Foundry binder

Details Foundry binder Foundry binder

1996-09-09

1998-01-27

Marcheschi, Michael

Compositions: coating or plastic

Coating or plastic compositions

Molds and mold coating compositions

106 382, 264219, 264319, 264225, B22C 118

Patent

active

057117926

DESCRIPTION:

BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATIONS

This is a 35 USC .sctn.371 application of international application No. PCT/GB94/02626, filed Nov. 30, 1994.
The present invention relates to a foundry binder, a water-dispersible core or mould prepared using the foundry binder and a process for making such a water-dispersible core or mould. More particularly, it relates to a foundry binder which when mixed with a water-insoluble particulate material gives a mixture having improved flowability.
Water-dispersible cores or moulds for use in making foundry castings or injection mouldings are known. In this respect, reference is made to published International application No WO 92/06808. Such water-dispersible cores or moulds are made according to a process comprising combining a water-insoluble particulate material such as sand with a binder which includes polyphosphate chains and/or borate ions, the chains and/or ions being dissolved in water and then forming the resulting mixture into a desired shape before removing the free water from the mixture. Typically, the binder is added to sand in the form of an aqueous solution of an inorganic glass, such as alkali metal polyphosphate or borate.
One of the main advantages of cores and moulds made using such inorganic binders compared to those made from traditional organic resin binders derives from the water-solubility of these inorganic binders. This feature provides the option to the foundryman of separating metal castings from cores and/or moulds made using such binders either by conventional shake-out methods or by dispersing the core or mould using water to dissolve the binder.
Three key measurable properties of systems containing such inorganic binders are: after purging with hot air and then cooled to room temperature, (referred to as P/O). casting operation.
The flowability of a binder/sand mix is a very important characteristic. This is especially the case when a binder/sand mix is intended to be blown to form a core or mould. Good flow will generally lead to cores and moulds which are well compacted when blown, which in turn maximises their strength and reduces their surface friability.
A binder/sand mix having good flowability characteristics is able, for example, to fill core boxes with complicated geometries and fill simple shapes more efficiently at a fast production rate. Mixes with good flow vacate the blowing head effectively. This helps to prevent the problem of "rat-holing" in the blowing head, where the high pressure air used in blowing drives a channel through a mix with poor flow rather than propelling a flowable mass of sand into the core box.
Sand mix flowability is, therefore, a key factor in determining both the production rates and quality of cores and is a property which should be quantified and improved wherever possible.
It is known to add flow promoters to sand mixes with traditional organic resin binders. For instance, U.S. Pat. No. 5,077,323 teaches the addition of flow promoters in the form of fatty acids and derivatives to organic binder/sand mixes. According to U.S. Pat. No. 4,996,249 the flowability of resin coated sand is improved by the addition of a fluorosurfactant to the sand/resin mixture.
The present invention provides a binder composition for binding a water-insoluble particulate material in the manufacture of a foundry mould or core which comprises a mixture of (1) an inorganic binder consisting of an aqueous solution containing polyphosphate chains and/or borate ions and (2) a water-soluble surfactant. The invention also provides a water dispersible core or mould for making a casting, the core or mould comprising a water-insoluble particulate material, a binder therefore and a water-soluble surfactant, the binder including polyphosphate chains and/or borate ions, the chains and/or ions being dissolved in water. The invention further provides a process for making a water dispersible core or mould for making a casting which process includes the steps of (a) providing a water-insoluble particulate material; (b) combining the parti

REFERENCES:
patent: 4541869 (1985-09-01), Maak et al.

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