A nylon oil-lubricated driving gear showed pitting upon visual inspection. The pitting produced numerous surface microcracks. Further investigation (visual inspection and 37x images) supported the conclusion that failure occurred in association with large-scale fragmentation (frictional wear). No recommendations were made.

A polyoxymethylene gear wheel that had been in operation in a boiler room failed. Investigation (visual inspection and 305x images) supported the conclusion that failure was due to postcrystallization causing considerable shrinkage. Breakdown along the crystalline superstructure started mainly at the mechanically stressed tooth flanks. In addition, oil vapors, humidity, and other degradative agents could also have contributed to the observed failure. No recommendations were made.