T-192
Table 17-33 Time Factor, Kh
* NOTE:
For a machine that operates 10 hours a day, 260 days a year; this number
corresponds to ten years of operating life.
17.5.5.K Allowable Stress Factor, Sc lim
Table 17-34 presents the allowable stress factors for various material combinations.
Note that the table also specifies governing limits of sliding speed, which must be adhered
to if scoring is to be avoided.
Table 17-34 Allowable Stress Factor for Surface Strength, Sc lim
Expected
Life
Uniform Load
Medium Impact
Strong Impact
Impact from Load
Kh
Impact from
Prime Mover
1500
Hours
5000
Hours
26000
Hours*
60000
Hours
1500
Hours
5000
Hours
26000
Hours*
60000
Hours
1500
Hours
5000
Hours
26000
Hours*
60000
Hours
Uniform Load
(Motor, Turbine,
Hydraulic Motor)
Light Impact
(Multicylinder
engine)
Medium Impact
(Single cylinder
engine)
0.80
0.90
1.0
1.25
0.90
1.0
1.25
1.50
1.0
1.25
1.50
1.75
0.90
1.0
1.25
1.50
1.0
1.25
1.50
1.75
1.25
1.50
1.70
2.0
1.0
1.25
1.50
1.75
1.25
1.50
1.75
2.0
1.50
1.75
2.0
2.25
Sliding Speed Limit
before Scoring
(m/s) *
Material of
Worm Gear
Material of Worm
SC lim
Phosphor Bronze
Centrifugal Casting
Phosphor Bronze
Chilled Casting
Phosphor Bronze
Sand Molding or Forging
Aluminum Bronze
Brass
Ductile Cast Iron
Alloy Steel Carburized & Quenched
Alloy Steel HB 400
Alloy Steel HB 250
Alloy Steel Carburized & Quenched
Alloy Steel HB 400
Alloy Steel HB 250
Alloy Steel Carburized & Quenched
Alloy Steel HB 400
Alloy Steel HB 250
Alloy Steel Carburized & Quenched
Alloy Steel HB 400
Alloy Steel HB 250
Alloy Steel HB 400
Alloy Steel HB 250
Ductile Cast Iron but with a higher
hardness than the worm gear
1.55
1.34
1.12
1.27
1.05
0.88
1.05
0.84
0.70
0.84
0.67
0.56
0.49
0.42
0.70
30
20
10
30
20
10
30
20
10
20
15
10
8
5
5
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