The Reduction of Quartz.

Cromwell Argus, Volume III, Issue 115, 23 January 1872, Page 6

The Reduction of Quartz.

(Thames Guardian, Jan. 9.J To some people it has often been a matter of surprise, that at the Thames goldfield, not a single “ore-crusher” has yet been employed. It is a well-known fact, however, that where mines have taken out of them auriferous stone at the rate of 200 tons and upwards per week, ore-crushers can bo used with great advantage, thereby enabling batteries to perform about double the usual amount of work. Amongst other well-known ore-crushing machines, there are Blake’s, Goodman’s, Archer’s, &c., but Blake’s are generally considered the best. These machines have two jaws ; the one fixed, the other moveable. Each revolution of an evcentric causes the lower end of the movable jaw to advance towards the fixed jaw about a quarter of an inch, and then return. Hence, if a stone be dropped in between the convergent faces of the jaws, it is broken by the next succeeding bite, the fragments then fall lower down, and are again broken ; —this process being repeated until the chipped stones are small enough to pass out beneath. The 15x7 machine, that is to say, the one which has jaws 15 inches long and 7 inches wide at top, requires 4 horse-power, and in 24 hours will reduce at least 100 tons of the hardest stone, from say 0 inches to 12, to the size of maize or nuts. The 20x9 requires 5 horse-power, and in 24 hours will reduce 150 tons, from say 8 inches to 16, to any size that may be required, as the distance between the jaws at the bottom can be regulated at | pleasure. Prior to the introduction of the I ore-crusher into mines, the ore was “ spalled” by hand-hamrpers, by hand-rollers, or by stamp’s weighing at least half a ton, and having a fall of several feet. Besides the ordinary kind of stamps, there are Wilson’s steam-stamp, Child’s atmospheric stamp, Beere’s spring stamp, Ac., &c., but the stamps most used are those which fall by their own gravity. The term “ battery” embraces the stamper, boxes, stamps, stamp-shanks, discs, shoes, false-bottoms, cams, cam-shaft, gratings, guides, and the framing. The number of stamps in a box vary from one to six, and considerable difference of opinion exists as to the most productive number of stamps in a box. Some people prefer two stamps in a box, with large openings in the end as well as in front, as it is found that the extra space for discharge greatly facilitates crushing, two stamps accomplishing as much work in that way as three would do with a front opening only. Others again are in favour of five stamps in a box, having front and back discharges, the stamps rising and falling in the order of 1, 3, 5, 2, 4, —1, 3, 5, 2, 4, and so on. Tiie discs used for raising stamps are of various kinds, viz. : —the plain disc with one or two keys, the screw disc, the screw disc in sections—as to be seen at the recent addition to the Caledonian battery,—and the “gib” disc, which is generally adopted in California. Cams are made with one, two, and three arms, and are sometimes made in two parts, so that in the event of one being broken, it can readily be replaced without the necessity of lifting the cam-shaft. Single-armed cams were tried at the New Zealand battery, Coromandel, but abandoned. In California, however, the use of the single-armed cam is pretty general, and it is said that it gives as many as ninety ten-inch drops per minute, with safety and economy. Even with a fly-wheel on the cam-shaft, the wear and tear must be something enormous, as the shaft revolving at the rate of ninety revolutions per minute must force the cams into violent collision with the discs, and as each disc carries a stamp some seven or eight hundred pounds weight, severe concussion must inevitably follow. The doublearmed cam, however, reduces the speed of the cam-shaft by half, thus enabling the disc to receive the cam much more gently; and the less the distance between the centre of the cam-shaft and the centre of the disc—that is to say, the closer the stamper-shank is to the cam-shaft—the less violent the concussion. If sixty blows per minute are wanted with a double-armed cam and a twelve-inch I drop, the cam-shaft must revolve at the rate i of 180 degrees in a second, and as each footfall occupies a quarter of a second, this gives 45 degrees for each fall, leaving 135 degrees for each pause and rise, the cam to be shaped I accordingly. But supposing that 120 blows i per minute are wanted, the cam-shaft must i revolve 360 deg. in a second, giving 180 deg. ; for each rise, fall, and pause. Gravity will only move at a given speed ; consequently, j for 120 blows per minute the’ height of fall must be greatly reduced. The throe-armed cam is useful when the ordinary fall of the stamp is increased in velocity by aid of springs, or otherwise, thus allowing double the number of blows to be given per minute, without catching the cams. The use of the spring enables a great reduction to bo made in the weight of the stamp, and instead of i the cam striking the disc at 700 ibs or SOOlbs, ! as in the ordinary stamp, it strikes only against 1501bs or 2001bs, the spring absorb-1 ing the further necessary power to give the | force of blow wanted. The spring-stamp is 1 perhaps the smoothest worker of all stamps, the force of fall being easily increased or di- I minished, so as to accommodate its crushing power to any quality of stuff that may be re-1 quired. In all cases it is necessary that the i shanks of stamps should work perfectly free | in the guides, so as to avoid heating, which i impedes the freedom of fall, and endangers the breakage of cams. Gratings arc generally made of Russia sheet-iron, of the very best quality-soft and tough ; a good test of which is to hammer a part of the sheet into a concave form. It has

been already stated that the larger the area allowed for gratings, the more is crushing facilitated. The same rule holds good with the number of holes in the gratings, for if a sheet of iron be perforated with a certain needle to the number of 10 holes to the lineal j inch (equal to 100 holes to the square inch), and another sheet perforated with the same j sized needle to the number of 12 holes to the j lineal inch (or 144 to the square inch), more | stone will be crushed with the latter than ! with the former. In the iron gratings menI tioned there are 10 or 12 holes to the lineal inch, but in brass-wire gratings there are 20 holes of the same size. By using wire gratings the quartz escapes as soon as it is reduced sufficiently fine to go through the holes, whereas by the use of thinly-perforated plate the stuff is over and over again thrown up against the spaces between the holes, thus materially retarding the progress of crushing ; and if tables are sufficiently wide to meet the increased production, there is certainly no good to be effected by retaining quartz in the stamper-box after it has been sufficiently crushed to admit of its escape.