Table of Contents
- Methods of Crushing Stone without a Crusher
- Construction of the Blake Stone Crusher
- The Capacity of Blake Ore Crushers
Methods of Crushing Stone without a Crusher
Up to the date of the invention of the Stone Crusher, stone for road-metal was broken by hand, with the aid of a hammer having a long, pliant handle, and a round, ball-like head, illustrative drawings of which may still be found in standard dictionaries of engineering.
Crushing stone by hand has always been slow, monotonous, tedious work; an occupation suitable to convicts, tramps or denizens of the poor-house. And even now convicts and tramps are occasionally so employed, as, for example, at Buffalo, N. Y.
Ragging and Spalling
Crushing stone by hand was a common sight a few years ago along the macadam roads of England, but much of this work is now done by portable machine stone-crushers.
So, also, in the mechanical preparation of ores, crushing by hand was common, and is still required at the tin-mines of Cornwall, and in some other mining-regions, where hand-sorting is essential. But by means of the stone-or ore-crusher in most instances the work can be much expedited and cheapened. The broken-up ore being received, either upon a revolving table or upon an endless belt, is easily picked over and assorted.
Much of the crushing by hammers in Cornwall is done by women. A mass of ore upon the ground is held in place by the ball of the foot while subjected to a sharp and quick blow from the hammer. The first rough crushing, known as “ ragging,” requires a hammer or sledge from 6 to 8 lb. in weight, and the second operation, known as “ spalling,” requires a hammer weighing about 1 lb.
In ore and rock-crushing, up to the time of the invention of the Blake stone-crusher, besides the ragging and spalling by hand, ores were roughly crushed by rolls, generally known as Cornish rolls, with the construction and use of which we are all familiar. While this is a very effective and useful machine when new and carefully fed, the product lacks evenness and uniformity in size. A large mass of hard rock fed to the rolls separates them to such a degree that smaller rocks drop through without being acted on, and so escape crushing. The space between the rolls varies with the size and resistance of the masses fed in to it; with the rock-crusher, the greatest width of the opening is invariably the same and is predetermined at will. In the rolls there is great friction and wear by rubbing and sliding of rocks upon the revolving crushing-surface, resulting in the rapid wearing-down of the medial portion of the face of the rolls, by which a large space is left between them, and the effective operation of the machine is quickly impaired.
Construction of the Blake Stone Crusher
The construction of the stone-crusher is best described in the language of the inventor:
“ As respects its principles, or its essential characteristics, it consists of a pair of cast-iron jaws, one fixed and the other movable, between which the stones are to be broken, having their acting faces nearly in an upright position and convergent downward one towards the other in such manner that, while the space between them at the top is such as to receive the stones that are to be broken that at the bottom is only sufficient to allow the fragments to pass when broken to the required size; and giving to the movable jaw a short and powerful vibration through a small space, say one-fourth of an inch, more or less. By means of this form and arrangement of the jaws, and this motion of the movable jaw, when a stone is dropped into the space between them it falls down until its further descent is arrested between their convergent faces : the movable jaw, advancing, crushes it, then receding, liberates the fragments and they again descend, and if too large are again crushed, and so on, until all the fragments, having been sufficiently reduced, have passed out through the narrow space [between the jaws] at the bottom.”
The claims made by the inventor in his application for a patent, which was granted June 15, 1858, and was reissued January 9, 1866, were as follows:
” What I claim as my invention in the herein-described machine, and desire to secure by Letters Patent, is :
- The combination in a Stone-crushing Machine of the upright convergent jaws with a revolving shaft and mechanism for imparting a definite reciprocating movement to one of the jaws from the revolving shaft, the whole being and operating substantially as set forth.
- The combination in a Stone-crushing Machine of the upright movable jaw with the revolving shaft and fly-wheel, the whole being and operating substantially as set forth.
- In combination with the upright converging jaws and the revolving shaft imparting a definitely limited vibration to the movable jaw, so arranging the jaws that they can be set at different distances from each other at the bottom, so as to produce fragments of any desired size.”
These claims were approved and allowed by the Board of Examiners-in-Chief on appeal, after a full and careful investigation.
One of the earliest forms of the machine, known generally as the “ Lever-Pattern,” is represented by Figs. 1, 1a and 2.
Fig. 1 is a side-view, or vertical, longitudinal section through the center of the machine, showing one-half of the heavy, cast-iron frame in the background. Fig. 1a is a perspective view of the same machine.
Fig. 2 represents the machine as seen from above, and shows the two fly-wheels and the opening between the jaws. The lettering corresponds in both figures.
The operation of the crusher is evident from the inspection of these figures. It is driven by a belt upon the pulley C.
The revolution of the crank-shaft D E alternately raises and lowers the pitman F and the long arm of the lever G, by which the vertical I is made to rise and fall between the toggles J J, thrusting the movable jaw M forwards towards the
fixed jaw K. The return-movement of the jaw is effected by a rubber-spring O, which is compressed when the jaw is thrust forwards. At the back-end of the frame an arrangement of two wedge-shaped blocks R and Q (seen only in the section, Fig. 1) permits of shortening or lengthening the distance in which the toggles move, thus determining the extent of the throw of the movable jaw, varying the size of the opening at the lower or discharge-end of the jaw, and also taking up the wear on the ends of the toggles and other parts.
This pattern has always been a very effective and popular form of the crusher, and is by some, to-day, preferred to any other. The lever-machine is, however, heavier and more cumbrous than one in which the lever is dispensed with and the pitman F operates the toggles directly.
The Eccentric Pattern
This form is shown in section in the above illustration, Fig. 3.
This is now the prevailing, and may be said to be the standard, form of the Blake stone-crusher. It has undergone some minor modifications of form and construction by different makers, but remains essentially the same as it left the hands of the inventor. It was early introduced into England by Mr. Marsden, the former employe and agent of the manufacturers, who built the machines for England at Leeds.
Fig. 4 gives a good perspective view of the construction of a frame, in which the strain is received chiefly upon steel rods, as now made by the Llewellyn Iron-Works, Los Angeles, Cal. It represents the usual eccentric pattern, as seen from the rear end.
Fig. 5 illustrates the construction of the rock-crusher of the eccentric type as now built by the Union Iron-Works, San Francisco. It shows the rear end of the frame and the arrangement of the bolts, the top of the pitman and of the swinging jaw. This form is made in two sizes, 8 by 12 in. and 10 by 16 in.
The immense strain upon the frame of the crusher, especially in the larger sizes, necessitates a great thickness and weight of cast-iron; the frame of the 20- by 12-in. machine weighing no less than 10,000 lb. This great weight is avoided by many manufacturers by throwing the stress upon
wrought-iron or steel rods passing through, or along side of, the cast-iron frame, which secures a lighter frame with equal or greater strength than when made wholly of cast-iron.
The Challenge Pattern
In the “ Challenge crusher,” a form designed and manufactured by Theodore A. Blake, the sides of the frame are replaced by timber, the ends of the frame, only, being of cast-iron and connected by heavy rods of steel in the line of greatest tensile stress, near the bottom of the jaws, as shown in Fig. 6. This form of crusher is sectional, so that it can be taken apart for convenience of transportation; the weight of the heaviest piece, in the 15 by 9 in. size, being only 2,400 lb.
The following description of the “ Challenge,” understood to be from the pen of Prof. H. M. Howe, which appeared in the correspondence of The Engineering and Mining Journal, N. Y., of November 17, 1883, in regard to Metallurgy and Engineering, at the Boston Fair, so well describes the points of difference between the “ Challenge ” and the “Eccentric” pattern crushers that it is given in full.
The letters used in the following description refer to the sectional view, Fig. 6.
“ This improved form of our old friend, the Blake crusher, has such marked advantages over the older form that it is likely to supersede it. The form of Blake crusher, now called the ‘ Eccentric,’ consisted of a fixed jaw F, and a moving jaw J, actuated by a toggle-joint, all of which were contained and rigidly supported by a very strong cast-iron frame or box. The upper end of the movable jaw was fixed, and the lower end was moved by a toggle-joint driven by a pitman R H, somewhat as shown in the accompanying cut. Of course, when the pitman ascended, forcing the movable jaw toward the fixed one and crushing the ore between them, there was a tremendous longitudinal strain in the cast-iron frame which contained the two jaws, and against the ends of which the fixed jaw and the outer toggle pressed violently. To resist this pressure, the frame needed great strength, and consequently a large cross-section and great weight per unit of length. To avoid excessive weight, the frame was made short, which necessitated making the toggles O O short also. Now the proportion of the downward pressure of the pitman, which is resolved into horizontal pressure against the jaw J, depends on the angle which the toggles make with each other. If they are nearly parallel with each other, most of the downward pressure of the pitman will be resolved into downward pressure on the hearings T T, and but a small portion into horizontal pressure ; of course, economical working demands that as much as possible of the power be resolved into useful horizontal pressure and as little as possible into vertical pressure, which is simply rigidly resisted by fixed parts of the machine. Now, if we suppose, for simplicity, that in every case the toggles are, approximately, in a straight line with each other at the end of the pitman’s downward stroke, it should be evident that, for a given length of stroke of the pitman, the longer the toggles are, the less will be their inclination to each other at the beginning of the stroke. Thus efficiency demands length of toggles, which in turn requires excessive length and weight of the containing cast-iron frame.”
