| 17.5.4
Surface Strength of Worm Gearing Mesh (1) Calculation of Basic Load Provided dimensions and materials of the worm pair are known, the allowable load is as follows:  (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. An equivalent load is needed to compare with the basic load in order to determine an actual design load, when the conditions deviate from the above. Equivalent load is then converted to an equivalent tangential force, Fte, in kgf: Fte = FtKhKs (17-53) and equivalent worm gear torque, T2e, in kgf.m: T2e = T2KhKS (17-54) (3) Determination of Load Under no impact condition, to have life expectancy of 26000 hours, the following relationships must be satisfied: Ft £ Ftlim or T2 £ T2lim (17-55) For all other conditions: Fte £ Ftlim or T2e £ T2lim (17-56) NOTE: If load is variable, the maximum load should be used as the criterion. |
17.5.5
Determination of Factors in Worm Gear Surface Strength Equations
17.5.5.A Tooth Width of Worm Gear, b2 (mm) Tooth width of worm gear is defined as in Figure 17-13.
where: Basic Zone Factor
is obtained from Table 17-28 |
420 
