Abstract: Sintered reaction-bonded silicon nitride components, e.g., automotive components, are made by forming a powder mixture comprising silicon and oxide or oxide precursor additives. These additives comprise alumina and a calcium compound. The powder is formed into a preform, the silicon is reacted with nitrogen in a nitriding process to form silicon nitride, and the so-formed silicon nitride is sintered.

Abstract: A grinding machine includes a rotating grinding wheel and workpiece moving apparatus operable to move a workpiece towards and away from the wheel. The apparatus is arranged to move a workpiece support arcuately about an axis to move a workpiece towards or away from the wheel. A motor turns the workpiece to present different parts of the workpiece to the wheel, and an orientation detector signals the orientation of the workpiece so that the operations of the workpiece moving apparatus, and the motor can be coordinated to cause a desired profile to be ground on the workpiece. The machine also comprises correcting apparatus operable in response to the operation of the workpiece moving apparatus to cause the output of the orientation detector to be altered to compensate for angular alterations in the point of contact of the workpiece with the grinding wheel caused by the arcuate movement of the workpiece support.