This machine is composed of one pair of fluted cylinders, x x, [fig. 628.], and of two pairs of smooth cylinders z z, z z, which serve altogether for crushing the ore. The two cylinders of each of the three pairs turn simultaneously in an inverse direction, by means of two toothed wheels, as at m, [fig. 629.], upon the shaft of every cylinder, which work by pairs in one another. The motion is given by a single water wheel, of which the circle a a a represents the outer circumference. One of the fluted cylinders is placed in the prolongation of the shaft of this wheel, which carries besides a cast-iron toothed wheel, geered with the toothed wheels e e, fixed upon the ends of two of the smooth cylinders. Above the fluted cylinders, there is a hopper, which discharges down between them, by means of a particular mechanism, the ore brought forward by the waggons A. These waggons advance upon a railway, stop above the hopper, and empty their contents into it through a trap-hole, which opens outwardly in the middle of their bottom. Below the hopper there is a small bucket called a shoe, into which the ore is shaken down, and which throws it without ceasing upon the cylinders, in consequence of the constant jolts given it by a crank-rod i ([fig. 629.]) attached to it, and moved by the teeth of the wheel m. The shoe is so regulated, that too much ore can never fall upon the cylinders, and obstruct their movement. A small stream of water is likewise led into the shoe, which spreads over the cylinders, and prevents them from growing hot. The ore, after passing between the fluted rollers, falls upon the inclined planes N, N, which turn it over to one or other of the pairs of smooth rolls.
These are the essential parts of this machine; they are made of iron, and the smooth ones are case-hardened, or chilled, by being cast in iron moulds. The gudgeons of both kinds move in brass bushes fixed upon iron supports k, made fast by bolts to the strong wood-work basis of the whole machine. Each of the horizontal bars has an oblong slot, at one of whose ends is solidly fixed one of the plummer-blocks or bearers of one of the cylinders f, and in the rest of the slot the plummer-block of the other cylinder g slides; a construction which permits the two cylinders to come into contact, or to recede to such a distance from each other, as circumstances may require. The movable cylinder is approximated to the fixed one by means of the iron levers X X, which carry at their ends the weights P, and rest upon wedges M, which may be slidden upon the inclined plane N. These wedges then press the iron bar O, and make it approach the movable cylinder by advancing the plummer-block which supports its axis. When matters are so arranged, should a very large or hard piece present itself to one of the pairs of cylinders, one of the rollers would move away, and let the piece pass without doing injury to the mechanism.
Besides the three pairs of cylinders which constitute essentially each crushing machine, there is sometimes a fourth, which serves to crush the ore when not in large fragments, for example, the chats and cuttings (the moderately rich and poorer pieces), produced by the first sifting with the brake sieve, to be presently described. The cylinders composing that accessory piece, which, on account of their ordinary use, are called chats-rollers, are smooth, and similar to the rollers z z, and z z. The one of them is usually placed upon the prolongation of the shaft of the water-wheel, of the side opposite to the principal machine; and the other, which is placed alongside, receives its motion from the first, by means of toothed wheel-work.
The stamp mill is employed in concurrence with the crushing cylinders. It serves particularly to pulverize those ores whose gangue is too hard to yield readily to the rollers, and also those which being already pulverized to a certain degree, require to be ground still more finely. The stamps employed in the neighbourhood of Alston Moor are moved by water wheels. They are similar to those described under [Tin].
Proper sifting or jigging apparatus.—The hand sieve made of iron wire meshes, of various sizes, is shaken with the two hands in a tub of water, the ore vat, being held sometimes horizontally, and at others in an inclined position. This sieve is now in general use only for the cuttings that have passed through the grating, and which though not poor enough to require finer grinding, are too poor for the brake sieve. When the workman has collected a sufficient quantity of these smaller pieces, he puts them in his round hand sieve, shakes it in the ore vat with much rapidity and a dexterous toss, till he has separated the very poor portions called cuttings, from the mingled parts called chats, as well as from the pure ore. He then removes the first two qualities, with a sheet-iron scraper called a limp, and he finds beneath them, a certain portion of ore which he reckons to be pure.
The brake sieve is rectangular, as well as the cistern in which it is agitated. The meshes are made of strong iron wire, three-eighths of an inch square. This sieve is suspended at the extremity of a forked lever, or brake, turning upon an axis by means of two upright arms about 5 feet long, which are pierced with holes for connecting them with bolts or pins, both to the sieve-frame and to the ends of the two branches of the lever. These two arms are made of wrought iron, but the lever is made of wood; as it receives the jolt. A child placed near its end, by the action of leaping, jerks it smartly up and down, so as to shake effectually the sieve suspended at the other extremity. Each jolt not only makes the fine parts pass through the meshes, but changes the relative position of those which remain on the wires, bringing the purer and heavier pieces eventually to the bottom. The mingled fragments of galena, and the stony substances called chats lie above them; while the poor and light pieces called cuttings, are at top. These are first scraped off by the limp, next the mixed lumps, or chats, and lastly the pure ore, which is carried to the bing heap. The cuttings are handed to a particular class of workmen, who by a new sifting, divide them into mere stones, or second cuttings, and into mixed ore analogous to chats.
The poor ore, called chats, is carried to a crushing machine, where it is bruised between two cylinders appropriated to this purpose under the name of chats rollers; after which it is sifted afresh. During the sifting many parcels of small ore and stony substances pass through the sieve, and accumulate at the bottom of the cistern. When it is two-thirds filled, water is run slowly over it, and the sediment called smitham is taken out, and piled up in heaps. More being put into the tub, a child lifts up the smitham, and lays it on the sieve, which retains still on its meshes the layer of fine ore. The sifter now agitates in the water nearly as at first, from time to time removing with the limp the lighter matters as they come to the surface; which being fit for washing only in boxes, are called buddler’s offal, and and are thrown into the buddle hole.
Mr. Petherick, the manager of Lanescot and the Fowey Consol mines, has contrived an ingenious jigging machine, in which a series of 8 sieves are fixed in a stationary circular frame, connected with a plunger or piston working in a hollow cylinder, whereby a body of water is alternately forced up through the crushed ore in the sieves, and then left to descend. In this way of operating, the indiscriminate or premature passage of the finer pulverulent matter through the meshes is avoided, because a regulated stream of water is made to traverse the particles up and down. This mode has proved profitable in washing the copper ores of the above mentioned copper mines.
Proper washing apparatus.—For washing the ore after sifting it, the running buddle already described is employed, along with several chests or buddles of other kinds.
1. The trunk buddle is a species of German chest (see [Metallurgy] and [Tin]) composed of two parts; of a cistern or box into which a stream of water flows, and of a large tank with a smooth level bottom. The ore to be trunked being placed in the box, the workman furnished with a shovel bent up at its sides, agitates it, and removes from time to time the coarser portions; while the smaller are swept off by the water and deposited upon the level area.