CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No.

62/053,982, filed on September 23, 2014, the entirety of which is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention is a pulp lifter with which a pulp chamber is associated having a transverse portion located in the pulp chamber for receiving at least part of a carryover portion of pulp directed through the pulp chamber.

BACKGROUND OF THE INVENTION

[0003] As is well known in the art, "carryover" of pulp in grinding mills (i.e., the incomplete discharge of pulp in pulp chambers within one revolution of a mill shell) is a serious problem. The extent of carryover may be as high as 50% or more, depending on the circumstances. Carryover imposes many costs on the operator.

[0004] As is well known in the art, the mill shell of a grinding mill defines a mill shell chamber upstream from the pulp chambers, which are located on a discharge end wall of the mill shell. When the grinding mill is operating, a charge is located in the mill shell chamber. The charge (i.e., ore, water, and grinding media, if grinding media are used) may fill the mill shell chamber up to a level indicated by a line "A" in Figs. 1A-1C. The direction of rotation of the mill shell is indicated by arrow "B" in Figs. 1A-1C. Typically, the ore is added into the grinding mill at an input end, and water is also added into the mill shell chamber. The charge is rotated as the mill shell of the grinding mill rotates, subjecting the ore to comminution and resulting in finely-ground ore particles that are included in a slurry or pulp that is passed to an output, or discharge, end of the grinding mill. As the mill shell rotates, the pulp chambers are also rotated, so each pulp chamber is successively immersed in the charge, and then raised above the charge. [0005] As each of the pulp chambers is immersed in the charge, the slurry or pulp flows into the pulp chamber. As can be seen in Figs. 1A-1C, depending on the amount of the charge in the mill shell chamber, a pulp chamber may be immersed (in whole or in part) as it is rotated from about the three o'clock position to about the nine o'clock position. When the pulp chambers are rotated to be above the charge, the pulp in them partially exits (i.e., is partially discharged). As a pulp chamber is moved from about the nine o'clock position to about the three o'clock position (i.e., above the line designated "A"), the pulp in that pulp chamber is directed by gravity toward the central hole by the pulp lifters that partially define that pulp chamber (i.e., one such pulp lifter being located on each side of the pulp chamber).

[0006] The pulp lifters also respectively support the pulp that is positioned on them respectively, and direct the pulp toward the central hole, when the pulp lifters are located above the charge.

[0007] As is well known in the art, the pulp chamber is covered with a discharge grate that permits the slurry or pulp to flow into the pulp chamber, when the pulp chamber is immersed. It will be understood that the top surface of the charge (identified as "A" in Figs. 1A-1C) typically varies significantly, depending on a number of parameters, and the level illustrated in Figs. 1A-1C is exemplary only. In addition, those skilled in the art would appreciate that the direction of rotation may be clockwise or counter-clockwise, depending on how the mill is manufactured and installed.

[0008] As is well known in the art, the pulp is a heterogeneous mixture of solid particles and water. Some finer particles may be suspended in the water. The ore and the ore particles typically include some waste material.

[0009] As can be seen in Figs. 1A-1C, a conventional discharge wall 20 in a typical grinding mill includes a number of pulp lifters 22 that extend inwardly (i.e., toward a central hole 24) from a shell wall or outer perimeter wall 26 of the mill shell. The pulp lifters 22 are at least partially mounted on an end wall 27 of the mill shell. The pulp lifters are intended to direct the pulp to the central hole 24, through which the pulp exits the grinding mill, when the pulp lifters are above the charge. In the example illustrated in Figs. 1A-1C, the pulp lifters 22 include shorter pulp lifters 22A and longer pulp lifters 22B. As is well known in the art, various arrangements of longer and shorter pulp lifters, and additional pulp lifters of intermediate length (not shown in Figs. 1A-1C), may be used. As is well known in the art, the optimum design of the pulp lifters depends on a number of parameters, e.g., the hardness of the ore, and the unit cost of energy inputs.

[0010] As is well known in the art, the pulp lifters 22, the shell wall 26, and the end wall 27 at least partially define pulp chambers 28 therebetween. The grates (not shown in Figs. 1A-1C) are located on the pulp chambers 28 to screen the flow of the pulp into the pulp chambers, i.e., to limit the solid particles in the pulp entering the pulp chambers to particles sized smaller than the apertures in the grates.

[0011] As is well known in the art, ideally, all the pulp in a particular pulp chamber should empty out of that pulp chamber 28 in the time that such pulp chamber 28 is moved from approximately the nine o'clock position to approximately the three o'clock position. That is, ideally, the pulp chamber should be emptied before it is next re-immersed in the charge. However, in practice, it often happens that a significant portion of the pulp does not exit the pulp chamber by the time that the pulp chamber has reached the three o'clock position. The pulp remaining in the pulp chamber at a point when the pulp should have been discharged therefrom is typically referred to as "carryover".

[0012] The movement of the pulp that is carried over is schematically illustrated in

Figs. 1A-1C. It will be understood that the illustrations in Figs. 1A-1C are based on computer-generated graphic simulations of the movement of the pulp in the pulp chambers as the mill shell rotates. (As will be described, embodiments of the invention are illustrated in the balance of the attached drawings.) The pulp includes solid particles and water.

