Abstract:
A centrifugal jig has a container mounted for rotation about its longitudinal axis ( 22 ), separated into an axial region ( 32 ) and a peripheral region by ragging material ( 41 ) supported by a screen ( 30 ). The peripheral region is composed of a series of hutch chambers ( 34 ) with reciprocating wall portions ( 45 ) located radially outside the screen ( 30 ), for repetitively dilating the ragging. 
     Also disclosed is a hutch chamber construction applicable to both rotary and non-rotary jigs, having a reciprocating wall portion ( 45 ) which includes convergent wall surfaces leading to the hutch chamber concentrate outlet ( 44 ).

Description:
This application is a continuation of U.S. patent application Ser. No. 09/486,081, filed Feb. 28, 2000 now U.S. Pat. No. 6,286,686, which was a National Stage filing of PCT/AU98/00657, filed Aug. 20, 1998 and claimed foreign priority to Australian Patent Application No. PO8691, filed Aug. 20, 1997. All priority documents are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF INVENTION 
     This invention relates to jigs which separate materials in a feed mixture on the basis of differing specific gravities and especially, but not exclusively, to centrifugal jigs of the general type described in International Patent Publication Nos. WO86/04269 and WO90/00090, in which a feed slurry is introduced into a rotating chamber bounded radially by a screen provided with ragging on its inner surface, the ragging being dilated repetitively to provide jigging action. 
     In WO86/04269, the ragging is dilated by pulsing the water in a hutch chamber which surrounds the screen. The water is pulsed by means of a diaphragm positioned at the base of the hutch chamber. In WO90/00090, a number of hutch chambers are circumferentially spaced about the jig screen, with the water in the hutch chambers being pulsed sequentially. Each hutch chamber has a diaphragm positioned below the screen, with the diaphragms being actuated by respective pushrods driven by a central crank assembly. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide an improved pulsating mechanism for a jig. 
     In a first form, the invention provides a centrifugal jig having a container mounted for rotation about a longitudinal axis, the container having an axial region, a peripheral region separated from the axial region by ragging which is radially restrained by screen means, means for introducing feed material to the axial region and means for pulsating fluid in said peripheral region so as to repetitively dilate said ragging, characterised in that the pulsating means is located directly radially outwards of said screen means. 
     A further form of the invention provides a method of separating components of a feed material on the basis of specific gravity in a container of a centrifugal jig which has an axial region, a peripheral region separated from the axial region by ragging which is radially restrained by screen means, including the steps of rotating the container about its longitudinal axis, introducing the feed material to the axial region and repetitively dilating the ragging by means of pulsating means located directly radially outwards of the screen means. 
     Preferably, the pulsating means includes a reciprocating wall portion of one or more hutch chambers which comprise the peripheral region, most preferably a portion of a radially outer wall of the hutch chamber, including convergent wall surfaces which lead to the hutch chamber concentrate outlet. 
     Preferably, the reciprocating wall portion of each hutch chamber reciprocates along a substantially radial line of action which intersects with the screen. 
     A yet further form of the invention, applicable both to centrifugal and gravity (non-rotary) jigs, provides a jig having at least one hutch chamber, said hutch chamber having a reciprocating wall portion which includes convergent wall surfaces leading to a hutch chamber concentrate outlet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further preferred embodiments of the invention shall now be described with reference to the accompanying drawings, in which: 
     FIG. 1 is a sectional elevation of a centrifugal jig employing a preferred pulsing hutch arrangement; and 
     FIG. 2 is a sectional elevation of the screen, hutch and pulsating assembly shown in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a centrifugal jig of the general type according to the Applicant&#39;s WO90/00090 but employing a pulsion mechanism according to the present invention. The general construction and operation of the jig are described in detail in that patent, the contents of which are incorporated herein by reference, and shall now be described here only briefly. 
     The centrifugal jig of FIG. 1 has a frame  10  supporting a jig drive motor  12 , a crank drive motor  13 , a fixed launder arrangement  14  and cover  16  and a jig main shaft  18  which is supported in bearings  20  to rotate about a rotational axis  22 . 
     The main shaft  18  is driven by the jig drive motor  12  through jig drive pulley  24  and jig drive belt  26 . Mounted on the main shaft is a screen housing  28  supporting a screen  30  defining an inner chamber  32  and a number of hutch chambers  34  circumferentially spaced about the screen. Mounted inside the jig main shaft for independent rotation in bearings  35  is a crankshaft  36  with crank  38  for reciprocating a respective pushrod  40  for each hutch chamber. 
     Ragging material  41  (shown in FIG.  2 ), such as run-of-mill garnet, aluminium alloy or lead glass balls, is provided on the inner surface of the screen  30 . The ragging is held against the surface of the screen due to the rotation of the jig. The feed slurry entering the inner chamber  32  through the feed tube  42  migrates to the inner surface of the ragging. 
     Hutch water is supplied to tube  43 , passing through bores (not shown) in the screen housing  30 , into each of the hutch chambers  34  circumferentially spaced about the screen. The crank  38  sequentially reciprocates a series of radially extending pushrods  40 , with each pushrod in turn reciprocating a respective hutch chamber  34 , as will be described below with reference to FIG.  2 . The reciprocation of the hutches causes pulsation of the water in the respective hutches. 
     The ragging is repetitively dilated by the pulsation of the hutch water. This dilation allows the higher specific gravity material in the feed slurry to pass through the ragging and the screen and enter the hutch chambers. The concentrate material then travels along the convergent walls  45  of the hutch to the radially outermost part of the hutch chamber and passes through concentrate outlet spigot  44 , which is aligned with a gap in the inner wall of a concentrate launder  46 . The lower specific gravity material in the feed slurry does not pass through the ragging, but passes upwardly and escapes past the open top  48  of the inner chamber and then to a tailings launder  50 . 
     The jig of FIG. 1 is mounted for rotation on an inclined axis  22  so that the ragging and feed material in the jig will fall to the lower side of the jig when the jig is stopped or is rotated only slowly. The inclined axis also requires the use of only one outlet from each of the tailings and concentrate launders. 
     Screen cleaning apparatus  54  is mounted on the stationary jig cover  16  and extends into the high side of the jig, pivoting and retracting between a cleaning position (shown in FIG. 1) for cleaning the screen and a withdrawn position (shown in ghost) radially inwards of the jig feed material, during normal operation of the jig. The cleaning apparatus includes a high pressure water spray  56  and a series of scraper wheels  58  depending from cantilevered cleaner head  59  and acting against the inner surface of the screen, which will typically have a large number of circumferentially elongate slots extending therethrough. The wheels have a series of projecting blades  60  disposed diagonally on their circumference for forcing particles accumulated on the screen to be sheared off at the screen surface and then forced through the screen by the water spray. The wheels are resiliently mounted so as not to cause damage to the screen when an unusually resistant particle is encountered. 
     In an unillustrated modification, the screen cleaner can include a plurality of spring-mounted buttons on the end face of an enlarged cantilevered cleaner head  59  instead of using scraper wheels  58 . The buttons may be moved up and down across the screen surface to shear off lodged particles for removal by the water spray  56 . 
     The screen cleaning arrangement is applicable to centrifugal jigs and other equipment employing rotating screens. 
     FIG. 2 illustrates the new pulsing hutch assembly in more detail. 
     With reference to FIG. 2, the inner surfaces of the hutch chamber walls are convergent in the direction of travel of a particle—i.e. radially outwards for a centrifugal jig as illustrated, or downwards for a non-rotary jig (not shown)—for example conical or rectangular pyramidal, with the concentrate outlet spigot  44  at its apex. The radially inwards portion  62  of the hutch is part of the casting of the jig screen housing  28 , while the radially outwards part surrounding and attached to the outlet spigot  44  is formed by a diaphragm  64  backed by a support block  66 . Each support block is attached to the upper end of the lever  68  pivoting about a fulcrum member  70  attached to the screen housing  28 . The lower end of each lever is attached to a respective pushrod  40 . 
     When each pushrod  40  is forced radially outwards by the crank  38 , the respective lever  68  forces radially inwards movement of the hutch diaphragm  64 , with the resultant pulsation of the hutch water in the hutch chamber causing dilation of the ragging. The concentrate material passes through the ragging and exits the hutch chamber via outlet spigot  44  as discussed above in relation to FIG.  1 . 
     The heavy block  66  behind the diaphragm causes the hutch to be strongly biased toward the radially outwards (non-pulsating) position under influence of the centrifugal motion of the jig. This causes the hutch to quickly and positively return to this position after actuation of the pushrod by the crank, holding the pushrods  40  against the crank  38  with little or no “bounce”. This is an advance over the prior art, in which the pulse water pressure was used to force the diaphragm return, and gives protection against damage to the machine in the event of the hutch water supply being interrupted. 
     A spring actuated lever return  72  may also be provided to hold the hutch in the non-pulsed position when the jig is stationary or is being rotated at very low speeds for routine maintenance. 
     By providing the pulsators directly and centrally opposite the respective portions of the screen, in accordance with the first form of the invention, the depth of water through which each pulse is transferred from the pulsator to the ragging is decreased. This allows higher pulsation rates with greater coupling between the pulsator and the ragging, resulting in less water hammer and smoother operation of the jig. 
     Other advantages of preferred forms of the invention are increased energy efficiency and smoother operation caused by a reduction in the volume of the hutch chamber, and thus the volume of water pulsated, as it is no longer necessary to extend the hutch chamber below the level of the screen. The volume of the hutch may be further reduced as the rapid pulsation of the hutch wall portion containing the convergent walls and concentrate outlet assists discharge of the concentrate from the hutch. Higher density concentrate slurries can pass through the hutch and the wall angle of the hutch can be reduced without accumulation of the concentrate on the hutch wall, thus allowing the use of a flatter, more compact hutch. The reduction in hutch volume gives scope for production of higher capacity jigs than capable with the prior art pulsion mechanisms. 
     A yet further advantage is more even dilation of the bed of ragging, allowing more efficient use of the screen area and therefore increasing the throughput capacity of the jig, due to the pulsator. 
     While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.