1、 WORLDWIDE ENGINEERING STANDARDS Test Procedure GMW16666 Coefficient of Friction Measurement for Elastomers Copyright 2011 General Motors Company All Rights Reserved November 2011 Originating Department: North American Engineering Standards Page 1 of 12 1 Scope Note: Nothing in this standard superce
2、des applicable laws and regulations. Note: In the event of conflict between the English and domestic language, the English language shall take precedence. 1.1 Purpose. See Table 1, Test Description. Table 1: Test Description Purpose/Technique Evaluation A1 Horizontal Dry Schedule 1 (subsection) To e
3、valuate the friction between dry test surfaces. A sled of specified material with the desired surface finish is pulled across a stationary flat elastomer slab at 23 C. Sled surface finish directional influences on friction are tested by rotating the sled 90 degrees and repeating the measurement proc
4、edure. Procedural control of significant test parameters (finish, finish direction, pull rate and time between measurements) provides repeatable and reproducible measurement. Material and finish effects on starting (static) and sliding (kinetic) coefficient of friction on clean, dry surfaces. A2 Hor
5、izontal Wet Schedule 2 (subsection) To evaluate the friction between wet test surfaces. A sled of specified material with the desired surface finish is pulled across a stationary flat elastomer slab. Both contact surfaces are covered with a designated liquid. Tests are run at 23 C. Sled surface fini
6、sh directional influences on friction are tested by rotating the sled 90 degrees and repeating the measurement procedure. Procedural control of significant test parameters (finish, finish direction, pull rate and time between measurements) provides repeatable and reproducible measurement. Material a
7、nd finish effects on starting (static) and sliding (kinetic) coefficient of friction on wet surfaces. 1.2 Foreword. This document is based on ISO 15113, Rubber - Determination of Frictional Properties. The coefficient of friction (CoF) depends on the rubber composition, test duration and type of tes
8、t rig. The latter affects the CoF mostly via the contact pressure and transport of debris from the contact area (on repeat measurements). The force to start the sled (static friction) and to keep the sled moving (kinetic friction) are both measured by the load cell, and recorded on a graphical devic
9、e or stored in a data acquisition system. The acquired force data is divided by the sled weight to mathematically determine the static and kinetic coefficient of friction. Static friction is derived from the first maximum peak (force) on the load curve, and the kinetic friction is derived from an av
10、eraged force value between two defined points within the region beyond the first peak on the load curve. 1.3 Applicability. To support finite element analysis of elastomeric parts for an assembled joint. 1.3.1 Measured Finishes. Such as cast and machined groove, or surface finishes for static mating
11、 surfaces (e.g., engine block, head, covers, etc.) It does not represent rotating or reciprocating surfaces like crankshaft or valve stems. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license
12、from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16666 Copyright 2011 General Motors Company All Rights Reserved November 2011 Page 2 of 12 1.4 Definitions. 1.4.1 Friction. The resistance between two contacting surfaces. See Figure 1 for graphic representation of friction. 1.4.2 Static Coefficient
13、 of Friction (s). Coefficient of friction at the instant motion between surfaces starts. 1.4.3 Kinetic Coefficient of Friction (k). Coefficient of friction after motion between surfaces is established. 1.4.4 Coefficient of Friction (CoF). The ratio of the force required to move one surface over anot
14、her to the total force applied normal to those surfaces. Coefficient of friction is dimensionless and its value is not restricted to numbers less than unity. Figure 1: Graphic Representation of Friction 1.4.5 Stick-Slip. A condition where the actual velocity between the surfaces oscillates, resultin
15、g in corresponding oscillations in the measured frictional force. See Figure 7. 1.4.6 Coating. A dry substance introduced between two surfaces to lower the coefficient of friction. 1.4.7 Wet Assembly Aids. Solutions used to temporarily reduce assembly force (friction) between press and interference
16、fit stationary mating elements (e.g., hose to fitting). The term lubricant is sometimes used to describe an assembly aid; however its proper usage is to describe fluids or greases as a maintained film between moving surfaces to reduce friction and wear. 1.4.8 Machine Direction. The direction the mac
