Description
Lagging is the term used to describe the application of a coating, cover, or wearing surface which is sometimes applied to pulley shells. Lagging is often applied in order to extend the life of the shell by providing a replaceable wearing surface or to improve the friction between the belt and the pulley.
Types of Lagging：
There are primarily three categories of lagging that are used on pulleys and these are described below:
a) Rubber lagging
Rubber lagging is applied to pulley shells in order to improve the friction between the pulley and the belt. Conveyor drive pulleys are often supplied with diamond grooved lagging as indicated in the adjacent sketch.
Rubber lagging material is manufactured in standard widths in either ‘plain’ or ‘diamond grooved’ pattern and is vulcanized to the pulley shell to prevent the lagging from peeling off of the shell.
b) Ceramic lagging
Ceramic lagging or lining of a pulley is used in instances where the pulley operates in extremely aggressive conditions. An example of such a condition is the pulleys on a bucket elevator, where the pulleys operate within the enclosed elevator housing and material cannot be prevented from becoming trapped between pulley shell and belt.
c) Replaceable Strip lagging
In applications where the required duty and/or the availability of a conveyor is such that downtime for maintenance is at a premium, pulley lagging can often be overlooked.
Lagging Specifications
Rubber pulley lagging is usually specified in terms of its type, hardness, thickness, and finish as follows :
a) Lagging Type and Finish
The type of lagging to be used is specified on the basis of the application, duty, and required life of the lagging as outlined above.
In general, the type of lagging used on troughed belt conveyors is indicated in the table below:-
| Pulley Location | Type of Lagging | ||
| Diamond Grooved | Plain | No Lagging | |
| Drive | X | X | |
| Tail | X | X | X |
| Bend | X | X | |
| Take-up | X | X | |
| Snub | X | X | |
Ceramic-type lagging is not usually applied to troughed belt conveyor pulleys, neither is strip lagging.
b) Lagging Hardness
The hardness of the rubber lagging to be used on a conveyor is generally dependent on the pulley location.
Pulleys that come into contact with the dirty- or carrying side of the belt including snub pulleys and bend pulleys, usually employ lagging with a hardness of 35 to 45 Shore ‘A’.
Drive, take-up, and tail pulleys should use lagging with a Shore ‘A’ hardness of between 55 and 65.
c) Lagging Thickness
Rubber lagging thickness varies extensively. Commonly used lagging thicknesses are as follows:-
Drive pulleys, grooved lagging: 10 to 12 mm.
Other pulleys, plain lagging: 6 to 10 mm.
Useful Tips for the Care and Maintenance of Pulley Lagging
Like all equipment, the life expectancy of rubber lagging is dependent on the operational environment, the quality and frequency of maintenance, and the manner in which the equipment is used.