“ In the ‘Challenge’ crusher, which is represented in Fig. 6, the tensile strains are taken up, not by weak cast-iron, with its puny strength of, say, 20,000 lb., perhaps seriously weakened by cooling strains, but by light steel bolts, many times as strong per unit of weight. The upper end of the jaws is held together by the powerful steel strap C, and the bottom of the fixed jaws is held firmly by the strong steel bolts B, to the block B, against which the outer toggle presses. These bolts are in the plane of the toggles, thus concentrating the material near the line of strain. This arrangement permits us to increase the length of the toggles, and thus to get high efficiency, and at the same time to get a very much lighter machine. The upward pressure of the eccentric shaft S is taken up by the wooden beams A A. It is evident that, as the toggles wear, not only will the opening between the jaws, but also the obliquity of the toggles to each other, be increased ; and as that obliquity increases, so will the horizontal travel of the jaw increase.”
The Monarch Pattern
In the form of crusher known as the “ Monarch,” Fig. 7, the main frame is of cast-iron, but the tensile strains due to crushing are wholly upon wrought metal. The rear toggle-block instead of being a rigid part of the frame is pivoted at the bottom. The main shaft and eccentric are placed below instead of above the toggles. These crushers, as the name indicates, are made of great size and capacity. The weights of three different sizes are, respectively, 45,000, 50,000 and 56,000 lb., and to drive them, from 25 to 30 H.P. are required.
The Multiple-Jaw Pattern
In the preparation of ores for concentration, especially if the ores are intended for jigging, it is usually necessary to obtain much smaller fragments than are yielded by the operation of the standard patterns of the crusher, before described. To meet this need, Mr. Theodore A. Blake has devised a machine with several parallel jaws, the construction of which is shown by Figs. 8 and 9.
This machine will receive the product of the ordinary single-jaw Blake crusher, and crush down to one-eighth of an inch or finer if required. The principle of crushing is the same as in the Blake single-jaw crusher, i.e., by simple pressure between upright convergent faces. Instead of a single jaw, there is a series of jaw openings—in the illustration, four—each opening having a receiving capacity of 20 by 2 in. The main jaw has a reciprocating motion, given to it by
means of a toggle-joint, pitman and eccentric shaft, as in the ordinary crusher. The motion and pressure necessary to crush the material are transmitted to each succeeding jaw through the material itself. The multiplicity of jaws, besides giving a large discharging capacity, operates as a safety-provision. In case a piece of iron or steel should get into one of the jaw openings, the stroke which that opening would have is taken up by the others and no breakage or stoppage ensues.
In the illustration shown, each jaw having a receiving-capacity of 20 by 2 in., and there being four of them, it is evident that the capacity of the machine is equal to that of a single-jaw crusher with a receiving capacity of 80 by 2 in.
Crushing can be carried by multiple crushers to one-eighth inch, or even finer, with far greater economy than by any other
method. These crushers are intended to be used “ in series ” precisely as in the case of “ Rolls,” for which they are an invaluable substitute. The jaw-faces are strips of steel and can be inverted when worn, or wholly renewed in a few minutes, thus causing but little or no interruption to the work.
The product for purposes of concentration will be found to be unequalled; a smaller percentage of “ fines ” being made than by any other method of crushing.
For preliminary crushing, preparatory to further comminution, they will be found to be far more economical than rolls or any other known device.
They will do the work for which they are intended with as much ease and certainty as the ordinary Blake single-jaw crusher, and with even greater economy per ton of ore crushed.
