US3078049A - Mill and process for autogenous grinding of friable material - Google Patents

Description

Feb. 19, 1963 H. HARDINGE MILL AND PRocEss FOR AUToGENoUs GRINDING OF' FRIABLE MATERIAL 4 Sheets-Sheet l Filed June 24, 1959 INVEN TOR H/QZL OWL' HQ60/NGE ATTORNEY Feb. 19, 1963 H HARDINGE l 3,078,049

MlLI.. AND PROCES FOR AUTOGENOUS GRINDING Filed June 24, 1959 OF FRIABLE MATERIAL 4 Sheets-Sheet Z ATTORNEY Feb. 19, 1963 H. HARDINGE MILL AND PROCESS FOR AUTOGENOUS GRINDING OF FRIABLE MATERIAL 4 Sheebs-Sheei'I 3 June 24, 1959 Filed lII llllllllll II I I I 0 l l l l.

Feb. 19, 1963 H. HARDINGE 3,078,049

MILL AND PROCESS FOR AUTOGENOUS GRINDING OF FRIABLE MATERIAL. Filed June 24, 1959 4 Sheets-Sheet 4 /22 //o /Zo//z l /36 /52 /40 /30 j /4-2 l j i /46 ATTORNEY 3,078,049 Patented Feb. 19, 1963 tice 3,078,649 MILL AND PROCESS FOR AUTOGENOUS @BIND- ING F FRIABLE MATEREAL Hariowe Hardinge, York, Pa., assigner to Hardinge Cornpany, lne., York, Pa., a corporation of New York Filed .fune 24, 1959, Ser. No. 822,612 27 (Jiaims. (Cl. Zei-26) This invention relates to reduction of solid friable material, such as ore, non-metallic minerals, coal and the like from a run-of-the-mine condition including coarse lumps, intermediate and relatively fine sizes to a desired range of fine particle sizes and, more particularly, to a process and mechanism to achieve such reduction in size, by autogenous grinding which, essentially, comprises causing the material to grind itself, with or without the aid of auxiliary means such as balls, rods or other aids within the mill.

Autogenous grinding, per se, is not new and a comprehensive review on this general subject by the present inventor is found in the Engineering and Mining Journal, June 1955, vol. 156, No. 6, at pages 84-90, entitled Malring Rock Grind Itself, and also in a paper presented before the American Mining Congress entitled Autogenous Grinding and reprinted in the American Congress Journal, pages 56-62, October 1958. Many of the problems confronting the mining industry with respect to autogenous grinding are discussed in said articles and, as of the publication dates thereof, the existing state of this art is described. The expression autogenous grinding means in effect, self reduction, that is, the material undergoing reduction in effect reduces itself during the reduction process.

The present invention relates to improvements in both a method and mill apparatus which solve many of the existing problems in autogenous grinding but, in order Ithat such problems can be appreciated adequately, some of the fundamental requisites of the operation of an autogenous mill for grinding and pulverizing ore, nonrnetallic minerals, coal and the like should be recounted preliminarily to form a basis for highlighting and appreciating the advantages and details of the invention which are set forth thereafter in this specification.

By the expression run-of-the-mine is meant a mixture normally of coarse, intermediate and fine sizes, the larger sizes being sufcient to reduce themselves along with the other sizes present, even though in some cases certain size ranges may be eliminated or partially treated separately.

There preferably should be a satisfactory ratio of fine and coarse material in an autogenous mill and process. The coarse material is essential to perform grinding of the intermediate and finer sizes until a desired range of fines are produced and are removed from the mill such as for further processing, either chemical or physical. The presence of some of the finer particles at all times is desired to somewhat cushion the coarse pieces relative to the mill while tumbling, thus minimizing abrasion on the liner of the mill and also somewhat retarding the decreasing of size of the coarse pieces which are the principal grinding media for the smaller particles, whereby enough of the coarse material should be present to drop onto each other and the other smaller material with desired crushing effect to be gradually reduced to finer sizes. The supply of runofthemine solid raw material to the mill usually insures an adequate supply of the coarse material to effect desired pulverizing not only of the coarse pieces themselves but also the intermediate sizes and finer particles of material. The material which has been reduced to the desired size is removed from the mill by any of a number of means, or combinations thereof, including if desired, such auxiliary aids as gaseous or liquid fluid currents regulated as to volume and velocity to entrain desired ranges of fine particles and particularly if greater speed is desired, after the material has passed through a grate or perforated diaphragm which effects retention of the coarser material within the mill and performs at least somewhat of a sizi-ng function.

During rotation of the autogeneous mill drum, the material therein is carried upwardly mainly by friction and centrifugal action until gravity overcomes these forces and the material then drops or rolls down the underlying material to provide a continuous tumbling action of the material in the mill. During such tumbling, the larger particles or lumps of material crush, grind, and ultimately pulverize the smaller particles; they themselves gradually becoming broken by such action and, in turn, being ground by incoming larger pieces.

One of the difiicult problems in autogenous grinding comprises maintaining an adequately thorough mixture of all sizes of material within the mill. There is a definite tendency for the material to become segregated due, primarily to .the natural phenomenon that when a mixture of material, ranging in sizes from coarse to ne particles, is discharged or dumped onto a pile, the coarser particles roll down the pile faster than the finer fraction with the result that more of the fines will remain nearer the top than the coarser fraction and the separate sizes thereby becoming segregated in such localities. This likewise occurs within a rotating drum type mill for autogenous grinding, where, during the rotation thereof the cascading mass at the top of the load rolls and falls down the incline formed by the tumbling action of the rotating mass within the drum.

When fluid currents are passed through the mill from the feed end to the exit end, for example, there is a tendency for these additional current forces to displace the material laterally, with the result that the larger pieces will tend to remain adjacent the feed end, while the finer material is moved more easily and concentrates adjacent the exit end, whereby the overall mass is not distributed as it should be throughout the mill for effective autogenous grinding.

Another problem of considerable extent comprises the lifting of the material in the mill as high as possible, for a given speed of rotation, before it falls onto the material lower down in the mill to effect crushing of boththe latter and the falling material. Attempts to achieve maximum lifting effects having included the employment of traus verse lifting bars extending radially inward from the inner peripheral surface of the drum of the mill a distance adequate to receive therebetween the material to be lifted and retain the same while moving upwardly as high as possible before gravity causes it to fall therefrom.

Obviously, the longer the material can be retained between the lifter bars before it falls, the higher it will be lifted and the greater will be the fall with resulting higher impact and longer distance of travel down the slope of the moving mass. To increase the retention of the material and thus achieve a higher lifting effect, greater heights of lifting bars in a radial direction have been used, even including those with undercut faces in some instances, with the result that the material fills the spaces between the bars to such an extent that movement therein virtually stops as the mass is being raised during the upward path of the material near the periphery. This condition exists until just at the time it falls away at the top of the upward travel. In other words, a very high lifter in effect tends to decrease the effective and active grinding volume and the active mass undergoing reduction tends to orbit and also slides over that stationary portion of the load held between the high litters. Such a design which produces a high lifting action tends therefore to defeat its own purpose.

The mills best suited for autogenous grinding comprise rotating drums provided with a feed inlet at one end and an exit at the opposite end, said inlet and exit preferably extending through hollow trunnions which support the drum during rotation. In order that the most effective type of grinding may be achieved, it is to be understood that the drums of the invention preferably should have a diameter compared to its effective grinding length which .is considerably greater than has been the practice heretofore where special grinding media or bodies have been employed to grind pre-sized material as the feed.

The principal object of the invention is to provide an autogenous mill of the type referred to above, and the `process of operating the same whereby a susbtantial increase in the height of drop of at least the larger material undergoing treatment will take place to produce more effective and efficient reduction in size of the material undergoing treatment.

Another object of the invention is to'provide an autogenous mill and a method of operating the same wherein thorough intermixing of all sizes Vof material, especially laterally, takes place constantly during the operation of the mill to minimize lateral segregation of the material.

A further object of the invention is to provide an autogenous mill and a method of operating the 'same wherein `practical and relatively fool-proof means are provided for lifting especially the larger material undergoing treatment within the mill to substantially greater heights within the mill than was heretofore possible before the same `falls by gravity and such means for achieving such lifting of the material are readily changeable for means of different sizes best suited for particular types and sizes 'of material which are to be subjected to grinding and comminuting within the mill, whereby maximum efciency of the operation of the mill is achieved relative to any given run of material.

