Lubrication of Gear Systems

Lubrication of Gear Systems

From large to small stationarygear sets

Lubrication is our World

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Front page: Worm gearPhoto courtesy of Rhein-Getriebe40667 Meerbusch, Germany

ASONICCENTOPLEXISOFLEXKlüberbioKlüberoilKlüberplexKlübersynthMICROLUBENONTROPPETAMOPOLYLUBSTRUCTOVISSYNTHESOUNIGEAR

are registered trademarks ofKlüber Lubrication München KG

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1 Introduction ............................................................................................................................................. 5

2 Gear systems .......................................................................................................................................... 7

2.1 Gear types .......................................................................................................................................... 72.1.1 Spur gears .......................................................................................................................................... 82.1.2 Planetary gears .................................................................................................................................. 82.1.3 Bevel gears ......................................................................................................................................... 82.1.4 Crossed helical gears ......................................................................................................................... 82.1.5 Hypoid gears ...................................................................................................................................... 92.1.6 Worm gears ........................................................................................................................................ 9

3 Gear components ................................................................................................................................. 10

3.1 Gear wheels ..................................................................................................................................... 103.1.1 Tooth geometry ................................................................................................................................ 103.1.2 Gear materials .................................................................................................................................. 113.2 Bearings ........................................................................................................................................... 123.2.1 Rolling bearings ................................................................................................................................ 123.2.2 Plain bearings ................................................................................................................................... 123.3 Seals ................................................................................................................................................. 133.3.1 Static seals ....................................................................................................................................... 133.3.2 Dynamic contact seals ...................................................................................................................... 133.3.3 Dynamic non-contact seals .............................................................................................................. 14

4 Gear lubrication basics ........................................................................................................................ 15

4.1 Types of movement and speed ........................................................................................................ 154.2 Lubrication condition ......................................................................................................................... 164.2.1 Full fluid film lubrication .................................................................................................................... 164.2.2 Mixed lubrication ............................................................................................................................... 17

5 Types and methods of lubrication ...................................................................................................... 18

5.1 Oil lubrication .................................................................................................................................... 185.1.1 Splash lubrication ............................................................................................................................. 185.1.2 Splash circulation lubrication ............................................................................................................ 195.1.3 Force-fed circulation lubrication (injection lubrication) ...................................................................... 205.2 Grease lubrication ............................................................................................................................ 205.2.1 Splash lubrication with gear greases ................................................................................................ 215.2.2 One-time lubrication of tooth flanks .................................................................................................. 215.3 Lubrication with adhesive lubricants ................................................................................................. 21

6 Energy losses and heating of gear systems ...................................................................................... 22

6.1 Efficiency of gear systems ................................................................................................................ 226.2 Power losses in gear systems .......................................................................................................... 236.2.1 Tooth related power loss PVZ ........................................................................................................... 236.2.2 Tooth related power loss PVZ0 .......................................................................................................... 236.2.3 Bearing related power loss PVB ........................................................................................................ 236.2.4 Sealing related power loss PVD ........................................................................................................ 246.2.5 Other power losses PVX ................................................................................................................... 246.3 Heating of gear systems ................................................................................................................... 256.3.1 Heat dissipation ................................................................................................................................ 25

6.4 Temperatures in gear systems ......................................................................................................... 256.4.1 Tooth flank temperatures .................................................................................................................. 266.4.2 Temperature limits ............................................................................................................................ 266.4.3 Oil temperatures (empirical values) .................................................................................................. 27

7 Lubricants for stationary gear systems ............................................................................................. 28

7.1 Tasks, requirements ......................................................................................................................... 287.2 Types of gear lubricants ................................................................................................................... 297.2.1 Gear oils with a mineral base oil ....................................................................................................... 29

– CL lubricating oils ......................................................................................................................... 29– CLP lubricating oils ....................................................................................................................... 29– Multi-purpose lubricating oils ........................................................................................................ 29

Page Contents

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Page

7.2.2 Gear oils with a synthetic base oil .................................................................................................... 31

– Application related advantages ..................................................................................................... 32– Enhancement of efficiency and wear reduction ............................................................................. 33– Extension of oil change intervals ................................................................................................... 34– Reduction of energy costs ............................................................................................................. 35– High temperature lubrication ......................................................................................................... 36– Reduction of maintenance and disposal costs .............................................................................. 38

7.2.3 Gear greases .................................................................................................................................... 39

7.2.4 Adhesive lubricants .......................................................................................................................... 39

7.3 Standard requirements for gear lubricants ....................................................................................... 40

7.4 Gear oil properties ............................................................................................................................ 417.4.1 Viscosity ........................................................................................................................................... 417.4.2 Ageing behaviour .............................................................................................................................. 437.4.3 Behaviour under mixed friction conditions ........................................................................................ 437.4.4 Anti-corrosion properties .................................................................................................................. 437.4.5 Behaviour towards air ....................................................................................................................... 437.4.6 Cold flow properties .......................................................................................................................... 447.4.7 Compatibility with elastomers (seals) ............................................................................................... 447.4.8 Compatibility with interior coatings ................................................................................................... 457.4.9 Miscibility of different gear oil types .................................................................................................. 45

8 Selection of gear lubricants ................................................................................................................. 46

8.1 Selection of lubricant type and application methods ........................................................................ 468.1.1 Notes on lubricant selection ............................................................................................................. 46

8.2 Determination of the required viscosity ............................................................................................ 488.2.1 Determination of the viscosity of mineral lubricating oils

in accordance with DIN 51 509 ......................................................................................................... 48

8.2.2 Determination of the viscosity of synthetic Klüber oils ...................................................................... 52

8.3 Selection of synthetic gear oils ......................................................................................................... 56

8.4 Selection of gear greases ................................................................................................................. 578.4.1 Determination of the grease's consistency ....................................................................................... 588.4.2 Determination of the required base oil viscosity ............................................................................... 608.4.3 Determination of the base oil type .................................................................................................... 608.4.4 Properties of the thickening agent .................................................................................................... 618.4.5 Behaviour of lubricating greases towards synthetic materials .......................................................... 63

8.5 Notes on the lubrication of small gears ............................................................................................ 64

9 Tooth flank damage .............................................................................................................................. 66

9.1 Abrasive wear ................................................................................................................................... 669.2 Scuffing wear .................................................................................................................................... 679.3 Pitting................................................................................................................................................ 679.4 Micro pitting ...................................................................................................................................... 68

Literature, photographs ............................................................................................................................ 70

Product survey .......................................................................................................................................... 70

Contents

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1 Introduction

Gear wheels and simple gear unitswere already common ancient timesand used in grain mills (Fig. 1),water pumping stations and windmills.

Even today, many centuries afterthe gear wheel was invented, thereis nothing better, more compact orefficient than a gear unit when itcomes to transferring power, con-verting torques and adapting speed.It is therefore not surprising to findgears in all fields of technology, e.g.in turbo-generator drives with an out-put of 100 MW and more, tube milland kiln drives, or small and minia-ture low-output drives used in mecha-nical equipment and computers.

The development of gear systemsis characterized by the requirementfor enhanced power and torquetransfer by means of smaller andlighter gears on all performancelevels.

This requirement resulted in verycompact gears with a high powerdensity. In other words, the power-weight ratio (kg/kW) of gears wasreduced considerably in the pastfew years.

Increased efficiency is mainlyachieved by means of gear mate-rials that are more resistant to wear(case hardened, high alloy steel),improved flank machining methodsand optimized tooth geometry.

The power-weight ratio of gear unitscan also be improved by means oftorque division (planetary gears),light weight construction (light metalor plastic casings, hollow shafts), orby increasing the thermal limit which,as far as standard gears areconcerned, often lies below theirmechanical load limit (e.g. by usingsynthetic lubricating fluids).

Fig.1: Roman corn mill with a right angle gear (acc. to Vitruv)

A4 10196 C 10193

The requirements of lubricants haveto meet in terms of anti-wear andanti-scuffing properties as well ashigh temperature resistance in-crease while the power-weight ratioof the gear units decreases. Excessheat must be dissipated from gearswith a very small housing surface.This often results in higher operatingtemperatures, which has a negativeeffect on the service life of gearsand lubricants.

Measures to decrease power lossesand reduce temperatures are gain-ing more and more importance.They include the reduction of frictionlosses in gear components as wellas gear cooling.

The use of synthetic lubricants witha low friction coefficient and highresistance to increased tempera-tures and oxidation turned out to bea cost effective way of decreasingpower losses and reducing opera-ting temperatures. In many cases

complicated cooling installations areno longer necessary.

But these are not the only reasonswhy synthetic lubricants, especiallysynthetic lubricating oils, are soimportant in gear units. Apart fromreducing gear temperatures, it ispossible to ensure a substantiallylonger lubricant life (in case of wormgears this can even mean lifetimelubrication) or transfer more powerby increasing the oil’s operatingtemperature. Costs and energy willbe saved in any case.

The importance of synthetic gearoils also increases in view of eco-logical concerns. Increased lubri-cant life (3 to 5 times longer thanmineral oil) means a lot lessconsumption and less used oil todispose, hence less damage to theenvironment.Reduced maintenance costs dueto less frequent oil changes is anadditional spin-off.

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This brochure will focus on synthe-tic gear oils and describes their ad-vantages as compared to mineralhydrocarbon oils. The application-related advantages such as im-proved performance, extension ofoil change intervals, reduced energycosts and high temperature lubri-cation will be explained in detail bymeans of practice related examples(see 7.2.2).

The selection of synthetic oils (7.2.2and 8.3) and determination of vis-cosity based on the new Klüberselection method (8.2.2) will alsobe described in detail.

A special lubricant manufacturer,Klüber offers a comprehensiverange of modern synthetic, highquality and high performance oilssuitable for all gear lubrication pur-poses, including food grade lubri-cants for the food processing andpharmaceutical industries andrapidly biodegradable gear oils.Gear oils are very important forstationary industrial gears that areused to transfer power. Gear greases,on the other hand, are mainly ap-plied in small and miniature gearmotors used in all industrial sectorsand, owing to automation and im-proved comfort, also in domesticequipment (household and gardenappliances, hobby tools).

Small and miniature gears are oftenlubricated with greases becausethey may not be oiltight, be installedin inaccessible or hard-to-reachplaces, because it may not be pos-sible to perform maintenance, thegear may not be stationary duringoperation, or because lifetime lubri-cation is required.

There is no such thing as a univer-sal gear grease because there aremany types of small gears whosecomponents are made of most dif-ferent materials (steel, nonferrousmetals, plastics, composites).

Application, operating and ambientconditions also vary considerably.

For the sake of completeness thisbrochure also briefly deals with thelubrication of large open girth geardrives and open gear stages. Thisspecial type of gear lubricationmainly relies on adhesive gearlubricants.

More detailed information about thelubrication of large gear drives withadhesive lubricants is contained inour brochure Lubrication of largegear drives, 9.2 e.

Therefore a large number of diffe-rent gear greases is required, andoffered by Klüber, with a consistencyvarying between fluid to soft, withdifferent base oils, additives suitablefor the specific gears and loads, andwith thickeners imparting specialproperties to the greases such asadhesiveness, resistance to media,noise damping, etc.

As compared to gear oils which areexclusively used in oiltight gears,the selection of a suitable geargrease is not that easy. Apart fromthe type of base oil and viscosity itis important to determine thegrease’s consistency and the re-quired type of thickener.

As there is not very much writteninformation available about geargreases, their application andselection, and because DIN stan-dards are restricted to an absoluteminimum, the selection of geargreases is treated in detail in thisbrochure.

This chapter, together with thesurvey of Klüber gear greases atthe end of the brochure, will make itrelatively easy even for the not-so-versed reader, to select a suitableproduct.

Fig. 2: High-performance worm gear, madeby ZAE-Antriebssysteme, Hamburg

F 10288

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The quality and efficiency of a gearunit depend on the amount of powerloss resulting from the tribo-systemmade up by the power transmittingtooth flanks (friction system).

2.1 Gear types

Gears are classified in three maingroups depending on the positionof the shafts relative to each other,the type of flank contact and thecharacteristic tooth traces:

● primarily rolling contact gears

● combined rolling and slidinggears

● primarily sliding contact gears

Table 1 is based on DIN 868 andthe GfT worksheet 2.4.2 and pro-vides a survey of gear types (GfT =Gesellschaft für Tribologie, GermanSociety of Tribology).

A gear unit performs rolling andsliding movements on the power

transmitting flanks of the meshingteeth. The load on the tooth flanksis a function of the tooth geometryand the forces generated by thesliding movement.

In gears mainly performing a rollingmovement (spur and bevel gears)the load on the tooth flanks isgenerally lower than in gears mainlyperforming a sliding movement(worm and hypoid gears), seetable 1, column "sliding percentage".

The higher the sliding percentage,the higher the wear load on thetooth flanks, the higher the require-ments a lubricant has to meet.

C 10194 a-e

Rol

ling

cont

act

Position ofthe shafts

parallel

line

line cylinders

Sliding percentage[ % ]

GearsTypes Gear components Type of movement

cones 20 to 40

point cylinders 60 to 70

line cones 60 to 70

line

Rol

ling

/ slid

ing

cont

act

Slid

ing

cont

act cylindrical

andgloboidelement

70 to 100

2 Gear systems

Being extremely versatile, gearunits are widely used in all industrialsectors. Their task is to modify thetorque and speed generated by apower source at the input end ofthe gear with maximum efficiencyand in such a way that it suits therequirements of the output end.Gear units are speed/torque con-verters which also provide thepossibility of reversing the directionof rotation. A simple gear unitcomprises:

● two shafts

● two meshing gear wheels, and

● the required number of shaftbearings.

These components are either fullyor semi-enclosed by a housing. Inopen gears the shafts of the drivingand the driven gear wheel are sup-ported by separate bearings (e.g.girth gear drives).

Tooth flank contact

Spurgears

Bevelgears

Crossedhelicalgears

Wormgears

crossing

Hypoidgears

crossing

crossing

inter-secting

increased sliding

increased sliding

rolling and sliding

rolling and sliding 10 to 30

mainly sliding

Table 1: Types of gears

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2.1.1 Spur gears

Spur gears are characterized by thecylindrical shape of the gear wheelsand the parallel shafts. A distinctionis made between straight toothed,helical, double helical and herring-bone gears depending on the toothtrace, and between internal orexternal gears depending on therelative position of the gear wheels.The contact of the intermeshingteeth is linear over the entire flankwidth.

By splitting it is possible to multiplythe transferrable power under thesame specific load.

Other advantages include low rol-ling and sliding speeds of the toothflanks.

2.1.3 Bevel gears

Bevel gears are characterized byintersecting axes, most frequentlyat 90°, and cone-shaped gearcomponents. The gear teeth meshin a line contact.

The tooth trace can be straight,inclined, curved or helical anddepends on the required powertransmission and smooth operation.

Fig. 3: Spur gear, external gear pair

Fig. 5: Planetary gear, three wheels

A4 10197 C 10195 a

C 10196 a

C 10196 bA4 10198

a

Straight-toothed spur gears usuallyhave one or two meshing pairs ofteeth. As they have to transfer thefull power, their load carryingcapacity is relatively low and theygenerate a lot of noise.

Helical gears are better becausetheir contact ratio is higher. Shocksduring meshing and running noisesare reduced as the flanks meshgradually. The manufacturing costsof helical gears are higher, and theshaft bearing design is more com-plicated due to the axial forces thatare generated.

Axial thrust can be eliminated bymeans of double helical or herring-bone gears. The latter are verycomplicated in design and aretherefore rarely used.

The combination of internal andexternal gear wheels provides theadvantage of a relatively shortcenter distance. Internal gears areoften used as an "annulus" inplanetary systems.

Fig. 4: Spur gear, internal gear pair

A4 10197 C 10195 b

a

2.1.2 Planetary gears

Planetary gears have a driving anda driven shaft located on the sameaxis. Their main advantage as com-pared to conventional spur gears isthe increased power density, i.e.they utilize the installation spacemuch better. The input torque issplit and transmitted to three ormore planetary wheels.

Fig. 6: Bevel gear pair

A4 10197 C 10195 c

∑

2.1.4 Crossed helical gears

These gears are characterized bycrossing shafts and cylindricalrolling elements. The teeth are thesame as in the case of helical spurgears. Owing to the offset axes theteeth only have a point contact, i.e.

Straight-toothed bevel gears gene-rate a lot of noise, whereas bevelgears with other types of teethoperate much more silently andpermit a higher degree of powertransfer. It is important to rememberthat bevel gears always generateaxial thrust.

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This results in a high sliding speedand, in consequence, high thermalload on the tooth flanks. Thereforecross helical gears are only suitableto transfer movements and can onlycarry low loads.

2.1.5 Hypoid gears

Hypoid gears are characterized byhyperbolic teeth, crossing shaftsand a pinion axis offset to the centerof the crown gear. The tooth tracesare curved. Owing to the staggeredaxes the hypoid pinion has a largerdiameter than that of a bevel gearwith the same crown diameter. Inconsequence, hypoid gears have abetter load carrying capacity whileensuring the same transmissionratio.

When the teeth are meshing thereis a point contact with an ellipsoidsurface, which results in verticalsliding movements and an in-creased percentage in the horizon-tal direction.

Owing to the increased contactratio and the additional slidingmotion, hypoid gears operate muchsmoother than bevel gears.

Their disadvantage, however, isthat the horizontal sliding movementreduces the scuffing load capacitythe more the axes are offset, resul-ting in a lower gear efficiency.

Special hypoid gear oils can help.As compared to bevel gears of thesame size, hypoid gears have abetter noise behavior, higher trans-mission ratio and increased powertransfer capacity. Their efficiency, incontrast, is worse.

2.1.6 Worm gears

These gears are characterized byshafts crossing at an angle of 90°.Fig. 10 shows the main worm andwheel types and the respectivegeometrical components. Cylindri-cal worm gears (Fig. 10 a) are mostcommon.

Having a high transmission ratio(i = 5 to 70), worm gears usually areof a single-stage design. They cantransfer increased forces and arestill small in size. As compared to allother gear units, they have the bestnoise behavior but also a very highsliding percentage which results infriction losses. Worm gears there-fore operate hotter and have a lowerefficiency.

Fig. 8: Hypoid gear pair

A4 10197 C 10195 e

a

∑

Fig. 9: Worm gear pair

A4 10197 C 10195 f

a ∑

when two flanks mesh there is noline as in the case of spur gearswith parallel shafts.

Fig. 7: Crossed helical gear pair

A4 10197 C 10195 d

a ∑

a) Cylindrical worm gear (cylindrical worm – globoid gear)

b) Spur-type worm gear (globoid worm – cylindrical gear)

c) Double enveloping worm gear (globoid worm – globoid gear)

A4 10199 C 10197 a-c

aa

a

Fig. 10: Worm gears

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Fig. 12: Nomenclature and dimensions of involute gears (no profile offset)

geometry has the following advan-tages:

– simple and precisemanufacturing

– exchangeable when used inspur gears

– uniform transfer of movementseven with center distancevariations

– uniform direction and amountof normal force

– one tool with variable profilescan be used for various toothgeometries and center distances.

Positive and negative profile correc-tions are made in order to avoidundercutting when the number ofteeth is low and to increase the

root’s load carrying capacity. Theyare also made to improve the flanks’load carrying capacity (larger curveradius) and reduce the slidingpercentage to decrease powerlosses.

Other gears such as cycloid gears(e.g. for pinion stands, clocks) andlantern gear drives (e.g. live ringdrives) are not used very often.

Even though cycloid gears operatemore precisely than involute gears,they are much more sensitive tovariations in the center distance,and are very expensive to manu-facture.

Fig. 11: Main components of a gear pair

The general terms relating to gearwheels, pairs and units are definedin DIN 868 which also explains thebasic principles.

Other relevant standards includeDIN 3960, 3971, 3975 and 3989.

3 .1.1 Tooth geometry

Involute gears are most widely usedin machine construction. As com-pared to other gears, the tooth

A4 10200 C 10198

▼

▲

2

1

1 pinion 2 wheel a center distance

C 10199 b

a

1

es p

b

2

3

4

5

ha

hf

d f

d ad

xyz

C 10199 a

l

C1

p

K

A

A1

T1 C2

B

C

α

α

g f1

g a1

g α r 1

r a1

treibend

D

E

E1

02

01

ra2

r2

Rad 2

Rad 1

T2

aa

O2

O2

c2

c1

3 Gear components

Gear systems are made up ofwheels, shafts, bearings andhousings. All components interactclosely, and lubricants play animportant role.

3.1 Gear wheels

A gear wheel is a machine elementrotating around a shaft. It consistsof a wheel body, contact surfaceand teeth. Depending on the posi-tion of the teeth relative to the wheelbody, a distinction is made betweeninternal and external gear wheels.

A gear pair consists of two gearwheels separated by the centerdistance a. The smaller wheel iscalled pinion, the larger wheel.

wheel 2

wheel 1

driving

1 Gear rim2 Left flank3 Right flank4 Reference cylinder

(operating pitch cylinder)5 Right tooth trace

a Center distanceb Face widthc Bottom clearanced Reference circle (pitch

circle)df Root circleda Addendum circlee Space widthgα Length of action A-C-Eα Pressure angleha Addendumhf Dedenduml Length of action (path

of rotation from start ofaction A1 to end ofaction E1)

p Pitchs Tooth thickness in

reference circle

A Start of actionB Internal point of action:

the leading teeth havejust ended action (E)

C Pitch pointD External point of action:

the following teeth arejust starting action. –B is the external point ofaction of wheel 2.

Designation(from this point:left or right flank)

Root circle

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3.1.2 Gear materials

In view of the ever increasingrequirements for higher gear out-put, smaller dimensions and lowerweight, the materials used for gearswere refined to an extremely highdegree and the flank machiningmethods were improved.

Table 2 illustrates how high gradematerials, improved flank surfaces,improved hardening methods andthe application of high performancelubricants made it possible to reducethe size, weight and manufacturingcosts of gear units considerably.

830 mm

10

Center distance a

Module m

Heattreatment

Material

Machiningmethod

Size(weldedhousing)

Weight of rollingbearings

Total weight

Total weight bypercentage

Price bypercentage

Reliability SH

Reliability SF

Pinion and gearwheelC 45

Pinion and gearwheel

42 Cr Mo 4


31 Cr Mo V 9


34 Cr Mo 4


20 Mn Cr 5

normalizinghardening and

tempering

Pinion: 20 Mn Cr 5Gear wheel: 42 Cr

Mo 4

gas nitridinginduction hardening

of flanks case hardening

hobbing hobbing fine milling milling and lapping grinding

650 mm

10

585 mm

10

490 mm

10

470 mm

14

390 mm

10

95 kg 95 kg 95 kg 105 kg 105 kg 120 kg

8 505 kg 4 860 kg 3 465 kg 2 620 kg 2 390 kg 1 581 kg

174 %

132 %

71 % 54 % 49 % 33 %

85 % 78 % 66 % 63 %

1.3

6.1

1.3

5.7

1.3

3.9

1.3

2.3

1.4

2.3

1.6

2.3

Table 2: Comparison of gear units equipped with gear wheels of different materials. Rated pinion moment 21 400 Nm ; n1 = 500 rpm; i = 3; application factor KA = 1.25; prevention of pittings: SH min = 1.3; root: SF min = 2.3; individual design

100 %

100 %

Today high performance gear unitsare usually equipped with gearwheels of alloyed steel and casehardened teeth which are groundafter heat treatment. Industrialworm gears subject to high loadsgenerally have a worm of alloyedcase hardened steel and a gearwheel made of a high grade bronzealloy material. Gears subject to lowloads are usually made of alloyedheat treatable steel, nitriding steel,alloyed cast steel or spheroidalgraphite iron.

Gear wheels made of syntheticmaterials are rarely used in indus-trial gears due to their inferior load

carrying capacity and low thermalresistance. They are mainly found insmall and miniature low capacitygears used to transfer movementsand speeds. In these cases lowvibrations and noises as well asemergency running properties areof greater importance, as the flanksare often lubricated only once.

C 10200 a-f

pinion: case-hardeningwheel: hardening and tempering

pinion: grinding

wheel: hobbing

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3.2 Bearings

3.2.1 Rolling bearings

Low to medium capacity gear unitsoperating at speeds up to approx.3000 rpm are mainly equipped withrolling bearings.

Advantages:

– low starting friction

– glow friction losses throughoutthe speed range

– the shaft material does not havean impact on the running proper-ties

– easy lubrication; lifetimelubrication is possible

– good emergency running proper-ties in case of bearing failure

– bearings are less wide and stillaccommodate the same loads

– international standardization

Disadvantages:

– limited suitability for high speeds(centrifugal forces)

– susceptible to contaminatedlubricants

– limited service life

Rolling bearings can be lubricatedwith grease or oil. In case of oillubrication the lubricant is usuallyapplied by immersion or splashing,in some cases by means of apressurized circulation system or byinjection.

Lifetime lubrication is possible if agrease is used (depending on theintended service life of the gear).

3.2.2 Plain bearings

Plain bearings are generally usedwherever the performance limit ofrolling bearings is exceeded (speed,load), for example in high speedturbo-gears (speeds between 3000and 70,000 rpm) or large scalegenerators (power plants, ships).

They are also used in gears whichhave to operate especially smoothly.

Fig. 13: Bevel / spur gear with rolling bearings

Advantages:

– simple design

– unlimited life if lubricatedadequately

– suitable for very high speeds

– not sensitive to the ingress ofdust

– good vibration, shock and noisedamping properties

Disadvantages:

– require complex lubrication andcooling systems

– plain hydrodynamic bearings:mixed friction occurs duringstarting and stopping

– hydrostatic jacking pumpsrequired for large gears

Plain bearings are normallylubricated with oil by immersion,splashing or pressurized circulation.Bearings generating a low amount

A4 10203 C 10202

A4 10202 C 10201

Fig. 14: Spur gear with plain bearings

of heat and subjectto low loads canalso be lubricatedwith grease.

Low-capacity smalland miniature gearsare often equippedwith plain sinteredmetal bearingswhich are lubricatedfor life with specialimpregnating fluidsand are suitable forhigh speeds.

Small bearings sub-ject to low speedsand loads may alsobe equipped withplain bearings madeof tribo-systemmaterials (drybearings).

13


3.3.2 Contact dynamic seals

are used on shafts and requireprecisely machined shaft surfacesas well as continuous lubrication tokeep wear to a minimum. The use ofsuch seals may be limited at highspeeds due to the high frictiontemperatures that are generated.

Radial shaft seals

These sealing elements are used onrotating shafts. They are standard-ized in DIN 3760. The standardtypes are A and AS, i.e. radial shaftseals with a rubber coating without(A) and with (AS) an additional dustlip. For special cases of applicationthere are also radial shaft seals with

Klüber offers semi-finished andready-to-use bearing bushingsmade of tribo-system materialsunder the trade name Klüberplast.

3.3 Seals

A distinction is made between staticand dynamic seals depending onwhether the machine elements to besealed have a relative movement ornot.

Dynamic seals are divided into non-contact gap type seals, contact sealsand sealing elements combining thefunctions of the first two types.

3.3.1 Static sealing elements

Flat seals

Flat seals are used to seal staticgear components such as flanges,housing parts or oil trays. Thesealing effect is generated by thefact that the two opposing surfacesexert pressure on the seal and thuscompress irregularities into the sealsurface.

Flat seals can be of the hard,composite or soft type, the latterbeing most common today.

Soft seals can be made of elasto-mers, rubber asbestos (IT materialsin acc. with DIN 3754), cork andrubber compounds, artificial resinand thermoplastic materials.

Sealing masses, tapes, and putty

In contrast to flat seals, pressure isnot required for these types of seals.They form a very thin sealing layerbetween the surfaces to be sealedwithout requiring any additional

Fig. 15: O-Ring cover seal

pressure. They are available in theform of removable rubber, knead-able and hardening masses and arepreferred over flat seals if an impacton center distances or the concen-tricity of split bores is possible.

O-ring seals

Such seals are standardized underDIN 3770 (compression moldedseals) and DIN 2693 (extrusionmolded seals). They are made ofelastomers and are used in gearsfor static sealing purposes, e.g. inbearing covers, inspection holes,threaded pipe connections, etc.

an outer metal case and seals withan outer case plus a (reinforcing)cap.

Radial shaft seals with a helix forreverse pumping action are used toimprove the sealing effect in case ofoil lubrication and to extend theservice time, especially if elastomerseals (acrylate or fluorinated rubber)are used at increased temperatures.

C 10203

The speed limit of radial shaft sealsdepends, among other things, onthe elastomer base material, the oillevel in case of oil lubrication

Type A DIN 3760

Type AS DIN 3760

Former type C DIN 3760

Former type B DIN 3760

Fig. 16: Radial shaft seals

C 10204 a-d

14


The sealing and dust lips must neverdry out and require greasing or oilingprior to installation. The sameapplies to the sealing surfaces onthe shaft. In case of oil lubricationthe oil must dissipate the frictionalheat generated at the sealing lip.

Axial lip seals

The sealing effect is generated byexerting axial pressure on theelastomer sealing lip, thus pressingit against a contact surface that isperpendicular to the shaft axis(Fig. 18 a).

Axial sliding seals

These seals rotate together with theshaft. The sealing lip slides against acontact surface at a right angle tothe shaft axis (Fig. 18 b).

a)

3.3.3 Non-contact, dynamic seals

Advantages as compared to contactdynamic seals:

– no wear at high speeds

– negligible frictional heat

– no special requirements in termsof chemical and heat resistanceof the seal material (temperature,medium).

A disadvantage is that these ele-ments do not provide static sealing,i.e. they must never be in contact

Smooth, gap type seal

Grooved, gap type seal

Gap type seal with conveyor grooves

Shield type Z

Rotating disk

Fig. 17: Bevel gear with a radial shaft seal

Fig. 19: Sealing disk– RS

Fig. 18: a) Axial lip sealb) Axial sliding seal

(dissipation of heat), the type oflubricant (oil, grease), the possibilityof dissipating frictional heat (hollowor solid shaft, shaft diameter) andthe surface roughness of the contactareas. If radial shaft seals are usedin front of grease lubricated bearings(fig. 17) the space between theprotective lip and the sealing lipmust be completely filled withgrease (NLGI 1 or 2) in order toprevent the seal from wearing andprotect the shaft against corrosion.It is important to test the compati-bility of the grease and the sealingmaterial prior to application.

Fig. 20: Gap type seals

A4 10204 C 10205

C 10207

C 10208

C 10209 a-e

Rolling bearings with sealing disks

Sealing disks located at one or bothsides of the bearing serve the pur-pose of retaining the initial fill ofgrease in the bearing and preven-ting the ingress of water and dust.These seals are not effectiveagainst fluids.

b)

C 10206

with the oil if the gear stands stillin order to avoid leakage. Splashlubrication is therefore only possibleto a limited extent because it isdependent on the oil level.

A basic distinction is made betweenseals with a smooth gap, (convey-ing) grooves, labyrinth gap, labyrinthand flinger.

Seals performing the function of agap type seal after a certain periodof running in are also countedamong the non-contact seals.These include felt rings, resilientlaminar rings and resilient sealingdisks.

O-ring

15


Fig. 21: Gap type seal with flinger

Fig. 23: Resilient sealing disk

Fig. 22: Labyrinth seal

Fig. 26: Sliding speeds on tooth flanks of rolling spiral and helical gears

a) rolling movement

b) sliding movementC 10210 a+b

C 10211 a-d

C 10212 a-d C 10215 a+b

C 10213 a+b

resilient lamellarring

V=0

V

4 Gear lubrication basics

4.1 Types of movement andspeed

In all types of gears described under2.1 the tooth flanks perform rollingand sliding movements while theteeth are meshing. Table 1 on page7 shows that the sliding percentageof the combined rolling/sliding move-ments varies depending on the typeof gear. The ratio of the sliding androlling speed is of vital importancefor the load to which the lubricant issubject.

In gears where the rolling movementis predominant the tooth flanks andthe lubricant are subject to less loadthan in gears with a predominantsliding movement (parallel/ helicalgears, helical gears).

Fig. 26 illustrates the speed condi-tions in parallel gears and parallel/helical gears. Point a) shows that inparallel gears the sliding speed isonly vertical. It is zero in the pitchpoint (pure rolling friction) and in-creases in the direction of the tip ofthe tooth. Point b) illustrates that inparallel/helical gears there is also asliding (spiral) movement in thehorizontal direction and that there iseven a certain percentage of slidingmovement in the pitch point.

This is the reason why the ratiobetween the sliding and the rollingspeed is relatively high in worm

gears and hypoid gears with offsetshafts. The direction of the slidingspeed is not constant but changesin the vertical direction. The "wiping"movement considerably impairs theformation of a lubricant film underpressure.

The load on the tooth flanks and thelubricant increases as the slidingpercentage grows.

x U1 ≠ U2: rolling and sliding movement

U1 = U2: mere rolling movement

Like symbols: surfaces touching at contactpoint

C 10214

U1

U2 +

+

Fig. 25: Schematic drawing of a combinedrolling and sliding movement

Fig. 24: Rolling and sliding movement

a

b

b

a

vGH

vGR

vGF

tip

tooth

referencecircle

0tooth tip

vGR = vGH

sliding speed vGRVGH: vertical sliding speedVGF: horizontal sliding speedVGR: resulting sliding speed on the tooth

16


Fig. 27: Full fluid film lubrication C 10216 Fig. 29: Typical friction areas on tooth flanks

A ... E: meshing pointsin acc. with DIN 3960

A initial meshing point

B internal individual meshingpoint of the driving gear,external individual meshingpoint of the driven gear,

C pitch point

D external individual meshingpoint of the driving wheel,internal individual meshingpoint of the driven wheel,

E final meshing point

FR full fluid film lubrication

MR mixed lubrication

a) low peripheral speed

b) high peripheral speed

a) no load(flatter and larger contact area),which leads to a greater lubricantgap and a thicker oil film.

The most favorable conditions for aseparating film are present in spurgears due the high percentage ofrolling movement and the linecontact when the teeth mesh.

Film thickness increases as thepressure related viscosity and theperipheral speed rise. It decreases,however, as the pressure increasesfurther and internal friction causesthe oil film temperature to rise which,in turn, results in a decrease ofviscosity.

4.2 Lubrication condition

4.2.1 Full fluid film lubrication

Full fluid film lubrication would bethe ideal condition of lubrication.The meshing tooth flanks would becompletely separated by a lubricantfilm. Due to the gap geometry andthe various movements, however,full fluid film lubrication on themeshing flanks is only achieved onsufficiently large flank areas undercertain operating conditions. Mixedfriction prevails on the other areas.The size of the full fluid film areasmainly depends on the tooth flankgeometry and is largest in spur andbevel gears.

The formation of a load-carrying andseparating lubricant film around thepitch point can be explained bymeans of the elasto-hydrodynamiclubrication theory (EHD), which isbased on the following:

– High pressures up to 10,000 baroccur in the contact zonesbetween the tooth flanks. Theyhave an impact on the oil’s visco-sity since pressure increasesviscosity.

– In the meshing phase the contactsurfaces are deformed elastically(contact stress).

The high surface pressure betweenthe tooth flanks results in a suddenincrease in the oil film’s viscositymaking the lubricant so viscous thatit cannot flow off. The oil filmpressure deforms the tooth flankselastically in the contact points

A4 10205C 10218 a+b

C 10217 a-c

A

ED

CB

A

ED

CB

MR FR

MR

MR

b) load, no movement

pressuredistribution

c) load and rotation with lubricant film

surface 1

deformationsurface 1 film

thickness hwithoutconstriction

defor-mationsurface 2

contact stressdistribution

EHD pressuredistribution

surface 2

inward turning sideoutwardturning side

2b

n1

n2(u2)

FN

h°

(u1)

FN

FN

surface 1

surface 2

Full fluid film

Fig. 28: Formation of a lubrication gap in case of elasto-hydrodynamic lubrication (EHD)

maximum pressure= sHz

17


2

1 OO 2

4.2.2 Mixed lubrication

Mixed lubrication is the lubricationcondition that includes both fluidfriction and dry friction.

The surfaces of the meshing teethare not completely separated by afluid film and are in direct contact insome parts.

Fig. 31: Gear motor with a three-stage helical gear, made by Getriebebau Nord, D - 22941 Bargteheide, Germany F 10241

Mixed friction occurs in cylindricaland bevel gears operating at highperipheral speeds and subject tohigh specific load. At increasedperipheral speeds mixed friction isreplaced by fluid friction (Fig. 30).

Worm and hypoid gears usuallyoperate under mixed friction condi-tions.

A lubricating oil with antiwear addi-tives forms reaction layers (bound-ary layers) on the flank surfaces.This largely prevents metal/metalcontact and avoids scoring andcoarse wear. The most commonextreme pressure additives are ofthe sulfur/phosphorous type.Chemical reactions with the toothmaterial produces iron sulfide andiron phosphorate layers.

The course and intensity of thesetribo-chemical reactions depend on

the following reaction parameters:pressure, temperature, type andquantity of the additives involved.The additives are usually combinedin such a way that they becomeactive with an increasing tooth flanktemperature.

As compared to the base materials,the reaction layers have a low shearstability. This ensures a continuousprocess of wear and renewal of theboundary layers (layer wear).

O Surface layer friction1 Lubricant2 Surface reaction layer C 10219

Full fluid film

Fig. 30: Mixed friction

18


Splash lubrication

Combined splash andcirculation lubrication

Force-fed lubrication(injection lubrication)

Splash lubrication

Splash lubrication with agear housing almost com-pletely filled with grease

Spray lubrication(total loss lubrication)Lifetime lubrication of thetooth flanks

Lubricant type Lubrication method

Oil

Splash lubrication

Splash lubrication(if fluids are used)Spray lubrication(intermittent andquasi-continuous)

Table 3: Types of lubricants and lubrication methods

Grease 1)

Adhesivelubricants 2)

1) See also table 17, page 47

2) See also our brochure 9.2 e, "Lubrication of large gear drives"

5 Types and methods of lubrication

There is a correlation between thetype of gear and its peripheralspeed, and the type and method oflubrication. See also table 17 onpage 47.

Depending on the type of lubricant,the application methods listed intable 3 are most common for thelubrication of gear systems.

5.1 Oil lubrication

The majority of closed industrialgears are lubricated with an oil bymeans of splash lubrication.

Other application methods includesplash/circulation lubrication (usedif heat dissipation is important) andforce-fed circulation lubrication (inlarge gears operating at highspeeds).

Other lubrication methods are irre-levant in context with stationary geardrives and will not be dealt with inthe following.

5.1.1 Splash lubrication

A lubricant depot in the gear housinginto which the teeth are immersed isthe easiest way of ensuring continu-ous lubrication. It is therefore themost common lubrication methodfor closed, oiltight gear systems.

It is especially economic, simple indesign and reliable. Its coolingeffect is sufficient for most applica-tions and can be improved bymeans of special housing designs(e.g. cooling ribs) or auxiliary units

C 10221 a+b

C 10220

Fig. 32: Splash lubrication. Oil lubrication ofrolling bearings via intermediatereservoirs

Fig. 33: Examples of oil guide plates

horizontal arrangement

vertical arrangement

Tests with single-stage spur gearshave shown that splash lubricationis efficient up to a peripheral speedof 60 m/s.

such as cooling fans or watercooling lines.

In splash lubrication one wheel pergear stage usually plunges into theoil sump and carries some oil to themeshing zone. Oil dripping off thegears and shafts due to centrifugalforces either runs into special oilreturn lines and is carried to thebearings that also require lubrica-tion, or runs directly back into thesump along the housing walls.

Splashing oil to a certain extent alsolubricates the wheels that are notimmersed. In some cases the shaftsare equipped with additional oilsplashers to intensify the splasheffect.

Oil splash lubrication without anyadditional design measures isfeasible up to a peripheral speedof approx. 20 m/s. Oil guides (baffleplates, oil pockets, etc.) are requiredfor increased peripheral speeds.

Fluid grease 1)

Splashing oil

Oil

19


Type of gear

Peripheral speed up to5 m/s

Peripheral speed> 5 ... 20 m/s

–

Spur gears

Bevel gears

Worm gears

Operating conditions Depth of immersion Oil level and immersion depth

With splash lubrication it is importantthat a certain oil level is retained atall times in order to prevent damageand ensure reliable operation.

If the oil level is too low, it may resultin starved lubrication, inadequateheat dissipation and increased wear.

If the oil level is too high, churninglosses may increase, resulting inhigher temperatures. This, in turn,accelerates oil ageing, decreasesthe oil’s service life, increases visco-sity and thus reduces the lubricant’spressure absorption capacity in themeshing zone. It also results in thegeneration of foam and noises.

When the peripheral speed is in-creased, the depth of immersion isreduced in order to keep churninglosses to a minimum. The followingrule of thumb applies to spur gears:

Depth of immersion

3 to 5 times the moduleup to 5 m/s

1 to 3 times the module> 5 to 20 m/s

With higher peripheral speeds itbecomes more difficult to wet thetooth flanks sufficiently, and the oillevel is reduced due to oil splashing.In case of very high peripheralspeeds it is therefore important toincrease the depth of immersion ofthe gear wheels irrespective ofpotential churning losses. Gearswith fully immersed pinions (e.g.bevel gears) are found quite often.A great difference in wheel dia-meters in the individual gear stagesmay also be a reason for deviatingfrom the immersion depths listed inthe following.

Worm on the top

Worm at the side

Worm at the bottom Wheel immersed to approx.the center of the meshing zone

Fig. 34: Planetary worm gear, Rhein-Getriebe GmbH, D-40667 Meerbusch, Germany F 10242

Table 4: Recommended depth of immersion

5.1.2 Combined splash and circulation lubrication

If additional cooling ribs, fans orducts in the housing are not enoughto compensate for the power lossesin a splash lubricated gear, heat canalso be dissipated by using a com-bined splash and circulation lubrica-tion system.

The easiest method is to install apump driven by the gear whichtakes a certain oil quantity out of theoil sump and returns it to the gear

via an oil cooler. Electrically ope-rated oil pumps (main and backuppumps) are also used.

Thermostatically controlled coolersand filters installed in the oil circuitmake it possible to extend the oilchange intervals. The depth ofwheel immersion is determined asdescribed for splash lubrication.

The oil fill quantity has to be some-what higher because a certainamount of oil is always circulating.

Wheel immersed to at least1/2 of the worm height

Wheel immersed to approx.1/3 of its diameter

Immersion of teeth over theentire width of the wheel

1 to 3 times the module

3 to 5 times the module

20


Fig. 35: Schematic drawing of a wet sump lubrication system

Fig. 36: Schematic drawing of a dry sump lubrication system

1 Flanged-on pump

2 Pressure relief valve

3 Filter with pressuredifference indicator

4 Manometer

5 Spray nozzles

6 Gearbox

C 10221

C 10222

1 Oil container

2 Motor/ pump unit

3 Pressure relief valve

4 Filter with pressure differenceindicator

5 Oil / water heat exchanger

6 Thermometer

7 Pressure control unit

8 Manometer

9 Gear box

1

2

3

4

5

6

7

8

9

M

6

5.2 Grease lubrication

Grease lubrication is normally usedfor gears that are not oiltight or, forsafety reasons (leakage), for oiltightgears installed in a position pre-venting maintenance and repair.Grease lubrication is also suitable

5.1.3 Force-fed circulation lubrication

(injection lubrication)

Force-fed circulation lubrication isused at peripheral speeds too highfor splash lubrication and in case ofgears equipped with plain bearings.This lubrication method is suitablefor even the highest peripheralspeeds encountered in gearsystems (approx. 250 m/s).

Oil is brought onto the tooth flanksvia slotted or perforated nozzles.The oil is injected into the contactzone, either at the initial or the finalmeshing zone. It is assumed that oilinjected into the initial meshing zoneis more benefitial to the lubricationprocess, while oil injected into thefinal meshing zone intensifies thecooling effect.

The injection quantity depends onthe amount of heat to be dissipated.As a rule of thumb we recommend0.5 to 1.0 l / min per cm of toothwidth.

The required oil circulation quantityis made up of the lubricant quantityrequired for the gear wheels plusthe quantity required for the bear-ings.

Depending on the type of circulation,a distinction is made between wetand dry sump lubrication. In wetsump lubrication (Fig. 35) the oilreservoir is the oil sump in thehousing from which the oils isbrought to the friction points.

In dry sump lubrication (Fig. 36)the oil which returns from the frictionpoints is collected in the housingand then transferred into a separateoil container from where it is broughtback to the friction points.

Dry sump lubrication is used if theoil volume is too big to be accom-modated in the gear housing.

With grease lubrication it is im-portant to take into account thatexchanging the grease is verycomplicated because the gearboxusually has to be taken apart com-pletely and cleaned thoroughly.

12

3

4

5

6

21


for gears with a limited life that aresuitable for lifetime lubrication.

As grease cannot dissipate heator only to a limited extent, greaselubrication is restricted to low andmedium capacity gears operating inshort or intermittent intervals.

Grease is mainly used on gearmotors and in all types of small andminiature gears, e.g. power tools,household and office equipment,automotive servo drives, etc.

Splash lubrication is the commonmethod of application. Gears witha low specific load that are mainlyused to transfer movements over alimited period of time or gears de-signed for a certain operating periodare usually lifetime lubricated. Withthis application method the peri-pheral speed is limited to 2 to 3 m/s.

5.2.1 Splash lubrication with gear greases

As already mentioned it is importantto take into consideration thatgreases have a considerably lowerheat dissipation capacity than lubri-cating oils.

Splash lubrication with gear greasesis therefore restricted to low to me-dium capacity gears. As the devel-opment and dissipation of heatlargely depend on the individualoperating conditions (permanent orintermittent operation) and thecasing design, it is not possible toindicate a specific capacity limit forgrease lubrication.

Unless the gears have a very lowcapacity we recommend carryingout tests to establish the gearheating rate.

Gears with high peripheral speedsoperating continuously and/or usedto transfer power require a grease

with a high base oil content toensure heat dissipation: a fluidgrease of consistency grade 000 or00 or at least a very soft grease ofgrade 0.

In continuous operation theperipheral speed limit is as follows:

5.3 Lubrication with adhesivelubricants

Adhesive lubricants are mainly usedfor the lubrication of open gears andgear systems of large to very largedimensions, e.g. drives of rotarykilns, tube mills, lifting cylinders,cranes and construction machines.

Depending on the operating modeand/or conditions and the drivedesign (with/without cover, with/without lubricant reservoir), thelubricant is applied

– once (or several times at verylarge intervals)

– continuously (long term lubrica-tion)

– intermittently (total loss lubrica-tion)

Fig. 37 on page 22 shows thecorrelation between the types oflubrication and the applicationmethods.

5.2.2 One-time lubrication of tooth flanks

See NOTE above.

000 6 to 8 00 4 to 5 0 2 to 3

NLGI gradeDIN 51 818

Peripheral speed[m/s]

The lubricant to be used determinesthe type of lubrication and the suit-able application method.

Adhesive lubricants used on opengears can be fluid or semi-solid andtherefore have an impact on theapplication method.

Table 5: Correlation between the peripheralspeed and the application methodin case of lubrication with adhesivelubricants

up to 2

Application method

manual application

up to approx. 8 splash or spray lubrication

> 8 to approx. 11 spray lubrication

Peripheral speeds[m/s]

Fluid gear greases have a lessfavorable flow behavior than oils.Excess grease thrown off the gearreturns to the lubricant sump at amuch lower speed. It is thereforeimportant to fill the grease immer-sion bath to a higher level than incase of oil lubrication in order toprevent starved lubrication.

Depending on the grease’s consis-tency the approximate depth of im-mersion should be between 1 and 3times the tooth depth.

Splash lubrication with a gear greaseat peripheral speeds above 8 to10 m/s in continuous operation ispossible if the following steps aretaken:

a) Use a gear grease of consistencygrade 0 or 00 and fill the casing toapprox. 30 to 40 % of its volume.

b) Use a gear grease of consistency1 or 2 and fill the casing almostcompletely.

Low capacity gears in short term orintermittent operation can be lubri-cated with a gear grease up to aperipheral speed of 25 m/s ifmethod b) is applied.

NOTE: For detailed informationabout lubrication with gear greasesrefer to section 8.4, page 57,Selection of gear greases.

22


Type of lubrication Application method Type of lubricant

Splash lubrication

Circulation lubrication

Transfer lubrication

Highly viscous gear oils orfluids with a mineral base oil(free from solvents andbitumen), with EP additives,with or without solid lubricants

Spray lubricationIntermittent (total loss)lubrication

Continuous (long term)lubrication

One-time lubrication

Fig. 37: Lubrication types and applicationmethods common with adhesivelubricants

6 Energy losses and heating of gear systems

6.1 Efficiency of gear systems

The efficiency η o gear systems isdefined as the ration of the inputpower Pb and the output power Pa.

η =Pa

Pa - Pv Pv

Pa = 1-

Pb = Pa - Pv (Pv = power loss)

Pb

Paη = < 1

A description of all commonmethods of application would gobeyond the scope of this brochure.

For details about lubrication withadhesive lubricants please refer toour brochure"Lubrication of large gear drives",9.2 e.

Type of gearOverall efficiency

under nominal loadapprox. [%]

Spur gears

single stage up to 98.5

two stage up to 97

three stage up to 95.5

four stage up to 94

Bevel gears up to 98

Straight bevelgears

two stage up to 96.5

three stage up to 95

four stage up to 93.5

Planetary gears

single stage up to 97

Crossed helicalgears 50 to 98.5

Hypoid gears

high transmission ratio 50 to 90

low transmission ratio 85 to 96Gears with a low sliding percentage,such as spur and bevel gears, havea very high efficiency (up to 99 % inthe case of single-stage spur gears),whereas gears with a high slidingpercentage, e.g. hypoid and wormgears, have a relatively low effi-ciency. Table 6 gives a generalsurvey on gear efficiency.

It is important to note that efficiencydecreases with an increasing num-ber of gear stages.

The efficiency of worm gearsdepends on the worm speed, thetransmission ratio and the overallsize of the gear system. Efficiencyincreases with a higher worm speed(increasing sliding speed of theteeth), lower transmission ratio(increasing pitch angle) and largercenter distance. Efficiency valuesstated in gear brochures usuallyrefer to the gears’ rated efficiencyand apply to full load operation.

The efficiency of gear systemsvaries as a function of the load. It isat its maximum under full load anddecreases under partial load.

Unless specified otherwise, theindicated efficiency applies tostandard gears lubricated with agear oil with a mineral hydrocarbonbase.

Synthetic gear oils can improve agear’s efficiency up to 30 %, espe-cially in the case of gears with ahigh sliding percentage, such ashypoid and worm gears. See alsosection 7.2.2, page 33.

Table 6: Efficiency of industrial gears

Application by brush, spatula,aerosol can or manual spray gun

Solid lubricant powder,bonded coatings, greasesand pastes, especially thosewith solid lubricants

Sprayable adhesive gearlubricants (free from solventsand bitumen), with or withoutsolid lubricants.Consistency gradesNLGI 0, 00, 000

23


Churning losses in high speedgears may result in increased tem-peratures which, depending on thegear oil, may be excessive.

Squeezing losses

Squeezing losses occur whenexcess lubricant is forced out of themeshing zone in a vertical and/orhorizontal direction. They areintensified with an increasing nomi-nal viscosity of the lubricant.

