AU5358386A

AU5358386A - Shell liner assembly

Info

Publication number: AU5358386A
Application number: AU53583/86A
Authority: AU
Inventors: Charles B. Dugger Jr.; David M. Kjos
Original assignee: Evans Products Co
Current assignee: Evans Products Co
Priority date: 1985-01-25
Filing date: 1986-01-24
Publication date: 1986-08-13
Anticipated expiration: 2006-01-24
Also published as: CN86100920A; FI863859A0; FI863859A; MX168532B; CA1298260C; SE8604053L; WO1986004267A1; SE8604053D0; PH22969A; AU607892B2; CN1017600B

Description

SHELL LINER ASSEMBLY

Technical Field The invention relates generally to ore pro¬ cessing, and is specifically directed to an improved liner assembly for the cylindrical shell of an ore grinding machine.

Background of the Invention Ore grinding or comminuting machines have long been used to reduce the size of ore fragments to small particles for further processing. One type of commonly used machine comprises a cylindrical shell in which ore particles enter through an opening in one axial end and reduced particles are discharged from the .opposite end. Comminution occurs by rotating the shell, causing the ore fragments to tumble on one another, resulting in grinding and a reduction in size.

Typically, the inner cylindrical surface of the shell is lined with a plurality of thick liner segments that cover substantially the entire shell sur- face. The exposed grinding surface of the liner assembly is configured to carry the ore fragments upwardly as the shell rotates, causing them to tumble back into the charge of ore fragments, resulting in comminution. It is well established that, in any rotary grinding mill, a portion of the tumbling charge of ore fragments consists of a relatively inactive region that is generally kidney shaped. In the "kidney", there is very little movement of the particulate matter, and as a result, very little useful grinding takes place. The size of the "kidney" is dependent on a number of factors including shell diameter, to what extent the mill is filled, rotational velocity of the shell, liner configuration, ball size (if balls are used to assist in comminution) and percent moisture in the ore charge. However, in any tumbling charge of ore par¬ ticles, a kidney exists which adversely affects ore com¬ minution.

With increased sizes of ore grinding mills, useful grinding work appears to be limited to and depen¬ dent upon a maximum depth of the ore charge (as measured from the bottom of the shell to the top of the charge at rest) .

Grinding efficiency drops as the ore charge depth is increased beyond an upper limit. It is believed that this efficiency loss is related to an increase in the size of the ore charge kidney, which is accompanied by- increased slippage of the active outer charge layers and the inactive layers in the kidney. Grinding efficiency refers to the volume of reduced particles discharged from the mill in a given unit of time. If the size of the charge is increased, it is potentially possible for more reduced particulate matter to be discharged from the mill in a given unit of time. However, the larger the ore charge, the greater the size of the kidney, which significantly reduces the overall efficiency. Consequently, even though the charge may be larger and the mill capacity increased, it takes a greater period of time to reduce the charge to ore particles of a predetermined size, and mill effi¬ ciency is therefore reduced.

The charge may be decreased in volume, which reduces the size of the kidney and comminutes the ore more quickly. However, with a reduced input of the charge, this necessarily limits the volume of ore par¬ ticles to be discharged in a unit of time, and grinding efficiency is decreased in this manner. Summary of the Invention It has been found that, by configuring the liner assembly in a particular manner, activity within the charge can be increased with a commensurate decrease in the size of the kidney by breaking it up to an extent.

More specifically, this is accomplished by creating a plurality of ramp-like surfaces that extend circumferentially to present sequential steps to the ore charge as the shell rotates. Advantageously, the liner assembly includes a plurality of axial sections with each section defining its own sequence of ramp-like sur¬ faces, and with the ramp-like surfaces staggered relati¬ vely from section to section. Rotation of the mill is such that any given point in the charge which is disposed in engagement with the liner surface is moved progressively closer to the center of the drum as it travels up the ramp, but then abruptly steps radially outward at the end of one ramp and the beginning of another. It will be appreciated that, since this occurs over and over as the ramp moves sequentially by the charge, the charge is "pulsed" at a rate which is a function of the effective circumferen¬ tial length of the ramp and the rotational velocity of the shell.

