Stock material or miscellaneous articles – Composite – Of quartz or glass
Patent
1996-08-23
1999-01-05
Group, Karl
Stock material or miscellaneous articles
Composite
Of quartz or glass
428472, 501 18, 501 19, 501 20, 501 21, 501 24, C04B 818, B32B 1706
Patent
active
058560157
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a glaze for refractory materials and, in particular, to a glaze for carbon-containing refractory materials.
2. The Prior Art
Refractories used in the continuous casting of steel often contain a percentage of elemental carbon, normally in the form of flake graphite. The inclusion of elemental carbon serves to protect the refractory from attack and erosion by molten metals and the accompanying slags. It also contributes towards the high thermal shock resistance required in certain applications. However, elemental carbon is itself susceptible to air oxidation at temperatures above 500.degree. C. Therefore, during preheat and casting operations, the refractory must be protected from the atmosphere if extended life of the component is required. An example of a component which requires extended oxidation protection is the submerged entry nozzle (SEN). This must typically survive preheat times of 2-3 hours at temperatures as high as 1400.degree. C. and casting times of up to 5 hours at temperatures approaching the melting point of steel.
EP-A-0252621 discloses a method of protecting an electric arc furnace graphite electrode with particulate matter comprising 35-70% by weight of a refractory filler, 20-40% by weight of a graphite-wetting, fusible material and 10-25% by weight of a metal or metalloid oxidisable to a refractory oxide whilst the electrode is at an elevated temperature such that the metal or metalloid oxidises and forms a coating adhering to the side of the electrode. The preferred metal for use is aluminium, whilst the preferred refractory filler is silicon carbide and the preferred graphite-wetting fusible material is a boron compound or a boron-containing glass. The specification teaches that the particulate matter is sprayed onto the hot graphite electrode, for example using the spraying apparatus as disclosed in EP-A-0070100.
Using dry powder spraying methods, it is difficult to obtain an even coating of the refractory composition onto the graphite electrodes and expensive spraying equipment is required. Furthermore, dry powder spraying methods are not particularly suitable for coating complex geometries, for example the interiors of tubes. The refractory compositions as disclosed in EP-A-0252621 are not designed for use as aqueous suspensions since the boron oxide would be very soluble and the lack of any suspension agent means that it would not form a stable glaze slip.
U.S. Pat. No. 4,260,662 is directed to a composition for the enamelling of metal parts, such as heat exchangers and exhaust systems. The composition disclosed comprises 30-60% by weight of a specified frit, 5 to 60% by weight of aluminium powder, optionally silicon, chromium trioxide, zirconium silicate, copper oxide and bentonite, and is applied as an aqueous slip. Evolution of hydrogen, by the contact of aluminium with water, is avoided by the particular nature of the frit used which contains very large quantities of boron trioxide.
SUMMARY OF THE INVENTION
We have now developed a glaze composition for application from aqueous suspensions which contains aluminium powder and silicon powder but which does not react significantly with the water, whereby the evolution of hydrogen is prevented. The composition provides oxidation protection to carbon-containing materials during high temperature use.
Accordingly, in one aspect the present invention provides a glaze composition for refractory materials which comprises:
______________________________________ % By Weight
______________________________________
at least one lead free and barium free
30 to 80
borosilicate, borophosphate or phosphate
glass frit having a dilatometric
softening point of below 600.degree. C.
aluminium powder or an aluminium
alloy powder 2 to 30
silicon powder or silicon alloy powder
2 to 30
inhibitor up to 2
refractory filler 0 to 20
clay 0 to 20
optional additives 0 to 10
______________________________________
In another aspect, the present invention
REFERENCES:
patent: 3348929 (1967-10-01), Valtschev et al.
patent: 3547098 (1970-12-01), Lee
patent: 4224074 (1980-09-01), Reade
patent: 4260662 (1981-04-01), Wratil
patent: 4340645 (1982-07-01), O'Conor
patent: 4588700 (1986-05-01), Reven
patent: 4717424 (1988-01-01), Wilfinger et al.
patent: 4814298 (1989-03-01), Nelson et al.
patent: 5252521 (1993-10-01), Roberts
patent: 5264398 (1993-11-01), Thometzek et al.
patent: 5306674 (1994-04-01), Ruderer et al.
patent: 5362687 (1994-11-01), Tokunaga
patent: 5547749 (1996-08-01), Chiba et al.
Chemical Abstracts, vol. 112, No. 6, Feb. 5, 1990, No. 41222y, "Dual-Phase Vitreous Enamels . . . ".
Cookson Matthey Ceramics & Materials Limited
Group Karl
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