WO2003013761A1

WO2003013761A1 - Method and device for the production of molds or cores for foundry purposes

Info

Publication number: WO2003013761A1
Application number: PCT/EP2002/007885
Authority: WO
Inventors: Bernd Kuhs
Original assignee: Dipl.-Ing. Laempe Gmbh
Priority date: 2001-08-10
Filing date: 2002-07-16
Publication date: 2003-02-20
Also published as: EA200400295A1; CN1538887A; EA005362B1; CA2457588A1; EP1417061A1; JP2005508252A; MXPA04001086A; US20040192806A1

Abstract

The invention relates to the production of molds or cores (2) for foundry purposes, wherein a mixture (3) of foundry sand and binder are produced and introduced into a mold or core tool (8), e.g. shot in a core shooter. A known binder or magnesium sulfate with and/or without at least one or additionally several crystallization waters is dispersed or dissolved in water and used as binder, which is then mixed with the foundry sand and introduced or shot into the mold tool or the core box (8). For hardening purposes, the water and a fraction of the crystallization water are vaporized by heating and driven out by a gaseous medium, all of which can be carried out very rapidly. After pouring, said core or mold consisting of foundry sand can be very rapidly removed from the tool with water and flushed due to the fact that the magnesium sulfate preserves its capability of dissolving.

Description

METHOD AND APPARATUS FOR THE PRODUCTION OF FORMS OR CORES F _O R GIES- SEREIZWECKE

The invention relates to a method for producing molds or cores for foundry purposes from a mixture of foundry sand and binder, wherein the foundry sand and the binder are mixed and introduced into a mold or core tool and the binder then hardens and the mold or core the necessary Gives strength.

It is known to do this in the manufacture of cores or molds for foundry purposes. In the majority of the current cases, organic binders are used, which give good curing, but produce gases during the casting process due to their combustion, which can lead to the formation of voids in the resulting cast workpiece. In addition, cores, in particular, which do not have sufficient dimensional stability at such a temperature in such a foundry sand mixture, expand. Due to the relatively large tendency of the organic binders to stick, cleaning the tools for the foundry molds or the cores is also complex.

It is to be seen as particularly unfavorable that especially cores whose sand mixture contains an organic binder can only be removed from the finished casting with great difficulty and with high mechanical or thermal expenditure.

It has therefore already been proposed to use inorganic binders, namely water glass, in the manufacture of molds or cores for foundry purposes for admixing with the sand. This can indeed cause the development of environmentally harmful gases can be avoided as far as possible, but the shaping or removal, in particular, of the cores from the finished casting is also difficult and complex.

The object is therefore to create a method of the type mentioned at the outset and also a device by means of which foundry molds and / or cores, which are said to have high dimensional stability and strength even during the casting process, can be produced, but which are nevertheless made from the finished casting are easily removable.

To solve this problem, the process defined at the outset is characterized in that magnesium sulfate is dispersed and / or dissolved in water and mixed as a binder with the foundry sand and then introduced or shot into the mold or core tool and then inside the mold - Or core tool, the water is heated and at least partially evaporated and expelled from the mold or core tool.

Experiments have shown that a stable core or a stable shape can be produced by such a method, the melting point being greatly increased by the binder chosen and the expulsion of water and optionally at least part of water of crystallization from hydrated magnesium sulfate, so that such a Foundry mold or such a core can also withstand the high temperatures of the casting material and withstand it without liberating harmful gases. The invention makes use of the fact that the expulsion of crystal water results in a chemical change in the material properties of the special binder, namely the magnesium sulfate. It has been shown that such foundry molds or cores can be flushed out with water after the casting workpiece has cooled, because the special binder then again tries to absorb water of crystallization and thereby chemically convert back into a soluble substance that can be or cleaning water and can therefore be removed from a complicated casting very easily, without the need for mechanical vibrations or the like. It may even be sufficient to simply dip the finished casting in a water bath. It has been shown that such an immersion can only be sufficient for half a minute to dissolve and flush out a complex core. In addition, the foundry sand is then practically unchanged again and does not require extensive cleaning and preparation, since no organic residues have to be removed.

The advantages that can be achieved by the invention thus relate on the one hand to the foundry shape or the cores and their properties during the casting process, in which no harmful gases are released, and on the other hand later to clean the finished casting, which is considerably simplified.

