AU704386B2 - Improvements relating to grinding mills - Google Patents

Description

-1- P/00/01 1 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT r Invention Title: Improvements Relating to Grinding Mills e r o r o The following statement is a full description of this invention, including the best method of performing it known to me/us: GH&CO REF: P16303W/JT:MR 2 The present invention is applicable to grinding mills, but may also be applicable to other machinery in which components such as wear liners are to be bolted to an outer structure. For illustrative purposes the invention will be described particularly with reference to grinding mills.

A grinding mill is a cylindrical container which is adapted to be rotated so that material in the mill is comminuted usually primarily by impacts and also to some extent by abrasive action. Typically grinding mills are used for grinding mineral ores and other material which is mined such as coal and chemical products. In some mills a grinding action is achieved due to larger mineral particles grinding against smaller particles and discharge from the mill is controlled to be limited to fine particles. Other grinding mills are designed to contain grinding media such as balls or rods which are tumbled in the rotating mill to achieve a grinding action on feed material. Grinding mills usually are cylindrical and internal liners of wear-resistant material are installed, the liners usually providing a profile which imparts a lifting action to the material being ground and the grinding media. Some grinding mills have liners which incorporate lifting bars for lifting the material.

It is conventional to bolt the liners onto the S.interior of the grinding mill. In some designs only some components are bolted to the interior of the mill, as these components wedge down on top of other components to hold them in position. Liner components are manufactured in a highly wear resistant material and provided with holes for accommodating fixing bolt heads. After a period of service the grinding mill will require replacement of its worn components. This is an expensive operation in terms of cost of components, labour time and the effect of down-time of the machinery. Therefore it is important that the maximum possible working life is achieved.

The present invention is directed to providing new S:16303W -3and useful alternatives to known arrangements whereby it is possible for grinding mills to operate reliably for extended periods, yet when relining is required it should be possible for old liners to be removed easily and quickly and for new liners to be installed also in a speedy and efficient manner.

The present invention manifests itself in several aspects which the applicants intend to claim separately and in combination. In one aspect, the present invention resides in a system of bolting a wear component in a machine and wherein the wear component is to be subjected to impact forces and abrasion forces; the system comprises providing an aperture for accommodating the shank of a bolt and a counter-bore for accommodating the head of the bolt at a location an extended distance below the wear surface of the wear component and at a location such that the wear component would usually be replaced when worn down to the location of the head of the bolt and providing an insert which fits into the counterbore, means being provided for retaining the insert in the counter-bore, the insert being of a wear-resistant material and being formed and mounted so as to protect the head of the bolt during normal use from the effects of impact and abrasion.

,:0o 25 Preferably the counter-bore is of non-circular Scross-sectional shape and the bolt head has a corresponding shape whereby rotation of the bolt in the counter-bore is prevented. A preferred embodiment utilises an oval cross-sectional shape.

Preferably the head of the bolt has a small axial extent e.g. of the order of 10i of the thickness of the wear component.

a Efficient and easy installation of bolts is required and this is preferably achieved by providing a recess in 35 the head of the bolt for receiving a complementary shaped Sotip of a tool whereby manipulation of the bolt can be achieved during the installation process. It should be ~noted that in typical machines each bolt weighs several S:16303W 4 kilograms and has a diameter of around 50mm and it is important therefore to design a system whereby a fitter can readily align che parts and install the bolt. This requirement is best met by preferred embodiments of the invention in which the surface of the head of the bolt leading from the shank is of part-spherical shape and a corresponding part-spherical seat is provided in the wear component. Advantageously the aperture in the wear component extending from the seat increases in diameter in the direction from the seat to the remote side of the wear component thereby permitting angling of the bolt to a small extent as maybe necessary during initial insertion.

Since the invention can be implemented with a bolt head of small axial extent this reduces the mass of metal and the cost of fabrication as well as permitting the head of the bolt to be as far as practicable below the surface of a new wear component, thereby providing for the maximum possible wear life before the bolt head might be exposed.

It has now been appreciated that a limitation on the working life of liners in known containers such as grinding mills can arise around bolt holes which can result in excess and premature wear as well as acting as 25 a structural "defect" which affects the strength of the Scomponents. In view of this problem a common approach is I to provide the fixing bolts with large, axially-extended forged heads which at least partially fill a counter-bore in the wear component, the bolt heads being intended to wear during a period of use. This approach however suffers from the disadvantage that bolts usually have to be of a material to adsorb very high tensile loads and the material is less resistant to wear than the liner itself and thus accelerated wear arises in the bolt head.

S 35 Furthermore, this reduced resistance to wear can cause premature failure of the system due to cracking of the liner component or condemning of the liner due to Slocalised wear around the bolt.

S:16303W 5 Many grinding mills are operated with grinding media which causes very severe impacts. For example, using steel balls of a diameter of 150mm provides a problem with very severe impacts which individually are measured as many tonnes and it is undesirable in these circumstances to have the heads of the bolts available for impact with such grinding balls, because the impacts would loosen the bolts. If such impacts occur then problems could arise with deformation of the head of the bolt, thereby causing a severe problem in removing a bolt when a change is to be made to the liner components.

The present invention is believed, at least in preferred embodiments, to provide significantly better options with extended life of components and thus 15 significantly better economic performance of a grinding S" mill or similar machine.

In a preferred embodiment, the insert for the ."counter-bore is of an axial length substantially corresponding to the depth of a counter-bore, the 20 counter-bore having an annular surface substantially at right angles to the axis of the bolt and for receiving in abutment a corresponding annular projection at the end of the insert. In the case of steel liners, after a few hours of operation impacts from grinding media will cause 2L deformation at the opposite free end of the insert whereby the insert becomes tightly wedged into the •counter-bore and because the insert can be made of the same or of similar material as the liner, no premature wear should be experienced in the region of the bolt.

Preferably the insert has a recess in its end adjacent to the head of the bolt, so that contact with the head of the bolt is obviated thereby avoiding the transfer of shock loads, which by vibration can cause loosening of the bolt and its associated nut, which is located outside the grinding mill.

Preferably the insert has a resilient retaining element extending across the insert and a, ed to enyage in a corresponding undercut in the coul -r-bore whereby S:16303W 6 the insert is initially retained. Conveniently this resilient element is located near the end of the insrt which is adjacent the bolt head. A preferred and important embodiment of resilient element is a generally U-shaped spring steel clip.

Furthermore, this reduced resistance to wear can cause the insert is initially retained. Conveniently this resilient element is located near the end of the insert which is adjacent the bolt head. A preferred and important embodiment of resilient element is a generally U-shaped spring steel clip.

In a further aspect, the present invention resides in a grinding mill fitted with li.ning components and using a system as described above. The invention also encompasses an insert for the system as described above and the bolt for the system as described above.

In a still further aspect, the invenzion resides in a kit of parts for bolting a wear component in a machine, the wear component having an aperture for accommodating the shank of a bolt and a counter-bore for accommodating the head of the bolt at a location an extended distance below the wear surface of the wear component and at a location such that the wear component would usually be rei,_aced when worn down to the location of the head of 25 the bolt, the kit of parts comprising a bolt and an insert, the bolt having a shank adapted to extend through "'the aperture in the wear component to a remote location S"for receiving a nut wherEmby the wear component can be clamped in position, and a head of non- circular crosssectional shape to be accommodated in the counter-bore which is of corresponding shape whereby rotation of the bolt is prevented and the head, on installation, is located an extended distance below the wear surface of the component, the insert being formed and adapted to be 35 mounted in the counter-bore to protect the head of the bolt during normal use from the effects of impact and abrasion.

6a Advantageously, the kit includes the wear component.

Typically, the retaining means of the insert comprises at least one laterally projecting element resiliently mounted for displacement on engagement with walls of the counter-bore in a direction inwardly relative to the insert at right angles to the direction of insertion ard adapted to resiliently displace outwardly upon alignment with a corresponding recess in the lower region of the wall of the counter-bore, and the bolt head has a generally T-shaped form with each arm of the T having a lower part spherical surface adapted to engage in a correspondingly shaped seat in the wear component.

For illustrative purposes only, an embodiment of the invention will be described with reference to the accompanying drawings of which:- Figure 1 is a cross-sectional enlarged view of a known bolt arrangement for securing a grinding mill liner in position; Figure 2 is an iscmetric view of a lifter bar for use in a grinding mill and adapted to be utilised in accordance with the present inventive concepts; Figure 3 is a cross-sectional view taken along the line A-A of Figure 2 illustrating the use of an embodiment of the invention when the lifter bar of Figure 25 2 is installed in a grinding mill according to the invention and before use of the grinding mil] i Figure 4 is an enlarged transverse cross-sectional S" view taken along the line B-B cf Figure 3; Figure 5 is an isometric view of the bolt of Figures 3 and 4; Figure 6 is a front elevation of the bolt of Figure :Figure 7 is a side elevation of the bolt end of Figure 35 Figlre 8 is a plan of the bolt head of Figure Figure 9 is a view of a steel spring clip; 70/BJN/704 6b Figure 10 is a cross-sectional view taken through the lifting bar in the plane of the undercut recess and showing its configuration; Figure 11 is d part sectional elevation of a preferred embodiment of insert for use in the embodiment of Figures 3 and 4; Figure 12 is a side view partly in section of Figure 11; Figure 13 is a plan of the embodiment of Figure 11; e.