Still another object of the invention is to provide an autogenous mill and method of operating the same wherein a discharge arrangement is provided that is operable to permit the discharge of material at a level below the trunnion exit of the mill, and the provision of means to protect the discharge arrangement from undue abrasion as well as aid in the lateral intermixing of the material within the mill.

Another object of the invention ancillary to the object immediately described above comprises the utilization of perforated diaphragm screening means as Such discharge arrangement, said screening means extending generally radially from the trunnionexit toward the inner peripheral wall of the mill but preferably spaced from said peripheral wall, there also being provided means to produce discharge of material from the screening means through the trunnion exit of the mill.

One further object of the invention is to provide an tautogenous mill and method of operating the same Whereby effective use is made of conical ends in the mill not 'only to aid in lateral mixing of the material undergoing 'treatment to minimize segregation, but also to aid in effecting higher lifting of at least the larger sizes of material to produce a more effective drop by more positive means than has heretofore been possible, such dropping of the material also being in a directed manner to aid in achieving the lateral mixing of the material undergoing -treatment.

Still another object of the invention is to utilize a number of dierent embodiments of sloping inner surfaces on the peripheral wall of an autogenous mill in "order that such sloping peripheral inner surfaces will cooperate with other structures and method of opera- `tion of the mill to aid still further in achieving maximum, substantially uniform intermixing of the material undergoing treatment throughout the entire mass thereof while the mill is operating.

Details of the foregoing objects and of the invention, as well as other objects thereof, are set forth in the following specification and illustrated in the accompanying drawings comprising a part thereof.

In the drawings:

FIG. 1 is a side elevation, partly broken away and the broken away part being illustrated in vertical elevation, of one embodiment of autogenous mill having conical ends and in which the principles of the present invention are utilized.

FIG. 2 is a view similar to FIG. 1 but showing an autogenous mill having parallel end walls and otherwise em bodying the principles of the present invention.

FIG. 3 is a sectional view of the mill shown in FIG. l, as seen on the line 3 3 of said figure, to illustrate an exemplary disposition of the material undergoing treatment within the mill, especially to show the lifting effect afforded by the mill.

FIG. 4 is a transverse sectional view of the mill taken within a plane parallel to the axis of the mill, on the line 4 4 of FIG. 3, but showing a slightly different form of peripheral liner than in FIG. 1 and also a slightly different height of lifting bars than those shown in FIG. l, said View primarily illustrating exemplary disposition of material within the mill and especially the manner in which mixing of the various sizes of material takes place especially in a lateral direction relative to the end walls of the mill.

FIG. 5 is a fragmentary vertical section sectional elevation of still another embodiment of the invention similar to that illustrated in FIG. l and showing a section of another embodiment of the peripheral wall and screening means of the mill.

FIG. 6 is a view similar to FIG. 5 showing a still further embodiment of peripheral Wall and screening means in a mill otherwise basically similar to the embodiment shown in FIG. l.

FIG. 7 is a vertical elevation of a mill drum embodying the present invention and similar to the embodiment shown in FIG. l but illustrating by exemplary arrows various paths taken by certain typical sizes of material within the mill while undergoing treatment therein.

FIG. 8 is a vertical sectional View similar to FIG. 7 but illustrating the embodiment of the invention shown in FIG. 2 and showing by exemplary arrows typical paths taken by various typical sizes of the material within the mill drum While undergoing treatment.

FIG. 9 is a fragmentary vertical sectional view taken on the line 9 9 of FIG. 1 and illustrating details of the liner members and the transverse peripheral lifting bars which maintain the liner members in operative position and also operate to lift the material within the mill drum, said lifting bars being illustrated in full lines to show one exemplary height thereof, and in dotted lines, showing another exemplary height thereof, selectively to provide variable lifting effect to suit a particular size range of material being treated.

FIG. 10 is a sectional view taken on the line 10 10 of FIG. 9, and showing details of the preferred bolt means by which the lifting bars are held connected to the mill drum.

FIG. 11 is a fragmentary sectional detail of a portion of the grate structure employed in the embodiment shown in FIG. 1, as seen on the line 1.1 11 of said ligure.

FIG. l2 is a fragmentary plan View of the embodiment shown in FIG. 5 as seen from the line 12 12 of said figure.

FIG. 13 is a fragmentary vertical elevation as seen on the line 13 13 of FIG. l2.

FIG. 14 is a sectional view similar to PIG. 9 but illustrating another embodiment of liner and lifter means.

It is to be understood that the various illustrations shown in the drawings primarily are intended to be exemplary and not restrictive. In autogenous grinding and comminuting of material by a rotating mill drum, and particularly for purposes of achieving the elevating of the material, and especially the larger particlesof material, to fall onto or roll down the uppermost surface of the main body within the mill to achieve desired reduction of size of all of the material within the mill, it is preferred that the diameter of the mill drum be considerably greater than the length thereof in an axial direction to provide a relatively narrow mill. Accordingly, all of the illustrated exemplary embodiments of mill within the attached drawings are so dimensioned, it being understood that the length in an axial direction is the effective length of the inner surfaces of the lining elements within the mill and exclusive of the projecting hollow trunnions connected respectively to the end walls of the mill drum and the effective diameter is the diameter of the exposed inner surfaces of the peripheral liner sections or members of the mill drum.

It also will be seen that mill drums having conical end walls as well as end walls which are substantially parallel to each other and transverse to the axis of the mill drum are illustrated inasmuch as at least certain of the embodiments of the invention are substantially equally applicable to both types of autogenous mills. In regard to other features of the invention however, the same are more effective in one type of mill than the other and these distinctions will be described in detail hereinafter.

In most of the embodiments illustrated in the drawings, grate means comprising screening diaphragm means are provided adjacent one end wall of the mill drum, said yscreening means comprising an important feature among a number of important features of the present invention. It is to be understood that there are certain important features of the invention which do not depend upon said screening structure however and are applicable to autogenous mills in which no such screening structure need be employed.

Referring to the embodiment shown in FIG. 1, the mill 1li is of the autogenous grinding type and comprising a cylindrical peripheral member or shell 12, to the opposite ends of which conical end shell members 14 and 16 are connected at the periphery thereof by any suitable means such as welding, riveting, or the like to form a drum. Connected coaxially with central openings in the end members 14 and 16 are hollow cylindrical trunnions 18 and 20. It will be understood that the trunnions 18 and 2t) are supported in suitable bearings such as those employed for a ball and rod mill, such bearings not being illustrated in order to simplify the illustration of the invention, and the mill 1t) is supported by such bearings for rotation about the axis of the trunnions 18 and 20. The trunnion 18 comprises the inlet or entrance to the mill and a feed chute 22 extends into trunnion 18 for purposes of feeding run-of-the-mine material into the interior of the mill 19. Preferably, a frusta-conical entrance cone 24 is formed within the trunnion 18 to guide the material readily into the interior of mill 1li.

Coaxial with the trunnion 18 on the interior of mill 10 and extending axially inward therefrom is an annular conical abrasion-resistant ring 26 providing a circumferential bulge projecting axially into the mill 10 for purposes to be described. The ring 26 preferably is formed from a plurality of arcuate segments which respectively are secured to the inner surface of the end shell 14 by any suitable means such as bolts 2S which extend through the shell and receive external clamping nuts. Such segments readily andvquickly may be replaced by additional segments of a different size which, -for example, may project a greater distance axially into the mill such as indicated by the exemplary dotted line illustration 26.

Also secured to the inner face of the end shell 14 are a plurality of segmental sections 30 of abrasion-resistant liner members which are made from material similar to that from which the segmental sections of conical ring 26 are formed. Particularly for use in mills of appreciable diameters, it is preferred that the segmental sections ?0 be of a size which permit convenient handling, especially for purposes of replacement or the substitution of different sections, whereby the sections 30 preferably do not extend as single sections radially between the conical ring 26 and the peripheral shell 12 of the mill. Rather, one or more additional annular segmental sets of liner sections 34 are utilized and are positioned between the sections 3@ .and the liner members on the peripheral shell 12 to be described.

The liner sections 30 and 34 preferably are secured to end 14 by radially extending wedge and lifting bars 36 and 38 which wedgingly engage adjacent edges of the segmental liner sections 30 and 34 and are secured to end 14 by bolts 32 having taper heads received in complementary holes in the bars, the bolts extending through the various circular rows of holes in end 14. The bars 36 and 38 may be replaced by similar bars respectively identified as 36 and 38 of different height than the bars 36 and 3S, thereby adapting the mill to handling a size range of material of a different average composition from that of another to secure the greatest efficiency, as determined by inspection of or as the result of tests made using the size composition of a run of material to be treated by the mill. In other words, the invention is concerned with changing the contour of the mill to produce therein a reduction characteristic which will result in the most efficient production of a range of fine sizes of product material at the minimum overall cost of reduction of the material to said range of tine sizes.