Machines can be made of almost any size and required capacity to suit various conditions of use or requirements.
Movable Dies for Jaws
In the original rock-crushers no provision was made for a movable face-plate, or die, for the oscillating jaw, to receive the wear, so as to be discarded when worn and replaced by another. The jaw at first was cast in one piece, but the corrugated face was chilled. A movable die was not so important in the Eastern and Central States, where crushers were not far from foundries, and the cost of transportation of worn-out jaws was not great; but it was far different upon the Pacific coast, and the necessity of providing a movable face-plate, or die, for the oscillating jaw, early became apparent. This want was supplied by the writer for the California-made machines at the Union Iron-Works of San Francisco, where the first patterns and castings were made.
Fig. 10, a sectional representation of mouth and the fixed and swinging jaw of the rock-crusher, shows the form of the jaw-plates, or dies, g and d, as now made by the Union Iron-Works, San Francisco. These movable dies are made of cast-steel. They are reversible and are held in place by the dove¬tail lugs and the locking-keys e and c.
The form of the die was such that it could be reversed, end for end, and could be securely attached to the front of the ponderous oscillating jaw. Such movable, reversible jaw-plates, or dies, are now a recognized necessity in all rock-crushers, just as shoes and dies are required in stamp-mills and new shells upon rolls.
These dies are so constructed by the insertion of wrought-iron strips in the castings that a true plane-surface bearing can be secured by planing, rendering the use of white-metal bearings unnecessary.
Fig. 11 shows the form of hardened jaw-plate, or die, for the oscillating jaw, as manufactured by the Allis-Chalmers Co.
for the Blake rock-crusher. The figure gives a front-, side- and end-view; the front- and end-views show the corrugations. These dies are reversible, end for end, and are easily attached to the jaw by means of lugs and slots in the castings.
Fig. 12 shows the form of the fixed jaw, which is a plane rectangular block with a corrugated face, and is also reversible, end for end.
In order to avoid the wear of the frame of the crusher at the sides or ends of the opening between the jaws, movable plates are provided, known as cheek-plates, which on becoming worn are renewed at small cost. Fig. 13 shows the form of these plates by a front-view D B H, an edge-view G, and an end-view, or section, A.
The Capacity of Blake Ore Crushers
The capacity of all the Blake crushers is determined by the size of the opening between the jaws at the top. This opening, which may properly be called the mouth, varies in the smaller sizes from 2 or 3 in., in the laboratory crusher, up to from 30 by 12 in. to 30 by 18 in. in the Monarch, and to 24 by 24 in. in a still larger and exceptional size, specially made by the inventor for the Calumet & Hecla Co., Lake Superior, which takes in masses of copper conglomerate 20 in. or more in diameter, and breaks them up sufficiently to permit the pieces to be fed to crushers of ordinary capacity.
The 15 by 11 in. size may be termed a medium coarse crusher —it will receive rocks 11 in. thick and break to 3 or 4 in. It is used by miners and, to some extent, at smelting-furnaces.
The 15 by 13 in. is what is termed a coarse or preliminary crusher. It is made, also, with a 24 by 18 in. mouth. It is used chiefly at copper-mines. It receives large masses of ore 15 by 13 in. thick, or 24 by 18 in., and breaks them to 6 or 8-in. pieces, which are thus prepared for further reduction by the smaller crushers.
The production in tons in a given time, of course, depends not only upon the hardness and weight or gravity of the material broken, but upon the size to which it is broken, and the rate of feeding. The size of the broken stone or ore is determined by the distance the jaws are set apart. In a 15- by 9-in. machine, when the jaws are set 1.5 in. apart at the bottom and the machine is run at its proper speed, and diligently fed, it will break 7 cu. yards of quartz per hour, or nearly 10 tons. This large product often induces the selection of a smaller machine, losing sight of the fact that the usefulness of a crusher is determined by the size of the rocks it will receive, rather than by the amount which can be broken by it. The largest size of the Monarch form is capable of receiving and crushing a rock measuring nearly 30 in. in length and 18 in. in thickness. The medium-sized crushers, known as the 15 by 7 in. and the 15 by 9 in., are the sizes best adapted to general purposes and for crushing stone for Macadam roads and ballasting railroads and for concrete. They are also used extensively at smelting-furnaces, also at copper- and other mines, to take the product of the coarse crushers and reduce it to proper size for feeding under the stamps.
