US2931583A - Grinding mills - Google Patents

Description

GRINDING MILLS 2 Sheets-Sheet 1 Filed May 21, 1957 Inventor Oscar 3+. J h

April 5, 1960 o. H. JOHNSON GRINDING MILLS Filed May 21, 1957 2 Sheets-Sheet 2 Inventor Oscar 31-.Johnson.

nlted States 2,931,533 I GRINDING MILLS Application May 21,1957, Serial No. 660,682 3 Claims. (Cl. 241-79) This invention relatesto an end liner for a grinding mill.

A common method of comminuting or pulverizing comparatively large particle size material such as ore as mined is to charge the same into a grinding mill to be subjected to the action of grinding media such'as ferrous metal balls, pebbles or the like. The mill includes a shell disposed to rotate about a horizontal'axis and is provided with vertical end walls which confine the charge. It is common practice to line both'the shell and the end .walls with liners of a wear resistant alloy exposed to the abrading actionof the charge and the grinding atentt media so asto protect the shell and end walls against" ldirect wear.

Such an end liner is relativefy expensive, and when worn out it is necessary to shut down the mill and replace the worn liner. It is therefore advantageons'to reduce wear on the end liner itself, and the accomplishment of this in a novel manner is'the primary object of the present invention.

Specifically, it is the object of .the present invention to provide the end liner of a grinding orso-called ball 'mill with a rib that projects from the wear surface thereof and which extends tangential to'the direction of mill rotation in such a way as to'substantiallyreduce the wearing action of the grinding media on the wear surface of the end liner.

As is well known in the art, an end liner for a grinding mill may be advantageously in the form of a. segment commonly designated and referred to as an end liner. An end liner in this form is assembled with the requisite number of like segments to afford a complete 360"end liner plate or disc assembly. Such an end liner maybe as large as 180", or smaller, say on the order .ofand when worn is readily replaceable in the complete 360 assembly. In other instances, the end liner may be cast as a one-piece 360 part. In any event, the assembly or the one-piece construction is complemental to the area of the end wall of the mill.

Where the construction includes a plurality .of end liners assembled in the foregoing manner, the individual segments can be cast one by one in a single mold, and under the present invention each segment will be formed with a rib that will be aligned in an arc with the ribs on the other liners making up the assembly, thereby affording a virtually closed ring of ribs extended for 360 about the resultant assembly. In a so-called dry or high discharge mill, the ends of the ribs on the several sections will usuaily abut one another within foundry tolerances and the end liner inmost instances will be the same both at the feed and discharge end of the dry mill.

In the instance of a so-called wet or low discharge mill wherein the charge is mixed with liquid which carries the comminuted fines out the discharge opening'at the discharge end of the mill, a grate or so-called'screen is interposed in front of the discharge opening so as to classify the fines prior to discharge. Such a grate or screen is .also known in the art as attend liner, "because 2,931,583 Patented Apr. 5, 1960 ice his forwardly of the discharge end wall ofthe'rnill and .is cast of wear resistant alloy to 1 take the wear. It 'is also conventional practice to construct "the end liner screen or grate as an assembly with .a plurality of liners of segmental form which areheld in place by elongated wedge bars which cooperate with complemental wedge surfaces representing the radial edge surfaces of the end liner grate segments. Under such circumstances, individual end liners for the discharge end of a wet mlll constructed in accordance with the present invention and when assembled by means of wedge bars will have the It is recognized that it is not new to form a rib on the end liner of a grinding mill so as to project inwardly from the wear surface of the liner. However, ribs as heretofore provided have been radial, that is, disposed normal to the direction of rotation of the mill. It was apparently intended that the ribs thus disposedradially would sweep through the grinding media in some manher .to reduce the abrading action of the grinding media on the wear surface of the liner. However, the grinding media, once lifted .by the radial ribs, roll back against the liner with rather violent impact forces. .Moreover, radial ribs present rather large andextended surface areas acting fiat against the crowded mass of grinding Other and further objects of the present invention i 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 I now consider .to bethe best mode in which I have contemplated applying these principles. ..bodiments of the invention embodying the same or equivalent principles may be used and structural changes may be. made as desired by those skilled in the art without Other emdeparting from the present invention and the purview of the appended claims.

