Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1995-04-05
1996-07-23
Hail, III, Joseph J.
Metal founding
Process
Shaping liquid metal against a forming surface
148 26, 75305, C21C 7076
Patent
active
055380700
DESCRIPTION:
BRIEF SUMMARY
This invention relates to mould fluxes and their use in the continuous casting of steel.
In the continuous casting of steel a mould flux is generally added to the surface of the molten steel in the mould. The flux provides lubrication between the mould wall and the steel, it reduces the loss of heat from the surface of the steel, it protects the surface from oxidation, and it may remove impurities such as alumina from the steel.
As granules evolve much less dust compared with powder, mould fluxes used in the continuous casting of steel are often used in the form of granules, which may be produced by, for example, spray-drying of the flux constituents. The excellent flowability of granules makes them particularly suitable for automatic feeding to the mould, for example, using a DAPSOL (trade mark) feeder. However once the flux is in the mould the flowability of the granules becomes a disadvantage since the granules tend to find their own level under high rates of flow of steel into the mould and the surface of the steel may become exposed in the corners of the mould.
It has now been found that the above problem can be alleviated if the granules contain a minor mount of an expandable material which will expand under the action of heat and will cause the granules to break down into powder on the surface of the steel.
According to the invention there is provided a granular mould flux comprising refractory metal oxide, one or more fluxing agents, a binder and an expanding agent, the expanding agent being present in an amount of 0.1% to 3% by weight based on the weight of the flux.
According to a further feature of the invention there is provided a method of continuously casting molten steel in a mould the method comprising adding to the mould prior to, during or after teeming of the molten steel a granular mould flux comprising one or more refractory metal oxides, one or more fluxing agents, a binder and an expanding agent, the expanding agent being present in an amount of 0.1% to 3% by weight based on the weight of the flux.
The refractory metal oxide is preferably made up of calcium oxide and silica but alumina and/or magnesia may also be present. Materials such as blast furnace slag which contains calcium oxide, silica and alumina, or feldspar (sodium potassium aluminium silicate) which contains alumina and silica may be used as a source of refractory metal oxides.
Wollastonite, which contains calcium oxide and silica, is a particularly useful component since it is capable of absorbing appreciable amounts of alumina from the steel into the flux without significantly affecting the viscosity or melting point of the flux. The wollastonite component may be, for example, a synthetic or natural calcium monosilicate (which may contain very small quantities of iron oxide and/or alumina), or it may be calcium monosilicate in solid solution with at least one of silica, calcium oxide or alumina, for example, a solid solution containing pseudo-wollastonite or rankinite.
The fluxing agent may be, for example, one or more of sodium carbonate, potassium carbonate, lithium carbonate, barium carbonate, sodium fluoride, aluminium fluoride, potassium fluoride, cryolite, fluorspar, manganese dioxide and olivine. The fluxing agent reduces the melting point of the flux and by the selection of particular fluxing agents and amounts the variation of the viscosity of the flux with temperature can be controlled.
The binder may be any suitable binder which will maintain the integrity of the granules from manufacture through storage, transport and use up to the point of expansion of the expanding agent when it is necessary for the granules to disintegrate back into the original powder form. Examples of suitable binders include resins, gums such as a polysaccharide gum and carbohydrate materials such as molasses.
The expanding agent may be, for example, expandable perlite, expandable vermiculite or expandable, e.g. acid-heated, graphite. The expanding agent is preferably present in an amount of 0.3% to 1.5% by weight based on the weight
REFERENCES:
patent: 4221595 (1980-09-01), Zebrowski
patent: 4321154 (1982-03-01), Ledru
patent: 4561912 (1985-12-01), Courtenay et al.
patent: 4785872 (1988-11-01), Koul et al.
patent: 5240492 (1993-08-01), Phillips et al.
The Making, Shaping and Treating of Steel, USS. edited by McGannon (1971) pp. 240-243.
Diehl Spencer C.
Phillips Royston J.
Foseco International Limited
Hail III Joseph J.
Herrick Randolph S.
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