1、Designation: G 181 04Standard Practice forConducting Friction Tests of Piston Ring and Cylinder LinerMaterials Under Lubricated Conditions1This standard is issued under the fixed designation G 181; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers procedures for conducting labora-tory bench-scale friction tests of m
3、aterials, coatings, andsurface treatments intended for use in piston rings and cylinderliners in diesel or spark-ignition engines. The goal of thisprocedure is to provide a means for preliminary, cost-effectivescreening or evaluation of candidate ring and liner materials. Areciprocating sliding arra
4、ngement is used to simulate thecontact that occurs between a piston ring and its mating linernear the top-dead-center position in the cylinder where liquidlubrication is least effective, and most wear is known to occur.Special attention is paid to specimen alignment, running-in,and lubricant conditi
5、on.1.2 This practice does not purport to simulate all aspects ofa fired engines operating environment, but is intended to serveas a means for preliminary screening for assessing the fric-tional characteristics of candidate piston ring and liner materialcombinations in the presence of fluids that beh
6、ave as use-conditioned engine oils. Therefore, it is beyond the scope ofthis practice to describe how one might establish correlationsbetween the described test results and the frictional character-istics of rings and cylinder bore materials for specific enginedesigns or operating conditions.1.3 Thi
7、s standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Document
8、s2.1 ASTM Standards:2D 6838 Test Method for Cummins M11 High Soot TestG 40 Terminology Relating to Wear and Erosion3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 conditioned oila lubricating oil whose viscosity,composition, and other function-related characteristics havebeen
9、altered by use in an operating engine, such that the oilseffects on friction and wear reflect those characteristic of thelong-term, steady-state engine operation.3.1.2 conformal contactin friction and wear testing, anymacro-geometric specimen configuration in which the curva-ture of one contact surf
10、ace matches that of the countersurface.3.1.2.1 DiscussionExamples of conformal contact includea flat surface sliding on a flat surface and a ball rotating in asocket that conforms to the shape of the ball. A pair of surfacesmay begin a wear or friction test in a non-conforming contactconfiguration,
11、but develop a conformal contact as a result ofwear.3.1.3 lubrication regimein liquid-lubricated sliding con-tact, a certain range of friction coefficients that results from acombination of contact geometry, lubricant viscosity charac-teristics, surface roughness, normal pressure, and the relativespe
12、ed of the bearing surfaces.3.1.3.1 DiscussionCommon designations for lubricationregimes are boundary lubrication, mixed film lubrication,elasto-hydrodyanmic lubrication and hydrodynamic lubrica-tion.4. Summary of Practice4.1 A reciprocating friction test apparatus is used to simu-late the back-and-f
13、orth motion of a piston ring within acylinder bore in the presence of a heated lubricant. Other typesof motions, like ring rotation, ring-groove fretting motion, andring rocking, are not simulated with this procedure. The contactgeometry, selection of testing parameters, and the methods ofspecimen s
14、urface finishing and characterization are described.The lubricating fluid is selected to simulate the effects of usedoil. A running-in procedure is used to increase the repeatabilityof results.5. Significance and Use5.1 The efficiency and fuel economy of spark ignition anddiesel engines is affected
15、in part to the friction between movingparts. Although no reliable, in situ friction measurements exist1This practice is under the jurisdiction of ASTM Committee G02 on Wear andErosion and is the direct responsibility of Subcommittee G02.40 on Non-AbrasiveWear.Current edition approved Nov 1, 2004. Pu
16、blished November 2004.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr
17、 Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.for fired internal combustion engines, it has been estimated thatat least half of the friction losses in such engines are due tothose at the ring and liner interface. This practice involves theuse of a reciprocating sliding
18、arrangement to simulate the typeof oscillating contact that occurs between a piston ring and itsmating cylinder bore surface near the top-dead-center positionin the cylinder where most severe surface contact conditionsoccur. There are many types of engines and engine operatingenvironments; therefore
19、, to allow the user the flexibility totailor this test to conditions representative of various engines,a practice is considered more appropriate than a standard testmethod in which specific test parameters are prescribed.Variables that can be adjusted in this procedure include: normalforce, speed of
20、 oscillation, stroke length, duration of testing,temperature of testing, method of specimen surface prepara-tion, and the materials and lubricants to be evaluated. Guidanceis provided here on the set-up of the test, the manner ofspecimen fixturing and alignment, the selection of a lubricantto simula
21、te conditioned oil characteristics (for a diesel engine),and the means to run-in the ring specimens to minimizevariability in test results.5.2 Engine oil spends the majority of its operating lifetimein a state that is representative of use-conditioned oil. That is,fresh oil is changed by exposure to
22、 the heat, chemical envi-ronment, and confinement in lubricated contact. It ages, chang-ing viscosity, atomic weight, solids content, acidity, andchemistry. Conducting piston ring and cylinder liner materialevaluations in fresh, non-conditioned oil is therefore unrealisticfor material screening. But
23、 additive-depleted, used oil canresult in high wear and corrosive attack of engine parts. Thecurrent test is intended for use with lubricants that simulatetribological behavior after in-service oil conditioning, butpreceding the point of severe engine damage.6. Reagents6.1 Cleaning SolventsSuitable
24、solvents may be used todegrease and clean specimens prior to conducting the describedprocedure. No specific solvents are recommended here, exceptthat they should not chemically attack the test surfaces, norleave a residual film or stain after cleaning.6.2 LubricantsLubricants shall be handled approp
25、riatelywith awareness of, and precautions taken against, any hazardsindicated in the Material Safety Data Sheets for those lubri-cants. A further description of simulated used engine oil isfurther described in an appendix to this standard.7. Apparatus and Specimen Preparation7.1 Description of the T
26、est ApparatusA schematic repre-sentation of the reciprocating contact geometry is shown inFig. 1. Two versions of this test are shown. In the first case(Fig. 1, bottom left), the lower specimen conforms to the shapeof the ring segment. In the second case (Fig. 1, bottom right),the ring segment slide
27、s on a flat lower specimen. Specimensare placed in a heated, temperature-controlled bath of lubricant.Alternate means of supplying the lubricant, such as drip feed,may be used.7.1.1 MotionThe test apparatus shall be capable of im-parting a back-and-forth (herein called reciprocating) motionof consta
28、nt stroke length and repeatable velocity profile to thesimulated piston ring specimen which slides against the simu-lated cylinder bore under a controlled normal force. The motorshall be sufficiently powered so that the velocity profile andconstancy of operation shall be unaffected by the friction f
29、orcedeveloped between the test specimens. The velocity versustime response of crank-driven devices tends to be approxi-mately sinusoidal, and this type of motion is appropriate tosimulate a piston driven by a crankshaft. The frequency ofreciprocation, given in cycles per second, shall be selected to
30、induce the appropriate lubrication regime experienced by thepiston ring during its slow down and reversal of direction in theengine of interest. Typical frequencies for slider-crank testingequipment of this type range between 5 and 40 cycles persecond. The average sliding speed for each stroke, s, i
31、n metresper second, is calculated as follows:s 5 2 fL (1)FIG. 1 Schematic Drawing of the Test Configuration Showing Conformal and Non-conformal ContactG181042where:f = frequency of reciprocation in cycles per second, andL = stroke length in meters.7.1.2 Stroke Length SelectionIt is unnecessary to se
32、t thestroke length equal to the full stroke of the piston in the enginebecause the greatest frictional influence of the materials isexperienced at the ends of the ring travel where operation in theboundary lubrication regime increases the likelihood thatcontact will occur between the surfaces of the
33、 ring and cylindermaterials. The stroke length should typically range between 5and 10 times the width of the worn-in contact face of the pistonring specimen.NOTE 1The design of certain testing machines and motor drivesystems limits the maximum frequency achievable for a given strokelength. Therefore
34、, a compromise may be necessary between the highestdesired stroke length and the desired reciprocating frequency.7.1.3 Specimen FixturingA means shall be provided toclamp the ring specimen to the reciprocating portion of themachine in such a way as to ensure correct alignment duringsliding. Likewise