It is expedient if the mixture of foundry sand and a dispersion and / or solution of magnesium sulfate in water is heated within the mold or core tool by means of a microwave and / or infrared radiator. This represents a particularly simple type of heating for expelling the water and, if appropriate, at least some of the water of crystallization. Microwaves can be used in a very targeted manner and also penetrate into the interior of larger cores. A particularly advantageous procedure can be that the mixture of foundry sand and a dispersion and / or solution of magnesium sulfate in water within the mold or core tool by applying an electrical voltage to the at least partially electrically conductive, mutually insulated parts of the separable mold. or core tools is heated. Electrical energy is available practically everywhere where molds or cores are manufactured, so that the heating for expelling the water from the mold or the core can be carried out correspondingly easily.

The electrically conductive core / form, consisting of a mixture of foundry sand and a dispersion and / or solution of magnesium sulfate in water, can be used in a simple and expedient manner as the electrical resistance of a resistance heater and via an electrical voltage and the current flowing through it is heated. The heat is thus generated directly where the water is to be driven out.

The electrical voltage can be applied to the core / mold contacting electrodes and for this the at least partially electrically conductive, mutually insulated parts of the separable mold or core tools can be used. Their internal cavities receiving the shape to be formed or the core to be formed thus contact the shape or the core as electrodes and provide the appropriate heating, since the shape or core is electrically conductive due to the moisture or moisture and the other constituents.

It is particularly favorable if an AC voltage is applied as the electrical voltage. A pulsed, in particular rectangular, voltage can be used as the electrical voltage be created. A suitable AC voltage can use the reactive properties of the sand mixture in the core or the mold to heat it. Particularly good results can be achieved with the pulsed and in particular rectangular voltages. In particular, this makes it possible to control or regulate the power input by changing the pulse width of the electrical voltage. The voltage can therefore be regulated and in particular selected to be greater than 1000 V or greater than 1500 V in order to achieve a correspondingly rapid and strong heating.

Good drying through in a short time can be achieved if an AC voltage with a frequency of over 1000 Hz, for example 3000 Hz or more, is selected. Since the entire core box or the core or molding tool is used as an electrode surface, the energy can be transferred very quickly and effectively and the corresponding core or shape can be dried in a very short time.

It may be expedient if the water evaporated by heating is expelled from the tool by means of a gaseous medium such as nitrogen and / or carbon dioxide and / or air, this gaseous medium used for the expulsion being under pressure or through suction and underpressure through the tool and thus can be transported through the foundry mold formed or through the core. Air in particular is practically unlimited and can be used to drive water vapor out of the tool without any problems.

It is advantageous if the water vapor generated by the heating in the tool is expelled with hot gas. This can prevent the water to be driven out Steam may condense again too soon or a slightly lower heating of this water vapor may be sufficient to be able to drive it out of the tool as far as possible.

An expedient embodiment of the process can consist in that the magnesium sulfate is dispersed and / or dissolved in water without or with at least one crystal water in a mixture with magnesium sulfate with several crystal waters, optionally with up to seven crystal waters, and is mixed as a binder with the foundry sand and that the water and part of the crystal water are evaporated by heating and then driven off.

Surprisingly, the amount of water to be expelled can thereby be reduced. The magnesium sulfate, which has little or no crystal water, can take over such crystal water from the magnesium sulfate containing more multi-crystal water during the heating, so that corresponding crystal formations within the foundry mold or the core and corresponding solidifications occur, without the crystal water of the entire mixture must be driven out completely.

It is known that magnesium sulfate with little or no, in particular with only one crystal water with one with several crystal waters with mutual reaction and heating causes interweaving of the respective crystals, which in the application according to the invention contribute to an extraordinarily strong core or a corresponding one to form a solid form.

Another or additional possibility of reducing the amount of water or steam to be expelled during the process according to the invention can be hen that a high or higher concentrated solution of magnesium sulfate is mixed with or without at least one water of crystallization with a hydrocolloid and this mixture is used as a binder. The addition of hydrocolloid can have the effect that higher salt concentrations can be achieved in a relatively small amount of dispersion and / or solution water, so that correspondingly less water has to be driven off.

A further embodiment of the method can consist in that more magnesium sulfate is mixed with the amount of solution water specified for a certain amount of foundry sand than is required for a saturated solution, and that part of the magnesium sulfate is dispersed in the solution and mixed as a dispersion with the foundry sand becomes. As a result, it is possible to introduce as much magnesium sulfate as binder into the foundry sand and to keep the required amount of solution water as low as possible, so that correspondingly little water vapor then has to be expelled. At the same time, the advantages of later removal of foundry sand residues from the casting are retained with the aid of a simple water rinse or immersion in water.

The foundry sand can be mixed with the dispersed or dissolved binder in a weight ratio of 97: 3 to about 80:20.

It is expedient if about 100 parts by weight of foundry sand are mixed with about 3 parts by weight to about 20 parts by weight of dispersed or dissolved binder, that is to say dissolved magnesium sulfate and / or without water of crystallization. An optimized procedure can consist in mixing about 5 to 10 parts by weight of binder in dispersed or dissolved form with about 100 parts by weight of sand. Attempts have shows that this leads to solid cores or foundry molds that can withstand the casting process well and in which as little water as possible has to be expelled from the tool.

The invention also relates to a device for producing foundry molds or cores with at least one heating device for curing, the device for producing foundry molds being a molding machine and the device for producing cores being a core shooter. This device can be characterized in that at least one microwave generator is installed as a heating device on the molding machine or on the core shooter and that at least one microwave antenna is arranged in the area of the molding tool for the foundry mold or for the core or cores, which is connected to the microwave generator via a waveguide can be coupled or coupled. A feed opening of a gas purging hood known per se can serve to expel gases and / or heated water vapor.

It should be mentioned at this point that the mold for the foundry mold or for the core can also be a multiple tool in which, for example, several cores are molded and / or heated at the same time.

The device according to the invention can thus advantageously be largely formed by a previously known molding machine or core shooter, which is additionally equipped with a heating device, namely with a microwave generator and a microwave antenna. It is also advantageous that the access openings for the foundry sand mixed with binder can be used to drive off gases or heated steam, so that overall an inexpensive device is available. Also already Standing core shooters or molding machines can optionally be retrofitted in order to be able to use the advantageous invention and in particular the method according to the invention.

It is expedient if, by setting the device to the gas purging process for expelling gases or water vapor, the microwave generator can simultaneously be coupled to the antenna via the waveguide. This can simplify the actuation of the device, since it practically only requires one adjustment movement in order to couple the microwave generator to the antenna and to trigger the heating process.

The adjustment movement to the gas purging process can thereby automatically couple the microwave generator to the antenna. For this purpose, only the corresponding coupling is to be designed such that the closing of the gas purging hood or the like simultaneously produces the corresponding coupling of the microwave generator with the antenna.

A structurally particularly simple arrangement can provide that the course of the waveguide is separable and has a coupling at the separation point and that the antenna-side part of the waveguide is either arranged or connected to the gas purging hood or in the tool. This coupling can therefore be closed or disconnected if appropriate movements are carried out in order to bring a gas flushing hood into the use position or to remove it again.

A further embodiment of the invention for amplifying and accelerating the heating oranges can consist in that the microwave generator has a branched waveguide or two waveguides with one in the gas purging hood and with an antenna arranged in the mold can be coupled or connected.

It has already been mentioned above that water vapor can be expelled when hardening. This is particularly expedient if the foundry mold or the core is made from a mixture of foundry sand and a binder, which is a dispersed or dissolved magnesium sulfate. In this case, the device can be adjusted to the gas purging process for expelling the water vapor generated during heating or heating, as has already been mentioned above.

Overall, it is advantageously achieved that the molding or core shooting machine and the actual molding tools can remain practically unchanged, since the existing ventilation can also be used in the device according to the invention and can be used to drive out the heated and evaporated solution water according to the invention. It is only necessary to additionally install an antenna for the microwave shaft, for example on the gas supply hood. Of course, the tools must be made from materials suitable for microwaves. However, this device with a heating device designed as a microwave generator and antenna can also be used in the production of molds or cores in which a binder other than the dispersed or dissolved magnesium sulfate mentioned is used and a heating process is required for curing. A further possibility of importance worthy of protection is provided by a device for producing foundry molds or cores with at least one heating device for curing, the device for producing foundry molds machine and the device for producing cores is a core shooting machine, in which machine a molding or core tool can be inserted or is inserted. An electrical resistance heater can be provided as the heating device, in which the electrically conductive core or the mold forms the electrical resistance and the mold or core tools which are composed of several parts for removing a mold or a core can be at least partially electrically conductive and insulated from one another at their contact points and the parts of the tools can each have at least one electrical connection for applying an electrical voltage for the resistance heating device.

In this way, the molds or cores which initially contain solution water and / or water of crystallization and which are therefore electrically conductive due to the further constituents contained in them, can be electrically heated in a structurally very simple manner in order to drive off water. The wet core or the wet form represents an impedance, so that there is electrical conductivity. The voltage applied to it can therefore be used for drying.

The resistance heating device can have a voltage source with a frequency converter for increasing the frequency and / or a pulse shaper for forming an impulsive voltage. With a pulsed voltage, good results can be achieved during heating.

The resistance heater may include a voltage source and a voltage increasing transformer connected by leads to the terminals on the parts of the mold or core tool. The effectiveness can thus be increased. At least part of the mold or core tool can have a plurality of electrical connections, and switches for changing or for optionally applying a voltage to the electrical connections can be provided between these connections and the voltage source, so that one switch is alternately closed and the others are open. As a result, any polarities that may occur on an electrode can be continuously reduced or changed. The heating of a mold or a core can take place correspondingly uniformly, it also being possible to take into account the most varied contours of such molds and cores by changing the respectively effective electrical connections.

In the case of a mold or core tool consisting of more than two parts, each part can have an electrical connection and electrical feed lines, and two parts of such a tool can always be connected to the power source in cycles. Such multi-part tools are often required, especially for complicated cores. Nevertheless, with the above-mentioned configuration it is possible to form a resistance heater using the voltage applied and to heat the core thoroughly.

All in all, there is a method and a device which enable the mechanical production of molds or cores in conventional core shooters and which can harden the molding sand within about half a minute. The process makes use of the extremely different melting points of magnesium sulfate in its hydrated form on the one hand and in its crystal water-free state on the other. Magnesium sulfate has a melting point of approximately 75 ° Celsius as heptahydrate and a melting point of 1124 ° Celsius in its crystal water-free form. Through the targeted Removal of the chemically bound crystal water, it is therefore possible to achieve an almost sudden hardening of the molding sand. A strong matting of partially hydrated and fully hydrated magnesium sulfate is an advantageous property that can be used to obtain very high strength even with small amounts of magnesium sulfate, for example 1% based on the molding sand.

The important gassing for removing the originally chemically bound water of crystallization after heating can optionally take place through specially arranged inlet and outlet nozzles, an excess pressure of 1 to 6 bar of a dry gas, preferably of heated room air, being expedient. The heating can be carried out favorably with microwaves, since the quartz sand normally used is “transparent” to the microwave radiation, so that it can penetrate completely into larger shapes or cores. In addition, only the magnesium sulfate containing water of crystallization is heated. As soon as the crystal water has escaped, this magnesium sulfate, which is then free of crystal water, is "transparent" and no longer an obstacle to the further penetration of the microwaves.

However, the heating can also be carried out in a favorable manner by resistance heating, as explained above.

It is therefore essential to remove the chemically bound water of crystallization - at least in part - from the magnesium sulfate. A very rapid hardening occurs here, which is advantageous for economical production. Sufficient strength is also achieved with a comparatively low concentration of magnesium sulfate. The molded parts or cores manufactured in this way are up to at least at least 1124 ° Celsius dimensionally stable and can be removed from the metal casting with a little water.

If conventional binders are used, accelerated hardening is also possible due to targeted heating using a microwave or electrical conductive heating.

Exemplary embodiments of a device for producing molds or cores for foundry egg purposes according to the invention are described in more detail with reference to the drawing. It shows in a partially schematic representation:

1 shows a diagram of a device for producing foundry molds or cores with a microwave generator and corresponding antenna in the form of a core shooter,

Fig. 2 On an enlarged scale and even more schematically, a longitudinal section through part of the shooting unit after the shooting of

Sand into a mold designed as a core box and before moving this core box together with a rinsing hood located above it and pressing it from below onto the shooting head or vice versa, the microwave antenna for

Heating the core and for expelling the solution water is arranged in this washing hood and the connection between the microwave generator and this transmitting antenna is still open and can be closed automatically when moving together or lifting and pressing, 3 shows a representation corresponding to FIG. 2, the transmitting antenna being arranged in the lower region of the core box designed as a molding tool,

Fig. 4 shows a modified embodiment compared to Fig. 2 and 3 in an analog representation, in which both in the washing hood and in the core box each in the use position with the microwave generator can be coupled or coupled

Antenna for heating the shot core is arranged,

5 shows a representation corresponding to FIGS. 2 to 4 of a modified embodiment, in which infrared heaters are arranged in the core box for heating the shot core,

Fig. 6 is a representation of FIGS. 2 to 5 corresponding to a modified embodiment, in which an electrical resistance heater is provided as a heating device, in which the shape for the electrically conductive core is also electrically conductive and its parts are insulated at their contact points and on each Part of the mold or core tools an electrical connection is provided for a resistance heating device,

FIG. 7 shows an arrangement corresponding to FIG. 6 and

Device in which a plurality of electrical connections are provided on one of the parts of the tool for the core, via switches can be connected alternatively and alternately to avoid polarization at one of the connections,

Fig. 8 is a modified device, in which the core tool consists of three mutually insulated and electrically conductive parts, each of which has an electrical connection, two of the three parts can be connected alternately to the voltage source via switches and

FIG. 9 shows an embodiment and arrangement corresponding to FIG. 6, in which however the pulse shaper and located behind the voltage source

Voltage transformer are reversed in order compared to the arrangement of FIG. 6.

