US 3834631 A
A tensile-type crushing system combined with autogenous grinding. A symmetrical bowl-shaped element is rotated at high speed, and is autogenously lined with centrifuged material in process. Combined intermediate crushing, fine crushing and grinding is accomplished as pieces of feed material are accelerated by frictional contact with the autogenous bowl lining to high rotative or spin velocities about their own centers of gravity on their spiral path out of the bowl such that internal fracture is obtained when internal centrifugal force exceeds the tensile strength of the material itself. Simultaneously, additional crushing and grinding is obtained in compression and shear as a result of impact, abrasion and attrition between the particles themselves and the autogenous bowl lining in the process of acceleration in the bowl, and the process of deceleration in a surrounding stationary annular trap chamber, also autogenously lined in the impact zone of projected material with material in process. Some recycle of material projected from the rotating bowl is obtained by rebound from the trap chamber. A novel method of gyro-stabilizing the rotating bowl is used to compensate for unbalanced forces inherent in large size feed material. Efficient crushing is obtained by centrifugally induced tensile stress which requires less energy than crushing by compression stress. Contamination of product from manufactured linings and grinding media is minimized. The system may be employed with standard closed circuit screening, classification or concentration processes.
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Description (OCR text may contain errors)
United States Patent King SPIN BREAKING PROCESS  Inventor: Thomas C. King, Florence, Ariz.
 Filed: Apr. 18, 1973  Appl. No.: 352,226
 US. Cl 241/26, 241/275, 241/30  int. Cl. B020 19/00  Field of Search 241/5, 26, 30, 275, 284
 References Cited UNITED STATES PATENTS 1,228,338 5/1917 Marks 241/275 1,300,192 4/1919 Overstrom 241/275 X 1,911,568 5/1933 Higby 241/275 X 2,248,927 7/1941 Ainsa 241/275 X 2,562,560 7/1951 Macartney 241/275 X 2,906,465 9/1959 Sweet 241/275 X 3,302,895 2/1967 Ryder 241/284 X 3,326,476 6/1967 lzquierdo 241/284 X Primary ExaminerGranville Y. Custer, Jr.
[111 3,834,631 [451 Sept. 10, 1974 centrifuged material in process. Combined intermediate crushing, fine crushing and grinding is accomplished as pieces of feed material are accelerated by frictional contact with the autogenous bowl lining to high rotative or spin velocities about their own centers of gravity on their spiral path out of the bowl such that internal fracture is obtained when internal centrifugal force exceeds the tensile strength of the material itself. Simultaneously, additional crushing and grinding is obtained in compression and shear as a result of impact, abrasion and attrition between the particles themselves and the autogenous bowl lining in the process of acceleration in the bowl, and the process of deceleration in a surrounding stationary annular trap chamber, also autogenously lined in the impact zone of projected material with material in process. Some recycle of material projected from the rotating bowl is obtained by rebound from the trap chamber. A novel method of gyro-stabilizing the rotating bowl is used to compensate for unbalanced forces inherent in large size feed material. Efficient crushing is obtained by centrifugally induced tensile stress which requires less energythan crushing by compression stress. Contami nation of product from manufactured linings and grinding media is minimized. The system may be employed with standard closed circuit screening, classification or concentration processes.
cznssrnsns cnncrurlmrnns PRUDUBTS ovsnslzsf ELEVATOR PAIENTED SEP 1 01974 sum 10F FEED MATERIAL SCREENS GLA SSIF IE RS GUNGE N TRA TORS ELEVATOR PRUDUG T8 0 VE RSIZ E PATEN'I'EUSEP 1 01974 sum 2 BF 5 UIUL Z 1 SPIN BREAKING PROCESS BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates to comminution, and comminution by tensile-type forces in the size ranges classified as intermediate crushing, fine crushing, and grinding. More particularily the present invention relates to an improved system for crushing and grinding solid material, especially hard, abrasive, or brittle materials whose tensile strength is less than their compressive or shear strengths; and, to an improved autogenous system for crushing and grinding utilizing centrifugal force. The present invention further relates to gyrostabilization of rotating elements designed to accelerate pieces of material to high individual rotational or spin velocities, and to means of pulling apart minerals and crystals at grain boundaries by tensile forces to effect a greater degree of liberation. The invention further relates to processes for minimizing contamination of comminuted product by manufactured linings and grinding media, and to improvements in efficiency of Comminution by taking advantage of the greatly re duced energy required to fracture materials in tension, rather than crush them by compression as is done in the present state of the art.
2. Description of the Prior Art In recent years industrial demand for beneficiated materials such as aggregates, slags, abrasives, ores and minerals has been on the rise, while methods employed for crushing and grinding have changed little in the past 50 years.
Comminution is normally the first step in beneficiation of solid minerals and materials. It is usually a stage process, utilizing in the successive steps machines especially suitablefor reduction of particular sizes. The stages, starting with the crude material as mined, guarried, or otherwise obtained or manufactured, and comprising successive reduction steps down to a final stage or stages employed for the production of finest. sizes, are called crushing. In contradistinction, comminution of 2 -mesh or finer is called grinding. There is a twilight zone in which the product is from .6-mesh to 14- mesh limiting size, which is either crushing or grinding according to the type of machine used. Primary crushing is the first crushing stage; secondary srushing isthe second stage, etc. Coarse crushing includes crushing operations discharging at sizes 4- to 6- or 8-inch maximum and making products down to one-half-or threeeighth-inch; fine crushing is reduction by crushing to one-fourth-inch or finer; the distinctions are not sharp.
Crushing is a mechanical operation in which a sufficient force is applied to relatively brittle solid particles in such directions that failure of the bonding forces in the particles is brought about. When the problem of crushing is thus approached, it becomes clear that crushing machines must be designed to exert either pushes or pulls on the individual particles, since there are no other kinds of'mechanical forces, and that the solid particles must be so introduced into and maintained in the force zone that the forces available can be applied to them. The study of the mechanics of materials has resulted in a classification of mechanical forces and of the structural elements for resisting them which, applied in reverse, supplies a terminology and basis for classification of crushing machines along mechanical lines. Thus the common load-bearing members are beams, columns and ties; stresses induced in these by loading are compressive, shearing, and tensile; and the applied loads are stationary, slow-moving, or impact.
