Coating compositions for inorganic casting molds and cores, containing salts, and use thereof

Abstract

The subject matter of the invention relates to sizing compositions as coating compositions for casting molds. The sizing composition is suitable for cores and molds, in particular those produced using water glass as a binder. The sizing composition contains certain salts.

Description

[0001]The invention relates to a sizing composition as a coating material for casting molds. The sizing composition is suitable for cores and molds, especially those produced using water glass as the binder. The sizing composition contains certain salts.PRIOR ART[0002]Casting molds can be produced from a refractory material, for example quartz sand, by shaping into a casting mold and binding using a suitable binder to guarantee adequate mechanical strength. Thus casting molds are produced using a refractory basic material and a suitable binder. The refractory basic mold material is preferably present in free-flowing form, so that it can be packed into a suitable hollow mold and compacted there. The binder produces firm cohesion between the particles of the basic mold material, so that the mold form achieves the necessary mechanical stability.[0003]Both organic and inorganic binders can be used for producing casting molds, and they can be cured by cold or hot processes. Cold processe...

AI Technical Summary

Benefits of technology

The patent text describes how adding certain salts to an aqueous sizing composition can improve the quality and shelf life of the sized cores and molds. This is surprising because it was previously thought that adding salts could damage the quality of the sizing. The technical effect of the patent is a more effective and reliable way to improve the quality and longevity of sized cores and molds.

Problems solved by technology

Regardless of the curing mechanism, all organic systems share the fact that they undergo thermal decomposition when the liquid metal is filled into the casting mold and in this process may release toxic materials, such as benzene, toluene, xylene, phenol, formaldehyde and other cracking products, some of which have not been identified.

It has become possible to minimize these emissions by various measures, but they cannot be avoided altogether in the case of organic binders.

However, theses references do not disclose the use of refractory materials as part of the size.

However, inorganic binders also have drawbacks compared with organic binders;

for example, the known inorganic binders result in low stability of the casting molds produced by using them toward high atmospheric humidity and toward water.

Thus storage of the moldings over a long period of time, as is customary with organic binders, is not definitely possible.

Under the process parameters typically used in mass production (rapid cycling, high temperatures), the casting molds lose their strength due to contact with water and to some extent also, to contact with alcohol; the surface softens and the casting mold loses its shape.