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EP3570993B1 - Casting method - Google Patents

Casting method Download PDF

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Publication number
EP3570993B1
EP3570993B1 EP18701010.3A EP18701010A EP3570993B1 EP 3570993 B1 EP3570993 B1 EP 3570993B1 EP 18701010 A EP18701010 A EP 18701010A EP 3570993 B1 EP3570993 B1 EP 3570993B1
Authority
EP
European Patent Office
Prior art keywords
charge
mould
filling
melting
casting mold
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
EP18701010.3A
Other languages
German (de)
French (fr)
Other versions
EP3570993A1 (en
EP3570993B8 (en
Inventor
Henrik Franz
Sergejs SPITANS
Ulrich Betz
Egon Bauer
Markus Holz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ALD Vacuum Technologies GmbH
Original Assignee
ALD Vacuum Technologies GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by ALD Vacuum Technologies GmbH filed Critical ALD Vacuum Technologies GmbH
Priority to SI201830128T priority Critical patent/SI3570993T1/en
Publication of EP3570993A1 publication Critical patent/EP3570993A1/en
Publication of EP3570993B1 publication Critical patent/EP3570993B1/en
Application granted granted Critical
Publication of EP3570993B8 publication Critical patent/EP3570993B8/en
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D13/00—Centrifugal casting; Casting by using centrifugal force
    • B22D13/02—Centrifugal casting; Casting by using centrifugal force of elongated solid or hollow bodies, e.g. pipes, in moulds rotating around their longitudinal axis
    • B22D13/026—Centrifugal casting; Casting by using centrifugal force of elongated solid or hollow bodies, e.g. pipes, in moulds rotating around their longitudinal axis the longitudinal axis being vertical
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D13/00—Centrifugal casting; Casting by using centrifugal force
    • B22D13/10—Accessories for centrifugal casting apparatus, e.g. moulds, linings therefor, means for feeding molten metal, cleansing moulds, removing castings
    • B22D13/107—Means for feeding molten metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D13/00—Centrifugal casting; Casting by using centrifugal force
    • B22D13/12—Controlling, supervising, specially adapted to centrifugal casting, e.g. for safety reasons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D18/00—Pressure casting; Vacuum casting
    • B22D18/06—Vacuum casting, i.e. making use of vacuum to fill the mould
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
    • B22D21/02—Casting exceedingly oxidisable non-ferrous metals, e.g. in inert atmosphere
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
    • B22D21/02—Casting exceedingly oxidisable non-ferrous metals, e.g. in inert atmosphere
    • B22D21/022—Casting heavy metals, with exceedingly high melting points, i.e. more than 1600 degrees C, e.g. W 3380 degrees C, Ta 3000 degrees C, Mo 2620 degrees C, Zr 1860 degrees C, Cr 1765 degrees C, V 1715 degrees C
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
    • B22D21/02—Casting exceedingly oxidisable non-ferrous metals, e.g. in inert atmosphere
    • B22D21/025—Casting heavy metals with high melting point, i.e. 1000 - 1600 degrees C, e.g. Co 1490 degrees C, Ni 1450 degrees C, Mn 1240 degrees C, Cu 1083 degrees C
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
    • B22D27/003—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting by using inert gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
    • B22D27/15—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting by using vacuum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D39/00—Equipment for supplying molten metal in rations
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D39/00—Equipment for supplying molten metal in rations
    • B22D39/003—Equipment for supplying molten metal in rations using electromagnetic field
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/22—Furnaces without an endless core
    • H05B6/32—Arrangements for simultaneous levitation and heating
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/36—Coil arrangements
    • H05B6/365—Coil arrangements using supplementary conductive or ferromagnetic pieces
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/36—Coil arrangements
    • H05B6/44—Coil arrangements having more than one coil or coil segment

