Operating fluids for stationary and mobile lubrication and hydraulic systems

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Operating fluids for stationary and mobile lubrication and hydraulic systems

Author Martin Reik, Grad. Eng.

Editors Susanne Lingemann, Melanie Gelf

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Publisher HYDAC Systems & Services GmbH Training Center Hirschbachstraße 2 D-66280 Sulzbach/Saar E-mail: E-learning@HYDAC.com SAP no.: 3557889

Figures Ifnototherwisespecified:HYDACInternationalGmbH

© 2019 by HYDAC International GmbHAll rights reserved.

www.HYDAC.com

Exclusion of liability

Every effort has been made to ensure the accuracy of the contents of this document. However, errors cannot be ruled out.Forthisreason,weassumenoliabilityforerrorsanddeficienciesinthedocumentnorforanyconsequentialdamagethatmayresult.Thecontentofthisdocumentischeckedregularly.Anycorrectionsrequiredwillbeincorporatedinfutureeditions. We are grateful for any recommendations or suggestions for improvement. The content of this document is subject to change without notice. Reprinting is possible only with our permission!

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Contents1 Introduction ---------------------------------------------------------------------------------------------------------------------------- 91.1 General ----------------------------------------------------------------------------------------------------------------------------------- 91.2 Particularrequirementsmadeofoperatingfluids -----------------------------------------------------------------------------121.2.1 In hydraulic systems -----------------------------------------------------------------------------------------------------------------121.2.2 In lubrication systems ----------------------------------------------------------------------------------------------------------------14

2 Operating fluids – an important element in tribological systems ---------------------------------------------------172.1 General ----------------------------------------------------------------------------------------------------------------------------------172.2 Friction -----------------------------------------------------------------------------------------------------------------------------------182.3 Wear--------------------------------------------------------------------------------------------------------------------------------------212.3.1 The mechanisms of wear ----------------------------------------------------------------------------------------------------------212.4 Functionoftheoperatingfluid -----------------------------------------------------------------------------------------------------22

3 Composition and production of operating fluids -------------------------------------------------------------------------233.1 General ----------------------------------------------------------------------------------------------------------------------------------233.2 The structure of molecular chains ------------------------------------------------------------------------------------------------253.3 Theproductionofoperatingfluids ------------------------------------------------------------------------------------------------323.3.1 Mineraloil-basedoperatingfluids -------------------------------------------------------------------------------------------------323.3.2 Base oils --------------------------------------------------------------------------------------------------------------------------------333.3.3 Vegetable-basedoperatingfluids(bio-oil,HETGtype) ----------------------------------------------------------------------383.3.4 Syntheticallyproducedoperatingfluids(bio-oil,HETG,HEES,HEPR,PAOtypes) ---------------------------------383.3.5 Semi-syntheticallyproducedoperatingfluids ----------------------------------------------------------------------------------393.3.6 Base oil characteristics --------------------------------------------------------------------------------------------------------------403.4 Additives --------------------------------------------------------------------------------------------------------------------------------413.4.1 General ----------------------------------------------------------------------------------------------------------------------------------413.4.2 Composition and function of the most important additives ----------------------------------------------------------------433.4.3 Effects of the most important additives ------------------------------------------------------------------------------------------443.4.3.1 Anti-ageingadditives(oxidationinhibitors) -------------------------------------------------------------------------------------443.4.3.2 Anti-corrosion and anti-rust additives --------------------------------------------------------------------------------------------453.4.3.3 Anti-wear additives ------------------------------------------------------------------------------------------------------------------453.4.3.4 Additives for improving viscosity characteristics ------------------------------------------------------------------------------463.4.3.5 Detergents/dispersantadditives(agentstocarrycontaminants) ---------------------------------------------------------483.4.3.6 Pour point improvers -----------------------------------------------------------------------------------------------------------------493.4.3.7 Anti-foaming additives ---------------------------------------------------------------------------------------------------------------493.4.3.8 Summary of the most important types of additive ----------------------------------------------------------------------------49

4 Properties, characteristic values and maintenance of operating fluids ------------------------------------------544.1 Laboratory determination of characteristic values ----------------------------------------------------------------------------544.1.1 Density -----------------------------------------------------------------------------------------------------------------------------------554.1.1.1 Temperaturedependency(temperature-densitycharacteristics) ---------------------------------------------------------564.1.1.2 Pressuredependency(pressure-densitycharacteristics) ------------------------------------------------------------------564.1.2 Compressibility ------------------------------------------------------------------------------------------------------------------------574.1.3 Viscosity ---------------------------------------------------------------------------------------------------------------------------------584.1.3.1 General ----------------------------------------------------------------------------------------------------------------------------------584.1.3.2 Dynamic viscosity ---------------------------------------------------------------------------------------------------------------------594.1.3.3 KinematicviscositytoDIN51562(alsoreferredtoastheviscosity-density

characteristicsofanoperatingfluid) ---------------------------------------------------------------------------------------------614.1.3.4 Temperature dependency -----------------------------------------------------------------------------------------------------------624.1.3.5 Viscosityindex(VI)accordingtoDINISO2909 ------------------------------------------------------------------------------644.1.3.6 Viscosity-pressure characteristics ------------------------------------------------------------------------------------------------654.1.3.7 Shear gradient D ----------------------------------------------------------------------------------------------------------------------664.1.3.8 Viscosity classes ----------------------------------------------------------------------------------------------------------------------674.1.3.9 Practical meaning of density and viscosity -------------------------------------------------------------------------------------734.1.4 Impuritiesinoperatingfluids -------------------------------------------------------------------------------------------------------754.1.4.1 Airinoperatingfluids -----------------------------------------------------------------------------------------------------------------764.1.4.2 Waterinoperatingfluids ------------------------------------------------------------------------------------------------------------824.1.4.3 Solidsinoperatingfluids ------------------------------------------------------------------------------------------------------------904.1.4.3.1 General ----------------------------------------------------------------------------------------------------------------------------------904.1.4.3.2 Determination of contamination by solid particles ----------------------------------------------------------------------------934.1.4.3.3 Classificationofsolidparticlecontamination --------------------------------------------------------------------------------- 1004.1.4.3.4 Cleanlinessrequirementsforlubricationandhydrauliccomponents -------------------------------------------------- 1044.1.4.3.5 Limitingsolidparticlecontaminationthroughtheuseofhigh-qualitylubricationorhydraulicfilters ---------- 1064.1.5 PourpointaccordingtoDINISO3016 -----------------------------------------------------------------------------------------1114.1.6 Cloud point ----------------------------------------------------------------------------------------------------------------------------1114.1.7 FlashpointaccordingtoDINISO2592 --------------------------------------------------------------------------------------- 1124.1.8 Combustion point ------------------------------------------------------------------------------------------------------------------- 1124.1.9 Neutralisationnumber(NN)DIN51558 --------------------------------------------------------------------------------------- 112

