CA1138398A - Liner assembly for ball mills - Google Patents

Abstract

ABSTRACT

The disclosure is directed to a multiple zone liner system for the cylindrical shell of a ball mill. The liner system comprises a plurality of liner sections which are con-structed for mounting on the inner shell surface of the mill in sequential relation along its rotational axis. Each liner sec-tion is formed with a plurality of elevated ridges disposed in substantial alignment with the shell access, and which are cir-cumferentially spaced therearound to define a comminuting sur-face. Each ridge defines a lifting surface that is disposed at a predetermined angle relative to a radius of the shell, and each ridge has a predetermined lifting dimension. The number of ridges of each liner section increases from section to sec-tion from the inlet to the outlet of the mill. The angle of the lifting surfaces of the ridges also increases from section to section toward the mill outlet. The lifting dimension of the ridges decreases from section to section from the mill inlet to the outlet. The result is a liner system capable of comminuting ore with greater effectiveness and efficiency.

Description

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Technical Field The invention generally relates to ore com-minuting ball mills, and is specifically directed to a multiple zone or section liner system for the shell of a ball mill in which each liner sec-tion has a profile of differen-t configuration.
Backgrolmd of Prior Art Ball mills are commonly used as one step in the process of reducing the size of ore in commercial mining operations. A ball mill typically consis-ts of a large cy-lindrical drum mounted on bearings for rotation about a substantially horizontal axis and driven by a powerful motor through conventional reduction gearing. The axial ends of the drum are open, and the ore which is to be com-minuted is continuously fed into the mill at one end with the product of reduced size continuously emerging from the other end.
In conventional ball mills, comminution occurs by the balls falling and tumbling onto the ore fragments as the drum is rotated. In an operation of this type, 40-50 percent of the overall charge consists of balls.
The term "ball mill" also encompasses a semiautogenously operated mill, in which 2~15 percent of -the total charge is balls. In a semiautogenous operation, part of the ore is comminuted by the balls, and part is self comminuted.
Generally, several steps are required to reduce the ore from the larger, randomly sized fragments resulting from the mining operation. Each s-tep requires large, heavy and sometimes complex equipment which repre-sen-ts a high initial cos-t and requires substantial energy ".

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(usually electrical) to operate. Ball mills, some of which are operated semiautogenously, constitute one type of e~uipment. Other types include rod mills, au-togenous mills (in which the ore is self-comminuted by tumbling in a drum or the like), gyra-tory crushers and roll crushers.
Each of these different types of machines is ordinarily used to reduce the ore fragments or particles in a par-ticular size range, and all may be necessary in a particu-lar comminu-ting process.
It is presently known to employ more than one reducing zone in ball mills. The multizone concept in-creases the efficiency of the comminuting process because it performs more than one reducing step with a single piece of equipment. ~Iowever, in order to effect the proper gradation of the ore fragments or particles, and to prevent larger particles from passing into subse~uent zones before being properly reduced in size, these ~all mills are compartmented through the use of sizing screens.
Accordingly, the fragments are tumbled in a particular zone until they have been reduced to a size which permits them to move through the grading screen to the next zone.
As of the present time, the multizone concept has not been possible with semiautogenous mills. Whereas the usage of balls increases the efficiency of a com-minuting process by crushing, nipping and rolling the ore fragments to a reduced size, they tend to destroy any grading screen which is used to re-tain the fragmen-ts in a given zone. Accordingly, to my knowledge, there are no multiple zone semiautogenous mills in the prior ar-t.
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Brief Summary of the Invention My invention is specifically directed to a semiau-togenous ball mill having a liner assembly for the rotating drum which defines a plurality of zones. The liner assembly is constructed and arranged so that -the ore moves se~uentially from one zone to the next. Each zone has a profile of different configuration, and each is specifically designed to reduce the ore fragments to a given size, after which the ore moves or migrates to the ne~t ~one.
In the preferred embodiment, each zone comprises a liner subassembly or section which is cylindrical in shape and lines a predetermined axial length of a cylin-drical rotating drum or shell. The liner subassemblies or sections are preferably of equal axial length; e.g., if three zones are used in the cylindrical drum, each occu-pies one-third of-the drum length.
Each of the liner sec-tions is formed wi-th a plurality of elevated ridges which project radially inward and extend in general alignment with -the shell axis. The ridges are circumferentially sp~ced around the inner cylindrical surface of the drum to define an ore com-minuting surface. The number of ridges per liner section increases in the direction of ore flow (inlet to outlet).
Each ridge defines a lifting surface -that is disposed a-t a predetermined angle relative to a radius of the drum. The angle is constant for -the ridges in a given liner section, but the angle increases from section to section in the direction of ore flow.

