Bearing Project

STUDY OF CONDITION MONITRING TECHNIQUES

TO

REDUCE BEARING FAILURE’S IN FINISHING MILL

OFWIRE ROD MILL

VIZAG STEEL PLANT

Project report submitted in partial fulfillment of the requirement

For the award of the degree of B.Tech

BY

E.S.ARAVIND M.ASHOK KUMAR

08L31A0316 08L31A0335

P.VASUDEV S.CHAITANYA

08L31A0344 08L31A0354

K.CHANDRA SHEKAR

09L35A0305

Under the guidance of

T.JAGADESWARA RAO

(Asst. General. Manager)

VIGNAN INSTITUTE OF INFORMATION TECHNOLOGY

DUVVADA

CERTIFICATE

This is to certify that the project report entitled “CONDITION MONITRING

TECHNIQUES TO REDUCE BEARINGS FAILURE IN FINISHING MILL OF

WIRE ROD MILL” is being submitted by

E.S.ARAVIND 08L31A0316

M.ASHOK KUMAR 08L31A0335

P.VASUDEV 08L31A0344

S.CHAITANYA 08L31A0354

K.CHANDRA SHEKAR 09L35A0305

In partial fulfillment of the degree of Bachelor of Technology in mechanical

branch in VIGNAN INSTITUTE OF INFORMATION TECHNOLOGY,

DUVVADA. Is a record of bonafied work carried out by them under my

guidance and supervision.

The results embodied in this project report have not been submitted to any other

University or Institute for the award of any Degree or Diploma.

MR. T.JAGADESWARA RAO

(Asst. General. Manager)

WRM DEPARTMENT, VSP

ACKNOWLEDGEMENT

It is my pleasure and duty to express my indebtedness to

Sir MR. T.JAGADESWARA RAO (AGM) WRM DEPARTMENT, VSP for

providing us the guidance and required assistance to enable us to undergo our project

work success.

I would like to thank B. Sateesh Head of the Mechanical engineering

Department, VIGNAN INSTITUTE OF INFORMATION TECHNOLOGY for his

constant encouragement and support in completing the project.

I also thank training and development centre (T&DC), VSP for introducing

us to the industry and for holding such useful project training.

Lastly, I would like to thank all the employees of vsp with kind cooperation

without whom it would not have been possible to travel through various departments in

the plant and complete the project successfully.

OVER VIEW OF VIZAG STEEL PLANT

Steel comprises one of the most important inputs in all sectors of economy. Steel

industry is both a basic and a core industry. The economy of any nation depends on a

strong base of iron and steel industry in that nation. Iron & steel making, as India has

known a craft for a long time. The growth of steel industry in India can be

conveniently studied by dividing the period into pre & post independence era. By

1950, the total installed capacity for ingot steel production was 1.5 million tonnes per

year. The capacity increased by 11 folds to about 16 million tones by nineties.

Presently in India, steel products are being produced from 4 different sources, namely

integrated Steel plants, Re-rolling Mills, Alloy & special steel plants. In integrated

steel plants, naturally occurring raw materials are processed into finished (steel)

products in various stages.

These plants are highly capital intensive. If needs approximately Rs.2500 crores of

money to establish a 1 million ton per year steel plant.

Visakhapatnam Steel Plant is an integrated steel plant, constructed with former USSR

collaboration. It is the first based and integrated steel plant constructed in South India,

with many modern technological features, some of them for the first time in the

country. Among these are:

7 meter tall coke ovens Dry quenching of coke

On ground blending of sinter base mix

Conveyer charging and bell less top for Blast furnace

Cast house slag granulation for Blast furnace

100% continuous casting of liquid steel

Gas expansion turbine for power generation utilizing Blast furnace top gas pressure

Hot metal desulphurization

Extensive treatment facilities of effluents for ensuring proper environmental

protection

Computerization for process control

Sophisticated high speed and high production rolling mills

Major Sources of Raw Materials:

Water Supply: Operational water requirement of 36 mgd is being met from the Yeluru Water Supply Scheme

Power Supply: Operational power requirement of 180 to 200 MW is being met

through Captive Power Plant. The capacity of power plant is 286.5 MW.VSP is

exporting 60 MW power to APSEB.

MAJOR DEPARTMENTS

Raw materials handling plant (RMHP):

VSP annually requires quality raw materials viz. iron ore, fluxes; coking and non

coking coals etc. to the tune of 12 to 3 million tons for producing 3 million tones of

liquid steel. To handle such a large volume of incoming raw materials received from

Raw Material Source Source

Iron Ore Lumps & Fines Bailadilla,MP

BF Lime Stone Jaggayyapeta,AP

SMS Lime Stone UAE

BF Dolomite Madharam,AP

SMS Dolomite Madharam,AP

Manganese Ore Chipurupalli,AP

Boiler Coal Talcer,Orissa

Coking Coal Australia

Medium Coking Coal (MCC) Gidi/Swang/Rajarappa/kargali

different sources and to ensure timely supply of consistent quality of feed materials to

different VSP consumers, Raw Material Handling Plant serves a vital function.

Coke Ovens and Coal Chemical Plant (CO and CCP):

Coke is manufactured by heating of crushed coking coal in the absence of

air at a temperature of 1000c and above for about 16 to 18 hours. At VSP there

are three coke oven batteries, 7m tall and having 67 ovens each. The carbonization

takes place at 1000 to 1050c in absence of air for 16 to 18 hours. The useful coal

chemicals are extracted in coal chemical plant from C. O. Gas. After recovering the

coal chemicals the gas is used as a byproduct fuel by mixing it with gases such as BF

Gas, LD Gas etc.

Sinter Plant (SP):

Sinter is a hard and porous ferrous material obtained by agglomeration of

iron fines, coke breeze, lime stone fines, metallurgical wastes viz. flue dust, mill scale,

LD slag etc.

Sinter is a better feed material to blast furnace in comparison to iron ore

lumps and its usage in blast furnaces help in increasing productivity, decreasing the

coke rate and improving the quality of hot metal produced.

Blast Furnaces (BF):

Hot metal is produced in the Blast Furnaces, which are tall vertical

furnaces. The furnace is named as Blast Furnace as it runs with a blast at high pressure

and temperature. Raw materials such as sinter, iron ore lumps, fluxes and coke are

charged from the top and hot blast at 1100c to 1300c and 5.75 KSCG pressure is blown

almost from the bottom. VSP has two 3200 cu.metre. Blast Furnaces namely Godavari

and Krishna named after the two rivers of AP.

Steel Melting Shop (SMS):

Steel is an alloy of iron with carbon up to 1.8%. Hot metal produced in

Blast Furnace contains impurities such as Carbon, Silicon, Manganese, and Sulphur

and phosphorous is not suitable as a common Engineering Material. To improve the

quality, the impurities are to be eliminated or decreasing by oxidation process.

VSP produces steel employing three numbers of top blown Oxygen Converters.

Each converter is having 133cu.metre volume capable of producing 3 million tones of

liquid steel annually. The hot metal, steel scrap, fluxes from a part of the charge to the

converters.

