Metallic Abrasives-Shot & Grit Abrasives
The abrasive blasting materials is important because they determine the surface profile produced. Metallic abrasives (shot & grit) are used primarily to blast clean steel and forged or cast iron where a surface profile is seldom critical on the finished product. Some examples of metallic abrasives include:
- Cast steel is a hard metallic abrasive used to remove scale and other hard surface deposits.
- Steel grit abrasives have irregular shapes and are effective in cutting away surface deposits or imperfections. Steel grit is expensive and is generally used only in recycling systems and when cheaper abrasives are unavailable. Because steel grit can be recycled, it reduces the overall waste stream.
- Steel shot is spherical; it can be produced accidentally as a byproduct or intention-ally for blast cleaning. Steel shot is good for heavy brittle deposits. Because of its spherical shape, it ricochets in enclosed areas and causes multiple impacts. Steel shot may stretch light materials and drive mill scale and other impurities into the surface.
- Cast iron is the hardest metallic abrasive and is used to remove scale and other hard surface deposits. Hardness should not be confused with toughness; hard abrasives sometimes have high breakdown rates because of their brittleness. This product should not be used in corrosive environments; it has a high initial cost, but can be recycled.
- Malleable iron is a relatively hard metallic abrasive used to remove scale and other hard deposits.
These metallic abrasives are often heat treated to different hardness’s to increase their life and the rate of cleaning. Hard abrasives, 62–65 HRC (HRC = Hardness, Rockwell C), are often used for etching, but they break down rapidly. Softer abrasives, 35–40 HRC, may be used for easier cleaning jobs. These materials may round up after use. The average hardness of metal abrasives is 45–50 HRC, which works well as an air blast abrasive.
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