Fig. 5.
Comparison of the efficiency of the two types has shown that the revolving-trough type is the better, giving a larger output per unit time with a reduced consumption of power. [Figs. 4] and [5] show a vertical section and plan respectively of this type of edge-runner. The trough G is turned by means of a toothed crown gearing with the bevel pinion O mounted on an overhead shaft C driven by a belt pulley N.
The bearings of the vertical shaft J of the trough are situated at L and M. The runners H are loosely mounted on the fixed horizontal shaft E and revolve in consequence of the friction between them and the material in the trough. As the latter revolves, the material is continuously pushed aside by the runners, and is again brought under them by the action of scrapers.
The great advantages afforded by edge-runners, in consequence of their simplicity, easy management and low wear in comparison with other grinding appliances, have led to their reintroduction on a large scale. It should, however, be borne in mind that the edge-runner mill must be of a pattern suitable to the materials it will have to treat. The method of drive usually depends on local conditions. The revolving-trough type is chiefly useful for mixing, on account of the ease with which the materials can be charged.
The capacity of edge-runner mills depends on the nature of the material, the diameter and weight of the runners, the speed at which they are run, and also on the rate at which the reduced material is discharged in order to give place to fresh portions of the charge. This is effected by means of two sets of scrapers, the individual members of which can be adjusted in any direction. Their ploughing action also greatly assists the mixing effect.
Fig. 6.
[Fig. 6] illustrates an edge-runner mill with revolving trough and overhead drive; and [Fig. 7] one with stationary trough and bottom drive; both made by the Badische Maschinenfabrik, Durlach. The runners are of grey cast-iron, chill-castings or cast-steel being used for crushing hard materials. The trough in all cases is lined with detachable chill-cast plates. Special attention is bestowed on the lubrication of all the moving parts, and all the lubricators are easily accessible.
Fig. 7.