It is the repeated impartation of "pulses" to the charge that produces directional physical forces and creates additional action within the kidney, thus serving to break it up. With the increased activity, there is a commensurate increase in total useful work done by the charge, resulting in increased grinding efficiency.

In addition to increased activity within the charge, the improved liner assembly can also result in secondary benefits of increased retention time and segregation of the charge based on size. Both of these benefits further enhance performance of the mill.

Where a plurality of axial sections are used, we have found that variation in the circumferential position of the ramps of one section relative to those of adjacent sections (i.e., "staggering" of the sections) will produce different desired results; e.g., retarding or advancing the rate of flow of the charge through the mill. With the improved liner assembly, overall efficiency in terms of volume of reduced throughput per unit of time is increased. Because ore grinders are typically operated on a twenty-four hour per day basis, increased comminution efficiency results in significant economic advantages to the user.

Brief Description of the Drawings Figure 1 is.an exemplary view of a portion of a liner assembly embodying the invention and installed in the shell of an ore grinding machine as viewed in a transverse sectional plane perpendicular to the axis of the cylindrical shell;

Figure 2 is a reduced perspective view which is schematic in nature showing a plurality of separate axial sections making up the inventive liner assembly and the relationship of these axial sections to each other;

Figure 3 is a view similar to Figure 2, and showing an alternative relationship of the axial sec¬ tions of the liner assembly; Figure 4 is a view similar to Figures 2 and 3 showing another alternative relationship between the axial sections of the inventive liner assembly;

Figure 5 is a generated fragmentary plan view of the specific structural configuration of a first embodiment of the inventive liner assembly; Figure 6 is a sectional view taken along the line 6-6 of Figure 5;

Figure 7 is an enlarged fragmentary sectional view taken along the line 7-7 of Figure 5; Figure 8 is a view similar to Figure 7 of a slightly modified version of the liner assembly shown in Figures 5-7;

Figure 9 is an end sectional view of a second embodiment of the inventive liner assembly as installed in the shell of an ore grinding machine;

Figure 10 is a generated fragmentary plan view of the second embodiment as viewed along the lines 10-10 of Figure 9;

Figure 11 is a sectional view taken along the line 11-11 of Figure 10; and

Figure 12 is an enlarged fragmentary sectional view taken along the line 12-12 of Figure 10. Detailed Description of the Invention Figure 1 shows one of a plurality of axial sections of a liner assembly which is represented generally by the numeral 11. Each axial section com¬ prises a plurality of individual liner segments which are installed in such a manner as to cover the entire inner circumferential surface of the cylindrical shell 12 of an ore grinding machine. One circumferential row of liner segments is shown in Figure 1. As will be discussed below, the liner segments also extend in axial rows within the cylindrical shell 12 so that substan¬ tially the entire inner cylindrical surface of the shell 12 is covered by the liner assembly 11.

In Figure 1, the individual liner segments are secured to the shell 12 by suitable means not shown, such as nut and bolt assemblies.

With continued reference to Figure 1, there are four different structural configurations of liner segments used, which respectively bear the reference numerals 13-16. As is apparent in Figure 1, the primary difference between the segments 13-16 is in their thickness or radial height, and a description of the structural details of one segment will otherwise be exemplary of all of the segments.

Segment 16 has a bottom surface 16a that is slightly convex to correspond to the inner cylindrical surface of the shell 12, and a top or grinding surface 16b which defines two axially extending ridges which serve to carry particles of the ore charge upwardly for subsequent tumbling upon rotation of the shell 12 in the direction shown in Figure 1.

Liner segment 16 has sides 16c, 16d, with the latter having a greater thickness or radial height than the former. Accordingly, the thickness or radial height of the segment 16 increases gradually from the side 16c to the side 16d.

Each of the liner segments 13-16 is structured with the same gradual increase in thickness, and the segments are interrelated in size so that together, the four grinding surfaces of the segments 13-16 generally define a ramp-like surface, but with undulations as defined by the axially extending ridges. As shown in Figure 1, there are six groups of segments 13-16 extending circumferentially around the inner cylindrical surface of the shell 12, with the lowest point (the shortest side of segment 13) of one segment group disposed adjacent the highest point (side 16d of segment 16) of another segment group. As such, this defines a plurality of circumferentially extending sequential steps to which the ore charge is exposed as the shell 12 rotates.

