Abstract
In a method of making a lifter bar for use in a grinding mill, a refurbished lifter bar and a mould for producing the refurbished lifter bar, the lifter bar has a predetermined form and has a base member, and the method includes providing a mould having an interior space that conforms at least partially to the predetermined form, joining the mould and the base member together to form a cavity defined by the base member and the interior space, and filling the cavity with polymer and allowing the polymer to attach to the base member to construct a lifter bar having the predetermined form.
Claims
1. A refurbished lifter bar for use in a grinding mill, the refurbished lifter bar having a predetermined form and comprising: a base member, said base member comprising a worn lifter bar or a part of a worn lifter bar and having a different form than the predetermined form; and a new wearing surface, wherein the new wearing surface is formed of polyurethane by moulding to the base member to form the refurbished lifter bar having the predetermined form, wherein the new polyurethane wearing surface comprises at least part of an outer side surface of the lifter bar, which is toward the moving direction of the grinding mill, and at least part of an outer top surface of the refurbished lifter bar, which is opposite the base member, wherein the refurbished lifter bar is configured to be connected to the grinding mill by the base member, and wherein the refurbished lifter bar comprises a contact surface through which the base member and the new wearing surface are chemically bonded together to form the refurbished lifter bar, the contact surface including a worn wearing surface of the base member which is roughened and/or chemically treated.
2. The refurbished lifter bar according to claim 1, wherein the polyurethane comprises additives.
3. The refurbished lifter bar according to claim 2, wherein the additives include metal particles, ceramics or carbide.
4. The refurbished lifter bar according to claim 1, wherein the base member comprises a rail or profile that connects the refurbished lifter bar to the grinding mill.
5. The refurbished lifter bar according to claim 4, wherein the rail or profile is made from aluminium.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which
(2) FIG. 1 shows a longitudinal cross-section of a grinding mill;
(3) FIG. 2 is a view in cross-section of the grinding mill shown in FIG. 1 taken at line A-A;
(4) FIG. 3 shows a typical wear profile of a lifter bar;
(5) FIG. 4 shows a mould for moulding a new wearing surface to a worn lifter bar together with said worn lifter bar;
(6) FIG. 5 shows the mould and the worn lifter bar as shown in FIG. 4 such that the mould is filled with polymer; and
(7) FIG. 6 shows a mould with a reinforced surface together with the worn lifter bar.
DETAILED DESCRIPTION OF THE INVENTION
(8) FIG. 1 shows a longitudinal cross-section of a grinding mill 2 having an inner cylindrical wall which comprises lifter bars 1a, 1b, 1c attached to the cylindrical wall. Shell plates, wear plates or similar elements are preferably attached to the shell of the grinding mill in between said lifter bars 1a, 1b, 1c such that the lifter bars 1a, 1b, 1c and shell plates together protect the inner surface of the grinding mill 2 and wear is subjected to them. The grinding mill 2 rotates about its central axis in the direction indicated by arrow B in FIG. 2.
(9) FIG. 2 shows a view in cross-section of the grinding mill 2 shown in FIG. 1 taken at line A-A. The grinding mill 2 rotates in the direction indicated by arrow B. The lifter bars 1a, 1b, 1c are arranged such that they are around the cylindrical wall of the grinding mill 2. Lifter bar 1a, 1b, 1c comprises a rail, a profile or an insert element on the bottom of the lifter bar 1a, 1b, 1c. The lifter bar 1a, 1b, 1c is secured to the shell of the grinding mill 2 with fasteners such as bolts extending from the outer surface of the grinding mill 2 to the bottom of the lifter bar 1a, 1b, 1c securing the lifter bar 1a, 1b, 1c to the interior wall of the grinding mill 2. The rail, the profile or the insert element alone can be a base member of the lifter bar such that a predetermined form of the lifter bar 1a, 1b, 1c is moulded over it or the rail, the profile or the insert element can form a part of the base member such that a worn lifter bar 1b, a part of the worn lifter bar 1b or a lifter bar 1a having a different form than the predetermined form forms another part of the base member. The lifter bars 1a, 1b, 1c are typically made of rubber or elastomer and attached to the inner wall of the grinding mill 2 by bolt connection. Over time the upper and/or side surface of the lifter bar 1a, 1b, 1c wears and the wearing surface becomes uneven and the solid material is not lifted upwards inside the grinding mill 2 as effectively as with the new lifter bars 1a, 1c.