Injection losses

Injection losses are generally lowerthan churning losses in case ofsplash lubrication. They occur whenthe oil is forced off the tooth flanksand the injected oil is acceleratedand deflected. They depend on theinjected oil quantity, the oil viscosity,the tooth width and the wheel dia-meter. Injection losses are intensi-fied when these factors are in-creased, but are reduced when themodule is increased.

6.2.3 Bearing related power lossPVB

This type of loss mainly depends onthe type of bearing, mounting posi-tion, lubrication, speed and load.Rolling bearings generally producelower losses than plain bearings.

Rolling bearings

Bearing related power losses aremade up of a load related portion(PVB) and a portion not related to theload (PVB0). Load related losses arecaused by the elastic deformation of

6.2.1 Tooth-related power loss Pvz

This type of loss occurs due to thesliding movement of the meshingtooth flanks operating under load.The individual coefficient of frictionon the tooth flanks is of decisiveimportance.The tooth related power loss Pvzdepends on the meshing positionof the teeth.

Fig. 38: Total loss in a gear system brokendown by individual losses as afunction of the peripheral speed (v) –(standard tooth load: 100 N per mmof tooth width)

PV = PVZ+PVZ0 +PVB+PVB0+PVD+PVX

Industrialgears

0.2 to 0.5 1.0 to 2.8

PVZ

% of Pa

PV

% of PaType of gear

Worm drive

i = 5 i = 10 i = 70

4.0 to 9.07.0 to 1124 to 35

C 10223

bearing related loss

total losstooth related loss

overall loss underno-load conditions

v

2

%

1,6

1,2

0,8

0,4

0 4 8 12 16 m/s 20

6.2 Power loss in gear systems

The total power loss PV of a gearsystem is made up of variousindividual types of losses:

PV = total power loss

PVZ = tooth related power loss,under load

PVZ0 = tooth related power loss,no-load condition

PVB = bearing related power loss,under load

PVB0 = bearing related power loss,no-load condition

PVD = sealing related power loss,irrespective of load

PVX = other lossesirrespective of load

Tooth and bearing related powerlosses are divided into losses underload and under no-load conditions.

Fig. 38 shows that, with referenceto the overall power loss (Pv), thelosses under load decrease and theno-load losses increase with anincreasing peripheral speed. Thecurve shown below applies to gearsequipped with rolling bearings.

ζ

0.8

1.2

1.6

0.4

6.2.2 Tooth related power loss PVZ0

In splash lubricated gears this typeof power loss comprises the chur-ning and squeezing losses, and incase of gears lubricated by oil injec-tion it is equivalent to the injectionloss.

Churning losses

Churning losses occur while thegear teeth plunge into the oil sump.It is determined by the followingfactors:

– width, diameter of the addendumcircle and number of plunginggears

– shape of gear casing (clearancevolume, juts, etc.)

– depth of immersion

– peripheral speed of the plunginggears

– operating viscosity of the lubricant

Fig. 39: Variation of the sliding frictioncoefficient µg, the sliding speedvgand the standard tooth load Fbt onthe tooth flank and the distance ofaction A - E

A B C D E

100%

50%

0%

Fbt

C 10224

bearing related loss under load

tooth related loss under no-load conditions

µgvg

C

Table 7: Average values of tooth relatedlosses PVZ and total losses PV pergear stage. Pa = driving power

24


the rolling elements and the race-ways and by sliding movements atthe points of contact. Losses notrelated to the load occur due to thesliding friction between the cage,the rolling elements and the guide-ways, and because there are hydro-dynamic losses in the lubricating oil.They depend on the lubricant’sviscosity and quantity as well as theaverage peripheral speed of thegear.

It is known from experience thatthe power loss per rolling bearingamounts to approx. 0.1 % of thegear’s efficiency.

Plain bearings

Losses in plain bearings are inten-sified with an increasing load.

Power losses are relatively high atlow speeds. In the mixed frictionregime they decrease with an in-creasing sliding speed, whereasunder fluid friction conditions theyincrease with an increasing speed.

The average power loss of standardplain bearings is approx. 0.5 to 1.5 %of the nominal efficiency and in caseof high performance bearingsapprox. 0.1 to 0.3 %.

6.2.4 Sealing related power loss P VD

These losses mainly depend on thetype of sealing. With respect to thetotal power losses they are relativelylow in case of non-rubbing seals.However, they play a more importantrole in case of rubbing seals.If radial shaft seals are used, sealingrelated losses increase with a largershaft diameter and with a higherperipheral speed at the sealing lip.The average loss is between 0.01and 0.04 kW per radial shaft seal.

Fig. 42: Shaft-mounted spur gearFig. 41: Three-stage straight bevel gear driving a stone crusher, VOITH F 10244

C 10225A4 10206

6.2.5 Other losses P VX

These include losses caused byfreewheels, couplings, oil pumpsand fans.

The average oil pump loss isbetween 0.15 % (large gears) and1 % (small gears) in relation to thenominal output.

Fan losses usually are below 0.5 %.

Fig. 40: Three-stage spur/bevel/spur gear motor, oil lubricatedSEW-EURODRIVE GmbH & Co, D-76646 Bruchsal

F 10251

25


This means that the total power lossPV is the same as the thermal lossQV dissipated via the casing surfaceto the environment.

6.3.1 Heat dissipation

Most of the heat generated by thepower losses is dissipated from thefriction points via the lubricating oiland transferred to the environmentthrough the gear casing. Only asmall share of the heat is dissipatedthrough the connected shafts andfoundations.

The gear casing dissipates heat tothe environment by way of convec-tion (the casing surface is cooled byair flowing past) and thermal radia-tion.

The thermal capacity of a gearsystem, i.e. to what extent wasteheat can be dissipated by way ofconvection and thermal radiation,is determined by

toil [°C] QV increased by ≈ [%]

100 14.7

110 29.4

120 44.1

PV = QV

.

the heat transmission coefficient α,the casing surface area A,

and

the temperature difference betweenthe oil bath and the ambient air(toil – tL)

QV = α · A (toil - tL).

A gear’s thermal capacity can alsobe increased by means of additionalcooling (fan, fan + oil cooler) or byreducing the ambient temperature(ventilation).

6.4 Temperatures in gearsystems

Heating of a gear system, individualgears, bearings and lubricants isone of the most important criteria toevaluate gear’s performance. Theexisting temperatures are indicativeof the power losses. Fig. 43 showsthe characteristic temperatures in agear system.

A4 10132

A

B

C

D

Fig. 43: Characteristic temperatures in a gear system

6.3 Heating of gear systems

The power losses produced in thefriction points between the teeth,bearings and seals result in exces-sive heat that has an impact on thegears and the lubricating oil.

The gears may be heated additio-nally by the sun or heat dissipatedfrom the motor. Heating occurs untilenough heat is exchanged with thesurrounding elements to reach athermal balance. In most gear sys-tems heat is only dissipated via thecasing.

The following equation applies ifthere is a thermal balance betweenthe gear system and the ambientelements:

.

From this equation it can be deduc-ted that the amount of heat (Qv) thatcan be dissipated from the gear canbe increased by increasing the oilsump temperature. This also impliesthat it is possible to increase thetotal power loss (Pv) that can bebalanced and in consequence alsothe transferrable power.

Whether the oil sump temperaturecan be increased depends on thetype of oil and the temperature limit.Mineral hydrocarbon oils have arelatively low temperature limit andare therefore not suitable to in-crease a gear’s thermal capacity byincreasing the oil sump temperature.

Synthetic high temperature gear oilsare suitable for oil sump tempera-tures between 100 and 150 °C andtherefore make it possible to in-crease a gear’s efficiency conside-rably by increasing its thermal capa-city (Qv). See also section 7.2.2,page 36.

Example:Temperature limit of a standardmineral oil: approx. 90 °CSupposed ambient temperature:22 °C

Increase of thermal capacity afterconversion to a synthetic oil andincrease of the oil sump tempera-ture:

.

.

The various temperature levelshave a decisive impact on

– the ratio between fluid frictionand mixed friction,

– the formation of pittings on thetooth flanks,

– the degree of scuffing,– the lubricant ageing rate,– the bearing’s service life, and– the gear’s efficiency.

Power loss = Thermal capacity

.

A Temperature of the gear body(roughly corresponds to thetemperature of the tooth center)

B Various tooth flank temperatures

C Bearing temperature

D Oil sump temperature

26


Case hardened steel 180 to 300

Tempered steel > 200

Bronze > 200

Rolling bearings

Standard bearings 120

High temperature bearings 300

Plain bearings

Standard bearings 90

High temperature bearings 150

Shaft seals

Nitrilorubber 100

Polyacrylate rubber 125

Fluorinated rubber 150

Lubricating oil (oil sump)

Mineral oil 100

Synthetic oil 160

It is important to ensure that thepertinent temperature limits are notexceeded when the individual gearcomponents, the lubricant and theaccessories (filter inserts, pumps,etc) are heated.

Synthetic gear oils, which have aconsiderably higher temperaturelimit than mineral oils, are suitablefor high temperature lubrication(lubricant temperature > 100 °C)and make it possible to increase thethermal limit and, in consequence,the transferrable power.

The lubricant’s operating tempera-ture (defined by Klüber as the oilsump temperature or the tempera-ture of the injected oil) is a decisiveparameter when selecting a suitableviscosity.

Operating temperatures aboveaverage or temperature peaksindicate malfunctions or incipientdamage.

6.4.1 Tooth flank temperatures

Fig. 44 illustrates the temperaturestypically found on a tooth flank of astraight or helical spur or bevel gear.

Contact temperature t C

The contact temperature tC is theflank temperature existing duringthe meshing phase at the individualcontact points along the action dis-tance E-A. In contact point C it isequal to the gear body temperaturetM.

Integral temperature t int

The integral temperature t int is thetooth flank temperature calculatedfrom the contact temperature curvetC. Scuffing occurs if a critical inte-gral temperature (depending on thelubricant and the gear material) isexceeded.

Gear body temperature t M

The gear body temperature tM, alsoknown as the mass or tooth center

6.4.2 Temperature limits

The temperature limit is the tem-perature which a (gear) componentcan sustain without sufferingdamage.

The temperature limit of a gear isdetermined by the component (in-cluding the lubricant) most suscep-tible to high temperatures. In mine-ral oil lubricated gears this usually is

tC = contact temperature

tint = integral temperature

tM = gear body (mass)temperature

toil = oil temperature

Fig. 44: Temperatures typically found on a tooth flank

Temperaturelimit [°C]

Component

Gear wheels

temperature, roughly corresponds tothe tooth flank temperature beforemeshing occurs. It lies between theintegral temperature tint and the oiltemperature toil in the casing (oilsump); toil < tM < tint.The gear body temperature deter-mines the temperature of the lubri-cating oil and its operating viscositybefore reaching the lubrication gap,which, in turn, is decisive for thethickness of the oil film in the gap.

Oil temperature t oil

The oil temperature toil, also knownas the oil’s operating temperature,is equal to the oil sump temperaturein case of splash lubrication and tothe injection temperature in case ofoil injection lubrication.

The temperature along the actiondistance E-D in the lubrication gapbetween the meshing teeth roughlycorresponds to the gear body tem-perature tM. In the remaining actiondistance it is almost equal to thecontact temperature tC. This alsoapplies to the oil film temperature.

The various tooth flank tempera-tures explained above are importantfor the calculation of the load carry-ing capacity of the flanks. GfT work-sheet no. 2.4.2 illustrates the calcu-lation principle to obtain the perti-nent temperatures and scuffingresistance. This worksheet is basedon DIN 3990 which describes howto calculate the load carrying capa-city of spur and bevel gears.

AB

C D E

tCtint

tM

toil

Table 8: Approximate temperature limits

27


Oil sumptemperature °CType of gear

80 to 100

50 to 80

40 to 60

6.4.3 Oil temperatures (empirical values)

The permanent oil temperature inindustrial gears is between 40 and150 °C, depending on the type ofgear, the application and the lubri-cant (mineral /synthetic oil).

Apart from design related influences,oil temperatures mainly depend onthe existing operating temperatures.They rise with an increasing ambienttemperature and if the oil is exposedto thermal radiation. They fall whenthe gear is operated under partialload conditions or intermittently.

the lubricating oil, which has a muchlower temperature limit than theother gear components.

Gear lubrication with a synthetic oilmakes it possible to increase geartemperatures by 20 to 30 °C whileensuring the same oil life than witha mineral oil.

This can increase the gear’s ther-mal capacity and the transferrablepower, provided the temperaturelimit of other components, materialsand substances is not below theoil’s operating temperature. In sucha case it might be necessary toreplace them with components witha higher thermal resistance.

This also applies to all componentsin contact with the gear oil but notlisted in table 8, such as filter inserts,hoses, inspection glasses andcouplings.

The temperature limit of the respec-tive lubricating oil also has to betaken into account!

F 10253

A permanent oil sumptemperature of 80 °C

should not be exceededif mineral gear oils are used.

Table 9: Permanent oil sump temperatures(empirical values) if a mineral oil isused. The lower values pertain toan ambient temperature of approx.20 °C, the higher values to highambient or room temperatures.

Splash lubrication

Worm gears

Spur and bevel gears

Force-fed lubrication

Gears equipped withrolling bearings

Gears equipped withplain bearings

Fig. 45: Two-stage spur/worm gear motor,oil lubricated, SEW-EURODRIVEGmbH & Co, D-76646 Bruchsal,Germany

28


7 Lubricants for stationary gear systems

7.1 Tasks, requirements

Lubricants for gear systems havethe following general tasks:

● transfer forces

● minimize wear

● reduce friction

Fluid lubricants also have to

● dissipate heat

and

● remove abrasive particles

Depending on the type of gear andthe operating conditions gear lubri-cants have to meet various require-ments, some of them even conflict-ing. There is no universal gear lubri-cant which would meet all require-ments. Instead there are differenttypes of gear lubricants, such asgear oil, greases and adhesive lubri-cants, whose properties have to suitthe individual operating conditions.

Gear oils may have to meet thefollowing requirements:

● excellent resistance to ageingand oxidation

● low foaming tendency

● good air separation behaviour

● good load carrying capacity

● neutrality towards the materialsinvolved (ferrous and nonferrousmetals, seals, paints)

● suitability for high and/or lowtemperatures

● good viscosity-temperaturebehaviour

Gear greases , in contrast, may berequired to ensure

● good adhesion

● low oil separation

● low starting torques

● compatibility with syntheticmaterials

● noise damping Fig. 46: Schematic drawing of multi-stage spur gears

Adhesive lubricants , e.g. for thelubrication of large open gear drives,have to meet the following require-ments:

● excellent adhesion

● optimum separating and lubrica-ting capacity under mixed frictionconditions

● good emergency running proper-ties in case of starved lubrication

● good pumping characteristics inautomatic spraying equipment

The natural properties of the startingmaterials, mineral or synthetic oilsor a mixture of both, usually are notsufficient to meet all the require-ments listed above. The base oilsare therefore equipped with addi-tives improving their natural proper-ties or imparting new properties.

The type and quantity of additivesdepends on the intended use andthe type of lubricant. In case of geargreases not only the additives butalso the thickening agents have animpact on the lubricant’s properties.

A4 10207 C 10227

▼

▼

▼

▼▼

▼

two-stagespur gear

three-stagespur gear

four-stagespur gear

29


as worm gears. CLP lubricating oilsare not suitable for bevel gears withoffset axis (hypoid gears) unlessthey contain specific EP additives.Hypoid gears are usually lubricatedwith special oils with enhanced EPadditives, so-called "HYP" oils(DIN 51 502).

DIN 51 517, Pt. 3 specifies theminimum requirements for lubri-cating oils containing antiwear addi-tives. It stipulates, among others, ascuffing load capacity of 12 in themechanical test on the FZG test rigin acc. with DIN 51 534, Pt. 2(FZG = Forschungsstelle für Zahn-rad- und Getriebebau, TU München– Technical Institute for the Study ofGears and Drive Systems of theMunich Technical University).

Multi-purpose oils

Such oils are not only suitable forthe lubrication of gear systems butalso for other machine components(clutches, backstops, etc.). They areoften used as a working mediumtransferring power in turbines,electric current transformers andhydraulic systems.

Multi-purpose oils are used inmachine tools equipped with onlyone circulation system for gearsystems and hydraulic units, or forthe lubrication and feedback controlof steam and gas turbines whilesimultaneously supplying connec-ted machines and gear systems.

They are also suitable for productstreamlining purposes if, forexample, one lubricating oil is to beused in various components in alarger system, provided it meets allthe different quality and viscosityrequirements.

Mineral multi-purpose oils include:

Just like type "C" oils, lubricating oilstype "CL" are not very important forgear lubrication.

CLP lubricating oils DIN 51 517

These are mineral oils containingadditives to improve corrosion pro-tection and ageing resistance ("L")plus additives to minimize wearunder mixed friction conditions ("P").

They are recommended if improvedwear protection is required becausethe friction point (meshing zone) issubject to increased load and/or iftooth flank damage (scuffing) shouldbe prevented in case of overloading.This type of oil is frequently used inindustrial gear systems.

The pertinent antiwear additives areclassified in two categories: addi-tives improving lubricity and EPadditives. Additives improving lubri-city are also called "polar additives".They enhance the base oil’s wettingand adhesion properties by meansof solid organic (animal or vege-table) or synthetic particles whichseparate the contact points byforming an adhesive, semi-solid,pressure resistant film, thus redu-cing friction and wear.

EP (extreme pressure) additives areused for increased wear protection.They mainly consist of organicphosphorous and sulfur compoundshaving a chemical impact on thelubricant.

When subject to increased tempera-tures these compounds form aprotective layer on the tooth flankswhich reduces metal contactsbetween the flank surfaces, preventswelding and scoring and minimizesfriction.

A combination of EP and lubricityenhancing additives is often used tomake a lubricating oil suitable formany types of gears including gearswith a high sliding percentage, such

7.2 Types of gear lubricants

7.2.1 Gear oil with a hydrocarbon base oil

Mineral oil lubricants are widelyused in closed industrial gears.

Paraffin base solvent raffinates areoften used as the standard base oilfor the various lubricant types.These raffinates are called plainmineral oils or simply "lubricatingoils ".

Plain mineral oils (in acc. with DIN51 517, Pt 1, lubricating oils "C")are no longer important for thelubrication of gear systems. Theyare only used if the requirements interms of ageing resistance, corro-sion and wear protection are verylow.Plain gear oils were largely re-placed by additive treated oils, i.e.mineral oils containing oil solubleadditives enhancing their propertiesand/or imparting new ones.

Depending on the additive types,a distinction is made between thefollowing gear oils:

CL lubricating oils DIN 51 517

These are mineral oils containingadditives to improve corrosionprotection and ageing resistance("L"). In accordance with the abovestandard they are recommended ifcorrosion may occur, for exampledue to the impact of water, or if oilsof the "C" type (plain mineral oils)would fail to achieve a sufficientservice life at increased tempera-tures.

CL lubricating oils do not containantiwear additives and are thereforemainly used in older gears subjectto low loads, with a peripheral speedbelow 30 m/s, which are equippedwith hardened and tempered gearwheels and are particularly resistantto fatigue.

30


Lubricating and control oils L-TDDIN 51 515

Turbine oils with a mineral base oilplus additives improving corrosionprotection and ageing resistance.They are used for the lubricationand/or feedback control of steamturbines, stationary gas turbines,machines operated electrically orby steam turbines, e.g. generators,compressors, pumps and gearsystems.

Hydraulic oils HLDIN 51 524, Pt. 1

Pressure fluids based on mineral oilplus additives enhancing corrosionprotection and ageing resistance.They are used to simultaneouslysupply hydraulic units and gearsystems.

F 10246

Fig. 47: Shaft-mounted gear motor with three-stage spur gears, make Getriebebau Nord, D-22941 Bargteheide, Germany

Hydraulic oils HLPDIN 51 524, Pt. 2

Pressure fluids based on mineral oilplus additives improving corrosionprotection and ageing resistanceand reducing fretting corrosionunder mixed friction conditions.They are used to simultaneouslysupply hydraulic units and gearsystems subject to high wear.

31


Possible disadvantages include:

● higher price

● reaction in the presence of water(hydrolysis, corrosion)

● material compatibility problems(paints, elastomers, certainmetals)

● limited miscibility with mineral oils

Application related advantagesusually prevail, so that syntheticlubricants will be increasingly usedfor gear lubrication, especiallyunder critical operating conditions.

Synthetic lubricants based on

synthetic hydrocarbon oils (SHCs),

polyglycols (PGs) and

ester oils (Es)

have proven particularly efficient ingear systems.

Lubricating oils based on synthetic hydrocarbon oils

They are similar to mineral hydro-carbons in their chemical structure.

They are equal to mineral oils as faras their compatibility with sealingmaterials, disposal, reprocessingand miscibility with mineral oils areconcerned. Their main advantage istheir excellent low temperaturebehaviour.

It is possible to manufacture foodgrade lubricants for the foodprocessing and pharmaceuticalindustries with SHC base oils andspecial additives.

7.2.2 Gear oils with a synthetic base oil

Synthetic gear oils are used when-ever mineral gear oils have reachedtheir performance limit and can nolonger meet the requirements, e.g.at very low or high temperatures,extremely high loads, extraordinaryambient conditions, or if they fail tomeet special requirements, e.g. interms of flammability.

Even though many properties ofmineral oils can be improved bymeans of additives, it is not possibleto exert an unlimited influence on alltheir properties. This applies espe-cially to material properties depen-ding on the chemical structure, suchas

● thermal resistance

● low temperature properties(fluidity, pour point)

● flash point

● evaporation losses

Synthetic oils provide a number ofadvantages. However, they do notnecessarily outperform mineral oilsin all respects and may even resultin some drawbacks despite theiradvantages.

The advantages of synthetic lubri-cating oils (depending on the baseoil) include:

● improved thermal and oxidationresistance

● improved viscosity-temperaturebehaviour, higher viscosity index

● improved low temperatureproperties

● lower evaporation losses

● reduced flammability

● improved lubricity

● lower tendency to form residues

● improved resistance to ambientmedia

Lubricating oils based on polyglycols

These lubricants ensure especiallylow friction coefficients, whichmakes them suitable for gears witha high sliding percentage (worm andhypoid gears).

Containing appropriate additives,they have an excellent antiweareffect, for example in steel/bronzeworm gears, and a very goodpressure absorption capacity.

Polyglycol oils may have a negativeimpact on sealing materials andmay dissolve paints. At operatingtemperatures above 100 °C onlyseals made of fluorinated rubber orPTFE are resistant, below that alsoseals made of NBR are resistant toPG oils.

This information is only a guideline.Before using PG oils in seriesapplications it is important to testcompatibility with paints, seals andinspection glass materials.

Miscibility with mineral oils is verylimited; mixtures should thereforebe avoided.

Polyglycols are neutral towardsferrous metals and almost all non-ferrous metals. In the case of frictionpairings with one component con-sisting of aluminum or aluminumalloys (e.g. rolling bearing cagescontaining aluminum) there may beincreased wear under dynamic load(sliding movement and high load).In such cases we recommendcarrying out compatibility tests.

32


Lubricating oils based on ester oils

Ester oils are the result of a reactionof acids and alcohols with waterbeing split off. They exist in nume-rous structures, all of them havingan impact on the chemical andphysical properties of lubricants.

In the past these lubricating oilswere mainly used in aviation tech-nology for the lubrication of aircraftengines and turbines as well asgear systems in pumps, starters,etc.

Ester oils have a high thermalresistance and excellent low tem-perature behavior. In industrialapplications rapidly biodegradableester oils will gain importancebecause it seems possible toachieve the same efficiency aswith polyglycol oils by selecting anappropriate ester base oil.

Application related advantages of synthetic lubricating oils

The following application relatedadvantages result from the improvedproperties of synthetic lubricatingoils as compared to mineral oils:

● improved efficiency due toreduced tooth related frictionlosses

● lower gearing losses due toreduced friction, thus less energyrequired

● oil change intervals 3 to 5 timesas long as compared to mineraloils operating under the sametemperature

● reduced operating temperaturesunder full load, thus increasedcomponent life; cooling devicesmay not be required.

The data were gathered empiricallyin many tests conducted on Klüber’sgear test rig. These results havebeen confirmed by gear manufac-turers and operators.

Advantages of synthetic gear oilsbased on reduced friction

Increased gear efficiency

● Smaller gears with smallermotors sufficient for equivalentoutput

● Higher output with the samepower input

Reduced oil temperatures

● Extension of the oil's life (5 timeslonger than mineral oils)

● Extended component life

● Cooling units may no longer berequired

Reduced energy consumption

● Reduced costs for lost electriccurrent due to lower total losses;30 % and more in the case ofworm gears

● Costs for electric power reducedup to 10 % due to improvedefficiency

30 % and more 20 % and more

up to 1 %15 % and more

20 °C and more up to 12 °C

Worm gears,Hypoid gears

Spur gearsBevel gears with axis not offset

Table 10: Potential reduction of gearing losses and improvement of efficiency if a syntheticgear oil is used instead of a mineral oil.

Type of gear

Reduction of gearing losses andefficiency improvement

Owing to their special molecularstructure, synthetic lubricating oilsbased on polyalphaolefins andpolyglycols ensure that tooth relatedfriction is considerably lower thanwith mineral oils. It may be up to30 % lower than if a regular mineralgear oil with EP additives were used.

As the friction coefficient of syntheticoils is lower, tooth related friction isreduced to a large extent, thusincreasing the gear’s efficiency.

The efficiency of gears with a highsliding percentage, worm andhypoid gears, may be increasedup to 15 % if a synthetic oil is usedinstead of a mineral oil. Even incase of spur and bevel gears, whichalready have a high degree of effi-ciency, it is possible to achieve anincrease of up to 1 % by using asynthetic gear oil. This may notseem very much at first sight, but itmay result in considerable costsavings depending on the nominaloutput of a gear or if several gearsare concerned.

