EP3597329B1 - Method for casting castings - Google Patents

Description

The invention relates to a method for casting castings, in which a molten metal is poured into a casting mold which encloses a cavity forming the casting to be produced, the casting mold being a lost mold consisting of one or more casting mold parts or cores. The casting 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 to adjust certain properties of the molding material.

In conventional processes of this type, the casting mold that forms the casting is usually first provided, the casting cores and moldings of which have been prefabricated in separate operations. The casting mold can be composed of a large number of casting cores as a so-called “core package”. It is also possible to use casting molds which, for example, are composed of only two mold halves, each made of molding material, into which the mold cavity forming the casting is formed, whereby mold cores can also be present here in order to form recesses, cavities, channels and the like in the casting .

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

In the field of iron casting, quartz sand mixed with bentonite, lustrous carbon formers and water are usually used as the molding material for the mold parts that form the outer end of the mold. The casting cores that form the internal cavities and channels of the casting, on the other hand, are usually formed from commercially available core sands that are coated with an organic or inorganic binder, e.g. B. mixed with a synthetic resin or water glass.

Regardless of the type of core sand and binder, the basic principle in the production of molds made from molding materials of the type mentioned above is that after shaping the binder is hardened by a suitable thermal or chemical treatment so that the grains of the core sand stick together and The dimensional stability of the respective molded part or core is guaranteed over a sufficient period of time.

Especially when casting large-volume cast iron parts, the internal pressure on the mold after the molten metal has been poured can be very high. In order to absorb this pressure and reliably avoid the mold from bursting, either thick-walled, Large-volume molds or support structures are used that support the mold on its outside.

One possibility for such a support structure is an enclosure that is placed over the mold. The housing is usually designed in the manner of a jacket that surrounds the mold on its peripheral sides, but has a sufficiently large opening on its top to enable the melt to be poured into the mold. The enclosure is dimensioned such that after placement, a filling space remains at least in the sections crucial for supporting the casting mold between the inner surfaces of the enclosure and the outer surfaces of the casting mold. This filling space is filled with a free-flowing filling material, so that large-area support of the respective surface section on the housing is guaranteed. In order to achieve the most uniform possible filling of the filling space, an equally uniform contact of the casting mold with the filling material and a correspondingly uniform support of the fragile casting mold material, fine-grained, free-flowing filling materials, such as sand or steel gravel, are generally used as filling material, which have a high Have bulk density. After filling, the filling material is additionally compacted. The aim here is to create the most compact filling compound possible, which ensures the direct transfer of the supporting forces from the enclosure to the casting mold in the manner of an incompressible monolith.

The molten metal is poured into the casting mold at high temperature, so that the casting mold parts and cores from which the casting mold is composed are also 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, releasing further heat. This causes the binder to lose its effectiveness. As a result of this decomposition of the binder, the binding of the grains of the molding material from which the casting mold parts and cores of the casting mold are made is lost and the casting mold or its parts and cores made of molding material break up into individual fragments.

It is known from practice that this effect can be used to remove the casting from the respective mold. For example, from the EP 0 546 210 B2 or the EP 0 612 276 B2 Heat treatment processes for castings are known, in which the casting mold with the castings enters a heat treatment furnace in a continuous process from the casting heat. When passing through the furnace, the mold and the castings will be exposed to a temperature for a sufficiently long period of time at which the condition of the casting desired through the heat treatment will be achieved. At the same time, the temperature of the heat treatment is selected so that the binder of the molding material decomposes. The fragments of the casting mold, which then automatically fall off the casting and are made of molding material, are still in the heat treatment furnace Sand bed collected. They remain there for a certain period of time in order to further promote the disintegration of the fragments of the mold parts and cores. The comminution of the mold material fragments falling from the mold can be supported by fluidizing the sand bed by blowing in a hot gas stream. The sufficiently crushed molding material fragments are finally sent to a processing facility in which the core sand is recovered so that it can be used for the production of new casting mold parts and cores.

The well-known procedure for demolding and preparing the molds required for casting cast parts has proven successful in practice when casting parts for internal combustion engines made of aluminum in large numbers. However, it requires an oven of considerable length and handling of the molds and castings, which proves to be complex with large-volume parts or molds that require additional support through an enclosure of the type described above. This applies in particular to those castings that are to be produced in small and medium quantities from cast iron.

The WO 01/08836 A1 relates to a method for removing a sand core from a casting and heat treating the casting.

Against this background, the object of the invention was to provide a method which is optimized Energy efficiency and in a particularly economical way enables the production of cast parts using casting technology.

The invention has solved this problem by the method specified in claim 1.

