EP2017022A1 - Component of a casting system which can be permeated by molten metal - Google Patents

Abstract

A non-fired component of a casting system, through which molten metal passes, has a wall thickness of less than 9 mm and is formed from a material (A) which is at least partially destroyed at the temperature of the molten metal.

Description

The invention relates to a component of a casting system through which a molten metal can flow. Such a casting system typically includes a gate, a so-called "run" and so-called "gates", collectively referred to as a runner system. This Gießkanalsystem is at least partially integrated into a mold having one or more cavities in which the casting is created. For this purpose, a molten metal is supplied via the Gießkanalsystem in / the cavities. Subsequently, the melt solidifies.

The components of the Gießkanalsystems are made of refractory ceramic products. These components are designed to withstand the high casting temperatures and remain dimensionally stable to prevent non-metallic components from entering these components in the molten metal and thus in the casting. Accordingly, the components have large wall thicknesses (> 10 mm) and highly refractory materials.

After the solidification and hardening of the melt, the casting mold, which generally consists of quartz or zircon sand, is dismantled (destroyed) in order to expose the casting. The mold material should be used again as possible. This disturbing the ceramic components of Gießkanalsystems that are usually mechanically destroyed during removal of the casting, but in the form of fragments in the sand (mold material) remain and must then be separated in a further process step.

Another disadvantage of known components of the type mentioned is that, for example, to create longer casting channels several components must be arranged one behind the other and connected to each other. This creates discontinuities in the region of the pouring channel wall. This increases the risk that ceramic sections or mold material get into the flowing molten metal.

The invention has for its object to optimize a generic component for metal casting. Among other things, it is about reducing the recycling costs after completion of the casting process, to minimize the risk of infiltration of non-metallic inclusions into the casting and to simplify the assembly of the pouring channel system within the casting mold.

The invention is based on the following idea: Usual casting times for metallic castings amount to a few minutes, for example 1.5 to 2.5 minutes. This is the time period during which a molten metal is introduced into the casting mold via the sprue system. Only during this time there is a risk that components of the Gießkanalsystems be entrained with the melt stream and get into the casting to be produced. After completion of the casting process, the Gießkanalsystem remains at least partially filled with molten metal, which then solidifies. However, this production phase no longer has a decisive influence on the quality of the casting.

In the prior art, care was taken to make the components of the Gießkanalsystems so stable that chipping or the like can be reliably avoided. According to the invention, the idea is to design the component in such a way that it has the necessary stability during the casting process in order to reliably guide the melt into the casting mold (the molding box), but on the other hand during disassembly of the molding box as little as possible components of the component remain in the mold material.

With this in mind, the invention is based on the consideration of forming the component from a material which is at least partially destroyed in contact with the molten metal, that is to say after being subjected to temperature by the molten metal. The destruction can be a chemical destruction, for example by breaking chemical bonds.

This destruction should take place in particular after completion of the casting process, ie at the time at which the cavity for forming the casting and the Gießkanalsystem are filled with metal and then, but can also already begin during the casting process, provided that the mechanical stability of the component by the way is ensured to distribute the molten metal in the mold.

In its most general embodiment, the invention then relates to a component of a casting system, wherein the component is flowed through by a molten metal and has a wall thickness <9 mm and consists of a material which is at least partially destroyed in contact with the molten metal.

From the idea of at least partial destruction also follows the idea to form the component as thin as possible, that is, with a wall thickness significantly below the known ceramic components. As a result, an inventive component massearm. In addition, the component should at least partially decompose under thermal load. As a result, only minimal amounts of solids enter the surrounding mold material and may remain in the mold material cycle.

Of course, the at least partial dissolution (destruction) of the component must be done in a manner that prevents non-metallic solids from entering the casting stream. One possibility is the use of a material of at least one temporary binder and at least one reinforcing agent. In this case, the reinforcing agent is quasi a kind of basic strength, while the temporary binder under the influence of the temperature of the molten metal at least partially and / or successively burns out. Since the surrounding mold material (such as quartz sand, zircon sand) within the mold box has a certain gas permeability, volatiles of the binder originating from the component can easily be led away from the mold box.

Suitable temporary binders are: phenolic resins, furan resins, polysaccharides, polymers based on polyvinyl acetate, polyvinyl alcohol, polyvinyl acrylate, phosphate binders such as aluminum phosphate, water glass, cellulose derivatives, lignosulfonates. The selection of individual of these binders and / or combinations thereof takes place depending on the application. While the polymers mentioned based on polyvinyl acetate evaporate relatively quickly, the service life of components based on phenolic resins and in particular furan resins is significantly higher. Using a material of, for example, 20 to 80% by mass of furan resin and 20 to 80% by mass of a (fibrous) reinforcing agent, a tubular member within the casting system keeps its basic shape smoothly during casting of the molten metal (assumed: 2 minutes), so that the Melt can be filled trouble-free. The abrasion is zero. However, soon after (possibly a few seconds) after the contact between the molten metal, the decomposition of the furan resin can begin, but only to an extent which does not endanger the stability of the pouring tube. Only after completion of the casting process (here:> 2 min), the furan resin decomposes further, for example, after a few hours more or less completely dissolved (without significant residual solids). This has the advantage for the further process steps that no appreciable foreign components remain in the molding sand (possibly combustion residues of the resin and the reinforcing agent). This makes it possible to reuse the mold material. Elaborate cleaning processes, as in the prior art omitted.

