GB2034220A

GB2034220A - A Method and Apparatus for Catalytically Hardening Mould Parts Made of Sand in the Manufacture of Metal Castings

Info

Publication number: GB2034220A
Application number: GB7909936A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-07-28
Filing date: 1979-03-21
Publication date: 1980-06-04
Also published as: ATA202279A; FR2431886B1; IT7968376A0; CH641067A5; IT7953372V0; IT1119310B; FR2431886A1; AT372317B; NL7902403A; GB2034220B; SE7902605L

Abstract

A liquid catalyst is vaporised and then injected with a compressed gas (air) into a foundry mould in a first period of a working cycle, the subsequent period being used to flush the catalyst throughout the mould using just compressed gas. The compressed gas fed to the mould is heated and vaporisation of the catalyst occurs during a period between injections in a shut-off zone of the apparatus.

Description

SPECIFICATION A Method and Apparatus for Catalytically Hardening Mould Parts made of Sand in the Manufacture of Metal Castings The present invention relates to a method for hardening mould parts, for example mould cores and hollow mould parts, made of sand with the addition of a catalytically hardenable binding agent or binding agents in the manufacture of metal castings.

The invention is thus based on a method developed by the applicant, in which a certain amount of a liquid catalyst mixed with compressed air was fed to the mould part, and then the mould part was flushed with catalystfree compressed air.

In the carrying out of this known method it is important to make certain that there is an even distribution of catalyst (injected as a mist) throughout the mould part (i.e. to prevent outer parts of the mould being deprived of catalyst due to drops being retained on some sand grains close to the injection point and not being transported fully to the more remote parts). For this reason the applicant suggested using a heating system for heating the mist downstream of the mixing zone so that the liquid catalyst is vaporised prior to injection into the sand. Using a compressed airvaporised catalyst mixture for injection into the mould part, makes for a more rapid movement of the catalyst through the mould part material and, concomitantly a more rapid hardening of the mould parts.

However, such a way of operating the method required the expenditure of substantial amounts of thermal energy, because the mist has to be heated up rapidly, generally speaking, from the temperature of the compressed air, which is typically between 0 and 200 C, to the vaporisation temperature of the liquid catalyst, this rapid heating up being necessary every time the mist is forced into the mould parts.

The starting temperature is normally towards the lower end of the temperature range given, because the compressed air is usually dehydrated by forcing it through a refrigeration dryer. If it is to be subsequently heated it is naturally necessary for the heat input to be sufficient to first offset the cooling of the compressed air effected for the purpose of drying it. Furthermore in this known method, the heating up must be effected in the short period allowed for the injection, and in practice it has not proved possible to ensure that there is a complete vaporisation of the catalyst in the time available.

The present invention seeks to provide a method of ensuring complete vaporisation of the liquid catalyst and while at the same time reducing the amount of thermal energy expended for the vaporisation.

According to the invention there is provided a method of hardening mould parts made from sand with the addition of a catalytically hardenable binding agent in the manufacture of metal castings, in which a certain volume of a catalyst is forced, by compressed gas into the mould part by mixing the catalyst with compressed gas and then the mould part is flushed with catalyst-free compressed gas, characterised in that the compressed gas fed to the mould part is heated and catalyst in liquid form is vaporised during a period between injections in a shut-off zone of the apparatus.

Thus, in accordance with the method of the present invention the rest time between injection periods, which will in any case occur, is used for vaporising the catalyst. The heating zone can be kept unchangingly at an elevated temperature so that it is no longer necessary for heating to take place from low values to the vaporising temperature, thus involving the expenditure of reduced amounts of thermal energy.

The use of heated compressed air for the hardening of mould parts, forms part of a suggestion given in German Auslegeschrift 2,546,032. However in this case a liquid catalyst is not employed and in fact the catalyst together with the heated compressed air in the form of a supporting gas-catalyst mixture is put into contact with the material to be conditioned. This prior art method however has a shortcoming in that the volume of catalyst is measured by fixing the opening times of the valves and furthermore is dependent on the pressure and temperature. In the method of the present invention on the other hand, the correct amount of catalyst may be supplied for each injection using a measuring or metering pump.For the prior-art method to employ, even approximately, a sufficient amount of catalyst, it was necessary to supply more catalyst than is actually needed, because it was only possible, using the prior art method, to make certain that a proportion of the catalyst supplied did in fact make its way into the mould part each time. The excess catalyst was passed to the ambient air with possible ill effects.

The invention also refates to an apparatus for carrying out the method of the invention according to which the apparatus comprises a mixing chamber, an inlet line for liquid catalyst to the mixing chamber, a heating system, and control valves for controlling the inlet of compressed gas and the inlet of liquid catalyst to the mixing chamber in synchronism with the injection periods, the heating system being joined to an inlet of the mixing chamber and a further shut off valve being provided between the mixing chamber and outlet to the mould part.

Using the apparatus of the invention the shutoff zone may be used as an evaporation chamber for the liquid catalyst, and this evaporation chamber can be kept at all times at a temperature making evaporation possible whereby the periods in between injections may be used for the evaporation operation. The heating system may be in the form of a heating chamber having a sufficiently large heat capacity for the vaporising operation. Because of this, the heating of the catalyst no longer has to take place from the compressed air temperature to the vaporising temperature during a short period at the beginning of the injection period. The input thermal energy requirement for the heating system need only be dimensioned to keep the heating system at the desired working temperature in question.For preventing heat going from the vaporising zone to a volumetric displacement pump for the catalyst to prevent premature vaporisation of the catalyst on its way to the shut-off zone, it is desirable, although not completely necessary, to have cooling means located between the pump and the vaporising zone, preferably as close as possible to the vaporising zone. This cooling may be effected by a heat exchanger on the inlet line for the catalyst through which heat exchanger cooled compressed gas is passed.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a graph of a working run, such as would take place a number of timers in a working day, and Figure 2 is a schematic diagram of an apparatus for carrying out the method of the invention.

In the graph of Figure 1 the abscissa represents time t, while the ordinate represents pressure P.

At the origin 0, a working run is started. It has a working period T and a rest period (of indeterminate length) 8. The upper curve represents the pressure of the inlet compressed air. Below it, at the beginning of each working period T, the decrease in the quantity of vaporised catalyst in a mixing zone is indicated by the arrow AC, while the iowermost chain-line curve represents the takeup of catalyst and the inlet of catalyst.

At the time t equals zero, that is to say at 0, the inlet compressed air has a pressure value of for example 2 bar, which is controlled by a valve system to be explained later with reference to Figure 2. In the working period T, the pressure first undergoes an increase of, for example, up to 6 bar, a pressure value which is attained at a point B. At the time t equals 0 at the pressure A, catalyst is present in gas form in the mixing zone (comprising a heating chamber and a mixing chamber to be described later). This catalyst is forced out of the mixing zone by the ingress thereto of compressed air and the catalyst concentration reduces to zero at the point C.

Starting at the time represented by the point C, a hardening period H terminates and a flushing period S commences which terminates at a time represented by a point D. At this point in time (represented by D) the system is shut off from the compressed air inlet, so that the pressure of the compressed air falls to a resting value at the point E which corresponds to the ambient pressure. The working period T thus ends at D and the rest period 6 starts.

At the time t equals zero, a takeup pump for the liquid catalyst is started and it goes on working till the time represented by the point F shown on the chain-line curve. The position of this point F will be dependent on the volume of liquid catalyst required for each working period.

On reaching the point F, the pump is stopped, which is indicated in Figure 1 by the chain line curve running parallel to the time axis. This parallel part of the chain line curve extends beyond the time represented by the point E as far as the time represented by the point G and from this time onwards the pump will be forcing the pre-set volume of the liquid catalyst into the mixing zone. The next working period will be started after a certain rest period 0 at a new starting point 0.A complete working cycle is, for this reason, made up of the working period time T and the rest period time 6. It is important to note that the rest period 6 is used for forcing the liquid catalyst into the mixing zone and, at the same time, the vaporisation of the liquid catalyst in preparation for the start of the next working period T. It is naturally necessary for the rest period 0, in cases in which for example the apparatus is turned off overnight, to be bridged over by turning on the heating before the start of the first working period on the next day in order, at the start of the working step time, to have a charge of vaporised catalyst available at time t equals zero.However this starting up does not require any change in the general operation or theory of the apparatus, that is to say that the compressed air injected includes vaporised catalyst for flow into the core or outer mould part.

In the apparatus shown in Figure 2, 1 represents a connection with a compressed air line, which for example has a pressure of 6 bar, and 2 is a water, oil and dirt trap for making certain that the apparatus only receives clean compressed air.

The inlet compressed air passes to an automatic pressure control valve 3, which is operated by a part of the apparatus to be detailed later. From the automatic control valve 3, the compressed air goes to a shut-off valve 4 by means of which it is possible for downstream units (i.e. units 7 and 9 to be described later) to be shut off from the compressed air line.

A safety check valve 5 and an overpressure valve 6 of conventional design are provided downstream of the valve 4.

The unit 7 is a heating chamber (e.g. of aluminium) which includes an integral duct for the passage of compressed air through the chamber.

It is of course possible to make use of any other arrangements to heat the air. In the arrangement shown a power connection 8, for example for electric power, to the heating chamber is also provided. From the heating chamber 7 the compressed air goes into a mixing chamber 9 and from there, through a shut-off valve 10, it flows in the direction of the arrow 11 to the core or box containing the mould material (not shown).

A duct 12 opens into the mixing chamber 9, the duct 12 leading from a pneumatic measuring pump 14 via a check valve 13. The measuring (or metering) pump 14 withdraws liquid catalyst through a take-up line 1 5 and a check valve 16 from a tank 17. The pump 14 removes a charge of liquid catalyst from the tank 1 7 and forces it, after shutting of the check valve 1 6, through the check valve 1 3 into the mixing chamber 9. In the duct 1 2 there is located a cooling tube 1 8 for making certain that heat from the heating chamber 7 and the mixing chamber 9 is not transmitted too far back along the duct 12, thus preventing premature evaporation of liquid catalyst.

The compressed air coming from the connection 1 is partly diverted at 1 9 through a duct 20 to serve as a control air supply. Some of this control air supply goes through a first pressure-decreasing valve 21 and a check valve 22 to a pneumatic control valve 23. Through a second pressure-decreasing valve 24 and a control choke 25, the second compressed air supply is available for the control valve 23. The air pressures of these first and second supplies are pre-fixed by adjustment and may be read on pressure gauges 26 and 27.Normally a time control clock (not shown) is'used for operating a control valve 28, this control valve 28 being used, on the one hand, for operating the valve 4 and on the other hand for operating the valve 23, so that initially a lower pressure, for example of 2 bar, will flow through the automatic control valve 3, the valve 4 and the check valve 5 into the line leading to the heating chamber 7. The line 20 also leads to a valve 29, which controls the supply of pressure air through a duct 30 to the measuring pump 14 so that the piston of the pump is moved downwards and the pre-set amount of liquid catalyst is taken into the pump from the tank 17.

This pump-filling operation is represented by the falling part of the curve Ill from the point 0 to the point F. The speed at which the pump makes its stroke may be adjusted with the aid of a choke valve 31. At the same time on working the valves 28 and 29 the valves 4 and 10 are opened via the lines shown in the drawing. In the unit comprising the heating chamber 7 and the mixing chamber 9, some gaseous catalyst air mixture will be present from the last operating step, this residual mixture being forced by the air, coming from the compressed air connection 1 through the open valves 4 and 10 to the core box.When this has been done, the valve 3 is smoothly opened further by virtue of the control valve 24, which is set to a higher pressure value, opening the valve 3 more and more, through the valves 25 and 23, until a certain pressure value is produced, i.e. the pressure represented by the point B in Figure 1.

The point B is reached after the full charge of gaseous catalyst has been forced into the core on getting to the point C, and then the clearing time S commences. At the end of the clearing time S, that is to say on getting to the point D in the graph of Figure 1, the valve 28 is switched over by the clock so that the valve 4 shuts off air flow to the chamber 7. The valve 10 is kept open for a longer period by the valve 29, which is controlled by a second clock (also not shown). The pressure of the compressed air in the core is for this reason made to undergo a decrease from the point D to the point E along the curve IV in Figure 1.It is only at point G that the valve 29 switches over effecting a shutting of the valve 10 so that there is now a shut off part of the apparatus (which includes the chambers 7 and 9), into which during the time between that corresponding to the point G and that corresponding to the start of the next period H, the volume of liquid catalyst taken up in the pump 14 from the tank 1 7, is forced into the shut-off volume of the apparatus made up by the heating chamber 7 and the mixing chamber 9. In this volume there is a mass of unexpanded compressed air, which because of the residual heat energy in it, is responsible for rapidly vaporising the catalyst into gaseous form. This vaporised catalyst is retained in the shut-off volume of the apparatus between the valves 5 and 10 and is to hand for the next dispensing operation, which, can if necessary be after a prolonged dwell time, and will take place in the same way as detailed above.

It is furthermore to be noted that it is possible, by reading the pressure on a gauge 32, to take note of the complete development of pressure of the compressed air as made clear by the curve for the compressed air of Figure 1. It is for this reason possible to modify the shape of the curves, as may be desired, by adjustment of the choke 25, and keeping an eye on the changes in the position of the pointer of the pressure gauge 32.

Claims

Claims

1. A method for hardening mould parts made from sand with the addition of a catalytically hardenable binding agent in the manufacture of metal castings, in which a certain volume of a catalyst is forced, by compressed gas into the mould part by mixing the catalyst with compressed gas and then the mould part is flushed with catalyst-free compressed gas, characterised in that the compressed gas fed to the mould part is heated and catalyst in liquid form is vaporised during a period between injections in a shut-off zone of the apparatus.

2. A method for hardening mould parts made from sand with the addition of a catalytically hardenable binding agent in the manufacture of metal castings substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

3. An apparatus for hardening mould parts made from sand with the addition of a catalytically hardenable binding agent in the manufacture of metal castings, in which a certain volume of a catalyst is forced, by compressed gas, into the mould part by mixing the catalyst with compressed gas and then the mould part is flushed with catalyst-free compressed gas, in which the compressed gas fed to the mould part is heated and the catalyst in liquid form is vaporised during a period between injections in a shut-off zone of the apparatus, said apparatus comprising a mixing chamber, an inlet line for liquid catalyst to the mixing chamber, a heating system, and control valves for controlling the inlet of compressed gas and the inlet of liquid catalyst to the mixing chamber in synchronism with the injection periods, the heating system being joined to an inlet of the mixing chamber and a further shut-off valve being provided between the mixing chamber and outlet to the mould part.

4. Apparatus as claimed in claim 2, characterised by a cooling unit in the inlet line for catalyst supplied to the mixing chamber.

5. Apparatus for hardening mould parts made from sand with the addition of a catalytically hardenable binding agent in the manufacture of metal castings, substantially as hereinbefore described with reference to, and as illustrated in, Figure 2 of the accompanying drawings.

New Claims or Amendments to Claims filed on 23 November, 1979.

Superseded Claims 1, 3, 4.

New or Amended Claims:

1. A method for hardening mould parts to be used for making metal castings which parts are made from sand and a binding agent capable of being catalyst hardened, which comprises the steps of providing a source of compressed gas, providing a passage connecting said source to the mould part, isolating a portion of the passage from both the compressed gas source and the mould part, introducing a controlled volume of vaporisable catalyst in liquid form into said portion, heating the catalyst while in said portion to vaporise all the catalyst; opening said portion to the mould part to permit flow of the gas/catalyst mix into the mould part and opening said source to said portion and releasing a quantity of catalyst-free, heated compressed gas at a higher pressure into said portion to force the entire gas/catalyst mix in said portion into the mould part; thereafter passing an additional quantity of the catalyst-free compressed gas through said portion and the mould part to clear it of residual catalyst, and terminating the flow of compressed gas.

2. A method according to claim 1 in which said steps of opening said portion to the mould part and releasing compressed gas to flow through said portion are performed simultaneously.

3. A method according to claim 1 or claim 2 in which said heating is continuous both when said passage is opened to said source and mould part and when it is isolated therefrom.

4. A method according to any preceding claim which includes intermittently releasing compressed gas from said source through said portion in pulses; causing a time interval to occur between each of said releases; isolating said portion from both said source and the mould part during each such interval; injecting the controlled volume of vaporisable catalyst into said portion during each such interval and heating said gas/catalyst mix in said portion to a temperature sufficient to vaporize all of the catalyst prior to the termination of the interval, opening said portion to the mould part and passing a pulse of compressed gas through said portion to force all the gas/catalyst mix into the mould part.

5. A method as claimed in any preceding claim, in which said portion of the passage is elongated and said heat is applied upstream of the point of catalyst injection with respect to the direction of flow of the gas therethrough.

6. A method according to claim 4, in which the catalyst is metered into separate charges of a predetermined volume before introduction and each charge is injected into the passage under pressure immediately after said portion of the passage has been isolated.

7. A method according to claim 4 or claim 6, in which the gas is maintained at an elevated pressure in said portion during the interval it is isolated; the pressure in the isolated portion is allowed to increase by the introduction and vaporisation of the catalyst; and the pulse of compressed gas is introduced at a substantially higher pressure than that of the gas/catalyst mix in said portion.

9. An apparatus for hardening sand mould parts of a saind and binder mixture by passing a catalyst through the parts, said apparatus having a source of compressed air and a passage connecting said source to the mould parts, a valve at each end of said passage for closing off said passage from both said source and the mould part, a heater in said passage; a source of liquid catalyst connected to said passage, said source including means for injecting a measured quantity of catalyst into said passage; said passage having a catalyst vaporising chamber and a heater for heating the air to above the vaporisation temperature of the catalyst; and timing means for intermittently opening said valves at each end of the passage to pass a pulse of compressed air through said passage; said timing means being connected to said injecting means for activating said injecting means only when said valves are closed.

10. Apparatus according to claim 9, in which said passage includes two chambers arranged in tandem, said heater being in one of said chambers and said catalyst injecting means being connected to the other of said chambers.

11. Apparatus according to claim 10, in which said one chamber is adjacent said source of compressed air and said other chamber is adjacent the mould parts.

12. Apparatus according to any of claims 9 to 11, in which a duct interconnects said catalyst source and said passage and a cooling element is mounted in said duct for preventing the conduct of heat from said passage to said catalyst source.