[0013] It will also be understood that the majority of the solid particles in the pulp

(i.e., primarily ore that has been ground), which exit the pulp chambers via the central hole 24, are omitted from Figs. 1A-1C for clarity of illustration.

[0014] The reasons for carryover are well-known in the art. The relatively high mill shell rotation speed, e.g., about 10 rpm, is an important factor. This relatively fast rotation speed means that the discharge wall completes one rotation every six seconds. Accordingly, the pulp in a particular pulp chamber has only approximately three seconds, at most, to exit the pulp chamber 28. In addition, due to the rotation of the mill shell, the pulp in each pulp chamber is urged outwardly by centrifugal force, i.e., away from the central hole 24, effectively slowing the exit of the pulp from the pulp chamber as the pulp chamber moves from approximately the nine o'clock position to approximately the three o'clock position. [0015] From the foregoing, it can be seen that carryover undermines the production rate (i.e., tph of throughput), and requires energy to be wasted in rotating a mill shell in which much of the pulp is carryover. It is also believed that carryover subjects elements of the discharge wall and the mill shell to significant wear.

[0016] It has been determined that the movement of the pulp that is carried over, inside the pulp chamber, is distinctive, and generally consistent. For example, in Fig. 1A, pulp chambers 28A-28E are shown with solid particles 30 of the pulp therein. (It will be understood that only a portion of the particles that are carried over are illustrated in Figs. 1 A- 1C.) As can be seen in Fig. 1A, pulp chamber 28A is partially defined between the pulp lifters 122 and 122A, which are a pair of the trailing and leading pulp lifters respectively, relative to the direction of rotation. For the purposes hereof, the pulp chamber 28A is said to be associated with the leading pulp lifter 122A. When the pulp chamber 28A is in the one o'clock position, the solid particles 30 start to fall from a leading edge 132 of the pulp lifter 122 (Fig. 1A).

[0017] Although only certain of the solid particles 30 of the pulp that is carried over are illustrated, it will also be understood that the pulp includes water that is omitted from the drawings for clarity of illustration.

[0018] In pulp chamber 28B, partially defined between a pair of the pulp lifters identified in Fig. 1A for convenience as 122 A and 122B, the movement of the solid particles 30 toward a trailing side 134B of the leading pulp lifter 122B is more pronounced, because the pulp chamber 28B as illustrated is further along the clockwise rotation than the pulp chamber 28A. It will be understood that of the pair of pulp lifters that partially define the pulp chamber 28B, the pulp lifter 122A is the trailing pulp lifter, and the pulp lifter 122B is the leading pulp lifter. For the purposes hereof, the pulp chamber 28B is said to be associated with the leading pulp lifter 122B.

[0019] In Figs. 1A and IB, pulp chambers 28C, 28D, and 28E show the solid particles

30 progressively moved further onto the trailing edge of the leading pulp lifter in each pulp chamber respectively, due to the positions of the pulp chambers and the effects of gravity on the solid particles 30. In particular, in Figs. 1A and IB, it can be seen that, in the pulp chambers 28D, 28E (located at the three o'clock position, or almost at such position) the particles 30 that will be carryover are positioned in a middle area 35 of the trailing edge 134, i.e., they are spaced apart from the shell wall 26 by a distance 36 (Fig. IB).

[0020] As can be seen in Fig. 1C, the solid particles 30 move downwardly, to pile on the shell wall 26, when the pulp chambers are at or close to the six o'clock position.

[0021] It can be seen in Figs. 1A-1C that, although the solid particles 30 in a particular pulp chamber have been moved part of the distance toward the central hole when the pulp chambers are at approximately the three o'clock position or prior thereto, the particles 30 that are illustrated, i.e., the particles that become carryover, do not reach the central hole.

[0022] The particles 30 that are destined to become carryover in the illustrated example are, at one point while the mill shell rotates, generally located in the middle area 35 of the pulp lifter, i.e., they are temporarily located a relatively short distance from the central hole. From Figs. 1A and IB, it can be seen that the particles 30 have moved from the shell wall 26 to the middle area 35 as the pulp chamber 28 in which the particles 30 are located has moved from approximately the nine o'clock position to approximately the three o'clock position. However, because the particles 30 that are illustrated do not reach the central hole 24, they are returned to engage the shell wall 26 as the pulp chamber in which they are located moves further (clockwise) from approximately the three o'clock position, due to gravity. For these particles 30, the gains achieved during this rotation (i.e., the distances moved toward the central hole) are lost when the pulp chamber moves past the three o'clock position.

[0023] It will also be appreciated that, in the arrangement illustrated in Figs. 1A-1C, the carried-over solid particles 30 move to the outer wall 26 as the pulp chambers are successively moved to below the three o'clock position. Also, the carried-over particles are buried under particles in the pulp that flows into the pulp chamber, when the pulp chamber in which the carried-over particles are located is next re-immersed in the charge, as illustrated in Fig. 1C. The carried-over particles 30 will only exit the mill (i.e., via the central hole 24) in the next rotation if such solid particles reach the central hole during such rotation. From the foregoing, it can be seen that some of the pulp that is carried over to the subsequent rotation may be carried over for several subsequent rotations. SUMMARY OF THE INVENTION

[0024] There is a need for a pulp lifter that overcomes or mitigates one or more of the defects or disadvantages of the prior art. Such disadvantages or defects are not necessarily included in those listed above.

[0025] In its broad aspect, the invention provides a pulp lifter mountable on a discharge end wall of a grinding mill that includes a mill shell having an outer perimeter wall partially defining the discharge end wall and rotatable in a predetermined direction of rotation. The discharge end wall has a central hole therein through which pulp exits the mill shell. The pulp lifter includes an elongate body portion extending between an outer end thereof located at the outer perimeter wall and an inner end thereof located between the central hole and the outer perimeter wall, the body portion having a trailing side of the pulp lifter thereof relative to the direction of rotation that partially defines a pulp chamber associated with the pulp lifter. The body portion is rotated with the mill shell successively between: a discharge condition, in which the outer end is raised above the inner end to cause the pulp in the pulp chamber associated with the pulp lifter including the body portion to flow toward the central hole under the influence of gravity, and a non-discharge condition, in which the pulp in the pulp chamber associated with the pulp lifter including the body portion is not flowable toward the central hole under the influence of gravity. The pulp lifter also includes a transverse portion positioned in the pulp chamber associated with the pulp lifter and formed for receiving at least a part of a carryover portion of the pulp that remains in the pulp chamber associated with the pulp lifter when the body portion of the pulp lifter is moved to the non-discharge condition thereof.

[0026] In another of its aspects, the invention provides a discharge wall system positionable on a discharge end wall of a mill shell in a grinding mill. The mill shell is rotatable about an axis of rotation thereof in a predetermined direction of rotation. The discharge end wall is at least partially defined by an outer perimeter wall of the mill shell and includes a central hole through which pulp exits the mill shell. The discharge wall system includes a number of pulp lifters radially mounted on the discharge end wall. Pairs of adjacent ones of the pulp lifters each respectively include a leading one of the pulp lifters in the pair and a trailing one of the pulp lifters in the pair relative to the direction of rotation. Each pair partially defines a pulp chamber therebetween through which the pulp is at least partially directed to the central hole. Each pulp chamber is associated with the leading one of the pulp lifters in the pair partially defining the pulp chamber. Each pulp lifter includes an elongate body portion extending between an outer end thereof located at the outer perimeter wall and an inner end thereof located proximal to the central hole. The body portion has a trailing side relative to the direction of rotation partially defining the pulp chamber associated with the leading one of the pulp lifters in each pair. The body portion is movable by rotation of the mill shell between: a discharge condition, in which the outer end is raised above the inner end sufficiently to cause the pulp in the pulp chamber associated with the pulp lifter including the body portion to flow toward the central hole under the influence of gravity, and a non-discharge condition, in which the pulp in the pulp chamber associated with the pulp lifter including the body portion is not flowable toward the central hole under the influence of gravity.

The discharge wall system also includes a number of transverse portions, each transverse portion being positioned in each pulp chamber. Each transverse portion is formed for receiving at least a part of a carryover portion of the pulp remaining in each pulp chamber respectively when the body portion of the pulp lifter with which the pulp chamber is associated respectively is moved to the non-discharge condition.

[0027] In another of its aspects, the invention provides a grinding mill including a mill shell with a mill shell chamber therein and having an outer perimeter wall partially defining a discharge end wall of the mill shell. The discharge end wall has a central hole therein through which pulp exits the mill shell. The mill shell is rotatable about an axis of rotation. The grinding mill includes a discharge wall system positionable on the discharge end wall, including a number of pulp lifters mounted on the discharge end wall. Pairs of adjacent ones of the pulp lifters respectively include a leading one of the pulp lifters in the pair and a trailing one of the pulp lifters in the pair relative to the direction of rotation. Each pair partially defines a pulp chamber therebetween through which the pulp is at least partially directed to the central hole. Each pulp chamber is associated with the leading one of the pulp lifters in the pair partially defining the pulp chamber. Each pulp lifter includes an elongate body portion extending between an outer end thereof located at the outer perimeter wall and an inner end thereof located proximal to the central hole, the body portion having a trailing side relative to the direction of rotation partially defining the pulp chamber associated with the leading one of the pulp lifters in each pair. The body portion is rotatable with the mill shell successively between: a discharge condition, in which the outer end is raised above the inner end to cause the pulp in the pulp chamber associated with the pulp lifter including the body portion to flow toward the central hole, under the influence of gravity, and a non-discharge condition, in which the pulp in the pulp chamber associated with the pulp lifter including the body portion is not flowable toward the central hole under the influence of gravity.

The discharge wall system includes a number of transverse portions, each transverse portion being positioned in each pulp chamber. Each transverse portion is formed for receiving at least a part of a carryover portion of the pulp that remains in each pulp chamber respectively when the body portion of the leading one of the pulp lifters with which the pulp chamber is associated respectively is moved to the non-discharge condition thereof.

