GB2589922A - Liner for a grinding mill - Google Patents

Abstract

A shell liner for use with a grinding mill, comprising a body 20 extending along a longitudinal axis 22, an upper surface 28 comprising a plurality of recesses 30, each recess defining a recess surface (32, fig. 4) and mouth, the recess 30 dimensioned to receive a lower portion of an insert (40, fig 6) where a portion of the insert may protrude. The recess surface 32 supports the lower portion of the insert in response to grinding forces imparted during the grinding, the mouth of the recess 30 grips the insert to retain it during this process. Body 20 may be an elastomer, it may comprise a support bar 26 and a plurality of fixtures to secure the liner to the mill. Upper surface 28 may be planar or concave, body 20 may define a convex lower surface. Each recess may be frusto-spherical, cylindrical, or cuboidal, the liner may comprise a plurality of different shaped recesses. Lateral portions 50 may extend from a lower part of the body 20. A grinding mill may comprise a plurality of shell liners 20, where the number of inserts exceeds the number of recesses.

Description

LINER FOR A GRINDING MILL

The present invention relates generally to crushing, grinding; comminution or similar processing of materials such as mineral ores, rock and other materials, and more particularly to apparatus for use in such processing, such as a grinding mill.

Grinding mills are one form of apparatus used for processing materials as described above. Typical grinding mills generally comprise a drum shaped shell mounted for rotation about its central axis. The axis of the shell is generally horizontally disposed or slightly inclined towards one end. The interior of the shell forms a comminution chamber into which the material to be reduced in size is fed.

In one form of mill known as a ball mill, a grinding medium (such as balls or rods) is fed to the treatment chamber (i.e. the inside of the shell) with the material to be processed. During rotation of the shell the grinding medium acts on the material to cause the crushing or grinding action. The grinding medium and material to be processed are carried up the side of the shell as a result of the centrifugal force created by rotation of the shell and lifer bars mounted circumferentially on an inner surface of the shell, and then afterwards it falls towards the bottom of the shell under the influence of gravity.

To protect the inner surface of the shell from damage during the grinding process, shell liners are mounted on the inner surface. These liners take many forms. One form comprises a base having fixtures by which it may be secured to the inner face of the shell, e.g. by fastening bolts, and an outer elastomeric surface surrounding the base. The elastomeric surface's main purpose is to absorb and disperse impact forces which arise as a result of ore and balls striking the shell liner as the shell rotates. Although the elastomeric surface disperses the impact forces, there is still a significant wear rate of the elastomeric surface. When the elastomeric surface has worn below a critical level, the ball mill must be stopped and the shell liner replaced. This adversely affects the operation of the grinding process by stopping throughput of ground ore when the ball mill is stopped.

It is among the objects of an embodiment of the present invention to obviate or mitigate the above disadvantage or other disadvantages of the prior art.

The various aspects detailed hereinafter are independent of each other, except where stated otherwise. Any claim corresponding to one aspect should not be construed as incorporating any element or feature of the other aspects unless explicitly stated in that claim.

According to a first aspect there is provided a shell liner for use with a grinding mill, the shell liner defining a longitudinal axis and comprising: a body extending along the longitudinal axis and having an upper surface defining a plurality of recesses therein, each recess defining a recess surface and a mouth, the recess being dimensioned to receive a lower portion of an insert used in the grinding mill and to allow an upper portion of the insert to protrude above the upper surface, wherein the recess surface is dimensioned to support the insert lower portion in response to forces impacting an upper portion thereof, and the mouth is dimensioned to grip the insert to retain the insert in the recess.

The body may comprise an elastomer. Alternatively, the body may comprise metal, steel, an alloy, a carbide (silicon carbide, boron carbide, or the like), or the like.

The body may comprise a longitudinal support bar surrounded (partially or fully) by an elastomer.

The body may comprise a plurality of fixtures for securing the shell liner to a grinding mill. The fixtures may include threaded bores defined by the longitudinal support bar.

The upper surface may define a planar surface, an arcuate surface (such as a concave surface) generally corresponding to a radius of a drum-shaped shell in which the shell liner may be mounted, or any other convenient shape.

Each recess may comprise a generally frusto-spherical depression, e.g. a hemispherical depression. Alternatively, the cross-sectional shape of the recesses may be of any suitable form.

