WO1998055249A1

WO1998055249A1 - Method and apparatus for supplying an optimised quantity of catalyst to a core shooting machine

Info

Publication number: WO1998055249A1
Application number: PCT/GB1998/001509
Authority: WO
Inventors: Heinz Josef Hemsen; Christoph Genzler
Original assignee: Foseco International Limited
Priority date: 1997-06-04
Filing date: 1998-05-22
Publication date: 1998-12-10
Also published as: AU741268B2; EP0986442A1; DE19723314C1; AR015384A1; AU7542198A; ATE234698T1; JP2002502317A; CN1265614A; KR20010013424A; BR9809723A; ZA984468B; DE69812354D1; TR199902962T2; EP0986442B1; TW396075B; CA2293507A1

Abstract

In a method and apparatus for the supply of an optimised quantity of catalyst to a core shooting machine for the manufacture of cores or moulds for casting processes wherein a catalyst is extracted from a pressurised vessel (11) in liquid or gaseous form and is mixed with a purging gas before it is introduced into the core shooting machine, firstly an optimised quantity of catalyst and secondly the purging gas at a pressure of 0.1 to 10 bar are fed into a pressure container (15), the catalyst and purging gas are mixed in the pressure container (15), and the resulting mixture is introduced into the core shooting machine. When the catalyst is used in liquid form it can be transformed from the liquid to the gaseous form in metering bellows (20) located between and connected to the pressurised vessel (15) and the pressure container (15).

Description

METHOD AND APPARATUS FOR SUPPLYING AN OPTIMISED QUANTITY OF CATALYST TO A CORE SHOOTING MACHINE

This invention relates to a method and apparatus for the supply of an optimised quantity of catalyst to a core shooting machine for the manufacture of cores and moulds for casting processes wherein the catalyst is extracted from a pressurised vessel in liquid or gaseous form and is mixed with a purging gas before it is introduced into the core shooting machine.

Methods are known for the manufacture of cores for casting processes. The application of amines as catalysts for the manufacture of cores according to the urethane Cold Box Process is described in the special issue of Giesserei 78 (1991), volume 11 , pages 372 to 374. In this known method for core and mould production a moulding material is used containing a benzyl ether resin (ortho-phenol resol) and an isocyanate which is cured with a tertiary amine catalyst. As the catalytic effect of the amine is particularly advantageous in the gaseous phase, tests were carried out using trimethylamine (TMA) whose boiling point is about 3 °C, and with which, for this reason, curing is possible in a relatively simple manner with a gaseous amine. The accelerating effect of a tertiary amine by the formation of reactive transitional compounds during the polyurethane reaction is described by the following reaction equation :

-RN=C=0 + (CH₃)₃N → -R-N=C-0» Isocyanate TMA N⁽⁺>(CH₃)₃

-R-N=C-0> + OH-R'-OH → -R-N(H)-C=0 + N(CH₃)_: N⁽⁺⁾(CH₃)₃ OR'-OH

Polyol Polyurethane When making cores by this known method it is disadvantageous that the tertiary amine is fed to the core shooting machine considerably in excess of the required amount. Although it has been shown that the application of trimethylamine makes it possible to advantageously reduce the amount of amine used by about 50% in comparison to other amines, the application of trimethylamine still has associated disadvantages. One problem is the extreme nuisance created by the odour which makes it essential that all parts of the equipment used are absolutely leak proof. All pipework must there be insulated at relatively high expense.

A method for the manufacture of cores for casting processes is described in DE 19706472.8 in which gaseous trimethylamine is conducted through parts of a metering device and then, in a concentration of from 0.01 to 0.12 wt-% based on the quantity of sand used per core, it is conducted into the core shooting machine, and is there brought into contact with the sand.

According to a preferred embodiment of this method it is envisaged that the gaseous trimethylamine is exposed to a purging gas. In general according to the method described in DE 19706472.8 it is envisaged to take the trimethylamine from a pressurised vessel and conduct it to the core shooting machine by means of a conduit. A connector is located in the conduit for the purging gas which in this manner is brought into contact with the catalyst. However it is disadvantageous when using this method that the quantity of catalyst which is conducted to the core shooting machine decreases as a result of a decrease of the pressure in the pressurised vessel. Therefore the addition of and/or the setting for an optimised quantity of catalyst is not possible. Furthermore, it is disadvantageous that the pressure at which the mixture of catalyst and purging gas is conducted to the core shooting machine is relatively low, as it is not possible to conduct the mixture of catalyst and purging gas through the core shooting machine at the desired speed. The object of the invention therefore is to provide a method and apparatus for adding an optimised quantity of catalyst to a core shooting machine for the production of cores or moulds for casting processes in which it is ensured that the core shooting machine is exposed to the optimised quantity of catalyst in the shortest possible time.

According to the invention there is provided a method for the supply of an optimised quantity of catalyst to a core shooting machine for the manufacture of cores or moulds for casting processes wherein a catalyst is extracted from a pressurised vessel (1) in liquid or gaseous form and is mixed with a purging gas before it is introduced into the core shooting machine, characterised in that firstly an optimised quantity of catalyst and secondly the purging gas at a pressure of 0.1 to 10 bar are fed into a pressure container (15), the catalyst and purging gas are mixed in the pressure container (15), and the resulting mixture is introduced into the core shooting machine.

As used herein the term "core shooting machine" shall be understood to include devices or apparatus used in foundries for the manufacture of moulds for casting processes.

The catalyst may be for example a tertiary amine (such as trimethylamine), methyl formate, sulphur dioxide or carbon dioxide. The method is particularly useful for producing cores or moulds using a benzyl ether resin and an isocyanate and a tertiary amine such as triethylamine as catalyst.

A gas bottle may be used for example as the pressurised vessel containing the catalyst. Usually air is used as the purging gas but other gases, for example carbon dioxide, may be used. The supply of purging gas to the pressure container at 0.1 to 10 bar makes it possible to adjust the pressure in the pressure container within the range from 0.1 to 10 bar. Advantageously the catalyst supply takes place through a valve. The optimised quantity of catalyst depends on the size of the core or mould being produced, and is determined in advance on the basis of various parameters for a particular core or mould.

Surprisingly it has been shown that in the process of supplying an optimised quantity of catalyst to a core shooting machine according to the invention it is possible in advantageous manner to conduct the optimised quantity of catalyst through the core shooting machine in an optimised time. The relationship between the quantity of catalyst on the one hand, and the quantity of purging gas on the other hand, which is adjusted to between 1 : 1000 and 1 : 10000 can be held constant while the mixture of the two is flowing through the core shooting machine. In this manner disadvantageous variations in pressure may be avoided. The optimised time is the shortest time which is necessary for the mixture to flow completely through the core shooting machine, and it is regulated by means of the pressure in the pressure container.

In a preferred embodiment of the method of the invention the catalyst in gaseous form is heated in the pressurised vessel to 3 to 80 °C to facilitate contact between the catalyst and the purging gas.

According to another preferred embodiment of the method of the invention the catalyst is conducted to metering bellows in liquid form before being fed in gaseous form to the pressure container. The use of the metering bellows is advantageous because although heat is extracted from the surroundings during the transformation of the catalyst from the liquid to the gaseous form the metering bellows remain able to continue to function over extended periods of operation when compared with other conveying equipment. It is particularly advantageous that the metering bellows can be installed in a relatively simple manner because older core or mould production plants can be adapted to use this embodiment of the method of the invention. According to a further preferred embodiment of the method of the invention trimethylamine is used as the catalyst, and it is advantageous that when using trimethylamine the quantity of catalyst can be kept relatively small because the nuisance from odour when cores are subsequently stored before use can largely be avoided.

According to a further preferred embodiment of the method of the invention, after the mixture of catalyst and purging gas have been introduced from the pressure container into the core shooting machine additional purging gas is fed into the core shooting machine via the pressure container. This measure has the additional advantage that it results in purging of the core shooting machine, and the core or mould, and appreciably reduces any nuisance due to the odour from the catalyst.

According to a further feature of the invention there is provided apparatus for the supply of an optimised quantity of catalyst to a core shooting machine for the manufacture of cores or mould for casting processes comprising a pressurised vessel (11 ) for containing the catalyst, means (12) for determining the quantity of catalyst in the pressurised container, means (14) for conducting the catalyst to a conduit (19) for supplying the catalyst to a core shooting machine, and means (16, 17) for supplying a purging gas to the apparatus, characterised in that the apparatus also has a pressure container (15) located between and connected to the pressurised vessel (11) and the supply conduit (19), and the purging gas supply means (16) is connected to the pressure container (15).

If desired the apparatus may also have a heater for heating the catalyst in the pressurised vessel.

Such apparatus is suitable for use when the catalyst in the pressurised vessel is in gaseous form. When the catalyst in the pressurised vessel is in liquid form the apparatus may have metering bellows located between the pressurised vessel and the pressure container so that the catalyst may be transformed into the gaseous form before being fed into the pressure container.

The invention is illustrated in the accompanying drawings in which :-

Figure 1 shows schematically apparatus used for producing cores of moulds by a known method in which a catalyst is exposed to purging air.

Figure 2 shows schematically apparatus according to the invention for supplying an optimised quantity of catalyst to a core shooting machine using the method of the invention and

Figure 3 shows schematically apparatus according to the invention for supplying an optimised quantity of catalyst to a core shooting machine using the method of the invention, wherein the catalyst is used in liquid form.

Referring to Figure 1 , a catalyst is contained in a pressurised vessel (1 ), which may be a simple gas bottle, and the pressurised vessel (1) is located on scales (2) in order to determine its contents. The pressurised vessel (1) can be heated by means of heater (3). In the production of a core or mould the catalyst is conducted through a valve (4) into supply conduit (5) which leads directly to the a core shooting machine (not shown). A purging gas is introduced directly into the supply conduit (5) through conduit (6). With decreasing pressure in the pressurised vessel (1) the quantity of catalyst which reaches supply conduit (5) is reduced. Furthermore, in order to prevent the purging gas from being introduced into the pressurised vessel (1) through the open valve (4) the pressure selected in the conduit (6) for the purging gas cannot be too great. The pressure which exists in the supply conduit (5) is therefore insufficient to conduct the quantity of catalyst through the core shooting machine in as short a time as is desirable. Referring to Figure 2, a catalyst is contained in a pressurised vessel (11), which may be a simple gas bottle, and the pressurised vessel (11) is located on scales (12) in order to determine its contents. The pressurised vessel (11) can be heated by means of heater (13). A previously determined optimum quantity of catalyst is introduced via first valve (14) into pressure container (15) and first valve (14) is closed. Purging gas is supplied to the pressure container (15) through conduit (16) via second valve (17) at a pressure of 0.1 to 10 bar. Second valve (17) is then closed and third valve (18) is opened so as to introduce a the mixture of catalyst and purging gas which is present in the pressure container (15) into supply conduit (19) and into the core shooting machine (not shown). If desired, in order to largely eliminate nuisance due to odour from the catalyst, second valve (17) can remain open while third valve (18) is open so that purging gas continues to be introduced into the core shooting machine through pressure container (15) after the mixture of catalyst and purging gas has passed into the core shooting machine.

Figure 3 shows similar apparatus to that shown in Figure 2 but the apparatus also has metering bellows (20) an additional fourth valve (21) located between first valve (14) and pressure container (15) and there is no heater.

When the apparatus is used liquid catalyst in the pressurised vessel (11) is conducted through first valve (14) into the metering bellows (20) where the catalyst is transformed from the liquid to the gaseous state. First valve (14) is then closed and fourth valve (21) is opened, and the gaseous optimised quantity of catalyst is introduced into the pressure container (15), while the second valve

(17) and the third valve (18) remain closed. After the fourth valve (21) has been closed the second valve (17) is opened and purging air is introduced into pressure container (15). The third valve (18) is then opened and the mixture of catalyst and purging gas is introduced to a core shooting machine (not shown) via supply conduit (19).

Claims

1. A method for the supply of an optimised quantity of catalyst to a core shooting machine for the manufacture of cores or moulds for casting processes wherein a catalyst is extracted from a pressurised vessel (11) in liquid or gaseous form and is mixed with a purging gas before it is introduced into the core shooting machine, characterised in that firstly an optimised quantity of catalyst and secondly the purging gas at a pressure of 0.1 to 10 bar are fed into a pressure container (15), the catalyst and purging gas are mixed in the pressure container (15), and the resulting mixture is introduced into the core shooting machine.

2. A method according to Claim 1 characterised in that the catalyst in gaseous form is heated to 3 to 80 ┬░C in the pressurised vessel (11).

3. A method according to Claim 1 characterised in that the catalyst in liquid form is conducted to metering bellows (20) before being fed in gaseous form to the pressure container (15).

4. A method according to any one of Claims 1 to 3 characterised in that the catalyst is trimethylamine.

5. A method according to any one of Claims 1 to 4 characterised in that after the introduction of the mixture of catalyst and purging gas into the core shooting machine additional purging gas is fed into the core shooting machine through pressure container (15).

6. Apparatus for the supply of an optimised quantity of catalyst to a core shooting machine for the manufacture of cores or mould for casting processes comprising a pressurised vessel (11) for containing the catalyst, means (12) for determining the quantity of catalyst in the pressurised container, means (14) for conducting the catalyst to a conduit (19) for supplying the catalyst to a core shooting machine, and means (16, 17) for supplying a purging gas to the apparatus, characterised in that the apparatus also has a pressure container (15) located between and connected to the pressurised vessel (11) and the supply conduit (19), and the purging gas supply means (16) is connected to the pressure container (15).

7. Apparatus according to Claim 6 characterised in that the apparatus has means (13) for heating the catalyst in the pressurised vessel (11).

8. Apparatus according to Claim 6 characterised in that the apparatus has metering bellows (20) located between the pressurised vessel (11) and the pressure container (15) so that the catalyst may be transformed into the gaseous form before being fed into the pressure container (15).