US2509919A - Method of reduction by attrition - Google Patents

Description

y 1950 o. C. GRUENDER 2,509,919

METHOD OF REDUCTION BY ATTRITION Filed Aug. 4, 1947 -s Sheets-Sheet 1 Jlfarneys May 30, 1950 o, c, R R 2,509,919

METHOD OF REDUCTION BY ATTRITION Filed Aug. 4, 1947 3 Shets-Sheet 3 172067? zar Uscar C. Qrzzewde'r 5y M/Mm Patented May 30, 1950 METHOD OF REDUCTION BY ATTRITION Oscar C. Gruender, Milwaukee, Wis., assignor to Nordberg Manufacturing Company, Milwaukee,- Wis., a corporation of Wisconsin Application August 4, 1947, Serial No. 766,043

1 Claim.

My invention relates to an improved reduction or comminuting method.

One purpose is to provide a comminuting method in which fine reduction is obtained without the use of a metal grinding medium such as the balls used in ball mills.

Another purpose is to provide a comminuting method in which some of the particles ground perform the function of the balls normally used in a ball mill.

Another purpose is to provide a reduction method in which a rapid reduction to great fineness is obtained in a mechanism of substantially less weight and less cost than a mechanism, such as a tube or ball mill, heretofore used in fine grinding.

Another purpose is to provide a reduction method in which an economical reduction to great fineness is obtained in a mechanism requiring substantially less power than a mechanism, such as a tube or ball mill, commonly used in fine grinding.

Another purpose is to provide a, reduction method in which an economical reduction to great fineness is obtained in a mechanism producing substantially less objectionable fines and slimming than a mechanism, such as a tube or ball mill, commonly used in fine grinding.

Another purpose is to provide a reduction method in a mechanism in which the oonsumption of steel will be substantially less than in a mechanism, such as a tube or ball mill, commonly used in fine grinding.

Other purposes will appear from time to time in the course of the specification and claim.

I illustrate my invention more or less diagrammatically in the accompanying drawings wherein:

Fig. 1 is a vertical, axial section through a mechanism I may employ;

Fig. 2 is a diagrammatic showing illustrating the relation of the material ground to the attrition members at successive nips; and

Fig. 3 is a diagram illustrating the particles in the attrition zone when the attrition members are in position of closest approach.

Referring to the drawings, Fig. 1 illustrates a structure which may be employed to carry out my method and which has some resemblance to currently manufactured gyratory crushers but differs basically from them in operation. Since the particular structure involved does not of itself form part of the reduction method, I have not fully shown it. The structure is more completely shown in my co-pending application Serial No.

766,044 filed on the same date as the present application.

Referring to Fig. 1, I generally indicates a circumferential main frame mounted on any suitable base not herein shown. 2 illustrates a central post which will be understood to be mounted on the main frame structure. 3 indicates an upward projection from the main frame structure. 4 is an eccentrically apertured sleeve which rotates about the fixed post 2 and may be rotated by any suitable means not herein shown. It has an upward extension or sleeve 5 which carries a feed plate support 6, to which is secured the centrifugal feed plate So. It will be understood that when the eccentric sleeve 4 is rotated the feed plate 6a is also rotated thereby.

Surrounding the exterior of the eccen'trically apertured sleeve 4 is a head I which is provided with a downwardly convex spherical bearing surface .8 received by an appropriately formed bearing ring 9 upon the frame portion 3. III, II are any suitable sealing members and I2 is a trough in which water may be received. The result is an adequate sealing structure which, however, forms no part of the present invention and will not be further discussed.

I4 is a bowl support ring resting on the abutment ring Me which, in turn, rests on themain frame I. I5 indicates the bowl which is adjustable upon the ring I 4 as by the interpenetrating threads IE. IT is any suitable conic hopper mounted on the bowl l5 and adapted to receive the feed centrifugally delivered by the rotating plate 6a. I8 is any suitable feed spout adapted to deliver the material to the top of the feed plate Ga.

