ASTM G181-04
(Practice)Standard Practice for Conducting Friction Tests of Piston Ring and Cylinder Liner Materials Under Lubricated Conditions
Standard Practice for Conducting Friction Tests of Piston Ring and Cylinder Liner Materials Under Lubricated Conditions
SIGNIFICANCE AND USE
The efficiency and fuel economy of spark ignition and diesel engines is affected in part to the friction between moving parts. Although no reliable, in situ friction measurements exist for fired internal combustion engines, it has been estimated that at least half of the friction losses in such engines are due to those at the ring and liner interface. This practice involves the use of a reciprocating sliding arrangement to simulate the type of oscillating contact that occurs between a piston ring and its mating cylinder bore surface near the top-dead-center position in the cylinder where most severe surface contact conditions occur. There are many types of engines and engine operating environments; therefore, to allow the user the flexibility to tailor this test to conditions representative of various engines, a practice is considered more appropriate than a standard test method in which specific test parameters are prescribed. Variables that can be adjusted in this procedure include: normal force, speed of oscillation, stroke length, duration of testing, temperature of testing, method of specimen surface preparation, and the materials and lubricants to be evaluated. Guidance is provided here on the set-up of the test, the manner of specimen fixturing and alignment, the selection of a lubricant to simulate conditioned oil characteristics (for a diesel engine), and the means to run-in the ring specimens to minimize variability in test results.
Engine oil spends the majority of its operating lifetime in a state that is representative of use-conditioned oil. That is, fresh oil is changed by exposure to the heat, chemical environment, and confinement in lubricated contact. It ages, changing viscosity, atomic weight, solids content, acidity, and chemistry. Conducting piston ring and cylinder liner material evaluations in fresh, non-conditioned oil is therefore unrealistic for material screening. But additive-depleted, used oil can result in high wear and corrosive atta...
SCOPE
1.1 This practice covers procedures for conducting laboratory bench-scale friction tests of materials, coatings, and surface treatments intended for use in piston rings and cylinder liners in diesel or spark-ignition engines. The goal of this procedure is to provide a means for preliminary, cost-effective screening or evaluation of candidate ring and liner materials. A reciprocating sliding arrangement is used to simulate the contact that occurs between a piston ring and its mating liner near the top-dead-center position in the cylinder where liquid lubrication is least effective, and most wear is known to occur. Special attention is paid to specimen alignment, running-in, and lubricant condition.
1.2 This practice does not purport to simulate all aspects of a fired engines operating environment, but is intended to serve as a means for preliminary screening for assessing the frictional characteristics of candidate piston ring and liner material combinations in the presence of fluids that behave as use-conditioned engine oils. Therefore, it is beyond the scope of this practice to describe how one might establish correlations between the described test results and the frictional characteristics of rings and cylinder bore materials for specific engine designs or operating conditions.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: G181 – 04
Standard Practice for
Conducting Friction Tests of Piston Ring and Cylinder Liner
Materials Under Lubricated Conditions
This standard is issued under the fixed designation G181; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This practice covers procedures for conducting labora- 3.1 Definitions of Terms Specific to This Standard:
tory bench-scale friction tests of materials, coatings, and 3.1.1 conditioned oil—a lubricating oil whose viscosity,
surface treatments intended for use in piston rings and cylinder composition, and other function-related characteristics have
liners in diesel or spark-ignition engines. The goal of this been altered by use in an operating engine, such that the oil’s
procedure is to provide a means for preliminary, cost-effective effects on friction and wear reflect those characteristic of the
screening or evaluation of candidate ring and liner materials.A long-term, steady-state engine operation.
reciprocating sliding arrangement is used to simulate the 3.1.2 conformal contact—in friction and wear testing, any
contact that occurs between a piston ring and its mating liner macro-geometric specimen configuration in which the curva-
near the top-dead-center position in the cylinder where liquid ture of one contact surface matches that of the countersurface.
lubrication is least effective, and most wear is known to occur. 3.1.2.1 Discussion—Examplesofconformalcontactinclude
Special attention is paid to specimen alignment, running-in, a flat surface sliding on a flat surface and a ball rotating in a
and lubricant condition. socket that conforms to the shape of the ball.Apair of surfaces
1.2 This practice does not purport to simulate all aspects of may begin a wear or friction test in a non-conforming contact
a fired engine’s operating environment, but is intended to serve configuration, but develop a conformal contact as a result of
as a means for preliminary screening for assessing the fric- wear.
tional characteristics of candidate piston ring and liner material 3.1.3 lubrication regime—in liquid-lubricated sliding con-
combinations in the presence of fluids that behave as use- tact, a certain range of friction coefficients that results from a
conditioned engine oils. Therefore, it is beyond the scope of combination of contact geometry, lubricant viscosity charac-
this practice to describe how one might establish correlations teristics, surface roughness, normal pressure, and the relative
between the described test results and the frictional character- speed of the bearing surfaces.
