On a belt conveyor, the fine material that stays stuck to the belt surface after discharge is called carryback. This material spills along the return run, sticks to return idlers and pulleys, and causes mistracking, idler failures and heavy cleaning labour. Belt scrapers (also called belt cleaners) are the equipment that cleans this material off the belt at the discharge point.
In this guide we cover primary and secondary scrapers, V-plough scrapers, blade materials, correct contact pressure, maintenance and replacement steps, and spare part selection. For general belt conveyor maintenance, see our belt conveyor guide.
Scraper Types
| Type | Location | Function |
|---|---|---|
| Primary scraper (pre-cleaner) | On the face of the drive/discharge pulley | Removes most of the material |
| Secondary scraper | Just behind the pulley, under the belt | Removes the remaining thin layer |
| Tertiary scraper | On the return run | Final cleaning for very sticky material |
| V-plough scraper | In front of the tail pulley, on the inside of the return belt | Throws off rocks before they enter the tail pulley |
Blade Materials
| Material | Characteristics | Use |
|---|---|---|
| Polyurethane | Gentle on the belt, economical | Primary scrapers |
| Tungsten carbide tipped | Very long life, effective cleaning | Secondary scrapers |
| Rubber | Flexible | V-ploughs and light applications |
On conveyors with mechanical belt fasteners, the blade type should be chosen so that it neither damages the fasteners nor is damaged by them.
Correct Contact Pressure
- If the pressure is too low, the scraper does not clean.
- If the pressure is too high, the belt cover wears, the blade wears out quickly and motor load increases.
- The scraper tensioner (spring, torsion rubber or pneumatic) should be set to the manufacturer’s value and readjusted as the blade wears.
Failure and Wear Signs
- Material building up under the return run,
- Build-up on return idlers and pulleys,
- Worn or broken blades,
- The scraper vibrating or making noise,
- Scraper marks on the belt cover.
Inspection and Maintenance
| Check | Interval | Method |
|---|---|---|
| Carryback | Daily | Observation under the return run |
| Blade wear and contact | Weekly | Checked with the conveyor locked out |
| Tensioner setting | Weekly | To the manufacturer’s value |
| Mounting brackets | Monthly | Tightness and damage |
Blade Replacement
- The conveyor is stopped and locked out.
- The tensioner is released and the scraper is moved away from the belt.
- The worn blades are removed and the carrier profile is cleaned.
- New blades are fitted; the scraper is brought back into contact with the belt and the tension is set.
- Cleaning performance is checked during operation.
Common Mistakes
- Relying on a primary scraper alone (insufficient for sticky material),
- Over-tensioning,
- Running blades until they are completely worn,
- Neglecting the V-plough scraper; rocks entering the tail pulley cut the belt.
Troubleshooting Table
| Symptom | Possible cause | Solution |
|---|---|---|
| Material on the return run | Worn blade, low tension | Blade replacement, tension adjustment |
| Belt cover wearing | Too much tension, unsuitable blade | Reduce the tension, change the blade |
| Scraper vibrating | Mechanical fastener, wrong angle | Fastener-compatible blade, angle adjustment |
| Rocks at the tail pulley | No V-plough or a worn one | V-plough scraper |
An Example from the Field
On a conveyor carrying wet sand, material was constantly sticking to the return idlers and the belt was mistracking. There was only a primary scraper. A tungsten carbide tipped secondary scraper was added and the tension of the primary scraper was corrected. Carryback fell markedly; the mistracking and idler failures stopped.
Pre-Purchase Checklist
- Have belt width, pulley diameter and belt speed been determined?
- Is the material sticky or abrasive?
- Are mechanical fasteners used?
- Have the primary, secondary and V-plough requirements been determined?
Frequently Asked Questions
Which scraper is more effective?
Using a primary and a secondary scraper together gives the best results in most applications.
Does a scraper wear the belt?
With correct tension and a suitable blade, wear is negligible.
The Hidden Cost of Carryback
Carryback is usually seen as a minor problem, yet its effect on plant costs is large:
- Cleaning labour: Shovelling or machine-cleaning material that builds up under the return run takes considerable time every shift and puts workers in risky jobs near the conveyor.
- Idler failures: Material stuck to return idlers increases their diameter and causes imbalance and bearing failure.
- Belt mistracking: Material building up on pulleys and idlers pushes the belt to one side.
- Belt and pulley wear: Abrasive material wears the pulley lagging and the belt’s bottom cover.
- Product loss: Spilled material is lost from saleable product.
An effective scraper system eliminates most of these costs and often pays for itself quickly.
Parameters to Consider When Choosing a Scraper
| Parameter | Effect on selection |
|---|---|
| Belt width and speed | Blade length and tensioner capacity |
| Pulley diameter | Mounting geometry of the primary scraper |
| Material stickiness and moisture | Number of scrapers (primary + secondary + tertiary) |
| Material abrasiveness | Blade material (polyurethane / carbide) |
| Belt splice type | Blade design compatible with mechanical fasteners |
| Belt cover condition | Flexible blades on a damaged belt |
Tensioning Systems
- Spring tensioner: Simple and common; needs periodic adjustment as the blade wears.
- Torsion rubber tensioner: Compact; easy to adjust.
- Pneumatic tensioner: Provides constant contact pressure; automatically compensates for blade wear.
- Weighted/counterweight tensioner: Used on some secondary scrapers.
Maintenance Record Form
| Field | Record |
|---|---|
| Conveyor and scraper type | Primary / secondary / V-plough |
| Blade condition | Remaining blade height |
| Tension setting | Date and value |
| Carryback observation | None / little / a lot |
| Blade replacement | Date and blade type |
Stock Planning
- Keep at least one set of spare blades in stock for each scraper.
- Tensioning elements (springs, torsion rubbers) should be on the critical spares list.
- V-plough rubbers should be stocked separately.
More Questions
How often are scraper blades replaced?
It depends on belt speed, the abrasiveness of the material and the tension setting; polyurethane blades are replaced more often than carbide-tipped blades.
What should be done if material still remains after the scraper?
First check the tension setting and blade condition; if that is not enough, consider adding a secondary or tertiary scraper or switching to a more suitable blade type.
Can a scraper damage belt splices?
Unsuitable rigid blades can catch on mechanical fasteners. Fastener-compatible blades with flexible mounting eliminate this risk.
Spare Parts and Service for Belt Scrapers
CSP Mühendislik supplies primary, secondary and V-plough scrapers and spare blades as part of its belt conveyor spare parts range, and provides service support for selecting and adjusting belt conveyor cleaning systems. You can share your belt details on WhatsApp.
