US3804346A

US3804346A - Liner for grinding mills

Info

Publication number: US3804346A
Application number: US00287779A
Authority: US
Inventors: T Norman
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-09-11
Filing date: 1972-09-11
Publication date: 1974-04-16
Anticipated expiration: 1991-04-16
Also published as: AU6020473A; CA1011315A

Abstract

Liners for grinding mills having alternating bars of alloy steel and strips of an elastomer, such as rubber, bonded together and to a backing plate which is sufficiently flexible that the liner may be manufactured flat, but drawn against an arcuate portion of the cylindrical side wall of the mill by attaching bolts. Converging slots formed in the center bar of the liner are engaged by bolt heads having converging sides. For a ball mill, the bars of each liner are of the same height and the strips are of the same height, with the bars initially slightly higher than the strips. The liners are installed so that the bars and strips extend longitudinally of the mill, the effect of the balls and material being ground being to produce a corrugated or ripple wave surface on each liner which provides a lifting effect to the grinding media and causes the balls to bounce or oscillate. For rod mills, each liner has several center bars and strips of a greater height, with a series of one bar and one strip of successively lesser heights on each side of the center bars and strips. Wear during use produces not only a ripple wave contour of the bars and strips but also a higher portion of the liner toward the direction of rotation from the initial highest portion, which accentuates the lifting effect on the grinding media. A liner for a segment of the end wall of the mill includes alternating bars and strips of alloy steel and rubber, with the center bar being disposed along a radius of the end wall and the remaining bars and strips parallel thereto.

Description

Norman LINER FOR GRINDING MILLS Teller E. Norman, 37 Hillside Dr., Denver, Colo. 80215 [22] Filed: Sept. 11, 1972 [21] Appl. No.: 287,779

[76] Inventor:

1521 Us. c1. 241/182, 241/300 [51] Int. Cl. 1302c 17/22 [58] a Field of Search 241/294, 295, 298,299, 241/300, 182, 183, DIG. 30

[56] References Cited UNITED STATES PATENTS 3,194,506 7/1965 Bourne et a1. 241/300 3,533,570 10/1970 Bernutatm; 241/300 X 2,476,505 7/1949 Mclntyren"; '241/182 3,378,209 4/1968 Crocheron.... 241/183 X 1,921,672 8/1933 Haushalter.... 241/183 1,631,971 Y 6/1927 Linhard 241/183 FOREIGN PATENTS OR APPLICATIONS 999,521 7/1965 Great Britain 241/183 399,990 8/1 924 Germany 241/182 OTHER PUBLICATIONS No. 178,351 Lining for Tube Mills The Canadian Patent Office Record, Vol. 45, July, 1917, Page 2,180.

7 Primary Examiner-Granville Y. Custer, Jr.

Attorney, Agent, or Firm-HoraceB. Van Valkenburgh; Frank C. Lowe 1451 Apr. 16, 1974 [5 7] ABSTRACT Liners for grinding mills having alternating bars of alloy steel and strips of an elastomer, such as rubber, bonded together and to a backing plate which is sufficiently flexible that the liner may be manufactured flat, but drawn against an arcuate portion of the cylindrical side wall of the mill by attaching bolts. Converging slots formed in the center bar of the liner are engaged by bolt heads having converging sides. For a ball mill, the bars of each liner'are of the same height and the strips are of the same height, with the bars initially slightly higher than the strips. The liners are installed so that the bars and strips extend longitudinally of the mill, the effect of the balls and material being ground being to produce a corrugated or ripple wave surface on each liner which provides a lifting effect to the grinding media and causes the balls to bounceor oscillate. For rod mills, each liner has several center bars and strips of a greater height, with a series of one bar and one strip of successively lesser heights on each side of the center bars and strips. Wear during use produces not only a ripple wave contour of the bars and strips but also a higher portion of the liner toward the direction of rotation from the initial highest portion, which accentuates the lifting: effect on the grinding media. A liner for a segment of the end wall of the mill includes alternating bars and strips of alloy steel and rubber, with the center bar being disposed along a radius of the end wall and the remaining bars and strips parallel thereto.