The principles of the present invention are best illus' Fig. 3 is a sectional view through the mill taken substantially on the line 3-3 of Fig. 2 and illustrating the cavitation eiiect on the ball charge;

Fig. 3A is a view similar to Fig. 3 but showing contrasting condition;

Fig. 4 is a plan view of a, 360 assembly of end liners constructed in accordance with the present invention;

Fig. 5 is a detail perspective view of one ofithe end liners used in the segment assembly of Fig. 4;

Fig. 6 is, a plan view illustrating the grate embodiment of the invention;

Fig. 7 is a perspective view of an individual end liner used in the segment assembly of Fig. 6 and illustrating the association of the wedge bar therewith; and

Fig. 8 is a sectional view substantially on the line 8-8 of Fig. 7 and showing the relation of the grate to the corresponding end wall of a wet mill.

In Figs. 1 and 2 of the drawings there is illustrated a dry or so-called high discharge grinding mill of the kind used to comminute to a finer state large particle ore material charged into the internal chamber 21 thereof. The mill 20 thus includes a conventional drum or shell 25 of cylindrical form disposed to rotate about a horizontal axis. The inner face or wall of the shell may be provided with removable liners (not shown), and secured to the opposed ends of the shell 25 are heads or end walls 27 and 28, Figs. 1 and 2. Associated with each end wall as 27 and 28 is a trunnion as 33 and 34. These trunnions are coaxial with'the axis of the shell and are respectively supported for rotation with the mill in respective bearings 31 and 32 which are a part of heavy duty standards 35 and 36 which carry the entire load of the mill. For rotating the mill, a ring gear 39 is secured to one of the end walls, and this gear is adapted to be driven in a conventional manner by a pinion gear at the end of a drive shaft (not shown).

The end walls 27 and 28 as well as the end liners associated therewith and to be described hereinafter, are formed with apertures at the centers thereof. The trunnions referred to above are in the nature of sleeves, and the inner ends thereof communicate with the apertures in the end walls and the end liners. Accordingly,-the trunnion as 33 at what constitutes the feed end of the mill enables the mill to be charged with the material to be ground or pulverized as well as with the grinding media. Likewise, the trunnion 34 associated with the end wall 28 atfords the discharge.

Under the present invention, the heads 27 and 28 of the mill 20 are provided with end liners 40 and 41, Fig. 2, of novel construction to be described in more detail hereinafter. The liners 40 and 41 are in the form of one-piece castings, but the liners may be in other and different forms as will be described hereinafter. Moreover, the end liner for the discharge end of a wet mill is of further modified form as will be described.

End liners as 40 and 41 for a dry mill will in most instances be of identical construction, and referring to Figs. 1, 2 and 3 it will be noted that these are in the form of relatively large discs each adapted to be disposed in a vertical plane inwardly of and parallel to the associated head or end wall 27 and 28. In the dry mill form of the invention, the end liners are anchored to the end walls usually by nuts and bolts, and for this purpose the linersv 40 and 41 are formed with square apertures 43, Fig. 3. Each liner includes a flat, smooth wear surface 40WS, and when oriented as in the foregoing manner the wear surfaces 40WS face inwardly of the mill chamber 21 and are disposed in true vertical planes.

Thus, liners 40 and 41 serve the known purpose of eliminating direct wear of the grinding media on the inner faces of the end walls 27 and 28 of the mill. Consequently, it is the wear surface 40WS of the end liner which is subjected to the abrading action of the grinding media so as to take the wear at the ends of the mill. Each end liner 40 and 41 includes an arcuate outer peripheral edge 46, Fig. 2, and an arcuate inner peripheral edge 47, Figs. 1 and 3, these edges lying on true concentric circles. The inner peripheral edge 47 corresponds to the diameter of the feed opening at the feed end of the mill, or'complementary to the discharge opening at the discharge end of the mill as the case may be. Where the feed and the discharge openings are of different internal diameter or configuration, the aperture 47 of the end liners 40 and. 41 will differ to this degree;

axis about which the mill rotates.

