This invention relates to a composition and more particularly, but not exclusively, a composition which is resistant to erosion, cavitation and abrasion.

In hydro electric power stations water can enter the turbines at a velocity in the order of 100 cubic metres/second and at a pressure of 75 bar. It can happen that under these conditions serious cavitation of the turbine casing can occur, particularly on the stay vanes. For example it has happened that cavitation of the stay vanes up to a depth of 6.0 mm was observed after only 500 hours of operation. Similarly low velocity, low pressure and turbulent flow can cause erosion cavitation of pump inlets, of pumping stations and of turbine draft tubes. A feature of cavitation in hydro electric plants is that it is not usually possible to predict in advance the precise site where it is going to occur. It is something which arises after the plant has been in service for some time. It would, of course, be possible to pre-treat the entire area of the stay vanes to render them resistant to cavitation. However, stay vanes, have quite a large area, for example 6 feet by 13 feet, so that would be very expensive. In addition it is not known whether prevention of cavitation at one place may increase it somewhere else.

A further problem is that equally serious cavitation can also occur on the turbine blades. Again it is difficult to predict the precise sites on the turbine blades where cavitation is likely to arise. It is somewhat easier to gain access to the turbine blades than to the stay vanes to treat the cavitation. However, any treatment of the turbine blades must be able to resist the dynamic load applied thereto when the turbine is rotated.

It has been proposed to deal with the problem once the cavitation sites have been identified by applying an appropriately resistant metal or alloy to those sites as by welding. However, access to the stay vanes is so limited that no-one could get to the sites to carry out such welding. Of course, the plant could be dismantled to enable a welder to get inside the turbine casing, but that could mean a shut down of from twelve to eighteen months which, added to the cost of dismantling and then re-assembling the plant, makes the proposal financially unacceptable.

Various attempts have been made to paint the area where cavitation occurs with some appropriately resistant material. All the known materials which have been tested have only remained in place at best for a short time.

The present invention has been made in order to deal with this problem.

According to the invention there is provided a composition comprising a hardenable resin having dispersed therein a major proportion of hard, angular particulate material, said particulate material having a wide particle size distribution so that spaces between larger particles are substantially filled by smaller particles.

The amount of resin used in composition of the invention is preferably the least that can be used to maintain the integrity of the composition when in use. More resin may be required when the size range of particulate material is smaller and conversely less resin may be needed when the particle size is bigger. Typically the proportion of hard, angular particulate material to resin, for example in the range 15 to 40% by weight of resin based on the total weight of the composition. A preferred composition includes particulate material and resin in the proportion 5:1 by weight.

The particulate material must be hard, preferably above 5 on Mohs scale of hardness and more preferably above 8. The particles can be of any hard material but particularly preferred are alumina and ceramic, for

example "Zirgrit" an alumina/zirconium material used for polishing and case hardening. It is preferred that provision is made to create a bond between the resin and the particulate material.

It is also important that the particulate material should be angular, that is to say it should not be spherical and that there should be a wide particle size range. The angular particles can be more firmly held in the resin than rounded particles and the wide particle size range enables spaces between larger particles to accommodate smaller particles. The particle size distribution is chosen having regard to the end use of the composition.

Because of the high proportion of hard, angular particles to resin the composition can be difficult to handle, for example to apply it as a coating to a surface. It is, therefore, preferred to include a thixotropic agent which controls the flow and viscosity of the composition. When the composition is cast in a mould rather than applied to a surface it may be more important that it flows in which case a thixotropic agent may not be necessary. Other uses may demand a rather more viscous composition.

The composition may also include reinforcement such as fibrous material for example of plastics such as

polypropylene fibres of natural material such as asbestos, cottgn, wool and the like, metal fibres and glass fibres. The fibres may also function so as to introduce secondary thixotropic effects.

It is, of course, highly important that the hard, angular particulate material should be held firmly in the resin after the resin has been cured. In order to enhance bonding between the resin and the particles a coupling agent, such as an organo-silicone is preferably included. Particularly preferred are coupling agents which also improve the bond between the composition and the surface on which the composition is coated.

The resin is preferably an epoxy resin having an average molecular weight of from 150 to 10,000 and which may include a reactive or non-reactive diluent, preferably the former. The viscosity of the composition can also be adjusted by means of the reactive diluent. The resin is preferably cured with a hardener, which may be a cross linking agent such as trimethyl hexamethylene diamine. The hardeners that can be used may be those with low viscosity and which readily wet the constituents of the composition and thus make the composition easier to work. The hardener may be one which provides for curing at room temperature or which requires heat.

The composition of the invention may contain other additives, for example a pigment such as black oxide which is an aid to checking the uniformity of mixing of the composition.

It is preferred that the composition should be prepared in such a way as to prevent or limit air being entrained therein. The presence of entrained air can lead to voids being formed in the cured composition which can weaken the resistance of the composition to erosion, cavitation or abrasion.

There are many ways by which the composition can be applied to a surface. For example it can be applied manually using a trowel or the like. If desired the outer surface of the coating of composition can, prior to curing, be smoothed or otherwise shaped by applying an appropriately shaped former to the coating. Alternatively the area to be coated can be enclosed, in the manner of a mould and the composition injected into the mould space thereby defined. Coating to repair cavitation is far quicker and cheaper than conventional welding.

Although there have been references to the composition being used as a coating it is not confined to that use. Products can be cast or moulded from the composition.

The following Examples further illustrate the invention.

Certain items in the Examples are further explained as follows:-

The Ceramic Filler consisted of 50% Alumina, 32% Zirconia and 16% Silica. The particle size distribution was as follows:-

Particle Size 1 0 - 0.125 mm

Particle Size 2 0.125 - 0.250 mm

Particle Size 3 0.250 - 0.50 mm

Particle Size 4 0.50 - 1.0 mm

Silica Flour 180-200's Mesh

EXAMPLE FORMULATIONS

1) UNMODIFIED EPOXY RESIN

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE

CERAMIC PARTICLE SIZE 1

CERAMIC PARTICLE SIZE 2

CERAMIC PARTICLE SIZE 3

CERAMIC PARTICLE SIZE 4

SILICA FLOUR

AMORPHOUS SILICON DIOXIDE

SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

2) UNMODIFIED EPOXY RESIN 3.000 PARTS 1.4 BUTANE DIOL 0.600

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE 0.100 CERAMIC PARTICLE SIZE 1 3.000 CERAMIC PARTICLE SIZE 2 3.000 CERAMIC PARTICLE SIZE 3 3.000 CERAMIC PARTICLE SIZE 4 3.000 SILICA FLOUR 3.200

AMORPHOUS SILICON DIOXIDE 0.250 SYNTHETIC POLYPROPYLENE FIBRE 0.025

TRIMETHYLHEXAMETHYLENE DIAMINE 0.900 PARTS AMORPHOUS SILICON DIOXIDE 0.100 " SYNTHETIC BLACK IRON OXIDE 0.010 "

3) UNMODIFIED EPOXY RESIN 1.4 BUTANE DIOL

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE CERAMIC PARTICLE SIZE 1 CERAMIC PARTICLE SIZE 2 CERAMIC PARTICLE SIZE 3 SILICA FLOUR

AMORPHOUS SILICON DIOXIDE SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

4) UNMODIFIED EPOXY RESIN ISO OCTYL GLYCIDYL ETHER

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE CERAMIC PARTICLE SIZE 1 CERAMIC PARTICLE SIZE 2 CERAMIC PARTICLE SIZE 3 CERAMIC PARTICLE SIZE 4 SILICA FLOUR

AMORPHOUS SILICON DIOXIDE SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

5) UNMODIFIED EPOXY RESIN

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE

CERAMIC PARTICLE SIZE 1

CERAMIC PARTICLE SIZE 2

CERAMIC PARTICLE SIZE 3

CERAMIC PARTICLE SIZE 4

SILICA FLOUR

SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

6) BISPHENOL A, BISPHENOL F RESIN

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE

CERAMIC PARTICLE SIZE 1

CERAMIC PARTICLE SIZE 2

CERAMIC PARΗCLE SIZE 3

CERAMIC PARΗCLE SIZE 4

SILICA FLOUR

AMORPHOUS SILICON DIOXIDE

SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

7) UNMODIFIED EPOXY RESIN 1.4 BUTANE DIOL

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE CERAMIC PARΗCLE SIZE 1 CERAMIC PARΗCLE SIZE 2 CERAMIC PARΗCLE SIZE 3 CERAMIC PARΗCLE SIZE 4 SILICA FLOUR

AMORPHOUS SILICON DIOXIDE SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

8) UNMODIFIED EPOXY RESIN 1.4 BUTANE DIOL GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE PHOSPHORUS BRONZE PARΗCLE SIZE 1 (300's mesh) PHOSPHORUS BRONZE PARΗCLE SIZE 2 (100's mesh) SILICA FLOUR

AMORPHOUS SILICON DIOXIDE SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

9) UNMODIFIED EPOXY RESIN

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE CRUSHED CERAMIC - RANDOM SIZE 3MM TO DUST SILICA FLOUR

AMORPHOUS SILICON DIOXIDE SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

10) UNMODIFIED EPOXY RESIN 2.000 PARTS 1.4 BUTANE DIOL 0.500 GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE 0.150 COBALT ALLOY 1 PARΗCLE SIZE 50'S MESH 5.000 COBALT ALLOY 2 PARΗCLE SIZE 350'S MESH 2.500 SILICA FLOUR 2.500

AMORPHOUS SILICON DIOXIDE 0.100 SYNTHETIC POLYPROPYLENE FIBRE 0.050

TRIMETHYLHEXAMETHYLENE DIAMINE 0.625 PARTS AMORPHOUS SILICON DIOXIDE 0.075 " SYNTHETIC BLACK IRON OXIDE 0.007 "

11) UNMODIFIED EPOXY RESIN

ISO OCTYL GLYCIDYL ETHER GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE COBALT ALLOY 1 PARΗCLE SIZE 50*S MESH COBALT ALLOY 2 PARΗCLE SIZE 350'S MESH SILICA FLOUR

AMORPHOUS SILICON DIOXIDE SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

12) UNMODIFIED EPOXY RESIN

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE

CERAMIC PARΗCLE SIZE 1

CERAMIC PARΗCLE SIZE 2

CERAMIC PARΗCLE SIZE 3

CERAMIC PARΗCLE SIZE 4

SILICA FLOUR

AMORPHOUS SILICON DIOXIDE

SYNTHETIC POLYPROPYLENE FIBRE

4.4'DIAMINODIPHENYLMETHANE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

13) UNMODIFIED EPOXY RESIN 1.4 BUTANE DIOL

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE CERAMIC PARΗCLE SIZE 1 CERAMIC PARΗCLE SIZE 2 CERAMIC PARΗCLE SIZE 3 CERAMIC PARΗCLE SIZE 4 SILICA FLOUR

AMORPHOUS SILICON DIOXIDE SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

14) UNMODIFIED EPOXY RESIN 1.4 BUTANE DIOL

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE CERAMIC PARΗCLE SIZE 1 CERAMIC PARΗCLE SIZE 2 CERAMIC PARΗCLE SIZE 3 SILICA FLOUR

AMORPHOUS SILICON DIOXIDE SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE . AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

15) UNMODIFIED EPOXY RESIN

GAMMA GLYCIDOXYPROPYLTRIMETHOXY SILANE

CERAMIC PARΗCLE SIZE 1

CERAMIC PARΗCLE SIZE 2

CERAMIC PARTICLE SIZE 3

CERAMIC PARΗCLE SIZE 4

SILICA FLOUR

AMORPHOUS SILICON DIOXIDE

SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE

16) UNMODIFIED EPOXY RESIN 1.4 BUTANE DIOL CERAMIC PARΗCLE SIZE 1 CERAMIC PARΗCLE SIZE 2 CERAMIC PARTICLE SIZE 3 CERAMIC PARΗCLE SIZE 4 SILICA FLOUR

AMORPHOUS SILICON DIOXIDE SYNTHETIC POLYPROPYLENE FIBRE

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

17) UNMODIFIED EPOXY RESIN

CRUSHED CERAMIC - RANDOM SIZE 3MM TO DUST

SILICA FLOUR

AMORPHOUS SILICON DIOXIDE

SYNTHETIC POLYPROPYLENE FIBRK

TRIMETHYLHEXAMETHYLENE DIAMINE AMORPHOUS SILICON DIOXIDE SYNTHETIC BLACK IRON OXIDE

SUBSTITUTE SHEET