WO2000009267A1

WO2000009267A1 - Grinding of particulate material

Info

Publication number: WO2000009267A1
Application number: PCT/AU1999/000648
Authority: WO
Inventors: George Veres
Original assignee: Bengold Holdings Pty. Ltd.
Priority date: 1998-08-10
Filing date: 1999-08-10
Publication date: 2000-02-24
Also published as: WO2000009267A9; AUPP518098A0

Abstract

An apparatus and method for processing particulate material to reduce the particle size thereof comprising means defining an enclosed path progressively decreasing in cross section and entraining the material in a high pressure liquid jet to carry it along the path in the direction of decrease of the path. The jet will carry the particles along said path to be impacted on the wall of the passage and the material therein to fracture the particles to reduce the size thereof, and delivering from said defined path particles below a selected size.

Description

GRINDING OF PARTICULATE MATERIAL

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 (HP 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 HP 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 HP 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.

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 high pressure liquid jets while the particles are restricted to move along a defined enclosed path that sequentially increases and decreases in cross sectional area while also progressively decreasing in overall area in the direction of flow along said path to there by repeatably impacting the particles with rigid surfaces defining said path and the high pressure jets, and collecting from the defined path those particles of a size below a predetermined value. Conveniently the rigid surfaces are configured and arranged so particles are repeatedly carried into the path of the high pressure liquid jets to be entrained therein and further impacted by the jet and with the rigid surface or surfaces defining the path.

Also there is provided an apparatus for grinding particulate material to reduce the particle size thereof comprising means defining an enclosed path of progressively decreasing in cross section, means to entrain particulate material in a high pressure 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 reduce the size thereof, and delivering from the defined path particles below a selected size.

Preferably the enclosed passage is defined by a rigid casing, the passage progressively decreases in cross section form the entry end where the particulate material enters and the high pressure liquid jet enters to a discharge end thereof. Preferably the rigid casing has axially spaced annular shoulders extending into the path of the particulate material to impact therewith and thereby promote breakdown of the particulate material.

The invention will be further described with reference to the accompanying drawings.

In the drawings:

Figure 1 is an elevational view of the apparatus.

Figure 2 is a longitudenal sectional view of the apparatus as shown in Figure 1.

Figure 3 is a cross sectional view of an alternative apparatus.

In Figures 1 qnd 2 of the drawings there is shown one embodiment of an apparatus for applying the method of reducing the particle size of reclaimed particulate material, such as rubber from vehicle tyres and other sources, and of other polymer materials. The apparatus comprises a processing column 10 communicating with a mixing chamber 11 into which the material to be treated is delivered through a processing passage 12 and into which fluid, such as water, is delivered at high or ultra high pressure through the passage 13.

The particulate material to be processed to reduce the size thereof are entrained in a gas to be conveyed to, and delivered into, the mixing chamber 11 through the passage 12. Compressed gas such as air is delivered through the gas passage 13 into the mixing chamber 11 at a pressure sufficient to entrain the particles and carry same through the converging guide passage 16 into an alignment passage 17. As the alignment passage 17 is of substantially reduced cross section, relative to the mixing chamber 11, the increased speed of the particles in the passage 17 promotes the alignment of the particles in the direction of travel as they pass therethrough.

The generally aligned particles are delivered from the alignment passage

17 into the first section of the processing chamber 12 at the upper or inlet end

18 thereof. As can be seen in Figure 2 the processing chamber comprises a series of axially aligned stripper rings 20 supported in the processing passage. Each stripping ring 20 has a tapered central aperture there-through with the smaller dimension end thereof downward with respect to the direction of flow through the aperture in the stripped ring.

It will be appreciated that each stripper ring 20, discharges the material being processed from the smaller aperture end of one ring into the larger aperture end of the next stripper ring. By this arrangement it is possible for the particles to undergo a change in orientation in the enlarged area before being presented to and passed through the small apertured end thereof. This configuration provides improved effectiveness in the reducing of the particle size to the required degree.

In one form of the apparatus there are a multiple of successive stripper rings 20, of the same external size, arranged in series so the material passes successively through each ring. With this arrangement there is a more effective reduction of a high percentage of the particles to the size of the small end of the aperture before passing to a stripped ring of a smaller size aperture. It is desirable for the number of rings of the same aperture size to be greater in the smaller aperture size rings than the larger aperture size rings at the initial entry end of the processing passage.

By way of example in the embodiment shown in Figures 1 and 2 there are a total of 15 rings and the internal diameter of the small end of the first three rings would be of a first diameter, the next five rings would be of a smaller second diameter and the final seven rings are of a yet smaller third diameter approximately the desired finished size of the particles produced by the processing. The greater number of rings of the smallest diameter, which diameter corresponds to the desired nominal particle size, reduces the percentage of oversized particles in the finished product.

The size of the final product is selected in relation to the intended future use or processing of the material, a typical particle size achievable with the present process and equipment can for example be of the order of 200 to 250 micron from a feed stock of the order of 600 micron. Another form of apparatus that can be used to process the particulate material is shown in Figure 3. This embodiment operates on the same principle as the apparatus described above with reference to Figures 1 and 2, but has a greater through-put capacity.

Referring now to Figure 3, there is shown a vertical cross-sectional view of the apparatus. In Figure 3 only the lower portion of the apparatus is shown in section, that portion above the break line 30 is not sectioned but the internal wall 31 thereof is shown in broken outline. The internal axial passage 32, is suitably communicated at the upper end 33 to a supply of high pressure fluid preferably a liquid such as water.

The lower end of the passage 32 communicates directly with the mixing chamber 36 and the latter is in direct communication with a plurality of feed passages 34. The feed passages 34 are equally spaced about the periphery of the chamber 36 and each is in communication with a supply of the particulate rubber material to be processed. The particles and the fluid mix in the chamber 36 to form a substantially uniform mixture in preparation for the further processing.

The rubber particles and high pressure fluid mix is passed into the annular passage 39 formed between conical inner wall 40 and the plurality of discs 41 mounted concentrically there about. Each disc 41 has the central bore 42 tapered to create a respective annular passage which decreases in width in the direction of flow therethrough. The diameter of the passages 42 is less than the diameter of the next adjacent disc to allow a degree of expansion of the particle mass as it is passed from one ring to the next. This construction performs the same function as the similar step formation previously discussed with reference to Figures 1 and 2.

The particles of rubber being processed are progressively reduced in size by passing through one disc to the next. Also the action of the particle mass being sequentially compacted and expanded promotes a reorientation of the particles between each disc and a resulting high degree of uniformity in particle size of the product output.

The processed particles are discharged into the enlarged annular passage 45 together with the fluid, normally water, in which they are carried, and are then passes to further processing dependent on the intended use thereof, or may be dried and stored.

The above described method and apparatus enables grinding particulate ductile material to reduce the existing (600-1000-micron) particle size, by subjecting the particles to an high pressure liquid jets while the particles are carried by the high velocity jets through a specially designed and formed disc assembly. The ductile material is forced by the liquid jets through progressively smaller orifices to tear them to smaller particles. With appropriate design of the equipment it is possible to apply the method to processing rubber and like material from a particle size of the order of 3,000 micron or more.

More specifically, the grinding of particulate ductile material reduces the particle size by subjecting it to high velocity high pressure liquid jets, while also passing through a defined space to impact the particles with the jets and with rigid and smaller orifices, reduces the ductile particle size to a selected level.

The high pressure liquid jets, having also a high velocity, carrying the accelerated ductile particles through the progressively consistently smaller orifices of the discs assembly, tearing the particles to the desired size relevant to the specific discs orifice as the ductile material is passed from point of entry to the point of exit.

Claims

1. A method of reducing the particle size of particulate material comprising subjecting the particles to high pressure liquid jets while the particles are restricted to move along a defined path that sequentially varies in cross-sectional area in a stepwise manner while also progressively decreasing in overall cross-sectional area in the direction of flow along said path to thereby repeatedly impact the particles with rigid surfaces defining said path and the high pressure jets, and collecting from the defined path those particles of a size below a predetermined value.

2. A method as claimed in Claim 1 wherein the particulate material is impacted as it passes the decreased cross-sectional parts of the passage, and the orientation of at least some of the particulate material is randomly charged as the particles traverse the increased cross-sectional parts of the passage.

3. An apparatus for processing particulate material to reduce the particle size thereof comprising means defining an enclosed path progressively decreasing in cross-section, means to entrain particulate material in a high pressure liquid jet and carry same along said path in the direction of decrease of said path, and means provided along said path to be impacted by particulate material during the passage therealong to fracture the particles to reduce the size thereof, and delivering from said defined path particles below a selected size.

4. An apparatus as claimed in Claim 3 wherein the enclosed passage is defined by a rigid casing and said passage decreases in cross-section from the entry end thereof where the high pressure liquid jet enters.

5. An apparatus as claimed in Claim 4 wherein the passage has axially spaced annular shoulders defining said path and areas of increased cross section between adjacent ends of successive shoulders.

6. An apparatus as claimed in Claim 4 wherein the passage is defined by a plurality of aligned elements rigidly secured in alignment, each element having a central aperture tapered in the direction of flow therethrough, the tapered aperature being configured to form an undercut surface at the interface of the abutting elements.

7. An apparatus as claimed in Claim 6 wherein the plurality of aligned elements are arranged in two or more sets with the element in respective sets having the aperatures therein of equal size.

8. An apparatus as claimed in Claim 4 wherein the passage is defined by a plurality of aligned elements rigidly secured in alignment centrally about a rigid column to define a tapered passage there-between decreasing in the direction of intended flow there-through.

9. An apparatus as claimed in Claim 8 wherein the elements are configured to form an undercut surface at the interface of the abutting elements.