Advantageous embodiments of the invention are specified in the dependent claims and are explained in detail below, as is the general idea of the invention.

The invention therefore provides a method for casting castings, in which a molten metal is poured into a casting mold which encloses a cavity that forms the casting to be produced. The mold is designed as a lost mold, which is composed of one or more mold parts or cores. These mold parts are each formed from a molding material which consists of a core sand, a binder and optionally one or more additives to adjust 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 includes the following work steps:

• Providing the mold;
• Housing the mold in a housing to form a filling space between at least one 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 mold,
• wherein the casting mold begins to radiate heat as the molten metal is poured in, which is the result of the heat input caused by the hot molten metal, and
• 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 mold falls into fragments.

According to the invention, the filling material filled into the filling space now has such a low bulk density that a gas flow can flow through the filling material pack formed there from the filling material after the filling space has been filled.

In addition, in the method according to the invention, the filling material has a minimum temperature when filling the filling space, starting from which the temperature of the filling material is formed by process heat, which is formed by the heat radiated by the casting mold and by the heat released during the combustion of the binder, up to above one Limit temperature of 700 °C rises.

The method according to the invention is therefore based on the idea of using the filling material in the sense of a heat storage and of tempering and designing this heat storage in such a way that the decomposition of the binder of the molding material from which the casting mold parts and cores of the casting mold are made is already during the Residence time in the enclosure is largely decomposed by the effects of temperature.

In this way it is achieved that the parts and cores of the mold made of molding material are as far in Fragments disintegrate are that these fragments fall off the casting and the casting is largely free of adhering molded parts or cores, at least in the area of its outer surfaces, after the enclosure has been removed.

At the same time, the cores, which form channels or cavities inside the casting, have also disintegrated at this point, so that the core sand and the molding material fragments of these cores either automatically trickle out of the casting in the enclosure or in a manner known per se, for example by mechanical methods , such as shaking, or by rinsing with a suitable fluid, can be removed from the casting.

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

What is crucial here is that, according to the invention, the filling material has a bulk density that is so low that a gas flow can still flow through it even after the filling space has been filled and the filling material filled into the filling space has been compressed if necessary. According to the invention, in contrast to the above-mentioned prior art, a highly compressed packing is expressly not produced in the filling space, which, although it ensures optimal support of the casting mold, is largely impermeable to gas. Rather, the filling material used according to the invention should be selected so that it is suitable for a Gas flow is permeable, which occurs, for example, as a result of thermal convection. This occurs when the casting mold is heated by the molten metal poured into it and the evaporating binder components of the molding material of the casting mold parts and cores begin to evaporate and burn, releasing heat.

When we talk about an evaporating and burning binder, we always mean those binder components that become vaporous and combustible when heat is applied. This does not rule out the possibility that other binder components remain in the mold in solid or other form, for example as cracking products, and are also optimally decomposed there by the influence of heat.

The ability to flow through the filling material filled into the filling space with a gas stream, which is to be provided according to the invention, not only creates the possibility that the binder evaporating from the mold burns in the area of the filling material itself and thereby further heats the filling material, but also allows the supply of oxygen, which Combustion of the binder is supported. In this way, the filling material is heated by the process heat supplied via the molten metal and released by the combustion of the binder to a temperature that is so high that the binder portions of the molded parts and cores that come into contact with the filling material and emerge from the mold burn or at least thermally decomposed in such a way that they no longer have a damaging effect on the environment or can be removed from the enclosure as exhaust gas and fed to an exhaust gas purification system.

The filling material pre-tempered according to the invention is preferably introduced into the filling space at a short time interval before the metal melt is poured in order to minimize temperature losses.

After a sufficient concentration of combustible outgassing from the molding material has been reached in the filling space, combustion begins through contact with the heated filling material. The combustion of the binder emerging from the mold continues and the filling material continues to be tempered for as long. This process continues until only small amounts of binder emerge from the mold that a combustible atmosphere no longer forms in the enclosure. However, the hot filling material now maintains a temperature above the limit temperature at which combustion of the binder occurs, in the manner of a heat accumulator. The casting mold accordingly remains at least at this temperature, so that any binder residues remaining in the casting mold are thermally decomposed.

Particularly suitable for the method according to the invention are casting molds whose molded parts and cores consist of molding material that is bound by an organic binder. For example, commercially available solvent-containing binders or binders whose effect is triggered by a chemical reaction come into consideration for this. Corresponding binder systems are now used in the so-called “cold box process”.

