Ball Mill - for Cement/Powders

Typically you would not slope the ball mill to assist flow. The outlet end of ball mills (for grinding to powder) have a screen that lets the ground material out but not the grinding media. Just beyond the screen are lifters that lift and funnel the material to the outlet that goes thru the center of the trunnion. The lifters often are static spiral slides that raise the material as the mill rotates. The speed the material passes thru the mill is usually determined by feed rate, outlet screen percent opening and other attributes.

The feed going in a ball mill usually has a product distribution (like a histogram) and the product coming out has a product distribution (histogram). This means that how outlet product size is specified is very important. It could be as simple as saying "at least 95% of the output must be smaller than 200 micrometers" or as complicated as defining the whole size distribution.

Many mills with simple product specifications just pass the material thru it once. You control the maximum particle size by feed rate, media level etc. You might have a screener on the output to scalp off oversize. More sophisticated systems pass the oversize material thru the mill again. The oversize separation is done with equipment suitable to the product size. Oftentimes this would be screens or air classifiers and back to the feed end.