ASTM G181-04(2009)
(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 engine’s 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 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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 (Reapproved 2009)
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 2. Referenced Documents
1.1 This practice covers procedures for conducting labora- 2.1 ASTM Standards:
tory bench-scale friction tests of materials, coatings, and D6838 Test Method for Cummins M11 High Soot Test
surface treatments intended for use in piston rings and cylinder G40 Terminology Relating to Wear and Erosion
liners in diesel or spark-ignition engines. The goal of this
3. Terminology
procedure is to provide a means for preliminary, cost-effective
3.1 For definitions, see Terminology G40.
screening or evaluation of candidate ring and liner materials.A
reciprocating sliding arrangement is used to simulate the 3.2 Definitions of Terms Specific to This Standard:
3.2.1 conditioned oil—a lubricating oil whose viscosity,
contact that occurs between a piston ring and its mating liner
near the top-dead-center position in the cylinder where liquid composition, and other function-related characteristics have
been altered by use in an operating engine, such that the oil’s
lubrication is least effective, and most wear is known to occur.
Special attention is paid to specimen alignment, running-in, effects on friction and wear reflect those characteristic of the
long-term, steady-state engine operation.
and lubricant condition.
1.2 This practice does not purport to simulate all aspects of 3.2.2 conformal contact—in friction and wear testing, any
macro-geometric specimen configuration in which the curva-
a fired engine’s operating environment, but is intended to serve
as a means for preliminary screening for assessing the fric- ture of one contact surface matches that of the countersurface.
3.2.2.1 Discussion—Examplesofconformalcontactinclude
tional characteristics of candidate piston ring and liner material
combinations in the presence of fluids that behave as use- a flat surface sliding on a flat surface and a ball rotating in a
socket that conforms to the shape of the ball.Apair of surfaces
conditioned engine oils. Therefore, it is beyond the scope of
may begin a wear or friction test in a non-conforming contact
this practice to describe how one might establish correlations
between the described test results and the frictional character- configuration, but develop a conformal contact as a result of
wear.
istics of rings and cylinder bore materials for specific engine
designs or operating conditions. 3.2.3 lubrication regime—in liquid-lubricated sliding con-
tact, a certain range of friction coefficients that results from a
1.3 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this combination of contact geometry, lubricant viscosity charac-
teristics, surface roughness, normal pressure, and the relative
standard.
1.4 This standard does not purport to address all of the speed of the bearing surfaces.
3.2.3.1 Discussion—Common designations for lubrication
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- regimes are boundary lubrication, mixed film lubrication,
elasto-hydrodynamic lubrication and hydrodynamic lubrica-
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. tion.
This practice is under the jurisdiction of ASTM Committee G02 on Wear and
Erosion and is the direct responsibility of Subcommittee G02.50 on Friction. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2009. Published February 2010. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2004. Last previous edition approved in 2004 as G181–04. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/G0181-04R09. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G181 – 04 (2009)
4. Summary of Practice 5.2 Engine oil spends the majority of its operating lifetime
in a state that is representative of use-conditioned oil. That is,
4.1 A reciprocating friction test apparatus is used to simu-
fresh oil is changed by exposure to the heat, chemical envi-
late the back-and-forth motion of a piston ring within a
ronment, and confinement in lubricated contact. It ages, chang-
cylinder bore in the presence of a heated lubricant. Other types
ing viscosity, atomic weight, solids content, acidity, and
of motions, like ring rotation, ring-groove fretting motion, and
chemistry. Conducting piston ring and cylinder liner material
ringrocking,arenotsimulatedwiththisprocedure.Thecontact
evaluationsinfresh,non-conditionedoilisthereforeunrealistic
geometry, selection of testing parameters, and the methods of
for material screening. But additive-depleted, used oil can
specimen surface finishing and characterization are described.
result in high wear and corrosive attack of engine parts. The
The lubricating fluid is selected to simulate the effects of used
current test is intended for use with lubricants that simulate
oil.Arunning-in procedure is used to increase the repeatability
tribological behavior after in-service oil conditioning, but
of results.
preceding the point of severe engine damage.
5. Significance and Use
6. Reagents
5.1 The efficiency and fuel economy of spark ignition and
6.1 Cleaning Solvents—Suitable solvents may be used to
dieselenginesisaffectedinparttothefrictionbetweenmoving
degreaseandcleanspecimenspriortoconductingthedescribed
parts.Although no reliable, in situ friction measurements exist
procedure. No specific solvents are recommended here, except
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,
a practice is considered more appropriate than a standard test 7.1 Description of the Test Apparatus—A schematic repre-
sentation of the reciprocating contact geometry is shown in
method in which specific test parameters are prescribed.
