US2980352A - Grinding mills - Google Patents

Description

April 18, 1961 o. H. JOHNSON 2,980,352

GRINDING MILLS Filed Dec. 22, 1958 5 sheets-sheet 1 (5 Fg E- April 18, 1961 o. H. .JoHNsoN 2980352 GRINDING MILLS Filed Dec. 22, 1958 5 Sheets-Sheet 2 ooooooooooo oooooocoooo I5 OOOOO INVENTOR.

OSCAR H. JOHNSON BY MM ff/W lil-.,15-

April 18, 1961 o. H. JOHNSON GRINDING MILLS 5 Sheets-Sheet 5 Filed Deo. 22, 1958 R. 0.9/ \;D\\\ s R. m Ll@ mm 5. :Yo 5-o? E H o I. u MDN .knw gx MJ H @l v I? mm m bm m/ mlllllElll m Ihm. K E. wom H 1 -I R M Il :mm l lm mm hm Non mm MM mm my nOu Q bm Ww n@ \om, O B M mom, f L @ma 4 mom |||JT Q, l

mm\ h\ \.n\\ mm \\om Emma@ m @I m\. I m,\ N1 M mw mv\ I im, `v\ W.m\ l l `Ml NW Guss smits @scar H. Johnson, Denver, Colo., assigner to American Brake Shoe Company, New York, NSY., a corporation of Delaware Filed Dee. 22, 195%, Ser. No. '782,222

IClaims. (Cl. 241-183) This invention relates to grinding mills which use rods or balls or selected pieces of ore as the grinding media, and is concerned in particular with the construction of the liner for the shell of the mill.

It is conventional practice in the grinding mill art to line both the shell and the end walls with replaceable linears of wear-resistant material such as maganese steel or like ferrous metal alloy which is resistant to attrition and impact types of wear. These liners are what take the wear, thereby protecting the more expensive shell and end Walls, and when the liners become unduly worn the mill is temporarily shut down and relined where necessary'.

Over the years, diierent shapes and configurations have been imparted to the liners for imparting certain types of action to the grinding media in order to either enhance the eiciency of the mill or prolong further the life of the liner elements. For instance, it is conventional to so form the liners for the shell as to account for a wave or rib-like appearance of the shell liner, but I have found that such rib-like shell liner constructions account for a great deal `of slippage of the grinding media whether these be rods, balls or selected pieces of ore. In this connection, it should be mentioned that the most eicient types of comminution within a grinding mill is that which follows from an actual forceful impact of the grinding media on the charge. Tnernext most eicient type of cornminution is that caused by a rolling action of the grinding media on the charge. Virtually no comminution occurs as a result of the grinding media simply sliding or slipping one over the other within the mill, and I have found that the wave-type or rib-type shell liners encourage a great deal of slippage within the mill thereby lowering the grinding eiciency. Accordingly, the primary object of the present invention is to so construct a shell liner for a grinding mill as to account for high eiiiciency in impact and attrition grinding. Specifically,l I achieve this by constructing the shell liner of alternate to be carried around with the shell with virtually no inemcient backsliding, and when theforce or" gravity on the grinding media overcomes the centrifugal force of the mill the grinding media take fiight and fall with a violent force downward in a deilected direction toward the opposite side ofthe mill with the consequent result of a great deal of impact gnindingon the charge within 4the mill. v V- v The foregoing explains the primary principle of the present invention, and this principle together with ancillary features will be more apparent from and will be explained in greater detail in `connection with the description of the present construction of grinding mill shell liners.

Other and further objects of the present invention will be apparent from the following description land claims and are illustrated in the accompanying drawings which, by way of illustration show a preferred embodiment of the present invention and the principle thereof and what is now considered to be the best mode contemplated for applying this principle. Other embodiments ofthe invention embodying the same or equivalent principle may be used and structural changes may be made as desired hy those skilled in the art without departing from the present invention and the purview of the appended claims.

in the drawings:

Fig. 1 is a perspective view of a grinding mill having a shell liner constructed in accordance with the present invention, one end of the mill being open to reveal the internal construction;

` Fig. 2 is a sectional view on an enlarged scale of a portion of the shell of the mill in Fig. l lined in accordance with one plan under the present invention;

