Abstract:
A method of fabricating a liner component for a grinding mill is described, the method including the steps of: providing a plate of hard material; cutting the plate to form a plurality of inserts, at least some of the inserts including a formation for mechanically engaging with a body of a resilient material; arranging the inserts in a mould, and—adding resilient material to the mould to form a resilient material body around the inserts to thereby form the liner component.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to crushing, grinding, or comminution methods for processing materials such as mineral ores, rock and other materials, and more particularly to the fabrication of apparatus for use in such processing. 
       BACKGROUND ART 
       [0002]    Grinding mills are one form of apparatus used for processing materials as described above. Typically 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 treatment chamber into which the material to be processed is fed. 
         [0003]    In one form of milling known as SAG (semi autogenous grinding), a grinding medium such as balls or rods is fed to the treatment chamber with the material to be processed and the shell rotates. 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 rotation of the shell whereafter it falls towards the bottom of the shell under the influence of gravity. 
         [0004]    The inside surfaces of the mill are typically protected by an arrangement of wear components collectively referred to as a mill liner. The mill liner usually includes lifter bars spaced around the inner circumference of the mill. The lifter bars assist in lifting the charge inside the mill up the side of the shell as the shell rotates. Further, the mill liner often includes wear plates which are provided in between each lifter bar. The lifter bars or wear plates may be formed as a resilient body, with a number of wear resistant inserts embedded in the resilient material. The inserts are produced by casting of molten metals in a mould. 
         [0005]    Over time, the components of the mill liner wear away and require replacement. This necessitates that the mill be stopped for a period of time which causes the cessation of the grinding of material, and may also necessitate the shutting down of other machinery in a plant which works on the material produced by the mill. There is a continued need to provide mill liner components with improved longer service lives to reduce the mill stoppage time. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    In a first aspect there is provided a method of fabricating a liner component for a grinding mill, the method including the steps of:
       providing a plate of hard material;   cutting the plate to form a plurality of inserts, at least some of the inserts including a formation for mechanically engaging with a body of a resilient material;   arranging the inserts in a mould, and   adding resilient material to the mould to form a resilient material body around the inserts to thereby form the liner component.       
 
         [0011]    Formation of the inserts by cutting them from a plate makes it possible to prepare inserts with a finer microstructure when compared to the more coarse microstructures found in metal components that have been formed by casting. A fine microstructure may be found in metal plates that have been subjected to a rolling process during their formation. An insert with a fine microstructure has improved toughness properties when compared with an insert with a coarser microstructure, which leads to increased impact resistance. This leads to increased service life of the mill liner components, and reduced mill downtime for replacing worn liners. Thus, the economic performance of the mill, and associated minerals processing operations, is improved. 
         [0012]    In one embodiment, the method can further includes the step of applying heat and pressure to the contents of the mould to cure the resilient material to thereby form the body. 
         [0013]    In one embodiment, the method step of cutting the plate can include any of laser, plasma or oxy cutting. 
         [0014]    In one embodiment, the plate can be formed from steel. 
         [0015]    In one embodiment, the formation can include a hooked portion. 
         [0016]    In a second aspect there is provided a liner component for a grinding mill formed by the method of the first aspect. 
         [0017]    In one embodiment of the liner component, the inserts can be distributed along the length of the component at a regular pitch. 
         [0018]    In one embodiment of the liner component, the pitch can be less than 120 mm. 
         [0019]    In one embodiment of the liner component, the inserts can be of a thickness in the range of 10 mm to 100 mm. 
         [0020]    In one embodiment of the liner component, the inserts can be of a thickness of about 65 mm. 
         [0021]    In one embodiment of the liner component, the resilient material can include an elastomeric material. 
         [0022]    In a third aspect there is provided a liner component for a grinding mill, the component including:
       a generally elongate body;   a plurality of inserts associated with the body, the inserts being distributed along the length of the body; and   at least some of the inserts including a formation which engages mechanically with the body;       
 
         [0026]    wherein the inserts have a measured Charpy v-notch test toughness of more than 10 J. 
         [0027]    Mill liner components including hardened inserts with Charpy v-notch test values of 10 J or higher have significantly improved toughness properties to mill liner components which include inserts formed by casting, which may have a Charpy v-notch test value of around 2-3 J. This can provide significant improvements in the impact resistance of the mill liner, with a consequential increased service life leading to reduced mill downtime. 
         [0028]    In one embodiment of the liner component, the inserts can have a measured Charpy v-notch test toughness of between 10 J and 45 J. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0030]      FIG. 1  is a side view of an insert for a component of a mill liner according to an embodiment of the invention; 
           [0031]      FIG. 2  is a front view of the insert of  FIG. 1 ; 
           [0032]      FIG. 3  is a front view of a lifter bar according to an embodiment of the invention; 
           [0033]      FIG. 4  is an end view of the lifter bar of  FIG. 3 ; and 
           [0034]      FIG. 5  is a cross sectional view along the line A of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0035]    Referring to  FIGS. 1 and 2 , an insert  10  for a mill liner of a grinding mill is shown. The insert  10  has a major dimension generally indicated by arrow A and opposed major surfaces being planar side faces  12 ,  14 . Between the planes of these side faces  12 ,  14  there is provided a formation for mechanically engaging with adjacent resilient material. The formation includes a hooked portion  16  which has a free end  20  and which is joined to the remainder of the insert by way of a shank portion  18 . 