In practice, a temperature of 700 °C is suitable as a limit temperature, particularly when processing iron casting melts. Burn especially at temperatures above 700 °C organic binders safe. At the same time, at these temperatures, other pollutants that emerge from the mold are oxidized or rendered harmless in some other way. The same applies to the crack products that form in the mold as a result of the temperature-related disintegration of the binder, which also decompose safely at such high temperatures.

By filling the filling material into the filling space preheated to a certain temperature, according to the invention, it is achieved that the filling material heats up to a temperature above the limit temperature as a result of the process heat supplied. Practical tests have shown that a temperature of 500 °C is sufficient as the minimum temperature of the filling material when filling it into the filling chamber.

Accompanied by the escape, combustion and decomposition of the binder, the parts and cores of the mold formed from molding material break down into loose fragments, which can either be disposed of after the enclosure has been removed and sent for processing or, advantageously, already during the period between After pouring out the molten metal and removing the enclosure, the time spent in the enclosure can be deducted. For this purpose, the mold can be placed on a sieve base and the fragments of the mold that trickle through the sieve base can be collected. Practically, the openings of the sieve base are designed so that the fragments of the mold and the filling material trickle together through the sieve base, are collected, processed and separated from each other after processing. This has the The advantage is that there is no longer any loose filling material in the enclosure when the enclosure is removed.

The enclosure of the mold can accordingly be provided by a jacket that surrounds the mold with a distance sufficient to form the filling space and is made of a thermally insulating and sufficiently dimensionally stable material, a perforated support plate that acts as a sieve plate on which the mold is placed, and a likewise thermal be formed with an insulating lid, which is placed after the mold has been filled. In order to enable a controlled removal of the exhaust gases that form in the filling space, an exhaust gas opening can also be provided.

In the method according to the invention, the filling material filled into the filling space can also be compacted in order to create a preload between the casting mold and the housing, which ensures a secure, precisely positioned cohesion of the casting mold even if the casting mold consists of a large number of molded parts and Core package composed of cores is formed. As mentioned, however, due to the low bulk density, the ability of a gas stream to flow through is ensured even with such a compacted filling material.

The effectiveness of the destruction of the molded parts and cores of the casting mold achieved according to the invention can be further increased by designing not only the filling material but also the casting mold itself so that gas can flow through it. For this purpose, channels can be specifically introduced into the mold through which the hot exhaust gas that forms in the filling space or accordingly preheated oxygen-containing gas flows. In this way, rapid evaporation, burning and other thermal decomposition of the molding material binder also occurs within the mold. This further accelerates the disintegration of the mold.

Channels specifically introduced into the casting mold can also be used to accelerate the 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 the case of a filling material according to the invention, after compaction, the prestress is transmitted through the grains of the filling material that come into contact with one another. In order to prevent the grains of the filling material from shifting uncontrollably despite the gas permeability of the filling material required according to the invention, the housing can be equipped with a structured surface on its inner surface assigned to the casting mold, on which the grains abutting against this surface are supported in a form-fitting manner at least in places .

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

Filling material that is optimally suitable for the purposes according to the invention thus combines a low bulk density with a low specific heat capacity, the material from which the individual parts that form the filling material are made.

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

Regardless of whether compaction is carried out, granules or other granular bulk materials have proven to be suitable 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 , are particularly suitable for the purposes according to the invention.

If a granular, pourable and free-flowing filling material is used, it has proven to be advantageous in practical tests if the average diameter of the grains is 1.5 - 100 mm, with optimally filling material being used whose grain sizes are in the range of 1.5 - 40 mm.

Filling material that consists of materials with a specific heat capacity of max. 1 kJ/kgK, ideally less than 0.5 kJ/kgK, shows optimal heating and heat storage behavior for the invention.

In principle, all thermally resilient bulk materials that meet the above-mentioned conditions and are sufficiently temperature-resistant are suitable as filling material. Non-metallic bulk materials, such as granules made of ceramic materials, are particularly suitable for this. These can be irregularly shaped, spherical or with cavities be provided in order to achieve good gassing of the filling material filled into the filling space while at the same time having low heat storage properties. The filling material can also consist of ring-shaped or polygonal elements, which only touch each other at points when they come into contact with each other, so that sufficient space remains between them to ensure good flow.

In order to avoid the oxygen-containing gas stream, which is optionally passed into the housing via a gas inlet, causing the filling material to cool down, 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 filling material. For example, the hot exhaust gas that is withdrawn from the enclosure can be used to heat the gas stream. A heat exchanger known per se can be used for this purpose. If a sieve base is provided, through which the fragments of the mold can possibly escape from the enclosure together with the filling material, the oxygen-containing gas stream can also be guided through this sieve base. This not only has the advantage of a large-area introduction, but also means that the supplied gas stream is heated through contact with the hot molding material fragments trickling out of the housing and the equally hot filling material.