~ ach ridge also defines a predetermined lifting dimension ~i.e., the height of the internally projecting ridge) which is constant in each liner section, but which decreases from section to section in the direction of ore flow.
The first liner section :includes the least number of elevated ridges. Each ridge has a more severe lifting angle (i.e., the lifting surface more closely approaches a radius of the cylindrical drum than -the other ridges) and its lifting dimension causes it to project internally a greater distance than that of the other ridges. Accordingly, the large ore fragments which are received from the inlet are carried higher as -the liner section rotates. With the added effect of the balls, which are also carried upward with rotation, comminution results from the impac-t of the ore fragments falling on other ore fra~nents and balls below, and from the balls dropping on ore fragments.
In the second zone, the number of elevated ridges increases because the size of the ore fragments has been reduced by one order of magnitude. The lift angle is increased relative to the drum radius, so that the frag~
ments and balls fall more easily from the ridges. Coupled with a decreased lifting dimension, the ore fragments are not carried as high with rotation of the drum as in the first zone, and the comminution process more closely resembles tumbling, as distinguished from fragmen-tation by dropping impact as in the first zone. In the second zone, there is a greater tendency for the balls to nip the ore ~0 fragments and thus reduce them in size.

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In the third zone, the number of ridges is again increased, the lift angle further increased and the liting dimension further decreased. This gives rise to a more gentle tumbling or rolling effect for the alread~ reduced fragments, further reducing them to small particulate size. The comminuted product is discharged from the outlet in this form.
I have found that the approach of comminution of ore by passing it through a plurality of com~inution zones in a noncompartmented ball mill is more efficient than in prior art devicesO Efficiency is usually referred to in terms of throughput per kilowatt-hour.
Another feature of the invention is that the ore fragments and balls migrate from one zone to another automatically as they become smaller. This is believed to result at least in part from an effective decrease in rotational velocity from one zone to the next in the direction of ore flow, coupled with the structural variations from section to section as described above.
This decrease in rotational velocity results from a decrease in the effective diameter from zone to zone in the direction of ore flow. This is accomplished by increasing the base thickness of each liner section relative to the preceding section. The resulting classifîcation oE both ore fragments and ~alls into the appropriate comminuting zone is also a factor in the increased efficiency of the process. It also insures that a fresh charge of balls will remain in the first zone until they become smaller through wear.
In one of its broadest forms, the invention resides in a multiple-zone liner system for the cylindrical shell of a ball mill having an inlet at one ,~

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axial end an outlet at the other. The liner system comprises a plurality of liner sections constructed for mounting on the inner shell surface in sequential rela-tion relative to the shell rotational axis, with each liner section de~ining a comminution zone. Each liner section is formed with a plurality o elevated ridges extending in general alignment with the shell axis and circumferentially spaced therearound to define a com-minuting surface. Each ridge defines a lifting sur~ace that is disposed at a predetermined angle relative to a radius of the shell, and each ridge has a predetermined lifting dimension. The number of ridges in each liner section increases from section to section from the inlet ~`
to the outlet, as does the angle of the lifting surfaces of the ridges. The lifting dimension of the ridges is substantially constant in each section but decreases from sec~ion to section from the inlet to the outlet~
In the other of its broadest forms, the inven-tion resides in a multiple-zone liner system for the cylindrical shell of a ball mill having an inlet at one ~ ;axial end and an outlet at the other. The liner system comprises a ~lurality of liner sections constructed for ~ ~`
mounting on the inner shell surface in sequential rela-tion relative to the shell rotational axis, with each liner section defining a comminution zone~ Each liner section coprises a base of predetermined substan~ially constant thickness, the base thickness increasing from section to section from the inlet to the outlet. Each liner section further comprises a plurality of elevated ridges projecting from the associated base and extending in general alignment with the shell axis, the elevated ridges being circumferentially spaced around the liner , ;, , section to define a comminuting surface. Each ridge defines a lifting surface that is disposed at a pre-determined angle relative to a radius of the shell, and each ridge has a predetermined lifting dimension. The number of ridges of each liner section and the angle of the lifting surfaces of the ridges increase from section to section from the inlet to the outlet. The lifting dimension of the ridges decreases from section to sec-tion from the inlet to the outlet.
Additional features and advantages of the invention will become apparent from the drawings and description below.

