Originally Posted by Simon McConnell

We installed a new screw conveyer for petcoke (similar to coal) feeding a bowl mill. The conveyer is inclined to about 20 degrees and the shaft is made out of steal. The petcoke sticks on the shaft and the paddles, harden and stuff the conveyer. It is worse when petcoke is humid because of rain.

Well, there's a surprise

Ditch the shaft and use a centreless screw

(if you don't know what one is use Google http://www.google.com/ ) ■

Originally Posted by Simon McConnell

The screw lenght and power is too much for a centerless; there would be a twisting.

So what are it's dimensions? ■

There are usually two problems when dealing with damp, fine materials; one is sticking on the flight and shaft and the other is the formation of a hard boundary layer under the screw that imposes a high tip drag and also wears the flights if, in this case, the product is abrasive. A screw at 20 degrees inclination has a lower handling capacity than if it were horizontal as there is a greater tendency for material to be carried round with the flights. Brute force is not the answer to either problem.

The situation calls for an experienced appraisal based on full information. Send all drawings and photo to lyn@ajax.co.uk for a provisional assessment. ■