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1、BRITISH STANDARD BS 903-A61: 1994 Physical testing of rubber Part A61: Determination of the frictional properties of rubber UDC 678.01:620.178.16 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 04:56:51 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 903-A61:1994
2、This British Standard, having been prepared under the direction of the Plastics and Rubber Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 January 1994 BSI 04-1999 The following BSI references relate to the work on this standard: Commi
3、ttee reference PRM/22 Draft for comment 92/43803 DC ISBN 0 580 22376 0 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Plastics and Rubber Standards Policy Committee (PRM/-) to Technical Committee PRM/22, upon which the following bodies
4、were represented: British Railways Board British Rubber Manufacturers Association GAMBICA (BEAMA Ltd.) Institution of Mechanical Engineers Institution of Water and Environmental Management Malaysian Rubber Producers Research Association Ministry of Defence RAPRA Technology Ltd. SATRA Footwear Techno
5、logy Centre Coopted member Amendments issued since publication Amd. No.DateComments Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 04:56:51 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 903-A61:1994 BSI 04-1999i Contents Page Committees responsibleInside front
6、cover Forewordii Introduction1 1Scope1 2References1 3Definitions2 4Principle2 5Apparatus2 6Test surfaces3 7Preparation4 8Conditioning5 9Test parameters5 10Cleaning or renewal of the test track5 11Procedure A (initial friction values)5 12Procedure B (service behaviour)6 13Procedure C (tests with adde
7、d lubricants or contaminants)6 14Stick-slip6 15Presentation of results6 16Test report8 Annex A (informative) Design principles9 Annex B (informative) Ball on flat geometry10 Annex C (informative) Static friction and “stiction”10 Annex D (informative) Other parameters11 Figure 1 Typical friction trac
8、es showing high and low points7 Figure 2 Typical drift of results in extended tests8 Figure 3 Typical stick-slip traces8 Figure A.1 Effect of offsetting the towing force and the force in the friction plane9 Figure A.2 An arrangement which keeps the towing force and the line of action of the load cel
9、l in the friction plane9 Figure D.1 Theoretical change in friction over a large velocity range, allowing for temperature increase at the interface12 Figure D.2 Experimental change in friction over a large velocity range, allowing for temperature increase at the interface12 Figure D.3 Effect of glass
10、 transition temperature on friction curves13 List of referencesInside back cover Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 04:56:51 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 903-A61:1994 ii BSI 04-1999 Foreword This Part of BS 903 has been prepared und
11、er the direction of the Plastics and Rubber Standards Policy Committee. In preparing this Part of BS 903 the committee was concerned to develop a method of test, which provided the greatest degree of operational flexibility, for investigating the frictional properties of rubbers. There are many appl
12、ications in the Defence, Aerospace, Public sector and private industry where frictional properties are extremely important. Attention is drawn in particular to the considerations discussed in the introduction. A British Standard does not purport to include all the necessary provisions of a contract.