[0028] In yet another of its aspects, the invention provides a method of grinding ore into ore particles including providing a mill shell rotatable in a direction of rotation about an axis of rotation, the mill shell defining a mill shell chamber therein and having an outer perimeter wall partially defining a discharge end wall of the mill shell, the discharge end wall having a central hole therein through which pulp including the ore particles and water exits the mill shell, the mill shell being rotatable about an axis of rotation in a direction of rotation. Also, a number of pulp lifters mounted on the discharge end wall is provided. Pairs of adjacent ones of the pulp lifters including a leading one of the pulp lifters in each pair and a trailing one of the pulp lifters in each pair relative to the direction of rotation, each pair partially defining a pulp chamber therebetween through which the pulp is at least partially directed to the central hole. Each pulp chamber is associated with the leading one of the pulp lifters in the pair partially defining the pulp chamber. Each pulp lifter includes an elongate body portion extending between an outer end thereof located at the outer perimeter wall and an inner end thereof located proximal to the central hole, the body portion including a trailing side relative to the direction of rotation partially defining the pulp chamber associated with the leading one of the pulp lifters in each pair. Each body portion is successively positionable between: a discharge condition, in which the outer end is raised above the inner end to cause the pulp in the pulp chamber associated with the pulp lifter including the body portion to flow toward the central hole, under the influence of gravity, and a non-discharge condition, in which the pulp in the pulp chamber associated with the pulp lifter including the body portion is not flowable toward the central hole under the influence of gravity.

A number of transverse portions are provided, each transverse portion being positioned in each pulp chamber. Each transverse portion is formed for receiving at least a part of a carryover portion of the pulp remaining in each pulp chamber respectively when the body portion of the leading one of the pulp lifters with which the pulp chamber is associated respectively is in the non-discharge condition thereof. A charge including the ore and the water is added into the mill shell chamber. The mill shell is rotated about the axis of rotation thereof in the direction of rotation to grind the ore into the ore particles. The ore particles and the water are permitted to flow into the pulp chambers by immersing the pulp chambers therein respectively as the mill shell rotates. An exiting portion of the pulp in each pulp chamber respectively is permitted to exit the mill shell via the central hole, when the body portion of the leading one of the pulp lifters with which each pulp chamber is respectively associated is in the discharge condition. The part of the carryover portion of the pulp is retained in each transverse portion respectively, when the body portion of the leading one of the pulp lifters with which the transverse portion is associated is in the non-discharge condition. The part of the carryover portion is permitted to move from each transverse portion toward the central hole under the influence of gravity when the body portion of the leading pulp lifter with which the pulp chamber in which the transverse portion is positioned is associated is in the discharge condition.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention will be better understood with reference to the attached drawings, in which: [0030] Fig. 1A (also described previously) is a schematic illustration showing certain selected solid particles in selected pulp chambers located at first locations between the nine o'clock and three o'clock positions thereof and moving along a clockwise rotation path;

[0031] Fig. IB (also described previously) is a schematic illustration of the pulp chambers of Fig. 1A and the selected solid particles therein further along the rotation path;

[0032] Fig. 1C (also described previously) is a schematic illustration of the pulp chambers of Figs. 1A and IB and the selected solid particles therein further along the rotation path;

[0033] Fig. 2 is an elevation view of an embodiment of a discharge wall system of the invention including an embodiment of a pulp lifter assembly of the invention, drawn at a larger scale;

[0034] Fig. 3 A is an elevation view of a portion of the discharge wall system of Fig. 2 in which movement of selected solid particles in selected pulp chambers as the pulp chambers move along the rotation path is schematically illustrated, drawn at a larger scale;

[0035] Fig. 3B is an elevation view of the portion of the discharge wall system of Fig.

3A in which the selected pulp chambers are shown after further rotation in the clockwise direction;

[0036] Fig. 3C is another elevation view of the portion of the discharge wall system of Figs. 3A and 3B in which the selected pulp chambers are shown after further rotation in the clockwise direction;

[0037] Fig. 4 is a longitudinal cross-section of a embodiment of a grinding mill of the invention, drawn at a smaller scale;

[0038] Fig. 5A is a cross-section of a pulp chamber of the discharge wall system illustrated in Fig. 2 along line A-A in Fig. 3B; and

[0039] Fig. 5B is a cross-section of pulp lifters of the discharge wall system illustrated in Fig. 2 along line B-B in Fig. 3C. DETAILED DESCRIPTION

[0040] In the attached drawings, like reference numerals designate corresponding elements throughout. In particular, to simplify the description, the reference numerals previously used in Figs. 1A-1C are used again in connection with the description of the invention hereinafter, except that each such reference numeral is raised by 100 (or by whole number multiples thereof, as the case may be), where the elements described correspond to elements referred to above.