10 Claims, 14 Drawing Figures 1 LINER FOR GRINDING MILLS This invention relates to liners for grinding mills, such as ball mills and roclmills used in grinding or comminuting ore and the like.

Grindingmills are used for the purpose of reducing the size of lumps or other pieces of ore or the like for various purposes. In the case of ore, the normal function of the grinding mill is to reduce the size of the ore to particles within a fine sieve range for flotation, in which through the use of suitable additives, the ore bearing particles are separated from the gangue. Both ball mills and rod mills have been used for grinding ores or the like, such a mill normally being a rotating cylinder containing a number of balls or rods formed of steel, usually special alloy steels, which crush and comminute the ore between them or against the side of the mill, or perhaps the end thereof. In addition to balls or rods, pebbles or natural rock have also been used as grinding media. A grinding mill thus normally consists of a cylindrical shell rotated about a-central horizontal axis, with ends which close theends of the shell. Various diameters and lengths of shells have been utilized, varying considerably but normally in proportion to the capacity of the mill. In view of the abrasive character of the material being ground, the wear on the inside of a grinding mill has been a serious problem. Normally, grinding mills have been lined with cast or wrought abrasion resistant ferrous alloy liners several inches thick, or in some cases, with rubber or ceramic liners. These liners have been made in sections, with various configurations, usually being held in place by bolts which hold the liner tightly against the interior of the 1 mill shell or the mill end. Cast ferrous alloy liners require molds for the production thereof, while liners manufactured from wrought steel require special rolls for forming to shape. a

During service; the liners tend to be worn easily by the abrasive action of the grinding media and the minerals being ground in the mill. The cost of periodic re- 1 placementof liners is thus a major item of cost in the operation of mills or plants which'grind ore or other minerals. ln'addition, the configuration of thesurface' of the liner, during its service life, has been found to be an importantconsideration affecting both the life of the' liner and the grinding efficiency or grinding rate of the mill. Furthermore, a configuration which produces the highest grinding efficiency or grinding rate for a ball mill is not necessarily the configuration which will produce the highest efficiency or grinding rate for a rod mill, and vice versa. j

Among the objects of this invention are to provide a .novel liner for grinding mills; to provide such a liner which may be adapted for use as a liner for the shell and also aliner for an end of the mill; to provide such a liner which has a longer life and therefore requires replacement at less frequent intervals; to provide such a liner which is'readily modified in construction, to provide a configuration most suitable for use in a ball mill or pebble mill, as well as a different configuration which is most suitable for use in a rod mill or an autogenous grinding mill using large diameter natural rock; to provide such a liner which may be readily manufactured in a flat or planar form but will fit tightly against the mill shell, irrespective of the'mill diameter, thereby avoiding the cost of machining or of molds for casting liners for shells of different diameters; to provide such liners which may be made in different lengths and widths without undue expense; to provide such liners which may be modified for use in grinding fine or soft materials; and to provide such liners which are economical to manufacture and are efficient and effective in use.

The foregoing objects are generally accomplished by utilizing a series of longitudinally extending, alternating strips of highly abrasion resistant material, such as hardened alloy steel, and strips of elastomer, such as rubber, which are bonded to each other and to a backing plate, to form a laminated composite liner. The backing plate, as of soft steel or the like, will conform to the inner diameter of the shell when attached thereto, while the resiliency of the elastomer strips permits compression thereof toaccommodate the curvature of the shell. For use in ball mills or pebble mills, the height of the more highly abrasion resistant strips or bars is slightly greater than the height of the alternating elastomer strips, in order to provide what may be characterized as a low wave ripple configuration. For rod mills or autogenous grinding mills, with large diameter natural rock as grinding media, the height of the strips and bars 'are varied to provide a greater height at the center of theliner, to produce what may be characterized as a high wave" ripple configuration. For lining the ends ofa cylindrical mill, the low wave configuration is conveniently utilized, with the bars and stripsextending radially of each liner, which forms a segment of the circle of the end of the mill. When fine or soft materials are ground, a good quality of abrasion resistant rubber or other elastomer may prove to have a greater abrasion resistance than steel or iron. In this case, higher bars should be made fromthe abrasion resistant rubber or other elastomer and the lesser abrasion resistant strips may be made of other suitable material, such as a harder, less abrasion resistant rubber or elastomer, a suitable plastic material or hard wood.

The attainment of the foregoing. and additional objects of this invention, as well asthe novel features thereof, will further be apparent from the following description of preferred embodiments of this invention, illustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view, on a reduced scale, of

a grinding mill in which the liner of this invention is particularly useful;

FIG. 2 is a fragmentary circumferential section, showing one segmental liner constructed in accordance with this invention, portions of two adjacent liners and a portion of the shell of the grinding mill in which the liners areinstalled, such liners being particularly useful for a ball mill;

FIG. 3 is a fragmentary section, on an enlarged scale,

I taken along line 3-3 of FIG. 2 and showing particularly the head of an installation bolt and associated parts;

FIG. 4 is a fragmentary section taken along line 4----4 of FIG. 3;

FIG. 5 is a fragmentary section, similar to FIG. 2 but showing the condition of the alternating steel and elastomer strips after wear to what may be characterized as a low, wave" configuration;

FIG. 6 is a transverse section of the of FIG. 2, prior to installation;

FIG. 7 is a. condensed top plan view of the liner of FIG. 6;

grinding mill liner FIG. 8 is a fragmentary section, similar to FIG. 2 but FIG. 9 is a fragmentary section, on an enlarged scale and taken along line 9-9 of FIG. 8;

FIG. 10 .is a fragmentary section, taken along line 10-10 of FIG. 9;

FIG. 1 1 is a fragmentary section, similar to F IG. 8 but showing the liner segment after wear to what may be characterized as a high wave configuration;

FIG. 12 is a transverse section of the grinding mill liner of FIG. 8, prior to installation;

FIG. 13 is an inside view of one end ofa grinding mill, also provided with liners constructed in accordance with this invention, the shell and shell liners being omitted for clarity of illustration; and

FIG. 14 is a planar section, on an enlarged scale, of one of the liners of FIG. 13.

A rotating cylindrical grinding mill, ofa type in which liners constructed in accordance with this invention may be used, is shown in FIG. 1 and includes a cylindrical shell 10 having bolts 11 by which the liners are attached to the inside of the shell, with the bolts extending therethrough. An end plate 12 is attached to one end of the shell 10 and a corresponding end plate is attached to the opposite end of the shell, while a cover 13 for a ring gear 14, having teeth (not shown), enclosed within the cover 13 is disposed at one end of the mill. The ring gear is engaged by a gear drive, which is conventional and therefore not shown. The grinding mill is mounted for rotation through

bearings

15 and 16 at opposite ends of the mill, with supports 17 and 18 for the respective bearing being mounted on any suitable type of foundation. The ore or other material to be ground is introduced into the mill through a feed tube 19, while the ground material is discharged from the mill through a discharge tube 20, as indicated by the arrows.

A liner L, constructed in accordance with this invention and illustrated in FIG. 2, is flanked by portions of additional liner sections L constructed in the same manner, all mounted on the inside of the shell 10 by bolts 11. Each liner L may cover a section of the circumference of the shell 10, with each liner or two or more liners placed end to end corresponding to the length of the shell so that the length of each liner L may be such that the weight thereof permits it to be relatively easy to handle. For a mill shell which has a 10 footinside diameter, there may be 20 rows of liners, each occupying an 18 segment of the shell. Thus, the chord width of an l8 segment for a 10 foot inside diameter shell would be 18.84 inches. However, a clearance or space 21 between adjacent liners is desirable, so that the liner L, in the instance under discussion, may be l8-5/l 6 inches wide. When more than one liner is placed end to end in the shell, a spacing between the ends of these two liners, similar to the spacing between adjacent liners, may be provided.

The liner L includes a series of hardened alloy steel bars 22 which alternate with a series of elastomer strips 23, such as formed of rubber, of the same width and length, and a pair of outside elastomer strips 23 of lesser width, for the liner illustrated. The alternating bars 22 and strips 23 may have a similar width, such as between inch and 2 inches, with the bars 22 and strips 23, as shown inFIG. 2, being approximately l-5/l6 inches in width and the outside elastomer strips 23 being inch in width. The upper ends of the steel bars 22, which may be rounded as shown, are spaced above the elastomer strips 23 a distance less than the width of the steel bars, such as approximately h inch, when the bars and strips have the dimensions indicated above. Of course, for other widths of bars and strips, or for a liner made for a grinding mill shell having a different diameter, the outside strips 23' may be unnecessary.

In accordance with this invention, each of the bars 22 and strips 23 and 23' are bonded to each other and to a backing plate 24, which may be formed of a low carbon steel, since it is not subjected to abrasion during use. A rubber strip 25 is conveniently disposed between the backing plate 24 and the bars and strips, for bonding purposes. Thus, the steel bars 22 and elastomer strips 23 and 23' may be bonded to each other and the backing plate 24, through the strip 25, by a suitable rubber cement mixture, followed by vulcanization, as in an autoclave, to produce a strong bond. Other suitable ways of attaching the bars 22 and strips 23 to each other and to the backing plate 24 may, of course, be utilized. The thickness of backing plate 24 need not be great, so that, when the liner is mounted against the inside of the shell 10 by a series of bolts 11, as in FIG. 2, the backing plate 24 will bend to conform to the inside of the shell. It will be noted that the liner L is initially formed in a straight or planar condition, as in FIG. 6, and that the backing plate 24 will be curved, when the backing plate is drawn into engagement with the inside of the shell, as in FIG. 2. The elasticity of the strips 23 will permit a slight compression, principally along the upper portion thereof, by the steel bars 22, when the liner is installed. Thus, there should be no difficulty in the liner conforming to the inside curvature of the shell 10, substantially irrespective of the diameter thereof.

For bolt attachment purposes, a series of slots 27, as in FIG. 7, corresponding to the number of bolts 11 utilized in attaching the liner to the shell, are provided between sections of center bar 22. Each slot 27 has a rectangular configuration down to an angular surface 28 at each side and which slants inwardly toward a hole 29 in the backing plate 24, when installed, is in alignment with a hole 32 in shell 10, through which the shank of a bolt 11 extends. Each bolt head 30, as in FIGS. 3 and 4, is generally rectangular in cross section down to opposed angular surfaces 31 which fit against the corresponding angular surface 28 of the corresponding slot 27, to permit the bolt to draw the liner tightly against the shell 10. The shell 10, in appropriate positions, is provided with a series of holes 32 through which the shank of each bolt 11 extends, as for attachment of a conventional washer and nut, as in FIG. 2.

Since the direction of impingement of the grinding media and the minerals on the liners is approximately perpendicular to the joint lines between the laminated bars and strips, the action of the grinding media and minerals tends to produce different rates of wear on the more abrasion resistant bars and less abrasion resistant strips, respectively. Thus, as the liner wears, it developes a ripple wave wearing surface, as shown in FIG. 5. This ripple wave or corrugated contour persists on the liner surface until it is worn down to. the steel backing plate. At that time, the worn liners may be replaced with a new set of liners. The ripple wave contour pro.- vides the desired lifting effect to the charge of grinding media, as the mill rotates, and also causes the balls to surface of a liner, as when each liner is formed from one material. As will be evident, the use of the liner construction of this invention reduces the wear of the liner and therefore increases its useful life, as compared with the types of liners used herefore.

As indicated previously, the alternating bars and strips, with the more abrasion resistant bars slightly higher than the less abrasion resistant strips, but with all of the bars normally of about the same height and all of the strips normally of about the same height, provides the low wave configuration illustrated in FIG. 5. As indicated previously, this low wave configuration is particularly useful for ball mills and pebble mills.

