GB2218653A - Mill linings and replacement thereof - Google Patents

Abstract

A batch mill has a lining composed of a plurality of interlocking lining elements 3 secured against the internal surface of the mill casing 2 by means of steel retaining bars 5 secured to the internal surface of the steel casing 2 by welds. Each element 3 is made of synthetic wear-resistant rubber of a type generally known for use in batch mill linings, there being a core 15 of relatively hard rubber material having a Shore hardness of 80 DEG and an outer body 16 of relatively soft material having a Shore hardness of 60 DEG . Lining can readily take place and is less time-consuming than in conventional lining practices. Removal of worn lining elements is particularly readily achieved and primarily responsible for savings of time. A stratum 20 of pigmented rubber may be present as a wear marker. <IMAGE>

Description

Improvements In Grinding Mills The invention relates to improvements In grinding mills and is particularly concerned with mill linings.

The grinding of solid materials Is a frequent requirement in connection with many commercial and industrial processes In order to reduce particle size to that desired for the process concerned or to assist In transportation and storage. For example, coke Is ground to provide a particle size sultable for use in blast furnace processes in the steel industry, animal bones are ground to provide a pulverulent raw materlal for use In the manufacture of bone china and Iron ore is ground prior to introduction to a blast furnace.

Grinding may be accomplished simply by causing attrition between particles of the materlal to be ground but in normal practice It is preferred to include a grinding aid such as steel rods, steel balls or flint rocks. In any event, the material to be ground Is set In motion, typically by rotatlon of a cylindrical mill upon Its longitudinal axis.

It will be readily appreciated that rotation of a mill In this way subJects the internal surface of the mill to abrasive forces and impact. After a period of operation, the internal surface of a mill will begin to show signs of wear and damage. This is undesirable in apparatus terms since eventually the mill would need to be replaced. However, a more minor disadvantage Is that abrasion of the Internal surface of the mill can result In the Introductlon of small amounts of impurities Into a mill product. Thus, a typical mill will be made of steel and It would be undesirable In the grlnding of bones to introduce small amounts of steel as an abrasldn product into the pulverulent mill product Intended to be used in the manufacture of bone china.

For the above reasons, it has been customary practice for many years for the Internal surfaces of mills such as batch mills to be lined. As the lining suffers wear and damage due to grinding operatlons, the time may be reached when the lining needs to be replaced but this Is, of course, more desirable than a circumstance where the Interlor surface of the mill itself has been damaged or worn.

Rubber mill linings have been used for the last ten to twelve years and have essentially replaced stone lInIngs.

However, some stone linings are still used. Stone linings have a number of drawbacks, largely associated with theIr considerable weight, both in terms of mill operatIon and Instal lation and removal operat Ions.

Rubber lInings avoid the latter disadvantages of stone linings but have been problematical to Install and more over when replacement Is required.

One system of rubber mill lining involves lining elements which are formed with a llp and shoulder construction.

Two adJacent lining elements-;abut by thelr llps so as to form between the respective shoulders a recessed area.

The elements are made of rubber. A rubber bar overiles the two abutting lips and fills the recessed area to maintain the two elements in place. The head of a bolt Is received In the body of the rubber bar and Its shank penetrates the mill casing to receive a fIxing bolt on the exterlor of the mill. The rubber mill lining elements are arranged on the Internal circumference of the mill and the retalning bars run longitudinally along the Internal surface in the previously mentloned recessed areas. Several end-to-end bars are needed to cover the entire length of the mill parallel to its axes.In the same fashion as In brick bonding In bulldlng construction, matters are arranged so that a Join between mill lining elements is not aligned with a Join between two of the rubber retaining bars. installation of this system of mill lining is rather time-consuming since the Inside of the mill has to be marked out for drilling purposes and then holes drilled through the mill casing.

This Is very tIme-consuming in practice. Post-lnitlal installation, the rubber linings are also difficult to remove, the practice usually being to grind off the fixing nuts on the outside of the mill as part of the overall operation and then to remove the linings manually. A more up-to-date system which has been In service for several years avolds the initial installation problem outlined above by having steel members Inserted Into the rubber Lining elements or platens. These elements form a tongue-and-groove arrangement, a plate on one end of a lining element having a configuratlon defining a groove and generally non-deformed steel plate upon the other end of an adjacent abutting element defining a tongue.The tongue Is recelved In the groove to secure the two adJacent elements together. The groove-defining steel plate is welded to the Internal surface of the mill. This system deals quite satisfactorily wlth the initial Installation problems outlined hereinbefore and achieves some materlals costs.