(10) FIG. 3 shows a typical wear profile of a worn lifter bar 1b. The outer surface 5 of the lifter bar 1a, 1b, 1c and especially the upper surface of the lifter bar 1a, 1b, 1c wears over time because of the impacts of the solid material that it carries and/or lifts upwards in the grinding mill 2. The upper surface comprises at least part of the top surface of the lifter bar as well as at least part of the side surface of the lifter bar which is toward the moving direction of the grinding mill 2. The outer surface 5 that wears over time is called wearing surface. As the wearing surface wears the lifting effect becomes less and the grinding mill 2 becomes ineffective and the lifter bar 1a, 1b, 1c has to be changed and replaced by a new lifter bar.
(11) FIG. 4 shows a mould 3 for moulding a new wearing surface 8 to a worn lifter bar 1b and said worn lifter bar 1b. The mould 3 is preferably made of sheet metal by bowing such that a new unused lifter bar 1a is used as a model for the mould. The mould 3 can be made according to new dimensions without having an existing lifter bar 1a as a model. The mould comprises plurality of walls for connecting the mould 3 to the base member of the lifter bar 1a, 1b, which said plurality of walls define an interior space 4a. The mould also comprises an opening (not shown in figure) for feeding polymer into said interior space 4a. When the lifter bar 1a has been in use for example six months the wearing surface of the lifter bar 1a has worn such that the lifter bar 1a, 1b, 1c has to be changed for a new one. The new lifter bar 1a can then be made by using the mould 3 for moulding a new wearing surface to the used lifter bar 1b. The aluminium profile or rail of the used lifter bar 1b from which the lifter bar is attached to the shell of the grinding mill 2 can be used again as well as the bottom part of the worn lifter bar 1b and only a new wearing surface 8 is moulded. The worn lifter bar 1b is first treated such that the new wearing surface 8 to be moulded will form a bond with the worn lifter bar 1b. The worn wearing surface is preferably heat treated such there isn't any moisture in the worn wearing surface of the worn lifter bar 1b. The worn wearing surface may also be roughened and/or chemically treated so that the chemical bond between the worn wearing surface and the new wearing surface 8 will be created. This bond is created in the contact surface 6 between the worn lifter bar 1b and the new wearing surface 8. The mould 3 is then preferably attached in a conventional way to the used worn lifter bar 1b such that at least part of the used lifter bar 1b is inside the mould 3 and such that the mould 3 and the base member of the lifter bar form a cavity 4b for the new wearing surface 8 to be moulded. The interior space 4a conforms at least partially to a predetermined form of the refurbished lifter bar 1c. Next step is to fill the cavity 4b in the mould 3 with polymer such as polyurethane to form a new wearing surface 8 to the lifter bar 1b. This is shown in FIG. 5. Polymer can comprise ceramics and/or carbides and/or other additives to change the properties of the polymer. The polymer can also comprise metal particles. When the polymer is hardened the lifter bar having a new wearing surface 8 may be heat treated.
(12) FIG. 6 shows a mould 3 with a reinforced surface 7 for moulding a new wearing surface 8 to a worn lifter bar 1 and said worn lifter bar 1. The mould 3 can additionally comprise a reinforced surface 7 to be moulded on the wearing surface 5 of the lifter bar 1. The reinforced surface 7 is for example metal piece or some other element that stays in shape longer and doesn't wear that easily. The reinforced surface 7 may be attached to the mould 3 with a screw connection such that after the polymer is hardened and the mould 3 and the screw connection is be separated from it, the reinforced surface 7 is on the surface of the new wearing surface 8. The reinforced surface 7 may comprise a fin or fins which protrude from the reinforced surface 7 inside to the wearing surface 8.
(13) The mould for producing a refurbished lifter bar for use in a grinding mill as shown in FIGS. 4 to 6 comprise a plurality of walls for connecting the mould to a worn lifter bar and for defining a cavity in co-operation with an abraded surface of the worn lifter bar, said cavity conforming to a worn-away portion of an unused lifter bar, and an opening (not shown in the figures) for admitting a polymer into said cavity.
(14) 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.
