Cold-setting moulding binders and their use (phenols and gaseous

Details Cold-setting moulding binders and their use (phenols and gaseous Cold-setting moulding binders and their use (phenols and gaseous

1988-07-13

1990-05-29

Kight, III, John

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

523146, 524596, 164 15, 264 82, C08J 6110

Patent

active

049296493

DESCRIPTION:

BRIEF SUMMARY
Where the manufacture of foundry mouldings is concerned, cold-setting binders have acquired increasing importance. In comparison with thermosetting binders, they offer marked advantages, particularly higher productivity for better working conditions and lower energy consumption. Without exception, these cold-setting binders consist of a cross-linkable reaction system which is processed with a basic mould material (e.g. quartz sand, zirconium sand, chromite sand or mixtures thereof) to produce a moulding mixture, a catalyst then assisting it to react to produce a solid highly cross-linked polymer. The catalyst is thereby in many cases added to the finished moulded mixture as a gas, but it can however also be worked into the moulding mixture together with the reaction system.
Typical examples of foundry working procedures using cold-setting binders are, if a gaseous catalyst is supplied, the coldbox process (isocyanate cross-linking of polyols with the action of gaseous tertiary amines), the SO.sub.2 process, the CO.sub.2 process or the formiate process, and if the catalyst is worked into the moulding mixture, the pepset process (isocyanate cross-linking of polyols under the action of higher amines). Of these, the coldbox process has been the most widely used for about 20 years. In this time, it has undergone constant improvement, but still suffers from a number of largely unavoidable disadvantages, some of which go back to the fact that the polyurethane formed during the cross-linking state is a thermoplast which has a relatively low thermal resistance and a relatively high pollutant emission during casting and is also very sensitive to moisture. In addition, the so-called "sand lifetime", i.e. the period of time during which a moulding mixture remains workable, is relatively short, the use of old sands is problematic and the polyols must be dissolved in organic solvents. The other cold-setting processes are by virtue of even greater disadvantages, less widely used in practice, because in the case of the formiate process, the strengths attainable are too low, while the SO.sub.2 process, the problematical handling of peroxides and SO.sub.2 gas speak against greater usage and the CO.sub.2 process is adversely influenced by low productivity and very poor disintegrating capacity of the mouldings after casting.
Therefore, in the foundry industry there is as ever a need for a binder having improved properties. The invention satisfies this need and provides practice with an improved binder, which is according to the invention characterised in that it comprises a solution of aldehyde-reactive phenol substances and gaseous acetals as reaction partners and strong acids as catalysts, the phenol substances and the acids being laid down in the mixture of moulding mixture, the acetals being added to the shaped moulding mixture.
It is well known that an aldehyde reactive phenol substance can in the presence of an aldehyde (preferably formaldehyde), by the addition of a strong acid, be brought to harden out while cold and it is furthermore known that acetals can indeed remain stable in the alkaline range but will, however, in the acid range easily hydrolyse into the corresponding alcohols and aldehydes. With the invention, these two facts are brought into connection with each other and are suitably used to provide a novel binder in that a moulding mixture containing the phenol substance and the acid is, after removal of the mould, gasified with a gaseous acetal acting as an aldehyde donor. The acid has thereby a dual function, it brings about hydrolysis of the acetal and at the same time catalyses the cross-linking of the phenol substance by the aldehyde released from the acetal. It has been found that in this way a binder having properties which are surprisingly good in every respect and offering manifold advantages can be obtained, these advantages extending both to the manufacture and handling of the moulding mixture and also to the mould parts and their use in the casting process. Therefore, the binder is predestined f

REFERENCES:
patent: 4287092 (1981-09-01), Stewart et al.
patent: 4584340 (1986-04-01), Chi

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