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4.1.10 Ageing --------------------------------------------------------------------------------------------------------------------------------- 1134.1.10.1 General -------------------------------------------------------------------------------------------------------------------------------- 1134.1.10.2 Teststodetermineahydraulicfluid'sresistancetoageing --------------------------------------------------------------- 1164.1.10.3 Devices for regeneration of the oil degradation products ----------------------------------------------------------------- 120 4.1.11 Corrosion characteristics ---------------------------------------------------------------------------------------------------------- 1224.1.11.1 General -------------------------------------------------------------------------------------------------------------------------------- 1224.1.11.2 Anti-corrosivecharacteristicsofsteamturbinesandhydraulicfluidscontainingadditives

compared to steel/iron, DIN 51 585 -------------------------------------------------------------------------------------------- 1234.1.12 Wearprotection(AW/EP) --------------------------------------------------------------------------------------------------------- 1234.1.12.1 VKAtest(accordingtoDIN51350) --------------------------------------------------------------------------------------------- 1244.1.12.2 Brugger test -------------------------------------------------------------------------------------------------------------------------- 1254.1.12.3 FZGtest(accordingtoDIN51354,-1and-2) ------------------------------------------------------------------------------ 1264.1.12.4 Vickerstest(accordingtoDIN51389-2) ------------------------------------------------------------------------------------- 1264.1.13 Filterability ---------------------------------------------------------------------------------------------------------------------------- 1274.1.13.1 Verificationofthefilterabilityoftheoperatingfluidconsideringflowpropertiesandthe

tendencyofthefiltermaterialtoclog ------------------------------------------------------------------------------------------ 1274.1.13.2 Verificationofoperatingfluidfilterabilitywithregardtomaterialcompatibilityand

stability of the additive system --------------------------------------------------------------------------------------------------- 1334.1.14 Electricalconductivityofpressuremedia(breakdownvoltageaccordingtoDINEN60156) ------------------- 1344.1.15 Thermal conductivity --------------------------------------------------------------------------------------------------------------- 1384.1.16 Infraredspectroscopy(determinationofalubricant'smolecularfingerprint) ----------------------------------------- 1384.1.16.1 RULERtest(RemainingUsefulLifeEvaluationRoutine) ----------------------------------------------------------------- 1394.1.17 Atomicemissionspectroscopy(AES) ----------------------------------------------------------------------------------------- 140

5 Brief description of operating fluids ---------------------------------------------------------------------------------------- 1495.1 General -------------------------------------------------------------------------------------------------------------------------------- 1495.2 Classification,propertiesandrequirementsofhydraulicfluidswiththecodeletter"H"--------------------------- 1505.3 Subgroupsofhydraulicfluidswiththecodeletter"H" --------------------------------------------------------------------- 1525.3.1 Mineraloil-basedhydraulicfluids ----------------------------------------------------------------------------------------------- 1535.3.1.1 Code letters, composition, typical properties/characteristics and applications -------------------------------------- 1545.3.2 Fireresistanthydraulicfluids ----------------------------------------------------------------------------------------------------- 1585.3.2.1 Code letters, composition, typical properties/characteristics and applications -------------------------------------- 1605.3.3 Rapidlybiodegradablehydraulicfluids ---------------------------------------------------------------------------------------- 1765.3.3.1 General -------------------------------------------------------------------------------------------------------------------------------- 1765.3.3.2 Definitionofbiodegradable ------------------------------------------------------------------------------------------------------- 1785.3.3.3 Water Resources Act --------------------------------------------------------------------------------------------------------------- 1805.3.3.4 Summary of the properties and performance characteristics of rapidly biodegradable hydraulic oils --------- 1875.3.4 Foodsafehydraulicfluids --------------------------------------------------------------------------------------------------------- 1915.3.5 Tractor oils ---------------------------------------------------------------------------------------------------------------------------- 1925.3.6 Hydraulicfluidsforaircraft -------------------------------------------------------------------------------------------------------- 1935.3.7 Transmissionfluidsforhydrokineticapplications(AutomaticTransmissionFluids(ATF)) ----------------------- 1935.3.8 Silicone oil or white oil ------------------------------------------------------------------------------------------------------------- 1945.3.9 Motor and gear oils ----------------------------------------------------------------------------------------------------------------- 1955.4 Classification,propertiesandrequirementsoflubricatingoilsorcirculatingoilswiththecodeletter"C" ---- 1975.4.1 General -------------------------------------------------------------------------------------------------------------------------------- 1975.4.2 Classification ------------------------------------------------------------------------------------------------------------------------- 1985.4.3 Requirements ------------------------------------------------------------------------------------------------------------------------ 1985.4.4 Properties ----------------------------------------------------------------------------------------------------------------------------- 1985.4.5 Requirementsofhydraulicandlubricatingoilsforspecialapplications ----------------------------------------------- 2005.4.5.1 Turbineoils(DIN51515-1and-2) ---------------------------------------------------------------------------------------------- 2005.4.5.2 Lubricating oils for circulating lubrication ------------------------------------------------------------------------------------- 2065.4.5.3 Lubricating oils for wind power applications ---------------------------------------------------------------------------------- 2075.4.5.4 Rolling oil ------------------------------------------------------------------------------------------------------------------------------ 209

6 The market for lubricants ------------------------------------------------------------------------------------------------------- 211

7 Lubricant selection and project planning considerations ----------------------------------------------------------- 2137.1 General -------------------------------------------------------------------------------------------------------------------------------- 2137.2 Project planning support ---------------------------------------------------------------------------------------------------------- 2177.2.1 Measures to consider when planning an oil conversion ------------------------------------------------------------------ 2177.2.2 Seals ----------------------------------------------------------------------------------------------------------------------------------- 218

8 Inspection and maintenance of lubricating oils and hydraulic fluids ------------------------------------------- 221

9 Standardisation of lubricating greases ------------------------------------------------------------------------------------ 2259.1 General -------------------------------------------------------------------------------------------------------------------------------- 2259.2 Requirementsoflubricatinggrease -------------------------------------------------------------------------------------------- 2269.3 Properties of lubricating greases ------------------------------------------------------------------------------------------------ 2269.4 Composition of lubricating greases --------------------------------------------------------------------------------------------- 2269.5 ClassificationoflubricatinggreasesaccordingtoDIN51502 ----------------------------------------------------------- 229

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9.6 Explanationoftermsandnotesforprojectplanning ----------------------------------------------------------------------- 231

Table of illustrations ------------------------------------------------------------------------------------------------------------- 235

Index of tables --------------------------------------------------------------------------------------------------------------------- 239

Notes:

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Preface

Thesafeanddependableoperationofstationaryequipment,suchas transfer lines,machiningcenters,pressesandpapermachinery,orheavyindustrialandmobileequipment,suchasexcavators,wheelloadersandbulldozers,ispossibleonlythroughtheuseofoperatingfluidsadaptedtotherespectiveapplication.

Theseoperatingfluidsareavitallyimportantcomponent,representingoneofthemostimportant,yetoftenoneofthemost neglected design elements in the system. Their properties and condition are decisive for the service life and the degreeofeffectivenessofthe,usuallyexpensive,componentsusedintheequipment,aswellasintheoverallsystem.

Themostimportantandessentialknowledgeaboutoperatingfluidsisusuallyavailableonlysuperficiallytothepersonsstipulatingandplanningthedesiredequipmentfunctions.