Likewise, the outer peripheral edges 46 of the end liners 40 and 41 are complemental to the inner diameter of the shell 25 so as to engage the inner diameter of the shell 25 about the circumference thereof corresponding to the related end liner, and it may be mentioned at this point that the shell or .drum 25 is illustrated in an unlined form although, as will be appreciated, it is conventional practice to line the inner diameter of the shell 25 to eliminate driect wear thereon. When so lined, the end and the shell liners will be so related as to present a complete internal lining for the mill.

In accordance with the present invention, each end liner 40 and 41 is formed with at least an outermost circular rib 50, Figs. 1, 2 and 3, which lies on a circle that is concentric to and between the inner and outer peripheral edges of the related end liner. In other words, the rib 50 is so disposed and oriented as to rotate with the related end liner 40 or 41 tangent to the direction of rotation of the mill indicated by arrows R in Figs. 1, 2 and 3. The particular effect achieved by the rib 50 will be described hereinbelow, and it is preferable that each end liner include a second or innermost rib 51, Figs. 1, 2 and 3, parallel to and spaced inwardly of the outermost rib 50.

As best shown in Figs. 2 and 3, the ribs 50 and 51 project forwardly from and perpendicular to the plane of the wear surfaces 40WS of the , end liners 40 and 41. In other words, the ribs 50 and 51 project inwardly toward the chamber 21 of the mill parallel to the horizontal In the form of the invention illustrated in Figs. 1, 2 and 3, the ribs 50 and 51 are endless, being cast integral with the one-piece end liners.

,The ribs 50 and 51 are so formed as to have fiat, continuous or uninterrupted forward surfaces 52 and 53, Fig. 3. ":In other words, all points on the rib surfaces 52 and 53 are'substantially coplanar. Moreover, the ribs 52 and 53 are of relatively narrow radial thickness, and therefore the ribs travel freely through the grinding media or balls B as well as the charge of ore or like material that is to be ground or pulverized by the grinding action of the grinding media. Additionally, the ribs 50 and 51 in the present instance have continuous uninterrupted outer surfaces 55 and 56, Figs. 1, 2 and 3 so that all points thereon have substantially the same surface in common. This is important inasmuch as the balls B are to able to backslide freely on the surfaces 55 and 56.

As is well known in the art, grinding balls, so-called pebbles and the like are furnished in standard dimension depending upon the character of the material to be ground and the extent to which the material is to be ground. Thus, grinding media as B in ball form are furnished in standard diameters, five inches being about maximum. Under the present invention, the outer surifaces 55 and 56 of the ribs 50 and 51 project inwardly perpendicular to the wear surfaces 40WS for a distance at least equal to the radius of the maximum size ball diameter to be used. Moreover, the outer surface 55 of the outermost .rib 50 is spaced inwardly of the outer peripheral edge of the end liner a distance at least equal to the combined diameters of several balls as shown in Fig. 3. The aforesaid spacing also prevails with respect to the distance that the outer surface 56 of the innermost rib 51 is spaced from the lower surface of the outermost rib 50. It will be understood that the relations thus set forth and defined will prevail for all modifications of the end liners such as those to,be described hereinafter in connection with Figs. 4 to 8. Thus, it is contemplated that the axial extent of the outer surfaces 55 and 56 of theribs 50 and 51 be sufiicient to afford a ledge enabling the balls to repose thereon during rotation of the mill. Moreover, the outer surfaces of the ribs are sufiiciently spaced radially from any opposed radial outer surface to enable a plurality of balls to in effect stack up on one another in the radial space between such outer surface $7 ofzthe rib iandflthe. outer radial surface opposed:thereto. This stacking isillustrated in Fig. 3.

