US3624797A

US3624797A - Multiple compartment grinding mills

Info

Publication number: US3624797A
Application number: US884149A
Authority: US
Inventors: Eugene P Waddell
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1969-12-11
Filing date: 1969-12-11
Publication date: 1971-11-30
Anticipated expiration: 1988-11-30
Also published as: DE2061214A1; ZA708149B; ES198759Y; GB1265637A; ES198759U; FR2073576A5; CA934724A

Abstract

A grinding mill is disclosed having a cylindrical shell for rotation about its central axis and a division head that divides the interior of the shell into axially disposed compartments, one compartment containing steel rods for relatively coarse grinding and another compartment containing steel balls for finer grinding. The division head is an assembly of elements in which a pair of the elements are annular bulkheads perpendicular to the central axis and spaced apart from each other. The annular bulkhead on the coarse grinding side of the division head assembly defines a central opening of smaller diameter than the central opening defined by the annular bulkhead on the fine grinding side of the division head assembly. A liner extends between the radially inner peripheries of the two annular bulkheads and defines a central passage through the division head assembly with a surface having the configuration of a truncated cone with its central axis coincident with the central axis of the shell and with its apex end pointed toward the coarse grinding compartment. A shielding disk is concentrically mounted within the conical central passage in a plane perpendicular to the shell axis and supported by a plurality of arcuately spaced mounting blocks between the outer periphery of the shielding disk and the inner periphery of the conical central passage. The shield blocks a mass of grinding balls which tends to surge from the ball compartment toward the rod compartment during periods of mill acceleration at startup and during periods of deceleration when being stopped. The normal flow of pulp from the rod compartment into the ball compartment passes through the passage in channels between the mounting blocks and radially outward of the shielding disk.

Description

United States Patent [72] inventor Eugene P. Waddell Brooktield, Wis.

[21 1 Appl. No. 884,149

[22] Filed Dec. I1, 1969 Nov. 30, 1971 Allis-Chalmers Manufacturing Company Milwaukee, Wis.

[45] Patented [73] Assignee [54] MULTIPLE COMPAR'IMENT GRINDING MILLS 4 Claims, 3 Drawing Figs.

Primary Examiner-Andrew Juhasz Assistant Examiner-Gary L. Smith Attorneys- Arthur M. Streich, Robert B. Benson and John P.

Hines ABSTRACT: A grinding mill is disclosed having a cylindrical shell for rotation about its central axis and a division head that divides the interior of the shell into axially disposed compartments, one compartment containing steel rods for relatively coarse grinding and another compartment containing steel balls for finer grinding. The division head is an assembly of elements in which a pair of the elements are annular bulkheads perpendicular to the central axis and spaced apart from each other. The annular bulkhead on the coarse grinding side of the division head assembly defines a central opening of smaller diameter than the central opening defined by the annular bulkhead on the fine grinding side of the division head assembly. A liner extends between the radially inner peripheries of the two annular bulkheads and defines a central passage through the division head assembly with a surface having the configuration of a truncated cone with its central axis coincident with the central axis of the shell and with its apex end pointed toward the coarse grinding compartment. A shielding disk is concentrically mounted within the conical central passage in a plane perpendicular to the shell axis and supported by a plurality of arcuately spaced mounting blocks between the outer periphery of the shielding disk and the inner periphery of the conical central passage. The shield blocks a mass of grinding balls which tends to surge from the ball compartment toward the rod compartment during periods of mill acceleration at startup and during periods of deceleration when being stopped. The normal flow of pulp from the rod compartment into the ball compartment passes through the passage in channels between the mounting blocks and radially outward of the shielding disk.

MULTIPLE COMPARTMENT GRINDING MILLS CROSS-REFERENCE TO RELATED PATENT APPLICATION This invention is disclosed and described as being applied to a mill which is the subject of a Pat. application of Raymond C. .lenness and Wayne C. Dannenbrink, Ser. No. 884,059 filed Jan. 26, 1970.

BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to multiple compartment cylindrical grinding mills having a compartment containing steel rods for coarse grinding and a compartment containing steel balls for finer grinding, and in particular to a division head assembly between the compartments.

2. Description of the Prior Art Grinding mills having a cylindrical shell divided into longitudinally disposed compartments by a division head assembly, are shown in prior art patents such as U.S. Pat. No. 2,052,426 of 1936; U.S. Pat. No. 3,144,212 of 1964; and U.S. Pat. No. 3,298,619 of 1967. The aforementioned U.S.Pat. No. 2,052,426 also discloses a division head assembly having a pair of spaced annular bulkheads, and a conical liner connected on its apex end to the central opening in each of the annular bulkheads of the division head assembly. In this prior art patent the conical liner connected to the coarse side bulkhead does not extend to the fine side bulkhead. Such an arrangement provides for pulp in both compartmentsflowing into a central discharge chamber rather than a one direction through-flow movement of pulp from the coarse grinding compartment, through the division head assembly, to the fine grinding compartment. With central discharge mill, rather than a one direction end to end movement of pulp, much greater classifier capacity must be provided because. partly ground material which needs further grinding and finely ground material needing no further grinding, are mixed and discharged together through a common discharge port in a central portion of the mill.

For a one direction through-flow movement of pulp requiring less classifier capacity, the prior art discloses division head assemblies and mill arrangements such as are disclosed in U.S. Pat. Nos. 3,144,212 and 3,298,619. However, in actual practice utilizing such mills with such division head assemblies, which include a slotted bulkhead on the fine grinding side of the division head, pieces of the steel grinding balls are forced through the slotted bulkhead and into the coarse grinding compartment containing steel grinding rods. Such pieces in the rod compartment get between rods and hold the rods apart, not allowing them to come sufficiently close together to break pulp material and these prior art constructions therefor, like the central discharge mills, also have disadvantages.

The copending Pat. application of Raymond C. Jenness and Wayne C. Dannenbrink, Ser. No. 884,049 filed Jan. 26, 1970, a grinding mill is disclosed having a cylindrical shell for rotation about its central axis and a division head that divides the interior of the shell into axially disposed compartments, one compartment containing steel rods for relatively coarse grinding and another compartment containing steel balls for finer grinding. The division head is an assembly of elements in which a pair of the elements are annular bulkheads perpendicular to the central axis and spaced apart from each other. The annular bulkhead on the coarse grinding side of the division head assembly defines a central opening of smaller diameter than the central opening defined by the annular bulkhead on the fine grinding side of the division head assembly. A liner extends between the radially inner peripheries of the two annular bulkheads and defines a central passage through the division head assembly with a surface having the configuration of a truncated cone with its central axis coincident with the central axis of the shell, and with the apex end of the configuration pointed toward the coarse grinding compartment. Such a conical configuration of the central opening through the division head from the rod compartment to the ball compartment eliminates the need for slotted openings in one of the bulkheads and provides a downwardly sloped path from the coarse grinding chamber to the fine grinding chamber. During normal operation of the mill the slope of the path prevents balls moving through the division head from the ball compartment into the rod compartment because during normal operation the grinding balls cannot roll up the slope. Balls that enter the rod compartment via a path external to the shell as in closed circuit grinding, can roll down the slope from the rod compartment back to the ball compartment. However, while such a division head does provide the described result during normal operation, during periods of mill acceleration at startup and during periods of deceleration when the mill is stopping, the charge of grinding balls in the fine grinding compartment tends to surge toward the division head. During such periods the grinding balls could move up the slope of the central passage through the division head and enter the rod compartment where they interfere with the grinding action of the rods. It is to this problem that the present invention is directed and the provision of a solution to this problem is a principal object of the present invention.

SUMMARY OF THE PRESENT INVENTION In a preferred embodiment of the present invention, as applied to a mill such as disclosed in the aforementioned Jenness and Dannenbrink patent application and which has hereinbefore been described, a shielding disk is concentrically mounted within the conical central passage through the division head assembly. The disk is arranged in a plane perpendicular to the shell axis and is supported by a plurality of arcuately spaced mounting blocks between the outer periphery of the shielding disk and the inner periphery of the conical central passage. The shielding disk blocks the surge of balls from moving into the rod compartment during acceleration and deceleration while the normal flow of pulp from the rod compartment to the ball compartment during normal operation of the mill, passes through channels between the mounting blocks and radially outward of the shielding disk.

Other features and objects of the invention that have been attained will appear from the more detailed description to follow with reference to an embodiment of the present invention shown in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the accompanying drawing shows a side elevation, in section, a grinding mill according to the present invention;

FIG. 2 shows to enlarged scale, a portion of a division head assembly in FIG. 1; and

FIG. 3 is an end view of the portion of the division head assembly shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The multistage grinding mill disclosed in FIG. 1 of the drawing comprises in general a rotary cylindrical shell casing 1 illustrated as having uniform or substantially uniform diameter throughout its length, the casing being provided with feed and discharge end heads 2, 3, respectively. The casing 1 is divided into a pair of grinding chambers 4 and 5 in a manner and by structure that will be described in detail later. The chamber 4 on the inlet end of the casing l is provided with a plurality of rods 6 that provide for relatively coarse grinding in the chamber 4. The chamber 5 is provided with a plurality of balls 7 for relatively fine grinding of material in the chamber 5. The mill is rotatably mounted in suitable end bearings which carry feed and discharge trunnions 11 and 12, respectively. Rotary motion about its horizontal central axis is imparted to the mill by means of power applied to a driving gear 13 secured either around the inlet end of the casing 1 as shown or around the feed trunnion (not shown). The feed end of the mill is provided with a feeder such as feeder 15 for introducing the material which is to be reduced into the inlet end of the coarse grinding chamber 4 through the feed trunnion ll.

The discharge end of chamber 5 is provided with a perforated plate .19 which is spaced from the end head 3. Located within the space between plate 19 and the end head 3 is a series of elevating vanes 20. The inner extremities of the elevating vanes 20 are located close to a central discharge cone 21, the apex of which is directed toward the discharge trunnion l2.

The arrangement shown in FIGS. 1 and 2 for dividing the casing 1 into the two grinding compartments 4 and 5, includes an arrangement of parts shown to enlarged scale in FIG. 2 and FIG. 3. A division head assembly is mounted within the mill comprising a pair of spaced

annular bulkheads

26, 27. The side of bulkhead 26 facing the feed head 2 and the side of bulkhead 27 facing the discharge head 3, are each provided with

replaceable wear liners

28, 29 respectively. Liner 29 projects farther radially inward than does bulkhead 27 but the reverse is true on the opposite side of the division head assembly where the liner 28 does not project as far radially as bulkhead 26 thus leaving an inner portion of bulkhead 26 unprotected by liner 28. The inner portion of bulkhead 26 not protected by liner 28 is however covered and protected by a liner 30 having both a radial portion 31 and an axially extending portion 32. A liner extends between the axial extending portion 32 of liner 30 and the radially inner portion of liner 29, and portion 32 and liner 35 together provide and define a central passage 36 through the division head assembly 25 having

openings

37, 38 and a configuration therebetween of a truncated cone with its apex end pointed toward the feed head 2 end of the mill and a base flange 39 on the end thereof facing the discharge head 3.

Shielding means comprising a disk 40 is mounted concentrically within the central passage 36 and perpendicular to the central axis -xx' A plurality of mounting blocks 41 are connected to the outer periphery of disk 40, as by welding, and blocks 41 are connected to the inner periphery of liner 35 by bolts 42 that pass through blocks 41, liner 35, bulkhead 26 and liner 30 to unite the assembly of those parts. A peripheral pulp channel 43 is defined between each adjacent pair of blocks 41, the outer circumference of disk 40 and an intermediate diameter on the inner surface of liner 35 indicated in FIG. 3 by the broken line circle 44.

In the operation of the mill assembly that has been described, material to be ground is delivered to the feeder such as feeder 15 and fed into the coarse grinding chamber 4 where the rods 6, which tumble as gear 13 turns casing 1, provide a preliminary grinding of the feed material to provide a coarse pulp which will overflow from chamber 4 through the passage 36 in the division head assembly 25, and into chamber 5. In chamber 5 the steel balls 7 tumble and provide a further grinding action to provide a finer pulp which flows through the perforated plate 19 to be picked up by the vanes 20 and dumped into the discharge cone 21. With the central passage 36 through division head assembly 25 being defined by liner 35 and portion 32 of liner 30, which in turn provide a configuration of a truncated cone with its central axis coincident with the central axis of the mill shell 1 and with the apex end of this configuration pointed toward the chamber 4, the bottom surface of this .passage 36 is sloped downwardly from the chamber 4 toward chamber 5. Thus in normal operation (i.e., steady speed neither accelerating nor decelerating) balls 7 do not roll up this inclined surface and they are kept out of the rod compartment 4, but balls or pieces of balls that get into chamber 4 via an external recirculation circuit (not shown) can roll out of chamber 4 into chamber 5 where they should be.