While six groups of segments 13-16 are shown in the preferred embodiment, it will be appreciated that the number of groups is variable depending on the mill diameter and bolt hole pattern.

With reference to Figure 2, it will be seen that, in the preferred embodiment, the liner assembly 11 comprises four individual sections lla-lld, each of which is structurally identical to the section shown in Figure 1. These axial sections lla-d are commonly cen¬ tered on the rotational axis of shell 12 and are disposed in side-by-side relation. Broadly speaking, each of the axial sections lla-d is annular in configuration, and as discussed in connection with Figure 1, each section defines a plura¬ lity of ramp-like surfaces that extend circumferentially and define sequential steps with the lowest point of one ramp-like surface adjacent the highest point of another. Further, and as shown in Figure 2, the ramps of each axial section are circumferentially staggered with respect to the ramps of an adjacent axial section.

More particularly, and as shown in Figure 2, the axial section lib is staggered or advanced in the forward or clockwise direction (as viewed from the left end of the liner assembly 11) by a distance X. In the preferred embodiment this staggering is followed uni¬ formly throughout the axial sections lla-lld, so that each of the sections llb-d is advanced by a distance of X relative to the section which immediately precedes it.

With reference to Figure 3, which shows an alternative form of staggering, the staggering distance between the adjacent sections lla-d is 2X in the forward direction, and this spacing is uniformly followed throughout the liner sections.

In Figure 4, which represents another alter¬ native, the distance of staggering is 3X in the forward direction, and in the preferred embodiment this staggering is also uniformly followed from section to section. This alternative may also be viewed as staggering each of the succeeding sections llb-d by a distance of X in the rearward direction, or counter¬ clockwise as viewed from the left end of the liner assembly 11.

As will be discussed below, different handling of the ore charge is accomplished with different staggering arrangements, and other variations are possible to accomplish desired functions. The distance "X" is based on the circumferential spacing of mounting holes in the cylindrical shell 12, and this distance is not critical. Neither is absolute uniformity of staggering between adjacent sections, although unifor¬ mity is preferred. Figures 5-7 disclose a first specific struc¬ tural embodiment of the liner segments of the inventive liner assembly. This liner assembly bears the general reference numeral 21, and in the generated plan view of Figure 5, three axial liner sections 21a-c are shown. In this embodiment, the length (i.e., the dimension extending in the direction of the rotational axis of shell 12) of the individual liner segments in liner sec¬ tions 21a and 21c is the same, and the liner segments of section 21b are somewhat shorter. This dimensional variation may be carried out as one of several approaches to accommodating the liner segments to a par¬ ticular mill, and demonstrates that the axial length of the liner segments in all of the axial sections 21a-21c need not be identical. With additional reference to Figures 6 and 7, axial sections 21a and 21c are made up of three dif¬ ferent individual liner segments 22-24, and axial sec¬ tion 21b is made up of individual liner segments 25-27. Each of the segments 22-27 is secured to the cylindrical shell 12 by two or three conventional tapered head bolt and nut assemblies that extend through mounting openings 29 in the individual segments and registering mounting openings 30 in the shell 12. As best appears in Figure 5, the mounting openings 30 in the shell 12 are uni- formly disposed in axial and circumferential rows, and the mounting openings 29 in the segments 22-27 must be appropriately disposed to register therewith. Also as shown in Figure 5, the cylindrical shell 12 of the pre¬ ferred embodiment is provided with one or more "manhole" access openings 31. In the embodiment shown in Figure 5, the access opening 31 is covered by one of the liner segments 26.

With specific reference to Figure 7, each of the liner segments 22 defines a bottom mounting surface 22a that is slightly convex to conform to the inner con¬ cave surface of the shell 12. Segment 22 further comprises unequal sides 22b, 22c that reflect the_ increasing thickness of the body of segment 22 from left to right as viewed in Figure 7. Each of the segments 22 further comprises an upper or comminuting surface defined by axially extending, elevated ridges 22d, 22e, each of which has a rounded top. With reference to Figure 5, each of the segments 22 includes three spaced, colinear ridges 22d and 22e which are of different length and staggered relative to one another. The number of ridges 22d, 22e, and their length and spacing is not critical. Of impor¬ tance is the performance of a lifting function to the ore particles as the shell 12 moves in the clockwise direction as shown in Figure 7.