17、hining method is applied to the work piece or the direction the work piece lead end was first fed into the finish machine (running direction). 1.4.9 Against Machine Direction. The 180 degree movement opposite of the machine direction. 1.4.10 Cross Direction. The direction perpendicular to the machin
18、e direction. 2 References Note: Only the latest approved standards are applicable unless otherwise specified. 2.1 External Standards/Specifications. ASME B46.1 ASTM D3182 ISO 15113 ASTM D412 ASTM E18 ISO 23529 ASTM D1329 ISO 2230 SAE AS7949 ASTM D1894 ISO 6194-4 SAE AS21443 2.2 GM Standards/Specific
19、ations. 9985662 2.3 Additional References. MIL-A-8625 MS20219A1 (Bearing, Ralmark Company) Commercial Grade - Specifications SD 117 2.3.1 Aluminum Alloys. 2024-T351 6061-T6 Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or netw
20、orking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16666 Copyright 2011 General Motors Company All Rights Reserved November 2011 Page 3 of 12 2.3.2 Air Atomizing Sprayer. 7054T8 (McMaster Carr Supply Company) 7054T41 (McMaster Carr Supply Company) 2.3.3 Horizontal Te
21、st Line. SC01217 (Loos and Company, Incorporated, Pomfret, Connecticut 06528) 3458T961 (McMaster Supply Company) 3 Resources 3.1 Facilities. 3.1.1 A suitable area or room for conduction testing with a stable and known environment (see 4.2.1). 3.2 Equipment. The following items are needed to perform
22、Test A. 3.2.1 Testing Machine. See ASTM D412 apparatus description. All tests are made on a power driven machine equipped to produce a uniform rate of grip separation that allows 1% strain per second in the test specimen. The testing machine must have a suitable dynamometer and indicating or recordi
23、ng system for measuring the applied force. The applied force must be within 1% of the readings throughout the entire range/distance of testing (to normalize readings). 3.2.2 Surface Finish Measuring Equipment. Test labs must be able to produce and measure/verify the desired test finish internally or
24、 have it performed by qualified pay for service facility. 3.2.3 Methods A1 and A2. Figure 2 shows the setup for attaching two horizontal friction surfaces. The test apparatus may be a dedicated device or a tensile testing machine adapted for that purpose. On the tensile test machine the load cell is
25、 mounted on the crosshead, and the friction fixture is mounted on the base of the test instrument. The crosshead moves up during the test. The equipment must be capable of providing linear motion between the surfaces for a distance of 50 mm to 100 mm, and a rate of 0.5 mm/minute to 150 mm/minute. Fi
26、gure 2: Friction Test Setup 3.2.4 Clamping Force or Load. 3.2.4.1 Weights. For Methods A1 and A2 to provide a 1 N to 20 N range over the minimum contact area (sled). The weight must not cause stick-slip or promote sled misalignment during measurement. 3.2.4.2 Clamps. For Methods A1 and A2 to provide
27、 a secure positioning of elastomer slab during testing. 3.2.5 Sled. A 50 mm 50 mm 6 mm platform made of the specified material with referenced standard, grade, process and finish. Examples include cast and machined surfaces of aluminum, magnesium and cast iron and 30% glass filled nylon. Eyelets are
28、 secured at the opposite ends of the leading edge to attach the horizontal test line. All edges will be rounded (not beveled). See Figure 3, Sled and Line Configuration. Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or network
29、ing permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16666 Copyright 2011 General Motors Company All Rights Reserved November 2011 Page 4 of 12 Figure 3: Sled and Line Configuration 3.2.6 Grooved Bearing Wheel with Mounting Feature. Provides alignment for the monofilament
30、 line between the test cell and the sled. Wheel is a metallic sheave, aluminum alloy 2024-T351. Aluminum sheaves are anodized per MIL-A-8625, Type II, Class I. Bearing retention sleeve is aluminum alloy 6061-T6. Bearing conforms to the requirements of SAE Aerospace Standard AS7949 and AS21443. Ralma
31、rk Company, MS20219A1 meets the requirements. See Figure 4, Bearing Wheel Dimensions. A B C D E Outside Diameter 0.005 Groove Diameter 0.005 Shoulder Diameter (approximately) Bore Diameter +0.0000/-0.0005 Width Inside Radius (IR) +0.000/-0.005 1.312 1.000 0.372 0.2500 0.438 F G H I Material Width Gr
32、oove Width +0.000/-0.010 Groove Radius +0.000/-0.003 +0.000/-0.010 0.310 Maximum 0.150 0.050 0.055 Figure 4: Bearing Wheel Dimensions (mm) 3.2.7 Load Cell. 0.1 N to 1 kN. 3.2.8 Horizontal Test Line. Nylon monofilament, Teflon coated, 5.4 kg test load. Spiderwire meets the requirements. Commercial Gr
33、ade - Specifications SD 117 - 302/304 stainless steel strand (1 7 construction, 0.3048 mm (0.012 in) diameter, 11.3 kg (25 lb) minimum break strength). 3.2.8.1 Manufacturer. Part Number SC01217, Loos and Company, Incorporated, Pomfret, Connecticut 06258, USA. This product is also available from McMa
