【国外标准】 Standard Test Method for Asbestos Strength Units (Withdrawn 2022)

5.1 This test method facilitates the comparison of different types and grades of chrysotile asbestos by the property most pertinent to its use in asbestos-cement, namely, the strength or reinforcing value it imparts to the product.5.2 While similar comparative results could be obtained on any given production equipment, this method allows the testing of small samples, avoids costly interruptions in production for numerous trial runs, and allows test values to be obtained by a single standard method so that results can be compared among different locations.5.3 Strength Unit (SU) value of a fiber blend used in asbestos-cement products may be estimated by taking the proportionate SU value of each component of the fiber blend.5.4 If the fiber blend is formulated with the aim to optimize another fiber property such as filterability, the SU calculation will assure that the blend will not fall below an acceptable strength level.5.5 This test method is restricted to grades of asbestos used in asbestos-cement products. Very long (Group 3) fibers are difficult to evaluate by this method because the test specimens produced may not be sufficiently homogeneous. Similarly, very short (Group 7) grades may not be retained satisfactorily in the mold during the pressing of test specimens or may not provide sufficient strength to meet the test requirements.NOTE 1: The term Group 3 or 7 refers to the standard designation for chrysotile asbestos grades established by the Quebec Asbestos Mining Association, See 2.2.5.6 Because of certain differences between this method and the many variations in plant production procedure commonly used in asbestos-cement manufacture, it is emphasized that the strength values obtained by this standardized procedure will not necessarily give exactly the same strength values as obtained at any one specific manufacturing plant.1.1 This test method gives a procedure for the evaluation of the strength-giving properties of asbestos fibers used to reinforce asbestos-cement products.1.2 The purpose of this test method is to determine the number of strength units that may be assigned to the sample tested.1.3 Asbestos fiber possesses the ability to impart strength to an asbestos-cement product. Every fiber grade may be regarded as possessing a certain quantity of strength-giving units. The quantity of fiber required in an asbestos-cement composition varies inversely with the number of strength units it possesses. For example, if an amount, designated by X, of a fiber possessing 100 strength units produces a product of a given strength, 2X would be required to produce a product of equivalent strength from fiber possessing only 50 strength units.1.4 The following definition is the basis for the strength unit test: An asbestos fiber that gives the standard strength at the standard density when used as 10 % of the furnish is defined as having 100 strength units. Therefore, by knowing the percent fiber required in the mix to give standard strength at the standard density, it is possible to calculate the strength units of a sample of asbestos.1.5 This procedure is intended primarily for chrysotile asbestos; it has not been verified whether or not it is applicable to other types.1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.1.7 Warning—Breathing of asbestos dust is hazardous. Asbestos and asbestos products present demonstrated health risks for users and for those with whom they come into contact. In addition to other precautions, when working with asbestos-cement products, minimize the dust that results. For information on the safe use of chrysoltile asbestos, refer to “Safe Use of Chrysotile Asbestos: A Manual on Preventive and Control Measures.”21.8 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. For specific precautionary statements see 6.7.2, 7.5, 9.2.2, and 1.7.1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.