EP0620866B1

EP0620866B1 - Wear surface

Info

Publication number: EP0620866B1
Application number: EP93901845A
Authority: EP
Inventors: Robert Kay
Original assignee: Alcan Aluminum Ltd; SIMEC Lochaber Hydropower 2 Ltd
Current assignee: Rio Tinto Alcan Inc; SIMEC Lochaber Hydropower 2 Ltd
Priority date: 1992-01-10
Filing date: 1993-01-08
Publication date: 1996-08-14
Anticipated expiration: 2013-01-08
Also published as: DE69304043D1; AU3262393A; EP0620866A1; WO1993014236A1; CA2127439A1

Abstract

A method of forming a wear surface on a base structure, the wear surface comprising a metal layer having distributed therein at least one solid, filler characterized by the steps of: 1) providing a self-supporting substrate having at least parts of one surface capable of intimately bonding with said layer; 2) applying the layer to said one surface by a high temperature spray technique selected from flame spraying, plasma spraying and arc spraying; and 3) thereafter securing the substrate to the base structure with a surface opposed to the one surface in contact therewith.

Description

WEAR SURFACE

This invention relates to the provision of a wear surface on a base structure.
In this specification the term "wear surface" has been used to include such a surface applied to a base structure to protect the structure from physical damage in arduous industrial conditions and/or to provide the base structure with an anti-skid surface to enhance the safety of operatives walking thereon or to improve the traction of vehicles. Such wear surfaces are commonplace in factories, shopping centres and in many other places. The base structure may, for example be a concrete floor or it may be a metal base plate.
In general anti-skid surfaces are made deliberately rough whereas surfaces to protect the structure from damage do not need a rough finish. Both kinds of surface may be of the same composition; variation in texture being obtained by differences in the way the surface is applied.
In EP 0331519A there is disclosed a method of producing a corrosion and mechanical wear resistant coating on a metal surface to be protected which comprises (a) providing a rod or wire formed of a metal matrix composite comprising a metal matrix having distributed therein a finely divided solid filler material and (b) applying a coating of said metal matrix composite on said metal surface to be protected by means of a flame spraying or arc spraying process.
The use of these proposals would be entirely satisfactory in many installations with the coating applied to metal base plates already incorporated in the installations.
Should the wear surface need replacement or repair this can be done on site by re-spraying. Alternatively a damaged base plate could be replaced even, as in some installations, where such a base plate may be a heavy steel structure up to 5 metres long and two metres wide, by using appropriate lifting apparatus.
However the prior proposals would not be appropriate for an installation which cannot be shut down or which is located in an environment where techniques involving high temperatures and naked flames cannot be used and where all risk of generating sparks must be avoided.
Such an installation may for example be an oil rig or support platform to be located at sea or installations such as refineries or petroleum product storage facilities. In such circumstances it would not be possible to use the process of EP 0331519A on an operational oil rig. It would also not be possible to replace a damaged steel base plate on site. Nevertheless it is very desirable that damaged wear surfaces on such installations should be removable and replaceable on site.
According to the present invention there is provided a method of forming a wear surface on a base structure, the wear surface comprising a metal layer having distributed therein at least one solid filler characterised by the steps of:-

1. providing a self-supporting substrate having at least parts of one surface capable of intimately bonding with said layer,
2. applying the layer to said one surface by a high temperature spray technique selected from flame spraying, plasma spraying and arc spraying, and
3. thereafter securing the substrate to the base structure with a surface opposed to the one surface in contact therewith.

Preferably the metal layer is of aluminium or an aluminium alloy.
According to another aspect of the present invention there is provided a self supporting substrate having a wear surface thereon in which the wear surface is a metal layer having distributed therein at least one solid filler and in which the layer is applied to one surface of the substrate at least parts of that one surface being capable of intimately bonding with said layer.
In the present specification we use the term "solid filler" to mean a fibrous or particulate material which is capable of being incorporated in and distributed through a suitable metal and which at least substantially maintains its integrity as incorporated rather than losing its form or identity by dissolution in or chemical combination with the metal. The filler may for example be selected from alumina, titanium diboride, silica, zirconia silicon carbide, silicon nitride and aluminium/titanium boride complexes. The size of filler particles may be from 5 to 30 µm (5 to 30 microns) and is preferably within the range 7 to 20 µm (7 to 20 microns). The filler may comprise 5.0 to 25 volume percent of the metal and is preferably 8.0 to 12.0 volume percent thereof.
Numerous embodiments of the present invention will now be described by way of example with reference to the single figure of the accompanying drawing which shows, diagrammatically a machine for making substrates having a wear coating.
Referring to the drawing a coil 1 of an aluminium alloy strip 2 is unwound and passes successively through an optional abrading zone 3 where its upper surface is roughened by grit blasting or scratch brushing and an induction heating zone 4 to raise the temperature of the strip 2 to about 200°C. The strip then passes over a heated table 5 to provide a firm support through a spray zone 6. Above the spray zone, one or more spraying devices 7 is movable to coat the upper surface of the strip 2 with a coating as described in EP 0331519A. This coating is of a metal matrix composition and constitutes a wear surface to the strip. The strip then passes between driven nip rolls 8 past a zone 9 having a flying shear mechanism 10 where the strip is cut into individual substrates constituting tiles 11.
When the strip 2 is of aluminium or an aluminium alloy as described the coating may be of such thickness as to weigh 0.5 to 3.0 kg/m² and preferably 1.0 to 2.0 kg/m². However it would be possible to use a ferrous strip and in this case the coating should be thicker to protect against corrosion. For example the coating may be of such thickness as to weigh 1.0 to 6.0 kg/m² and preferably 2.0 to 5.0 kg/m². Thicker coatings may, if desired be provided by more than one spraying operation.
Prior to the nip rolls 8 a roll of sheet impact adhesive material 12 (with a strippable backing sheet) may be located below the strip 2 and unwound by being passed with the strip 2 through the nip rolls 8 so that the material 12 is bonded to the lower surface of the strip 2. If this arrangement is used the abrading zone 3 may also suitably prepare the lower surface to enhance bonding of the material 12 thereto.
In an alternative arrangement, prior to the nip rolls 8, the lower surface of the strip 2 may be coated with a non-curing pressure-sensitive, adhesive, formulated on the basis of synthetic resins such as polyisobutylene ["Oppanol" from BASF for example] or a polyvinylisobutyl ether, or based on combinations of nitrile rubber and tackifier resin based on terpene oil. The coating may be applied by a blade (not shown) from a heated melt of the adhesive or directly from a slot (not shown) in a suitable applicator. A roll of release-coated backing paper is interleaved in the manner of the material 12 immediately after the adhesive application.
The tiles 11 may be rectangular or square and of a readily handleable size, say 750 mm square. Alternatively the tiles may each be in the form of an elongated strip. Although comparatively thin tiles or strip are, in general, envisaged by this invention such tiles or strips may have a thickness of up to 20 mm or more.
The abrading zone 3 is referred to above as "optional" since it has sometimes been found that merely heating the strip 2 to about 200°C is sufficient. Indeed in some cases even this metal heating step may not be necessary. In addition the heated table 5 may be omitted from the arrangement of the drawing.
When the tiles are to be applied to a metal base plate the surface of the latter is cleaned. In locations such as on an oil drilling platform such cleaning may be by blasting with a grit having a composition that precludes the generation of sparks. The blasted surface may be primed with a coating compatible with the tile adhesive and capable of protecting the surface against corrosion and/or damage until the tile is laid.
Although pressure sensitive non-curing adhesives as described above can be used it will be understood that other ways of sticking the tiles or strips to a base plate may be employed. For example a high strength adhesive may be used with tiles subjected to heavy applied loads especially impact or shear loads. The adhesive may have considerable inherent strength so that it contributes to the physical properties of the structure comprising tiles, the adhesive and the base plate.
Another variation is to use an adhesive that never completely sets so that a damaged tile can be readily peeled from its base plate for replacement.
The tiles may be relatively thick and may be of a strong aluminium alloy or relatively thin and may be a soft, ductile alloy, for example a lxxx alloy, which can be deformed to follow irregularities in the base plate.
If desired a polymerisable two part adhesive may be used that has considerable inherent strength so that it contributes to the physical properties of the structure comprising the tiles, the adhesive and the base plate. For convenience the two parts of the adhesive may be mixed together and applied to the tiles or the base plate as the tiles are laid.
In all these arrangements the adhesive may be applied only to parts of the surface of each tile.
Where the base plates are located on an oil drilling platform at sea or are on some other structure that may be subjected to an electrolyte the adhesive may incorporate electrically conducting particles. In such case when the base plate is of a ferrous alloy, aluminium alloy tiles can constitute sacrificial anodes therefor. In an alternative arrangement the tiles could be electrically connected with the base plate by a mechanical link.
When the tiles or strips are themselves of aluminium or an aluminium alloy it is desirable that the filler used should not corrode or assist the corrosion of the tiles. Thus copper or graphite particles should not be used whereas all the particles referred to above are satisfactory.
It will also be understood that tiles may be pre-shaped before application of the wear resistant layer. Although metal tiles of aluminium or an aluminium alloy have been described above it will be understood that these may be of other metals such as steel.
In a modification of the present invention the substrate may be a self-supporting web of a non-metallic material to which the wear layer is capable of bonding. Such a web may be a mat incorporating glass particles or glass fibres such as a glass reinforced plastics material.
The plastics material may incorporate a resin that constitutes one component of a two part adhesive, the other part of which is applied to the base plate. Alternatively the resin may itself be a low temperature heat setting adhesive.
A commonly used example of such a plastic material substrate would be a conventional floor tile, usually about 2.0 mm thick in which a mat of glass fibre is embedded in a thermoplastic plastics material. Such a tile (or sheet during a continuous manufacturing process) could be abraded as by shot blasting on one surface to expose sufficient of the glass fibre mat to receive the wear resistant layer. We have found however that arc spraying directly on to a glass reinforced plastics surface is less satisfactory than flame spraying or plasma spraying. However, a flame sprayed layer may be followed by an arc sprayed layer.
It will be understood that the self supporting web may have any convenient combination of layered materials both to receive the sprayed on layer and also to fulfil requirements of strength, convenient handling and securing to a base. For example an additional mat of glass reinforced fibre could be applied during manufacture of the tile to be exposed on one surface thereof so as to eliminate the abrading step or at least materially reduce it.
The resultant tile thickness is likely to be at least 2.0 mm and may be much thicker. The wear resistant layer is likely to be between 0.2 mm and 0.7 mm thick.
In all the above arrangements the peel resistance of even a high strength adhesive may be comparatively low. Thus to remove a worn or damaged tile one corner may be prized up and a slotted bar (not shown) engaged therewith. The bar may have one end formed for engagement with a ratchet handle to rotate it and wind the tile around the bar to peel it off the base plate.
The wear resistant layer may be of variable thickness to provide surface channels to facilitate shedding of liquid or solid detritus from vehicle wheels passing thereover.
Although it is preferred to stick the tiles to the base plate it will be understood that mechanical fasteners could be used.
It will also be understood that the spraying techniques of the present invention should preferably be carried out at atmospheric pressure. The alloy and temper of the wire used for spraying may be 1060-H 18; aluminium oxide particles in the wire may be 8-10 µm in size and the metallising wire may contain 10 volume percent of the oxide particles.
Tiles according to the present invention have been tested under arduous conditions both with respect to surface grip and wear and skid resistance. The surface grip results mentioned below were derived from tests conducted by the Flight Systems and Measurement Laboratory, of the Cranfield Institute of Technology and are based on standards used for helideck surfaces on offshore oil rigs. A Grip Test value of 0.7 or above (wet or dry surface) represents a surface with good deck friction where no helideck nets are required and where no check on surface frictional properties needs to be made for one year.
The tests were carried out in the hot rolling department of an aluminium rolling mill. The monthly traffic volume was predicted to be 250,000 tonnes of forklift truck movement with maximum individual axle loadings of 68 tonnes. The floor location chosen was an area in the path of forklift trucks where they needed to change direction through 90° at their maximum permissible speed.
The floor conditions were generally oily and wet depending on external weather conditions as the truck movements were partly from the exterior of the building.

In these tests various adhesives were used as set out in the following table:

SIKAFLEX 221	SIKA LIMITED	Single component, moisture curing polyurethane (elastomeric adhesive)
PERMABOND F245	PERMABOND ADHESIVES Ltd	2 part toughened acrylic cured by an activator applied to one surface
PERMABOND V501	AS ABOVE	2 part toughened Acrylic - Epoxy hybrid
PERMABOND V6018	AS ABOVE	2 part toughened Acrylic Epoxy Hybrid
PERMABOND E04	AS ABOVE	2 part toughened epoxy

Phase One

The floor area comprised a sound flat concrete floor.
Four steel plates numbered A, B, C and D, each 1200 mm x 2400 mm by 7 mm thick formed the basis of the trial. Each were prepared as below prior to being bolted side by side to the concrete floor in the Plate order C B A D.

Tiles

Substrate aluminium alloy sheet in alloy 1050A to BS 1470, of nominal thickness 0.25 mm and 0.9 mm were grit blasted to Sa 2½ to provide an anchor tooth profile and were coated with nominally 1.22 kg/m² of a wear surface according to the present invention which was applied by arc spraying.
Substrate tile size 500 mm x 500 mm x 0.25 mm and 0.9 mm thickness, weighing 0.68 kg/m² and 2.44 kg/m² respectively.
Total weight of tile at 0.25 mm thick was 1.9 kg/m² and at 0.9 mm thick was 3.66 kg/m².
Surface Grip Test reading, although not measured on the finished tile was the same as that recorded at Cranfield averaging over 1.00 in the wet.

Plate A

1. Grit blasted to Sa 2½ anchor tooth profile
2. Coated with one brush applied coat of W & J Leigh Epigrip J984 primer followed by one brush applied coat of W & J Leigh Epigrip M 330 seal coat
3. Adhesive Sikaflex 221 applied by roller
4. Aluminium tile 0.9 mm thick x 500 mm x 500 mm surface coated as above applied on to the adhesive
5. 50% of the surface painted with one brush applied seal coat Epigrip M 330

Plate B

1. As 1 to 3 for Plate A
2. Aluminium tile 0.25 mm thick x 500 mm x 500 mm surface coated as above applied on to the adhesive
3. 50% of the surface painted with one brush applied seal coat Epigrip M 330

Plate C

1. Grit blasted to Sa 2½ anchor tooth profile
2. Coated directly with a first arc sprayed coat to provide a wear/corrosion coating at application rate of 1.22 kg/m²
3. The coating of 2 above coated with an arc sprayed anti-skid surface at an application rate of 1.22 kg/m²
4. 50% of the surface painted with one brush applied seal coat Epigrip M 330

Plate D

1. As 1 to 3 for Plate C
2. No additional seal coat applied.

Phase Two

Tiles according to the invention were bonded to worn and cleaned surfaces simulating repair and refurbishment conditions after approximately 750,000 tonnes of traffic movements over the tiles on Plates A, B, C and D above. The following procedure was adopted.

Cleaning

All surfaces of the Plates A to D were cleaned with water and standard detergent using a conventional industrial powered floor cleaner with nylon bristle brushes. The cleaning was also applied to the concrete area surrounding the four Plates.

Grip testing

The surfaces of Plates A to D were tested using the Cranfield Grip-Tester both dry and wet with four runs being made across the full width of all plates. The Grip factor had reduced on average from 1.0 to 0.8.

Tile removal

The 0.25 mm thick tiles still remaining on Plate B were removed exposing a part adhesive covered and part painted steel surface. A proportion of the old adhesive material was removed with the use of solvents and scraping.

Tile replacement

A simulated in-service resurfacing repair was applied to Plate B by applying new 0.9 mm thick anti-skid coated tiles with two different adhesives, Permabond V 6018 and F 245.

Surface repair

A patch repair was simulated on Plate C by applying four new 0.9 mm thick anti-skid coated tiles with two different types of adhesive, Permabond V 501 and V 6018, to the previously cleaned existing part sealed and part un-sealed anti-skid surface.
A patch repair was also simulated on Plate D by applying four new 0.9 mm thick tiles with two types of adhesive, Permabond F 245 and V 501 to the previously cleaned existing anti-skid surface.
The remainder of the surface on both Plates C and D and the whole of the surface of Plate A with the original 0.9 mm tiles attached were left to continue the original surface test programme.

Application to concrete

Three groups of four new 0.9 mm thick anti-skid coated tiles were bonded to the surrounding previously cleaned concrete floor area using three types of adhesive, Permabond F 245, V 6018 and E 04.

Bonding materials

In Phase One of the trials Sikaflex 221 adhesive was used.
The adhesives used in Phase Two were Permabond F 245, V 501, V 6018 and E 04.

COMMENTS ON TRIALS

Phase One

Grip reading

Prior to the tests, samples of aluminium plates with the anti-skid surface applied, and having degrees of roughness covering that applied to the tiles, were tested by Cranfield using the Grip-tester approved for recording the "Grip" on offshore helidecks.
This Grip-testing established a mean "Grip" of just over 1.00 under both wet and dry conditions.
At the end of Phase One the "Grip" reading was over 1.00 in the dry condition and over 0.7 on average in the wet condition.

Vehicle movement

During the first Phase lasting three months approximately 750,000 tonnes of fork lift truck movements passed over the test area, with the trucks turning through 90° over the tiled area.

Tile performance

During Phase One of the trial 60% of the 0.25 mm thick tiles on Plate B became detached. The tiles failed as a result of the severe twisting action caused by the steering wheels of the fork lift trucks being turned whilst the trucks were static. The 40% balance of these tiles remained in good condition.
The other surfaces on Plate A remained in good condition and tiles were 100% intact except for 3 points of mechanical damage where the steel forks had been "grounded" with full load. A very localised part of one tile had been removed.
Direct applied anti-skid surface performance.
On Plate D the-overall surface was in good condition with a good anti-skid surface coating retained.
On Plate C the overall surface was in good condition with a good anti-skid surface coating retained. No apparent difference between the painted and un-painted surfaces.

Phase Two

Vehicle movement

During the second Phase also lasting three months approximately 250,000 tonnes of fork lift truck movements passed over the test area each month, with the trucks turning through 90° over the tiled area.

Tile performance

The tiles bonded to the concrete floor with the adhesive V 6018 detached within 1 week.
The tiles bonded to Plate C with adhesive V 6018 became detached after approximately 250,000 tonnes of traffic movement.
All the tiles bonded with adhesives F 245, V 501 and E 04 were remaining in place after approximately 500,000 tonnes of traffic movement.
The tiles on Plate A bonded with the Sikaflex 221 adhesive remained in place after approximately a total of 1,250,000 tonnes of traffic movement.

Claims

A method of forming a wear surface on a base structure, the wear surface comprising a metal layer having distributed therein at least one solid, filler characterised by the steps of:-
1. providing a self-supporting substrate having at least parts of one surface capable of intimately bonding with said layer,

2. applying the layer to said one surface by a high temperature spray technique selected from flame spraying, plasma spraying and arc spraying, and

3. thereafter securing the substrate to the base structure with a surface opposed to the one surface in contact therewith.
A method according to claim 1 in which the metal layer is of aluminium or an aluminium alloy.
A method according to claim 1 or claim 2 in which the base structure is a ferrous base plate.
A method according to any one of claims 1 to 3 in which the substrate is a metal tile or strip having said one surface physically abraded or chemically or thermally treated to enhance bonding of the layer.
A method according to claim 4 in which the substrate is of an aluminium alloy.
A method according to claim 5 in which the substrate is of a thin, ductile aluminium alloy so that after application of the layer thereon it can be formed to follow irregularities in the base plate.
A method according to any one of the preceding claims in which the substrate is stuck to the base structure.
A method according to claim 7 in which the substrate is stuck with an adhesive that contributes to the physical properties of the structural unit comprising the substrate, the adhesive and the base structure.
A method according to claim 8 in which the adhesive has such characteristics that the substrate may readily be peeled away from the base structure to permit easy replacement.
A method according to any one of claims 6 to 9 in which the adhesive is a two part cold setting adhesive the parts being mixed and applied to the substrate or the base plate.
A method according to any one of claims 6 to 9 in which the adhesive is a non-curing pressure-sensitive adhesive.
A method according to claim 11 in which the adhesive is selected from a moisture curing polyurethane; a two part acrylic a two part epoxy or a two part epoxy hybrid.
A method according to claim 5 and claim 8 in which the substrate and the base plate are electrically connected together by electrically conducting particles incorporated in the adhesive so that when the base plate is of a ferrous alloy and is located in an electrolyte an aluminium alloy substrate constitutes a sacrificial anode therefor.
A method according to any one of claims 1 to 3 in which the substrate is a self supporting web of a non-metallic material incorporating particles or fibres to which the layer is capable of bonding.
A method according to claim 14 in which the substrate is of glass reinforced plastics material.
A method according to claim 14 in which the substrate is itself a one component heat settable adhesive.
A method according to claim 14 in which the substrate is itself one component of a two component cold setting adhesive the other component of which is applied to the base plate.
A method according to any one of the preceding claims in which the layer is formed of variable thickness to facilitate shedding of liquid or solid detritus from vehicle wheels passing thereover.
A structure provided with a wear surface which comprises a metal layer having distributed therein at least one solid filler, characterised in that said metal layer is applied no one surface of a self supporting substrate having at least parts of said one surface capable of intimately bonding with said layer, by a high temperature spray technique selected from flame spraying and arc spraying, and the substrate is secured to a base structure with a surface or the substrate opposed to the said one surface in contact with the base structure.
A structure according to claim 19 wherein said base structure is a ferrous metal base plate.
An oil drilling or support platform which is, or comprises, a structure according to claim 19 or claim 20.