WO1999010112A1

WO1999010112A1 - Improved mineral screen

Info

Publication number: WO1999010112A1
Application number: PCT/GB1998/002487
Authority: WO
Inventors: Hans Vello Wilhelm Haasma; Mikael Krantz
Original assignee: Scapa Group Plc
Priority date: 1997-08-21
Filing date: 1998-08-19
Publication date: 1999-03-04
Also published as: ZA987434B; GB9717614D0; AU8815798A

Abstract

An improved mineral screen comprises a nonwoven mesh membrane (10) in the form of an endless belt, made from a thermoplastics material. The mesh comprises lands (12, 13) surrounding apertures formed through the membrane. Reinforcing yarns (14) are embedded in and extend through the lands (12) in at least one direction, preferably the machine direction of the endless belt.

Description

IMPROVED MINERAL SCREEN

This invention relates to an improved mineral screen, for use in

separating mineral particles according to size.

The larger mesh sizes of screens are commonly made from meshes

of metal rods or wires, whilst finer sizes can be woven fabrics of synthetic

or metal yarns. A problem with the existing woven fabrics is that it is

difficult to ensure a regular mesh size in the weaving and heat setting steps,

requiring close attention to detail. Variations in mesh size can result in

undersized particles being retained or oversized particles passing through

the mesh, possibly in different areas of the same screen, and resulting in the

possible contamination of valuable material with gangue or loss of valuable

material.

A further problem is that polyamide yarns such as nylon cannot be

used . These are much more abrasion resistant that the polyester or

polypropylene monofilaments used at present for making woven mineral

screens, but lack dimensional stability and therefore cannot be used as a

regular and precise mesh structure would be unobtainable.

It is accordingly an object of the invention to provide an improved

mineral screen whereby the problems of obtaining regular and precise mesh

structure during weaving are eliminated.

According to the invention therefore, an improved mineral screen comprises a nonwoven mesh membrane in the form of an endless belt made

of a thermoplastics material, the mesh comprising lands surrounding

apertures formed through the membrane.

The membrane may be made by perforating a sheet of the

thermoplastics material, eg by passing it in contact with a studded or spiked

roiier. By carefui machining even spacing and equality in size of the studs

or spikes can be ensured, so that the spacing and dimensions of the

apertures in the membrane can be assured.

The membrane may be made from any thermoplastic or thermosetting

polymer, and high abrasion resistance materials such as polyamides,

polyurethanes and silicones may be used.

The aperture size may be provided in a wide range, depending upon

the upper size limit of the particles to be passed, or the lower size limit of

the particles to be retained. Also the ratio of land area to aperture area may

be selected as required, depending upon the rate of screening and water

drainage required through the screen.

The screen may be provided in the form of an endless belt without

the use of clipper seams which avoids the problem of flex fatigue failure

caused by the region of adhesive used to fill the voids in the seam area to

prevent escape of particles. A seam such as that disclosed in GB-A-

2231838 may be used to make the belt endless, or the membrane may be endless and lack a noticeable seam, or be manufactured in endless form.

The membrane is preferably rigid, but need not be resilient. The

membrane preferably is highly abrasion resistant which is important not only

to withstand wear and tear due to contact with the particulate material, but

also to withstand continuous operation on heavy duty mining machinery

which is frequently corroded or encrusted with dirt and deposits etc.

The mesh size may be in the range of 5-4000 microns, but is

preferably in the range of 400-1000 microns, and the screen is preferably

from 1 .0-3.5mm thick..

Yarn members may be incorporated in the machine direction lands of

the membrane so as to reinforce the screen and provide adequate strength

in the running direction of the screen. Cross-direction rigidity can be

improved by incorporating yarn members into the cross machine direction

lands of the membrane.

An embodiment of mineral screen according to the invention will now

be described by way of example, with reference to the accompanying

drawing, which is a fragmentary view of part of the screen.

The mineral screen belt of the invention comprises a membrane 10

of a rigid abrasion resistant material which is formed with an array of regular

rectangular equal apertures 1 1 , between which are provided lands 1 2,

extending in the longitudinal direction of the belt, and cross-lands 1 3, extending across the belt direction. Reinforcing yarns 1 4 extend in the

longitudinal direction of the belt.

The belt 10 is formed as an endless loop, so that the provision of a

joining seam is avoided. The belt is made from an abrasion resistant nylon

or polyurethane matrix, reinforced with dimensionally stable PET or PEN

mono or multi filament yarns as the yarns 14.

The membrane forming the belt may conveniently be manufactured

in accordance with the process described in US 4,740,409. This allows a

full range of thermoplastic or thermoset polymers to be used as matrix

material enabling abrasion resistance and other properties to be optimised

for use as a mineral screen belt. The membrane may be formed as an

endless tube as described in GB-A- 2254287. Although not preferred, the

belt may instead include a seam arrangement of the type described in US

5, 1 69,570 or EP-A-0518494.

In the embodiment shown, the apertures 1 1 are shown as elongated

rectangles. The shape and size of the apertures may be designed to be as

desired or best suited to a particular material, for example, square or

rounded apertures may be generally found to be optimum. The mesh size

of the apertures is in the range of 400-1000 microns, but may be in the

range of 5-4000 microns, and the membrane is from 1 .0-3.5mm in

thickness.

Claims

CLA1MS

1 . A mineral screen comprising a nonwoven mesh membrane in the form

of an endless belt made of a thermoplastics material, the mesh comprising

lands surrounding apertures formed through the membrane.

2. A mineral screen according to claim 1 wherein the membrane

comprises a sheet of the thermoplastics material which has been perforated.

3. A mineral screen according to claim 2 wherein the perforation is

carried out using a studded or spiked roller.

4. A mineral screen according to any preceding claim wherein the

membrane is made from a thermoplastic or thermosetting polymer.

5. A mineral screen according to claim 4 wherein the membrane is made

from a high abrasion resistance material.

6. A mineral screen according to claim 5 wherein said high abrasion

resistance material is one of polyamides, polyurethanes or silicones.

7. A mineral screen according to any preceding claim which is in the

form of an endless belt.

8. A mineral screen according to any preceding claim wherein the mesh

apertures have a diameter in the range of 5-4000 microns.

9. A mineral screen according to claim 8 wherein the mesh apertures

have a diameter in the range of 400-1000 microns.

10. A mineral screen according to any preceding claim wherein the lands run on machine direction and cross-machine direction axes, and incorporate

yarn members within at least the machine direction lands.

1 1 . A mineral screen according to claim 10 wherein the cross-machine

direction lands also incorporate yarn members.

1 2. A mineral screen substantially as hereinbefore described with

reference to and as illustrated in the accompanying drawings.