EP3119545B1 - Method for casting castings - Google Patents

Description

The invention relates to a method for casting cast parts, in which a molten metal is poured into a casting mold, which surrounds a cavity forming the casting to be produced, wherein the casting mold consists of one or more mold parts or cores as a lost mold. The mold parts or casting cores are formed from a molding material which consists of a core sand, a binder and optionally one or more additives for adjusting certain properties of the molding material.

In conventional methods of this type, the casting mold is usually first provided, the casting cores and moldings have been prefabricated in separate operations. The casting mold can be composed as a so-called "core package" of a plurality of casting cores. In the same way it is possible to use casting molds which are composed, for example, of only two mold halves, in which the mold cavity forming the casting is formed, wherein mold cores may also be present in order to image recesses, cavities, channels and the like in the casting ,

Typical examples of castings produced by a method according to the invention are cylinder crankcases and cylinder heads. For larger and highly stressed engines, they are made of cast iron by sand casting.

As molding material for the mold parts forming the outer end of the casting mold, quartz sands mixed with bentonites, lustrous carbon formers and water are usually used in the region of iron casting. By contrast, the casting cores reproducing the internal cavities and channels of the casting are usually formed from commercially available core sands, which are filled with an organic or inorganic binder, eg. B. with a synthetic resin or water glass, are mixed.

Regardless of the nature of the core sands and binders, the basic principle in the production of molds formed from molding materials of the above-mentioned type is that after the molding of the binder is cured by a suitable thermal or chemical treatment, so that the grains of the core sand stick together and over a sufficient period the dimensional stability of the respective molded part or core is ensured.

Especially when casting large-volume castings made of cast iron, the pressure on the mold after pouring the molten metal internal pressure can be very high. In order to absorb this pressure and to reliably avoid bursting of the casting mold, either thick-walled, large-volume molds or support structures are used, which support the mold on its outside.

One possibility of such a support structure is an enclosure which is slipped over the mold. The housing is usually formed in the manner of a jacket which surrounds the mold on its peripheral sides, but on its upper side has a sufficiently large opening to allow the pouring of the melt into the mold. The enclosure is dimensioned so that after filling at least in the decisive for the support of the mold sections between the inner surfaces of the housing and the outer surfaces of the mold remains a filling space. This filling space is filled with a free-flowing filling material, so that a large-area support of the respective surface portion is ensured at the housing. In order to achieve the most uniform possible filling of the filling space, an equally uniform contact of the mold with the filler and a correspondingly uniform support of the fragile casting material, are used as filling usually fine-grained, free-flowing filler materials, such as sand or steel gravel, which has a high Own bulk density. After filling, the contents are additionally compacted. The aim here is to produce a very compact filling compound, which ensures the direct transfer of the supporting forces from the housing to the casting mold in the manner of an incompressible monolith.

The molten metal is poured into the mold at high temperature, so that the mold parts and cores from which the mold is composed, are heated strongly. As a result, the mold begins to radiate heat. If the temperature of the mold exceeds a certain minimum temperature, the binder of the molding material begins to evaporate and burn with the release of further heat. The binder loses its effect. As a result of this decomposition of the binder, the bonding of the grains of the molding material from which the mold parts and cores of the mold are made is lost, and the mold or its parts made of molding material and cores disintegrate into individual fragments.

It is known from practice that this effect can be used for demoulding the casting from the respective casting mold. For example, from the EP 0 546 210 B2 , the WO 01/08836 A1 or the EP 0 612 276 B2 Heat treatment process for castings known in which the casting mold with the castings in a continuous process flow from the casting heat in a heat treatment furnace. When passing through the furnace, the casting mold and the castings will be exposed for a sufficiently long duration to a temperature at which the condition of the casting desired by the heat treatment will be attained. At the same time, the temperature of the heat treatment is chosen so that the binder of the molding material decomposes. The then automatically falling from the casting, consisting of molding fragments of the mold are still in the heat treatment furnace in a Sandbed caught. There they linger over a certain period of time in order to continue the disintegration of the fragments of the mold parts and cores. The crushing of the falling off of the mold molding material fragments can be supported by the fact that the sand bed is fluidized by blowing a hot gas stream. The sufficiently shredded shaped material fragments are finally fed to a treatment, in which the core sand is recovered so that it can be used for the production of new mold parts and cores.

The known procedure in the demolding and processing of the casting molds required for the casting has proven in practice in the casting of parts for internal combustion engines made of aluminum in large numbers. However, it requires a furnace of considerable length and a handling of the molds and castings, which proves to be costly in large-volume parts or molds, which require additional support by an enclosure of the type described above. This is especially true for such castings, which are to be produced in small and medium quantities of cast iron.

Against this background, the object of the invention was to provide a method which enables the casting production of castings with optimized Energieeffiziens and in a particularly economical manner.

The invention has achieved this object by the method specified in claim 1.

Advantageous embodiments of the invention are specified in the dependent claims and are explained below as the general inventive concept in detail.

The invention thus provides a method for casting castings, wherein a molten metal is poured into a mold enclosing a cavity forming the casting to be formed. The mold is formed as a lost mold composed of one or more mold parts or cores. These mold parts are each formed from a molding material consisting of a core sand, a binder and optionally one or more additives for adjusting certain properties of the molding material.

• Bereitstellen der Gießform;
• Einhausen der Gießform in ein Gehäuse unter Ausbildung eines Füllraums zwischen mindestens einem Innenflächenabschnitt des Gehäuses und einem zugeordneten Außenflächenabschnitt der Gießform;
• Befüllen des Füllraums mit einem rieselfähigen Füllgut;
• Abgießen der Metallschmelze in die Gießform,
• wobei die Gießform einhergehend mit dem Eingießen der Metallschmelze beginnt, Wärme abzustrahlen, die Folge des durch die heiße Metallschmelze bewirkten Wärmeeintrags ist, und
• wobei in Folge des durch die Metallschmelze bewirkten Wärmeeintrags der Binder des Formstoffs zu verdampfen und zu verbrennen beginnt, so dass er seine Wirkung verliert und die Gießform in Bruchstücke zerfällt.