o e o 7 Figure 14 is a cross-sectional view taken along the line XlV,XlV; Figure 15 shows a cross-sectional partial view of an assembly comprising a linear plate wedged between two modified lifting bars (as illstrated in Figure 16) and secured onto a side wall of a grinding mill container; Figure 16 is a cross-sectional enlarged view of a modified lifting bar shown in Figure 15 to be utilised in accordance with the present inventive concept; Figure 17 is a front elevation of an insert in a second embodiment for use with the lifting bar of Figures and 16; Figure 18 is a side elevation of the insert of Figure 17; and o Figure 19 is a plan view of the insert of Figure 17.

A conventional arrangement shown in Figure 1 comprises a grinding mill lifting bar 10 made of wear- :....resistant alloy steel, which is clamped to the interior of a grinding mill 11 by a bolt 12, a clearance 13 being 20 provided between the interior of the lifting bar and the grinding mill body as in this instarce the lifting bar (which can be as shown in Figure 3) has a wedging action against chamfered sides of liner plates.

The lifting bar has a bore 14 in which the shank of the bolt is a clearance fit, a conical seat 16 for accommodating a conical surface 17 of the bolt and a counter-bore 18 in which a head 19 of the bolt is a clearance fit. The head 19 could be e.g. oval in shape to prevent rotation in the counter-bore during installation of the bolt. It will be seen that the bolt head is of extended axial length, so as to provide an extended mass of metal which the fitter needs to grip during installation of the bolt and also provides a portion of the bolt which is designed to wear when in use.

The illustrated embodiment of the invention using the components as shown in Figures 3 to 8 is described as applied to securing a lifting bar 20 shown in Figure 2.

S:16303W 8 The lifting bar is of wear-resistant material such as chrome-molybdenum steel or white iron and is cast into the appropriate shape and provided with an oval counterbore 21 for each bolt, and a wedge shape is provided by a pair of chamfered surfaces 22 near the leading edge which engage against corresponding end surfaces of mill liner plates which are slightly spaced apart.

The lifting bar 20 is bolted to the cylindrical grinding mill 11 by a series of bolts which in this embodiment of the invention have generally T-shaped heads of oval profile as best seen from Figures 5 to 8. Each bolt 23 has a circular cross-sectional shank with a threaded end portion and is typically of the order of 50mm diameter. A T-shaped head 24 is in plan view oval 15 in that it has part-spherical ends 25 blended by a smoothly curved shoulder 26 into the shank. Generally flat approximately semi-circular opposed side walls 26 are forged to a sm.-1 relief angle as shown in Figure 8 and are tapered a few degrees in the downward direction S 20 as the embodintent adopts a preferred feature of avoiding parallel surfaces so that a used bolt can be released and removed from a worn liner.

For the purpose of facilitating manipulation of the bolt during insertion, a tapered slot 27 is provided in the centre of the head of the bolt and extending along •the major axis.

Since it is necessary to apply high torque when tightening a bolt to secure a mill liner into position, the bolts must be of a suitable tensile strength steel such as grade 8.8. Such steel however does not have a wear resistance comparable with mill liner material and in accordance with this embodiment of the invention where and impact on the bolt head is obviated by the use of a novel insert. As shown in Figure 3, the bolt head 25 is located nearer the bottom surface 22A of the lifting bar and the location of the head is chosen such that when the lifting bar has been worn down to just above the head of the bolt, then the lifting bar requires replacement.

S:16303W 9- Lifting bars when eroded to a certain extent need to be replaced as otherwise performance of the mill and in particular the lifting action of the lifting bar becomes unacceptable inefficient.

As shown in Figure 3, the lifting bar has for each bolt a bore 30 which increases in diameter towards the bottom 22A of the lifting bar, has part-spherical seats 31 for each of the part-spherical ends of the bolt head and has a counter-bore 21 which is also oval, but of significantly greater dimensions than the head of the bolt, the counter-bore terminating in an annular shoulder 32 surrounding the bolt head.