Alternatively or additionally, it is also conceivable to mix a partial stream of the exhaust gas stream with the oxygen-containing gas stream and to return the hot gas mixture thus obtained into the filling space. In this regard, it may make sense that The oxygen-containing gas stream fed into the filling space consists of 10 - 90% by volume of exhaust gas.

The oxygen-containing gas stream supplied to the filling space can 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 designed 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 stream into the filling space at a certain pressure using a blower or the like.

An optional regulation of the gas flow introduced into the filling space can be carried out depending on the exhaust gas volume flow emerging from the enclosure in order to avoid the creation of excess pressure in the atmosphere prevailing in the filling space. For this purpose, the respective gas inlet can be equipped with a mechanism that regulates the supply air depending on the flow speed. A suitable pendulum flap, for example, is suitable for this purpose and is suspended and loaded in such a way that the flow pressure of the gas flow passing through it automatically regulates the flow speed and thus the combustion air supply depending on counterweights.

It is also conceivable to carry out an exhaust gas measurement at the exhaust gas outlet and to regulate the oxygen-containing gas flow depending on the result of this measurement in order to ensure complete combustion of the binder and the others to ensure possible gases escaping from the mold in the filling space.

A minimization of pollutant emissions can also be achieved in the method according to the invention by equipping the enclosure with a catalyst device for decomposing pollutants contained in the combustion products of the binder.

The casting exposed after demolding according to the invention can, after the mold has disintegrated, undergo a heat treatment in which it is cooled in a controlled manner in a manner known per se in accordance with a specific cooling curve in order to produce a specific state of the casting.

Of course, with the procedure according to the invention, several casting molds can be accommodated together in one housing and these casting molds can be filled with molten metal in parallel or in close succession.

In principle, the method according to the invention is suitable for any type of metallic casting materials, the processing of which generates sufficiently high process heat. The method according to the invention is particularly suitable for producing cast parts from cast iron because, due to the high temperature of the iron casting melt, the temperatures intended for the combustion of the binder according to the invention can be achieved particularly reliably. In particular, in accordance with the invention Process GJL, GJS and GJV cast iron materials as well as cast steel.

If it is said here that the casting mold used according to the invention consists of molded parts or cores that are formed from molding material, this of course includes the possibility of producing individual parts, such as cooling chills, supports and the like, from other materials within such a mold . The only decisive factor is that the casting mold contains so much molding material volume that binder evaporates during the pouring of the respective molten metal, which then burns in the filling space and heats the filling material to such an extent that it has a largely complete decomposition of the binder Molding material maintains a temperature above the limit temperature for a sufficient period of time.

The exhaust gas stream emerging from the enclosure provided according to the invention can be cleaned by post-burning the combustible substances still present in the exhaust gas in an exhaust air combustion system. The heat released can in turn be used to preheat the oxygen-containing gas stream fed into the enclosure.

If castings are produced in the manner according to the invention with several casting molds according to the invention parallel to one another, it may be expedient if the casting molds with the housings assigned to them stand together in a tunnel or the like the resulting exhaust gases are discharged via a common exhaust pipe.

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

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

The regenerated sand obtained after processing can be mixed with new sand in a manner known per se.

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 is explained in more detail below using a drawing showing an exemplary embodiment. Their figures each show schematically:

Fig. 1

a flowchart depicting the process according to the invention;

Fig. 2 - 8

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

Fig. 9

the thermoreactor opened to remove the casting in one of the Figures 2 - 8 corresponding view;

Fig. 10

a device for cooling a casting;

Fig. 11

the finished casting;

Fig. 12

a collecting container of the thermoreactor in one Figures 2 - 8 corresponding view;

Fig. 13

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

Fig. 14

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

Fig. 15

a storage container filled with contents in one of the Figures 2 - 8 corresponding view.

In Fig. 1 The circuit that results from carrying out the method according to the invention is shown as a diagram. It starts with casting mold parts and cores made from molding material made from new, previously unused core sand, e.g. B. quartz sand, and a conventional binder, for example a commercially available cold box binder, is mixed. In the same way, new filling material, for example ceramic granules with an average grain size of 1.5 - 25 mm, is used, which for the first use is heated to the required minimum temperature, e.g. B. 500 °C, must be heated before it can be used. Furthermore, these starting materials can be reused in the cycle, as explained below.

The one in the Fig. 2 - 8 Thermoreactor T shown in various phases of the method according to the invention has a sieve 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 internal combustion engine.

