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Lubrication and Reliability Handbook PDF

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INTRODUCTION This handbook is intended to help engineers in industry filters and coolers as well as the interconnecting piping with the operation and maintenance of machinery. It systems and the necessary instrumentation and warning gives the information that these engineers need in a devices. form that is instantly accessible and easy to read. The manufacturers of machinery provide guidance on Machine operation the operation, lubrication and maintenance required for their particular machines. However, there are, of course, The machine manufacturers and/or process designers many different machines in an industrial plant or service will usually provide the necessary guidance on machine organisation, supplied by various manufacturers, and operating conditions. The operating engineers can there is a need to select as many similar lubricants as however benefit from additional guidance on running in possible, and to use related maintenance techniques. procedures, and on lubricant related operating prob- This book attempts to bridge the gap which exists lems, such as potential lubricant deterioration due to between the available data on the various machines, by high or low temperatures, and the effect of contaminant providing overall guidance on how to co-ordinate the process gases and liquids. Information is provided on recommendations of the various manufacturers. these areas, together with data on fire or health hazards The handbook is structured in a number of sections to from lubricants. make it easier to use, and to bring together related subjects, so that the reader when focusing on a particular Machine maintenance problem can also refer to related material that is likely to be of interest. The various sections are listed here in this To keep the machines in a plant or fleet operating introduction, to provide some overall guidance, addi- effectively, requires good maintenance procedures. The tional to that available in the contents list and the handbook reviews the suitability of the various main- index. tenance methods for various types of machines and gives guidance on their selection. Condition based main- tenance is covered in detail with the various methods by Lubricants which the condition of a machine can be monitored while it is in operation, so that future essential main- This section describes the various types of lubricant that tenance can be planned. Such methods include tem- are available with guidance on their overall properties perature measurement, vibration analysis, wear debris and performance. Detailed information is provided on analysis, and lubricant tests, as well as methods of mineral oils, synthetic oils, greases and solid lubricants, assessing the operating performance of machine as well as on the various oil additives that are commonly components. used. Since some machines are now lubricated by their own process fluids information is also given on the viscosity of water, refrigerants and various hydrocarbons Component failure and chemicals. When a failure does occur on one of the working components of a machine, such as a bearing, gear, seal or Lubrication of components coupling, it is useful to have guidance on understanding the causes of the failure from the appearance of the The lubrication of machines relates to the lubrication of failed component. This section therefore includes a their various moving components. This section gives