Continuous Casting Department (CCD):

Continuous casting may be defined as teaming of liquid steel in a mould

with a false bottom through which partially solidified ingot is continuously withdrawn

at the same rate at which liquid steel is teamed in the mould.

At VSP there are six-4 strand continuous casting machines capable of producing 2.82 Million tons per year, Blooms of size 250250 mm and 250320 mm.

ROLLING MILLS :

Blooms produced in SMS-CCD do not find much applications as such and are required

to be shaped into products such as billets, round, squares, angles (equal and unequal,

channels, I-PE beams, HE beams, wire rod and reinforcements by rolling them in, there

sophisticated high capacity, high speed, fully automated rolling mills, namely Light

and Medium Merchant Mills (LMMM), Wire Rod Mills (WRM) and Medium

Merchant and Structural Mill (MMSM).

1. Light and Medium Merchant Mills: - LMMM comprises of two units in

the billets/break down mill 250 320 mm size blooms are rolled into billets of 125 mm

size after heating them in two nos. of walking beam furnaces of 200T/hr capacity each.

This unit comprises of 7 stands (2 horizontal 859 1200mm) and 5 alternations vertical

and horizontal stands (730 1000 mm and 630 1000 mm) billets are supplied from this mill

to bar mill of LMMM, wire rod mills (WRM).

2. Wire Rod Mills (WRM):- Wire rod mill is a 4 strand, 25 strands fully

sophisticated mill. The mill has 4 zone combination type reheating furnace (walking

beam cum walking hearth ) of 200T/hr capacity for heating the billet received from the

billet mill of LMMM to rolling temperature of 1200c.

3. Medium Merchant and Structural Mill (MMSM) :- This mill is a high

capacity continuous of 20 strands arranged in 3 trains. Roughing train having 8 strands (4

two high horizontal strands, two vertical strands and two combination)

Intermediate train has six mill strands as per details given below.

2 high horizontal strands

2 combination strands

2 horizontal strands/two universal strands

Finishing train – consists of 6 strands namely

2 combination strands

4 horizontal strands/4 universal strands.

WIRERODMILL

Introduction Wire Rod mills (WRM): wire rod mill is a 4 strand, 25 stands fully sophisticated

mill. The mill has 4 zone combination type reheating furnace (wailing beam cum

walking hearth ) of 200t/hr capacity for heating the billets received from billet mill of

LMMM to rolling temperature of 1200 degrees centigrade. The continuous 4 strand

wire mill for the RASHTRIYA ISPAT NIGAM LIMITED is a high speed roll mill

of modern technological design, including equipment for controlled cooling of rolled

product from rolling heat by stelmor method. The mill is designer for low and high

carbon Steel up to 0.9% carbon.

CHARACTERISTIC DESIGN FEATURES OF THE WIRE ROD MILL

High production after a short starting time.

Reliable loading at high speeds.

High wire qualities.

Charging material:BILLET WEIGHT: 1250 kg

CROSS SECTION DIMENSIONS: 125 x 125 mm

BILLET LENGTH: 1044 mm

Rolling Program:

5.5 to 12 mm round

6.0 to 12.7 mm rebar

Maximum coil weight 1200 kg

Outside coil diameter 1250mm

Inside coil diameter 850 mm

Coil height not compacted:

Round approximately 2200mm

Rebar “ 2200mm

Coil height compacted

Round approximately 1200 mm

Rebar “ 1350mm

Charging material:The charging material –rolled billets from the billets from the billet mill be straight,

free from shells, free from shrinkages cavities and additionally free from cracks as far

as quality steel grades are concerned, so that a continuous at the required quality is

guaranteed.

Finished Material :Based on max temperature difference across the billet cross section of 25 degree

centigrade on entering the mill train, the following tolerance values are obtained:

5.5mm – 8 mm round (+/-) 0.15 mm

9 mm – 12 mm round (+/-) 0.20 mm

Capacity of the PlantThe annual capacity of the rod mill be 850 000 tons of finished wire rods by three shift

operation and specified product mix.

Figure 1.0 : Layout drawing of Wire Rod Mill

EQUIPMENTS OF WIRE ROD MILL: 1. Roughing train

5 two high horizontal stands 600 mm dia.


2. Intermediate train



3. Intermediate Block

4 single stands two high roughing blocks in HV arrangement.

4. Finishing train

4 one stand wire rod finishing blocks (Morgan type ) with 10 no twist two high rolling units

each in 45 degree arrangement

5. Billet deposing grids, inclined hoist, billet collect device.

6. Furnace approach roller table ejector for rejected billets.

7. Billets ejector.

8. With drawing pinch roll set, billet switch, pendulum shear.

9. 4 cropping and chopping shears.

10. 4 Horizons lopper.

11. Water cooling sections with 3 water cooling boxes each.

12. 4 Rotary cropping and cross cutting shears.

13. 2 Chopping shears.

14. Horizontal loppers.

15. 4 Water cooling sections with 3 water cooling boxes each.

16. 4 Pinch roll sets and 4 laying heads.

17. 4 Stelmor conveyors for delayed cooling, 10 cooling zones each.

18. 4 Coil forming chambers with dividing shears.

4 coil receiving stations.

4 Up ender loading stations

19. Power and free hook conveyor.

20. 6 coil compacting presses.

21. 6 coil unloading stations.

22. 4 coil weighing machines.

23. 2 Large coil compactor circuit’s comprising power and free conveyor, coil Transfer station, large

size coil compactor and unloading station.

Description of Mill Mechanical Equipment:

The inspected billets rolled by the billet unit to the size 125 x 125 x

10400mm are taken from the billet store and where placed down on the first of the two

charging grids in larders of 8 to 10 billets each. The weight capacity of the charging

grid is 200tons which conforms to a storage capacity sufficient to store the production

of one hour.

The billets deposited are by means of for operated pawl transfers with

electromechanical drive moved towards the billet cross transport on the grids are

passed to over to that transport on the grids are passed to over to that transport one by

one.

The billet cross transport which is also arranged at (+/-)0 m takes the

individual billets with drag chains and transports them step by step from the billet

charging grid NO.2.

In to the area of the inclined elevator. Nine billets in total can be deposited

in the area between billet charging grid and inclined elevator; they rest on roller chain

carrier plates during transport.

The furnace roller table extends from the area of the billet positioning

device up on the charging side of the walking beam the 48 driven rollers of the table

are subdivided into two groups with three disappearing stops between and two fixed

stops arranged on both ends of the roller table.

The billets lying on the roller table are carried to the furnace by means of

electrically combined roller table sections with separately divided reversible rollers.

The roller table is limited by a fixed stop at its rear end.

Pneumatically operated disappearing stops prevented succeeding billets from

colliding with proceeding once on individual roller tables. With bottom heaters in the

soaking zone has a nominal through input capacity of 200t/hr.

The charging of the furnace will be done by walking beams, which transfers the

4 billets together. The walking beams can be lifted and lowered as well as displaced in

the longitudinal direction to transfer the billets through the furnace step at a cycle of 72

sec per stroke.

