Compositions: coating or plastic – Coating or plastic compositions – Molds and mold coating compositions
Patent
1980-10-27
1982-05-11
Hayes, Lorenzo B.
Compositions: coating or plastic
Coating or plastic compositions
Molds and mold coating compositions
106 385R, 106 80, 106 84, 106162, 106213, 106214, B28B 734, C08L 302
Patent
active
043291775
DESCRIPTION:
BRIEF SUMMARY
This invention relates to alkali metal silicate binder compositions, particularly for use in the production of foundry moulds and cores.
It is common practice to use alkali metal silicate aqueous solutions, particularly sodium silicate solutions, as binders for sand for the production of foundry moulds and cores. These solutions usually contain 40-50% by weight of a sodium silicate having a SiO.sub.2 :Na.sub.2 O ratio of from 2.0:1 to 3.0:1. In one process the sodium silicate solution is mixed with sand, and the resultant mixture is formed into a mould or core. Carbon dioxide gas is then blown through the mould or core, and due to chemical reaction between the sodium silicate and the carbon dioxide a bonded mould or core results. In another process a so-called hardener, which may be for example, a mixture of diacetin and triacetin, is mixed with sodium silicate and sand, and the mixture is formed into a mould or core, which on standing hardens due to chemical reaction between the hardener and the sodium silicate.
A disadvantage of both processes is that after casting the moulds and cores are difficult to break down and remove from the solidified cast metal. This can be particularly disadvantageous in the case of cores of complex shape, or when the moulds and cores are used for the production of castings in metals which are cast at high temperatures, e.g. steel castings. Accordingly numerous proposals have been made in the past to add materials, so-called breakdown agents, to the mixture of sand and sodium silicate, which will aid the breakdown or disintegration ability of the sand mould or core after casting.
Among the breakdown agents used is a variety of carbohydrate-containing materials such as cellulose derivatives, starches, and sugars, e.g. sucrose and dextrose.
It has now been found that improved results can be obtained in the production of foundry sand moulds and cores bonded with an alkali metal silicate binder by using a binder composition which contains in addition to the alkali metal silicate and a carbohydrate, urea.
According to the invention there is provided a binder composition in aqueous solution obtained by mixing: monosaccharides, disaccharides, polysaccharides and derivatives of any of these and
According to a further feature of the invention there is provided a method of making an article of bonded particulate material such as a foundry mould or core, which comprises forming to the desired shape a mixture comprising particulate material and a binder composition in aqueous solution obtained by mixing: monosaccharides, disaccharides, polysaccharides and derivatives of any of these and
The preferred alkali metal silicate is sodium silicate. The SiO.sub.2 :Na.sub.2 O ratio of the sodium silicate may vary widely, e.g. from 2.0:1 to 3.5:1 but sodium silicates having a ratio of from 2.0:1 to about 2.5:1 are preferred.
Examples of suitable monosaccharides include glucose, mannose and fructose, and examples of suitable disaccharides include sucrose, maltose and lactose.
Polysaccharides, also known as glycans, are polymers of monosaccharides with or without reducing terminal groups.
The monosaccharide constituent may be an aldose or a ketose. Examples of glycans are glucans (polymers of glucose), xylans (polymers of xylose) and gluco-xylans (copolymers of glucose and xylose).
In general high molecular weight glycans, such as starch, amylose and amylopectin, are unsuitable for use in binder compositions according to the invention since they are not soluble in water. Suitable glycans are available as components of starch hydrolysates or glucose syrups.
Suitable polysaccharide derivatives include glycanitols. Glycanitols are products obtained by the reduction of glycans. The monosaccharide constituent of the glycan may be an aldose or a ketose. During production of a glycanitol the stereo-chemical configuration of the substituted aldose or ketose end group may be retained or there may be conversion in the derived polyhydric alcohol derivative. For example, the reduction of a substituted reducing e
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Foseco International Limited
Hayes Lorenzo B.
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