Discharge end wall system

Abstract

A discharge end wall system including a discharge wall assembly in which a number of pulp chambers are defined, and one or more plug elements at least partially occupying one or more of the pulp chambers.

Claims

1. A grinding mill comprising: a mill shell comprising a mill shell chamber therein and having an outer perimeter wall partially defining a discharge end wall of the mill shell, rotatable in a direction of rotation to produce a pulp including ore particles and water; the discharge end wall having a central hole therein through which the pulp exits the mill shell; a discharge end wall assembly comprising: a plurality of pulp lifters mounted on the discharge end wall, the pulp lifters being arranged in pairs of adjacent ones of the pulp lifters respectively comprising 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, a trailing edge surface of the leading one of the pulp lifters and a leading edge surface of the trailing one of the pulp lifters partially defining respective pulp chambers therebetween; at least one plug element located in at least one selected one of the pulp chambers, said at least one plug element being formed to occupy at least a portion of said at least one selected pulp chamber to define at least one reduced pulp chamber therein, the pulp chambers other than said at least one selected pulp chamber comprising a plurality of open pulp chambers, said at least one plug element being sized and located for optimal flow of the pulp through the open pulp chambers and said at least one reduced pulp chamber.

2. The grinding mill according to claim 1 in which said open pulp chambers comprise three quarters of the pulp chambers in the discharge end wall assembly.

3. The grinding mill according to claim 1 in which a proportion of the pulp chambers that comprise the open pulp chambers is selected for maximizing throughput of the pulp through the discharge end wall assembly.

4. A method of minimizing carryover of a pulp including ore particles and water in a discharge end wall assembly, the method comprising: (a) providing at least one plug element, to be positioned in at least a predetermined portion of at least one selected pulp chamber; (b) selecting said at least one selected pulp chamber, for receiving said at least one plug element; and (c) installing said at least one plug element in said at least one selected pulp chamber, to occupy the predetermined portion of said at least one selected pulp chamber.

5. A method of mitigating wear in a discharge end wall assembly comprising a discharge end wall of a mill shell, the mill shell being rotatable about an axis of rotation in a direction of rotation and defining a mill shell chamber therein in which a pulp including ore particles and water is produced by comminution, the discharge end wall assembly comprising a plurality of pulp chambers at least partially radially located relative to the axis of rotation, the method comprising the steps of: (a) providing at least one plug element, to be positioned in at least one selected pulp chamber, for occupying at least a portion of said at least one selected pulp chamber; (b) determining a proportion of the pulp chambers in the discharge end wall assembly that comprise a plurality of open pulp chambers, the proportion being determined for maximizing throughput of the pulp through the discharge end wall assembly; and (c) positioning said at least one plug element in said at least one selected pulp chamber, to define at least one reduced pulp chamber therein, wherein the pulp flows through the open pulp chambers and said at least one reduced pulp chamber as the discharge end wall assembly rotates.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood with reference to the attached drawings, in which:

(2) FIG. 1A (also described previously) is a schematic illustration showing certain selected solid particles in selected pulp chambers in a discharge wall assembly of the prior art located at first locations between the nine o'clock and three o'clock positions thereof and moving in a counter-clockwise rotation direction;

(3) FIG. 1B (also described previously) is an illustration of a portion of the discharge wall assembly of FIG. 1A, drawn at a larger scale;

(4) FIG. 1C (also described previously) is a schematic illustration of the pulp chambers of FIG. 1A and the selected solid particles therein further in the rotation direction;

(5) FIG. 1D (also described previously) is a schematic illustration of the pulp chambers of FIGS. 1A and 1B and the selected solid particles therein further in the rotation direction;

(6) FIG. 1E (also described previously) is a longitudinal cross-section of a conventional grinding mill, drawn at a smaller scale;

(7) FIG. 2A is an elevation view of an embodiment of a discharge end wall assembly of the invention including a number of partially occupied pulp chambers, drawn at a larger scale;

(8) FIG. 2B is a cross-section of the discharge end wall assembly of FIG. 2A, drawn at a larger scale;

(9) FIG. 2C is a longitudinal cross-section of an embodiment of a grinding mill of the invention, drawn at a smaller scale;

(10) FIG. 2D is a cross-section of one of the partially occupied pulp chambers of the discharge wall assembly of FIG. 2A, drawn at a larger scale;

(11) FIG. 3A is a portion of the discharge end wall assembly of FIG. 2A, drawn at a larger scale;

(12) FIG. 3B is a portion of an alternative embodiment of the discharge wall assembly of the invention; and

(13) FIG. 3C is a portion of another alternative embodiment of the discharge wall of the invention.

