AU4527300A - Ball mill - Google Patents

Description

WO 00/71258 PCT/AUOO/00492 BALL MILL FIELD OF THE INVENTION This invention relates to the art of comminution of frangible and friable material such as ore samples. In particular this invention relates to a mill for milling an ore sample. 5 BACKGROUND ART Various types of ball mill have previously been described, the most commonly known type being a horizontal cylinder containing hard balls or beads (usually steel or sometimes ceramic), with the horizontal cylinder being rotated about its central axial extent. When the cylinder is rotated, the balls roll against the internal 10 periphery of the cylinder, pulverising material fed to the ball mill. Planetary ball mills have also been described, where a planetary action of the cylinder increases the gravitational effect acting on the balls in the mill. These ball mills often have more than one cylinder, to assist with dynamic balancing, although there have been such ball mills described with a single cylinder and a 15 counterweight. Planetary ball mills may have their cylinders disposed horizontally or vertically, but the axial extent of the cylinders is always disposed in the same direction, commonly parallel with, as the axial extent of a main shaft about which the cylinders are mounted. In these planetary ball mills, the cylinders are mounted 20 about a rotating main shaft. The cylinder(s) have their central axial extents offset in parallel relation from the central axis of the main shaft. In some arrangements, the cylinders are fixed in relation to the main shaft, so that as the main shaft undergoes one revolution, the cylinders undergo one revolution with the main shaft. Alternatively, the cylinders may rotate, being driven by the movement of 25 the main shaft, or being driven by independent motors.

WO 00/71258 PCT/AUOO/00492 -2 Planetary ball mills lend themselves to batch grinding/milling operations for assay purposes, although planetary ball mills have been described which are suitable for continuous milling operations. An object of the present invention is to provide a ball mill suitable for batch 5 grinding/milling operations, or to at least provide an alternative to existing planetary ball mills. While the ball mill of the invention is suitable in particular for assay purposes, it may lend itself to automated continuous operation with the addition of suitable loading and unloading facilities. Throughout the specification, unless the context requires otherwise, the word 10 "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. DISCLOSURE OF THE INVENTION In accordance with the invention there is provided a ball mill having a fixed base 15 with a mount for receiving a main body rotatable along a main axis, said main body defining mounts for receiving at least one planetary body having a planetary axis located distal from and parallel to said main shaft axis, wherein said planetary body supports at least one tubular ball mill pot having a central axial extent perpendicular to said main shaft axis. 20 Preferably, said at least one planetary body is rotatable about said planetary axis. It is preferred that there be two planetary bodies mounted in pairs on opposite sides of the main axis. In a more preferred form, there are four planetary bodies mounted as two such pairs. In practice there may be any number of planetary bodies, as long as dynamic balancing is maintained. For example, there may be 25 five planetary bodies , or three pairs comprising six planetary bodies. Preferably each said planetary body supports a plurality of said tubular ball mill pots. To maintain dynamic balancing, there should be an equal number of tubular WO 00/71258 PCT/AUOO/00492 -3 ball mill pots supported by each planetary body, although this is not necessary with adequate counter-balancing in compensation for unequal numbers of said tubular ball mill pots. Preferably each said planetary body is associated with drive means to rotate said 5 planetary body relative to said main body. The drive means may comprise any known means for transferring motion such as gears or belts or chain and sprocket assemblies or toothed belt and cog assemblies, but it is most preferred that the drive means be one that can maintain the planetary bodies in synchronisation, in order to prevent the ball mill from becoming unbalanced. Thus belts which are 10 prone to slippage are not preferred. Alternatively the drive means may comprise any known means for imparting motion, such as an independent motor, the speed of which is preferably controllable in order to maintain the planetary bodies in synchronisation. Preferably said drive means is arranged to impart a rotary motion in said 15 planetary bodies which is opposite in direction to the rotary motion of said main body. Preferably said drive means includes at least one central gear, each being mounted along said main axis and being fixed relative to said base in operation, with a drive train extending from each said at least one central gear to drive each 20 said at least one planetary body about its planetary axis. Preferably said at least one central gear comprises at least one central toothed sprocket, and said drive chain comprises at least one endless chain engaging therewith and with at least one planetary sprocket fixed for rotation with each planetary body 25 Preferably the absolute ratio of rotary motion of the planetary bodies and said main body, considered with respect to said base, lies between 4:1 and 0.5:1.

WO 00/71258 PCT/AUOO/00492 -4 Preferably the absolute ratio of rotary motion of the planetary bodies and said main body, considered with respect to said base, lies between 2:1 and 0.5:1. Preferably the ratio of rotary motion of the planetary bodies and said main body, considered with respect to said base, is -1:1. 5 Preferably said planetary body includes means for retaining access covers on said tubular ball mill pots. The means for retaining may comprise any known arrangement such as threading engagement of a lid, or clips or the like. However, it is most preferred that the means for retaining comprises a mechanism adapted in a first position to 10 retain said access covers on said tubular ball mill pots and in a second position to allow any one or more of said access covers to be removed from said tubular ball mill pots. Preferably said mechanism comprises an arm pivotally attached along an axis parallel to said planetary axis. 15 Preferably said mechanism includes adjustment means to allow clearance adjustment from said arm to each said access covers, in order to ensure that said access covers are retained tightly on said tubular ball mill pots. Preferably said mechanism is associated with clip means to retain said mechanism locked in said first position. 20 Preferably said tubular ball mill pots are each received in holders located in said planetary body. This arrangement allows for removal of a tubular ball mill pot for refurbishing or replacement. Preferably a clutch is provided between said drive means and any said planetary body.

WO 00/71258 PCT/AUOO/00492 -5 Preferably said clutch is provided between said drive means and each said planetary body, each said clutch allowing selective disengagement of a said planetary body from the drive means with which it is associated. When so disengaged, a planetary body may be manually rotated, to allow the tubular ball 5 mill pots to be emptied in unison. In order to maintain the rotational synchronisation, the clutch includes a spring loaded mechanism which engages in only one relative angular disposition of said planetary body. Alternatively, means for emptying the mill pots may be provided by means for 10 rotating said at least one central gear relative to said base. The means for emptying the mill pots is used only when the main body is not rotating. Preferably said means for rotating rotates all of said at least one central gears. Preferably said means for rotating includes a hydraulic ram linked to said at least one central gear. When it is desired to empty the mill pots, the ball mill is stopped 15 operating (ie drive to the main body is stopped), the lids of the mill pots on the appropriate planetary body are removed, and the means for rotating is actuated until the mill pots empty. Preferably said hydraulic ram is actuated by a hand operated rotary pump. Operation in this manner ensures that fine control can be achieved manually. 20 BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention will now be described in the following description made with reference to the drawings, in which Figure 1 is a perspective view from the front of a planetary ball mill according to the embodiment; 25 Figure 2 is an end elevation from the front, showing the mill at 0O rotation; Figure 3 is an end elevation from the front, showing the mill at 22.50 anticlockwise rotation; WO 00/71258 PCT/AUOO/00492 -6 Figure 4 is an end elevation from the front, showing the mill at 450 anticlockwise rotation; Figure 5 is an end elevation from the front, showing the mill at 67.50 anticlockwise rotation; 5 Figure 6 is an end elevation from the front, showing the mill at 900 anticlockwise rotation; Figure 7 is a side elevation of the mill showing only one of the planetary bodies for simplicity; Figure 8 is an end elevation showing means for retaining access covers in 10 a closed position; Figure 9 is an end elevation showing means for retaining access covers of figure 8, in an open position; Figure 10 is a front end elevation showing one of the clutch means for the planetary bodies 15 Figure 11 is a side elevation showing the clutch means of figure 10; and Figure 12 is a perspective view of one of the tubular ball mill pots and its access cover being handled. BEST MODE FOR CARRYING OUT THE INVENTION The embodiment is directed toward a batch milling ball mill suitable for preparing 20 ore samples for analysis. In particular the ball mill of the embodiment can be used for fine comminution and lixiviation in a single rapid step. Referring to figure 1, the ball mill indicated generally at 11 includes a base 13 having a mount 15 at each end thereof in which is received a main body 17 for rotation about a main axis. The main body is rotatably driven by a 5.5kW three 25 phase electric motor 19 via a reduction belt 21 and pulley 23 arrangement, and a 13:1 reduction gearbox 25. The motor 19 has its speed controlled by a variable voltage and frequency switch-mode power-supply which is controlled by a programmable logic controller (not shown). The motor 19 is generally run at speeds sufficient to achieve between 50rpm and 150rpm in the main body, with 30 the optimum main-body rotation speed being 90rpm. Higher speeds could WO 00/71258 PCT/AU00/00492 -7 achieve effective grinding, but the upper limit is dictated by physical constraints which if exceeded could lead to self destruction. The main body 17 includes a central shaft 27 extending along the main axis. The main body 17 has four arms 29 extending from the central shaft 27 near each end 5 thereof, the arms 29 supporting at their distal ends 31 planetary bodies 33a, 33b, 33c, and 33d, the latter two being shown in dashed outline for clarity and ease of viewing. The planetary bodies 33 are elongate in configuration, and arranged in two opposing pairs 35a and 35b comprising planetary bodies 33a and 33c, and planetary bodies 33b and 33d respectively, each pair being located on either side 10 of the axis of the main body 17. The planetary bodies 33a, 33b, 33c, and 33d are each mounted for rotation about a planetary axis which extends between the respective arms 29 in which they are mounted. A sprocket mount 37 is secured to the base 13, and supports sprockets 39a and 39b, which are fixedly secured thereto in spaced apart relation, concentrically 15 along the main axis. The sprockets 39a and 39b do not rotate with respect to the base 13. The sprocket mount 37 includes a bore (not shown) concentric with both sprockets 39a and 39b, which carries bearings to support the central shaft for rotation therewithin. Each planetary body 33 has a sprocket 41 secured for rotation therewith via a 20 clutch mechanism 42 which is normally in an engaged condition. A drive chain 43 extends between the sprocket 39a and the sprockets 41 connected with planetary bodies 33a and 33b, and a drive chain 45 extends between the sprocket 39b and the sprockets 41 connected with planetary bodies 33c and 33d. As the main body 17 is rotated, driven by the motor 19, orbiting movement of the 25 planetary bodies 33 results in rotation being imparted to the planetary bodies 33, through the chains 43 and 45 riding over respective stationary sprockets 39a and 39b, and driving the sprockets 41. The direction of rotation of the planetary bodies 33 is opposite to the direction of rotation of their orbit. Referring to figures 2 to 6, a sequence of views shows the relative movement of main body 17 and WO 00/71258 PCT/AUOO/00492 -8 planetary bodies 33, through 900 of anticlockwise rotation of the main body 17. It will be observed that the planetary bodies undergo 1800 clockwise rotation relative to the main body 17, which is a 90 rotation relative to the base 13. This arises due to the gearing ratio of planetary bodies 33 to the main body 17 being 5 1:2; the ratio of relative rotational movement of planetary bodies 33 and the main body 17, considered with respect to said base, being -1:1. With these ratios, and with the combined effect of the main body rotation and the counter planetary body rotation as observed with respect to the base 13, the net effect is believed to be end-to-end axial movement of the contents within the tubular ball mill pots, 10 resulting in very efficient milling. The planetary bodies 33 each have a base 47 and side walls 49, and apertures (not shown) in which are received thirteen individual tubular ball mill pots 51. Referring to figure 12, the tubular ball mill pots 51 each have a cover 53 which has an annular recess 55 to receive the inner lip 57 of a tubular ball mill pot 51. 15 In use, between eight and twenty steel or ceramic balls or beads of a nominal diameter of 8mm are placed inside the tubular ball mill pots 51 along with a sample to be milled, and optionally simultaneously lixiviated, before the covers 53 are placed on top of the tubular ball mill pots 51. Each planetary body 33 includes, associated therewith, means for retaining the 20 covers 53 in closed condition on the tubular ball mill pots 51. This means is in the form of a mechanism comprising a horizontal bar 55 attached to the planetary body 33 by way of articulated levers 57. The horizontal bar is moveable from a first position as shown in figure 8 in which the covers 53 are retained in a closed condition on the tubular ball mill pots 51, and a second position, shown in figure 9 25 where the covers 53 are accessible for removal. Attached to the horizontal bar 55 are a plurality of adjustment screws 58, aligned one for each cover 53, which adjustment screws 58 can be adjusted so that the covers 53 are retained tightly, in the first position of the mechanism. A handle 59 is provided, attached to the horizontal bar 55, so a user can operate the mechanism. The horizontal bar 55 30 engages in the first position by way of an over-centre action, although other methods of engagement could be employed such as a clip or fastener assembly.

WO 00/71258 PCT/AUOO/00492 -9 Referring to figures 10 and 11, the clutch mechanism 42 is shown in greater detail. The sprockets 41 connect to an outer casing 61 which is normally held engaged by a spring loaded pin 63 with an inner casing 65. The inner casing 65 is connected with a planetary body 33. An axially extending pin 67 provides 5 leverage support for an actuating lever 69 which, with the mill stopped, is used by an operator to access the spring-loaded pin 63 to allow disengagement of the clutch 42. With the clutch 42 disengaged, the operator may manually rotate the planetary body 33 to empty the pots 51. The arrangement of the clutch mechanisms 42 with each of the planetary bodies 10 33, in effect provides means for emptying the mill pots. In an alternative arrangement envisaged by the inventor, the clutch mechanisms 42 can be omitted, which would result in the sprockets 41 being fixed for rotation with their respective planetary bodies 33. With such an arrangement, means for emptying the mill pots is provided through means for rotating the normally stationary 15 sprockets 39a and 39b. Such means for rotating can be provided by a hydraulic ram fixed at one end to the base 13 and at the other end to a position on the stationary sprockets 39a and 39b. Operation of the hydraulic ram will rotate the sprockets, causing all of the planetary bodies to rotate, while the main body 17 remains stationary. 20 The hydraulic ram can be operated by a manual rotary pump, so the user has precise control over rotation of the planetary bodes 33 when emptying the pots 51. As will be understood, when it is desired to operate the hydraulic ram, it is necessary to stop the motor 19. Alternative means for rotation may comprise a hydraulic rotary motor or an 25 electric motor, with reducing gearbox providing a drive train to the normally stationary sprockets 39a and 39b. It may be desirable to include a locking pin or pawl arrangement to lock the stationary sprockets 39a and 39b in the normal stationary operating position, in order to remove stress from the hydraulic ram when the ball mill is operated.

WO 00/71258 PCT/AUOO/00492 -10 When the pots 51 are to be emptied, they may be emptied into a trough or into individual containers. The linear configuration of the arrangement of the pots 51 lends itself to emptying into a trough. A screen can be used, located above the trough, to separate ground sample from the grinding medium (steel or ceramic 5 balls or beads). Once the pots 51 have been emptied, they can be washed out, and the grinding medium washed, before the grinding medium is returned to the pots 51 and fresh sample for grinding is introduced. The ground sample in the trough can be washed down to a collection point for further processing or assay. If required, the discharge from one or more (or all) of the pots can be "dry" 10 sampled by pouring past a sampling cup on emptying the pots 51. These dry samples can be taken away for analysis. Other methods for handling the ground sample will be clear to a person skilled in the art, or an operator of the ball mill. While the ball mill of the invention has been designed for mineral assay, its 15 design lends itself to other applications where high efficiency milling is required. In mineral assay applications, the ball mill of the invention allows a maximised sample size, the use of wet or dry coarse samples produced either directly during drilling or as prepared by minimal preparation such as crushing or splitting, and achieves fast and efficient lixiviation of values from the sample for subsequent 20 analysis. It will be understood that where lixiviation is to take place simultaneously with milling, the material of construction of the mill pots or liners therefor must be taken into account to allow this. Benefits of combined milling and lixiviation ensures good mass transfer conditions, as well as imparting Rehbinder energy to the particles which both 25 enhance the rate of dissolution of desired mineral species. Further, any surface fouling or tarnishing which might exist in the samples, or be induced on some materials during lixiviation, will be removed during the intense milling.

WO 00/71258 PCT/AUOO/00492 -11 A particular benefit of this invention is ore samples directly received from sample drilling or light crushing with no prior drying can be handled, with allowance made for the typical moisture content associated with the ore type being sampled. By not requiring pre-drying of samples, a very large labour requirement, and sample 5 delay time of 6-12 hours can be avoided. It should be appreciated that the scope of the invention is not limited to the particular embodiment described herein.

Claims (25)

1. A ball mill having a fixed base with a mount for receiving a main body rotatable along a main axis, said main body defining mounts for receiving at least one planetary body having a planetary axis located distal from and 5 parallel to said main shaft axis, wherein said planetary body supports at least one tubular ball mill pot having a central axial extent perpendicular to said main shaft axis.

2. A ball mill as claimed in claim 1 wherein each said planetary body supports a plurality of said tubular ball mill pots. 10

3. A ball mill as claimed in claim 1 or 2 wherein said at least one planetary body is rotatable about said planetary axis.

4. A ball mill as claimed in claim 3 wherein each said planetary body is associated with drive means to rotate said planetary body relative to said main body. 15

5. A ball mill as claimed in claim 4 wherein the drive means is adapted to maintain the planetary bodies in synchronisation, in order to prevent the ball mill from becoming unbalanced.

6. A ball mill as claimed in claim 4 or 5 wherein said drive means is arranged to impart a rotary motion in said planetary bodies which is opposite in direction 20 to the rotary motion of said main body.

7. A ball mill as claimed in any one of claims 4 to 6 wherein said drive means includes at least one central gear, each being mounted along said main axis and being fixed relative to said base in operation, with a said drive train extending from each said at least one central gear to drive each said at least 25 one planetary body about its planetary axis. WO 00/71258 PCT/AUOO/00492 -13

8. A ball mill as claimed in claim 7 wherein said at least one central gear comprises at least one central toothed sprocket, and said drive chain comprises at least one endless chain engaging therewith and with at least one planetary sprocket fixed for rotation with each planetary body. 5

9. A ball mill as claimed in any one of claims 4 to 8 wherein the absolute ratio of rotary motion of the planetary bodies and said main body, considered with respect to said base, lies between 4:1 and 0.5:1.

10. A ball mill as claimed in claim 9 wherein the absolute ratio of rotary motion of the planetary bodies and said main body, considered with respect to said 10 base, lies between 2:1 and 0.5:1.

11. A ball mill as claimed in any one of claims 6 to 8- wherein the ratio of rotary motion of the planetary bodies and said main body, considered with respect to said base, is -1:1.

12. A ball mill as claimed in any one of the preceding claims wherein said 15 planetary body includes means for retaining access covers on said tubular ball mill pots.

13. A ball mill as claimed in claim 12 wherein the means for retaining comprises a mechanism adapted in a first position to retain said access covers on said tubular ball mill pots and in a second position to allow any one or more of 20 said access covers to be removed from said tubular ball mill pots.

14. A ball mill as claimed in claim 13 wherein said mechanism comprises an arm pivotally attached along an axis parallel to said planetary axis.

15. A ball mill as claimed in claim 14 wherein said mechanism includes adjustment means to allow clearance adjustment from said arm to each said 25 access covers, in order to ensure that said access covers are retained tightly on said tubular ball mill pots. WO 00/71258 PCT/AUOO/00492 -14

16. A ball mill as claimed in claim 13 to 15 wherein clip means is provided to retain said mechanism locked in said first position.

17. A ball mill as claimed in any one of claims 2 to 16 wherein said tubular ball mill pots are each received in holders located in said planetary body. 5

18. A ball mill as claimed in any one of the preceding claims wherein a clutch is provided between said drive means and any said planetary body.

19. A ball mill as claimed in claim 18 wherein said clutch is provided between said drive means and each said planetary body, each said clutch allowing selective disengagement of a said planetary body from the drive means with 10 which it is associated.

20. A ball mill as claimed in claim 18 or 19 wherein, in order to maintain rotational synchronisation, the clutch includes a spring-loaded mechanism which engages in only one relative angular disposition of said planetary body. 15

21. A ball mill as claimed in any one of claims 1 to 17 wherein, means for emptying the mill pots may be provided by means for rotating said at least one central gear relative to said base.

22. A ball mill as claimed in claim 21 wherein said means for rotating rotates all of said at least one central gears. 20

23. A ball mill as claimed in claim 21 or 22 wherein said means for rotating includes a hydraulic ram linked to said at least one central gear.

24. A ball mill as claimed in claim 23 wherein said hydraulic ram is actuated by a hand operated rotary pump.

25. A ball mill substantially as herein described with reference to the drawings.