Uniform heating of the billets is ensured by bottom and top heating to improve

the temperature compensation in the billets, they are pushed together on the soaking

hearth in solid masonry at the end of the furnace. This hearth made of temperature

changes resistant and abrasion resistant material has no load bearing cooled rails, so

that no local cold spots can occur on the billets and existing temperature differences

are compared.

THE WALKING BEAM FURNACE OFFERS SEVERAL ADVANTAGES :

Smaller temperature difference across the billet cross section

Safe possibilities to vary billet length and billet cross section

Small heat losses due to water cooled rails

Simply emptying of furnace

Smaller wear of lining

The discharging temperature will be 12000 c depending on the steel quality.

On the discharging side of the furnace a billet discharging machine pushes the

single billet from furnace to the stand no1 by help of rollers then it again aligned the

following billet.

After discharging 4 billets, the walking beam moves a further step to refill the

empty space left by the billet ejected.

A hydraulically operated switch guides the billet to the respective stand.

The billet switch, a v-shaped CI design with open top, is lowered and moved

underneath the stand to be charged in the rise working position it is on pass line

level and guides the billet into the free groove in each case. After the initial pass has

been carried out the switch is lowered again and moves underneath the running

billet into the receiving position for the next stand.

A four stand pendulum shear with hydraulic drive is arranged. The shear

serves for chopping and dividing the hot billet in case of “cold head “or rolling mal

functions. The rolling mill train is sub divided into seven roughing mills, an 8 stand

intermediate mill and 10 stand rod finishing mill. Rotary shears, snap shears,

cooling sections and controlled material cooling and placed between or in front of

the coil handling facilities.

From stand no.1 to stand no.13 the stands are designed as 4 strands stands.

Behind stand no.13 the intermediate mill is sub divided into 4 single stand

lines. A sum of 25 roll stands results thus for each stand. The roughing

comprises of 7 continuous 4 stands horizontal to high mill stand into sizes.

Five stand 21” with a roll diameter of 600mm and the barrel length of

1000mm and stand 16” with roll diameter of 480mm and a barrel length of 920mm.

For all mill stands the pass line is 900mm above mill floor (=+5350mm). All stands

are fitted with variable speed dc drives.

Post arranged to the roughing train four rotary shears, one for each stand, is

placed for cropping and chopping if malfunction should occur. Each shear has a

variable speed dc drive mounted on common base plate, which can be hydraulically

moved out of the pass line for maintenance purposes. The shears are operated for

start-stop mode.

Every shear is controlled via a photo cell which transmits the cutting command

for the front crop end on the bar head and for the rear crop end at the bar end in

connection with the pulse generator of the last stand of preliminary train and making

allowance for the forward slip and shear staring distance.

In case of malfunctions, the shear chops the running bar and this operation

different from cropping in so far as the shear blades are not stopped after every cut but

keep running with this operating mode, the dividing lengths are approximately 500mm.

The intermediate mill comprises of six continuous four stand horizontal two

high stands and four single stand 8” HV intermediate blocks, the pre finishers.

At all, the complete intermediate train consists of 8 stands with 3different sizes

Three stands 16” with a roll diameter of 480mm and a barrel length of 800mm,

Three stands 12” with a roll dia of 375mm and a barrel length of 700mm and

four pre finisher block 8” with roll rings 210.5mm dia and the width of 72mm the

six horizontal stands are identical in the design of roughing mill but smaller sized,

depending on the reduced rod size.

Behind stand no 13 the roll stand change in to single strand stands.

Guided by rod delivery pipes the 4 stands where spread up to4 uniform finishing

lines.

A horizontal looper for each strand ensures stress relieved rolling. A loop is

formed on the loop table with the aid of loop. Supporting roll and being monitored

continuously by a photo cell and controlled by changing pre finisher speed.

Immediately before the rolling stock enters the pre finisher stand, it passes through

a snap shear which interrupts the further supply in to the stand in case of a

malfunction of the running strand.

The pre finisher roll stands; H-V compact stands are in their design like those

of finishing block. Additional roller in entry guides for all in going ovals and free

passage of the roll stock without guide troughs between the horizontal stands as

well as the single strand no twist intermediate blocks with the horizontal loopers in

front ensures optimal surface quality and tolerances of the material as it leaves the

intermediate mill.

To permit adoption of the “HOT ROLLING TRECHNOLOGY” that means:

reduction of material in entry temperature upstream the finishing block plus

additional cooling of rolled stock inside the finishing blocks, one water box 4

finishing blocks. Guide troughs with hinge-mounted covers are located ahead of

behind the water box.

4 cooling pipes in the water box were supplied with 6 bar cooling water.

Stripper nozzles at the entrance and exit side whose jets are directed against the

rolling direction got water with air pressure of 12 bar. On each stand a rotary shear

is arranged ahead of the switch and looper table. The shear operates by the start-

stop mode with a variable speed dc drive to crop or to divide the rod.

Before the material enters the finishing block, it passes another horizontal

looper and a snap shear in front of the block. Their functions and their construction

are like those in front of the pre finishing blocks.

Four single strand 10 stand high speed MORGAN finishing block, which

permit the final speed above 80mts per second at a wire diameter of 5.5mm can be

considered one of the high elements of a high capacity rolling mill. The entire

single piece block comprises a base frame with 10 roll units and roll rings in

cantilevered arrangement that are mounted in horizontal /vertical arrangement in

pairs offset by 90 degrees against each other. The main axis is inclined by 45

degrees. This allows free rolling of the wire.

Tungsten carbide is the only material used for rolling rings. This leads to

prolonged tool life, close tolerances and dimensional stability of the groove.

However, constant cooling of the roll discs must be guaranteed to avoid

inadmissibly high temperatures. The first two roll units are designed as 8 inches

stands because of the high roll pressures and roll movements produced.

The 6 inches size is sufficient for the remaining 8 stands that follow.

These sizes allow an extremely favorable elongation of the rolling stock.

Two couple 2000 K. W. Dc motors drives the roll units.

The finishing blocks are covered with protective hoods.

Since the roll disc cooling is very important for the wear-resistant material

used, the finishing block is automatically locked against further material supply if

cooling water supply fail. The blocks are integrated with facilities for hot rolling.

Provisions will be kept to install in further a size measuring unit and defect scope

after finishing blocks.

At the back of the finishing block, the rolling stock enters the rod cooling line.

This cooling line is a combination of a water cooling section with cooling and equalizing

zones, one pinch roll set, one loop layer and one roller stelmor roller transport system to

cool down the rolling stock as desired, with a delay of insulating hoods, by thermal

rolling heat in such a way that wire has subsequently specific properties that exercise a

favorable influence on further working. The intension is to lower the temperature level to

such a extent that a scorbutic structure results which is maintained has uniform as

possible throughout the entire rolling length which corresponds to one coil weight.

Different temperatures can be obtained in front loop layers for different grades, so the

desired optimum properties with regard to metallurgical and mechanical features also

obtained.

The following temperature at the loop layer apply for most customary steel grades:

Reinforced steel bars approx 780oc

Normal commercial grades 840oc

Soft grades approx 9000c

It is particular important for the consumer that a uniform material guide is

supplied against his order, so that a constant temperature can be maintained at the laying

head by manufacture.

