US2993656A - Grinding mills - Google Patents

Description

July 25, 1961 "r. A. RATKOWSKI GRINDING MILLS 3 Sheets-Sheet 1 Filed March 6, 1959 United States Patent Filed Mar. 6, 1959, Ser. No. 797,740 Claims. (Cl. 241-183) This invention relates to a shell liner for a grinding Grinding mills of the kind wherein material such as ore and the like is to be ground or cornrninuted to a more finely divided state have a rotating shell in which the material to be ground is confined together with the grinding media. The grinding media can be in the form of rods, in which case the mill is known as a rod mill, or the grinding media can be in the form of balls, in which case the mill is known as a ball mill. The present invention contemplates both forms of mills, and in either event it is common practice to line the shell with removable liners which serve the purpose of preventing wear of the material and the grinding media on the shell. Thus, the shell liner is what will take the beating during operation of the mill, and when the liner is unduly worn the same can be removed and replaced by a new liner.

It has heretofore been proposed to construct a shell liner for a grinding mill so as to have raised lifter ribs. These ribs project from the inner faces of the liners and extend parallel to the axis of the mill, and the spacing between the ribs is sufiicient to enable the grinding media to lie between the lifter ribs. Accordingly, during rotation of the shell, the lifter ribs in effect carry the grinding media upward and prevent ineflicient slippage or backsliding of the grinding media. When so lifted, the grinding media eventually reach a point where gravity overcomes the centrifugal force of the mill, whereupon the grinding media at the top or crest of the mass take flight and drop with a violent force upon the material being ground. Thus, the lifter elements actually elevate the grinding media, and the advantage of this is that the grinding mediaare prevented from slipping or backsliding, noting that slippage or back-sliding of the grinding media is not nearly as elfective in comminuting the material as is the case of lifting and dropping the grinding media.

During operation of the mill, the lifter ribs are gradually worn down by erosion so that their eifectiveness becomes less and less after prolonged use of a mill equipped with a liner installation having lifter ribs. The primary object of the present invention is toso construct a liner for a grinding mill as to present-a new lifter rib once the original lifter rib has been worn to the extent that it is no longer practically eifective. Specifically, it is an object of the present invention to construct a grinding mill liner having a lifter rib superimposed over a recess in the body of the lifter rib whereby when the original lifter is in a sloped state worn through to expose the recess, the recess will be effective to present a new rib as will be explained. In other words, the present invention can be viewed as a liner having a hollow rib, the original rib actually being a wall bounding the hollow or the recess within the rib, and hence when this wall is worn through the recess is exposed constituting an open pocket in which the grinding medium can be reposed to be lifted with the pocket.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way'of illustration, show preferred embodiments of the present invention and the principles thereof and what is now considered to be the best mode contemplated for,

applying these principles. Other embodiments of the in Patented July 25, 1961 .accordance with the present invention;

FIG. 3 is a sectional view of a liner element constructed in accordance with the present invention;

FIG. 4 is a plan view of the liner element in FIG. 3, being partly broken away;

FIG. 5 is a sectional view illustrating the condition of the liner element of FIG. 3 at a time when the original rib wall has been worn away;

FIG. 6 is a sectional view of a modified form of the present invention; and

FIG. 7 is a plan view of the liner element in FIG. 6.

A typical form of a grinding mill contemplated by the present invention is illustrated schematically at 10 in FIG. 1. A mill of this kind includes a cylindrical shell 11 and a pair of end walls as 12 of which only one is illustrated so as to enable the construction and conditions at the interior of the mill to be visualized. The end walls as 12 are provided with trunnions that are mounted in bearings that in turn are supported by end blocks 13. It is common practice to provide one of the end walls with a ring gear whereby the mill can be rotated by a conventional gear drive. Grinding mills of the kind under consideration are operated on various difierent principles insofar as wet or dry operation is concerned, and also in respect of the particular manner in which the charge to be ground is admitted to the interior of the shell and the manner of with drawing the comminuted fines from the mill. Accordingly, it is to be understood that these principles and various methods of operation are immaterial under the present invention, which is concerned primarily with the construction of the liner which is used to line circumferentially the interior of the shell 11. It should finally be pointed out that it is assumed that the mill 10 is to operate with grinding media in the form of rods R, but balls can be used as well.