I illustrate two opposed and replaceable attrition liners or dies. 20 is an upper liner assembly secured to the bowl l5, as by the securing structure 2|, the details of which do not form part of the present invention. 22 is a lower die or attrition member which is held in position by the combined hopper and thrust member 23, which, in turn, is held by the locking ring 24 secured to the upward extension 25 of the head 1. Whereas the various details do not of themselves form part of the present invention, it will be understood that the result of the rotation of the eccentric sleeve 4 will be a simultaneous rotation of the feed plate 6a and gyration of the head I. With the upper attrition member 20 normally fixed, the result will be a movement of the lower member or die 22 toward and away from the fixed member 20, as indicated diagrammatically in Fig. 2. Appropriate sealing means entry st into the mechanism rotary movement of the plate Ga and gyratory moveme of the head 3. Thus the ring 25 has upward scaling connection Qiia which whe trates into an appropriate channel 2% in the bottom oithemembe': r

in considering. the nature (if my method, I employ an initial feed which may vary widely from mine to mine. It is certainly important, and, in general, necessary that there he a. pro.- portion of oversize particles which will perform functions of the metal balls or pebbles or the conventional ball mill. in addition to this function, the coarse particles tend to maintain a satisfactory volume of voids and prevent packing. As an example of a useful range of size, I may employ a feed having about coarse particles and 80% fine particles. The coarse particles may be plus V8" to minus The fine particles may be minus and plus 65 mesh. While I do not wish to be limited to a specific range, the one above described is practical.

In carrying out my method, the coarser particles should be generally uniformly distributed throughout the mass, to prevent segregation and unequal grinding. Y

My method can be carried out e'ther dry or wet, and with various proportions of water. For example, I may have water to the extent of 40% or,50% of the whole, throughout a substantial range. However, I cannot use so large a proportion of water as to cause a. rapid cascading or flushing of the particles through the attrition zone.

With reference to Figs. 1 and 3, and with a feed conforming to the general characteristics above discussed, the rotation of the fee-:1 plate So will deliver the particles violently outwardly against the hopper l1. fine and coarse particles are delivered downwardly through the spout 18 in segregated condition, the rotation of the plate 6a is effective to provide adequate mixture, and the particles, with the coarse elements satisfactorily scattered through the mass, will move gravitally down the slope of the hopper ll. As shown in Fig. 3, the crushing cavity normally will be bridged as at A. Fig. 3 shows the upper and lower attrition members 20 and 22 at their closest approach. But even when they are at their greatest recession, normally there will still be a bridging mass at A, which serves as a restriction and control for the entry of the particles to the grinding zone proper at B, between the opposed members 20 and 22.

At each recession of the member 22 downwardly away from the normally fixed member 20 there will be an entry, from the zone A, of particles into the opening of the zone B. As a matter of fact, the upper, inner end of the grinding cavity B normally will be substantiall entirely filled with a mixed mass of fine and coarse particles. As a result, when the attrition excursion begins, the material or mass caught by the first nip is directly compressed. However, there are sufficient voids in the mass to prevent its reduction to an incompressible packed mass. The length of stroke and the timing of the movement of the head are such that, after the initial nip, the head, with the lower attrition member 22, is withdrawn faster than the previously crushed mass is accelerated by gravty. Thus, the member 22 recedes downwardly away from the falling mass. Significantly, the timing and excursion In the event that the are such member 22 has reached its lowe t position is again rapidly moving upy tower the member 2i) before it receives the The result is a shattering or oi the causing the particles to assume a new position in the mass, with the stroke terminating in a. compression nip.

At no stage is there a single layer crushing or grinding effect. is to say, there are no particles of sumcient size to be directly gripped between the members 20 and 22. On the contrary, the mass is squeezed or nipped between the opposed surfaces the members 20 and 22, with a resultant grinding of particle on particle, and a reduction by attrition of a multi-layered mac I After the iirst compremlng nip with a full cavity, there is a. sequence, at each nip, of a free gravital fall terminated by an impact against the falling mass. However, since the compressing or impacting nip is delivered perpendicularly to the grinding surfaces, there is a minimum of abrasive or glancing or cutting action on the metal surfaces of the opposed attrition members.

It will be noted that the angle of the upper surface of the lower member 22 is less than the angle of repose of the material undergoing reduction. Thus, it the member 22 were at rest, the material delivered to its upper surface would not of itself slide downwardly through the attrition zone. The propulsion of the material through the attrition zone, or zone of treatment B, is generally positive, in response to the carrying movement of the head. There is only an incidental or slight sliding movement of the particles outwardly through the discharge zone. This propulsiv action is well illustrated in Fig. 2. The

form 50 indicates the compressed mass in the polsaition in which it is placed by the nip of the mem- As the member 22 recedes downwardly, the mass 50 may theoretically be considered to be falling to the position 5011. When it is again picked up by the lower member 22 it is moved outwardly, and, owing to the slope of th member 22, is carried or lifted to the advanced position 50b. The space left at the upper or inner end is filled by particles flowing in from the space A. The particles at the end of the form 50b fall downwardly out of or away from the zone of treatment. It will thus b evident that with the proportion Of the parts 20 and 22, as shown, and with the center of gyration located at X in Fig. 1, the mass undergoing treatment will be moved progressively outwardly through the zone B in a series of relatively short steps, and that the ratio of reduction of the mass during the first step or initial compression nip will be considerably greater than the ratio of reduction of th mass during the subsequent steps or compression nips.