The wire leaving the wire rod mill is to show good properties, and has a

uniform strength curve has possible for the entire wire length and across the wire cross

section after cooling down. As the first stage of controlled cooling down in stelmor

cooling line, a water cooling section is used immediately at the back of finishing block.

To further guide the loops, two guide plates are additionally provided on the

exit side of the protection door in order to make the loops tilt and over transfer them the

stelmor conveyor.

As the machine is running, at particular attention should be paid to vibrations due to

unbalances caused by irregularities in mechanical system.

THE ADVANTAGES OF THE STELMOR PROCESS ARE FOLLING:

Less scale formation and thus a higher yield.

Higher drawing speeds due to the uniform properties of wire throughout the coli.

Improved uncoling properties before drawing I the draw shop.

Lower picking costs due to shorter picking times with uniformly thin scale

layers that can easily be pickled and mainly consists of FEO, instead of the

sticking Fe3o4

The stelmor conveyor has an overall length of 60mts and a width of 1.45mts.

Furnace Details:

Type : Combined type walking beam cum earth furnace.

Capacity : 200 T/hr

Dimensions : 42m X 10.92m

Fuel used : Mixed Gases (co+ coke oven gas)

Calorific Value : 27,000 k cal/Nm3

Gas Flow : 2, 70,000 K cal/t

Thermal efficiency : 70%

Number of billets that can be accommodated 187.

Number of burners : 60 number flat flame

: 6 number long flame

Cycle time : 72secs

There were totally four zones in furnace. The temperatures in the four zones are:-

First Zone : 750 to 850

Second Zone: 850 to 1000

Third Zone : 1100 to 1200

Fourth Zone : 1100 to 1200

(Gas safety precautions: It is unsafe when CO gas exceeding 50 rpm.)

Equipment Features: - Combined type walking beam cum earth furnace.

- Capacity is 200 T/hr.

- Air and gas recuperates for waste heat recovery

- Mixed gases (bf gas co+ coke gas) of 2200 K cal/ Nm 3

- Microprocessor system for temperature control.

- Four strand mill with 25 stands, Morgan Construction Company from stand 14

to 25

- Morgan No twist finishing blocks facilitating high mill speed of 76 m/sec (5.5

mm wire).

- Controlled cooling of wire rods with Stelmor cooling system for achieving

superior mechanical properties.

- Process control automation by computer and PLC.

- Hook circuit and online coil compactors for packing of wire rod coils.

Ring grinding shop equipped with CNC

TOPIC: CONDITION MONITRING TECHNIQUES TO REDUCE BEARING FAILURES IN FINISHING MILL OF WIRE ROD MILL- VISAKHAPATNAM STEEL PLANT, VISAKHAPATNAM

Finishing mill of wire rod mill consists of two strand intermediate block, horizontal lopper, flying shear, 10 strand finishing block, pinch roll and laying head. This mill is a high speed mill which will facilitate making of finished products of required size. Rolling of stock is done in intermediate block and finishing block and the finished product is pulled in pinch roll and fed to laying head for laying in the circular coil shape. MORGAN BLOCK REPAIR SHOP (MBRS) is meant for maintaining the equipment in the finishing mill, like assembly of the roll bearings, bevel gears, housings that include bearing changes in the equipment periodically.

Various types of bearings used in finishing mill are as follows:

1. DEEP GROOVE BALL BEARINGS.2. ANGULAR CONTACT BALL BEARINGS.3. SELF ALIGNING BALL BEARINGS.4. CYLINGRICAL BALL BEARINGS.5. NEEDLE ROLLER BEARINGS.6. TAPPERED ROLLER BEARINGS.7. BARREL ROLLER BEARINGS.8. SPHERICAL ROLLER BEARINGS.9. THRUST BALL BEARINGS.10.ANGULAR CONTACT THRUST BALL BEARINGS.11.CYCLINDRICAL ROLLER THRUST BEARING.12.SPHERICAL ROLLER THRUST BEARINGS.

PLAIN BEARING

DESCRIPTION: The plain bearings of the roll shafts feature hydrodynamic lubrication i.e. the rotary movement of the shaft and its shifting off the center due to the roll separating force produces an oil film of adequate load carrying capacity between shaft and bearings. Each plain bearing consist of two semicircular base elements. The inner diameter of the basic element carries a lining of copper- lead based alloy. This lining is covered by a thin layer of Babbitt metal of a thickness of 0.05mm.

PRINCIPLE:

The roll side and drive side bearing trunnions of the roll shafts feature a tapered shape is necessary because of the fact that due to bearing clearance the roll shaft is susceptible to certain amount of tilt. This tilting effect results in certain amount heavily loaded roll shaft adds to this misalignment.

TYPES OF BEARINGS

1. DEEP GROOVE BALL BEARINGS

2. ANGULAR CONTACT BALL BEARINGS

3. SELF-ALIGNING BALL BEARINGS

4. CYLINDRICAL BALL BEARINGS

5. NEEDLE ROLLER BEARINGS

6. TAPERERED ROLLER BEARINGS

7. BARREL ROLLER BEARINGS

8. SPHERICAL ROLLER BEARINGS

9. THRUST BALL BEARINGS

10. ANGULAR CONTACT THRUST BEARINGS

11. CYLINDRICAL ROLLER THRUST BEARINGS

12. SPERICAL ROLLER THRUST BEARINGS

DEEP GROOVE BALL BEARINGS

Single row deep groove ball bearings accommodate radial and thrust loads and are capable of operating at high speeds. For these reasons and their economical price, they are most widely used

Double row deep groove ball bearings feature a filling slot and, consequently, can carry only low thrust loads.

ANGULAR CONTACT BALL BEARINGS

Single row angular contact ball bearings can carry thrust load in one direction only, and should always be adjusted against bearing which accommodates the opposed thrust load. Single row angular contact ball bearings are non-separable.

SELF- ALIGNING BALL BEARINGS

The self-aligning ball bearings are of the double row type with a spherical raceway in the outer ring. This feature gives the bearing self-aligning properties and makes it insensitive to misalignment and shaft deflections.

CYLINDRICAL ROLLER BEARINGS

Cylindrical roller bearings are separable. This simplifies mountings and dismounting. Rollers and raceways feature a modified line contact to eliminate edge stressing.

NEEDLE ROLLAR AND CAGE ASSEMBLIES

The small cross section of needle rollers and cage assemblies provides particularly compact and light constructions. The needle rollers which are long relative to their diameter result in rigid bearing mountings of high load carrying capacity. Due to controlled contour of the needle roller ends edge stressing is eliminated.

TAPPERED ROLLER BEARINGS

Tapered roller bearings are separable i.e. cup and cone can be assembled separately. The modified line contact between rollers and raceways prevents edge stresses. Since tapered roller bearings can carry thrust in one direction only, two such bearings are usually installed in opposition to each other.

BARREL ROLLER BEARINGS

The barrel roller bearing is a single row self-aligning roller bearing. It is used where radial loads are high and misalignment has to be compensated. Its sturdy design makes the barrel roller bearing excellently suited for the absorption of high radial shock loads. Barrel roller bearings cannot transmit high thrust loads.

