To present all the particles of the material to the action of the chasers— which do not follow the same path, but roll upon annular portions of the bed-plate—scrapers (B) are set obliquely on and secured to a cross-bar, which is turned by the vertical shaft (b). These scrapers in going around gather the crushed material in the trough (C) and push it alternately out ward and inward, thus placing it for most effective crushing in the paths of the slowly-revolving chasers (A, 13), which, in consequence of their great weight and the differential motion of the surfaces in contact, exert not only a crushing effect, hut also a grinding one. Such machines can be driven by horse- or steam-power through the transmitting mechanism (c, a', e). Figure 6 (fii. 6) shows another form of chaser, in which the motive power is a steam-engine attached to the frame and acting on the bevel gearing at the top instead of at the base of the machine. In another form of the machine (fig. 7) the extremities of the shaft (a) are fixed against turning circumferentially, but are permitted to slide vertically in two slotted columns placed outside and clear of the trough (C), which is arranged to revolve and to carry the material around and under the peripheries of the cylinders. The scrapers are also immovable. The above-described edge-stone mills are extensively used in various manufac turing processes, especially where comminution and intimate mixture of the materials are required. In expressing oils they serve for crushing oleaginous seeds; in the pottery industry, for pulverizing the earths and stones; in building operations, for mixing sand and lime: they are also employed for the tempering of putty and in the manufacture of drugs, chocolate, etc.
singular application of the principle of the edge stone mill is exhibited by the quartz-crusher, shown in Figure 9. In place of the two heavy cylinders there are three wheels, which have their bearings on a centrally-guided triangular axle, and which are so placed as to roll in and around an annular trough, in which the material to be crushed is deposited. The crushing weight is secured by loading with stone or other materials the circular basin placed above and resting on the wheels. As seen in the Figure, the horses attached give rotatory motion to the basin, which causes the wheels to revolve by contact with the annular trough, and thus to crush the material.
The Cycloidal Mill (fig. 8) is a peculiar modification of the edge-stone mill (fig. 6). The two cones (E, F), which are driven by the vertical shaft (B) and the arms (C, D), move in a circle upon a conical granite bed-plate (A). They do not run, however, upon their peripheries, but upon their level ends; hence they actually slide. These cones (runners) are fitted upon the cylindrical pivots of the arm (C, D), so that they can revolve and rest with their entire weight upon A and the material placed upon it. The resistances upon the diameter of contact to be overcome by the runners being unequal, in making their circuit they revolve at the same time around their own axis, which insures their uniform wear. The entire grinding-apparatus is enclosed in a wooden or metal casing, which keeps the material upon A together. The introduction of the material is effected from the centre by means of a hopper placed at a higher level, while the removal is mostly left to the air, which, being slightly set in motion by the rotation of the runners, carries the most finely pulverized portion of the material over the edge of the casing. Hence, by surround ing the machine with a large wooden box, the finely ground product can be collected upon the bottom, and from time to time can be removed. This
arrangement, being especially suitable for the production of the finest dust like powder for pharmaceutical purposes (for example, gum-arabic), is ex tensively used in drug-mills. The name of the machine is derived from the cycloidal form of the tracks which the various points of the runners describe.
Roller Cru —111 the mills shown in Figures 1-3 (p1. 7) the grinding-surfaces arc cylindrical; two hollow cylinders roll upon each other, as in Figure 1, or a solid cylinder (A) revolves in a fixed concave (P), as in Figure 3. In the first form both cylinders revolve either at the same speed, though in all opposite direction to each other, whereby they exert only a crushing effect, or at different speeds, whereby a grinding effect is added to the crushing.
r represents in vertical section a malt-mill, chiefly employed in breweries. 'flue more finely the material is to be ground, the more closely the cylinders are set; so that, as in grinding flour, for which purpose cylinder-mills are now generally used, the circumferences of the cylinders run very near each other. The same is the case with mills which serve for the subtilization of dough-like materials (chocolate-paste, printers' ink, etc.), and whose arrangement is shown in Figure 2. The mate rial contained in the hopper (a) passes between the first two cylinders (b, , of which one (c) revolves at the greater speed. Now, as areas of equal size of the surfaces of these cylinders take along equal quantities of adhering material, it is evident that the larger portion of the latter is transported a greater distance by c. A further trituration takes place between c and the cylinder d, which latter runs at a still greater speed than c. The larger portion of the material being transferred to d, a third and a fourth tritura tion take place between the pair of cylinders d, c and c, f, until the mate rial is reduced to the requisite fineness, after which it is scraped from the periphery of the last cylthder by the blade g.
AM. —In the cylinder-mill, shown in Figure 3, a solid cyl inder (A) works in connection with a concave (B), the material being intro duced into the intermediate space from the hopper (C) by the feeding-cyl inder E). The adjusting-screws b) serve to regulate the interspace between A and B according to the condition of the material itself and the degree of fineness to which it is to be reduced. By the cylinder (A), revolv ing toward the left (in the Figure), the sufficiently ground material is car ried to a funnel-shaped space (F), through which it leaves the mill. The arrangement shown here is of interest, as in a slightly modified form it is met with in the so-called " Hollander," used in preparing paper pulp.
The Gates (fig. 4) consists of a pair of Cornish rolls inside of and surrounded by a revolving screen, which has elevating buckets on its inner surface for returning the partly-crushed material repeatedly back to the rolls until it is crushed fine enough to pass through the screen. The machine is simple, compact, and free from noisy and expensive gearing, the whole of it resting upon and secured in line on a strong iron bed-frame cast in one piece. The roller-shells are sepa rate from their shafts, for inexpensive renewal. The rolls are driven separately, but at the same speed, and give a finished product direct from the one machine. The battery of springs gives the desired pressure. The journals of the rolls are large and well provided with ample bearing-sur face and means for lubrication.