Page 220 - Improving Machinery Reliability

Machinery Reliability Audits and Reviews 191

IT
UI
g 50,000
3
Z 40.000
v)
0)
$ 30.000
k- 0)
a
b 20,000
0
z
3 15,000
220 240 260 280 300 320 340 360 50 52 54 56 58
BRINELL ROCKWELL C
MATERIAL HARDNESS
Figure 3-76. Bending stress numbers.
In this expression, the previously defined parameters are joined by N,, the pinion
speed (rpm).
The following may be assumed:

S.I. < 14,000: slight probability of scoring
14,000 < S.1. < 18,000: moderate probability
S.I. > 18,000: high probability of scoring
Reviewing our example shows

and

23,700 '75 (8,088Y5 -
S.I., = - ___ -
[ 18.25 1 (8.%).25
Both offers are completely acceptable from the point of view of scoring.

Gear-Tooth Backlash Review

Many gear manufacturers consider the backlash values found in Table 3-22 appro-
priate for solid or forged-steel gears.
These backlash values have sometimes been viewed as relatively tight. However,
even these seemingly close backlash tolerances take into account a 50°F temperature
rise and gear growth due to centrifugal force at a pitch-line velocity of 25,000 fpm.