The trunnion 2t? comprises part of the exit of the mill and has a grate 40 comprising perforated screening means of one or more slots or size-limiting openings associated therewith, as Well as a circular conical ring 42 which provides a circumferential bulge extending axially inward toward ring 26 for purposes to be described. A frustreconical exit member 44, having an end wall 46 therein, is mounted to extend coaxially into the reversely-angled conical exit shell 4S which projects through the hollow exit trunnion 2t? in spaced relationship thereto. The exit member d4 is carried by conical ring 42 as clearly shown in FIG. 1. Ring 42 is sectional and is clamped to the end shell by bolts 54 which extend through the sections and spacer sleeves 56 arranged between the grate members 40 and the inner surface of end shell 16. Preferably, the grate 40 comprises a plurality of segmental sections having radial division lines therebetween.

As best shown in detail in FIG. 1l, adjacent edges of the sections of the grate 40 are connected to the end shell 16 by radially extending lifter bars 60 which receive clamping bolts 62 which extend through spacer sleeves 56 to maintain the grate 46 in desired spaced relationship from the liner plate 58 and end shell 16 of the mill.

Preferably the radially extending lifter bars 60 have beveled sides 64, as shown in FIG. 1l, which are complementary to adjacent side edges of the sections of the grate 40 whereby when said bars 60 are clamped into operative position by the bolts `62, firm wedging-type clamping of the grate sections 49 will take place. As also shown in FIG. ll, the radial lifting bars 60 which clamp the grate sections 40 may be replaced by other lifting and clamping bars 60 of different height as illustrated in dotted lines. Said radial lifting bars 60 clamp the various grate sections into operative position.

Another segmental annular ring 66 having a conical inner surface is clamped against the inner surface of end shell 16 as shown in FfG. 1, said ring forming the periphery of an annular chamber 68 within which the material passing through the slots or openings of the grate 40 is received and from which discharge is effected by means to be described. Ring 66 is secured to the end shell 16 by bolts 70. The detachable securing of the annular ring 66 to the end shell 16 permits said ring to be replaced by a ring of diffeernt height.

Positioned between the annular bulge ring 66 and the liner means within the cylindrical shell 12 are additional segmental liner members '74 secured to end 16 by radial wedge bars 76 which are bolted to end 16 by bolts 78 similar to bolts 32 and 36. The detachable mounting of the wedge bars 76 permits the same to be substituted by other bars of different heights, as indicated by dotted lines 76 in FIG. 1. Liner sections 74 and ring 66 define an annular space within the mill comprising an expanding zone 79 for purposes to be described.

Liner elements also are detachably connected to the inner cylindrical peripheral wall of shell 12 of the mill 10 and such sections, in this embodiment of the invention, are formed and positioned so as to slope from the end members of the mill axially inward and radially outward toward the shell 12 of the mill. Even a gradual slope of a few degrees is highly effective. In this specific illustration of FIG. 1, it will be seen that a plurality of central liner sections St) are secured by transverse wedge and lifting bars 82 affixed to shell 12 by bolts 84 similar to bolts 32, 36 and 78, The bars 82 may be replaced by other wedge and lifter bars 82 of a different height and the sections 80 thus are wedgingly clamped thereby in endtoend relationship around the inner periphery of shell 12. 4Bars 82 readily may be replaced by other bars with substantially no disturbance to liner sections 80.

Oppositely sloping liner sections 86 are disposed between the opposite edges of the liner sections 80 and the liner sections 34 and 74 respectively adjacent the opposite shell ends 14 and 16. The sections 86 may be maintained in such sloping relationship by filler members 88 such as wedge-shaped pieces of wood. The sections 86 are secured to shell 12 by wedge and lifter bars 90 which are shaped to extend substantially in continuation, or otherwise, to the bars 82 and the bars 90 are secured to the shell 12 by bolts 92. As in regard to the other liner sections of the mill 10, wedging and lifter bars 86 may be replaced by other bars 90' of a different height.

In the preferred operation of the mill 10 as shown in FIG. 1, run-ofthemine material is introduced through feed chute 22 at a rate in accordance with the grinding rate of the mill. As said material is reduced in size, that which is reduced sutciently fine to pass through lthe slots of the screening means 40 is discharged therethrough into annular chamber 63. As the mill revolves, the material within said space which is above the axis of the mill will fall onto the conical exterior of exit member 44 and slides down the same to be discharged through the exit shell of discharge spout 4S. Lifting of the material within the chamber 68 is accomplished by the provision of lifting means such as plates 94 which extend from the annular ring 66 radially inward toward the axis of the mill to preferably near the outer end of Athe exit member 44 as shown in FIGS. 1 and 3. Such lifting action is further facilitated if such plates 94 are curved so as to comprise spiral scoops 95 as shown in FIG. 3.

The grinding and comminuting action which takes place within the mill 1t) is best illustrated in FIGS. 3, 4 and 7. It is preferred that in the operation of the mill, grinding and treating of the material be of an autogenous nature and that run-of-the-mine material be ground and reduced in size to a desired range of ne material for desired purposes, the largest of which are determined by the openings in the screening means 40. It has been found that, contrary to previous attempts, the use of relatively low, as distinguished from' relatively high transverse lifter bars or ribs S2 operate more effectively tomaintain relative motion between the various size ranges undergoing reduction than when the lifter bars are higher than need be to prevent undue slippage against the peripheral shell liners, particularly when utilizing radial lifter bars in association with the end liners, which radial bars extend along the interior of the ends of the mill. Hence, the radial lifting bars 36 and 3S at one end of the mill cooperate with the radial lifting bars 60 and 76 on the opposite end of the mill and, in view of the fact that the length or axial dimension of the mill is relatively short in proportion to the diameter thereof, a substantial quantity of coarse ma- *but of the material of the mass which it contacts.

terial within the mixture being treated will be elevatedto a point higher than the same ordinarily would take place if relatively high transverse lifter bars 82 were used. The disadvantage of using relatively high transverse lifter bars which project radially inward from the cylindrical shall 12 is that part of the mass of the material within the mill tends to become locked and relative movement between said lifter bars ceases or at least to such an extent that the major portion ofthe spaces between the bars are filled with dead material and the bars then have substantially no lifting effect upon the larger segment of the material and the effective grinding volume of the mill is reduced thereby. As a result, when such relatively high transverse lifter bars are used, much of the material tends to orbit within the rotating mass of the material directly above the innermost edges of the relatively high transverse lifter bars and is not carried as high within the mill as it would be if bars were employed only of sufficient height to discharge lthe material onto the top of the mass so as to prevent slippage against the shell liners by the size characteristics of the material undergoing reduction. A different average size piece of the mass undergoing reduction calls for a different size lifting effect. Hence, the height of the bars should be subject to adjustment and testing at minimum expense for operation of the mill at optimum eiciency.

By the use of relatively low transverse lifter bars 82 in conjunction with radial lifterbars on the end shell mem- Ibers of the mill, particularly where the heights of the radial lifter bars are selected in accordance with the overall composition of the material, substantially firm lodgment of the material taltes place between the transverse lifter Ibars 32. Moreover, there is a tendency especially for the coarser particles of material when falling or rolling down the sloping mass within the mill to become momentarily held on the radial lifter bars so that they are elevated to a higher position within the mill than heretofore possible, even though some of the finer material may fall from between the coarser material, until finally, as illustrated in exemplary manner in FIG. 3, the coarser material is freed by gravity from between the radial lifter bars so that it falls and effects impact upon tthe sloping mass of the material within the mill, the most of which, at that instant, is substantially stationary to receive maximum impact, such coarser material also rolling `down the upper surface of the mass to effect reduction not only of itself Of equal, if not more, importance is the fact that such operation maintains a thorough intermixing action of all sizes laterally, a condition that is important to maintain in an autogenous grinding mill of the type here described as opposed to the desired classification for best operation ofthe conventional ball or pebble mill.

It is diicult to illustrate or indicate exactly 4the motion of the various segments or particles of material within the mill but an attempt has been made to do this somewhat diagrammatically in FIG. 7, which is at a right angle to 'the view in FIG. 3, and wherein the release of the larger pieces in particular from between the radial lbars 36, 38 and 60, 76 is denoted by the arrows 96. When said larger particles, as well as some of the smaller particles fall from between the radial bars or ribs, they will engage the sloping annular surfaces or bulges 98 of rings 26 and 42, whereby the falling material will be deflected toward the center as indicated by the arrows 100. Such deflection of the material will tend to direct it toward the center of the mill while other material will be falling substantially directly downward, the falling material colliding to some extent with itself, whereby even further distribution takes place throughout and particularly transversely across the 4mass of the material in the direction of the axis of the mill as is evident in exemplary manner in FIG. 4.