Definitions

  • This invention relates to a casting method for making castings.
  • the process is a levitation melting process in which the melt does not come into contact with the material of a crucible, so that contamination from the crucible material or from reaction of the melt with the crucible material is avoided.
  • metals and alloys with high melting points are, for example, titanium, zirconium, vanadium, tantalum, tungsten, hafnium, niobium, rhenium and molybdenum. But this is also important for other metals and alloys such as nickel, iron and aluminum.
  • U.S. 2,686,864 A also describes a method in which a conductive melt material, for example in a vacuum, is suspended under the influence of one or more coils without the use of a crucible.
  • two coaxial coils are used to stabilize the suspended material. After it has melted, the material is dropped or poured into a mold. With the method described there, a 60 g portion of aluminum could be kept in suspension. The molten metal is removed by reducing the field strength, so that the melt escapes downwards through the conical coil. If the field strength is reduced very quickly, the metal falls out of the device in a molten state. It has already been recognized that the "weak spot" of such coil arrangements lies in the center of the coils, so that the amount of material that can be melted in this way is limited.
  • U.S. 4,578,552 A discloses an apparatus and method for levitation melting.
  • the same coil is used for both heating and holding the melt, while doing so the frequency of the alternating current applied to regulate the heating power is varied while the current strength is kept constant.
  • levitation melting contamination of the melt by a crucible material or other materials that are in contact with the melt in other processes is avoided.
  • the floating melt is only in contact with the surrounding atmosphere, which can be a vacuum or protective gas, for example. Since a chemical reaction with a crucible material is not to be feared, the melt can be heated to very high temperatures. In addition, the waste of contaminated material is reduced, especially in comparison to the melt in the cold crucible.
  • levitation melting has not caught on in practice. The reason for this is that with the levitation melting process only a relatively small amount of molten material can be kept in suspension (cf. DE 696 17 103 T2 , Page 2, paragraph 1).
  • JP 2012 166207 A a centrifugal casting process for zirconium-based alloys in which the metal is melted levitatingly in the field of a coil and then poured into a centrifugal casting mold located below.
  • the durability of the casting mold is improved by a coating with Ti and / or Ti compounds, in particular TiN, TiAlN, TiO2, TiC and TiAlISiCON.
  • JP 2012 040590 A a centrifugal casting process in which the metal is melted levitatingly in the field of a coil and then poured into a centrifugal casting mold arranged below.
  • an electromagnetic shield is arranged between the coil and the centrifugal casting mold, which is intended to prevent the shape from being influenced by the magnetic field of the coil in order to be able to better control the cooling rates of the melt in the mold.
  • the method should enable a high throughput and be able to melt a sufficient amount of material without the use of a supporting platform in order to enable the economical production of castings of very high quality.
  • the casting mold When the casting mold is filled, it is allowed to cool or is cooled with coolant so that the material solidifies in the mold.
  • the cast body can then be removed from the mold.
  • the casting can consist of dropping the charge, in particular by switching off the electromagnetic alternating field; or the casting can be slowed down by an alternating electromagnetic field, e.g. by using a coil.
  • the method comprises the step of moving the filled casting mold out of the filling area after casting but before removing the solidified cast body.
  • This embodiment is used particularly advantageously when using lost molds, since the filling area is thus released for another lost mold.
  • the cast body in particular when using a permanent mold, can be removed in the filling area.
  • the solidified cast body can be removed in different ways.
  • the casting mold is destroyed when the casting is removed.
  • the casting mold can be designed as a permanent mold, in particular as a permanent mold. Permanent molds are preferably made of a metallic material. They are suitable for simpler components.
  • a permanent mold preferably has two or more mold elements that can be separated from one another in order to demold the cast body. When demolding from permanent molds, one or more ejectors can be used.
  • a “conductive material” is understood to mean a material which has a suitable conductivity in order to inductively heat the material and to keep it in suspension.
  • a “state of suspension” is understood to mean a state of complete suspension, so that the batch being treated has no contact whatsoever with a crucible or a platform or the like.
  • a “filling volume” of a casting mold is understood to mean a volume that fills the casting mold to an extent that is sufficient for the production of one or more complete cast bodies to be formed with the casting mold. This does not necessarily have to correspond to a complete filling of the casting mold; nor does it have to correspond to a minimum volume necessary for the production of a cast body. It is crucial that it is not necessary to fill the mold beyond the filling volume.
  • a casting mold can have channels or filler sections, the filling of which is not necessary in order to produce complete cast bodies, but which merely serve to fill the melt into the casting mold or to distribute it therein. According to the invention, the casting mold is in particular not filled beyond the volume of the molten charge.
  • the casting molds used according to the invention have cavities which correspond to the shape of the cast bodies to be produced. In the context of this invention, it is also possible to use casting molds which have more than one such cavity and are therefore suitable for the simultaneous production of several cast bodies.
