What is vacuum impregnation? I have been told that it can be used when plating porous substrates. G.G.
Vacuum impregnation can be used when working with materials that have a high degree of porosity. The two major categories of materials that suffer with this problem are castings made from aluminum, iron and zinc; and items made from powdered metal.
Any electroplater who has worked with zinc diecasts can attest to the problems with porosity. Cleaning and plating solutions are trapped in the pores and leach out after processing, and the results are a ruined part. Vacuum impregnation allows you to seal the part so that these liquids cannot be trapped. Plastic sealants that are heat-curable are used. As the name implies, the resin is “drawn” into the pores under a vacuum. After a set period of time the parts are removed from the vacuum chamber, washed and cured. After this treatment, the parts can be electroplated.
You can find information on the various types of vacuum impregnation and its history from the Society of Vacuum Coaters, www.svc.org. Vendors of equipment and supplies can be found in the 2002 PRODUCTS FINISHING DIRECTORY AND TECHNOLOGY GUIDE, Vacuum Impregnation Equipment, materials or on the Suppliers page at www.pfonline.com.