For. themost part, the novel. effects achieved. under the. present invention are illustrated in Figs. 2 and 3 whereby the abrading action of the material within the mill on the wear surfaces 40WS of the end liners is materially lessened and reduced. When the mill has been charged and is at rest, the grinding media B and the material-to be ground fill the chamber 21 to a level corresponding approximately to the. horizontal axis, and the charge and the grinding media are of course in contact with the. lower sections of the end liners 40 and 41 up to a corresponding level. Accordingly, the grinding media are in contact with corresponding areas of the wear surfaces 40WS of the end liners between the peripheral edges 46 and 47 thereof, which is to say that the lower areas of the end liners between and radially outwardly and inwardly of the ribs 50. and 51 are filled with grinding media. When the mill rotates, the ribs 50 and 51 by virtue of the smooth uninterrupted surfaces thereof travel freely through the grinding media without encountering any significant resistance. Operative conditions in the mill at the time of normal rotation thereof areillustrated in Figs. 2 and 3. Thus, as shown particularly in Fig. 3, grinding media are carried upwardly by and on the outer surfaces 55 and 56 of the ribs 50 and 51 incident to rotation of the mill.

During mill rotation," the ore charge and the grinding media shift .to one side of the mill because of centrifugal force, and the free or exposed surface thereof assumes what can be viewed as a downwardly sloped incline surface down which the'grinding media tumble from the crest or peak of the inciine adjacent the shell as viewed inFig. 3 to the trough or bottomofthe incline adjacent thediarnetrical oppositepart of the shell at the lower periphery. thereof. Under the present invention, the grinding media in the chamber 21 of the mill axially inwardly of the forwardsurfaces 52 and'53 of the ribs 55 and 51 for the most part slide straight'down the incline as indicated by the directional arrows K in Fig. 2, inasmuch as these grinding media are denied contact with the wear sufaces4iWS of the end walls by virtue of the grinding media riding on the radial outer surfaces 55 and 56 of Fig. 3. Thus, the aforementioned voidsat the peak of the incline are created inwardly of the ribs 50 and 51,

and the aforementioned ba'ck-sliding balls tumble inwardlyoff the ribs 56 and 51 into these voids, and at the same time drive more and more of the grinding media B away from the end liners. The effect is therefore synergistic to this extent, namely, as the back-sliding balls move contra-rotative to the mill and tumble off the ribs 50 and 51, these balls in the first instance'are directed away from the end liners, and because of their inward path drive the grinding media which they impact away from the end liners.

The foregoing effect is bestillustrated in Fig. 2 wherein directional arrows ES outwardly of the arrows K. illustrate the manner in which grinding media at the peak of the incline are directed in a constant stream away from the wear surfaces of the end liners during operation of the mill. There is thus a main stream of balls straight down the slope at K, Fig.2, and two end streams ES down and away from the end liners in an axial inward sense.

It will be, realized from the foregoing description that it.is. important that theouter surfaces as 55 and56 of theribs be. angled-relativeto the flatv vertical wear surfaces 40WS of the end liners so. as at least. to bep'efr.

pendicular thereto, that is, the included angle between the outer or ledge surfaces 55 and 56 of the ribs and the wear surfaces 40WS outwardly thereof should be at least' 90, since otherwise the ribs 55 and 56 will not shed freely to the maximum desired extent the back-sliding balls that are initially carried upwardly thereby. In this same connection, it will be realized that the smooth and,

especially, the continuous nature of the surfaces 55 and 56, that is, unbroken by deep recesses or raised projections throughout the axial and circumferential extent thereof, encourages back-sliding of the balls as described. in connection with Fig. 3.