[0041] Reference is made to Figs. 2-5B to describe an embodiment of a pulp lifter of the invention indicated generally by the numeral 240. The pulp lifter 240 preferably is mountable on a discharge end wall 227 of a grinding mill 242 including a mill shell 244 (Fig. 4) with an outer perimeter wall 226 (Figs. 2-3C) partially defining the discharge end wall 227 and rotatable in a predetermined direction of rotation, designated by the arrow "Bi" in Figs. 2-3C. The discharge end wall 227 preferably includes a central hole 224 therein through which pulp (Figs. 3A-3C) exits the mill shell 244. Preferably, and as can be seen in Fig. 2, the pulp lifter 240 includes an elongate body portion 250 extending between an outer end 252 thereof located at the outer perimeter wall 226 and an inner end 254 thereof located between the central hole 224 and the outer perimeter wall 226. The body portion 250 preferably includes a trailing side 256 of the pulp lifter 240 thereof relative to the direction of rotation that partially defines a pulp chamber 228 associated with the pulp lifter 240. It is also preferred that the body portion 250 is rotated with the mill shell 244 successively between a discharge condition, in which the outer end 252 is raised above the inner end 254 to cause the pulp in the pulp chamber 228 associated with the pulp lifter 240 including the body portion 250 to flow generally toward the central hole 224 under the influence of gravity, and a non- discharge condition, in which the pulp in the pulp chamber associated with the pulp lifter 240 including the body portion 250 is not flowable toward the central hole 224 under the influence of gravity. Preferably, and as will be described, the pulp lifter 240 also includes a transverse portion 260 positioned in the pulp chamber 228 associated with the pulp lifter 240 and formed for receiving at least a part of a carryover portion of the pulp that remains in the pulp chamber associated with the pulp lifter when the body portion 250 of the pulp lifter 240 is moved to the non-discharge condition thereof.

[0042] As can be seen in Fig. 2, the inner end 254 of the body portion 250 of the pulp lifter 240 is located at an edge of an exit cone "EC" that directs the pulp out via the central hole. For the purposes hereof, the pulp chamber that is associated with the relatively long leading pulp lifter 240 is at least partially defined by the trailing side 256 of the leading pulp lifter 240 and a leading side 258 of the next trailing pulp lifter 240', relative to the direction of rotation. The pulp lifter 240' has a body portion 250' (Fig. 2).

[0043] Another pulp chamber 228X is also illustrated in Fig. 2. The pulp chamber

228X is associated with a leading pulp lifter which is designated 240X for convenience, and the trailing pulp lifter relative to the pulp chamber 228X is designated 240X', for clarity of illustration. That is, the pulp chamber 228X extends in the counter-clockwise direction from a trailing side 256X of a body portion 25 OX of the leading pulp lifter 240X to a leading side 258X of a body portion 250X of the trailing pulp lifter 240X, as indicated by line "L". It will be understood that, in the examples illustrated in Fig. 2, the pulp chamber 228X' located immediately counter-clockwise relative to the pulp lifter 240X' is associated with that pulp lifter. That is, as can be seen in Fig. 2, the pulp lifter 240X' is the leading pulp lifter relative to the pulp chamber 228X.

[0044] As can also be seen in Fig. 2, in one embodiment, one or more intermediate vanes 222 preferably are mounted to the discharge end wall 227, inside the pulp chamber 228. In the pulp chamber 228 as illustrated, the intermediate vanes include a longer vane 221 _L and a shorter vane 221 _s (Figs. 3A, 3C, 5B). Those skilled in the art would appreciate that a suitable number of intermediate vanes may be positioned in the pulp chamber, having any suitable lengths. Alternatively, the pulp chamber may not include any intermediate vanes. In each case, the optimum design of the pulp chambers is subject to a variety of factors known to those skilled in the art.

[0045] For the purposes hereof, it will be understood that the intermediate vanes are positioned in the pulp chamber, i.e., between the pair of the leading pulp lifter and the trailing pulp lifter, relative to the direction of rotation, for that pulp chamber. The intermediate vanes are shorter in length than the leading and trailing pulp lifters. It will also be understood that the intermediate vanes are therefore distinguished from the pulp lifters herein. As described above, the pulp lifters partially define the pulp chambers.

[0046] Those skilled in the art would also appreciate that the transverse portion 260 may have any suitable form. In one embodiment, the transverse portion 260 preferably includes an at least partially concave pocket 261 facing, or open, toward the central hole 224 (Fig. 3A). It is also preferred that the transverse portion 260 includes an arc segment 262 extending away from the direction of rotation between an inner end 264 thereof, at which the arc segment 262 joins the trailing side 256 of the body portion 250, and an outer end 266 thereof spaced apart from the trailing side 256, to at least partially define an opening 268 to the concave pocket 261.

[0047] In one embodiment, the transverse portion 260 preferably also includes an extension segment 270 extending between first and second ends thereof 271, 272, the first end 271 being connected with the outer end 266 of the arc segment 262, and the second end 272 being located substantially between the outer end 266 of the arc segment 262 and the central hole 224. In effect, the extension segment 270 extends the pocket 261. As can be seen in Fig. 3B, for example, the extension segment 270 serves the purpose of helping to hold the part of the carried-over particles in the pocket 261. That is, due to the extension segment 270, more particles can be retained in the pocket 261.

[0048] Preferably, and as can be seen in Fig. 3A, the arc segment 262 of the transverse portion 260 is located a preselected distance "D" apart from the central hole 224. Preferably, the preselected distance "D" is selected so that the part of the carryover portion retained in the transverse portion 260 of the pulp lifter 240 is flowable toward the central hole 224 when the body portion 250 is in the discharge condition. As will be described, the transverse portion preferably is positioned sufficiently proximal to the central hole that, when the body portion of the pulp lifter with which the relevant pulp chamber is associated is in the non-discharge condition, the part of the carried-over proportion of the pulp moves to the central hole 224, and exits the mill shell. In this way, carryover of the pulp for more than one rotation is minimized or mitigated.