The method according to the invention comprises the following steps:

• Providing the mold;
• Einhausen the mold into a housing to form a filling space between at least an inner surface portion of the housing and an associated outer surface portion of the mold;
• Filling the filling space with a free-flowing filling material;
• Pouring the molten metal into the casting mold,
• wherein the mold commences, along with the pouring of the molten metal, to radiate heat, which is the result of the heat input caused by the molten metal, and
• wherein, as a result of the heat input caused by the molten metal, the binder of the molding material begins to evaporate and burn, so that it loses its effect and the casting mold breaks up into fragments.

According to the invention, the filling material filled in the filling space now has such a low bulk density that a gas flow can flow through the filling product pack formed there from the filling material after filling the filling space. In addition, the filling material in the inventive method when filling the filling chamber to a minimum temperature of at least 500 ° C, starting from the temperature of the filling by process heat, which is formed by the radiated heat from the mold and by the heat released during the combustion of the binder will rise above a limit temperature of 700 ° C.

The method according to the invention is therefore based on the idea to use the filling material in the sense of a heat storage and to temper and form this heat storage so that the decomposition of the binder of the molding material from which the mold parts and cores of the mold are made, already during the Dwell time in the enclosure is largely decomposed by the effect of temperature.

In this way it is achieved that the parts made of molding material and cores of the mold so far in Fragments have fallen apart, these fragments fall off the casting and the casting after removal of the enclosure, at least in the region of its outer surfaces is largely free of adhering moldings or cores.

At the same time, the cores that break channels or cavities in the interior of the casting are also disintegrated at this time, so that the core sand and the shaped material fragments of these cores automatically trickle out of the casting already in the enclosure or in a manner known per se, for example by mechanical methods such as shaking, or by flushing with a suitable fluid, can be removed from the casting.

The present invention filled in the formed between the casting and housing filling space filling material is free-flowing, so that it also completely fills the filling space when in the area of the outer surfaces of the mold undercuts, cavities and the like are present.

It is crucial that according to the invention, the filling material has a bulk density which is so low that it is still permeable by a gas flow after filling the filling space and an optionally carried out compression of the filled into the filling space filling material. According to the invention, therefore, in contrast to the above-mentioned prior art, expressly no highly compressed packing is produced in the filling space, which indeed ensures optimum support of the casting mold, but is largely gas-impermeable. Rather, the filling material used according to the invention is to be selected such that it is suitable for a Gas flow is permeable, which sets, for example, as a result of thermal convection. This occurs when the mold is heated by the molten metal poured into it and the vaporizing binder components of the molding material of the mold parts and cores begin to evaporate and begin to burn with the release of heat.

If we speak here of a vaporizing and combusting binder, then this always means those binder components which become vaporous due to the supply of heat and are combustible. This does not exclude that other binder components remain in solid or other form, for example as cracking products in the mold and there optimally also decomposed by heat influence.

The inventively provided flowability of the filled into the filling space filling with a gas stream not only creates the possibility that the evaporating from the mold binder in the region of the medium itself burns and thereby further heats the contents, but additionally allows the supply of oxygen, the Combustor combustion supported. In this way, the contents are heated by the supplied via the molten metal and released by the combustion of the binder process heat to a temperature which is so high that the coming into contact with the filling material, emerging from the mold binder components of the moldings and cores burn or thermally decomposed at least so that they no longer have the effect of damaging the environment more or can be deducted as exhaust from the enclosure and fed to an exhaust gas purification.

The pre-tempered product according to the invention is preferably introduced into the filling space at a short time interval before the casting of the molten metal in order to minimize temperature losses.

After a sufficient concentration of combustible outgassing of the molding material has been reached in the filling chamber, the combustion begins by the contact with the heated product. The combustion of the binder emerging from the casting mold proceeds and the contents are kept at a temperature as long as possible. This process continues until only such small amounts of binder escape from the casting mold that no combustible atmosphere forms in the enclosure. However, the hot medium now holds in the manner of a heat storage a temperature above the limit temperature at which it comes to the combustion of the binder. Accordingly, the casting mold remains at least likewise at this temperature, so that binder residues remaining in the casting mold are thermally decomposed.

Casting molds whose shaped parts and cores are made of molding material which is bound by an organic binder are particularly suitable for the process according to the invention. Commercially available solvent-borne binders or binders are suitable for this purpose, the effect of which is triggered by a chemical reaction. Corresponding binder systems are used today in the so-called "cold-box process".

In practice, the limit temperature is 700 ° C., especially when processing cast iron melt. At above 700 ° C burn in particular safe organic binders. At the same time, other pollutants emanating from the mold are oxidized or otherwise rendered harmless at these temperatures. The same applies to the cracking products which form in the casting mold as a consequence of the temperature-induced decomposition of the binder and which also decompose safely at such high temperatures.

According to the invention, the contents are pre-heated to a certain temperature in the filling space is filled, it is ensured that the filling material heats up as a result of the supplied process heat to a temperature above the limit temperature. Practical experiments have shown here that a minimum temperature of 500 ° C is sufficient when filling into the filling space.

Along with the discharge, combustion and decomposition of the binder, the mold-molded parts and cores of the mold disintegrate into loose fragments, which may either be disposed of after removal of the casing and sent for treatment or, advantageously, during the interval between them Discharge of the molten metal and the removal of the housing can be deducted from the housing. For this purpose, the mold can be placed on a sieve and collected by the sieve bottom trickling fragments of the mold. Practically, the openings of the sieve tray are designed so that the fragments of the mold and the contents trickle together through the sieve tray, collected, processed and separated from each other after the preparation. This has the Advantage that no loose filling material is more in the housing is available when the housing is removed.

The enclosure of the mold can accordingly by a mold surrounding the mold with a sufficient for the formation of the filling space, consisting of a thermally insulating and sufficiently dimensionally stable material jacket, acting as a sieve plate perforated support plate on which the mold is placed, and also thermally be formed insulating cover, which is placed after filling the mold. In order to enable a controlled discharge of the exhaust gases forming in the filling space, an exhaust gas opening may additionally be provided.

Also in the method according to the invention, the filling material filled in the filling space can be compressed to produce a bias between the mold and the enclosure, through which a secure, positionally accurate cohesion of the mold is also guaranteed if the mold as from a variety of moldings and Nuclear composite core package is formed. As mentioned, however, due to the low bulk density, even with such a compacted filling material the flowability is secured with a gas stream.

The effectiveness of the present invention achieved destruction of the moldings and cores of the mold can be further increased by not only the contents, but also the mold itself is designed to flow through gas. For this purpose, channels can be deliberately introduced into the casting mold, through which the hot exhaust gas forming in the filling space or correspondingly preheated oxygen-containing gas flows. In this way, a rapid evaporation, burning and other thermal decomposition of the molding material binder is also within the mold. The disintegration of the mold is thus additionally accelerated.

Targeted channels introduced into the casting mold can also be used to accelerate cooling of certain zones on or in the casting or to avoid such accelerated cooling in order to achieve certain properties of the casting in the respective zone.

In a filling material according to the invention, the bias is transmitted by the contacting grains of the medium after the compression. In order to avoid despite the inventively required gas permeability of the contents that the grains of the contents move uncontrollably, the housing can be equipped on its inner surface associated with the mold with a textured surface on which the abutting against this surface grains are at least partially positively supported ,

The contents should at the same time have a low suitability for storing heat, so that the product heats up quickly and can be kept at a temperature above the limit temperature for as long as possible.

Optimal for the purposes of the invention suitable filling thus combines a low bulk density with a low specific heat capacity of the material from which the items that make up the contents are made.

Practical investigations have shown here that product in which the product P of bulk density Sd and specific heat capacity cp of the material from which the product is made, is at most 1 kJ / dm ³ K (P = Sd x cp ≤ 1 kJ / dm ³ K), wherein product, in which the product P = Sd x cp is at most 0.5 kJ / dm ³ K, is particularly well suited.

Regardless of whether a compaction is carried out, granules or other granular bulk material have proven to be good as filling material. Such bulk materials with bulk densities of max. 4 kg / dm ³ , in particular less than 1 kg / dm ³ or even less than 0.5 kg / dm ³ , particularly suitable for the purposes of the invention.

If a granular, pourable and pourable filling material is used, it has proven to be advantageous in practical experiments if the mean diameter of the grains is 1.5-100 mm, with optimum use of filling material whose grain sizes are in the range of 1.5 - 40 mm.

This shows contents made of materials with a specific heat capacity of max. 1 kJ / kgK, ideally less than 0.5 kJ / kgK, is an optimum heating and heat storage behavior for the invention.

As a product are basically all thermally stable bulk materials suitable that meet the above conditions and are sufficiently temperature resistant. For this purpose, in particular non-metallic bulk materials, such as granules of ceramic materials are suitable. These can be irregularly shaped, spherical or with cavities be provided in order to achieve a good gasification of the filling material filled in the filling space at the same time low heat storage property. Also, the contents may consist of annular or polygonal elements that touch each other only in point contact upon contact, so that between them enough space remains to ensure a good flow.

In order to prevent the oxygen-containing gas stream optionally conducted into the enclosure via a gas inlet from causing a cooling of the filling material, the gas stream can be heated to a temperature above room temperature before it enters the filling space. Optimally, the temperature of the gas stream is at least at the level of the minimum temperature of the medium. For the heating of the gas stream, for example, the hot exhaust gas can be used, which is deducted from the enclosure. For this purpose, a known heat exchanger can be used. If a sieve bottom is provided, over which the fragments of the casting mold can optionally pass out of the housing together with the contents, the oxygen-containing gas stream can also be passed through this sieve bottom. This not only has the advantage of a large-scale introduction, but also causes the supplied gas stream is heated by contact with the hot, trickling out of the housing molding material fragments and the equally hot contents.

Alternatively or additionally, it is also conceivable to mix a partial flow of the exhaust gas stream with the oxygen-containing gas stream and to recycle the resulting hot gas mixture into the filling space. For this it can be useful that the oxygen-containing gas stream fed into the filling space consists of 10 to 90% by volume of waste gas.

The oxygen-containing gas stream supplied to the filling space may be, for example, ambient air.

The oxygen-containing gas stream supplied to the filling space can be sucked into the filling space via a suitably formed inlet as a result of the flow triggered by heat convection within the filling space. Alternatively, it is of course also conceivable to introduce the gas flow by means of a blower or the like with a certain pressure in the filling space.

An optional regulation of the gas flow introduced into the filling space can take place as a function of the exhaust gas volume flow exiting the housing in order to prevent the formation of overpressure in the atmosphere prevailing in the filling space. For this purpose, the respective gas inlet can be equipped with a mechanism which regulates the supply air as a function of the flow velocity. Suitable for this purpose is, for example, a per se known pendulum flap, which is suspended and loaded so that the flow pressure of the gas flow passing it regulates the flow rate and thus the combustion air supply automatically depending on counterweights.

Likewise, it is conceivable to carry out an exhaust gas measurement at the exhaust gas outlet and to regulate the oxygen-containing gas flow as a function of the result of this measurement in order to ensure complete combustion of the binder and the other possibly to escape from the mold escaping gases in the filling space.

A minimization of pollutant emissions can also be achieved in the method according to the invention in that the housing is equipped with a catalyst device for the decomposition of pollutants contained in the combustion products of the binder.

The cast part exposed after demoulding according to the invention can be subjected to a heat treatment after the decay of the casting mold, in which it is cooled in a controlled manner according to a specific cooling curve in order to produce a specific state of the casting.

Of course, in the case of the procedure according to the invention, a plurality of casting molds can be accommodated simultaneously in an enclosure and these casting molds can be filled with molten metal in parallel or in a chronologically closely successive sequence.

In principle, the method according to the invention is suitable for any type of metallic cast materials, the processing of which produces a sufficiently high process heat. The method according to the invention is particularly suitable for the production of castings from cast iron, because due to the high temperature of the cast iron melt, the temperatures provided for the combustion of the binder according to the invention are achieved particularly reliably. In particular, can be in inventive GJL, GJS and GJV cast iron materials and cast steel.

If it is mentioned here that the mold used in the invention consists of molded parts or cores, which are molded from molding material, so of course includes the possibility to produce within such a mold items, such as chills, supports and the like, from other materials , It is only important that the mold contains so much molding material volume that it comes in the course of pouring the respective molten metal for evaporation of binder, which then burns in the filling and heats up the contents to the extent that it has a for a complete complete decomposition of the binder of the Formstoffs sufficient duration maintains a temperature above the limit temperature.

The cleaning of the effluent gas stream exiting from the housing provided according to the invention can be carried out by combusting the flammable substances still present in the exhaust gas in an exhaust air combustion system. The heat released in turn can be used to preheat the oxygen-containing gas stream fed into the enclosure.

If castings are produced in accordance with the invention with several casting molds according to the invention in parallel, it may be expedient if the casting molds together with the housings assigned to them are in a tunnel or the like and the forming exhaust gases are removed via a common exhaust pipe.

The inventive method is particularly suitable for the casting production of cylinder crankcases and cylinder heads for internal combustion engines. In particular, when the components in question are intended for commercial vehicles, they and the respective mold required for their production have a comparably large volume, in which the advantages of the procedure according to the invention have a particularly pronounced effect.

The core sand fragments obtained according to the invention, when they emerge from the enclosure, are usually still so hot that they can be comminuted in a conventional grinder without additional heat input. If the core sand fragments are present as a mixture with the contents, the separation takes place after the grinding. This is very simple, because the grain size of the core sand obtained after milling is much smaller than the grain size of the medium. The grinder can be designed so that it causes a mechanical preconditioning of the core sand. Such a preconditioning can consist, for example, in the fact that the surface roughness of the sand grains is increased by the contact of the core sand with the product granulate and thus the adhesion of the binder to the core sand is improved in the subsequent processing into a molded part or core.

The regenerated sand obtained after the preparation can be mixed in a conventional manner with new sand.

Fig. 1

ein Ablaufdiagramm, dass den erfindungsgemäßen Prozess darstellt;

Fig. 2 - 8

einen Thermoreaktor in verschiedenen Phasen der Durchführung des erfindungsgemäßen Verfahrens jeweils in einem Schnitt entlang seiner Längsachse;

Fig. 9

den zum Entnehmen des Gussteils geöffneten Thermoreaktor in einer den Figuren 2 - 8 entsprechenden Ansicht;

Fig. 10

eine Einrichtung zum Abkühlen eines Gussteils;

Fig. 11

das fertige Gussteil;

Fig. 12

einen Sammelbehälter des Thermoreaktors in einer den Figuren 2 - 8 entsprechenden Ansicht;

Fig. 13

ein Mahlwerk zum Regenieren von Kernsand in einem Schnitt quer zu seiner Längsachse;

Fig. 14

eine Gießform zum Gießen eines Gussteils in einer den Figuren 2 - 8 entsprechenden Ansicht;

Fig. 15

einen mit Füllgut gefüllten Vorratsbehälter in einer den Figuren 2 - 8 entsprechenden Ansicht.

The invention will be explained in more detail with reference to a drawing illustrating an exemplary embodiment. Their figures show each schematically:

Fig. 1

a flowchart illustrating the process according to the invention;

Fig. 2-8

a thermoreactor in different phases of carrying out the method according to the invention in each case in a section along its longitudinal axis;

Fig. 9

the open to remove the casting thermoreactor in a Figures 2 - 8 corresponding view;

Fig. 10

a device for cooling a casting;

Fig. 11

the finished casting;

Fig. 12

a sump of the thermoreactor in a Figures 2 - 8 corresponding view;

Fig. 13

a grinder for regenerating core sand in a section transverse to its longitudinal axis;

Fig. 14

a casting mold for casting a casting in a die Figures 2 - 8 corresponding view;

Fig. 15

a filled with filling reservoir in a Figures 2 - 8 corresponding view.

In Fig. 1 is shown as a diagram of the cycle that results in the execution of the method according to the invention. It is started with mold parts and cores made of molding material, the new, previously unused core sand, z. As quartz sand, and a conventional binder, for example, a commercial cold box binder is mixed. Likewise, new filler material, for example, ceramic granules with a mean particle size of 1.5 - 25 mm, used, which for the first use to the required minimum temperature, eg. B. 500 ° C, must be heated before it can be used. Furthermore, these starting materials can be reused in the circulation, as explained below.

The in the Fig. 2-8 Thermoreactor T shown in different phases of the process according to the invention has a screen plate 1, on which a casting mold 2 prepared for pouring an iron casting melt is placed. The casting mold 2 is intended for the casting production of a casting G, which in the present example is a cylinder crankcase for a commercial vehicle engine.

The mold 2 is conventionally assembled as a core package from a plurality of outer cores or moldings arranged externally and internally arranged casting cores. In addition, the casting mold 2 may comprise components made of steel or other indestructible materials. These include, for example, chill molds and the like, which are arranged in the mold 2, to achieve a directional solidification of the casting G by accelerated solidification of each coming in contact with the chill melt.

The casting mold 2 delimits a mold cavity 3 from the environment U into which the iron casting melt is poured off to form the casting G. The molten iron flows through a gate system in the mold cavity 3, which is not shown here for clarity.