Fig. 3 is a plan view showing the precise manner in which'liner plates are arranged under one plan;

Fig. 4 is a perspective view showing the Various kinds of liner plates designated iu Fig. 3;

Fig. `5 isa plan view of another installation constructed in laccordance with the present invention;

Fig. 6 is a plan View on an enlarged scale of two of the lifter plates shown in Fig. 5;

Fig. 7 is a sectional View through either of the plates Sil and 31 in Fig. 6;

Fig. 8 is a sectional View through either of the plates fi-il and 41 in Fig. 5;

Fig. 9 is a sectional view of a conveyor plate for the installation shown in Fig. 5.

Grinding mills in actual practice are constructed in many ditferent forms for different purposes depending primarily upon the type of material to be comminuted and the manner in which the charge is to be fed to and withdrawn from the mill. The mill l@ in Fig. l of the drawings is illustrated schematically for the most part,

since the present invention is concerned with the construction yof a shell liner `rather than the operation details of the mill as a whole. cylindrical shell or drum 11. which yaiords the chamber which the charge and the grinding media are confined foraction.v The ends of such a mill are closed oi by end weils as l2 securely locked to the shell, and these end walls are provided with trunnions (not shown) that are supported in bearings which in turn are part of the standards or bearing blocks as 'BB which support the mill' for rotation. One of the end walls-is usually provided with an inlet of one kind or another for the charge that is to be commiDuted, and the other end Wall is usually provided with a take-oft" for the resultant fines. Movement of the charge through the mill can be Ione of 4gravity as a result of tipping the mill slightly or oan'be ciples ofthe present invention are applicable to mills which use 'other type grinding media such as balls Vand gore,` and hence various forms of grinding Vmedia capable of rolling on one anotherrare contemplated. f It will be The mill 10 includes a l Y be explained.'Y A Y Y Y :Each shell'liner row in the mill is made up of individual Yto be expected. A, v d d The lifter linery rows alsocomprise individual plates Vthat are secured in a conventional style to the shell of shell'isf lined jso as to have alternating rows of dissimilar liners which are so constructed as to greatly improvethe action of the grinding media, and this construction will nowV be explained'inidetail. Y l

Referring to Fig.VA l, the reference characters R1 and R2 are used to identify respectively-the conveyor liner rows jandethe lifter liner'rows, andthese rows of liners v alternate circumferentially about the mill. VVIt will moreoverbe'noted that each lifter liner row` has spaced projecprising the lifter liner,and these media, asV will be observed inFigs.V 1 and Z,` occupy elevated positions'in comparison Ato the grinding media which engagezthe conltionsV of quitelgenerous area, whereas the` conveyor liner Y :row'has no such projections. Thisrpartiular construction enables Vseveral of the grindingmedia to rest on Y,the y elevated surfaces of thejprojecting'members comveyor liners. Additionally, lthe, rows of lifter liners are Y oil-set longitudinally of the mill, andA this produces an advantageous tortuous ow of iin'es within themill as will plates secured to the shell in a conventional style, andY referring to lFig."ytheconveyor linervplates include a 'f'pluralit'yf ofV short plates CA Vwhich arefof rectangular dimension and which'arelaid end to end in Va row along the len'gtliio'fgthemill parallelto the longitudinal axis.

CB will be Vapproximately one-third longer. ForV instance, inY a mill of approximately sixteen feet axiallength lifter plates. Also included in the lifter liner rows are lifter plates LB and LC of somewhat dilerent contguration or dimension as will now be explained. The lifter plates LB, like the plates LA, are of the same length and width dimension as the conveyor plates CA. However, kthe plates LB have two spaced projecting pads or blocks 16 and 17 atthe two ends thereof, and these parts 16 and 17 are separated by a shallow 0r depressed portion 18 which in the assembly will be coplanar with the wear surfaces'of the ledges 174g and'lonthe. plates LA. The pads 16 and 17, and the depressed surface 1S therebetween, are equal in'area dimension Vand are equal in area dimension to the parts 13, 14.and115 of the plates LA- Y Y The lifter plates LC have the length and width dimensions of the conveyor plates CB. The lifterV plates LC have projecting blocksV or pads arranged in spaced relation thereon, identied at 20 and r2.1. These blocks project above the adjacent ledgesurfaces 22 and`23 to the same height as the blocks 13, 16V and 17 described above, and

