Belt conveyors are the arteries of crushing and screening plants: they connect crushers, screens, bins and stockpiles. A typical aggregate plant has dozens of conveyors, and just one of them stopping can stop the whole line. Conveyor maintenance is therefore not a matter of “small jobs” but a cornerstone of plant availability.
In this guide you will find the main components of a belt conveyor, how to correct belt mistracking — the most common problem — correct tension values, cleaning systems and a maintenance schedule that can be applied in the field.
Main Components of a Belt Conveyor
| Component | Function |
|---|---|
| Conveyor belt | A rubber belt reinforced with textile (EP) or steel cord that carries the material |
| Drive pulley and motor-gearbox | Moves the belt; the pulley lagging provides traction |
| Tail (take-up) pulley | The end where the belt turns back; usually connected to the take-up |
| Snub and bend pulleys | Increase the belt’s wrap angle and change its direction |
| Carrying (troughing) idlers | Carry the loaded belt and give it a trough shape |
| Return idlers | Carry the empty return belt |
| Impact idlers / impact bed | Absorb impact at the loading point |
| Take-up (screw, gravity, hydraulic) | Provides belt tension |
| Skirt rubber and loading chute | Prevent spillage at the loading point |
| Belt cleaners (scrapers) | Remove material stuck to the belt (carryback) |
| Safety equipment | Emergency stop pull cord, slip (speed) sensor, misalignment switch, guards |
Choosing a Conveyor Belt
- Carcass: Aggregate plants usually use belts with an EP (polyester-polyamide) textile carcass; steel cord belts are preferred on long, high-tension conveyors.
- Cover grade: The abrasion grade (such as DIN-Y, DIN-X, DIN-W) is chosen according to the abrasiveness and particle size of the material. Large, sharp-edged rock needs covers with high cut and tear resistance.
- Cover thickness: The top cover is thicker than the bottom cover; on short belts loaded frequently, the top cover wears faster.
- Special belts: Chevron belts are used for steep inclines, heat-resistant belts for hot material and oil-resistant belts for oily material.
For details on belt types, see our conveyor belt rubber guide and our article on chevron conveyor belts.
How to Correct Belt Mistracking
A belt running to one side is the most common conveyor problem, causing the belt edge to rub on the structure and tear, material spillage and idler damage. Mistracking usually results not from one cause but from a combination of several small faults.
Basic rules for diagnosis
- The belt moves towards the end of the idler it touches first. In other words, if an idler is skewed with one end ahead in the direction of belt travel, the belt runs towards that side.
- The belt moves towards the high (larger-diameter) side of a pulley. This is why material build-up on a pulley causes mistracking.
- If the belt runs off in one place when empty and another when loaded, the problem is most likely related to loading (off-centre loading).
- If the same section of belt runs off in the same place on every revolution, the problem may be in the belt itself (crooked splice, cambered belt).
Step-by-step correction
- Check that the conveyor structure is straight and level, and that the pulleys are square and parallel to the belt.
- Clean material stuck to pulleys and idlers; replace idlers that are not turning or are seized.
- Make sure loading is in the centre of the belt; add deflector plates to the loading chute if necessary.
- Starting a few idlers before the point where the belt runs off, adjust the idler brackets in very small steps; after each adjustment, let the belt run a few revolutions.
- If necessary, use self-aligning carrying and return idler sets.
- Check that the belt splices are square; a crooked splice must be remade.
Belt Tension
- Insufficient tension causes slip on the drive pulley and excessive sag between idlers; material spills and the belt wears quickly.
- Excessive tension overloads the pulleys, bearings and belt splices and shortens belt life.
- On a loaded belt, sag between carrying idlers should not exceed about 2–3% of the idler spacing (CEMA recommendation).
- On screw take-ups, both sides must be tensioned equally; tensioning one side makes the belt run off. On long conveyors, a gravity take-up is preferred because it provides constant tension.
Idlers, Pulleys and Pulley Lagging
- Every accessible idler should be turned by hand and checked for free rotation, play, wobble and flattened surfaces. A seized idler wears and can cut the belt; a seized bearing is a fire risk.
- Impact idlers or impact beds should be used at the loading point, and the drop height kept as low as possible.
- Drive pulley lagging should be checked for worn grooves, glazing, cracks and separation. In wet and muddy applications, ceramic lagging increases traction considerably. See pulley lagging: rubber and ceramic.
Belt Cleaning and Spillage Control
Material that sticks to the belt and comes back (carryback) builds up on return idlers, causes mistracking and idler failure, and creates a cleaning burden around the plant.
- Primary scraper: On the drive pulley; removes most of the material.
- Secondary scraper: Just behind the pulley; removes the remaining thin layer.
- Check the contact pressure and wear of scraper blades weekly; too much pressure wears the belt, too little does not clean. Details: primary and secondary belt scrapers.
- At the loading point, skirt rubber should touch the belt lightly; dust curtains and an enclosed loading chute should be used to reduce dust.
Maintenance Schedule
| Interval | Check |
|---|---|
| Daily (walk-around) | Belt tracking, spillage, idlers not turning, unusual noise, scrapers, accessibility of the emergency stop cord |
| Weekly | Belt tension and sag, splices, skirt rubber, scraper blades, pulley cleanliness |
| Monthly | Pulley lagging, idler bearings, gearbox oil level, coupling, testing safety switches |
| 3–6 months | Gearbox oil analysis/change, greasing pulley bearings (at the manufacturer’s interval), measuring belt cover thickness |
| Yearly | Structure and steelwork, pulley shafts, belt life assessment |
Safety
- Most conveyor accidents happen at pulley and idler nip points while cleaning or adjusting a running belt. Never clean a running conveyor.
