Steel abrasive is a term generally applied to two types of steel abrasive mediums: steel shot and steel grit. These mediums are presented in the form of spherical or irregularly-shaped grains or particles, which are projected at high velocity against the surface of a workpiece to remove rust, scale or paint, to impart a texture or even to work-harden the surface. The steel abrasive particles may be projected by means of a high-pressure jet of compressed air or by the centrifugal action of a spinning wheel or impeller. Steel abrasives of both types are available in a selection of grades which are defined by grain size, hardness and impurity levels.
Abrasive blasting is a technique used to achieve a wide range of surface effects on materials as diverse as stainless steel, glass and denim. Decorative finishes such as patterned frosting, simulated wear and engraving may be achieved with bead and sand blasting on materials such as glass, plastics, and fabrics. Steel abrasive techniques employing either steel shot or steel grit are particularly useful for heavier applications where they are used to remove surface imperfections, rust, grime and scale from metal items in preparation for painting, polishing or powder coating. Metal parts may also be work-hardened by exposure to a steel abrasive action known as shot peening. The same techniques may also be employed in other areas such as road surface reconditioning and masonry or concrete finishes.
There are two basic types of steel abrasive both, featuring a selection of different grades and sizes. The first of these is steel shot, which consists of spherical steel particles or grains. The second type is steel grit, which consists of angular or irregularly-shaped steel grains. Both types have specific applications to which they are particularly well-suited, but may also be applied to a range of common applications. The application methods for both shot and grit are also similar.
In both cases, the grains are projected at the work surface at high velocity in one of two ways. The first is pressure blasting, which utilizes a powerful jet of compressed air to transport the steel abrasive. The second is a centrifugal action process which sees the abrasives spun off rapidly-revolving discs or impellers. Both of these processes are often carried out in specially-designed booths which allow the shot or grit to be collected for further use, makes dust collection easy and contains much of the noise generated. Abrasive blasting operators should also wear protective clothing and respirators to ensure safety at all times.
Varieties of grade for both types of steel abrasive take into account levels of impurities, such as oxides, in the steel. Common sizes for both types include grains of between 0.007 and 0.1 inch (0.2 and 2.5 mm). Steel grit tends to be harder than shot, with average values for both in the range of 40 to 65 on the Rockwell scale.