[0049] As can be seen in Fig. 3B, the arc segment 262 is positioned for retaining the part of the carryover portion when the pulp lifter 240 is in the non-discharge condition and to permit the part of the carryover portion to move toward the central hole 224 under the influence of gravity when the pulp lifter 240 is in the discharge condition. In Fig. 3A, the body portion 250 of the pulp lifter 240 is shown as being in the discharge condition thereof. Those skilled in the art would appreciate that, when the transverse portion 260 is positioned relative to the central hole 224 as illustrated in Fig. 3A, any of the pulp that had been positioned in the concave pocket 261 falls from the pocket 261 due to gravity. [0050] As can be seen in Fig. 3B, the transverse portion 260 is positioned relative to the central hole 224 so that the transverse portion 260 catches the part of the carryover portion before it reaches the outer perimeter wall 226. The particles that are the part of the carryover portion that is received in the transverse portion are identified by the reference numeral 23 OA in Fig. 3B for convenience.

[0051] Preferably, an embodiment of a discharge wall system 274 of the invention includes a number of the pulp lifters 240 mounted on the discharge end wall 227 (Fig. 2).

[0052] The movement of certain solid particles identified generally by the reference numeral 230 in the pulp chamber 228 is schematically illustrated in Figs. 3A-3C. In Figs. 3A-3C, the mill shell 226 is rotated in the direction indicated by arrow "Bi". Other solid particles 230A, located in another pulp chamber identified for convenience by the reference numeral 228A, are also schematically illustrated in Figs. 3A-3C. (It will be understood that the other solid particles that would be present in operation, whether carryover or not, are omitted from Figs. 3A-3C for clarity of illustration.) The pulp chamber 228 is partially defined by the leading pulp lifter 240. The pulp chamber 228 is associated with the pulp lifter 240, which is leading, relative to the direction of rotation, with respect to the associated pulp chamber 228. The pulp chamber 228 is also partially defined by the trailing pulp lifter 240'.

[0053] For example, in Fig. 3A, the pulp chamber 228 (described above, as illustrated in Fig. 2) is located generally between the twelve o'clock and one o'clock positions. Because of the orientation of the pulp chamber 228 relative to the central hole 224 and the body portions 250, 250' of the pulp lifters 240, 240', the solid particles 230 fall (i.e., under the influence of gravity, in the direction indicated by arrow "C" in Fig. 3 A) from a leading side 268 of the intermediate vane 221 _L to the trailing side 256 of the body portion 250 of the pulp lifter 240.

[0054] In Fig. 3A, a body portion 250A of a pulp lifter 240A is shown positioned at approximately the three o'clock position. At this point, solid particles 230A are located on a trailing side 256A of the body portion 25 OA of the pulp lifter 240A. Specifically, when the pulp lifter 240A is approximately at the three o'clock position, the particles 230 are located a relatively short distance "Y" from the center of the central hole 224 (Fig. 3A). A pulp chamber 228A is associated with the leading pulp lifter 240A. The pulp lifter 240 is the trailing pulp lifter relative to the pulp chamber 228A. The pulp lifter 240A preferably includes a transverse portion 260A that is positioned in the pulp chamber 228A. The transverse portion 260A preferably defines a concave pocket 261A.

[0055] It can be seen in Fig. 3A that the particles 230A will be carryover.

[0056] As noted above, because the mill shell is rotating relatively rapidly, the particles 230 will, when the body portion 250 is in the three o'clock position, be located in a position similar to that of the particles 230A illustrated in Fig. 3A, i.e., spaced apart from the central hole by approximately the distance "Y". Accordingly, and as shown in Fig. 3B, the particles 230 will also become carryover.

[0057] In Fig. 3B, the pulp chambers 228, 228A are shown located at approximately the four o'clock position and the five o'clock position, respectively. In Fig. 3B, the body portions 250, 250' of the pulp lifters 240, 240' are at the four o'clock and the six o'clock positions respectively, i.e., both of the body portions are in non-discharge conditions. As can be seen in Fig. 3B, when the pulp chamber 228 is in such position, the solid particles 230 tend to slide down the trailing side 256 of the body portion 250 of the pulp lifter 240 (i.e., in the direction indicated by arrow "E" in Fig. 3B), under the influence of gravity. In Fig. 3B it can be seen that, as the pulp lifter 240 moves toward the six o'clock position, the particles 230 tend to fall or slide into the concave pocket 261.

[0058] The transverse portion 260 is described herein as receiving and retaining at least the part of the carryover portion, and not necessarily the entire carryover portion, because in practice, some of the carryover portion may not be retained in the transverse portion. However, as can be seen in Figs. 2-3C, the transverse portion is formed and positioned so that it may retain at least a substantial part of the carryover portion of the pulp. Accordingly, as a practical matter, some of the carryover portion may not be caught or received by the transverse portion 260. However, for clarity of illustration, only the particles 230 and 230A that are ultimately retained in the transverse portions 260, 260A are shown.