However, installation of replacement linings, as distinct from installation of linings when a new mill Is brought into service, will, of course, require removal of existing linings. In the system Just descrlbed, existing linings can only be removed by breaking the original welds, removing the mlll linings elements and then Installing new lining elements by re-welding. Thus, although there is a saving in initial Installation costs, the system does not avoid the down-llne problems which had already existed for some years before this particular system was proposed. This system makes no material change to the cost of replacing worn out linings.

Steel linings have also been used, for example, for the grinding of coke In the steel industry. Steel lining plates in such a system are secured In place by bolting and this of course gives rise to many of the Installation and re-lnstallation problems outlined above In connection wlth other lining systems.

According to the inventlon, there Is provided a grinding mill wherein a grinding cavity Is defined by a wall whose surfaces are at least partly lined with natural or synthetic rubber I ining members secured thereto characterized In that said members each are provided with a vold therein and In that a cooperating element secured to the wall has an enlargement lodged In the vold and retained therein by confrontation of enlargement surfaces and abutting surfaces of the vold.

Conveniently, as for example In the case of a typical batch mill, the grinding cavity Is of right circular cylindrical form, the mill conveniently being mounted for rotation upon the longitudinal central axes of sald cavity.

In practice, all or substantially all of the mill surface cylindrical side walls are usually lined, the end wails optionally belng lined In the case of a mill having closed ends. Thus, In practice, all or substantlally all cavity-defIning surfaces In use Impacted by material charged to the mill for grinding purposes are lined.

In preferred forms of the Invention, the lining members are each formed with a void in the form of a channel therein, a plurality of spaced apart enlargements being convenlently received in sald channel.

Preferably, In any event, a pluralIty of spaced apart enlargements are received in respective void locations, eg In respective distinct voids, in each of the lining members.

Each cooperating element Is conveniently of elongate form having an elongate upstanding portion of enlarged cross sect ion spaced from the cavity wall. For example, each cooperating element may have an elongate enlargement of bead-llke form. Preferably, each cooperating element has a pair of generally parallel elongate upstanding portions for reception In spaced apart voids in a respective one of said lining elements. In particular, each said cooperating element has a generally U-shaped crosssection including a base welded to the cavity wall and a pair of upstanding sides each having an enlargement for engagement In a respective spaced apart void in a lining element.

Each lining element Is made of a region of relatively soft natural or synthetic rubber and a region of relatively hard natural or synthetic rubber* the latter having the or each enlargement-receiving vold formed thereln. The relatively hard natural or synthetic rubber typically has a Shore Hardness of at least 750, eg 800 or more.

In a particular embodiment of the Invention, a grinding mill comprlses: (I) a mill wall defining a right circular cylindrical grinding cavity; (ill) means mounting sald mill for driven rotation upon the central longitudinal axis of sald grinding cavity; (iii) a plurallty of llning elements preferably made of a natural or synthetic rubber composition and collectively lining at least the cylindrical surfaces of said mill wall and each formed with a channel In material thereof having a Shore Hardness of 750 or more; and (iv) a plurality of metallic elements secured to the wall one at each of a plurality of spaced apart locations, each element comprising an elongate bead-like enlargement recelved In a lining element channel to secure such lining element to the mill wall.

The following is a specific descriptlon intended to Illustrate the Invention, by way of example only, reference being made to the accompanying drawings in which:- Flgure 1 is an internal view of a batch mill for the grinding of bones to produce raw material for use in bone china production; Figure 2 Is a view similar to Figure 1 but shown wlth the Lining removed; Figure 3 Is a partial cross-section of the batch mill as shown in Figure 2; Figure 4 Is a view similar to that shown In Figure 2 but showing the state of the batch mill after partial Installation of fresh lining; Figure 5 is a cross-sectlon taken through a portion of the lining installed in the batch mill shown in Flgure 4;; Figure 6 shows a portion of the lined surface of the batch mill of Figure 4 on an enlarged scale and in more detail; and Flgures 7a to 7e show various configurations of Lining element for instal lation in the batch mill shown In Figure 2.

