Abrasive Material
Blasting is carried out with abrasive materials such as chilled iron grit, steel or aluminium oxide grit. Sand or other substances containing free silica must not be used, as anyone exposed to dust from it could develop silicosis.76
In a factory, blasting operations should be carried out in a suitable enclosure or room to protect other personnel from injury and nearby machinery from damage. The ‘blast room’ should be provided with an efficient system of exhaust ventilation, preferably of the down-draught type. During the blasting operation super abrasive material rebounds from the surface of the article with a high velocity. Consequently the operator must be given special protective clothing such as gloves, apron and leggings. A helmet supplied with fresh air at a positive pressure is also necessary to protect the blaster from both flying particles and harmful dust.82
Very hard surfaces can be studied by the abrasion of the surface with a sheet of abrasive material, such as silicon carbide or carborundum paper. At this point a number of different methods may be used to analyze the abraded material. In essence, any solid sampling technique that is capable of handling fine powders—KBr pellet, diffuse reflectance, ATR, photoacoustic, etc.—may be used to study the material. An interesting variant is to use diffuse reflectance to study the abrasive (see the reference to the silicon carbide method in Section 4) for the residual material.
Materials used as abrasives include both natural minerals and synthetic products. Abrasive materials can be considered as cutting tools with geometrically unspecified cutting edges that are characterized by high hardness, sharp edges, and good cutting ability. The sharpness of abrasive grains may be described in terms of edge radius and apex angle. As grain size increases, the percentage of sharp apex angles decreases, indicating a deterioration of grain cutting ability. In addition, cutting ability depends on specific features such as grain structure and cleavage, which are connected with the ability of cutting grains to regenerate new sharp cutting edges and points.