Stock material or miscellaneous articles – Composite – Of inorganic material
Patent
1996-03-13
1998-11-24
Krynski, William
Stock material or miscellaneous articles
Composite
Of inorganic material
428 344, 428 346, 428323, 428384, 428403, 428408, 428446, 428469, 428472, 428699, 428701, 428702, 4274432, 106 3835, 501 95, 501100, 501133, B32B 900
Patent
active
058404333
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATION
This is a U.S. national phase of PCT/GB94/02127 filed Sep. 30, 1994.
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to coated articles made from graphite-alumina refractory material and which are used, for example, as nozzles or shrouds in the casting of metals, especially steel.
Articles such as pouring nozzles for molten metal-containing vessels, e.g. ladles and tundishes, and shrouds which surround the metal stream flowing from one vessel to another, e.g. a ladle to a tundish, are commonly made in a graphite-alumina refractory material having a carbon bond produced by the decomposition of a phenolic resin binder.
Such a material has poor thermal shock resistance and tends to crack so it is necessary to treat nozzles and shrouds in some way so as to minimise the thermal shock produced when they are heated rapidly to elevated temperatures.
One method of treatment which is commonly used is to subject the article to a decarburisation treatment prior to use. The article is heated in an oxidising atmosphere so as to oxidise or burn out carbon at the surface of the article and leave a surface layer of porous, essentially unbonded alumina.
In the case of nozzles, another practice is to apply a ceramic fibre-containing insulating paper around the outside of the nozzle. However, this practice is expensive and time-consuming as it is necessary to cut the paper sheet and wrap and wire it in order to fit it properly around the nozzle.
It has also been proposed to coat nozzles with an insulating coating and Canadian Patent No. 1301780 describes the use of a coating composition comprising about 30% to about 85% by weight of a finely divided constituent selected from one or more of fused silica grains, alumina powder, zirconia powder, mullite powder and alumina bubbles; 0 to about 10% by weight of ceramic fibre selected from aluminosilicate fibre, zirconia fibre, titania fibre, alumina-chrome fibre, alumina bubbles and zirconia bubbles; about 15% to about 30% by weight water; 0 to about 7% by weight of a binder constituent selected from Glass H, sodium silicate and acrylic resins; and 0 to about 40% by weight of a glass forming frit material.
GB-A-2 100744 describes a composition which is useful as a heat-resistant coating material on the surface of a metal or ceramic article and which contains a refractory oxide powder such as alumina or silica, an inorganic powder having cation-exchangeability and a layered structure, such as mica, and an alkali metal silicate or aluminate as binder.
JP-A-60238080 describes a heat-resistant coating for use on the inner surface of ladles for molten metals and particularly for ladles for molten aluminium. The coating contains refractory aggregate which is mixed with zirconia, titania and kaolinite, and a binder consisting of colloidal silica, sodium silicate and potassium silicate.
SU-A-876249 describes an aqueous suspension for use in making lost wax or investment casting moulds. The suspension contains 30 to 40% by weight of water glass, 5 to 40% by weight of mica and a balance of refractory filler such as quartz dust.
GB-A-1268128 describes an aqueous coating composition for protecting metal or refractory surfaces, particularly ingot mould bottom plates, against attack or erosion by molten metals. The composition contains siliceous and carbonaceous refractory materials, sodium silicate and a polysaccharide gum and, optionally, a clay such as montmorillonite.
It has now been found that a coating containing one or more minerals having a sheet structure and bonded with a refractory oxide is particularly satisfactory for protecting graphite-alumina articles such as nozzles and shrouds against thermal shock.
DETAILED DESCRIPTION
According to the invention there is provided an article of graphite-alumina refractory material having a coating thereon comprising one or more minerals having a sheet structure and a refractory oxide bond.
Suitable minerals having a sheet structure include talc, micas, vermiculite, antigorite (lamella
REFERENCES:
patent: 4041199 (1977-08-01), Cartwright
patent: 4304605 (1981-12-01), Keibler
patent: 4951852 (1990-08-01), Rancoulle
Bahta Abraham
Foseco International Limited
Krynski William
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