Machinery's Handbook, 31st Edition
2600 Variable Speed Belts Belt Size Designation: Variable-speed belt sizes are identified by a standard belt num - ber. The first two digits denote the belt top width in sixteenths of an inch; the third and fourth digits indicate the angle of the groove in which the belt is designed to operate. Letter V (for variable) follows the first four digits. The digits after the V indicate pitch length to the nearest 0.1 in. For example, 1422V450 is a belt of 7 ⁄ 8 in. ( 14 ⁄ 16 in.) nominal top width designed to operate in a sheave of 22 degree groove angle and having a pitch length of 45.0 in. Sheave Groove Data: A variable speed sheave is an assembly of movable parts, designed to permit one or both flanges of the sheave to be moved axially causing a radial movement of the variable speed belt in the sheave groove. This radial movement permits stepless speed variation within the physical limits of the sheave and the belt. A companion sheave may be a solid sheave having a constant diameter and groove profile or another variable sheave. Variable speed sheave designs should conform to the dimensions in Table 33 and Fig. 10. The included angle of the sheaves, top width, and clearance are boundary dimen sions. Groove angles and dimensions of companion sheaves should conform to Table 33 and Fig. 11. Various tolerance values are also given in Table 33.
α b g / b e
a
b go
a v
Closed Variable Sheave
Closed Variable Sheave
S g
Open Multiple Groove Variable Sheave Fig. 10. Variable Sheaves
Variable-Speed Drive Design: Variable-speed belts are designed to operate in sheaves that are an assembly of movable parts. The sheave design permits one or both flanges of the sheave to be moved axially, causing a radial movement of the variable-speed belt in the sheave groove. The result is a stepless speed variation within the physical limits of the sheave and the variable-speed belt. Therefore, besides transmitting power, variable- speed belt drives provide speed variation.
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