Similarly, improperequipmentmaintenancecannegativelyaffect thecharacteristicsof theoperatingfluidsdeployed.Dependableandspecificoperatingfluidmaintenancemeasuresmakepossiblelongerretentiontimesfortheoperatingfluidintheequipmentalongwithanincreaseoncomponentoperatinglives.Downtimesformaintenanceandrepairsarereduced.

This book provides an in-depth look at the subject matter. In so doing, the author deals with the composition, the characteristicvaluesandthestandardsofoperatingfluidsandgreases.

The author would like to thank Mr. Bock, Fuchs Co., Mr. Spilker, Total Co., Mr. Lämmle, Panolin Co. and Mr. Thieme for their professional advice.

Notes:

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1 Introduction1.1 General

TheEgyptianswerealreadyawarethattheconstructionofpyramidswithouttheuseofoperatingfluidswasonlypossiblewithhighmaterialandphysicallosses.Withouttheoliveoilappliedtoheavystonesandwoodenbeamsas"operatingfluid",itwouldnothavebeenpossibletokeeptotheconstructiontimesspecifiedbythePharaoh.Uptothebeginningofthe19thcentury,operatingfluidswereobtainedfromplantsandanimalssuchasforexample olives, oilseed rape, castor oil plant seeds and fruits of the oil palm for lubricating bearings and for slow-running machines.Theinventionofthesteamenginein1765meantthattheseorganic,animalandvegetablelubricantsprovedinsufficientand had to be replaced with mineral oils.Thedisadvantageoftheseorganicandmineraloilswasmainlythattheydifferedimmenselyinquality.Theproductionofoil of a consistent quality was not possible until base oil was refined. This process was developed around 1880.Technologicaladvancementshaveshownthatthequalityoftheoperatingfluidsproducedintherefinerywasstillnotsufficientandthattheyhadtobesupplementedbyadditivestoimprovethequality(fromapprox.1910).Researchingthesesupplements(additives)isstillofahighprioritytoday.

Thesafeandreliableoperationofstationaryequipment,suchastransferlines,machiningcentres,pressesandpapermachinery,orheavyindustrialandmobileequipment,suchasexcavators,wheelloadersandbulldozers,ispossibleonlythroughtheuseofoperatingfluidswhichareadaptedtotherespectiveapplication.These are therefore used widely in industry. The main task is the transmission of pressure from the pump to the consumer.

Withouttheseoperatingfluids,systemsandmachineswouldnotfunctionasthefrictionbetweenthefrictionpartnersishigh and would lead to rapid destruction of the respective components.Inthiswaytheoperatingfluidhasadecisiveinfluenceonthereliabilityandlongevityofmachinesandsystems.Thismeans thatanyknowledgeabout theoperatingfluid, thecorrectselectionofoperatingfluidsand theirhandlingand application is of major importance.

Operatingfluidscompriseofanextremelywidespectrumofverydifferentproductsandqualities.Theyareoftenpurchasedorselected forsystemsbasedongivenspecificationssuchasAPI,ACEA,MIL,DINor theapprovals issuedby the manufacturer. This is perhaps the easier way, but it does not take into account the economic and ecological viewpoints. Thisisbecausespecificationsandstandardsonlydescribetheminimumrequirementsonalubricantandthereforemakenostatementsonforexampletheirqualityreservesoftheirrangeofapplications.Wemustalsorememberthatthereisno lubricant which completely and ideally covers all technical, health and environmental viewpoints. When selecting the most suitable lubricant, therefore, the entire environment of the lubrication must be taken into account, such as the transport, storage, handling, application, toxicology and disposal. Contradictory requirements must be carefully setagainst each other and balanced.

The maintenance of the value of a machine starts with the selection of the correct lubricant. Lubricant must be able to guaranteecorrectfunctioneveninthemostadverseofconditions.Inordertofulfilalllubricantspecifications,anumberofdifferentproductsarerequired.Thesecanbefullysyntheticorbasedonmineralproducts.

Unfortunately, this vital element "operating fluid" is generally neglected during the design of a machine or system, and the development objectives:

•High reliability of the entire unit•Longcomponentlifeexpectancy•Highdegreeofefficiencyontheoverallsystemthroughreductionoftheenergycosts•Largest possible environment protection•Low maintenance costs due to long intervals between replacements•Low noise emissionsarethereforeonlyachievedtoacertainextent.

Thecondition,characteristicsandcareoftheoperatingfluidsplayanimportantroleinfulfillingtheexpectedlifeexpectancyandthedegreeofefficiencyofthecomponentsandtheentiresystem.

Increased requirements placed on the system, such as:

•Reduced or no leakage•Compact design of the overall system and individual components•Increased power density•Reduced tank content•Longer maintenance intervals consistentlyincreasethequalityrequirementsontheoperatingfluidused.

Dependingontheapplicationcaseinthedevices,theoperatingfluidsmustfulfilimportantfunctions.

Therapiddevelopmentofmachinesandsystemsforcesmanufacturersofoperatingfluidstorevisetheirproductrangesor to supplement them with new products.

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Rising temperatures and pressures, higher performance densities, smaller filling quantities and the resulting highcirculationindexesareonlysomeoftheconsistentlyincreasingloadsonlubrication.Thismeansthatthepurchaseofa"cheap"lubricantwhich,forexample,justaboutfulfilstheDIN,APIorACEArequirements,mightinfactprovetohavebeenanexpensivedecision.Highamountsofwear,frequentoperatingmalfunctionsandfailures,substantialeffortforrepairsandspareparts,shortusageperiodsforoilfillingsandhighdisposalcostsmayresult.Inaddition,theeconomicbalanceofacompanywillhardlybenegativelyaffectedthroughtheprocurementofahighqualitylubricant.Experiencehasshownthatlubricantcoststotallessthan1%ofalloperatingcostswhichcanbeinfluenced,whereasforexamplerepairs, maintenance and care costs total almost 50 %.

Onlyproblem-freeoperationof high-performance systemsandmachines justifies their high investment costs, andalubricantwithsubstantialqualityreservesisoneoftheprerequisitesforit.

Dependingontheapplicationcaseinthedevices,theoperatingfluidsmustfulfilimportantfunctions.

These are, for the most part:

•Pressure transmission•Lubrication of components to reduce friction and wear•Reliableformationofthelubricatingfilmevenunderhighpressures•Coolingofcomponentssuchasforexamplevalves,pumpsandbearings•Support of seals in their sealing function•Absorbmoistureandneutraliseexistingacidstoprotectcomponentsfromcorrosion•Keepingsolidparticlecontaminationsuspendedandtransportingittothefilter

Corrosion protection Vibration damper

Lubrication

Pressure transmission

Conduction of heat

Fig. 1 Operatingfluidasanelementofdesign

Asalreadymentioned,operatingfluidsareaveryimportantmachineelement.

So that the reliability and the life expectancy of the components is guaranteed, the system manufacturer must choose:

•The proper type of lubricant•A suitable lubrication procedure •Asuitableviscosityclassforsufficientlubricationfilmformation

for each component.

Furthermore, it must be ensured that operating fluid is available:

•Insufficientquantityandpressure•With a low degree of contamination for the lubrication and/or the hydraulic circuit.

