In order to produce rubber bonds, natural and synthetic rubbers are mixed. To this mixture, sulphur is added as a vulcanisation agent. The sheet is produced by means of a multistage rolling of the abrasive grits. The rolling process is repeated several times, in the course of which the very heavy sheets are tuned by the operator by hand.
Subsequently, the internal and external diameters are punched out of the sheet. Several of these punched-out grinding wheel components are then put on placed of each other until the desired grinding wheel width is reached. Then these blanks are pressed and vulcanised in a furnace at 150°C [HADE66, N. N.9].
3.4.2 The Manufacture of Superabrasive Grinding Wheels
Superabrasive grits, like conventional grits, are fixed to the grinding wheel by vitrified, metallic or synthetic resin bonds. Bond production is described in the following.
In binding superabrasives using synthetic resin bonds, phenol resins are used as a rule, whereby the bond characteristics can be adjusted by means of fillers. These serve to change wear resistance and heat conductivity or to act as dry lubricants. Besides phenol resins, polyamides and polyimides are also utilised. These are stronger and have more thermal consistency and elasticity. In synthetic resin bonds, the abrasive is generally furnished with a nickel or copper coating in order to improve temperature conductivity and adhesion to the bond matrix. Wear resistance against abrasion is much lower than with metal bonds.
The manufacture of abrasive coatings bonded with ceramics or synthetic resins with the abrasives cBN and diamond is essentially analogous to that of corundum and silicon carbide. In the case of grinding wheels bonded in synthetic resin, the hot press method is the most often used.
The grit is placed in a premixture consisting of synthetic resin powder (phenol resin) and additives (silicon carbide, boron carbide, aluminium oxide etc.). The components are distributed evenly by mixing [COLL88]. Then the premixture is poured into a mould and the coating is hot-pressed onto the body. In special cases, surface rings are also made that are either stuck to the body or rear pressing with body mixtures.
While synthetic resin and metallic bonds are manufactured without pores due to their bond formulae and productions conditions in general, normally burned vitrified bonds have a definite amount of pores in the bond. Because of the mechanical and thermal properties of superabrasives, these bonds are however fundamentally different from those of vitrified bonds with conventional abrasives. Moreover, the firing temperatures and burning behaviour are different. Vitrified bonds can also be produced without pores by hot-pressing. Such grinding tools can also be manufactured in a segmented fashion depending on the diameter of the grinding wheel.