New coatings based on silicon dioxide or silane are modified to have hydrophilic or hydrophobic properties [KUNZ91, SETH11]. The coatings repel infiltration of
cooling lubricant between grit and bond and therefore protect the resin bond [KLOC05a, p. 25, MARI04, p. 377]. Corundum grits can be coated with silane to optimize their performance in some resin bonds. Coated abrasive tools for example can fail if water separates the backing material from the bond [SETH11].
Another advantage of coatings is a more controlled breakdown behavior of the abrasive grits [HERB81]. Metal coatings envelope friable grit particles and retain their integrity even if parts are removed by impacts in the abrasive process [DYER79].
The characteristics of the abrasive grits are important variables controlling the process. Evaluating the characteristics is a complex problem due to the non-uniform grit geometry [BREC73]. The grit properties are influenced by the chemical composition, crystal structure, grit size, and much more. Unfortunately, many properties for ideal process performance are contradictory, such as toughness and hardness. Furthermore, tool manufacturing is affected substantially by the grit properties. Grit properties have always to be balanced between optimal properties for tool use and for tool manufacturing. The following discussion of grit characteristics aims to clarify the difficulties in the choice of abrasives.