34、ster Carr Supply Company, Part Number 3458T961. 3.2.8.2 A wire test/tow line may be necessary for material combinations found to have excessive stick-slip tendency, in which the kinetic portion of the test degenerates into a series of static tests as a result of rapid jumps from the sled. This neces
35、sitates making separate measurements for static and kinetic friction coefficients. The test technician can determine what level of stick-slip is considered excessive for its materials. If there is disagreement, the nylon tow line remains the prevailing choice. 3.2.9 Air Atomizing Sprayer. A 250 mL o
36、r 500 mL corrosion resistant bottle or carafe shaped container with nozzle capable of delivering a uniform wet coating of wet assembly aids containing water/soap or emulsion type solutions. The unit is pressurized with filtered compressed air in a range suitable for multiple applications without los
37、s of uniform coating coverage. After repeated use the container can be depressurized, refilled and recharged. 3.2.9.1 This product is available from McMaster Carr Supply Company, Part Number 7054T41 or 7054T8. 3.2.9.2 Spray Nozzle (Mist). A unit capable of a full cone pattern with a 70 degree or lar
38、ger coverage angle. A built-in pressure activated check valve is desired to eliminate drip with strainer to prevent fluid contaminant transfer to the tested surface. Nozzle material shall be corrosion resistant to wet assembly aids containing water/soap or emulsion type solutions. Copyright General
39、Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW16666 Copyright 2011 General Motors Company All Rights Reserved November 2011 Page 5 of 12 3.3 Test Vehicle
40、/Test Piece. Elastomer test surfaces are as molded or with a dry friction reduction coating. The production release intent coating is applied using the same production method as the coated part. Allowances for pilot or lab scale coating application are permitted if coating by full scale production i
41、s impractical. Test specimen surfaces are fully coated with no cracks, flow lines or other surface imperfections at 2X magnification using an optical device. The coating must be uniform and represent the intended production intent application thickness. One has the option of coating the entire slab
42、or individual test strips. 3.4 Test Time. Numbers are based upon cleaning, conditioning (4.1.1.4) and set up for three (3) runs on one specimen. Values are independent of specimen molding time (4.1.1.3). Calendar time: 1 day Test hours: 0.5 hours Coordination hours: 4 hours 3.5 Test Required Informa
43、tion. Report the static and kinetic coefficients of friction. See 5.3. 3.6 Personnel/Skills. Technician with lab experience (one (1) month or more), proficiency and training in this technique and instrumentation use. 4 Procedure 4.1 Preparation. 4.1.1 Elastomer Preparation. Test slabs shall be molde
44、d from the same batch of rubber and cured under the same conditions as the molded parts they represent. 4.1.1.1 Specimen Profile. Flat specimens from ASTM D3182 or ISO 23529 slabs for horizontal tests. The entire slab may be used but completed measurements shall be made 10 mm from any perimeter edge
45、. The top and bottom of a molded slab may be used in testing. 4.1.1.1.1 Elastomer Finish. Molded specimens are to be smooth, flat, and free of surface defects. Any film of suitable material placed above and below the sheet in the mold to prevent contamination from previous cures and sticking shall n
46、ot contribute any measureable effect on friction versus non-film use. All tested slabs are produced in a manner so as not to have significantly different surface directional friction properties based on slab orientation. 4.1.1.1.2 Other Finishes. If stipple or grain effects are part of the finished
47、article, the requester must identify and approve the replicated molded specimen finish before start of test. This condition must be reported in the test documentation (5.3). Since these finishes may produce different friction results with specimen orientation, evaluate and report an additional 90 de
48、gree rotational measurement. 4.1.1.2 Mount Rubber to Test Sled. Secure the molded specimen using clamps. Do not test cracked or improperly surface coated specimens. 4.1.1.3 Specimen Aging Before Testing (All Tests). The minimum time between vulcanization and testing shall be 16 hours. For ASTM D3182
49、 slab specimens, the maximum time between vulcanization and testing shall be 28 days and, for evaluations intended to be comparable, the tests shall, as far as possible, be carried out after the same time interval. 4.1.1.4 Conditioning of Test Specimens. Condition prepared test pieces for a minimum of 3 hours at 23 C 3 C. For tests at temperatures other than standard laboratory temperature, condition the test pieces at the temperature at which the