The casting mold 2 is assembled in a conventional manner as a core package from a large number of outer cores or molded parts arranged on the outside and casting cores arranged on the inside. In addition, the mold 2 may include components made of steel or other indestructible materials. These include, for example, cooling molds and the like, which are arranged in the casting mold 2 in order to achieve a directed solidification of the casting G through accelerated solidification of the melt that comes into contact with the cooling mold.

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

The cores and molded parts of the casting mold 2 are manufactured in a conventional manner using the cold box process from a conventional molding material, which is a mixture of a commercially available core sand, an equally commercially available organic binder and optionally added additives, for example the better ones The binder serves to wet the grains of the core sand. The casting cores and molded parts of the casting mold 2 are formed from the molding material. The resulting casting cores and molded parts are then gassed with a reaction gas in order to harden the binder through a chemical reaction thereby giving the cores and molded parts the necessary dimensional rigidity.

The sieve plate 1 is supported with its edge on a circumferential edge shoulder 4 of a collecting container 5. A sealing element 6 is incorporated into the circumferential contact area of the edge shoulder 4.

After the mold 2 has been positioned on the sieve plate 1, an enclosure 7, which also belongs to the thermoreactor T, is placed on the circumferential edge shoulder 4 of the collecting container 5. The housing 7 is designed in the manner of a hood and encases the mold 2 on its outer peripheral surfaces 8. The circumference of the space delimited by the housing 7 is oversized compared to the circumference of the casting mold 2, so that after the housing 7 has been placed on the sieve base 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 its edge assigned to the collecting container 5, the housing sits on the sealing element 6, so that a tight seal of the filling space 10 with respect to the environment U is guaranteed. The enclosure consists of a thermally insulating material, which can consist of several layers, one layer of which ensures the necessary dimensional stability of the enclosure 7 and another layer ensures the thermal insulation. On its upper side, the housing 7 delimits a large opening 11, through which the casting mold 2 can be filled with cast iron melt and the filling space 10 with filling material F ( Fig. 3 ).

To fill the filling space 10 with a filling material F designed as a granular material and tempered to a temperature Tmin of at least 500 ° C, a storage container V is positioned above the opening 11, from which the hot filling material F is then fed into the filling space 10 via a distribution system 12 lets trickle down ( Fig. 4 ).

When the filling process is completed, the filling material package filled into the filling space 10 can be compacted if necessary. A cover 13 is then placed on the opening 11, which also has an opening 14 through which the iron casting melt can be filled into the casting mold 2 ( Fig. 5 ).

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

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

The intentional destruction of the casting mold 2 that begins with the casting of the iron casting melt and the associated removal of the casting G from the mold takes place in two phases.

In the first phase, the solvent contained in the binder evaporates. That emerging from the mold 2 Vaporous solvent reaches a concentration in the filling space 10 at which it automatically ignites and burns off. Due to the heat released, the granular filling material F, brought to a temperature Tmin of approximately 500 °C, is heated beyond the limit temperature Tlimit of 700 °C until its temperature reaches the maximum temperature Tmax of approximately 900 °C.

If the concentration of the binder components evaporating from the mold 2 is no longer sufficient for independent combustion, the filling material heated in this way takes on the function of a heat storage, through which the temperature of the mold 2 and in the filling space 10 is above a temperature limit of 700 ° C level is maintained. In this way, the combustion of the binder components and other potential pollutants emerging from the mold 2 continues until no more binder evaporates from the mold 2. The vaporous substances that may then still emerge from the mold 2 are oxidized or otherwise rendered harmless by the high temperature prevailing in the filling space 10.

The oxygen-containing gas streams S1, S2, which are formed from ambient air and which reach the filling space 10 of the enclosure 7 via the gas inlet 15 and the sieve base 1, also contribute to the completeness of the combustion of the gases emerging from the casting mold 2.

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

The flow of the gases emerging from the casting mold 2 through the filling material F causes good mixing with the supplied gas flow S1, S2, a longer residence time and good reactivity. The casting mold 2 is 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 material F. As a result, the binder system holding the molded parts and cores of the mold 2 together is almost completely destroyed. The molded parts and cores then break down into fragments B or individual grains of sand.

The fragments B and the loose sand fall through the sieve base 1 into the collecting container 5 and are collected there. Depending on the progress of the destruction of the mold 2, the sieve base 1 can be opened in such a way that filling material F also gets into the collecting container 5 ( Fig. 8 ).

