Belt conveyor: belt, splices, take-up and loading zone bearings: arrangement, lubrication and failures
Most belt conveyor problems are not bearing problems. They start at the loading point, at a splice, at a dirty idler or at a take-up that is set wrong, and the bearings are the last victims. This view opens the conveyor as a system: the belt, how it is joined, what carries it and what keeps it tensioned and centred. For the bearings in the pulleys and idlers, open Belt conveyors (pulley and idler bearings).
Typical duty
| Speed | Load | Temperature | Typical life |
|---|---|---|---|
| Set by the capacity needed; the pulleys turn slowly and the belt moves at a steady speed | Belt tension, the weight of the load and shock where material lands | Ambient for most; the temperature of the material decides which belt cover to use | Belt and splices last for years when loading, tracking and cleaning are right |
How the bearings are arranged
Belt and splices · the part that carries the load
Used when: Choosing, joining and repairing the belt on any conveyor
A belt has three layers. The top cover takes the abrasion and impact, the carcass in the middle carries the tension, and the bottom cover runs on the pulleys and idlers. The carcass is either layers of woven fabric or a row of steel cords. The two ends are joined into a loop with a splice, and the splice is usually the weakest point on the belt.
Pulleys, lagging and take-up · drive, turn and tension
Used when: Head, tail, snub, bend and take-up positions on every conveyor
The head pulley usually drives the belt by friction. A snub pulley next to it adds wrap, so more of the belt touches the drive pulley. The tail pulley turns the belt at the loading end. A take-up keeps the belt tight enough to grip the drive pulley and to hold its shape at the loading point, and it makes up for stretch.
Idlers, loading zone and cleaning · supporting and protecting the belt
Used when: Between the pulleys, and especially at the loading point and the discharge
Troughing idlers shape the loaded belt into a trough so it carries more. Return idlers support the empty belt on the way back. At the loading point, the chute, skirtboards and impact idlers decide how much damage the belt takes, and cleaners at the head keep dirt from being carried round to the return rolls.
Common failures and how to prevent them
| Failure | What you see | Why it happens | Prevention |
|---|---|---|---|
| Belt runs off to one side | Edge wear, spillage and a belt rubbing the structure. | Off-centre loading, idlers or pulleys out of square or level, material build-up on rolls, a crooked splice or a belt that has taken a set. | Load on the centre in the belt direction, keep rolls clean and free, square every pulley and idler first, and use training idlers only as a last step. |
| Belt slips on the drive pulley | Heat and wear at the head pulley, a belt that stalls on starting. | Worn or wet lagging, too little take-up tension, too little wrap, material build-up, or an underbelted drive. | Lag the drive pulley, use grooved lagging when wet, add a snub pulley for wrap and set the take-up from the calculated tension. |
| Gouged or stripped top cover | Cuts, grooves and stripped rubber near the loading point. | Heavy impact, skirtboards set too tight, material hanging up in the chute or the wrong skirt rubber. | Improve the chute, add impact idlers, land fines first, and open skirtboard clearance in the direction of travel. |
| Splice separation or pulled fasteners | Splice opens, fasteners tear out or the belt breaks behind them. | A poorly made splice, pulleys too small, tension too high, trapped material or a short transition at the pulley. | Follow the splice procedure, use the specified step lengths, check the transition distance, and inspect fasteners on a schedule. |
| Stuck idler rolls | Flat spots on rolls, grooved bottom cover and a hotter drive. | Dust and water in the idler bearing, worn seals or no lubrication. | Walk the line with a hot-spot check and listening, replace seized rolls early and keep spillage away from the rolls. |
| Rain, ice and wet pulleys Moisture corrosion | Slip in wet weather and stopped belts in frost. | No cover, wind-blown rain on the return run or a wet drive pulley. | Use half or three-quarter covers, wind breaks and wind hoops where needed, and grooved lagging on the drive pulley. |
Lubrication
Idlers
Most idler rolls are filled for life. Check for hot rolls and noise rather than relying on a grease schedule.
Gearbox and drive
Check the reducer oil level at a static inspection and the condition of the drive belts or coupling.
Grease near the belt
Over-greasing idlers pushes grease onto the belt. Oil or grease on the belt can make the rubber cover swell in spots, so use only the amount needed.
Sealing
- Skirt rubber: Rubber edging on skirtboards seals the gap above the belt. It should rest lightly on the belt, contain no fabric and never be made from old belt, which wears the belt cover.
- Idler seals: Each idler roll is a sealed bearing unit in a dusty place. A worn seal lets dust in and the roll seizes. See Belt conveyors for the bearing view.
- Covers and shields: Half covers, three-quarter covers and wind breaks keep rain and sun off the belt and keep wind from lifting an empty belt off the rolls.
What to watch
- Belt tracking along the full length, loaded and empty, on both runs.
- Rolls that are seized, worn or caked with material.
- Splice condition, cuts, holes and fastener tightness.
- Lagging wear and material build-up at head, tail and snub pulleys.
- Take-up position and travel left, and the condition of skirt rubber.
- Drift switch, zero-speed switch, plug detector and pull-cord condition.
Questions
Which bearings are used in belt conveyor: belt, splices, take-up and loading zone?
Belt and splices · the part that carries the load: Choosing, joining and repairing the belt on any conveyor. Pulleys, lagging and take-up · drive, turn and tension: Head, tail, snub, bend and take-up positions on every conveyor. Idlers, loading zone and cleaning · supporting and protecting the belt: Between the pulleys, and especially at the loading point and the discharge.
What are the common bearing failures in belt conveyor: belt, splices, take-up and loading zone?
Belt runs off to one side: Off-centre loading, idlers or pulleys out of square or level, material build-up on rolls, a crooked splice or a belt that has taken a set. Belt slips on the drive pulley: Worn or wet lagging, too little take-up tension, too little wrap, material build-up, or an underbelted drive. Gouged or stripped top cover: Heavy impact, skirtboards set too tight, material hanging up in the chute or the wrong skirt rubber.
How should belt conveyor: belt, splices, take-up and loading zone bearings be lubricated?
Idlers: Most idler rolls are filled for life. Check for hot rolls and noise rather than relying on a grease schedule. Gearbox and drive: Check the reducer oil level at a static inspection and the condition of the drive belts or coupling.