Abstract:
The invention relates to a shell plate, to method for making a shell plate and to a grinding mill for ore grinding. The shell plate is mountable to a shell of a grinding mill for grinding ore, said shell plate comprises a shell plate body having a first portion comprising a fixing surface for fixing the shell plate body to the shell and a second portion comprising a wear surface facing toward interior of the grinding mill, said first portion and said second portion forming a continuous shell plate body, the second portion comprises polyurethane such that the wear surface is made of polyurethane.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a shell plate, and more particularly to a shell plate as defined in the independent claim  1 . The invention further relates to a method for making a shell plate as defined in the independent claim  12  and to a grinding mill as defined in the independent claim  15 . 
       BACKGROUND OF THE INVENTION 
       [0002]    Grinding mills are used for processing hard solid material such that large solid material is grinded into smaller pieces. Lifting bars assist in lifting the solid material that is being processed in the drum as it rotates and the shell plates&#39; function is to protect the shell of the grinding mill. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    The shell plate according to the invention, the method for making a shell plate according to the invention and the grinding mill according to the invention are characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims. 
         [0004]    The solid material is crushed in a drum shaped shell mounted for rotation about its central axis in the grinding mill. The axis of the rotatable shell is generally horizontally arranged or slightly inclined towards one end in the grinding mill. The interior of the shell forms a treatment chamber and has a cylindrical wall. The inner surface of the chamber is plated with a lining for protecting the shell because the material to be processed is fed to the treatment chamber and grinding it causes wear in the chamber. The interior wall of the shell is equipped with lifter bars for lifting the material inside the shell along the rotation so that as the shell rotates the shell plates lift up the solid material along the inside wall of the shell to a point where gravity causes the solid material to fall down inside the shell and by falling down the solid material is crushed. In order to protect the shell of the grinding mill shell plates are arranged in between adjacent lifter bars. 
         [0005]    Lifter bars as well as shell plates extend from one end of the drum to another end and they are arranged in a short spacing adjacently along the cylindrical wall of the shell. The shell plates do not protrude from the shell wall as much as the lifter bars which assist in lifting the solid material. The shell plates have an outer surface and comprise a shell plate body having a fixing surface for connecting the shell plate to the shell of the grinding mill. The shell plate body has an outer surface comprising a fixing surface to be arranged against the shell and a wear surface facing toward interior of the grinding mill. The shell plate body comprise a first portion and a second portion forming a continuous shell plate body, said first portion comprises the fixing surface which is arranged against the shell when connected to the grinding mill. 
         [0006]    The shell plate is mountable to a shell of a grinding mill for grinding ore. The shell plate may be secured to the shell of the grinding mill such that the adjacent lifter bars interlock the shell plate to its place or the shell plate may have a fixing element embedded to the shell plate which forms part of the fixing surface of the shell plate. When mounted to the shell the fixing surface is arranged against the shell and the shell plate is secured to the shell through the fixing element in the shell plate or through adjacent lifter bars. When having a fixing element the shell plates are mechanically fastened to the inner surface of the shell with fastening means such as a bolt connection through the fixing element. When the shell plate is installed to the shell of the grinding mill the fixing surface of the shell plate body is faced against the inner surface of the shell of the grinding mill. 
         [0007]    A grinding mill for ore grinding comprises multiple shell plates arranged to a shell of the grinding mill, the shell plates being as described earlier. The shell plate is used in grinding mills having grinding energy per ton of ore of 1-30 kWh/t and preferably 3-20 kWh/t. The diameter of the grinding mill is 1-15 m, and most typically 1.5-10 m. The length of the grinding mill in horizontal direction is between 1 and 15 meter, and most typically from 2 to 8 m. Thickness of the shell of the grinding mill is 0.5-10 cm. Grinding mills can be for example SAG mills, AG mills, Ball mills, rod mills, scrubbers or regrinds. 
         [0008]    The grinding mill comprises multiple lifter bars arranged to the shell, which the lifter bars comprise a lifter bar body having a fixing surface for fixing the lifter bar to the shell and a wear surface facing toward interior of the grinding mill, the wear surface of the lifter bars and the wear surface of the shell plates comprise polyurethane. The grinding mill is arranged to grind input material of which at least 80% has particle size between 0.1-300 mm, preferably 1-250 mm and most preferably 80-220 mm to grinded output material of which 80% has particle size between 0.02-3 mm, preferably 0.05-2.5 mm and most preferably 0.2-2 mm. 
         [0009]    The grinding mill comprises a lifter bar arranged to the shell, which the lifter bar has a volume. The lifter bar further has an outer surface comprising a fixing surface to be arranged against the shell and a wear surface facing toward interior of the grinding mill. The lifter bar comprises a lifter bar body having an outer surface conforming the outer surface of the lifter bar and a fixing element for connecting the lifter bar to the shell of the grinding mill. The lifter bar body further comprising a first portion and a second portion forming a continuous lifter bar body, the fixing element is embedded to the first portion such that it forms part of the fixing surface of the lifter bar. The second portion is made of polyurethane and forms 35-85% of the volume of the lifter bar and the first portion of the lifter bar body is made of rubber or the first portion of the lifter bar body is made of other polyurethane than the polyurethane in the second portion of the lifter bar body. 
