Standard Practices for Sampling Metal Powders
4.1 Specifications and test methods for metal powders and metal powder products require the sampling, testing, and performance evaluation of small samples taken from large quantities of powder. The sampling procedure is equally as important as the testing and evaluation; the sampling methods used must include every precaution to ensure that the samples obtained will show the true nature and condition of the large powder quantity that they represent.
4.2 The primary objective of any sampling procedure is to obtain a small quantity of material that is truly representative of the larger amount from which it is taken, a condition that is readily comprehended but difficult to define, quantify, and prove. Certain criteria are desirable to meet this condition:3
4.2.1 Every sampling increment should have a non-zero probability of being selected.
4.2.2 All increments should have an equal probability of being selected.
4.2.3 The sampling procedure should not alter the material (for example, by changing the particle size or chemical composition).
4.3 Sampling a moving powder helps to satisfy these criteria; therefore, Practice 1A should be used whenever possible to obtain the composite sample. Similarly, Practice 2 should be used to obtain the test portions; use of a spinning riffler is preferred when possible and practicable.
4.4 Although not always meeting all the criteria of 4.2.1 – 4.2.3, the other sampling practices described in this standard are based on time-proven experience in the PM industry in sampling granular metal powders. These practices have been shown to produce samples that give reliable and representative evaluation data.
4.5 Since many tests are performed using very small amounts of powder meant to represent much larger quantities, it is most important that the test portions be obtained in a standardized manner. The practices described here take into account the possibility of segregation of the metal powder during and after filling of containers.
4.6 Sample quantities of metal powder are used for chemical analysis and to determine the physical characteristics of the powder. These data are used for production control and quality inspection of finished lots.
4.7 Green compacts produced from powder samples are used to evaluate the compactability properties of metal powders, information that is important to the use of these powders in the manufacture of PM bearings and structural parts.
4.8 Test specimens produced from metal powder samples are compacted and sintered and used to measure physical and mechanical properties of solid PM materials. The data obtained are included in PM material specifications to assist with material selection for PM applications.
4.9 Solid PM articles—structural parts, bearings, etc.—are produced from metal powder samples to evaluate powder performance in the manufacturing and end use of such articles.
1.1 These practices cover sampling methods used to collect a small quantity of metal powder that is as representative of the entire starting material as possible, and detail the procedures that are recommended for reducing this quantity into smaller test portions on which chemical, physical, and mechanical property data may be determined.
1.2 Several sampling practices are described, depending on their applicability to the conditions of storage and transport of the sampled powders:
1.2.1 Practice 1A (Described in Section 6)—Applicable to sampling moving powders, as when being transferred from one container to another or to a process stream; or when falling from a conveyor; or in a moving process stream. This is the preferred practice for obtaining the several increments that are combined to form the gross sample.
1.2.2 Practice 1B (Described in Section 7)—Applicable to sampling powders that have already been packaged for transport, as in a bag or drum. A hollow tubular slot sampler is the recommended way to sample these packaged powders to obtain the increments (7.1.1). Alternatively, when other methods are not possible or available, a procedure specified here (7.1.2) may be used to randomly scoop samples from the powder, using a scoop of specified material and configuration.
1.2.3 Practice 2 (Described in Section 8)—Applicable to obtaining test portions from the composite sample. For larger quantities of powder, a chute splitter is generally used, while a spinning riffler is used for smaller quantities.
1.3 These practices apply to particulate materials or mixtures of particulates with particle sizes generally less than one millimetre and include mixtures containing lubricant, with or without other non-metallic additives, that are ready for compacting.
1.4 These practices do not cover the sampling of flake powders or pastes. For procedures on the sampling and testing of flake metal powders and pastes, refer to Test Methods D480.
1.5 Units—The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.6 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 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.
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