Specifying Impact and Return Rollers: Maximizing Conveyor Belt Lifespan with Rubber and Polyurethane Lagging

Conveyor belts represent the single largest capital investment in a bulk material handling system, often accounting for 50% to 70% of the total system cost. Protecting this asset from premature wear and catastrophic damage is a top priority for plant managers and maintenance engineers.

The two areas where conveyor belts are most vulnerable to damage are:

1. The Loading Zone: Where high-velocity, falling bulk materials cause severe impact damage, punctures, and carcass bruising.
2. The Return Run: Where sticky material carryback clings to the belt, building up on steel rollers and causing abrasive cover wear and tracking errors.

To mitigate these risks, engineers specify rubber-lagged impact rollers and polyurethane-coated return rollers. This technical guide analyzes the material properties, application criteria, and cost-benefit ratios of lagged rollers.

---

1. The Physics of the Loading Zone: Specifying Impact Idlers

When heavy, jagged materials (such as run-of-mine ore, limestone, or coal) drop from a feeder chute onto a conveyor belt, the kinetic energy must be absorbed. Standard steel rollers cannot deform; this forces the conveyor belt to absorb the entire impact, leading to cuts in the top cover and fractures in the internal fabric or steel cord carcass.

Rubber Disc Impact Rollers

Impact rollers are positioned directly beneath the loading chute. Instead of a bare steel shell, they feature a series of high-durometer rubber rings (discs) assembled along the tube.

• Cushioning Effect: The rubber discs compress under impact, distributing the force over a larger area and reducing the peak impact stress on the belt by up to 70%.
• Material Specifications: Premium impact rollers utilize natural or synthetic rubber with a hardness of 60 to 65 Shore A and excellent abrasion resistance.

Impact Roller Spacing

In the loading zone, idler spacing must be significantly tighter than along the normal conveyor run to prevent the belt from sagging between rollers:

• Typical Spacing: 300mm to 600mm (12 to 24 inches) depending on the material drop height and lump size.

---

2. Managing Carryback: Rubber & Polyurethane Return Rollers

After the conveyor belt discharges its load at the head pulley, it travels back along the return run. Despite scrapers and cleaners, a small amount of fine, sticky material (carryback) always remains on the belt.

If standard steel rollers are used on the return run, this carryback transfers to the roller shell, hardening into a jagged crust (scaling). This scaling causes:

• Belt Cover Wear: The abrasive crust grinds away the bottom cover of the belt.
• Tracking Issues: Uneven buildup creates an artificial crown on the roller, causing the belt to drift.

Rubber Disc Return Rollers (Flat & V-Return)

By replacing flat steel return rollers with rubber disc return rollers, the contact area between the belt and the roller is minimized. The rubber discs are spaced along the shaft, and as the belt flexes over them, any accumulated material is broken loose and shed, preventing scaling.

Polyurethane-Coated Rollers: The Premium Standard

For highly abrasive, sticky, or corrosive materials (such as fertilizer, chemical salts, or wet sand), polyurethane (PU) lagging is the superior choice.

---

3. Calculating Impact Energy to Specify the Correct Roller

To determine whether standard rubber disc rollers are sufficient or if a heavy-duty impact bed is required, engineers calculate the impact energy (E_impact):

Where:

• m = Mass of the largest material lump (kg)
• g = Acceleration due to gravity (9.81 m/s²)
• H = Material drop height (m) (the vertical distance from the discharge pulley to the belt)

Specification Thresholds:

• E_impact under 200 Joules: Standard rubber disc impact rollers are sufficient.
• E_impact between 200 and 1,000 Joules: Heavy-duty rubber impact rollers with C3 bearings and reinforced shafts are required.
• E_impact over 1,000 Joules: A dedicated impact slider bed (featuring UHMW polyethylene sliding bars backed by high-damping rubber cores) must be installed to prevent belt puncturing.

---

Conclusion: Protect Your Belt Investment with VOTNE

Every conveyor system has unique challenge zones. Using the wrong roller coating can lead to premature wear of both the roller and the conveyor belt.

At VOTNE, we manufacture a comprehensive range of rubber disc impact rollers, rubber return rollers, and premium polyurethane-sleeved rollers. Our polyurethane formulations are specifically engineered for maximum cut-growth resistance and low coefficient of friction to ensure your belt slides smoothly without material buildup.

Contact our application engineers today to calculate your loading zone impact forces and specify the optimum lagging solution.

• Email: engineering@votne.com
• Technical Support: Fill out our Contact Form to consult with a B2B parts specialist.