As shown in Figure 4, on opposed sides the lifting bar 20 has undercuts 33, which are used for accommodating curved arms 42 of a generally U-shaped spring steel retaining clip 34, which is secured in the lower end portion of an insert 40. The insert is of oval shape and has a clearance fit within the counter-bore 21 and has a recess 41 in its lower end for accommodating with a clearance the head 25 of the bolt, thereby leaving an annular collar projecting from the body of the insert for abutment on the shoulder 32. The purpose of the spring clip 34 is to retain the insert in position during initial operation of the grinding mill. During this period impact of grinding media cause deformation of the S"metal of the lifting bar around the counter-bore 21 and to some extent the insert thereby causing a peening action to occur whereby the portion of the insert near the surface acquires an interference fit with the lifting bar.

Operation of the mill normally continues until the body of the insert has been worn away, at which time the head of the bolt is exposed so it can be driven out after removal of the nut. Speedy and efficient replacement of the components in a grinding mill are very important as down time is of great economic significance, particularly in mines where mining production comes to a standstill while the grinding mill is off-line.

S:16303W 10 Referring now to Figure 10, the undercut 33 is illustrated and accommodates the spring ears 42 of the spring clip which is shown in Figure 9. The spring clip is retained in the insert which is shown in detail in a preferred embodiment in Figures 11 to 14.

As best appreciated from Figure 13, in p-an view the insert 40 is oval with semi-circular ends and a central substantially parallel-sided section 42 which in its upper region has curved tabs 43 which extend laterally to fill corresponding tapering recesses in the oval counterbore 21 in the lifting bar which are provided to receive and press inwardly the spring ears 42 of the clip during initial installation of the insert.

At its lower end the insert has a recess 45 provided •0go 15 for the purpose of indicating visually when the insert is nearly worn down so that operators can plan a mill shut down for replacement of the lifting bar. As best seen from Figure 12, lateral slots 46 are provided for accommodating the ears 42 of the spring clip when installed, the body of the spring clip being retained within the oval base recess 47 as best shown in Figure 14.

In Figures 15 and 16 are illustrated modified S grinding mill lifting bars 100, 101 whi h are used to wedge between them a liner plate 102 to securely fix the latter abutingly onto the interior surface of a side wall 103 of the grinding mill vessel. The lifting bars 100, 101 are clamper against the side wall 103 as hereinbefore described by suitably formed bolts 104 in accordance with the invention which are secured by nuts 106 to the side wall.

As can be seen in Figures 15 and 16, the lifting bars 100, 101 as well as the liner plate 102 are provided with mounting ears 105 to aid in the installation of these heavy structures.

Figure 16 illustrates in greater detail the lifting bar 100 as well as a mudified insert 140 received in the generally oval-shaped counter-bore 121 of the lifting bar S:16303W 11 to cover the T-shaped bolt head 124 and terminate flush with the upper surface of the lifting bar. As an alternative to the metal insert described above, the modified insert 140 is a rubber-like component which provides enhanced safety. As can be best appreciated in Figures 14 to 19, the upper section of the insert is shaped generally as hereinabove described with reference to Figures 11 to 14, whereas the lower section is modified in that it has a cavity 145 of generally rectangular parallelopiped shape extending into the insert body from an also generally rectangular parallelopiped shaped recess 146 in the lower surface of the insert. Two cylindrical steel pins 148 are embedded in a bore 14'i extending perpendicular to the longitudinal oo 15 axis of the insert 149 parallel-sided surfaces 150 such as to protrude with their half-spherical ends from the parallel-sided surfaces 150 of the insert and leave a gap (in which to receive the T-head of the bolt) between the flat terminal inner ends within the cavity 145.

Thus, the insert 149 can be secured by means of t>e protruding pin ends within an enlarged diameter annular recess ±22 of the counter-bore 121 without the necessity of providing a separate spring clip as has been described with reference to the first embodiment (Figures 4 to 9) Further, as is indicated at 123 in Figures 15 and 15, a rubber sleeve surrounds the bolt shank 115 within the lifting bar 100. This modified embodiment comprising the rubber bolt cap insert 140 and bolt 104 enables restricted swivel movement of components without negatively affecting retention of the lifting bar and linear plate on the mill vessel surface.

