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ASTM D3157-05(R2020) pdf free download

ASTM D3157-05(R2020) pdf free download.Standard Test Method for Rubber from Natural Sources—Color
1. Scope
1.1 This test method covers a method of classifying the color of raw rubber according to a standard color scale. 1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 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 appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.4 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Summary of Test Method
3.1 The raw rubber is prepared in the form of a molded disk of specified thickness, and the color of this disk is compared and matched as closely as possible with that of colored glass disks referred to as standard glasses. The standard glasses used are calibrated according to the intensity of their amber color. Occasionally the color of the rubber cannot be matched due to the presence of strong yellow, green, or gray tints. Color matching is carried out under diffuse daylight illumination against a matt white background, preferably by use of a comparator that suitably locates and shrouds the test specimen and standard glass. The standard glasses used are calibrated according to the intensity oftheir color to provide a color index scale in which higher index values correspond to deeper color.
4. Significance and Use
4.1 Color of material rubber is of importance in compounds where product color is determined by the color of the raw rubber.
5. Apparatus
5.1 Laboratory Mill, as described in Practice D3182. 5.2 Hydraulic Press, capable of giving a molding pressure of not less than 3.5 MPa (500 psi) over the platen surface and platen temperatures of 150 6 3°C (302 6 5°F). 5.3 Mold, stainless steel or aluminum, 1.60 6 0.05 mm (0.063 6 0.002 in.) thick having holes approximately 14 mm (0.55 in.) in diameter in accordance with Fig. 1. 5.4 Mold Plates, two, of similar material, 1.60 6 0.05 mm (0.063 6 0.002 in.) in thickness. 5.5 Comparator or Standard Glass Disks 3 —Standard col- ored glasses with color index scale: 1 to 5 in half-integral steps and 5 to 16 in integral steps. 5.6 Test Specimen Cutting Die, as described in Test Method D926. 5.7 Thickness Gage, capable ofmeasuring the test specimen to the nearest 0.02 mm (0.001 in.) in accordance with Practice D3767, Procedure A1.
7. Test Specimen and Sample
7.1 Homogenize the piece to be tested in accordance with Test Methods D1485, omitting the weighing procedure unless that is required for other tests. 7.2 Take a test portion of about 30 g from the homogenized piece and pass not more than three times (doubling the sheet between passes) between the mill rolls at room temperature with the nip adjusted so that the final sheet thickness is 1.6 to 1.8 mm (0.06 to 0.07 in.). Immediately double the sheet, which should be uniform in texture and free of holes, and press the two halves lightly together by hand, avoiding the formation of air bubbles. From the sheet, which is 3.2 to 3.6 mm (0.10 to 0.15 in.) thick, punch two pellets (each weighing about 0.3 g) and laminate together by lightly pressing with the fingers. Press the rubber specimen in the mold between sheets of polyester (or cellophane) using mold plates at not less than 3.5 MPa (500 psi) pressure on the mold surface for 5 min at 150°C (302°F). The molded test piece should be 1.4 to 1.8 mm (0.05 to 0.07 in.) thick. The sample should be smooth, free of air bubbles, mold lubricant, rust, grease, soot, or other contaminants and the transparent polyester sheet left in place.

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