DETAILED DESCRIPTION

(14) 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-1E 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.

(15) Reference is made to FIGS. 2A-3A to describe an embodiment of a discharge end wall system of the invention indicated generally by the numeral 240. The discharge end wall system 240 preferably is mounted on a discharge end wall 227 of a mill shell 223 in a grinding mill 221. The mill shell 223 is rotatable about an axis of rotation “AX.sub.1” thereof in a direction of rotation to produce a pulp including ore particles and water. The discharge end wall 227 is partially defined by an outer perimeter wall 226 of the mill shell 223 and includes a central hole 224 through which the pulp exits the mill shell 223. In one embodiment, the discharge end wall system 240 preferably includes a discharge end wall assembly 242.

(16) As will be described, the discharge end wall assembly 242 preferably includes a number of pulp lifters 222 that are arranged on the discharge end wall 227 relative to the axis of rotation “AX.sub.1”. It is preferred that the pulp lifters 222 are arranged in pairs of adjacent ones thereof. Each pair respectively includes 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. As will also be described, a trailing edge surface 244 of the leading one of the pulp lifters 222 and a leading edge surface 246 of the trailing one of the pulp lifters partially define respective pulp chambers 228 therebetween (FIG. 3A).

(17) It is also preferred that the discharge end wall system 240 includes one or more plug elements 248 located in one or more selected pulp chambers 228′. Preferably, the plug element 248 is formed to occupy at least a portion of the selected pulp chamber 228′. For the purposes hereof, the pulp chambers other than the selected pulp chamber(s) 228′ are referred to as open pulp chambers 228.sub.O. In the cases where the plug element 248 does not fill the selected chamber 228′ completely, a modified or reduced pulp chamber 229 is defined in the selected chamber 228′ at least in part by the plug element 248 therein. The volume of the reduced pulp chamber 229 is the difference between the volume of the selected pulp chamber 228′ (i.e., prior to the insertion of the plug element 248 therein) and the volume of the plug element 248. In one embodiment, the pulp is receivable in the reduced pulp chamber 229.

(18) As will be described, it has been found that the size and location of the plug elements 248 may be selected for optimum flow of the pulp through the discharge wall assembly 240. Surprisingly, the optimum flow rate may be achieved by including the plug elements in the selected pulp chambers 228′. The optimum flow rate brings advantages further described below. It will be understood that the optimum flow rate of the pulp through the discharge wall assembly 240 preferably is achieved when the discharge wall assembly rotates at a preselected rotation speed.

(19) As will be described, it is believed that, in at least most cases, the plug element 248 preferably occupies only a predetermined portion of the volume of the selected pulp chamber 228′, in the optimum design. The reduced pulp chamber 229 is a portion of the pulp chamber 228′ that is not occupied by the plug element 248. It is also believed that in the optimum design, in at least most cases, the plug element preferably is included only in certain pulp chambers of the discharge wall assembly, i.e., in one embodiment, the plug element 248 preferably is not positioned in every pulp chamber in the discharge end wall assembly. For instance, in the example illustrated in FIG. 2A, one-quarter of the pulp chambers in the discharge end wall assembly are selected for the plug elements to be positioned therein. Also, and as illustrated in FIG. 2A, the selected pulp chambers 228′ preferably are uniformly distributed throughout the discharge wall assembly.

(20) However, the discharge end wall system of the invention may include the plug elements in each of the pulp chambers therein. It will be understood that the optimum design in each case would depend on a number of parameters. As a practical matter, the optimum design may be determined by trial and error, e.g., using computer simulation.

(21) It will be understood that the plug element 248 may be located in a pulp chamber having any suitable configuration. For instance, in the attached drawings the pulp lifters as illustrated are straight, and positioned substantially equidistant from each other, radially relative to the axis of rotation. However, it will be understood that, alternatively, the pulp lifters may be curved.

(22) Those skilled in the art would appreciate that, as a practical matter, the plug elements 248 may be retrofitted into an existing discharge end wall assembly, to improve the overall performance thereof. Alternatively, the discharge end wall system may include the plug element when initially installed.