[0059] In Fig. 3B, the solid particles 230A in the pulp chamber 228A are shown as having accumulated in the pocket 261 A, due to the influence of gravity as the pulp lifter 240A was rotated from approximately the three o'clock position to approximately the six o'clock position. [0060] It will also be understood that, as the body portions 250, 250A of the pulp lifters 240, 240A are moved from approximately the six o'clock position to approximately the nine o'clock position respectively, the solid particles 230, 230A remain in the respective pockets 261, 261A of the respective transverse portions in the pulp chambers 228, 228A. However, as illustrated in Fig. 3C, once the body portion 250 of the pulp lifter 240 is at the nine o'clock position and further rotated in the clockwise direction, the solid particles 230 tend to empty out of the pocket 261.

[0061] It will be understood that the pulp (the particles) that flows into the pulp chambers as the pulp chambers move from approximately the three o'clock position to approximately the nine o'clock position (i.e., as the pulp chambers are successively immersed in the charge), and subsequently exits therefrom, is omitted from Figs. 3A-3C for clarity of illustration.

[0062] The manner in which the solid particles 230, 230A are positioned by the transverse portions 260, 260A for exit from the pulp chambers 228, 228A via the central hole 224 can be seen in Fig. 3C.

[0063] In Fig. 3C, the body portion 250 of the pulp lifter 240 is shown at approximately the ten o'clock position. The body portion 250' of the pulp lifter 240' is shown at approximately the nine o'clock position. As illustrated in Fig. 3C, the particles 230 are falling out of the pocket 261 (i.e., under the influence of gravity), in the direction indicated by arrows "F". It can be seen that such particles will accumulate on a leading edge 258' of the body portion 250', generally at an intermediate location designated "W" in Fig. 3C.

[0064] The location "W" is spaced apart from the center of the central hole 224 by a distance "Z".

[0065] It will be understood that the particles 230A that had been received in the transition portion 260A (i.e., upon the body portion 250A being located approximately in the six o'clock position, and subsequently) had fallen out of the transition portion 260A when the body portion 250A was approximately at the ten o'clock position. Under the influence of gravity, the particles 23 OA fell onto the leading side 258 of the body portion 250. Further rotation in the direction of rotation (indicated by arrow "Bi" in Fig. 3C) causes the particles 230A to move further downwardly on the leading side 258, to the location (identified as "G" in Fig. 3C) where the particles 230A are located as illustrated in Fig. 3C. As can be seen in Fig. 3C, at this point in the rotation of the body portion 250A, the particles 230A are about to fall into the central hole 224, as schematically represented by arrow "H".

[0066] From the foregoing, it can be seen that the particles 23 OA will not be carried over further. Those skilled in the art would appreciate that the particles 230 will also be positioned to exit via the central hole when the body portion 250 is slightly past the twelve o'clock position, i.e., it can be seen that the particles 230 also will not be carried over further for another rotation. Accordingly, due to the transverse portions and their location relative to the central hole 224, the carryover particles exit the mill shell after approximately one rotation of the discharge end wall.

[0067] In one embodiment, a discharge wall system 274 (Figs. 2, 4) preferably is positionable on the discharge end wall 227 of the mill shell 244 in the grinding mill 242. Preferably, the discharge wall system 274 includes a number of pulp lifters 240 radially mounted on the discharge end wall 227. Pairs of adjacent ones of the pulp lifters 240 each respectively include a leading one of the pulp lifters in the pair and a trailing one of the pulp lifters in the pair relative to the direction of rotation of the mill shell 244. Each pair partially defines the pulp chamber 228 therebetween through which the pulp is at least partially directed to the central hole 224. Each pulp chamber 228 is associated with the leading one of the pulp lifters in the pair partially defining the pulp chamber, as described above. It is also preferred that each pulp lifter 240 includes the elongate body portion 250 thereof, extending between the outer end 252 thereof located at the outer perimeter wall 226 and the inner end 254 thereof located proximal to the central hole 224. The body portion 250 includes the trailing side 256 relative to the direction of rotation partially defining the pulp chamber associated with the leading one of the pulp lifters in each pair. The body portion 250 is movable by rotation of the mill shell 244 between: the discharge condition, in which the outer end 252 thereof is raised above the inner end 254 thereof sufficiently to cause the pulp in the pulp chamber associated with the pulp lifter 240 that includes the body portion 250 to flow toward the central hole 224 under the influence of gravity, and the non-discharge condition, in which the pulp in the pulp chamber associated with the pulp lifter 240 that includes the body portion 250 is not flowable toward the central hole under the influence of gravity. It is also preferred that the discharge wall system 274 includes a number of the transverse portions 260 positioned in each pulp chamber 228. Preferably, each transverse portion 260 is formed for receiving at least the part of the carryover portion of the pulp remaining in each pulp chamber respectively when the body portion of the pulp lifter with which the pulp chamber is associated respectively is moved to the non-discharge condition.