The alternate rows of lifterV .liners are, however, in elect a off-set with respect to one another: Thus, considering the and having twenty rows of liners in accordancewith the Y present invention, the plates'CA'are two feet eleven'v and one-half inches inA length with a width" of :nineteen and three-fourths'inchesl The platesk CB have the same width f y but have a length of three feet eleven andl one-half inches. u V'Ifhe plates CA and CB have ay thickness idimensionof three inches under these circumstances, but this dimension can be changed depending upon the severity. ofVY the mill, and these lifterrows alternate 'withY the conveyorv i'jeitherside thereof a `distance equal'toatjleastone-thirdV the diameter'of the grinding rod orV ballusedin the mill,

platesLA liein the plane Vor' the wear surfacesvWSY of 4 the conveyor plates CA and CB as willbe apparent from Eig. 2such that theV plates LA have a thicknessdimension Y Y yequal Yto Ythat ofthe plates CA and CB measured between jrows as was mentioned` above. In constructing and assem-- Y tive rows of liners illustrated in Fig. 3 as being numbered from topto bottom, it` will benoted that the first row is Y' a lifter row, and the left handend platel of this row is occupied by a lifter plate'LB havingtwo upstanding blocks 516 and 17. Continuing kdown the row, the platesalter? nate between LA and'LB until the righthandA end of the lifter row is finished oiffby a large end plate LC. The third rowV of liners is again'a lifter row, but in vthis instance, the leftV hand end commences with a lifter plate VLA and so on'.- v

TheV advantageous relationships 'achieved'. under the present construction are illustrated in Figs. l and 2. Thus, by oli-setting alternate rows of Ylifter liners so that the pas 13 on a Vplate LA, Fig. 1, is aligned with the spaceof a plate LB` in thej next lifter row, the ledges as 15 and'18 account for ,a tortuouspath for the material being ground iup as indicated bygthe dashed'V arrows in Fig.v 1. lnV this manner, the inesaregradually allowed fto move and sift from the fhigh.` part of the charge Y toward the bottom ofthe mill o r toerg'of the charge whereVV there occurs highly eEective impact as will be explained; This flow' Vis,not'straight'.through: to

' 'the contraryfitis a divided flow Vallowing substantial amount of line attrition crunching to oceur'intheconveyorchannels under the influence v`of grinding Ymedia Y v yrotating on Vtheir'own'axes'insthefconveyor Ychannels a projecting pad'or lblock 13'wh1chV projects above the plane ofthe depressed surfaces o1' ledges -14and 151 on a ,'Statedinother words, the wear-surfaces 1'4'anjd15 onlthe Y' 1 which are continuousialong the Vlength ofthe mill; This,

together with similar action'of theY grinding media sup-Y tom orto one side of'ther'mill, accomphshedin-amanner the wear surface 14 or 15 andthe opposing surface which Y e engages the inner wall of the shell.Y 'This'dimensio is iu- Y dicated at MA in Fig. 4 andis utilized in fall the liner-,plates "Shswninrigsg and@ Y *Y Referring `to nig-2, if spbs'rvedthat 'the width Vof 'the liner plates rinffeach, instance'isjsuch as to allow Y A,a Vsubstantial number of then :mediazto'repose in yside ,by side relationship, yon the .elevatedl surface of theY projectingY pads orjblocks'on the'lifterplates. In yother words, the wearsurfaces WS presented bythe c011- iveyor plate, andthel wear stu'faeesA presented "byftheV vzlifter pads aref-cfa 'width 'equalvat least to'the'icombined diameters` rof V*several ,of vtheY vgrind/ing media. i The'. net

7e euecff this' is that the" leadihdgredgesjef :heurter pads as 13 and 17, whichare angled substantially normal to the wear surfaces WS, push ahead the grinding media within the long channels defined by the conveyor plates.