The shell liner may comprise a plurality of different shapes of insert, each having a corresponding shape of recess into which it is mounted.

Optionally, the body defines a convex lower surface complementary to a concave lower surface of the grinding mill.

Optionally, each recess comprises a generally frusto-spherical depression.

Alternatively, each recess comprises a cylindrical or cuboid shape, or a cross-sectional shape of any desired form.

Optionally, the shell liner comprises a plurality of different shapes of recess on the upper surface.

A shell liner according to any preceding claim, wherein the recesses are arranged in a plurality of rows along the upper surface, with adjacent rows being mutually offset.

Optionally, the shell liner further comprises lateral portions extending from a lower part of the body from either side thereof.

Optionally, the upper surface is raised above the lateral portions.

According to a second aspect there is provided a grinding mill comprising a drum-shaped shell mounted for rotation about its central axis, a plurality of shell liners according to the first aspect mounted on an inner surface thereof, and a plurality of inserts, where the number of inserts exceed the number of recesses in the shell liners, and the excess inserts crush or grind material in the grinding mill.

Optionally, each insert comprises a material selected from a metal, steel, another alloy, and a ceramic.

Optionally, each insert is retained in the corresponding recess as an interference fit.

Optionally, each recess defines a recess entrance narrower than a cross-sectional width of the corresponding insert so that the corresponding insert is held in place by the narrower entrance on insertion of the insert.

Each insert may define a generally spherical shape. Alternatively, each insert may define a generally rectangular, circular, triangular, diamond, or oblong shape, or any other convenient shape, such as a generally polygonal, generally circular, generally quadrilateral, such as square or rectangular, or generally polyhedral shape. The recess surface may be straight, curved or a combination of the above or any other suitable shape.

Each insert may comprise metal, steel, another alloy, a ceramic (silicon carbide, boron carbide, boron nitride, or the like), or the like.

The inserts may be arranged in a plurality of rows along the upper surface. 30 Adjacent rows may be offset so that every second, third, or nth row is aligned. Each insert may be retained as an interference fit in the corresponding recess. A recess entrance may be narrower than a cross-sectional width of the corresponding insert so that the corresponding insert is held in place by the narrower entrance.

Each insert may be dimensionally similar to a charge medium used in a grinding mill in which the shell liner is to be mounted.

The shell liner may further comprise lateral portions extending from a lower part of the body from either side thereof.

The upper surface may be raised from the lateral portions.

Optionally, at least 15% of the area of the upper surface comprises recesses, i.e. when populated, at least 15% of the area of the upper surface is covered by inserts. Advantageously, at least 20% of the upper surface is covered by recesses.

In some embodiments, at least 30%, 40%, 50%, 60% or 70% of the upper surface may be covered by recesses.

As used herein, the term "ball mill" refers to a grinding mill that includes a charge of at least 18% (i.e. 18% of the usable volume in the grinding mill is taken up by the grinding medium) and includes a grinding medium, regardless of the shape of the grinding medium (spherical, rod, or the like).

In this aspect, the grinding medium comprises inserts (i.e. the inserts are the charge that is used in the grinding mill to break down the ore or the like), and the shell liner recesses are dimensioned to accommodate the grinding medium during use. As a result, when the shell liner is mounted in a grinding mill, and the grinding medium (inserts) are added, the recesses are filled by the inserts as the grinding mill rotates the shell on which the shell liners are mounted. It is possible that some recesses may be temporarily blocked by ore particles, but these will typically fall out of the recesses as the shell rotates, thereby allowing the recesses to be filled during the next rotation.

By virtue of this aspect, the shell liners are protected from wear by the inserts mounted in the recesses, which protect the upper surface from impact of both the grinding medium and the ore being ground, during operation of the grinding mill. Any inserts that fall out during operation of the grinding mill will be replaced by other inserts in the grinding mill.

According to a third aspect there is provided a grinding mill comprising a drum-shaped shell mounted for rotation about its central axis, and a plurality of shell liners according to the first aspect mounted on an inner surface of the drum shaped shell and a plurality of inserts dimensioned to be accommodated within the corresponding recesses.

The inserts may be dimensioned to be accommodated within the corresponding recesses as an interference fit.

According to a fourth aspect there is provided a method of manufacturing a shell liner, the method comprising: providing a shell liner body comprising a plurality of recesses disposed on an upper surface thereof; each insert being dimensioned to correspond to a shape of the recess.

According to a fifth aspect there is provided a grinding mill comprising a charge and a shell liner defining recesses therein, wherein the charge is operable to grind material in the mill and also to populate the recesses in the shell liner. These and other aspects will be apparent from the following specific description, given by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a side view of a shell of a grinding mill, where the shell comprises a plurality of shell liners, according to a first embodiment of the present invention; Fig. 2 is a perspective view of half of the shell of Fig. 1, showing the shell liners in more detail; Fig. 3 is a perspective view of one of the shell liners of Fig. 2 showing an upper surface thereof; Fig. 4 is a cross sectional side view of the shell liner of Fig. 3; Fig. 5 is an enlarged side view of a ball of the type used in the grinding mill shell of Fig. 1; Fig. 6 is a side view of the shell liner of Fig. 3 showing the upper surface recesses fully populated with balls of the type shown in Fig. 5; Fig. 7 is a perspective view of the populated shell liner of Fig. 6; Fig. 8 is a perspective view of part of the shell of Fig. 1, showing some shell liners populated with balls and some unpopulated shell liners; and Fig. 9 is an enlarged side view of the shell of Fig. 8.

Reference is now made to the drawings, and particularly to Figs. 1 and 2, which are a side view of a cylindrical shell 10 of a grinding mill, and a perspective view of half of the shell 10, respectively. The shell 10 defines a longitudinal axis 12, and includes a plurality of conventional lifter bars 14 mounted circumferentially on an inner surface 16 of the shell 10, and a plurality of elongate shell liners 20 mounted circumferentially around the shell 10, such that a shell liner 20 is mounted between adjacent lifter bars 14, and vice versa. In this embodiment, four shell liners 20 are mounted end to end at each circumferential position, and five lifter bars 14 are mounted end to end at each circumferential position.

Reference is now particularly made to Figs. 3 and 4, which are perspective and cross-sectional side views of one of the shell liners 20. The cross section is along line 4-4 in Fig. 3. The shell liner 20 defines a longitudinal axis 22 and comprises: a body 24 extending along the longitudinal axis 22 and a longitudinal steel bar 26 extending through the body 24 (shown in outline in Figs. 3 and 6) to provide rigidity thereto, and fully enclosed by an elastomer housing that defines an upper surface 28. The body 24 has a slightly convex underside to match the concave shape of the shell inner surface 16.

The upper surface 28 defines a plurality of recesses 30. Each recess 30 is identical to the other recesses 30 and defines a generally hemispherical support surface 32 (best seen in Fig. 4) and a pinch mouth (or recess entrance) 34. However, in other embodiments, the recesses 30 may have a plurality of different shapes, e.g. some pad spherical, some part cylindrical, and the like.

The recesses 30 are arranged in a plurality of rows (twenty seven rows in this embodiment) and columns (five columns in this embodiment) along the upper surface 28. In this embodiment, adjacent rows are offset so that every second row is aligned. However, the recesses 30 may be aligned in a different configuration, or disposed randomly, in other embodiments.

As shown in Figs. 5 and 6, the charge used in the shell 10 during operation of the grinding mill are spherical steel balls 40 (also referred to herein as inserts), although in other embodiments a different charge shape (e.g. cylindrical) may be used, or a different material (e.g. other types of metal, alloy, or ceramic) may be used for the charge. The balls 40 define a centreline 42 (shown in broken line in Figs. 5 and 6) and arrows 44 indicate a pinch point on the ball 40 at which the recess pinch mouth 34 can grip the ball 40 so that the ball 40 is retained in the recess 30 using an interference fit.

In this embodiment, the recesses 30 are slightly larger than a hemisphere so that more than half of a ball 40 can be accommodated therein.

The shell liner 20 further comprises lateral portions 50 extending from a lower part of the body 24 from either side thereof. The upper surface 28 is higher than the lateral portions 50 and is generally planar in this embodiment; although in other embodiments the upper surface 28 may have a concave shape matching that of the inner surface 16 of the shell 10. The lifter bars 14 sit on top of (straddle) the lateral portions 50 of adjacent shell liners 20 (best seen in Fig. 9).

In this embodiment, the shell liner body 24 (which does not include the lateral portions 50) may have a width in the range of 150mm to 400mm, and a length in the range of 100mm to 2m. These are suitable for use in grinding mills having a diameter of between 1.5m and 6.5m.

Reference is now also made to Fig. 6, which is a side view of the shell liner 20 showing the upper surface recesses 30 fully populated with balls 40, which are held in place in the recesses 30 by the pinch mouth 34 acting on the pinch points 44 of the balls 40. Fig. 6 illustrates in an enlarged portion thereof one recess 30 having a ball 40, partly shown in broken line, mounted therein. When a ball 40 is mounted in a corresponding recess 30, it is held in place by an interference fit (also known as a press fit or friction fit) because the pinch mouth 34 of the recess 30 is narrower than the widest point of the ball 40, so the pinch mouth 34 is a tight fit against the insert 20 at the pinch points 44.

When mounted in a corresponding recess 30, each ball 40 protrudes above the upper surface 28, as best seen in Figs. 6 and 7.

Reference is now made to Figs. 8 and 9, which are partial perspective and side views, respectively, of the shell 10, and part of the grinding mill 60 (Fig. 9) supporting and rotating the shell 10. In this example, the shell liners 20 are initially mounted in the grinding mill 60 without any balls 40 mounted in the recesses 30.

During operation of the grinding mill 60, the grinding mill 60 is filled with balls 40 and ore or other material to be crushed or ground down and the recesses 30 are populated automatically as the grinding mill 60 rotates (as described below). Alternatively, the shell liners 20 may be manually populated with the balls 40 prior to starting the grinding mill 60.

During operation of the grinding mill 60, the shell 10 rotates and balls 40 within the shell 10 are raised by the lifter bars 14 and fall on ore in the grinding mill 60 thereby crushing the ore. As the shell 10 is rotated, balls 40 are pushed into the recesses 30 by outward forces exerted by the other balls 40 and the ore. This provides a bed of steel balls 40 on which ore and loose balls 40 fall and slide, thereby aiding the comminution process by increasing the abrasion and attrition compared with using only falling balls.

This also reduces the wear on the upper surface 28 as it is primarily the balls (rather than the upper surface 28) that receive the blows from falling balls 40 and ore. Thus, providing a bed of steel balls ensures that the shell liner 10 lasts longer before it is worn down and needs to be replaced.

If any of the balls 40 are displaced from the recesses 30 during operation of the grinding mill 60, then the removed balls 40 will provide additional charge for the operation of the grinding mill 60, and some of the balls 40 used in the grinding mill 60 may take the place of the removed ball 40 in the now empty recess 30 as the shell 10 continues to rotate.

If the grinding mill 60 is stopped for any reason, for example to inspect the shell liners 20 or the lifter bars 14, then any empty recesses 30 can be manually filled using the balls 40 in the grinding mill 60, if desired.

As best seen in Fig. 9, the lifter bars 14 are mounted to the shell 10 in a conventional manner using a bolt fixture 62 comprising a T-shaped bolt (a T-shaped head having a threaded arm extending therefrom). The lifter bars 14 include a longitudinal recess having a narrow opening, defined by flanges. The T-shaped head of the bolt 62 is inserted side on through the narrow opening, then rotated. When rotated, the T-shaped head engages with the flanges, and the threaded arm extends through an aperture in the shell 10, and a nut is threaded onto the threaded arm from outside the shell 10 to pin the T-shaped head to the flanges and thereby to secure the shell liner lateral portions 50 from adjacent shell liners 20 to the inner surface 16 of the shell 10.

Various modifications may be made to the above described embodiments within the scope of the present invention. For example, in other embodiments, the shape of the upper surface 28 may differ from that described above. The shell liners 20 may be used in other types of grinding mills, such as SAG mills.

As shown in Fig. 8, one shell liner 20 is located between adjacent lifter bars 14 in this embodiment, but in other embodiments, multiple shell liners 20 may be provided between adjacent lifter bars 14.

In other embodiments, a different securing mechanism may be used to hold the balls 40 (or other charge) in the recesses 30. For example, the balls 40 may include a threaded stub that screws into the recess support surface 32.

