Page 157 - Analysis and Design of Machine Elements

1.25 Belt Drives 135
1.2
Belt length correction factors, K L 1.05
1.15
1.1

1

0.95
0.9
Type B belt
0.85 Type A belt
Type C belt
0.8
500 1500 2500 3500 4500 5500 6500 7500 8500 9500 10500
Standard V-belt datum lengths L d , mm
Figure 6.11 Standard V-belt datum lengths L versus length correction factors K [4].
d L

6.4 Design of Belt Drives

6.4.1 Introduction
Belt drive design involves either the selection of a proper belt to transmit a required
power or the determination of a power that can be transmitted by a belt drive. When
designing a belt drive, the data provided are the rated power of driving motor or other
prime mover, the rotational speed of driving sheave n and driven sheave n (or speed
1
2
ratio), the type of driver and driven machine and the layout requirement of the belt drive.
The data that need to be determined include belt type, length and the number of
belts; centre distance; the size, materials and structure of driving and driven sheaves,
as well as the initial tension on the belt. The design procedure and factors involved
in the selection of a V-belt and driving and driven sheaves are introduced in this
section.

6.4.2 Design Criteria
As discussed in Section 6.2.5, principal failure modes in a belt drive are fatigue and
slippage. To prevent these failures, design criteria for a belt drive are to prevent belts
from slippage and at the same time to ensure belts have sufficient fatigue strength and
service life.

6.4.3 Design Procedure and Guidelines
The design procedure and guidelines for variable selection are given as follows: