GB1592166A - Production of a foundry core or mould - Google Patents

Description

(54) IMPROVEMENTS RELATING TO THE PRODUCTION OF A FOUNDRY CORE OR MOULD (71) We, STONE WALLWORK LIMITED.

a Company incorporated under the laws of Great Britain, of Woolwich Road, London S.E.7, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns improvements relating to the production of a foundry core or mould.

In a known method of bonding foundry moulding and core-making materials, the refractory grains, hereinafter referred to as sand, are coated with a resin and an isocyanate in suitable known proportions. Reaction between the resin and isocyanate takes time, usually about 1+ hours, to complete, the sand grains becoming bonded to each other by the solid reaction product.

In the presence of a tertiary amine catalyst, the reaction is greatly accelerated. The reaction is completed almost instantaneously at ambient temperature and, in the final stage of the reaction, the grains become bonded by the end product, polyurethane, the catalyst being released.

If freshly mixed material is placed on a pattern tor in a core-box and is exposed to the catalyst, it will set hard almost immediately and may be removed intact. Molten metal can subsequently be poured into a mould or around a core produced from sand bonded as just described.

The catalyst has been admitted to the sand-resin-isocyanate mixture under a pressure above atmospheric pressure, using a gas, typically air, nitrogen or carbon dioxide or a, mixture of these, as vehicle. The pressure was intended to be high enough to ensure that the amine penetrated all interstices in the sand-resin-cyanate mixture.

Tertiary anrines have a high saturated vapour pressure and when subjected to pressure above atmospheric pressure, their vapours condense at ambient temperature.

Consequently, upon entering the mixture at ambient temperature under pressure, the condensing amine tended to saturate the mixture at the point of entry, thereafter requiring a higher pressure to effect its distribution within the mixture, causing further condensation with a cumulative effect. After the mixture had hardened, residual amine, which is highly toxic, was removed by purging, usually by means of compressed air.

After a purging time of up to 15 seconds, some liquid amine remained in the hardened mould or core. It later evaporated at atmospheric pressure. The vapours had to be collected and rendered harmless. Hitherto, the amine vapour conduits have been heated or the vehicle (CO2, N or air) has been preheated to inhibit amine condensation.

To facilitate penetration of the catalyst, for instance trimethyl amine, into the whole of the mould or core to be hardened, it has also been proposed that liquid amine should be converted into a vapour or gaseous state and maintained in that state by heating the conduit through which it was conveyed to the core or mould- box. However, contrary to what appcars to have been intended, the catalyst did not remain in the vapour state during its penetration into the mixture in the box, conventionally at ambient temperature, but condensed upon entry into the mixture and was forced through the same as finely dispersed liquid or as droplets under a pressure which was, necessarily, higher than atmospheric pressure. In this case also, a cumulative deleterious effect resulted in which the increasing pressure necessary to force the liquid through the core or mould being formed produced even earlier condensation and involved yet higher pressure.

In either case the process was employed in an uneconomical manner and was necessarily operated under closely controlled conditions. Condensation could not be -avoided and total removal of amine con densate within the core-box was impracticable. Because of the toxicity of the amines, core boxes had to be effectively sealed or enclosed to prevent escape of toxic vapour.

Vapour scavenged during purging had to be rendered harmless by incineration, by chemical decomposition in acid scrubbing devices, or by ion-exchange devices. Metering pumps and associated equipment for the liquid amine could not easily be completely cleansed prior to removal for adjustment or maintenance.

In the Specification of United Kingdom Patent No. 1,296,649, a process has been proposed, for curing a foundry mould or core comprising a mixture of sand and resin binder and using vacuum to facilitate a curing reaction between the binder and a reagent gas such as trimethyl or triethyl amine,- wherein the curing is carried out in at least two reaction cycles, each cycle com- prising the steps of evacuating a chamber containing the article and, when a predetermined high vacuum of from 12 to 50 mm.

Hg. is reached, introducing the reagent gas into the chamber until the chamber pressure is increased by the gas to a value of from 50 to 100 mm. Hg., and then introducing atmospheric air into the chamber to increase the chamber pressure further to approximately 735 mm. Hg. This is a relatively complex process.

The present invention seeks to avoid the difficulties in a simple manner.

According to the present invention, in a method for the production of a foundry core or mould by a hardening reaction within a core or mould box between resin components of a sand-resin coremaking or moulding mixture with the assistance of a tertiary amine catalyst, the pressure in the box charged with the mixture is reduced, by connection of the box to a source of -low pressure less than the saturated vapour pressure of the catalyst at the ambient temperature of the box, and liquid amine catalyst vaporised in a vessel is supplied in vapour state through conduit to the box, the whole system comprising the said vessel and conduit, the box with the mixture within it and the connection to the said source being maintained at a pressure less than the saturated vapour pressure of the catalyst at the ambient temperature for the duration of the supply of said catalyst vapour and of the hardening reaction, whereafter the supply of catalyst vapour is cut off and purge gas is admitted to the box which remains connected to the source of the said low pressure until the catalyst has been purged from the core or mould in the box, whereby the catalyst is maintained in the vapour state at ambient temperature throughout the supply, reaction and purging stages. The components of the mixture may be, typically, a phenol-formaldehyde resin oomponent and an isocyanite component and the catalyst is a, tertiary amine such as triethyl amine or dimethyl ethyl amine.