large number of photographs of machine components guidance on the selection of lubricants to match the showing the typical surface appearance associated with needs of the components under a range of operating the various failure modes. conditions. The components covered are plain and rolling bearings, gears, roller chains, wire ropes, flexible Component repair couplings and slides. Finally, after a failure has occurred it is useful to have Lubrication systems guidance on how a worn surface can be rebuilt or refaced, or how a bearing or friction surface can be The next subject requiring review is the optimum relined. method of feeding the lubricant to the various machines This handbook is based on experience from around and their components. This can range from manual the world, over many years, of the investigation of greasing to automated centralising greasing systems, and problems with machines of all kinds, and of dealing with from splash, wick and ring oil feeding to pressurised mist these by practical and economical solutions. It is hoped systems and full size oil circulation systems. Detailed that it will be helpful to the many engineers involved in guidance is also given on the selection and design of machine operation and maintenance of all kinds of circulation system components such as oil tanks, pumps, machinery and plant. CONTRIBUTORS Section Author Selection of lubricant type .A .R Lansdown MSc, PhD, FRIC, FlnstPet Mineral oils .T .I Fowle BSc(Hons), ACGI, CEng, FIMechE Synthetic oils .A .R Lansdown MSc, PhD, FRIC, FInstPet Greases N. Robinson & .A .R Lansdown MSc, PhD, FRIC, FInstPet Solid lubricants and coatings J. .K Lancaster PhD, DSc, FInstP Other liquids .D .T Jamieson FRIC Plain bearing lubrication J. c. Bell BSc, PhD Rolling bearing lubrication .E .L Padmore CEng, MIMechE Gear and roller chain lubrication J. Bathgate BSc, CEng, MIMechE Wire rope lubrication D. .M Sharp Lubrication of flexible couplings J. D. Summers-Smith BSc, PhD, CEng, FIMechE Slide lubrication M.J. Neale OBE, BSc(Eng), DIC, FCGI, WhSch, FEng, FIMechE Lubricant selection .R .S Burton Selection of lubrication systems .W J. J. Crump BSc, ACGI, FInstP Total loss grease systems .P .L Langborne ,AB CEng, MIMechE Total loss oil and fluid grease systems E G. E Seldon CEng, MIMechE Mist systems .R .E Knight BSc, FCGI Dip splash systems J. Bathgate BSc, CEng, MIMechE Circulation systems .D .R Parkinson FInstPet Design of oil tanks .A G. .R Thomson BSc(Eng), CEng, AFRAeS Selection of oil pumps A.j. Twidale Selection of filters and centrifuges .R H. Lowres CEng, MIMechE, MIProdE, MIMarE, MSAE, MBIM Selection of heaters and coolers J. H. Gilbertson CEng, MIMechE, AMIMarE A guide to piping design .P D. Swales BSc, PhD, CEng, MIMechE Selection of warning and protection devices A.J. Twidale Commissioning lubrication systems N. .R .W Morris Running-in procedures .W .C Pike BSc, ACGI, CEng, MIMechE Industrial plant environmental data .R .L .G Keith cSB High pressure and vacuum .A .R Lansdown MSc, PhD, FRIC, FInstPet J. D. Summers-Smith BSc, PhD, CEng, FIMechE High and low temperatures M.J. Todd MA Chemical effects H. H. Anderson BSc(Hons), CEng, FIMechE Maintenance methods M.J. Neale OBE, BSc(Eng), DIC, FCGI, WhSch, FEng, FIMechE Condition monitoring M.J. Neale OBE, BSc(Eng), DIC, FCGI, WhSch, FEng, FIMechE Operating temperature limits J. D. Summers-Smith BSc, PhD, CEng, FIMechE Vibration analysis M.J. Neale OBE, BSc(Eng), DIC, FCGI, WhSch, FEng, FIMechE Wear debris analysis .M H. Jones BSc(Hons), CEng, MIMechE, MInstNDT M.J. Neale