Most crushers load the solid particles they crush as beams or short columns, but explosive shattering, whether by dynamite or by steam, loads them as ties. So also does centrifugal force about their own centers of gyration. The induced stresses are mostly those of compression and shear, but tensile stresses arise in beam loading as well as in explosive shattering. The rate of loading in the majority of crushing machines is gradual; impact crushers form an important class, however; stationary loading is unknown.
With one or two relatively unimportant exceptions, all rock crushers taking coarse feeds apply pressure gradually to particles which take the load as simple beams or short columns. Two general types of mechanism are employed, viz., (l reciprocating breakers in which the crushing surfaces alternately approach and withdraw from each other, and (2) continuous breakers in which, in the crushing zone, there is continuous approach of the crushing surfaces to asubstantially fixed predetermined minimum spacing. Reciprocating pressure breakers include jaw, gyratory, cone, and gyrasphere crushers; continuous-pressure breakers are typified by rolls, single-roll crushers, and the so called roller mills. Impact crushers form a group comprising mechanisms some of which e.g., stamps, load the particles primarily as short columns, whereas others load by striking particle in suspension or by hurling them at high speed against stationary surfaces; hammer mills are typical of this latter class. Tumbling mills (ball mills, rod mills, etc.) utilize both continuous-pressure and impact mechanisms. Blasting, exphosive shattering, and decrepitation (fire-setting) are tension-type breaking operations; all three are relatively unimportant as crushing operations, although blasting is, of course, preeminently useful in rock excavation.
A crushing machine must not only break the rock but mustprovide means for continuous presentation of uncrushed material to the crushing zone and continuous discharge of crushed material therefrom. Gravity is the force employed for presentation in the great majority of machines; gravity, gravity aided by the carrying force of a fluid (air or water), and gravity aided by the mechanical impulse of the crushing surfaces are the usual means of discharge. In some cases, however, gravity is used as a retarding force against the discharge of a stream of fluid by putting a weir-type baffle in the path of the discharge stream; in other cases discharge is regulated and retarded by a screen or similar perforate septum.
The size characteristics of a crushed product are determined, all other things being equal, by the mechanical principles employed in the crushing machine. Gradual application of load, loading particles as beams and short columns, and rapid and unhindered discharge from the crushing zone make for a. grandular product with a minimum of very fine material; impact, shear, and slow restricted discharge all tend to produce fines. Cumulative weight-percent size curves for the product of crushers employing the first group of principles exclusively approach nearest to straight lines; the product of the grinding pan, which employs shear.(abrasion) for breaking and interposes a high weir in the path of the water-borne discharge, plots as a highly concave curve. With doubtful exceptions the sizing curves of the products of all other comminuters fall between these limits.
Coarse crushers or breakers for rock are the jaw crusher, gyratory crusher, single-roll crusher, sledging or slugging rolls, and occasionally, the hammer'mill. Intermediate crushers are the reduction gyratory, cone crusher, hammer mill, stamp, and, occasionally, rolls. Fine crushers are rolls, hammer mills, short-head cones, fine-reduction gyratories, and stamps; certain grinding machines, e.g., the rod mill may be used for fine crushing.
In general, jaw and gyratory crushers are preeminently adapted to breaking hard, tough, abrasive rocks. They are, therefore, used for the majority of metalliferous ores and aggregates, which, it so happens, occur mostly with gangues or other materials of this description. The primary roll crushers and the hammer mill cannot break such materials or rocks economically but are particularily useful with the relatively soft, friable and sticky rocks that are characteristic of many nonmetallic mineral deposits.
Grinding is powdering or pulverizing by pressure an abrasion. The essential elementof all grinding apparatus is, therefore, a means for applying compression and shear to particles in such a way as to cause their rupture. Since fine powder is the desired product, it follows that in most cases the comminuting means must come close together in order to apply the necessary rupture forces. Hence one definition of a grinding machine is that it is a crushing machine in which the crushing elements touch except in so far as they are prevented from doing so by the material being broken.
Grinding mills thus differ fundamentally from crushers, in which contact of the crushing faces is prevented by the mechanism itself.
Grinding in some form or other is the only commercially practicable method of comminution available to produce material at maximum sizes of 20-mesh or finer, and it is at least debatable whether it is not the economical method for production of lO-mesh or even 6-mesh sizes. Limiting reduction ratio is usually large. On the other hand there are unquestionable both a maximum feed size for efficient work and a maximum reduction ratio for a given type of grinding or a given maximum size of a given rock.
Grinding machines most frequently used are tumbling mills, comprising a rotating container partly filled with loose hard bodies free to move as the container revolves. Other tyyes are roller mills, in which heavy rolling bodies are constrained to travel a fixed circular path pressed against a track or tire; rubbing mills, consisting of a heavy movable part or parts arranged to rub against a fixed surface; and stamps, in which a heavy mechanically actuated pestle strikes material on a fixed die in a mortar. Grinding is ordinarily continuous, but there is some batch operation, e.g., barrel amalgamation and certain processing of nonmetallics to very fine sizes.
Purposes of grinding differ with the material being ground. In concentrating plants the primary purpose is severance sufficient to liberate the bulk of the valuable minerals from the gangue and. in many cases, from each other; secondarily it may be necessary to reduce the size of liberated valuable mineral sufficiently to effect differential movement in the subsequent concentration, e.g., flotation.' In some nonmetallic beneficiation, grinding is practiced to satisfy market requirements, no question of separation being involved. In hydrometallurgical work, exposure of the valuable mineral to the leach solution, rather than severance, is the sole purpose.
