Fine Rock Crushing with Jaw Crushers

Fine Rock Crushing with Jaw Crushers

The introduction of a new machine for fine crushing, or The Blake multiple-jaw crusher, which, in combination with the ordinary Blake breaker, could be used in the reduction of ores or any hard and brittle substance to almost any degree of fineness.  How can you use a jaw crusher to crush fine enough to feed a ball mill?

The construction of the multiple jaw-crusher, since the date of my first paper, is the same, except in the substitution of main swinging, instead of main sliding, or toggle jaw,—thus doing away with the upward thrust on the tension rods and the wear incident thereunto. (See Fig. 1.) It has also been found, in case of the fine crusher, that is, in machines of not over ½ inch width of opening, that the use of several small machines with a series of jaw openings, say 15 inches by ½ inch, is better than one large machine with a series of openings 24 by ½ inch, or 36 inches by ½ inch, as at first constructed. Many details of the method of holding in jaw-plates, etc., have been perfected.

Without giving any details with respect to the different mills built upon the Blake system, let me state that, although it has proved possible to carry any hard and brittle material with crushers alone to a fineness such that all particles will pass a 30-mesh wire screen, still the economical limit of such crushing will be found somewhere between 14 and 20. If it is necessary to carry all the material to a fineness greater than this, the system must be supplemented with other arrangements. Furthermore, the material to be operated upon must be sufficiently dry to screen readily, to take out the fine as rapidly as made, or fed with such an excess of water as will insure successful screening. It is, of course, evident that if fines are not removed as rapidly as made, there must be an accumulation and consequent slowing down of feed, and greatly diminished product, or a stoppage.multiple-jaw-crusher

The first mill on the Blake system was that built for the Chateaugay Ore and Iron Company in 1882, which was designed to crush two hundred tons per day down to pass a quarter inch round hole. This was run at irregular intervals, and idle much of the time up to the summer of 1886, owing to the depression of prices of iron ore. Since the summer of 1886 it has been running continuously, crushing many thousands of tons of the tough magnetic ores of that company. I am not informed as to the exact product and cost of operations of this mill, but they have been approximately the same as that of a mill of treble the capacity built for the same company oil the same general plan in the summer of 1886, for exact and accurate details respecting the operations of which I am indebted to the Chateaugay Ore and Iron Company, and enabled to give statistics which will be found in another part of this paper.

The second mill of any considerable magnitude is that of the Haile Gold-Mining Company, Lancaster County, South Carolina. The gold-ores derived from the different veins or mines upon the property are altered magnesian slates. That of the “ Blauvelt ” mine is a very tough, coarse quartzite, carrying a large percentage of sulphurets. Free gold is rarely, if ever, found in these mines. For purposes of amalgamation, the ore must be crushed extremely fine.

The mill was built in the most substantial and durable manner, timbers for the frame-work of any required dimensions being readily obtainable and cheap. Power was derived from a 150 horse-power Harris-Corliss engine and three 60 horse-power boilers, and the plant was complete in the three departments of crushing, amalgamating and concentration. As at first arranged, the crushing appliances of the system consisted of one 20 by 10 Blake breaker, the product of that going to a 30 by 5, product of the 30 by 5 going to two 60 by 2 multiple-jaw crushers, each with three jaws, receiving capacity of 20 by 2 inches. The product of the 60 by 2 multiple crushers, approximately of corn-grain size, was elevated and screened through one-quarter inch holes. That which did not pass the holes of the screens went to finer crushers. The material, ¼ inch fine and finer, was elevated, screened through 40-mesh wire screens, and all that did not pass 40-mesh, that is, material between ¼ inch and 40- mesh, went to two pairs of Krom’s new swinging-block rolls, each 30 inches in diameter and 16 inches face, main driving pulleys 8 feet in diameter, 14 inches face. The product of the rolls was discharged into No. 2 elevator, elevated and screened; that which would not pass 40-mesh returning to them, together with the new supplies of coarse material from the fine crushers. The finer crushed product, 40 fine and under, was discharged from the spouts of hoppers beneath the fine screens, where it encountered a stream of water, mixing it and conveying to 10 Atwood amalgamators in two groups of 5 each. The “pulp” from each group of amalgamators, discharged at their lower ends, was carried by troughs to 20 Embrey tables, two groups of 10 each, arranged in pairs, each pair being fed from a spitzkasten on the line of the troughs conveying the pulp.