(23) As illustrated in FIGS. 2A and 3A, the mill shell 223 is rotated in a counter-clockwise direction, indicated by arrow “2R”. The discharge end wall system 240 is mounted on the discharge end wall 227, and therefore the discharge end wall system 240 rotates with the mill shell 223. The charge “CH” is introduced into the grinding mill 221 at its intake end, as indicated by arrow “IN.sub.2” in FIG. 2C. The pulp flows into the immersed pulp chambers 228 (or at least the portions of the pulp chambers that are immersed, when they are only partially immersed), via discharge grates 250, as indicated by the arrows “OP.sub.2” in FIG. 2C. It will be understood that, for clarity of illustration, only two open pulp chambers 228.sub.O are illustrated in FIG. 2C. It will also be understood that the selected pulp chambers 228′ are also immersed in turn as the discharge end wall assembly rotates.

(24) It will also be understood that the grinding mill 221 of the invention preferably includes the discharge end wall system 240 of the invention. As noted above, the discharge end wall system 240 preferably includes one or more selected pulp chambers 228′, in which the plug elements 248 are respectively located, to define the reduced pulp chambers 229 therein. The discharge end wall system 240 also preferably includes a number of the open pulp chambers 228.sub.O. The open pulp chambers 228.sub.O do not include any plug elements 248.

(25) The plug elements 248 have been found to provide certain advantages. Surprisingly, it has been found that the throughput of the grinding mill 221 of the invention is at least equal to, and may be significantly larger than, the throughput of the prior art grinding mill of equivalent size, in which all of the pulp chambers are open. The reasons for this are unclear. Without wishing to be bound by any theory, it is believed that this is due to a reduction in carryover, which results from the presence of the plug elements in the selected pulp chambers 228′, occupying at least a predetermined portion of each of the selected pulp chambers 228′.

(26) In the prior art, “carryover” (described above) is believed to be a result of allowing insufficient time (i.e., during approximately one-half of the total time needed for one rotation of the discharge wall) for all of the pulp to exit from each of the pulp chambers. Due to the presence of the plug elements 248 in the selected pulp chambers 228′, the volume of the pulp that may be received in each of the reduced pulp chambers 229 is reduced (i.e., as compared to the volume receivable in any one of the open pulp chambers 228.sub.O), in a proportion based on the size of the plug element 248 relative to the size of the open pulp chamber 228.sub.O.

(27) Because the open volume available for receiving the pulp in the selected pulp chamber 228′ has been reduced to the volume of the reduced pulp chamber 229, a smaller volume of the pulp is receivable in the reduced pulp chamber 229 than would have been receivable in the selected pulp chamber 228′, i.e., before insertion of the pulp element 248. As noted above, in one embodiment, only a certain proportion of the pulp chambers in the discharge end wall assembly are selected to have the plug elements 248 positioned therein. It is believed that, because less pulp is received in the discharge end wall system 240 as it rotates, there is less carryover. Specifically, in the reduced pulp chambers 229, there will be less carryover than in one of the open pulp chambers 228.sub.O.

(28) One advantage of this is that the reduced carryover volume (in the reduced pulp chambers 229) means that the elements defining the reduced pulp chamber 229 are subjected to less wear. The net result appears to be that the throughput is not decreased by the introduction of the plug elements, and may increase somewhat, due to the reduced carryover. The foregoing is achieved without a decrease in throughput.

(29) An increase in throughput after the plug elements 248 are installed is surprising. Without wishing to be bound by any theory, it may be that the carryover that, in the absence of any plug elements, often occurs in the pulp chamber may have the effect of hindering the exit of a portion of the pulp that otherwise (i.e., in the absence of carryover) would have successfully exited the open pulp chamber. For example, if the fines of the pulp are “dammed” (and held in the pulp chamber) due to a more coarse portion of the carryover located near the exit from the pulp chamber, then those fines would be able to exit successfully, in the absence of carryover. It is thought that, in this way, a slight decrease in the amount of carryover may result in a slight increase in throughput.

(30) As noted above, the mechanisms controlling the movement of the pulp are not well understood. Another possibility is that, for the same input, the result of inserting the plug element 248 into one or more selected pulp chambers 228′ is to cause the portion of the pulp that otherwise would have flowed through the selected pulp chambers 228′ to flow instead through the open pulp chambers 228.sub.O. This portion of the pulp, which is effectively redirected from the selected pulp chambers 228′, is thus added to the pulp that would otherwise have flowed into and at least partially out of the open pulp chambers, i.e., in the absence of the plug elements 248 in the system 240. Accordingly, in the discharge end wall system 240, the amount of the pulp flowing through the open pulp chambers 228.sub.O is increased, if compared to the flow of the pulp through each pulp chamber in the prior art grinding mill.

(31) It may be that increasing the amount of the pulp that is located in each open pulp chamber 228.sub.O increases the overall throughput of the pulp through the grinding mill 221. However, what might cause this improvement is not clear at this time. It may be that, when the pulp flows through the open pulp chambers 228.sub.O, the friction between the particles of the pulp therein tends to cause the pulp to move together, so that the pulp tends to exit the open pulp chamber 228.sub.O en masse. In short, in the discharge end wall system 240 of the invention, it may be that the pulp that flows into the open pulp chambers 228.sub.O is packed into them more tightly than in the prior art, but not so tightly that the flow of the pulp through the open pulp chambers 228.sub.O (and in particular, exit therefrom) is thereby impeded. It may be that the carryover in the open pulp chambers is somewhat less, as a result. As noted above, it is believed that the carryover in the reduced pulp chamber is also much reduced at the same time, as described above.

(32) It will be understood that the plug element 248 may be in any suitable form or configuration. An embodiment of the plug element 248, positioned in a predetermined portion of the selected pulp chamber 228′, is illustrated in FIGS. 2B and 2D. As illustrated in FIGS. 2B and 2D, in one embodiment, the plug element 248 preferably occupies approximately one-half of the volume of an outer portion of the selected pulp chamber 228′. The configuration illustrated in FIGS. 2A-2D is also illustrated in FIG. 3A.

(33) In FIG. 3A, the plug element (identified for convenience by reference character A248 in FIG. 3A) that is located in the selected pulp chamber identified for convenience in FIG. 3A by reference character A228′ is cross-hatched, so that the extent of the plug element A248 can be seen. As illustrated in FIG. 3A, the pulp chamber A228′ has an overall length 252, and includes an inner portion 254 and an outer portion 256. The outer portion 256 of the selected pulp chamber 228′ is partially occupied by the plug element A248 (FIG. 3A).

(34) In the embodiment illustrated in FIG. 3A, the plug element has a width “W” and a length “L”. The width “W” is approximately one-half of the total width “TW” of the selected pulp chamber 228′, at the outer perimeter wall 226 of the mill shell 223. The length “L” of the plug element only extends along the outer portion 256 of the pulp chamber, i.e., in this embodiment, the plug element does not extend into the inner portion of the selected pulp chamber 228′. As will be described, other versions of the plug element may alternatively be utilized.

(35) It will be understood that the grate and the blind plate that are normally positioned to cover the pulp chamber A228′ (i.e., when the grinding mill is in use) are omitted from FIGS. 2A and 3A, to simplify the illustrations. It will also be understood that the outer portion 256 of the pulp chamber A228′ is covered by the grate 250 and the inner portion 254 is covered by the blind plate. Similarly, the outer portions of the other pulp chambers (both open and selected) are covered by discharge grates respectively, and the inner portions thereof are covered by blind plates.

(36) When a particular open pulp chamber 228.sub.O or selected pulp chamber 228′ is at least immersed in the charge, the pulp flows through the discharge plate into that open, unoccupied pulp chamber 228.sub.O or into the reduced pulp chamber 229 (as the case may be) under the influence of gravity, to the extent that at least a part of the pulp chamber is located below a top surface “S” of the charge “CH” (FIGS. 2A, 2C). For the purposes hereof, the pulp chamber is said to be in an “intake condition” while it is at least partially immersed in the charge, and the pulp is able to flow into that pulp chamber under the influence of gravity. Similarly, for the purposes hereof, while the pulp chamber is at least partially located above the top surface “S” of the charge, and therefore located so that the pulp therein may flow to the central hole 224 and thus exit the grinding mill, the pulp chamber is said to be in a “discharge condition”.

(37) Accordingly, it can be seen in FIGS. 2A-3A that, when one of the selected pulp chambers 228′ is in the intake condition thereof, the pulp flows through the discharge grate into the reduced pulp chamber 229 thereof. When one of the selected pulp chambers 228′ is in the discharge condition thereof, the pulp located in the reduced pulp chamber 229 thereof exits the reduced pulp chamber 229, and flows to the central hole 224 and subsequently exits the grinding mill.