Particularly in regard to the material which rolls down -the sloping surface of the mass of the material within the mill, when at least some of the larger pieces of said rolling material stop rolling adjacent the' instantaneous Abottom of said mass of material, the sloping surfaces of the peripheral liner sections 86 will tend to direct said material toward the center of the mill. Such material also includes the larger, faster rolling pieces especially, and these will be trapped between the transverse ribs or bars 82 and be covered by the oncoming mass of material, whereby said pieces will not be released for dropping or rolling until they have been elevated to a relatively high position within the mill so as to be free either to drop onto the mass or roll down the same, some pieces rolling more or less centrally, while other particles thereof will tend to roll toward the feed or discharge end of the mill because of the tendency of the mass of the material to assume an angle of repose while being constantly moved by tumbling within the mill, whereby such rolling down the sides of the mass will take place from the theoretical crest of the material within the center of the mill. At least some of the larger particles will become momentarily entrapped between the radial bars or ribs along the ends of the mill during such rolling and falling thereof, whereby a thorough mixing of both large, medium and small segments takes place.

An additional lifting effect is achieved by reason of some of the material being momentarily wedged or entrapped by the undercut surfaces 98 of the rings or bulges 26 and 42, see FIGS. l and 7, so as to insure relatively high elevation of such material before being overcome by the force of gravity so as to cause the same to drop or roll relatively to the tumbling mass of material in the mill. Still further, momentary entrapment is afforded by the undercut surfaces of the annular ring 66 which produces a similar effect to the undercut surfaces of rings 26 and t2 but in an area closer to the periphery of the mill. Additionally however, the undercut surfaces of the ring 66 on that portion in the upper part of the mill assures deflection of the material, as indicated by the arrows 96 in FIG. 7, away from the grate surface 40 when the elevated material falls so as to minimize abrasive contact of the material with said grate surface. Likewise, the sloping surface of the annular ring 42 nearest the axis of the mill deflects falling material from the grinding Zone of the mill as well as that which falls or flows against end member 44 and wall 46 such as shown, for example, in FIGS. l and 4, toward the center of the mill and away from said grate so as to protect the surface thereof from direct impact by such falling material. The radial bars 60 which extend across the grate 40 likewise aid in protecting the grate from abrasive action, in addition to aiding in elevation of the material. Hence, passage of material through the slots or other openings through the grate takes place primarily from rolling action of the mass of material as distinguished from impact against the grate.

From the foregoing description, especially with reference to FIGS. 3 and 7, it will be seen that the operational results of the mill produce a thorough mixing of the coarse, intermediate, and fine segments of the material as it is rolled and tumbled within the mill and before the particles are submerged by the oncoming mass. The ability to change the various lifter bars and particularly those sections adjacent the ends 14 and 16 of the mill for bars of different heights permits the mill to operate effectively upon a wide range of size compositions of run-of-the-mine material. Accordingly, the mill is provided with radial and/or transverse lifting bars of desired heights after making a preliminary inspection of a run of material to be treated by the mill. Further, the conical ends of the mill, as shown in FIG. 1, offer advantages over the parallel ends in the embodiment shown in FIG. 2, due primarily to the natural spreading effect afforded by the conical ends which taper axially toward the peripheral section 12 of the mill, whereby the rolling material naturally tends to spread and then contract momentarily during rolling and tumbling down the slope 10 of material within the mill and as it hits the tapered liners of the shell 12. The whole mass is then inescapably being somewhat wedged between the sloping end walls which are relatively near to each other as distinguished from the relatively far apart end walls in a conventional ball or pebble mill.

Referring to the embodiment 'basically illustrated in FlG. 2, wherein the mill 102 has a cylindrical peripheral member or shell 104 and parallel end members 106 and 108 which comprise large discs which are centrally apertured and the peripheries of which are secured by welding or otherwise to the opposite ends of the cylindrical shell 104, said mill is supported at opposite ends by hollow trunnions 110 and 112 which correspond and function similarly to trunnions 1S and 26 respectively shown in FIG. l. It will be understood that many of the details shown in FIG. 2 correspond to similar details shown in FIG. l, whereby such details will not be described as minutely as in regard to the structure shown in FIG. l, reference being had where convenient to the details concerning FIG. l.

A feed chute 114 extends into entrance `trunnion 110 and a reversely angled conical exit shell 116 is connected to the end wall 108 and extends through exit trunnion 112. Annular rings or bulges 118 and 120, formed similarly to the rings 26 and Li2 respectively of the embodiment shown in FIG. l, extend around the central openings in the end walls 106 and 168 respectively and are attached by suitable bolt means for ready replacement and substitution. A frustro-conical exit member 122 is mounted in operative position concentrically with the exit shell 116 and in spaced relationship thereto.

The interior of the end wall 106 supports segmental liner plates 124 and 126 respectively clamped to end 106 by bars 12S and 134B which serve as radial lifter bars in similar manner as the bars 36 and 38 of the embodiment shown in FIG. l. The lifter and wedge bars 128 and 130 readily are replaceable due to conveniently being held in operative position by bolts 131 clearly illustrated in FIG. 2, whereby other lifter and wedge bars 128 and 130 having different heights than bars 128 and 130 may be mounted upon the end member 106. While wedge bars are described and illustrated in the various embodiments, it is to be understood that any type of separate clamping bar will also serve the same clamping purpose.

The end member 163 supports an annular grate 13-2 comprising a perforated diaphragm screening means which is illustrated as being substantially parallel to end member 168 and is supported in spaced relationship thereto by spacer sleeves 134. Radial lifter and clamping bars 136 preferably wedgingly clamp the segmental sections of the grate 132 in spaced relationship to the end lmember 108 to provide an annular chamber 138 to receive the material which has been reduced to a sufficient state of ineness that it passes through the slots or other openings in said grates. The radial bars 136 are replaceable by bars of different heights as indicated for example by the dotted line 136'. Another annular ring 148', similar in structure to ring 66 of FIG. l, defines the periphery of annular chamber 138 and also provides an undercut surface 142. The ring 140 is secured to end member 168 'by taper head bolts 143.

End member 10S also supports additional segmental liner sections 144 secured to the end member by radial lifter and wedge bars 146 which are connected to end 103 by taper head bolts, whereby the same may be replaced by other radial lifter bars 146 of different height, as desired. The cylindrical shell 104 of the mill 102 is lined intermediately of the edges thereof by liner segments 14S which are secured to the shell by transverse lifter and wedge bars 150 extending substantially in parallel relationship to the axis of the mill, the bars 150 being secured detachably by taper head bolts to the cylindrical shell 104,

11 whereby the same may be substituted by lifter bars having a different height.

Disposed between each end of the mill and the opposite ends of thetransverse liner segments 148 are sloping liner segments 152 secured by lifter and wedge bars 154 which extend in the same general direction as bars 150 and may be replaced by bars of different heights. Further, it will be noted from FIG. 2 that the lifter bars 150 as well as the segments 148 slope upwardly and outwardly -from the center thereof as seen in the lower part of the mill, whereby the associated liner segments connected to the cylindrical shell 104 provide oppositely sloping surfaces extending inward and radially outward from the axis of the mill, preferably at a gradual angle but which angle nevertheless is adequate to eifect lateral motion of the various sizes of material within the mill during the rotation thereof, such lateral motion principally being toward the center of the mill.

The annular rings 118 and 120 serve to deect falling material toward the center of the mill in a similar manner to that performed by rings 28 and 42 of the embodiment shown in FIG. 1. The ring 120 additionally protects the grate 132 from direct impact by falling material, while that portion of the additional ring 140 in the upper part of the mill serves to deflect falling material away from direct impact with grate 132 and, further, that portion thereof in the rising side of the mill affords limited wedging action of material within the mill while rotating, whereby at least some of the material and particularly the larger segments thereof are elevated to a relatively high position within the mill before gravity causes the same to drop or roll against the sloping mass of material within the mill.