         [0036]    The insert  10  is formed by cutting the shape of the outline of the major faces  12 ,  14 , including the hooked portion  16  and shank  18  as shown in  FIG. 1 , from a plate of hardened steel. For example, such steel plate can be manufactured from Bisalloy® 450 which is available from Bisalloy Steels Pty Ltd, of Unanderra, New South Wales, Australia (www.bissalloy.com.au). The plate is cut by various available techniques, including laser, plasma or oxy cutting techniques. Other equivalent cutting techniques are also possible alternatives. It can be seen from  FIG. 1  that the outline of the insert  10  is a continuous outline with no closed sections, such as through-holes. This allows the laser cutting operation to be carried out with a continuous single cut, with no need to stop and start the laser or any need to reposition the workpiece between cutting operations. In the illustrated embodiment, the insert  10  has been cut from a plate of Bisalloy® that was 65 mm thick. Hence, the insert has a thickness of 65 mm between its major surfaces  12 ,  14 . Many other thicknesses of steel plate are possible. 
         [0037]    The hardened steel used for forming the inserts has a Charpy v-notch test hardness value of between 10 to 45 J at a test temperature of −40 C. In contrast, prior art inserts that are produced by casting of metal have a Charpy v-notch test toughness value of around 2 J. A higher toughness provides for an increased resistance to impact wear. 
         [0038]    The insert  10  and its method of formation finds use in the fabrication of components for a mill liner as will now be described. Referring to  FIGS. 3 to 5 , a component for a mill liner is shown in the form of a lifter bar  100 . The lifter bar includes a body  102  formed from an elastomeric material and a total of fifteen inserts  10  which are evenly distributed along the length of lifter bar  100  and which are associated with the lifter bar by being embedded into the elastomeric body  102  to create a composite structure. The inserts are distributed along the length of the lifter bar at a pitch of about 82 mm, with each insert being 65 mm thick and each being spaced from an adjacent insert by about a 17 mm thickness of elastomeric material. 
         [0039]    A channel  104  is embedded in the body  102  and is used to affix the assembled lifter bar  100  to the inside of the shell of a grinding mill using T-headed bolts in a known fashion. Thus, when installed, mounting surface  106  faces against the inside surface of the shell of the grinding mill. 
         [0040]    The lifter bar  100  is formed by placing fifteen inserts  10  into the bottom of a mould. A resilient material is then added to the mould and channel  104  is held at an upper region of the mould. In one example, the resilient material can be an elastomeric material, for instance a combination of a natural and synthetic rubber compounds. 
         [0041]    Prior to being introduced into the mould, the channel  104  is cleaned and primed. Once the steel inserts and the elastomer has been positioned in the mould, the contents of the mould are then simultaneously heated and compressed for a period of time to cause the elastomeric material to cure. The lifter bar  100  is removed hot from the mould and then allowed to cool. Subsequently the lifter bar is inspected ultrasonically for voids, and excess flashing of elastomeric material is trimmed away. 
         [0042]    As a result of the moulding process, a chemical bond is formed between the inserts  10  and the elastomeric material at the boundary  108  between these component parts. Furthermore, the hook  16  becomes mechanically engaged with the elastomeric material. The insert  10  cannot separate from the elastomeric body  102  without mechanical disruption to the lifter bar  100 . This mechanical engagement with the body provides additional resistance to separation of the inserts  10  from the body  102  as a result of the high stresses put on the lifter bar  100  during use. 
         [0043]    The hook  16  is joined to the remainder of insert  10  by way of a shank portion  18  and the hook  16  also includes a free end  20 . It can be seen that the shank portion  18  is disposed closer to the mounting surface  106  than the free end  20 . The reason for this is that, as the lifter bar wears away during use, material is lost from the inserts  10  as they gradually wear down. By providing the shank  18  low down within the lifter bar  100 , the shank  18  is one of the last parts of the insert  10  to wear away, thus maintaining a degree of mechanical engagement between the insert  10  and elastomeric body  102  and extending the service life of the lifter bar  100 . 
         [0044]    In use, a grinding media consisting of steel balls is agitated in the grinding mill along with the material being processed. The size of the steel balls is selected according to the task at hand, but typically ranges in size from about 50 mm to 140 mm in diameter. By providing inserts with a thickness of 65 mm, this means that multiple simultaneous ball impacts across the width of the exposed face of the insert are avoided, thereby prolonging the life of these components. Achieving the narrow width of such inserts is also more convenient and cost effective when produced by a cutting technique rather than trying to use a conventional casting process to produce sufficiently thin inserts, which are prone to breakage or shattering on impact from a steel ball. 
         [0045]    In the embodiment described above, the mill liner component was a lifter bar  100 . The invention can also be applied to other mill liner component such as shell flat liner wear plates. 
         [0046]    In the embodiment described above the insert was formed from a plate of hardened steel that was 65 mm thick. In other embodiments the inserts may be of other thicknesses and may be from 10 mm up to 100 mm thick. 
         [0047]    In the embodiment described above the formation of the insert which mechanically engages with the body was provided in the form of a hooked portion. Similarly, other types of formation can be used to provide mechanical engagement such as formations with an “L” shaped profile, “T” shaped profile, some sharp spikes, and so on. Common to each of these shapes is that the formation can be produced by making a continuous outline of the insert and the formation in a single cutting operation with no need to stop and start the cutting instrument, and that the resulting formation cannot be pulled from the body without significant disruption to material forming the body due to an improved mechanical engagement between the insert and the material of the body. 
         [0048]    In the embodiment described above the resilient material was formed as an elastomeric body  102 , which comprised a mixture of natural and synthetic rubbers. In other embodiments, the body may be formed from another resilient material such as polyurethane, or a combination of polyurethane with other materials. 
         [0049]    Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated. 
         [0050]    Finally, it is to be appreciated that various alterations or additions may be made to the parts previously described without departing from the spirit or ambit of the present invention.