SECTION IV.-BREAKING, CRUSHING, AND GRIND

ING ORES.

CHAPTER LXXVIII.

BREAKING AND CRUSHING.

Ores which reach the surface in large solid blocks require to be broken into fragments that can be easily handled before they can be placed in machines for reducing them to still smaller fragments, or to powder.

The sledge is the simplest and most common tool for this purpose; and it is followed by spalling hammers, until none of the fragments are much larger than the fist. Until within a few years this was the common and only way of breaking up ore into sizes suitable to be fed into the mortars of stamp-batteries, and it is still used where only small quantities are to be broken, and the extent of the operations do not justify the expense of obtaining suitable machines for the purpose.

HEAVY STAMPS.

The first attempts upon the Pacific coast to substitute machine for hand labor in spalling ore were in the direction of stamps of unusual weight, raised by cams to a height of four feet, and allowed to drop upou the mass of rock to be broken. Stamps of this kind, either single or two in a battery, were placed at the superb mills erected near Aurora, at the Real del Monte, and at the Antelope. They weighed 2,000 pounds each. There were no mortars, but a solid bed or anvil was surrounded with massive grates, made of bar iron, through which the fragments could drop. Masses of ore, from one to two feet in diameter, could be rolled in and subjected to a succession of blows. The two heads could break up about two tons an hour, but with an enormous expenditure of power, as is evident when we consider that for each blow a ton weight of stamp was to be raised four feet, and also that the smaller the mass to be broken the greater was the force of the blow. Thus when a mass of quartz, say six inches in height, lay upon the anvil, the stamp fell upon it from a height of three feet six inches; but when a block two feet high, which needed a much harder blow, was upon the anvil, the stamp fell only two feet. Similar stamps were in use at Washoe and at Virginia, but were soon abandoned because of their manifest defects and cost.

BLAKE'S ROCK BREAKER.

The machine for breaking up rock_now most in use is the invention. of Mr. Eli Whitney Blake, of New Haven, Connecticut, and is gener ally known as Blake's Rock Breaker. It was designed at first to break up trap-rock into fragments for macadamizing roads. Its value for breaking ores into sizes suitable for feeding to stamps or jigs was quickly seen, and in 1861 it was introduced into California. Its first operation in the mines was at the Benton Mills upon the Merced River. The ore

delivered there from the Pine-tree vein is noted for its hardness and massive character, and it required the constant labor of thirty Chinamen to spall enough to keep the stamps supplied. The same and a greater amount of work was better performed by the machine in a few hours, and effected a saving of seventy-five dollars a day, when sufficient rock was furnished to keep the machine running. From that time it has been extensively used, and is recognized as an indispensable adjunct to every well-appointed stamp mill.

The general construction of this machine has been rendered familiar by numerous figures and publications in the United States and in Europe. It consists, essentially, of a strong iron frame, supporting upright convergent iron jaws, actuated by a revolving shaft. The stones or masses of ore to be broken are dropped between these jaws, and a short reciprocating or vibratory motion being given to one or both of them, the stones are crushed, and drop lower and lower in the converg ing or wedge-shaped space, until they are sufficiently broken to drop out at the bottom. The size of the broken fragments may be regulated by increasing or diminishing the size of this opening between the jaws. But the construction and operation of the machine will be made more clear by the inspection of the annexed figure, accompanied by a description in detail of the various parts.

This figure is a sectional side view or elevation of the machine, representing the parts in place as they would be presented to view by removing one side of the frame. The parts of this figure which are shaded by diagonal lines are sections of those parts of the frame which connect its two sides, and which are supposed to be cut asunder in order to remove one side and present the other parts to view. The dotted circle D is a section of the fly-wheel shaft; and the circle E is a section of the crank. F is a pitman or connecting rod, which connects the crank with the lever G. This lever has its fulcrum on the

frame at H. A vertical piece, I, stands upon the lever, against the top of which piece the toggles J J have their bearings, forming an elbow or toggle-joint. K is the fixed jaw against which the stones are crushed.

This is bedded in zinc against the end of the frame, and held back to its place by cheeks, L, that fit in recesses in the interior of the frame on each side. M is the movable jaw. This is supported by the round bar of iron N, which passes freely through it and forms the pivot upon which it vibrates. O is a spring of India-rubber, which is compressed by the forward movement of the jaw and aids its return.

Every revolution of the crank causes the lower end of the movable jaw to advance toward the fixed jaw about one-fourth of an inch and return. Hence, if a stone be dropped in between the convergent faces of the jaws, it will be broken by the next succeeding bite; the resulting fragments will then fall lower down and be broken again, and so on until they are made small enough to pass out at the bottom. The readiness with which the hardest stones yield at once to the influence of this gentle and quiet movement, and break down into small fragments, surprises and astonishes every one who witnesses the operation of the machine.

It will be seen that the distance between the jaws at the bottom limits the size of the fragments. This distance, and consequently the size of the fragments, may be regulated at pleasure. A variation to the extent of five-eighths of an inch may be made by turning the screw-nut P, which raises or lowers the wedge Q, and moves the toggle-block R forward or back. Further variations may be made by substituting for the toggles J J, or either of them, others that are longer or shorter; extra toggles of different lengths being furnished for this purpose.

Machines are made of various sizes. Each size will break any stone, one end of which can be entered into the opening between the jaws at the top. The size of the machine is designated by the size of this opening; thus, if the width of the jaws be 15 inches, and the distance between them at the top 9 inches, the size is called 15 by 9.