In operation, the embodiment shown in FIG. 2 is illustrated essentially in FIG. 8, wherein exemplary arrows have been placed to illustrate in a diagrammatic manner what is observed to be approximate paths of certain seg- -ments of the material within the mill during the operation thereof. The embodiment shown in FIGS. 2 and 8 primarily relies for effective lifting upon a cooperation between the transverse lifting ribs or bars 150, 154 and the radial lifting ribs or bars 128, 130 at one end of the mill and radial lifting bars 136, 142 and 146 on the grate and opposite end of the mill, which lifting bars have been selected by test or otherwise as to height for greatest elieiency relative to a certain run of material. Thus, at least some of the larger segments of the material will become stationary momentarily particularly between the radial lifting bars or ribs so as to insure substantial elevation thereof within the mill before they are released by gravity to fall or roll onto the mass of material in the mill, such falling movement being indicated by the arrows 156. As the material is dislodged from between said radial ribs, at least some of the same may strike the annular rings or bulges 118 and 140, being deflected thereby toward the center of the mill. Still other large and intermediate, as well as some finer segments of the mass will be carried by the transverse lifter bars 150, 154 to a substantial height within the mill, and drop more or less centrally in the mill as indicated by the arrows 158. Such -falling material will roll down the upper surface of the sloping mass of the material and some of the larger elements, because of the angle of repose phenomenon, will roll toward the radial lifter bars, and rest therebetween until they again are released as the rotation of the mill brings them to the top of the load.

As treatment of the material continues, while thorough mixing thereof takes place especially in a transverse direction parallel to the axis of the mill, falling material is deected from contact with the grate screening means 136 but passage of relatively tine material through the grate takes place in a manner similar to that described relative to FIG. l, above, including lifting of the material Within the chamber 138 by plates 162 or the like, for discharge '12 onto the conical surface of exit member 122, as indicated by the arrows i.

Except for the increased holding, spreading and mixing action afforded by the conical ends of the embodiment of the invention shown in FIGS. 1 and 7, the embodiment shown in FIGS. 2 and 8, wherein the ends of the mill are substantially parallel to each other and perpendicular to the axis of the mill, is capable of performing a number of the benecial results of the embodiment shown in FIGS. l and 7 insofar as autogenous grinding is concerned.

Referring to FIG. 5, a slightly different embodiment of mill construction from that shown in FIGS. 1 and 9 is illustrated, particularly in regard to the transverse lifting ribs or bars adjacent the periphery of the mill and the disposition of the grate relative to the end member nearest the exit trunnion. The same basic reference characters are used in FIG. 5 as in FIGS. l and 9 for the elements which are common to both embodiments. In the embodiment of FIG. 5, it will be seen that the grate 40, rather than being substantially parallel to the end 16 of the mill, is perpendicular to the axis of the mill, thereby affording an annular chamber 164 of somewhat greater capacity than the annular chamber 68 in the embodiment shown in FIGS. 1 and 7. This embodiment necessitates the employment of spacing sleeves 166 of graduated lengths. Further the angle between the grate and opposite end of the mill in the embodiment shown in FIG. 5 is less than in the embodiment shown in FIGS. 1 and 7, whereby somewhat greater momentary wedging or compacting of the material takes place in the embodiment of FIG. 5 as it rolls and falls toward the bottom of the mill during rotation thereof as compared with the embodiment shown in FIGS. l and 7, thus enhancing the lifting of the material by the structure in FIG. 5 before the material falls.

The liner segments 168 are held in position by transverse lifter and wedge bars 172, as shown in detail in IFIGS. 12 and A13. Bars 172 have a substantially straight upper surface and are secured to shell 12 by clamping bolts 174. Similar lifter bars 176 are disposed between the liner segments 170, the ends of the lifter bars 176 nearest the lifter bars 3S and 76 respectively and preferably being shaped to merge therewith. Bolts 174 secure the lifter bars 176 detachably to the cylindrical shell 12. 'Ihe straight upper surface of lifter bars 172 and 176, in conjunction with the sloping surfaces of the liner segments atford greater lifting capacity than the arrangement shown in FIGS. 1 and 2, due to the greater areas of the lifter bars -in the centers thereof than at the ends of the bars.

A still further embodiment is illustrated in FIG. 6, this embodiment being similar in some respects to that shown in FIG. 5 and also being related to that shown in FIGS. 1 and 7. In FIG. 6, it will be seen that the feature which is principally different comprises the grate structure or screening means. There has been added in FIG. 6 an additional grate or screening member 178 which is substantially perpendicular to the axis of the mill 10, while the screening section 40, which is similar to that shown in FIGS. 1 and 7, also is employed. Such disposition of screening means close to the periphery of the mill places said means adjacent the location of maximum impact of the falling coarse pieces with the bed of the material, especially when the mill is loaded relatively lightly. This increased grate or screening area permits an increased rate of removal of the finer particles of material from the coarser pieces which are retained within the mill for further processing. The screening section 40 is connected to the end shell 16 by means similar to that shown in FIGS. l and 7, while the screening secetion 178, which preferably is formed from similar segments, is secured t0 the end shell 12 by radial lifter and wedge bars 180 which extend in wedging relationship between adjacent edges of the segments of the grate section 178. The relationship of the lifter bars 60 and 180 to the lifter bars 36 and 38 on the opposite end of the mill will afford a variation in wedging of material therebetween over that shown in the preceding embodiments.

The radial clamping bars lll are secured against the segments of grate section 178 by bolts lZ which extend through spacer sleeves 184.

It will be seen therefore from FIG. 6 that in addition to the annular chamber 68 between conical ring 42, grate screening means 4t? and end shell i6, an additional annular chamber lS extends between the grate means l't and end shell 16 and communicates with annular chamber 63 to comprise an extension thereof, thereby affording an even greater annular chamber into which the liner particles of material may pass than that afforded in the embodiment sho-wn in FIG. 5. To provide desired lifting effect within chamber E38, the radial plates or scoops 9d in chamber 68 preferably are supplemented by scoop-like members 95 within chamber 188 which are similar in shape, as viewed from the end, to the scoops 95 shown in FIG. 3, which facilitate the rate of travel of material behind grate 173 to discharge cone dft when the mill is running at relatively high speed.

While the various foregoing descriptions of the several embodiments of mills illustrated in the different figures of vthe drawings have included lifting bars which are searable from the lining segments of the mill, it is to be understood that the lifting within the mills may be effected by bars or ribs 19t) which may be integral with the liner segments 192 as illustrated in exemplary manner in FIG. 14, which is a vertical sectional view similar to FIG. 9. Bolts 194 are used to secure the segments 192 to the shell 12' of the mill. It is to be understood that the segments i922 may be replaced by other segments having ribs 190 of different'height than ribs 19d, thereby to vary the lifting effects of the ribs. The height of the ribs is selected in the same manner as that employed to select the detachable lifting bars of the other embodiments described hereinabove.

Whereas a conventional conical mill straties the material in accordance with the intended purpose thereof to achieve its desired objectives, the present invention utilizes, in at least several embodiments, sloped ends somewhat similar to a conical mill but prevents stratification of the material therein through the employment of a relatively narrow mill, applying specific deflecting means, using radial and transverse retaining and lifting bars on ends and peripheral shell of mill, as well as annular expansion spaces extending axially outward of mill on at least one end. By means of these, individual pieces or particles of material are caused to have lateral movements between the ends and assume no regular, repeated or stratifying lateral paths, thereby resulting in relatively uniform mixing and dispersion of all sizes of material throughout the mass in the mill. As an example of typical paths of certain exemplary particles, reference is made in FIG. 4 in which various typical large or coarse pieces of material are shown moving through certain typical paths, said pieces being numbered l1. through to show progressive positions thereof within the mill and mass of material therein.

In the embodiments of the invention described in detail above, no specific reference has been made to fluid currents which may be employed with such embodiments to enhance removal particularly of the finer particles of material from the mill. When the end wall 46 in FIG. l, for example, is employed in the exit end of the mill, liquid currents readily may be circulated within the mill to eect wet grinding and enhance the flowing of at least the finer particles through the grate screening means of the mill. If screening means is not employed, the exit end of the mill may be modied, especially to provide a passage to the hollow exit trunnion, so that flowing of the material entrained within the discharging liquid may take place. lf gaseous currents are to be employed to circulate through the mill, especially to entrain the finer particles and carry them from the mill, the exit end of the mill can be modified to permit this such as by omitting end Wall 46 and arrange an entrance end of a conduit relative to the exit trunnion of the mill, whereby either a negative or a positive pressure fluid current may be imposed upon such conduit in a direction to effect removal of the fluid current and entrained material from the mill through the yexit trunnion in accordance with well known principles. .Because of the constant, through mixing of the material within the mill arrangement as herein specified, when either a liquid or gaseous current is circulated through the mill, no objectionable stratification of the material will take place as is otherwise the case where fluid currents are employed. The so-called stratifying or classifying action caused by fluid current or other means is in fact a desirable feature when separate grinding media other than the material itself is employed such as in the so-called standard ball, pebble, or rod mill, but is not desirable in autogenous grinding of the type described hereinabove.