The size characteristics of broken rock particles are determined, other things being equal, by the way in which the particle broken was loaded, and by the degree of hindrance offered to egress from the breaking zonefln general, shear loading (abrasion) is more productive of fines than loading a particle as a short column; impact produces more fines than gradual loading; the greater the hindrance offered to egress,'the finer the product. Hence grinding machines are designed to strike the particles to be ground sudden, hard blows, and/or to cause them to be rubbed wth considerable pressure against each other and against hard surfaces; also some device is always used to hnder escape of unground material from the grinding zone. The nature of the expedients used to effect these ends determines the type of machine. Since the particles to be broken are relatively small, of highly varied size, and substantially infinite in number, it is not feasible to lead them through a restricted crushing zone, as in coarse and intermediate crushers, with the certainty that all .will be reduces to some predetermined maximum thickness. Hence repetitive chance is called upon to effect presentation to the crushing surfaces. Two methods are employed. In tumbling mills the stream of pulp is broken up into a large number of small branches and is thus led relatively rapidly over a crushing surface of large extent. In roller and rubbing mills the crushing surface, on the other hand, is of relatively small area, and repetition is had either by repeated circulation or by tremendously slow travel. Hindrance to egress is effected by a screeen or a weir. In all cases the crushing surfaces alternately approach to and recede from each other; this motion is positively controlled and is substantially regular and uniform in the roller and rubbing mills, but less regular and definitely nonuniform in tumbling mills.
Capacity depends, in all types, upon the force exerted between the crushing surfaces and upon the proportion of time that the particles are in active crushing zones.
To summarize, process systems and apparatus long used in the art involve separate machines to accomplish intermediate crushing and grinding. Each machine involves relatively slow moving parts of low capacity per unit of weight and/or size, with attendant high capital and maintenance costs. Crushing machnes do not accomplish size reduction in an autogeneous manner, and grinding machines which are operated with autogeneous grinding media, e.g., the autogeneous tumbling mill, still expose the entire shell lining to direct attack and abrasion of the tumbling charge. With the exception of highcost systems using gas under heat and pressure, substantially all crushing and grinding systems expose considerable manufactured parts to abrasion. High maintenance costs and contamination of product result. Portability or mobility of such crushing and grinding systems is severely limited in the larger capacities by size and weight. Crushing systems fail to take advantage of the fact that the tensile strength of most hard, abrasive materials processed is from one-tenth to one-twentieth that of their compressive strength. By
crushing in compression there is required from to 20 times the power which theoretically would be required if crushing could be accomplished in tension. Crushing systems fail to take advantage of the fact also that minerals liberate better if pulled apart at grain boundaries or at zones of weakness, rather than be fractured across grain boundaries or zones of weakness as is often the case with compressive and shear fracture.
The combination of these shortcomings leads to significant increase in the costs of the beneficiated materials over that which theoretically should be achievable. Of course it will be appreciated that even a small percentage reduction in the cost of crushing and grinding of materials beneficiated would have significant commercial impact.
The present invention overcomes many of the shortcomings of the prior art, providing a novel system for crushing and grinding, and for simultaneously crushing and grinding in the same comminution zone.
If the previously described terminology and classification is used for the present inventive system, the load bearing members in the larger pieces of material being crushed are primarily loaded as ties, rather tahn beams and columns as is the case with prior art systems. The applied loads in the present inventive system are high speed, rather than slow moving as is the case with prior art systems; and the acceleration due to gravity is supplanted with centrifugal acceleration, thus, more work is accomplished faster in less space and with less weight of apparatus.
The present inventive system uses the material to crush and grind itself, and uses the material being crushed and ground to automatically and continuously re-line ro re-surface the exposed portions of the comminution zone, thus reducing maintenance and repair, especially with abrasive materials. Contamination of the products with grinding media is much less than other prior art systems. No special grinding media or lining is required.
The present inventive system places crushing and grinding stresses on a gyro-stabilized bowl gradually transferring these stresses through the bearings to the frame, thus greatly reducing bearing sizes, bearing stresses, frame weight and foundations required as compared with present art systems.
The present inventive system combines the operations of intermediate and fine crushing with grinding in one apparatus with only one moving part to accomplish comminution, as compared with multiple operations in multiple machines as is the case with the present state of the art, thus greatly simplifying the crushing and grinding process. The rotative speed and direction of rotation of the bowl may be varied to adapt to special crushing and grinding situations.
In Marks Standard Handbook for Mechanical Engineers, 7th Edition 1967, section 5, page 6, table 3 is the following quote:
Other strength functions: shearing strength of brick and stone is from 10 to 20 percent of the compressive strength; tensile strength is 4 percent of compressive strength; modulus of rupture is percent of compressive strength; Poissons ration is 1.
By loading the larger pieces of material as ties the present inventive system does much crushing by tension rather than compression, as is the case with prior art systems. An increase in efficiency in crushing and a reduction in power requirements is thus attainable with the present invention.
If one climbs to a very high rocky place with steep clifflike areas, and disloges some stones, it will be noted that in their acceleration down hill that their frictional contact with the surface of the hill results in their attaining high rotational velocities. Some rockes will attain such high rotational velocities that they will spin to pieces in mid air. Here we see an example of crushing in tension, for the centrifugal force induces tensile stress within the rocks themselves which is greater than their tensile strength along their weakest zones or unlike mineral surfaces.
This problem is how to accomplish this process of tensile-type crushing wthin an apparatus adaptable to mineral beneficiation. The present inventive system solves this problem in a simple and efficient manner by introducing the material to be crushed into a high speed spinning bowl which induces the rotational velocity into the pieces of material to be crushed, or torn apart by internal tensile stress.
In order to withstand the unbalanced forces inherent in feeding large pieces of material to such a spinning bowl without imposing large stresses on the bearings the present inventive system employes the principles of the gyroscope. One of these principles is that the end of the axle of a rotating gyroscope always tends to move at right angles to any force impressed upon it. We could express this in a different way: that the gyroscopic force leads the impressed force by and in the direction of rotation. By fixing the axle relative to the bowl in a flexible mounting in such a way that angular deflection of the rotating element is held within reasonable limits, the bowl is allowed to precess, and thus is self-stabilizing as its geometric center is urged back into alignment gradually by the restrictive action of the flexible bearing mounting. The sudden impact of large unbalanced forces resulting from relatively large pieces of material passing through the rotating bowl is thus absorbed in the kinetic energy of the rotating bowl and in its gyroscopic precession, and transferred either to other pieces of material, or, if no other material passes through the bowl, then gradually to the bearings and frame as the gyroscopic precession is reduced by the restrictive flexible bearing support.
SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a novel comminution system for crushing and grinding materials, particularily solid materials whose tensile strength is less than their compressive strength, or which materials have areas or planes of weakness which may be pulled apart or fractured under tensile stress. The inventive system employes a novel method of applying tensile stress within pieces of material being crushed and ground as well as applying shear and compressive stress in the comminution zones.
To effectuate the application of tensile stress within the particles of material a bowl-shaped rotating element is used of cylindrical or frustro-conical cross section; open at the larger end and closed at the smaller. The bowl is smooth, having no radial projections such as impellers, hammers, baffles or the like. Attached to or a part of the bow] at the open end is a rim or ring, preferable relatively heavy. Attached to (or a part of the bowl) at the closed end at its concentric rotating axis is a driving and/or supporting shaft, extending either or both directions along the rotating axis from the closed end of the bowl. The bowl is of such depth relative to its diaemter that feed material reaching the inside is centrifuged against its inner surface thereby forming an autogeneous lining which is automatically renewed out of incoming material as it wears away. Surrounding the bowl radially outward from its rim is a shelf, enclosing sides and a lid, forming a trap chamber for material thrown outward from the spinning bowl. The shelf is set at such an angle that material being processed collects upon it as a dead bed lining in the direct path of the material thrown outward by the bowl, which lining is automatically renewed out of incoming material as it wears away. A hole in the lid provides means of feeding material to the bowl; and, the opening between the bowl and the shelf, or other openings in the shelf,-or shell together with collecting and discharge chutes provide means for removing the processed material. The rotational axis is preferably set vertical as the self-lining nature of the shelf in the trap chamber is more properly presented for minimum maintenance, but the rotational axis may be in any position from vertical to horizontal. The shaft bearing support or supports is preferably made flexible with restricted motion to allow the spinning bowl to vary its axis of gyration off its rotational center to automatically compensate for off-center and unbalanced loads; thus, the rotating element is gyrostabilized. Conventional means may be provided to classify, screen, or process the discharging material with or without means of elevating and returning oversize material or middlings back to the bowl for re-crushing or re-grinding.
The action of the inventive system is as follows:
As material is fed into the rotating bowl some of it is thrown against the inner surface and is held in place by centrifugal force. As more material is fed the lining builds up to an equilibrium shape in the form of a paraboloid-like surface with its open end toward the open end of the bowl. Thereafter material is discharged from the' bowl as fast as it enters. Since there are no radial baffles, impellers or projections in the bowl the particles are acted upon largely by their frction against the moving bowl surface in the direction of rotation; by centrifugal force radially outward; by inertia opposite the direction of rotation (and acceleration) and opposite the centrifugal force; and in a very minor way by the force of gravity. Since the friction forces and forward drag of the inner bowl lining surface at the peripheral surface of the particle is opposite the inertia of the particle, and is separted by a distance equal to the average radius of the particle to its center of gravity, force couples are formed which tend to produce rotation of the particle itself. The action of the centrifugal force is to multiply the force the particle applies to the inner lining surface of the bowl, thus forcing the particles to act like planetary gears on their spiral path out of the bowl, such that they attain very high rotative velocities, and burst when their internal tensile strength is exceeded.
As the particles reach the rim of the rotating bowl they attain about half the velocity of the rim, as there is considerable slip between the bowl surface and. the particles which has been translated into rotary motion of the particles themselves. At the rim there is a sudden change in direction of the path of the particles and again a couple is formed which tends to produce rotation, composed of the centrifugal force and inertia of the particles outward at their centers of gravity, opposed by the rim of the bowl at the periphery of the particles. The effect is similar to the mechanism a baseball pitcher uses in throwing a curve ball over his index finger to achieve high spin velocity. High rotative speeds are imparted to the particles themselves. Again fracture by tensile stress is obtained. Fragments of material then fly outward and impact into the surrounding lining of the trap chamber where the discharging material expends the balance of its kinetic energy in shear and compression, thus accomplishing additional crushing and grinding before discharge. The bowls action gives two important areas of comminution by means of tensile-type forces induces in the individual particles by centrifugal force as a result of high spin velocities imparted to them; that due to slip at the inner lining surface, and that due to escape conditions at the lip.
The net effect of the action of the bowl is to cause a large portion of the pieces and particles to reach such high spin velocities that centrifugal force within them exceeds their tensile strength, and they fly into fragments. There is also considerable grinding by impact and attrition in the process as the particles are accelerated and decelerated in their spiral path out of the spinning bowl.
For example a prototype machine was constructed which could be considered a small commercial unit. The inside bowl diameter is 30 inches, and the diameter inside the wearing lip and centrifuged lining at the top of the bowl is 28 inches.
It has been found by limited experimentation that rotative speeds sufficient to give peripheral speeds of over 100 feet per second accomplishes good crushing and grinding of brittle siliceous materials such as vein quartz, quartz-pegmatite and some porphyry ores. Relatively homogeneous tough materials such as limestone or dolomite require much higher speeds for best results, and efficiencies appear to increase to peripheral speeds of 500 feet per second or more. Peripheral speeds above 300 feet per second require special alloy steels to withstand tangential rim stress, which may reach 70,000 pounds per square inch under operating conditions at peripheral speeds of 500 feet per second.
Additional weight was added to the bowl by welding a heavy steelring at the upper lip 3 inches by 3 inches in cross section. This counterbalancing ring adds to the gyroscopic stabilization of the bowl and permits feed up to 6 inches or larger in diameter.
Freedom to precess within limits is accomplished by mounting the bearing assembly for the rotating element on six resilient automotive motor mounts. its
Test material fed into the unit failed first at planes of weakness, such as boundaries of crystals or mineral grain broundaries. A quartz-pegmatite-mica ore fed to the unit at minus 6-inches size lumps resulted in effe cient crushing. About percent of the material was reduced in one pass to one-fourth qts previous size or smaller. Substantially all the mica defoliated and was blown out the feed hole by the current of air generated by the rotating element.
It was noted further in the inventive system test unit that the material flying off the bowl rim has an upward trajectory of about 15 above the radius of the bowl at right angles to the rotational axis, and said material spun off the lip at an angle about half way between the tangent to the rim and the radius, indicating considerable slip between the material and the inner bowl surface.