The final discharge of superfluous water and finest slimes was opposite to the central point of the concentrating room, where the flow of tailings from the two groups of Embrey tables (10 in each) was united, and finally discharged into the waste weir.

It is evident that from the 30 by 5 crusher on, the rest of the mill was arranged in two symmetrical halves, either of which, in case of necessity, could be run independently of the other. As so arranged, about 1000 tons were put through the mill, when it became evident that a change was imperative. The Krom rolls, one pair on each side of the mill, were the chief cause of frequent stoppages, often becoming surcharged and coming suddenly to a full stop, resulting either in throwing the belts or their slipping upon the pulleys, running at about 100 revolutions per minute.

Although the greatest care was taken to insure their being properly fed, this surcharging would happen. The shells or tires had in crushing 500 tons each worn down one-quarter inch; that is, one-half in the entire diameter. The surfaces had become more or less pitted and corrugated. The returns to them were increasing rapidly, and the cost of the wear of the wire cloth had been at least $1 per ton. It became evident that for purposes of fine crushing their use must be abandoned.

Accidental knowledge of the results obtained by many years’ use of a Chili mill at glass-sand works, near Pittsburgh, Pa., led to the immediate substitution of two Chili mills (see Figs. 2 and 3) for the two pairs of Krom rolls, and running the material after being crushed to one-quarter inch wet instead of dry. This proved at once to be a solution of the question of crushing and the difficulties of fine screening.


The capacity of these mills, run as they were, was something wonderful,—no one who has not seen one run as it should be can form an idea of the rapidity, economy and certainty of their work, when dealing with material already carried to one-quarter of an inch and finer. The central spindle, carrying horizontal axis on which the wheels revolved, had a speed of 40 revolutions per minute. Each wheel of the mill, weighing about a ton, was 4 feet in diameter and 8 inches face. The distance from outside to outside of the wheels was 50 inches, and the tires were of hard white iron, having a cross-section 8 by 8 inches. The segmental dies on which the wheels ran were of best chilled iron. The shallow pan holding the dies was surrounded by an enclosure of sheet iron 4 feet high, to prevent water and ore being thrown out by the splash of the rapidly revolving wheels. On each side of each Chili mill was a revolving tub-shaped screen, 8 feet in diameter and 18 inches face, turning on a horizontal axis extending from the side furthest from the mill.


The outer periphery of this was covered with wire cloth 35 meshes to the linear inch, of the coarsest possible steel wire, equivalent to 40 meshes to the linear inch with wire of ordinary fineness. The inner periphery of this tub-shaped screen, provided with a rim about 4 inches deep, was divided into six segments by wooden pieces across its face, forming so many buckets which served to elevate the material which failed to pass the screens, and throw it on to an apron which carried it back to the mill. This screen was run in water, submerged to the depth of the rim,—i. e., about 4 inches,— and at the rate of 12 revolutions per minute.

No screens were used in the Chili mill itself; the crushed ore issued from openings on opposite sides and was, by the aid of water, discharged on to the inner periphery of revolving screens.

The substitution of Chili mills for the rolls, and the adoption of the wet method, had solved not only the problem of crushing, but that of screening. The wear of the wire cloth was at once reduced to about 10 cents per ton, and the two Chili mills proved their capacity to readily handle 7½ tons per hour of the hardest and toughest quartzite from the Blauvelt mine—on the softer and in some cases decomposed ores, as high as 20 tons per hour were put through them ; in fact, the crusher could not supply the amount of softer ores they were enabled to handle.

