Normal abrasives were formed during primitive time by volcanic cast iron fusion. Even to date, the normal corundum and emeries are employed occasionally, although their structural composition was purely coincident and the abrasive sheets resulting from execution to be wished much. At the end of the century the artificially built abrasives were made in electric furnaces. With this fine silicon carbide of the crystals were produced by melting the sand and the coke of quartz. One discovered another process by which alumina was transformed into aluminous oxide and then out of electric corundum, also by using the electric method of fusion.



Special molten alumina is derived from very pure bauxite. Thus, we have a certain number of basic abrasives which must be attached to a material of support in order to make them technically useful. Institutional link as well as the agents inorganic of connection are employed. Among the connection inorganic the agents are clay, feldspar, kaolin and a sand of quartz which is molded, compressed and made cook with the furnace as well as the abrasive grain. Generally, the liaison officers determine the approved maximum speed of circumference for the abrasive tool the organic agents of connection which can be found for example in the fiber-constant resin-stuck discs stick the abrasive grain with phenol resin. Cut granulation the size of the abrasive granulation is mainly responsible for the quality of the result of sandpapering.

The unit of the mesh of measurement is employed to describe the size of granulation. This measuring unit is based on a screen which has a certain number of openings (mesh) each inch length. 8 openings per inch choose the abrasive grains with a diameter of roughly 2 millimeters. The number of mesh is indicated for all the abrasives to describe the size of granulation, with 8 being roughest and the 1200 finest category. The following exposures of table which cuts granulation that you can employ for which application of sandpapering:

- 8 of sandpapering crudes, 10, 16, 20, 24, 30 - medium sandpapering 30, 36, 40, 46, 50, 60 - 80 of sandpapering ends, 100, 120 - amends superb sandpapering 220, 240, 300, 400 - to roll up 400, the 1200 discs of grinding and rough cuts have a size of granulation to extend between 16 and 30.

Hardness the abrasive grains are extremely hard; if they were not, the grains would be not very suitable for sandpapering. While referring to abrasives, hardness means usually the hardness of the bond. An abrasive mol is composed of the extremely hard grains which can break easily of their connection. The hardness of connection of limit would be more suitable.

It is indicated by an order of the letters: - E, F, G very gently - H, I, J, K soft - L, M, NR, medium of O - P, Q, R, S hard - T, U, V, W very hard - X, Y, Z extremely hard.

Structure This limit refers to the distribution abrasives on the material of carrier. The more open the structure is, the more thermal dissipation and the cooler the process of sandpapering is better. Texture is indicated by an order of the numbers: 1-4 dense texture (much abrasive grains) 5-7 standard texture 8-10 open texture 11-14 very open texture 15-18 strongly porous texture All the abrasive tools should include these characteristics.

To mark abrasive tools is governed by DIN 69120. The discs of cutting of BOSCH and the discs of rough grinding colored labels with the following significance: - green = for the stone - blue = for steel an additional diagonal band indicates the approved maximum circumferential speed: the red = approved the maximum speed of circumference: 80 m/sec blue = approved the maximum speed of circumference: 45 m/sec the abrasives are available in many various forms and for a large variety applications, such as the discs of rough grinding or the discs of cut, the conical discs of sandpapering or apartment, the points of grinding, the wheels of grinding, the wheels of cup, the sheets of sandpapering, the emery paper, the fabric of sandpapering, the belts of sandpapering, the rings of grinding, the wheels of ventilator and much more. Abrasive pastes can be applied like agents of polishing and to be distributed with the grinder to contribute to the process of grinding.