During periods when the mill is being started and being accelerated to operating speed and when the mill is being slowed in preparation for shutdown, surges of grinding balls toward the division head assembly 25 are prevented from passing through the passage 36 to the rod compartment 4, by the shielding disk 40. During normal operation of the mill when the mill IS being rotated at steady and constant rate, pulp flows freely from the rod compartment 4, through the channels 43 and into the ball compartment 5.

From the foregoing detailed description of the present invention, it has been shown how the objects of the invention have been attained in a preferred manner. However, modifications and equivalents of the disclosed concepts such as readily occur to those skilled in the art are intended to be included within the scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a grinding mill having a cylindrical shell mounted for rotation about its central axis, a compartment containing media for coarse grinding and a compartment containing media for finer grinding separated by a division head assembly, said division head assembly comprising a first and a second annular bulkhead perpendicular to said axis and spaced apart from each other, the annular bulkhead on the coarse grinding side of the division head assembly defining a central opening of smaller diameter than a central opening defined by the annular bulkhead on the finer grinding side of the division head assembly, an axially extending liner extending between and connected to the radially inner peripheries of the first and second bulkheads and with said liner having an inner surface defining a central passage through the division head assembly with a surface having a configuration of a truncated cone with a central axis coincident with the central axis of the shell and with an apex end pointed toward the coarse grinding compartment, and shielding means within said central passage presenting a surface blocking a central portion of said passage and defining arcuate peripheral channels therethrough to block surging masses of fine grinding media from passing therethrough into the coarse grinding compartment and provide pulp channels therethrough from the coarse grinding compartment to the fine grinding compartment.

2. The structure of claim 1 characterized in that both annular bulkheads are imperforate thus making the channels defined within the central passage the sole path of communication within the shell between the two compartments.

3. ln a grinding mill having a cylindrical shell mounted for rotation about its central axis, a compartment containing rods for coarse grinding and a compartment containing balls for finer grinding separated by a division head assembly, said division head assembly comprising a first and a second annular bulkhead perpendicular to said axis and spaced apart from each other, the annular bulkhead on the rod compartment side of thedivision head assembly defining a central opening of smaller diameter than a central opening defined by the annular bulkhead on the ball compartment side of the division head assembly, an axially extending liner extending between and connected to the radially inner peripheries of the first and second bulkheads and with said liner having an inner surface defining a central passage through the division head assembly with a surface having a configuration of a truncated cone with a central axis coincident with the central axis of the shell and with an apex end pointed toward the rod compartment, a shielding disk concentrically mounted within said central passage and perpendicular to said central axis, and a plurality of mounting blocks connecting the disk to the liner and supporting the disk to block a central portion of the central passage and provide a plurality of arcuate pulp channels between the outer periphery of the disk and the inner periphery of the liner.

4. The structure of claim 3 characterized in that the disk has a diameter larger than the central opening defined by the annular bulkhead on the rod compartment side of the division head assembly and smaller than the central opening defined by the annular bulkhead on the ball compartment side of the division head assembly.

Claims

3. In a grinding mill having a cylindrical shell mounted for rotation about its central axis, a compartment containing rods for coarse grinding and a compartment containing balls for finer grinding separated by a division head assembly, said division head assembly comprising a first and a second annular bulkhead perpendicular to said axis and spaced apart from each other, the annular bulkhead on the rod compartment side of the division head assembly defining a central opening of smaller diameter than a central opening defined by the annular bulkhead on the ball compartment side of the division head assembly, an axially extending liner extending between and connected to the radially inner peripheries of the first and second bulkheads and with said liner having an inner surface defining a central passage through the division head assembly with a surface having a configuration of a truncated cone with a central axis coincident with the central axis of the shell and with an apex end pointed toward the rod compartment, a shielding disk concentrically mounted within said central passage and perpendicular to said central axis, and a plurality of mounting blocks connecting the disk to the liner and supporting the disk to block a central portion of the central passage and provide a plurality of arcuate pulp channels between the outer periphery of the disk and the inner periphery of the liner.