For rod mills, i.e. mills in which elongated rods are placed in the mill, rather than balls, or mills using an autogenous grinding media of relatively large diameter or sized rocks of the material being ground, the high wave" configuration shown in FIG. 11, produced by the configuration of FIG. 8, as it wears, is particularly useful. As in FIG. 8, a high wave liner L will include a pair of longitudinally abutting center bars 35 of alloy steel provided with bolt slots 27', with another pair of bars 36 outside the center bars, but with elastomer strips 37 interposed therebetween. The

central bars

35, 36 and strips 37 are the highest of the bars or strips utilized in this embodiment, for a purpose described later. On each side of the center bars 36 is an elastomer strip 38 and then a hardened alloy steel bar 39, each of lesser height than the central bars and strips; then strips 40 and bars 41 of lesser height and strips 42 and bars 43 of successively lesser height. A pair of narrower elastomer strips 44, of the same height as bars 43, complete the assembly of bars and strips onthe outside. A space 21', between liners L, is provided, as before. As before, the bars and strips of the liner L are bonded together and to a backing plate 24' by a rubber strip 25, as in the manner described previously. The respective liners L are attached to the interior of the shell of the mill by bolts II, with each liner occupying a predetermined arcuate portion of the inner circumference of the shell and the liners having either a length corresponding to the shell, or two or three liners placed end to end longitudinally of the shells, for shells with increasing longitudinal dimensions. Slot 27' of each bolt 11 is again rectangular in cross section to an inwardly angular surface 28' at each side but is formed between aligned sections of the two center bars 35, rather than between sections of a single bar. Head 30' of bolt 11' is similar in configuration to the bolt heads 30 of FIG. 3, except for the height, being provided with a longer angular surface 31' adjacent the shank of the bolt, with the angular surfaces of the bolts being longer than the angular surfaces 30 of the bolt 11, to compensate for the greater weight of the liner of the "high wave configuration. For the high wave" configuration, the center bars 35, strips 37 and bars 36 may be on the order of 6 inches high, with the strips 38 and bars 39 being the order of inch and V2 inch wide, or a total width of 18% inches. The width of the liners may, of course, vary considerably, such as ranging from about 15 inches to about 24 inches in width.

During the use of liners L' of FIG. 8, when rotated in the direction of the arrow 45 of FIG. 11, the impingement of the grinding media and material being ground, on the bars andstrips, will tend to wear away to a greater extent the bars 35 and strips 37, as well as the bars and strips on the side opposite the direction of rotation, so that the generally higher portion of the liner will become the bars and strips disposed toward the direction of rotation. Such wear will produce a pronounced peak, as well as a series of peaks and valleys of a generally lesser height. However, the differential effect of the differences in height of the portions of the liner toward and away from the direction of rotation will accentuate the lifting effect on the rods in the rod mill, or large diameter rock utilized in an autogenous grinding mill.

For lining either end of the mill, such as end 12 of FIG. I or the opposite endof the grinding mill, the low wave ripple configuration is preferable. Thus, each end of the grinding mill may be provided with a series of liners L", each corresponding to a segment of the annulus between the inner circle 50 and outer circle 51 of the grinding mill end. Spaces 52 may be provided between the liners L, similar to the spaces 21 of FIG. 2 and 21' of FIG. 8. Each liner L" or segment may have the construction illustrated in FIG. 14, such as including a center bar 53 formed of hardened alloy steel and a pair of elastomer strips 54 on each side thereof and disposed parallel thereto. It will be noted that the center bar 53 extends radially of the end of the mill.

Additional bars

55, 56 and 57 may also extend parallel to the center bar 53, interspersed with elastomer strips 58, 59 and 60 of the same or different width, and again extending parallel to the center bar. The bars and strips of FIGS. 13 and 14 have relative heights similar to the bars and strips of FIG. 2. During use, the alternating bars and strips will tend to become worn to a low wave ripple configuration, similar to that shown in FIG. 5. The center bar 53 is provided with bolt slots 27 between sections, similar to the bolt slots 26 of FIG. 3 and adapted to receive the boltsfor attaching the liner L" to the end plate,such as the end plate 12 of FIG. 1, or the opposite end plate. With respect to the liner L, it will be noted that these liners are not only manufactured in a flat form, but also utilized in a flat form, or they may deform when bolted in the mill to fit the slightly conical surface which exists at the ends of many grinding mills. As before, the alternating strips and bars are bonded to each other and may be bonded to asuitable backing plate corresponding to backing plate 24 of FIG. 6, with a rubber strip interposed between the backing plate and the alternating bars and strips to fa- 'cilitate bonding, as in the manner described, through a rubber cement mix and vulcanizing.