         [0010]    The shell plate comprises a shell plate body which has a first portion comprising a fixing surface for fixing the shell plate body to the shell and a second portion comprising a wear surface facing toward interior of the grinding mill, said first portion and said second portion forming a continuous shell plate body. The second portion comprises polyurethane such that the wear surface is made of polyurethane. 
         [0011]    The polyurethane in the context of this application means polyurethane material that may comprise additives, such as metal particles, ceramics or carbide. The polyurethane material comprises at least 50% and preferably at least 80% pure polyurethane the rest being additives and possible impurities. 
         [0012]    The polyurethane may comprise additives, such as metal particles, ceramics or carbide. 
         [0013]    In one embodiment of the shell plate the second portion is made of polyurethane. 
         [0014]    In another embodiment of the shell plate the first portion is made of polyurethane. 
         [0015]    In still another embodiment of the shell plate the first portion is made of recycled polyurethane. 
         [0016]    In still another embodiment of the shell plate the second portion is made of more wear resistant polyurethane than the first portion. 
         [0017]    In an embodiment of the shell plate the first portion comprises rubber. In another embodiment of the shell plate the first portion is made of rubber. The rubber may be recycled rubber. 
         [0018]    Between 40 to 80%, preferably between 45 to 70%, of the second portion of the shell plate body is polyurethane. The shell plate has a thickness between 3 to 20 cm, preferably between 4 to 15 cm. 
         [0019]    Method for making a shell plate as described earlier comprises steps of providing a mould for moulding the shell plate, adding polyurethane into the mould for forming the shell plate body. The polyurethane is in such a state that it is arranged to react in the mould and form a connection with a material of the first portion of the shell plate body and adding material into the mould for forming the first portion of the shell plate body such that the polyurethane is arranged to react in the mould with the material for forming a continuous shell plate body with the second portion of the shell plate body. Shell plates can be made with moulds made of sheet metal having a thickness between 0.1 to 10 mm, preferably less than 5 mm and most preferably 0.2-2 mm. 
         [0020]    In an embodiment of the method the step of adding material into the mould comprises adding material other than the polyurethane of the second portion into the mould for forming the first portion of the shell plate body. 
         [0021]    In another embodiment of the method the step of adding material into the mould comprises adding polyurethane into the mould for moulding the first portion of the shell plate body. 
         [0022]    When arranging polyurethane into the mould the polyurethane is in such a state that it is arranged to react in the mould and form a connection with a material of the first or the second portion of the shell plate body. 
         [0023]    The first portion of the shell plate body may be the same material as the second portion of the shell plate body or it may be different material than the second portion, for example rubber, recycled rubber or polyurethane having different properties than the polyurethane in the second portion of the shell plate body. The method may further comprise a step of adding other material than the polyurethane of the second portion into the mould for forming the first portion of the shell plate body, the material of the first portion is in such a state that it is arranged to react in the mould such that the polyurethane in the second portion and the material in the first portion form a connection with each other for forming a continuous shell plate body. 
         [0024]    In still another embodiment of the method the mould has an interior space and the step of adding material into the mould comprises adding material in a form of providing a base member. In this embodiment the method further comprises the steps of joining the mould and the base member together to form a cavity defined by the base member and the interior space; and the step of adding polyurethane comprises adding the polyurethane to fill the cavity with polyurethane. 
         [0025]    Effect of a shell plate comprising polyurethane is that the polyurethane needs less pressure and heat than other materials, such as rubber, and energy consumption can be reduced in manufacturing. Also the manufacturing process is easier because shell plate comprising polyurethane can be made using mould made from sheet metal. The shell plates can be retreated with new polyurethane when the wear surface has worn away. This retreatment can be made in smaller scale near to the factory so the need for transportation is less. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which 
           [0027]      FIG. 1  shows a grinding mill; 
           [0028]      FIG. 2  shows a cross section of the grinding mill in  FIG. 1 ; 
           [0029]      FIG. 3  shows a shell plate; and 
           [0030]      FIGS. 4 a , 4 b  and 4 c    show embodiments of a shell plate. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]      FIG. 1  shows a longitudinal cross-section of a horizontal grinding mill  3  having an inner shell  2  comprising a cylindrical wall which the shell  2  comprises lifter bars  11  mounted to the cylindrical wall of the shell  2  and in between the lifter bars  11  there are shell plates  1 . The grinding mill  3  rotates about its central axis x in a predetermined direction. The axis of the shell  2  is horizontally disposed or slightly inclined toward the other end of the shell  2 . The surface of the inner shell  2  is plated with shell plates  1  for protecting the drum against wear caused by grinding. The shell plates  1  is attached between the lifter bars  11  such that the lifter bars  11  and the shell plates  1  together protect the surface of the inner shell  2  of the grinding mill  3 . 
         [0032]      FIG. 2  shows a cross-section of the grinding mill  3  shown in  FIG. 1  taken along line A-A. The grinding mill  3  rotates in a predetermined direction around its axis indicated by x. The shell plates  1  and the lifter bars  11  are arranged such that they are mounted to the shell  2  of the grinding mill  3  extending in the longitudinal direction of the horizontally arranged grinding mill  3 . The shell plate  1  is secured to the shell  2  of the grinding mill  3  with fasteners such as bolts extending from the shell  2  of the grinding mill  3  to a fixing element embedded to the shell plate  1  or the shell plate  1  is secured with an interlocking effect provided by adjacent lifter bars  11 . 
         [0033]    The shell plate  1  has the same or substantially same degree of curvature as the shell  2  of the grinding mill  3 . The curvature is especially on the fixing surface  13  of the shell plate  1  but the same or similar curvature may be also on the wear surface  12  of the shell plate  1 . 
         [0034]    The shell plate  1  may be made of polyurethane such that the whole shell plate  1  is made of same polyurethane or the shell plate  1  may comprise rubber, which is preferably but not necessarily recycled rubber, and polyurethane such that the polyurethane forms at least part of the wear surface  12  of the shell plate  1 , or the shell plate may comprise polyurethane such that at least the wear surface  12  comprises new polyurethane and the rest of the shell plate  1  comprises recycled polyurethane or other polyurethane than that of the polyurethane in the wear surface  12 . The difference in polyurethanes comes from different properties in polyurethane, such as additives. 
         [0035]    The polyurethane may comprise additives, such as metal particles, ceramics or carbide. The parts of the shell plate body that are formed by polyurethane are mostly polyurethane and if there are the additives, the additives form smaller part than the polyurethane. 
         [0036]      FIG. 3  shows a shell plate  1  together with the adjacent lifter bars  11  arranged to a shell  2  of a grinding mill. The shell plate  1  comprises a shell plate body  10  which is divided into a first portion  10   a  comprising a fixing surface  13  for fixing the shell plate body  10  to the shell  2  and into a second portion  10   b  comprising a wear surface  12  facing toward interior of the grinding mill  3 . The first portion  10   a  and the second portion  10   b  form a continuous shell plate body  10 . At least part of the shell plate body  10  comprises polyurethane. The division into the first portion  10   a  and into the second portion  10   b  is imaginary when the shell plate body is completely made of polyurethane. When the shell plate body  10  comprises different materials for example such that polyurethane forms the second portion  10   b  of the shell plate body  10  and rubber forms the first portion  10   b  of the shell plate body  10  then the division is according to the materials. 
         [0037]    The shell plate  1  is in this embodiment mounted to the shell  2  of the grinding mill with an interlocking effect by adjacent lifter bars  11 . The shell plates  1  are first arranged against the shell  2  and then the lifter bars  11  are arranged such that part of the lifter bars  11  are on top of the side of the shell plates  1  so that part of the shell plate  1  is compressed between the shell  2  and the lifter bar  11  when the lifter bar  11  is secured to the shell with fixing means. 
         [0038]      FIG. 4 a    shows an embodiment of a shell plate  1  completely made of polyurethane. The completely means that the complete shell plate body  10  having a first portion  10   a  and a second portions  10   b  is made of polyurethane but the polyurethane may comprise additives as earlier described. The shell plate body  10  is now imaginarily dived into the first portion  10   a  and into the second portion  10   b  because the whole shell plate body  10  is of one material. The second portion  10   b  comprises a wear surface  12  and the first portion  10   a  comprises a fixing surface  13 . 
         [0039]      FIG. 4 b    shows an embodiment of the shell plate  1  comprising only polyurethane. First example of the embodiment shown in  FIG. 4 b    is such that the first portion  10   a  is made of polyurethane and the second portion  10   b  is made of other polyurethane than that of the first portion  10   a . The polyurethane in the first portion  10   a  and the polyurethane in the second portion  10   b  have different properties. The difference in properties may be for example such that the polyurethanes in different portions have difference in wear resistance for example such that the difference in wear resistance is 10%. Another example of the embodiment shown in  FIG. 4 b    is such that the first and the second portion  10   a ,  10   b  both are made of the same polyurethane but they are made at different times, i.e. not simultaneously. The other polyurethane may be for example recycled polyurethane. 
         [0040]      FIG. 4 c    shows an embodiment of a shell plate  1  comprising a first portion  10   a  made of rubber and a second portion  10   b  made of polyurethane. The first portion  10   a  made of rubber may be made of recycled rubber. 
         [0041]    The curvature of the shell plates  1  are exaggerated in  FIGS. 4 a -4 c    and in reality they are much less curved. Radius of the outer surface of the first portion could be for example between 0.3-10 m. Radius of the outer surface of second portion could be at least 0.3 m, preferably 0.3 m-10 m. The outer surface of the second portion could even be straight. The outer surface of the second portion  10   b  is the wear surface  12  of the shell plate  1  which is toward the interior of the grinding mill and the outer surface of the first portion  10   a  is the fixing surface  13 . The shell plates  1  are 3-20 cm thick, preferably 4-15 cm, for example 10 cm. The shell plates  1  comprise polyurethane 40-80% and preferably 45-70%. 
         [0042]    It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.