Flank Breakage on Gears for Energy Systems

摘要

Gear flank breakage can be observed on edge zone-hardened gears. It occurs, for example, on bevel gears for water turbines, on spur gears for wind energy converters and on single- and double-helical gears for other industrial applications. The nature of flank breakage is described in this paper. An ultrasonic inspection technique has been shown to be suitable for carrying out an inspection within the volume of case-hardened teeth. The nature of various ultrasonic indications could be identified by means of metallographic and fractographic investigations. Various phenomena such as white etching areas, nonmetallic inclusions and large cracks are involved. Recurring inspections have shown that indications associated with increases in reflectivity and in the lengthwise extent, or in individual indications growing together, have appeared. This confirms a cyclic crack growth under vacuum. Over time, it can be noticed that the cylindrical form of gears has lost as much as several tenths of a millimeter. Measurements of retained austenite have shown that the content decreases in areas with visible high temperature and loading. Within the framework of an earlier research project-Flank Breakage with Spur Gears - a calculation model was developed that shows good correlation with the investigated gears that have suffered flank breakage.