(38) In FIGS. 2A and 3A, the discharge end wall system 240 is illustrated as rotating in a counter-clockwise rotation. Accordingly, and as can be seen in FIG. 2A, any particular open pulp chamber 228.sub.O or selected chamber 228′ is generally in the discharge condition while the pulp chamber is moved from approximately the three o'clock position to approximately the nine o'clock position.

(39) Those skilled in the art would appreciate that in each rotation, each of the pulp chambers 228.sub.O, 228′ may be very briefly positioned between the intake and discharge conditions, so that the charge flows neither into, nor out of, the pulp chamber 228.sub.O, 228′. The pulp chamber 228.sub.O, 228′ is between the intake and the discharge conditions when it is approximately at the three o'clock position and approximately at the nine o'clock position, subject to the amount of the charge in the grinding mill.

(40) Those skilled in the art also would appreciate that the mill shell may, alternatively, be rotated in a clockwise direction. In the drawings, the mill shell is illustrated only as rotating in the counter-clockwise direction for clarity of illustration.

(41) It will be understood that the optimum proportion of the pulp chambers in the discharge wall assembly that are the selected (i.e., occupied) pulp chambers 228′ may vary. For example, in one embodiment, the open pulp chambers 228.sub.O in the discharge end wall assembly 242 preferably include three quarters of the total number of pulp chambers therein. That is, in one embodiment of the discharge end wall system 240, one-quarter of the pulp chambers in the discharge wall assembly 242 are the selected pulp chambers 228′, that are at least partially occupied by the plug elements 248 respectively.

(42) Those skilled in the art would appreciate that a proportion of the pulp chambers that include the open pulp chambers preferably is selected for maximizing throughput of the pulp through the discharge end wall assembly 242. As a practical matter, it is believed that the optimum proportions for any particular grinding mill may best be determined by trial and error, in view of the large number of inter-related factors that would need to be considered, if attempting to calculate the optimum proportion of open pulp chambers.

(43) The plug element 248 may include any suitable material. For example, the plug element 248 may be made of concrete.

(44) As can be seen, e.g., in FIG. 2C, the invention preferably includes the grinding mill 221. The grinding mill 221 preferably includes the mill shell 223 and the discharge end wall system 240. The system 240 is mounted on the discharge end wall 227.

(45) The discharge end wall system 240 of the invention may be configured in an existing (prior art) grinding mill, e.g., a grinding mill of the prior art such as that illustrated in FIGS. 1A-1E. In order to retrofit the system 240 of the invention into a conventional grinding mill, the discharge grates preferably are first removed. Next, the size and shape of the plug element is to be determined. Next, the optimum number of the selected pulp chambers for the embodiment of the plug element that is to be used is determined. The pulp elements 248 that are selected are then located in the selected pulp chambers 228′. Those skilled in the art would appreciate that the plug elements 248 may be secured in the selected pulp chambers 228′ using any suitable means therefor.

(46) It will be understood that the design process, generally outlined above, may be iterative in nature, i.e., after the plug element's size and shape are initially determined and the optimum number of selected pulp chambers is determined based on that form of the plug element, it may be prudent to amend the design of the plug element, and then reconsider the number of selected pulp chambers. This process may be repeated until satisfactory results are obtained that permit the design to be finalized.

(47) As noted above, the form of the plug element that is positioned in the selected pulp chamber 228′ may be any suitable size or shape. In FIG. 3A, for example, the plug element 248 has a width “W” at the mill shell wall that is approximately one-half of the total width “TW” of the selected pulp chamber 228′ at the outer perimeter wall 226 of the mill shell 223. In the embodiment of the system 240 illustrated in FIG. 3A, the plug element 248 also occupies only part of the outer portion 256 of the selected pulp chamber 228′, and does not occupy part of the inner portion 254 of the selected pulp chamber 228′.

(48) An alternative embodiment of the plug element 348 is illustrated in FIG. 3B, included in another embodiment of the discharge end wall system 340 of the invention. The discharge end wall system 340 includes the discharge end wall assembly 342.