As so arranged, the mill was run, crushing about 3000 more tons of ore. Very great improvements in economy of screening could be made, but all alterations had been made under the greatest pressure, and within the shortest possible limit of time. Material one-quarter of an inch coarse should not be thrown on to wire cloth 35 to 40 fine, especially when containing a large percentage of heavy sulphurets, as was the case in this instance, but should first go to a hydraulic separator or coarser screen. Only the approximately sufficiently fine should go to the screens, the remainder being carried back to the mill without touching the wire cloth.

For purposes of amalgamation, where concentration is not desired, it is evident that the use of the Richards-Coggin hydraulic separator would enable one to dispense with screening entirely. As to the power required, the mill showed the greatest possible economy. It was often run with capacity of 7½ tons per hour, with boilers carrying only 40 pounds of steam; engine with 80 pounds of steam rating at 150 horse-power, and I think with consumption of about 4 cords of wood per diem.

The following is a statement of percentages of different fineness of the finished pulp from the Chili mill, from sample taken and tested by Mr. Raymond, assayer of the Company:


It is to be hoped that Mr. E. Gybbon Spilsbury, then general manager and now consulting engineer of the Haile Gold-Mining Company, will in time give in detail many points and facts here necessarily omitted. I am without special items of cost of milling per ton of ore in the Blake mill at the Haile mine, and can only state in a very general way that it showed great economy of power and material after the introduction of the Chili mills. Its operations were not sufficiently great to determine the real facts with accuracy. Enough was shown by its working to prove that mills on this system for crushing and amalgamating or concentrating, or both, may in future come into general use, that their economy per ton of ore crushed, of power and material, is greater than that of the stamp mill, and that there is no reason why they should not run with quite as much if not with more certainty and as continuously as the best stamp mill ever built.

In the summer of 1886 I furnished plans and machinery for a second mill on the Blake system to the Chateaugay Ore and Iron Co., Lyon Mt., N. Y. This was a complete crushing and concentrating plant, the crushing being done entirely by Blake crushers, and with a daily capacity of 600 long tons, from 15 inches down to ¼ of an inch, and it was built in accordance with plans shown in Figs. 4, 5, and 6. The iron-ores of this company are well known as being among the best, if not the best, Bessemer ores in the country. The deposit or vein of magnetic iron-ore is enormous, and the output from this mine often exceeds 1500 tons daily. The richer portions are sorted out and shipped, the leaner ores, consisting of magnetic iron-ore in grains, disseminated through a tough quartzose and feldspathic gangue, are sent to the mills for concentration. In order to effect this by jigging, with best results, it must be reduced to a size to pass a ¼-inch or 5/16 ths inch round hole. The jigs used are those known as the Conkling, with an annular revolving sieve and central discharge, said to be the invention of Mr. Hooper, of the American Graphite Co., Ticonderoga, and improved in some details by Mr. W. B. Hodgson, Superintendent of Separators for the Chateaugay Ore and Iron Co. The concentrates pass into a hutch from whence they are taken out by belt elevators. The capacity of one of the jigs, as run at Chateaugay, is 100 tons of crude ore in twenty hours, or 5 tons per hour. The elevation and plans of this mill, in accompanying plates, show very clearly its construction. The ore is brought to the mill by rail, in side dumping cars, carrying on the average 7½ to 8 long tons each from the various dumps one-quarter to one-half of a mile distant. It consists of two groups or systems of crushers, with elevating and screening appliances, each group being an exact duplicate of the other; a “jack-pulley” on main-line shafting being placed centrally between them. Power is derived from a 250 horse-power Harris-Corliss engine, and battery of three 100 horse-power boilers of Parks Bros, best steel. Each group consists of the following crushers, all of Challenge pattern, one 20 x 15, crushing from 15 inches to 2 or 2½ inches.

Product of each 20 by 15 is divided, going to two 30 by 5s.

