35

C—3

with a collar upon it at a suitable distance from the end, and between this collar and the bottom flange of the sleeve are inserted, as required, a series of interlocking horse-shoe-shape plate washers, each half an inch thick (illustrated in Fig. II.). All that is necessary is, at the intervals of time corresponding to about half an inch Of wear of shoe and die, to slacken back the three keys, raise the sleeve, insert one of the washers, allow the sleeve to drop again, and tighten up the keys. No measurements whatever are necessary, and, so far as the operation of the stamp is concerned, the man in charge need not even know that a piston and port enter into its constitution. These washers fulfil the additional important function of compensating for the reduction in the total weight of the stamp caused by the wearing-away of the shoe. The tabulated statement in Fig. 11. shows that, in the case of a 1,4001b. "High-Speed" stamp, the gain in the crushing-capacity of a ten-head mill, due to compensation, amounts to no less than 4 tons per day, or 5-26 per cent. A y groove is turned in the bottom flange of the adjusting-sleeve to receive a rope by means of whichthe stamp is turned. The turning-gear, also illustrated in Fig. 11., is extremely simple and effective. Each set of turning-gear for one stamp consists of a small rope pulley fitted with a ratchet and carried on a pin at the end of one arm of a bell-crank lever, on the other arm of which is fixed a weight for the purpose of maintaining the required tension in the rope. The bellcrank lever is hung freely upon a shaft common to the set of five turning-gears, and to the same shaft is fixed an arm carrying a weighted pawl engaging with the lower portion of the ratchetwheel. A piece of ordinary rope establishes connection between the ratchet rope pulley and the rope groove on the adjusting-sleeve. By means of this gear its own reciprocating motion is utilised to effect the turning of the stamp. During the fall of the stamp the rope pulley is free to swing about the centre of the suspension-shaft, and to turn around its own centre, and therefore no transfer of rope takes place to create a turning moment about the axis of the stamp. On the lift, however, the rope pulley is prevented from turning around its own centre by means of the pawl, and consequently a transfer of rope takes place to provide for the difference in the lengths of the two sides of the rope created by the angular motion of the sleeve relatively to the rope pulley, and to permit of this transfer taking place the stamp has to turn. There are many more or less obvious methods of causing a recriprocating stamp to turn regularly at any predetermined rate ; but after an unsatisfactory experience with several gears of the frictional type it was realised that any frictional or positive gear embodying more or less rigid parts would not withstand the hard wear-and-tear accompanying a high speed under the trying conditions existing in a stamp-mill. It was therefore decided that the gear must be connected to the stamp by means of a flexible connection, and that the motion of its parts should be as small as possible. It will be seen, on an inspection of the " High-Speed " stamp-battery illustrated in Fig. V., that the turning-gear can be conveniently placed under the platform above the feeder. The holding-up gear is illustrated in Fig. 111., and its action is so simple and obvious that there is no need for any explanation. It may be pointed out, however, that it has to be called into use only when it is necessary to change the shoes and dies or clean out the mortar-box, because when it is only desired to stop a stamp, without having it raised above the die, it is readily accomplished by means of the cylinder drain-plug described above. In Fig. IV. is shown a typical modern ten-head cam-stamp mill, suitable for 1,150.1b. stamps running at ninety-five drops per minute, and in Fig. V. is shown the same mill converted into a " High-Speed" gravitation stamp-mill with 1,4001b. stamps running at 132 drops per minute. It will be seen that the mortar-box, battery-framing, floor, platforms, and feeder remain unaltered, whilst the old heads are utilised, the additional weight being partly obtained by means of auxiliary heads, which are very similar to the chuck-shoes sometimes used. The portions of the cam-stamp mill which are dispensed with are the cam-shaft, cams, bearings, stems, tappets, upper guides, and the jack-shaft and finger-posts. The general construction of the " High-Speed " stamp will be understood from an inspection of Fig. V. The five-throw crank-shaft D, which can be designed for any required order and height of drop, is carried in seven bearings formed in the cast-iron entablature E, which is bolted to two special beams B, attached to the king-posts of the battery-framing. The cylinders are each guided by two round guides G, connected to the top and bottom cast-iron crossbeams F, which are carried by two cast-iron side frames, bolted to the entablature. The component parts of the machine being thus rigidly connected together, the maintenance of their true relative positions is therefore quite independent of the timber framing; whilst in cases where the weight is not too great for transport, the machine complete, with the connecting-rods, cylinders, and pistons, can be fitted together in the makers' shops, so that when it arrives at the mine it can be easily and speedily erected in place. In the case of the relative weights and numbers of drops per minute (of the same height) assumed above, and which represent a perfectly normal example of conversion, the crushing-capacity would be increased by 70 per cent, as calculated below: — 1,400 Ib. x 7** x 132 IK ™, ~ . . - .. J = 115,500 ft.-lb. per minute. LA 1,150 lb. x 7j" X 95 = 68,280 ft.-lb. per minute. 12 47,220 Difference = 69 per cent. On this basis :— 14 "High-Speed" stamps are equivalent to 25 cam-stamps. 30 „ „ „ 50 60 „ „ „ 100 120 „ „ „ 200