Resin Impregnation
Resin impregnation is a secondary operation in which plastic resins are applied to compact metal powder parts in order to act as a seal and reduce porosity. Sintering, the final step in powder metallurgy, results in porous products as the raw materials are fused rather than melted together. In many applications the pores resulting from sintering are unacceptable as they can lead to leaks and the unwanted transmission of materials. Resin impregnation is needed in some processes to seal parts and reduce porosity in order to increase product longevity and improve functionality. Automotive companies, for example, use resin sealing services to protect power steering pumps against exposure to many engine gases and liquids. In some applications, resin impregnation is also used as a primer to prevent bleed-out and blistering of final finishes. This use is common in electroplating industries. In addition to electroplating and automotive manufacturers, military, electronic, aerospace, oil and gas industries make frequent use of resin impregnation. Air regulators, gas meters, pumps, gear housing, valves and compressors commonly utilize sintered metal parts that require resin sealants. While oil and other viscous materials can be used for the same purpose, resin provides the best seal and most often the best resistance to water and corrosives. Natural resin is a compound secreted by plants, but synthetic resins are gaining popularity as they offer a more stable, predictable and uniform seal.
There are several different techniques used for resin impregnation and the selection of which technique to use depends largely on the intended purpose of the seal. Dry vacuum pressure services, for example, use a pressure chamber to coat the surface pores. Vacuum pressure impregnation also uses a pressure chamber, but forces resins into pores for deeper penetration. Internal impregnation forces liquids through leak paths in a similar manner. Rather than using pressurized chambers, wet vacuum services submerge sintered metal parts in a liquid bath and trickle impregnation uses surface tension to allow resins to be absorbed by the internal porosity of a material. In general, wet impregnation provides higher outputs than dry variations. Advantages to resin impregnation, wet or dry, include improved resistance to chemicals and high temperatures, decreased part vibration and a smoother finish on the surface of the part. Resin impregnated parts made from compressed iron, bronze, steel, aluminum, zinc, magnesium, copper and many other metals exhibit these advantages while still retaining dimensional machine tolerances and their original color. In addition to these powdered metal parts, resin impregnation offers vast improvements to machined components made of plastics and ceramics.