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Brief Description of the Drawin~s Figure 1 is a somewhat schematic view in side elevation of a semiautogenous ore grinding mill in which the inventive multiple section liner assembly is used;
Figure 2 is an enlarged fragmentary view showing the multiple zone liner assembly of the grinding mill ac-cording to the invention and viewed radially outward from within the mill;
Figure 3 is a sectional view of the multiple zone liner assembly taken along the line 3-3 of Figure 2, showing in particular the relative diference in size of the individual liner segments between grinding zones, and the fastening of the liner segments to the cylindrical dxum or shell of the mill;
Figure 4 is an enlarged fragmentary sectional view of the means for fastening a liner se~ment to the drum or shell, as taken along the line 4-4 of Figure 2;
Figure 5 is a perspective sectional view of several individual se~ments of the first comminution zone as generally taken along the line 5-5 of Figure 2;
Figure 6 is a perspective sectional view of several individual segments of the second comminution zone as generally taken along the line 6-6 of Figure 2;
Figure 7 is a perspective sectional view of several individual segments of the third comminution zone as generally taken along the line 7-7 of Figure 2.
Figures 8-10 are enlarged sectional vlews of the individual liner se~ments for -the first, second and -third grinding zones, respectively; and '~' -6- ~:

3~3 Figures 11-13 are schematic representations of the material mass profiles in the firs-t, second and third grinding zones, respectively.
Detailed Description of the Invention With ini-tial reference to Figure 1, a semiauto-genous mill employing the inventive multiple zone or sec~
tion liner assembly is referred to generally by the numer-al 11. The mill 11 includes a hollow cylindrical drum or shell 12 having end walls 13, 14 with large central axial openings (not shown) and arranged for rotation abou-t a substantially horizontal axis in suitable bearings 15, 16 by a drive of conven-tional na-ture and a suitab:Le housing 17. A chute 18 communicating with the axial inlet receives ore fragments 19 from a conveyor 21. The com-minuted material leaves the drum 12 through the opposite axial opening in end wall 14, and is discharged from the mill 11 through an outlet 22. The fully comminuted ore is represen-ted by reference numeral 23.
Cylindrical drum 12 is made up a plurality of cylindrical sections 24-26, each of which is in turn assembled from a set of cylindrical ~uadran-ts by bol-ts extending through axial flanges. For example, section 24 consists of quadrants 24a-24c (one ~uadrant is not shown) which are secured together circumferentially by a plu-rality of bolts passing through radially extending, axially aligned flanges 27, 28. The cylindrical sections 24, 25 are secured together axially by a plurality of bolts passing through circumferential flanges 29, 30 extending radially from the periphery of each side.
Cylindrical sec-tions 25, 26 are secured in an identical }3~