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To fulfil these tasks, operating fluids must meet certain requirements:

•Definedflowproperties,meaningoptimalviscosity-temperaturecharacteristics•Deployable over a wide range of temperatures•Shear stable•Largely resistant to ageing•Friction and wear reducing•High degree of protection against corrosion•Good air release capacity•Low degree of foaming•Seal material compatibility•Physiologically harmless•Resistant to deposit formation•Largely incompressible•Notreadilyflammable•Rapidly biodegradable•Goodfilterabilityproperties•Good contaminant release properties•Good electrical conductivity•Good thermal conductivity

Different operating fluids are used to realise these requirements:

•Mineral oils•Rapidly biodegradable oils•Synthetically produced oils•Flame-retardantfluids•Phosphate ester•Water

Thecontinually rising levelofdemandand the requirements thatoperatingfluidsaresubject tohave resulted in the development of high-tech products based on one or more mineral, synthetic or semi-synthetic base oils, such as esters or glycols, that are adapted to the desired characteristics through the addition of additives.

The most commonly used additives are:

•Antioxidants–improvedresistancetoageing•Corrosioninhibitors–protectionagainstcorrosion•Anti-wearadditives–reductionofwear•Anti-foamingadditives–curbthetendencytofoam•VIimprovers–improvetheviscosity-temperaturecharacteristics•Pourpointdepressants–ensurefluidflowevenatlowertemperatures•Specialapplicationsrequireadditiveswithdetergentanddispersantproperties.

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1.2 Particular requirements made of operating fluids

1.2.1 In hydraulic systems

Inhydraulicsystems,theprimaryfunctionoftheoperatingfluidisthetransferofpressure.Atthesametime,ithasthetask of providing the pressure generated by the pump to every point in the system.

This is based on Pascal's principle, as stipulated already in the 17th century:

"Anychangeinpressureexertedatanypointinachamberinastatic,incompressiblefluidwhichdoesnotdisturbtheequilibriumofthefluidistransferredequallytoallotherpointsthroughoutthefluid.Assumingthepressureforcesaregreaterthanthemassforces,thenthestaticpressureinthefluidwillactequallyatallpoints."

Thestaticpressurealwaysactsatrightanglestothecontainer'sboundarysurfaces.Usingthestaticpressureofafluid,it is thus possible to transmit forces and power.

OperatingfluidFF

AA

ss

p FA

FA

1

2

1

2

2

1

1

1

2

2

= = = =

Fig. 2 HydrostaticprincipleaccordingtoPascal(source:MrBock,Hydraulicfluidsasanelementofdesign)

Operatingfluid

Fig. 3 Theprincipleofahydraulicpress(source:MrBock,Hydraulicfluidsasanelementofdesign)

Inahydraulicsystem,fluidispumpedthroughlinesbymeansofapump,withapistonattheendbeingmovedbythehydraulicfluid.Acomparativelysmallamountofpumpingpowerisrequiredtotransmitalargeamountofforceduetotheprinciple of the lever, or leverage. This is demonstrated in the following illustration.

Load

Surface 100 cm2

Surface 1 cm21 cm

Piston'sdisplacement in the pump 100 cm

Displacement of the piston to lift the loadPumpForce

Fig. 4 Basicprincipleofahydraulicsystem(source:VSI)

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Whatappearsatfirstglancetobeaverysimpleproduct,revealsitselfuponcloserinspectiontobequiteanelaborateone. This, of course, is because hydraulic systems are not constructed as simply as the illustration implies but, as such, posespecialrequirementsonthehydraulicfluidsused.Thefollowingillustrationdepictstheelementsinatypicalhydraulicsystem.Thedemandsplacedonthefluidbytheindividualelementsarelistednexttoeachelement.

Cylinder Viscosity Coldflowcharacter-istics Wear protection

Lines/seals Oilcompatibility

Hydraulic pump Viscosity Shear stability Wear protection Air separation

Oilreservoir/tank Oilcompatibility Foam characteristics Corrosion protection Air separation

Fluid maintenance Filterability Oilpurity Air and water separation Heat conductivity

Filter Filterability Demulsification Oilpurity

Valve Oxidationstability Thermal stability Oilpurity Demulsification

Motor

Fig. 5 Requirementsonthehydraulicfluid

In order for the hydraulic fluid to meet these requirements, the following properties and flow processes must be considered more closely:

• Fluid properties:• Density• Viscosity(thickness)• Elasticity(compressibilityandmodulusofelasticity)• Specificheatcapacity• Surfacetension(capillaryaction)• Solubility of gases, air and water

• Hydrostatics:• Pressure• Buoyancy

• Theoretical description of the flow processes:• Consideration as kinematic or dynamic• Continuity condition, conservation of mass• Linear momentum• Equationofmotion(Euler'sequationofmotion)• Energyequationsandsimpleformulasrelatedtotheflowcalculation(Bernoulli'senergyequation)• Hagen–Poiseuillelaw• Laminarflow• Turbulentflow• Hydromechanically dimensionless numbers: Froude number, Reynolds number, Euler number

• Real flows:• Flows within pipelines and tanks• Flows within valves and bearings• Flows within pumps and cylinders

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1.2.2 In lubrication systems

Withregardtothelubricationofcomponents,suchasshaftbearings,pumps(cylinderliners),tracks,etc.,theprimarytaskoftheoperatingfluidistoreducefriction.Inaddition,itisessentialthatthelubricantformsasufficientlubricatingfilmthicknessthatpreventscontactbetweenthesliding surfaces.

Fig. 6 Fluidfriction:bothbodiesarecompletelyseparatedfromeachotherbythefluidlayer,meaningthatthebodiesareliterallyswimmingonalayeroflubricant.Thereispracticallynowear.(source:BP)

ω1

ω2

Elastohydrodynamic lubricant film in the contact zone: 2.5to7.5μmthick(elliptical pressure distribution over the width of thetooth)

Lubricant inflow

Surface roughness RH 0.7 - 0.8

Lubricant outflow

Max.contactpressure

Surface roughness RH 0.7 - 0.8

Fig. 7 Lubricationofaspurgear:thelubricatingfilmservestotransmittheforcebetweenthedrivinggearwheeland the gearwheel being driven.

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The actual lubrication is distinguished between the following lubrication processes:

Boundary lubrication:In this process, the lubricant permeates the solid body and forms a reaction layer, which does not cover the asperity contact area of the solid body. The load is transferred to the friction partner via the asperity contact area. The component lifeexpectancyistherebyseverelylimited.Forthisreason,thelubricantmustbedevelopedinsuchamannerthatthiscondition does not occur.

Semi-fluid lubrication:

Theloadistransferredinpartbythelubricatingfilmandinpartbycontactwithintheasperitycontactarea.

Fluid-film lubrication:

The load is taken up completely by the lubricant. The contact surfaces are separated. Fluid-film lubrication can be further subdivided into:

•Hydrostatic lubrication •Hydrodynamic lubrication •Elastohydrodynamic lubrication

Hydrostatic lubrication:

Separation of the contact surfaces takes place by pumping the lubricant into the lubrication gap. From the technical perspective, this form of lubrication is very complicated, and from the design perspective it is very challenging.