With continued reference to Figure 7, each of the segments 23 also comprises a similar mounting sur¬ face 23a, but which also includes axially extending recesses 23b, 23c facing the shell 12 that conserve material without affecting the strength and wearability of the segment 23. The recesses 23b, 23c are of gra¬ duated depth, corresponding to the increased thickness of the body of segment 23.

Segment 23 further comprises a short side 23d that is slightly greater in height or radial dimension than the adjacent side 22c of segment 22, and a long side 23e.

The top or comminuting surface is also defined by axially extending, elevated ridges 23f, 23g that, in the preferred embodiment, are structurally similar to the liner segments disclosed in the commonly owned U.S. Patent No. 4,270,705, which issued on June 2, 1981 in the name of Darrell R. Larsen, and U.S. Patent No. 4,295,615, which issued on October 20, 1981 in the name of James E. Mishek. Axially extending longitudinal channels 23h, 23i having closed ends and tapered sides that converge toward the mounting surface are formed in each segment 23. Inserts 23j, 23k are subsequently cast in the respective longitudinal channels. The resulting elevated ridges 23f, 23g are flat topped in this embodi¬ ment.

Alternatively, the longitucinal channels 23h, 23i may be open ended and extend over the entire length of the associated segment, and the inserts 23j, 23k may be of commensurate length and inserted by sliding in from one end thereof, as disclosed in U.S. Patent Nos. 4,270,705 and 4,295,615.

Preferably, the body of segment 23 is cast from a material which is softer and less brittle than the material of the inserts 23j, 23k, which are pre¬ ferably cast from an extremely hard, long-wearing material such as martensitic white iron. Other materials are suitable.

The structural configuration of segment 24 is the same as that of segment 23 except for its thickness, which increases from the largest radial dimension of segment 23.

Mounted together, the liner segments 22-24 define a ramp-like surface that increases in dimension from the shortest side of segment 22 to the longest side of segment 24, then stepping off to the short side of another segment 22 in a sequential manner.

With the exception of axial lengths and the number of axially extending elevated ridges, the liner segments 25-27 have the same structure as the segments 22-24 as shown in Figure 7.

With specific reference to Figure 6, the ends of segments 22-27 are disposed in parallel, spaced rela¬ tion. However, just above the inner surface of the shell 12, these mutually parallel sides diverge from each other in the direction of the shell 12, and define a pocket in which an insert 32 is retained. The func¬ tion o^"f the insert is to prevent the entry and com¬ pacting of ore particles between adjacent liner segments to the extent that removal of the segments for replace¬ ment purposes becomes extremely difficult.

In the preferred embodiment, the insert 32 is made of rubber and is generally triangular in con¬ figuration and dimensioned to be loosely retained within the pocket. Reference is made to the commonly assigned U.S. Patent No. 4,165,041 for further structural details and features of the insert and pocket.

In the preferred embodiment of liner assembly 21 as shown in Figure 5, the liner segments 25-27 of axial section 21b are advanced by a distance of one axial row of mounting openings 30 in the shell 12 by advancement of one axial row of mounting openings 30. Liner assembly 21 thus generally conforms to the embodi¬ ment shown in Figure 2. Figure 8 discloses a liner assembly 21' that is quite similar to liner assembly 21 with one varia¬ tion. The individual segments 22', 23', 24' are dif¬ ferent than their counterparts in liner assembly 21 in that each has a substantially constant thickness or radial dimension (aside from thickness variations due to the elevated ridges) . However, the overall thickness of the segment body of liner segment 23' is greater than that of liner segment 22' and less than that of liner segment 24*. Consequently, each of the ramp-like sur- faces is defined by incremental steps. These steps do not adversely affect comminution and function in substantially the same manner as the elevated ridges themselves.

Liner assembly 21' offers certain advantages because the individual liner segments 22'-24^* are sym¬ metric. These include less difficulty in manufacture and reversability of the liner section within the shell when the leading edges of the elevated ridges become worn. Liner assembly 21' may also be configured to receive rubber inserts 32 in a similar manner to liner assembly 21.