The prototype machine showed practically no wear within the machine itself, as'the principal surfaces subject to abrasion and impact are covered with a selfreplacing lining of the material being crushed and gound. Only a thin line surface on the bowl lip and the shelf lip surrounding the bowl are subject to abrasion, and these were hard surfaced. The lip suffers some abrasion from splatter as material bounced off thedead bed lining on the shelf below, but this abrasion of the lid was minor in itself.
Material remains in the bowl but a fraction of a second, thus capacity per unit weight is high and the device is readily portable.
The prototype machine adapted readily to either wet or dry crushing and grinding, and could take 6-inch feed and reduce it to 65-mesh when proper closed circult classification means was provided to remove the fines and recycle the oversize into the feed hole.
Thus it is an object of the present invention to provide a unique system for comminution using tensiontype forces without the use of heat, or gas or liquids under differential pressure.
Another object of the present invention is to provide a unique system for comminution by combining tension-type and compressive-type forces simultaneously applied to the material being crushed and ground.
It is another object of the present invention to provide a unique system of comminution by combined tension and compression using centrifugal force for acceleration.
It is yet another object of the present invention to provide a unique system for comminution by combined tension and compression using centrifugal forces for acceleration which has a higher capacity to unit weight ratio than present art methods, and is thus more portable.
It is yet another object of the present invention to provide a unique system for comminution by combined tension and compression using centrifugal forces for acceleration which crushes and grinds and lines itself autogeneously, that is, with the material itself.
It is another object of the present invention to provide a novel technique and apparatus for causing crystal aggregates, minerals, and unlike substances aggregating a material to separate or fracture under tension at planes or zones of weakness.
Wt is another object of the present invention to provide a comminution system which can combine the functions of intermediate, finecrushing, and grinding in a single apparatus with a single moving part in actual contact with the material being crushed and ground.
Another object of the present invention is to provide a comminution system which minimizes contamination of the comminuted product with foreign materials or grinding media.
Yet another object of the present invention is to provide a unique system of comminution using tensile-type force for a portion of the crushing and grinding so as to take advantage of the much lower tensile strength of brittle materials than compressive and shear strength, thus crushing and grinding them with less power and at higher efficiencies.
Yet another object of the present invention is to provide a gyroscopic means of automatically compensating for unbalanced forces in systems and apparatus designed for comminution using centrifugal force to accelerate particles in spin velocity.
Another object of the present invention is to provide a system of comminution using combinedtensile-type and compressive forces applied by high speed rotation which combines intermediate crushing with grinding at a high capacity per unit volume, so that the ground product may be pumped or blown from restricted areas, such as from mines, rather than being conveyed, hoisted or hauled.
It is yet another object of the present invention to provide a system of comminution utilizing tensile-type forces induced by the action of a rotating element, which rotating element is fully reversible in rotatative direction.
It is still another object of the present invention to provide a system of comminution utilizing tensile-type forces induced by the action of a rotating element, which may operate either wet or dry, or with either fluids or gases.
It is another object of the present invention to provide a system of comminution utilizing tensile-type forces induced by the action of a rotating element, the peripheral discharge from which rotating element impacts into a surrounding trap chamber, thus utilizing the kinetic energy of the projected pieces or particles in accomplishing additional crushing and grinding and re-entry of some material into the comminution zone.
It is another object of the present invention to provide a system of comminution utilizing surfaces which neither approach and recede from each other, nor in which there is continuous approach of crushing surfaces to a substantially fixed, predetermined minimum spacing.
It is yet another object of the present invention to provide a system of comminution in which grinding of smaller pieces is accomplished by larger pieces of the same material during acceleration of the larger pieces in rotative or spin velocity.
BRIEF DESCRIPTION OF THE DRAWINGS Still other objects, features and attendant advantages of the present invention will become apparent to those skilled in the art of a reading of the following detailed description of the preferred embodiement constructed in accordance therewith, taken in conjunction with the accompanying drawings wherein like numerals designate like parts in the several figures, and wherein:
FIG. I is a sectional side view of the tensile-crushing and compressive-grinding system for comminution. Conventional external processing operations used in conjunction therewith are shown diagrammatically in flowsheet form.
FIG. 2 is a 45 oblique perspective view showing the inventive system with portions cut away to illustrate the annular nature of the various components, and the plane upon which sectional views shown in FIG. 1 and FIG. 3 are taken is shown by a broken line.
FIG. 3 is a sectional side view showing the deflection of the rotating element with gyroscopic precession due to unbalanced load.
The inventive system employs gravity means of feed and discharge to and from the comminutive zones. As is shown in FIG. ll, the feed material enters through feed hole I and falls by gravity to the botton or deepest portion of the inside of rotating bowl 4. Pieces of material are urged into frictional contact with the centrifuged autogenous lining 7 first by gravity and then by centrifugal force with increasing distance from the rotational axis of bowl 4. An equilibrium angle of repose is established for centrifuged autogenous lining 7, the inner surface of which resembles a paraboloid opening upward. Material scoured from lining 7 by frictional contact with incoming feed material is automaticallyreplaced out of the feed material itself, and is held in place by centrifugal force against the inner surface of bowl 4 and against wearing lip 6 at the point of discharge.
Material accelerated in a spiral path upward and outward of rotating bowl 4 is projected outward into a surrounding annular trap chamber composed of lid 2, shell 15, bottom shelf 3, and autogenous dead bed lining 8 which consists of material in process which has collected on top of shelf 3 and is held in place by gravity. Projected material impacting into dead bed 8 accomplishes autogenous crushing and grinding, and the recycle of some material back into bowl'4 by rebound off dead bed lining 8 and lid 2.
Material whose kinetic energy is spent after impact with dead bed lining 8 falls freely out of the comminution zones between shelf 3 and counterbalance ring of bowl 4, and may fall free of the entire assembly or be collected by discharge chute l6, and be removed.
Conventional screens, classifiers or concentrators may then be used in closed circuit with the inventive system in conjunction with suitable pumps, conveyors or elevators to adapt the present inventive system to specific situations and applications. The use of these devices would be obvious to one skilled in the art. For example:
The comminution zones may be swept with air or other gas to remove fines for further classification, and the oversize material elevated and returned to feed hole 1 for further comminution.
