AGMA 12FTM04-2012 Energy Efficient Industrial Gear Lubricants.pdf

1、12FTM04AGMA Technical PaperEnergy EfficientIndustrial GearLubricantsBy D. Blain and A. Galiano-Roth,ExxonMobil Research andEngineering, R. Russo andK. Harrington ExxonMobil Fuels,Lubricants and SpecialtiesEnergy Efficient Industrial Gear LubricantsDavid Blain and Angela Galiano-Roth, ExxonMobil Rese

2、arch and Engineering,Rick Russo and Kevin Harrington ExxonMobil Fuels, Lubricants and SpecialtiesThe statements and opinions contained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractGlobal energy deman

3、d is predicted to be about 30 percent higher in 2040 compared to 2010 (1). Energydemand growth will slow as economies mature, population growth moderates and efficiency gainsaccelerate. This paper will focus on the third factor: energy efficiency. The industrial sector consumesalmost 48% of global e

4、nergy, with the remainder being used for residential/commercial and transportation.Clearly, improvements in energy efficiency in the industrial setting can have a major impact on overall globalenergy use and resultant CO2emissions.Therearemultiplesourcesoflubricant-relatedenergylossinindustrialequip

5、mentingeneral,andgearboxesin particular. These include frictional losses due to metal-to-metal contact, frictional traction losses underelasto-hydrodynamic lubrication conditions and windage/churning loses in the bulk oil. All three of thesefactors can be improved by using a properly formulated lubr

6、icant, with carefully selected base oils andadditives to improve efficiency.ExxonMobilhasdevelopedaseriesofindustriallubricantsthatcanreduceenergyusagebyupto4%relativeto conventional lubricants. These savings have been documented in both carefully controlled laboratorytesting and in extensive evalua

7、tions in actual industrial equipment in the field. Experiments to measurelubricant-relatedenergyefficiencybenefitsareinherentlychallenging. Validdeterminationsofthesebenefitsrequire precise measurements and controls, meticulous attention to detail and appropriate statisticalanalysis. In addition to

8、the energy efficiency benefits, these oils can reduce equipment operatingtemperatures,resultinginincreasedcomponentandlubricantlife. Thisleadstolongeroildrainintervals,andless used oil disposal.ExxonMobil defines sustainability as having three components: social development, economic growth andenvir

9、onmental protection. In addition to discussing all of the points above, this paper will also describe howthe new energy efficient lubricants contribute to each of these sustainability attributes.Copyright 2012American Gear Manufacturers Association1001 N. Fairfax Street, Suite 500Alexandria, Virgini

10、a 22314October 2012ISBN: 978-1-61481-035-33 12FTM04Energy Efficient Industrial Gear LubricantsDavid Blain and Angela Galiano-Roth, ExxonMobil Research and Engineering,Rick Russo and Kevin Harrington ExxonMobil Fuels, Lubricants and SpecialtiesWorld energy use 1Global energy demand is predicted to be

11、 about 30 percent higher in 2040 compared to 2010, as economicoutputmorethandoublesandprosperityexpandsacrossaworldwhosepopulationwillgrowtonearly9billionpeople. Theuseofenergyhaspropelledtheworldfromearliestcivilizations,throughtheindustrialrevolution,tothecurrenttechnologyenabledworld. Itallowsust

12、oheatandcoolourhomes,travelto andfrom work,andutilize the multitude of manufactured goods we rely on.Energy demand growth will slow as economies mature and populationgrowth moderates. Overall,countriesbelonging to the Organization for Economic Cooperation and Development (OECD 2) will see energy use

13、remain essentially flat through 2040, whereas non-OECD countries will have energy demand grow by closeto 60% (Figure 1). Demand growth will also slow as energy efficiency gains accelerate.This paper will focus on increasing energy efficiency. The industrial sector consumes almost 48% of globalenergy

14、, with the remainder being used for residential/commercial and transportation. This translates to 193Quadrillion BTUs1)for industrial use out of a total of 406 Quadrillion BTUs in 2010. These amounts grow to251 Quadrillion BTUs out of 535 Quadrillion BTUs in 2040 (Figure 2).SustainabilityThere are m

15、ultiple definitions of sustainability available 3 4. Exxon Mobil Corporation defines“Sustainability” as balancing economic growth, social development and environmental protection (Figure 3and 5), so that future generations are not compromised by actions taken today.Thissustainabilityplatformreflects

16、ExxonMobilssixcorporatecitizenshipfocusareas- protectinghealthandsafety, managingclimatechangerisks, respecting humanrightsandsecurityconcerns, promotingeconomicdevelopment, ensuring industry leading corporate governance, and reducing environmental impacts.Figure 1. Percent increase in energy demand

