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......