The comminuted material falling from the system or emerging from discharge chute 16 may be screened, wet or dry, and the oversize returned to feed hole l. The undersize from the screen may be a final product, or if dry, may be further air classified into a number of products, one or more of which may be returned to feed hole 1 by suitable elevating means, and the balance of the products removed for beneficiation. If the undersize from the screen be wet, it may be classified wet by any of the devices well known in the art such as pump and wet hydraulic cyclone, the oversize returned to feed hole 1 and the undersize sent to concentrative means such as flotation. One or more products from the screen undersize may be concentrated by gracity means such as jigs and film separators, or magnetic separators, and the oversize or middlings returned to feed hole 1.
The action of the inventive system is as follows: As material falls through feed hole 1 into the inside and bottom of rotating bowl 4 it encounters the rapidly revolving centrifuged lining 7. As the material is accelerated in a spiral course upward and outward from the botton of bowl 4, the forward frictional drag of the inner bowl lining 7 atthe outer surface of the particles of material countered by the retarding inertia of the mass of the particles themselves acting at the center of gravity of the particles, separated by the distance between the center of gravity and the surface of the particles, results in force couples which tend to produce rotation. Thus the particles are accelerated in rotational velocity as well as being accelerated in their spiral, bouncing path out of bowl 4. At some point in this journey out of bowl 4, as illustrated by the piece of material shown in FIG. 1, number 23, internal centrifugal force becomes so great due to increasing spin velocity that tensile strength of the weakest zones is exceeded and the particles fly to pieces.
Again as illustrated by the piece of material 24 in FIG. 1, an additional force couple tending to produce rotation is formed at the point of discharge from bowl 4 at wearing lip 6. At this point the centrifugal force which may amount to several hundred times the force of gravity acts outward at the center of gravity of the particles and is separated by the radius of the particles from the retarding force of the wearing lip 6 acting in opposite direction.
The effect of the force couple acting on a piece of material 24 as illustrated in FIG. 1 is similar to that of a baseball picher throwing a curve ball over his index finger. Very high rotational velocities which may exceed 40,000 RPM are attainable at this point and again the centrifugal forces within the particles radially outward from their own centers of gravity become so great due to the accelerated spin velocities that tensile strength of the material is exceeded and the particles fly to pieces.
Acceleration of the particles in spin velocity in their bouncing spiral path out of bowl 4 is accompanied by considerable grinding by compression and shear forces between the particles themselves and between the particles and the centrifuged autogenous lining 7. Thus it is seen that the larger particles grind the smaller in the process of acceleration. Grinding forces are greatly multiplied by the centrifugal forces imposed.
Material flying outward from bowl 4 over wearing lip 6 impacts into annular dead bed lining 8 resting on shelf 3 where additional crushing and grinding is accomplished by shear and compression. Some of the material impacting into dead bed lining 8 climbs by rotation and forward velocity into rebounding off trap chamber lid 2 and recycles back into bowl 4 for additional comminution.
Crushing and grinding in bowl 4 is somewhat a function of repetitive change as some pieces undergo the proper acceleration in spin velocity to effect rupture by centrifugally induced tensile forces, whereas others bounce out of the bowl by impact. It has been found by experience that in practical crushing and grinding situations either wet or dry that as the size range of the material is reduced it becomes increasingly difficult to accelerate the particles to sufficiently high spin velocities to effect fracture by centrifugally induced tensile forces. It is believed that this size limitation is due to the drag on the surface of the particles as their surface area relative to their weights increases as their size is reduced. At feed sizes less than 2 millimeters diameter fracture by tension in the present invention is practically non-existant. However, if larger size feed is cointroduced, material finer than 2 millimeter diameter is readily ground by compression and shear. This size limitation would not apply to material crushed in a vacuum, but, of course crushing and grinding in a vacuum is not a particularily practical condition.
Mechanical details of the preferred embodiment of the present inventive system are as follows:
Referring to FIG. 1, bowl 4 is typically of alloy steel, formed into one piece by forging or welding. It may be manufactured from a standard high-pressure forged tank bell-end of halfspherical or frusto-conical shape. As a rough rule of the thumb the depth should be about equal to the inside diameter for dry crushing; and, the depth sould be about 1 /2 times the inside diameter for wet crushing.
counterbalance ring 5 may be fashioned so that the ratio of its outer to inner diameter equals about 1.25, but other ratios of course may be used.
Fashioned as a portion of the top or outer rim of bowl 4 is wearing rim 6 which projects concentrically inward to act as a darn for centrifuged autogenous lining 7. It should be of wear resistant alloy or should be hard surfaced on its inner edge.
The supporting and driving shaft 10 attaches to the center bottom of bowl 4. It may extend upward through the inside center of bowl 4 and through feed hole 1 to a bearing assembly on top or above lid 2. However, such a configuration exposes shaft 10 to severe wear and abrasion, requiring a liner.
In the preferred embodiment the supporting and driving shaft 10 attaches to the center bottom of bowl 4 and extends downward as is shown in FIG. 1, 2 and 3. The inner surface of any section of bowl 4 at right angles to its central axis is circular.
Rotating bowl 4 and supporting and driving shaft 6 attached rigidly thereto is set in bearing assembly 11, within which are standard sealed ball, roller, or sleeve bearings 13 and 14.
As is illustrated by FIG. 1 and FIG. 2, bearing assembly 11 contains bearings 13 and 14 rigidly attached to it. Bearing assembly 11 is then flexibly mounted by means of resilient material 12 to the frame members 21 and 17. This type mounting of bearing assembly 11 allows rotating bowl 4 to precess as a gyroscope and at the same time cushions shocks along the axis of rotation.
In operating bowl 4 is rotated by standard driving means such as through flexible coupling 19 and electric driving motor 18. It has been found that the tire-type flexible coupling 18 is preferred as this type allows considerable lateral as well as angular shaft deflections. Of course other driving meanssuch as V-Belt drives, may be substituted for flexible coupling 19, and other power sources may be substituted for electric motor 18. Such other power sources may be turbine, deisel, or internal combustion engines with or without angle gears to change the direction of drive from horizontal to vertical.