S:16303W

Claims (14)

1. A system of bolting a wear component in a machine and wherein the wear component is co be subjected to impact forces and abrasion forces; the system comprising providing an aperture for accommodating the shank of a bolt and a counter-bore for accommodating the head of the bolt at a location an extended distance below the wear surface of the wear component and at a location such that the wear c nponent would usually be replaced when wo:n down to ne location of the head of the bolt and providing an insert which fits into the counter-bore, means being provided for r-taining the insert in the counter-bore, the insert being of a wear- resistant material and being formed and mounted so as to protect the head of the bolt during normal use from the effects of impact and abrasion.

2. A system as claimed in claim 1 wherein the counter- bore is of non-circular cross-sectional shape and the bolt head has a corresponding shape whereby rotation of the bolt in the counter-bore is preve -d.

3. A system as claimed in claim 1 or im 2 wherein the head of the bolt has a small axial extent e.g. of the order of 10% of the thickness of the wear component.

4. A system as claimed in any one of the preceding claims wherein there is provided a recess in the head of the bolt for receiving a complementary shaped tip of a o tool whereby manipulation of the bolt can be achieved during the installation process.

5. A system as claimed in any one of the preceding claims wherein the surface of the head of the bolt leading from the shank is of part-spherical shape and a 4 corresponding part-spherical seat is provided in the wear component.

6. A system as claimed in any one of the preceding claims wherein the insert for the counter-bore is of an axial length substantially corresponding to the depth of z/IR a counter-bore, the counter-bore h-iving an annular 13 surface substantially at right angles to the axis of the bolt and for receiving in abutment a corresponding annular projection at the end of the insert.

7. A system as claimed in claim 6 and wherein the insert has a recess in its end adjacent to the head of the bolt, so that contact with the head of the bolt is obviated thereby avoiding the transfer of shock loads, which by vibration can cause loosening of the bolt and its associated nut, which is located outside the grinding mill.

8. A system as claimed in any one of the preceding claims wherein the insert has a resilient retaining element and adapted to engage in a corresponding undercut in the counter-bore whereby the insert is initially retained.

9. A grinding mill fitted with lining components and using a system as defined in any one of claims 1 to 8. An insert for the system as claimed in any one 2- of claims 1 to 8.

11. A bolt for the system as claimed in any one of claims 1 to 8.

12. A method of managing wear of components in a grinding mill comprising using a system as claimed in any oo 25 one of claims 1 to 8.

13. A kit of parts for bolting a wear component in a machine, the wear component having an aperture for accommodating the shank of a bolt and a counter-bore for .accommodating the head of the bolt at a location an extended distance below the wear surface of the wear component and at a location such that the wear component would usually be replaced when worn down to the location of the head of the bolt, the kit of parts comprising e. bolt and an insert, the bolt having a shank adapted to extend through the aperture in the wear component to a remote location for receiving a nut whereby the wear component can be clamped in position, and a head of non- circular cross-sectional shape to be accomn,:ddtted in the BJN/704 14 counter-bore which is of corresponding shape whereby rotation of the bolt is prevented and the head, on installation, is located an extended distance below the wear surface of the component, the insert being formed and adapted to be mounted in the counter-bore to protect the head of the bolt during normal use from the effects of impact and abrasion.

14. A kit of parts as claimed in claim 13 and including the wear component.

15. A kit of parts as claimed in claim 13 or claim 14 and wherein the retaining means of the insert comprises at least one laterally projecting element resiliently mounted for displacement on engagement with walls of the counter-bore in a direction inwardly relative to the insert at right angles to the direction of insertion and adapted to resiliently displace outwardly upon alignment with a corresponding recess in the lower region of the wall of the counter-bore, and the bolt head has a generally T-shaped form with each arm of the T having a lower part spherical surface adapted to engage in a correspondingly shaped seat in the wear component. DATED this 29th day of January 1999 THE ANI CORPORATION LIMITED 4 25 By its Patent Attorney GRIFFITH HACK 00*00: 0V VS 9 V V ABSTRACT A system for fixing a wear component into a machine such as a ball grinding mill consists in providing in the wear component an aperture for accommodating the shank of a bolt and a counter-bore for accommodating the head of the bolt at a location an extended distance below the wear surface of the wear component and at a location such that the wear component would usually be replaced when worn down to the location 1 0 of the head of the bolt and providing an insert which S fits into the counter-bore, means being provided for retaining the insert in the counter-bore, the insert O Sbeing of a wear-resistant material and being formed and mounted so as to protect the head of the bolt during normal use from the effects of impact and abrasion. The .or counter-bore preferably is non-circular such as oval and "the head of the bolt had a generally T-shaped form with part-spherical surfaces to engage on corresponding part- spherical surfaces constituting a seat in the wear component. oeo S:16303W