Designation:D1894–001An American National Standard
Standard Test Method for
Static and Kinetic Coefficients of Friction of Plastic Film and
Sheeting1
This standard is issued under thefixed designation D1894;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(e)indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1.Scope*
1.1This test method covers determination of the coefficients of starting and sliding friction of plasticfilm and sheeting when sliding over itself or other substances at specified test conditions.The procedure permits the use of a stationary sled with a moving plane,or a moving sled with a stationary plane.Both procedures yield the same coefficients of friction values for a given sample. N OTE1—For the frictional characteristics of plasticfilms partially wrapped around a cylinder,or capstan,see Test Method G143under the jurisdiction of ASTM Subcommittee G0
2.50.
1.2Test data obtained by this test method is relevant and appropriate for use in engineering design.
1.2.1As an option to this test,coefficient of friction may be run at temperatures other than23°C by heating only the plane while the sled is at ambient temperature.
1.3The values stated in SI units are to be regarded as the standard.The values given in parentheses are for information only.
1.4This 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.For a specific precautionary statement,see Note6.7.
N OTE2—This test method and ISO/DIS8295–1994are not technically equivalent.
2.Referenced Documents
2.1ASTM Standards:
1This test method is under the jurisdiction of ASTM Committee D20on Plastics and is the direct responsibility of Subcommittee D20.10on Mechanical Properties.
Current edition approved July March10,20001.Published October2000.June2001.Originally published as D1894–61T.Last previous edition D1894–9900.
1
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version.Because it may not be technically possible to adequately depict all changes accurately,ASTM recommends that users consult prior editions as appropriate.In all cases only the current version of the standard as published by ASTM is to be considered the official document.
*A Summary of Changes section appears at the end of this standard.
Copyright©ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA19428-2959,United States.
D618Practice for Conditioning Plastics and Electrical Insulating Materials for Testing2
D883Terminology Relating to Plastics2
D3574Test Methods for Flexible Cellular Materials—Slab,Bonded,and Molded Urethane Foams3
D4000Classification System for Specifying Plastic Materials3
E691Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method4
G143Test Method for Measurement of Web/Roller Friction Characteristics5
2.2ISO/DIS Standard:
ISO/DIS8295–19946
3.Terminology
3.1Definitions:
3.1.1friction,n—resistance to relative motion between two bodies in contact.
3.1.1.1coeffıcient of friction—the ratio of the force required to move one surface over another to the total force applied normal to those surfaces.
3.1.1.2kinetic coeffıcient of friction—the ratio of the force required to move one surface over another to the total force applied normal to those surfaces,once that motion is in progress.
3.1.1.3static coeffıcient of friction—the ratio of the force required to move one surface over another to the total force applied normal to those surfaces,at the instant motion starts.D996,D10 3.2Definitions of Terms Specific to This Standard:
3.2.1slip—in plasticfilms,lubricity of two surfaces sliding in contact with each other.
4.Significance and Use
4.1Measurements of frictional properties may be made on afilm or sheeting specimen when sliding over itself or over another substance.The coefficients of friction are related to the slip properties of plasticfilms that are of wide interest in packaging applications.These methods yield empirical data for control purposes infilm production.Correlation of test results with actual performance can usually be established.
4.1.1This test method includes testing at temperatures other than23°C by heating only the plane while the sled is at ambient
temperature.
4.2Slip properties are generated by additives in some plasticfilms,for example,polyethylene.These additives have varying degrees of compatibility with thefilm matrix.Some of them bloom,or exude to the surface,lubricating it and making it more slippery.Because this blooming action may not always be uniform on all areas of thefilm surface,values from these tests may be limited in reproducibility.
4.3The frictional properties of plasticfilm and sheeting may be dependent on the uniformity of the rate of motion between the two surfaces.Care should be exercised to ensure that the rate of motion of the equipment is as carefully controlled as possible.
4.4Data obtained by these procedures may be extremely sensitive to the age of thefilm or sheet and the condition of the surfaces.The blooming action of many slip additives is time-dependent.For this reason,it is sometimes meaningless to compare slip and friction properties offilms or sheets produced at different times,unless it is desired to study this effect.
4.5Frictional and slip properties of plasticfilm and sheeting are based on measurements of surface phenomena.Where products have been made by different processes,or even on different machines by the same process,their surfaces may be dependent on the equipment or its running conditions.Such factors must be weighed in evaluating data from these methods.
4.6The measurement of the static coefficient of friction is highly dependent on the rate of loading and on the amount of blocking occurring between the loaded sled and the platform due to variation in time before motion is initiated.
