Component Selection

Many factors influence the amount of power which may safely be transmitted by a chain assembly. Generally the larger the pitch size and the larger the sprocket diameters the greater the power that can be transmitted but the slower the speed that the chain can operate at.

This is because the larger the pitch, the larger the pin and bush sizes. The link is thus stronger and the bushes have greater resistance to wear for a given power and speed (hence torque and tooth load). Conversely, for a given reduction ratio, the larger the chain pitch the larger the sprockets and hence peripheral speed. For a limiting operational chain velocity, smaller pitch chains will operate at higher rotational speeds. In addition to chain size, the recommended maximum operating power and speed will depend upon factors such as the number of teeth in the sprocket, the severity of use, the lubrication system and the number of strands used.

The application suitability of a chain drive depends upon the type of drive and also the class of load. Typically each is categorised into three levels as follows :

Types of Drive      - Steady (e.g. 'soft start' electric motors)
                        - Medium Impulsive (e.g. multi-cylinder i.c. engines)
                          - Highly Impulsive (e.g. single-cylinder i.c. engines)

Types of Load      - Class 1 for Smooth loads
                          - Class 2 for Moderate Shock loads
                          - Class 3 for Heavy Shock loads

Service Factors for the three classes of load severity are displayed below based on a Driving Sprocket with 15 teeth.

It is desirable from power considerations to have larger sprockets since the greater the diameter the more teeth there are to share the load. Based on a reference sprocket size of 15 teeth the following modification factors are used :

Using a multi-strand chain increases the power that can be transmitted for a given pitch size but not fully in proportion with the number of strands used. Typically, the following power rating factors are widely used.

No. of Strands	Multi-Strand Rating Factor
1 2 3 4	1 1.7 2.5 33

Multi-Strand Power Rating Factors

The required type of chain for a given application is identified from a manufacturers Rating Chart. To minimise the number of charts needed in a catalogue it is necessary to calculate the Selection Power (or Design Power as it is sometimes referred). This obtained from :

A ŚTransmission Rating Chartą using a sprocket with 15 teeth is illustrated in Figure 7.