manner, as are the end walls 13, 1~ to the cylindrical sec-tions 24, 26, respectively.
Each of the cylindrical sections 2~-26 of drum 12 is formed with a plurality of liner mounting holes 31 which are positioned in a pattexn defining axial rows, -the rows being spaced equiangularly about the drum, and in circumferential rows which are equidistantly spaced within each of the sections 24-26.
With additional reference to Figures 2-4, an lQ inner circumferential liner assembly for the drum 12 is bolted to the drum 12 to virtually co~er i-ts inner cylin-drical surface. The inner circumferential liner assembly comprises three separate liner sections for the respective cylindrical sections 24-26, which bear reference numerals 32-34, respectively. For reasons o~ manufacturing sim-plicity and ~ase o~ liner replacement, each of the liner sections 32-34 comprises a subassembly of individual liner segments respectively numbered ~1, 51, 61. With particu-lar reference to Figure 2, each of the liner segments 41, 61 defines an outer end which is perpendicular to the segment longitudinal axis and parallel to the end walls 13, 14 of drum 12. The inner ends of each of these seg ments gl~ 61 are truncated to complement the ends of the adjacent segments 51, which are -trape~oidal in shape.
Each of the liner segments, 41, 51, 61 is mounted to the shell by mounting bolts 35 and nuts 36.
Figure 4 is an enlarged sectional view showing the mount~
ing of one of the segments 61, which is typical. Each segment is formed with three countersunk bores 37 that are 30 registrable with the liner mounting holes 31 to receive ~ ~
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the bolts 35. The enlarge~ head of the bolt 35 has flat, parallel sides, and the countersunk portion of the bore 37 is shaped accordingly (see Eigure 2). This insures that the bolt 35 will not turn when the nut 36 is tightened during installation or loosened during replacement. The beveled underside of the bolt head and the corresponding bevel of the countersunk recess insures that the segment 61 is drawn tight and flush to the inner mounting surface of the drum 12.
Figures 5-7 disclose each of the liner sections 32-34 in perspective. Figures 8-10 are sectional views of the individual segmen-ts 41, 51, 61 which make up the liner sections.
With reference to Figures 5 and 8, each of the liner segments 41 comprises a body defining a base 42 and a ridge 43 which projects upwardly from the base at one side thereof. The base 42 defines a slightly arcua-te mdersurface 42a that mounts flush with -the inner cylin-drical surface of the shell 12. The height or thickness of base 42 is represented by A, and -the distance which ridge 43 projects above base ~2 (the lif-ting dimension) is represented by B. Apart from the base 42, the ridge 43 is symmetrical and defines identical substantially flat sides 43a, 43b, each of which subtends an angle ~ rela-tive to a true radius of the shell 12, which appears as the vertical line ~ in Figure 8. The top surface o~ ridge 43 is flat, as shown at 43c, and side 43b blends smoothly into the upper surface 42b of base 42.
With specific reference to Figure 5, the "tail"
of segment 41 (i.e., that portion of base 42 extending _9_ 33~

laterally from side 43b) defines the spacing between elevated ridges 43 when the segments are mounted in side-by-side relation. An ore carrying recess (defined by opposed sides or faces 43a, 43b and the upper surface 42b of base 42) is disposed between each of -the ridges 43.
The size of the recess between ridges 43, which permits the carrying of larger ore fragments, is determined by the number of ridges and the spacing therebetween. As shown in Figure 5, there is one elevated ridge 41 for a given chordal distance C of the drum 12, or two ridges 41 for -two chordal distances C.
With reference to Figures 6 and 9, each of the segments 51 comprises a base 52, one full elevated ridge 53 and a partial elevated ridge 53'. Base 52 has a moun-t-ing surface 52a the arcuate length of which is identical to mounting surface 42a, and an upper surface 52b from which the ridges 53, 53' project. The thickness or radial height of base 52 is represented by A'.
Each of the ridges 53, 53' projects a radial distance B'. Ridge 53 has substantially flat symmetrical sides 53a, 53b each of which sub-tends an angle 0 ' wi-th the true radius R, and a flat top surface 53c. Ridge 53' has an identically angled side 53a' and a side 53b' which :
lies on a true radius of shell 12.
As constructed, and as particularly shown in Figure 6, the segments 51 are mounted front -to back and back to front in alternating relation, so that the sides 53b' of adjacent segments are disposed side by side to define a full elevated ridge 53. The spacing between the \

elevated ridges 53 is such that two of the chordal dis-tances C emcompass three elevated ridges.
Each of -the se~ments 61 comprises a base 62 and two ridges 63 which project symmetrically from the upper surface 6~b of base 62. The mounting surface 62a is iden-tical in length and curva-ture to the surfaces 42a, 52a.
The thickness of base 62 is greater than the thickness of both bases 42 and 52, and is represented by ~". The lifting dimension of the ridges 63, however, is less than that of ridges 43, 53, and is represented by B".
The ridges 63 have rounded sides, blending smoothly into the rounded upper base surface or top 62b and definin~ a sinusoidal pa-ttern. Although rounded, the ridge sides generally subtend an angle ~' with a true radius R o~ the shell 12, which angle is greater than ~ and ~.
With specific reference to Figure 7, it will be noted that the ridges 63 of a given segment are so spaced that, when the segment is mounted adjacent another seg-ment, all of the ridges 63 are equidistan-tly spaced. This is accomplished by providing a half recess on the outboard side of each ridge 63 which combines wi-th an adjacent half recess to define a full recess.
Also as shown in Figure 7, there are two full ridges 63 within liner section 34 for the same chordal distance C, or four ridges 63 for two of the chordal dis-tances C.
As described, i-t will be apparent from the fore-going that the liner sec-tions 32-34 differ from each other in several importan-t respects. First, althouyh not nec-essarily in order of importance, is the number of ridges ,~ , 3~3~