OBE, BSc(Eng), DIC, FCGI, WhSch, FEng, FIMechE Lubricant change periods and tests J. D. Summers-Smith BSc, PhD, CEng, FIMechE Lubricant biological deterioration .E .C Hill MSc, FInstPet Component performance analysis M.J. Neale OBE, BSc(Eng), DIC, FCGI, WhSch, FEng, FIMechE Allowable wear limits H. H. Heath FIMechE CONTRIBUTORS Section Author Failure patterns and failure analysis j. .D Summers-Smith BSc, PhD, CEng, FIMechE M.J. Neale OBE, BSc(Eng), DIC, FCGI, WhSch, FEng, FIMechE Plain bearing failures E .T Holingan BSc(Tech), MIF Rolling bearing failures .W J. J. Crump BSc, ACGI, FInstP Gear failures .T .I Fowle BSc(Hons), ACGI, CEng, FIMechE H.J. Watson BSc(Eng), CEng, MIMechE Piston and ring failures M.J. Neale OBE, BSc(Eng), DIC, FCGI, WhSch, FEng, FIMechE Seal failures .B .S Nau BSc, PhD, ARCS, CEng, FIMechE, MemASME Brake and clutch failures .T .P Newcombe DSc, CEng, FIMechE, FInstP .R .T Spurr BSc, PhD Wire rope failures .S waM ,AM CEng, MIMechE Fretting of surfaces .R .B Waterhouse ,AM PhD, MIF Wear mechanisms .K H. .R Wright PhD, FInstP Repair of worn surfaces .G .R Bell BSc, ARSM, CEng, FIM, FWeldI, FRIC Wear resistant materials H. Hocke CEng, MIMechE, FIPlantE, MIMH, FIL .M Bartle CEng, MIM, DipIM, MIIM, AMWeldI Repair of plain bearings .P .T Holligan cSB (Tech), MIF Repair of friction surfaces .T E Newcomb DSc, CEng, FIMechE, FInstP .R .T Spurr BSc, PhD Viscosity of lubricants H. Naylor BSc, PhD, CEng, FIMechE Surface hardness M.J. Neale OBE, BSc(Eng), DIC, FCGI, WhSch, FEng, FIMechE Surface finish and shape .R .E Reason DSc, ARCS, SRF Shape tolerances of components J.J. Crabtree BSc(Tech) Hons S.I. units and conversion factors M.J. Neale OBE, BSc(Eng), DIC, FCGI, WhSch, FEng, FIMechE Selection of lubricant type 1A elbaT 1.1 Importance of lubricant properties in relation to bearing type ~ epyT o f tnenopmoc nialP lanwoj nepO ,sraeg kcolC dna ,segniH .sedils tnacirbuL ytreporp ~ gniraeb gnilioR gniraeb Closed&,,. ,,tpo, c~, .~, ~ut t~o, t,~,. .~, .1 Boundarylubricating properties + ++ +++ ++ ++ + 2. Cooling + + + + +++ 3. Friction or torque + + + ++ -- ++ + 4. Ability to remain in bearing + + + + +++ + 5. Ability to seal out contaminants -- + + + -- + 6. Temperature range + + + ++ + -- + 7. Protection against corrosion + + + ++ -- + 8. Volatility + + ++ ++ + Note: The relative importance of each lubricant property in a particular class of component is indicated on a scale from + + + = highly important to - --- quite unimportant. Speed, ft/min 2 10 100 1000 10000 100000 1000000 100000 (cid:12)9 100000 10000 l _ - . - ",,~. ~."...- ;!N~,, ~,~,. - 1 10000 ~ . . . . ~/~,,,. ~ ~------~ \ oo E z Limit rof esaerg ~ 1000 .- i/I - Ii ".0 6. :"'"7:::::".:.'.:'.:';;.:" ::-: ".' :-.: .";;-:~ .~,'.-".~-,,".'.:.'..:::.;".~,!( ~ - 1000 8. :.-- _, '.. 100 . > All:i!;;:il t. t;7 I I3 ~ l!:i:: IN - 7".' .. ;~,'." ".. ~,, ,,,,- 100 :.:-;:-I,,,I.::.;.., , , ,,,,,,, ;.:t, ,,, ,,,,,I , 14.5 10 ...... I(Xi 1000 10000 100000 1000000 Speed at bearing contact, mm/s Figure 1.1 daol~deepS limitations for different types of lubricant A1.1 1A Selection fo lubricant type 600 500 , o o ~ ~ ~ ~ -.THERMAL STABILITY LIMIT .':-'::::::;:::'.~::.:-:i I ...... . ...... " ~ ~ ~ - ~ ~ (INSIGNIFICANT OXYGEN PRESENT) ' 111 I------- EFIL NI THIS REGION DEPENDS NO AMOUNT FO OXYGEN PRESENT AND ! .... ~ ~ ~1 7J6u ~. 300 --'-----PRESENCE RO ABSENCE FO STSYLATAC --.+- , ~ , t i lio ..-i ~,~~2~,~-yo,~:~?I . I!! I I ,I ~ , ~.o~~ ,~ .,o,,,o,xo ,, ~ u..,..o~o ~ m 200 E= ~~ w"~"~ ox.o~. ~o..~. ~, o.~,.,.~o JIL -.-i ~ ~ ~ ~ ~ ~ ~ ....... ~ ~ ~ ~ ~ ..... 