The cores and moldings of the mold 2 are made in a conventional manner in a cold box process from a conventional molding material, which is a mixture of a commercially available core sand, an equally commercial organic binder and optionally added additives, for example, the better Wetting of the grains of the core sand by the binder serve. From the molding material, the cores and moldings of the mold 2 are formed. Subsequently, the obtained cores and moldings are gassed with a reaction gas to cure the binder by a chemical reaction and thereby giving the cores and moldings the necessary stiffness.

The screen plate 1 is supported with its edge on a peripheral edge shoulder 4 of a collecting container 5. In the circumferential footprint of the edge paragraph 4, a sealing element 6 is incorporated.

After the casting mold 2 is positioned on the sieve plate 1, an enclosure 7, which likewise belongs to the thermoreactor T, is placed on the peripheral edge shoulder 4 of the collecting container 5. The housing 7 is formed in the manner of a hood and encases the mold 2 at its outer peripheral surfaces 8. In this case, the circumference of the space enclosed by the housing 7 an excess of the circumference of the mold 2, so that after placing the housing 7 on the sieve bottom 1 between the outer peripheral surface of the mold 2 and the inner surface 9 of the housing 7, a filling space 10 is formed. With their collection container 5 associated edge of the enclosure sits on the sealing element 6, so that here a tight closure of the filling space 10 is ensured with respect to the environment U. The enclosure consists of a thermally insulating material, which may consist of several layers, of which one layer ensures the necessary dimensional stability of the enclosure 7 and another layer thermal insulation. At its upper side, the housing 7 delimits a large opening 11, via which the casting mold 2 can be filled with iron casting melt and the filling space 10 with filling material F ( Fig. 3 ).

For filling the filling space 10 with a granular material designed as granular and tempered to a temperature Tmin of at least 500 ° C contents F a reservoir V is positioned over the opening 11, from which then the hot medium F via a distribution system 12 into the filling space 10th trickle down ( Fig. 4 ).

When the filling process is completed, the filled in the filling space 10 filling package can be compacted if necessary. Subsequently, a lid 13 is placed on the opening 11, which also has an opening 14 through which the molten cast iron can be filled into the mold 2 ( Fig. 5 ).

The cast iron melt is then poured into the casting mold 2 (FIG. Fig. 6 ).

Meanwhile, oxygen-containing ambient air may enter the filling space 10 via a gas inlet 15 formed in the lower edge region of the housing 7. Likewise, ambient air, which passes through an access 16 in the collecting container 5, sucked through the sieve bottom 1 in the filling space 10 ( Fig. 7 ).

The deliberate destruction of the casting mold 2, which starts with casting of the iron casting melt, and the associated demolding of the casting G takes place in two phases.

In the first phase, solvent contained in the binder evaporates. The emerging from the mold 2 vaporous solvent reaches in the filling chamber 10, a concentration at which it ignites and burns off automatically. Due to the heat released in the process, the granular product F, which has been brought to a temperature Tmin of about 500 ° C., is heated above the limit temperature TGrenz of 700 ° C. until its temperature reaches the maximum temperature Tmax of approximately 900 ° C.

If the concentration of the binder constituents evaporating from the casting mold 2 is no longer sufficient for independent combustion, the product heated in this way assumes the function of a heat accumulator, through which the temperature of the casting mold 2 and in the filling chamber 10 are at a temperature above 700 ° C. Level is maintained. In this way, the combustion of leaving the mold 2 Binder components and other potential pollutants stops until no more binder from the mold 2 evaporates. The then possibly still emerging from the mold 2 vaporous substances are oxidized by the prevailing in the filling chamber 10 high temperature or rendered harmless in any other way.

Likewise contribute to the completeness of the combustion of passing from the mold 2 gases, the oxygen-containing, formed from ambient air gas streams S1, S2, which pass through the gas inlet 15 and the sieve bottom 1 in the filling chamber 10 of the housing 7.

Since the bulk density of the product F is so low that even after compression a good gas permeability ensured in the filling chamber 10 filling material package is a good mixing of the emerging from the mold 2 gases with the oxygen for its combustion-providing gas streams S1, S2 guaranteed. At the same time, the filling material pack in the filling space 10 supports the casting mold 2 at its peripheral surfaces and thus prevents the iron casting melt from breaking through.

The flow through the gases emerging from the casting mold 2 through the filling material F causes a good mixing with the supplied gas flow S1, S2, a longer residence time and a good reactivity. The casting mold 2 is thus heated both by the combustion of the binder system and the heat introduced by the metal poured into the casting mold 2, as well as by the preheated filling F. As a result, the binding parts and cores of the mold 2 cohesive binder system is almost completely destroyed. The moldings and cores then break up into fragments B or individual grains of sand.

The fragments B and the loose sand fall through the sieve tray 1 in the sump 5 and is collected there. Depending on the progress of the destruction of the casting mold 2, the sieve bottom 1 can be opened in such a way that also contents F reach the collecting container 5 ( Fig. 8 ).

For optimal combustion of outgassing from the mold 2 gases and for the regeneration of the core sand already in the enclosure are the Temperatures of product F and the gases flowing in the filling chamber 10 optimally each well above 700 ° C. The conditions in the thermoreactor T are designed in such a way that the regeneration process and the exhaust gas treatment are independent of system availability. Determining and set sizes are the starting temperature of the filler F, the oxygen-containing gas streams S1, S2 flowing in via the gas inlet 15 and the inlet 16 and the casting mold 2 itself.

The progress of the destruction of the casting mold 2 and the solidification course of the cast iron melt poured into the casting mold 2 are adapted to each other so that the casting G is sufficiently solidified when the disintegration of the casting mold 2 begins.

After the casting mold 2 has essentially completely disintegrated, the collecting container 5 with the molding material / product mixture contained in it is separated from the sieve bottom 1 and the housing 7 likewise removed from the sieve bottom 1. The largely sanded casting G is now freely accessible and can be cooled in a controlled tunnel-like space 17 controlled ( Fig. 10 ). Due to the process, the casting G has a high picking temperature at which the austenite transformation is not yet completed and rapid cooling would lead to residual stresses and thus to cracks. For this reason, the casting G is cooled in a cooling tunnel 17 slowly according to the glow curves during stress relief annealing. The supplied cooling air is measured so that the cooling profile is achieved product specific.

The still contained in the container 5, still hot mixture of filling F, core sand and fragments B is in a grinder 18, which may be, for example, a rotary tube, mixed intensively and mixed with sufficient oxidation air, so that possibly still existing binder residues afterburn. In this process step, the contents F of core sand can be separated and both fed to a separate cooling. Such post-regeneration ensures the safe maintenance of complete combustion of the binder system and additionally prepares by mechanical friction, the core sand surface for a good adhesion of the binder for reuse as core sand.

The resulting core sand is cooled down to near room temperature and, after fractionation, recycled to casting moldings or casting cores for a new casting mold 2.

The contents F, however, cooled to the intended start temperature Tmin and filled in the circuit for re-filling of the filling chamber 10 in the reservoir V.

The amount of combustion gas conducted into the filling chamber 10 as gas streams S1, S2 is regulated by means of mechanically adjustable flaps or slides, with which the opening cross-sections of the gas inlet 15 and of the access 16 can be adjusted. The respective setting can first be determined via the stoichiometrically required air quantity for combustion of the binder system and then finely adjusted via measurements of CO, NO x and O 2 at the exhaust outlet 19 formed here through the opening 14 of the cover 13, which is molded into the cover 13 and over the resulting in the filling chamber 10 exhaust gases are discharged from the enclosure 7.

How out Fig. 16 shows, in the filling chamber 10 immediately after the casting by the evaporation of the solvent from the binder system of the mold 2 and the other fumes of the mold 2 a high pollutant concentration represented by the curve KSchadstoff achieved, which would burn even at room temperatures independently. The boundary KGrenz, from which at room temperature a pollutant concentration is reached that is combustible, is in Fig. 16 indicated by the dashed line. Because of the high minimum temperature Tmin of 500 ° C, which prevails in the filling chamber 10 through the introduced there hot filling F, the combustion of the reaching into the filling chamber 10 from the mold 2 but already at a much lower concentration (s. Fig. 16 ).

Due to the combustion within the granulate in phase 1, the granules heat up and its temperature TFüllgut exceeds after a short time the limit temperature TGrenz of 700 ° C, in the organic substances known to be sufficient oxygen content oxidize independently and thus burn. The course of temperature TFüllgut is in Fig. 16 shown as a dashed line.

This phase ("phase 1") intensive combustion of the evaporating from the mold 2 binder continues until the concentration KSchadstoff of reaching into the filling chamber 10 from the mold 2, essentially formed by the vaporizing binder combustible gases decreases so much that at Room temperature no combustion would take place.

Due to the high product temperature of more than 700 ° C, as described above, this oxidation or combustion in the subsequent phase 2 is still continued, the heat released is sufficient to increase the temperature of the medium 10 further until the maximum temperature Tmax is reached. At this temperature, the filling material 10 remains until the decomposition process of the casting mold 2 has progressed so far that no appreciable outgassing take place, the casting mold 2 disintegrates in small parts and the molding material residues fall into the container 5. However, as long as combustion processes take place in the filling chamber 10, so much heat is still generated that the filling material F remains in a range over a sufficiently long period of time, whose upper limit is the temperature Tmax and whose lower limit is the temperature limit.

According to the invention is thus by the choice of the temperature at which the filling material is filled in the filling chamber 10, the time at which the limit temperature TGrenz of 700 ° C is exceeded, so determined that this is reached before by low pollutant concentrations KSchadstoff the process of combustion in the filling space 10 is no longer reliably takes place with the necessary intensity. The then highly heated filling material F then ensures that the decomposition and residual combustion of the gases still evaporating from the casting mold 2 takes place, even if the concentration of combustible gases present in the filling space would be too low at temperatures below the temperature limit.

It could be proven that with the evaporating and combustible substances contained in the casting mold 2 so much chemical energy is available for a combustion that product temperatures of well over 1000 ° C could be reached. In this case, however, the cooling of the casting would be delayed much longer, so that long residence times would be necessary. This can also be determined by the starting temperature at which the filling material F is filled into the filling space 10. Likewise, an excessive increase in temperature can be prevented by increasing the then acting as cooling air gas streams S1, S2.

When choosing the filling material F, which is, for example, ceramic filling body, care is taken that the individual grains of the filling material F have a high compressive strength in order to absorb the pressure forces during casting and to keep the abrasion loss as low as possible in circulation. Another selection criterion is a low heat capacity in Combination with the bulk density of the product F to get a temperature rise above the 700 ° C as quickly as possible from phase 1. Due to the oxidation in the bulk material, with adapted combustion air supply and relatively low temperature, a nitrogen oxide formation is largely avoided.

Since the outgoing exhaust gases according to the invention substantially heat up the Füllgutschüttung even in the first phase, there is a temperature profile within the bed, which ensures clean combustion. The combustion air follows due to the resulting in the filling chamber 10 Wärmekonvektionsströmung a vertical upward direction and the outgassing of the pollutants from the mold 2 due to the strong vapor formation in the first phase of a horizontal direction in the package inside. By crossing the gas streams within the product F good mixing is ensured.

In the region above the casting mold 2, the gas streams are then rectified and can sufficiently afterburn in the hottest region of the exhaust system in the combustion chamber between the lid 13 and filling F before exiting the exhaust outlet 19 above the sprue.

In an example calculation, on the basis of the parameters and material values given in Table 1 for a process according to the invention, the thermal energy Qa released by the cooling of the melt and the combustion of the binder as well as for the heating of the contents and the heating of the core sand of the mold required heat energy Qb has been determined.

It was assumed that a cast iron melt is poured into a mold as a melt, the moldings and cores are made in the conventional cold box process of molding material, which consists of conventional core sand, d. H. made of quartz sand, and for this purpose just as common binder.