17、 (vs. 2010)_1)BTU is the amount of energy required to heat 1 pound of pure liquid water 10F. It is a common unit of energy used in the UnitedStates.4 12FTM04Advanced synthetic lubricants can address several of these areas of interest (Figure 4). For example, oilsthat extend oil drain intervals can c

18、ontribute to health and safety by reducing the amount of interactionbetween humans and the machines. Longer oil life can also help reduce waste and transportation relatedenergy use. The choice of proper lubricant can also help extend equipment life. This gives advantages inenhanced reliability and e

19、quipment availability leading to increased return on capital.Figure 2. Projected energy use by sector (quadrillion BTU)Figure 3. Sustainability What is it?Figure 4. Lubricants help drive productivity, sustainably5 12FTM04Oneofthekeysustainabilityareasistoreduceenvironmentalimpact. Onewaytodothis,and

20、thefocusoftherest of this paper, is by using advanced lubricants that can improve energy efficiency of the equipment theylubricate.Sources of energy loss in industrial equipmentTherearemultiplesourcesoflubricant-relatedenergylossinindustrialequipment ingeneral, andgearboxesin particular (Figure 5).

21、The causes of efficiency loss in gearboxes generally fall into two categories, thosewhicharelargelyspeeddependent andthose whichare largelyload dependent6. There isthe possibilitytoimprove efficiency through hardware modifications 7 8 9, but this paper will focus on lubricant effects.These lubricant

22、 related causes include windage/churning losses in the bulk oil, frictional losses due tometal-to-metal contact, and frictional traction losses under elasto-hydrodynamic lubrication conditions. Allthree of these factors can be improved by using a properly formulated lubricant, with carefully selecte

23、d baseoils and additives to improve efficiency.Windage/churning losses can be minimized by using the correct viscosity lubricant for the equipment. Thelubricant viscosity should be chosen to be able to keep the metal surfaces separated under a variety ofconditions. The viscosity index (VI) of the lu

24、bricant is also critical, as higher VI oils will provide larger filmthicknesses at higher temperatures.Inindustrialequipment,themechanicalenergylosttofrictiontypicallyrepresentsonlyasmall fractionof allofthe energy that is transmitted but it can still have a significant value to a customer as the am

25、ounts of energytransmitted can be very large. In addition, the frictional energy is converted to heat, and the consequenttemperature rise can have adverse effects, such as reduced oxidation life or reduced hydrodynamic or EHLprotection through reduced viscosity.Frictional losses can occur under all

26、three lubrication regimes: hydrodynamic, elasto-hydrodynamic (EHL)and most significantly under boundary lubrication, where metal surfaces are actually in contact.2)Hydrodynamic lubrication exists in systems where the contact occurs over a relatively large area(Figure 6).Bearings operating under hydr

27、odynamic conditions can be found in a large number of applications:S Inindustrialapplications,bothjournalandthrust bearingscan befound ina widevariety ofconfigurationsand sizes.S In automobile engines,journal bearingsare usedto supportthe crankshaftand atboth endsof thepistonconnecting rod.Figure 5.

28、 Source of energy loss in a gearbox_2)See AGMA 925-A03 for more detailed review.6 12FTM04Figure 6. Hydrodynamic lubricationIn hydrodynamic bearings, the load is spread over a relatively large area. Consequently the pressure in thecontact region is not too high. Thus the pressure ”felt” by the lubric

29、ant is not high. A significant part of thelosses in these systems are related to the viscosity of the oil under ambient conditionsThemaindifferencebetweenhydrodynamiclubricationandEHListhepressureinthecontact. EHLisassoci-atedwithcomponentswheretheloadissupportedoverasmallarea.(Figure 7). Examplesin

30、cludealltypesofrolling element bearings, cams such as those found in the valve train of automobile engines and gears. Inthese contacts, the load is so high that the surface elastically deforms to form a small contact patch. Thelubricant film is drawn into this area and separates the surfaces:S The l

31、ubricant is sheared under these high pressure conditions. Pressures of the order of 1 GPa andabove are common in EHL contacts.S The losses are determined by how the oil behaves under these extreme conditions. As we will see, thecharacteristics of the oil is very different under these circumstances.F

32、igure 7. Elastohydrodynamic lubrication (EHL)7 12FTM04A typical contact may consist of many types of interaction. If bare metal touches, as shown by A in theFigure 8, there is obviously no lubricant film present. However, even in the absence of a lubricant, the oxidelayer formed on the surface of ma

33、ny metals, as shown by B, will have different physical characteristics andhence will alter friction and wear characteristics. Most lubricants contain components commonly referred toasanti-wearadditivesandsomemayincludefrictionmodifiersasshownbyC. Theseformachemicalfilmonthesurfaceandpreventdirectmet