It is well known in the art that it is advantageous to lift the grinding media as R by a positive acting force as distinguished from merely having the grinding media carried around with the mill due to the resultant centrifugal forces that are established during mill rotation. Such a positive acting force for lifting the grinding media heretofore has been afiorded conventionally by lifter ribs that are formed on cast liner plates or blocks which are secured to the inside of the shell. These lifterribs extend longitudinally of the mill in parallel spaced relation one to another and parallel to the axis of mill rotation. The ribs thus afforded act as back-up members for the grinding media and tend to push ahead the grinding media during mill rotation. This prevents ineffective slippage or back-sliding of the grinding media since it is a known fact in this art that slippage or back-sliding of the grinding media results in poor comminution. Thus, by providing lifter ribs, the grinding media will be lifted to a greater extent and will be carried around to a higher point on the arc of rotation such that the grinding media I as R will not take flight in an inward and downward direction until quite high along the are of rotation. This tive. to ,liftthe grinding media.

In accordance with the present invention, the interior of the shell 11 is lined with individual liner elements 15, FIGS. 1 to 6 inclusive which are extended for 360 about the inside of the shell. The individual liners will of course be of predetermined segmental angle, and this angle and resultant width dimension of the liner element will vary for different types of installation, and will 'vary in accordance with optimum operating conditions. The view illustrated in FIG. 1 is exemplary of actual practice wherein the individual liners are of a size corresponding approximately to 20 of are. It will be appreciated that for smaller arcs there will be a greater number of liner plates and for larger arcs a corresponding lesser number of liner plates. Additionally, it will be realized that the liners 15 will be of a predetermined length in the direction of the longitudinal axis of the mill. Thus, the liners could be of a length such that each extends for the full length of the mill as a lone one-piece part, but preferably the liners will be in individual block form laid end to end as will be evident from FIG. 1 wherein it will be noted that three liner blocks 15-1, 15-2 and 15-3 are positioned in end-to-end relation along one liner row with slight spacing between the adjacent ends of the individual blocks thus identified. It will be moreover noted in FIG. 1 that there is some spacing between adjacent rows, indicated at S, and such is in accordance with conventional liner installation practice. It is advantageous that the dividing areas between the adjacent blocks alternate or be off-set along adjacent rows of liner blocks. This is accomplished by starting every alternate row with an over-sized liner block designated at 15-5 in FIG. 1, such that the dividing line between the over-sized liner block 15-5 and the normal-sized block 15-6 next adjacent thereto in the same row occurs at the transverse medial line of the normalsized liner block 15-2 in the next trailing row of liner blocks.

As shown in FIGS. 2 and 3, each liner, of whatever length or of whatever width, includes: an arcuate back or outer face which is curved complemental to the curvature at the inside face of the shell 11 so as to be capable of fitting complementally thereagainst. Additionally, each liner is preferably cast of manganese steel or like wear-resistant alloy so as to have a relatively thick body portion 2 1, that is radially thick and inasmuch as the liners in nearly all instances will in fact be segments having arcuate backs, the outer sides of the castings are preferably tapered at 22 and 23 so that the desired full 360 substantially closed arc will be established in the assembly.

The face of the liner which will project inward of the mill, that is, the face that is opposite the back 20, is formed with a single lifter rib 25. In the form of the liner illustrated in FIG. 3, the rib 25 is located medially of the width of the liner, and resultantly the rib 25 will in part be defined by shoulders 26 and 27 which are sloped down from the crest 25C of the rib in depending relation so as to diverge in a direction proceeding from the crest or outer wear face 25C of the rib toward a pair of depressed ledge surfaces 28 and 29. The ledge surfaces 28 and 29 thus are located at the base of the rib, and as will be apparent from FIG. 2, the ledges 28 and 29 of adjacent liner elements 15 secured to the shell of the mill will lie in a substantially common plane. The width of the crest of the rib 25C is sufilcient, as shown in FIG. 2, to enable several of the grinding media to repose thereon. Likewise, the adjacent ledges 28 and 29 which lie below the top surfaces or crests 25C enable several of the grinding media to lie in the spaces between the adjacent ribs circumferentially about the mill. The ribs 25 project outward of the ledges 28 and 29 a distance at least equal to the radius of the grinding media, and hence, as the shell rotates, a leading shoulder as 26 on a rib will serve to push ahead'or lift the grinding media by a positive acting force which is the primary function of a lifter rib. The directions of assumedrota- 4 tion are indicated by the bold arrows A in FIGS. 1 and 2, and if the mill should be operating in the opposite direction, then it will be the shoulders 27 of the ribs which will apply the positive acting force to the grinding media.