While the invention has been described and illustrated in its several preferred embodiments, and has included certain details, it should be understood that the invention is not to be limited to the precise details herein illustrated and described since the same may be carried out in other Ways falling Nithin the scope of the invention as claimed.

I claim: 1. A rotatable tumbling mill for treating friable material to reduce the size thereof and having opposed ends of lconvex congurations sloping away from each other from Athe inner surface of said screening means being exposed to the material undergoing reduction and the outer periphery of said screening means being spaced inwardly from the outer periphery of the grinding zone of the mill, and deflecting means adjacent the outer periphery of said screening means having a substantially annular deecting surface extending angularly inward away from the exit end of the mill contiguous to said screening means and toward the axis of rotation of the mill, said annular deilecting surface being operable to be engaged by material falling within the mill and deect the same away from said screening means to protect the same and also to produce an added intermixing action upon said material within said grinding zone.

2. A rotatable tumbling mill for treating friable material to reduce the size thereof and having opposed ends of convex configurations sloping away from each other from the periphery to the axis of the mill and the diameter of the internal grinding Zone of the mill being substantially greater than the axial length thereof, the ends of the mill being provided respectively with substantially coaxial inlet and exit opening means and the interior surface of the end having said exit means being provided with an annular space extending axially away from the center of the mill adjacent the periphery thereof and extending radially inward toward the axis a predetermined distance to provide a laterally expanded grinding Zone in said mill, and perforated screening means carried by the exit end of the mill and positioned at least partially opposite the grinding zone of the mill and converging radially toward the exit opening means of the mill from the inner periphery of said annular expanded zone, the circumferential surface of said screening means being exposed to the material undergoing reduction to deflect the same away from said screening means toward the center of the mill to minimize stratication of material within said grinding zone.

3. A rotatable tumbling mill for treating friable material to reduce the size thereof and comprising a drum having opposed ends connected by a peripheral shell means and said ends respectively having substantially coaxial inlet and exit means therein and the interior of 'said drum defining an internal grinding zone having a substantially greater diameter than the length thereof in an axial direction, perforated screening means carried by the end of the drum having exit means therein and extending radially into the grinding zone, the circumferential perimeter of said screening means being of lesser diameter than that of said grinding zone and exposed to the material undergoing reduction, and defiecting means extending angularly in an axial direction into the grinding zone adjacent the outer periphery of said screening means and being operable to deect falling material from direct impacting engagement with said screening means, thereby minimizing abrasion of said screening means and effecting mixing of all size segments of material in a transverse direction within said grinding zone.

4. A rotatable tumbling mill for treating friable material to reduce the size thereof and comprising a drum having opposed ends respectively having substantially coaxial inlet and exit means therein and defining an internal grinding zone having a substantially greater diameter than the length thereof in an axial direction, the end of the mill having the exit means therein being provided with an annular recess extending between the periphery fof the drum and extending radially toward the axis thereof a predetermined distance and also extending axial- 1y outward from the center of the mill to provide a laterally expanded grinding zone, and perforated screening means converging radially inwardly from the inner periphery of said expanded zone toward the axis of said drum, the inner surface of said screening means being exposed to the material undergoing reduction and the surface comprising said inner periphery of said expanded zone projecting in an axial direction into said mill and being operable to deflect material from direct impacting engagement with said screening means, thereby minimizing abra- 4`sion of said screening means and effecting mixing of all size segments of material in a transverse direction within said grinding zone.

5. A rotatable drum-type mill for subjecting friable material to reduction of size and having ends thereon, the diameter of the interior of the mill being substantially greater than the length thereof in an axial direction and said ends having substantially coaxial inlet and exit means for material fed to and discharged from said mill, wear resistant lining means extending around the interior of said mill, the surfaces thereof defining the inner periphery of said mill sloping radially outward from the perim- `eter of the ends of the mill toward the center of the mill,

whereby material falling upon said peripheral lining means laterally outwardly from t-he center thereof will move toward the center of the mill, and lifter bars extending radially inward from and transversely across said peripheral lining means at spaced circumferential intervals, said bars having substantially straight inner surfaces exposed to the material undergoing reduction, thereby providing transverse pockets increasing in depth from the outer ends toward the centers thereof.

6. A rotatable drum-type mill for subjecting a range of sizes of friable material to self-reduction of all sizes simultaneously and having opposed convex ends sloping 'away from each other from the periphery to the axis of the mill, the diameter of the interior of the mill being substantially greater than the length thereof in an axial direction and said ends having substantially coaxial inlet and exit means for material fed t-o and discharged from said mill, wear resistant lining means extending around the interior of said mill, the surfaces thereof defining the yinner periphery of said mill sloping radially outward from the perimeter of the ends of the mill toward the center of the mill, whereby materia-l falling upon said peripheral lining means laterally outward from the center thereof will move toward the center of the mill, and lifter bars extending radially inward from and transversely across i6 said peripheral lining means at spaced circumferential intervals, said bars having substantially straight inner surfaces exposed to the material undergoing reduction whereby the greatest lifting area of said bars is substantially in the center of the mill.

7. A rotatable tumbling mill for treating friable material to reduce the size thereof and comprising a drum having opposed ends respectively having substantially coaxial inlet and exit means therein and defining an internal grinding zone having a substantially greater diameter than the length thereof in an axial direction, perforated diaphragm screening means extending radially into the grinding zone and carried by the end of the drum having the exit means therein and the inner surface of said screening means being exposed to the material undergoing reduction, the circumferential perimeter of said screening means extending in an axial direction into the grinding zone beyond the adjacent areas of the end wall and the inner peripheral surface of the drum sloping radially outward from the perimeter of the drum toward the center thereof, and lifter bars extending radially inward from and transversely across said inner peripheral surface of the drum at spaced circumferential intervals, said bars having substantially straight inner surfaces exposed to the material undergoing reduction, whereby the greatest lifting area of said bars is substantially in the center of said drum and the inwardly extending circumferential perimeter of said screening means being operable to defiect materia-l falling thereonto away from said diaphragm means to cooperate with said sloping peripheral surfaces of said drum to effect mixing of all size segments of material in a transverse direction within the grinding zone of said drum.

8. A rotatable tumbling mill for treating friable material to reduce the size thereof and having opposed ends of convex configurations sloping away from each other from the periphery to the axis of the mill, the diameter of the Vinternal grinding zone of the mill being substantially greater than the axial length thereof and the ends of the mill being provided respectively with inlet and exit means, annular perforated diaphragm screening means carried by the end of the mill having the exit means therein and spaced from said end in an axial direction, said diaphragm means converging substantially radially inwardly from the periphery of said mill a predetermined distance toward the axis thereof but spaced therefrom, a circumferential portion of said diaphragm screening means being substantially parallel to said end of the mill and another circumferential portion thereof being substantially vertical to the axis of the mill, and deliecting means adjacent the circumferential portion of said diaphragm screening means nearest the axis of said mill and extending laterally inward from said circumferential portion to effect defiection of falling material in a direction away from said diaphragm means.

9. A rotatable tumbling mill for treating friable material to reduce the size thereof and comprising a drum having opposed ends respectively having substantially coaxial inlet and exit means therein, the interior of the drum comprising a grinding zone the diameter of which 4is substantially greater than the length thereof in an axial direction, annular perforated diaphragm screening means spaced inwardly in an axial direction from the end of said drum having the exit means therein and the inner and outer perimeters of said diaphragm means respectively being spaced from the axis and the peripheral surface of the grinding zone, there being an annular grinding space of predetermined appreciable radial depth defined by the periphery of the mill and the outer perimeter of said diaphragm means, and substantially annular detlecting means extending respectively around said perimeters of said diaphragm means and at least one of said deecting means projecting into said drum axially beyond the inner surfaces of said diaphragm screening means and said deecting means being operable to deflect material from direct falling impact with said diaphragm surface, thereby minimizing abrasion of said grate means and effecting transverse mixing of the material undergoing treatment.

