1. Blasting (Abrasive blast cleaning): This method is widely used for removing all classes of scale and rust from forgings, Castings, weld elements, and heat treated parts. Depending on the finish requirements, Blasting alone or blasting with pickling is used. In this process the parts are generally cleaned by the use of abrasive particles such as sand, steel grit or shot impelled against the surface to be cleaned. Some cleaning is performed by means of high-velocity air blast, with the blast directed by hand. In many cases, an airless blast machine that cleans by impact is also used. The abrasive is fed from an overhead storage hopper to the center of a radially rotating wheel, whereupon the metallic shot or grit is thrown in a controlled stream upon the work to be cleaned. All traces of sand, scale, oxides and other material are removed, providing an excellent surface for bonding final finishes.
2. Tumbling: It is least expensive process for removing rust and scale from metal parts. This operation is accomplished by placing work pieces in a drum or barrel, together with stars, jacks, slugs, or abrasive materials. The abrasive materials can be sand, granite chips, and slag or aluminum oxide pallets. In this operation, the barrel is rotated and the movement of the work pieces and the accompanying slugs or abrasive materials against each other produces by friction a fine cutting action which removes fins, flashes, and scales from the products.