Figures 9-12 disclose a second specific struc¬ tural embodiment of a liner assembly 41 embodying the invention. Liner assembly 41 utilizes the general inventive concept of plural axial sections each of which defines a plurality of ramp-like surfaces that extend circumferentially in sequential steps. However, most of the liner segments of liner assembly 41 are of a com- posite rather than an integral structure. Consequently, and as best shown in Figures 9 and 12, a single wear cap 42 may be commonly utilized throughout the assembly 41.

With reference to Figure 10, liner assembly 41 comprises two circumferential rows 41a, 41b of liner segments that together comprise a single axial section; i.e., there is no staggering of adjacent liner segments. Each of the rows 41a, 41b comprises three liner segments represented generally by the numerals 43-45. As shown in Figures 10 and 11, the liner segments 43-45 are of the same length or axial dimension.

In addition, to compensate for the manhole access openings 31, each circumferential row 41a, 41b further comprises a liner segment 43' of reduced length. The liner segment 43' ' is sized to cover the manhole access opening 31 and fits between liner segments 43' as shown.

With reference to Figure 12, and as briefly discussed above, each of the liner segments 43-45 is of composite structure, comprising carrier or holder segments 43a-45a, respectively, with wear caps 42 respectively superimposed thereover. Each of the holder segments 43a-45a increases in thickness, with wear segment 43a the lowest of the three. As shown in Figure 12, the increasing thicknesses of the holder segments 43a-45a are dimensioned so that, with the wear caps 42 attached, a ramp-like surface is defined extending in the circumferential direction in sequential steps as described above.

To resist shear stresses on the mounting bolt assemblies (discussed below), and to resist relative movement, each of the wear caps 42 of the preferred embodiment is cast with three circular, downwardly pro¬ jecting bosses 42a. As shown in Figure 10, the holder segment 43a is cast with three corresponding recesses 43b to receive the associated bosses 42a. As shown in Figures 11 and 12, registering mounting openings for mounting bolt assemblies 46 extend through the bosses 42a and recesses 43b. The mounting bolt of assembly 46 is a standard oval-head bolt that is recessed below the grinding surface of the wear cap 42 for protective pur¬ poses. The mounting bolt assemblies 46 commonly secure both the wear cap 42 and holder segment 43a to the cylindrical shell 12. The mounting arrangement of the holder segments 44a and 45a and their respective wear caps 42 is the same, although the mounting bolt assemblies 46 are somewhat longer due to the increased thickness of the holder segment bodies.

With reference to Figures 10 and 11, each of the holder segments 43a-45a is formed with four equi- distantly spaced mounting openings. Liner segment 45 is exemplary, and these mounting openings bear the reference numeral 45c. The circular recesses 45b register with three of these openings 45c to receive the associated bosses 42a. The mounting opening 45a for which there is no recess 45b receives a short bolt assembly 46 the head of which is recessed within this mounting opening, as shown in Figure 11. As such, one of the four mounting bolt assemblies 46 secures the holder segment 45a directly to the shell 12 indepen¬ dently of the associated wear cap 42, whereas the other three mounting bolt assemblies 46 extend through both the wear cap 42 and underlying holder segment 45a to commonly secure both to the shell 12.

The same mounting arrangement exists for all of the liner segments 43-45. With such construction, it is possible to remove the wear caps 42 for replacement without removing the underlying holder segments 43a-45a.

With continued reference to Figure 11, the opposed ends of adjacent wear caps 42 diverge toward the bottom or mounting surfaces to receive an insert 32. As exemplified by the holder segments 45a in Figure 11, the ends of the holder segments 43a-45a also diverge to receive an insert 32, such construction being similar to that shown in the embodiment of Figures 5-7.

With reference to Figures 10 and 12, the liner segment 43' is of single-piece construction, but has the same thickness and grinding surface as liner segment 43. Liner segment 43' ' is also of single-piece construction, and aside from its shorter length, is otherwise struc¬ turally the same as liner segments 43'. The composite approach to the liner segments

43-45 is advantageous in that the wear caps 42 and holder segments 43a-45a may be cast from different materials appropriate to their respective functions. For example, the wear caps 42 are continuously and directly exposed to the ore comminution process, and in the preferred embodiment are cast from material having a high resistance to abrasion, such as martensitic white iron or martensitic steel. The holder segments 43a-45a are not directly exposed to the comminution process, and their primary function is to support the wear caps 42 in the ramp configuration. Consequently, they can be cast frOtø a material which is less hard and less brittle, such as pearlitic chrome-molybdenum.