Under and in accordance with the present invention, the ribs 25 includingthe crest and the shoulders in reality line the top of a recess 30, FIG. 3, which extends parallel to the rib and which is of quite generous size as will be explained. It willbe noted that each recess 30 is in effect bounded or covered over at the top or upper half and partly at the sides by what can be considered a web W which represents the effective thickness of the rib 25.

The recesses 30 are quite deep so that the lower half of each recess extends well into the body portion 21 of the liner directly behind the crest of the rib whereby a solid part of the body portion of the liner at the interior thereof bounds the remainder or bottom part of the recess 30. In other words, if a plane P, FIG. 3, be assumed as the plane of the ledge 28 or 29 outward of the adjacent shoulder 26 or 27, the bottom half of the recess 30 extends below this plane and is bounded by a solid surface within the body 21. Referring to 'FIG. 2, it will be noted that each recess 30 is of a width slightly greater than the diameter of a grinding medium. During operation of the mill the shoulders 26 and 27 are graduallyworn away and rounded off. The shoulders thus become less and less efiective as lifting surfaces, and eventually the ribs are worn down to the dotted lines D indicated in FIG. 3, whereat there is virtually no longer any positive acting force. In other words, the web W covering the top of the recess 30 is eventually worn through as shown in FIG. 5 leaving only fragments W; whereupon the recess or pocket -30, FIG. 5, is exposed. The pocket 30 is of a depth at least slightly greater than the radius of a grinding medium to repose therein when the web is worn through. Hence, when the web W is worn through, a grinding medium can fit therein, and the pocket 30 thus becomes effective to aflord a new lifter rib, 25A or 25B, FIG. 5, depending on the direction of mill rotation. In this connection, it will be noted, particularly in FIGS. 3 and 5, that the side walls SW and S of the recess slope upwardly and outwardly from the bottom wall BW of the recess. Furthermore, the slopes of these side walls present internal shoulders which respectively are substantially parallel with the non-adjacent one of the shoulders 26 and 27. Therefore, when the crest has worn through the resultant new ribs 25A and 25B have the proper slope to continue with the lifting action, which is to say that the new lifting surface 25A has approximately the slope of the original non-adjacent shoulder 27, and the new lifter surface 25B has approximately the slope of the non-adjacent shoulder 26. This also applies to the embodiment of the invention illustrated in FIG. 6 hereinafter described.

Various modes of securing the liners 15 to the shell can be resorted to, and one way of easily accomplishing this is to provide the body portion of the liner with a pair of elongated openings 35 extended inward from the arcuate back 120 as to communicate with the recess 30. These openings are provided with transverse T-head slots 36 that communicate with the recess 30 and which are disposed at right angles to the long dimension of the opening 85. The long dimension of the opening 35 is such to enable the correspondingly sized head of a T-bolt B, FIG. 2, to pass therethrough, whereupon the head of the bolt can then be turned to fit in the transverse slot 36. The manner of attachment will be apparent from FIG. 2. Thus, it is common practice to use bolts to secure shell liners in place, and in the present instance the shanks of these bolts are extended outward through the shell where lock nuts, washers and like securing elements as N, FIG. 2, are aiforded. The shell will be lined from the inside of course, and the heads of the bolts can be turned in such a manner as to enable each liner block or plate to be passed down over the T-heads of the bol s located inside the shell. The bolts are then turned to dispose the T-heads in the slots 36, whereafter the lock nuts or the like are tightened down.

