RULES / CONVEYING
Carry-back and belt cleaner selection
Carry-back is material that stays on the belt past the discharge. Nine rules for belt cleaner selection and set-up — primary, secondary, tertiary, wash box, V-plough — and what cleaners cannot fix.
Part of the guide: Transfer point design: dust, spillage and chutes
Every belt discharges most of its load at the head pulley and keeps a little. That little — fines pressed into the cover, a damp film, a smear of clay — travels round the return strand and falls off along the way. Per hour it is nothing. Per year it is the pile under the conveyor and the reason someone is shovelling next to moving parts.
What is carry-back, and what does it cost?
Carry-back is the material still adhering to the carrying cover after the belt has passed the discharge point. It leaves the belt along the return, so the costs appear far from the head pulley and are rarely charged back to it.
- Spillage along the return — a line of material under the conveyor, cleared by hand or not at all.
- Build-up on return idlers and pulleys — rolls go eccentric, pulleys grow a crust, and the belt starts to run off centre.
- Cover wear — material trapped between belt and pulley cuts the cover.
- Dust — dried carry-back is a dust source along the whole return.
- Housekeeping and safety — cleaning around a running conveyor is one of the commonest ways people are hurt on one.
How do we choose and set up belt cleaners?
Nine rules, in the order we apply them.
Clean at the head pulley first
The primary cleaner sits on the pulley face, below the material trajectory, and takes the bulk while the belt is fully supported. The secondary sits just past where the belt leaves the pulley and removes the film. Anything further along the return is tidying up, not cleaning.
Match the blade to the material
A polyurethane primary blade gives a compliant edge for bulk removal; a hard-metal tipped secondary holds a sharp edge against the fine film. Wet or sticky material may need a tertiary blade or a wash box; hot material needs compounds rated for it; dry dust on a cleated belt wants a brush.
More pressure is not more cleaning
Beyond the maker's setting, extra blade pressure removes no more material. It heats the cover, wears blade and belt faster, and lets the blade ride over a lump instead of shearing the film. Set the tension as specified and let the tensioner follow the wear.
Tension and inspect on a schedule
A blade wears, and the tension that was right last month is light now. Put cleaners on the same round as the idlers: blade contact across the full width, wear, tensioner travel, build-up behind the blade. A cleaner never adjusted becomes a roll of packed material.
Splices and covers set the ceiling
A mechanical splice is a row of steel across the belt and a hard-metal blade will catch it: use compliant blades or a vulcanised splice. Gouges in the cover hold material no blade reaches, and a thin, hard cover cleans worse than one chosen with the cleaners in mind.
Protect the tail pulley with a plough
Material landing on the inside of the return strand — spillage, a leaking chute, loosened carry-back — is carried into the tail pulley and crushed between belt and drum. A V-plough resting on the belt ahead of the pulley sweeps it off; it protects the pulley, not the belt.
Put cleaners where they can be serviced
A cleaner is a wear part with a tensioner to reset and a blade to change. Inside a head chute with no door, no room to slide the blade out sideways and no dust seal at the shaft, it is serviced once. Design the access with the cleaner.
Measure carry-back before judging
Scrape a known area of belt after the last cleaner, or collect what falls along a marked length of return over a set time. The figure, in grams per square metre, says whether a cleaner works and sets a target for whatever is changed next.
Cleaners do not fix a bad transfer
Wet fines pressed into the cover, a stream landing across the belt or a belt loaded to its edges make carry-back that cleaners chase and never catch. The transfer point note covers the loading side; the retrofit or replace note covers when a belt change should take the head end with it.
Which cleaner goes where?
| Cleaner | Position | Best for | Limits |
|---|---|---|---|
| Primary (pre-cleaner) | Head pulley face, below the trajectory | Bulk removal on most materials | Leaves a film; short blade life on abrasive material |
| Secondary | Just after the belt leaves the pulley, belt supported | The fine film; final cleaning | Catches mechanical splices; needs correct tension |
| Tertiary | Further along the return | Very sticky or wet material | Another wear part; diminishing returns |
| Wash box | After the secondaries, enclosed, with sprays | Sticky, wet or hygiene-sensitive duties | Needs water, drainage, frost protection |
| V-plough or diagonal plough | Return strand ahead of the tail pulley | Protecting the tail pulley | Does not remove carry-back; needs room to discharge sideways |
| Rotating brush | After the head, on the return | Dry dust; chevron and cleated belts | Clogs on damp material; needs a drive and enclosure |
Cleaners are among the components we supply and set up under equipment, components and spares, with the return idlers that suffer when they fail; the idler note covers rubber-disc returns for sticky duties.
QUESTIONS WE HEAR
How much carry-back is acceptable on a conveyor?
There is no universal figure; it depends on the material and on what the return strand runs over. Measure it — scraped from a known belt area, in grams per square metre — and set a site target. A well-set primary and secondary pair usually leaves a film that dries rather than piles.
Do I need both a primary and a secondary cleaner?
For most materials, yes. The primary takes the bulk at the pulley face and protects the secondary; the secondary removes the film the primary cannot reach. One blade asked to do both is over-tensioned, wears fast and still leaves a film. Dry, coarse, free-flowing materials are the exception.
Why does my belt cleaner stop working after a few weeks?
Usually because the blade has worn and the tensioner has not followed, or the blade was over-tensioned and wore quickly, or material has packed behind it. Occasionally the belt is the cause: a new splice, or cover damage. Inspection on a fixed round and a carry-back measurement tell you which.