Metal founding – Process – Shaping a forming surface
Patent
1995-11-28
1997-05-27
Lin, Kuang Y.
Metal founding
Process
Shaping a forming surface
501 80, 164 53, 164359, B22C 100
Patent
active
056323263
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a mould and a method for the casting of metals, and particularly for the casting of steel, and to refractory compositions for use therein.
When molten metal is cast into a mould and allowed to solidify the metal shrinks during solidification. In order to compensate for this shrinkage and to ensure that a sound casting is produced it is usually necessary to employ so-called feeders located above and/or at the side of the casting. When the casting solidifies and shrinks molten metal is fed from the feeder(s) into the casting and prevents the formation of shrinkage cavities. In order to improve the feeding effect and to enable the feeder volume to be reduced to a minimum it is common practice to surround the feeder cavity and hence the feeder itself with a refractory exothermic and/or heat-insulating material which retains the feeder metal in the molten state for as long as possible.
For the same reason it is also common practice in the casting of ingots, for example steel ingots, to line the head of an ingot mould or head box fitted to an ingot mould with a refractory exothermic and/or heat-insulating composition.
In both applications the refractory exothermic and/or heat-insulating compositions are used in the form of preformed shapes such as cylindrical sleeves for lining the feeders of foundry casting moulds and boards for the lining of ingot mould heads or head boxes.
The exothermic compositions employed in the applications described above usually consist essentially of a metal which is readily capable of oxidation, usually aluminium, and an oxidising agent therefor, for example iron oxide, sodium nitrate or manganese dioxide. The composition will usually contain a particulate refractory filler, and a binder to bond the composition into a preformed shape. Preformed shapes which are to heat-insulating as well as exothermic will usually contain a fibrous material and/or a light-weight particulate refractory material.
In order to improve the sensitivity, of the exothermic composition, i.e. reduce the time lag between applying to the composition a temperature at which it will ignite and the actual ignition of the composition, it was proposed some years ago to include in the composition a proportion of an inorganic fluoride salt. Examples of inorganic fluoride salts which may be used for this purpose include simple fluorides such as sodium fluoride or magnesium fluoride, and complex fluorides such as sodium silicofluoride, potassium silicofluoride, sodium aluminium fluoride or potassium aluminium fluoride. Exothermic compositions containing inorganic fluoride salts are described in British Patents 627678, 774491, 889484 and 939541.
Non-exothermic refractory compositions usually consist of particulate refractory material, inorganic and/or organic fibres and a binder.
In both types of composition the particulate refractory material used is commonly alumina, Silica or an aluminosilicate, and aluminosilicate fibres are commonly used as the fibrous component of compositions which are to be used for the casting of steel.
When refractory compositions which are to be used in the form of sleeves for feeding steel castings contain both alumina and silica, it has been found in practice that the quantity of alumina present in the composition expressed as a percentage of the total of alumina plus silica should be at least about 55% by weight in the case of a heat insulating composition and at least about 70% by weight when the composition is an exothermic composition containing a fluoride.
Fibres are incorporated in exothermic and heat-insulating compositions, and in heat-insulating compositions in order to reduce the density of the compositions and to improve their heat-insulation properties and hence, their performance in feeding metal castings or ingots. Such compositions are usually formed to shape, for example, as sleeves or boards, by a method which involves forming a slurry of the components of the composition in water and sucking or forcing the slurry on to a pervious former of appropriat
REFERENCES:
patent: 3198640 (1965-08-01), Walsh
patent: 4687752 (1987-08-01), Peters
Foseco International Limited
Lin Kuang Y.
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