4.7Care should be exercised to make certain that the speed of response of the recorder,either electronic or mechanical,is not exceeded.
4.8For many materials,there may be a specification that requires the use of this test method,but with some procedural modifications that take precedence when adhering to the specification.Therefore,it is advisable to refer to that material specification before using this test method.Table1of Classification System D4000lists the ASTM materials standards that currently exist.
5.Apparatus
5.1Sled—A metal block63.5mm(21⁄2in.)square by approximately6mm(0.25in.)thick with a suitable eye screw fastened in one end.When aflexiblefilm(see
6.2)is to be attached,the block shall be wrapped with a sponge rubber63.5mm(21⁄2in.) in width and3.2mm(1⁄8in.)in thickness.The foam shall beflexible,smooth-faced,and have a nominal density of0.25g/cm3 2Annual Book of ASTM Standards,V ol08.01.
3Annual Book of ASTM Standards,V ol08.02.
4Annual Book of ASTM Standards,V ol14.02.
5Annual Book of ASTM Standards,V ol03.02.
6Available from American National Standards Institute,11W.42nd St.,13th Floor,New York,NY10036.
when measured in accordance with the Density Test of Methods D3574.The pressure required to comp
ress the foam25%shall be85615kPa(12.562.5psi).The foam shall also have a high hysteresis when deformed.7The rubber shall be wrapped snugly around the sled and held in place against the bottom and top of the sled with double-faced masking tape.When a sheet(see6.3) is to be attached,double-faced tape shall be used to attach the specimen.The total weight of the(wrapped)sled and specimen shall be20065g.
N OTE3—Round-robin testing8has shown that the physical properties of the backing can drastically affect both the coefficient of friction and stick-slip behavior of thefilm.
5.2Plane—A polished plastic,wood,or metal sheet,9approximately150by300by1mm(6by12by0.040in.).A smooth,flat piece of glass may cover the upper surface of the plane.This provides a smooth support for the specimen.
pulleys5.2.1When it is desirable to run tests at temperatures above23°C,a heating unit shall be provided that is capable of maintaining
the temperature of the plane within62°C of the desired temperature.The temperature should be maintained within62°C of the desired temperature over the entire traverse of the sled(that is,over the full surface of the plane).
N OTE4—If the equipment has a plane with a heater,a cover may be used to help maintain the temperature of the plane within62°C of the desired temperature.
5.3Scissors or Cutter,suitable for cutting specimens to the desired dimensions.
5.4Adhesive Tape,cellophane or pressure-sensitive.
5.5Adhesive Tape,double-faced.
5.6Nylon Monofilament,having a0.3360.05-mm(0.01360.002-in.)diameter and capable of supporting a3.6-kg(8-lb)load.
5.7Beaded Chain,flexible metal cable,or equivalent,having a spring rate no less than600lbs per inch of stretch per inch of length(40lbs/in.(7000N/m)for a15-in.chain)in the range of50to150g of tension(such as beaded lampswitch pull chain).
5.8Low-Friction Pulleys—A phenolic type pulley mounted in hardened steel cone bearings on a metal fork.A ball-bearing type pulley may also be used.
5.9Force-Measuring Device,capable of measuring the frictional force to65%of its value.A spring gage10(Note3),universal testing machine,or strain gage may be used.
N
OTE45—The capacity of the spring gage(Fig.1(a and b))needed will depend upon the range of values to be measured.For most plastic,a500-g capacity gage with10-g or smaller subdivisions will be satisfactory.This spring will measure coefficients of friction up to and including2.5.
5.10Supporting Base—A smooth wood or metal base approximately200by380mm(8by15in.)is necessary to support the plane.The supporting base may be a simple rectangular box.If a universal testing machine is used to pull a moving plane,a supporting base of sufficient structural strength and rigidity to maintain afirm position between the moving crosshead and the force-measuring device will be necessary.
5.11Driving or Pulling Device for Sled or Plane—The plane may be pulled by a driven pair of rubber-coated rolls not less than 200mm(8in.)long,capable of maintaining a uniform surface speed150630mm/min(0.560.1ft/min)(Fig.1(b)),by the crosshead of a universal testing machine(Fig.1(d))(Note6),7),or a worm drive driven with a synchronous motor(Fig.1(e)).
A constant-speed chain drive system has also been found satisfactory(Fig.1(a)).A power-operated source may be used for pulling the sled over the horizontally-mounted specimen at a uniform speed of150630mm/min(0.560.1ft/min).A universal testing machine equipped with a load cell in its upper crosshead and a constant rate-of-motion lower crosshead has been found satisfactory (see Fig.1(c)).