in each liner section, which also may be ~iewed as thenumber of ridges in a uniform chordal distance. For sub-s~antially the same diameter, liner section 32 has the least number of ridges, and each of the liner sections 33, 34 has progressively more ridges. This is necessary because the ore fragments are largest when they enter the mill 11, and more space is thus required ~e-tween the ridges 43. ~s the ore becomes more fxagmented during the comminu-tion process, lesser space is needed between ridges, and an increased number of ridges assists in carrying the ore fragments upwardly.
Second, the lifting dimension B of the ridges 43 of liner section 32 is grea-ter than the li.fting dimensions B' and B" of liner sections 33 and 3~, respectively.
~gain, the size of the ore fragments as they enter the mill 11 requires a greatex projection or lifting dimension on the part of the ridges 43, permitting the fragments to be carried upwardly as the mill rotates. After -the initial stage of comminution, the lifting dimension is decreased in accordance with ore ragment size.
Third, the lifting angle ~ is at a minimum within the liner section 32, with the angles ~ ' and ~
increasing progressively. The smaller the lift angle, the more nearly it approaches a true radius of the shell 12, which permits the ridge to carry the ore fragments higher as the shell rotates. As the angle increases, there is a greater tendency of` -the ore fragmen-ts to fall off the ridge earlier; and~ in the case of liner section 33, the increased lift angle results in more o a tumbling action -than the lifting and dropping of ore fragments which ~12-occurs with liner section 32; and the configuration of liner section 34 results in a more rolling movement of the ore fragments and balls.
Fourth, the thickness A of liner segments 41 is at a minimum, and this dimension increases for -the liner sections 33 and 34, as shown at A' and A", respectively.
Increasing the thickness of the base slightly reduces -the average inside diame-ter of the liner section. Since cir-cumferential velocity is a direct f~mc-tion of diameter size, it follows that the ore fragments travel at a greater speed within liner section 32, and -this speed progressively decreases for the liner sections 33, 34. It is believed that this difference in circumferential velocity is at least partly responsible for migration of -the ore fragments from one liner section -to another in the forward direc-tion (inlet to outlet) as the ore is com-minuted.
This difference or variation between liner sec-tions may also be characterized in terms of the ratio of the lif-ting dimension of the elevated ridges of each liner section to the base thickness of the associated section.
Since the lifting dimension decreases from section -to sec-tion, whereas the base thickness increases, the ratio of these dimensions decreases from section to sec-tion; i.e., B/A is greater -than B'/A', which is greater than B"/A".
Last, -the configuration of -the ridges is gener-ally more angular for liner sections 32 and 33, and becomes rounded for liner section 34. This facili-tates the falling, tumbling and rolling movement of ore frag-ments within each liner section.

Preferably, the liner segments 41, 51, 61 are formed from material which is resistant to abrasion, a typical example of which is martensitic steel. Although such materials may not be as resistant to impact, it has been found that the extremely hard, abrasion-resistant characteristic enables the segment to wear longer over long periods of use.
It is also possible to employ a composite approach to each of the individual segments, such as that disclosed in U.S. Patent No. 4,046,326 entitled "Shell Liner Assembly", and which issued to Darrell R.
Larsen on September 6, 1977. With this approach, a segment body is provided of material which has a greater resistance to impact but is lesser resistant to abra-sion. One or more wedge-shaped wear inserts are uni-quely secured with the segment body to the liner shell in a position of exposure to the ore fragments during comminution. In another approach, which is disclosed in U.S. Patent No. 4,235,386, entitled "Shell Liner Assembly for Ore Grinding Mills", and which issued to Darrell R. Larsen on November 25, 1980, the abrasion-resistant wear insert takes the form o~ a cap which is connected directly to the segment body, the latter being connected directly to the liner shell.
The material of both the segment bodies and wear inserts for these composite structures is preferably martensitic steel, which can be heat ~ -treated to be either impact resistant, ox highly resistant to abrasion. The procedures for obtaining these performance characteristics are well known in the metallurgical art. Another suitable . . , , , ~

