apart of the rollers and the fineness of the grinding can be adjusted. It will be seen that the driving-shaft of the machine is the lowest of the six shown. It drives by means of spur gearing roller number three, and through it the other rollers of the mill. No two rollers working together revolve at the same speed, and hence one rubs over the other, and they thoroughly grind the material between them. In the common three-roller mills it is necessary to pass the material to be ground through the mill twice, but in this machine one passage is sufficient, so that both time and floor space are saved, as the machine, it is claimed, does the work of two ordinary mills. Another noteworthy feature of this mill is that on No. 2 roller is a
Fig. 44.—Clark’s Patent Granite-roller Mill.
lateral motion giving a sidewise movement of ¾ inch. This is also applied to No. 4 roller, and gives the same movement. Each roller can be separately and easily adjusted by means of adjusting screws. The fifth roller is the delivery roller. The weight of No. 2 roller is carried by a strong spring fixed between the bearings of rollers Nos. 2 and 3, so that by the movement of the adjusting screw, the No. 2 roller can be brought down upon No. 3 with the required pressure.
The principle of mounting the rollers of most machines, is that the centre roll shall revolve in fixed bearings, and the two outer ones shall revolve in bearings made to slide backward and forward in grooves in the framework. There is no means of adjusting the rollers in order to keep them in perfect parallel plane, or to compensate for the wear of the brasses. The consequence is, that immediately the bearings begin to wear, the rolls are not then in parallel plane with each other, and the longer they work the worse they get; until they only grind a small distance in the centre of the roll, causing the machine not only to perform imperfect work, but the rolls to wear hollow in the centre.
Hind and Lund, Limited, of the Atlas Works, Preston, Lancashire, claim that in their machine ([Fig. 45]) these defects are entirely obviated. The centre roll is mounted in a similar manner to other machines, but the two outer rolls are hung upon excentric studs at each side. Should the journals wear at all unevenly, this is at once detached, and by a single turn of the excentric stud at either one side or the other as the case may be, the rolls are kept always in perfect parallel plane.
This machine is fitted with relieving apparatus for throwing the two outer rolls apart whilst working, in case of accident, or for cleaning purposes. Thus the machine may be run for an indefinite period without the granite touching, hence no wear can take place; while the rollers may be instantly put back to their working distances, just exactly as they were before the rolls were thrown apart.
As will be readily understood, this is a very valuable improvement, as the machine can be put in and out of actual grinding work as often as may be desired, without once altering the pressure upon the springs or the grinding distances.