(49) In FIG. 3B, the outer portion 256 of the selected pulp chamber 228′ is occupied by the plug element 348. For clarity of illustration, the plug elements 348 are marked with cross-hatching in FIG. 3B. The plug elements 348 occupy the outer portions 256 of the selected pulp chambers 228′, but do not extend into the inner portions 254 of the selected pulp chambers 228′.

(50) It will be understood that the optimum proportion of the pulp chambers in the discharge wall assembly 342 that are the selected (i.e., occupied) pulp chambers 228′ may vary. For example, in one embodiment, the open pulp chambers 228.sub.O in the discharge end wall assembly 342 preferably include three quarters of the total number of pulp chambers therein. That is, in one embodiment, one quarter of the pulp chambers in the discharge wall assembly are the selected pulp chambers 228′, that are at least partially occupied by the plug elements 348 respectively.

(51) Those skilled in the art would appreciate that the proportion of the pulp chambers of the total in any discharge end wall assembly would depend on a number of parameters. As noted above, due to the large number of parameters involved and the interrelated relationships therebetween, the optimum configuration of the plug element, and the optimum proportion of the selected pulp chambers in which the plug element is received, is best determined via trial and error.

(52) The discharge end wall system 340 is rotated in the direction indicated by arrow “3R” (FIG. 3B). It will be understood that discharge grates and blind plates are omitted from FIG. 3B, for clarity of illustration.

(53) As the discharge end wall system 340 is rotated about the grinding mill's axis, the pulp chambers are respectively moved between intake conditions and discharge conditions thereof. When one of the selected pulp chambers 228′ is in the intake condition, virtually no pulp flows into the reduced pulp chamber 229, because the reduced pulp chamber 229 in this embodiment is the inner portion 254 of the selected pulp chamber 228′, which located substantially entirely behind a blind plate (not shown in FIG. 3B).

(54) An alternative embodiment of the plug element 448 is illustrated in FIG. 3C, included in another embodiment of the discharge end wall system 440 of the invention. The discharge end wall system 440 includes a discharge end wall assembly 442.

(55) In FIG. 3C, a selected part 458 of the outer portion 256 of the selected pulp chamber 228′ is occupied by the plug element 448. For clarity of illustration, the plug elements 448 are marked with cross-hatching in FIG. 3C. The plug elements 448 occupy the parts 458 of the outer portions 256 of the selected pulp chambers 228′, but do not extend into the inner portions 254 of the selected pulp chambers 228′. Preferably, a part 460 of the outer portion 256 remains unoccupied, or open (FIG. 3C). Accordingly, it can be seen in FIG. 3C that, in this embodiment, the reduced pulp chamber 229 includes the inner portion 254 of the selected pulp chamber 228′ and the part 460 of the outer portion 256.

(56) It will be understood that the optimum proportion of the pulp chambers in the discharge end wall system 440 that are the selected (i.e., occupied) pulp chambers 228′ may vary. For example, in one embodiment, the open pulp chambers 228.sub.O in the discharge end wall assembly 442 preferably include three quarters of the total number of pulp chambers therein. That is, in one embodiment, one-quarter of the pulp chambers in the discharge wall assembly are the selected pulp chambers 228′, that are at least partially occupied by the plug elements 448 respectively.

(57) Those skilled in the art would appreciate that the proportion of the pulp chambers of the total in any discharge end wall assembly would depend on a number of parameters. As noted above, due to the large number of parameters involved and the interrelated relationships therebetween, the optimum configuration of the plug element, and the optimum proportion of the selected pulp chambers in which the plug element is received, is best determined via trial and error.

(58) The discharge end wall system 440 is rotated in the direction indicated by arrow “4R” (FIG. 3C). It will be understood that discharge grates and blind plates are omitted from FIG. 3C, for clarity of illustration.

(59) As the discharge end wall system 440 is rotated about the grinding mill's axis, the pulp chambers are respectively moved between intake conditions and discharge conditions thereof. The pulp chambers include the open pulp chambers 228.sub.O and the selected pulp chambers 228′. When one of the selected pulp chambers 228′ is in the intake condition, pulp flows into the part 460.

(60) Those skilled in the art would appreciate that other configurations of the plug element may be utilized. In addition, although one-quarter of the pulp chambers include plug elements in those embodiments of the discharge end wall system that are illustrated, those skilled in the art would appreciate that other proportions of selected pulp chambers may be utilized, if appropriate.

(61) It will also 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.