Table 10 shows to what extent syn-thetic gear oils can reduce losses,especially in gear systems with ahigh share of load dependent losses.

Reduction of totallosses

Reduction of operating(steady-state) tempera-ture

Improved efficiency

Effect

33


The following test results andcalculation examples illustrate theadvantages of synthetic gear oilsover mineral oils.

Improved efficiency andreduced wear when usingsynthetic oils

Synthetic gear oils can reducepower losses and operating tem-peratures in almost any gear typeand thus increase gear efficiency.This applies particularly to gearswith high or predominant slidingpercentages (hypoid and wormgears) if oils on a polyglycol basisare used.

Previously it was assumed that theefficiency of spur and bevel gearscould be increased up to 1 % andthat of worm gears up to 10 % byusing synthetic gear oils.

Tests comparing high grade CLPoils and modern synthetic gear oils,however, prove that the efficiencyof spur, bevel and worm gears canbe increased far beyond the valuesstated above.

Such tests were carried out withKlüber gear oils on our in-housetest rig for worm gears.

The results show clearly that syn-thetic oils make the gears moreefficient than mineral oils.

Klübersynth GH 6 , a polyglycollubricating oil, resulted in the high-est degree of efficiency: 18 % morethan with Klüberoil GEM 1 , a highperformance CLP oil. This provesonce again that PG oils are particu-larly suitable for the lubrication ofworm gears.

Klübersynth GEM 4 andKlüberoil 4 UH 1 , two SHC gearoils, also made the test gears 8 to9 % more efficient. The performanceof Klüberoil 4 UH 1, which is author-ized as a food grade lubricant in

accordance with USDA-H1, is ex-cellent. Food grade lubricants areoften thought to be inferior to"normal" lubricants as far as theirperformance is concerned, anopinion which the test resultsdefinitely disprove.

The results are also confirmed byvery positive practical experience inall sectors of the food processingand pharmaceutical industries.

Synthetic base oils already have anexcellent wear protection behaviourwhich is even enhanced by appro-priate antiwear additives containedin Klüber lubricants.

The diagrams in Fig. 48 show thatthe antiwear behavior of syntheticlubricating oils is superior to that ofmineral gear oils.

Wear was particularly low whenKlübersynth GH 6 was used.

All this is convincing proof that PGbase gear oils containing specificadditives are most suitable for thelubrication of gears with a highsliding percentage, especiallyworm gears.

Fig. 48: Test diagrams a) Efficiency b) Wear

Test oils

Klüberoil GEM 1 - 460 (mineral oil)

Klüberoil 4 UH1 - 460 (SHC oil)Food grade lubricant

Klübersynth GEM 4 - 460 (SHC oil)

Klübersynth GH 6 - 460 (PG oil)

Test gear

Standard worm geari = 1 : 39 center distance a = 63 mmWorm shaft: steel 16 Mn Cr S5Worm wheel: GZ - Cu Sn12 Ni

Test conditionsInput speed: 350 rpmOutput speed: 300 NmTest duration: 300 h

Wea

r [µ

m]

b)

Test results: Wear

Klüberoil GEM 1 - 460 ... 225 µm

Klüberoil 4 UH 1 - 460 ... 142 µm

Klüberoil GEM 4 - 460 ..... 40 µm

Klübersynth GH 6 - 460 .... 2 µm

Mineralöl

Klübersynth GEM 4-460

Klüberoil 4 UH 1-460

Klübersynth GH 6-460

0 50 100 150 200 250 300

100

95

90

85

80

75

70

65

60

55

50

Laufzeit [h]

250

200

150

100

50

0

Laufzeit [h]

Mineralöl

Klüberoil 4 UH 1-460

Klübersynth GH 6-460

Klübersynth GEM 4-460

0 50 100 150 200 250 300

Effi

cien

cy [

%]

Running time [h]

Mineral oil

Mineral oil

Running time [h] C 10228 a+b

Test results: Efficiency

Klüberoil GEM 1 - 460 ...... 60 %

Klüberoil 4 UH 1 - 460 ...... 69 %

Klüberoil GEM 4 - 460 ...... 68 %

Klübersynth GH 6 - 460 ... 78 %

a)

34


Fig. 49: Approximate oil change intervals in gears with oil sump lubrication. Comparison ofsynthetic oils Klübersynth GEM 4 (SHC oil) and Klübersynth GH 6 (PG oil) withKlüberoil GEM 1 (mineral oil)

Klüberoil GEM 1-460 800 op. hours

Klübersynth GEM 4-460 7,500 op. hours

Klübersynth GH 6-460 approx. 25,000 op. hours

The life extension factors of syn-thetic oils as compared to mineraloil are as follows:

GEM 4 (SHC oil) / GEM 1 (min. oil):approx. 9.4

GH 6 (PG oil) / GEM 1 (min. oil):approx. 31

These test results indicate quiteclearly that a synthetic gear oilreduces the oil sump temperaturedrastically. It is also obvious thatKlübersynth GH 6, a polyglycolgear oil, is particularly suitable forthe lubrication of worm gears. Thisoil allows especially long oil changeintervals, or even lifetime lubrication.

Klüber gear oils on a PG basis, e.g.SYNTHESO D...EP, are also suit-able for the lubrication of hypoidgears which are mainly used inautomotive transmissions. Hypoidgears are increasingly used inindustrial applications because oftheir advantages over bevel gears(see section 2.1) and becauselubrication is quite simple.

shaft casing sump ambient area

For data on test gears and conditions seebox on page 33

Klübersynth GEM 4 - 460

Klübersynth GH 6 - 460

Klüberoil GEM 1 - 460

Synthetic oils have a lower gearrelated friction coefficient thanmineral oils (up to 30 % lower) anda more favorable viscosity-tempera-ture behaviour. This generally per-mits the use of an oil of a lowerviscosity grade and makes it pos-sible to reduce the oil temperature.

The extension factors for oil changeintervals of synthetic oils are longerthan the values stated above, whichrefer to an identical oil temperature.

The following comparison of testresults illustrates this advantage.

Three high-performance Klüberlubricants were tested in a splashlubricated worm gear mounted onan in-house test rig.

Results and evaluation

The test records (Fig. 50) show thefollowing oil sump temperaturesafter 300 operating hours:

Klüberoil GEM 1-460 ............110 °C

Klübersynth GEM 4-460 ........ 90 °C

Klübersynth GH 6-460 ........... 75 °C

Based on these results the diagramin Fig. 49 indicates the followingapproximate oil change intervals: Fig. 50: Gear temperatures

30000

0

5000

10000

15000

20000

25000

80 90 100 110 120 130 140 150 160

Oil sump temperature [°C]

Oil

chan

ge in

terv

als

[h]

Mineral oil

SHC oil

PG oil

C 10229

running hours [h]

C 10230 a-c

110

90

75

Extended oil change intervalsusing synthetic oils

Synthetic oils have a much betterresistance to ageing and hightemperatures and a longer servicelife than mineral oils.

Depending on the base oil (SHC orPG), the oil change intervals are3 to 5 times longer at the same oiltemperature.

running hours [h]

running hours [h]

Approximate oil change intervals at an oiltemperature of 80 °C:

Mineral oil: 5 000 operating hours

SHC oil: 15 000 op.h. (extension factor 3)

PG oil: 25 000 op.h. (extension factor 5)

35


Pv A

Pv B( ) · 100 [%] = 1 –( 21

30)· 100 = 30 %

With a synthetic oil the reduction of friction results in power losses Pv of only 21 kW. In consequence:

The reduced power input saves the following energy costs:

Assumption: 5 worm gears, 2-shift operation (4000 operating hours per year), electric energy costDEM 0.23/kWh, reduced power input: 5 x 11.4 = 57 kW

Calculation: 57 kW x 4000 hrs x DEM 0.23/kWh = DEM 52,440 less per year

Advantages of a synthetic gear oil based on increased gear efficiency:

● Higher power output Pb – increase from 70 to 79 kW with the same input Pa = 100 kW.

= increased efficiency of 13 % (see chart B1), or

● Reduced power input Pa with the predefined output of Pb = 70 kW

Pb 70 = 88.6 kW Reduction of power input of 11.4 kW (see chart B2).Pa =

η =0.79

▲ ▲

▲

Pv

PbPa

= 1

00 k

W

30 k

W70

kW

▲

▲

Pv

Pb

▲

▲

▲

79 k

W

▲

21 k

W

Pb

▲

70 k

W

123456789012312345678901231234567890123123456789012312345678901231234567890123

▲

▲

▲

Pv

18.6

kW

Pa

= 8

8.6

kW

▲

▲

∆ Pv = 9 kW

∆ Pa = 11.4 kW

▲

▲

A B1 B2▲

▲

21= 1 –( )·100 = 79 %

100ηB100

30= 1 –( )·100 = 70 %ηA

1 –Reduced overall power loss: ∆Pv =

Increased efficiency:

AWorm gear lubricated with a mineral oil

Power input Pa = 100 kW

Power output Pb = 70 kW

Power loss Pv = Pa - Pb = 100 - 70 = 30 kW

BWorm gear lubricated with a synthetic oil

Power input Pa = 100 kW

Power output Pb = 79 kW

Power loss Pv = Pa - Pb = 100 - 79 = 21 kW

Efficiency η ( ) ·100 [%]Pv

= 1 –Pa

∆η = ηB – ηA = 79 – 70 = 9 %

How to save energy costs by using a synthetic lubricating oil, calculation example

36


High temperature lubrication with synthetic oils

Synthetic gear oils are much moreresistant to high temperatures andageing than mineral gear oils, whichmakes it possible to increase thethermal load limit of gear systemsand their overall performance.

The term "thermal load limit" refersto a gear’s power output at a tem-perature at which even the leaststressed component and the lubri-cant will not suffer any damage.Many gear systems are still lubri-cated with a mineral oil, a factwhich limits the maximum tempera-ture and thus a gear’s output. Table11 shows that mineral oil has one ofthe lowest temperature limits of allgear components.

The temperature limit of syntheticgear oils is much higher than that ofmineral oils. The gear temperaturecan therefore be increased by 20 to30 % while still achieving the sameoil life. The thermal load limit and thetransferrable power are increasedaccordingly.

This, however, is only feasible if thetemperature limit of all other ele-ments and materials used in a gearsystem is not below the limit of thepertinent synthetic oil.

If a mineral oil is used, the mecha-nical capacity (nominal output) ofsplash lubricated standard gears isgenerally higher than its thermalload limit. This difference indicatesto what extent the gear’s perfor-mance could be enhanced by in-creasing the thermal load limit.

The thermal limit can be increasedby installing additional cooling units(fans, internal coolers, etc.) or byapplying a synthetic, high tempera-ture lubricating oil (permanent oilsump temperatures between 100and 150 °C), which in most cases isthe less expensive solution, espe-cially for gears that are alreadyoperating.

The following practice relatedexample shows how a synthetic,high temperature oil can increase agear’s thermal capacity while en-suring an extended lubricant life.

The synthetic oils of theKlübersynth GEM 4 andKlübersynth GH 6 series are parti-cularly suitable for high temperaturelubrication of gear systems.

Example

A standard single-stage splashlubricated spur gear is required todrive an axial fan without any addi-tional cooling units.

Operating conditions:

Electric motor Pa = 100 kW

Driven machine(axial fan) Pe = 96 kW

Motor speed 1500 rpm

Fan speed 425 rpm

Nominal transmission ratioiN = 3.55

Operating time 24 h / day

Starts per hour 5

Ambient temperature 20 °C

1. Determination of the gear'snominal capacity

PN = Pe x c

(c = machine output correctionfactor, to be determined as speci-fied by the gear manufacturer)

PN = 96 x 1.44 = 138 kW

2. Determination of the gear’sthermal capacity during opera-tion without additional cooling

Pth = Pe x cw

(cw = thermal factor depending onthe ambient temperature and theoperating time per hour, to bedetermined as specified by thegear manufacturer)

Pth = 96 x 1.0 = 96 kW

3. Selection of a suitable gear froma standard brochure

Based to the values PN und Pthcalculated above, a gear is requiredthat has a nominal capacity of295 kW and, without additionalcooling, a thermal load limit of105 kW when lubricated with a CLPgear oil which would be sufficient inview of the required thermal limit of96 kW (fig. 51).

However, the difference betweenthe nominal capacity of the standardgear (295 kW) and the requiredcapacity (138 kW) is too big, i.e. thegear is too large for the intendeduse.

A gear of the next smaller sizewould be sufficient as far as thenominal output (185 kW) is con-

Table 11: Temperature limit of componentsand lubricants used in gears

Component/Lubricant

Gear wheels

case-hardened steel 180 / 300

tempered steel > 200

bronze > 200

Rolling bearings

standard bearings 120

heat stabilizedbearings 300

Plain bearings

standard bearings 90

heat stabilizedbearings 150

Shaft seals

nitrile rubber 100

polyacrylate rubber 125

fluorinated rubber 150

Lubricating oil (oil bath)

mineral oil 100

synthetic oil 160

Temperaturelimit [°C]

37


Fig. 51: Excerpt from a gear brochure, VOITH TURBO

Ratio

iN

Speeds (rpm) n1 n2

Gear unit size

014 016 018

15001000

1500100075015001000750150010007501500100075015001000750

1340890

425280210375250187335220166300200150270180134

020 022

1400 *1000

700480380650450350560380290480340260420290220

025

920620550870600490820580460680480375580410310

028

1250860700

1230850660

1100800620

1000720550900610460

032

17001150920155011008301400102078013008807001150800620

036

280210

1259070

1107560856045755040704535

730500

390280220320220175270185150220145110200140105

1000 *680

510340270500330260380260200370260195300205160

Thermal limit capacities Pth (kW)

Gear unit size

Pth1

Pth2

Pth3

Pth4

014 016 018 020 022 025 028 032 036

63

100

162

199

86

131

208

253

105

167

245

307

129

206

288

365

162

259

366

436

201

321

437

557

251

402

516

667

329

536

737

934

411

657

879

1125

C 10231

Nom. power rating PN (kW)

410300

18513511016011085

1409575

1258665

1057555

500400

295200150230160115200140105160106851409075

cerned, but its thermal capacity of86 kW without additional cooling istoo low.

As additional cooling will not beprovided, this problem can only besolved by means of a synthetic, hightemperature lubricant with a highthermal capacity (permanent oilsump temperature between 100and 150 °C). The thermal capacityof standard gears with a mineral oillubricant is generally limited to100 °C (thermal limit of the oil) andcannot be increased without addi-tional cooling.

4. Determination of the anticipatedoil sump temperature and lubri-cant life when increasing thethermal load limit from 86 kW to96 kW by using a synthetic oil

4.1 Anticipated oil sumptemperature

The possible increase of the thermallimit and the transferrable power canbe deducted from the thermal capa-city equation Qv (see section 6.3.1,p. 25).

Qv = α · A · (t oil - t L)

whereby:

α = thermal transfer coefficient[W/m2 · K]

A = housing surface [m2]

toil = oil bath temperature [°C]

tL = ambient air temperature [°C]

To achieve the required thermal limitof 96 kW it is necessary to increasethe gear’s thermal limit (86 kW) by11.62 %, i.e. the thermal capacity(Qv) must also be increased by thesame amount.

With an oil bath temperature (toil) of100 °C and an ambient air tempera-ture (tL) of 20 °C the gear’s thermalcapacity is as follows:

Qv1 = 23·0.85·(100 – 20)

= 1564 W

W·m2·°C

m2·K

.

.

.

Qv1 increased by 11.62 %

Qv2 = 1746 W

By rearranging the Qv equation itis now possible to calculate the oilbath temperature expected afterincreasing the thermal limit from86 to 96 kW.

.

.

toil = + t L(α · A)

= + 2019.55

1746Qv2

.

= approx. 110 °C

.

This calculation did not take intoaccount that synthetic lubricating oilsreduce the friction losses occurringin gear systems up to 25 %, whichmeans that the permanent oil bathtemperature is expected to remainunder 110 °C during operation.

4.2 Determination of the lubricant’sservice life

The diagram in Fig. 49, page 34,shows that the service life of a syn-thetic gear oil at an oil bath tem-perature of 100 °C is twice(Klübersynth GEM 4) or approx.three times (Klübersynth GH 6) aslong as the life of a mineral oil at anoil sump temperature of 100 °C.

Assuming an identical service life,the oil sump temperature could beincreased to approx. 123 °C whenKlübersynth GH 6 is used insteadof a mineral oil.

It would therefore be possible toincrease the thermal limit of theselected gear by approx. 29 %from 86 kW to about 111 kW.

.

without cooling

with fan

with built-in cooler

with fan and built-incooler

Cooling required

1.12

3.55

4

4.5

5

5.6

* Additional injection lubrication required

38


Synthetic oils help to savemaintenance and disposalcosts

As compared to mineral oils, the oilchange intervals of synthetic oils areusually five times longer under thesame thermal conditions.

Despite the fact that the purchaseprice and the costs of disposal of asynthetic oil are higher than that ofa mineral oil, the extended oil

change intervals save purchase anddisposal costs when taking intoaccount the gear’s service life.

Table 12 shows a comparison ofthe costs for mineral and syntheticoils which proves that it is possibleto save a lot of money by using asynthetic oil while at the same timeconserving resources and reducingenvironmental impacts by reducinglubricant consumption.

Notes on high temperature lubrication

High-temperature lubrication, whichis possible with synthetic gear oils,is only feasible if the temperaturelimits of all other gear components,gear wheels, bearings, seals, filtersinserts, internal coatings, are notexceeded. It may be required toinstall new seals or replace otherheat sensitive components.

If standard gears are convertedfrom a mineral to a synthetic oil, itis indispensable to coordinate thisprocess with the gear manufacturerand the lubricant supplier.

Advantages of high temperaturelubrication with synthetic gear oils

● The thermal limit (Pth)of the gearsystem can be increased by upto 50 %.

● Due to the increased thermal limit(Pth) a gear with a smaller nomi-nal performance (PN) can beselected from a gear brochure toachieve the same output (seeexample calculation above),provided Pth < Pmech .

● In many cases additional coolingunits are not required.

● Future gears can be designedwith an increased performance(smaller gears with a higherpower transfer).

Table 12: Comparison of costs incurred when using a mineral and a synthetic oil

Synthetic oil(Klübersynth GH6 - 220)

Purchase price / l * DEM 7.30 DEM 11.90

Total costof DEM 7,665.00 DEM 2,499.00lubricant

Disposal costs DEM 157.50 DEM 210.00(DEM 15.00 /100 l) (DEM 100.00 /100 l)

Maintenance costs DEM 2,800.00 DEM 400.00( 2 hours à DEM (14 x DEM 200.00) (2 x DEM 200.00)100.00 per cycle)

Overall costs DEM 10,622.50 DEM 3,109.00

Cost savingswith a DEM 7,513.00synthetic oil

* Price per liter if a 200 l drum is purchased, as of May 1994

Filling quantity ( l ) 70 70

Oil change interval annually every 5 years

Gear life (years) 15 15

Amount of lubricantrequired ( l ) 1 050 210

Mineral oil(Klüberoil GEM1 - 220)

The above data is the basis of the following calculation:

39


7.2.3 Gear greases

Lubricating greases are used ingear systems instead of lubricatingoils if they are more suitable fortechnical or economical reasons,or if it is not possible to use a lubri-cating oil, for example in open gears,closed gears that are not oiltight,for safety reasons (leakages) ingears that are difficult to access,and wherever it is not possible toperform maintenance work orexchange the lubricant.

Fluid greases of NLGI 00 and 000(DIN 51 818) are typically used ingear systems, mainly for splashlubrication in gear motors.

Gear greases are widely used insmall and miniature gears, forexample in office machines, domes-tic appliances, DIY machines, powertools, automobiles, model toys, etc.

Greases with a higher consistency(NLGI 0, 1 and 2 ) are mainly usedin such gears because quite oftenthey are not oiltight or the toothflanks are only lubricated once.

Gear greases are selected in accor-dance with DIN 51 509, Pt. 2. Theminimum requirements thesegreases have to fulfill are listed inDIN 51 826, "lubricating greasestype G".

Gear greases, like lubricatinggreases in general, consist of amineral or synthetic base oil or amixture of both plus a thickeningagent.

The most common thickeningagents include metal soaps suchas aluminum, barium, calcium andlithium soaps, but also non-soapthickeners such as gels, polyureaand bentonite. Fig. 70 on page 63shows the general structure of alubricating grease.

The oils incorporated in the thicke-ners are similar to those in gear oils:raffinates, hydrocracking oils, syn-thetic hydrocarbons or polyglycols.Depending on the type and theconsistency of the grease, thethickener share is between 5 and25 %, i.e. the oil share prevails.

Synthetic base gear greases havethe same advantages as syntheticgear oils: reduction of friction losses,good low and high temperaturebehavior, high resistance to ageing,suitability for lifetime lubrication.

Additives are incorporated in thegreases in order to obtain specificproperties such as resistance toageing, corrosion protection, in-creased pressure absorption capa-city, wear protection, etc. Theirshare is up to 5 %.

The theory that soaps contained inlubricating greases are nothing buta carrier medium and have no lubri-cating effect has been disproved.The base oil and the thickener bothhave a lubricating function.

7.2.4 Adhesive lubricants

This type of lubricant is used onlarge open gears, e.g. the drives of

rotary kilns, cement mills, liftingcylinders, cranes, constructionmachinery, etc. They are called"gear greases type OG" in accor-dance with DIN 51 509, Pt. 2, andare divided into two categories:adhesive lubricants without bitumenand adhesive lubricants containingbitumen.

Klüber only manufactures highquality adhesive lubricants free frombitumen and solvents which aresuitable for many applications.

These lubricants are available for alltypes of lubrication and applicationmethods. Modern adhesive fluidsare used for splash and circulationlubrication, and grease type adhe-sive spray lubricants of NLGI 0 and00 are suitable for applicationthrough automatic spray systems.

Modern adhesive lubricants containEP additives to ensure optimumlubrication under mixed friction con-ditions (which are often found inlarge open drives), adhesion impro-vers to optimize adhesion on thetooth flanks and solid lubricantparticles to increase the load carry-ing capacity and improve emergencylubrication properties.

See also our brochure "Lubricationof large gear drives", 9.2 e.

F 10247

Fig. 52: Combined worm and spur gear unit with IEC-Motor, Rhein-Getriebe, Meerbusch, Germany

40


7.3 Standard requirements forgear lubricants

Gear lubricants have to fulfill anumber of standard requirements interms of application, composition,and lubrication properties which arechecked for compliance with thepertinent standard.

The standards’ purpose is to makelubricants of the same type inter-changeable.

Mineral oils with additivesenhancing resistance tocorrosion and ageing, andreducing wear under mixedfriction conditions.FZG scuffing load stage(A/8.3/90): at least 12

CLP lubricatingoils

DIN 51 517, Pt 3 Gears with high flankloads and/or a highsliding percentage;permanent oil bathtemperature up to100 °C

L - TD lubricatingand control oils

DIN 51 515, Pt 1 Mineral oil base turbine oilswith additives enhancingresistance against corrosionand ageing

Gears in steam and gasturbines

HL hydraulic oils DIN 51 524, Pt 1 Pressure fluids made ofmineral oils containing additi-ves to enhance resistanceagainst corrosion and ageing

HLP hydraulic oils DIN 51 524, Pt 2 Pressure fluids made ofmineral oils containing additi-ves to enhance resistanceagainst corrosion and ageingand to reduce wear.FZG scuffing load stage(A/8.3/90): at least 10

Combined application inhydraulic systems andgears

Combined application inhydraulic systems andgears subject to a highdegree of wear

Lubricatinggreases type G

DIN 51 526 Fluid to very soft greases ofNLGI grade 000 to 1, basedon mineral oil and/or syntheticoil plus thickener

Splash lubrication ofclosed gears, e.g. gearmotors, drum motors,actuators

Klüberoil GEM 1

LAMORA HLP

Table 13: Standard requirements for common gear greases

DIN standards only indicate theminimum requirements for gearlubricants. Modern products, espe-cially synthetic gear oils and greasesand most of the gear lubricantsoffered by Klüber, exceed theserequirements by far.

Similar to new technologies, newtypes of lubricants are only includedin standards if they have been usedsuccessfully for some time and havegained acceptance on a wide basis.

See product survey

p. 75-77: Greasesfor industrial gearsp. 78-82: Greasesfor small gears

State of the art lubrication techno-logy proves that lubricants havekept pace with the general techno-logical development and are wellahead of standardization.

Table 13 lists all gear lubricantsmeeting DIN requirements.

Standardizedlubricants

Requirements Type of lubricant Application Klüber lubricants

41


7.4 Properties of gear oils

Gear oil properties are determinedby the base oil (mixture) and theadditives and are described instandards, classifications andspecifications.

Individual properties are divided intoselection parameters and qualityparameters (see table 14).

Selection parameters include thoseproperties which are important forthe individual case of applicationbut do not provide any informationabout the oil’s quality or operationalproperties (e.g. viscosity).

Quality parameters, in contrast, areindicative of the service propertiesof a particular product.

The distinction between primary andsecondary properties does not indi-cate a qualitative graduation.

Instead, primary properties describethe gear related requirements suchas antiwear and antiscuffing beha-viour.

Secondary properties, on the otherhand, are important from a generalpoint of view. For example, it isimportant that the base oil and addi-tives contained in a specific gear oildo not attack the sealing material.

7.4.1 Viscosity

Gear oils change their flow behaviourdepending on temperature and pres-sure. Their viscosity1) decreaseswith a rising temperature andincreases with a rising pressure.

This crucial behaviour of gear oilsis therefore of primary importancewhen determining the requiredviscosity and selecting a suitabletype of oil (mineral, synthetic).