10. A rotatable tumbling mill for treating friable material to reduce the size thereof and having opposed ends of convex configurations sloping away from each other from the periphery to the axis of the mill, the diameter of the internal grinding zone of the mill being substantially greater than the axial length thereof and the ends of the mill being provided respectively with inlet and exit means, annular perforated diaphragm screening means carried by the .exit end of the mill and spaced in an axial direction into the mill and at least portions of said screening means being substantially parallel to the adjacent convex ends of the mill, the inner and outer perimeters of said diaphragm means respectively being spaced from the axis and the peripheral inner surface of said mill, deflecting substantially annular means respectively extending around the perimeters of said diaphragm means and projecting in an axial direction into the grinding zone of the mill respectively beyond the adjacent perimeter of said diaphragm means and said deflecting surfaces being operable to be engaged by falling material to deflect the same away from said diaphragm screening means to protect the same and also minimize stratification of material within said grinding zone.

11. A rotatable tumbling mill for treating mixtures of various sizes of friable material to reduce the same to a predetermined range of fine sizes thereof by self-reduction of all sizes simultaneously and comprising a drum having opposed ends and the diameter of the internal grinding zone of the mill being substantially greater than the axial length thereof, the ends of the mill being provided respectively with substantially coaxial inlet and exit means, substantially annular and radially extending perforated diaphragm screening means carried by the exit end of the mill to define at least a portion of one end of the grinding zone within the mill, means comprising a set of material lifter means having a predetermined height and detachably connectable relative to the inner surface of the mill in directions substantially perpendicular thereto and perable to provide the mill with a certain lifting effect upon a given run of material and produce a determinable rate of reduction of material within the mill, additional sets of material lifter means respectively having heights different from each other and the predetermined height of said aforementioned set, said sets selectively being exchangeable one for the other respectively to produce different lifting effects within the mill if said determinable rate of reduction of said given run of material is not a desired optimum, and means to connect a selected set of said material lifter means detachably to the interior of the mill in spaced relationship to each other, whereby a selected set of said material lifter means of a given height may be exchanged for another set of material lifter means of a different height to produce an optimum reduction rate of a given run of material within the mill.

l2. A rotatable tumbling mill for treating mixtures of various sizes of friable material to reduce the sizes thereof to a predetermined range of fine sizes thereof and comprising a drum having opposed ends respectively provided with substantially coaxial inlet and exit means therein, perforated diaphragm screening means carried by the exit end of the mill and extending radially, the perimeter of said diaphragm screening means being spaced from the interior periphery of the drum and the interior surface of the end of the mill carrying said diaphragm screening means being positioned axially outward from said diaphragm screening means to provide a substantially annular expanded zone within the drum adjacent the periphery thereof, and radial lifter bars connected to the interior surface of said end of the drum in circumferentially spaced relationship to each other within said expanded zone.

13. A rotatable tumbling mill for treating mixtures of various sizes of friable material to reduce the sizes thereof to Ya predetermined range of fine sizes'thereof and comprising a drum having opposed ends respectively provided with substantially coaxial inlet and exit means therein, perforated diaphragm screening means carried by the exit end of the mill and extending radially, the perimeter of said diaphragm means being spaced from the interior periphery of the drum and the interior surface of the end of the mill carrying said diaphragm means being positioned axially outward from said diaphragm to provide a substantially annular expanded zone within the drum adjacent the periphery thereof, means comprising a set of material lifter means of a given height connectable detachably against the end wall in said expanded zone in circumferentially spaced relationship to each other and operable to provide the drum with a certain lifting effect in said expanded zone relative to a given run of material and thereby produce a mixing of the various sizes of material within the drum by action of the lifted material within said expanded zone in being deflected laterally from said zone and thereby produce a determinable rate of reduction, additional sets of material lifter means respectively having heights different from each other and the given height of said aforementioned set, said sets selectively being exchangeable one for the other to produce different lifting effects within said expanded zone if said determinable rate of reduction of a given run of material is not a desired optimum, and means to connect a selected set of said material lifter means detachably to said end wall within said expanded zone, whereby said selected set of said material lifter means of a given height may be exchanged for another of said sets of material lifter means of a different height to produce an optimum lifting effect in said expanded zone upon a given run of material to produce thorough mixing of all sizes of material within the drum as a result of the lifted material Within said expanded zone being deflected laterally from said expanded zone and thereby produce an optimum reduction rate of a given run of material within the mill.

14. A rotatable mill for subjecting a mixture of friable material of different sizes to reduction to a range of finer sizes within a desired range, said mill having ends respectively provided with substantially coaxial inlet and exit means and the diameter of the interior of the mill being substantially greater than the length thereof in an axial direction, annular perforated diaphragm screening means carried by the end of the mill having the exit means therein and spaced from said end in an axial direction, said diaphragm means extending substantially radially within said mill and defining at least a portion of one end of the grinding zone of the mill and operable to permit discharge therethrough for passage to said exit means of a range of products less than a predetermined maximum, guiding and lifting means on the interior peripheral surface of the mill between the ends thereof, said means having angularly related guiding surfaces on said interior periphery of the mill for engagement of the material as tumbled within said mill to cause all sizes of said material to be intermixed and moved in opposite axial directions and said guiding and lifting means comprising a set of material lifter means of a given height detachably connectable relative to said aforementioned inner peripheral surface of the mill and projecting inwardly therefrom, said set of means being operable to produce a certain lifting effect upon a given run of material to produce a determinable rate of reduction of material within the mill, additional sets of material lifter means similar to the aforementioned set but all of said sets respectively having heights different from the other sets, said sets selectively being exchangeable one for the other to produce different lifting effects within the mill if said determinable rate of reduction of a given run of material is not a desired optimum, and means detachably connecting a selected set of said material lifter means to the periphery of said mill to provide the mill with optimum lifting effect relative to a given run of material.

15. A process of treating run-of-the-mine solid material consisting of a mixture of large, intermediate and relatively fine sizes of the material to grind and reduce all sizes of the same simultaneously and progressively and autogenously to a predetermined range of fine sizes by tumbling the same within a rotatable mill while thoroughly mixing all sizes by substantially unobstructed transverse movement from end to end within the mill in a direction parallel to the axis of rotation of the mill, retaining the coarser particles of unwanted sizes for further reduction in size, separating the finer sizes of a predetermined range therefrom continuously by screening incident to removal from the mill, and further subjecting the retained coarse particles of an unwanted size adjacent to the screening zone to additional movement toward and away from said screening zone to enhance the mixing action of the retained coarse particles adjacent the screening zone within the mill and thereby cause grinding engagement thereof with the other sizes of material therein present when the coarse particles are out of contact with the screening means to facilitate discharge of the desired sufficiently reduced size ranges when in said screening zone.

16. The method of operating a tumbling mill provided with interior protrusions in the comminution of a mixture of ranges of various sizes of friable material autogenously to effect optimum efficiency in simultaneous reduction in size of all sizes of material in said mixture by the impinging forces of the material acting upon itself and the interior surfaces of the mill while tumbling, said method comprising the steps of feeding to said tumbling mill at a selected rate a mixture of said friable material of unknown reduction characteristics and consisting of coarse sizes mixed with intermediate and fine sizes, grinding said material autogenously within said mill while employing material lifters of a selected contour for a trial period of time sucient substantially to stabilize the material load size range and size ratios within the mill, determining the reduction characteristics as established by said load in the mill, then altering the contour of the interior of the mill sufficiently to vary the reduction characteristics therein to produce a size range and ratio of the various size ranges of the material load within the mill different from that produced during the trial period if said ratio is not substantially that having a desired size range and ratio of said various sizes of material enabling said mill to produce a product of the desired characteristics at optimum efiiciency under the existing conditions.

17. The method of operating a tumbling mill as set forth in claim 16 and further characterized by said grinding occurring in a confined zone while moving the mass of the material axially therein between the ends of the mill to maintain all sizes thereof axially mixed and moving said mass of the material vertically a substantially greater distance than it is moved axially, and removing said product from a discharge zone adjacent one end of said mill at a location below the load level in said mill.

18. The method of operating a tumbling mill provided with interior protrusions in the comminution of a mixture of ranges of various sizes of friable material autogenously to effect optimum eiciency in simultaneous reduction in size of all sizes of material in said mixture by the impinging forces of the material acting upon itself and the interior surfaces of the mill while tumbling, said method comprising the steps of feeding to said tumbling mill at a selected rate a mixture of said friable material of unknown reduction characteristics and consisting of coarse sizes mixed with intermediate and fine sizes, grinding said material autogenously within said mill while employing material lifters of a selected contour for a trial period of time sufficient substantially to stabilize the material load size range and size ratios within the mill, determining the reduction characteristics as established by said load in the mill, and altering the contour of the mill to cause greater impact of coarse sizes of material for more rapid disintegration thereof if the ratio of said coarse sizes to the 2f) smaller sizes is determined to be too high for a desired reduction rate.

