A single diameter shaft having no steps or shoulders drives

A single diameter shaft, having no steps or shoulders, drives a machine with a fairly heavy load. The shaft rotates at 1200 rpm and extends from the bearing several times its diameter. A vee-pulley is mounted on the shaft. Belts drive the pulley from a motor, causing a considerable side stress. The bearing is kept in place with a snap-ring that is in a narrow groove around the shaft at the edge of the bearing. The shaft has to be replaced several times a year at considerable cost in lost man-hours and material. Every time the shaft is severed, the mill-wright notices that it is at the location of the snap-ring groove. The break has a smooth surface with tiny grooves and a round section at the center that has a rough crystalline surface as in Figure 23.23. Can you identify the problem and name the type of failure? Name as many changes that could be made to correct the problem.

Solution

The problem seems to be the belts which drive the pulley from a motor, causing a considerable side stress. The sbap ring groove at the bearing seems to be unable to handle the fatigure stress. It is a sudden , brittle like fatigue failure .

Changes that can be made

1) Increase the diameter of the shaft

2) Use shaft material of higher strength

3) Instead of the snap ring use a bearing of exact shaft diameter