- All pulleys and nip points must have fixed guards; any work that involves removing a guard must be done under LOTO.
- Emergency stop cords must run continuously along the conveyor and be tested.
Frequently Asked Questions
Why does the belt keep running to the same side?
The most common causes are off-centre loading, material build-up on pulleys or idlers, skewed idler brackets and a structure that is not level. Correction should always start with cleaning and checking the loading.
How can conveyor belt life be extended?
The right cover choice, impact absorption and a low drop height at the loading point, effective scrapers, correct tension and timely idler replacement are the main factors determining belt life.
When should pulley lagging be renewed?
When the lagging has lost its pattern, when cracks and separation are seen, or when the belt starts to slip.
Conveyor Capacity and Belt Width Selection
Belt conveyor capacity depends on belt width, troughing angle, the material’s surcharge (dynamic repose) angle, belt speed and bulk density. In simplified form:
Capacity (t/h) = Cross-sectional area (m²) × Belt speed (m/s) × 3,600 × Bulk density (t/m³)
The cross-sectional area is taken from standard tables according to belt width and trough geometry. For example, on an 800 mm wide belt with 30° troughing, the typical cross-sectional area is about 0.06–0.07 m²; at a speed of 2 m/s and a density of 1.6 t/m³, capacity reaches a theoretical value of about 0.065 × 2 × 3,600 × 1.6 ≈ 750 t/h. In practice, design capacity is kept below this because of fill level and irregular loading.
Besides capacity, the largest particle size is also decisive in choosing belt width: for large rocks, the belt width should be several times the largest particle size; otherwise rocks roll off the belt and strain the skirt rubber.
Choosing Belt Speed
- Higher speed means a narrower, lighter belt for the same capacity; but wear, dust and impact at transfer points increase.
- Lower speeds are preferred for large, sharp rock and on conveyors under crushers and feed conveyors.
- With fine, light material, very high speed increases dust generation.
- On stockpile conveyors, speed also affects how the stockpile forms and segregation.
Incline Limits
On flat belts, the conveying incline is limited by the angle at which material can be carried without sliding back on the belt; for crushed rock it is typically around 16–20°. With wet, rounded or fine material, this limit is lower. For steeper inclines, chevron belts or special belts with sidewalls and cleats are used.
Belt Splices: Vulcanised or Mechanical?
| Splice type | Advantage | Disadvantage |
|---|---|---|
| Hot vulcanised splice | Highest strength and life, smooth surface | Requires a specialist team, equipment and a longer shutdown |
| Cold vulcanised splice | More practical than a hot splice | May be weaker than a hot splice |
| Mechanical splice (hinged, bolted) | Very quick to apply, emergency repair | Can wear scrapers and pulleys, can leak fines |
Vulcanised splices are preferred on main conveyors; mechanical splices are suitable for emergencies and short-life applications. The splice must always be made square to the belt axis (or at the angle recommended by the manufacturer) and straight; a crooked splice is one of the most common causes of permanent mistracking.
Spare Parts Stock
- Always in stock: Carrying and return idlers for each conveyor type, impact idlers, scraper blades, skirt rubber, a mechanical splice kit, belts.
- Critical spares: For main conveyors, a drive pulley (lagged), gearbox or motor-gearbox unit, coupling, bearings.
- Planned: A belt roll (of suitable length for main conveyors), tail pulley, take-up parts.
Standardising idler, bearing and motor sizes across the plant reduces stock variety and cost.
An Example from the Field: A Stockpile Conveyor That Kept Slipping
At one plant, a chippings stockpile conveyor kept slipping on rainy days, with the belt spinning on the drive pulley. Increasing tension gave a temporary fix but led to bearing failures. The investigation found that the rubber pulley lagging was glazed and that wet material stuck to the return belt was getting between the pulley and the belt. The pulley was relagged with ceramic lagging, primary and secondary scrapers were added and tension was brought back to normal. The slipping problem was solved and the bearing failures ended.
Pre-Purchase Checklist
- Have peak capacity, material density and largest particle size been determined?
- Are the conveyor length, lift and incline known?
- Are the belt type and cover grade suited to the abrasiveness of the material?
- Has the take-up type (screw/gravity) been chosen to suit the length?
- Have impact and dust control at the loading point been planned?
- Is safety equipment (pull cord, misalignment and slip switches) included?
- Have walkways and access for maintenance been planned?
More Questions
Why does the conveyor belt wear at the edge?
Rubbing on the structure because of constant mistracking, badly adjusted skirt rubber or damaged edge guide rollers cause edge wear.
Why do idlers fail quickly?
The most common causes are inadequate sealing against dust and water, material stuck to the belt building up on the idlers, overload and the wrong choice of idler.
Is there a fire risk on conveyors?
A seized idler or slipping belt can heat up through friction and cause a fire. Regular idler checks, slip sensors and cleaning reduce this risk.
Conveyor Solutions from CSP Mühendislik
CSP Mühendislik designs and manufactures belt conveyors for your plant and supplies belt conveyor spare parts such as belts, idlers, pulleys, scrapers and take-up systems. Contact us to reduce stoppages on your conveyor line.
