Coating processes – Spraying – Heated coating material
Patent
1997-05-27
1998-07-14
Marcantoni, Paul
Coating processes
Spraying
Heated coating material
427427, 264 30, 501133, 501154, C04B 3502, C04B 3560
Patent
active
057801142
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for making a crystalline siliceous refractory mass comprising cristobalite. This process may be for the purpose of producing the mass as such, for example in making refractory building bricks or blocks to be used in the construction or repair of furnaces, or may be a process for in situ repairing a worn surface of a siliceous refractory material, for example in industrial furnaces such as glassmaking furnaces.
2. Description of the Related Art
The process uses a technique of the type generally known as "ceramic welding", in which a mixture of solid refractory particles and solid combustible fuel particles of a metal or semi-metal such as aluminum and silicon are projected against the surface to be repaired and are there reacted with oxygen-rich gas, usually substantially pure oxygen, such that the heat of reaction of the fuel is released against the surface so that a coherent refractory repair mass is formed.
Such "ceramic welding" is described in GB patent 1,330,894 (Glaverbel) and GB 2,170,191 (Glaverbel), in which a coherent refractory mass is formed against a surface by projecting onto the latter a mixture of refractory particles and combustible particles in the presence of oxygen. The combustible particles are particles whose composition and granulometry are such that they react in an exothermic manner with the oxygen to form a refractory oxide while releasing the necessary heat for melting, at least superficially, the projected refractory particles. The projection of particles is conveniently and safely achieved by using the oxygen as a carrier gas for the particle mixture. In this manner a coherent refractory mass is formed against the surface onto which the particles are projected.
These known ceramic welding processes can be employed for forming a refractory article, for example, a block having a particular shape, but they are most widely used for forming coatings or for repairing bricks or walls and are particularly useful for repairing or reinforcing existing refractory structures, for example, furnace walls in glassmaking or coke furnaces.
The process is particularly suitable for the repair of a hot substrate surface. This makes it possible to repair worn surfaces while the equipment remains substantially at its working temperature and in many cases while the furnace as a whole remains in operation. Such repairs while the furnace remains in use are especially useful in glassmaking and coke ovens since the intended life of the furnace is measured in years, often as long as twenty years, with the furnace being maintained continuously in operation over the whole period.
The composition of the ceramic welding mixture is generally selected to produce a repair mass which has a chemical composition similar or close to that of the basic refractory. This helps to ensure compatibility with and adhesion to the new material and the base material on which it is formed.
Even with such chemical compatibility there can however be a problem in ensuring adhesion of the repair mass to the substrate, especially if the adhesion is to be maintained over prolonged periods. The problem tends to increase if the repaired surface is subjected to very high temperatures. In this case a high grade refractory is necessary, as for example for the vault of a glass tank.
The breaking away of a repair mass is to be avoided if at all possible. In glassmaking the broken mass is likely to fall into the molten glass and introduce unacceptable impurities, sometimes necessitating a huge batch of molten glass to be discarded.
SUMMARY OF THE INVENTION
We have now found that highly refractory masses comprising cristobalite can be easily formed, provided that the temperature is maintained at a very high level, from a solid refractory particulate material which has traditionally been avoided on the ground that it would be incompatible with the base material. Specifically the material which according to the present invention can now be used
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Meynckens Jean-Pierre
Somerhausen Bernard
Glaverbel
Marcantoni Paul
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