The product of these machines per hour, in cubic yards of fragments, will vary considerably with the character of the stone broken. Stone that is brittle, like quartz, granite, and most kinds of sandstone, will pass through more rapidly than that which is more tough. The kind of stone being the same, the product per hour will be in proportion to the width of the jaws, the distance between them at the bottom, and the speed. The proper speed is about 180 revolutions per minute; and to make good road metal from hard, compact stone, or to prepare ores for stamps, the jaws should be set from 14 to 14 inches apart at the bottom. For softer and for granular stones they may be set wider.

The following table shows the several sizes of machines commonly made, the product per hour of broken stuff from the hardest materials, when run with a speed of 180; the power required to perform this duty; the whole weight of each size in round numbers, and the weight of the heaviest piece when separated for transportation.

The whole length of the machines to the back-side of the fly-wheels is from 8 to 8 feet; height to top of fly-wheels, 5 feet; width, from 4 to 5 feet.

The machine may be driven by any power less than that given in the table, yielding a product per hour smaller in the same proportion.

Either of the sizes mentioned will break quartz enough in a few hours to feed a forty-stamp mill for one day. A machine of less capacity would of course have a smaller mouth and would not take large stones. It is usual therefore for mill-men to use the largest mouthed machine, and to run it a few hours each day. The rough quartz in blocks as it comes from the mine being ready on the platform near the mouth of the breaker, two men can feed it into the machine and break it up at the rate of five to ten tous per hour, according to the size of the machine.

Breakers have been made larger than any of the above for breaking very large blocks of ore. They are in use at Lake Superior, where they take in masses of ore eighteen inches in diameter by twenty-four in length, and crush them without difficulty. The fragments from these large breakers are received by two or three of the machines of the ordinary sizes and are broken again, so that the pieces will all pass through a two-inch ring. The metallic copper is readily picked out by hand from this broken ore. These large machines would be useful at many mines in California and Nevada, and would permit sledging to be dispensed with. The machine is made without the lever, and works very slowly, but without loss of power; since, when it is not crushing, the only power consumed is that required to overcome the friction, whereas with the heavy stamps, as we have seen, the greatest expenditure of power is when the least work is performed.

There are some modifications of the construction of this machine as here described. In England and France they are commonly made without the lever, the eccentric shaft being mounted on the top of the frame directly over the toggles. A pitman connects the eccentric shaft with

these toggles, and thus produces the oscillating motion of the jaw. This construction is shown by a sectional view as before, one-half of the frame being supposed to be removed. One only of the fly-wheels is represented. This is the form of the machine exhibited at the Paris Exhibition by the manufacturers under the patent in France. The mouth of this machine is expanded, hopper-like, so as to be more convenient for the reception of the masses to be broken. This may be a desirable addition in some cases, where comparatively small stuff is to be broken and is to be shoveled in from a floor lower than the mouth of the machine; but when the mouth is placed, as it should be, on a level with the floor of the dump pile, the hopper is not required.

The rock breaker may be successfully used instead of stamps to obtain either coarse or fine fragments suited to concentration. It has been attempted to increase the fineness of the product of the machine by placing an "obturator" or obstruction, such as a triangular bar of iron, under the outlet between the jaws, arranging it so that it can be raised or lowered by means of screws, in order to diminish or increase the size of the outlet for the delivery of the crushed stuff. The effect of this obstruction is to retain the stuff between the jaws until it is so much broken and comminuted that it will sift through the narrow slits left on each side of the bar. This method of operating may be successful with some materials but involves a considerable expenditure of power. It is also attended with some danger to the machine, since with materials that are easily impacted to a hard mass, the entire space between the jaws may become so tightly filled that some part of the machine must give way. The massive frame of a machine in California was broken asunder in this manner, simply by permitting the outlet between the jaws to become closed by the accumulation of a heap of broken stuff below it. Obturators have been tried; but the discharge from the machines is rendered so slow by them that they have been discarded as not practically valuable. A better way to accomplish the object is to first break the ores in an ordinary machine and then pass the fragments through a machine with a mouth 10 by 2 inches, the jaws of which move only about one-eighth of an inch and make 600 bites in a minute. Machines of this kind have been successfully used in preparing ores for jigs.

At the Churprinz mine, Freiberg, Saxony, two rock breakers are used to prepare the lead ores for the various concentrating machines. One breaker takes the rough ore as it comes from the mine and breaks it up into coarse fragments; these pass to a second breaker with the jaws set nearer together, so as to make fragments small enough for jigging. The finer portions of the first product are separated from the coarse by means of revolving screens.

The fragments of ores produced by rock breakers are better adapted in size and shape to the operation of concentration by jigging than the fragments made by rollers and stamps. When set coarse, for breaking. quartz to be fed to stamps, the product consists of masses which do not exceed a certain size, and this permits a uniformity in the action of the stamps which cannot be obtained upon quartz broken up by hand, since in the latter case there is great irregularity in the size of the masses, and, as a general rule, the hardest and toughest are the largest. With selffeeding batteries, it is very important that the ore should be uniformly broken, and machine-broken rock is especially well adapted to automatic feeding. When the masses fed into batteries do not exceed a certain size, the wear and tear of grates is less than when the size is irregular. It is easy also with breakers to reduce the whole quantity of the ore to