As shown In Flgure 1 of the drawings, the batch mill designated generally by the reference numeral 1 comprises a right circular cylindrical steel casing 2 closed at its two axially opposed ends by a steel plate (not shown) having an internal lining of sheet natural or synthetic rubber. In use, the batch mill shown in Flgure 1 will be deployed as such although It is far more likely In the case of larger mills (eg for use in the cement industry) that a serles of mill chambers will be used in combination, each mill chamber In a series belng disposed end-to-end with adjacent mlll chambers.A screen (not shown) would In such instances normally be provided at the Interface between each mill chamber to ensure that only ground material of certain size characteristics passes from one chamber to the next. In this way, it can be ensured that the fInal mill product Is comprIsed of particles of a particular size distribution as desired for the product in any particular Instance. In use, conveyance of material from one axial end of such a mill assembly to the other Is achieved by the charging of new material to the input end of the mill, thus causing ground materlal to move towards the output end. To assist this, such mills may be rotated with their longitudinal central axis slightly Inclined to horizontal although this Is in practice not normally the case.

In practice, a batch mill or other mill is rotated about Its longitudinal central axis by electrical power means (not shown), approprlate gearlng and transmission being provided to couple drive to stub axles (not shown) provided on the previously referred to axial end plates of the mill. Such details will be well known to those skil led in this particular -art and do not require exposition wherein.

As shown In Figure 1, the mill 1 has a lining composed of a plurality of interlocking lining elements of a configuration designed to ensure optimum grinding efficiency. The lining element configuration represented in Figure t Is also reflected in Flgures 4, 5 and 6 of the drawings but various configurations can be used depending upon operational requirements in any particular grinding facility. Various alternative configurations for the lining elements are represented In Figures 7a to 7e of the drawings.

As shown in Flgure 1, the batch mill Is provided wlth a manhole 4 to enable access Into the cavity of the mill for both materials Input purposes and lining Inspectlon.

The linlng elements 3 are secured against the Internal surface of the mill casing 2 by means of retaining bars 5 (Flgures 2 to 6). Retaining bars 5 are made of steel and have a generally U-shaped cross-sectlon as best seen from Figure 5. Thus, each retaining bar 5 has a base 6, a pair of laterally opposed webs 7 upstanding from the base 6 and a palr of beads 8 integral wlth each web 7. The retaining bars 5 are disposed lengthwise wlthin the cavity of the batch mill 1, as best seen from Figure 2, and are secured to the Internal surface of the steel mill casing 2 by welds. Retaining bar 5a, as shown in Flgure 2, is discontinuous In order to facilitate penetration into the cavity of the batch mill by manhole 4.

Needless to say, the retaining bars 5 could adopt alternative configurations and a wide varlety of alternative configuratlons are likely to be efficacious in the batch mlll shown In the drawings and also to be readily available through existing steel extrusion processes. Thus, for example, the retaining bars 5 could have an Inverted T-shaped configuration comprising a base, an upstanding single web similar to the web 7 shown In Figure 5 and a single bead similar to the bead 8 shown In Figure 5. The bead 8 could, of course, In any form of the retaining bars 5 have a sllghtly different configuration. For example, the bead 8 could be provided wlth a much more Irregular cross-section.

The mill lining elements 3, as shown In detail In Figure 5 of the drawings, have a confIguration comprising a leg portion 9 having a gently sloping upwardly facing surface 10. A step 11 rises from the slope 10 to a flat surface 12. Flat surface 12 leads into a step 13 having an Initial sloping surface followed by a vertical surface.

It will be seen from Figure 5 that the vertical surface of step 13 is adJacent a recess 14 Into which Is recelved the extremity of a leg portlon 9 of an adJacent lining element 3.

Each lining element 3 is made of synthetic wear-resistant rubber of a type generally known for use In batch mill linings. In the particular embodiment represented in Flgure 5 of the drawings, the lining element 3 comprises a core of a relatively hard rubber material having a Shore Hardness of 800 and an outer body 16 of relatively soft rubber material having a Shore Hardness of 600. It will be observed from Figure 5 that the retaining bar 5 has a large proportlon of Its beads 8 engaged against surfaces of the relatively hard rubber material of the core 15.The core rubber material because of its relative hardness yields to a smaller extent under the lateral forces experlenced by the lining elements 3 In operation of the mill and serves better to provide security of retention of the lining elements 3 against the Internal surface of the mill casing 2 by the retalning bars 5.

To provide stiffness in the leg portion 9 of the lining elements 3, a stiffner 19 In the form of a steel plate embeded in the body of rubber material 16 is provided.

In the embodiment shown in Figure 5, a wear marker 20 is also provided in the body of rubber materlal 16. This takes the form of a vertical stratum of pigmented rubber material, yellow pigment being typical. The rubber lining elements 3, particularly In the reglon of the inclined surfaces 11, suffer wear durlng thelr normal use life due to abrasive contact with the contents of the mill during grinding. When the wear is such as to expose the wear marker 20, visual Inspection via manhole 4, of course, being necessary to detect a limiting wear condition, replacement of linings may be made.

As shown In Flgure 1 of the drawings, the batch mill Is rotated In clockwise fashlon so that It is the gently sloping surface 10 and the inclined surface 11 which act against material charged to the mill cavity. This avoids the risk of mill materlal Insurgence Into the Junction between two linlng elements 3 (which would tend to happen at the socket Joint between the extremity of the leg portlon 9 of a lining element 3 and recess 14 If rotation was counter clockwise).

In the case of conventional lining systems where lining elements are bolted to the mill casing, Installatlon for the first lining requires marking out and drilling of the mill casing followed by bolting In of the mill lining elements. Replacement of Linings after service of the mill for a sufficient period requires unbolting of existing linings followed by manual removal of old linings and installation of replacement linings with rebolting. Bolts are in practice too difficult and timeconsuming to remove by unthreading and therefore normal custom is to remove the heads by grinding. In a typical batch mill, this can mean a down-time of six days.In the case of the prior art welded lining systems referred to earlier, a first lining operation Involves welding In the linings via their steel components. Re-lining operatlons after service of the mill for a sufficient period requires removing the old linings by breaking the welds, repairlng damage done by this operatlon and rewelding new linings in place. This leads to down-tlme of three to four days In a typical batch mill. Stone linings require a higher level of skill for fitting and both initial installation and replacement of linings leads to a down-time of between two to four weeks for a typical batch mill.

In the linlng system of the present Invention described with reference to the accompanying drawings, marking out of the Internal surface of the mill casing 2 for correct positioning of the retalning bars 5 Is much easler than marking out for drilling purposes. Welding of the retaining bars 5 then takes place and this requires a smaller number of welds than In the conventional welded lining systems referred to above. The lining elements 3 can then be located over respective retalning bars wlth an interlocking relatlonship wlth already installed lining elements 3. Installation of lining elements 3 over retaining bars 5 is a relatively simple and unskilled force-fitting operatlon. The final lining element 3 In each annular band would be cut and rebated to the correct size to finish that band of lining.

Llning elements 3 adjacent manhole 4 would be cut and trimmed to shape and In some case speclal measures such as bolting and sealing in this particular viscinity would be required in practice. For initial Installation of the lining system of the Invention, a down-time for a typical batch mill would be three to four days. Re-installation of fresh linings when replacement is required would require removal of worn lining elements by a relatively simple operation involving peeling the elements off from their force-fitted securement to the retaining bars 5.

This might be moderately dlfficult in the case of the first lining element 3 of any particular annular band where such tools as crowbars would probably need to be used. However, subsequent elements in any particular band can be removed very easily. New elements are also relatively easy to fit with the result that durlng a typical re-lnstallatlon programme for a typical batch mill there would be a significantly smaller down-time than In the case of existing welded lining systems, a typical down-time being two days.

The invention as described earlier without reference to the drawings may include any one or more features of the Invent ion as descrlbed with reference to the drawings.

Claims (23)

Claims

1. A grinding mill wherein a grinding cavity is defined by a wall whose surfaces are at least partly lined with natural or synthetic rubber I ining members secured thereto, characterized in that sald members each are provided with a void thereln and In that a cooperating element secured to the wall has an enlargement lodged In the void and retalned therein by confrontatlon of enlargement surfaces and abutting surfaces of the void so that the lining member Is secured to the grinding cavity wall.

