Page 170 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
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P transmitted power, kW t link plate thickness, mm
P 0 basic power rating of a chain drive, v avg average speed of a chain, m s −1
kW v instantaneous velocity along the
P actual power rating of a chain chain, m s −1
r
drive, kW v ′ instantaneous velocity vertical to
p pitch, mm the chain, m s −1
p strand spacing, mm z number of teeth of a sprocket
t
∘
q mass of chain per unit length, contact angle, or rad
kg m −1 pitch angle, ∘
Q limiting tensile load of angular velocity, rad s −1
single-strand chain, N
R pitch radius of a sprocket, mm Subscripts
r chordal radius of a sprocket, mm 1 driving sprocket
S ca safety factor 2 driven sprocket

7.1 Introduction

7.1.1 Applications, Characteristics and Structures

A chain drive is another major type of flexible drive used to transmit power over com-
paratively long centre distances. They are commonly used in conveyor systems, automo-
biles, motorcycles, bicycles and many other similar applications. Contrary to belt drives,

chain drives are desirable at low to moderate speeds, high torque applications and usu-
ally at lower speed stage of a power transmission system. Figure 6.1 shows a chain drive
together with a gear reducer and a belt drive in a power transmission system.
Chain drives combine some features of belt drives and gear drives. Compared with belt
drives, chain drives have high transmission efficiency, great power transmitting capac-
ity and long life, as no slippage or creep is involved between the chain and sprocket
teeth. Besides, chain drives can operate in hostile environments, such as high ambient
temperature, high moisture, oily, dusty or dirty situations. Furthermore, chain drives
can be applied to an arbitrary centre distance compared with gear drives. The main
disadvantage of a chain drive is the impact and noise due to variable angular veloc-
ity ratio and velocity. Besides, chains may elongate and even jump off sprockets due
to wear [1–4].
A chain drive consists of a driving sprocket 1, a driven sprocket 3 and a chain loop 2,
as illustrated in Figure 7.1. A chain is a flexible power transmission element composed
of a series of pin-connected links. When transmitting power, the chain engages toothed
wheels, called sprockets. The driving sprocket imparts constant tension to the chain,
forcing the driven sprocket rotates. As a joint enters and leaves a sprocket, adjacent
links rotate relatively to each other. Chains obtain flexibility from pin-connected links
that articulate at each joint during operation [5].

7.1.2 Types of Chains
Chains include three types according to their applications, that is, power transmission
chains, drag chains and lifting chains. Drag chains and lifting chains are used mostly in