istics of rings and cylinder bore materials for specific engine 3.1.3.1 Discussion—Common designations for lubrication
designs or operating conditions. regimes are boundary lubrication, mixed film lubrication,
1.3 This standard does not purport to address all of the elasto-hydrodyanmic lubrication and hydrodynamic lubrica-
safety concerns, if any, associated with its use. It is the tion.
responsibility of the user of this standard to establish appro-
4. Summary of Practice
priate safety and health practices and determine the applica-
4.1 A reciprocating friction test apparatus is used to simu-
bility of regulatory limitations prior to use.
late the back-and-forth motion of a piston ring within a
2. Referenced Documents
cylinder bore in the presence of a heated lubricant. Other types
2.1 ASTM Standards: of motions, like ring rotation, ring-groove fretting motion, and
D6838 Test Method for Cummins M11 High Soot Test ringrocking,arenotsimulatedwiththisprocedure.Thecontact
G40 Terminology Relating to Wear and Erosion geometry, selection of testing parameters, and the methods of
specimen surface finishing and characterization are described.
The lubricating fluid is selected to simulate the effects of used
oil.Arunning-in procedure is used to increase the repeatability
This practice is under the jurisdiction of ASTM Committee G02 on Wear and
of results.
Erosion and is the direct responsibility of Subcommittee G02.50 on Friction.
Current edition approved Nov. 1, 2004. Published November 2004. DOI:
5. Significance and Use
10.1520/G0181-04.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.1 The efficiency and fuel economy of spark ignition and
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
dieselenginesisaffectedinparttothefrictionbetweenmoving
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. parts.Although no reliable, in situ friction measurements exist
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G181 – 04
forfiredinternalcombustionengines,ithasbeenestimatedthat that they should not chemically attack the test surfaces, nor
at least half of the friction losses in such engines are due to leave a residual film or stain after cleaning.
those at the ring and liner interface. This practice involves the
6.2 Lubricants—Lubricants shall be handled appropriately
use of a reciprocating sliding arrangement to simulate the type
with awareness of, and precautions taken against, any hazards
of oscillating contact that occurs between a piston ring and its
indicated in the Material Safety Data Sheets for those lubri-
mating cylinder bore surface near the top-dead-center position
cants. A further description of simulated used engine oil is
in the cylinder where most severe surface contact conditions
further described in an appendix to this standard.
occur. There are many types of engines and engine operating
environments; therefore, to allow the user the flexibility to
7. Apparatus and Specimen Preparation
tailor this test to conditions representative of various engines,
7.1 Description of the Test Apparatus—A schematic repre-
a practice is considered more appropriate than a standard test
sentation of the reciprocating contact geometry is shown in
method in which specific test parameters are prescribed.
Fig. 1. Two versions of this test are shown. In the first case
Variablesthatcanbeadjustedinthisprocedureinclude:normal
(Fig. 1, bottom left), the lower specimen conforms to the shape
force, speed of oscillation, stroke length, duration of testing,
of the ring segment. In the second case (Fig. 1, bottom right),
temperature of testing, method of specimen surface prepara-
the ring segment slides on a flat lower specimen. Specimens
tion,andthematerialsandlubricantstobeevaluated.Guidance
areplacedinaheated,temperature-controlledbathoflubricant.
is provided here on the set-up of the test, the manner of
Alternate means of supplying the lubricant, such as drip feed,
specimen fixturing and alignment, the selection of a lubricant
may be used.
to simulate conditioned oil characteristics (for a diesel engine),
7.1.1 Motion—The test apparatus shall be capable of im-
and the means to run-in the ring specimens to minimize
parting a back-and-forth (herein called reciprocating) motion
variability in test results.
of constant stroke length and repeatable velocity profile to the
5.2 Engine oil spends the majority of its operating lifetime
simulated piston ring specimen which slides against the simu-
in a state that is representative of use-conditioned oil. That is,
lated cylinder bore under a controlled normal force. The motor
fresh oil is changed by exposure to the heat, chemical envi-
shall be sufficiently powered so that the velocity profile and
ronment, and confinement in lubricated contact. It ages, chang-
constancy of operation shall be unaffected by the friction force
ing viscosity, atomic weight, solids content, acidity, and
developed between the test specimens. The velocity versus
chemistry. Conducting piston ring and cylinder liner material
time response of crank-driven devices tends to be approxi-
evaluationsinfresh,non-conditionedoilisthereforeunrealistic
mately sinusoidal, and this type of motion is appropriate to
for material screening. But additive-depleted, used oil can
simulate a piston driven by a crankshaft. The frequency of
result in high wear and corrosive attack of engine parts. The
reciprocation, given in cycles per second, shall be selected to
current test is intended for use with lubricants that simulate
induce the appropriate lubrication regime experienced by the
tribological behavior after in-service oil conditioning, but
pistonringduringitsslowdownandreversalofdirectioninthe
preceding the point of severe engine damage.
