Why Do “Dirty Side” Pulleys Wear Out Faster?

Over time every conveyor belt system will experience wear to both the belt and the pulleys. But if you’ve ever noticed that reverse bend pulleys (commonly referred to as “dirty side” pulleys) wear out faster, you’re not alone.

These pulleys, often found at the top of Gravity Take-Up (GTU) systems, contact the carry side of the belt; the side that faces the material load. This side tends to be dirtier, with leftover material (carryback) sticking to the worn, uneven surface. As the belt wraps around the pulley, this carryback gets trapped between the belt and the pulley lagging, increasing friction and wear.

When Wear Accelerates Without Warning

Sometimes you might see a sudden increase in wear on the belt or pulley even though nothing has changed and belt speed, cleaning systems, and material loads all seem normal. It’s easy to blame poor cleaning or excess carryback, but in many cases, they’re not the root cause.

Instead, the issue often lies in how the belt’s internal structure (the carcass) influences the interaction of the belt and pulley lagging surfaces, especially when slippage occurs.

What Is Slippage?

Slippage happens when the belt and pulley move at slightly different speeds. This causes the belt to slide against the pulley instead of gripping it firmly, causing heat and wear from friction on both surfaces.

When a new belt is installed on freshly lagged pulleys, everything fits snugly. The belt lies flat, and even if there’s some carryback, wear is minimal because there’s no slippage.

But as the belt wears down or carryback builds up, the contact surface changes. This can lead to slippage, and that’s when wear starts to accelerate.

When Fenner Conveyors belt engineers are supporting clients experiencing this problem, they calculate the rotational speed of the pulley in relation to the belt speed, with consideration to the belt’s thickness (especially the carcass) as this affects how it interacts with the pulley.

What Happens When the Belt Wears Down?

As the carry cover wears or carryback builds up in localised areas across the belt width, the effective radius of the belt surface changes. This affects the surface speed at the point of contact with the pulley.

This means that the worn areas of the belt move faster than the pulley surface, causing slip – and that slip grinds dirt into the belt and lagging, accelerating wear.

As wear increases, so does slip speed, and with it, the rate of wear.

Where Does Slip Happen?

It might seem like slip would happen evenly across the pulley, but it usually occurs toward the point where the belt leaves the pulley. This is due to the elastic nature of rubber covers applied to the belt, which stretch under shear forces.

The belt grips the pulley until the shear strain (internal stretching) becomes too much, then it slips suddenly. This creates a “slip-grip” cycle, where the belt alternates between gripping and slipping, causing localized wear and heat.

The Takeaway

This simplified explanation doesn’t account for every factor, like stress distribution or lagging compression, however it does highlight a key mechanism behind accelerated wear on dirty side pulleys.

Understanding this helps explain why wear can increase even when cleaning systems are working fine. It also explains why belt design and carcass structure play a critical role in long-term performance.

Read on here to learn more about belt wear and how our custom compounds help compensate for this to extend belt life and improve operational efficiencies.