Metal founding – Process – Shaping a forming surface
Patent
1982-09-30
1985-11-12
Godici, Nicholas P.
Metal founding
Process
Shaping a forming surface
106 3835, B22C 118, C01B 3332
Patent
active
045522022
DESCRIPTION:
BRIEF SUMMARY
Aqueous sodium silicate solutions are widely used as binders in the production of foundry moulds or cores. Large volumes of the binder are used by a foundry and it is obviously preferable that it should be made by an inexpensive process.
Accordingly such solutions are normally made by melting sand and soda ash at a temperature of around 1450.degree. C., crushing the resultant glass and dissolving it in water, and if necessary evaporating the resultant solution to the desired solids content. While offering a relatively low cost material for foundary use, the process suffers from the disadvantages that it requires expensive apparatus and, in particular, high energy input.
It is known that aqueous sodium silicate can be formed by dissolving very fine particulate silica (fumed silica such as the material sold under the trade name "Aerosil") in aqueous sodium hydroxide. However the cost of producing the fumed silica is so high that this process is not commercially practicable for the production of binder solutions. It is also known that impure particulate silica can be used to form solutions of sodium silicate. Thus it is disclosed in Chemical Abstract Vol. 86 1977 No. 142342n and in Japanese Application No. 75/44686 that silicon dioxide dust form ferroalloy smelting may be heated with aqueous sodium hydroxide in the presence of an anionic, non-ionic or amphoteric surfactant to prevent viscosity increase, and these additives are also proposed in German OLS No. 2856267. In Chemical Abstracts Vol. 92 1980 No. 96294x and in Japanese Application No. 7855634 it is described that dust from ferrosilicon manufacture may be reacted with sodium hydroxide to form a product that can be used for preparing casting moulds.
Although this latter abstract states that the product is stable in fact dust collected from manufacturing ferrosilicon will normally contain insoluble impurities and in practice these will inevitably tend to settle out from the main solution.
British Patent Specification No. 1518772 also describes the use of the dust and states that impurities can be removed using a press filter. It also alleges that binders made from the dust give products of greater water resistance, irrespective of whether or not the binder is purified. Any such improvement must therefore be due solely to the pressure of dissolved impurities and so the filtered, undissolved, impurities are regarded as having no effect on bonding properties.
In commercial practice it is absolutely essential that the solution should be of completely uniform composition throughout and that it does not deposit a precipitate or coating on equipment used for storing or transporting it, for instance drums or pipes. If it is not of completely uniform composition its use will lead to variable results, and this is intolerable in practice. If precipitates or coatings are formed on equipment this can clog the equipment and this again is intolerable. If such precipitates or coatings are formed they have to be removed and disposed of, and this can be difficult and costly because they are contaminated with alkali metal silicate. Accordingly although these proposals have been made to use dust contaminated with impurities in practice they are not commercially satisfactory.
It has been our object to provide an alkali metal silicate solution using low cost raw materials and methods and which can be suitable for use as a binder for foundry moulds.
The invention is based on the surprising discoveries that it is possible to put the insoluble impurities into stable suspension in the solution, and that when such solutions are used in foundry processes they give a very desirable improvement in initial strength and a very desirable decrease in retained strength after use.
In the invention an aqueous alkali metal silicate solution is made by a method comprising dissolving in aqueous alkali a silica powder containing impurities that are insoluble in aqueous alkali and suspending the impurities as a stable suspension in the solution by means of a suspending agent.
An aqueous alkali
REFERENCES:
patent: 3135029 (1964-06-01), Cooper et al.
patent: 3179523 (1965-04-01), Moren
patent: 3428464 (1969-02-01), Pollard
patent: 4070196 (1978-01-01), Kraak et al.
patent: 4341559 (1982-07-01), Friedemann et al.
Chemical Abstracts, vol. 86, No. 20, May 16, 1977, p. 140, Abstract 142342n.
Chemical Abstracts, vol. 92, No. 12, Mar. 24, 1980, p. 117, Abstract 96294x.
Bugg John W. J.
Houlden Stephen
Batten, Jr. J. Reed
Godici Nicholas P.
Rosen Lawrence
The White Sea & Baltic Company Limited
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