For optimal combustion of the gases escaping from the casting mold 2 and for the regeneration of the core sand, they are already in the enclosure Temperatures of the filling material F and the gases flowing in the filling space 10 are optimally well above 700 ° C. The conditions in the thermal reactor T are designed in such a way that the regeneration process and the exhaust gas treatment take place independently of system availability. Determining and set variables are the starting temperature of the filler F, the oxygen-containing gas streams S1, S2 flowing in via the gas inlet 15 and the access 16 and the casting mold 2 itself.

The progress of the destruction of the casting mold 2 and the solidification process of the iron casting melt poured into the casting mold 2 are adapted to one another in such a way that the casting G has solidified sufficiently when the casting mold 2 begins to disintegrate.

After the mold 2 has essentially completely disintegrated, the collecting container 5 with the molding material-filling material mixture contained in it is separated from the sieve base 1 and the housing 7 is also removed from the sieve base 1. The cast part G, which has been largely removed from sand, is now freely accessible and can be cooled in a controlled manner in a tunnel-like space 17 provided for this purpose ( Fig. 10 ). The casting G has a high temperature when removed due to the process in which the austenite transformation is not yet complete and rapid cooling would lead to internal stresses and thus cracks. For this reason, the casting G is slowly cooled in a cooling tunnel 17 according to the annealing curves during stress-relieving annealing. The The cooling air supplied is dimensioned so that the cooling profile is achieved in a product-specific manner.

The still hot mixture of filling material F, core sand and fragments B contained in the collecting container 5 is intensively mixed in a grinder 18, which can be a rotary tube, for example, and sufficient oxidation air is added so that any remaining binder residues may still be present afterburn. In this process stage, the filling material F can also be separated from the core sand and both can be fed to separate cooling. Such regeneration ensures that the binder system is completely burned and also prepares the core sand surface through mechanical friction for good adhesion of the binder for reuse as core sand.

The core sand obtained is cooled down to almost room temperature and, after fraction separation, is processed again into casting mold parts or casting cores for a new casting mold 2.

The filling material F, on the other hand, is cooled to the intended starting temperature Tmin and filled into the storage container V in the circuit for refilling the filling space 10.

The amount of combustion air passed into the filling space 10 as gas streams S1, S2 is regulated via mechanically adjustable flaps or slides, with which the opening cross sections of the gas inlet 15 and of access 16 can be adjusted. The respective setting can first be determined via the stoichiometric amount of air required for combustion of the binder system and then fine-tuned via measurements of CO, NO through which the exhaust gases arising in the filling space 10 are removed from the housing 7.

How out Fig. 16 As can be seen, a high pollutant concentration shown by the curve Kpollutant is reached in the filling space 10 immediately after casting due to the evaporation of the solvent from the binder system of the mold 2 and the other vapors from the mold 2, which would burn independently even at room temperatures. The limit Klimit, from which a pollutant concentration that is flammable is reached at room temperature, is in Fig. 16 indicated by the dash-dotted line. Because of the high minimum temperature Tmin of 500 ° C, which prevails in the filling space 10 due to the hot filling material F introduced there, the combustion of the gases entering the filling space 10 from the casting mold 2 begins at a significantly lower concentration (see Fig. Fig. 16 ).

As a result of the combustion within the granulate in phase 1, the granulate heats up and its temperature T after a short time exceeds the limit temperature T limit of 700 ° C, at which organic substances are known to have sufficient oxygen content oxidize independently and thus burn. The course of the temperature of the filling material is in Fig. 16 shown as a dashed line.

This phase ("Phase 1") of intensive combustion of the binder evaporating from the mold 2 lasts until the concentration Kpollutant of the combustible gases entering the filling space 10 from the mold 2, essentially formed by the evaporating binder, decreases so much that at Combustion would no longer take place at room temperature.

Due to the high filling material temperature of more than 700 ° C, this oxidation or combustion continues in the subsequent phase 2, as described above, with the heat released thereby being sufficient to further increase the temperature of the filling material 10 until the maximum temperature Tmax is reached. The filling material 10 remains at this temperature until the decomposition process of the casting mold 2 has progressed to such an extent that no significant outgassing occurs anymore, the casting mold 2 disintegrates into small pieces and the molding material residues fall into the container 5. However, as long as combustion processes take place in the filling space 10, so much heat is still generated that the filling material F remains in a range for a sufficiently long period of time, the upper limit of which is the temperature Tmax and the lower limit of which is the temperature Tlimit.

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

It has been proven that with the evaporating and combustible substances contained in the mold 2, so much chemical energy is available for combustion that filling material temperatures of well over 1,000 °C could be achieved. In this case, the cooling of the casting would be delayed, 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 rise in temperature can be prevented by increasing the gas flows S1, S2, which then act as cooling air.