The impact of an oil’s viscosity ongear lubrication can be summarizedas follows:

Increased viscosity results in athicker lubricant film, thus improvingantiwear and damping behaviourand, to a certain extent, the oil’sscuffing load capacity.

If the viscosity is too high, in-creased churning and squeezinglosses result in excessive heat,especially at an increased periphe-ral speed. The operating viscositywill finally decrease.Decreased viscosity improves theflow behaviour at low temperatures,the air separation properties andidling losses.

If the viscosity is too low, mixedfriction conditions prevail and willresult in increased wear.

Viscosity-temperature behaviour

An oil’s viscosity-temperature (VT)behaviour describes the fact thatviscosity changes as a function ofthe existing temperature. It in-creases when the temperature rises.

The degree to which viscositychanges with the temperature variesfrom oil to oil. It depends on thebase oil (mineral or synthetic) andthe additives influencing (improving)the oil’s VT behaviour.

An oil’s VT behaviour is generallydepicted on an Ubbelohde VT chart.The coordinates were defined in away to make it possible to describethe VT characteristics of minerallubricating oils as a straight line.

Synthetic hydrocarbon base oils(SHC) also show a straight VT line,whereas PG (polyglycol) base oilsresult in a curve.

Fig. 53 on page 42 shows thegeneral viscosity temperaturecharacteristics of gear oils withdifferent base oils.

The flatter the VT line, the lessviscosity depends on temperature.The viscosity index (VI) generallydescribes the temperature-relatedchange of viscosity. It is calculatedaccording to DIN ISO 2909 and is adimensionless number.

Primary properties Secondary propertiesSelection

parameters

Quality parameters

Table 14: Gear oil properties

1)

Viscosity is the property of a fluid that en-ables it to resist the laminar shearing forces(deformation) of two adjacent layers (internalfriction, shear stress).DIN 1342, DIN 51 550, DIN ISO 3104Viscosity

Servicetemperaturerange

Friction behaviour

Viscosity/temperature behaviour

Antiwear behaviour

Antiscuffing behaviour

Running-in behaviour

High temperature behaviour

Low temperature behaviour

Chemical behaviour (corrosion,attack on nonferrous metals)

Thermal resistance(oxidation)

Foaming properties

42


Comparison of VIs:

Gear oils on the basis ofMineral oil VI approx. 85 to 100Synth. hydrocarbons VI approx. 130 to 160Polyglycols VI approx. 150 to 260

In practice a high viscosity indexmeans that a gear will start smoothlyunder low temperature conditionsand have only minimum powerlosses, or that a load bearing lubri-cant film is formed at increasedtemperatures that provides goodprotection against wear.

This comparison above shows thatsynthetic gear oils have a clearlyhigher viscosity index than mineralgear oils. In consequence, they alsohave a wider service temperaturerange. It is between approx. -50 and160 °C, depending on the base oiltype.

The service temperature of mineralgear oil ranges between approx.-20 and 100 °C.

Viscosity-pressure behaviour

A lubricating oil’s viscosity increaseswhen the pressure rises. Elasto-hydrodynamic processes occurring

The higher a gear oil’s viscosityindex, the smaller the change inviscosity depending on temperature,i.e. the wider its service temperaturerange.

Fig. 53: Viscosity-temperature curves of different types of gear oils

in the lubrication gap between theintermeshing flanks produce pres-sures up to 10,000 bar or more.This results in an increase of visco-sity that may be some powers of tenhigher than the initial viscosity of theoil under atmospheric pressure(Fig. 54).

Viscosity measurement

Viscosity is measured by meansof a viscometer. Viscometer typesinclude:

● capillary viscometer(kinematic viscosity)

● drop-ball viscometer(dynamic viscosity)

● rotational viscometer(dynamic viscosity)

Capillary and drop-ball viscometersare used for measurements above0 °C, rotational viscometers below0 °C.If the lubricant flows out of themeasuring equipment only due to itsown gravity, like in a capillary visco-meter, it is possible to determine thekinematic viscosity ν using the SIunit [mm2 · s-1].

Fig. 54: Pressure-temperature behaviour of a synthetic oil ISO VG 220 at 60 °C and 100 °C

The gear manufacturers’ instruc-tions, the lubricant manufacturers’product information leaflets andtechnical brochures, and the DINstandards almost exclusively con-tain information about a lubricants’kinematic viscosity.

If viscosity is measured by meansof additional parameters, e.g. drop-ping ball, pressure, torque, it ispossible to determine the dynamicviscosity η using the SI unit [MPa · s].

A lubricating oil’s kinematic viscosityν is obtained by dividing its dynamicviscosity η by its density ρ.

Viscosity units:

Kinematic viscosity

SI unit: m2 · s -1

Derived SI unit: mm2 · s -1

Conversion factor: 1 m2·s -1 = 10 6 mm2·s -1

Dynamic viscosity

SI unit: N · s · m-2 = Pa · s (Pascal second)

Derived SI unit: MPa · s

Conversion factor: 1 Pa · s = 103 MPa · s

= 60 °C Isotherme

= 100 °C Isotherme

1000 2000 3000 40000101

102

103

104

2

5

2

5

2

5

2

5

p [bar] →

� [M

Pa·

s] →

40 °C

Vis

cosi

ty →

123

Temperature → C 10232

C 10233

ν = η / ρ

1 Mineral oil2 Synthetic hydrocarbon oil3 Polyglycol oil

43


sive decomposition productsgenerated during ageing.

DIN 51 355 and DIN 51 385 de-scribe standardized tests to deter-mine an oil’s rust prevention ability.

Compatibility with nonferrous metals

Gear oils containing EP additives(to form boundary layers) must notreact with nonferrous metals, i.e.they must not lead to corrosion onsuch materials, especially on copperor copper alloys (bronze, brass),throughout the entire service life.Components made of nonferrousmetals are found, for example, inworm gears (bronze wheels), shut-off valves, cooling units (copperalloys).

According to the requirementsspecified in DIN 51 517 Pt 3, CLPlubrication oils must not be corrosiveon copper. The corrosion behaviourof lubricating oils on copper is testedin accordance with DIN 51 759(copper strip test).

All CLP and synthetic gear oilsoffered by Klüber comply with thisrequirement and are not corrosiveon copper.

7.4.5 Behaviour towards air

Gear oils should be able to separaterapidly from dispersed air and pre-vent the formation of stable surfacefoam. Foam is generated by airbubbles rising to the surface. Thebubbles should burst as quickly aspossible to keep the foam to aminimum.In case of splash lubrication atmedium to high peripheral speeds,the oil has a pronounced foamingtendency due to the air that is con-stantly introduced. Contaminantssuch as water, dust, corrosionparticles and ageing residues mayeven increase the foaming tendency.Foaming has a high negative impact

7.4.3 Behaviour in the mixed friction regime

Under mixed friction conditions, fluidand dry friction occurs on the inter-meshing tooth flanks. In order tominimize the effects of dry friction,scuffing and abrasive wear, it isimportant that the lubricating oilscontain antiwear additives preven-ting direct metal contact between thetooth flanks (boundary lubrication).

The effects of the additives aredescribed in section 7.2.1, page 29,"CL lubricating oils".

7.4.4 Anti-corrosion properties

Anti-corrosion properties are eva-luated from two points of view:

– corrosion protection on steel(rust prevention)

– corrosion protection on copper(compatibility with nonferrousmetals)

Rust prevention

If there is water in a gear system,either leakage or condensationwater, it will combine with ambientoxygen and lead to rust forming oninadequately protected steel sur-faces.

Wear is the result of corrosioncaused by rust particles containedin the oil that are returned to themeshing zone and the bearings,where they have an abrasive effect.

Rust also has a negative impacton an oil’s ageing resistance anddemulsification (water separation)properties, and may result in theformation of sludge.To enhance their rust preventionproperties, gear oils contain polarrust inhibitors forming a compactand protective, water repelling layer.Other additives neutralize the corro-

7.4.2 Ageing behaviour

External impacts continuouslychange an oil’s chemical structure,thus causing it to age. Changesmainly occur under high tempera-tures, when the oil mixes with air,and when it is in contact with metalcatalysts (e.g. copper, iron). Thespeed of the ageing process prima-rily depends on the oil’s structureand the amount and duration ofheat to which the oil is subject. Theageing process can be retarded bymeans of additives.

Contaminants like water, rust or dustalso have a negative impact on oilageing. Ageing is indicated by oildiscolorations, increased viscosity,formation of acids enhancing corro-sion, as well as residues in the formof lacquer, gum or sludge cloggingoil lines and filters.

Ageing also has a negative impacton the oil’s demulsifying and anti-foaming capacity, its anticorrosionand antiwear properties, and, to acertain extent, its air separationcapacity.

When using a mineral oil it must beensured that the permanent oil bathtemperature never exceeds 80 °Cbecause the ageing speed doubleswith every temperature increase by10 K. As compared to mineral oils,synthetic gear oils in similar appli-cations are much more resistant toageing. Depending on the oil type,oil change intervals can be 5 timesas long and service temperaturescan be increased (Fig. 49).

Even though there are a number ofageing tests, there is no generallyaccepted test method. One of themethods used to determine theageing properties of gear oils is laiddown in DIN 51 586 (CLP lubricatingoils).

44


on the lubricant’s properties, suchas oxidation, pressure absorptioncapacity, etc. Excessive foamingmay cause the foam to be forcedout of the breather vent; in case ofpressurized circulation lubricationthere is the danger of foam beingsucked into the oil pump.

The foaming tendency can bereduced by means of anti-foam (AF)additives. However, a too high con-centration may have a negativeimpact on the air separation capa-city.

The foaming tendency of a lubrica-tion oil is determined in accordancewith DIN E 51 566.

7.4.6 Cold flow behaviour

Depending on the base oil type,lubricating oils solidify at low tem-peratures due to their increasedviscosity (synthetic oils) or waxcrystallization (paraffin mineral oils).An oil’s pour point is indicative of itscold flow behaviour. The pour pointis the lowest temperature at whichthe oil still flows if it is cooled downunder specified test conditions. It isdetermined in accordance with DINISO 3016.

In order to ensure rapid and suffi-cient lubricant supply during a coldstart, the lowest temperature occur-ring in a gear (starting temperature)should always be several degreesabove the pour point.

Synthetic gear oils show a muchmore favorable cold flow behaviourthan mineral oils. Their pour point ismuch lower, sometimes even below-50 °C. Due to their high viscosityindex, synthetic oils are less viscousat lower temperatures than mineraloils with the same nominal viscosity.Their cold starting behaviour istherefore particularly good at verylow temperatures. Friction points inthe gear are supplied with lubricantmore rapidly, which makes oil pre-heating elements unnecessary. In

Klüberoil GEM 1-220(mineral oil)

Klübersynth GEM 4-220(Synthetic hydrocarbon/ester oil)

Klübersynth GH 6-220(PG oil)

Pour point

DIN ISO30 16

[°C]

Viscosityindex

DIN ISO29 09

approx.

< – 10

< – 40

< – 30

95

> 150

> 220

Product

addition, friction losses are reducedduring the heating phase which isoften very long.

7.4.7 Compatibility with elastomers (seals)

The term "elastomers" refers to anumber of different synthetic mate-rials used to manufacture rotaryshaft lip seals. When exposed tooperating temperatures, the gear oiland its additives must neither em-brittle nor soften the seals or impairtheir sealing effect. A certain amountof swelling is desired in order tocompensate for minimum wear ofthe sealing lips.

Gear oils must be compatible withshaft seals and all other nonmetalliccomponents installed in a gearsystem or in a connected oil circu-lation system. These componentsinclude flat, O-ring and moldedseals, sealing putty, rolling bearingcages, and filter inserts.

The nonmetallic materials must notrelease any particles into the gearoil which would change the oil’sproperties or have a negative effecton the gear’s performance.

The impact of a gear oil on a seal’sswelling behavior and Shore-A hard-ness are determined in accordancewith DIN 53 521 and DIN 53 505.

The extent to which a gear oil hasan impact on elastomers depends

on the oil’s composition and itsviscosity. Low viscosity promotesswelling, which, in turn, can resultin excessive seal wear. Sulfur addi-tives may lead to embrittlement andimpair the sealing effect.

With increasing oil temperatures theinteraction between the lubricatingoil and the seals intensifies.Table 16 gives a general survey ofthe compatibility of gear oils withvarious sealing materials.

Converting a gear from a mineralto a synthetic oil is often done toimprove performance at higheroperating temperatures.

Compabitility with the sealingmaterial, however, must also betaken into account. This pertainsespecially to the base oil type(SHC/PG oil) and the temperaturesoccurring at the sealing points.

220

220

ISO VG

DIN 51 519

220

Table 15: Comparison of approximate low-temperature values of a mineral gear oil andsynthetic gears oils (Klüber gear oils)

45


Sealing material

Mineral gearoils for indus-

trial gears

SHC baseoils

PG baseoils

Lubricating oil

ACM

VQM

NBR to 100 °C

to 125 °C

Compatible with all gear oils, but impact onair separation capacity

to 150 °CPTFE

Acrylonitrile-buta-diene-rubber,e.g. Buna-N

Acrylate rubber

Silicone rubber

Fluorinated rubber,e.g. Viton

Polytetrafluoro-ethylene

FKM to 150 °C

= compatible

= no or limited compatibility

= mineral oils suitable for sealing point only up to 125 °C

Table 16: Compatibility of gear oils with sealing materials, e.g. radial shaft lip seals

TypeAbbre-viation

Thermalresistance

to 125 °C

Legend:

7.4.8 Compatibility with interior coatings

Gear housings made of grey castiron or sheet steel are usuallycoated to protect them againstcorrosion during storage, transportor extended periods of standstill.Artificial resin primers are generallyresistant to mineral gear oils up toa temperature of 100 °C. However,they are not resistant at higher tem-peratures (> 100 °C) or to syntheticgear oils, especially those with a PGbase oil. The coatings may get soft,dissolve or form blisters and chip off,thus causing gear malfunctions ordamage by clogging oil lines, filtersand deaeration holes.

We recommend to have the paintmanufacturer carry out compatibilitytests prior to series applications.

7.4.9 Miscibility of different types of gear oils

Different mineral gear oils aremiscible with each other. However,we recommend to mix only such oilswhich meet the gear manufacturer’sinstructions in terms of quality andviscosity (observe collective lubri-cant charts).

Lubricants of different manufacturersgenerally vary in their composition(base oil, additives) and properties.Mixing such oils may therefore resultin quality impairment, for example, areduction of antiwear properties and/or viscosity-temperature behaviour.If possible, the same type of oilshould be used for refilling.

Mineral and synthetic gear oils arenot miscible or only to a certain ex-tent. Synthetic oils with a differentbase oil (PG/SHC) must not bemixed. The following is importantwhen changing from a mineral to asynthetic gear oil:

SHC gear oils

These gear oils (e.g. Klübersynthseries GEM 4) are miscible withmineral oil residues (up to approx.5 %) which cannot be removed bynormal draining and remain in thegear system (including the oil con-tainer and filter).

PG gear oils

These gear oils (e.g. Klübersynthseries GH 6) are neither misciblewith mineral oils nor synthetic HCoils. Before changing over to a PGoil the previous oil has to be re-moved completely by flushing thesystem with the new product. Filterinserts have to be changed. ThePG oil used for flushing must notbe used for lubrication purposes.It can, however, be re-used forflushing purposes. The gear shouldthen be filled with fresh oil.

Residual amounts of mineral orSHC oil (up to 5 %) in polyglycolare not problematic.

46


Fluid greases of NLGI grade 00 and000 are particularly suitable to lubri-cate the various stages of gearmotors.

Lubricating greases of NLGI 0, 1,and 2 are often used in small andminiature gears in office machines,domestic appliances, automotivegear motors, power tools, etc.

Lubrication with adhesivelubricants

Adhesive lubricants are mainlyused on the tooth flanks of open orencased gears (girth gear drives,open gear stages). State-of-the-artadhesive lubricants are high-perfor-mance specialty lubricants free frombitumen and solvents. They areavailable in the form of fluids (forsplash and circulation lubrication)or grease-like adhesive spray lubri-cants for application through auto-matic spray systems.

The main characteristics of modernadhesive lubricants are determinedby excellent EP additives, adhesionimprovers and solid lubricants en-hancing the load-carrying andemergency lubrication capacity.

Being a specialty lubricant manu-facturer, Klüber has developed asystematic lubrication method forlarge girth gear drives (tube mills,rotary kilns, etc.) known and appliedworldwide under the name "A-B-Clubrication ".

8.1.1 Notes on lubricantselection

Oil lubrication

Oil lubrication is preferred in closedgears because a fluid lubricant notonly lubricates the meshing teethbut also dissipates heat from thefriction points.

Another decisive edge: All otherfriction points in a gear system,such as rolling and plain bearings,seals, couplings, backstops, etc.can be lubricated with only one pro-duct. In individual cases, however,additional grease lubrication maybe required for the rolling bearings.

Lubrication with gear greases

Gear greases are only used in ex-ceptional cases and under certaindesign conditions, for example if itis not possible to change the lubri-cant on a regular basis (long-termor lifetime lubrication), or in closedgears that are not oiltight. Geargreases are frequently used insmall closed gears whose mountingposition is unknown or whose posi-tion changes during operation,because such gears are often notcompletely tight. Gear greases havea lower heat dissipation capacitythan oils, which makes them onlysuitable for low-performance gears.

The general peripheral speed limit is4 m/s. It is, however, possible to usefluid greases in gear motors up to20 m/s.

Fluid greases are only applied byway of splash lubrication supplyingboth the gear wheels and thebearing.

8 Selection of gear lubricants

Maximum operational securitythroughout a gear’s service life canonly be ensured if lubricants are notonly considered necessary ingre-dients but are taken into accountduring all design phases as integralstructural elements.

Lubricants should already be selec-ted in the initial design phase.Based on the gear’s performance,speed, ambient influences andoperating conditions (e.g. connec-tion to an oil circulation system), thefollowing parameters are important:

● type of lubricant

● application method

● viscosity and consistency

● lubricant quality

8.1 Selection of lubricant typeand application method

The selection of a suitable lubricanttype and application method de-pends on the type of gear and itsperipheral speed.

Table 17 shows correlations andmakes it possible to determineappropriate lubricants and appli-cation methods.

The indicated peripheral speeds areguide values that can be exceededif appropriate design measures aretaken, e.g. oil pockets, depots, baffleplates or cooling units. The decisiveselection parameter is the gearstage with the highest peripheralspeed.

47


to ≈ 20 immersion

from ≈ 20 to 250 spraying

Lubricating oil Gear grease (fluid grease) Adhesive lubricant(grease, fluid)

Peripheral Application speed method [m · s -1]

to 4 immersion

Spur and bevelgears

to 4 immersionWorm gears(immersing worm)

Worm gears(immersing wheel)

to ≈ 12 immersion

from ≈ 12 spraying in direction of action

to ≈ 8 immersion

from ≈ 8 spraying in direction of action

to 1 immersion

▼

Type of gear

_ _

Closed gear,oiltight

Closed gear,not oiltight

Open gear

Type of lubricant


to 2 manual

to ≈ 8 immersion or spraying

from ≈ 8 to 11 spraying


Table 17: Guide values to determine the lubricant type and application method depending on the type of gear and its peripheral speed.

▼

Type of gearsystem

▼

_ _

Fig. 55: Closed oiltight gear F 10248 Fig. 56: Closed gear, not oiltight (exposedminiature gear) F 10249

Fig. 57: Open gear (girth gear drive) F 10250

48


8.2 Determination of the required viscosity

8.2.1 Determination of theviscosity of minerallubricating oilsDIN 51 509

Due to the different kinematic con-ditions it is important to distinguishbetween spur and bevel gears onthe one hand and worm gears onthe other hand.

for spur and bevel gears for worm gears

= · KA ks / v T2

a3 · nsks / v =

Ft

b · d1· · Z

2· Z

2·KA v

u + 1

u H

ks / v = Force-speed factor [N · s /mm2 · m = MPa·s·m-1]

v = Peripheral speed on the reference circle [m· s-1]ks = Stribeck's rolling pressure [N /mm2]Ft = (Nominal) Peripheral force [N]b = Tooth width [mm]d1 = (Pitch) Reference circle diameter [mm]u = Gear ratio z2 / z1 (z2 > z1)ZH = Zone factor *

Ze = Contact ratio factor *

KA = Application factor **

ks / v = Force-speed factor[N·min /m2]

v = Peripheral speed [m·s-1]

T2 = Initial torque [Nm]

a = Center distance [m]

ns = Worm speed [min-1]KA = Application factor **

Calculation examples

Example 1:

Determination of the nominal kinematic viscosityrequired for a single-stage spur gear driving a fan

Operating conditions

Peripheral speedon the reference circle v = 4 m · s-1

(Nominal) Peripheral force Ft = 3 000 N

Tooth width b = 25 mm

(Pitch) Reference circle diameter d1 = 230 mm

Gear ration z2/z1 u = 2.5

Application factor KA = 1 (Table 21)

Drive motor Electric motor

ks = Ft

b · d1

u +1

u· · Z2 · Z2 · KA

Calculation of Stribeck's rolling pressure k s

Depending on the type of gear, thenominal kinematic viscosity is deter-mined in mm2 • s-1 at 40 °C (mid-point viscosity) as a function of theforce-speed factor (ks/v) by meansof the curves shown in fig. 58 and59.

They are based on practical gearlubrication experience. The force-speed factor (ks/v) takes into con-sideration the specific load on thegear. The indicated viscosities areguide values referring to an ambient

temperature of approx. 20 °C andan oil service temperature of 70 °C.

Viscosity values will differ in caseof other ambient temperatures andspecial operating conditions.

See also notes on page 50/51.

The power-speed factor is calcu-lated in accordance with thefollowing equations:

Calculation of the force-speed factor

e

[N/mm2]

* ZH and Ze are determined in accordance with DIN 3990 Pt 2.The following equation can be taken as the basis of a roughestimate: Z2 · Z2 ≈ 3

** Approximate values of the application factor KA are listedin table 21. This table as well as tables 22, 23 and 24were taken from DIN 3990 Pt6.

eH

H e

49


For a rough calculation of Stribeck's rollingpressure (except for hypoid gears) it is possibleto use the equation

Ze Z2 · Z2 = 3 as a base.

Fig. 59: Determination of the required viscosity for worm gears

N · s

mm2 · m

ks

v=

2.2

4= 0.55 MPa·s·m-1

Having calculated the force-speed factor, it is possibleto determine the required nominal kinematic viscosity inFig. 58.In our example the nominal kinematic viscosity at 40 °C= 150 mm2 · s-1.According to table 18, page 50, the oil suitable for thisapplication would be ISO VG 150.

Force-speed factor k s / v

Kin

emat

ic v

isco

sity

ν a

t 40

°C in

mm

2 /s

→

Force-speed factor ks

v in N · s

mm2 · m→

C 10246

Kin

emat

ic v

isco

sity

ν a

t 40

°C in

mm

2 /s

→

Force-speed factor T2

a3 · nsin

Nmin

m2 →

Fig. 58: Determination of the required viscosity for spur and bevel gears (except for hypoid gears)

C 10245

1,5

eH

ks = 3000

25 · 230

2.5 + 1

2.5·

= 2.2 N

mm 2

· 3 · 1 N

mm · mm

50


Example 2:

Determination of the nominal kinematic viscosityrequired for a worm gear driving a light-weightelevator


Initial torque T2 = 1000 Nm

Center distance a = 0.125 m

Worm speed ns = 1000 min-1



Mid-point

viscosityat 40 °C

[mm2· s-1]

Kinematic viscosity limitsat 40 °C

[mm2· s-1]

ISO VG 2ISO VG 3ISO VG 5






2.23.24.6

6.81015

223246

68100150

220320460

68010001500

1.982.884.14

6.129.0013.5

19.828.841.4

61.290.0135

198288414

612900

1350

2.423.525.06

7.4811.016.5

24.235.250.6

74.8110165

242352506

74811001650

min. max.

Table 18: ISO viscosity grades for industrial lubricating oils acc. to DIN 51 519

N· min

m2

1000

0.1253 · 1000

ks

v=

T2

a3 · ns=

= 512

· 1 Nm

m3 · min-1

Force-speed factor k s / v

On the basis of this force-speed factor it is possible todetermine the required nominal kinematic viscosity inFig. 59.

In our example the nominal kinematic viscosity at 40 °C= 360 mm2 · s-1.

As the determined value exceeds the limits of ISO VG320 (see table 18) an oil of the next higher viscosity– in this case ISO VG 460 – has to be selected.

NOTE

When determining the force-speedfactor (Ks/v) for the viscosity calcu-lations, it is important to take intoaccount that in multi-stage gears theindividual gear steps are subject todifferent operating conditions.

In case of two-stage gears theoperating conditions existing at thefinal stage are important for thecalculations.

In case of triple-stage gears theforce-speed factor (ks/v) has to bedetermined for the second and thethird stage. The average of thesetwo values is required to calculatethe nominal kinematic viscosity forthe entire gear system. The calcu-lation process for gears with morethan three stages is the same.

Conditions for increased viscosityvalues

● If the ambient temperature ispermanently above 25 °C, thenominal kinematic viscosity hasto be increased by approx. 10 %for every 10 °C.

● If the gear pairs consist of similarsteels or CrNi steel, the nominalkinematic viscosity has to be in-creased by 35 %. This does notrefer to surface-hardened ornitride steel.

● Gear pairs susceptible to scuffing(no or inadequate elasto-hydro-dynamic lubricating film) alsorequire an increased nominalkinematic viscosity. The sameapplies to lubricants not con-taining antiwear additives.

Viscositygrade ISO

Correction of the nominal kinematic viscosity

The nominal kinematic viscosityvalues determined in Fig. 58 and 59are valid for normal operating con-ditions and an average ambienttemperature of approx. 20 °C(tolerance range: 10 °C to 25 °C).

