Failure of a Polyoxymethylene Gear Wheel
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.