13、 Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 14, an inside back cover
14、and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 04:56:51 GMT+00:00 2006, Unco
15、ntrolled Copy, (c) BSI BS 903-A61:1994 BSI 04-19991 Introduction Various geometrical arrangements can be used when measuring friction, but each is likely to give a different value for m, the coefficient of friction. Each may be appropriate in particular circumstances but it is desirable that some st
16、andard method utilizing specified test conditions be employed when comparisons between materials are undertaken. Rubber samples are most readily available in sheet form and for many practical applications measurement between two planar surfaces most nearly approaches service behaviour. Consequently
17、this is the most widely used geometry. For this geometry the apparatus used needs careful design in order to ensure reproducible contact between the surfaces and this is discussed in Annex A. Where rubber moulding facilities are available, some workers prefer to use a hemispherical rubber slider and
18、 a planar test track. This gives a more definable contact area and minimizes the errors involved if the friction plane does not contain both the line of action of the load cell and the line of the towing force. However, when this geometry is used, frictional force is not proportional to normal load
19、(see Annex B) and contact area is estimated from a knowledge of the modulus of the rubber. Hence care should be taken when quoting values for coefficient of friction. The big disadvantage of the method is that special test pieces need to be moulded from unvulcanized rubber and rubber products cannot
20、 be accommodated. Finally, since some degree of wear is inseparable from friction, extended testing will produce a “flat” on the hemispherical test piece. Frequent inspection of the test surface is recommended therefore, to ensure that the initial contact geometry is maintained. The alternative “bal
21、l on flat” geometry where a hard ball slides on a flat rubber surface is not an exact equivalent. The ploughing action of the ball through the rubber results in an energy loss by hysteresis which gives a higher measured coefficient of friction. However, in some circumstances this may be an appropria
22、te test procedure. Although there may be some uncertainty in the contact area using plane on plane geometry, this Part of BS 903 is based on this geometry because of its wide practical applicability. However, it is emphasized that it is necessary to have a well designed apparatus with the line of ac
23、tion of the load cell contained by the plane of contact of the test pieces (see Annex A). The method can be adapted to cover other contact geometries to suit particular products, including the ball on flat geometry set out in Annex B. This Part of BS 903 is based on linear motion and guidance on the
24、 experimental arrangement is given in Annex A. Because friction generates heat it is usual to restrict testing to velocities typically below 1 000 mm/min in order to avoid a large temperature rise at the interface. If service conditions involve high speeds then an entirely different method based on
25、rotary motion is more appropriate as discussed in Annex A. The method of test set out here enables kinetic friction to be measured at a number of fixed velocities. It can be arranged that the lowest velocity is such that movement is barely discernible and this gives an approximation to frictional be
26、haviour close to zero velocity (static friction). This may be different from the starting friction which may involve some element of adhesion (stiction) as discussed in Annex C. This method is suitable for measuring the initial friction only if the machine has a constant rate of load facility and a
27、sufficiently compliant load cell. A discussion on static friction and the correct approach to its measurement is given in Annex C. Rubber friction is complex and the coefficient of friction is dependent on the contact geometry, normal load, velocity and temperature, as well as the composition of the
28、 rubber. A discussion of the influence of these parameters and some other factors which affect measurement is presented in Annex D. 1 Scope This Part of BS 903 outlines the principles governing the measurement of coefficient of friction and describes a method suitable for measuring the coefficient o
29、f friction of a rubber against standard comparators, against itself, or against any other specified surface. 2 References 2.1 Normative references This Part of BS 903 incorporates, by reference, provisions from specific editions of other publications. These normative references are cited at the appr
30、opriate points in the text and the publications are listed on the inside back cover. Subsequent amendments to, or revisions of, any of these publications apply to this Part of BS 903 only when incorporated in it by updating or revision. 2.2 Informative references This Part of BS 903 refers to other
31、publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions. Licensed Copy: London South Bank University, London South Bank University, Fri Dec
32、 08 04:56:51 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 903-A61:1994 2 BSI 04-1999 3 Definitions For the purposes of this Part of BS 903, the following definitions apply. 3.1 coefficient of friction the ratio of the frictional force opposing motion between two surfaces to the normal force between