For convenient reference, the direction of `rotation of the mill in Figs. l and 2 is assumed to be that of a clock- Wise direction indicated by the arrow CR. This pushing effect prevails until the force of gravity overcomes the centrifugal force of the mill, and this can be considered as occurring at the top crest of the grinding media' mass. When the crest is reached, and the point of the crest will of course depend upon the speed of the mill, the grinding media take flight Iinward toward the centrall aids of the mill as indicated by the flight arrows F in Figs. l and 2.

Thus it will be seen that there is no backsliding or slippage of the grinding media R until the crest is reached, and as a consequence of this the grinding media tumble and fall down toward the toe of the charge near the bottom of the mill with a tremendous impact on the charge at the toe. This impact on the charge at the toe of the mill Vrepresents the primary comminuting force.

It should be here pointed out that for purposes of sim-` plicity all the levels of grinding media present in the mill are not illustrated in Figs. l and 2. tice-the mill is approximately forty-five percent full of grinding media, and hence there will be various loop flights F characterizing each successive level of grinding media considered as levels between the shell l1 and the central axis of the mill. When the top or outer shell takes llight in the manner illustrated in Figs. l and 2, it inuences all succeeding rows, and as a consequence of this there is no so-called quiet center of idle media R which can be observed in mills which employ wave-top liners. In other words, all of the rods or balls in the present instanceare effectively working either by impact due to ight or as a result of rolling on the liners or on one another.

In Figs. 5 to 9 there are illustrated aspects of a commercial rorm of installation that has proven eminently satisfactory in use, and to further facilitate an appreciation of the sort of dimensions that can be involved in installations of this kind, it is to be pointed out that Fig. 5 represents a plan view on scale of a complete installation for a commercial ball mill. The long dimension C indicated in Fig. 5 is that of the internal circumference of the shell of the commercial'mill and this dimension is 29-l0.l424. lThe short dimension A in Fig. 5 is the axial length of the millshell and this di- .mension is 9-G. As inthe embodiments described above, the assembly illustrated in Fig. 5 is made up'o alternating rows of lifter plates and conveyor plates. Thus, half of the total rows of liftery platesconsistof two plates 39 and Si which' have sloped edges '36E and 31E, Fig. 6, which in the `installation are abutted as shown in Fig. 5. It is fpund that Ythis type of abutment results in less wear at the division in 'comparison to `a straight division. Y Y Y Y g Each of lifter plates 3i) and 3l is provided with a pair of full dimension lifter pads 35, and the areas where.

these plates are abutted are cast with truncated half lifter pads 35H. The pads or `blocks 35 are spaced as in the Vforegoing embodimentsdescribed above to .provide depressed feeder ledges 37 between the lifter pads. The pads-and ledges have equal area dimensions, and the pads are wide enough to support several of the grinding media in side-ey-side relation. Inasmuch as the assembly will of course be circular within the shell, the long-edges of the plates 3l) and 31 are sloped at and 31S as shown in Fig, 6, and these plates are formed with openings 3S enabling fastening studs or bolts to be set therein to secure Vthe liner plates 343 and 3l to the shell of the mill.

lt will be noted in Fig. 5 that the lifter pads in sucln actual pracf cessive rows of lifter plates are off-set to account `for the advantageous cross-how of pulp as explained above. Consequently, the remaining rows of lifter liners alternate among the rows consisting of the lifter plates 30 and 31, and these remaining rows consist of lifter platesA 40 and 41, Figs. 5 and 8. The pads or lifter blocks 45 of the plates 41 and 42 are positioned in alignment with the ledges 37 of the lifter plates 30 and 31, and the depressed ledges 47 between the pads 45 are aligned with the lifter pads 35. It will be recognized further that whereas a lifter row represented by the plates 3i? and 31 is terminated at both ends by lifter pads, the next Iadjacent lifter row is terminated at its end by ledges 47. Moreover, Whereas the plates 30 and 31 are cast with half lifter pads 35H at their abutted edges, the plates 4l) and 41 are cast at their abutted edges with half ledges 47H, Fig. 5. The assembly is also cast at two points with conventional holes H1 and H2 that will be closed by caps.

