Belt feeders are the backbone of high-capacity bulk material feeding in mining and heavy industry.
They can be designed to handle a great variety of bulk materials ranging from abrasive, large, lumpy iron ore to fine, wet, sticky filter cakes. Belt feeders use common, cost effective components and the method of operation and design principles are well understood.
“But there are limitations to belt feeders,” Bulk Handling Technologies (BHT) Senior Mechanical Design Engineer Sebastien Poulinet said.
“Feeders pulling out of very large hoppers tend to have very high tensions which typically require extremely large pulleys to meet the minimum radius requirements of stiff, heavy fabric belts or steel corded belts. The large pulley diameters increase the height of the feeder which in turn raises the entire hopper and structure. Steel corded belts can reduce the pulley diameters (and hence the height) when compared to heavy fabric belts, but they can be difficult to procure in short lengths and involve a complex hot vulcanisation process to correctly splice.”
An apron belt feeder eliminates the high pull-out tension carried by the belt by transferring this tension directly into two strands of dozer chain via connecting cross beams (similar to apron feeder pans). This allows small diameter sprockets which drive the chain, reducing the overall height of the machine when compare to the equivalent conventional belt feeder.
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They also remove the need for expensive, time consuming hot vulcanised belt splicing by employing a mechanical joint which is permitted due to the very low tensions on the belt.
“An extra feature of using sprockets on the apron belt feeder vs the pulley on the belt feeder is the elimination of belt slippage,” Poulinet said.
“A drawback of belt feeders is that they rely on friction to move the belt which necessitates the need for very high take-up tensions – especially if the belt and pulley are wet. This take-up tension must be always monitored as the belt will stretch over time, and so a continuous tensioning system (such as a gravity take-up) or regular adjustments are required.
“Apron belt feeders eliminate the need for friction for driving, by using a positively driven sprocket and chain. Typically tension only needs to be checked and adjusted annually as the chain wears.”
In situations where restrictions in the allowable hopper lip height exist (for example due to the maximum reach of a front-end loader) and the feeder is required to discharge at an elevation, often the capacity of the hopper must be compromised or an expensive FEL loading ramp must be installed.
Apron belt feeders however, can incorporate an incline bend, allowing the lower section to be low and horizontal with an incline after the feed hopper.
“This unique feature allows hopper volumes to be maximised, reduces the length of the machine and often eliminates the need for ramps altogether, “ Poulinet said.