33、 the surfaces under specified test conditions NOTECoefficient of friction is dimensionless and its value is not restricted to numbers less than unity. 3.2 area of contact the whole of the apparent area made between the two test surfaces NOTEThe real area of contact may well be less than this. 3.3 re
34、al area of contact the sum total of the minute contact areas at which the two surfaces touch 3.4 velocity of test the velocity with which one surface is driven relative to the other NOTEIf stick-slip occurs this will then be the mean velocity with which one surface moves relative to the other. 3.5 s
35、tick-slip a condition in which the actual velocity between the surfaces oscillates between two extremes about the test velocity, resulting in corresponding oscillations in the measured frictional force 3.6 test track the surface against which the rubber is to be tested NOTEThe test track may be made
36、 from the same material as the rubber under test or may be different. 3.7 temperature of test the temperature of the test apparatus and its environment NOTESince friction generates heat this may differ from the actual temperature of one or both of the test surfaces. 3.8 lubricant a substance introdu
37、ced between two surfaces to lower the coefficient of friction NOTEA lubricant is usually a liquid, but in some circumstances solid powders are used, e.g. talc. Usually, lubricants are introduced deliberately. 3.9 contaminant any substance present on either test surface not of the same composition as
38、 that surface NOTEA contaminant may act as a lubricant. Usually, in service contaminants are introduced inadvertently. 3.10 stiction the force needed to move one surface over another when the external normal load is reduced to zero NOTEThis is an apparent frictional force, but no coefficient of fric
39、tion can be calculated since the normal force is zero. See Annex C. 3.11 static friction the frictional force needed to start motion (i.e. the frictional force at zero velocity) NOTEWhen there is an external normal load a coefficient of static friction can be calculated. Static friction often involv
40、es some element of stiction. See Annex C. 4 Principle Two test surfaces are brought together under the action of a measured normal load. A mechanism slides one of the surfaces at a measured velocity and the force opposing motion is monitored and recorded. The ratio of this frictional force to the no
41、rmal load at any instant is the coefficient of friction at that time. Since the test itself will alter the surfaces and may change the temperature at the interface, the measured coefficient of friction may change as the test proceeds. In an ideal apparatus the line of action of the force-measuring e
42、quipment will lie in the plane of the two contacting surfaces, which may be either a horizontal or a vertical plane. 5 Apparatus 5.1 A device, with provision for attaching two friction surfaces, capable of providing linear motion between the surfaces for a distance of typically 100 mm, at a number o
43、f fixed velocities, typically between 0.5 mm/min and 1 000 mm/min. This may be a dedicated device or alternatively a tensile testing machine may be adapted for the purpose. 5.2 Means of providing several measured normal loads, between the surfaces within the range 1 N to 200 N. When the test track i
44、s horizontal, suitable weights may be used directly to provide the normal load, but on a machine with a vertical test track it will be necessary to use a bell crank lever system to convert the vertical gravitational force into a horizontal normal force. Licensed Copy: London South Bank University, L
45、ondon South Bank University, Fri Dec 08 04:56:51 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 903-A61:1994 BSI 04-19993 5.3 A series of load cells, or alternatively a load cell with multiple ranging, conforming to grade A of BS 5214-1:1975, fitted with a means of recording the output and fastened t
46、o one of the friction surfaces, with ranging or other means of indicating the frictional force to an accuracy of 1 % throughout the range of measurement. NOTECorresponding to the range of normal loads stated in 5.2, the measured frictional forces are likely to be within the range 0.1 N to 1 kN. 5.4
47、An environmental cabinet, if the effects of temperature are to be studied, to contain the apparatus and the two surfaces under test (but not the load cell) with a means of measuring and recording temperature to an accuracy of 0.5 C. The environmental chamber shall not make physical contact with any
48、moving parts. NOTE 1The exclusion of a condensation forming atmosphere from the test environment is extremely difficult, and the formation of ice crystals or particles or films on the test surfaces can only be assessed visually. NOTE 2To avoid the formation of ice when testing at temperatures at or
49、below 0 C, a very dry atmosphere (e.g. 5 % to 10 % r.h.) is needed. 5.5 Means to avoid stick-slip, as the whole apparatus (including the load cell) needs to be as stiff as possible. All connections shall be made with rods and not with wire. Where an apparatus is designed to be attached to a tensile testing machine, then a testing machine with a high degree of stiffness shall be chosen. In practice this means a tensile testing machine with a load capacity some 20 times greater than the maximum frictional force being measured. 5.6 Means of separating the sur