Variablesthatcanbeadjustedinthisprocedureinclude:normal Fig. 1. Two versions of this test are shown. In the first case
force, speed of oscillation, stroke length, duration of testing, (Fig. 1, bottom left), the lower specimen conforms to the shape
temperature of testing, method of specimen surface prepara- of the ring segment. In the second case (Fig. 1, bottom right),
tion,andthematerialsandlubricantstobeevaluated.Guidance the ring segment slides on a flat lower specimen. Specimens
is provided here on the set-up of the test, the manner of areplacedinaheated,temperature-controlledbathoflubricant.
specimen fixturing and alignment, the selection of a lubricant Alternate means of supplying the lubricant, such as drip feed,
to simulate conditioned oil characteristics (for a diesel engine), may be used.
and the means to run-in the ring specimens to minimize 7.1.1 Motion—The test apparatus shall be capable of im-
variability in test results. parting a back-and-forth (herein called reciprocating) motion
FIG. 1 Schematic Drawing of the Test Configuration Showing Conformal and Non-conformal Contact
G181 – 04 (2009)
achieve with conformal starting geometry. When testing ring and cylinder
of constant stroke length and repeatable velocity profile to the
materials from the same type of engine, the ring curvature in the actual
simulated piston ring specimen which slides against the simu-
engine is produced by elastically confining the ring in its groove. The
lated cylinder bore under a controlled normal force. The motor
same ring, out of the engine, will tend to have a larger curvature, and
shall be sufficiently powered so that the velocity profile and
hence rest on the edges of the corresponding cylinder bore specimen
constancy of operation shall be unaffected by the friction force
unless the ring can be pre-stressed or in some other way forced into a
developed between the test specimens. The velocity versus
radius of curvature that precisely matches that of the opposing specimen
time response of crank-driven devices tends to be approxi- cut from the cylinder. A non-conformal, ring-on-flat geometry with a
suitable running-in procedure, has been shown to produce a more
mately sinusoidal, and this type of motion is appropriate to
repeatable worn-in condition for friction testing.
simulate a piston driven by a crankshaft. The frequency of
reciprocation, given in cycles per second, shall be selected to 7.1.5 Normal Force Application—The apparatus shall have
induce the appropriate lubrication regime experienced by the
the ability to apply a controlled normal force to the ring and
pistonringduringitsslowdownandreversalofdirectioninthe cylinder specimens. The loading mechanism can be a dead-
engine of interest. Typical frequencies for slider-crank testing
weight system, a levered type of device, or a hydraulic or
equipment of this type range between 5 and 40 cycles per electromagnetic actuator. The loading system shall have suffi-
second. The average sliding speed for each stroke, s, in metres cient rigidity and damping capacity to avoid excessive deflec-
per second, is calculated as follows:
tions or vibrations during testing, and to maintain the desired
normal force within 2 % of the intended value.
s 5 2fL (1)
7.2 Specimen Preparation—Test specimens are herein re-
where:
ferred to as the ring specimen and the cylinder bore specimen.
f = frequency of reciprocation in cycles per second, and
Theprecisemannerofpreparingtestspecimensdependsinpart
L = stroke length in meters.
on the kinds of materials, coatings, or surface treatments to be
7.1.2 Stroke Length Selection—It is unnecessary to set the
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
area of the contact, shall be measured by a suitable method and
NOTE 1—The design of certain testing machines and motor drive
included in the test record. All pertinent descriptors (type of
systems limits the maximum frequency achievable for a given stroke
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.
7.2.2 Cylinder Bore Specimen—The specimen intended to
7.1.3 Specimen Fixturing—A means shall be provided to
simulate the cylinder bore surface shall constitute either a cut
clamp the ring specimen to the reciprocating portion of the
section of a production-finished cylinder or a flat specimen
machine in such a way as to ensure correct alignment during
whose form and finish is similar to that of the cylinders used in
sliding. Likewise, the cylinder bore specimen shall be mounted
the engine of interest. Methods have been developed to
in a suitable, heated lubricant container such that no loosening
simulate the roughness and lay of production cylinder liners on
orothermisalignmentoccursduringthetest.Forringsegments
flat cast iron test coupons. Alternatively, a polished surface
with a rectangular cross-section, a suitable flat-faced ring-
may be used to simulate the worn condition of a cylinder bore
segment grip may be used. For non parallel-sided piston rings
near at the top-dead-center position. In certain cases, the
(for example, those with keystone-like cross-sections), it may
cylinder bore specimen may be fabricated from experimental
benecessarytoprepareaholderfromanactualpistonordesign
materials, coated, or surface-treated. The surface roughness of
a holder that clamps the inclined sides of the ring firmly.
the cylinder bore specimen shall be measured by a suitable
7.1.4 Specimen Alignment—Proper alignment and centering
method and included in the test record. With stylus-type
between sliding surfaces is a critical factor for ensuring
instruments, it is traditional to measure and report the surface
repeatable friction test results. Alignment affects the distribu-
roughnessprofileparalleltothedirectionofmotionofthering,
tion of normal forces on the contact surface as well as the
that is, parallel to the cylinder axis. All pertinent descriptors
lubrication regimes that change as the ring specimen moves
(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
...
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