The first vitrified bonded wheels were considered as inappropriate for large temperature variations because the bond was not elastic enough to withstand thermal expansion differences within the tool [KING86, p. 87]. Certain bond elasticity is important to equalize the volumetric expansion of the abrasive grits induced by the grinding process heat [STAD62, p. 51]. Vitrified bonds are thermally highly stable. However, Stade reports about molten beads of vitrified bond in the grinding debris [STAD62, p. 51].
Grit retention in vitrified bonds is partially mechanical because the bond encloses the grits. In addition, the bond often reacts chemically with the grit surface. For example, the vitrified bond dissolves the grit surface in corundum wheels [JACK11, p. 62]. For CBN, the early vitrified bonds were just transferred from conventional applications and happened to be so reactive that they dissolved the CBN into the bond and converted it into boric oxide [MARI04, p. 419]. However, the bond composition was changed over the years so that well dressable CBN bond systems became state of the art [MARI04, p. 419]. CBN grits can be coated to avoid chemical reactions between CBN grits and alkali or water present in most glass frits at temperatures above 800 °C [MALK08, p. 26].
Diamond, however, does not show significant chemical bonding with the components of a vitreous bond [MARI04, p. 418]. Retention of diamond grits is mostly mechanical. However, diamond is reactive with oxygen at temperatures above 650 °C. Therefore, diamond wheels must be fired at low temperatures or in inert or reducing atmosphere [MARI04, p. 418]. However, titanium based coatings on diamond or CBN grits have a protective function during the sintering process.
Reaction layers between the vitrified bond and corundum white or sol-gel corundum consists from bond and grit material and can be adjusted by the sintering process. The characteristics of the layer affects grit retention. Sol-gel corundum grits expose thicker reaction layers than white corundum due to microcrystalline structure and higher number of grit boundaries. [KLOC06a]
The first vitrified bonded CBN grinding wheels needed separate profiling and sharpening processes [STUC88]. However, this problem has been overcome by new bonding compositions. Today, vitrified bonded grinding wheels are easy to profile and sharpen in one step. The dressing mechanisms are mainly grit breakage, grit splintering, bonding breakage, grit break-out off the bonding, and grit deformation [MARI04, WIMM95, MINK88, MESS83, KLOC08b]. Linke found that the dressing forces likely induce cracks or support crack propagation in the tool bond, so that the abrasive layer is weakend by the dressing process [LINK07]. However, hot pressed vitrified bonded wheels are difficult to dress und need a separate sharpening process similar to resin and metal bonded wheels [MARI04, p. 418].