Belt or screw conveying for cement and powders

The question of whether to use a belt conveyor or a screw conveyor for cement and similar powders comes up on nearly every plant layout. The answer usually follows from distance, duty and dust control.

## Distance decides more than anything

A screw conveyor becomes expensive per metre as length increases, because screw and casing weight rise with the run and the drive has to overcome the friction. Beyond roughly 15 metres, a belt conveyor is normally cheaper to supply and much cheaper to run.

Below about 6 metres, a screw is usually the better choice: it is compact, it can be dropped into a tight plant layout, and it does not need the headroom a belt discharge demands.

## Dust and material behaviour

Cement, fly ash and fine powders behave well in an enclosed screw. A screw is dust-tight by design, which matters where a fine powder is being transferred inside a building and local air quality is regulated.

A belt is harder to seal. Covered belts are available and work well, but the transfer points – loading and discharge – still need capture and extraction, and those are the points that leak in practice.

## Where each one fails

– **Screw with wet or lumpy material.** Damp powder compacts and blocks the flights. If your material can get damp, either dry the feed or choose a belt.
– **Screw with abrasive minerals.** Wear accelerates sharply. Wear plate lining and segmented flights help, but check the wear rate rather than assuming.
– **Belt with fine powder in the open.** Wind losses from an uncovered belt can be significant, and the losses become a housekeeping and air quality problem.
– **Belt with very steep inclines.** Standard troughed belts manage about 22 degrees. Beyond that, you are looking at a different machine, not a steeper belt.

## A practical rule

For short, enclosed, vertical or near-vertical movement of powders inside a building, screw conveyors and bucket elevators do the job. For long horizontal or moderate-incline movement of aggregate, minerals or clinker, use a belt. Where a plant needs both, the layout usually decides itself once you draw the material route.