34、altometalcontact. Thisisoftenreferredtoasboundarylubrication. Finally,the surface may be separated by an oil film so no contact is formed between the two surfaces.Therecanbeconfusion betweenthe termstraction andfriction. When weuse theword friction,it isgenerallyassumedthatwearediscussingtheboundary

35、lubricationeffectscorrespondingtosomelevelofsurfaceinter-action such as those shown in A, B and C. When the word traction is used, it is generally related to the forcedeveloped by shearing the oil film under the high EHL contact pressures. Since friction is associated withboundary films, it is gener

36、ally the case that the lubricant additives have the most direct effect.The traction properties depend primarily on the selection of base stock type. Since traction is related toshearing the oil without any surface contact the selection of additives has little influence (Figure 9).Figure 8. Mixed and

37、 boundary lubricationFigure 9. Traction fundamentals8 12FTM04Thus, the use of a properly formulated synthetic lubricant can significantly reduce energy losses caused bytraction. This in turn also results in lower equipment operating temperatures, prolonging both equipmentcomponent life and oil drain

38、 interval.Synthetic lubricant technologyAs notedabove, syntheticlubricants canbe usedto improveenergy efficiency10 1112. However, notallsynthetic lubricants give the same benefits, and some may cause harm in other areas such as sealcompatibility and water separability 13.For example, in controlled t

39、esting in a worm gear box (to be described in more detail below), three syntheticoils were tested, as shown in Figure 10. Results were as follows:S Efficiency: API Group IV 14 Polyalpha olefin (PAO)-only based gear oil showed an average of 6%efficiency over an API Group III/PIB-based gear oil. (Note

40、 gradually declining efficiency curves forPolyisobutylene (PIB) containing oils. This is caused by two factors: 1) wear on bronze gear; and2) decreasing viscosity due to shear.)S Viscosity change: PIB-containing gear oils showed significant shear loss versus PAO-only based gearoil.S Wear: higher lev

41、els of wear metals in used oil indicate higher wear rates and shorter equipment life forPIB-containing gear oilsAdvanced synthetic lubricantsTheadvancedsyntheticindustriallubricants usedin thisstudy can reduceenergy usageby upto 4%relativeto conventional mineral oil based lubricants. These savings h

42、ave been documented in both carefully con-trolled laboratory testing and in extensive evaluations in actualindustrial equipmentin thefield. Experimentsto measure lubricant-related energy efficiency benefits are inherently challenging. Valid determinations ofthese benefits require precise measurement

43、s and controls, meticulous attention to detail and appropriatestatistical analysis.Figure 10. Case study results, efficiency and oil analysis data9 12FTM04Initialtestingtodocumentenergyefficiencybenefitswasconductedusing laboratorybench topapparatuses.The Mini Traction Machine (MTM), available comme

44、rcially from PCS Instruments, is widely accepted toperform tribological experiments (Figure 11). It reproduces a lubricated contact under highly controlled EHLconditions and measures the traction forces transmitted across a lubricant film under varying amounts ofsliding while controlling load, speed

45、 and temperature.Figure 12 of actual traction coefficient measurement over a range of slide to roll ratios shows that syntheticshave much lower traction coefficient than typical mineral oil based products. This leads to more energyefficient operation, reduced heat generated, and lower overall system

46、 operating temperatures.Testing was also carried out using an conventional EHL ball on disc rig equipped with temperature mappingusing infrared imaging 15. The test determines a temperature map of a lubricated contact under highlyloaded EHL conditions with varying amounts of sliding, while controlli

47、ng load, speed and inlet temperature.Figure 11. Mini traction machine (MTM)Figure 12. Low traction benefit10 12FTM04Data was generated in this assessment with color showing the variation in temperature as the disk surfaceisheated due to shearing of the fluid in the contact zone (Figure 13). The temp

48、erature rise is a function of theheat generation per unit area, which is the product of the fluid shear stress under the contact conditions andsliding speed.For a given sliding speed, fluids with lower shear stress will give lower temperature rise across the EHLcontact. For a given fluid, temperatur

49、e rise across the contact increases with increasing sliding speed.Advancedsyntheticlubricantswereevaluatedvsaconventionalmineraloilbasedlubes. Thesyntheticlubric-ant reduced the temperature in the contact zone by 4C, leading to reduced heat generated and loweroverall system operating temperatures (Figure 14).After the bench top testing, the next phase of testing was done in a highly instrumented worm gear boxspecifically developed by ExxonMobil to evaluate lubricant efficiencies.Figure 13. EHL