A pronounced clearly observable effect of the foregoing is appreciably reduced wear on the wear surfaces of the end liners particularly at the areas thereof adjacent the bottom of the ball incline. This effect is illustrated in Fig. 3 wherein it will be observed that cavita tions CA are produced at the bottom of the ball incline, that is, relatively large vacant areas void of grinding media. This condition can be best appreciated by (3011-. sidering the contrasting normal condition prevailing in a mill not provided with ribs in accordance with the present invention. Thus, there is shown in Fig. 3A a section of a conventional mill 20A having a shell 25A and a conven-. tional one-piece end liner 40A at one end of the shell 25A. It will be noted that the mill 29A is illustrated as rotating in the same direction as the mill 20. However, the grinding media incline adjacent the end liner 40A as illustrated in Fig. 3A covers a continuous 'chordal area of the end liner 40A unbroken by any cavitations or voids as CA, Fig. 3. Moreover, as is .well known, the balls at the trough or toe T, Fig. 3A, of the ball incline in a conventional mill as 29A slide violently against conventional end liners as 40A practically to'the samenegree that the balls slide down the incline inwardly of the endliners as MA. This of course represents rather."

severe abrading action on the end liner. In contrast to this, it is observed that the grinding media, Fig. 3, collected in the circumferential spaces between the ribs 5%) and S1 and between the rib 50 and the shell 25 are significantly slowed insofar as their sliding action against the wear surfaces of the end liners 4i and 41 adjacent thetoes T, Fig. 3, is concerned. In fact there is, scarcely any observable sliding of balls at the toes T of the ball incline. Thus, during operation of a mill as 20 constructed in accordance with the present invention, it is observed that inwardly of the end liners, that is axially inwardly of the ribs 50 and 51, there occurs the normal violent tumbling action of the ball or grinding media accompanied by the novel effects described above, but insofar as the grinding balls immediately in contact with the bottom-most wear surfaces 40WS of the end liners 40 and 41 are concerned, sliding action is practically nonexistant. p I

As was mentioned above, end liners may be segmental form of the kind illustrated in Fig. 5, and these when assembled'in the required number afford a continuous 360' end liner segment assembly 60AS shown in Fig. 4. Thus, under this form of the invention, each end liner 60 is conveniently in the form of a 45 segment having arcuate outer and inner peripheral edges 61 and 62 respectively. Each end liner 60 further includes inclined side edges 63 and 64 that are angled to afford the desired segment angle. As in the foregoing embodiment, each end liner 60 has a wear surface 60WS adapted to be disposed in a vertical plane and. face inwardly of the mill, and all points on the wear surfaces 60WS lie in a common plane. Apertures as 65 are formed in the end liner. 60 at pre: determined selected locations to enable the same to be secured to the end walls of the mill. 1

Disposed inwardly ofand between the peripheral edges 61 and 62 are parallel ribs 70 and 71 which additionally are parallel to the outer peripheral edge 61 of thdfend liner so as to rotate with the end liner 60 tangent; o

the direction of mill rotation. The ribs 70 and 71 project from the wear surface 40WS normal thereto and have continuous uninterrupted forward and upper surfaces as described above in connection with the ribs 50 and 51. The ribs 70 and 71 additionally are spaced apart one from another and from opposing surfaces in the manner described above. When assembled in the manner illustrated in Fig. 4, the end edges 70A and 71A, Fig. 5, of the respective ribs on the respective end liners 60 closely abut one another to afford a pair of endless rib rings, and the inner peripheral edges 62 of the end liners are configured and sized to afford a feed or discharge opening 75, Fig. 4, as the case may be of the desired diameter.

The foregoing embodiments of the end liner of the present invention are for both ends of a dry or high discharge mill. In a wet discharge mill, the end liner associated with the discharge end of the mill is of grate or screen nature, and an end liner 80 of this kind is illustrated in Fig. 7.

The end liners 80 are also illustrated in the form of 45 segments, but in this instance are provided with screen or grate openings 808 formed in a desired pattern. It will be appreciated of course that the openings 808 open at the opposed surfaces of the end liner 80 and extend all the way through the body thereof.

