A mixture of lumps only in which 95% or more are lumps ranging from maximum size to one half of the maximum size; and 5% or less are lumps less than one tenth of the maximum size.
The Maximum lump size table shows the recommended maximum lump size for each customary screw diameter and the three lump classes. The ratio, R, is included to show the average factor used for the normal screw diameters which then may be used as a guide for special screw sizes and constructions. The allowable size of a lump in a screw conveyor is a function of the radial clearance between the outside diameter of the central pipe and the radius of the inside of the screw trough, as well as the proportion of lumps in the mix. The following illustration illustrates this relationship.