Grit blasting is a process by which abrasive particles are made to impinge on a component to clean or modify its surface properties.
Particles range from walnut shells (relatively soft), through various sands, to silicon carbide, alumina or emery particles, depending on the application.
Methods of propelling the particles also vary and include entrainment in compressed air, liquid (usually water) or vapour (usually steam) streams, and mechanical projection methods (e.g. rotating paddles).
Grit blasting is used to remove sand and scale in the fettling of castings, and for dressing of stampings and billets, etc. It is often used to prepare surfaces before welding (removal of scale, rust or paint), and afterwards to improve the adhesion of coatings (e.g. paint, or galvanising).
The impact of the grit on the metal surface puts the surface layer into compression, and this effect can be beneficial, for example, in reducing stress corrosion cracking in aluminium alloys.
Grinding and Abrasive Processes: Blasting Processes, section D4 pp.D4/22-D4/25 in Kempe's Engineers Year Book, Volume 1. 97th Edition. Publ: Tonbridge, Kent, TN9 1RQ, UK; Benn Business Information Services Ltd; 1992.
or the equivalent section in other editions.