Conveyor belt tracking problems: causes and fixes

A belt that runs off centre wears its edge on the structure, spills along one side and, given long enough, tears itself. The reflex is to knock over an idler wherever the belt is seen wandering. Sometimes that is the fix; more often it moves the problem twenty metres downstream. Tracking is a diagnosis before it is an adjustment.

What is the belt telling you?

Before touching anything, note where the belt runs off and when, and whether the bad spot stays on the structure or comes round with the belt: a fault that passes once per revolution is in the belt, not the conveyor.

What should you check, and in what order?

Structure first, then rolling parts, then loading, then the belt. Fixing a later item while an earlier one is wrong gives a belt that runs straight on Monday and wanders on Tuesday.

• Structure square and levelA twisted or offset frame skews every idler on it. String-line the length, level the stringers, correct the steel first.
• Idlers square to the belt centrelineOne idler a few millimetres out at one end steers a belt: it moves toward the end of an idler it touches first.
• Pulleys parallel, level and squareHead, tail, snub and bend pulleys parallel to each other and square to the belt line; an unevenly wound screw take-up is a classic.
• No build-up on pulleys or rollsMaterial stuck to a pulley or roll makes it conical and steers the belt; usually it is carry-back the cleaners are missing.
• No seized or dragging rollsA roll that does not turn drags one side and wears a flat that makes it worse. Walk the return strand too.
• Loading centred, in the direction of travelA stream landing to one side pushes the belt the other way; the transfer point note covers landing it centrally.
• Skirt seals set evenlyA skirt rubber pressed harder on one side drags that edge; set both sides to the same light contact.
• Belt camber and splice squareLay a length flat and measure its bow; check the splice against a marked centreline. Neither fault can be tracked out with idlers.
• Tension and take-up correctToo little tension lets an empty belt float; a gravity take-up jammed or hanging off centre pulls the tail pulley crooked.
• Transition distance adequate at the pulleysWhere a troughed belt flattens onto a pulley the edges travel further than the centre; a short transition overstresses them. Commonly quoted as a multiple of belt width.
• Training idlers used sparingly, set neutralA self-aligning idler answers drift; it does not remove the cause. Fit them centred, for a small residual drift, never first.
• Weather on open beltsWind pushes a lightly loaded belt across the trough; rain or a leaking chute wets one side. Covers and repaired leaks count as tracking measures.

Which structural causes come first?

Alignment of the steel and the rolling parts is the foundation. Idlers answer to a string line and patience: adjust one, wait a few belt cycles, then the next. Pulleys come last, because a pulley moves the belt a long way either side of it. The idler selection note covers the transition and return sets that are tracking by design.

Why does a belt run true empty and drift when loaded?

Because the load is applying the force. A stream that lands off centre, or across the belt, pushes the belt away from itself until the trough re-centres it, at every start-up and every surge. When drift only appears downstream of the transfer, the transfer is the cause and the idlers are the victims.

What can the belt itself do wrong?

A belt that is not straight when unrolled, or a splice cut out of square, gives a drift no idler can correct, because it moves with the belt; the tell is that it runs off at the same point on itself every revolution. Damaged edges and covers of uneven thickness after a repair behave the same way. Raise camber tolerance and splice procedure with the belt supplier before the belt is cut.

What can training idlers do, and what can they not?

They hold a belt that drifts a little. They cannot cure an off-square structure, an off-centre chute or a cambered belt; used for that they work constantly, wear the belt edge and hide the problem until the pivot sticks. Knocking idlers over all along a belt to chase a drift is the other misuse: each moved idler steers, and the belt becomes sensitive to load, tension and temperature. Square everything first, then correct with as few idlers as possible, and mark each one you move.

Tracking is also a specification item: camber tolerance, transition geometry and training idler placement belong in the conveyor specification, and the components and spares we supply — idlers, pulleys, cleaners — are chosen with the belt they sit under in mind.