Section 17 Strength and Durability of Gears - SDP/SI

ELEMENTS OF METRIC GEAR TECHNOLOGY
I
Coefficient of Friction
0.150
0.120
0.100
0.090
0.080
0.070
0.060
0.050
0.040
0.030
0.020
0.015
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R
T
1
2
3
4
0.012
0 0.001 0.01 0.05 0.1 0.2 0.4 0.6 1 1.5 2 3 4 5 6 7 8 9 10 12 14 16 18 20 22 24 26 30
Sliding Speed
Fig. 17-12 Friction Coefficient, µ
Table 17-27 Combinations of Materials and Their Coefficients of Friction, µ
Combination of Materials
Cast Iron and Phosphor Bronze
Cast Iron and Cast Iron
Quenched Steel and Aluminum Alloy
Steel and Steel
17.5.4 Surface Strength of Worm Gearing Mesh
µ
µ in Figure 17-12 times 1.15
µ in Figure 17-12 times 1.33
µ in Figure 17-12 times 1.33
µ in Figure 17-12 times 2.00
(1) Calculation of Basic Load
Provided dimensions and materials of the worm pair are known, the allowable load is
as follows:
F t lim = Allowable tangential force (kgf)
Z L Z M Z
0.8
= 3.82 K R
v K n S c lim Zd 2 m x –––––– (17-51)
K C
T 2 lim = Allowable worm gear torque (kgf • m)
Z L Z M Z
1.8
= 0.00191 K R
v K n S c lim Zd 2 m x ––––– (17-52)
(2) Calculation of Equivalent Load
The basic load Equations (17-51) and (17-52) are applicable under the conditions of
no impact and the pair can operate for 26000 hours minimum. The condition of "no impact"
is defined as the starting torque which must be less than 200% of the rated torque; and the
frequency of starting should be less than twice per hour.
K C
5
6
7
8
9
10
11
12
13
14
15
T-187
A