engine of interest. Typical frequencies for slider-crank testing
6. Reagents equipment of this type range between 5 and 40 cycles per
second. The average sliding speed for each stroke, s, in metres
6.1 Cleaning Solvents—Suitable solvents may be used to
per second, is calculated as follows:
degreaseandcleanspecimenspriortoconductingthedescribed
procedure. No specific solvents are recommended here, except s 5 2fL (1)
FIG. 1 Schematic Drawing of the Test Configuration Showing Conformal and Non-conformal Contact
G181 – 04
7.2 Specimen Preparation—Test specimens are herein re-
where:
ferred to as the ‘ring specimen’ and the ‘cylinder bore
f = frequency of reciprocation in cycles per second, and
specimen.’ The precise manner of preparing test specimens
L = stroke length in meters.
depends in part on the kinds of materials, coatings, or surface
7.1.2 Stroke Length Selection—It is unnecessary to set the
treatments to be evaluated.
stroke length equal to the full stroke of the piston in the engine
7.2.1 Ring Specimen—The ring specimen shall be prepared
because the greatest frictional influence of the materials is
by cutting a segment from a production piston ring, or
experiencedattheendsoftheringtravelwhereoperationinthe
machining a test piece of equal dimensions and finish to a
boundary lubrication regime increases the likelihood that
production piston ring. The ring specimen may be used in its
contactwilloccurbetweenthesurfacesoftheringandcylinder
original, factory-finished condition or it may be altered by
materials. The stroke length should typically range between 5
applying a coating or surface treatment. The surface shall be
and10timesthewidthoftheworn-incontactfaceofthepiston
prepared to simulate that for a particular engine or class of
ring specimen.
engines. The surface roughness of the ring specimen, in the
NOTE 1—The design of certain testing machines and motor drive
area of the contact, shall be measured by a suitable method and
systems limits the maximum frequency achievable for a given stroke
included in the test record. All pertinent descriptors (type of
length. Therefore, a compromise may be necessary between the highest
profiling method, surface finish parameters, and measuring
desired stroke length and the desired reciprocating frequency.
conditions) shall be reported.
7.1.3 Specimen Fixturing—A means shall be provided to
7.2.2 Cylinder Bore Specimen—The specimen intended to
clamp the ring specimen to the reciprocating portion of the
simulate the cylinder bore surface shall constitute either a cut
machine in such a way as to ensure correct alignment during
section of a production-finished cylinder or a flat specimen
sliding.Likewise,thecylinderborespecimenshallbemounted
whose form and finish is similar to that of the cylinders used in
in a suitable, heated lubricant container such that no loosening
the engine of interest. Methods have been developed to
orothermisalignmentoccursduringthetest.Forringsegments
simulate the roughness and lay of production cylinder liners on
with a rectangular cross-section, a suitable flat-faced ring-
flat cast iron test coupons. Alternatively, a polished surface
segment grip may be used. For non parallel-sided piston rings
may be used to simulate the worn condition of a cylinder bore
(for example, those with keystone-like cross-sections), it may
near at the top-dead-center position. In certain cases, the
benecessarytoprepareaholderfromanactualpistonordesign
cylinder bore specimen may be fabricated from experimental
a holder that clamps the inclined sides of the ring firmly.
materials, coated, or surface-treated. The surface roughness of
7.1.4 Specimen Alignment—Proper alignment and centering the cylinder bore specimen shall be measured by a suitable
method and included in the test record. With stylus-type
between sliding surfaces is a critical factor for ensuring
repeatable friction test results. Alignment affects the distribu- instruments, it is traditional to measure and report the surface
roughnessprofileparalleltothedirectionofmotionofthering,
tion of normal forces on the contact surface as well as the
lubrication regimes that change as the ring specimen moves that is, parallel to the cylinder axis. All pertinent descriptors
(type of profiling method, surface finish parameters, and
back and forth. Two approaches are used together to ensure
measuring conditions) shall be reported.
proper alignment: (1) mechanical alignment of the test fixtures
7.3 Lubricant Selection—The lubricant should be in a
during the initial test set-up, and (2) running-in of the ring
condition that is representative of that found in the engine of
specimenagainstthecounterfacesurface.Theformerapproach
interest after a period of running. Studies of experimental
addresses macro-contact aspects of alignment and the latter
piston ring and liner materials have shown that fresh engine
micro-scale aspects of alignment. A method for running in
lubricants do not in general produce friction and wear test
specimens is given in Appendix X1.
results equal to those obtained with used engine oils under
NOTE 2—Mechanical specimen alignment tends to be difficult to 4
otherwise similar testing conditions. A guide to formulating
achieve with conformal starting geometry. When testing ring and cylinder
fluidswithcharacteristicssimilartothoseofuseddieselengine
materials from the same type of engine, the ring curvature in the actual
oil is given in Appendix X2.
engine is produced by elastically confining the ring in its groove. The
7.4 Friction Force Measurement and Calibration:
same ring, out of the engine, will tend to have a larger curvature, and
hence rest on the edges of the corresponding cylinder bore specimen 7.4.1 Friction Force Measurement and Recording—A
unless the ring can be pre-stressed or in some other way forced into a
means shall be provided for measuring and recording the
radius of curvature that precisely matches that of the opposing specimen
magnitude of the friction force. This can inv
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