  • the casting molds used according to the invention have precisely one cavity for producing precisely one cast body.
  • the casting mold has a filling section which has a larger diameter than the cavity of the casting mold to be filled. Such a filling section can in particular be designed in the shape of a funnel. Its purpose is to facilitate entry of the molten charge into the casting mold.
  • the casting mold preferably consists of a ceramic, in particular oxide-ceramic, material, such as in particular Al 2 O 3 , ZrO 2 , Y 2 O 3 or mixtures thereof.
  • This mold material has proven itself in practice and is particularly advantageous for lost forms.
  • Permanent forms that can also be used according to the invention can be made of a metallic material, that is to say a metal or a metal alloy.
  • another empty casting mold is moved into the filling area.
  • the cast body can still be removed from the casting mold in the filling area without the casting mold having to be moved out of the filling area.
  • another batch of the conductive material can be introduced into the area of influence of the electromagnetic alternating field. The next batch can also be melted and poured into the further casting mold. This process can be repeated any number of times, especially since no crucible is required that would be subject to wear and tear.
  • the method according to the invention can be carried out in such a clocked manner that exactly one casting mold is assigned to each batch of conductive material.
  • the mold is sufficiently filled with one batch and can be moved out of the filling area to make space for the next mold to receive the next batch. In this way, a particularly efficient process is made possible, which enables a high throughput even with the relatively limited capacity of the levitation melting process.
  • the casting mold is preheated before filling.
  • a preheated casting mold has the advantage that the molten charge does not solidify immediately upon contact with the casting mold.
  • the casting mold can be rotated about a vertical axis, in particular a vertical axis of symmetry, during filling.
  • the melt in the casting mold is, as it were, thrown into the cavities.
  • a material that shows a pronounced dependence of the viscosity on the temperature is titanium and titanium alloys, in particular TiAl, so that the casting mold should be rotated, particularly with titanium and titanium alloys as conductive material.
  • the rotation also prevents turbulence, which has an extremely harmful effect on the quality of the cast body.
  • both the melting of the conductive material and the filling of the casting mold are preferably carried out under vacuum or under protective gas.
  • Preferred protective gases are nitrogen, one of the noble gases or mixtures thereof. Argon or helium is particularly preferably used.
  • the use of protective gas or vacuum serves to avoid undesirable reactions of the material with components of the atmosphere, in particular with oxygen.
  • the melting and / or the filling of the casting mold is preferably carried out in a vacuum, in particular at a pressure of at most 1000 Pa.
  • the casting mold is set in a translational movement parallel to the pouring direction of the batch, in particular in the pouring direction, at the moment of filling.
  • the casting mold triggered by the casting process, is moved up or down.
  • This controls the filling speed of the mold i.e. accelerates or decelerates it.
  • This translation measure can be carried out together with the rotation described above become. Both measures contribute to an optimal filling in the sense of a filling of the casting mold that is as complete and as rapid as possible, but at the same time with little turbulence, so that the quality of the cast bodies obtained is improved.
  • a translation in the pouring direction takes place at a speed which is less than the falling speed of the molten charge.
  • the acceleration of the mold in the pouring direction should be less than the acceleration due to gravity of the batch.
  • sensors can be provided that detect the casting and send a signal to a drive unit that triggers rotation and / or translation on the casting mold.
  • Suitable sensors can, for example, detect a change or shutdown of the electromagnetic alternating field or the presence of the molten charge in a transition area between a melting area and the casting mold (e.g. by means of a light barrier).
  • Many other sensors are also conceivable in order to trigger a corresponding signal.
  • the conductive material used according to the invention has at least one high-melting metal from the following group: titanium, zirconium, vanadium, tantalum, tungsten, hafnium, niobium, rhenium, molybdenum.
  • a metal with a lower melting point such as nickel, iron or aluminum can be used.
  • a mixture or alloy with one or more of the aforementioned metals can also be used as the conductive material.
  • the metal preferably has a proportion of at least 50% by weight, in particular at least 60% by weight or at least 70% by weight, of the conductive material. It has been shown that these metals particularly benefit from the advantages of the present invention.
  • the conductive material is titanium or a titanium alloy, in particular TiAl or TiAlV.
  • These metals or alloys can be processed particularly advantageously because they have a pronounced dependency the viscosity of the temperature and, moreover, are particularly reactive, in particular with regard to the materials of the casting mold. Since the method according to the invention combines contactless melting in suspension with extremely fast filling of the casting mold, a particular advantage can be realized for such metals in particular. With the method according to the invention, cast bodies can be produced which have a particularly thin or even no oxide layer from the reaction of the melt with the material of the casting mold.
  • the conductive material is superheated during melting to a temperature which is at least 10 ° C., at least 20 ° C. or at least 30 ° C. above the melting point of the material. Overheating prevents the material from solidifying instantly when it comes into contact with the casting mold, the temperature of which is below the melting temperature. The result is that the charge can be distributed in the mold before the viscosity of the material becomes too high. It is an advantage of levitation melting that there is no need to use a crucible that is in contact with the melt. This avoids the high loss of material in the cold crucible process as well as contamination of the melt with crucible components.
  • melt can be heated to a relatively high level, since operation in a vacuum or under protective gas is possible and there is no contact with reactive materials. However, most materials cannot be overheated at will, since otherwise a violent reaction with the mold is to be feared.
  • the overheating is therefore preferably limited to at most 300 ° C., in particular at most 200 ° C. and particularly preferably at most 100 ° C. above the melting point of the conductive material.
  • melting is preferably carried out for a period of 0.5 min to 20 min, in particular 1 min to 10 min. These melting times can be easily achieved in the levitation melting process, since a very efficient heat input into the charge is possible and, due to the induced eddy currents, a very good temperature distribution takes place within a very short time.
  • the molten batch is poured into the casting mold.
  • the casting can consist of dropping the molten charge or it can be controlled by electromagnetic interference, for example with a (further) coil suitable for this purpose.
  • the filled casting mold is moved and preferably replaced by a new, empty casting mold, so that casting molds can be filled every few minutes.
  • a batch of conductive material can preferably have masses of 50 g to 2 kg, in particular 100 g to 1 kg. In one embodiment the mass is at least 200 g. These masses are sufficient to produce turbine blades, turbocharger wheels or prostheses. But there are also any other shapes conceivable, especially since the process can also be used to produce complex shapes with fine and branched cavities.
  • the combination of high melting temperature and thus low viscosity, vacuum or protective gas to avoid reactions, rotation for rapid distribution of the melt in the casting mold, translation for setting an optimal filling speed and clocked filling of the casting molds in just one filling step lead to an extremely versatile process which can be optimized depending on the material to be melted and the casting mold used.
  • At least two electromagnetic fields of different alternating current frequencies are used to bring the charge into suspension.
  • one or more conical coils are used to generate the required electromagnetic fields.
  • Such a classic levitation melting process with conical coils can also be used according to the invention.
  • the batch sizes are then very limited, since in the area of the axis of symmetry only the surface tension of the molten batch prevents it from flowing off.
  • This disadvantage can be avoided by using at least two electromagnetic fields with different frequencies (cf. Spitans et al., Magnetohydrodynamics Vol. 51 (2015), No.1, pp.121-132 ).
  • the magnetic fields should preferably run horizontally and in particular at right angles to one another. In this way, relatively large masses of conductive material can be processed in a full suspension melting process.
  • the use of different frequencies prevents the sample from rotating; a frequency difference of at least 1 kHz in each case is preferred.
  • At least one ferromagnetic element is arranged horizontally around the area in which the charge is melted.
  • the ferromagnetic element can be arranged in a ring around the melting area, with "ring-shaped" not only being understood to mean circular elements, but also angular, in particular square or polygonal ring elements.
  • the element can have several rod sections, which in particular protrude horizontally in the direction of the melting area.
  • the ferromagnetic element consists of a ferromagnetic material, preferably with an amplitude permeability ⁇ a > 10, more preferably ⁇ a > 50 and particularly preferably ⁇ a > 100.
  • the amplitude permeability relates in particular to the permeability in a temperature range between 25 ° C and 100 ° C and at a magnetic flux density between 0 and 400 mT.
  • the amplitude permeability is in particular at least one hundredth, in particular at least 10 hundredths or 25 hundredths of the amplitude permeability of soft magnetic ferrite (for example 3C92). Suitable materials are known to those skilled in the art.
  • the electromagnetic fields are generated by at least two pairs of induction coils, the axes of which are horizontally aligned, so the conductors of the coils are preferably each wound on a horizontally aligned coil former.
  • the coils can each be arranged around a rod section of the ferromagnetic element protruding in the direction of the melting area.
  • the coils can have coolant-cooled conductors.
  • a coil in particular a conical coil, with a vertical axis of symmetry is additionally arranged below the charge to be melted in order to influence the casting speed.
  • this coil can generate an electromagnetic field of a third alternating current frequency (cf. Spitans et al., Numerical and experimental investigations of a large scale electromagnetic levitation melting of metals, Conference Paper 10th PAMIR International Conference - Fundamental and Applied MHD, June 20-24, 2016, Cagliari, Italy ).
  • This coil can preferably also serve to protect the ferromagnetic element from the influence of excessive heat.
  • a coolant can flow through the conductor of this coil.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Continuous Casting (AREA)
  • Molds, Cores, And Manufacturing Methods Thereof (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • General Induction Heating (AREA)