A device designated overall by 1 and shown schematically and partially broken open in FIG. 1 serves for the production of cores, but could also be used for the production of casting molds. In the exemplary embodiment, it is a core shooter.

The cores 2 to be produced therewith (FIGS. 2 to 9) - or in an analogous manner foundry molds - are formed from a mixture 3 of foundry sand and binder, which is a magnesium sulfate dissolved in water, preferably with at least one water of crystallization or another binder, whereby this mixture 3 of sand and binder is introduced in a known manner into a sand feed hopper 4 and thereby filled into the shooting head 5 of a shooting unit, designated as a whole by 6 becomes. In Fig. 1, the air boiler 7 essential for the shooting process is shown in a partially cut shape.

This device 1 in the form of a core shooter includes the core box 8 shown in FIGS. 2 to 9, which is assembled from a core box upper part 8a and a core box lower part 8b in the position of use, but could also be a correspondingly differently shaped mold for the production of foundry molds , 8 shows an embodiment in which the core box upper part 8a is in turn subdivided in order to enable the removal of a correspondingly complicated core after it has hardened.

With this device it is possible to produce molds or cores for foundry purposes from the mixture 3 of foundry sand and binder, the foundry sand and the binder first being mixed and then introduced with the help of the shooting unit 6 into the mold or core tool - in the exemplary embodiment the core box 8 , This has already taken place in FIGS. 2 to 9 and the binder can harden and give the mold or core 2 the required strength. As a binder, magnesium sulfate is preferably dispersed and / or dissolved in water with at least one water of crystallization and mixed with the foundry sand to form the mixture 3. This is then introduced or shot into the mold or core tool 8.

Thereafter, the dispersing and / or solution water and at least some of the water of crystallization are evaporated by heating within this tool, the core box 8, and expelled from the mold or core tool, that is to say from the core box 8, by means of a gaseous medium. To carry out this method, at least one heating device to be described in more detail is provided on the molding or core shooting machine 1, with which the solution and / or crystal water can thus be heated and driven off.

In the embodiments according to 1 to 4, a microwave generator 9 is installed on the core shooter 1 as a heating device and, depending on the exemplary embodiment, at least one microwave antenna 10 is arranged in the region of the mold, that is to say the core box 8, which is connected to the microwave generator 9 via a Waveguide 11 can be coupled and coupled in the use position. In the exemplary embodiment, the corresponding coupling 12 is still open, since a core 2 has already been shot, but the core box 8 is still before moving together with a gas flushing hood 13 and before being heated and hardened by means of a microwave.

In all of the exemplary embodiments, this recognizes a feed opening 14 with which, for example, hot air can be introduced to expel the heated water or water vapor, which is produced by heating with the aid of the heating device, that is to say the microwave 9 in the use position.

In Figures 1 to 4, the connection between the microwave generator 9 and antenna 10 is still open. By setting the device 1 to the gas purging process to expel the water vapor, that is to say by the relative lifting movement of the core box 1 against the gas purging hood 13 and against the shooting head 5 or vice versa, the microwave generator 9 can simultaneously be coupled to the antenna 10 via the waveguide 11 by closing the clutch 12 during the relative movement mentioned. Then the heating can be done with the help of microwave energy and, at the same time or somewhat thereafter, the resulting water vapor is expelled.

The adjustment movement to the gas purging process can automatically effect the coupling of the microwave generator 9 to the antenna 10, so that the entire process can be carried out quickly.

The course of the waveguide 11 is thus separable and the aforementioned coupling 12 is provided at the separation point, the antenna-side part of the waveguide 11 optionally according to. Fig. 2 on the gas purging hood 13 or gem. Fig. 3 in the mold or core box 8 or gem. Fig. 4 can even be arranged and connected at both points. Fig. 4 shows that the microwave generator 9 can be coupled and connected via two waveguides 11 with an in the gas purging hood 13 and an antenna 10 arranged in the molding tool or core box 8, so that the foundry mold or the core 2 heats accordingly and quickly and strongly the time for expelling the solution and / or crystal water can be reduced.