If the ambient temperature is per-manently outside the tolerancerange it is necessary to correct thenominal viscosity in order to ensurethat the operating viscosity remainsthe same.

Apart from temperature relatedcorrections, it may also be neces-sary to correct the nominal viscositydue to loads, materials involved ortooth-related reasons.

51


Conditions for decreased viscosityvalues

● If the ambient temperature ispermanently below 10 °C, thenominal kinematic viscosity hasto be decreased by approx. 10 %for every 3 °C.

● The nominal kinematic viscositycan be decreased up to 25 % ifthe tooth flanks are phosphatedor copper-coated.

If temperature-related viscositycorrections are required becausethe actual ambient temperaturesdiffer from the normal temperaturerange (10 °C to 25 °C), it is possibleto use the viscosity-temperature dia-gram shown in Fig. 60 to determinea suitable viscosity. The indicatedexample shows how to proceed.

Fig. 60: Viscosity-temperature diagram / Example of oil selection at ambient temperatures outside the normal range

In case of doubt always select thenext higher viscosity grade. At lowtemperatures it is important toobserve the lubricant’s flow limit.

IMPORTANT

After having determined a viscositygrade suitable for your gear, we re-commend to calculate the scuffingresistance, for instance by meansof the GfT Worksheet 2.4.2 (GfT =German Tribological Society).In addition, it is important to take intoaccount the viscosity requirementsof the other friction points in the gearsystem which will also be lubricatedwith the gear oil, e.g. rolling or plainbearings, mechanical or hydrauliccouplings, oil pumps and connectedhydraulic systems.

C 10234

100 000

10 000

1000

100

10

54

3

mm2/sNormal ambienttemperature range

ISO-VG150100 68 46

ISO-VG680460320220

Vis

cosi

ty →

-40 -20 200 40 60 80 100 °CTemperature →35

Example:Normal ambient temperature ofthe gear: 10 ... 25 °C. Requiredviscosity grade: ISO VG 68.

Ambient temperature changes to35 °C.

As shown in the diagram therequired viscosity grade is nowISO VG 220.

52


8.2.2 Determination of theviscosity of syntheticKlüber oils

Viscosity calculations in accordancewith DIN 51 509 are only valid formineral oils with a viscosity indexbetween 90 and 95. These calcula-tions only take into account a speci-fic viscosity-temperature behaviour.In case of synthetic lubricating oils,whose viscosity is not determinedby way of calculation (e.g. on thebasis of the EHD theory), it is impor-tant to take into account the differentviscosity-temperature behaviour ofsynthetic oils as well as their tem-perature-related pressure-viscositybehaviour.

As there are no standardized pro-cedures to determine the required

Examples for the determination of the viscosity according to the Klüber selection process:

Example 1:

Determination of the viscosity grade required for asingle-stage spur gear driving a fan


Peripheral speed onthe reference circle v = 4 m·s-1

Nominal peripheral force Ft = 3 000 N

Tooth width b = 25 mm

Reference circle diameter d1 = 230 mm

Gear ratio z2/z1 u = 2.5



Expected oil temperature approx. 90 °C

Selected lubricant: Klübersynth GEM 4(SHC oil)

Determination of the force-speed factor k s /v

Calculation corresponding to page 48,"Determination of the nominal kinematic viscosityrequired for a single-stage spur gear ... "

Determination of the Klüber viscosity number (KVZ)The Klüber viscosity number is determined inTable 19.The example calculation results in a force-speedfactor of 0.55 MPa· s·m-1.The corresponding Klüber viscosity number is 4.

1

2

3

4

5

6

7

8

Klüber viscosity numberKVZ

Force-speed factorks/v [MPa·s·m-1]

≤ 0.02

> 0.02 to 0.08

> 0.08 to 0.3

> 0.3 to 0.8

> 0.8 to 1.8

> 1.8 to 3.5

> 3.5 to 7.0

> 7.0

▲▲

Table 19: Klüber viscosity number as a function of the force-speedfactor (ks/v) for spur and bevel gears (except for hypoidgears)

Determination of the viscosity gradeThe required viscosity grade is determined on thebasis of the viscosity selection diagram (Fig. 61).

Assuming a Klüber viscosity number (KVZ) of 4 andan expected oil service temperature of approx. 90 °C,the diagram indicates a suitable viscosity grade ofISO VG 220. In other words:Klübersynth GEM 4-220 is the suitable lubricant.

viscosity of synthetic oils and themethods currently used are quitecomplicated, we have developedspecial worksheets for our new syn-thetic gear oils (Klübersynth GEM 4and Klübersynth GH 6 series). Theseworksheets make it quite easy toselect an appropriate ISO VG grade.

The selection process is partlybased on DIN 51 509. Calculate theforce-speed factor (ks/v) – taking intoaccount the type of gear – and usethe result to determine the Klüberviscosity number. With this viscositynumber and the expected oil ope-rating temperature it is possible todetermine the required ISO VGgrade in the selection diagram(Fig. 61 and 62) pertaining to therespective Klüber oil series. Theselection diagrams take into account

the specific viscosity-temperatureand viscosity-pressure behaviourof synthetic oils.

NOTE

Klüber defines the oil operatingtemperature as the oil sump tem-perature or the temperature of theinjected oil.

The expected oil operating tem-perature is determined on the basisof the gear’s thermal economy(considering losses) or, in case ofinstalled gears, is simply measured.

ks

v= 0.55 MPa·s·m-1

53


Fig. 61: Viscosity selection diagram for Klübersynth GEM 4 - 32 ... 680 lubricating oils (see notes on page 54 on how to use the diagram)

5

6

7

8

9

Output torque T2 = 300 Nm

Worm speed ns = 350 min-1

Center distance a = 0.063 m


Expected oil temperature approx. 85 °C


Selected lubricant: Klübersynth GH 6(PG oil)

Example 2:Determination of the viscosity grade required for theworm gear stage of a gear motor driving a circularconveyor


Table 20: Klüber viscosity number (KSV) as a function of the force- speed factor (ks/v) for worm gears

Klüber viscosity numberKVZ

Force-speed factorks/v [N · min / m2]

≤ 60

> 60 to 400

> 400 to 1800

> 1800 to 6000

> 6000

The Klüber viscosity number is determined inTable 20.The example calculation results in a force-speedfactor of 3428.6 N · min / m2. The correspondingKlüber viscosity number is 8.

▲▲

Determination of the Klüber viscosity number (KVZ)

Determination of the force-speed factor k s /v

ks

v=

T2

a3 · ns

300

0.0633 · 350

= 3428.6 N· min

m2

· 1· KA=

Determination of the viscosity gradeThe required viscosity grade is determined on thebasis of the viscosity selection diagram (Fig. 62).

Assuming a Klüber viscosity number (KVZ) of 8 andan expected oil service temperature of approx. 85 °Cthe diagram indicates a suitable viscosity grade ofISO VG 460. In other words:Klübersynth GH 6 - 460 is the suitable lubricant.

8

7

6

5

4

3

2

1

10 20 30 40 50 60 70 80 90 100 110 120 130 140... 220

... 320

... 460

... 680

...100 ...150...68...46...32

▲

Operating oil temperature [°C] → C 10235

Klü

ber

visc

osity

num

ber

KV

Z

→

9

54


NOTES

– In example 1 the viscosity gradecan be determined quite easilybecause the coordinates of theKlüber viscosity number and theoil service temperature (90 °C)intersect exactly on the VG 220curve.If the point of intersection islocated between two curves (seeexample 2: between VG 320 andVG 460), always select the higherviscosity grade (in this caseVG 460).

– Viscosity selection as shown inexample 1 and 2 is only valid forone gear stage. In case of multi-stage gears each stage has to beconsidered individually. From allthe determined viscosity grades

Note on page 55:

Tables 21 - 24 were taken fromDIN 3990 Pt 1/12.87, Appendix A.

Fig. 62: Viscosity selection diagram for Klübersynth GH 6 - 32 ... 1000 lubricating oils (see notes below on how to use the diagram)

select the one which is the bestcompromise to ensure reliablelubrication of the gear stagesand the other gear componentsinvolved.

– In order to ensure adequate lubri-cation during cold start and at lowambient temperatures it may benecessary to select a lower visco-sity grade. Check the viscositiesat the pertinent starting tempera-ture (especially in case of oilcirculation lubrication) and testthe involved components underthe expected starting tempera-tures (especially in case ofsplash lubrication).

– When determining a suitableviscosity grade in accordancewith the Klüber selection process,

take into account that the selec-tion diagrams only pertain to oneKlüber oil series. The differenttypes of lubricating oils havedifferent synthetic base oils andvary considerably in their visco-sity-temperature behaviour.Before determining a suitableviscosity grade it is thereforeimportant to know the type of oilto be used.

The viscosity selection diagramsfor Klübersynth GEM 4 andKlübersynth GH 6 products areshown in Fig. 61 and 62.

9

8

7

6

5

4

3

2

1

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

... 220

... 150

... 460

... 680

... 320

... 1000

...32 ...80 ...100

C 10236

▲

8

85

... 460

Operating oil temperature [°C] →

Klü

ber

visc

osity

num

ber

KV

Z

→

55


1.25

1.35

1.50

1.75

1.50

1.60

1.75

2.0

1.75

1.85

2.0

2.25 or more

The values pertain to the nominal torque of the driving unit, alternatively to the nominal torque of the drive motor if it corresponds to the torque re-quired by the driven unit. They are only valid for machines not operating in the resonance range and only if they have a uniform power requirement.In applications with exceptional loads, motors with a high starting moment, intermittent operation, extreme and recurring shock loads, the gears haveto be checked for static and fatigue strength. For examples see DIN 3990 Pt 6, page 9.

Table 21: Application factor KA

Driving unitMode of operation

Electric motor (e.g. direct current), steam or gas turbine operating uniformly *)(low, infrequent starting torques) **)

Steam or gas turbines, hydraulic or electric motor (high, frequent starting torques) **)

Multi-cylinder combustion engine

Single-cylinder combustion engine

Table 22: Examples of driving units with different modes of operation

Driven unitMode of operation

Power generators, uniformly fed belt conveyors or apron feeders, light-weight elevators, packagingmachines, feed drives of machine tools, fans, light-weight centrifuges, rotary pumps, agitators andmixers for light fluids or substances of a uniform density, cutters, presses, punches 1); rotary units,drive units 2).

Uniform

Intermittently fed belt conveyors or apron feeders, main drive of machine tools, heavy elevators, rotaryunits of cranes, industrial and mining fan systems, heavy centrifuges, rotary pumps, agitators andmixers for viscous fluids or substances of varying density, multi-cylinder piston pumps, feeding pumps,extruders in general, calenders, rotary kilns, rolling mills 3) (continuous zinc and aluminum belt rollingmills, wire and rod mills).

Rubber extruders, intermittently operating mixers for rubber and synthetic materials, light-weight ballmills, woodworking machines (automatic saws, lathes), blooming mills 3), 4); lifting units, single-cylinderpiston pumps

Medium shocks

Excavators, bucket wheel and chain drives, screen drives, dredging shovels, rubber kneaders, stoneand ore crushers, mining machinery, heavy feed pumps, rotary drilling installations, brick presses,debarking drums, peeling machines, cold belt rolling mills 3), 5); briquetting presses; edge mills

Heavy shocks

Table 23: Industrial gears, examples of operating modes of driven units

Driven unitMode of operation

Radial compressor in a/c systems (for process gas), power test rig, generator and exciter for base orpermanent load, main drive of paper machines

Uniform

Moderate shocks Radial compressor for air or pipelines, axial compressor, centrifugal fan, generator and exciter for peakloads, all types of rotary pumps except rotary axial-flow pumps, gear pumps, paper industry: Jordanrefiner, secondary drives of paper machines, pulp compactors

Table 24: High-speed gears, examples of operating modes of driven units

*) As determined in frequency tests or as known by experience

**) Comparative life curves ZNT; YNT of the material in DIN 3990 Pt 2 and 3 takes into account short-term overload torques

1.00

1.10

1.25

1.50

Uniform

Light shocks

Moderate shocks

Heavy shocks

Operation of driven unit

uniformOperation of driving unit moderate shocks medium shocks heavy shocks

Uniform

Light shocks

Moderate shocks

Heavy shocks

Moderate shocks

1) Nominal torque = maximum cutting, pressing, punching torque 2) Nominal torque = maximum starting torque 3) Nominal torque = maximum rolling torque4) Torque based on power limit 5) KA up to 2.0 due to frequent belt breakage

Medium shocks Rotary cam blower, rotary radial-flow cam compressor, piston compressor (3 or more cylinders),suction fans for industrial or mining applications, (large units with frequent starts), rotary boiler feedpump, rotary cam pump, piston pump (3 or more cylinders)

Heavy shocks Double-cylinder piston compressor; rotary pump (surge tank); slurry pump; double-cylinder pistonpump

56


1

1

2

1/2

1

1

1

2

1

1

1

2

2 - 3

2

2

2

1

1

1

1

2

1

2

2

1

1

2

2

2

3

3

1

1

1 - 2

1

1

1

3

1

4

3

2

1

Viscosity-temperature behaviour

Low-temperature properties

Wear protection

Friction behaviour

Oxidation resistance

Water separation capacity

Corrosion protection

Miscibility with mineral oil

Behaviour towards paints

Compatibility with sealingmaterials

Low evaporation loss

Properties

Table 25: Comparison of the properties of mineral and synthetic gear oils (Klüber products). 1 = excellent, 2 = good, 3 = sufficient, 4 = poor

Gear oils with a PGbase oil

Klübersynth GH 6 series

Gear oils with aester base oil

Klüberbio series

High-quality EP gear oilswith a mineral base oil

Klüberoil GEM 1 series

Gear oils with a SHCbase oil

Klübersynth GEM 4 series

Type of oil

8.3 Selection of syntheticgear oils

Lubricating oils with a synthetichydrocarbon (SHC), polyalkyleneglycol (PG) or ester base oil haveproven particularly efficient in thelubrication of gear systems.Lubricants with a PG base oil areusually referred to as polyglycol oils.

Disadvantages

● not miscible with mineral oils

● may change sealing materials anddissolve paints; only resistant to fluori-nated rubber or PTFE seals as well asepoxy resin coatings

● may change sealing materials anddissolve paints; compatibility testsrequired

● antiwear properties not as good as thatof PG oils

● antiwear behaviour inferior to that of PGoils

● less favorable lubricating behaviour thanPG oils

Advantages

● low friction coefficient, therefore espe-cially suitable for the lubrication of gearswith a high sliding percentage (worm andhypoid gears)

● excellent viscosity-temperaturebehaviour (high VI)

● excellent antiwear behaviour

● very good pressure absorption capacity

● good low-temperature behaviour

● low friction coefficients possible

● high viscosity index (VI)

● high resistance to oxidation

● rapidly biodegradable

● excellent low-temperature behaviour

● miscible with mineral oil residues

● compatibility with paints and sealingmaterials equal to that of mineral oils

● very low evaporation losses up to 140 °C(also in case of low viscosity)

● disposal or treatment same as formineral oil

● SHC suitable as a base oil for food gradelubricants

SHC base lubricating oils PG base lubricating oils Ester oil base lubricating oils

A direct comparison of the properties of SHC, PG, and ester oil base lubricating oils gives the following hints onlubricants selection:

Synthetic gear oils have the follow-ing advantages over mineral lubri-cating oils:

● better resistance to temperaturesand ageing

● lower tooth-related frictioncoefficient

● better cold flow properties

● more favorable viscosity-temperature behaviour

Table 25 shows a comparison of theproperties of high quality mineral oilbase gear oils and synthetic oil baselubricating oils.

57


Gear greases type OG

These are used for the lubricationof open gear systems or girth gearsof large or very large dimensionswith steel/steel gear teeth, e.g.drives of rotary kilns, tube mills,lifting cylinders, cranes, construc-tion machinery.

They are not suitable for thelubrication of small open gears!

Today large open drives are mainlylubricated with special adhesivelubricants free from bitumen andsolvents, such as the products ofKlüber’s GRAFLOSCON orKlüberfluid series.

Depending on the type of lubricationand the application method, theselubricants are available as consistentspray lubricants of NLGI grade 00,0 and 1 or in the form of fluidsclassified in NLGI grade 000.

Selection criteria for gear greases

To select a suitable gear grease it isimportant to take into considerationthe type of gear, lubricant applicationmethod, gear performance, opera-ting conditions and ambient in-fluences. In addition, the followingparameters have to be determined:

● suitable grease consistency

● required base oil viscosity

● type of base oil

● thickener properties

8.4 Selection of gear greases

In DIN 51 509 Pt 2 lubricatinggreases for gear systems are divi-ded into two groups:

Gear greases type GLubricating greases for closedgears and splash lubrication,where grease lubrication is pre-ferred over oil lubrication due tothe sealing or operating conditions.

Gear greases type OG

Adhesive lubricants free frombitumen or bituminous adhesivelubricants for open gear systems.

Gear greases type G

These are lubricating greases ofNLGI grade 000 to 1, DIN 51 818,which are very soft or fluid atambient temperatures between 18and 28 °C according to DIN 51 014.They contain an increased amountof mineral and/or synthetic oil aswell as a thickener (typically a metalsoap).

They may also contain additivesreducing friction and wear and/orincreasing the load-carrying capa-city.

The minimum requirements forsuch a grease are specified inDIN 51 826. According to this stan-dard the application range of thesegreases is very limited because itonly mentions closed gears withsplash lubrication, e.g. gear motors,axial cylinder motors, actuators andgear couplings.

The standard does not refer to smalland miniature gears, which are alsolubricated with gear greases type Gof NLGI grade 0 and 1 as well aslubricating greases of NLGI grade 2.Gear greases type OG are notsuitable for such gears. Fig. 65: Open gears and gear stages – appli-

cation of gear greases type OG in theform of adhesive sprays (NLGI 00, 0and 1) or fluids (NLGI 000)

Fig. 63: Power tools – main field of applica-tion of gear greases type G of NLGI1 and 2

Fig. 64: Gear motors – classical field of appli-cation of gear greases type G ofNLGI 00 and 000

Two-stage spur gear motor

Rotary kiln with girth gear drive

Power hand drill gear system

C 10237A4 10208

C 10238A4 10209

C 10186

58


000

00

0

1

2

8.4.1 Determination of greaseconsistency

Consistency is the resistance of agrease to deformation, similar to anoil’s viscosity. In order to ensurereliable gear lubrication, gear greasesmust have a certain degree of flui-dity, which is why mainly soft to fluidgrease are applied in gear systems.

Table 26 gives a survey of greaseconsistencies and indicates all

NLGI gradeDIN 51 818

Application method

details on gear types, peripheralspeeds and lubrication methodsthat are important to determine asuitable consistency.

The table is based on DIN 51 528but also includes NLGI grade 2.These greases are also used forgear lubrication, especially on toothflanks in small gears or for forced-feed lubrication of gears operatingat high peripheral speeds (20 to25 m/s) with a complete fill of thegear housing.

Table 26 only lists the main selec-tion criteria for consistency deter-mination. Other criteria include:

● extent of gear sealing

● heat dissipation capacity

● adhesion properties.

Workedpenetration

DIN ISO 21 37

Units 1)

445 to 475

355 to 385

310 to 340

285 to 295

400 to 430

fluid

almost fluid

extremelysoft

very soft

soft

Greasetexture

closed,oiltight

closed,not oiltight 5)

semi-open, open

closed,oiltight

closed,not oiltight

closed,not oiltight

semi-open, open

Suitability forgear types

Permanentoperation

6 to 8

4 to 5

2 to 3

up to 8

–

up to 10

up to 10

–

Peripheral speed

[m · s -1]

up to 10

up to 7

Short-term orintermittentoperation

up to 5

up to 11

20 to 25

up to 4

20 to 25

2 to 3

immersion

immersion

immersion

spraying (total loss lubrication) 2)

one-time greasing 3)

one-time greasing 3)

immersion with almost complete filling ofthe gear housing 4)

immersion with almost complete filling ofthe gear housing 4)

semi-open, open – 2 to 3 one-time greasing 3)

1) One unit = 0.1 mm

2) Under permanent operation and if powerhas to be transferred it is important thatthe lubricant film, which is continuouslydestroyed by the friction components(tooth flanks), is rebuilt regularly in orderto maintain a minimum film thicknessthat prevents scuffing due to occasionalstarved lubrication. Relubrication is mostreliable if carried out by means of anautomatic spraying equipment whichsupplies the required lubricant quantityto the tooth flanks intermittently. Otherrelubrication methods: manual applica-tion by brush or spatula (when gear is notoperating) or with a pneumatic spraying

unit – e.g. Klübermatic LB – while thegear is operating up to a maximumperipheral speed of 2 m · s -1.

IMPORTANT: Only if heat dissipation isnot mandatory

3) One-time greasing of the tooth flankssufficient for the entire service life is onlysuitable for gears used to convert torquesand/or transfer movements in short-timeor intermittent operation.

4) Lubrication method ensuring reliable gearlubrication at increased peripheralspeeds.

Approx. 10 % of the grease quantity areused for lubrication, the rest serves as a

barrier to prevent the lubricant fromleaving the meshing zone. This type ofimmersion lubrication is only suitable forsmall gears transmitting power in short-time or intermittent operation, in order toavoid the destruction of the grease dueto excessive heating.

5) This also includes so-called semi-openand open gears provided they areencased and equipped with a lubricantreservoir making them suitable forimmersion lubrication.

Table 26: Determination of the required grease consistency as a function of the gear type, peripheral speed and lubrication method

^

59


However, this type of immersionlubrication is only suitable for gearstransmitting power in intermittentoperation in order to avoid greasedestruction due to excessive heating.

Heat dissipation capacity

Greases, in contrast to lubricatingoils, only have a low heat dissipationcapacity. Gears operating perma-nently at increased peripheralspeeds and/or used for power trans-fer purposes require greases with ahigh base oil content for heatdissipation, i.e. fluid greases ofNLGI 000 and 00. The only suitablelubrication method is splash lubrica-tion, and the gears have to be oil-tight.

Adhesion capacity

Gears mainly used to converttorques or transfer movements andlow power are often lubricated forlife. For this type of lubrication it isimportant for the grease to remainin the meshing zone throughout thegear’s service life. It must not bethrown off nor lose its lubricity dueto oil separation.

Gear sealing

The extent of gear sealing is ofspecial importance if gear greaseswith a consistency of NLGI 000 and00 are to be used, so-called fluidgreases with a base oil content of90 to 95 %. In such a case a gearshould be as oiltight as possible, orgreases with a higher consistencyshould be applied.

Especially splash-lubricated smallgears, whose position may constant-ly change (e.g. in power hand tools,machines for craftsmen, gears inproduction robots), there is thedanger of oil leakage. In thesecases we recommend at least anNLGI 0 grease, if possible even agrease of consistency 1 or 1-2.

As lubricating greases of such aconsistency are no longer fluid, aquasi-complete filling of the gearhousing is required to ensure reli-able gear lubrication in all operatingpositions.

NOTE

If NLGI 1 and 2 greases are usedfor immersion lubrication, it has tobe taken into consideration that theyhave a channeling tendency, i.e.upon immersion into the lubricantsump, the gear wheels leave achannel in the grease. Greases ofthis consistency have no backflowbehaviour, and gear wheels or wormsare subject to starved lubricationand increased wear after a veryshort period of time.

Channeling can be avoided by meansof grease scrapers where the greasewhich is removed from the sumpaccumulates until it falls back intothe sump by force of gravity.

Another way to prevent channelingis to fill the gear housing completelywith grease. This also makes itpossible to operate the gear at ahigher peripheral speed (up to25 m/s) because the grease is notthrown off.

Gear greases with an increasedconsistency, i.e. of NLGI grade 1and 2, are most suitable to meetthese requirements.

Greases of NLGI grade 0 are alsosuitable for tooth flank lubricationprovided they have special adhe-sion properties. These greases areadhesive greases without solidlubricant particles and must not beconfused with gear greases of theOG type.

Fig. 66: Cylinder-worm gear

A4 10211

60


if good vibration and noise dampingis required. High base oil viscositiesresult in a thicker lubricant film onthe meshing points, which increasesvibration and noise damping.

In case of immersion lubricatedgears with modules < 3 mm thebase oil viscosity should not behigher than 460 mm2/s in order toensure that the grease flows backinto the space between the teeth.Higher base oil viscosities arepossible with modules > 3 mm.

8.4.3 Determination of thebase oil type

Lubricating greases generally con-sist of a base oil and a thickeningagent. Depending on the type andconsistency of the grease thethickener share is between approx.5 and 25 %, i.e. the oil is the mainconstituent. Greases are nothingbut oils prevented from flowing bymeans of a thickening agent. Whenselecting a gear grease the base oiltype is therefore just as importantas in the case of a gear oil.

Base oils used for gear greases in-clude mineral, synthetic ester, syn-thetic hydrocarbon and polyglycoloils. To obtain certain characteristicsit is also possible to use a mixture ofthese base oil types, e.g. a mineral

oil plus a synthetic hydrocarbon oil,or ester oil / paraffin oil / synthetichydrocarbon oil.

Gear greases with a synthetic baseoil have the same advantages assynthetic gear oils:

● increased resistance to hightemperatures and ageing

● reduced tooth-related frictioncoefficient

● improved behaviour at lowtemperatures

● more favorable viscosity/temperature behaviour

Gear greases with a polyglycol baseoil are especially suitable for smallgears subject to high loads (also incase of an increased peripheralspeed), e.g. worm gears with aworm/wheel combination made ofsteel/bronze, because they have anexcellent pressure absorption capa-city, hardly change their viscosity atvarying service temperatures andhave a very low friction coefficient.

