ELIOT K. BUCKINGHAM
Buckingham Associates, Inc.
Gear Consultants
Springfield, Vt.

Surface wear and pitting effects are almost identical on rolls and gears, so you can get all the materials information you need from simple roll tests.

Accelerated life tests won't tell you everything about gear behavior, but they'll get the design program moving with reasonable confidence. By combining materials data from experiments on rolls with design data from prototype gear trials, you can predict wear life with confidence.

IDEAL GEAR-LIFE PREDICTIONS would be based on complete field tests that precisely duplicate expected drive use (and misuse). But for many drives, complete real-time tests are impractical. A machine-tool drive, for example, would be obsolete before testing was complete. But a combination of material tests and accelerated life tests with the material tests guiding the life tests gives relatively quick, inexpensive predictions of drive life. Furthermore, the combination gives you data that can be used to predict lives of brand-new designs.

Accelerated life tests cannot replace long-term testing. Full life tests should be performed where possible, because materials may deteriorate with time, with continued exposure to heat, and from other factors that do not show up in the first few hours of operation. But accelerated tests can give good estimates of the load-carrying capacity of specific drive elements, designs, or materials, without the time and expense associated with long-term testing.

An example: Engineers designing a high-capacity three-stage planetary drive faced a critical question on load sharing. Would the maximum load on...