The composite approach and the mounting con- figuration also enable the wear caps 42 to be replaced when worn without replacement of the holder segments 43a-45a.

Summarizing, each of the embodiments disclosed utilizes a plurality of ramp-like surfaces extending circumferentially to present sequential steps to the ore charge as the shell rotates. The repeated impartation of "pulses" to the ore charge decrease the size of the kidney by breaking it up, increasing the total useful work done by the charge and grinding efficiency.

Claims

WHAT IS CLAIMED IS:

1. An improved liner assembly for the cylindrical shell of an ore grinding machine comprising: a plurality of individual liner segments covering substantially the entire inner cylindrical sur¬ face of said shell; means for mounting the liner segments to said shell; the liner segments being arranged in a plura¬ lity of axial sections commonly centered on the shell at rotational axis and disposed in side-by-side relation; each section being generally annular in configuration and comprising a plurality of ramp-like surfaces that extend circumferentially and define sequential steps with the lowest point of one ramp-like surface adjacent the highest point of another; the ramp-like surfaces of each axial section being circumferentially staggered with respect to the ramp-like surfaces of an adjacent annular section.

2. The liner assembly defined by claim 1, wherein the circumferential staggering of the axial sections is uniform from section to section.

3. The liner assembly defined by claim 1, wherein the liner assembly is disposed so that a fresh charge of ore enters at one axial end and comminuted ore leaves at the other, and each axial section is circumferentially staggered by the same amount relative to the preceding axial section, and in the same circumferential direction.

4. The liner assembly defined by claim 3, wherein the cylindrical shell includes a plurality of mounting openings disposed in axially and circumferentially extending rows, and the mounting means comprises: a plurality of mounting openings formed in the respective liner segments and disposed for selective registration with the mounting openings of the cylindri¬ cal shell; and a plurality of mounting bolts sized to fit through the registered openings.

5. The liner assembly defined by claim 3, wherein the circumferential direction of staggering is clockwise as viewed from the axial inlet of the liner assembly.

6. The liner assembly defined by claim 3, wherein the circumferential direction of staggering is counter¬ clockwise as viewed from the axial inlet of the liner assembly.

7. The liner assembly defined by claim 1, wherein the respective liner segments are formed with elevated ridges that extend axially.

8. The liner assembly defined by claim 7, wherein the elevated ridges are axially aligned from axial sec¬ tion to axial section.

9. The liner assembly defined by claim 8, wherein at least part of the ridges comprise round-topped undu¬ lations. 10. The liner assembly defined by claim 8, wherein at least part of the ridges are flat topped.

11. The liner assembly defined by claim 1, wherein at least part of the liner segments are of composite structure, comprising: a holder segment secured to the cylindrical shell by the mounting means; and a wear segment carried by the holder segment.

12. The liner assembly defined by claim 11, wherein the wear segments are of identical construction, and the holder segments are constructed and arranged to progressively elevate the wear segments to define said ramp-like surfaces.

13. The liner assembly defined by claim 11, ■ wherein the wear segments are formed from material having a greater resistance to abrasion than that of the holder segments.

14. The liner assembly defined by claim 13, wherein the wear segments are cast from a martensitic alloy.

AMENDED CLAIMS

[received by the International Bureau on 15 May 1986 (15.05.86); original claims 1-14 replaced by new claims 1-22 (5 pages)]

1. (New) An ore comminuting machine, comprising: a cylindrical shell having a predetermined cylindrical axis; means for supporting the cylindrical shell for rotation about said cylindrical axis; a plurality of individual liner segments covering substantially the entire inner cylindrical surface of the shell; means for removably mounting the liner segments to the shell; the liner segments defining a plurality of ramp¬ like surfaces that extend circumferentially and define sequential steps with the lowest point of one ramp-like sur¬ face adjacent the highest point of another; and means for rotating the cylindrical shell in a direction so that the ore fragments are caused to move rela¬ tively up each ramp-like surface to the next adjacent sur¬ face in a pulsating manner.

