6.6.1 Introduction
A number of considerations must be taken into account when selecting vitrified bond for diamond that places different demands relative to conventional wheels. These are primarily the effects of:
Hard work materials
Low chemical bonding
High grinding forces
Reactivity with air at high temperatures
These considerations are discussed as follows.
6.6.2 Hard Work Materials
Materials ground with diamond tend to be hard, nonmetallic, brittle materials. Therefore, there are limited issues with wheels loading up with grinding debris and wheel porosity can be relatively low. On the other hand, hard workpiece debris is likely to cause much greater bond erosion than other work materials. Therefore, either the bond erosion resistance must be higher or, more practically, a lot more bond must be used.
6.6.3 Low Chemical Bonding
Diamond does not show significant chemical bonding with components in a vitrified bond. The bond must, therefore, rely primarily on mechanical bonding sometimes enhanced with various diamond grain coatings either to improve wetting or mechanical anchorage.
6.6.4 High Grinding Forces
Grinding forces with diamond can be very high and efforts are made to limit the forces by reducing the number of cutting points by significantly lowering the volume of diamond from 50%. This introduces the term Concentration, which is a measure of the volume of superabrasive per unit volume of wheel. Two hundred concentration is equivalent to 8.8 ct/cm3 by weight or 50% by volume. Most diamond wheels are typically 12 to 100 concentration.