Simplifying it has also been assumed that the casting metal gives off its heat to the casting mold and the filling material after casting and that also the binder used to internal chemical energy in the form of heat of combustion is completely available for heating the filling material.

somit im vorliegenden Beispiel zu $$\mathrm{Hfus}=170\mathrm{kg}\times 96\mathrm{kJ}/\mathrm{kg}\times 1/1000\mathrm{MJ}/\mathrm{kJ}=\mathrm{16,3}\mathrm{MJ}.$$

The melt heat Hfus dissipated to solidify the melt is then calculated according to the formula $$\mathrm{HFUS}={\mathrm{m}}_{\mathrm{melt}}\times \mathrm{HFUS}\times 1/1000\mathrm{MJ}/\mathrm{kJ}$$

thus in the present example too $$\mathrm{HFUS}=170\mathrm{kg}\times 96\mathrm{kJ}/\mathrm{kg}\times 1/1000\mathrm{MJ}/\mathrm{kJ}=16.3\mathrm{MJ},$$

im vorliegenden Beispiel mit $$\mathrm{\Delta }\mathrm{T}=\left(\mathrm{T}1-\mathrm{T}2\right)=\left(850\mathrm{K}-1500\mathrm{K}\right)=-650\mathrm{K}\mathrm{zu}$$

$$\mathrm{Qa}1=950\mathrm{J}/\mathrm{kgK}\times -650\mathrm{K}\times \mathrm{170kg}\times 1/1000\mathrm{MJ}/\mathrm{kJ}-\mathrm{16,3}\mathrm{MJ}$$

$$\mathrm{Qa}1=-121\mathrm{MJ}.$$

The heat energy Qa1 released from the melt as it cools is then calculated according to the formula $$\mathrm{Qa}$$$$1=\mathrm{cp}\times \mathrm{\Delta }\mathrm{T}\times \mathrm{m}\times 1/1000\mathrm{MJ}/\mathrm{kJ}-\mathrm{HFUS}$$

in the present example with $$\mathrm{\Delta }\mathrm{T}=\left(\mathrm{T}1-\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">T</figure-callout>}2\right)=\left(850\mathrm{K}-1500\mathrm{K}\right)=-650\mathrm{K}\mathrm{to}$$

$$\mathrm{<figure-callout\; id="1"\; label="Qa"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">Qa</figure-callout>}1=950\mathrm{J}/\mathrm{kgK}\times -650\mathrm{K}\times \mathrm{170kg}\times 1/1000\mathrm{MJ}/\mathrm{kJ}-16.3\mathrm{<figure-callout\; id="1"\; label="MJ\; Qa"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">MJ\; </figure-callout>}$$

$$\mathrm{Qa}$$$$1=-121\mathrm{MJ},$$

zu $$\mathrm{Qa}2=30\mathrm{MJ}/\mathrm{kg}\times 4\mathrm{kg}\times \left(-1\right)=-120\mathrm{MJ}\mathrm{.}$$

In a corresponding calculation results from the combustion of the binder contained in the molding material released heat energy Qa2 according to the formula $$\mathrm{Qa}$$$$2=\mathrm{Hi}\times {\mathrm{m}}_{\mathrm{binder}}\times \left(-1\right)$$

to $$\mathrm{<figure-callout\; id="2"\; label="Qa"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">Qa</figure-callout>}2=30\mathrm{MJ}/\mathrm{kg}\times 4\mathrm{kg}\times \left(-1\right)=-120\mathrm{MJ}\mathrm{,}$$

The sum of the released heat energy Qa = Qa1 + Qa2 is then -241MJ.

zu $$\mathrm{Qb}1=835\mathrm{J}/\mathrm{kgK}\times \left(800\mathrm{K}-20\mathrm{K}\right)\times 255\mathrm{kg}=166\left[\mathrm{MJ}\right].$$

The thermal energy Qb1 required for heating the core sand of the casting mold from the temperature T1 to the temperature T2 is calculated according to the formula $$\mathrm{Qb}$$$$1={\mathrm{cp}}_{\mathrm{core\; sand}}\times \left(\mathrm{T}2-\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">T</figure-callout>}1\right)\times {\mathrm{m}}_{\mathrm{core\; sand}}$$

to $$\mathrm{<figure-callout\; id="1"\; label="Qb"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">Qb</figure-callout>}1=835\mathrm{J}/\mathrm{kgK}\times \left(800\mathrm{K}-20\mathrm{K}\right)\times 255\mathrm{kg}=166\left[\mathrm{MJ}\right],$$

zu $$\mathrm{Qb}2=754\mathrm{J}/\mathrm{kgK}\times \left(800\mathrm{K}-500\mathrm{K}\right)\times 125\mathrm{kg}=28\left[\mathrm{MJ}\right].$$

Likewise, the heat energy Qb2 required for heating the core sand of the mold from the temperature T1 to the temperature T2 is calculated according to the formula $$\mathrm{Qb}$$$$2={\mathrm{cp}}_{\mathrm{filling}}\times \left(\mathrm{T}2-\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="imgf0002.png,imgf0004.png"\; state="\{\{state\}\}">T</figure-callout>}1\right)\times {\mathrm{m}}_{\mathrm{filling}}$$

to $$\mathrm{<figure-callout\; id="2"\; label="Qb"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">Qb</figure-callout>}2=754\mathrm{J}/\mathrm{kgK}\times \left(800\mathrm{K}-500\mathrm{K}\right)\times 125\mathrm{kg}=28\left[\mathrm{MJ}\right],$$

The heat requirement Qb = Qb1 + Qb2 required for heating the core sand of the casting mold, which is still initially at room temperature of 20 ° C., and the filling material filled with the temperature T1 of 500 ° C. to the final temperature T2 of 800 ° C. then amounts to a total $$\mathrm{Qb}=166\mathrm{MJ}+28\mathrm{MJ}=194\mathrm{MJ},$$

According to the parameters given in Table 1, as a result of the heat input through the melt and the combustion of the binder emerging from the casting mold, there is an energy surplus of 47 MJ available for heating the filling material F and compensating for tolerances and losses.

The determination given in Table 1 of an energy balance achievable when casting a gray cast iron molten metal casting shows that there is a significant excess capacity of thermal energy when conventional moldings are produced on the basis of a conventional binder system and using quartz sand. The supplied oxygen-containing gas streams S1, S2 are neglected in this consideration, since their influence is energetically very low.

Table 2 shows the bulk densities Sd, the specific heat capacities cp and the product P = Sd x cp for different bulk materials, which in principle would be suitable for use as filling material in terms of their temperature resistance. It turns out that, for example, steel gravel has a significantly lower specific heat capacity cp than a ceramic granulate of the type mentioned here, but has a much too high bulk density in order to ensure the gas permeability of the invention provided for in the filling space around the mold Füllgutpackung.

REFERENCE NUMBERS

1

sieve plate

2

mold

3

mold cavity

4

circumferential heel

5

Clippings

6

sealing element

7

Enclosure (housing)

8th

Peripheral surfaces of the mold 2

9

Inner surface of the enclosure 7

10

filling space

11

Opening of the enclosure

12

distribution system

13

cover

14

Opening the lid 13

15

gas inlet

16

Access

17

cooling tunnel

18

grinder

19

exhaust outlet

B

fragments

F

filling

G

casting

S1, S2

oxygen-containing gas streams

T

thermoreactor

U

Surroundings

V

reservoir

Table 1 Material value / parameter filling core sand cast metal binder unit ceramic granules quartz sand cast iron Cold box binder melting enthalpy HFUS 96 kJ / kg Heat capacity at 800 ° C cp 754 835 950 J / kg / K calorific value Hi 30 MJ / kg Dimensions m 125 255 170 4 kg inlet temperature T1 500 20 1500 ° C outlet temperature T2 800 800 850 ° C Table 2 filling Bulk density SD [kg / dm ³ ] Specific heat capacity cp [J / kgK] P = Sd x cp ceramics 0.61 754 460 steel shot 4.20 470 1974 quartz sand 1.40 835 1169

Claims (14)

1. Method for casting cast parts (G), in which a molten metal is poured into a casting mould which encloses a cavity (3) forming the cast part which is to be produced, wherein the casting mould (2), designed as a lost mould, consists of one or more casting mould parts or cores which are formed of a mould material which consists of a core sand, a binder and, optionally, one or more additives for adjusting particular properties of the mould material, comprising the following working steps:

   - provision of the casting mould (2);

   - enclosure of the casting mould (2) in a housing (7) forming a filling space (10) between at least one inner surface section (9) of the housing (7) and an associated outer surface section (8) of the casting mould (2);

   - filling the filling space (10) with a free-flowing filling material (F);

   - pouring the molten metal into the casting mould (2),

   - wherein, as a result of the pouring of the molten metal, the casting mould (2) begins to radiate heat, the consequence of the input of heat caused by the hot molten metal, and

   - wherein, as a consequence of the input of heat caused by the molten metal, the binder of the mould material begins to vaporise and combust, so that it loses its effect and the casting mould (2) disintegrates into fragments (B);

   characterised in that
   the filling material (F) poured into the filling space (10) has such a low bulk density that the filling material packing formed by the filling material (F) following filling of the filling space (10) can be permeated by a gas flow (S1, S2) and that, on filling the filling space (10), the filling material (F) has a minimum temperature (Tmin) to at least 500°C starting out from which the temperature of the filling material (F) rises as a result of process heat which is generated through the heat radiated from the casting mould (2) and through the heat released during the combustion of the binder, to above a boundary temperature (Tbound) at which the binder evaporating from the casting mould (2) and coming into contact with the filling material (F) ignites and begins to combust.
2. Method according to claim 1, characterised in that the product P of bulk density Sd and specific heat capacity cp amounts to a maximum of 1 kJ/dm³K.
3. Method according to one of the preceding claims, characterised in that the bulk density Sd amounts to a maximum of 4 kg/dm³.
4. Method according to one of the preceding claims, characterised in that the filling material (F) possesses a specific heat capacity cp of max. 1 kJ/kgK.
5. Method according to one of the preceding claims, characterised in that the filling material (F) is formed of granules with an average diameter of 1.5 - 100 mm.
6. Method according to one of the preceding claims, characterised in that the boundary temperature (Tbound) amounts to 700°C.
7. Method according to one of the preceding claims, characterised in that the enclosure has a gas inlet (15) and an exhaust gas outlet (19) and that the filling material (F) contained in the filling space (10) is, at least at times and in certain sections, flowed through by an oxygen-containing gas flow (S1, S2).
8. Method according to claim 6, characterised in that the gas flow (S1, S2) is heated to a temperature above room temperature.
9. Method according to one of the claims 6 to 8, characterised in that the gas flow (S1, S2) is regulated depending on the exhaust gas volume flow issuing from the exhaust gas outlet (19).
10. Method according to one of the claims 6 to 9, characterised in that an exhaust gas measurement is carried out at the exhaust gas outlet (19) and that the gas flow (S1, S2) is regulated depending on the result of this measurement.
11. Method according to one of the claims 6 to 10, characterised in that a partial flow of the combustion gases issuing from the exhaust gas outlet (19) is mixed with the oxygen-containing gas flow (S1, S2) and the resulting mixture is fed into the housing (7).
12. Method according to one of the preceding claims, characterised in that the housing (7) is equipped with a catalytic converter for decomposing the toxic substances contained in the combustion products of the binder.
13. Method according to one of the preceding claims, characterised in that the casting mould (2) is placed on a sieve base (1), and that the fragments (B) of the casting mould (2) and the filling material (F) trickle together through the sieve base (1), are collected and processed together and are separated from one another following processing.
14. Method according to one of the preceding claims, characterised in that, following disintegration of the casting mould (2), the cast part (G) passes through a heat treatment during which it is cooled in a controlled manner according to a specified cooling curve.

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