The advantages of the liners of grinding mills constructed in accordance with this invention are numerous. Thus, the liners of this invention have a longer life, primarily due to the ripple wave contour which persists throughout the life of the liner. A contributing factor is that unusually hard and abrasion resistant metal bars can be used in the construction of these liners, since each bar is well supported by and securely bonded to the tough rubber bars and to the mild steel backing plate, so that even if a metal bar cracks in service, it willcontinue to be held in place and perform its desired function throughout the life of the liner. Thus, the liners can be worn down to a very thin section before replacement is necessary. The liners of this invention also have a lower first cost than homogeneous liners of equivalent volume or thickness, due to the fact that the metal bars can be made from standard and relatively light sections, either rolled or cast, which can be produced at a lower cost per unit weight than the special heavier sections required in homogeneous cast or rolled liners. The alloying elements needed for the lighter section bars to produce full hardening is also less than for heavy sections. The rubber or elastomer strips in the composite liner can also be produced at a sub- Y stantially lower cost per unit volume than a homogeneous metal liner of heavysection. For making up composite liners, it is desirable to use only a few sizes or preferably one size of steel bars in a standard and therefore readily available dimension. If necessary, a greater number of sizes of rubber bars may be used to provide the desired width of the liner. The length of the individual bars, as supplied to the shop, can be variable, since they can be cut or trimmed at the shop to a desired length. Cuts on the ends of the sections of the bars which abut the bolts can be made accurately with an abrasive cut off wheel, or by any other suitable means available for cutting hardened tool steel. While there is an additional assembly cost involved in the production of composite ripple wave" liners, this cost is relatively low and is only a small fraction of the cost of materials.

The liners of this invention produce an increased grinding rate in the mill, due to the fact that the grinding media are activated andoscillated by the ripple wave" effect. When desired, relatively thin liners may be used to increase the effective interior diameter of the grinding mill.

The liners of this invention require less shut down time of the mill for liner changes, due to the inherently longer life of the liners and also to their ease of handling. If desired, the number of pieces to be handled can be reduced by the use of longer liners, which lend themselveswell to production in the ripple wave" configuration.

It will be understood that the method or design of bolt attachment may be changed from the forms shown. For instance, a series of cap screws extending through the wall of the mill may be utilized to attach each liner to the inside of the mill. In such an instance, it may be desirable to use a softer steel strip, such as S.A.E. 1040, which is more readily tapped, for anchoring the cap screws. Such a softer steel strip may be flanked by thin strips of rubber or the like and harder steel bars on each side thereof. Such a construction avoids cutting the softer steel strip and also eliminates the hole or socket at each bolt head.

Although certain preferred embodiments of this invention have been illustrated and described, it will be understood that other embodiments may exist and that various changes may also be made, such as in methods or designs of bolt attachment, or in widths of the indi- 8 vidual bars and strips forming the laminated composite, without departing from the spirit and scope of this invention.

What is claimed is:

l. A liner for at least a portion of the interior of a grinding mill adapted to utilize iron balls, steel balls, iron rods, steel rods, pebbles, rocks and the like as the grinding media, comprising:

bars formed of a relatively high abrasion resistant material;

strips formed of less abrasion resistant material and alternating with said bars; and

means for maintaining said bars and strips in alternating relation, whereby when installed in said mill, said bars and strips will engage the material to be ground and will wear differentially to produce a corrugated or ripple wave surface contour.

2. A liner as defined in claim 1, wherein:

said bars have the abrasion resistant qualities of alloy steel; and

said strips are formed of an elastomer having substantially the abrasion resistant qualities of rubber.

3. A liner as defined in claim 1, wherein:

said bars are formed of an elastomer having the abrasion resistant qualities of rubber; and

said strips are formed of a less abrasion resistant material.