It is characteristic of my method that the particles are maintained in a multi-layer condition, with the coarse particles scattered reasonably uniformly through the mass. passes through the zone of treatment, th number and size of the coarser particles are progressively reduced, as indicated diagrammatically in Fig. 3. However, I find it important to operate my method in closed circuit. The product of each stage of the attrition method is subjected to separation by size, by means not herein shown. The properly reduced material is removed from the circuit and the oversize, with additional feed, is returned to the closed circuit, to form part of the feed of the ensuing passage. In practice, as in the As the material conventional ball mill, the circulating load may be as low as 300% and as high as 600% or more, depending upon the nature of the feed and of the mat-"rial materials being fed.

It will be observed that I provide an attrition zone that is more or less continuously restricted in depth, from the feed end to the discharge end, as shown in Fig. 3; and that the attrition members 22 and 20 are set relatively far apart. In other words, close setting of th attrition mem hers is not required to produce a product which contains a, large percentag of extremely fine sizes.

It will be realized that-whereas I have shown an adequate mechanism for carrying out my method, the method maybe carried out by different mechanisms and is not a mere function of th particular mechanism shown.

I illustrate a method, and a structure for carrying it out, in which an attrition zone is proimportant that the attrition members, at their closest approach, are still separated by a distance suflicient to admit a layer of small particles of substantial thickness. .These particles are arranged in a layer of a depth many times the diameter of the largest particles passing through the attrition zone, at all positions of the movable member.

In the normal use of the structure illustrated in the drawings it will be understood that the lower attrition member 22 need not have any substantial rotation. Whereas the hub or sleeve I is free to rotate about the exterior bearing surface of the eccentric 4, no means for rotating it are provided, and it rotates merely in response to frictional contact with the material undergoing crushing, and at a rate insufficient to have any perceptible effect on the crushing method. However, I find it advantageous to provide a positi-ve mixing and feeding of the particles to the attrition zone. I therefore rotate the feed plate 6a in response to rotation of the eccentric 4. In the particular structure herein shown, I illustrate the plate So as directly driven by the upward extension 5 of the eccentric 4. The rate of rotation of the eccentric is, in practice, suflicient to impart a very substantial centrifugal outward delivery of the particles, as is diagrammatically indicated in Figure 1. Th particles, in mixed sizes, are de-- livered downwardly through the spout t8, and, in response to the mixing and centrifugal delivering movement of the plate 6a, the particles are fed in a relatively thin stream or layer, under conditions and ate. rate of speed adapted to maintain a substantially uniform mixture of coarse particles throughout the mass. The outward movement of the fed particles is terminated by conof repose of the material undergoing reduction,

while keeping the attrition members at all times substantially apart; providing a. feed in which a proportion of coarse particles is mixed in a mass of fine particles; centrifugally mixing and delivering the feed in a relatively thin and generally horizontal stream at a. suflicient rate of speed to maintain a substantiall uniform mixtur of coarse particles throughout the mass, as the mass enters the attrition zone; normally delivering sufficient feed into the receiving aperture of the attrition zone to maintain a bridge of material between the opposed attrition members at all positions of the attrition members; initially subjecting the entering mass to compression between the opposed attrition members; withdrawing the lower attrition member downwardly from the upper at a rate and through an excursion suflicient to withdraw it, after each compression, faster than the acceleration under gravity of the previously compressed material; returning the lower attrition member upwardly toward the falling mass and catching the falling mass thereon when the lower member is moving upwardly with suflicient rapidity to impact and scatter the falling mass; maintaining the sequence of free fall of the mass and of impact against the'mass, until the particles undergoing attrition escape from the attrition zone, while employing the lower member as the means for conveying the mass through the attrition zone, with the particles arranged in a layer of a depth many times the diameter of the largest particles passing through the! attrition zone, at all positions of the movable attrition member.

OSCAR C. GRU'ENDER.

REFERENCES CITED The following references are of record in the file of -this patent:

UNITED STATES PATENTS Number Name Date 933,669 Rusager Sept. 7, 1909 1,057,773 Pratt Apr. 1, 1913 1,226,275 Symons May 15, 1917 2,254,425 Fahrenwald .Sept. 2, 1941 FOREIGN PATENTS Number Country Date 656,857 Germany b. 17, 1938

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