WO1997030790A1

WO1997030790A1 - Method and apparatus for grinding particulate material using ultra high pressure jets

Info

Publication number: WO1997030790A1
Application number: PCT/AU1997/000099
Authority: WO
Inventors: George Veres
Original assignee: Water Jet Technologies Pty. Ltd.
Priority date: 1996-02-23
Filing date: 1997-02-24
Publication date: 1997-08-28
Also published as: AUPN829796A0

Abstract

A method of grinding particulate material to reduce the particle size thereof by subjecting the particles to impacting by UHP liquid jets while the particles are restrained within a defined space to thereby be repeatedly impacted with a rigid surface in a manner to be fractured into smaller particles and rebounded there off to be again entrained in the UHP liquid jets to further impact with the surface of the defined space.

Description

METHOD AND APPARATUS FOR GRINDING PARTICULATE MATERIAL USING ULTRA HIGH PRESSURE JETS

This invention relates to a method and apparatus for the grinding of particulate materials to reduce the particle size thereof by the use of ultra high pressure jets (UHP jets) and although not restricted, it is particularly suitable for the grinding of rubber or polymer particles such as produced in the reclaiming of such materials from used or rejected products, including vehicle tyres and insulated electrical cables.

The value of many reclaimed granular materials, intended to be subsequently used in production processes, is improved and hence the value thereof is increased proportional to the level of reduction in the material particle size. This is so in regard to rubber or polymer particles produced by various recovery techniques, in particular in regard to rubber particles produced from the tread portion of a tyre which is of a high grade rubber than that normally available from the side walls and beads of the tyre.

There has previously been proposed methods of processing products such as vehicle tyres wherein the rubber is exposed to treatment by UHP jets to remove the rubber from the metal fibre reinforcement structure of the tyre. Similarly, polymer materials recovered from the casing surrounding the conductors of electrical cables by UHP jets can be re-used if the particle size thereof is sufficiently small. However, in order to maintain an acceptable through put rate, the size of the particles produced is such that it does not render the recovered particulate material suitable for use in some areas of recycling, particularly in the areas of high quality products produced from recycled materials. As a consequence, the resale value of the particulate material is limited and the overall viability of recycling such material can become questionable.

It is therefore the object of the present invention to provide a method and an apparatus for the treatment of materials in a particulate form to reduce the particle size to below a selected value. It is a further object of the invention to produce an apparatus for carrying out this method.

There is thus firstly provided by the present invention a method of grinding particulate material to reduce the particle size thereof comprising subjecting the particles to UHP liquid jets while the particles are restrained within an area to be repeatedly impacted with the UHP jets, and removing particles of a size below a predetermined value from the influence of the jets whilst further treating the remaining particles.

More specifically, there is provided a method of grinding particulate material to reduce the particle size thereof comprising subjecting the particles to UHP liquid jets whilst contained in a defined space to impact the particles with the jets and with a rigid surface forming at least part of said defined space and removing from said defined space particles below a selected particle size.

Conveniently the surfaces of the defined space, with which the particulate material contact, are configured and arranged so particles entrained in the liquid are repeatedly carried into the path of the UHP liquid jets to be entrained therein and further impacted by the jet and for the rigid surface or surfaces. The UHP liquid jets, with the particles entrained therein, impact the surface of the defined space in a manner to be fractured into smaller particles and rebounded there off to be again entrained in the UHP liquid jets, and hence again impacted with the surface of the defined space. This sequence of impact of the particles by the UHP liquid jets and with the surface of the defined area is repeated over a period of time until the material is reduced to or below a required particle size.

Conveniently the particulate material entrained in the liquid travel through a defined passage which presents to the liquid entrained particle material a series of surfaces inclined to the general direction of travel of the particles from the point of entry to the point of exit. In this way the particle material will bounce off the inclined surfaces to provide an irregular non-unitary flow path of the particles from the point of entry to the point of exit. This action enhances the degree of grinding action to which the particles are subject, and hence increases the degree of reduction of particle size, as the material passes from the point of entry to the point of exit. Preferably, downstream from the exit location, there is provided a fine screen through which the liquid and particles below the selected particle size may pass and are thereafter subsequently separated. Particles that will not pass through the screen are returned into the UHP liquid upstream of the impact surfaces for further treatment.

In an alternative construction, the feed stock particles are delivered into a chamber having a rotating or oscillating member carrying a plurality of pockets into which the particle material to be treated is delivered. About the periphery of a portion of this chamber is an array of UHP jets directed towards the path of the pockets carrying the particle material. As the pocket assembly rotates or oscillates, the particulate material is subject to a bombardment by the UHP liquid jets to break the particle material down into the required particle size. Conveniently, the base of the pockets may be in the form of a classifier member so that the liquid and the fine component of the mass of particles pass therethrough to be collected and subsequently separated into the respective components of fine particles and liquid. In one form, a further classifier is provided at a location substantially isolated from the area where the UHP jets are arranged to bombard the particle material, and where the material after the bombardment is deposited on a further classifier, together with the liquid in which it is entrained, so that the liquid and fine particles can pass through the classifier. Those particles of a size too great to pass through the classifier are again picked up in the pockets and carried forward to pass again through the area where they are bombarded by the UHP liquid jets.

The invention will now be described with reference to the accompanying drawings wherein the specific embodiments of the invention are illustrated. In the drawings,

Figure 1 is a diagrammatic cross sectional view of one apparatus for performing the invention;

Figure 2 is a diagrammatic cross sectional view of an alternative apparatus for carrying out the present invention;

Figure 3 is a cross sectional view of a third form of apparatus for carrying out the present invention. Referring now to Figure 1 , the apparatus comprises a central processing chamber 1 defining an annular passage 6 between respective inner and outer walls 2 and 3 arranged in a co-axial configuration. The annular passage 6 has a form which generally decreases in cross section from the upper to the lower ends 4 and 5 respectively. In addition, the inner and outer walls 2 and 3, are formed by respective stacks of annular rings 2a and 3a spaced apart to define the annular passage 6, having opposing non-smooth surfaces formed by oppositely inclined faces 8 and 9, on the opposing faces of the annular rings.

The inclination of the faces 8 and 9 may vary down the length of the passage 6 so that more severe inclinations are at the upper end and the degree of inclinations reduces down the length of the passage to the lower end.

There is thus provided an annular passage 6 which generally decreases in cross section from the upper entry end to the lower discharge end, and thus would give rise to an increase in the general speed of the materials passing downwardly through the annular passage 6.

The oppositely inclined faces 8 and 9 on each of the annular rings define faces and recesses to be impacted at high speed by the particles passing through the passage 6 to effect a breaking up of the particles into smaller sized particles.

The upper end of the annular passage 6 communicates with a continuous conical passage 12, or a plurality of passages, outwardly inclined from the central delivery duct 13 to communicate with the annular passage 6 at spaced intervals around its periphery. The duct 13 is provided as the entry passage for material to be processed, such as rubber or polymers in particle form, which is entrained in a liquid, such as water, which is introduced into the duct 13 by minor ducts 15 and 16.

The lower end of the annular passage 6 discharges onto a sieve assembly 11 having a sieve screen 14 with aperture sized to permit passage therethrough of particles of the material being processed that are at or below a selected size. The material passing through the sieve screen 14 is collected in the hopper 17, and discharged therefrom through the delivery duct 18 to further processing, storing or whatever additional processing or purpose to which that particular material is to be applied.

The refining or size reduction of the particles is performed by ultra high pressure jets of water or other suitable liquid being directed into the upper end of the annular passage 6 in the area where the particulate material also enters the passage 6 through a series of nozzles 10 arranged about the upper periphery of the passage 6 so that the ultra high pressured jets in themselves produce a degree of break down of the particles and also cause the particles to impact on the plurality of inclined faces 8,9, defining the opposite walls 2 and 3 of the annular passage 6, thereby contributing to break down the particles to further reduce the particle size, and causing the particles to be bounced back into the ultra high pressure jets for further breakdown thereby.

The combined effect of the ultra high pressured jets and the configuration of the inner and outer surfaces of the annular passage 6 substantially increases the impact forces to which the particles are subjected, both by the impact of the water jets, and the impact with and rebounding from the inclined surfaces, to produce a high degree of reduction in the particle size during a single passage through the annular passage 6. The particles following a somewhat tortuous path compared with a generally linear movement which would occur if the walls of the annular passage 6 were not irregular as previously described.

An alternative form of this construction is shown in Figure 2 wherein the annular passage is replaced by a single passage 20 which also tapers inwardly in cross section from the upper entry to the lower delivery end 21 and 22 respectively. The internal surface of the passage 20 is somewhat in the form of a plurality of steps 18, each step forming an annular shoulder 19 on the internal surface of the tapered passage 20 and hence of stepwise reducing diameter of the passage. The coupling 25 is sealably secured at 27 into the upper end of the casing 26, and is connectable to a source of high pressure liquid for passage through the jet unit 21.

In this example the single ultra high pressured jet unit 21 delivers by jet, directly into the upper end 22 of the passage 20, and is preferably inclined at a small angle to the axis of the passage 20. The particlised material, is delivered through a side passage 23 into the path of the ultra high pressured jet unit 21 which then carries the particles into the stepped tapered passage 20, forming the series of internal annular shoulders or steps 18, to create a similar effect as previously described with respect to Figure 1. in a modification to the structure shown in Figure 2, the stepped passage 20 can be formed from a plurality of inserts assembled in a plain bore as a stack arrangement. Each of the inserts has a central aperture therein with the diameter of the apertures progressively decreasing from the top or entry end to the bottom or exit end of the stack. This construction is more simple to manufacture and maintain as the inserts can be readily removable and new inserts assembled therein as they wear and thereby permit the particle size of the processed material to changed if required by changing the aperture size of the inserts. There is depicted in Figure 3 an alternative construction of the general type of mechanism as shown in Figure 2 of the drawings comprising three generally cylindrical interconnecting coaxial sections 31 , 32 and 33 secured together by respective threaded fastenings as indicated at 34 and 35. The high pressure jet unit 36 is located in the upper portion of the section 31 and held in abutting sealed relation therewith by screws 37. The UHP injector unit 36 abuts the shoulder 38 so that in operation, the high pressure liquid issues into the cavity area 39, into which the particulate material to be processed is also delivered by a conduit (not shown) which is engaged with the threaded inlet for the wall of the chamber 39. Having regard to the nature of the jet of high pressure water delivered into the chamber 39, the particulate material to be further processed does not intimately intermix with the high pressure liquid issuing from the unit 36, but primarily is attached to the peripheral surface of the jet, which is in the form of a divergent cone as indicated at 41. In the light of this attachment of the particulate material to the surface of the jet cone 41 , the particulate material will initially impact with the slightly upwardly inclined perimetal surface 42 of the break up ring 43 mounted fixedly in the centre housing portion 32, and secured in position between the shoulders 45 and 46.

Having regard to the configuration of the cavity 44 including the upswept base, the particulate material is subjected to significant battering by the high pressure liquid, and against the walls of the chamber 44 to effect a breaking down of the particulate material to substantially smaller sized particles. This particulate material including the further broken down component thereof, is progressively passed over the upper peripheral edge 49 of the cavity 44, together with the liquid material delivered by the high pressure nozzle 36, which has now collapsed from the initial hollow conical shape, and hence has reduced in velocity. This portion of the fluid, together with particulate material entrained therein, then passes onto the screen 50 and the liquid and the solid particles which have been broken down to a size adequate to pass through the screen 50, so pass and are collected in an appropriate vessel.

That portion of the particulate material which has not been broken down sufficiently to pass through the screen 50 will progressively accumulate in the cavity 44 until it reaches a height to be discharged laterally through the series of apertures 52 in the internal wall 51 to the exit passage 55. The oversized particulate material is then separated from the liquid and returned by an appropriate pump (not shown) to the inlet port 40 to re-enter the chamber 37 for further processing until it is broken down to the required degree to pass through the screen.

The construction described with reference to Figure 3 has the advantage that the process can readily recycle material that is not broken down sufficiently in the first past, and such material is automatically recycled to be further subjected to the breaking down treatment without interrupting the continuity of the process.

The method and apparatus herein described and illustrated is suitable for processing materials such as rubbers or polymers that have previously been subjected to an initial breaking down treatment to be in a particulate form of up to about 7 mm maximum dimension. Normally they would be in the range of 2.5 to 5 mm. The UHP jet will normally operate at a delivery pressure of 500 to 2,500 Bar with the finished particle size of the material being processed being in the range of 100 to 200 microns. To achieve this performance, the UHP jet has a velocity, in the vicinity of the break-up ring 43 in Figure 3, of the order of at least 500 m/second. The figures referred to in the paragraph are by way of example only and the invention is not limited thereby.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method of grinding particulate material to reduce the particle size thereof comprising subjecting the particles to UHP liquid jets while the particles are restrained within a defined area to thereby be repeatedly impacted with a rigid surface and/or the UHP jets, and removing particles of a size below a predetermined value from the defined area whilst treating particles within said area.

2. A method of grinding particulate material to reduce the particle size thereof comprising subjecting the particles to UHP liquid jets whilst contained in a defined space to impact the particles with the jets and with a rigid surface forming at least part of said defined space, and removing from said defined space particles below a selected particle size while the UHP liquid jets continue operating.

3. A method as claimed in claim 1 wherein the rigid surface of the defined space is configured and arranged so particles are repeatedly carried into the path of the UHP liquid jets to be entrained therein and further impacted by the jet and with the rigid surface or surfaces.

4. A method as claimed in claim 1 wherein the UHP liquid jets, with the particles entrained therein, impact the surface of the defined space in a manner to be fractured into smaller particles and rebounded there off the be again entrained in the UHP liquid jets to further impacted with the surface of the defined space.

5. A method as claimed in claim 1 wherein the particulate material entrained in the UHP liquid jet are passed through a defined passage that presents to the liquid entrained particle material a series of surfaces inclined to the general direction of travel of the particles form the point of entry to the point of exit.

6. A method as claimed in claim 5 wherein the surfaces are arranged to define a circular passage that progressively decreases in cross sectional area between said point of entry and point of exit.

7. A method as claimed in claim 2 wherein the particulate material entrained in the UHP liquid jet are passed through a defined passage of a tapered conical shape with axial spaced internal circular shoulders, and the particulate material is impacted with said shoulders as it is driven through the tapered conical passage by the UHP liquid jet.

8. Apparatus for grinding particulate material to reduce the partical size thereof comprising means defining an enclosed path of progressively decreasing cross section, means to entrain particulate material in a UHP liquid jet and direct same along said path in the direction of decrease of the enclosed path, and means provided along said path to be impacted by the particulate material during the passage thereof therethrough to fracture the particles to a smaller particle size.

9. Apparatus as claimed in claim 8 wherein the enclosed path has projections extending into the path to be impacted by the particulate material as it traverses the path to promote break down of the particulate material.

10. Apparatus as claimed in claim 8 wherein the enclosed passage is defined by a rigid casing the passage progressively decreases in cross section form the entry end where the particulate material and the UHP liquid jet enters to a discharge end.

11. Apparatus as claimed in claim 10 wherein the rigid casing has axually spaced annular shoulders extending into the path of the particulate material to impact therewith to promote breakdown of the particulate material.

12. Apparatus as claimed in claim 10 wherein the passage is defined by a series of co-axial abutting elements each having a central aperture the aperture of the respective element progressively decreasing in size from the entry to the exit end of the passage.

13. Apparatus as claimed in claim 8 wherein an annular should is provided in the passage arranged to define an upwardly open annular cavity directly in the path of the UHP liquid jet so the particulate material is delivered in thereinto to be reduced in partical size by the UHP liquid jet.

14. Apparatus as claimed in claim 13 having separating means downstream of the annular shoulder to receive particulate material discharged from the upwardly open cavity and arranged to separate partical material above a preset size from the remainder, and means to return said separated partical material intothe UHP liquid jet.