Product of 30 by 5s is elevated and screened; that passing a ¼ inch round hole is finished product, as far as crushing is concerned, and is carried to the jigs. The “ coarse,” 1½ to ¼ inch, goes to three 60 by 2 Multiple Crushers, each with three jaw openings 20 by 2 inches. Product of these is elevated in No. 2 elevator and screened, formerly through holes ¼ of an inch in diameter, now through 5/16ths holes. That passing through the 5/16-ths screen-holes goes to jigs; that going through 11/16ths inch holes goes to two 15 by ½ fine-crushers. Each of the 15 by ½ crushers has 7 jaw openings, with 7 openings each 15 by ½ inch. Material not passing 11/16ths-inch holes, but going out the end of screen, goes back to the 60 by 2 Multiple Crushers. Product 15 by ½ fine-crushers is elevated and screened, material not passing 5/16ths-holes returning to them. Each group of crushers has three Conkling jigs.

The mill was completed and started September the 26th, 1886, and was run in a desultory sort of way until the organization of day- and night-shifts, October 18th following, when its operations may be said to have commenced. Its normal capacity on ore reasonably dry was shown to be 30 long tons per hour. This was the average amount crushed hourly up to the 8th of November; then a heavy snow-storm came and difficulties due to the presence of fine wet ore interfering with proper screening were encountered. Grizzlies were



put in at the 20 by 15 crushers, the idea being to take out the fine wet ore and send it to the wet screens below. This was fairly successful, but soon, owing to the rigorous climate of that latitude, bringing heavy snows and severe cold, the fine wet ore would freeze in solid mass on the dumps or in the cars bringing it to the mill, and would fail to pass the grizzlies, but go to the crushers. It would pass the


first two crushers well enough, giving no trouble, but by the time it reached the 60 by 2 multiple crushers the heat evolved in the crushing would thaw out the cementing ice, giving damp product which would not screen readily. In this way, or by imperfect screening, the actual product of the mill was greatly reduced, and notwithstanding the impossibility of sending the ore to the mill dry, or the absence of a sufficient supply of water to run the mill wet, and in that way obviate the difficulties of screening fine or wet and frozen ore, the mill has since that day been running uninterruptedly and continuously, day and night, to this time.

The actual amount crushed from September 26th, 1886, to January 1st, 1888, being 122,814 long tons or 137,551 short tons, at a cost for crushing and concentration of $42,200.55, or 34.36 cents per long ton or 30.67 cents per short ton, distributed as follows:


This economy is certainly remarkable, and still more so when we consider the prevailing unfavorable conditions as regards successful screening of the ore. Had the ore been reasonably dry instead of being generally wet and, during the winter months, frozen, or if the crushing after the passage of the 30 by 5 crushers had been “ wet” instead of “dry” and the screening in that way made perfect as it can be, the actual, average, daily product could have been increased, even doubled, and the cost of crushing and concentrating per ton of crude ore reduced to less than twenty-five cents. In a recent number of the Engineering and Mining Journal, January 28th, 1888, giving a description of the Tamarack steam-stamp, built by Messrs. E. P. Allis & Co., of Milwaukee, the capacity is given at 225 tons per day of 24 hours, on the basis of 34 to 36 tons of ore for every ton of coal consumed. In the Chateaugay mill the total consumption of coal in crushing from 15 inches down to ¼ inch, as opposed to 3 inches down to 3/16ths of an inch at Lake Superior, as proved by the results already stated, is one ton of coal to 68 tons of ore. If allowance were made for the coal used at Chateaugay mill in heating the mill itself and the water used in concentration, it is perfectly safe to assert that the Ball stamp, in its highest condition of development and efficiency will give crushed product in tons not more than half as great per ton of fuel burned as a mill constructed and run upon the Blake system. But the consumption of fuel in any method of stamping is, as a rule, a matter of small consequence compared to the losses due to the production of slimes not susceptible of concentration. This is, and must always be, an insuperable objection to their use where subsequent concentration or lixiviation are proposed.

