GB2231054A

GB2231054A - Mineral separation equipment manufacturing method from polyurethanes

Info

Publication number: GB2231054A
Application number: GB9005315A
Authority: GB
Inventors: Hans Jurgens Grobler
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-03-09
Filing date: 1990-03-09
Publication date: 1990-11-07
Anticipated expiration: 2010-03-09
Also published as: DE4007569A1; GB2231054B; GB9005315D0; BR9001104A; AU5115490A; AU630165B2; ZA895958B

Description

A :3:L (Z!is 'I 1 - MINERAL SEPARATION EQUIPMENT MANUFACTURING METHOD

FIELD OF INVENTION

The invention relates to a method for the manufacture of equipment used in a process of mineral separation with particular reference to the mining industry 5 although it is not restricted thereto.

BACKGROUND TO THE INVENTION

In the mining industry it has long been common practice to use abrasion resistant materials to protect the working surfaces of equipment used in processes for the treatment of abrasive minerals.

This protection has been effected by various methods, for example by rubber lining of steel vessels and latterly by the use of plastics and even ceramic linings. Steel vessels tend to be heavy and expensive in manufacture and to overcome this problem a lighter material having sufficient strength was sought and found in what is known as FRP (Fibre Reinforced Plastic) or more commonly as fibreglass.

This material, which is formed using polyester resins reinforced with glass fibre mat, is relatively inexpensive, although it has a fairly high flammability and is thus dangerous. It has good structural integrity and can be moulded at room temperature into almost any shape.

The material was adapted in the mineral process industry for the manufacture of equipment, in particular that for gravity separation, which includes spirals, cones and shaking tables. It was then necessary to find a wear resistant material for 1 n - J - application to this glass fibre carcass to render it sufficiently abrasion resistant for economic viability. Natural or synthetic rubbers, which could be conveniently glued to the fibre glass were initially chosen. However, due to their tendency to perish when exposed to sunlight and high humidity/water and the susceptibility of wear resistant grades to bacteriological degradation and the further disadvantage that rubbers did not possess wear resistant properties of sufficiently long lasting duration for equipment in highly abrasive conditions, consideration was given to the use of more wear resistant polymers having a polyether base such as polyurethane.

Polyurethane exhibits abrasion resistant properties which c:znnot be achieved by rubber and was chosen as a solution to the Droblem. However, in turn, a further problem was then presented, namely that of the adhesion between polyester and polyether based plastics, the two materials being chemically incompatible on an adhesion basis under almost any conditions.

Over the past two decades many methods and means of effecting adhesion have been attempted but none completely successfully, although many manufacturers have laid claims in this regard. When put to the test, however, in the hot and humid conditions existing in metallurgical plants, attempts by these methods have resulted in a tendency for the two layers to be separated by a process going by various names, e.g. blistering, bubbling or delamination. This has resulted in the suffering of the metallurgical efficiencies of the equipment in all cases.

Methods used f or the actual nanuf acture have been as f ollows:

1. STANDARD METHOD A fibreglass carcass is manufactured first and the method involves the steps of a.

applying a suitable release agent to a mould prior to applying a layer of gelcoat thereon. Laying up of the mould using fibreglass mat impregnated with polyester resin b.

allowing time for precure C.

trimming the GRP (Glass Reinforced Plastic) to exact mould dimensions d.

curing to complete hardening e.

demoulding the carcass.

The carcass is then sprayed with a layer of wear resistant- polyurethane, which involves various methods of first cleaning and then priming the GRP surface to be sprayed. obviously only the actual future wear surface of the carcass is to be treatedt but in the spray process other parts may be treated in addition.

Delanination occurs under certain conditions and the working surface may sometimes be less than perfect, resulting in decreases in equipment efficiencies.

As a result of these deficiencies, suppliers decided to develop and test "reverse" laminating or "reverse" casting techniques.

2. REVERSE CASTING OR - LAMINATING METHOD In this method, the mould surface is treated with a release agent (normally wax or silicon based). What will become the wear or working surface is then applied by spraying (or casting) the polyurethane layer directly on to the treated mould surface and this is then followed by the laminating procedure as in the standard method when the GRP is applied on to the as yet uncured polyurethane. Various methods are used, probably the most successful of which is that developed by Mineral Deposits Ltd of Australia, wherein a so called alloy layer comprised of equal volumetric amounts of polyester and polyurethane are intimately mixed during a special spraying process in order to form a layer that should in theory bond to both polyurethane and polyester FRP. After exhaustive tests and serious problems experienced at both Richards Bay Minerals and Du Pont in the USA, this method does not provide the answer.

Also tried have been methods whereby fibreglass strands are allowed physically to intrude into the polyurethane and these have not shown much success.

1 1 An additional problem is encountered due to the sensitivity of polyester based plastics to ultra violet light and moisture and this necessitates the non working surfaces which are subject to these factors being treated with some form of ultra violet shielding and moisture resistance e.g. by coatings of pigmented flow coat paints or even pigmented polyurethane. This is a necessary addition to both methods of manufacture.

Yet a further serious problem arises due to the fact that all polyurethanes tend to absorb waterwhen exposed thereto. This then brings the moisture sensitive polyester resin in contact with the water in the polyurethane with catastrophic results.

Of the two methods, that of reverse - casting or - laminating, in allowing for production of almost perfect working surfaces, is seen to be the best answer for optimum reproducibility and metallurgical efficiency and is therefore preferred.

It is an object of this invention to provide a method 20 of manufacture of mineral separation equipment which 1 avoids the problems which have previously been encountered.

SUMMARY OF THE INVENTION

According to this invention there is provided a method for the manufacture of equipment for use in a process for the treatment of materials of an abrasive nature, the method comprising:

r.2!,k-4-- the eTliPr.Pnt with a body of a structural grade of polyurethane and wear surf aces of a wear resistant grade of polyurethane bonded thereto.

Further features of the invention provide for making the equipment by use of a mould formed to the configuration required by the equipment and prepared by coating with a release agent.

Still further, according to the invention, the wear resistant grade of polyurethane is applied to the prepared surface of the mould and thereover in areas of the equipment requiring structural integrity the structural grade of polyurethane is applied, precured and trimmed, the polyurethanes are allowed to achieve a full cure and the equipment is withdrawn from the mould.

Still further, according to the invention, the structural grade of polyurethane may be applied to the prepared surface of the mould, precured, trimmed, allowed to achieve a full cure, be withdrawn from the mould and thereafter the wear resistant grade of polyurethane is applied to the areas of the equipment whereon wear resistance is required.

Still further, according to the invention, application of the structural grade of polyurethane may be performed by spraying, casting, or by laminating and the wear resistant grade by spraying or casting.

Still further, according to the invention, the structural grade of polyurethane may include a fibre reinforcement which is fibreglass mat.

Still further, according to the invention, the structural grade of polyurethane may include a colour pigmentation.

The method of the invention is further described by the following examples which illustrate practical ways in which the method may be employed for any one process where this type of equipment is required.

EXAMPLE 1

Form the required mould f rom the data supplied having the inside configuration of the equipment on its outer surface.

Apply a release agent to the mould surface.

3.

Spray the wear resistant grade of polyurethane on to the mould surface.

4. Apply the structural grade of polyurethane where required to give the necessary structural integrity.

5. Allow the structural polyurethane to precure for between 10 and 20 minutes and trim to facilitate and accelerate finishing off.

is 6. Allow the urethanes to cure sufficiently to achieve properties which allow of handling.

Remove finished product from the mould.

8. Allow to achieve complete cure before placing equipment in service.

EXAMPLE 2

1. Form the required mould f rom the data supplied having the inside configuration of the equipment on its inner surface.

2. Apply a release agent to the mould surfaces.

3. Cast the wear resistant polyurethane into the mould.

4. Allow the wear resistant polyurethane to cure fully.- 5. Remove the casting from the mould i 2 - 6.

Spray or laminate the structural polyurethane to the outside of the casting where required Precure and trim the structural polyurethane 8. Allow full cure of the structural polyurethane and the equipment is ready f or service or 6a Using a further mould or moulds cast the structural polyurethane to the outside of the casting where required 7a Precure and trim the structural polyurethane 8a. Allow cure of the structural polyurethane sufficiently to achieve properties which allow of handling.

Demould the integral twin layer casting.

Allow full cure before placing equipment in service.

With this method, twin layer castings may be made, where either of the two grades of urethane nay be cast first, followed by the other grade.

EXAMPLE 3 is Form the required mould from the data supplied having the outside configuration of the equipment on its inner surface.

2. Apply a release agent to the mould surfaces 3. Apply the structural polyurethane to the mould surface using any of the methods aforementioned 4. Allow the urethane to precure and trim to facilitate and acceler.ate finishing off Allow the urethane to cure sufficiently to achieve properties whih allow of handling.

6. Remove the carcass from the mould Spray or cast the required wear resistant urethane onto the structural carcass.

Allow full cure before placing equipment in service.

In any of the above examples, elevated temperatures for curing are not a necessity, but the rate of reaction is increased thereby, allowing for faster turn around times.

In all cases structural urethanes, may be used with or without fibre reinforcement, depending on economics and final properties required for the equipment. Also. application of the structural urethane may be by spraying, casting or laminating techniques, the choice 15 again being determined by the aforementioned criteria.

It will be understood that the invention provides a method of manufacture of equipment for mineral separation processes using a structural grade of polyurethane in substitution for the previously used 1 - is - polyester resin structure thus obviating adhesion and othcr problems encountered when polyester resin is in contact with polyurethane. The method also avoids the use of all gel coats, flow coats and alloy layers.

It will further be appreciated that other variations of the practical uses of the method are envisaged beyond those hereinbefore exemplified.

9

Claims

A method for the manufacture of equipment for use in a process for the treatment of materials of an abrasive nature, the method comprising:

making the equipment with a body of a structural grade of polyurethane and wear surfaces of a wear resistant grade of polyurethane bonded thereto.

2. A method as claimed in claim 1 wherein the equipment is made by use of a mould formed to the configuration required by the equipment and coated with a release agent.

A method as claimed in claim 2 wherein the wear resistant grade of polyurethane is applied to the prepared surface of the mould and thereover, in areas of the equipment requiring structural integrity, the structural grade of polyurethane is applied, precured and trimmed; the polyurethanes are allowed to cure sufficiently for handling and the equipment is withdrawn from the mould.

4. A method as claimed in claim 2 wherein the structural grade of polyurethane is applied to the prepared surface of the mould, precured, trimmed, allowed to achieve a cure sufficient for handling, withdrawn from the mould and thereafter the wear resistant grade of polyurethane is applied to the areas of the equipment whereon wear resistance is required.

5. A method as claimed in either of claims 3 or 4 wherein the wear resistant and structural grades of polyurethane are applied by spraying.

A method as claimed in either of claims 3 or 4 wherein the wear resistant grade and structural grades of polyurethane are applied by casting.

7.

A method as claimed in either of claims 3 or 4 wherein the wear resistant grade of polyurethane is applied by spraying and the structural grade of polyurethane is applied by casting.

- 1 R, - 8. A method as claimed in either of claims 3 or 4 wherein the wear resistant grade of polyurethane is applied by spraying and the structural grade of polyurethane is applied by laminating.

1 9. A method as claimed in either of claims 3 or 4 wherein the wear resistant grade of polyurethane is applied by casting and the structural grade of polyurethane is applied by spraying.

10. A method as claimed in either of claims 3 or 4 wherein the wear resistant grade of polyurethane is applied by casting and the structural grade of polyurethane is applied by laminating.

A method as claimed in any one of the preceding claims wherein the structural grade of polyurethane includes a fibre reinforcement.

is 12. A method as claimed in claim 11 wherein the fibre reinforcement is a fibreglass mat.

13. A method as claimed in any one of the preceding claims wherein the wear resistant and structural 1 - 19 k grades of polyurethane include a colour pigmentation.

14. A method as claimed in claim 13 wherein the colour pigmentation of the wear resistant grade is different from the colour pigmentation in the structural grade.

15. A method as clained in claim 1 for the manufacture of equit for use in a process f or the treatment of materials of an abrasive nature as hereinbefore described and exemplified.

16. Equipment for use in a process for the treatment of materials of an abrasive nature, comprising a body of a structural grade of polyurethane and wear resistant surfaces of a wear resistant grade of polyurethane bonded thereto.

The Patent Office.

2b12hed 1990as The Patent Office, State House, 66171 HIgh Holborn, London WC1R4TP. Furtlier copies maybe obtainedfrom Sales Branch, St Mary C-ray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187