WO2005016540A1

WO2005016540A1 - Advanced jigging apparatus

Info

Publication number: WO2005016540A1
Application number: PCT/ZA2004/000100
Authority: WO
Inventors: Cicero Combrinck; Daniël Booyens STEYN
Original assignee: Cicero Combrinck; Steyn Daniel Booyens
Priority date: 2003-08-18
Filing date: 2004-08-17
Publication date: 2005-02-24
Also published as: ZA200601634B

Abstract

Apparatus (1) for wet jigging comprises an conical displacement member (8) forming a floor of the hutch chamber (7), reciprocated by a actuating mechanism (10) to deliver succesive positive pulses in water into the hutch chamber jigging screen (3). A pumping chamber (11) is formed below the cone, one-way valves (12) in the wall of the pumping chamber for draw water into the pumping chamber when the cone rises, one-way valves (14) in the cone for transfer water from the pumping chamber to the hutch when the cone falls and a make up water is supplied at (16) into the hutch. A supplementary supply at (17) is provided to the pumping chamber to prevent cavitation. A normally fixed underpass barrier (35) and a movable vent (43) controlled by an interface level detector (44) are provided at the discharge end (6).

Description

ADVANCED JIGGING APPARATUS

FIELD OF THE INVENTION

This invention lies in the field of wet jigging and concerns methods and apparatus for separating particulate materials.

BACKGROUND

Jigging is widely used to separate mineral materials into fractions of different densities. A typical wet jig consists of a jig chamber with a screen bottom. Feed apparatus introduces material to be separated as a bed at one end of the screen and discharge means removes the stratified fractions at the other end or from below. A space underneath the screen is called a hutch in which apparatus generates a pulsation in water or medium that fills the hutch and the stratifying space above the screen.

A problem encountered in jigging, is that if the pulsation generates a downward phase as well as an upward phase that is the propulsion phase, the downward phase causes a suction on the bed. The repeated dilations of the bed produced by the propulsion phases of the pulsation, which enhances the stratification of the bed, are disturbed by the interposed suction phases. The stratification of the bed tends to be counteracted during the suction phases when the less dense particles tend to be sucked back between the denser particles. Stratification and hence separation deteriorates.

This problem is encountered and has adverse effects in both through the bed jigging and on the bed jigging.

through the bed jigging is typically used where only slight density differences occur and is usually more suitable for finer particles. In through the bed jigging the apertures in the screen pass the particles of the material to be separated. A layer of particles, which are larger than the apertures is located on the screen and commonly referred to as ragging. The ragging particles are less dense than the denser particles to be separated but more dense than the tailings. While the pulsing of the water proceeds, the denser materials work their way through the ragging into the hutch below, from which they are removed e.g. by screw or pump.

In through the bed jigging a suction phase causes the less dense materials to tend to be sucked through the ragging. This problem occurs even when a so called neutral hutch water pressure is maintained, by introducing water into the hutch to compensate for water losses, which arise when removing the denser fraction from the hutch chamber.

On the bed jigging is typically used for separation of course particles. The particles do not pass the apertures of the screen thus preventing the particles from entering the hutch. The material stratifies into heavier particles in lower strata and lighter particles in higher strata, as the material moves over the screen towards the discharge end. The lower fractions are separated by discharging through a discharge gate or gates and the lighter fractions, commonly the tailings, are discharged over a weir, thus effecting the separation.

Also in the case of on the bed jigging, if the pulsation causes a suction through the bed, especially if this occurs in the vicinity of the gate, the suction tends to disturb the stratification. This results in a flow of some of the less dense material from the upper strata of the bed through the gate and hence less effective separation.

A further problem is experienced in on the bed jigging in regard to the discharge gate. This is typically adjusted to a position at or close to the screen, according to the required control of the rate of discharge of the denser fraction and dependant on the degree of stratification of the bed. The adjustment is usually automated by mechanically or electronically tracking the height of the interface between the denser and lighter fractions. Since the separating action of the gate is mechanical, particles on the bed can and often do prevent the gate being properly adjusted downwards. This results in a poorer separation, even if there were adequate stratification ahead of the gate. Severe problems often arise in this control function, due to obstruction of the gate movement caused by particles in the gate.