By using a temporary, destructible binder, the reinforcing agent has a significant importance within the selected material. The reinforcing agent also ensures an at least temporary stability of the component during the successive decomposition of the further component. Reinforcing agents from the group oxide fibers and carbon fibers are particularly suitable. The invention includes reinforcing agents which also decompose at least partially under temperature load.

Oxidic fibers include, for example, stone fibers, glass fibers, ceramic fibers. Non-oxidic fibers are conceivable, but expensive.

The fibers can be "continuous fibers". Such fibers are used in particular when producing tubular components. The endless fiber can be wound, for example, on a mandrel. It is brought into contact either before or during the winding with the binder, which ensures the connection of adjacent fiber sections and formation of the desired tubular body. After curing of the binder, the component is ready. Due to the aforementioned winding technique, it has an extremely smooth inner surface. This benefits the desired application. Another advantage is that even large components, especially long pipes can be made so that undesirable junctions of adjacent pipe sections are avoided. This also minimizes the risk that unwanted components get into the pouring stream.

Likewise, "finite" fibers can be used, with fiber lengths between 20 μm and several cm.

Tubular components can also be produced in the so-called spin process. For this purpose, the binder is fed via a lance of a rotating die together with the reinforcing agent, for example mineral fibers. After curing of the binder, the tubular body can be removed from the die. Also in this way can be produced large pipe lengths.

For more complicated components, such as manifolds, coupling parts or the like, other manufacturing methods are possible.

The mixture of temporary resistant matrix material and reinforcement can alternatively be processed by fiber resin spraying, compression molding, transfer molding or injection molding as well as lamination to the desired component.

A component according to the invention only has to be sufficiently dimensionally stable during the actual casting phase (during which molten metal is introduced into the casting mold) to pass the melt, often only for a few minutes (<5, often <3, even <2 min). This makes it possible to significantly reduce the wall thickness compared to known ceramic components. Wall thicknesses <5 mm, <4 mm, <3 mm, <2 mm to <1 mm are possible and desired.

The use of thin reinforcing materials makes it possible to realize wall thicknesses well below 1 mm. For example, fiber materials may have a fiber diameter <20 microns, in particular <12 microns have. Carbon fibers usually have a diameter <8μm. The diameter of mineral fibers (stone fibers, glass fibers) is usually between 2 microns and 7 microns. This results in the possibility of forming the wall thickness of components of approximately the same order of magnitude, since the binder does not substantially change the wall thickness. Wall thicknesses of <50 μm, even <20 μm or <10 μm are possible, but also <100 μm, <250 μm or <500 μm. The length of the components can range from a few centimeters to several meters, the most circular flow channel have a diameter of 2 to 30 cm.

A component according to the invention can consist exclusively of said temporary matrix material in combination with the described reinforcing agent, but it can also have further constituents. These other constituents may be, for example, ceramic materials which are also resistant to high temperatures (refractory), for example clay, carbon, alumina, zirconium. However, their share is therefore kept as low as possible in order not to endanger the goal of avoiding metallic inclusions in the pouring stream.

According to one embodiment, the proportion of the temporary binder therefore regularly ≥ 30% by mass, often ≥ 40% by mass, but also ≥ 50% by mass as needed, while the mass fraction of the reinforcing agent is adjusted either to 100% by mass or so that a maximum of 30% by mass, according to embodiments ≤ 20% by mass or ≤ 10% by mass, if appropriate also ≤ 5% by mass of foreign components are taken into account.

An inventive component is easily transportable due to the small wall thickness. It can be cut easily and thus adapted to the respective casting systems. It can have lengths of several meters as a tube. Other component forms are possible.

Other features of the invention will become apparent from the features of the claims and the other application documents.

It follows from the above explanations that a component according to the invention - in comparison with the prior art - is a non-fired component. It therefore has a significantly reduced stability. It only has to have stability during the actual casting process, which allows a proper feeding of the pouring stream into the casting mold. Incidentally, the component is designed such that it dissolves (destroys) as much as possible at least partially, after the end of the casting process, so that a reprocessing of the surrounding mold material in comparison with the aforementioned prior art is significantly facilitated. Ideally, only coking residues of the resin and / or fiber residues that may remain in the mold material for the next molding process remain in the mold material.

The reinforcing agents for a component according to the invention are not limited to fiber materials. Rather, also platelet-shaped or granular reinforcing materials are suitable, provided that they meet the other criteria mentioned above. These include, for example: carbon particles, expanded perlite, expanded vermiculite, expanded glass, pumice, preferably in small particle sizes, in order to keep the wall thickness of the component low. The compound of the particles between each other again takes place primarily via a temporary binder of the type mentioned.

Again, after burning (decomposition) of the only temporarily resistant material component, the reinforcing materials can easily remain in the mold material, especially since they are small-grained (usually <5mm, often <2mm, even <1mm) and temperature resistant.

Claims (7)

By a molten metal flow-through component of a casting system, which has a wall thickness <9mm and consists of a material which is at least partially destroyed in contact with the molten metal. Component according to claim 1, whose material comprises at least one temporary binder and at least one reinforcing agent. Component according to claim 1, whose material comprises ≥ 20% by mass of at least one temporary binder and ≥ 30% by mass of at least one reinforcing agent. Component according to claim 1, whose material comprises a maximum of 20% by mass, in particular a maximum of 10% by mass of other components. Component according to claim 2 or 3, whose temporary binder is selected from the group: phenol resins, furan resins, polysaccharides, polymers based on polyvinyl acetate, polyvinyl alcohol, polyacrylate. Component according to Claim 2 or 3, the reinforcing agent of which originates from the group of oxidic fibers, carbon fibers. Component according to claim 2 or 3, whose reinforcing means comprises wound long fibers.