Flexible or resilient mounting material 12 may be a rubber compound vulcanized to steel mounting brackets, or may be steel or metal alloy springs, with or without shock absorbers. Automotive motor mounts have been found to be quite satisfactory on smaller units.
The rotative speed of bowl 4 should be sufficient to impart a centrifugal force to feed material at least one hundred times the force of gravity. For example with 50 percent slippage between the inner bowl surface and the feed material bowl speeds to impart radial accelerations of 100 times gravity are about as follows:
for inner rim diameter of 2 feet, rotate at 1,083
R.P.M., for inner rim diameter of 3 feet, rotate at 891 R.P.M.,
for inner rim diameter of 4 feet, rotate at 767 R.P.M.,
for inner rim diameter of 6 feet, rotate at 626 R.P.M. In fact in most applications rotative speeds should be as high as the materials of construction can safely endure without failure, which may place centrifugal forces on the centrifuged lining in excess of 500 times gravity. Such high rotative speeds require the driving means 18 to be regulated within a narrow range of rotation speed, hence the pre' ferred use of the AC electric motor, or an internal combustion engine with governer control.
In the stationary portions of the cominutive system of the present invention, lid 2 is preferably of heavy steel plate to absorb severe impact from large, heavy foreign objects such as sledge hammers, dipper teeth and the like which may inadvertantly be introduced into the feed stream. Refering to FIG. 2, shell 15 including shelf 3 and safety chamber 9 is supported by a plurality of legs 20, to which is attached frame members 17 and 21 to support resilient mounting 12 for the bearing assembly 1 1.
Safety chamber 9 is preferably filled with some energy absorbing material such as sand and surrounds the top half of bowl 4 including counterbalancing ring 5 in case of structural failure of the rotating element to protect personnel from flying pieces of metal. This safety feature is considered essential at the high rotative speeds employed.
Gyroscopic stabilization is illustrated in FIG. 3 in which can be seen the result of a large unbalanced load 22 due to the gyroscopic effect. It has been found that the new axis of rotation as a result of the unbalanced load 22 tends to be about the center of gravity of the combined load 22 and bowl 4. Thus if the unbalanced load 22 centrifuges to lining 7 for a moment, the entire assembly including bowl 4 and bearing assembly 11 is seen to gyrate until the unbalanced load is dislodged, after which the entire assembly consistng of bowl 4 and bearing assembly 11 is seen to precess about the normally central axis of rotation. This precession is coun tered by other unbalanced loads so that repetitive chance enters under operating conditions to bring about a random precession of the spinning bowl 4 as continuous successive unbalanced loads are passed through bowl 4. This precession is restricted in amplitude of deflection by the restricted motion permitted by flexible or resilient bearing assembly mount 12. The energy of these large unbalanced loads is thus absorbed by the kinetic energy of the rotating mass of bowl 4 including its counterbalancing ring 5, and centrifuged lining 7. Thus, very little stress is transferred to bearings 13 and 14 or to frame members 21 and 17.
In accordance with the present invention, comminution of solid materials is accomplished in a completely novel manner. While the invention has been described with respect to a preferred physical embodiment constructed in accordance therewith, it will be apparent to those skilled in the art that various modifications and improvements may be made without departing from the scope and spirit of the invention. Iclaim 1. A process for comminution of solid materials, said process comprising the steps of:
providing a bowl-shaped element rotating on its axis of revolution, its inner autogenously sutogenously lined with said solid material,
supplying the inside of said bowl-shaped rotating element with pieces of said solid material by gravity feed,
accelerating said pieces of solid material by frictional contact with the inside surface of said bowl-shaped rotating element to such high rotation velocities about their own centers of gravity that centrifugal force within such pieces exceeds the tensile strength of said solid material, and fracture is obtained along zones of weakness within the pieces themselves,
simultaneously grinding the smaller particles with the larger pieces of said solid material during said acceleration,
providing a surrounding annular trap chamber into such said solid material projects, utilizing residual kinetic energy of the projected material to accomplish further crushing and grinding in compression and shear as the material is decelerated, and accomplishing some recycle of material by rebound from other material back into the bowl-shaped rotating element,
removing said solid material from the surrounding annular trap chamber.
2. A process as defined in claim 1 wherein said bow]- shaped element rotating on its axis of revolution is mounted in a bearing assembly which allows the axis of revolution to deflect within restricted limits so that the said bowl-shaped rotating element may precess as a gryroscope.
3. A process as defined in claim 2 wherein said axis of revolution may gyrate within restricted limits while the bowl-shaped element is rotating.
4. A process as defined in claim 1 wherein the bottom and impact zone of the surrounding annular trap chamber is autogenously lined with said solid material being processed, and wherein said autogenous lining is held in place by gravity.
5. The process defined in claim 1 wherein the rotating speed of said bowl-shaped element is sufficient to impart radial centrifugal forces for particles centrifuged at the inside point of maximum diameter of the bowl shaped element of more than one hundred times the force of gravity.
6. The process as defined in claim 1 wherein solid material removed from the surrounding annular trap chamber is screened, classified and oversize are recycled back into said bowl-shaped rotating element in closed circuit.
7. The rpocess as defined in claim 1 wherein the axis of the bowl-shaped element is substantially vertical.
8. The process as defined in claim 1 wherein the direction of rotation of the bowl-shaped rotating element is reversible.
9. The process as defined in claim 1 wherein the surrounding annular trap chamber is swept by a current of air to remove fines.
10. A process for comminution of solid materials which combines the operations of intermediate and fine crushing with grinding in one apparatus in'which the comminution is accomplished with a single moving part in contact with the said solid material, said process comprising the steps of:
providing a bowl-shaped element rotating on its axis of revolution, its inner surface autogenously lined with said solid material, gyro-stabilized by providing a bearing assembly which allows the axis of revolution to deflect within restricted limits so that said axis of revolution may gyrate and so that said bowl-shaped element may precess as a gyroscope.
supplying the inside of said bowl-shaped rotating element with pieces and particles of solid material ranging in maximum size classified as feed for intermediate crushing,
accelerating said pieces of solid material to such high rotational velocities about their own centers of gravity that internal centrifugal force within such pieces exceeds their tensile strength, and fracture is obtained along zones of weakness within the pieces themselves,
simultaneously grinding the smaller particles with the larger pieces between themselves and the autogenous inner lining of the bowl-shaped rotating element during acceleration,
providing a stationary surrounding annular trap chamber, autogenously lined, in the path of material projected from the said bowl-shaped rotating element,
impacting the projected material into the autogenous lining of the annular trap chamber to accomplish further crushing and grinding by shear and compression as the kinetic energy of the projected material is expended in deceleration,
removing the comminuted material from the annular trap chamber,
classifying the comminuted material into a fine ground product and a coarser oversize,
removing the fine ground product for beneficiation,
returning the coarser oversize to the inside of said bowl-shaped rotating element for further comminution.
ill. The process as defined in claim 10 wherein the annular trap chamber is swept by a current of gas such as air to remove the fines for subsequent classification.