example of an abrasion resistant material from which the individual segments may be formed is martensitic white ron .
Preferably, the balls used with tbe multiple 20ne liner assembly are also formed from martensitic s-teel, but they ar~ heat trea-ted to be somewhat more resistant to impact -than -the individual liner segments, and not quite as resistant to abrasion. As such, the balls tend to wear slightly faster than the individual liner segments, and they gradually become reduced in size As discussed below, this works to an advantage by reason of the inherent migration of smaller balls to the down-stream zones where smaller ore fragments are comminuted.
Operation of the mill 11 is subs-tantially con-tinuous, wi-th ore fragments 19 supplied by conveyor 21 through chute 18 to the axial inlet of the drum 12. A
fresh charge of uniform sized balls is added intermittently as the balls in use become worn and reduced in size to the point that-they are no longer useful.
With specific reference -to Figures 5, 8 and 11, the large ore fragmen-ts are initially subjected to com-minu-tion in the first zone, which is defined by liner section 32~ As described above, each of the segrnents 41 of liner sec-tion 32 imparts subs-tantial lift to the ore fragments as the drum 12 ro-ta-tes, by reason of -the lifting dimension B and the lift angle ~. Because of these factors, the ore fragments and the balls are lifted upward a significant vertical distance by rotation of the drum 12, and ultimately are dropped onto the fra~nents and balls below. This results in crushing and breaking of the }3~

fragments by impa~t with other fragments and balls. The resulting profile of the mass within the drum 12 generally takes the form of a kidney, and is schematically repre-sen-ted in Figure 11.
In the second zone, which is defined by liner section 33 (Figures 6, 9 and 12), the reduced ore frag-ments are subjected to communication by the segments 51, which include a greater number of elevated ridges 53 than the number of ridges 43. However, each of the ridges 53 has a lesser lifting dimension B' and a lifting angle which permits the ore fragments to slide off more readily.
Consequently, these smaller ore fragments are not carried as high as in the ~irst comminuting zone as the drum 12 rotates. As a result, there is more of a tumbling action by the balls and ore fragments, and size reduction is by the rock par-ticles being "nipped" by the balls. The resulting kidney profile is moderated relative to the first zone, as shown in ~igure 12.
In the -third comminuting zone, liner section 34 defines an increased number of elevated ridges 63, each of which has a lesser lifting dimension B" and an increased lift angle O ". Coupled with the rounded profile of each ridge 63, the smaller ore fragments are carried upward a lesser vertical distance than in the prior zones, and com-minution results from ball-to-ball rolling abrasion on the fragmen-ts. As shown in Figure 13, the mass profile is further moderated, although it continues to be substan=~
tially kidney shaped.
The small comminuted rock particles leave the third comminuting zone and drum 12 through the axial outlet 22.

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a3~1 As described above, migration of the ore frag-ments and balls from one zone to the next is inheren-t with reduction in size. This results in classification of larger balls with larger fragments in the first zone, intermediate balls and fragments in the second zone and the smallest balls and fragments in the third zone. This migration results in a subs-tantial increase in efficiency of the comminution process, since there is a minimum amount of intermixture of ore fragments and balls of different size within each zone.
Each of the ridges 43, 53, 63 is symmetrical in profile, as shown in ~igures 8-10. This is not a neces-sity, but it is advantageous because i-t enables the direction of ro-tation of drum 12 to be reversed after -the lifting faces have become worn in one direc-tion. The symmetrical approach also increases the amount of material in the segment, which also increases life of the liner section.
As described, the multiple zone liner assembly performs a significant size reduction in ore fragments between the inlet and outlet, and also is of increased efficiency as compared with existing processes, as measured by total throughpu-t per ~ilowatt hour.

Claims (26)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A multiple zone liner system for the cylindrical shell of a ball mill having an inlet at one axial end and an outlet at the other, the liner system comprising:
(a) a plurality of liner sections constructed for mounting on the inner shell surface in sequential relation relative to the shell rotational axis, each liner section defining a comminution zone;
(b) each liner section formed with a plurality of ele-vated ridges extending in general alignment with the shell axis and circumferentially spaced therearound to define a comminuting surface;
(c) each ridge defining a lifting surface that is disposed at a predetermined angle relative to a radius of the shell, and each ridge having a predetermined lifting dimension;
(d) the number of ridges of each liner section increasing from section to section from the inlet to the outlet;
(e) the angle of the lifting surfaces of the ridges increasing from section to section from the inlet to the outlet;
(f) and the lifting dimension of the ridges being substantially constant in each section but decreasing from section to section from the inlet to the outlet.