2. A grinding mill as claimed In Clalm 1 wherein the grinding cavity is of right circular cyllndrical form.

3. A grinding mill as clalmed In Claim 2 whereln the mill Is mounted for rotation upon the longitudinal central axis of said cavity.

4. A grinding mill as claimed In Claim 2 or Claim 3 wherein all or substantially all of the mill surface cyllndrical side walls are lined.

5. A grinding mill as clalmed in any preceding claim whereln all or substantially all of the cavity-defining surfaces In use Impacted by material charged to the mill for grinding purposes are lined.

6. A grinding mill as claimed In any preceding claim wherein the lining members are each formed wlth a void In the form of a channel thereln.

7. A grinding mill as claimed in any preceding clalm wherein a plurality of spaced apart enlargements are recelved in respective void locations Ih each of the lining members.

8. A grinding mlll as claimed In Claim 6 wherein a plurality of spaced apart enlargements are received in said channel.

9. A grinding mill as claimed In any preceding claim wherein a plurality of spaced apart enlargements are recelved In respective distinct volds of each of the lining members.

10. A grinding mill as clalmed in any preceding claim whereln each cooperating element has an elongate enlargement of bead-like form.

11. A grinding mill as clalmed in any preceding claim whereln each cooperating element Is of elongate form having an elongate upstanding portion of enlarged crosssection spaced from the cavity wall.

12. A grinding mill as claimed In Claim 11 wherein each cooperating element has a pair of generally parallel elongate upstanding portions for reception in spaced apart volds In a respective one of sald lining elements.

13. A grinding mill as claimed In Claim 12 wherein each said cooperating element has a generally U-shaped crosssection Including a base welded to the cavity wall and a palr of upstanding sides each having an enlargement for engagement In a respective spaced apart void In a lining element.

14. A grinding mill as claimed in any preceding claim wherein each lining element is made of a region of relatively soft natural or synthetic rubber and a reglon of relatively hard natural or synthetic rubber, the latter having the or each enlargement-receiving void formed therein.

15. A grinding mill as clalmed In Claim 14 whereln the relatively hard natural or synthetic rubber has a Shore Hardness of at least 750.

16. A grinding mill as claimed In Clalm 14 wherein the relatively hard natural or synthetic rubber has a Shore Hardness of at least 800.

17. A grinding mill as claimed In any preceding clalm wherein each lining member comprises a body of natural or synthetic rubber having a generally flat bottom surface, an upper surface configured with a raised portion connecting to the balance of the upper surface by means of inclined surfaces, a relatively thin leg portion at one lateral extremity and relatively thick portion at opposed lateral extremity, the relatively thick portion defining with the bottom surface a socket in which to recelve a leg portion of an adJacent lining member in interlocking relationship of the two lining members.

18. A grinding mill as claimed In Claim 1 and comprising:- (I) a mill wall defining a right circular cylindrical grinding cavity; (ill) means mounting said mill for driven rotation upon the central longitudinal axis of sald grinding cavity; (liy) a plurality of natural or synthetic rubber lining elements collectively lining at least the cylindrical surfaces of said mill wall and each formed with a channel In material thereof having a Shore Hardness of 750 or more; and (Iv) a plurality of metallic elements secured to the wall one at each of a plurallty of spaced apart locations, each element comprising an elongate bead-like enlargement received in a Lining element channel to secure such lining element to the mill wall.

19. A grinding mill substantlally as hereinbefore described with reference to, and as illustrated in, any one of the accompanying drawings.

20. A method of re-lining a grinding mill as claimed in any preceding claim which method comprises accessing the grinding cavity, urging a first lining member from the grinding cavity wall to dislodge the enlargement of a respective cooperating element from the lining member void, performing the aforesaid operation In relation to one or more further lining members so that a plurality of lining members have been removed from the grinding cavity wail, disposing each of an equal number of further lining members In Juxtaposition between void(s) thereof and cooperating element enlargement(s) and applying force to sald lining members to lodge the or each enlargement In a respective vold.

21. A method as clalmed In Claim 20 wherein the first lining member is destructively removed from the grinding cavity wall.

22. A method as claimed In Claim 20 or Claim 21 wherein the further lining member(s) Is non-destructively removed from the grinding cavity wall.

23. A method of re-lining a grinding mill as claimed in Claim 1, substantially as hereinbefore described with reference to the accompanying drawings.