001 SLIO w..ou~ ..~.-o.,.o,,.~s: - ~ , I, : ~ ~ ........... ~ ~ ~ ~ :~ ~ ' - ~ ~ ~ ~ "' ~ ~~~:_.~~ 671671~ ~'~'::'~'~ 'ii~~'ii~~'~'~' ~i!ii'~'~'~ ~iiiiiiiiii~ili~ii~!~ii~ii! N~I~_~ li~N~.....~:,::...:.......i!~ | I I I I I I i ! I 1 ! LOWER s?u.c~, TEMPERATURE vlsc?s,,,,, ,,,~,,,.~.,~ LIMIT IMPOSED ,,~v,.,oo,.,~,o.,,. YB POUR POINT, ~ WHICH VARIES WITH OIL-" 1 2 3 4 5 01 20 03 40 50 001 002 300 004 500 0001 2000 300040005000 | 10000 LIFE, h Figure 2.1 Temperature limits for mineral oils 600 . . . . . ~_.~,_,.~__. 9(cid:12)LAMREHT-l STABILITY LIMIT ROF POLYPHENYL ETHERS 50C __ ,.~,._..,.~._.,...,~..~ ,, ~ . . . . . . . . . . . . . 1 1 1 1 1 1 ' "~~" ~,-~\l\\', "" T ~ ~TAB~r'OXIDATION TIMIL ROF SREHTE~~.._~~LYNEHPYLOP ~,.....~ ' !I"" 300 2~ . i,Jnu{ 200 ..... T ! "--_l LIMIT RCF ESTERS DNA SILICONES- Z 1001,, I Ill i ~ "-- ~ - - " - - - ~'--" ~-,~,-,,-== i -100 LpOUR POINT LIMIT ROF SILICONES DNA ESTERS_ ! "1 2 3 4 5 10 20 30 40 50 001 200 300400500 0001 2000 300040005000 10000 LIFE, h Figure 3.1 Temperature limits for some synthetic oils A1.2 Selection fo lubricant type 1A 600 005 400 - , NOITADIXO LIMIT ROF SYNTHETIC GREASES PORD- POINT LIMIT ROF CITEHTNYS HTIW UNLIMITED OXYGEN PRESENT GREASES WITH INORGANIC THICKENERS o O 003 :;Xi 200 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ju ~ NOITADIXO FO MINERAL GREASES NI SIHT :~ ~ ~ ~ REGION DEPENDS NO AMOUNT FO NEGYXO UJ -~ UPPER LIMIT IMPOSED YB DROP TNIOP ~ PRESENT 100-OF MINERAL LIO GREASES DEPENDS NO ITHICKENER ' -'- / WITH UNLIMITED OXYGEN , -100 ~ um,u=~^, P.o~^e=e ~ LOWEST LIMIT NO SYNTHETIC GREASES IMPOSED T O R Q' YBU HEG' IH, I I ! DESOPMli I I YB IHIGH I EUQROT I I [ 1 2 3 4 5 01 20 03 40 05 001 002 300 400500 0001 2000 300040005000 01 000 LIFE, h Figure 4.1 Temperature limits for greases. nI many cases eht grease life will be controlled by volatility or The effective viscosity of a lubricant in a bearing may be migration. This cannot be depicted simply, as it varies different from the quoted viscosity measured by a with pressure and eht degree of ventilation, but ni standard test method, and the difference depends on the general eht limits may be slightly below eht oxidation shear rate in the bearing. stimil 400 Typical SAE 30 mineral oil at 20~ ~ ~ ( k ~ ~ ~ ~ Note: A steep slope shows a rapid j change of viscosity with I temperature and therefore I 10000 a reduced operating J OO3 temperature range, and si ~ ~ undesirable ,,, I . . . . . I 0001 ~ enOC~S _ %,,, ;~ 200 ~_. 8 raehS rate in raehS rate in ' 100 50 ~ ~ ' ~ , " ~ ' ~ ~ "~200 --- standard test ~ sgniraeb may --- -' - methods si low eb high o_ , .... , 4.J o 20 , i ' i I 2 ' X f . , o ... xl 001 ~ 5 . . . . . 4 I Typical EAS 20/50 mineral oil at 100~ I I i i l i i I i | | | i i i i i i | I J J 30 20 10 0 10 20 30 40 50 60 70 80 90100120 1 Temperature, o C 100 1000 10000 100000 1000000 raehS rate (s -1 ) Figure 5.1 Viscosity/temperature characteristics of various oils Figure 6.1 Variation of viscosity with shear rate A1.3 A2 Mineral oils CLASSIFICATION Traditional use Mineral oils are basically hydrocarbons, but all contain Dating from before viscosity could be measured accu- thousands of different types of varying structure, molec- rately, mineral oils were roughly classified into viscosity ular weight and volatility, as well as minor but important grades by their typical uses as follows: amounts of hydrocarbon derivatives containing one or Spindle oils Low viscosity oils (e.g. below about more of the elements nitrogen, oxygen and sulphur. 