In the embodiment of the invention described above, each liner has but one rib, and is of a relatively small segment angle. The liner plates can of course be of larger size and of different configuration, and in FIGS. 6 and 7 a modification is illustrated at 40. Thus, the liner 40 is a relatively thick casting having the main body portion 41 formed with an arcuate back 42 which has a curvature complemental to the curvature of the inside wall of the shell of the mill. The side faces of the liner 40 are tapered at 43 and 44 so that there will be a neat fitting of the several liners in adjacent rows about the shell. The liner 40 is cast with a pair of ribs of sinusoidal shape projecting from the face of the liner opposite the arcuate back face 42. These ribs have rounded crests 43 in contradistinction to the relatively fiat crests 25C formed on the liners 15 described above. Each rib in FIG. 6, has a pair of shoulders 45 and 46 depending from the crest 43 and which gradually slope into depressed ledges 47 well below the crest of the rib, and the grinding media will repose on the ledges 47 whereby the shoulders 44 or 45 will exert a positive acting lifting force thereagainst during the rotation of the mill.

A relatively large recess 50 is formed in the interior of body 41 of the liner 40 so as to be coextensive in length with and lie directly behind the crest 43 of each rib, so that again each recess 50 is closed 01f or bounded at the top and partly along the sides by a web as WB representing the thickness of the related rib. The remainder of each recess 50 is bounded by the solid surface within the body 41 of the liner, FIG. 6.

It will be observed that the upper portion of each recess bounded by the inner face of the related Web WB projects slightly above or beyond the low points of the ledges 47, and as in the foregoing embodiment the recesses 50 are of a width at least slightly greater than the diameter of a grinding medium and are of a height at least equal to the radius of the grinding medium. Hence, when a web WB is worn through, the related recess 50 will be opened thereby affording a new lifter rib in the manner explained above.

Advantageously, the liners 40 are formed with apertures A that are medially located between the ribs. These apertures A open at the back of the liner and open at the intermediate ledge that lies between the two ribs. It will be noted that the apertures A are countersunk to receive fillet-head fastening bolts of a known kind.

It will be seen from the foregoing that under the present invention there is aflorded a liner for a grinding mill wherein the liner has a cored or recessed lifter rib projecting from the wear face of the liner. The size of the recess is sufiicient to effectively carry a grinding medium when the rib is worn through, and the parts are so dimensioned, based on field experience, that the original rib will wear through approximately at the time when it has been worn through to an inefiective condition. Preferably, the liner elements of the present invention are in block form, as is standard practice, but it will be realized that so far as over-all size is concerned, any desired dimension which is practical can be used.

Hence, while I have illustrated and described preferred embodiments of my invention, it is to be understood that these are capable of variation and modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a grinding mill having a rotatable cylindrical shell for confining material to be comminuted by grinding media within the shell, a renewable liner element for preventing direct wear of the material and the grinding media on the inside wall of the shell and for elevating the grinding media by a positive acting force, said liner element comprising a body portion having a rear face disposed toward the inside wall of the shell, a raised lifter rib projecting from the opposite face of said body portion, said rib having a crest and having a pair of shoulders joining the crest, said rib extending parallel to the axis of rotation of said shell, said opposite face having depressed ledges adjacent the shoulders of said rib on which the grinding media can lie to be forced around with the shell by the adjacent shoulder surface of the rib, and said rib being formed with a recess in the interior thereof behind the crest and the shoulders so that the crest and shoulders of said rib have internal surfaces which in part line said recess, the crest of the rib having a thickness substantially less than that of said depressed ledges so as to be adapted to wear through prior to Wearing down of the depressed ledges, said recess being coextensive in length with said rib and of a width to receive a grinding medium when the rib is worn through after prolonged operation of the mill having said liner element, said recess having a bottom wall and side walls which extend upwardly and outwardly from the bottom wall of the recess so as to present internal shoulders which respectively are substantially parallel with the non-adjacent one of the first-named shoulders, and the bottom wall of said recess being completely free of projecting elements to facilitate reception of the grinding media therein after wearing through of the crest.