Hydrodynamic lubrication:

The lubricant is conveyed to the narrowing lubrication gap through the movement of the contact surfaces relative to each other. The lubricant pressure is so high that the contact surfaces are lifted apart from each other.

Elastohydrodynamic lubrication (EHD):

This form of lubrication is common with highly stressed, moving roller bodies such as gearwheels and roller bearings. In additiontothebasichydrodynamicequations,elastohydrodynamictheoryalsoconsiderstheelasticdeformationofthebodies in contact. Characteristic for this type of lubrication is a narrowing of the lubrication gap at the end of the contact zone. EHD theory provides the basis for calculating the effect of the lubrication on gearwheel damage such as pitting, scuffingorgreystaining.

Depending on the arrangement of the lubricating points and how these points are supplied, a distinction is drawn between:

Total-loss lubrication:Total-loss lubrication designates exclusively the supply of lubricant to the lubrication points. Supply can take place manually, semi-automatically or automatically. Following usage, the lubricant is forced out of the lubrication gap provided it is still present.

Circulating lubrication:

Circulating lubrication describes a lubricant dispensing circuit. The circuit comprises a reservoir, such as an oil pan, supply to the friction point and the return line. It is recommended to interconnect a lubricant reconditioning element, such asanoilfilter,intheline.Circulatinglubricationrequireslesslubricantduetoitsreuse.Thelubricantisnotabletoescapeintotheenvironmentbecause of the closed system.

Lifetime lubrication:

Lifetime lubrication can be understood as a one-time provision of lubricant to a friction point, which will not be renewed or replaced to the end of its service life.Thisiscommonlyusedinrollerbearings,butalsofindsapplicationinlinearguidingsystems,forexample.Thesesystemsareusuallyprovidedwithalubricantgreasepacking(lubricatingoilfilmwithspecialthickeners)thatisretainedinthebearing or guiding system through sealing rings.

Individual lubrication:

An individual lubrication is used when only one lubrication point is present, when a central lubrication system is to be used or when the lubrication point cannot be reached by the central lubrication system.

Manual individual lubrication:

Manual individual lubrication is always a total-loss lubrication.

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Central lubrication:

Centrallubricationsystemsshouldbeconsideredwhenmultiplelubricationpointsneedtobeserviced.Oneadvantageexistsinthereductioninoverallmaintenanceefforts.Bothwearandlubricantconsumptionarereducedbecauseoftheregular lubrication at the proper dosing.

In order to meet the requirements:

•Reduction of friction and thus of wear•Transmission of force•Cooling•Damping of vibrations•Sealing effect•Corrosion protectionthe lubricant must be matched to•Pressure and shearing stress at the lubrication point•Heat build-up and dissipation•Any chemical interaction with substances from the friction partner or seals, or from the surrounding area•Lubricant ageinginfluences.

From this, the most important physical characteristic values for lubricants are derived:

•Density•Viscosity•Dropping point•Pointofsolidification,pourpoint•Flashpoint,combustionpoint,inflammationpoint

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2 Operating fluids – an important element in tribological systems2.1 General

Tribology is the science and engineering of surfaces in contact and interacting in opposing relative motion, as well as their corresponding processes. Itconsidersthescientificdescriptionoffriction,wearandlubrication,aswellasthedevelopmentoftechnologiesfortheoptimisation of friction processes. Its objective is the optimal design of lubrication and hydraulic system components in ordertoensuredamage-freeoperationoftheoverallsystemtothegreatestextentpossible.

Atribologicalsystemiscomprisedoftwomaterialsurfaceswhosefictionisreducedthroughtheuseofalubricant,aswellas their surrounding area.

1:Primarybody(material1) 2:Counterbody(material2) 3: Media in between, e.g. lubricant 4: Environment

Fig. 8 Tribologicalsystem–twomaterials,lubricantanditsenvironment

The basic tasks of a tribological system are to:

•Separatetheprimaryandcounterbodiesthroughasuitableoperatingfluidmatchedtotheapplicationconcerned•Providegoodlubricationbetweenthebodiesthroughsufficientoperatingfluidload-bearingcapacity•Preventwearingofthebodies(lowmaterialloss)•Minimisefrictionbetweenthebodies(lowenergyrequirement)•Prevent corrosion

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2.2 Friction

Frictionisaphysicalprocesswhichcanalsopossesspositivepropertiesformanydevices.Forexample,withoutfriction,a screw could not be securely tightened. Friction is generated by the relative motion of the primary body to the counter body. This causes dissipation, which means that friction retards the relative motion between the primary body and the counter body.

In most lubrication and hydraulic applications, the following friction conditions emerge:

Dry friction (also known as stiction):Dry friction results from the contact of two surfaces sliding over one another. In the process, the surface elevations are levelled(abrasionorwear).Withadversematerialpairingorhighsurfacepressureintensities,surfacefusingtakesplace(adhesion).Solidbodyfriction,forexample,occurswhenalubricantisnotusedorthelubricationprocesshasfailed.Thistypeoffrictionistypicallypresentinstandingsystemswhoseseparatingoilfilmhasbeenpressedaway.Whenthesystem(e.g.aturbine)isrestartedwithamissingoilfilm,ahighdegreeofwearandpermanentdamagetothecomponentsresults.

Possible remedies:

•Artificialdevelopmentofasufficientoilfilmpriortostartupbymeansofanancillaryunit•High oil viscosity or the addition of suitable additives

Counter body

Primary body

Fig. 9 Dryfriction(source:BP)

Mixed friction:

Mixedfrictioncanoccurduetoinsufficientlubricationorduringtheinitialmotionoftwolubricatedfrictionpartners,suchas during system startup. Pointed contact thereby occurs at the peaks of the sliding surfaces. The frictional force is less thanwithsolidbodyorfluidfriction.Thewear,however,ishigherthanwithpurefluidfriction.Forthisreason,itisalwaysan undesirable, yet sometimes unavoidable condition for continuous operations, but prevention efforts may be so complicated that the costs of wear-related repairs are considered acceptable.

Fig. 10 Mixedfriction(source:BP)

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Stick-slip effect:

Stick-slip (in thecontextofstickingandslipping) refers to the "chattering"ofsolidbodiesas theymoveagainstone another. It designates the rapid jerking motion of two slightly coupled surfaces alternatively sticking, bracing, separating andslidingagainstoneanother.Dependingonthetribologicalsystem,thiscanresultinoscillatoryexcitationthatradiatesas noise from resonating surfaces. The effect diminishes for the most part as soon as the friction partners are separated by an intermediary or a lubricant.

Fig. 11 Schematic representation of the stick-slip effect

Effects:

The stick-slip effect is usually undesirable. The negative effects of stick-slip effect can be seen in bearings and linear motion technology guide systems, as well as in other components or machine elements.