12. The process defined in claim 10 in which the rotative speed of the bowl-shaped element is sufficient for a peripheral speed at the inside bowl lip of more than one hundred feet per second.
13. The process of claim 10 in which the axis of the bowl-shaped rotating element is substantially vertical.
14. The process of claim 10 in which the direction of rotation of said bowl-shaped element is reversible.
15. A process for comminution of solid materials which loads pieces of said solid material as ties, and accomplishes fracture in tension along zones of weakness, said process comprising the steps of:
providing a bowl-shaped element rotating on its axis of revolution, its inner surface autogenously lined with said solid material, gyro-stabilized by providing a bearing assembly which allows the axis of revolution to deflect within restricted limits so that said axis of revolution may gyrate, and so that said bowl-shaped element may precess as a gyroscope,
supplying the inside of said bowl-shaped rotating element with pieces and particles of solid material,
accelerating the pieces and particles of solid material by frictional contact with said autogenous lining to such high rotative velocities about their own centers of gravity that centrifugal force within the pieces of solid material exceeds their tensile strength along zones of weakness, and the pieces are pulled apart.
16. The process as defined in claim in which unlike minerals or crystals aggregating the said solid material are liberated one from another by being pulled apart at grain boundaries. 1
17. The process as defined in claim 16 in which the said solid material is mica ore and the mica is defoliated and pulled from the gangue by imposed tensile forces as a result of centrifugal acceleration of the individual pieces of ore.
18. A process of autogenous comminution of solid materials, said process comprising the steps of:
providing a bowl-shaped element rotating on its axis of revolution, with its open end facing upward, lining the inner surface of said bowl-shaped element autogenously with said solid material,
holding said autogenous lining place with centrifugal force,
providing a surrounding annular trap chamber with a flat bottom, or with a bottom sloping less than the angle of repose of the solid material in process of comminution,
holding said autogenous lining in place by gravity,
supplying a feed of said solid material to said bowlshaped rotating element,
accelerating pieces of said solid material by frictional contact with the inner surface of the autogenous lining of said bowl-shaped rotating element to high rotative and spin velocities in their path out of the bowl-shaped rotating element,
crushing and grinding said solid material as a result of said acceleration by centrifugally induced tensile forces and by compression and shear in the process of acceleration in the bowl-shaped rotating element, and by impact of the material projected from the lip of the bowl-shaped rotating element into the autogenous lining of the stationary surrounding annular trap chamber, in the process of deceleration,
removing the comminuted solid' material from the annular trap chamber.
19. The process as defined in claim 18 including the steps of classification of the comminuted material into oversize and undersize returning the oversize to the bowl-shaped rotating element, removing the undersize.
20. A process for reducing the power requirements in comminution of solid material whose tensile strength is substantially less than compressive strength, said process comprising the steps of:
providing a bowl-shaped element rotating on its axis of revolution, its inner surface autogenously lined with said solid material.
supplying the inside of said bowl-shaped rotating element with pieces and particles of said solid material,
accelerating the pieces of said solid material by frictional contact with the autogenous lining of said bowl-shaped rotating element to such high rotative velocities about their own centers of gravity that centrifugal force within the pieces of solid material exceeds the tensile strength of the material itself, thus, effecting fracture be tensile stress which requires less power than fracture by compressive stress,
autogenously crushing and grinding said solid material without expending power in abrading manufactured linings and manufactured grinding media,
providing a surrounding annular trap chamber, au-
togenously lined to collect the material projected from the lip of the rotating bowl-shaped element,
decelerating said projected material in said trap chamber,
removing the comminuted solid material.
21. The process as defined in claim 20 wherein energy is conserved by:
providing a flywheel ring intergal with the open end of said bowl-shaped rotating element, and providing a bearing assembly for the rotating bowlshaped element which allows the axis of revolution to deflect within restricted'limits so that said axis of revolution may gyrate, and so that said bowlshaped element may precess as a gyroscope.
22. A process for reducing size and weight of apparatus for a given capacity in autogenous comminution of solid materials by increasing the speed of comminution and increasing the speed of removal of the comminuted material from the comminution zone, said process comprising the steps of:
providing a bowl-shaped element rotating on its axis of revolution, rotating at such a speed that a particle centrifuged at the inner surface at the lip of said bowl-shaped element is acted upon by centrifugal force greater than one hundred times gravity, its inner surface autogenously lined by particles of centrifuged solid material, and which said bowlshaped element is gyro-stabilized by providing a bearing assembly which allows the axis of revolution to deflect within restricted limits so that said axis of revolution may gyrate, and so that said bowl-shaped element may precess as a gyroscope,
accelerating the pieces and particles of solid material by frictional contact with the autogenous lining of said bowl-shaped rotating element to high rotative and radial velocities such that fracture is attained by exceeding the tensile strength of the pieces of solid material by centrifugal force of their individual rotation, and by attrition, abrasion and impact between themselves and against the autogenous lining of the bowl-shaped rotating element, the pressure of contact of said pieces against said autogenous lining being multiplied by the radial centrifugal forces generated in their spiral path out of the bowl-shaped rotating element,
ejecting the pieces of solid material from and out of the bowl-shaped rotating element at high speeds by means of centrifugal force,
providing a surrounding annular trap chamber to quickly decelerate the projected material by impact into an autogenous lining of said solid material resting at its angle of repose on the bottom of said annular trap chamber, and
removing said comminuted material by free fall from said annular trap chamber.