SPHERICAL ROLLER BEARINGS

The spherical roller bearings are well known for its heavy-duty features. It contains two rows of barrel-shaped rollers that can align themselves freely in the sphere outer ring raceway. This provides compensation for bearing seat misalignment and shaft deflection. Spherical roller bearings incorporate a maximum number of large diameter and extra long rollers. The high degree of roller raceway conformity ensures even load distributions and high load carrying capacity.

THRUST BALL BEARINGS

Thrust ball bearings are available in both the single and double acting designs. Either one can take high thrust but no radial load.

ANGULAR CONTACT THRUST BALL BEARINGS

The design of angular contact thrust ball bearings is such that the thrust bearing location can be either side of the tapered seat.

CYLINDRICAL ROLLER THRUST BEARINGS

These bearings provide rigid bearing mountings which have a high load carrying capacity and are insensitive to shock loads. These bearings are applied where the load carrying capacity of thrust ball bearings and needle roller thrust bearings is insufficient.

SPHERICAL ROLLER THRUST BEARINGS

Spherical roller thrust bearings can accommodate heavy thrust loads; they are adapted to high speeds. Since the raceways are inclined relative to the bearings axis a

certain amount of radial load can be applied. The radial should be less than 55% of thrust load. These bearings should always be lubricated with oil.

Plastic Bearings

Plastic Bearings are Lightweight, Low Friction, Lube Free, and Can be Run In Liquids. Bearing Rings Can Be Molded To Integrate With Customer Applications. Specials Made In Low/High

Quantities. Services Include Prototyping, Pilot Runs & Custom Designs.

Many different types of plastics have properties which make them suitable for bearing applications, the most commonly used are phenolics, acetals, UHMWPE, and nylon. The major limitations involved in the use of plastics have to do with high temperatures and possible cold flow under heavy loads.

Journal BearingA journal bearing, simply stated, is a cylinder which surrounds the shaft and is filled with

some form of fluid lubricant. In this bearing a fluid is the medium that supports the shaft

preventing metal to metal contact. The most common fluid used is oil, with special applications using water or a gas. This application note will concentrate on oil

lubricated journal bearings.

Hydrostatic Bearing

Hydrostatic Bearing: Hydrostatic bearings provide accurate, highly damped, friction free linear and rotary motion. These bearings also average the form errors of the surfaces that make up the bearing components. This averaging allows the bearings to exhibit smaller error motions than would otherwise be possible. The small error motions attainable when hydrostatic bearings are used make them the bearing technology of choice for ultra precise ways and spindles for instruments and machines.

Hydrodynamic Bearing:Hydrodynamic Bearing, which are active as the shaft rotates, create an oil wedge that supports the shaft and relocates it within the bearing clearances. In a horizontally split bearing the oil wedge will lift and support the shaft, relocating the centerline slightly up and to one side into a normal attitude position in a lower quadrant of the bearing. The normal attitude angle will depend upon the shaft rotation direction with a clockwise rotation having an attitude angle in the lower left quadrant. External influences, such as hydraulic volute pressures in pumps or generator electrical load can produce additional relocating forces on the shaft attitude angle and centerline position

Hydrodynamic Bearing

hydrodynamic journal bearings

Single Row Deep Groove Ball Bearings:This bearing consists of inner and outer rings with deep symmetrical ball race, ways, separator and complement of Balls. This beading is designed primarily for radial load but due to it's design features it is capable of carrying equal amount of thrust load in either direction and is capable of operating at high speed too.This bearing has the lowest frictional losses and therefore, it is the most widely used among all types

of bearings.

Double Row Deep Groove Ball Bearings: Double row deep groove bearing embodied the same design principle as that of the single row deep groove ball bearings.The bearing has a lower axial displacement than it occurs in the single row deep groove ball bearing. These bearings are capable of carrying substantial thrust loads in either direction and due to double rows of ball they are also capable of carrying high radial loads too.

Magneto Type Ball Bearings:In this type of bearings the inner ring is same to that of deep groove ball bearings but the track on outer race has one shoulder.At the deepest position the groove track merges into the cylindrical track and therefore this bearing has a character of separable outer race.Magneto type bearings may be loaded radially and in one direction axially, generally they are mounted in pairs and adjusted against each other with a small amount of end play. Usually these bearings are available in smaller size only.

Angular Contact Ball Bearings:Angular contact bearings are single row ball bearings but designed in such a way that the central line of the contact between balls and race ways is at an angle. This angle is called a contact angle and as per the manufactured design these vary between 15o, 25o,45o

In this type of bearings contact angles between balls and tracks have been swung to an angle between 20o to 40o to the radial plane.These bearings are capable of carrying higher axial loads than the corresponding deep groove ball bearings, but in one direction only. These bearings are eminently suitable where heavy thrust loads are encountered at high speeds.Usually these bearings are mounted in pairs and adjusted axially against each other so that they may support combination of heavy radial and thrust loads.

BEARING FAILURES AND THEIR CAUSES

Accurate and complete knowledge of the causes responsible for the breakdown of a machine is necessary. The future usefulness of a machine often depends on correct understanding of the causes of failure. Since the bearings of a machine are among its most vital components, the ability to draw the correct inferences from bearing failures is of utmost importance.

The calculated life expectancy of any bearing is based on the assumption:

1. That good lubrication in proper quantity will always be available to the bearing.

2. The bearing will be mounted without damage.3. The dimensions of parts related to the bearing will be correct.4. There are no defects inherent in the bearing.

However, even properly applied and maintained the bearing will still be subjected to one cause of failure: FATIGUE of the bearing material. Fatigue is the result of shear stress cyclically applied immediately below the load carrying surfaces and is observed as spelling away of surface metal.

The three major classifications of premature spelling are:

1. Lubrication2. Mechanical damage and3. Material defects

Most bearing failures can be attributed to one or more of the following causes:

1. Defective bearing seats on shafts and in housings.2. Misalignment3. Faulty mounting practice4. Incorrect shaft and housing fits.5. Inadequate lubrication6. Ineffective sealing.7. Vibration while the bearing is not rotating.8. The passage of electric current through the bearing during welding etc.

FAILURE DUE TO DEFECTIVE BEARING SEATS ON SHAFTS AND IN HOUSINGS

The calculated life expectancy of a roller bearing pre-supposes that its comparatively thin rings will be fitted on shafts or in housings. There are unfortunately factors that produce shafts seats and housing bores that are over size or under size, tapered or oval.

The above diagram illustrates the condition resulting when a bearing outer ring is not fully supported the impression made on the bearing outer diameter by a turning chip in the housing when the bearing was installed. The heavy specific load imposed on that part of the ring immediately over the turning chip produced the premature spalling, that results a condition called fragment denting which occurred when the fragment from the flaked surface were trapped between rollers and raceway.

When the contact between a bearing and its seat is not intimate relative movement results. Small movements between the bearing and its seat produce a condition called fretting corrosion. Fretting started the crack which in turn triggered the spalling. Shafts seats or journals as well as housing bores can yield and produce fretting corrosion.