The rows of conveyor liners, Fig. 5, also consist of two plates 56 and 5i, and these plates are butted at sloped edges S. It will be further observed that by having Vthe plates in the several rows abutting at sloped edges, there is no continuous break. The conveyors 5l? and 51 are plain, that is, the wear surfaces 'WS, Fig. 9, thereof are uninterrupted for the full length. These wear surfaces WS will lie in the plane of the exposed surfaces of the ledges 37 and 47 of the lifter plates.

The mill equipped with the liner assembly illustrated in Fig. 5 is one that operates at approximately 20 r.p.m which represents about 76 percent of the critical speed of the mill. lt was mentioned above that mills of this kind are actually -lled with grinding media to approximately 45 percent of their volume. This load coupled with the speed of the mill makes it possible to have the lifter pads or blocks projecting abovethe adjacent depressed ledges and wear surfaces by approximately one-third the diameter of the maximum-sized grinding media used in the mill, and of course this height differential prevails throughout the grinding media mass in respect of successive concentric shells of grinding media. Thus, were it not for the speed of the mill and the load of the grinding media, the most advantageous projecting distance for the lifting pads would be the radius or half lthe diameter of the maximum-sized grinding media to assure pushing of the grinding media and prevent backsliding but as eX- plained, operating conditions make it possible to reduce this distance to one-third the diameter of the maximum- 'sized grinding media. However, even at the slow speed of 20 percent of critical speed, where considerable cascading and backsliding has heretofore been encountered under the prior practices (cascading and backslidin'g are even observed at 75 percent critical speed) there is no observable cascading or backslidin-g under the present practice where the lifter pads projectnf'or one-thrd'the diameter of the sized grinding media. It might 'also be mentioned that in most instances a 'mill of the kind under consideration is lilled with 75 percent of the maximum-sized grinding media, three or four inches in diameter for example. Extending this illustration, 15 percent ofthe grinding media are represented by diameters of 2%' inches,` and the remaining amount/of 10 percent is represented by 2 inch diameter grinding media. This is simply for purposes or explanation and represents the average practice. Y

Thus it will be seen from the foregoing that the present arrangement of liners accounts for highly effective impact `and rolling or attrition grinding. Ineffective slippage and uncontrolled cascading is prevented by the leading shoulders of the lifter pads pushing ahead the grinding media until the apex or crest point is reached. The

- spaced pads which provide the circumferential or cross feeder channels, through which the dashed arrows in Fig. l `are' drawn, account for separation and some slowing down of the back pulp ow down the mill. The pulp or charge fines escape easily but the coarse charge ma Y terial remains behindy in the longitudinal conveyor channels where the'grinding media are effective with'a rolling action, `and in this connection it will be recognized that inasmuch as' the full Width of theV liner plates are used in providing the lifter pads or in-affording the Ydepressed conveyor channels,rthere is plenty of; room for Veffective rolling action of the grinding media. Moreover, and dueV l to theV occurrence' ofgrinding media rolling'otithe thick lifter pads onto thedepressed wear surfaces WS afforded by theY conveyor plates.V Hence, while I have illustrated Y Y j and described preferred embodiments of my invention, it is4 to'be yunderstood'that. thesefare capable of variation and. modification, Vand I therefore do not wish to be Y purview of the `following claims.V

" limited vto the precise details set forth,'but desire to avail myself of such .changes'andfalterations'as fall within the Iclaim:1 1

' -1.111 aV grinding bf the Vkind described having a s rotatable Vshell Vandlwhich is to contain grindin-g rodsv havingpredetermined diameters, andthe charge to be comminutedaby the grinding rods: alternating rows of surfacesdening elongated conveyor channels each of a,widthsubstantiallyequal to the combined diametersrof several ofvtheegrinding rods -to enable atleast .several of the' grindingrods to'be confined therein in side-byside Y relation, `s airdV channels being-uninterrupted substantially fromQone end of themill to the other,` andthe remaining one from'ianotheralongthe-length of those rows, said equal to thev combined diameters of Yseveral of the Vgrinding rodsgto enable at least several'of vthe `grinding rods to be confined in such 'channel in side-by-'side relation, said channel being uninterrupted `substantially Vrrom one end of the mill to the other, and the next adjacent liner rowcomprising a plurality of lifterfplatesv assembled l in end-to-end relationV andV in the assembly having raised lifterV pads that are spaced apart one yfrom anotherY along the length of that row, saidrlifter pads having Wear surfaces spaced above the Vdepressed wear Vsurface of said channel by ya distance at least one-third'the diameter of `the maximum-sized grinding rods-.used inthe mill, the