Polyglycol gear greases are notsuitable for the lubrication of gearsconsisting of aluminum alloys. Theirsuitability for plastic gears has to bechecked on a case-to-case basis.

Gear greases with synthetic hydro-carbon oils have proven effective inthe lubrication of plastic/plastic and

Fig. 67: Worm gear motor, servo drive for car seat adjustment F 10252

8.4.2 Determination of the re-quired base oil viscosity

The required base oil viscositydepends on the operating conditionsand the intended use of the gear.

In case of gears used to transferpower the required base oil viscosity(nominal kinematic viscosity at 40 °C)should always be based on concretecalculations in order to preventpittings and wear.

The required nominal viscosity canbe determined in accordance withDIN 51 509 Pt 1 (section 8.2.1, page48), no matter whether the base oilis of the synthetic or mineral hydro-carbon type.

Temperature or load-related visco-sity corrections can only be effectedto a limited extent in case of geargreases because pertinent data isonly available for the most commonbase oil viscosities. When in doubtalways select the lubricating grease– taking into consideration a suitableconsistency – whose base oil visco-sity is above the calculated nominalviscosity.

When determining the required baseoil viscosity for grease lubricatedgears that are used to converttorques or transfer movements –mainly low-performance small orminiature gears – the requirementsin terms of smooth operation, lowstarting torques, vibration and noisedamping are most important.

Smooth operation and low startingtorques are ensured by means ofdynamically light greases, i.e.greases with a very low base oilviscosity. Most suitable greaseshave a nominal kinematic base oilviscosity of 30 mm2 · s-1 and lowerat 40 °C.

Gear greases with a higher base oilviscosity should be used (between200 and 1000 mm2 · s-1 dependingon the peripheral speed and load)

61


steel/plastic gears because of theircompatibility with many syntheticmaterials.

In addition, SHC gear greases havea very good low-temperature beha-viour and are very suitable forlifetime lubrication of tooth flanksdue to their low evaporation loss.

Gear greases with a mineral baseoil are the most inexpensive typeof grease. They are mainly used asfluid greases for splash lubricationof gear motors subject to normalloads and operating permanentlyat almost the same service tempera-ture. Their service temperaturerange is considerably smaller thanthat of synthetic gear greases.

In permanent operation the greasesump temperature should not ex-ceed 60 °C in order to avoid pre-mature grease ageing and bearingfailure due to a diminishing lubri-cating effect.

Gear greases with a base oil mix-ture, e.g. mineral / SHC oil, permitan extended service temperaturerange.

8.4.4 Properties of thethickening agent

Thickening agents used in geargreases – mainly single or complexmetal soaps (Li, Ca, Al and Basoaps) – do more than perform thefunction of a base oil carrier. Theyalso have a lubricating effect andimpart certain characteristics to thegrease.

They are decisive for the servicetemperature range, the pressureabsorption capacity and thegrease’s resistance to ambientmedia.

Depending on the thickening agent,metal soap greases have thefollowing properties:

2

3

G PG 00 K - 30

upper service temperature andbehaviour towards water

lower service temperature in °C

NLGI grade (see table 26, page 58)letter(s) identifying base oil andadditives

lubricating grease for:

Fig. 68: Denomination of lubricating greases in acc. with DIN 51 502

1

Lubricating grease for:

G Closed gears DIN 51 826

OG Open gears

K Rolling and plain bearings, sliding surfacesDIN 52 825

M Plain bearings and seals(lower requirements than K)

1

3 Upper service temperature and behaviour towards water under test temperature conditions *)

Temperature Behaviour towards Test tempe- limit water rature

C +60°C 0 or 1 40 °CD 2 or 3

E +80 °C 0 or 1 40 °CF 2 or 3

G +100 °C 0 or 1 90 °CH 2 or 3

K +120 °C 0 or 1 90 °CM 2 or 3

N +140 °C

P +160 °C

R +180 °C As required

S +200 °C

T +220 °C

U > +220 °C

0 = no change1 = minor change2 = moderate change3 = major change

*) DIN 51 807,Pt 1, static test

2 Additional letters identifying

Base oil types

E Ester oils

FK Fluorinated hydrocarbons

HC Synthetic hydrocarbons

PG Polyglycol

SI Silicone oils

Additives

P Extreme pressure additives

F Solid lubricant particles, e.g. MoS2

62


carbon base oil are suitable for life-time lubrication of small gears withsteel/plastic and plastic/plastic gearwheels subject to increased specificloads.

Due to their good flow propertiesCa greases of increased consis-tency are suitable for splash lubri-cation of gears that are not oiltightwith little free housing space and aquasi-complete fill.

Greases with low-viscosity base oilshave good low-temperature proper-ties and ensure low starting torques.

Barium complex soap greases

Lubricating greases with bariumcomplex soap as a thickening agentare very resistant to working, havean excellent resistance to water, ahigh load-carrying capacity and verygood wetting properties.

The thickener share is very high,which gives these greases anti-noise and anti-vibration properties.As their backflow behaviour is not

very good, they are mainly used forlifetime lubrication of tooth flanks.

Such greases usually have a low-viscosity base oil in order to improvegear starting properties, especiallyin case of low input performance.Barium complex soap greases areparticularly suitable for the lubri-cation of small gears with steel/steel components.

Aluminum complex soap greases

Greases of this type show goodadherence to metal surfaces, arevery resistant to water and have agood wetting behaviour due to theirspecial rheological behaviour (theybecome softer under mechanicalload). For this reason they areespecially suitable for the lubricationof tooth flanks of large open gearswith steel/steel gear wheels subjectto increased loads. They are alsosuitable for splash lubrication.

Lithium soap greases

Lithium soap greases are waterrepellent, have a high drop pointand, depending on the type andconsistency of the base oil, verygood low-temperature properties.

Li soap greases of NLGI grade 1 or2 with a synthetic hydrocarbon baseoil or a mixture of mineral and syn-thetic hydrocarbon oils are particu-larly suitable for lifetime lubricationof small gears with steel/plastic andplastic/plastic gear wheels, especial-ly for gears with a high centrifugalacceleration, where oil/thickenerseparation must not occur. Greaseswith a low base oil viscosity permitvery low starting torques. Li soapgreases with a polyglycol base oilof low consistency are preferred forsplash lubrication of small gearsand gear motors subject to lowloads, also for increased peripheraland sliding speeds. They are alsosuitable for the lubrication of wormgears with steel/bronze materialpairings.

Calcium soap greases

Compared to other metal soapgreases, Ca greases have a betterflow behaviour and are more resis-tant to working. They also have agood pressure absorption capacity.Ca greases with a synthetic hydro-

Fig. 69: Small gear motor (worm/spur gear) for flap adjustment in automotive a/c systems,manufactured by Bühler Nachfolger GmbH, Nürnberg, Germany F 10255

63


8.4.5 Behaviour of lubricatinggreases towards syn-thetic materials

Lubricating greases are mainly usedfor long-term or lifetime lubricationof small and miniature gears pro-duced in large series. In these gearssynthetic materials are increasinglyreplacing metals in gear wheel,bearing and housing components.

However, long-term lubrication ofgears with plastic components isonly possible if the affected syn-thetic parts are lubricated as reliablyas if they were made of metal.

As the interaction between plasticsand greases is different than thatbetween metals and greases, it isnecessary to perform componenttests under service conditions be-fore starting production in order toensure that the synthetic materials

● Raffinate

● Hydrocrack oil

● Synthetic oil

● Biodegradableoils

Fatty acid 1)

+

Metal hydroxide 2)

Silicic acid Clay Polyurea

● Al greases● Li greases● Na greases● Ca greases● Ba greases● Mixed soap

greases 3)● Complex

greases 4)

Lubricating grease =base oil, thickener, additives

Additives

1) Fatty acids on a vegetable or animal base2) Aluminum hydroxide, lithium hydroxide, sodium hydroxide, calcium hydroxide,

barium hydroxide (lead hydroxide)3) e.g. Li/Ca soap, Na/Al soap4) Al, Ba, Na, Ca, Li complex soap greases; complex soap greases need two or

more fatty acids to form a metal soap.

Non-soap thickenerSoap thickener

Base oil Thickener

Fig. 70: Structure and manufacturing method of lubricating greases

are sufficiently compatible with thelubricants. These practice-relatedtests are required because conven-tional compatibility tests are onlycarried out under static conditionswith standardized test rods, dis-regarding

– that additives only becomeeffective when the lubricant issubjected to tribological loads,and

– that oil ageing under serviceconditions is much faster thanunder static loads due to theformation of aggressive oilproducts under mechano-dynamical loads.

There are no standardized or quasi-standardized tests or guidelines toidentify mechano-dynamical loads.

Describing the problems of compa-tibility of plastic materials and lubri-

cants would go beyond the scope ofthis brochure. For more information,please refer to our technicalbrochure "Lubrication of syntheticmaterials" 9.19 e, where you willfind everything you need to knowabout the interaction between lubri-cants and plastics, and which willhelp you select a suitable lubricant.

Table 27 on page 64 provides ageneral survey of the compatibilityof various thermoplastic materialswith specialty lubricating greases.

The data indicated in this table isonly intended as a guideline anddoes in no way substitute specifictests!

Protection against:

● ageing

● corrosion

● wear

Improvement ofpressure absorp-tion capacity

Gel greases Bentonitegreases

Polyureagreases

64


not resistant

not resistant

resistant

not resistant

resistant

partly resistant

mostly resistant

partly resistant

not resistant

not resistant

resistant

not resistant

not resistant

A B C

Abbre-viation

ABS

CA

PA

PC

PE

ABS-copolymer

Cellulose acetate

Polyamide

Polycarbonate

Polyethylene

high-density

low-density

Polyoxymethylene

Polypropylene

Polyphenylene oxide

Polystyrene

Polytetrafluoro-ethylene

Polyurethane

Polyvinyl chloride

POM

PP

PPO

PS

PTFE

PUR

PVC

not resistant

not resistant

resistant

not resistant

resistant

partly resistant

mostly resistant

partly resistant

not resistant

not resistant

resistant

not resistant

not resistant

resistant

resistant

resistant

resistant

resistant

resistant

mostly resistant

resistant

resistant

resistant

resistant

resistant

resistant

A = Special ester oil greases with - alkaline earth complex soap - lithium soap - inorganic thickener

C = Synthetic hydrocarbon oil greases with - alkaline earth complex soaps and other metal soap thickener

B = Special ester oil greases with

lithium soap

8.5 Notes on the lubricationof small gears

There is no general definition of theterm "small gear". In order todistinguish them from so-called"industrial gears", Klüber definessmall gears as gears with an outputtorque of less than 100 Nm.

Gears with an output torque below10 Nm are called "miniature gears".

Basically there is no differencebetween the lubrication of industrialand small gears.

The type of lubrication (with an oil,fluid grease or grease) and theapplication method (immersion,spraying, manual application) arenot dependent on the size of thegear but on the type of gear and theperipheral speed of gear stageoperating at the highest speed.

Table 28: Classification of gears in terms of output torque (Klüber)

Table 27: Behaviour of special lubricating greases towards thermoplastic materials

Grease groups

Output torque [Nm]

> 100

< 100 to 10

< 10

Type of gear

Industrial gear

Small gear

Miniature gear

The same applies to the selectionof a suitable lubricant, which doesnot depend on the gear size but onthe operating and ambient condi-tions, the gear materials and thetype of gear.

For small gears this means that agear stage with an output torque ofless than 100 Nm used for perma-nent power transfer (maximumperipheral speed: 18 m · s-1) canonly be lubricated with an oil, andnot with a grease. On the one handit is required to dissipate excessiveheat, on the other hand a fluid

grease of NLGI 000 is only suitablefor a peripheral speed up to 8 m · s-1

when used in permanent operation(see tables 17 and 26 on page 47and 58).

The gear housing must be oiltightand the gear motor installed in away to allow oil changes.

For the following reasons small andminiature gears are mainly greaselubricated:

Thermoplastics

65


– it is often not possible to makegear housings or seals absolute-ly oiltight,

– they are often not accessible ordifficult to access, which makesit impossible to change the lubri-cant (long-term or lifetime lubri-cation required),

– they are of the open or semi-open type

– the gear position during opera-tion varies

– lifetime lubrication is required.

Fig. 71: Spur gear stage of a miniature gear motor for universal application (copyingmachines, vending machines, equipment of all types), manufactured by BühlerNachfolger GmbH, Nürnberg, Germany F 10254

66


9 Tooth flank damage

More than 50 % of the damage inindustrial gears occurs on the gearteeth. Table 29 gives a survey of thedifferent types of tooth flank damageand their causes. Damage mainlydue to deficient lubrication is listedat the bottom of the table. Fig. 72indicates the load limits and thepertinent tooth flank damage. Toothflank damage can manifest itself invarious forms.

Based on the cause of the damagea distinction is made between

Insufficient surface quality

Mis-alignment

Corro-sion

DeformationCracksChippingWear

Toothbreak-

age

Slag inclusion

Non-metal inclusions

Wrong tooth geometry

Meshing interference

Wrong backlash

Deficient forging

Excessive heat during mechanicaltreatment

Inadequate heat treatment

Inadequate surface quality

Insufficient insulation

Frequent load alternations

Shocks, vibrations

Overloading

Inadequate running in

Insufficient lubricant quantity

Wrong viscosity

Insufficient quality

Solid / fluid contaminants

Peripheral speedtoo high / low

● ● ● ●

● ●

●Inadequate material pairing

Wrong dimensions

●● ● ●

● ● ●

Forging marks

● ●

● ●

●

● ●

●

● ●

● ● ● ● ●

● ●

● ●● ● ●

●

● ●

● ●

●

● ● ● ● ● ●

● ● ● ● ● ● ● ● ●

● ●

● ● ● ●

● ● ● ●

● ● ● ● ● ● ●

● ● ● ● ● ●

●

● ● ● ● ● ●

●

●Def

icie

nt

lub

rica

tio

nO

per

atin

gco

nd

itio

ns

Fau

lty

as-

sem

bly

Def

icie

nt

pro

du

ctio

nD

efic

ien

td

esig

nM

ater

ial

def

ects

Damage caused by

●

●

Table 29: Causes and types of gear damage

Tooth flank damageType of damage

● abrasive wear● scuffing wear● pitting.

DIN 3979 describes the damageeffects in detail.

Abrasive and scuffing wear aremainly caused by deficient lubrica-tion, whereas the formation of pit-tings can only be influenced by thelubricant to a limited extent.

The lubricant does not have animmediate impact on surface fatigue.However, in case of high peripheral

speeds and high lubricant viscosityin the lubricating gap, there may bea damping effect on the additionaldynamic forces, thus exerting in-direct influence on surface fatigue.

9.1 Abrasive wear

In the context of gear damage"abrasive wear" is a generic termincluding grinding, scratching andscoring wear. Abrasive tooth flankwear is caused by

● furrowing effects of surfaceroughness

Ove

rload

bre

akag

e

Fat

igue

bre

akag

e

Nor

mal

wea

r

Abr

asiv

e w

ear

Inte

rfer

ence

wea

r

Scr

atch

ing

Sco

ring

Scu

ffing

Pitt

ing

Spa

lling

Fla

king

Grin

ding

cra

cks

Que

nchi

ng c

rack

s

Mat

eria

l cra

cks

Fat

igue

cra

cks

Inde

ntat

ions

Rip

plin

g

Hot

flow

ing

Col

d flo

win

g

Che

mic

al c

orro

sion

Fre

tting

cor

rosi

on

Cav

itatio

n

Ero

sion

Ele

ctric

dis

char

ge

Sca

ling

Ove

rhea

ting

Other damage

67


Fig. 72: Schematic drawing of load limits of hardened steel gears.The location of the curves relative to each other and theirgradients are exemplary and do not pertain to a certaintype of gear

C 10240

no-damage range

peripheral speed

tooth breakage limit

scuffing load limit

wear limit

pitting limit

exte

rnal

load

00

● solid contaminants in the lubri-cant (dust, rust, scale, metal wearparticles, molding sand residues,etc.) which reach the lubricatinggap and result in grooves in thetooth flanks.

The degree of contamination of alubricant and the extent of surfaceroughness of the gear material aredecisive for the speed of wear.Wear usually occurs most rapidlyon the tooth tip and the base.

9.2 Scuffing (adhesive) wear

Scuffing wear occurs if the lubricantfilm is destroyed by excessive tem-peratures or loads, causing themetal tooth flank surfaces to touch.Gears are susceptible to scuffingwear if they operate at high peri-pheral speeds (hot scuffing) or atlow peripheral speeds and highflank pressure (cold scuffing)

Hot scuffing

In case of high friction temperaturesand sliding speeds the lubricant filmfails due to excessive heating.

Cold scuffing

The lubricant film fails due to highlocal flank pressure at low peripheralspeeds (up to approx. 4 m · s-1).Cold scuffing mainly occurs in heat-treated gears with a rough toothsurface.

Scuffing is characterized by localseizures which are torn apart by therelative movement of the tooth flanks,causing rough spots of varyingwidths and depths (individual spotsor over the entire flank width) on thetooth flanks (Fig. 74). The particlesremoved from the tooth surface arecarried along and deposited on otherspots, where they are subject toplastic deformation. Scuffing wear isespecially pronounced at the toothtip and base because this is wherethe sliding speed is highest.

Practical experi-ence shows thata gear’s scuffingload capacitydepends on fourmain parameterswhich have animpact on its per-formance limit:

1. Lubricant

2. Tooth geo-metry

3. Surface,material

4. Operatingconditions

Table 30 showsthe range of vari-ation of the transferable torque (hotscuffing limit) as a function of theseparameters. Contrary to pittings andtooth breakage, there is no fatiguestrength as far scuffing wear isconcerned. Even a short period ofoverloading can initiate scuffingwear and damage the tooth flanks.

It is therefore important to take intoaccount a gear’s scuffing resistancein the pertinent design calculations.

DIN 3990, ISO DP 6336 providesinformation on how to calculate agear’s scuffing load limit andscuffing wear resistance.

Fig. 74: Scuffing (adhesive wear) C 10242Fig. 73: Abrasive wear C 10241

9.3 Pitting

Pitting is a form of tooth flank mate-rial fatigue. It occurs if a material’spermanent rolling resistance is ex-ceeded by loads applied locally orover the entire tooth width.

The damage manifests itself in theform of flat, crater-like indentationscalled "pittings". Their size varies

from 0.01 mm (micro-pitting) toseveral mm. In spur gears theymainly occur in the area below thepitch circle. Lubricants can have alimited effect on the formation ofpittings, but an increased operatingviscosity retards their development.

For measures to increases a gear’spitting load capacity see Fig. 76.

68


ParametersRange of variation of the

transferable torque

Additives, same base oil viscosity

Oil viscosity, e.g. doubled

Service oil temperature, e.g. reduced by 20 °C

Tooth geometry

Tip relief

Surface roughness, e.g. reduction of

flank roughness to 1/16

Phosphatized flanks

Nitriding

Peripheral speed

2

1

4

3

1 : 5

up to 1 : 1.5

1 : 1.2

1 : 1.6

1 : 2

1 : 1.5

1 : 1.4

1 : 1.8

1 : 2.5

Table 30: Range of variation of the transferable torque (hot scuffing limit) .Change of main parameters: 1 = lubricant, 2 = teeth, 3 = material surface4 = operating conditionsThe individual parameters cannot be combined to obtain synergistic effects.

9.4 Micro-pitting

Micro-pitting is a lubricant relateddamage manifesting itself in theform of dull spots on the tooth flanksof surface-hardened gear wheels.It is characterized as follows:

– dull areas consisting of nume-rous chippings of microscopicsize (depth approx. 20 µm),

– direction and development ofcracks depending on sliding/rolling conditions (as in the caseof "conventional" pittings), i.e. thecracks start on the surface and,at a flat angle, develop in thedirection of the frictional force,

– occurs mainly at mediumperipheral speeds when low-viscosity oils are used on thetooth flanks of hardened gearwheels,

– the operating time until micro-pitting occurs may be quite shortand the loads may be significant-ly below the pitting load capacity,

– the incipient damage is wear-like,the progressive damage isfatigue-like,

Fig. 76: Measures to increase a gear’s pitting load capacity

Increased viscosity

Positive addendum modificationIncreased meshing angleVertical gearsHelical gearsTip relief

HardeningCopper-platingLow flank roughness

Increased peripheral speedLow flank pressure

Lubricating oils ▼▼

▼▼

▼▼

Tooth geometry

Material, surface

▼▼

▼

Operating conditions ▼▼

Fig. 75: Pittings C 10243

– lubricant viscosity and additiveshave a great impact on micro-pitting,

– lubricants with a low micro-pittingresistance may lead to erosion inthe micro-pitting area, resultingin increased internal dynamicforces and gear noises as wellas a reduced pitting loadcapacity.

The impact of a lubricant on micro-pitting is determined in a modifiedFZG test based on DIN 51 354 withgear wheels less susceptible toscuffing. The load is increased in

Fig. 77: Micro-pitting of case-hardened gear C 10244

69


Pittings

initial pittings

progressive pittings

ductile fracture

Weargrinding wear

wavy wear

Flank scaling

Overload breakage

▼

often results infatigue breakage

heavy wear

scores

hot flowing

cold flowing

normal wear

scuffing marks,frictional welding

Cracks

Corrosion

Electric discharge

Cavitation

(hot, cold)

Plasticdeformation

Types of gear damage

Flank damageTooth breakage

(increasing noise, unsteady operation, heating – incase of further increase: interruption of operation)

(immediate interruption of operation)

overloading cracks

quenching cracks

grinding cracks

material cracks

Fatigue breakage

idle corrosion

chemical corrosionfretting corrosion

Brittle fractureDuctile fracture

Scuffing

Overheating

Fig. 78: Types of gear damage

steps until the dimensional changeof the flank is twice as high as in thebeginning. If this damage criterion isonly reached in the 8th or an evenhigher load stage, the oil generallyprovides sufficient resistance tomicro-pitting.

To confirm the result and obtaininformation of the course of thedamage (which may be degressive)over extended periods of operation,the progressive load test is followedby an endurance test with10 ... 50 · 106 load alternations.

= occurs frequently

scratching, chipping

70


Additional literature:

(1) Bartz W.J.: Getriebeschmierung,Expert publishing house, 1989

(2) Dubbel: Taschenbuch für denMaschinenbau, Springer publishinghouse, 16th edition, 1987

(3) Klüber Lubrication: Lubrication oflarge girth gear drives, edition07.1993

(4) Niemann G., Winter H.: Maschinen-elemente, Vol. II, Springer publish-ing house, 1985

(5) Wollhofen G.P. and 17 co-authors:Getriebeschmierung in der Anlagen-technik, Expert publishing house,1990

Sources of photographs (numbers inparentheses refer to the additionalliterature indicated above):

Fig. 1: Private photo/Klüber

Fig. 3, 4: from (4), page 4

Fig. 5: Source unknown

Fig. 6,7,8,9: from (4), page 4

Fig. 10: from (2), G 128

Fig. 11: (1), page 9

Fig. 12: (4), page 37

Fig. 13: from (2), G 138

Fig. 14: Sartorius

Fig. 15: Freudenberg

Fig. 16: Freudenberg

Fig. 17: Klüber

Fig. 18,12,20,21,22,12: GfT Worksheet 2.42.

Fig. 24: from (1), page 15



Fig. 27: Klüber

Fig. 28: Schmiertechnik und Tribologie, 1973, No. 5, page 148

Fig. 29: Klüber

Fig. 30: Klüber

Fig. 32: acc. to P. Walter

Fig. 35, 36: Klüber

Fig. 38: acc. to Ohlendorf

Fig. 39: GfT Worksheet 2.4.2

Fig. 42: Klüber

Fig. 43: acc. to GfT Worksheet 2.4.2Fig. 44: acc. to GfT Worksheet 2.4.2

Fig. 46: Klüber

Fig. 48: Klüber

Fig. 49: Klüber

Fig. 50: Klüber

Fig. 51: VOITH TURBO gear brochure

Fig. 53: Klüber

Fig. 54: Klüber

Fig. 58,59,60: GfT Worksheet 2.4.2

Fig. 61: Klüber

Fig. 62: Klüber

Fig. 63: Klüber

Fig. 64: Bauer Getriebe, Esslingen/ Klüber

Fig. 65: FLS

Fig. 66: Klüber

Fig. 70: ÖMV brochure: Schmierstoffe für Kraftfahrzeuge, 1993

Fig. 72,73,74,75: GfT Worksheet 2.4.2

Fig. 76: Klüber

Fig. 77: Forschungsstelle für Zahnräder und Getriebebau (FZG), TU München

Fig. 78: acc. to Bartz

Gear oils

Mineral oils .......................................................................................................................................................71

Synthetic oils, HC base .................................................................................................................................... 71

Synthetic oils, HC base – food grade lubricants ..............................................................................................72

Synthetic oils, PG base .................................................................................................................................... 73

Synthetic oils, ester oil base – rapidly biodegradable ...................................................................................... 74

Gear greases for industrial gears

Lubricating greases with a mineral base oil .....................................................................................................75

Lubricating greases with a synthetic base oil ................................................................................................... 76

Gear greases for small gears

Lubricating greases with a mineral base oil .....................................................................................................78

Lubricating greases with a synthetic base oil ................................................................................................... 79

Product survey

71

Lubrication of Gear SystemsGear oilsProduct survey

ISO

VG

DIN

51 5

19

Klü

bero

il G

EM

1-N

ser

ies

Klü

bers

ynth

GE

M 4

-N s

erie

s

Klü

bers

ynth

EG

4-s

erie

s

Klü

bero

il 4

UH

1N

ser

ies

Klü

bers

ynth

GH

6-s

erie

s

SY

NT

HE

SO

D …

EP

-ser

ies

Klü

berb

io C

A 2

-460

Klü

bers

ynth

GE

M 2

-ser

ies

Pro

per

ties

, Ap

plic

atio

n n

ote

s (f

or

det

aile

d in

form

atio

n,

ple

ase

see

pro

du

ct in

form

atio

n le

afle

t)T

ype

of

oil

Ser

vice

tem

per

atu

rera

ng

e*°C

, ap

pro

x.in

cas

e of

spl

ash

lubr

icat

ion

Lu

bri

can

t

Par

amet

ers

46–6

80

32–6

80

150–

1000

32–1

500

32–1

000

68–1

000

460

220–

320

-15

to 1

00

-45

to 1

40

-35

to 1

40

-30

to 1

10

-45

to 1

60

-35

to 1

00

-20

to 1

10

-25

to 1

10

min

eral

oil

synt

hetic

hyd

roca

rbon

oil

Hig

h pe

rfor

man

ce g

ear

and

mul

ti-pu

rpos

e oi

ls w

hich

mee

t CLP

req

uire

men

ts.