Thus, each end liner 80 includes arcuate outer and inner peripheral edges 81 and 82 together with angled or inclined side edges 83. The side edges 83 in this instance, however, are of wedge shape as clearly shown in Fig. 7, and each such edge 83 is adapted to be engaged by the related complementally shaped wedge-shaped edge 84 of a so-called wedge bar 35. In affording the complete assembly 80AS, Fig. 6, the required number of wedge bars 85 are positioned between the opposed wedgeshaped side edges 83 of a pair of side-by-side end liners 80. The wedge bars 85 are formed with spaced apart apertures 87, Fig. 7, so that the shanks of bolts can be passed therethrough to anchor the end liner assembly 80AS to the end wall 88, Fig. 8, of the mill at the wet or discharge end thereof. This is accomplished in a well known manner so as to afford a discharge space 90 between the end wall 88 and the liner assembly 80AS into which suspended fines pass from the screen openings 80S incident to classification of the fines.

Ribs 91 and 92 are formed on the end liner 80 so as to project therefrom normal to the plane of the wear surface 80WS, and the ribs 91 and 92 are parallel one to another and parallel to the peripheral edges 81 and 32 of the end liner 80 so as to rotate tangent to the direction of mill rotation. The ribs 90 and 91 of the adjacent end liners in the end liner assembly 80AS will of course be spaced apart by the Wedge bars 85, but the effects achieved are wholly similar to what was described above in connection with Figs. 2 and 3. It may be moreover pointed out that the outer surfaces 93 and 94 of the ribs 91 and 92 may be slightly sloped radiallv inwardly away from the peripheral edge 81 of the end liner 80 to facilitate shedding of the grinding media, and resort may be had to such sloping in the embodiments of the end liner described above.

As mentioned, a wedge bar as 85 will of course be disposed between an immediately adjacent pair of grate or screen-type end liners as 80, and will, therefore. be interposed between the adjacent ends of the ribs on the respective liners in such a pair, inasmuch as a wedge bar as S usually projects outwardly of the wear face of the liner two to three inches as shown in Fig. 7. Ina completed 360 grate liner assembly, therefore, mounted operatively in the mill, the resultant rings of ribs disposed on projected 360 arcs as shown in Fig. 6, will be discontinuous at points where the wedge bars radially intersect the 360 arc common to the ribs 90 and 91 in the assembly. Even so, the outer ledge surfaces 93 and 94 of the ribs between the wedge bars are uninterrupted, that is, all points are substantially coplanar as in the foregoing embodiments, and hence the grinding media shed freely The travel freely through the grinding media substantially in the manner described hereinabove.

Of course in the instance of a one-piece 360 cast end liner as 40 and 41, the ribs 50 and 51 are completely closed and endless, that is, are in the form of circumferentially continuous 360 ribs. In the instance of an end liner assembly of the kid shown in Fig. 4, the ribs 70 and 71 in the assembly afford virtually endless rib rings, and by this I mean that the ends of the ribs 70 and 71 virtually abut and will be spaced apart only to the extent of foundry tolerances or such foundry grinding that may be imparted thereto.

Preferably, I use at least two ribs on an end liner located respectively at the one-third and two-thirds radius points. One or more ribs may be used, however, as long as the spacing between the outer rib surface and any opposed radial outer surface is sufiicient to enable a plurality of grinding media to stack up between such opposed surfaces. It was mentioned that the axial dimension of a rib should be at least equal to the radius of the grinding medium to be used. This is of course the minimum dimension and may be greater.

It will be seen from the foregoing that under the present invention, wear on the end liner of a grinding mill is significantly reduced by providing the end liner with at least an outermost rib that is disposed to rotate with the end liner tangent to the direction of mill rotation. Inasmuch as the outer and inner peripheral edges of the end liners will lie on concentric circles, the ribs will then be normal, that is, perpendicular to the radius drawn between such edges. In those instances where the liner is in the form of relatively small angle segment, it is possible for the ribs to be straight, since for all practical purposes the resultant ring rib of the assembly will be arcuate. The radial rib known in the prior art cannot achieve the effects induced in the mill under the present invention.

It is to be additionally pointed out that in a wet mill, a further advantage of the present invention is that by directing the grinding media away from the grate end liner, a more pronounced liquid condition is attained at areas about the grate openings thereby rendering discharge of classified fines more effective.