The above figure illustrates damage by movement on a shaft. The fretting corrosion covers a large portion of the surface of both the inner ring bore and the journal. The axial crack though the inner started from surface damage caused by fretting

Bearing seats that are concave, convex or tapered also cause bearing damage. On such a seat, a bearing ring cannot make contact throughout its width. The ring therefore deflects under loads and fatigue cracks commonly appear axially the raceway.

MISALIGNMENT

Misalignment occurs when an inner ring is against a shaft shoulder that is not square

with journal, is where a housing shoulder is out of square with the housing bore.

Misalignment arises when two housings are not on the same centre line. A bearing ring

can be misaligned even though it is mounted on a tight fit but is not pressed against its

shoulder and so left cocked on its seat.

Ball thrust bearings suffer early fatigue when mounted on supports that

not perpendicular to the shaft axis, because one shaft load zone of the stationary ring

carries the entire load. When the rotating ring of the ball trust bearings is mounted on a

out-of-square shaft shoulder, the ring wobbles as it rotates. The wobbling rotating ring

loads only a small portion of a stationary ring and causes early fatigue.

1) The two rings may not be parallel to each other during operation.

2) The load may not be sufficient at the operating speed to hold the bearing in its

designed operational attitude.

If the condition arises from non-parallelism of the rings, the smearing occurs

when the balls pass from the loaded in to the unloaded zone. Secondly, if the rings are

parallel to each other but the speed is too high in relation to the load, centrifugal force

causes each ball to spin instead of roll at its contact with the race way. Smearing

results. Smearing from misalignment will be localized in one zone of the stationary

ring where as smearing from gyral forces will be generally around both rings.

Cylindrical and tapered roller bearings, although crowned, can

accommodate only very small misalignments. If misalignment is appreciable, edge

loading results in premature fatigue. Edge loading from misalignment was responsible

for the spalling in the bearing ring as shown in fig. Advanced spalling due to the same

causes can be seen on the inner ring and roller of a tapered roller bearing.

FAULTY MOUNTING PRACTICE

The origin of premature fatigue and other failure lies too many times in

abuse and neglected before and during mounting. Prominent among the causes of early

fatigue is the presence of foreign matter in the bearing and its housing during

operation. If foreign matter traps between the race way and the rollers causes brindled

depressions. This condition is called “fragment denting” each of these small dents is

the potential start of premature fatigue. Foreign matter of small particle size results in

wear and the original internal geometry is changed and calculated life expectancy

cannot be achieved.

Impact damage during handling or mounting results in brindled

depressions that become the start of premature fatigue. The bearing has obviously

suffered impact if it is installed, the fault should be apparent by the noise or vibration

during operation.

Cylindrical roller bearings are easily damaged in mounting especially when the

rotating part with the inner ring mounted on it is assembled in to a stationary part with

its outer ring and roller set assembled. If the bearing is subjected to loads greater than

those calculated to arrive at the life expectancy. Premature fatigue results.

Unanticipated are parasitic loads can arise from faulty mounting practice. If a bearing

that should be free in its housing but because of pinching or cocking, cannot move with

thermal expansion and a parasitic thrust is induced on the bearing. Due to parasitic

thrust, the damaged area is not in the centre of the ball groove as it should be normally

but is high on the shoulder of the groove.

Interference between rotating and stationary parts can result in destructive cracks in

the rotating bearing ring. The roller bearing inner ring in the following figure shows

the effect of contact with an end cover while the bearing ring rotated.

DAMAGE DUE TO IMPROPER FITS:

Selection of the type of fir used for bearing rings depends upon rotation of

the ring with interference to the direction of the load. The degree of tightness or

looseness is governed by the magnitude of the load and the speed. If the bearing ring

rotates relative to the load direction, an interference fit is required. If the ring is

stationary with reference to the load, it is fitted with some clearance and is called as

slip fit. The degree of fit is governed by the concept that heavier loads require greater

interference. For shock and continuous vibrations a heavier interference fit is required

whereas for lightly loaded the rings and at extremely slow speeds lighter fit or in some

cases, a slip fit is required.

For example in an automobi le front wheel the direction of the load is

constant, i.e. to say that pavement is always exerting an upward force on the wheel. In

this case the outer rings are rotating and are press-fitted into the wheel hub while the

inner rings are stationary rings and are slip-fitted on the spindle. In some cases where it

appears necessary to mount both inner and outer rings of a bearing with interference

fits.

The above shows the bore surface of an inner ring that has been damaged by relative

movement between it and its shaft while rotating under a constant direction load. This

relative movement called “CREEP”, can result in the “scoring” as shown. When a

normally tight fitted inner ring does creep, the damage is not confined to the bore

surface but can have its effect on the faces of the ring. Severe rubbing cracks can occur

when there is a contact with the shaft shoulders

This illustrates an inner ring that cracked because of excessive interference fit.

Housing fits that are unnecessarily loose allow the outer ring to fret, creep, or even

spin. Lack of support to the outer ring results from excessive looseness as well as from

faulty housing bore contact.

INADEQUATE OR UNSUITABLE LUBRICATION

In the normal working of the bearing there is sliding motion and rolling

between the rolling element and raceway. In most type of roller bearings, there are

roller end faces, which slide against a flange or a cage. For this reason, adequate

lubrication is more important. The term “LUBRICATION FAILURE” often implies

that there is no oil or grease in the bearing.

The reasons for the failure of the bearings due to insufficient lubrication are:

1. Properties of lubricant.

2. Quantity applied to the bearing.

3. Operating conditions.

These three concepts comprise the adequacy of lubrication. If any one of the concepts

does meet requirements, the bearing can said to have failed from inadequate

lubrication.

Damages caused due to insufficient lubrication are:

1. Spalling.

2. Discoloration and softening of metal.

3. Glazing.

4. Smearing.

Viscosity of the oil is the primary characteristic of adequate lubrication. For

the bearing itself the quantity of lubricant required at any one time is small, but the

supply must be sufficient and constantly available. If the lubricant is also a heat

removal medium, then a large quantity is required. An insufficient quantity of lubricant

results in temperature raise and whistling sound. An excessive amount of lubricant

produces a sharp temperature raise due to churning, except in slow speed bearings.

When lubrication is inadequate, surface damage will result. This damage will

progress rapidly to failures that are often difficult to differentiate from a primary

fatigue failure “ SPALLING” will occur. Different stages of surface damage are shown

in the figure.

The first visible indication of trouble is usually a fine roughening or waviness

on the surface. Later, fine cracks develop followed by spalling. If there is insufficient

heat removal the temperature may raise high enough to cause discoloration and

softening. In some cases, due to insufficient lubrication, a “highly glazed” or “glossy

surface” which, as damage progresses, takes on a “frosty” appearances which

eventually “spalls”. The frosted area will feel smooth in one direction but have a

distinct roughness in the other. As the metal is pulled from the surface, pits appear and

so frosting advances to pulling.

Another fore of surface damage is called “smearing”. It appears when two surfaces

slide and the lubricant cannot prevent adhesion.

INEFFECTIVE SEALING

The effect of dirt and abrasive during bearing operation was described

under the section concerning mounting practices. Foreign matter can enter the bearing

during mounting and its most direct and sustained area of entry can be the housing

seals. Bearing manufacturers realize the damaging effect of dirt and take extreme

precautions to deliver clean bearings. Not only assembled bearings but also parts in

process are washed and cleaned freedom from abrasive matter is so important that

some bearings are assembled in air conditioned white rooms.