Pitting:

Pittingisatermthatdesignatesatypeofdamageontheprimaryandcounterbodies.Itisalsodefinedasblisteringandnear-surfacemicrocrackingwithrespecttotribologicalloads.Thisoccursinrollerbearingsandgearwheels,forexample.Pitformationwithrespecttotribologicalrequirementsisbroughtaboutbyalocaltransgressionoftherespectivematerial'ssolidity due to Hertzian stressing between the roller body and the inner or outer ring of the roller bearing, or the tooth flanksofthegearwheel.Decisiveisthefactthat,withHertziansurfacestressing,themaximumcomponentstressdoesnot occur at the component surface but at a characteristic depth beneath the surface.Otherinfluencingvariables,besidesHertzianstressing,aresurfacehardnessandhardnesspenetrationdepth,surfacequality,flankformdefectsandcircumferentialspeed(withgearwheels),oilviscosity,temperatureandsimilarfactors.

Fluid friction:

Fluidfrictionoccurswhenapermanentlubricatingfilmhasformedbetweentheslidingsurfaces.Theslidingsurfacesarecompletely separated from one another. The ensuing friction is based on the lubricant molecules sliding over one another. To ensure that these shearing forces result only in an acceptable lubricant temperature increase, the heat generated must be dissipated by suitable means via the lubrication gap.Fluid friction is the desired condition in bearings and guide systems when endurance strength, high gliding speeds and heavy loading are needed.The transition frommixed friction to fluid friction is depicted in theStribeck curve. Fluid friction in a laminar flow isproportionaltothevelocityv,whileinaturbulentflowitisproportionaltothesquareofthevelocity(v²).

Fig. 12 Fluidfriction(source:BP)

20

Internal friction:

Internalfrictionconsumesenergythroughthemotionofamaterial'satomsormoleculesagainstoneanother,suchasinflowswithinanoil.External forcessuchasgravitycaneffecteach liquidparticlewhilepressuredifferencescanevokeaccelerations. Internal friction iswhatmakesmaterialsductileandfluidsviscous.Forevery liquidparticle, theexternalforces, the pressure forces, the friction forces and the inertia forces must remain in balance if the tribological system should not be accelerated.

Stribeck curve:

The Stribeck curve describes the progression of frictional force with relation to friction velocity in the case of hydrodynamic friction. It is named after the researcher, Richard Stribeck, who concerned himself with material hardness and the shaft bearing, among other problems.

�� ��

� �

��

�

FN = normal force R = surface roughness d = distance between bodies

Hydrodynamics(d>R)Mixedfriction (d~R)

High degree of wear

Low degree of wear

Sliding speed

No wear

Solidbodyfriction(d~0)

Coefficientoffriction

Fig. 13 Stribeckcurve(source:Dr.TillwichGmbH)

If no relative motion takes place, then static friction predominates. As soon as a force imposes itself that is larger than the staticfriction,relativemotionwillbegin.Atfirst,onlyafewmoleculesof lubricantseparatetheprimarybodyfromthecounterbodyandboundaryfrictionpredominates.Assoonasathinfilmoflubricantforms,andwithonlyafewasperitiesontheprimaryandcounterbodiesstillslidingoveroneanotherwithoutseparationbythelubricant,thenmixedfrictionispresent. The transition frommixed friction to fluid friction (hydrodynamic or elastohydrodynamic friction), where the primary and counter bodies are completely separated by lubricant, is designated as the release point.Ascontinuallymorelayersoflubricantareslidingoveroneanotherwithincreasingvelocity,thefrictionforcesinthefluidfrictionrangebeginrisingonceagain.Asarule,wearisataminimumwithinthefluidfrictionrange.

21

2.3 Wear

Wear(abrasion)isthelossofmassofamaterialsurface(surfaceabrasion)duetogrinding,rolling,impacting,scratching,chemical or thermal stress.These,forthemostpartundesirable,alterationsofthesurfaceoccur,forexample,inbearings,couplings,gears,nozzlesand brakes. Wear is one of the main reasons for component damage and the corresponding failure of machinery and equipment.For this reason, thereductionofwearplaysanessential role towards increasing the lifeexpectanciesofmachineryandequipmentand,correspondingly,savingcostsandreducingrawmaterialconsumption.

Definition according to DIN 50320 (standard retracted in 1997):

Wearistheprogressivelossofmaterialfromthesurfaceofasolidbody(primarybody),broughtaboutbymechanicalcauses,referringtothecontactandrelativemotionofasolid,liquidorgaseouscounterbody.

Variables having an effect on wear:

•Primarybody(material,form,surface)•Intermediary(type,particlesize,andthelike)•Counterbody(material,form,surface)•Load(size,progressionovertime)•Typeofmotion(sliding,rolling,impacting)•Surroundingatmosphere(e.g.air,protectivegas,vacuum)•Temperature(degree,progressionovertime)

Wear is always a property of the system, not a property of the components involved.

2.3.1 The mechanisms of wear

Wear is determined primarily by four different wear mechanisms:

Adhesive wear:Iftwocontactingcomponentsarepressedfirmlytogether,thecontactsurfacesadheretooneanotherduetoadhesion.Particles will be sheared off when gliding. Holes and scale-like material particles ensue that often remain on the sliding surfaceof theharderpartner.Thiswearmechanism iscalledadhesivewear.Adhesivewearoccurswith insufficient lubrication.Adhesive wear arises when components slide against one another without an intermediary or when the intermediary is displaced due to the high surface pressure intensity. Surface layer particles are sheared off due to adhesive friction.

Abrasive wear:

When hard particles in a lubricant or asperity contact area penetrate the boundary layer of the friction partner, scoring and micro-chipping results. This type of wear is designated as abrasive wear.In order to prevent abrasive wear, lubricants should be monitored and renewed as necessary. Fundamentally, measures can be taken even during the design stage of a tribological system to prevent abrasive wear. Instead of metal-metal pairing, metal-synthetic or metal-ceramic pairing should be preferred. As a rule, a favourable relationship between hard-ness and ductility should be pursued with metal pairing, such as the use of hard carbide in a ductile intermediary.Abrasive wear plays a particular role in systems in which media are conveyed that contains hard, sharp-edged particles. Abrasivewearisprevalentinpipelinesandpumps,forexample,throughwhichwaterwithsuspendedmatter(sand),plas-terandcement(aggregates)orsyntheticfilledcompositions(filler)aretobeconveyed,suchaswithcastingsystems.Inthesecases,abrasivewearissignificantlyresponsibleforshorteningthelifeexpectanciesofthethrough-flowcomponents.Abrasivewearcanbedeterminedbyamechanicaltestingprocedure,viatheso-calledTaberAbraser,accordingtoISO9352,ASTMD1044orDINENstandard438-2.6.Inthistest,wheelsfittedwithsandpaperarepressedatadefinedpressure against the rotating surface of the test specimen. The measured variable usually relates to the loss of mass of thetestspecimenafteraspecificnumberofrevolutions.Abrasivewearisachippinginthemicro-range.

Surface fatigue:

Surface fatigue is a mechanism of wear that is brought about by repeated alternating mechanical stresses. A breakdown of the surface results, leading to the formation and propagation of cracks in the layers of material close to the surface. Surfacefatigueisprevalentinrollerbearings,forexample,duetothecontinuousrollingcontactstress.Thistypeofwear,also referred to as roller wear, causes the formation of pits, or pitting. As tensile stresses in the surface promote surface fatigue, compressive stresses can be introduced into the surface as a counter measure. Suitable processes for this includenitration,oxidationorball-peeningofthesurfaces.