0.01Ns/m 2 at 60~ suitable for the They are classified in various ways as follows. lubrication of high-speed beatings such as textile spindles. Types of crude petroleum Light machine oils Medium viscosity oils (e.g. 0.01-0.02 Ns/m )2 at 60~ suitable for machin- Paraffinic Contains significant amounts of waxy hydro- ery running at moderate speeds. carbons and has 'wax' pour point (see Heavy machine oils Higher viscosity oils (e.g. 0.02-0.10 below) but little or no asphaltic matter. Ns/m )2 at 60~ suitable for slow- Their naphthenes have long side-chains. moving machinery. Naphthenic Contains asphaltic matter in least volatile Cylinder oils Suitable for the lubrication of steam fractions, but little or no wax. Their naph- engine cylinder; viscosities from 0.12 thenes have short side-chains. Has 'viscosity' to 0.3 Ns/m 2 at 60~ pour point. Mixed base Contains both waxy and asphaltic materials. Their naphthenes have moderate to long sidechains. Has 'wax' pour point. Hydrocarbon types Viscosity index The various hydrocarbon types are classified as follows: Lubricating oils are also commonly classified by their change in kinematic viscosity with temperature, i.e. by (a) Chemically saturated (i.e. no double valence bonds) their kinematic viscosity index or KVI. Formerly, KVIs straight and branched chain. (Paraffins or alkanes.) ranged between 0 and 100 only, the higher figures )b( Saturated 5- and 6-membered tings with attached representing lower degrees of viscosity change with side-chains of various lengths up to 20 carbon atoms temperature, but nowadays oils may be obtained with long. (Naphthenes.) KVIs outside these limits. They are generally grouped )c( As (b) but also containing ,1 2 or more 6-membered into high, medium and low, as in Table 2.1. unsaturated ring groups, i.e. containing double valence bonds, e.g. mono-aromafics, di-aromatics, polynuclear aromatics, respectively. Table 2.1 Classification by viscosity index A typical paraffinic lubricating oil may have these hydrocarbon types in the proportions given in Table 2.2. puorG citameniK dscosity xedni Low viscosity index (LVI) Below 35 Table 2.2 Hydrocarbon types in Venezuelan 95 VI solvent extracted and dewaxed distillate Medium viscosity index (MVI) 35-80 High viscosity index (HVI) 80-110 nobracordyH t~s % emuloV Very high viscosity index (VHVI) Over 011 Saturates f Paraffins 51 (KVI-- 105) ~ Naphthenes 60 I Mono-aromatics 81 Aromatics Di-aromatics 6 It should be noted, however, that in Table 2.5 viscosity Poly-aromatics 1 index has been determined from dynamic viscosities by the method of Roelands, Blok and Vlugter, l since this is a more fundamental system and allows truer comparison between mineral oils. Except for low viscosity oils, when The VI of the saturates has a predominant influence on DVIs are higher than KVIs, there is little difference the VI of the oil. In paraffinic oils the VI of the saturates between IVK and DVI for mineral oils. may be 105-120 and 60-80 in naphthenic oils. A2.1 Mineral oils A2 Structural group analyses This is a useful way of accurately charactersing mineral atoms in aromatic groups (% CA), in naphthenic groups oils and of obtaining a general picture of their structure (% CN), in paraffinic groups (% Cp), and the total which is particularly relevant to physical properties, e.g. number (RT) of naphthenic and aromatic rings (RN and increase of viscosity with pressure. From certain other )AR joined together. Table 2.3 presents examples on a physical properties the statistical distribution of carbon number of typical oils. Table 2.3 Typical structural group analyses (courtesy: Institution of Mechanical Engineers) st,,c~ oamO % % % Oil epyt at .5! ~6 ls'N .socsiV m2 ~" m naeMortar aC xC ,C AR NR TR at 1 0O ~ thgiew LVI spindle oil 0.926 0.0027 280 22 32 46 0.8 1.4 2.2 LVI heavy machine oil 0.943 0.0074 370 23 26 15 1.1 1.6 2.7 MVI light machine oil 0.882 0.0039 385 4 37 59 0.2 2.1 2.3 MVI heavy machine oil 0.910 0.0075 440 8 37 54 0.4 2.7 3.1 HVI light machine oil 0.871 0.0043 405 6 26 68 0.3 1.4 1.7 HVI heavy machine oil 0.883 0.0091 520 7 23 70 0.4 1.8 2.2 HVI cylinder oil 0.899 0.0268 685 8 22 70 0.7 2.3 3.0 Medicinal white oil 0.890 0.0065 445 0 42 58 0 2.8 2.8 REFINING used as such on some plain bearings subject to high temperatures and as blending components in oils and Distillation greases to form very viscous lubricants for open gears, etc. Lubricants are produced from crude petroleum by distillation according to the outline scheme given in Refining processes Figure 2.1. The distillates and residues are used to a minor extent as The second distillation is carried out under vacuum to such, but generally they are treated or refined both before avoid subjecting the oil to temperatures over about 370~ and after vacuum distillation to fit them for the more which would rapidly crack the oil. stringent requirements. The principal processes listed in The vacuum residues of naphthenic crudes are bitu- Table 2.4 are selected to suit the type of crude oil and the mens. These are not usually classified as lubricants but are properties required. Elimination of aromatics increases the VI of an oil. A lightly refined naphthenic oil may be LVI but MVI if l ceuo,: LIO, I highly refined. Similarly a lightly refined mixed-base oil may be MVI but HVI if highly refined. Elimination of tC~TS~0 TA CIREHPSOMTA ~EssuREI aromatics also reduces nitrogen, oxygen and sulphur contents. ETALLITSID "l ENILOSAG I The distillates and residues may be used alone or __. blended together. Additionally, minor amounts of fatty ,, oils or of special oil-soluble chemicals (additives) are I--' sAG, o"I blended in to form additive engine oils, cutting oils, gear :EUDISER DEPPOT EDURC oils, hydraulic oils, turbine oils, and so on, with superior I RO GNOL EUDISER I properties to plain oils, as discussed below. The tolerance in blend viscosity for commercial branded oils is typically LLITSID UNDER MUUCAV i +4% but official standards usually have wider limits, e.g. ~sPINDLE OIL! +10% for ISO 3448. l DISTILLATE >i THGIL! ENIHCAM L!O j TROHSI IEUDISER I-~EAVY JLIO'ENIHCAM PHYSICAL PROPERTIES EsABCINIFFARAP( fEDNILYCI~DEXIM)sLIoDNA R ISLIO Viscos ity-te m perat u re Figure 1.2 (courtesy: Institution of Mechanical Figure 2.4 illustrates the variation of viscosity with Engineers) temperature for a series of oils with kinematic viscosity A2.2 A2 Mineral oils Table 2.4 Refining processes (Courtesy: Institution 5O000 of Mechanical Engineers) ssecorP es~r~P 5000 ' De-waxing Removes waxy materials from paraf- finic and mixed-base oils to prevent early solidification when the oil is cooled to low temperatures, i.e. to reduce pour point OO5 k A De-asphalting Removes asphaltic matter, particu- E larly from mixed-base short residues, 200,- which would separate out at high Z E and low temperatures and block v a. 100 oil-ways u Solvent extraction Removes more highly aromatic mat- ~" 50 erials, chiefly the polyaromadcs, 0 ! VI ~~ - in order to improve oxidation stability 20 Hydrotreating Reduces sulphur content, and accord- ing to severity, reduces aromatic IVK " ~ content by conversion to naphthenes 1 = 8.0 Acid treatment Now mainly