width of the lifter pad '-wear surfaces being at least the Y combined diameters of several of Ythe-grinding rods to enable at least several of the grinding rods Vto be supportedV thereon insidefby-siderelatiomj said adjacent liner row having depressed. ledge portions presenting wear surfacesbetweenand separating the lifter pads, and

said ledge portions Ibeing substantially -of the .same thickness` as the"conveyor'platesso that the Weary surfaces of saidledge portions aresubstantiallyY coplanarfwith the depressed wear surface of said'channelenablingfthe coin-V minuted charge to move in a vcross-llo 1 into the `conveyor channel. Y Y Y dissimilar Vshell'liners secured for rotation with the shell,

certainones of the liner rows presenting depressed wear Vpast' said pads and 4. VA liner construction for' agrindin-g mill ofV the kind whichV includes a generally cylindrical shell containing grinding rods havingV predetermined diameter for comminuting acharg'e by impact and relative rotation between l. Y said grinding rods produced by rotation offsaid shell, said yliftery pads Y`having wearsurfaces spaced above said de- .e Ypressed channel wear surfaces byaV distance at least one- 'third the diameter of the maximum sized-grindingY rods usedin the'mill, the Vwidth of the lifter pad wearsurfaces being at least the combined diameters of vseveral of the rods tofenable at leasteseveral of the lgrinding rods to -besupported thereon in side-by-side relation; said Y remaining liner rows having'depressed ledges presenting Vdepressedzwear surfaces between and separating the lifter padsby distances substantially equal -to the length of Vthe vlifter pads and which are substantiallyscoplanar with the' iirst-nan'ied depressed wear surfacesfenabling the comlminuted charge Vtowmove freely vinra Vcross-flow past said Y pads and Vinto ith'econveyor channelsl,`

f2.1A grinding mill according to'clairn Vl wherein the rowsoi` liners having'raised lifterY pads are olf-set along v the` length lof the mill whereby a lifter pad inY one lifter flinerrow is located opposite-a depressed ledgein the-next .1

' ,adjacent lifterlinerrow. Y

' 3.In ag'rindinglm'ill of rotatableV shellv and lwhich is to containA grinding -rods having predetermined diameters,V and the charge to be comminuted by the grinding rods: valternating rows of dissimilar shell liners securedifor'rotation with theshell, one liner row :comprising a pluraltyof conveyorplates Q ofsubstantially the same thickness aligned in end-toend relation Vpresenting a depressed wear surface defining the kinddescribed having a)` liners,-said lifter liners having 'pads projecting radially `inwardly-for lifting said grinding rods during `rotation of said shell and depressed ledgessubstantially coplanar` with the wear'surfaces of the conveyor liners, said projecting pads being` longitudinally spaced'from one another by said depressed ledges todene channels therebetween of substantially the same longitudinal extent asthe projecting Y' pads for ythe passage of ground material between con- Varijelongated conveyor channel'of a width substantially vbetweenfduring rotation of said shell.

veyorY-rows,VA and each of said YrowsnofV conveyor liners Yhaving 'a width which'is greater than Vthe combined diameters'of several of saidgrinding rods, whereby several of said grinding rodsV are freely rotatable Vwithineach of said rows of conveyor linersr to eiectgrinding there- 5. A liner'construction as defined in vclaim 4`wherein the pads in one row of said Ylitter linersV are longitudinally ofisetfronr4 the padsinthenex-t adjacent row of said lifter liners. A. Y l iV I i I References Citedlthe vtile thisfpatent `Insurer):s'frATEs PATENTS@ 221,548 1 Golding- Y fNdff11,-V1879 688,2294 Hundeshagen'f. Dec. 3 `1901 2,268,661 Kennedy f lan. 6, l1942 V2,670,149' Douglarsrl-, renza, 1954 Y FoRErdN PATENTSv 166,073V ...Austria Jude 1o, 195o

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