2. (New) The ore comminuting machine defined by claim

1, wherein the liner segments are arranged in a plurality of axial sections commonly centered on the shell rotational axis and disposed in side-by-side relation, each axial sec¬ tion being annular in configuration and comprising a plura¬ lity of said ramp-like surfaces.

3. (New) The ore comminuting machine defined by claim

2, wherein the ramp-like surfaces of each axial section are circumferentially staggered with respect to the ramp-like surfaces of an adjacent annular section. 4. (New) The ore comminuting machine defined by claim 1, wherein each ramp-like surface is itself formed from a group of liner segments, the liner segments within each group increasing substantially uniformly in thickness with the highest point of one segment adjacent and corresponding in thickness to the lowest point of the next segment.

5. (New) The liner assembly defined by claim 3, wherein the circumferential staggering of the axial sections is uni¬ form from section to section.

6. (New) The liner assembly defined by claim 3, wherein the liner assembly is disposed so that a fresh charge of ore enters at one axial end and comminuted ore leaves at the other, and each axial section is circumferentially staggered by the same amount relative to the preceding axial section, and in the same" circumferential direction.

7. (New) The liner assembly defined by claim 1, wherein the cylindrical shell includes a plurality of mounting ope¬ nings disposed in axially and circumferentially extending rows, and the mounting means comprises: a plurality of mounting openings formed in the respective liner segments and disposed for selective registration with the mounting openings of the cylindrical shell; and a plurality of mounting bolts sized to fit through the registered openings. 8. (New) The liner assembly defined by claim 6, wherein the circumferential direction of staggering is clockwise as viewed from the axial inlet of the liner assembly.

9. (New) The liner assembly defined by claim 6, wherein the circumferential direction of staggering is counter¬ clockwise as viewed from the axial inlet of the liner assembly.

10. (New) The liner assembly defined by claim 1, wherein the respective liner segments are formed with elevated ridges that extend axially.

11. (New) The liner assembly defined by claim 10, wherein the elevated ridges are axially aligned from axial section to axial section.

12. (New) The liner assembly defined by claim 11, wherein at least part of the ridges comprise round-topped undulations.

13. (New) The liner assembly defined by claim 11, wherein at least part of the ridges are flat topped.

14. (New) The liner assembly defined by claim 3, wherein at least part of the liner segments are of composite struc¬ ture, comprising: a holder segment secured to the cylindrical shell by the mounting means; and a wear segment carried by the holder segment.

15. (New) The liner assembly defined by claim 14, wherein the wear segments are of identical construction, and the holder segments are constructed and arranged to progressively elevate the wear segments to define said ramp¬ like surfaces.

16. (New) The liner assembly defined by claim 14, wherein the wear segments are formed from material having a greater resistance to abrasion than that of the holder segments.

17. (New) The liner assembly defined by claim 16, wherein the wear segments are cast from a martensitic alloy.

18. (New) A method of comminuting ore, comprising:

^* introducing the ore into the cylindrical drum of an ore mill, the cylindrical drum having on its inner surface a liner assembly comprising a plurality of liner segments disposed in an annular configuration and having a plurality of ramp-like surfaces extending circumferentially and defining sequential steps with the lowest point of one ramp¬ like surface adjacent the highest point of another; and rotating the cylindrical drum in a direction so that the ore fragments are caused to move relatively up each ramp-like surface to the next adjacent surface in a pulsating manner.

86/ 4

19. (New) An improved liner assembly for the cylindrical shell of an ore grinding machine, comprising: a plurality of individual liner segments covering substantially the entire inner cylindrical surface of the cylindrical shell; means for mounting the liner segments to the cylindrical shell; the liner segments being disposed generally in an annular configuration and comprising an plurality of ramp¬ like surfaces that extend circumferentially and define sequential steps with the lowest point of one ramp-like sur¬ face adjacent the highest point of another; each ramp-like surface itself being formed from a group of liner segments, with the liner segments within each group increasing substantially uniformly in thickness with the highest point of one segment adjacent and corresponding in thickrfess to the lowest point of the next segment.

20. (New) The liner assembly defined by claim 19, wherein the respective liner segments are formed with ele¬ vated ridges that extend axially.

21. (New) The liner assembly defined by claim 20, wherein at least part of the ridges comprise round-topped undulations.

22. (New) The liner assembly defined by claim 20, wherein at least part of the ridges are flat topped.