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

Since, according to the invention, the excreting exhaust gases essentially heat up the filling material bed even in the first phase, a temperature profile results within the bed which ensures clean combustion. The combustion air follows a vertical upward direction due to the heat convection flow arising in the filling space 10 and the outgassing of pollutants from the mold 2 follows a horizontal direction into the filling material package due to the strong steam formation in the first phase. The crossing of the gas streams within the filling material F ensures good mixing.

In the area above the casting mold 2, the gas flows are then rectified and can burn sufficiently in the hottest area of the exhaust gas duct in the combustion chamber between the lid 13 and the filling material F before exiting the exhaust gas outlet 19 above the pouring funnel.

In an example calculation, based on 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 that for heating the filling material as well as the heating of the core sand of the casting mold required thermal energy Qb was determined.

It was assumed that the melt is a gray cast iron melt that is poured into a casting mold, the molded parts and cores of which are made in the conventional cold box process from molding material that is made from conventional core sand, i.e. H. consists of quartz sand and a binder that is also commercially available for these purposes.

To simplify matters, it has also been assumed that the cast metal gives off its heat to the casting mold and the filling material after casting and that the chemical energy inherent in the binder used is also fully available in the form of combustion heat to heat up 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 heat of fusion Hfus to be 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 $$\mathrm{Hfus}=170\mathrm{kg}\times 96\mathrm{kJ}/\mathrm{kg}\times 1/1000\mathrm{MJ}/\mathrm{kJ}=16.3\mathrm{MJ}.$$

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

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

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

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

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

to $$\mathrm{<figure-callout\; id="1"\; label="Qa"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">Qa</figure-callout>}1=950\mathrm{J}/\mathrm{kgK}\times -650\mathrm{K}\times 170\mathrm{kg}\times 1/1000\mathrm{MJ}/\mathrm{kJ}-16.3\mathrm{<figure-callout\; id="1"\; label="MJ\; Qa"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">MJ\; </figure-callout>}$$

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

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

Correspondingly, the thermal energy Qa2 released by the combustion of the binder contained in the molding material is calculated according to the formula $$\mathrm{Qa}$$$$2=\mathrm{Hi}\times {\mathrm{m}}_{\mathrm{binder}}\times \left(-1\right)$$

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

The sum of the heat energy released 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 to heat the core sand of the mold from the temperature T1 to the temperature T2 is calculated using the formula $$\mathrm{Qb}$$$$1={\mathrm{cp}}_{\mathrm{core\; sand}}\times \left(\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">T</figure-callout>}2-\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">T</figure-callout>}1\right)\times {\mathrm{m}}_{\mathrm{core\; sand}}$$

to $$\mathrm{<figure-callout\; id="1"\; label="Qb"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">Qb</figure-callout>}1=835\mathrm{J}/\mathrm{kgK}\times \left(800\mathrm{K}-20\mathrm{K}\right)\times 255\mathrm{kg}=166\left[\mathrm{MJ}\right].$$

zu $$\mathrm{Qb2}=754\mathrm{J}/\mathrm{kgK}\times \left(800\mathrm{K}-500\mathrm{K}\right)\times 125\mathrm{kg}=28\left[\mathrm{MJ}\right].$$

In the same way, the thermal energy Qb2 required to heat the core sand of the mold from the temperature T1 to the temperature T2 is calculated using the formula $$\mathrm{Qb2}={\mathrm{cp}}_{\mathrm{filling\; material}}\times \left(\mathrm{T2}-\mathrm{T1}\right)\times {\mathrm{m}}_{\mathrm{filling\; material}}$$

to $$\mathrm{Qb2}=754\mathrm{J}/\mathrm{kgK}\times \left(800\mathrm{K}-500\mathrm{K}\right)\times 125\mathrm{kg}=28\left[\mathrm{MJ}\right].$$

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

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

The determination of the energy balance that can be achieved when casting a gray cast iron melt shown in Table 1 shows that when using conventional molding materials based on a conventional binder system and using quartz sand, there is a significant excess capacity of thermal energy. The supplied oxygen-containing gas streams S1, S2 are neglected in this consideration because their energetic influence is very small.

Table 2 shows the bulk densities Sd, the specific heat capacities cp and the product P = Sd x cp for various bulk materials that are generally suitable for use as filling materials in terms of their temperature resistance. It turns out that, for example, steel gravel has a significantly lower specific heat capacity cp than ceramic granules of the type mentioned here, but has a bulk density that is significantly too high to ensure the gas permeability of the filling material package provided in the filling space around the mold, as prescribed according to the invention.

REFERENCE MARKS

1

Sieve plate

2

Mold

3

Mold cavity

4

circumferential edge heel

5

collection container

6

Sealing element

7

Enclosure (housing)

8th

Circumferential surfaces of the mold 2

9

Inner surface of the enclosure 7

10

filling space

11

Opening the enclosure

12

Distribution system

13

Lid

14

Opening the lid 13

15

Gas inlet

16

Access

17

Cooling tunnel

18

grinder

19

exhaust outlet

b

Fragments

F

filling material

G

casting

S1,S2

oxygen-containing gas streams

T

Thermoreactor

U

Vicinity

v

storage container

Table 1 Material value / parameters filling material core sand Cast metal binder Unit Ceramic granules Quartz sand Gray cast iron Cold box binder Enthalpy of fusion 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 Input temperature T1 500 20 1500 °C Initial temperature T2 800 800 850 °C Table 2 filling material Bulk density Sd [kg/dm ³ ] Specific heat capacity cp [J/kgK] P = Sd x cp Ceramics 0.61 754 460 steel gravel 4.20 470 1,974 Quartz sand 1.40 835 1,169

Claims (15)

1. Method for casting castings (G), in which a molten metal is poured into a casting mold which encloses a cavity (3) forming the casting to be produced, wherein the casting mold (2) consists as a lost mold of one or more casting mold parts or -cores which are 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, comprising the following working steps:

   - providing the casting mold (2);

   - enclosing the casting mold (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 mold (2);

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

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

   - wherein the casting mold (2) begins to radiate heat as the molten metal is poured in, as a result of the heat input caused by the hot 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 combust, so that it loses its effect and the casting mold (2) breaks up into fragments (B),

   characterized in that
   the filling material (F) filled into the filling space (10) has such a low bulk density that a gas stream (S1, S2) can flow through the filling material package formed there from the filling material (F) after the filling space (10) has been filled, and in that the filling material (F) has a minimum temperature (Tmin) when the filling space (10) is filled, starting from which the temperature of the filling material (F) rises by process heat, which is generated by the heat radiated by the casting mold (2) and by the heat released during the combustion of the binder, to above a limit temperature (TGrenz) at which the binder evaporating from the casting mold (2) and coming into contact with the filling material (F) ignites and its combustion begins.
2. Method according to claim 1, characterized in that the product P of bulk density Sd and specific heat capacity cp is at most 1 kJ/dm³K.
3. Method according to any one of the preceding claims, characterized in that the bulk density Sd is at maximum 4 kg/dm³.
4. Method according to any one of the preceding claims, characterized in that the filling material (F) has a specific heat capacity cp of at maximum 1 kJ/kgK.
5. Method according to any one of the preceding claims, characterized in that the filling material (F) is formed from granules having an average diameter of 1.5 - 100 mm.
6. Method according to any one of the preceding claims, characterized in that the temperature of the filling material (F) during filling of the filling space (10) is at least 500 °C.
7. Method according to any one of the preceding claims, characterized in that the limit temperature (TGrenz) is 700 °C.
8. Method according to any one of the preceding claims, characterized in that the enclosure has a gas inlet (15) and an exhaust gas outlet (19) and in that the filling material (F) contained in the filling space (10) is flowed through at least temporarily and in sections by an oxygen-containing gas stream (S1, S2).
9. Method according to claim 7, characterized in that the gas stream (S1, S2) is heated to a temperature above room temperature.
10. Method according to any one of claims 7 to 9, characterized in that the gas stream (S1, S2) is controlled as a function of the exhaust gas volume stream emerging from the exhaust gas outlet (19).
11. Method according to any one of claims 7 to 10, characterized in that an exhaust gas measurement is carried out at the exhaust gas outlet (19) and in that the gas stream (S1, S2) is controlled as a function of the result of this measurement.
12. Method according to any one of claims 7 to 11, characterized in that a partial stream of the combustion gases emerging from the exhaust gas outlet (19) is mixed with the oxygen-containing gas stream (S1, S2) and the resulting mixture is passed into the housing (7).
13. Method according to any one of the preceding claims, characterized in that the housing (7) is equipped with a catalyst device for decomposing pollutants contained in the combustion products of the binder.
14. Method according to any one of the preceding claims, characterized in that the casting mold (2) is placed on a sieve bottom (1), and in that the fragments (B) of the casting mold (2) and the filling material (F) trickle together through the sieve bottom (1), are collected, processed and separated from each other after processing.
15. Method according to any one of the preceding claims, characterized in that the casting (G) undergoes a heat treatment after the break-up of the casting mold (2), in which it is cooled in a controlled manner in accordance with a specific cooling curve.

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