Technical Field [0001] This specification relates to grinding discs and particularly relates to grinding discs suitable for use in stirred-medium grinding machines with horizontally oriented driveshafts such as the type of mill known as the IsaMillTM.

Background

[0002] The IsaMill™ is a stirred-medium grinding mill, in which the grinding medium and the ore being ground are stirred rather than being subjected to the tumbling action of older high-throughput mills (such as ball mills and rod mills). Stirred medium mills often consist of stirrers known as grinding discs (see A in figure 1) mounted on a rotating shaft located along the central axis of the mill. The mixing chamber is filled with the grinding medium (normally sand, smelter slag, or ceramic or steel beads) and a suspension of water and ore particles, referred to in the minerals industry as a slurry. In contrast, ball mills, rod mills and other tumbling mills are only partially filled by the grinding medium and the ore.

[0003] In stirred-medium mills, the stirrers set the contents of the mixing chamber in motion, causing intensive collisions between the grinding medium and the ore particles and between the ore particles themselves. The grinding action is by attrition and abrasion, in which very fine particles are chipped from the surfaces of larger particles, rather than impact breakage. This results in the generation of fine particles at greater energy efficiency than tumbling mills. For example, grinding a pyrite concentrate so that 80% of the particles are less than 12 μπι (0.012 mm) consumes over 120 kilowatt-hours per tonne (kWh/t) of ore in a ball mill using 9 mm balls, but only 40 kWh/t in an IsaMill™ using a 2 mm grinding medium.

[0004] An IsaMill™ usually consists of a series of eight grinding discs mounted on a rotating driveshaft inside a cylindrical shell. The mill is 70-80% filled with the grinding medium, and is operated under a pressure of 100 to 200 kilopascals. The discs contain slots to allow the ore slurry to pass from the feed end to the discharge end. Referring to Figure 2, the area between each disc is effectively an individual grinding chamber, and the grinding medium is set in motion by the rotation of the discs, which accelerate the medium toward the shell. This action is most pronounced close to the discs. The medium flows back toward the shaft in the zone near the midpoint between the discs, creating a circulation of the grinding medium between each pair of discs.

[0005] The grinding discs are usually manufactured from rubber which is applied to the exterior of an internal metal reinforcing frame. The reinforcing frame includes a central aperture with holes drilled about the aperture to mount the disc to a reusable hub. The hub mounts the disc to the driveshaft. The metal reinforcing frame is of a smaller diameter than the rubber, so that the peripheral region of the manufactured disc is entirely formed from rubber. [0006] Over time, the rubber material wears away. This has the effect of reducing the efficiency of the grinding mill. From time to time the mill must be stopped and disassembled to replace the grinding discs resulting in down time of the mill and potential disruption to related mineral processing stages that occur upstream and downstream of the grinding mill.

Summary

[0007] In a first aspect there is provided a grinding disc for a grinding machine including:

- a support member, the support member includes a central aperture; and

- a rim member,

wherein the rim member is mounted to the support member and surrounds the support member. [0008] In one embodiment, the grinding disc further includes at least one region of elastomeric material.

[0009] In one embodiment, the elastomeric material is affixed to the support member.

[0010] In one embodiment, the rim member is formed from a harder material than the support member.

[0011] In one embodiment, the rim member is formed from white cast iron.

[0012] In one embodiment, the rim member is a circumferential ring. [0013] In one embodiment, the rim member includes formations which positively engage with the support member to transmit torque from the support member to the rim member.

[0014] In one embodiment, the grinding disc further includes a clamp arrangement which clamps the rim member to the support member.

[0015] In one embodiment, the support member is formed from a mild steel material. [0016] In a second aspect there is provided a grinding disc for a grinding machine including:

a support member, the support member includes a central aperture;

at least one region of elastomeric material is affixed to the support member; and a number of objects are embedded in the elastomeric material, the objects being formed from a material of a hardness which is greater than the hardness of the elastomeric material.

[0017] In one embodiment, the objects are formed from a ceramic material. [0018] In one embodiment, the ceramic material has a Knoop hardness of greater than 1300GPa.

[0019] In one embodiment, the ceramic material has a Knoop hardness of about 1400GPa

[0020] In one embodiment, the objects are generally spherical or cylindrical. [0021] In one embodiment, the objects have a diameter of between 6mm and 50 mm.

[0022] In one embodiment, objects have a diameter of approximately 10mm. [0023] In one embodiment, the objects are embedded in a region around the periphery of the grinding disc.

[0024] In one embodiment, the grinding disc includes a series of apertures and the objects are embedded in regions around the periphery of the apertures.

[0025] In a third aspect, there is provided a grinding machine including at least one grinding disc in accordance with the first aspect.

[0026] In one embodiment, the grinding machine is a stirred-medium grinding mill.

[0027] In one embodiment, a plurality of grinding discs are coupled to a horizontally oriented driveshaft. [0028] Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of inventions disclosed.

Brief Description of the Drawings

[0029] An embodiment will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0030] Figure 1 shows grinding discs in a prior art IsaMill™ type mill, one of which is in the process of being pushed into place along a drive shaft;

[0031] Figure 2 is a schematic diagram showing the principle of operation of an IsaMill™ type mill;

[0032] Figure 3 shows a partially manufactured grinding disc, before the step of applying elastomeric material in accordance with the present disclosure;

[0033] Figure 4 is a cross sectional view along the line A-A of Figure 3;

[0034] Figure 5 is an enlarged view of detail B of Figure 4;

[0035] Figure 6 shows the frame of the grinding disc of Figure 3;

[0036] Figure 7 shows the clamping ring of the grinding disc of Figure 3;

[0037] Figure 8 shows the wear ring of the grinding disc of Figure 3;

[0038] Figure 9 is a cross sectional view along the line B-B of Figure 8;

[0039] Figure 10 is a perspective view of the partially assembled grinding disc of Figure 3;

[0040] Figure 11 is a cross-sectional view similar to the view in Figure 5 but after the step of applying elastomeric material to the grinding disc has been carried out;

[0041] Figure 12 is a front view of an alternative embodiment of a grinding disc; and

[0042] Figure 13 is a cross sectional view along the line A-A of figure 12. Detailed Description

[0043] Referring to Figure 3, a partially manufactured grinding disc is shown including a support member in the form of a frame 1 and a rim member in the form of a wear ring 3. The wear ring 3 is mounted to the frame 1 and is held in place by a clamp arrangement formed from a removable clamp ring 2 and a backing ring 4 (visible in Figure 5). The backing ring 4 is permanently attached to the frame 1 by spot welds. The clamp ring 2 is removably attached to the frame 1 by a series of bolts which pass through apertures provided in the clamping ring and which screw into corresponding threaded holes provided in the frame 1.

[0044] The frame 1 includes a central aperture 11 which is surrounded by a series of holes 12 which are arranged to mount the frame 1 to a reusable hub (not shown in Figure 3 but labelled B in Figure 1) in a known fashion. The frame 1 also includes kidney shaped apertures 14 which are provided to allow passage of mill contents through the disc in use, again in a known fashion.

[0045] The frame 1 is formed from mild steel. The wear ring 3 is formed from high chrome white cast iron such as A05, A61 or A300 alloys available from Weir Minerals www.weirminerals.com. White cast iron contains carbides (for example chromium or niobium carbides) and is resistant to wear.

[0046] Referring to Figure 6, the frame 1 includes a series of five notches 16 provided around its periphery. Referring to Figure 8, the wear ring 3 includes a central rib 31 which includes a series of formations in the form of five projections 32. When assembled together, the projections 32 of the wear ring 3 sit in notches 16 of the frame 1. In use, the engagement of the projections 32 in the notches 16 enables full torque to be transmitted from the frame 1 to the wear ring 3 without the need to rely on the strength of the rubber spanning the join between the frame 1 and the wear ring 3 or relying on the strength of the clamp ring arrangement. In other embodiments, the wear ring can be fastened by a different arrangement or number of interfitting projections and recesses in use to join it to the frame. [0047] After the wear ring 3 is clamped in place on the frame 1, the resulting assembly is moulded over with an elastomeric material in the form of rubber 5. As can be seen in Figure 9, the region of rubber 5 overlies the clamping arrangement, thus preventing any loosening of the clamping bolts. The rubber extends for the width of the outer thickness of wear ring 3 and extends across the apertures 14. The apertures 14 become partly filled with rubber around their edges but they are not completely filled to leave slots for the passage of ore slurry through the grinding disc and along the mill in the usual fashion. The side faces and outer face of the wear ring 3 remain exposed.

[0048] Grinding discs according to the embodiment above have superior wear resistance characteristics which result in longer intervals between maintenance operations on a mill to replace worn grinding discs. [0049] Furthermore, the provision of a separate wear ring leads to the ability to fine tune the disc to the mill through the ability to change the carbide alloy grade of the material used to form the wear ring to the best suited material with respect to wear resistance for each particular mill application. The change of carbide is simply a matter of changing the wear ring.

[0050] The inclusion of projections and slots which engage the wear ring to the frame, along with the associated clamping arrangement provided, allows the carbide wear rings to be made without the need for machining, which can still be securely attached to the frame for adequate torque transmission from the driveshaft.

[0051] The disc weight may be increased with respect to prior art grinding discs, but the weight is still within the tolerance of most IsaMill™ shaft and bearing assemblies. Furthermore, the outer peripheral tip speed may be increased beyond the maximum allowable tip speed of elastomers.

[0052] The shape of the wear ring allows the use of processes such as centrifugal casting to produce a wear ring with a hard outermost later. The wear ring can also be made of A300 (containing niobium carbides) and other higher grade carbide materials prolonging the life even further.

[0053] The rubber mould process is unchanged from the prior art as the assembled disc is installed to the mould prior to moulding. The rubber-to-carbide interface and the coverage of the clamp rings means no chance of the clamp ring loosening.

[0054] Referring now to figures 12 and 13, an alternative approach will now be described. A metal support frame 100 (shown in dotted outline) is formed with a series of kidney shaped apertures 1 14 (also shown in dotted outline). The support frame is then introduced into a mould and raw elastomeric material is introduced into the mould along with a number of ceramic spheres. The ceramic spheres are introduced at regions in the mould around the periphery of the support frame and also around the periphery of the kidney shaped apertures. The elastomeric material is then cured in the mould in a known fashion. The resultant grinding disc has ceramic spheres located in a region 200 around the periphery of the grinding disc and also in region 214 around the periphery of each kidney shaped apertures.

[0055] The ceramic spheres are formed from a material which has a hardness greater than the hardness of the elastomeric material and also of a hardness greater than the hardness of the grinding media that is used in the mill. In one embodiment the material used is of a Knoop hardness of about 1400GPa. A suitable material is an alumina oxide material known as FG-995 available from CoorsTek, Inc. of Colorada, USA (www.coorstek.com). [0056] The ceramic spheres can be selected in a size range of between 6mm and

50mm and are preferably of about 10mm in diameter. Using this approach allows the use of pre-existing moulds to form the grinding discs. In other emodiments ceramic rods may be used in place of ceramic spheres. The rods are preferably of cylindrical cross section with a diameter of between 6mm to 50mm. The length of the rods is equal to or greater than their diameter.

[0057] In the foregoing description of preferred embodiments, specific terminology has been resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "front" and "rear", "inner" and "outer", "above", "below", "upper" and "lower" and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

[0058] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0059] In this specification, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

[0060] In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

[0061] Furthermore, invention(s) have been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.