Lagging Design Engineered To Allow Ceramic Tiles To Move Under Load And Minimise Slippage / Belt Cover Wear
Belt cover wear occurs when there is slippage between the lagging and the conveyor belt. When ceramic drive lagging is used and there is slippage the wear occurs in the rubber belt cover as this is the softer less abrasion resistant surface.
All conveyor belts stretch or elongate under tension. The amount of elongation depends on a number of factors including
- belt stiffness or modulus
- the level of applied tension or shear stress
Figure #1 shows that as the conveyor belt transitions from higher tension on the incoming side of the drive pulley to lower tension on the outgoing side the belting wants to retract/return to its original untensioned length. Slippage occurs when the lagging in contact with the belt cover is unable to move with the belt as it reduces its elongation. Slippage/wear is greatest for:
- fabric belts as they have higher elongation than steel cord belts
- higher tension belts as these produce higher belt elongation
- Direct Bond Ceramic Drive Lagging which has rigid mounting of the tiles to the pulley shell.
Figure #1. Drive Pulley and Belt
Figure #2. Friction Summary
Figure #2 illustrates the impact that friction, belt type and lagging type can have on slippage and hence belt cover wear. This illustration compares steel cord belt and fabric belt with both rubber and ceramic drive lagging.
In this example for the steel cord belt being used with rubber drive lagging localized slippage will occur. If ceramic lagging is used then the slippage will not occur with the steel cord belt.
As fabric belt has higher elongation than steel cord belt slippage will occur with both rubber and ceramic lagging. This illustration also shows that increasing the thickness of the rubber backing layer for the ceramic lagging reduces the slippage.
When considering design changes to reduce slippage/belt cover wear, the lagging parameters such as lagging rubber thickness, and lagging stiffness are much easier to adjust than other conveyor parameters.
Figure #3 illustrates the effect of the type of ceramic lagging on the degrees of slippage that can occur as the conveyor belt transitions around the drive pulley. The increase in strain occurs up to the point where slippage occurs – this is shown by the blue line. Once slippage occurs there is a drop in strain force between the ceramic lagging and the belt cover. For the Direct Bond Ceramic Lagging (DBCL) the arc of slippage is larger than for the rubber backed ceramic.
This is due to the rigid nature of the DBCL where there is no flexibility for the ceramic tiles to move with the conveyor belt as it retracts with the reducing tension.
The rubber backed ceramic lagging produces a reduced degree of slippage compared to the DBCL. Also illustrated is the effect of increasing thickness of the rubber backing on the ceramic lagging in further reducing the likelihood of slippage occurring.
Elastotec Hot and Cold Vulcanised Ceramic Lagging is available in a range of thicknesses to suit various conveyor design requirements. These thicknesses include 12,15,20 and 25 mm. Additionally assistance can be provided with design and selection lagging of the correct ceramic lagging type to maximise service life of both the conveyor belt and the ceramic lagging.
Figure #3. Degrees of Slip
For additional information on the lagging factors that effect belt cover wear please refer to the following articles available on our blog: