Metal founding – Process – Shaping a forming surface
Patent
1990-06-05
1992-10-27
Seidel, Richard K.
Metal founding
Process
Shaping a forming surface
164522, 164 15, B22C 100, B22C 118
Patent
active
051581302
DESCRIPTION:
BRIEF SUMMARY
The subject of the present invention is a method for the preparation of moulds and cores used in the casting of metals, wherein the moulds and cores are prepared out of a granular moulding material as well as out of a binder agent that binds the moulding-material granules together.
For the preparation of moulds and cores used in the casting of metals, in prior art, methods are known in which the granules of moulding sand are bound together by means of organic and/or anorganic binder agents, whose hardening takes place in the moulding mix substantially as a result of a chemical reaction. As the reaction result of such a chemical reaction, a chemical compound is produced which binds the granules of the moulding mix together. A considerable drawback of these prior-art methods is commonly that the disassembling quality of the moulds and cores after the casting is not satisfactory, being even difficult to carry out.
In these methods described above, organic binder agent components are frequently used, which remain in the binder agent as compounded in the moulding mix and which form pyrolysis gases during or after the casting. These pyrolysis gases are again highly detrimental, for they may be dangerous for the health of the workers and cause environmental problems. Moreover, pyrolysis gases cause gas porousity in the cast pieces. Moreover, in these prior-art methods, the compounds produced as a result of the chemical reaction taking place in the hardening of the binder agent restrict the re-use of the moulding material granules substantially as well as increase the cost of regeneration of the moulding material. This comes from the fact that the compounds produced as a result of the chemical reaction are of a stable nature, and breaking up of the binder-agent bond requires a very large amount of energy if the moulding material is supposed to be obtained even as tolerably pure granules for re-use. Moreover, disassembling of the cast and regeneration of the moulding sand require mechanical working steps, wherein an abundance of dust and waste are produced, causing problems of safety at work, environmental problems, high investment costs for reduction of the emissions, as well as costs of disposal of the waste. It is, among other things, because of the pyrolysis gases, dust and waste mentioned above that efficient and costly air-conditioning and filtering systems must be constructed in foundries.
In prior art, such methods for the preparation of casting moulds and cores are also known wherein anorganic salts soluble in water are also used as a binder agent. However, in these methods the hardening of the binder agent takes place by the intermediate of a chemical reaction. One such method has been described earlier, e.g. in the U.S. Pat. No. 4,399,858. It is a considerable drawback of such methods that the reaction products that bind the granules of moulding material together have a low melting point. This again results in the circumstance that the granules of moulding material are detached and carried along with the molten metal flow in particular when alloys of a high melting point are cast.
A prior-art method is the so-called water-glass method, wherein water-glass is used as the binder agent, said water-glass being a technical product developed expressly for the water-glass binder-agent method. However, in such a method it is essential that the water-glass must contain an abundant excess quantity of the silicate component. This results in the fact that the binder agent is not dissolved in water completely, but it forms a readily hydrolyzable pseudo-solution, whereby the excess SiO.sub.2 gel is liberated. When such a Na.sub.2 O.multidot.SiO.sub.2 compound, whose SiO.sub.2 concentration is, as a rule, about 2.5-fold as compared with normal sodiummetasilicate, loses its solvent, i.e. water, out of it a fully insoluble compound, is formed between the moulding granules. This is why a mould or core prepared by means of the water-glass method cannot be disassembled or emptied so that the binder agent is dissolved off fr
REFERENCES:
patent: 4043380 (1977-08-01), Valentine
patent: 4331197 (1982-05-01), Cole
patent: 4347890 (1982-09-01), Ailin-Pyzik
patent: 4399858 (1983-08-01), Kurabe
patent: 4678020 (1987-07-01), Hayes
Pelto Rex E.
Seidel Richard K.
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