Stock material or miscellaneous articles – Composite – Of quartz or glass
Patent
1993-12-07
1996-05-14
Robinson, Ellis P.
Stock material or miscellaneous articles
Composite
Of quartz or glass
428209, 428210, 428469, 428471, 428472, 4285395, 428697, 428701, 428702, 148403, 148516, 148537, 427192, 427205, 427330, 427367, 427404, 427405, 4274192, 4274196, 427422, 427456, B32B 1504
Patent
active
055165869
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention concerns the protection of metal surfaces against corrosion.
According to the invention there is provided a method of protecting a metal surface comprising the steps of coating the surface with vitreous enamel, spraying an atomized protective metal or alloy whilst the enamel is in a hot viscous condition thereby to form a layer of the protective metal or alloy on the enamel, and carrying out a spray peening operation on the layer of protective metal or alloy whilst the protective metal or alloy is in a hot condition.
The invention also provides an article or structure having at least part of a metallic surface thereof coated with a vitreous enamel, the coating of enamel having applied thereto a spray-coated layer of a protective metal or alloy, with penetration of the enamel at the interface between the enamel and the protective metal or alloy, the protective metal or alloy layer being peened.
Corrosion is a major hazard where articles or structures are required to operate for long periods under adverse weather conditions, particularly marine conditions. Typical cases are those of marine oil platforms and ships.
In the case of marine oil platforms the structure can be weakened, particularly near the waterline and in the splash zone. Painting of the structure is not of itself sufficient protection and sacrificial anodes of zinc are frequently used to diminish corrosion in the danger areas. Despite the use of antifouling paint the formation of barnacles causes further problems because it increases the drag on the structure caused by waves and water currents.
Similar problems occur with ships although the liberal use of antifouling paints and the relative simplicity of inspection ease the problem somewhat.
Many other solutions to the problem of corrosion have been tried including cladding with cupro-nickel or other corrosion resistant metals. This has the special advantage of presenting the seawater side of the combination with a corrosion resistant surface which is toxic to barnacles and therefore permanently antifouling. Unfortunately cupro-nickel and steel form a galvanic cell in the presence of sea water leading to severe corrosion of the steel if penetration of the cupro-nickel occurs. An intermediate layer of rubber can be used to prevent such penetration and separate the components of the galvanic cell but to be effective it must be thick and it is therefore expensive and bulky.
SUMMARY OF THE INVENTION
The method according to the invention allows a steel structure to be coated with, for example, cupro-nickel which is separated by a thin and cheap electrically insulating layer from the steel structure thus giving it effective corrosion protection in any area required and at the same time having antifouling properties.
More specifically the method comprises the steps of covering parts of a steel structure with a protective coating consisting firstly of a coating of vitreous enamel and secondly of a layer of a corrosion resistant metal or alloy applied as a metal spray, the first coating of vitreous enamel being heated to a temperature at which it flows over the steel surface and bonds to it, the composition of which vitreous enamel is selected such that it is softened and is viscous at the spraying temperature of the layer of metal or alloy, with the effect that the spray coating of corrosion resistant metal or alloy bonds to the vitreous enamel but the sprayed metal droplets do not penetrate the vitreous enamel completely, and spray peening the layer of metal or alloy. The sprayed layer of corrosion resistant metal can be applied by metal spraying using a thermal spray gun, plasma arc spray or spray from an atomised melt of corrosion resistant metal, or alternatively the process of simultaneous spray peening described in British Patent No. 1605035 can be used in which latter case a smooth pore-free external surface having controlled internal stress can be produced.
Vitreous enamelling is a well-known and much used procedure but the combination of vitreous
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Davies Gordon I.
Roche Allen D.
Singer Alfred R. E.
Robinson Ellis P.
Speer Timothy M.
Sprayforming Developments
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