used as additional to other treatments to produce special 6.0 qualifies such as tramformer oils, ,5 white oils and medicinal oils 4.0 Earth treatment Mainly tO obtain rapid separation of 3.0 , , , , J oil from water, i.e. good demulsi- -20 -10 0 10 20 60 80 100 120 bility Temperatu re, o C Figure 2.2 150 grade ISO 3448 oils of 0 and 95 KVI index of 95 (dynamic viscosity index 93). Figure 2.2 thenic oils, in contrast, simply become so viscous with shows the difference between 150 Grade ISO 3448 oils decreasing temperature that they fail to flow, although with KVIs of 0 and 95. no wax crystal structure develops. Paraffinic oils are therefore said to have 'wax' pour points while naph- thenic oils are said to have 'viscosity' pour points. Viscosity-pressure The viscosity of oils increases significantly under pres- sure. Naphthenic oils are more affected than paraffinic ........................................... ................L .... i 4~ but, very roughly, both double their viscosity for every !iiiiiii!iiii!iii!ili!ii!iii!i!!iiiiiiiiliiii!iiii!iiiiiili!!i!ili iiiii!i!iiii!i!iiiiiii (cid:1)84 35MN/m 2 increase of pressure. Figure 2.3 gives an impression of the variation in viscosity of an SAE 20 W ISO 3448 or medium machine oil, HVI type, with both temperature and pressure. In elastohydrodynamic (ehl) formulae it is usually i!i!iiiiiiiiiiiiiiiiiIliiiiiiiiiiii, iiiiii!!iiiiiiiiiii !ii ililii!fi ! assumed that the viscosity increases exponentially with pressure. Though in fact considerable deviations from an exponential increase may occur at high pressures, the ,ooo assumption is valid up to pressures which control ehl iii !iiii!iiiiiii!iii!iii behaviour, i.e. about 35 MN/m .2 Typical pressure vis- cosity coefficients are given in Table 2.5, together with other physical properties. Pour point De-waxed paraffinic oils still contain 1% or so of waxy hydrocarbons, whereas naphthenic oils only have traces of them. At about 0~ according to the degree of / / .... o / 60oC (140,F) dewaxing, the waxes in paraffinic oils crystallise out of o' solution and at about-10~ the crystals grow to the 20 000 tbf/in 10 000 extent that the remaining oil can no longer flow. This Figure 2.3 Variation of viscosity with temperature temperature, or close to it, when determined under and pressure of an SAE 20 W (HVI) oil (Courtesy: specified conditions is known as the pour point. Naph- Institution of Mechanical Engineers) A2.3 04 i~ ~=~ 04 C) l > tr o r >: r Q. ~- I.~ 3.5 4.0- 4.5- 5.0 6.01 7.0- 8.0- 9.0 10.0" 12.5 15 20- 25 30 40 50 75 100"- 150 200 300 400 500 750 1000 1500 2000 5000 7500 10000 15000 20000 U. A I r ! ~ I " '" ]- I- "= ...... ii~ __ I ur~ o I ~ ~ ul r,, ~ -6~ -~>~ "-- ~ i u. ~> _%'6 0 0r ~ ~e5 _ ,--'tel .~-~ m ~~ e'~ =5" ~ I N 1"3 Temperature, 04 O Mineral ..._._.,,..._ A2.4 03 o (cid:12)9 ~ ~. o oils 143 o tD r~ O O ~~~ .~$'=;" "-==.~=J ~N' YgN ,~t~ ,'=- -'~ =t ~ 8.~ ~= _~: --O ~_mm . ~ "0"-- >,.m e- ~mm Iomm~" (cid:12)9 -- ,Q., L ..'-- t" 0 o~ ~ ~.-= =~ >o ~ ,,,.=. = T: E,-~o_ ~ ~ E i" :~ C ea.,.~ ~_ C .. c ~ .c L r ~ ._~:~ ~.~ (cid:12)9 -- r g e=,- ~v'o~ X > .^o ._-~ r.~ 0 I--' m ~.co ~_>, ~ ,. ~r c~'~ ,,,| ..too ,~m'~ >'ou ,_= O " "" t~ or" ~ ~ o.., m I I 00 O ! N~~NI , ,~ ,-- o , i ~ ...':..-~_~ "~ ~ "~~ -- cOl, t} = ~.E -E.'-.= E ~z'_.~ ~ "10 I 8 i.".-'-3ii= , .- o "o "O ~ U. A -== u e" ~i i m S uJ "6 .-- g 10w Min. 15W, min t min min min -t- O~ o 04 E tg x u~ <1~ ,- e- E 0 ra i- X n r- o c- ,nd 75 for 20W for for 80 for 25 for 85 A2 w W W W ~, o r o) ~o ~= o .E

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