Fig. 5 shows a modified embodiment in which infrared heaters 15 are provided as a heating device on or in the mold, in this case in the core box 8, which can be provided as an alternative to heating by means of a microwave or possibly even additionally if for example in the gas purging hood additionally an antenna 10 acc. Fig. 2 would be provided. 6 to 9 again show modified embodiments in which an electrical resistance heater is provided as the heating device, in which the electrically conductive core 2 forms the electrical resistance. That for removing a core 2 in turn from two (FIGS. 6, 7 and 9) or three (FIG. 8) parts assembled core tool 8 is at least partially or expediently completely electrically conductive, for example, made of aluminum or cast iron or steel. The parts 8a and 8b are insulated from one another at their contact points and this insulation 16 is shown schematically in FIGS. 6 to 9.

It can also be seen that the parts 8a and 8b of the tools or of the core box 8 each have an electrical connection 17 for applying an electrical voltage for the resistance heating device.

Core box upper part 8a and core box lower part 8b, that is to say the parts of the core tool 8 thus belong to the resistance heater in which the core 2 forms the actual resistance.

In a conventional manner, this resistance heating device has a voltage source 19, which in the present case leads through a three-phase network 20 to a frequency converter for increasing the frequency and / or a pulse shaper 21 to form a pulsed voltage.

This resistance heating device also has a transformer 22 for increasing the voltage, from which leads 23 lead to the connections 17 on the parts 8a and 8b of the core tool 8. If the voltage is switched on, the moist core 2 acts within the tool 8 as a corresponding resistance or as an impedance, so that current flows to dry the core. The level of the tension can be chosen according to the thickness of the core 2. A very intensive and effective drying is achieved because the parts 8a and 8b as electrodes which are in contact with and contact the core, to which the electrical voltage is applied, these “electrodes” 8a and 8b being separated from one another by the insulation 16 in order to avoid a short circuit.

The electrical voltage can expediently be a sinusoidal or pulse-shaped, in particular rectangular, voltage, an alternating voltage of high frequency of more than 1000 Hz, for example 3000 Hz or more, being particularly effective. The voltage can also be regulated and selected greater than 1000 V. By changing the pulse width of the electrical voltage, the power input can be controlled or regulated and adapted to the shape and size of a core 2 - and in the case of producing a shape in a mold to the shape.

While two parts 8a and 8b form the core box 8 in the embodiment according to FIG. 6 and each have an electrical connection 17, the embodiment according to FIG. 7 shows four such electrical connections 17 on the core box lower part 8b, which are connected in parallel, between these connections 17 and the voltage source 19 switches 24 are provided for alternating or optional application of a voltage to the various electrical connections 17, alternately one switch 24 being closed and the others being open. As a result, polarization at a connection point of the core box lower part 8b can be avoided and the core 2 can be heated as uniformly as possible. FIG. 8 shows an embodiment in which the core tool 8 consists of more than two parts, the core box upper part 8a in turn being divided into two parts, which parts are electrically separated from one another by insulation 25 are. Correspondingly complicated cores 2 can thus be produced.

8 shows that each of these three parts has an electrical connection 17 and an electrical feed line 23, which initially consists of two parallel strands 23a and 23b, in which switches 26 are arranged. These parallel-connected strands 23b allow two parts 8a or 8b of such a multi-divided tool 8 to be connected to the voltage source 19 in cycles, by opening and closing the switches 26 in a clocked manner. At intervals, therefore, only two parts of the core box 8 are always live in order to use and heat the core 2 located therein as a resistor.

In the embodiment according to FIG. 9, which essentially corresponds to that according to FIG. 6, it is shown that the order of arrangement of the pulse shaper 21 and the transformer 22 can also be interchanged such that first the voltage transformer 22 and then the pulse shaper 21 are provided in a row.

In the embodiments according to FIGS. 6 to 9, as in the exemplary embodiments according to FIGS. 2 to 5, a gas purging hood 13 is provided with a feed opening 14, with which, for example, hot air can be introduced to expel the heated water or water vapor, which is produced by heating with the help the electrical voltage arises in the position of use. For the gas purging process, the gas purging hood 13 can be delivered analogously to the previously described exemplary embodiments. To drive off the evaporated water, a gaseous medium, for example nitrogen and / or carbon dioxide and / or air, preferably hot air or hot gas, can be supplied via the feed opening 14. The best way to expel the evaporated water is to use positive pressure.

The mixture 3 contains, as already mentioned, magnesium sulfate dissolved in water as a binder without and / or with one or possibly also several crystal waters. For example, magnesium sulfate without, with one crystal water and magnesium sulfate with several crystal waters together and / or also mixed with a hydrocolloid can be used as a binder. It is particularly advantageous if only magnesium sulfate or magnesium sulfate with hydrocolloid is used, because magnesium sulfate is well dispersed and / or dissolved in water with crystal water and mixed as a binder with foundry sand, but later it can also be dissolved out of a cast workpiece with the help of water can.

An example of a suitable mixture of foundry sand and dispersed or dissolved binder can provide that about 100 parts by weight of foundry sand are mixed with about 3 parts by weight to about 20 parts by weight of dissolved binder, consisting primarily of magnesium sulfate in dissolved form.

About 100 parts by weight of sand can preferably be mixed with about 5 to 10 parts by weight of binder in dispersed or dissolved form. Correspondingly little water has to be expelled from the core box 8 by heating and with a gas and the process can be carried out correspondingly quickly. To produce molds or cores 2 for foundry purposes, a mixture 3 of foundry sand and binder is produced and introduced into a mold or core tool 8, for example shot in a core shooter. In this case, a known binder or magnesium sulfate without and / or with at least one or more crystal waters is dispersed or dissolved in water as a binder and mixed with the foundry sand and introduced or shot into the mold or core box 8. For hardening, the water and some of the water of crystallization are then evaporated by heating and expelled using a gaseous medium, which can be carried out very quickly. After casting, such a core or such a mold consisting of foundry sand can be very quickly detached from the workpiece and washed out by means of water, since the magnesium sulfate retains its ability to dissolve.

Expectations

Claims

Expectations

1. A method for producing molds or cores (2) for foundry purposes from a mixture (3) of foundry sand and binder, wherein the foundry sand and the binder are mixed and introduced into a mold or core tool (8) and the binder then cures and gives the mold or core (2) the required strength, characterized in that magnesium sulfate, dispersed and / or dissolved in water and mixed as a binder with the foundry sand and then introduced or shot into the mold or core tool (8) and that then the water is heated within the mold or core tool and at least partially evaporated and expelled from the mold or core tool (8).

2. The method according to claim 1, characterized in that the mixture (3) of foundry sand and a dispersion and / or solution of magnesium sulfate in water within the mold or core tool (8) is heated by means of a microwave and / or infrared radiator.

3. The method according to claim 1, characterized in that the mixture of foundry sand and a dispersion and / or solution of magnesium sulfate in water within the mold or core tool (8) by applying an electrical voltage to the at least partially electrically conductive, isolated from each other Parts of the separable mold or core tools (8) is heated.

4. The method according to claim 1 or 3, characterized in that the / of a mixture of foundry sand and a dispersion and / or solution of magnesium sulfate in water existing, electrically conductive core / form is used as the electrical resistance of a resistance heater and is heated via an electrical voltage applied to it and the current flowing through it.

5. The method according to claim 3 or 4, characterized in that the electrical voltage is applied to the core / mold contacting electrodes and that preferably the at least partially electrically conductive, mutually insulated parts (8a, 8b) of the separable mold or core tools ( 8) can be used.

6. The method according to any one of claims 3 to 5, characterized in that an AC voltage is applied as the electrical voltage.

7. The method according to any one of claims 3 to 6, characterized in that a pulse-shaped, in particular rectangular voltage is applied as the electrical voltage.

8. The method according to claim 6 or 7, characterized in that an alternating voltage of high frequency of over 1000 Hz, for example 3000 Hz or more is selected.

9. The method according to any one of claims 3 to 8, characterized in that the voltage is adjustable and in particular greater than 1000 V or greater than 1500 V is selected.

10. The method according to any one of claims 3 to 9, characterized in that the performance input by change the pulse width of the electrical voltage is controlled or regulated.

11. The method according to any one of claims 1 to 10, characterized in that the water evaporated by heating is expelled from the tool (8) by means of a gaseous medium such as nitrogen and / or carbon dioxide and / or air, this serving for expelling gaseous medium is transported with pressure or by suction and vacuum through the tool and thus through the foundry mold or through the core.

12. The method according to any one of claims 1 to 11, characterized in that the water vapor generated by the heating in the tool (8) is expelled with hot gas.

13. The method according to any one of claims 1 to 12, characterized in that magnesium sulfate dispersed and / or dissolved in water without or with at least one crystal water in a mixture with magnesium sulfate with a plurality of crystal waters, optionally with up to seven crystal waters, and as a binder with the foundry sand is mixed and that the water and part of the crystal water are evaporated by heating and then driven off.

14. The method according to any one of claims 1 to 13, characterized in that a highly or highly concentrated dispersion or solution of magnesium sulfate is mixed with or without at least one water of crystallization with hydrocolloid and this mixture (3) is used as a binder.

15. The method according to any one of claims 1 to 14, characterized in that with the for a certain amount Foundry sand given the amount of solution water more magnesium sulfate is mixed with water of crystallization than is required for a saturated solution, and that part of the magnesium sulfate is dispersed in the solution and mixed as a dispersion with the foundry sand.

16. The method according to any one of claims 1 to 15, characterized in that the foundry sand is mixed with the dispersed or dissolved binder in a weight ratio of 97: 3 to about 80:20.

17. The method according to any one of claims 1 to 16, characterized in that about 100 parts by weight of foundry sand are mixed with about 3 parts by weight to about 20 parts by weight of dispersed or dissolved binder.

18. The method according to claim 17, characterized in that about 5 to 10 parts by weight of binder in dispersed or dissolved form are mixed with about 100 parts by weight of sand.

19. Device (1) for producing foundry molds or cores (2) with at least one heating device for curing, the device (1) for producing foundry molds being a molding machine and the device for producing cores being a core shooter, characterized in that that at least one microwave generator (9) is installed as a heating device on the molding machine or on the core shooter (1) and that at least one microwave antenna (10) is arranged in the area of the molding tool (8) for the foundry mold or for the core, which is connected to the microwave generator (9) can be coupled or coupled via a waveguide (11).

20. The apparatus according to claim 19, characterized in that the microwave generator (9) via the waveguide (11) can be coupled to the antenna (10) at the same time by setting the device (1) to a gas purging process for expelling gases or water vapor ,

21. The apparatus according to claim 19 or 20, characterized in that the adjusting movement to the gas purging process automatically causes the coupling of the microwave generator (9) with the microwave antenna (10).

22. Device according to one of claims 19 to 21, characterized in that the course of the waveguide (11) is separable and has a coupling (12) at the separation point and that the antenna-side part of the waveguide (11) optionally on the gas purging hood (3rd ) or is arranged or connected in the mold (8).

23. Device according to one of claims 19 to 22, characterized in that the microwave generator (9) via a branched waveguide (11) or via two waveguides (11) with one in the gas purging hood (3) and with one in the mold (8 ) arranged antenna (10) can be coupled or connected.

24. Device for producing foundry molds or cores

(2) with at least one heating device for curing, the device for producing foundry molds being a molding machine and the device for producing cores being a core shooting machine, in which machine a molding or core tool (8) can be inserted or inserted, characterized in that an electrical resistance heater is provided as a heating device, in which the electrically conductive core (2) or the mold forms the electrical resistance and that the mold or core tool (8) composed of several parts (8a, 8b) for removing a mold or a core (2) is at least partially electrically conductive and at its contact points is insulated and that the parts (8a, 8b) of the tool (8) each have at least one electrical connection (17) for applying an electrical voltage for the resistance heating device.

25. The device according to claim 24, characterized in that the resistance heating device has a voltage source (19) with a frequency converter for increasing the frequency and / or a pulse shaper (21) for forming a pulsed voltage.

26. Device according to one of claims 24 or 25, that the resistance heating device has a voltage source and a transformer (22) for increasing the voltage, which leads via lines with the connections (17) to the parts (8a, 8b) of the form or Core tool (8) are connected.

27. Device according to one of claims 24 to 26, characterized in that at least part (8b) of the mold or core tool (8) has a plurality of electrical connections (17) and that between these connections (17) and the voltage source (19) switches (24) are provided for alternating or optional application of a voltage to the electrical connections, so that alternately a switch (24) is closed and the rest are open.

28. Device according to one of claims 24 to 27, characterized in that in the case of a molding or core tool (8) from more than two parts (8a, 8b), each part has an electrical connection (17) and electrical feed lines and two parts of such a tool are always connected to the voltage source (19) in cycles.

29. Device according to one of claims 19 to 28, wherein the foundry mold or the core can be produced from a mixture of foundry sand and a binder which is a dispersed or dissolved magnesium sulfate, characterized in that the device (1) on the gas - Flushing process for expelling the water vapor generated during heating and heating is adjustable.

Summary