VIBRATION

Rolling bearings exposed to vibration while the shafts are not rotating are subject to

a damage called false brinelling. The evidence can be either bright polished

depressions or the characteristic red brown stain of fretting. Oxidation rate at the point

of contact determines the appearance. Variation in the vibrating load causes minute

sliding in the area of contact between rolling elements and race ways. Small particles

of materials are set free from the contact surfaces and may or may not be immediately

oxidized. The debris thus formed acts as a lapping agent (iron oxide) and accelerates

the wear. If the bearing is rotated slightly between periods of vibration more than one

pattern of false brinelling damage may be seen. A combination of vibration and

abrasive in a rotating bearing is seen in the wavy pattern as in the above figure, when

these waves are more closely spaced the pattern is called fluting.

False brinelling is a true wear scondition; such damage can be observed

even though the forces applied during vibration are much smaller than those

corresponding to the static carrying capacity of the bearing. False brinelling most

frequently occurs during transportation of assembled machines. It can be minimized

and usually eliminated by temporary structural members that will prevent any rotation

or axial movement of the shaft.

PASSAGE OF ELECTRIC CURRENT THROUGH THE BEARING

In certain applications of bearings to electrical machinery there is the possibility

that electric current will pass through a bearing. Current that seeks ground through the

bearing can be generated from stray magnetic fields in the machinery or can be caused

by welding on some part of the machine with the ground attached so that the current is

broken at the contact surfaces between rolling elements and raceways, arcing results

and this produces very localized high temperature and consequent damage.

Illustrates a series of electrical pits in a raceway of spherical roller bearings. The pit

was from each time the current broken in its passage between raceway and roller. In

fact this specific bearing was returned to service and operated successfully for several

additional years. Hence, moderate amounts of electrical pitting do not necessarily

result in failure.

Another type of In certain applications of bearings to electrical machinery there is

the possibility that electric current will pass through a bearing.. Flutes can develop

considerable depth producing noise and vibration during operation and eventual fatigue

from local overstressing.

Both alternating and direct currents can cause damage. Individual electric marks, pits,

and fluting have been produced in bearings running in the laboratory. When bearing is

under radial load, greater internal looseness in the bearing appears to result in greter

electrical damage.

CONDITION MONITRING TECHNIQUES

INTRODUCTION:-

The aim of the maintenance policy of an industry is to meet the changing needs of the plant & its equipment and to achieve the desired levels of reliability & planned availability. To meet this challenge, we at , Vizag Steel have designed a system to monitor the health of machinery & equipment

MAINTENENACE PRACTICES AT VSP

VSP adopted the following Maintenance practices.

PREVENTIVE MAINTENANCE

A data base is prepared for all the equipments & their sub assemblies. 3 year long term maintenance plan is prepared based on the recommendation of the OEM. It is further modified & fine tuned considering the site conditions & the experience gained subsequently after commissioning of the Plant. Based on this Annual , Monthly & weekly plans are generated .

Since the Preventive maintenance cannot predict the condition of the equipment and its life , it is being overshadowed by more systematic methods namely conditioned based maintenance.

CONDITION BASED MAINENANCE

Condition based Maintenance is the core of maintenance philosophy to access the equipment health periodically. More and more number of Condition based

Maintenance techniques are being introduced and almost all equipments has been brought under condition monitoring .Due to identification & liquidation of equipment defects in time , the primary damages to the components are reduced and secondary failures are minimized.

REACTIVE MAINTENANCE

All failures are meticulously analyzed and action plan is made for each failures. Repetitive failures and major failures are analyzed for corrective and preventive actions through a better scientific tools like root cause failure analysis etc .

PROACTIVE MAINTENANCE

Root cause failure analysis (RCFA) is a disciplined process used to investigate , rectify & eliminate equipment failure and is most effective when directed at chronic breakdowns. RCFA is being used for all major breakdowns to avoid their recurrence and also to generate the preventive steps. The Proactive maintenance is being strengthened by various online management tools available.

Condition based maintenance:

Machine component health monitoring is a developing field in which new technologies are being applied to assess the health of operating equipment. These techniques give maintenance personal the ability to know the operating condition of equipment at any point in time. It lets them detect the progressive deterioration of components like bearings, couplings, gears, brakes, etc which are designed to wear out and be replaced, without physically inspecting the individual components. However in some critical cases depending on a single technique often leads to misinterpreting the problem.

An Integrated steel plant is a combination of process units with various technologies and environments. Each process has its own criticality while contributing to end product. Maintenance needs of every unit are of a vital importance not only to meet the production targets, but also for safety & reliability.

All the advanced maintenance philosophies are pivoted on the foundation of predicting the equipment health in a scientific way and addressing the equipment specific needs at an appropriate time. At Visakhapatnam Steel Plant, the following Predictive Technologies are practiced.

1. Vibration Analysis.2. Thermograph.3. Wear Debris Analysis.4. Ultrasonic Leak and Crack Detection.5. Motor Current Analysis.6. Stroboscope.7. Acoustic emission.8. Shock pulse method.

Vibration Monitoring:

Vibration Analysis is invariably used for all rotating equipments. At VSP, the equipment speeds are

ranging from very low speed such as 20 rpm to very high speed 20,000 rpm. Vibration displacement, velocity, acceleration are used for low speed machines to high speed machines. Velocity measured in rms - mm/sec is standardized as a parameter for comparative study and trend monitoring. ISO 2372, IS 10816 standards are used for general classification of the equipments and severity evaluation criteria.

Machines running at moderate speeds with anti fiction bearings are generally analyzed with FFT analysis which gives amplitudes at different frequencies. Frequencies with dominant amplitudes are traced back to machine configuration and layout to find out fault frequencies and in-turn arriving at defects.

Low speed machines are analyzed with time wave analysis for better impact identification rather than over all level measurement. Very low speed machines are analyzed with a combination of acceleration enveloping and time wave.

High speed large capacity machines like compressors, turbo-generators are analyzed with shaft vibration signatures, usually available in horizontal direction. Bearings with installed proximity probes are analyzed with orbits. Filtered orbits are used to isolate shaft induced problems from resonance and other multiple faults. Defect which are functionally related to machine speed are analyzed with coast up/down plots. Frequency-Phase-Amplitude plots are used to pinpoint the major defect in case of

multiple defects. Cause and effect diagrams are used to eliminate trivial many from vital few.

Gear boxes are analyzed with FFT and TD analysis depending on the speed and accessibility of bearing points. Gearbox deterioration is better understood with the help of trend monitoring than a single measurement.

Out of all the above techniques, vibration monitoring remained the friendliest and widely used by maintenance engineers for a few decades in detecting and analyzing the problems of rotating equipments like fans, pumps, compressors and gearboxes. Because of the extensive research and development that took place in this field of vibration monitoring and due to advent of several vibration analysis techniques like Fast Fourier transformation(FFT), time wave form, synchronous time averaging, true order tracking, phase analysis, amplitude demodulation, stress wave analysis, operating deflecting shape analysis, model analysis, etc. maintenance engineers continued to believe that just vibration analysis is sufficient to detect the machine and motor problems. The development of various software’s, portable tools also made them become complacent and remain to a single field.