FZ

G te

st A

/8.3

/90,

scu

ffing

load

sta

ge ≥

12.

Hig

h m

icro

pitti

ng lo

ad c

apab

ility

.

Syn

thet

ic h

igh-

perf

orm

ance

gea

r oi

ls fo

r sp

ur, b

evel

and

wor

m g

ears

with

exc

elle

ntlo

w-t

empe

ratu

re b

ehav

iour

. The

y m

eet C

LP a

nd A

GM

A r

equi

rem

ents

. Mis

cibl

ew

ith m

iner

al o

ils. C

ompa

tible

with

com

mon

sea

ling

mat

eria

ls a

nd p

aint

s. F

ZG

test

A/8

.3/9

0, s

cuffi

ng lo

ad s

tage

> 1

2. H

igh

mic

ropi

tting

load

cap

abili

ty.

Syn

thet

ic h

igh-

perf

orm

ance

gea

r oi

ls fo

r sp

ur, b

evel

and

wor

m g

ears

with

exce

llent

low

-tem

pera

ture

beh

avio

ur. T

hey

mee

t CLP

and

AG

MA

req

uire

men

ts.

Mis

cibl

e w

ith m

iner

al o

ils. C

ompa

tible

with

com

mon

sea

ling

mat

eria

ls a

nd p

aint

s.F

ZG

A10

/16.

6R/9

0, s

cuffi

ng lo

ad s

tage

> 1

2. A

PI G

L 4.

Foo

d gr

ade

lubr

ican

ts a

utho

rized

in a

ccor

danc

e w

ith U

SD

A-H

1. E

spec

ially

sui

tabl

efo

r th

e lu

bric

atio

n of

spu

r, b

evel

and

wor

m g

ears

use

d in

the

food

pro

cess

ing

and

phar

mac

eutic

al in

dust

ries.

The

y m

eet C

LP. C

ompa

tible

with

com

mon

sea

ling

mat

eria

ls a

nd p

aint

s. F

ZG

test

A/8

.3/9

0, s

cuffi

ng lo

ad s

tage

> 1

2.

Hig

h-te

mpe

ratu

re g

ear

oils

with

a h

igh

scuf

fing

load

cap

acity

and

goo

d w

ear

pro-

tect

ion,

esp

ecia

lly s

uita

ble

for

the

lubr

icat

ion

of w

orm

gea

rs. F

ZG

test

A/1

6.6/

140,

scuf

fing

load

sta

ge >

12.

Not

mis

cibl

e w

ith m

iner

al o

ils. C

ompa

tibili

ty te

sts

with

seal

ing

mat

eria

ls a

nd p

aint

s ar

e re

quire

d.

Syn

thet

ic h

igh-

perf

orm

ance

gea

r oi

ls fo

r sp

ur a

nd b

evel

gea

rs o

pera

ting

unde

rex

trem

e lo

ads,

als

o su

itabl

e fo

r th

e lu

bric

atio

n of

hyp

oid

gear

s. O

ils o

f IS

O V

G 2

20an

d 46

0 pa

ss th

e F

ZG

-L-4

2 te

st, A

PI G

L 5.

Hig

h m

icro

pitti

ng lo

ad c

apab

ility

. Not

mis

cibl

e w

ith m

iner

al o

ils. C

ompa

tibili

ty te

sts

with

sea

ling

mat

eria

ls a

nd p

aint

s ar

ere

quire

d.

Esp

ecia

lly s

uita

ble

for

the

lubr

icat

ion

of w

orm

gea

rs w

hich

are

use

d in

app

licat

ions

whe

re le

akin

g lu

bric

ant m

ay b

e da

nger

ous

to th

e en

viro

nmen

t. B

iode

grad

abili

tyac

c. to

CE

C-L

-33-

A-9

4 af

ter

21 d

ays

> 7

0%.

Syn

thet

ic h

igh-

perf

orm

ance

gea

r oi

ls fo

r sp

ur, b

evel

and

wor

m g

ears

. The

y m

eet

CLP

req

uire

men

ts. M

isci

ble

with

min

eral

oils

. Com

patib

le w

ith c

omm

on s

ealin

gm

ater

ials

and

pai

nts.

FZ

G te

st A

/8.3

/90,

scu

ffing

load

sta

ge ≥

12.

Hig

h m

icro

pitti

nglo

ad c

apab

ility

. Bio

degr

adab

ility

acc

. to

CE

C-L

-33-

A-9

4 af

ter

21 d

ays

> 7

0%.

* se

e pa

ge 7

8

synt

hetic

hyd

roca

rbon

oil

synt

hetic

hyd

roca

rbon

oil

poly

glyc

ols

poly

glyc

ols

biod

egra

dabl

e es

ter

biod

egra

dabl

e es

ter

72

Lubrication of Gear SystemsGear greases for industrial gearsProduct survey

MIC

RO

LUB

E G

B 0

and

00

Klü

berp

lex

GE

11-

680

UN

IGE

AR

ST

2 M

Klü

bers

ynth

GE

46-

1200

ISO

FLE

X T

OP

AS

NC

A 5

051

ISO

FLE

X T

OP

AS

L 3

2

ISO

FLE

X T

OP

AS

NC

A 5

2

Bas

e o

il/th

icke

ner

Flu

id g

ear

grea

se fo

r sp

lash

lubr

icat

ion

of g

ear

syst

ems

subj

ect t

oin

crea

sed

load

s at

nor

mal

tem

pera

ture

s: F

ZG

test

A/2

.76/

50, l

oad

stag

e >

12.

Noi

se d

ampe

ning

adh

esiv

e gr

ease

for

spra

y lu

bric

atio

n of

ope

nge

ars,

als

o su

itabl

e fo

r sp

lash

lubr

icat

ion

of g

earb

oxes

ope

ratin

gat

nor

mal

tem

pera

ture

s. F

ZG

test

A/2

.76/

50, l

oad

stag

e >

12.

Gea

r gr

ease

for

open

and

clo

sed

spur

gea

rs o

f lar

ger

dim

ensi

ons

subj

ect t

o hi

gh lo

ads.

FZ

G te

st A

/8.3

/90,

load

sta

ge >

12.

Syn

thet

ic s

emi f

luid

gre

ase

for

spla

sh lu

bric

atio

n at

low

and

hig

hte

mpe

ratu

res.

For

hig

h lo

ads

as w

ell a

s lo

ng-t

erm

and

life

time

lubr

icat

ion,

up

to 8

m/s

phe

riper

al s

peed

. FZ

G te

st A

/8.3

/90,

load

stag

e >

12.

Not

sui

tabl

e fo

r ge

ars

mad

e of

pla

stic

s or

alu

min

ium

allo

ys.

Noi

se d

ampe

ning

gre

ase

for

spla

sh lu

bric

atio

n op

en g

ears

that

are

not o

il tig

ht. S

uita

ble

for

flank

gre

asin

g. E

spec

ially

sui

tabl

e fo

rge

ars

mad

e of

pla

stic

com

pone

nts.

Low

tem

pera

ture

gre

ase

for

toot

h fla

nks

with

a w

ide

serv

ice

tem

-pe

ratu

re r

ange

. Esp

ecia

lly s

uita

ble

for

plas

tic/p

last

ic a

nd p

last

ic/

stee

l whe

els.

Ens

ures

low

sta

rtin

g to

rque

s an

d sm

ooth

ope

ratio

nat

low

tem

pera

ture

s. M

eets

spe

cific

atio

ns o

f var

ious

aut

omob

ilem

anuf

actu

rers

.

Lubr

icat

ing

grea

se w

ith a

wid

e se

rvic

e te

mpe

ratu

re r

ange

for

toot

hfla

nks

and

lifet

ime

lubr

icat

ion

of s

mal

l gea

rs s

ubje

ct to

incr

ease

dlo

ads.

Esp

ecia

lly s

uita

ble

for

plas

tic/p

last

ic a

nd p

last

ic/s

teel

gea

rw

heel

s. L

ow b

ase

oil v

isco

sity

, thu

s lo

w s

tart

ing

torq

ues

at lo

wte

mpe

ratu

res.

* se

e pa

ge 7

8

Lu

bri

can

t

Par

amet

ers

Pro

per

ties

, Ap

plic

atio

n n

ote

s (f

or

det

aile

d in

form

atio

n,

ple

ase

see

pro

du

ct in

form

atio

n le

afle

t)S

ervi

cete

mp

erat

ure

ran

ge*

°C, a

pp

rox.

in c

ase

of s

plas

h

lubr

icat

ion

NL

GI

Gra

de

Co

lou

rU

se in

smal

lg

ears

x x x x x x

redd

ish

brow

n

brow

n

dark

brow

n

brow

n

yello

wis

h

beig

e

beig

e

min

eral

oil/

silic

ate

min

eral

oil/

Al c

ompl

ex

min

eral

oil/

sodi

um/M

oS2

poly

glyc

ol/

lithi

um

synt

h. h

ydro

-ca

rbon

oil/

spec

ial C

a

synt

h. h

ydro

-ca

rbon

oil/

lithi

um

synt

h. h

ydro

-ca

rbon

oil/

spec

ial C

a

0 / 0

00

0 / 0

0

0 / 1 00 0 2 2

-10

to 1

50

-10

to 1

40

-10

to 1

50

-30

to 1

20

-30

to 1

50

-60

to 1

30

-50

to 1

50

x x x x

Use

inin

du

stri

alg

ears

73

Lubrication of Gear SystemsGear greases for industrial gearsProduct survey

Klü

bers

ynth

GE

14-

151

Klü

bers

ynth

UH

1 14

-151

Klü

bers

ynth

UH

1 14

-160

0

Bas

e o

il/th

icke

ner

Lubr

icat

ing

grea

se fo

r th

e lu

bric

atio

n of

gea

rs b

earin

gs, j

oint

s in

smal

l gea

rs s

ubje

ct to

hig

h lo

ads,

e.g

. pow

er to

ols.

Sui

tabl

e fo

rap

plic

atio

ns w

ith a

hig

h sl

idin

g pe

rcen

tage

and

per

iphe

ral s

peed

of 2

0 m

/s a

t sho

rt te

rm o

pera

tions

.

Foo

d gr

ade

lubr

ican

t app

rove

d in

acc

. to

US

DA

-H1

grea

se fo

r th

efo

od p

roce

ssin

g an

d ph

arm

aceu

tical

indu

strie

s. E

xcel

lent

prot

ectio

n ag

ains

t wea

r, g

ood

resi

stan

ce to

cor

rosi

on, v

ery

good

low

-tem

pera

ture

beh

avio

ur.

Foo

d gr

ade

lubr

ican

t aut

horiz

ed in

acc

. US

DA

-H1.

Sem

i flu

idgr

ease

for

the

food

pro

cess

ing

and

phar

mac

eutic

al in

dust

ries.

Exc

elle

nt p

rote

ctio

n ag

ains

t wea

r, g

ood

resi

stan

ce to

cor

rosi

on,

very

goo

d lo

w-t

empe

ratu

re b

ehav

iour

. FZ

G te

st A

/2.7

6/50

load

stag

e 12

.

* se

e pa

ge 7

8

Lu

bri

can

t

Par

amet

ers

Pro

per

ties

, Ap

plic

atio

n n

ote

s (f

or

det

aile

d in

form

atio

n,

ple

ase

see

pro

du

ct in

form

atio

n le

afle

t)S

ervi

cete

mp

erat

ure

ran

ge*

° C, a

pp

rox.

in c

ase

of s

plas

h

lubr

icat

ion

NL

GI

Gra

de

Co

lou

rU

se in

smal

lg

ears

xye

llow

beig

e

yello

wis

h

synt

h. h

ydro

-ca

rbon

oil/

Al c

ompl

ex

synt

h. h

ydro

-ca

rbon

oil/

Al c

ompl

ex

synt

h. h

ydro

-ca

rbon

oil/

Al c

ompl

ex

1 1 00

-35

to 1

40

-45

to 1

20

-45

to 1

20

x x

Use

inin

du

stri

alg

ears

74

Lubrication of Gear SystemsGear greases for small gears

Min

eral

oil

bas

elu

bri

cati

ng

gre

ases

MIC

RO

LUB

EG

B 0

0

Klü

berp

lex

GE

11-

680

Min

eral

oil/

silic

ate

Min

eral

oil/

Al c

ompl

ex

EL L

Flu

id g

ear

grea

se fo

r sp

lash

lubr

icat

ion

of s

pur

and

beve

l gea

rs o

pera

ting

in th

eno

rmal

tem

pera

ture

ran

gean

d su

bjec

t to

high

load

s.G

ood

prot

ectio

n ag

ains

tw

ear

and

corr

osio

n.S

cuffi

ng lo

ad s

tage

>12

in th

e sp

ecia

l FZ

G te

stA

/2.7

6/50

and

a w

ork-

rela

ted

chan

ge in

wei

ght

< 0

.2 m

g/kW

h.

Noi

se-d

ampi

ng a

dhes

ive

grea

se fo

r th

e lu

bric

atio

n of

toot

h fla

nks

of o

pen

gear

sof

larg

er d

imen

sion

s(m

odul

e >

3 m

m)

subj

ect t

oin

crea

sed

load

s. A

lso

suita

ble

for

spla

sh lu

bric

a-tio

n. T

o be

app

lied

in th

eno

rmal

tem

pera

ture

ran

geon

ste

el/s

teel

gea

r w

heel

s.

Scu

ffing

load

sta

ge >

12 in

the

spec

ial F

ZG

test

A/2

.76/

50.

*, *

* an

d **

* se

e pa

ge 7

8

-10

to 1

50

-10

to 1

40

0.90

0.94

700

680

35 35

redd

ish

brow

n

brow

n

–

> 1

60

– –

00 /

000

0 / 0

0

430

to 4

75

380

to 4

20

4010

0

Product surveyB

ase

oil/

thic

ken

erA

pp

aren

tvi

sco

sity

Klü

ber

visc

osity

rang

e***

Par

amet

ers

Pro

per

ties

Ap

plic

atio

n n

ote

sS

ervi

cete

mp

erat

ure

ran

ge*

° C, a

pp

rox.

in c

ase

of s

plas

hlu

bric

atio

n

Den

sity

DIN

51 7

57(g

/cm

3)

at 2

0 °C

≈

Bas

e o

ilvi

sco

sity

DIN

51

562

(mm

2 /s

), a

t °C

≈

Co

lou

rD

rop

po

int

DIN

ISO

2176

(°C

) ≈

Sp

eed

fact

or*

*n

· dm

(mm

/min

)

Co

n-

sist

ency

gra

de

DIN

51 8

18

Wo

rked

pen

etra

tio

nD

IN IS

O21

37(0

.1 m

m)

≈L

ub

rica

nt

75


Lu

bri

cati

ng

gre

ases

wit

h a

min

eral

bas

e o

il

MIC

RO

LUB

EG

B 0

Lu

bri

cati

ng

gre

ases

wit

h a

syn

thet

ic b

ase

oil

Klü

bers

ynth

GE

46-

1200

Min

eral

oil/

silic

ate

Pol

ygly

col/

lithi

um

L EL

Gea

r gr

ease

for

spla

shlu

bric

atio

n or

toot

h fla

nkgr

easi

ng o

f sm

all g

ears

subj

ect t

o hi

gh lo

ads.

Goo

d pr

otec

tion

agai

nst

wea

r an

d co

rros

ion.

Scu

ffing

load

sta

ge >

12in

the

spec

ial F

ZG

test

A/2

.76/

50 a

nd w

ork-

rela

ted

chan

ge in

wei

ght

< 0

.2 m

g/kW

h.

Flu

id g

ear

grea

se fo

rsp

lash

lubr

icat

ion

e.g.

gea

rm

otor

s su

bjec

t to

high

load

s (u

p to

8 m

/spe

riphe

ral s

peed

) w

ith g

ear

stag

es in

the

form

of s

pur,

beve

l and

wor

m g

ears

.

Not

sui

tabl

e fo

r ge

arw

heel

s m

ade

of s

ynth

etic

mat

eria

ls o

r al

lum

inum

allo

ys.

Can

be

appl

ied

on m

ini-

atur

e ge

ars.

Scu

ffing

load

sta

ge >

12 in

the

FZ

G te

st A

/8.3

/90,

DIN

51

354,

Pt 2

.

*, *

* an

d **

* se

e pa

ge 7

8

-25

to 1

50in

cas

e of

spl

ash

lubr

icat

ion

-30

to 1

20

0.90

0.99

400

120

25 20

redd

ish

brow

n

brow

n

> 1

80

> 1

60

– –

4010

0

0 00

355

to 3

85

400

to 4

30

Product surveyB

ase

oil/

thic

ken

erA

pp

aren

tvi

sco

sity

Klü

ber

visc

osity

rang

e***

Par

amet

ers

Pro

per

ties

Ap

plic

atio

n n

ote

sS

ervi

cete

mp

erat

ure

ran

ge*

° C, a

pp

rox.

Den

sity

DIN

51 7

57(g

/cm

3)

at 2

0 °C

≈

Bas

e o

ilvi

sco

sity

DIN

51

562

(mm

2 /s

), a

t °C

≈

Co

lou

rD

rop

po

int

DIN

ISO

2176

(°C

) ≈

Sp

eed

fact

or*

*n

· dm

(mm

/min

)

Co

n-

sist

ency

gra

de

DIN

51 8

18

Wo

rked

pen

etra

tio

nD

IN IS

O21

37(0

.1 m

m)

≈L

ub

rica

nt

76


Lu

bri

cati

ng

gre

ases

wit

h a

syn

thet

ic b

ase

oil

ISO

FLE

X T

OP

AS

NC

A 5

051

Klü

bers

ynth

G 3

4-13

0

Syn

thet

ichy

dro-

carb

on o

il/sp

ecia

l Ca

Syn

thet

ichy

dro-

carb

on o

il/m

iner

al o

il/sp

ecia

l Ca

EL

EL

Noi

se-d

ampi

ng g

reas

e fo

rsp

lash

lubr

icat

ion

of g

ears

that

are

not

oilt

ight

. Sui

tabl

efo

r fla

nk g

reas

ing.

Esp

ecia

lly s

uita

ble

for

gear

sw

ith p

last

ic c

ompo

nent

s.E

xcel

lent

low

-tem

pera

ture

beha

vioe

r; lo

w s

tart

ing

torq

ues

poss

ible

.

Spe

cial

gre

ase

for

smal

lge

ars,

e.g

. in

pow

er h

and

tool

s an

d eq

uipm

ent f

orcr

afts

men

. Sui

tabl

e fo

rsp

lash

lubr

icat

ion

(up

to5

m/s

per

iphe

ral s

peed

) an

dfla

nk g

reas

ing

(up

to 4

m/s

).W

ide

serv

ice

tem

pera

ture

rang

e.

Esp

ecia

lly s

uita

ble

for

plas

tic/p

last

ic a

nd p

last

ic/

stee

l gea

rs.

*, *

* an

d **

* se

e pa

ge 7

8

4010

0

1 00

0 00

0

–

beig

e

beig

e,br

owni

sh

> 1

80

> 1

80

0.85

0.87

30 130

6

15.5

-50

to 1

40

-30

to 1

50in

cas

e of

spl

ash

lubr

icat

ion

0 / 0

0

0

385

to 4

15

355

to 3

85

Product surveyB

ase

oil/

thic

ken

erP

aram

eter

sP

rop

erti

esA

pp

licat

ion

no

tes

Ser

vice

tem

per

atu

rera

ng

e*°C

, ap

pro

x.in

cas

e of

spl

ash

lubr

icat

ion

Den

sity

DIN

51 7

57(g

/cm

3)

at 2

0 °C

≈

Bas

e o

ilvi

sco

sity

DIN

51

562

(mm

2 /s

), a

t °C

≈

Co

lou

rD

rop

po

int

DIN

ISO

2176

(°C

) ≈

Co

n-

sist

ency

gra

de

DIN

51 8

18

Wo

rked

pen

etra

tio

nD

IN IS

O21

37(0

.1 m

m)

≈L

ub

rica

nt

Sp

eed

fact

or *

*n

· dm

(mm

/min

)

Ap

par

ent

visc

osi

tyK

lübe

rvi

scos

ityra

nge*

**

77


Lu

bri

cati

ng

gre

ases

wit

h a

syn

thet

ic b

ase

oil

ISO

FLE

X T

OP

AS

L 32

ISO

FLE

X T

OP

AS

NC

A 5

2

Klü

bers

ynth

GE

14-

151

Klü

bers

ynth

UH

1 14

-151

Syn

thet

ichy

dro-

carb

on o

il /

Li

Syn

thet

ichy

dro-

carb

on o

il /

spec

ial C

a

Est

er o

il /

poly

urea

L

L / M L

Low

-tem

pera

ture

gre

ase

for

toot

h fla

nks

with

a w

ide

serv

ice

tem

pera

ture

ran

ge.

Esp

ecia

lly s

uita

ble

for

plas

tic/p

last

ic a

nd p

last

ic/

stee

l whe

els.

Ens

ures

low

sta

rtin

gto

rque

s an

d sm

ooth

ope

ra-

tion

at lo

w te

mpe

ratu

res.

Mee

ts s

peci

ficat

ions

of

vario

us a

utom

obile

man

ufac

ture

rs.

Lubr

icat

ing

grea

se w

ith a

wid

e se

rvic

e te

mpe

ratu

rera

nge

for

toot

h fla

nks

and

lifet

ime

lubr

icat

ion

of s

mal

lge

ars

subj

ect t

o in

crea

sed

load

s.

Esp

ecia

lly s

uita

ble

for

plas

tic/p

last

ic a

nd p

last

ic/

stee

l gea

r w

heel

s.

Low

bas

e oi

l vis

cosi

ty, t

hus

low

sta

rtin

g to

rque

s at

low

tem

pera

ture

s.

Hig

h-te

mpe

ratu

re lu

bri-

catin

g gr

ease

with

a w

ide

serv

ice

tem

pera

ture

ran

gefo

r fla

nk g

reas

ing.

Ens

ures

low

driv

ing

torq

ues

at lo

w a

mbi

ent

tem

pera

ture

s (s

moo

thop

erat

ion)

.

*, *

* an

d **

* se

e pa

ge 7

8

4010

0

1 00

0 00

0

1 00

0 00

0

600

000

> 1

85

> 2

20

> 2

50

beig

e

beig

e

beig

e

3.8

5.5

9.4

17.5

30 70

0.88

0.89

0.96

-60

to 1

30

-50

to 1

50

-40

to 1

80

2 2

2 / 3

265

to 2

95

265

to 2

95

250

to 2

80

Gear greases for small gearsProduct survey

Bas

e o

il/th

icke

ner

Par

amet

ers

Pro

per

ties

Ap

plic

atio

n n

ote

s

Lu

bri

can

t

Co

n-

sist

ency

gra

de

DIN

51 8

18

Wo

rked

pen

etra

tio

nD

IN IS

O21

37(0

.1 m

m)

≈

Ser

vice

tem

per

atu

rera

ng

e*°C

, ap

pro

x.

Den

sity

DIN

51 7

57(g

/cm

3)

at 2

0 °C

≈

Bas

e o

ilvi

sco

sity

DIN

51

562

(mm

2 /s

), a

t °C

≈

Co

lou

rD

rop

po

int

DIN

ISO

2176

(°C

) ≈

Sp

eed

fact

or *

*n

· dm

(mm

/min

)

Ap

par

ent

visc

osi

tyK

lübe

rvi

scos

ityra

nge*

***

78


Notes

* Service temperatures are guide valueswhich depend on the lubricant’s composi-tion, the intended use and the applicationmethod. Lubricants change their con-sistency, apparent dynamic viscosity orviscosity depending on the mechano-dynamical loads, time, pressure andtemperature. These changes in productcharacteristics may affect the function ofa component.

** Speed factors are guide values whichdepend on the type and size of the rollingbearing type and the local operatingconditions, which is why they have to beconfirmed in tests carried out by the userin each individual case.

*** Klüber viscosity grades:EL = extra light lubricating grease;L = light lubricating grease; M = mediumlubricating grease; S = heavy lubricatinggrease; ES = extra heavy lubricatinggrease

79


Publisher and Copyright:Klüber Lubrication München KG

Reprints, total or in part, are permitted ifsource is indicated and voucher copy isforwarded.

9.3/9.4 eEdition 11.03, replaces edition 12.98

The data in this technical brochure isbased on our general experience andknowledge at the time of printing and isintended to give information of possibleapplications to a reader with technicalexperience. It constitutes neither anassurance of product properties nordoes it release the user from the obliga-tion of performing preliminary tests withthe selected product. We recommendcontacting our Technical ConsultingStaff to discuss your specific applica-tion. If required and possible we will bepleased to provide a sample for testing.

Klüber products are continually im-proved. Therefore, Klüber Lubricationreserves the right to change all thetechnical data in this technical brochureat any time without notice.

Lubrication of Gear Systems

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