Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1979-08-07
1982-03-16
Cockeram, H. S.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
525453, 525534, 528 75, C08L 9100, C08L 9300, C08L 7504, C08G 7104
Patent
active
043200370
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of preparing a foundry core or mould and to a binder for use in the method. In known methods of preparing foundry moulds and cores, a binder composition is mixed with an aggregate, usually sand, and the mixture is introduced into a mould to form the mixture into the required shape. The binder is then caused or allowed to cure and thereby produce a mould or core which is sufficiently robust to be used in a metal casting process.
BACKGROUND ART
There have been proposed a number of foundry binder compositions which are cured by reacting with a polyisocyanate. Some examples of these are disclosed in U.S. Pat. No. 3,925,296 which discloses binders comprising, in combination with an organic polyisocyanate, either a phenolic compound having at least two phenolic-OH groups, or a condensation product of a furan alcohol and an aldehyde, or a mixture of both of these. We have found that cores formed by use of binders disclosed in this U.S. Patent suffer from the disadvantage that the strength of the cores deteriorates unduly if the cured cores are stored.
Further examples of foundry binder compositions which are used in conjunction with polyisocyanates are disclosed in U.S. Pat. No. 3,429,848. This patent discloses the use, as a foundry binder, of condensation products obtained by reacting phenols with aldehydes. One disadvantage of the use of these condensation products as foundry binders is that water is produced in the condensation reaction. If water is present in the binder when this is mixed with the polyisocyanate, the water tends to react with the polyisocyanate so that the amount of polyisocyanate necessary to achieve a core having a required strength is greater than the amount which would be necessary if the foundry binder was anhydrous.
SUMMARY OF THE INVENTION
The qualities which are required in a foundry binder depend upon a variety of factors, including the use which is to be made of the mould or core, the equipment which is available for and the circumstances under which the core is to be produced and the nature of the aggregate.
There is no single binder which is ideally suited for all purposes. Furthermore, the binders which have been proposed heretofore exhibit various advantages and disadvantages to different degrees. Whilst it is desirable to produce a binder having qualities which are superior to those of binders presently available, it is also advantageous to provide a novel binder having a mix of qualities which is different from the mix of qualities provided by any known binder.
One object of the present invention is the provision of a foundry binder which has a different mix of qualities from that possessed by known binders. It is a further object of the invention to provide a foundry binder which can impart to cores a greater strength than that achieved by using the same quantity of a known foundry binder, or can achieve the same strength with the use of a smaller quantity than would be required to achieve that strength with a known binder.
According to a first aspect of the invention, there is provided a method of preparing a foundry core or mould wherein there is mixed with a foundry aggregate a polyisocyanate and a polymeric addition product of a phenol.
By a polymeric addition product of a phenol, we mean a product of an addition reaction between a phenol and a co-reactant to produce a product having, in each polymeric chain, at least two units derived from the phenol connected by a unit derived from the co-reactant.
The co-reactant preferably comprises, in each molecule, at least two carbon-carbon double bonds. Preferably, these bonds are not conjugated. Alternatively, the co-reactant may comprise a carbon-carbon triple bond.
The binder composition may incorporate a further aromatic hydroxy compound which reacts with the polyisocyanate more rapidly than does the aforesaid addition product. Bisphenols and other monomeric polyhydroxy phenols react relatively quickly with polyisocyanates in the presence of catalysts which are well kn
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Cockeram H. S.
Fordath Limited
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