4. A liner as defined in claim 2, including:

a backing plate extending beneath said bars and strips, said bars and strips being bonded to each other and to said backing plate.

5. A liner as defined in claim 4, wherein:

said backing plate is sufficiently flexible to permit said backing plate to be manufactured with said backing plate flat, but said backing plate conforming to an arcuate portion of a cylindrical side wall of said grinding mill when installed with said bars and strips extending longitudinally of said mill through the compression of said elastomer strips.

6. A liner as defined in claim 1, wherein:

said liner has a configuration conforming to a segment of an end wall of said mill, with a center bar or strip extending in a direction corresponding to a radius of said end wall and the remaining bars and strips generally parallel to said center bar or strip.

7. In a liner as defined in claim 1, wherein:

each of said bars is initially of substantially the same height; and

each of said strips is initially of substantially the same height.

8. A liner as defined in claim 1, including:

a series of centrally disposed bars and strips of a predetermined height; and

a plurality of series of at least one bar and one strip disposed laterally at each side of said centrally disposed bars and strips, with each series having a successively lesser height.

9. A liner as defined in claim 1, wherein:

the composite assembly has sufficient lateral elasticity to permit it to be manufactured with a flat back but said flat back will conform to an arcuate portion of a side wall of said mill, with said bars and strips extending longitudinally of said mill.

10. A liner as defined in claim 1, for installation on a cylindrical side wall of a mill, wherein:

10 with converging side surfaces to engage the converging side portions of the corresponding slots, whereby the bars may extend longitudinally of said mill.

Claims

1. A liner for at least a portion of the interior of a grinding mill adapted to utilize iron balls, steel balls, iron rods, steel rods, pebbles, rocks and the like as the grinding media, comprising: bars formed of a relatively high abrasion resistAnt material; strips formed of less abrasion resistant material and alternating with said bars; and means for maintaining said bars and strips in alternating relation, whereby when installed in said mill, said bars and strips will engage the material to be ground and will wear differentially to produce a corrugated or ripple wave surface contour.

2. A liner as defined in claim 1, wherein: said bars have the abrasion resistant qualities of alloy steel; and said strips are formed of an elastomer having substantially the abrasion resistant qualities of rubber.

3. A liner as defined in claim 1, wherein: said bars are formed of an elastomer having the abrasion resistant qualities of rubber; and said strips are formed of a less abrasion resistant material.

4. A liner as defined in claim 2, including: a backing plate extending beneath said bars and strips, said bars and strips being bonded to each other and to said backing plate.

5. A liner as defined in claim 4, wherein: said backing plate is sufficiently flexible to permit said backing plate to be manufactured with said backing plate flat, but said backing plate conforming to an arcuate portion of a cylindrical side wall of said grinding mill when installed with said bars and strips extending longitudinally of said mill through the compression of said elastomer strips.

6. A liner as defined in claim 1, wherein: said liner has a configuration conforming to a segment of an end wall of said mill, with a center bar or strip extending in a direction corresponding to a radius of said end wall and the remaining bars and strips generally parallel to said center bar or strip.

7. In a liner as defined in claim 1, wherein: each of said bars is initially of substantially the same height; and each of said strips is initially of substantially the same height.

8. A liner as defined in claim 1, including: a series of centrally disposed bars and strips of a predetermined height; and a plurality of series of at least one bar and one strip disposed laterally at each side of said centrally disposed bars and strips, with each series having a successively lesser height.

9. A liner as defined in claim 1, wherein: the composite assembly has sufficient lateral elasticity to permit it to be manufactured with a flat back but said flat back will conform to an arcuate portion of a side wall of said mill, with said bars and strips extending longitudinally of said mill.

10. A liner as defined in claim 1, for installation on a cylindrical side wall of a mill, wherein: a central bar of said liner is divided into sections, with the ends of adjacent sections formed to provide a slot, at least a portion of the sides of which converge toward said side wall; and a series of bolts for attaching said liners to said side wall of said mill, said bolts having heads provided with converging side surfaces to engage the converging side portions of the corresponding slots, whereby the bars may extend longitudinally of said mill.