14.3.1 The Type of Diamond Abrasive
Diamonds, used for grinding ceramics, are mainly synthetic diamonds. The synthesis process permits control of diamond characteristics generating either blocky grit shapes with very high impact strength, or friable grits with low-impact strength. Diamonds are also classified by grit size and grit size distribution. The grit system can be used to control the desired working result within a wide range [Carius 2002].
The abrasive grains employed for ELID grinding usually consist of synthetic diamond. Diamond is the most efficient superabrasive material used for grinding all sorts of hard, nonmetallic materials. Depending on the materials to be ground, different strength and wear characteristics are required for the diamond used. For best economic performance, the abrasive grain formulation must be matched with a correct bond formulation.
The main property of diamond is its hardness (10 on Mohs hardness scale). Not only do different diamonds have appreciably different structures and mechanical properties, but also different parts of the same stone may differ appreciably.
The characteristics of diamond are
• Material pure carbon (C)
• Atomic weight 12
• Melting point 3,700 K
Diamond has the following properties:
• Behaves more like a nonmetal
• Is an electrical insulator but conducts heat very well
• Is truly stable only at high pressures
• Crystals form in the area of pressure and temperature where diamond is stable.
For ELID grinding, the grinding wheel is normally a metal-bonded diamond wheel. This structure presents a very different challenge for dressing compared with a vitrified diamond wheel or a resin — bond diamond wheel or even an electroplated diamond wheel.