Section 17 Strength and Durability of Gears - SDP/SI

ELEMENTS OF METRIC GEAR TECHNOLOGY
b
–––
d 1
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
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Table 17-11 Tooth Flank Load Distribution Factor for Surface Strength, K H β
Gear
Equidistant
from Bearings
1.0
1.0
1.05
1.1
1.2
1.3
1.4
1.5
1.8
2.1
Method of Gear Shaft Support
Bearings on Both Ends
Gear Close to
One End
(Rugged Shaft)
1.0
1.1
1.2
1.3
1.45
1.6
1.8
2.05
–––
–––
Gear Close
to One End
(Weak Shaft)
1.1
1.3
1.5
1.7
1.85
2.0
2.1
2.2
–––
–––
NOTES: 1. The b means effective face width of spur & helical gears. For double
helical gears, b is face width including central groove.
2. Tooth contact must be good under no load.
3. The values in this table are not applicable to gears with two or more mesh
points, such as an idler.
(b) When tooth contact under load is good: In this case, the shafts are rugged and
the bearings are in good close proximity to the gears, resulting in good contact over the
full width and working depth of the tooth flanks. Then the factor is in a narrow range, as
specified below:
K H β = 1.0 … 1.2 (17-22)
17.2.13 Dynamic Load Factor, K V
Dynamic load factor is obtainable from Table 17-3 according to the gear's precision
grade and pitch line linear speed.
17.2.14 Overload Factor, K o
The overload factor is obtained from either Equation (17-11) or from Table 17-4.
17.2.15 Safety Factor For Pitting, S H
The causes of pitting involves many environmental factors and usually is difficult to
precisely define. Therefore, it is advised that a factor of at least 1.15 be used.
Bearing
on One End
1.2
1.45
1.65
1.85
2.0
2.15
–––
–––
–––
–––
I
R
T
1
2
3
4
5
6
7
8
9
10
11
12
17.2.16 Allowable Hertz Stress, σ H lim
The values of allowable Hertz stress for various gear materials are listed in Tables
17-12 through 17-16. Values for hardness not listed can be estimated by interpolation.
Surface hardness is defined as hardness in the pitch circle region.
13
14
15
T-165
A