Large-diameter driveshafts are used in hot and cold rolling machines, etc. and must possess a high degree of reliability because of the harsh environments in which they are used. Small/medium-diameter driveshafts for use in steel bar rolling machines, continuous casting machines, paper mill equipment, etc., on the other hand, normally do not have such severe spec requirements, and therefore customers tend to place greater emphasis on cost.

JTEKT has succeeded in lowering the cost of small/medium-diameter driveshafts by reducing the size of the universal joint area by 10 percent. Normally, downsizing of this area reduces the fatigue strength of the bolts holding the bearing and shortens the flaking life of the cross surface functioning as the bearing inner ring. However, to resolve the bearing bolt problem we improved fatigue strength by adopting a process of thread rolling after heat treatment, and we improved cross flaking life by applying a type of plastic working called burnishing on the cross surface. The additional costs incurred by adopting thread rolling and burnishing were more than offset by the downsizing of the universal joint, resulting in an overall cost reduction for the driveshaft.

Burnishing is a type of plastic working whereby high-hardness ceramic balls are rolled on a part’s surface to achieve a highly durable surface finish.