Page 215 - Improving Machinery Reliability

186 Improving Machinery Reliability

Example: You receive two proposals for a gear-speed increaser with an input
speed of 1792 rpm, an output speed of 8088 rpm, and a rated power output of 13,200
HP. Given the following data, which gear should you buy?

Pinion Data Vendor A Vendor B
Pinion diameter d 9.48 in 8.92 in
Face width F
(total) 18.00 in 18.25 in
Minimum Brinell
hardness 388 412

For shortcut design appraisal, use Cd = 2.0. Next, for Vendor A, calculate

Similarly, for B:

then
(2.0) (21,700) 1
(9.48) (18) (0.194) (538)2 8'77
N, = 3.8 x IO-
~
= 13.68 x 10" cycles = 32 years (Vendor A)

and
(2.0) (23,063) 1
(8.92) (18.25) (0.190) (562)' 8'77
N, = 3.8 x 10-
= 9.51 x lo2' cycles = 22 years (Vendor B)

This example calculation establishes that Vendor A's offer ranks ahead of Vendor
B's offer.

Alternative Gear Strength Comparison. An alternative method of comparing the
relative strength of several gears is available to the engineer. Based on work per-
formed by Lufkin Gear Company's James Partridge, we have often found this
approach quite helpful for rapid screening studies. It consists of five steps: