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Today's specifications for magnetic materials are based on the testing of material as supplied by the materials producer. These test methods are so designed that the specification qualifies the material only as purchased. However, additional operations, such as machining, welding, binding, etc., alter the magnetic properties from those of the raw material. The same problem arises with powder metallurgy (P/M) parts because, although their properties may be equivalent to a well-sintered part fabricated from the raw material, the parts are too small to evaluate using the test methods used to evaluate the raw material. Magnetic properties of sintered parts are predominantly a result of the sintering practice employed. Quality of these parts can vary appreciably as a result of the sintering practice employed in manufacture. Although the powders or the starting material may satisfy specification, there is no guarantee that the end user may receive a quality product after processing is complete. For P/M technology, rings can be fabricated from specified powders under conditions similar to parts being processed, and can be sintered in conjunction with the parts. The magnetic properties of the rings will be equivalent to the magnetic properties of the parts. A quality control procedure is proposed that will guarantee performance of P/M parts in accordance with currently existing P/M material specifications.
quality control, P/M magnetic parts, sintering furnaces, sintering atmospheres, phosphorus irons, ferritic stainless steels
President, Magna-Tech P/M Parts Labs, Cinnaminson, NJ