Description

Diese Erfindung betrifft ein Gießverfahren zur Herstellung von Gusskörpern. Das Verfahren ist ein Schwebeschmelzverfahren, bei dem die Schmelze nicht mit dem Material eines Tiegels in Berührung kommt, so dass Verunreinigungen durch das Tiegelmaterial oder durch Reaktion der Schmelze mit Tiegelmaterial vermieden werden.This invention relates to a casting method for making castings. The process is a levitation melting process in which the melt does not come into contact with the material of a crucible, so that contamination from the crucible material or from reaction of the melt with the crucible material is avoided.

Die Vermeidung solcher Verunreinigungen ist gerade bei Metallen und Legierungen mit hohen Schmelzpunkten von Bedeutung. Solche Metalle sind beispielsweise Titan, Zirkonium, Vanadium, Tantal, Wolfram, Hafnium, Niob, Rhenium und Molybdän. Doch auch bei anderen Metallen und Legierungen wie Nickel, Eisen und Aluminium ist dies von Bedeutung.Avoiding such contamination is particularly important with metals and alloys with high melting points. Such metals are, for example, titanium, zirconium, vanadium, tantalum, tungsten, hafnium, niobium, rhenium and molybdenum. But this is also important for other metals and alloys such as nickel, iron and aluminum.

Stand der TechnikState of the art

Schwebeschmelzverfahren sind aus dem Stand der Technik bekannt. So offenbart bereits DE 422 004 A ein Schmelzverfahren, bei dem das leitfähige Schmelzgut durch induktive Ströme erhitzt und gleichzeitig durch elektrodynamische Wirkung frei schwebend erhalten wird. Dort wird auch ein Gießverfahren beschrieben, bei dem das geschmolzene Gut vermittelt durch einen Magneten in eine Form gedrückt wird (elektrodynamischer Pressguss). Das Verfahren kann im Vakuum durchgeführt werden. Es wird dort allerdings nicht gelehrt, dass eine geschmolzene Charge zur Füllung der Gussform ausreichend ist.Levitation melting processes are known from the prior art. So already revealed DE 422 004 A a melting process in which the conductive melt material is heated by inductive currents and at the same time is kept floating freely by an electrodynamic effect. A casting process is also described there in which the molten material is pressed into a mold by means of a magnet (electrodynamic compression molding). The process can be carried out in a vacuum. However, there is no teaching that a molten charge is sufficient to fill the mold.

US 2,686,864 A beschreibt ebenfalls ein Verfahren, bei dem ein leitfähiges Schmelzgut z.B. in einem Vakuum unter dem Einfluss von einer oder mehreren Spulen ohne die Verwendung eines Tiegels in einen Schwebezustand versetzt wird. In einer Ausführungsform werden zwei koaxiale Spulen verwendet, um das Material in der Schwebe zu stabilisieren. Nach erfolgter Schmelze wird das Material in eine Form fallen gelassen bzw. abgegossen. Mit dem dort beschriebenen Verfahren ließ sich eine 60 g schwere Aluminiumportion in der Schwebe halten. Die Entnahme des geschmolzenen Metalls erfolgt durch Reduktion der Feldstärke, so dass die Schmelze nach unten durch die konisch zulaufende Spule entweicht. Wird die Feldstärke sehr schnell reduziert, fällt das Metall in geschmolzenem Zustand aus der Vorrichtung. Es wurde bereits erkannt, dass der "weak spot" solcher Spulenanordnungen in der Mitte der Spulen liegt, so dass die Menge an Material, die so geschmolzen werden kann, begrenzt ist. U.S. 2,686,864 A also describes a method in which a conductive melt material, for example in a vacuum, is suspended under the influence of one or more coils without the use of a crucible. In one embodiment, two coaxial coils are used to stabilize the suspended material. After it has melted, the material is dropped or poured into a mold. With the method described there, a 60 g portion of aluminum could be kept in suspension. The molten metal is removed by reducing the field strength, so that the melt escapes downwards through the conical coil. If the field strength is reduced very quickly, the metal falls out of the device in a molten state. It has already been recognized that the "weak spot" of such coil arrangements lies in the center of the coils, so that the amount of material that can be melted in this way is limited.

Auch US 4,578,552 A offenbart eine Vorrichtung und ein Verfahren zum Schwebeschmelzen. Es wird dieselbe Spule sowohl zum Heizen als auch zum Halten der Schmelze verwendet, dabei wird die Frequenz des angelegten Wechselstroms zur Regelung der Heizleistung variiert, während die Stromstärke konstant gehalten wird.Also U.S. 4,578,552 A discloses an apparatus and method for levitation melting. The same coil is used for both heating and holding the melt, while doing so the frequency of the alternating current applied to regulate the heating power is varied while the current strength is kept constant.

Die besonderen Vorteile des Schwebeschmelzens bestehen darin, dass eine Verunreinigung der Schmelze durch ein Tiegelmaterial oder andere Materialien, die bei anderen Verfahren in Kontakt mit der Schmelze stehen, vermieden wird. Die schwebende Schmelze steht nur in Kontakt zu der sie umgebenden Atmosphäre, bei der es sich z.B. um Vakuum oder Schutzgas handeln kann. Dadurch, dass eine chemische Reaktion mit einem Tiegelmaterial nicht zu befürchten ist, kann die Schmelze auf sehr hohe Temperaturen erhitzt werden. Darüber hinaus wird, insbesondere im Vergleich zur Schmelze im Kalttiegel, der Ausschuss an kontaminiertem Material verringert. Dennoch hat sich das Schwebeschmelzen in der Praxis nicht durchgesetzt. Der Grund dafür ist, dass beim Schwebeschmelzverfahren nur eine verhältnismäßig kleine Menge an geschmolzenem Material in der Schwebe gehalten werden kann (vgl. DE 696 17 103 T2 , Seite 2, Absatz 1).The particular advantages of levitation melting are that contamination of the melt by a crucible material or other materials that are in contact with the melt in other processes is avoided. The floating melt is only in contact with the surrounding atmosphere, which can be a vacuum or protective gas, for example. Since a chemical reaction with a crucible material is not to be feared, the melt can be heated to very high temperatures. In addition, the waste of contaminated material is reduced, especially in comparison to the melt in the cold crucible. However, levitation melting has not caught on in practice. The reason for this is that with the levitation melting process only a relatively small amount of molten material can be kept in suspension (cf. DE 696 17 103 T2 , Page 2, paragraph 1).