On the other hand for example vibration monitoring and temperature monitoring of the gearbox indicates problem externally onl

MS - MILL STAND - 2STAND - 2 -MIA MOTOR DE A

Trend Display of OVERALL VALUE

-- Baseline -- Value: .421 Date: 04-OCT-01

0 400 800 1200 1600 2000

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Days: 04-OCT-01 To 12-DEC-06

RM

S Ve

loci

ty in

mm

/Sec

Date: Time: Ampl:

23-AUG-04 14:42:04 .946 y after

sufficient damage or irreversible process has already taken place to the parts. To generate excessive vibration or temperature, damage to the internals of the gears box or bearings should be high and at this stage only replacement of part can restore the normalcy but the process of damage cannot be stopped to avoid premature or early replacement of spares. Whereas WDA can identify the problem in incipient stage itself.

Shock pulse monitoring:

Only rolling element bearings are analyzed with the help of shock pulse meters. Meter deciphers the impact generated by both bearing inherent deformities and also induced mechanical defects. The signals are separated and numbered to compare with standard test available for each bearing type under standard conditions. 32+/- 5.0 khZ range signals are filtered to identify bearing faults. Condition codes like A, B, C, D will be generated in the order of severity along with Lubrication index to indicate the lubrication condition like starvation or inadequate lubrication.

This technique fails to detect Race ways slippages as there is no shock generated during race slippages. This technique is best suited for rolling element bearings along with temperature

Wear Debris/Oil Monitoring:

Oil Monitoring: Lubricating Oil Monitoring is one of the important condition monitoring practices. Oil monitoring is necessary after usage for some time to know whether oil properties are as per the requirement or not. Cleaner the oil betters the equipment performance. Lubricating oil monitoring methods indicate oil properties, but not equipment condition.

Ferrogaphy: During operation of the equipment all rotating/moving/sliding parts wear and generate wear particles. Mechanical abnormalities increase the generation of these particles over a period time. Size, shape and concentration of these particles give an early indication of abnormality associated with parts in motion. To identify and quantify these wear particles, ‘Ferrography’ is used. Particle materials are analyzed for constituent metals, like copper, bronze, ferrous, nickel etc., parameters generated by ferrography can broadly be divided into four criteria. Size indicates severity of wear. Shape indicates wear mechanism/cause of wear. Composition indicates wearing

component. Concentration indicates Severity of wear. Ferro graphic analysis is primarily a trend monitoring method to establish wear pattern of the moving parts and inferring the early warning signal about impending mechanical abnormality. Industrial terminology for this technique is ‘Wear Debris Analysis’ (WDA).

Identifying damage process at the incipient level is only possible with Wear Debris Analysis for equipments with dedicated oil lubrication systems. For equipments with centralized lubrication systems, equipment specific fault identification is not possible but stream of equipments can be monitored over a period time to arrive at wear pattern with mechanical abnormalities. However In case of a Gearbox the material of all gears are same & almost all bearing elements are made of similar material, hence pinpointing the problematic element only with WDA is not possible and accurate.

s

Motor Current Signature Analysis:

Current Signature Analysis (CSA) is a diagnostic and analysis technique that is being used to analyze motors, generators, alternators, transformers, and other electric equipment. This new technology has the ability to test operating electrical equipment and to identify a variety of mechanical and electrical problems. CSA traces can be used to analyze the driven load, the power supply, and perform inrush testing on motors. As

a preventative maintenance tool, CSA can be used to perform a one-time test or periodic testing to track and trend equipment performance. CSA is remote, and non-intrusive. CSA used only for motors is popularly known as Motor Current Signature Analysis(MCSA). MCSA is a powerful technique for detection of motor abnormalities like rotor bar failures, power quality, starting and load current harmonics, air-gap and eccentricity defects.

Motor Current Signature Analysis (MCSA) is a popular technique to diagnose motor problems. Mechanical abnormalities of motor or driven equipment, such as gearbox, fan, compressor etc., are also diagnosed using MCSA. Since all the defects which have dominant influence on machine performance during operation are reflected in motor load current, especially in AC motors. Harmonics developed in motor load current are used to detect abnormalities, but the accuracy of diagnosis is poor and analysis is cumbersome for mechanical defects in drive or driven equipment,

In an integrated steel plant like Visakhapatnam Steel plant, Identifying & pinpointing the problem accurately is very important since an failure in area has an cascading effect on downstream equipment/plants. The table below provides an insight into various techniques used to identify various problems which are faced generally and their success rate to pinpoint the problem. Here we can clearly see that Vibration can mostly identify most of the problems, but it is not the only technique which can identify all problems. Hence instead of depending on a single technique a combination of techniques is being used to pinpoint the problem accurately. Some of the case studies are presented below.

Fault WDA/Oil

Vibration

Thermography

Ultrasonics

Acoustic

Strobe

Motor Current

Shock pulse

Rolling Bearing

X 1 X X X 1

Journal bearing

X 1 X

Misalignment

1 X

Unbalance 1

Gears X 1 X

Lubrication X X 1

Oil contamination/ Wear rate

1

Cavitation X X X 1

Resonance 1

Elec. Unbalance/ Rotor bar

X 1

Belt/coupling

X 1

Cracks/leaks

X 1

“1” - Well Suited, “X” – Average, “ “ – Not suited/Not applicable

FTF BSF BPFO BPFI GMF

292.46 2409.4 5558.2 7304.8 8124

From the FFT the peaks were checked with all the possible fault frequencies, but neither the fundamental nor the harmonics of them are matching. Temperature is normal at 65 deg. Cent. Strobe was used and all the coupling bolts condition and universal shaft was inspected and no abnormality was observed. So finally, bearing problem was suspected and it was decided to stop the machine and check the oil. On draining the oil, small metal pieces were found indicating bearing problem. The rolling was suspended and the Plummer block was opened to check the bearing condition and was found that the outer race was cracked on the top as shown in fig (). After the bearing was replaced the vibration signature is as shown in fig (). From the above case it is clear that even though there is a problem it could not be pinpointed with vibration & temperature and only after checking the condition of oil it was confirmed that it is a bearing problem.

Table - 1

Conclusions

Condition monitoring has started in a humble way with visual monitoring and monitoring of vibration with handheld instruments in a small way. In due course it has assimilated new techniques and technologies; there are significant benefits when these techniques are integrated. When we integrate analysis reports from various condition monitoring techniques of some equipment and take a comprehensive decision we get the following benefits like early detection of problem, more scientific and effective decisions, root cause failure analysis. Condition monitoring has contributed immensely for the maintenance fraternity. VSP is marching ahead and is attaining new highs every day. It is our constant endeavor to upgrade our predictive technologies and maintenance philosophies to meet these requirements.

Thus by adopting these techniques failure of bearings can be reduced.

This in turn results in increase of production and decrease of accidents due to failure of bearing.

Bearing Project

Documents

Transcript of Bearing Project