AU2480592A

AU2480592A - Ore sorting

Info

Publication number: AU2480592A
Application number: AU24805/92A
Authority: AU
Inventors: Albert Peter Hawkins
Original assignee: Technological Resources Pty Ltd
Current assignee: Technological Resources Pty Ltd
Priority date: 1991-08-22
Filing date: 1992-08-24
Publication date: 1993-03-16
Anticipated expiration: 2012-08-24
Also published as: AU661713B2

Description

Title

Ore Sorting Field of the Invention

This invention relates to ore sorting and includes a method and apparatus for use in automatic ore sorting. Discussion of Prior Art

In order to successfully sort particulate matter automatically at high throughput rates, it is necessary to accelerate the matter from a slow moving, multilayered stream, usually drawn by a vibrating feeder from a feed hopper, to a high speed of 2m/sec or more where rock particles are separated from their neighbours. Such a fast moving, monolayered stream is usually launched into free air away from support surfaces, so that the path each particle travels is predictable to high accuracy. The accuracy must be sufficient for rock particles to be timed electronically as they proceed from an inspection position, to a position where, by action of a high speed fluid valve, they may be deflected from their normal motion separately from their neighbours. The rock particles selected for separation usually have a distinguishing property that can be sensed at high speed. In the majority of sorting methods in current use, it is necessary to wash the rock particles with water prior to such inspection and deflection. This is generall for one or both of the following reasons:

(a) in order to present the rock particles with clean surfaces for optical sensing; and/or

(b) in order to minimise the generation of hazardous airborne dust, as in uranium ore sorting.

Currently, known ore sorting rock presentation systems can be divided into three classes, namely:- (i) conveyor belt systems, where the rocks are fed from a vibrating feeder onto a solid rubber conveyor belt, where they are borne as a monolayer and then launched into air as the belt proceeds around a head-pulley, usually, both sensing and deflection take place whilst the rocks are in mid-air.

(ii) Free fall systems, as (i) above except that rocks are maintained in a monolayer at the discharge lip of the vibrating feeder, and simply drop off into a free fall under gravity. Again, the sensing and deflection are done with the rocks in free air.

(iii) Slide-plate systems, where rocks in a monolayer at the discharge of a vibrating feeder are caused to slide down a surface inclined at substantially 45 degrees. The rocks accelerate away from each other, over a sensing station usually located under the slide plate (e.g. electro-magnetic coils), and launch off the bottom end of the plate towards the deflection station.

All of these systems have difficulty in presenting relatively small sized material, typically between 6 and 25mm square mesh, when the material must be presented wet at high rates. These problems are due to:

(a) effects of surface tension which tend to make it difficult for small particles to cleanly separate from the feeding surfaces prior to their launch into free air;

(b) inability to sufficiently wash the materia whilst removing excess water and fine solid particles too small to sort; (c) inability to stabilise the particles at th stage where they must separate under acceleration from their neighbours for final washing and inspection and deflection; and

(d) inability to wash each separate particle over virtually its entire surface. If the material being sorted is prone to generate slimes, it is important to was the entire surface to avoid optical inspection taking plac on surface contaminated by such slimes which may obscure the true colour/reflectivity of the rock surface. It is an object of the present invention to provide equipment that can overcome some and perhaps all o the difficulties referred to above. Summary of the Invention

According to one aspect of the present invention there is provided apparatus for sorting particulate material comprising a mesh conveyor belt with washing nozzles positioned above and below the belt to wash particulate material on the belt from both sides of the belt. Preferably the mesh of the belt defines openings that are approximately 50% of the linear screen size of th bottom size material sorted by the apparatus, and the conveyor belt is formed of a balanced weave of stainless steel that runs at a speed of 2 metres/sec. In a preferred embodiment the mesh conveyor belt is positioned below the end of a vibrating feeder. Scanning and ejection means may be positioned downstream and below the mesh conveyor belt to act on particulate material launched in free fall from the end of the mesh belt.

According to another aspect of the invention there is provided apparatus for sorting particulate material comprising: a feed hopper arranged to feed particulate material onto a vibrating feeder, means to wash the particulate material whilst on the feeder, a conveyor belt of open mesh construction arranged to run below one end of the feeder, washing jets positioned on both sides of the mesh belt, and scanning and ejection means downstream and below the mesh belt to, in use, act on particulate material launched in free fall from the end of the mesh belt.

According to a still further aspect of the invention there is provided a method of sorting particulate material comprising the steps of: a) releasing the particulate material from a feed hopper onto a vibrating feeder, b) washing the particulate material whilst on the vibrating feeder, c) causing said particulate material to free fall onto a mesh belt, d) accelerating said particulate material on said mesh belt past washing jets positioned above and below said belt, e) washing said particulate material by use of the washing jets, f) launching said particulate material at the en of the mesh belt into free fall, g) scanning the particulate material during free fall, and h) ejecting particles from the path of the free fall by high pressure fluid released from ejector valves controlled by the scanner.

Preferably the method includes controlling the speeds of the vibrating feeder and mesh belt so that the horizontal velocity change of particulate material at transfer from the feeder to the mesh belt up to 5:1. Description of the Drawings

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which:-

Figure 1 is a schematic view of the layout of or sorting apparatus embracing the invention, and

Figure 2 is a plan view of a mesh belt forming part of the apparatus. Description of the Preferred Embodiment

Apparatus for ore sorting is shown in Figure 1. Ore in the form of rocks are drawn out of feed hopper 1 by linear vibrating feeder 2. The rocks 3 are fed along the deck of the feeder at a velocity of about 0.5m/sec. By th time the rocks reach the discharge edge 2A of the feeder they are between 1 and 4 layers thick.

During their travel along the feeder, the rocks undergo preliminary washing by means of high velocity sprays 4. Wash water is partially drained through wedge-wire screens 14 in the base of the feeder near the discharge end 2A. A cylindrical device 13 assists in deflecting via surface tension, excess water and accompanying slimes which pass to the rear of a splitting plate 15. The rocks fall typically 200mm onto a mesh wire belt 6, moving at a high horizontal velocity compared with the horizontal component of the rock velocity off the vibrating feeder 2. The belt velocity may be around 2m/sec.

By allowing the rocks to fall through about 200m (the distance D in Figure 1), the rocks tend to separate vertically under gravity so that when they land on the mes belt 6, they maintain the separation. The mesh, if appropriately selected, acts to capture each rock at the speed of the belt, and discourages rolling and bouncing which would occur in the normally used solid belts. It ha been accepted previously that the maximum horizontal velocity change at such a transfer point is 2:1. The use of the mesh belt 6 has enabled this to be increased to better than 5:1.

As the rocks fall on the mesh belt 6, they are presented to the final washing station with sprays 5 and 11 positioned above and below the belt to act through the mesh of the belt 6. The double sided washing allows removal of any residual slimes adhering to each rock surface, and further allows the water to drain through the belt before arriving at the head pulley 16.

As the belt is moved through a reasonably tight radius on the head pulley, the rocks 9 are launched into free air, and follow a parabolic trajectory under the influence of their forward horizontal motion due to the belt speed, and to gravity accelerating the rocks downward. Usually a sensing system 7 (typically a line-scan optical scanner), and fluid ejector valves 8 act to select individual particles in the stream that require removal, and these particles are blasted to the opposite side of a splitter plate 17 to the bulk of the feed material.

Further water sprays 12 are used on the belt return, in order to clear out any small particles which m have become stuck in the mesh. A tundish 10 collects water, slimes, and fine material.

In selecting the features of the mesh belt there is an important trade off between the wire thickness and open area of the belt. Thicker wire provides more resistance to stretching under tension. However, there needs to be adequate clear area to provide drainage of water and fine material. The openings should be around 50 of the linear screen size of bottom size material to be sorted.

It has been discovered that for +6-20mm material a mesh with 60 loops per foot across the belt, and 55 spirals per foot of length, with 16 gauge 304 stainless steel provides an optimum arrangement. The mesh belt 6 is shown in plan in Figure 2.

By use of such a mesh belt 6, where the mesh opening is typically about one-third the linear dimension of the bottom size of feed particles, it has been possible to demonstrate a feed presentation system which exhibits superior performance to all known sorter presentation systems in its ability to accelerate rocks with stability up to required sorting speeds, whilst at the same time providing superior means for washing the full surface of each particle and allowing proper removal of excess water without surface tension effects disturbing the trajectory of the stream as it launches in free fall.

In some applications, it may be desirable to use a different arrangement e.g. a non-metallic belt when usin electromagnetic sensors placed under the belt in order to select rocks with specific conductive or magnetic properties.

Claims

CLAIMS :

1. Apparatus for sorting particulate material comprising conveyor belt of open mesh construction with washing nozzles positioned above and below the belt to was particulate material on the belt from both sides of the belt.

2. Apparatus according to Claim 1 wherein the mesh of the belt defines openings that are approximately 50% of the linear screen size of the bottom size material sorted by the apparatus.

3. Apparatus according to either Claim 1 or 2 wherein the conveyor belt is formed of a balanced weave of stainless steel.

4. Apparatus according to any one of the preceding claims wherein the mesh conveyor belt is positioned below the end of a vibrating feeder.

5. Apparatus according to Claim 4 wherein in use the mesh conveyor belt is driven at up to five times the speed of the vibrating feeder.

6. Apparatus according to any one of the preceding claims wherein scanning and ejection means are positioned downstream and below the mesh conveyor belt to, in use, act on particulate material launched in free fall from the end of the mesh belt.

7. Apparatus according to any one of the preceding claims wherein washing sprays are positioned at the return of the belt.

8. Apparatus for sorting particulate material comprising: a feed hopper arranged to feed particulate material onto a vibrating feeder, means to wash the particulate material whilst on the feeder, a conveyor belt of open mesh construction arranged to run below one end of the feeder, washing jets positioned on both sides of the mes belt, and scanning and ejection means downstream and below the mesh belt to, in use, act on particulate material launched in free fall from the end of the mesh belt.

9. Apparatus for sorting particulate materials substantially as described herein with reference to and as illustrated in the accompanying drawings.

10. A method of sorting particulate material comprising the steps of: a) releasing the particulate material from a fee hopper onto a vibrating feeder, b) washing the particulate material whilst on th vibrating feeder, c) causing said particulate material to free fall onto a mesh belt, d) accelerating said particulate material on said mesh belt past washing jets positioned above and below said belt, e) washing said particulate material by use of the washing jets, f) launching said particulate material at the end of the mesh belt into free fall, g) scanning the particulate material during free fall, and h) ejecting particles from the path of the free fall by high pressure fluid released from ejector valves controlled by the scanner.

11. The method according to Claim 10 further comprising the steps of controlling the speeds of the vibrating feeder and mesh belt so that the horizontal velocity change of particulate material at transfer from the feeder to the mesh belt is up to 5:1.

12. The method according to either Claim 10 or Claim 11 comprising the further step of washing the mesh belt on its return.

13. A method of sorting particulate material substantially as described herein with reference to and as illustrated in the accompanying drawings.