The metallic shots

General points
The metallic shots are the most used for:
- their compatibility to the projection processes (with air or blast wheel),
- their shape diversity (spherical, angular, or cylindrical),
- their nature and structure diversity (ferrous, or non ferrous),
- their hardness diversity (obtained through heat treatments),
- their granulometry diversity (great range of choices),
- their use diversity (preparing, finishing, or shot peening).

Shapes
The metallic shots are under 3 different shapes:
- spherical, obtained through atomization with fusion in an electric furnace and quick quenching of a metal.
- angular, with irregular edges and shapes, obtained through the crushing of spherical grains.
- cylindrical, obtained through a regular cutting of a metallic wire.

The casting steel shots

Manufacturing
In the electric arc furnace, after a fusion of top grade scrap iron, the liquid metal is atomized by a water jet in order to obtain round grains which are then quenched.
The grains are removed through a selection of the bad shaped particles and are then gauged through screening and filed according to the granulometry. They are then subjected to a heat treatment and a tempering operation in order to adjust the hardness level.
The angular shot is obtained through the crushing of bad shaped grains, or round grains coming from the surplus of the less demanded granulometries.

Structure and calibres
They have a fine structure made of carbon and iron and are presented in:
- a spherical form (Shot) with dimensions ranging between 0.2 and 2 mm. (S-70 to S-780)
- an angular form (Grit) with dimensions ranging between 0.07 and 2 mm. (G-200 to G-10)
Adapted heat treatments allow adjusting the hardness of these shots and extending the applications to the most varied areas. (see chart uses)

Hardness and uses
The shots are classified into 4 hardness with variable range and symbol according to the manufacturers:
1 = about 40-50 HRc
2 = about 50-55 HRc
3 = about 55-60 HRc
4 = superior to 60 HRc
Their uses vary according to the granulomety and the hardness:
- the round shot, treated for a hardness ranging between 45-50 Rc, is almost used with a blast wheel machine for the cleaning of the ferrous metallic surfaces and for the shot-peening operations.
- the angular shot, treated for a hardness ranging between 50-55 Rc, is used in the same machines for applications which require a most important efficiency, such as stripping before paint coating.
- the angular steel shot with a hardness ranging between 55-60 Rc is used with blast wheel or compressed air machine for the surface preparation requiring at once cleanness and roughness.
- the angular steel shot with a hardness superior to 60 Rc is used with blast wheel or compressed air machine when the grains hardness is necessary for the surface preparation before some plating and for the cleaning which require at once cleanness and a high roughness.

Charts
Granulometric ranges of the casting steel shots
Spherical metallic shots recommended for some applications
Angular metallic shots recommended for some applications

Nota: Besides the granulometry, the shot hardness will have to be taken into account for a good choice.