N OTE56—Where the moving crosshead of a universal testing machine is used to pull the moving plane through a pulley system(Fig.1(d)),the strain
gage load cell,or other load-sensing instrument in the testing machine,acts as the force-measuring device.
6.Test Specimens
6.1The test specimen that is to be attached to the plane shall be cut approximately250mm(10in.)in the machine direction and130mm(5in.)in the transverse direction when such extrusion directions exist and are identifiable.
6.2Afilm specimen that is to be attached to the sled shall be cut approximately120mm(41⁄2in.)square.Film is defined as sheeting having a nominal thickness of not greater than0.254mm as indicated in Terminology D883.
6.3A sheeting specimen(greater than0.254mm nominal thickness)or another substance that is to be attached to the sled shall be cut63.5mm(21⁄2in.)square.
6.4Sheeting specimens shall beflat and free of warpage.Edges of specimens shall be rounded smooth.
6.5Five specimens shall be tested for each sample unless otherwise specified.
N OTE67—Plasticfilms and sheeting may exhibit different frictional properties in their respective principal directions due to anisotropy or extrusion effects.Specimens may be tested with their long dimension in either the machine or transverse direction of the sample,but it is more common practice to test the specimen as described in6.1with its long dimension parallel to the machine direction.
7Sheet stock,available from Greene Rubber Co.,59Broadway,North Haven,CT06473,has been found satisfactory.
8Supporting data are available from ASTM Headquarters.Request RR:D20-1065.
9Acrylic or rigid poly(vinyl chloride)sheeting has been found satisfactory for this purpose.
10Model L-500,available from Hunter Spring Co.,Lansdale,PA,has been found satisfactory for this purpose.
N OTE7—8—Caution:Extreme care must be taken in handling the specimens.The test surface must be kept free of all dust,lint,finger prints,or any foreign matter that might change the surface characteristics of the specimens.
7.Preparation of Apparatus
7.1Fig.1showsfive ways in which the apparatus may be assembled.The support bases for all apparatus assemblies shall be level.
7.2If the apparatus of Fig.1(a)or(b)is used,calibrate the scale of the spring gage as follows:
7.2.1Mount the low-friction pulley in front of the spring gage.
7.2.2Fasten one end of the nylonfilament to the spring gage,bring thefilament over the pulley,and suspend a known weight on the lower end of thefilament to act downward.
N OTE89—The reading on the scale shall correspond to the known weight within65%.The weight used for this calibration shall be between50and 75%of the scale range on the gage.
7.3The drive speed for the apparatus of Fig.1(a and b)shall be adjusted to150630mm/min(0.5(6.060.1ft/min).1.2 in./min).This speed may be checked by marking off a150-mm(0.5-ft)(6.0in.)section beside the plane and determining the time required for the plane to travel150mm(0.5ft).mm.
7.4If the apparatus of Fig.1(c and d)employing a universal testing machine is used,select the proper speed setting for a crosshead motion of150630mm/min(0.5(6.060.1ft/min).1.2in./min).A similar speed for the load-displacement recorder is desirable.However,the speed of the recorder can be adjusted to give the desired
accuracy
in reading
the
pen
trace.
7.5When the apparatus of Fig.1(c)(moving sled-stationary plane)is used,wipe the support base free of foreign matter and
A.Sled H.Constant-speed drive rolls
B.Plane I.Nylon monofilament
C.Supporting base J.Low-friction pulley
D.Gage K.Worm screw
E.Spring gage L.Half nut
F.
Constant-speed chain drive M.Hysteresis,synchronous motor
G.Constant-speed tensile tester crosshead
FIG.1Five Methods of Assembly of Apparatus for Determination of Coefficients of Friction of Plastic Film
D1894–001
4
lay down two strips of double-faced adhesive tape along the length of the supporting base so that they are approximately100mm (4in.)between centers.
7.6Fix the plane in position on the tape strips andfirmly press in place.
8.Conditioning
8.1Conditioning—Condition the test specimens at2362°C(73.463.6°F)and5065%relative humidity for not less than 40h prior to test in accordance with Procedure A of Practice D618,for those tests where conditioning is required.In cases of disagreement,the tolerances shall be61°C(61.8°F)and62%relative humidity.
