Belt tracking is the most common call we receive about belt conveyors, and the most commonly mistreated. Tightening the belt or adjusting the nearest snub roller can move the problem a metre downstream. The seven causes below cover almost every case we have seen in the field.
Key takeaways
- Check the frame and pulley alignment before touching the belt tension.
- Most tracking faults appear at the head pulley, the tail pulley or the first idler after the load point.
- A belt that is cambered or spliced out of square cannot be trained by adjustment alone.
- Off-centre loading is a design problem, not an operator problem.
1. Pulley misalignment
The head and tail pulleys must be parallel to each other and square to the frame. A pulley that is out of square by 1 mm over a 500 mm width will pull the belt to the tight side. Check with a string line or a laser across the pulley faces, and measure the diagonal distances between the frame corners. If the frame is square but the pulleys are not, shim the bearing blocks rather than forcing the belt.
2. Uneven belt tension
If one side of the belt is tighter than the other, the belt will run toward the slack side. This often happens after a splice or after one take-up screw has been adjusted more than the other. Measure the take-up position on both sides and equalise it before adjusting anything else.
3. Off-centre loading
A belt loaded consistently to one side will migrate to that side. The load should be centred within about 10% of the belt width. If the feed chute or the transfer point cannot be moved, add a guide or a baffle to centre the product. Do not compensate with idler adjustment; the belt will track when empty and run off when loaded.
4. Seized or misaligned idlers
A single seized idler creates a flat spot and a drag on one side. A misaligned idler acts like a steering roller. Check every idler by hand for free rotation and alignment. On a long conveyor, walk the length with the belt stopped and look for idlers that are not perpendicular to the frame.
5. Belt camber or a bad splice
No amount of training will fix a belt that is not straight. A cambered belt curves to one side by nature. A splice that is not square creates a repeated kick at the same point in every revolution. Check the splice by measuring the diagonal across the joint. If the belt is cambered beyond the manufacturer's tolerance, replace it.
6. Build-up on pulleys or rollers
Material stuck to a pulley changes its effective diameter and pulls the belt. This is common with sticky products, in humid conditions or after a washdown that was not followed by drying. Clean the pulleys and install a scraper if the product tends to build up.
7. Frame distortion or insufficient support
A long frame that sags in the middle changes the belt path. Check the frame for level and straightness, especially on conveyors longer than 6 metres. Add support legs rather than shimming the existing ones if the frame is visibly sagging.
| Symptom | Most likely cause | First check |
|---|---|---|
| Drifts one way when empty and loaded | Pulley or frame alignment | Diagonal measurements, string line |
| Drifts only when loaded | Off-centre load | Load position at the feed point |
| Kicks once per revolution | Splice out of square | Diagonal across the splice |
| Drifts gradually over days | Belt stretch or take-up uneven | Take-up positions both sides |
| Noisy and hot at one point | Seized idler or bearing | Hand rotation, temperature |
The correct adjustment sequence
Start with the frame and pulleys, then the belt tension, then the load, and only then the training idlers. Adjust one idler at a time, a small amount, and run the belt for several revolutions before adjusting again. Moving two idlers at once makes it impossible to know which change had an effect.
If the belt still will not train after these checks, stop adjusting. A belt that has been over-tensioned to compensate for a misalignment will fail at the splice or the bearing. Replacing a belt is cheaper than replacing a pulley shaft.
Frequently asked questions
How tight should a conveyor belt be?
Tight enough to transmit the load without slipping at the drive pulley, and no tighter. Use the manufacturer's sag specification, typically 1–2% of the centre distance on the slack side. Over-tensioning is a common cause of bearing failure.
Can I train a belt while it is running?
Only with extreme caution and only on idlers designed for it. Adjusting a running belt can trap hands or tools. Stop the conveyor, adjust, then restart and observe.
Why does the belt track differently after a splice?
The splice changes the belt length on one side. If the splice is not square or the belt was not cut straight, the belt will steer. Re-splice or replace the belt; idler adjustment will not correct it.
If tracking problems persist after these checks, send a short video and the conveyor drawing to our engineers via the contact page. We also cover belt selection in the belt conveyor section.