2. The liner system defined by claim 1, wherein the elevated ridges of each liner section are equiangularly spaced.

3. The liner system defined by claim 1, wherein the liner sections are of equivalent axial length.

4. The liner system defined by claim 1, wherein each liner section comprises a plurality of liner seg-ments.

5. The liner system defined by claim 4, wherein the liner segments of each section are structurally identical.

6. The liner system defined by claim 4, wherein each liner segment defines a mounting surface and a com-minuting surface, and is secured to the shell by fastening means.

7. The liner system defined by claim 4, wherein each liner segment comprises a body defining a base and at least one elevated ridge projecting therefrom.

8. The liner system defined by claim 7, wherein the thickness of the base of each segment body is substan-tially constant in each section, said base thickness increasing from section to section from the inlet to the outlet.

9. The liner system defined by claim 8, wherein the ratio of the lifting dimension to the base thickness de-creases from section to section from the inlet to the out-let, whereby the effective inside diameter of the liner sections decreases from section to section from the inlet to the outlet.

10. The liner system defined by claim 1, which com-prises three liner sections.

11. The liner system defined by claim 10, wherein each elevated ridge of the first liner section has a substantially flat lifting surface, and terminates in a flat top surface.

12. The liner system defined by claim 10, wherein each elevated ridge of the second liner section has a substantially flat lifting surface, and terminates in a flat top surface.

13. The liner system defined by claim 10, wherein each elevated ridge of the third liner section has a curved lifting surface that merges smoothly into a rounded top.

14. The liner system defined by claim 10, wherein the first liner section comprises a plurality of identical liner segments, each segment comprising a body defining a base and one elevated ridge projecting therefrom.

15. The liner system defined by claim 14, wherein the ridge is disposed within the segment body so that uniformly positioned adjacent segments define equi-distantly spaced elevated ridges with equidistantly spaced recesses therebetween.

16. The liner system defined by claim 10, wherein the second liner section comprises a plurality of iden-tical liner segments, each segment comprising a body defining a base and having one full and one-half ridge projecting therefrom.

17. The liner system defined by claim 16, wherein the full and half ridges are so disposed within the seg-ment body that alternately positioned segments define full, equidistantly spaced ridges with equidistantly spaced recesses therebetween.

18. The liner system defined by claim 10, wherein the third liner section comprises a plurality of identical liner segments, each segment comprising a body defining a base and having two ridges projecting therefrom.

19. The liner system defined by claim 18, wherein the two ridges are so disposed within the segment body that uniformly positioned segments define equidistantly spaced ridges with equidistantly spaced recesses therebetween.

20. The liner system defined by claims 15, 17 or 19, wherein the lifting surfaces of each elevated ridge merge smoothly into the associated base.

21. The liner system defined by claims 15, 17 or 19, wherein the elevated ridges are symmetrical in cross section.

22. The liner system defined by claim 10, wherein for a given chordal distance of the shell, the first liner section defines two elevated ridges, the second liner section defines three elevated ridges, and the third liner section defines four elevated ridges.

23. The liner system defined by claim 1, wherein the ele-vated ridges of each liner section are symmetrical in cross sec-tion.

24. The liner system defined by claim 1, wherein each liner section is formed from material that is resistant to abrasion.

25. The liner system defined by claim 24, wherein the liner section material is martensitic steel.

26. A multiple zone liner system for the cylindrical shell of a ball mill having an inlet at one axial end and an outlet at the other, the liner system comprising:
(a) a plurality of liner sections constructed for mounting on the inner shell surface in sequential relation relative to the shell rotational axis, each liner section defining a comminution zone;
(b) each liner section comprises a base of predeter-mined substantially constant thickness, the base thickness increasing from section to section from the inlet to the outlet;
(c) each liner section further comprising a plurality of elevated ridges projecting from the associated base and extending in general alignment with the shell axis, the elevated ridges being circum-ferentially spaced around the liner section to define a comminuting surface;
(d) each ridge defining a lifting surface that is disposed at a predetermined angle relative to a radius of the shell, and each ridge having a prede-termined lifting dimension;
(e) the number of ridges of each liner section increasing from section to section from the inlet to the outlet;
(f) the angle of the lifting surfaces of the ridges increasing from section to section from the inlet to the outlet;
(g) and the lifting dimension of the ridges decreasing from section to section from the inlet to the outlet.