[0068] As described above, it is preferred that the transverse portion 260 is at least partially located the preselected distance "D" apart from the central hole 224. The preselected distance "D" is selected so that the part of the carryover portion retained in the transverse portion 260 is movable into the central hole 224 under the influence of gravity when the body portion 250 is in the discharge condition thereof.

[0069] Preferably, the body portion of each pulp lifter is substantially straight and radially mounted on the discharge end wall relative to the axis of rotation, and the transverse portion extends from the trailing side of the body portion of the leading pulp lifter away from the direction of rotation.

[0070] It is also preferred that the discharge wall system 274 additionally includes a number of elongate intermediate vanes mounted onto the discharge end wall and located in the pulp chambers respectively, for guiding the pulp toward the central hole when the body portions of the pulp lifters partially defining the respective pulp chambers are in the discharge condition.

[0071] An embodiment of the grinding mill 242 of the invention preferably includes the discharge wall system 274, described above (Fig. 4). The mill shell 244 preferably defines a mill shell chamber 276 in which a charge 280 is located. The mill shell 244 is rotatable in the direction of rotation about its axis of rotation "AX". As indicated by arrow "I", the charge 280 preferably is added at the mill shell's intake end generally. The top surface of the charge 280 is identified by "Ai". The pulp moves through discharge grates 282 into a pulp chamber identified as 228L for convenience. The movement of the pulp through the discharge grates 282 is schematically represented by arrows "J". (The transverse portions are omitted from Fig. 4 for clarity of illustration.) The pulp chamber that is raised above the charge is identified as 228u for convenience. As described above, when the pulp chamber is raised to positions above the charge 280, the pulp exits the mill shell 244 via the central hole 224, as indicated by arrow "K". It will be understood that such exiting pulp includes the part of the carryover portion retained in the transverse portions.

INDUSTRIAL APPLICABILITY

[0072] In use, an embodiment of a method of the invention of grinding ore into ore particles includes providing the mill shell rotatable in a direction of rotation about an axis of rotation, the mill shell defining the mill shell chamber 276 (Fig. 4) therein and having the outer perimeter wall 226 partially defining the discharge end wall 227 of the mill shell 244. The discharge end wall has the central hole 224 therein through which pulp including the ore particles and water exits the mill shell 244, the mill shell being rotatable about the axis of rotation in the direction of rotation. A number of pulp lifters is provided, mounted on the discharge end wall 227. Pairs of adjacent ones of the pulp lifters include the leading one of the pulp lifters in the pair and the trailing one of the pulp lifters in the pair relative to the direction of rotation. Each pair partially defines the pulp chamber therebetween through which the pulp is at least partially directed to the central hole. Each pulp chamber is associated with the leading one of the pulp lifters in the pair partially defining the pulp chamber. Each pulp lifter includes the elongate body portion 250 extending between the outer end thereof located at the outer perimeter wall and the inner end thereof located proximal to the central hole. The body portion includes the trailing side 256 relative to the direction of rotation partially defining the pulp chamber associated with the leading one of the pulp lifters in each pair. Each body portion 250 is successively positionable between: the discharge condition, in which the outer end is raised above the inner end to cause the pulp in the pulp chamber associated with the pulp lifter including the body portion to flow toward the central hole, under the influence of gravity, and the non-discharge condition, in which the pulp in the pulp chamber associated with the pulp lifter including the body portion is not flowable toward the central hole under the influence of gravity.

A number of transverse portions are provided. The transverse portions are positioned in each pulp chamber and formed for receiving at least a part of a carryover portion of the pulp remaining in each pulp chamber respectively when the body portion of the leading one of the pulp lifters with which the pulp chamber is associated respectively is in the non-discharge condition thereof. The charge, including the ore and the water, is added into the mill shell chamber 276. The mill shell is rotated about the axis of rotation thereof in the direction of rotation to grind the ore into the ore particles. The ore particles and the water are permitted to flow into the pulp chambers by immersing the pulp chambers therein respectively as the mill shell rotates. An exiting portion of the pulp in each pulp chamber respectively is permitted to exit the mill shell via the central hole, when the body portion of the leading one of the pulp lifters with which each pulp chamber is respectively associated is in the discharge condition. The part of the carryover portion of the pulp is retained in each transverse portion respectively, when the body portion of the leading one of the pulp lifters with which the transverse portion is associated is in the non-discharge condition. The part of the carryover portion is permitted to move from each transverse portion toward the central hole under the influence of gravity when the body portion of the leading pulp lifter with which the pulp chamber is associated is in the discharge condition.

[0073] Fig. 5A is a cross-section taken along line A-A in Fig. 3B, and Fig. 5B is a cross-section taken along line B-B in Fig. 3C. As can be seen in Fig. 5A, the pulp chamber 228 is partially defined by the discharge end wall 227 and the outer perimeter wall 226. The discharge grate 282 is included in Figs. 5A and 5B although discharge grates are omitted from Figs. 2-3C for clarity of illustration. The pulp chamber is also partially defined by the discharge grate 282. Apertures 284 of the discharge grates 282, through which the pulp is flowable into the pulp chamber 228, can be seen in Figs. 5A and 5B.

[0074] It will be appreciated by those skilled in the art that the invention can take many forms, and that such forms are within the scope of the invention as claimed. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.