Since the amine is a true catalyst, it is theoretically 100% recoverable. -In the vapour state, almost all of the amine can be extracted from the hardened core. After extraction from the core, the amine vapour can be compressed to a pressure exceeding its vapour pressure, whereupon it condenses.

The condensed amine is returned into the system for re-cycling, substantially all of the amine being recovered. Even if this recovery were not justified on economic grounds, the substantially complete elimination of escape of amine to atmosphere is of great importance with respect to the improvement of operating conditions.

Since all components in the vapour-phase region are always at a pressure less than atmospheric, there is no possibility of escape of toxic vapour. As the catalysis is by vapour, it is effected rapidly. As the corebox, in which the reaction occurs, is a lowpressure region, amine vapour will reach all interstices within the sand-resin-isocyanate mixture, thereby avoiding risk of unhardened zones. Discharge of amine from the system is slight and can be confined to one point.

Destruction of this minimal amount is a correspondingly simple matter. Almost all of the mechanically wearing parts in the system are subject solely to vapour, not liquid, amine. Almost complete cleansing of these parts can readily be accomplished in situ by purging with controlled ingress of atmospheric air. Leakage at worn parts will not involve escape of toxic amine into the surroundings. Liquified amine can be directed into a single vessel, at a selected time.

One manner of carrying the invention into effect will now be more fully described by way of example and with reference to the accompanying drawing, in which: Figure 1 is a diagram for a complete catalysis system for producing a polyurethane bond, and Figures 2 and 3 illustrate modifications.

Referring to Figure 1, an opened cannister 1 containing a tertiary-amine catalyst, suitably trimethyl amine or dimethyl ethyl amine, is placed in an evaporating chamber 2 sealed by a lid 3. A pipe with valve 4 connects the chamber 2 to a core-box 5.

The core-box cavity is filled by any known means with sand, resin, isocyanate mixture 6 through a top aperture 7 and is sealed by a cover plate 8. A pipe with a valve 9 connects the core-box with a chamber 10.

A pump 11, which is controlled by a pressure switch 12 responsive to the pressure in the chamber 10 and connected in the powersupply circuit td the pump motor 13, main tains a predetermined pressure, less than the saturated vapour pressure of the amine at the ambient temperature, on the suction side of the pump. When the valve 9 is opened, air is drawn from the interstices within the mixture 6. The pressure within the mixture falls to a value less than the saturated vapour pressure of the amine. The valve 4 is opened and the pressure in the evaporating chamber 2 falls. Amine is evaporated and drawn through the mixture 6 into the chamber 10, so that the mixture hardens. The valve 4 is then closed and a pressure-sensitive, pressure-reducing, valve 14 is opened, allowing air at less than the saturated vapour pressure of the amine into the hardened mass. Incoming air expels the amine in vapour state from the core-box 5 to the chamber 10. The valve 9 is closed.

The air and amine vapour are drawn from the chamber 10 by the pump 11 and delivered at a pressure exceeding the saturated vapour pressure into a cooling coil 15 within the evaporating chamber 2. Amine condenses in the coil, heat exchange assisting both evaporation and condensation. Condensed amine is delivered from the coil 15 into a condensate vessel 16, together with the air introduced through the valve 14.

Condensate is returned to the chamber 2 through a pressure-sensitive non-return valve 17. Accumulating air is released from the vessel 16 through a blow-off valve 18.

Released air may contain traces of amine, which should be destroyed by means such as have been described. The catalyst content can be observed at a level glass 19. A filter 20 serves to prevent particles of sand and/or of binder components from entering the system downstream of the core-bore 5.

Figures 2 and 3 illustrate modified arrangements for introducing the catalyst into the core-box 5. Figure 2 shows an arrangement particularly suitable for a box with a vertical plane of separation of its two halves. The amine catalyst is supplied through the cover plate 8 and is withdrawn via side chambers of the box. Figure 3 shows an arrangement more suitable for a, box with a horizontal plane of separation.

The catalyst is again supplied through the cover plate 8, but is withdrawn via a bottom chamber.

Except for the traces of amine which are destroyed as just mentioned, the amine is recycled in a substantially closed circuit for which the vapour phase extends, clockwise in Figure 1, from a to b and the liquid phase on from b to a If the amine used is triethyl amine, provision may be made for enhancing evaporation by maintaining the chamber 2 at an elevated temperature, suitably a temperature not exceeding 60"C. An elevated temperature is unnecessary with dimethyl ethyl amine.