Tribo-oxidation:

Theformationofintermediarylayers,suchasoxidelayers,resultingfromchemicalreactionsandtheirdestructionduetocomponentmotion is referred to as tribo-oxidation or reaction layer wear. This almost always occurs together with adhesive wear. This wear mechanism, occurring as a result of chemical reaction and mechanical destruction in the reactionlayer,isatribo-chemicalreaction.Oneexampleoftribo-oxidationisfrettingcorrosion.

22

2.4 Function of the operating fluid

General:

Pressure media are energy savers in that they reduce friction and material savers in that they reduce component wear. Inadditiontotheseprimarytasks,theytakeonmanymoretasksrelatedtothemachineoritssurroundings(installationsite).

These include, among other tasks:

•Tribo-system cooling•Lubrication of cylinder and pump seals•Protection of components against corrosion

Lubricating film thickness:

Thelifeexpectanciesofthecomponentsinlubricationandhydraulicunitswillbeaffectedbythelubricatingfilmpresent.

The required lubricating film thickness will be affected by:

•Thepropertiesoftheoperatingfluid•The operating conditions•The geometry of the contact surfaces.

Aboveall,operatingfluidviscositythroughouttheoperatingtemperaturerangewillhaveadominanteffectontherequiredgap width between the moving bodies and the oil film thickness. This means that in a colder environment with acorrespondinglyhighviscositythemachinewillexhibitgreaterenergyconsumptionatthesystemdrives,whileathigheroperatingtemperatureswithacorrespondinglylowviscositytheoilfilmwillseparateandresultinseriousdamagetothecomponents.

Tribological characteristics:

The addition of additives to the base oil has the primary function of improving the tribological characteristics of the operatingfluidselected.

Tasks of the pressure media:

•Toseparateslidingpartners(movingbodies)•To seal lubrication points•To remove energy fed into the system and transfer it to the cooling system•To protect components

23

3 Composition and production of operating fluids3.1 General

Operatingfluidsaremainlyproducedfromcrudeoil,alsoknownasrawoil.Thiscrudeoil,emergingoutofprehistorictimesfromtheremainsofdead,single-celledmicroorganismscutofffromoxygenandexposedtoextremepressureandheat,mustbebroughtupbyhigh-qualityconveyorsystemsfromdeposits(e.g.poroussandstone)lyingmanythousandsof feet below the surface.

Evenwiththemostmodernconveyorsystems,amaximumofonly50%ofthecrudeoilstoredinthesestonereservoirsisrecoverable.Thequalityofthecrudeoilextractedisheavilydependentonthelocationandtheregion.Thetypicaloilproducing regions are depicted in the following table.

Region Trade name

Libya Zueitina

Great Britain Forties

Middle East Agha Jari

Middle East Arabian Heavy

Middle East Safaniya

GasesPetrol

1%22%

3%19%

2%20%

2%15%

2%13%

Middle distillates(e.g.heatingoilEL)

39% 37% 30% 26% 25%

Residue 38% 41% 48% 57% 60%

Density g/ml 0.817 0.840 0.855 0.887 0.890

Sulphur wt% 0.21 0.30 1.40 3.00 2.80

Price Ascending

Typical features Rich in naphthenes

Low sulphur content

High sulphur content

High sulphur content

Tab. 1 Typicalproducingregionsandqualitiesofextractedcrudeoil(source:VSI)

Basically, crude oil is made up of multiple chemical compounds and molecules.

The most important are:

•Carbon(C)•Hydrogen(H)•Sulphurcompounds•Nitrogencompounds•Oxygen•Varioustraceelements

82 - 87% by weight carbon(C)

0.01 - 2.2% by weight nitrogen,oxygen,metal

0.01 - 7% by weight sulphur

10 - 14% by weight hydrogen(H)

Fig. 14 Compositionofcrudeoil(source:VSI)

24

The main proportion of base oils used today is comprised of hydrocarbons derived directly from crude oil. This is primarily foreconomicreasons.Baseoilfractionsarederivedfromthecrudeoilbymeansofvariousphysical(distillation,extraction)andchemical(hydrogenation)processes.Forthemostpart,thesefractionsarecomposedofsaturatedhydrocarbons(paraffins)fromstraight-chain(n-paraffins),double-chain(isoparaffins)orcyclicstructures(naphthenes).

The base oils for lubricating and hydraulic fluids are:

•Raffinates•Hydro-crackoils•Syntheticoils(polyalphaolefins,polyglycols,esters)•Vegetableoils

Baseoilsintheirnaturalformcannolongerfulfilthecontinuouslyincreasinglevelofdemandplacedonlubricatingandhydraulicoils.Throughtheadditionofactivechemicalsubstances,additives,thepropertiesofoperatingfluidscanbespecificallyalteredsothat,today,virtuallyeverysuchfluidorgreasecontainsaso-calledadditivepackagecomprisedofa combination of carefully tested active substances.

Also known as a compound-ed lubricant

Hydraulic and lubrication oils Base oil Additive package

In general, the following applies:

The base oils for lubricating and hydraulic oil are responsible for the abilityof the lubricatingfilm to bear a load. The additive package used has the main task of protecting the surface of the components or the effective area.

25

3.2 The structure of molecular chains

The structure and number of carbon and hydrogen atoms in molecular chains determine the resulting basic products for theproductionoflubricationandhydraulicfluids.

Possible structure of the hydrocarbon molecule:

Thehydrogenatomismonovalent(i.e.ithasavalenceofone).Thismeansthatthehydrogenatomcanonlybindonesingle atom to itself. The carbon atom is tetravalent, meaning that it can bind four atoms to itself. It forms the framework for the hydrocarbon molecule.

hydrogenatom(H)

Ο— monovalent

carbonatom(C)

l

tetravalent

Fig. 15 Valency of the C and H atoms

Formula:

CnH2n+2

Hydrocarbon molecules can string themselves together in a:

•Chain-like(acyclical)or•Ring-like(cyclical)manner. Chain-like compound Ring-like(cyclical)compound

Fig. 16 Frameworkofthehydrocarbonmolecules(saturated)(source:BP)

Single or multiple bonds can ensue when the hydrogen atoms are linked to the carbon atoms.

With a single bond, also designated as saturated, an inert hydrocarbon compound forms. These compounds feature a high degree of ageing stability and thus make possible long intervals between oil changes without serious change to the oil.

The compounds with one or more double bonds, also referred to a unsaturated hydrocarbons, are reactive. These split apartwiththeintroductionofoxygen.Theformationofageingproductsresults.

Fig. 17 Unsaturatedtriplecompound(Source:BP) Fig. 18 Unsaturateddoublecompound(source:BP)

26

Molecular structures:

The various binding forms of the C atoms in hydrocarbons are summarised in molecular structure groups. The designation of these structures is listed in the following table.