8.2Test Conditions—Conduct tests in the standard laboratory atmosphere of2362°C(73.463.6°F)and5065%relative humidity,unless otherwise specified in the test methods or in this test method.In cases of disagreement,the tolerances shall be 61°C(61.8°F)and62%relative humidit
y.In specific cases,such as control testing,where the conditioning requirements cannot be met and the data still may be of direct assistance to the operation,other conditioning procedures may be used and recorded in the report.Frictional properties should be measured only after sufficient time has been allowed for the specimens to reach essential equilibrium with the ambient atmosphere.
9.Procedure
9.1Tape the250by130-mm(10by5-in.)film or sheet specimen to the plane with the machine direction of the specimen in the250-mm direction.Smooth thefilm specimen to eliminate wrinkles if necessary,taking care not to alter the specimen surface throughfinger oils,etc.
N OTE910—For some samples it has been found necessary to tape only the leading edge of the specimen to the plane.In some cases the specimen has
been pulled through the nip rolls apparatus of Fig.1(b)without the plane.However,should any dispute arise,taping of all four edges will be the referee method.
N OTE101—For the sake of uniformity and later comparison when testing a specimen sliding over itself,the specimens shall be mounted so that the same side of the specimen shall be used as the contact surface for both the moving and stationary specimens.
N OTE112—Coefficient of friction measurements may be made on afilm or sheeting specimen when sliding over itself or over other substance surfaces wherein the movement is made in the transverse direction of the specimen.However,the methods described here will be confined to movements in the machine direction of the specimens.
9.2Forfilm specimens,tape the edges of the120-mm(41⁄2-in.)squarefilm specimen to the back of the sled,using adhesive tape and pulling the specimen tight to eliminate wrinkles without stretching it.For sheet specimens,tape the63.5-mm(21⁄2-in.) square sheet specimen or second substrate to the sled face with double faced tape.Keep the machine direction of the specimen parallel to the length of the sled(where such a direction exists and is identifiable).
9.3Attach the specimen-covered sled through its eye screw to the nylonfilament.If a universal testing machine is used(Fig. 1(c and d)),pass thefilament through pulley(s)and upward to the bottom of the load-sensing device and attach securely.If a spring gage is used(Fig.1(a and b)),securely attach thefila
ment to it.The nylonfilament shall be of sufficient length to allow maximum sled or plane travel.With some slack in the nylonfilament,lightly place the sled in position on the horizontal plane(Note112).
The positioning of the sled shall be such that the length of the sled,the adjacent length of nylonfilament,and the long dimension (machine direction)of the plane-mounted specimen are parallel.For material combinations found to have an excessive stick-slip tendency,wherein the kinetic portion of the test degenerates into a series of static tests interspersed by rapid jumps of the sled, it is advisable but not mandatory to substitute the metal tow line(5.7)for the nylon tow line to make kinetic measurements.This will necessitate making separate measurements for static and kinetic friction coefficients.Each laboratory will determine what level of stick-slip is considered excessive for its materials.In case of disagreement between testing laboratories,the nylon tow line remains the referee procedure.
N OTE123—The purpose of using a nylonfilament for the static friction and sometimes a metallic tow line for kinetic friction is to avoid a faster force
buildup in the static measurement than the recorder can respond to,and to allow time for the recorder to separate the buildup of static friction force in the nylonfilament from the mass acceleration force as the sled breaks loose.The opposite effect is needed from the metallic tow line during kinetic friction measurement to prevent the occurrence of repeated stick-slips instead of steady motion.
N OTE134—The sled must be placed very lightly and gently on the plane to prevent any unnatural bond from developing.A high starting coefficient of friction may be caused by undue pressure on the sled when mounting it onto the plane.
9.4Start the driving mechanism(which has been adjusted previously to provide a speed of150630mm/min(0.5(6.060.1 ft/min)).1.2in./min)).As a result of the frictional force between the contacting surfaces,no immediate relative motion may take
place between the sled and the moving plane until the pull on the sled is equal to,or exceeds,the static frictional force acting at the contact surfaces.Record this initial,maximum reading as the force component of the static coefficient of friction.
9.4.1If conducting the test at temperatures above23°C(the temperature of the plane),ensure that sufficient time for the interface to reach the temperature of the plane has elapsed before starting the driving mechanism.
9.5Record the visual average reading during a run of approximately130mm(5in.)while the surfaces are sliding uniformly over one another.This is equivalent to the kinetic force required to sustain motion between the surfaces and normally is lower than the static force required to initiate motion.After the sled has traveled over130mm(5in.)stop the apparatus and return to the starting position.
9.6If a strain gage and load-displacement recorder are used,either draw the best straight line midway between the maximum points and minimum points shown on the chart while the sled is in motion,or obtain the average load by integration of the recorder
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