If it were possible, and I believe it is, to so construct a crushing- plant consisting of crushers alone as to handle the copper-ores of Lake Superior, crushing first down to ½ inch or larger, then jigging, recrushing, and jigging again, and so on, it would certainly be a great improvement on the very simple but extravagant methods at present pursued. Certainly a large percentage of the loss there is due to the abrasion of copper beneath the stamp, necessarily involved in carrying all the material to 3/16ths of an inch before it can escape from the battery. Only costly experiment can determine this, but there is every reason to believe that multiple-jaw crushers can be built of such design and strength as to enable them to flatten out and pass masses of “ included copper ” which may by accident escape the attention of the attendant and go to them. Ordinary Blake crushers are and have been in general use at Lake Superior for many years in preparing the rock for the stamp; that is, in breaking it down to 2½ to 3 inches, pieces of metallic copper that will not pass the lower jaw opening being picked out by hand before going to them.

In the operation of multiple-jaw crushers as already built, the intrusion of foreign material, such as cast iron, bits of steel, pick, gad and drill points, is a frequent occurrence. They are either crushed or simply render the jaw in which they are found inoperative until they are removed, which is very easily done. No breakage of the machine has ever been known to occur from such causes. In a fine crusher I have known a ½ inch steel set screw to remain for a day and to be actually drawn down to a perfect wedge-shaped mass, without any injury to the machine. The packing of all the jaws with damp, fine ore intermingled with the coarse is a far more serious matter, and must be avoided by proper screening.

Experience has fully demonstrated this remarkable fact, that the Blake multiple crusher will do its work with as much ease and certainty and with greater absolute economy for wear and tear per ton of ore crushed, than an ordinary Blake breaker. The explanation of this lies first, in the multiplicity of jaws affording a safety provision, and secondly, in the economy of the use of the finest quality of hardened tool-steel for wearing-surfaces.

Whether the quartz-mill of the future will consist of a system of breakers supplemented by Chili mills or other fine crushing devices, remains to be seen. Certainly, if we combine the results of crushing at the Chateaugay mill down to ¼ inch and at the Haile mill from ¼ inch down to 40 fine by means of a Chili mill, we show the greatest possible economy in crushing. The wear on the Chili mills used at the Haile mine, in crushing 3000 tons of ore was, on the diameter of the wheels, ¼ inch; on the segmental dies, ¼ to 3/8 of an inch. The total wear of iron in these mills per ton of ore is easily calculated. On the four wheels of the two Chili mills it would be 156.64 pounds, and on the two sets of segmental dies it would be 205 pounds, making a total of 361.64 pounds, equal, on 3000 tons, to .12 of a pound of iron to a ton of ore.

It would seem probable that multiple-jaw crushers could be used with advantage in supplementing the ordinary crusher for preliminary crushing before feeding stamps. This is only true to a certain extent. But if the crushing be carried beyond a certain limit or down to coarse sand, for example, the practical result would be to reduce the product of the stamp mill rather than to increase its capacity. The reason of it is that ore so crushed, when fed to the stamps would simply bank up or pack beneath them. It requires coarse with the fine to “ root up ” the fine under the stamp and prevent its packing. It is probable, also, that if material were confined in a Chili mill by screens surrounding it instead of being sent to screens entirely outside of the mill, as was the case at Haile, it would pack beneath the wheels and the results have fallen short of those obtained.

The Blake crusher, as a machine, has an extended and enviable reputation for strength, simplicity, and durability. Their use in a “system” forming complete crushing plants has already led to many improvements and perfection in their details. Their combination in a system so as to run continuously and without interruption is indeed a matter demanding no inconsiderable skill, care, and experience. But the results at Chateaugay and at the Haile mine have been such as to completely demonstrate the economy of this method of crushing, and it seems to me that these results possess more than ordinary interest for the engineer.