19. The method of operating a tumbling mill provided with interior protrusions in the comminution of `a mixture of ranges of various sizes of friable material autogenously to effect optimum efficiency in simultaneous reduction in size of all sizes of material in said mixture by the impinging forces of the material acting upon itself and the in terior surfaces of the mill while tumbling, said method comprising the steps of feeding to said tumbling mill at a selected rate a mixture of said friable material of unknown reduction characteristics and consisting of coarse sizes mixed with intermediate and fine sizes, grinding said material autogenously within said mill while employing material lifters of a selected contour for a trial period of time sufficient substantially to stabilize the material load size range and size ratios within the mill, determining the reduction characteristics as established by said load in the mill, and altering the contour of the mill to produce a decreased rate of disintegration of the coarse sizes of material if the ratio of smaller sizes of material to the coarse sizes thereof is determined to be too high for a desired reduction rate.

20. A process of treating run-of-the-mine solid material consisting of a mixture of large, intermediate and relatively fine sizes of material to grind and reduce all sizes of the same simultaneously and progressively and autogenously to a predetermined range of fire sizes by tumbling the same within a rotatable mill having a diameter substantially greater than the length thereof while thoroughly mixing all sizes by substantial transverse movement from end to end within the mill in a direction parallel to the axis of rotation of the mill, retaining the coarser particles of unwanted sizes for further reduction in size, and separating the finer sizes of a predetermined range therefrom continuously by screening adjacent the location of maximum impact of falling pieces of material and facilitating the removal of said finer sizes from the mill by said mixing action in a direction parallel to the axis of rotation of the mill serving constantly to move the coarser particles of material away from the screening zone to free the same for said finer sizes to discharge therethrough.

2l. A rotatable tumbling mill for treating friablle material to reduce the size thereof and having opposed ends, the diameter of the internal grinding Zone of the mill being substantially greater than the axial length thereof and the ends of the mill being provided respectively with inlet and exit means, annular perforated diaphragm screening means carried by the end of the mill having the exit means therein and spaced from said end in an axial direction, said diaphragm screening means extending radially substantially from the periphery of said mill a predetermined distance toward the axis thereof, whereby screening of the material for discharge of a range of sizes less than a predetermined maximum may occur adjacent the location of maximum impact of falling material, and means within the mill and movable therewith for engagement by falling material as the mill rotates and operable to effect mixing movement of the various sizes of material in directions extending axially of the mill.

22. The -mill set forth in claim 2l further characterized by said means to effect mixing movement including annular defiector means adjacent the inner periphery of said screening means and operable to dcfiect material from direct falling impact with said screening means, thereby, to minimize abrasion of said means.

23. The mill set forth in claim 22 further including end Wall means within said annular deflector means and extending radially toward the axis of said mill, said end wall means retaining within the mill the material undergoing reduction within the zone of the mill adjacent said end wall means.

24 The mill set forth in claim 2l further characterized 21 by said means to effect mixing movement including variations in the contour of the inner surface of at least one end wall of said mill arranged so as to be engaged by all sizes of said material being treated within the mill and said means also being shaped so as to be capable of. eecting inter-mixing and axial movement of all sizes of the material for substantially the full length of the mill.

25. The mill set forth in claim 21 further characterized by said means to effect mixing movement including variations in the contour of the interior peripheral surface of the mill comprising augularly related guiding surfaces extending generally transversely across substantially the full width of said peripheral surface and engagea-ble by said material as tumbled within said mill to cause all sizes of said material to be intermixed and moved axially in opposite directions.

26. A rotatable tumbling mill for treating friable material to reduce the size thereof and having opposed ends, the diameter of the internal grinding zone of the mill being substantially greater than the axial length thereof and the ends of the mill being provided respectively with inlet and exit means, the exit end of the mill having size- 4limiting discharge opening means therein operable to permit passage therethrough of material of a predetermined maximum size while retaining material of larger size within the mill for further reduction in size, and annular deilector means adjacent said size-limiting discharge opening means and engageable by material being tumbled within the mill while falling from or toward said sizelimiting discharge opening means and operable to deflect said falling material away from said size-limiting discharge opening means, thereby to minimize abrasion of said means and also effect Imovement of said material substantially axially within said mill.

27. A rotatable tumbling mill for treating friable material to reduce the size thereof and having opposed ends, said mill having an interal grinding zone which is substantially unobstructed between the opposite peripheral surfaces and the diameter of said internal grinding zone being substantially greater than the axial length thereof, the ends of the mill respectively having inlet and exit means, diaphragm means having size-limiting discharge opening means carried by the end of the mill having the exit means therein and spaced from said end in an axial direction, said discharge opening means extending radially a predetermined distance toward the axis of the mill and permitting discharge therethrough of a range of sizes of material of a predetermined maximum size from the grinding zone of the mill at a level substantially below the level of discharge of material through the exit in said end of the mill, and means detachably connected to the interior of the ends of the mill and movable therewith and positioned to be engaged by material falling within the substantially unobstructed interior portion of the mill as it rotates and deflected thereby to effect mixing of all sizes of the material axially in opposite directions substantially from one end of the mill to the other.

References Cited in the file of this patent UNITED STATES PATENTS 928,967 Hardinge July 27, 1909 1,080,768 Marcy Dec. 9, 1913 1,222,184 Cole Apr. 10, 1917 1,282,914 Mitchell et al Oct. 29, 1918 1,295,726 Garrow Feb. 25, 1919 1,315,025 Lawler Sept. 2, 1919 1,335,269 Ball Mar. 30, 1920 1,451,472 Pomeroy Apr. 10, 1923 1,589,741 Bonnot et al June 22, 1926 l1,591,938 Harrison July 6, 1926 1,690,493 Marcy Nov. 6, 1928 1,690,495 Marcy Nov. 6, 1928 1,690,497 Willard Nov. 6, 1928 2,185,960 Vogel-Jorgensen Jan. 2, 1940 2,381,351 Hardinge Aug. 7, 1945 2,555,171 Weston May 29, 1951 2,566,103 Weston Aug. 28, 1951 2,678,167 Weston May 11, 1954 FOREIGN PATENTS 118,840 Sweden May 20, 1947 272,033 Switzerland Mar. 1, 1951 OTHER REFERENCES Hardinge Company, Bulletin 18-A, page 8. Mineral Industry, volume 47, page 682 (1938).

Claims (1)

1. A ROTATABLE TUMBLING MILL FOR TREATING FRIABLE MATERIAL TO REDUCE THE SIZE THEREOF AND HAVING OPPOSED ENDS OF CONVEX CONFIGURATIONS SLOPING AWAY FROM EACH OTHER FROM THE PERIPHERY TO THE AXIS OF THE MILL, THE DIAMETER OF THE INTERNAL GRINDING ZONE OF THE MILL BEING SUBSTANTIALLY GREATER THAN THE AXIAL LENGTH THEREOF AND THE ENDS OF THE MILL BEING PROVIDED RESPECTIVELY WITH INLET AND EXIT MEANS, PERFORATED SCREENING MEANS CARRIED BY THE EXIT END OF THE MILL AND EXTENDING SUBSTANTIALLY RADIALLY INTO THE GRINDING ZONE OF THE MILL AWAY FROM THE EXIT MEANS ON SAID END, THE INNER SURFACE OF SAID SCREENING MEANS BEING EXPOSED TO THE MATERIAL UNDERGOING REDUCTION AND THE OUTER PERIPHERY OF SAID SCREENING MEANS BEING SPACED INWARDLY FROM THE OUTER PERIPHERY OF THE GRINDING ZONE OF THE MILL, AND DEFLECTING MEANS ADJACENT THE OUTER PERIPHERY OF SAID SCREENING MEANS HAVING A SUBSTANTIALLY ANNULAR DEFLECTING SURFACE EXTENDING ANGULARLY INWARD AWAY FROM THE EXIT END OF THE MILL CONTIGUOUS TO SAID SCREENING MEANS AND TOWARD THE AXIS OF ROTATION OF THE MILL, SAID ANNULAR DEFLECTING SURFACE BEING OPERABLE TO BE ENGAGED BY MATERIAL FALLING WITHIN THE MILL AND DEFLECT THE SAME AWAY FROM SAID SCREENING MEANS TO PROTECT THE SAME AND ALSO TO PRODUCE AN ADDED INTERMIXING ACTION UPON SAID MATERIAL WITHIN SAID GRINDING ZONE.

Images