DSM Engineering Plastics is a producer ofnylon plastic materials used for gears. In the past two years, they
have been running fatiguetests on actual molded gears in orderto provide design data. This experimentused
spur gears that are fully lubricated and temperature controlled. Testing for the materials has been done at
DSM Research, whilethegeartestsarebeing conducted attheUniversityofBerlin. Thepurposeofthetesting
is to see if there is a good correlation between fatigue data, generated on test bars, versus the actual fatigue
performance in a gear.
In order to do this, the theories of gear calculations to get root stresses also had to be examined. Advanced
FEA showed that there are corrections needed to account for high loading or high temperatures in plastic
gears. This corroborates other work within the industry.
With proper corrections to get accurate root stresses, there can be shown good correlation between tensile
bar fatigue and actual spur gear fatigue.
The chemistry of various nylons used in gears is explained. A high crystalline nylon has been found which is
an excellent material for gears in demanding applications and can withstand high torques and operating
temperatures. The material has a crystallinity of 70%, which results in very good wear properties and
excellent retention of mechanical properties (strength, stiffness, and fatigue) especially at elevated
temperatures.

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