WHAT WE CLAIM IS:- 1. A method for the production of a foundry core or mould by a hardening reaction within a core or mould box between resin components of a sand-resin coremaking or moulding mixture with the assistance of a tertiary amine catalyst, wherein the pressure in the box charged with the mixture is reduced, by connection of the box to a source of low pressure less than the saturated vapour pressure of the catalyst at the ambient temperature of the box, and liquid amine catalyst vaporised in a vessel is supplied in vapour state through a, conduit to the box, the whole system comprising the said vessel and conduit, the box with the mixture within it and the connection to the said source being maintained at a pressure less than the saturated vapour pressure of the catalyst at the ambient temperature for the duration of supply of the said catalyst vapour and of the hardening reaction, whereafter the supply of catalyst vapour is cut off and purge gas is admitted to the box which remains connected to the source of the said low pressure until the catalyst has been purged from the core or mould in the box, whereby the catalyst is maintained in the vapour state at ambient temperature throughout the supply, reaction and purging stages.

2. A method according to claim 1, wherein the pressure in the box is reduced to a value less than the said saturated vapour pressure and the box is then connected to the said vessel, whereby vaporised catalyst is drawn into the box and through the mixture within it.

3. A method according to claim 1 or 2, wherein the catalyst is recovered after the reaction.

4. A method according to claim 3, wherein the catalyst is recycled after recovery.

5. A method according to any one of claims 1 to 4, wherein the purge gas is air.

6. A method of producing a foundry mould or core substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. tains a predetermined pressure, less than the saturated vapour pressure of the amine at the ambient temperature, on the suction side of the pump. When the valve 9 is opened, air is drawn from the interstices within the mixture 6. The pressure within the mixture falls to a value less than the saturated vapour pressure of the amine. The valve 4 is opened and the pressure in the evaporating chamber 2 falls. Amine is evaporated and drawn through the mixture 6 into the chamber 10, so that the mixture hardens. The valve 4 is then closed and a pressure-sensitive, pressure-reducing, valve 14 is opened, allowing air at less than the saturated vapour pressure of the amine into the hardened mass. Incoming air expels the amine in vapour state from the core-box 5 to the chamber 10. The valve 9 is closed. The air and amine vapour are drawn from the chamber 10 by the pump 11 and delivered at a pressure exceeding the saturated vapour pressure into a cooling coil 15 within the evaporating chamber 2. Amine condenses in the coil, heat exchange assisting both evaporation and condensation. Condensed amine is delivered from the coil 15 into a condensate vessel 16, together with the air introduced through the valve 14. Condensate is returned to the chamber 2 through a pressure-sensitive non-return valve 17. Accumulating air is released from the vessel 16 through a blow-off valve 18. Released air may contain traces of amine, which should be destroyed by means such as have been described. The catalyst content can be observed at a level glass 19. A filter 20 serves to prevent particles of sand and/or of binder components from entering the system downstream of the core-bore 5. Figures 2 and 3 illustrate modified arrangements for introducing the catalyst into the core-box 5. Figure 2 shows an arrangement particularly suitable for a box with a vertical plane of separation of its two halves. The amine catalyst is supplied through the cover plate 8 and is withdrawn via side chambers of the box. Figure 3 shows an arrangement more suitable for a, box with a horizontal plane of separation. The catalyst is again supplied through the cover plate 8, but is withdrawn via a bottom chamber. Except for the traces of amine which are destroyed as just mentioned, the amine is recycled in a substantially closed circuit for which the vapour phase extends, clockwise in Figure 1, from a to b and the liquid phase on from b to a If the amine used is triethyl amine, provision may be made for enhancing evaporation by maintaining the chamber 2 at an elevated temperature, suitably a temperature not exceeding 60"C. An elevated temperature is unnecessary with dimethyl ethyl amine. WHAT WE CLAIM IS:-

1. A method for the production of a foundry core or mould by a hardening reaction within a core or mould box between resin components of a sand-resin coremaking or moulding mixture with the assistance of a tertiary amine catalyst, wherein the pressure in the box charged with the mixture is reduced, by connection of the box to a source of low pressure less than the saturated vapour pressure of the catalyst at the ambient temperature of the box, and liquid amine catalyst vaporised in a vessel is supplied in vapour state through a, conduit to the box, the whole system comprising the said vessel and conduit, the box with the mixture within it and the connection to the said source being maintained at a pressure less than the saturated vapour pressure of the catalyst at the ambient temperature for the duration of supply of the said catalyst vapour and of the hardening reaction, whereafter the supply of catalyst vapour is cut off and purge gas is admitted to the box which remains connected to the source of the said low pressure until the catalyst has been purged from the core or mould in the box, whereby the catalyst is maintained in the vapour state at ambient temperature throughout the supply, reaction and purging stages.

2. A method according to claim 1, wherein the pressure in the box is reduced to a value less than the said saturated vapour pressure and the box is then connected to the said vessel, whereby vaporised catalyst is drawn into the box and through the mixture within it.

3. A method according to claim 1 or 2, wherein the catalyst is recovered after the reaction.

4. A method according to claim 3, wherein the catalyst is recycled after recovery.

5. A method according to any one of claims 1 to 4, wherein the purge gas is air.

6. A method of producing a foundry mould or core substantially as hereinbefore described.