In an aggregate facility, conveyor belt slippage can be a problem. One possible solution is the use of lagging-in a variety of forms-on the conveyor pulley.

When applied to a conveyor pulley, lagging material performs two functions. Its primary function is to aid in gripping the conveyor belt, thus helping transmit torque from the drive to the pulley in order to carry the load on the conveyor belt. Lagging also prolongs the wear life of the pulley.

There are several types of lagging used in aggregate facilities. Many conveyor pulley manufacturers sell conveyor pulleys with lagging already applied. Frequently, this lagging is steam-cured, or coated with a rubber compound that has been cured in an autoclave under steam pressure. After curing, the lagging is grooved and then shipped to customers.

One potential challenge to this type of system, however, is that when removed from the autoclave, the lagging continues to cure and the durometer or hardness of the rubber will increase. For instance, the measure of the durometer of the lagging material when first taken from the autoclave may be approximately 60, nearly equal to the durometer of the conveyor belt. After several days or weeks, additional curing may significantly increase the lagging's durometer. If the durometer of the lagging exceeds the durometer of the conveyor belt, slippage can occur, causing a new conveyor pulley to slip against the belt.

Aggregate facilities combat slippage by applying more tension to the conveyor belt or by roughening the lagging surface with a hand-held grinder. Chemicals should not be applied to the lagging or belting to improve traction because they can disintegrate the rubber compound over time, making the problem worse.

Strip or slide lagging also is widely used in the aggregate industry. Like pre-applied lagging, the rubber compound in strip lagging undergoes a similar steam-cure process. Strip lagging applieseasily: retaining strips are welded to the face of a conveyor pulley and the lagging strips slip into the grooves between the retaining strips and the pulleys.

One might think simply replacing worn-out strips would make for a quick installation and more simple maintenance. However, the retaining strips may be bent by belt tension or the weight of the load, making maintenance difficult. Many times maintenance personnel cut off the old strips with a torch, creating a maintenance and downtime problem.

Lagging also may be manufactured using a molding process. The benefit of molded rubber lagging is that it is not cured under steam pressure and therefore will remain stable. The average durometer of this product is approximately 60. Though more expensive than other types of lagging, molded rubber lagging provides substantially better gripping action than the steam-cured product and lasts three to four times longer. This type of lagging material is applied by qualified rubber technicians using a cold vulcanizing process. The conveyor pulley surface is prepared and the lagging applied using special adhesives.

Ceramic lagging is used to combat chronic belt slippage and can provide twice the gripping power of molded rubber lagging. Ceramic lagging costs two to three times more than any of the lagging products previously mentioned and is applied much like the cold vulcanized lagging process.

No matter what type of lagging chosen, always remember to disconnect the power when working on conveyor equipment and follow all company safety procedures.

If conveyor belt slippage is causing reduced productivity or high maintenance costs, contact a local industrial distributor to discuss the features of lagged conveyor pulleys.