2. In a grinding mill having a rotatable cylindrical shell for confining material to be comminuted by grinding media within the shell, a renewable liner for preventing direct wear of the material and the grinding media on the inside wall of the shell and for elevating the grinding media by a positive acting force, said liner element comprising a plurality of individual liner blocks arranged in parallel rows about the inside wall of said shell and arranged in end-to-end relation in each row axially of said shell, each of said blocks being of generally rectangular shape and having a rear face disposed toward said shell and a front face disposed toward the cavity afforded by said shell, each of said blocks having at least one raised lifter rib on the front face thereof, said rib having a crest and a pair of shoulders spaced inward of the sides of the related block thereby affording a pair of depressed ledges at the front face of the related block and below said crest of the related rib, the crest of the rib having a thickness substantially less than that of said depressed ledges so as to be adapted to wear through prior to wearing down of the depressed ledges, said rib extending parallel to the axis of rotation of the mill, and the rib on each block being formed with a recess in the interior thereof so that the crest and shoulders of the related rib have internal surfaces which in part line said recess, the dimensions of said recess being related to the diameter of a grinding medium such that the shoulders of the rib are adapted to engage a grinding medium in lifting relation upon wearing through of the crest of the rib, said recess having a bottom wall and side walls which extend upwardly and outwardly from the bottom wall of the recess so as to present internal shoulders which respectively are substantially parallel with the non-adjacent one of the first-named shoulders, and the bottom wall of said recess being completely free of projecting elements to facilitate reception of the grinding media therein after wearing through of the crest.

3. In a grinding mill having a rotatable cylindrical shell for confining material to be comminuted by grinding media within the shell, a renewable liner element for preventing direct wear of the material and the grinding media on the inside wall of the shell and for elevating the grinding media by a positive acting force, said liner element comprising a body portion having a rear face disposed toward the inside wall of the shell, a raised lifter rib projecting from the opposite face of said body portion, said rib having a crest and having a pair of shoulders disposed generally normal thereto, said rib extending parallel to me axis of rotation of said shell, said opposite face having depressed ledges adjacent the shoulders of said'rib and on which the grinding media can lie to be forced around with the shell by the adjacent shoulder surface of the rib, and said rib being formed With a re-v cess in the interior thereof so that the crest and shoulders of said rib have internal surfaces which in part line said recess, the crest of the rib having a thickness substantially less than that'of said depressed ledges so as to be adapted to Wear through prior to wearing down of the depressed ledges, said recess being coextensive in length with said rib and of a width related to the diameter of the grinding medium to receive a grinding medium when the rib is worn through after prolonged operation of the mill having said liner element, said recess having a bottom portion extended well into said body portion directly behind said rib and lying below the planes of said ledges, said recess having a bottom wall and side walls which extend upwardly and outwardly from the bottom wall of the recess so as to present internal shoulders which respectively are substantially parallel with the non-adjacent one of the first-named shoulders, and the bottom wall of said recess being completely free of projecting elements to facilitate reception of the grinding media therein after wearing through of the crest.

4; A grinding mill as defined in claim 3 including fastening means disposed substantially flush withthe surface of the bottom wall of the recess for attaching the liner element to the shell.

5. In a mill of the kind described, a shell liner element including a body portion formed with a lifter rib on one face thereof and having a depressed ledge on either side of the rib, said rib including a pair of shoulders and a crest having arecess inthe interior thereof; the crest of the rib having a-thiokness substantially'less than that of said depressed ledges so as to be adapted to wear through prior to wearing down of the depressed ledges, said recess being coextensivein length with said rib and having awidth between said shoulders related to the diameter of grinding media in the mill for receiving a grinding medium within the recess wheneversaid recess is exposed by wearing through the crest, said recess having a bottom wall and side walls which extend upwardly and outwardly from the bottom wall of the recess so as to present internal shoulders which respectively are substantially parallel with the non-adjacent one of the firstnamed shoulders, and the bottom wall of said recesses being completely free of projecting elements to facilitate reception of the grinding media therein after wearing through of the crest, whereby. a shoulder of said recess alfords a new lifter rib.

References Cited in the file of this patent UNITED STATES PATENTS 1,291,008 Jensen Jan. 14, 1919 1,591,938 Harrison July 6, 1926 2,213,713 -Maxson Sept. 3, 1940 2,268,661 Kennedy Jan. 6, 1942 2,275,992 Rahner Mar. 10, 1942 2,611,546 Posselt Sept. 23, 1952 FOREIGN PATENTS 178,729 Germany Nov. 17, 1906 404,342 France Oct. 16, 1909 608,249 Belgium Jan. 31, 1952

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