Nomenclature for molecular structuresAcc. to IUPAC* Commonly called

Alkanes Normal alkanes Isoalkanes Cycloalkanes

Paraffins Normalparaffins Isoparaffins Naphthenes(cycloparaffins)

Alkenes Alkadienes

Olefins Diolefins

Alkynes AcetylenesAromatic compounds Aromatic compounds

* International Union of Pure and Applied Chemistry

Tab. 2 Molecular structures

Alkanes (paraffins):

In alkane molecules, the carbon atoms are only linked through a standard single bond; all free bonds are saturated with hydrogenatoms–theirmoleculesthereforecontainnofunctionalgroupsandtheythusbelongtothemostinertorganiccompounds.These are saturated hydrocarbons and are thus inert.

Formula:

CnH2n+2

Paraffins are further differentiated into:

•NormalparaffinswithCatomsinarow•IsoparaffinswithCatomsinarowwithbranches

This group includes:

•Methane(CH4)–gaseous,principleconstituentofnaturalgas•Ethane(C2H6)–gaseous•Propane(C3H6)–gaseous,liquidstatewithslightpressure•Butane(C6H14)–gaseous,liquidstatewithslightpressure•Pentane•Hexane•Heptane liquid

•Octane

Paraffinsaresolidfrom17Catomsonwards. Methane CH4 Ethane C2H6 Propane C3H6 HexaneC6H14

etc.

Fig. 19 Structureoftheindividualparaffin(alkane)groups Saturatedhydrocarbonswithstraight(normalparaffin)andbranched(isoparaffin)chains(source:BP)

Simplified skeletal formula:

CH3

CH3

H3C

27

Properties:

•High pour point•Poor temperature characteristics•Viscosityindex>90

Fig. 20 Naphthenes(cycloalkanes) Saturatedhydrocarbonswithringsofmostlyfive,sixorsevencarbonatoms(alsoreferredtoascycloparaffins),

distinguished by their low-temperature stability (source:BP)Formula:CnH2n

Fig. 21 Naphthenes(cycloalkanes) Simplifiedskeletalformula

Properties:

•Good temperature characteristics•Lowviscosityindex

Alkenes (double bonds):

These are unsaturated hydrocarbons. They usually occur with local overheating in distillation systems. They are distinguished fromparaffins in that theyarehighly reactive.Olefinsarenot contained in crudeoil.Theyareusually created during further processing, such as with the cracking process.

Doubleandtriplebondspossesstheabilitytoaddonotheratomsoratomgroups(accumulation).Compoundswithdoubleand triple bonds behave like unsaturated ones and are less inert than alkanes.

Formula:

CnH2n

This group includes:

•Ethene(alsocalledethylene)–gaseous,mostlyusedintheproductionofplastics•Propene•Pentene•Hexene

Propene C3H6 HexeneC6H12Ethene C2H4

etc.

Fig. 22 Structureoftheindividualolefingroups Unsaturatedhydrocarbons,morereactivethanparaffinsandthereforeabasicsubstanceforfurtherchemical

processing(source:BP)

28

Alkynes (triple bonds):

Alkynes and alkenes are reactive compounds; unsaturated hydrocarbons.

Formula:

CnH2n-2

Organic acids:

Formula:

COOH

Simplified skeletal formula:

CH3H3C

Aromatic compounds:

These are unsaturated hydrocarbons.

Formula:

CnHn or CnHn-2

Benzene C6H6

CH3

Fig. 23 Structureofthearomaticcompound"benze-ne"C6H6(source:BP)

Fig. 24 Simplifiedskeletalformula:

Thebasicframeworkforthearomaticcompoundsistheparticularlystabilebenzeneringcomprisedofsixcarbonatomswith three double rings and three single rings.Aromatic compounds are temperature resistant, exhibit good knockresistanceinmotorsandareasourcematerialforthechemicalindustry.(source:Aral)

Properties:

•Very good solubility of additives•Usuallytoxic(poisonous)•ComponentingroupIbaseoils(notcontainedingroupIIandgroupIIIbaseoils)

29

Group

Normal alka-nes

Normal (n)-paraffins

ISO-alkanes ISO

(i)- paraffins

Alkenes Normal

(n)-olefins

Alkadienes ISO (i)-olefins

Cyclo-alka-nes

Naphthenes

Aromatic compounds

Structure Straight chain Branched chain Straight chain Branched

chain Ring-shaped Ring-shaped

Chemical character Saturated Saturated Unsaturated Unsaturated Saturated Unsaturated

Example n-Hexane i-Hexane n-Hexane i-Hexane Cyclohexane Benzene

Ο=H l = C

Manufacturing processes Distillation catalyt. cracking Catalyt. cracking Distillation Catalyt.

crackingTendency to

react Inert Highly reactive Inert Highly reactive

Energy content High Medium Low

Density 0.66 0.63 0.67 0.78 0.88Ignitability Good Low Low Medium Bad

Low-temperature

characteristicsBad Good Good Good Medium

Tab. 3 Summaryofthecompositionandpropertiesoftheindividualhydrocarbons(source:VW)

Alkanes, paraffin-based Alkenes, naphthene-basedCarboninaparaffinbond >60% <60 %Density Low HigherViscosity-temperature characteristics Good MediumResistance to ageing Good BadThermal resistance Medium GoodFlash point high MediumEvaporation tendency Low MediumLow-temperature characteristics Bad GoodAdditive solubility Medium GoodWettability Medium GoodAromatic content Low MediumAmount of polycyclical aromatics contained

Extremelylow Very low

Elastomer compatibility Good Good

Tab. 4 Comparisonofparaffin/naphthene-basedoils

30

Characteristic data of various hydrocarbons:

The size of the molecule chain determines the evaporation characteristics of the hydrocarbon. The smaller the carbon atoms, the lower the boiling temperature.

Hydrocarbon Formula Boiling point (liquid → gaseous)

Melting point (liquid → solid)

Methane C1H4 -150 °C -160 °CPropane C3H8 -60 °C -120 °CHeptane C7H16 +120 °C -40 °C

Tab. 5 Boiling and melting points of hydrocarbons

A simple division is as follows:

C1 to C4 = gasApprox.C5 toapprox.C12 = benzineApprox.C10 toapprox.C22 = fuel oil EL/dieselApprox.C20 toapprox.C35 = lubricating and hydraulic oils Uptoapprox.C36 = grease Aboveapprox.C37 =vacuumresidue

The approximate characteristic values in the following table are applicable for the most important hydrocarbons:

Molecule size Molecular weight Boiling range Flash point t°C Density g/lBenzines C5 - C12 72 - 170 30 - 200 up to -50 715 - 790Diesel, heating oil EL C10 - C22 142 - 310 180 - 360 58 - 65 820 - 860

Lubricating and hydraulic oil

C20 - C35C20 H42 - C35 H72

280 - 455 210 - 600 100 - 260 840 - 910

Tab. 6 Characteristicdataforvarioushydrocarbons(approximatevalues)

Temperature

Gaseous

Melting point

Solid

Liquid

Boiling point

Met

hane

Eth

ane

Pro

pane

But

ane

Pen

tane

Hexane

Hep

tane

Octane

Non

ane

Dec

ane

Und

ecan

e

Dod

ecan

e

Trid

ecan

e

Tetra

deca

ne

Fig. 25 Meltingandboilingtemperaturesofnormalparaffins(source:BP)

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