In other embodiments, more or fewer than four shell liners 20 may be mounted end to end on the shell inner surface 16, and more or fewer than five lifter bars 14 may be mounted end to end at each circumferential position. The number of shell liners 20 and lifter bars 14 used typically depends on the size of the shell 10, the shell liners 20, and the lifter bars 14 used.

In other embodiments, the shell liner body 24 may have a width exceeding 10 400mm, and a length exceeding 2m; such shell liners may be used in grinding mills having the diameters listed above, or in grinding mills having a diameter larger than 6.5m.

The terms "comprising", "including", "incorporating", and "having" are used herein to recite an open-ended list of one or more elements or steps, not a closed list. When such terms are used, those elements or steps recited in the list are not exclusive of other elements or steps that may be added to the list.

Unless otherwise indicated by the context, the terms "a" and "an" are used herein to denote at least one of the elements, integers, steps, features, operations, or components mentioned thereafter, but do not exclude additional elements, zo integers, steps, features, operations, or components.

The presence of broadening words and phrases such as "one or more," "at least," "but not limited to" or other similar phrases in some instances does not mean, and should not be construed as meaning, that the narrower case is intended or required in instances where such broadening phrases are not used.

List of Reference Numerals and Associated Features Cylindrical shell 10 Shell longitudinal axis 12 Lifter bars 14 Shell inner surface 16 Elongate shell liners 20 Shell liner longitudinal axis 22 Shell liner body 24 Longitudinal steel bar 26 Upper surface 28 Recesses 30 Support surface 32 Pinch mouth (or recess entrance) 34 Spherical balls 40 Ball centreline 42 Ball pinch point 44 Shell liner lateral portions 50 Grinding mill 60 Bolt fixture 62

Claims (17)

1. CLAIMS1. A shell liner for use with a grinding mill, the shell liner defining a longitudinal axis and comprising: a body extending along the longitudinal axis and having an upper surface defining a plurality of recesses therein, each recess defining a recess surface and a mouth, the recess being dimensioned to receive a lower portion of an insert used in the grinding mill and to allow an upper portion of the insert to protrude above the upper surface, wherein the recess surface is dimensioned to support the lower portion in response to forces impacting an upper portion thereof, and the mouth is dimensioned to grip the insert to retain the insert in the recess.
2. 2. A shell liner according to claim 1, wherein the body comprises an elastomer.
3. 3. A shell liner according to claim 1 or 2, wherein the body comprises a support bar extending along the longitudinal axis.
4. 4. A shell liner according to any preceding claim, wherein the body comprises a plurality of fixtures for securing the shell liner to a grinding mill.
5. 5. A shell liner according to any preceding claim, wherein the upper surface defines a generally planar surface.
6. 6. A shell liner according to any of claims 1 to 4, wherein the upper zo surface defines a concave surface.
7. 7. A shell liner according to any preceding claim, wherein the body defines a convex lower surface complementary to a concave lower surface of the grinding mill.
8. 8. A shell liner according to any preceding claim, wherein each recess comprises a generally frusto-spherical depression.
9. 9. A shell liner according to any of claims 1 to 7, wherein each recess comprises a cylindrical or cuboid shape.
10. 10. A shell liner according to any preceding claim, wherein the shell liner comprises a plurality of different shapes of recess on the upper surface.
11. 11. A shell liner according to any preceding claim, wherein the recesses are arranged in a plurality of rows along the upper surface, with adjacent rows being mutually offset.
12. 12. A shell liner according to any preceding claim, wherein the shell liner further comprises lateral portions extending from a lower part of the body from either side thereof.
13. 13. A shell liner according to any preceding claim, wherein the upper surface is raised from the lateral portions.
14. 14. A grinding mill comprising a drum-shaped shell mounted for rotation about its central axis, a plurality of shell liners according to any preceding claim mounted on an inner surface thereof, and a plurality of inserts, where the number of inserts exceed the number of recesses in the shell liners, and the excess inserts crush or grind material in the grinding mill.
15. 15. A grinding mill according to claim 14, wherein each insert comprises a material selected from steel, an alloy, and a ceramic
16. 16. A grinding mill according to claim 14 or 15, wherein each insert is mounted in the corresponding recess as an interference fit.
17. 17. A grinding mill according to any of claims 14 to 16, wherein each recess defines a recess entrance narrower than a cross-sectional width of the corresponding insert so that the corresponding insert is held in place by the narrower entrance on insertion of the insert.