Position and Feeding of Crushers
The mouth of the crusher should not be raised above the level of the feeding-floor, but should be on the same level, so that rocks, or ores, may be easily pushed forward into the opening without being lifted. Crushers for effective service in the large way are not provided with hoppers to receive the material to be broken; the cheeks and the upper part of the oscillating jaw being sufficient to receive and hold the rock. It is necessary that the mouth should not be filled before starting a crusher. Feeding is deferred until the usual speed is attained.
In respect of feeding the rock-crusher, and in regard to the amount of ore broken, the following is pertinent, from the published memoir by John Hays Hammond, E.M.
“ The rock-crusher is placed directly below and in front of the coarse ore- bin. The chute leads from the gate of the bin into the jaws of the rock-crusher. The gate opening from the coarse ore-bin into this chute is worked by rack and pinion. By this gate the supply of ore delivered to the rock-crusher is controlled. This arrangement insures an almost continuous supply of ore to the rock-crusher, thereby greatly increasing the capacity of that machine. In most mills the coarse ore is discharged over the grizzly on to the rock-crusher floor, where it is picked up by the man who feeds the rock-crusher. This not only occasions unnecessary labor, but decreases the capacity of the rock-crusher through failure to keep it constantly supplied with ore. At the North Star mill [Grass Valley, Cal.], where the above arrangement has been introduced, one rock-crusher (15 x 9 in.) crushes from 30 to 40 tons of hard rock in from 5 to 7 hours, effecting a saving of wages of two or three men, as compared with the labor required in mills arranged according to the system generally adopted. As further evidence of the comparatively un-intermittent working of the rock-crusher, it requires 12 H.P. instead of 8, as is usually computed for machines of the above dimensions.” “Where the fall permits, it will be found advantageous to have two sets of rock-crushers, the first crushing coarse and delivering the crushed ore to the second set of rock-crushers, to be crushed finer than is the present custom. This would greatly increase the capacity of the stamp. The rock-crushers are adjusted to crush the ore to pieces smaller than from 2 to 3 in- The rock-crusher shoes and dies last from 6 to 8 months. When of steel, they wear about twice as long.”
At the Copper Cliff mine, Sudbury, Ontario, where the Blake crushers were used to break the ore for the roasting-heaps, the 15- by 9-in. machine had a capacity of about 20 tons an hour of ore, broken so that the largest pieces passed a 4-in. ring; the medium size a 1.75-in. ring, and the fines through a screen of 0.75 in.
In a description by A. J. Bowie, Jr., of the Father de Smet gold-mill, where the 15- by 9-in. size crushers were used, it is stated that the capacity of the mill was from 4400 to 5400 tons of quartz, and, with the addition of 2 more crushers, the capacity was increased to 6200 tons of quartz, and to 7000 when slate was milled. It was proved that in milling low- grade quartz there is great economy in large rock-crusher capacity.
The inventor claimed that each 15- by 9-in. machine would break at least 50 cu. yards of stone per day, doing the work of 100 men, and that the saving of cost per yard was at least $1, or $50 per day. But these figures are below, rather than above, those actually realized in crushing and in saving.
The nature of the material to be crushed or broken is an important factor. Hard, brittle rocks are broken up faster than soft, earthy rocks. The softer rocks or ores, especially if damp, do not fall through the machine as rapidly as dry rocks. They tend to pack and clog the crusher. For such materials a stream of water is sometimes fed into the machine to promote the discharge. Clean quartzose-ore is most readily broken.
Corundum, one of the hardest of minerals, yields readily to the jaws of the crusher. Emery-rock is another example. Abrasive machines or grinding-mills are speedily cut to pieces by these minerals, but in a properly-constructed crusher, without any sliding motion of the jaws, these typical abrasives are reduced, economically, with a minimum of wear of iron or steel.
Crushers at the Anna Ore-Dressing House, Pribram, Bohemia, in 1880, were made with jaw-openings 0.42 meter (16.5 in.) long and 0.25 meter (9.8 in.) wide, and gave 200 bites a minute of 4 mm. (0.16 in.) each. The material passing the three sieves went direct to jigs or in part to be re-crushed. The product between 1.5 mm. and 10 mm. (gries) was 10 per cent, of the amount crushed.