35、, the cylinder bore specimen shall be mountedin a suitable, heated lubricant container such that no looseningor other misalignment occurs during the test. For ring segmentswith a rectangular cross-section, a suitable flat-faced ring-segment grip may be used. For non parallel-sided piston rings(for e
36、xample, those with keystone-like cross-sections), it maybe necessary to prepare a holder from an actual piston or designa holder that clamps the inclined sides of the ring firmly.7.1.4 Specimen AlignmentProper alignment and centeringbetween sliding surfaces is a critical factor for ensuringrepeatabl
37、e friction test results. Alignment affects the distribu-tion of normal forces on the contact surface as well as thelubrication regimes that change as the ring specimen movesback and forth. Two approaches are used together to ensureproper alignment: (1) mechanical alignment of the test fixturesduring
38、 the initial test set-up, and (2) running-in of the ringspecimen against the counterface surface. The former approachaddresses macro-contact aspects of alignment and the lattermicro-scale aspects of alignment. A method for running inspecimens is given in Appendix X1.NOTE 2Mechanical specimen alignme
39、nt tends to be difficult toachieve with conformal starting geometry. When testing ring and cylindermaterials from the same type of engine, the ring curvature in the actualengine is produced by elastically confining the ring in its groove. Thesame ring, out of the engine, will tend to have a larger c
40、urvature, andhence rest on the edges of the corresponding cylinder bore specimenunless the ring can be pre-stressed or in some other way forced into aradius of curvature that precisely matches that of the opposing specimencut from the cylinder. A non-conformal, ring-on-flat geometry with asuitable r
41、unning-in procedure, has been shown to produce a morerepeatable worn-in condition for friction testing.7.1.5 Normal Force ApplicationThe apparatus shall havethe ability to apply a controlled normal force to the ring andcylinder specimens. The loading mechanism can be a dead-weight system, a levered
42、type of device, or a hydraulic orelectromagnetic actuator. The loading system shall have suffi-cient rigidity and damping capacity to avoid excessive deflec-tions or vibrations during testing, and to maintain the desirednormal force within 2 % of the intended value.7.2 Specimen PreparationTest speci
43、mens are herein re-ferred to as the ring specimen and the cylinder borespecimen. The precise manner of preparing test specimensdepends in part on the kinds of materials, coatings, or surfacetreatments to be evaluated.7.2.1 Ring SpecimenThe ring specimen shall be preparedby cutting a segment from a p
44、roduction piston ring, ormachining a test piece of equal dimensions and finish to aproduction piston ring. The ring specimen may be used in itsoriginal, factory-finished condition or it may be altered byapplying a coating or surface treatment. The surface shall beprepared to simulate that for a part
45、icular engine or class ofengines. The surface roughness of the ring specimen, in thearea of the contact, shall be measured by a suitable method andincluded in the test record. All pertinent descriptors (type ofprofiling method, surface finish parameters, and measuringconditions) shall be reported.7.
46、2.2 Cylinder Bore SpecimenThe specimen intended tosimulate the cylinder bore surface shall constitute either a cutsection of a production-finished cylinder or a flat specimenwhose form and finish is similar to that of the cylinders used inthe engine of interest. Methods have been developed tosimulat
47、e the roughness and lay of production cylinder liners onflat cast iron test coupons.3Alternatively, a polished surfacemay be used to simulate the worn condition of a cylinder borenear at the top-dead-center position. In certain cases, thecylinder bore specimen may be fabricated from experimentalmate
48、rials, coated, or surface-treated. The surface roughness ofthe cylinder bore specimen shall be measured by a suitablemethod and included in the test record. With stylus-typeinstruments, it is traditional to measure and report the surfaceroughness profile parallel to the direction of motion of the ri
49、ng,that is, parallel to the cylinder axis. All pertinent descriptors(type of profiling method, surface finish parameters, andmeasuring conditions) shall be reported.7.3 Lubricant SelectionThe lubricant should be in acondition that is representative of that found in the engine ofinterest after a period of running. Studies of experimentalpiston ring and liner materials have shown that fresh enginelubricants do not in general produce friction and wear testresults equal to those obtained with used engine oils underotherwise similar testing conditions.4A guide to for