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. An end liner for vertical disposition inwardly of and substantially parallel to the vertical end wall of a rotary grinding mill having grinding balls and the charge to be comminuted contained in a chamber afforded by a cylindrical shell, said liner when oriented in a vertical plane including: a flat vertical wear surface adapted to face toward the chamber of the mill and be exposed to the abrading action of the grinding media, said liner having inner and outer peripheral edges lying on concentric circles, an outermost rib provided on said surface of said liner and disposed in spaced relation inwardly of said outer edge thereof a distance equal to at least several grinding ball diameters, said rib projecting forwardly from said surface of said liner substantially perpendicular to the plane of said surface and for a distance at least equal to the radius of the maximum size grinding ball in said mill, said rib being aligned substantially parallel to the outer peripheral edge of said liner so as to be disposed tangent to a radius between said edges and thereby rotate with the liner tangent to the direction of mill rotation, said rib having an uninterrupted flat forward surface movable freely through grinding media in the mill, and said rib having an uninterrupted outer ledge surface on which grinding media are adapted to be carried and back-slide freely thereon and shed freely therefrom away from said wear surface of said liner.

2. An end liner for vertical disposition inwardly of and substantially parallel to the vertical end wall of a rotary grinding mill having grinding balls and the charge to be comminuted contained in a chamber afforded by a cylindrical shell, said liner when oriented in a vertical plane including: a fiat vertical Wear surface adapted to face toward the chamber of the mill and be exposed to the abrading action of the grinding media, said liner having inner and outer peripheraledges lying on concentric circles, an outermost rib and an innermost rib provided on said surface of said liner and disposed in parallel spaced relation to one another and inwardly of said edges of said liner, said ribs projecting forwardly from said surface of said liner substantially perpendicular to the plane of said surface and for a distance at least equal to the radius of the maximum size grinding ball'in said mill, said ribs being aligned substantially parallel to said edges of said liner so as to be disposed tangent to a radius between said edges and thereby rotate with the liner tangent to the, direction of mill rotation, said outermost rib being spaced from said outer edge of said liner and said innermost rib being spaced from said outermost rib a distance equal to at least several ball diameters, said ribs each having an uninterrupted flat forward surface movable freely through grinding media in the mill, and said ribs each having an uninterrupted outer ledge surface disposed at an angle at least perpendicular to said wear surface of said liner on which grinding media are adapted to be carried and back-slide freely thereon and shed freely therefrom away from said wear surface of said liner. 7

3. An end liner for vertical disposition inwardly of l0 and substantially parallel to the vertical end wall of a rotary grinding mill having grinding balls and the charge to be comrninuted contained in a chamber afforded by a cylindrical shell, said liner when oriented in a vertical plane including: a flat vertical wear surface adapted to face toward the chamber of the mill and be exposed to the abrading action of the grinding balls, said liner having inner and outer peripheral edges lying on concentric circles, an outermost rib provided on said surface of said liner and disposed in spaced relation inward of said outer edge a distance more than a grinding ball diameter, said rib projecting forwardly from said surface of said liner substantially perpendicular to the plane of said surface and for a distance at least equal to the radius of a maximum size grinding ball in said mill, said rib being aligned substantially parallel to the outer peripheral edge of said liner so as to be disposed tangent to the direction of mill rotation, said rib having an uninterrupted flat forward surface movable freely through grinding media in the mill, and said rib having an uninterrupted outer ledge surface on which grinding mediaare adapted to be carried and back-slide freely thereon and shed freely therefrom away from said wear surface of said liner.

References Cited in the file of this patent UNITED STATES PATENTS 1,018,320 Holthoff Feb. 20, 1912 1,282,914 Mitchell et al. Oct. 29, 1918 7 51,451,472 Pomeroy Apr. 10, 1923 1,770,850 Hartman July 15, 1930 2,678,167 Weston May 11, 1954 2,704,636 Weston Mar. 22, 1955 FOREIGN PATENTS 7,801 Great Britain of 1911 452,305 Germany Nov. 8, 1927 579,651 France Aug. 8, 1924

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