German Patent 887 181 issued in 1953, despite being an early proposal and using mechanical cranks to reciprocate pistons, is interesting in proposing a cylinder on one side of the hutch that generates a compensating discharge to neutralise the suction effect or provide an under- or over-compensation (page 3, lines 16 to 27). The action according to this invention is thus a series of positive pulses (propulsions) interposed by quiescent stages. The directions of the positive pulses and the compensating discharge are, however, unsatisfactory.

PCT patent application PCT/ZA01/00008, published 1 August 2001 , by one of the present inventors discloses an hydraulically driven displacement member that forms a flat base of the settling vessel (i.e. hutch) above and an expansion chamber below the base (page 3, lines 21 -23). The displacement member has a lower diaphragm that is of larger area than an upper one and has one-way valves. On downward movement of the member, water is propelled from the expansion chamber to the hutch to neutralise the suction effect or even produce a propulsion pulse through the bed is produced (page 12, lines 25 to 33). On upward movement of the displacement member a propulsion pulse through the bed is also produced and an ongoing sequence of propulsion pulses is produced in the bed.

However, due to engineering disadvantages development work diverted away from this design. The main reason was the excessive forces required to produce pulses in the large mass of water above the displacement member. A further problem is that as the water is introduced at one side and discharges at the other, forces tending to tilt the displacement member result in the large forces that are due to the large mass of the water having a horizontal component that has to be carried. This is carried by the hydraulic pistons and cylinders in that design, causing premature wear and high maintenance cost. For example, working jigs have been found to require the cylinder seals and piston chrome plating to be renewed at six-monthly intervals. PCT patent application PCT/ZA02/00135 (not yet published) discloses a design in many respects similar but with the flat displacement member located alongside the hutch in a pumping chamber. The same problem, however, of a large mass of water to be pulsed in the hutch still exists and very large forces in the hydraulic cylinders, including the horizontal component of forces.

In both designs according to these two PCT applications a further difficulty is the flexible seals at the edges of the flat displacement member which are subject to the large forces and it is difficult to make them long lasting and durable.

THE INVENTION

The features of a jigging apparatus design according to the invention relate to solving the problem with the production of the pulses and to solving the problem with the discharge of material at the discharge end of the screen.

An apparatus for wet jigging in accordance with the first aspect of this invention, in which particulate material to be separated is fed to a feeder end of a jigging screen forming a bottom of a jigging chamber and stratified material is removed at one selected from a discharge end of the screen and a hutch chamber below the screen, comprises an inverted truncated conical displacement member forming a floor of the hutch chamber, connected at the truncated narrow lower end of the cone to an actuating mechanism that produces a reciprocation up and down of the cone to deliver successive positive pulses in water into the hutch chamber and thence upwardly through the jigging screen, a pumping chamber formed below the cone, one-way valves in the wall of the pumping chamber for drawing water into the pumping chamber when the cone rises, one-way valves in the cone for transferring water from the pumping chamber to the hutch when the cone falls and a make up water supply provided into the hutch.

Preferably a further water supply is provided into the space in the pumping chamber below the cone, to prevent or reduce cavitation effects arising under the cone when it rises. The apparatus includes a supply of water to the pumping chamber via the oneway valves, which preferably comprises a tank alongside the apparatus with pipes that feed water to the one way valves of the pumping chamber.

The reciprocating drive of the cone is preferably a beam that is linked to the narrow truncated base of the cone at an intermediate position and a hydraulic cylinder at an end of the beam that is pivoted at an opposite end.

An optional design that has some advantage can be two or more truncated inverted cones forming the floor of the hutch, these can be driven by a yoke or other beam arrangement by a hydraulic cylinder or directly by two or more hydraulic cylinders or other arrangement.

As is known by the inventor, the positive displacement mechanism has a high efficiency of transfer of driving energy to the pulse energy.

The upper large truncated end of the cone must be substantially sealed against side-walls of the hutch chamber and this can be done by sliding seals against the inner surfaces of the hutch chamber walls, for example.

By providing sufficient make-up water a method is realised, in which there is no reverse or suction flow through the screen, eliminating the adverse effects of suction flow on the stratification process.

Furthermore, the stratification is enhanced by quiescent periods between the upward (positive) pulses, during which the bed settles, quiescent period being adjustable by adjusting the rate of make-up water flow. Pulsating bed dilation and active stratification can be optimised, optimising the rate of stratification and hence discharge of separated material, in comparison with the art.

The problems associated with the discharge of material at the discharge end of the screen for the heavier fractions in on the bed jigging, are solved in accordance with the second aspect of the invention. According to the second aspect of the invention, the discharge means comprises an underpass barrier, located just short of a discharge end of the screen, defining an end region of the screen, an underflow chute that has a communicating region that communicates with the end region of the screen and a delivery channel, the underflow chute and channel being filled with water, a means interposed in the channel of separating the discharged heavier fraction from the water, the channel returning the water to the communicating region of the underflow chute that communicates with the end region of the screen, creating a closed circuit and a vent in the discharge means in the communicating region that communicates with the end region of the screen.

Preferably a sensor means that senses an interface level in the stratified bed is added with a control means responsive to the interface level, to control the opening and closing of the vent.

A method of control of discharge from the jigging apparatus according to the invention comprises setting an underpass barrier at a level, somewhat lower than the height of the interface between the heavier fraction and the lighter fractions in the stratified bed, this height pre-selected and generally stable during jigging, maintaining a closed circuit of zero flow or quiescent condition in a region where the end region of the screen communicates with a chute, to have the result that pulses do not pass through the end region of the screen and bed and no discharge occurs, opening a vent in the underflow channel to divert pulses to pass through the end region of the screen and bed, bringing about a drop in the interface level to the underpass barrier level and a discharge of the heavier fraction into the underflow channel and to the delivery channel.

Preferably the vent is controlled automatically by a level sensing device that senses the interface level continuously.

As a result, the discharge of heavier fraction is not controlled by mechanical movement of a gate (with incumbent problems of the prior art) but control of the level of the interface between heavier and lighter fractions and control of the pulses at the end region of the screen to lift the heavier fraction over the discharge end of the screen. This is a new principle of discharge control and can be used to achieve more effective separation.

The underpass barrier level is only changed if there is a change in jigging parameters and material being treated, the underpass barrier is not continuously height adjusted to control the discharge of the heavier fraction.

The rest periods between pulses can be made very brief, a very small fraction of the period occupied by the pulses. This reduces the quiescent periods between pulses, a pulsing dilation of the bed is maintained and the rate of stratification of the bed is enhanced, with significant economic benefits.

THE DRAWINGS

The invention will be more fully described by way of non-limiting example, with reference to the accompanying drawings, in which: -

figure 1 is a simplified schematic side elevation of an apparatus in accordance with a preferred embodiment of the invention,

figure 1 A is a schematic plan view of an alternative arrangement,

figure 1 B is an enlarged side elevation of a discharge end,

figure 2 is an end elevation of a further embodiment,

figure 3 is a plan view of the embodiment shown in figure 2, and

figure 4 is a side elevation of a still further embodiment. THE PREFERRED EMBODIMENTS

Referring to figure 1 , the apparatus for wet jigging 1 , has particulate material to be separated fed to a feeder end 2 of a jigging screen 3 forming a bottom of a jigging chamber 4 and stratified material 5 is removed at a discharge end 6 of the screen. A hutch chamber 7 is defined by an inverted truncated conical displacement member 8 forming a floor of the hutch chamber. The displacement member is in the form of a truncated square or rectangular truncated cone, the hutch chamber and jig chamber having the same shape in plan view. Connected at the truncated narrow lower end 9 of the conical displacement member is an actuating mechanism 10 that produces a reciprocation up and down of the displacement member to deliver successive positive pulses in water into the hutch chamber and thence upwardly through the jigging screen. A pumping chamber 11 is formed below the displacement member and one-way valves 12 are located in the wall 13 of the pumping chamber for drawing water into the pumping chamber when the displacement member rises. One-way valves 14 are located in the displacement member wall 15 for transferring water from the pumping chamber to the hutch when the displacement member falls. A make up water supply is provided by a pipe 16 into the hutch chamber.

A further water supply is provided by a pipe 17 into the space in the pumping chamber below the cone, to prevent or reduce cavitation effects arising under the cone when it rises.

The apparatus includes a supply of water to the pumping chamber via the oneway valves, which comprises a tank 18 alongside the apparatus with pipes 19 that feed water to the one-way valves of the pumping chamber.

The reciprocating drive of the cone is a beam 20 that is linked at 21 to a pipe 22 depending from the narrow truncated base of the conical displacement member at an intermediate position and a hydraulic cylinder 23 has its piston rod 49 connected at an end 24 of the beam that is pivoted to a fixed structure at an opposite end 25. The depending pipe communicates with the hutch chamber and can be used to remove material that has been separated into the hutch in through-the-screen jigging. A seal 30 is provided in the floor of the pumping chamber where the depending pipe passes through.

As shown in figure 1 A, an optional design that has some advantage can be two or more truncated inverted rectangular conical displacement members 26 and 27 forming the floor of the hutch. These can be driven by a beam that is in the form of a yoke 28 or other beam arrangement by a hydraulic cylinder 29 or directly by two or more hydraulic cylinders or other suitable arrangement.

The upper large truncated end 31 of the cone is substantially sealed against side- walls 32 of the hutch chamber by sliding seals 33 that bear against the inner surfaces of the hutch chamber walls.

A discharge means 34 comprises an underpass barrier 35, located just short of a discharge end 36 of the screen, leaving an end region 37 of the screen. An underflow chute 38 has a communicating region 39 that communicates with the end region of the screen. A delivery channel 40 leads to a sieve bend 41 for separating the discharged heavier fraction from the water. The delivery channel return 42 returns the water to the communicating region of the underflow chute that communicates with the end region of the screen, creating a closed circuit. A vent 43 is located in the underflow chute in the region that communicates with the end region of the screen.

A sensor 44 that senses an interface level 45 in the stratified bed is added with a control means (not shown) responsive to the interface level, to control the opening and closing of the vent. As is shown in more detail in figure 1 B, control of discharge from the jigging apparatus is achieved by setting the underpass barrier 35 at a level 46, somewhat lower than the level 45 of the interface between the heavier fraction and the lighter fractions in the stratified bed. This level of the underpass barrier is pre-selected and generally stable during jigging. The maintenance of a closed circuit of water flow through the underflow chute 38, the delivery channel 40 and the return channel 42 results in a zero flow or quiescent condition in the communication region 39 where the end region 37 of the screen communicates with a chute 38. Thus although there is no physical or mechanical barrier, because the water is incompressible, the result is that pulses do not pass through the end region of the screen and bed to the region 39. Consequently no discharge of the heavier fraction occurs. Opening the vent 43 in the underflow channel allows water to discharge from the region 39 and hence pulses to pass through the end region of the screen and bed. This brings about a drop in the interface level to the level of the underpass barrier in a manner indicated by broken lines 47 and the pulse produces a discharge of the heavier fraction from the end region of the screen over the discharge end into the underflow channel and to the delivery channel and sieve bend.

The separated material is delivered from the sieve bend as indicated by arrow 48 (figure 1). If through the bed jigging is done, the separated material is delivered through the pipe 49 at the bottom of the displacement member. This is usually the end product of the jigging apparatus.

The vent is controlled automatically by the level sensing device that senses the interface level continuously.

As a result, the discharge of heavier fraction is not controlled by mechanical movement of the gate avoiding the problems of the prior art, but by control of the level of the interface between heavier and lighter fractions and control of the pulses at the end region of the screen to lift the heavier fraction over the discharge end of the screen. This is a new principle of discharge control and can be used to achieve more effective separation. The underpass barrier level is only changed if there is a change in jigging parameters and material being treated, the underpass barrier is not continuously height adjusted to control the discharge of the heavier fraction.

Figure 2 to 4 are engineering design drawings of jigging apparatuses that use the principles described above. The same reference numerals have been used for parts that correspond to those indicated in the preceding figures and the description of them is referred to. Figures 3 and 4 show a design in which there are two jigging chambers, each served by two displacement memeebrs of inverted conical or pyramidal shape.

REFERENCE NUMERALS

1 apparatus for wet jigging

2 feeder end 3 jigging screen

4 jigging chamber

5 stratified material

6 discharge end

7 hutch chamber 8 displacement member

9 narrow lower end

10 actuating mechanism

11 pumping chamber

12 one-way valves 13 pumping chamber wall

14 one-way valve

15 displacement member wall

16 make up water supply pipe

17 cavitation prevention supply pipe 18 water supply tank

19 water supply pipes

20 beam

21 pivot

22 depending pipe 23 hydraulic cylinder

24 pivotal connection of hydraulic piston

25 pivot of beam

26 displacement member

27 displacement member 28 yoke

29 hydraulic cylinder

30 seal for depending pipe

31 upper large truncated end of displacement member hutch side-walls seal discharge means underpass barrier discharge end end region underflow chute communicating region delivery channel sieve bend delivery channel return vent heavier fraction level sensor interface between stratified fractions underpass barrier level broken lines showing modified interface level arrow showing delivery of material from sieve bend hydraulic piston rod.

Claims

1. An apparatus for wet jigging, in which particulate material to be separated is fed to a feeder end of a jigging screen forming a bottom of a jigging chamber and stratified material is removed at one selected from a discharge end of the screen and a hutch chamber below the screen, comprises an inverted truncated conical displacement member forming a floor of the hutch chamber, connected at the truncated narrow lower end of the cone to an actuating mechanism that produces a reciprocation up and down of the cone to deliver successive positive pulses in water into the hutch chamber and thence upwardly through the jigging screen, a pumping chamber formed below the cone, one-way valves in the wall of the pumping chamber for drawing water into the pumping chamber when the cone rises, one-way valves in the cone for transferring water from the pumping chamber to the hutch when the cone falls and a make up water supply provided into the hutch.

2. An apparatus for wet jigging as claimed in claim 1 , in which a further water supply is provided into the space in the pumping chamber below the cone, to prevent or reduce cavitation effects arising under the cone when it rises.

3. An apparatus for wet jigging as claimed in claim 2, in which the further water supply comprises a tank alongside the apparatus with pipes that feed water to the one way valves of the pumping chamber.

4. An apparatus for wet jigging as claimed in any one of claims 1 to 3, in which the actuating mechanism comprises a beam that is linked to the narrow truncated base of the cone at an intermediate position and a hydraulic cylinder at an end of the beam that is pivoted at an opposite end.

5. An apparatus for wet jigging as claimed in any one of claims 1 to 4, in which two or more truncated inverted cones form the floor of the hutch.

6. An apparatus for wet jigging as claimed in claim 5, in which the two or more cones are driven by a yoke beam arrangement by hydraulic cylinder means. 7. An apparatus for wet jigging as claimed in any one of claims 1 to 6, in which the upper large truncated end of the/each cone is substantially sealed against side-walls of the hutch chamber by sliding seals against the inner surfaces of the hutch chamber walls. 8. An apparatus for wet jigging as herein described and as illustrated in the drawings.

9. A method of wet jigging, which comprises operating an apparatus as claimed in any one of claims 1 to 9, in which there is no reverse or suction flow through the screen and stratification is enhanced by quiescent periods between the upward (positive) pulses, during which quiescent periods the bed settles, the quiescent period being adjustable by adjusting the rate of make-up water flow. 10. An apparatus for wet jigging as claimed in any one of claims 1 to 8, in which the discharge means comprises an underpass barrier, located just short of a discharge end of the screen, defining an end region of the screen, an underflow chute that has a communicating region that communicates with the end region of the screen and a delivery channel, _Γ the underflow chute and channel being filled with water, a means interposed in the channel of separating the discharged heavier fraction from the water, the channel returning the water to the communicating region of the underflow chute that communicates with the end region of the screen, creating a closed circuit and a vent in the discharge means in the communicating region that communicates with the end region of the screen.

11. An apparatus for wet jigging as claimed in claim 10, in which a sensor means that senses an interface level in the stratified bed is added with a control means responsive to the interface level, to control the opening and closing of the vent.

12. A method of control of discharge from jigging apparatus as claimed in either one of claims 10 or 11 , which comprises setting an underpass barrier at a level, somewhat lower than the height of the interface between the heavier fraction and the lighter fractions in the stratified bed, this height pre-selected and generally stable during jigging, maintaining a closed circuit of zero flow or quiescent condition in a region where the end region of the screen communicates with a chute, to have the result that pulses do not pass through the end region of the screen and bed and no discharge occurs, opening a vent in the underflow channel to divert pulses to pass through the end region of the screen and bed, bringing about a drop in the interface level to the underpass barrier level and a discharge of the heavier fraction into the underflow channel and to the delivery channel.

13. A method as claimed in claim 12, in which the vent is controlled automatically by a level sensing device that senses the interface level continuously.

14. A method as claimed in either one of claims 12 or 13, in which the discharge of heavier fraction is not controlled by mechanical movement of a gate, but by control of the level of the interface between heavier and lighter fractions and control of the pulses at the end region of the screen to lift the heavier fraction over the discharge end of the screen.

15. A method as claimed in any one of claims 12 to 14, in which the rest periods between pulses are made very brief, a very small fraction of the period occupied by the pulses, to reduce the quiescent periods between pulses and maintain a pulsing dilation of the bed and enhance the rate of stratification of the bed.

6. A method of operating the apparatus as claimed in any one of claims 1 to 8, 10 and 11 and as herein described.

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