Daher wurde teilweise auf ein Halbschwebeverfahren zurück gegriffen, bei dem ein geschmolzenes Material nicht in der Schwebe gehalten, sondern nach einem ähnlichen Prinzip aufgerichtet wird, während das Material nicht schwebt, sondern auf einer Plattform liegt. Ein solches Verfahren wird in DE 696 17 103 T2 und DE 690 31 479 T2 beschrieben. Allerdings gestaltet sich der Abguss des so geschmolzenen Materials in eine Gussform als schwierig. Ferner entsteht hier ein erheblicher Anteil an unbrauchbarem Material, welches durch den Kontakt mit der Plattform verunreinigt wurde. In DE 690 31 479 T2 wird mit einer Plattform gearbeitet, die eine kreisrunde Öffnung aufweist, die mit arteigenem Material verschlossen ist. Nach dem kompletten Aufschmelzen fließt die Schmelze durch die Öffnung aus dem Schmelzbereich hinaus.For this reason, a semi-levitation method was used in some cases, in which a molten material is not kept in suspension, but instead is erected according to a similar principle, while the material does not float, but lies on a platform. Such a procedure is used in DE 696 17 103 T2 and DE 690 31 479 T2 described. However, it is difficult to pour the molten material into a mold. Furthermore, a considerable proportion of unusable material is created here, which has been contaminated through contact with the platform. In DE 690 31 479 T2 a platform is used that has a circular opening that is closed with material from its own species. After complete melting, the melt flows out of the melting area through the opening.

Weiterhin beschreibt die JP 2012 166207 A ein Schleudergussverfahren für zirkonbasierte Legierungen, bei dem das Metall im Feld einer Spule levitierend geschmolzen und dann in eine darunter angeordnete Schleudergussform abgegossen wird. Die Haltbarkeit der Gussform wird durch eine Beschichtung mit Ti und/oder Ti-Verbindungen, insbesondere TiN, TiAIN, TiO2, TiC und TiAISiCON verbessert.Furthermore describes the JP 2012 166207 A a centrifugal casting process for zirconium-based alloys in which the metal is melted levitatingly in the field of a coil and then poured into a centrifugal casting mold located below. The durability of the casting mold is improved by a coating with Ti and / or Ti compounds, in particular TiN, TiAlN, TiO2, TiC and TiAlISiCON.

Ebenso offenbart die JP 2012 040590 A ein Schleudergussverfahren, bei dem das Metall im Feld einer Spule levitierend geschmolzen und dann in eine darunter angeordnete Schleudergussform abgegossen wird. Hierbei ist zwischen der Spule und der Schleudergussform eine elektromagnetische Abschirmung angeordnet, die eine Beeinflussung der Form durch das Magnetfeld der Spule verhindern soll, um die Abkühlraten der Schmelze in der Form besser kontrollieren zu können.Likewise reveals the JP 2012 040590 A a centrifugal casting process in which the metal is melted levitatingly in the field of a coil and then poured into a centrifugal casting mold arranged below. Here, an electromagnetic shield is arranged between the coil and the centrifugal casting mold, which is intended to prevent the shape from being influenced by the magnetic field of the coil in order to be able to better control the cooling rates of the melt in the mold.

Die Nachteile der aus dem Stand der Technik bekannten Verfahren lassen sich wie folgt zusammenfassen. Vollschwebeschmelzverfahren lassen sich nur mit kleinen Materialmengen durchführen, so dass eine industrielle Anwendung bisher noch nicht erfolgt ist. Halbschwebeschmelzverfahren haben den Nachteil, dass derjenige Anteil des eingesetzten Materials verworfen werden muss, der mit der Plattform in Kontakt gekommen ist. Ferner gestaltet sich das Abgießen in Gussformen schwierig. Im Ergebnis ist ein Vollschwebeschmelzverfahren zur Herstellung von Gusskörpern bislang nicht wirtschaftlich durchführbar.The disadvantages of the methods known from the prior art can be summarized as follows. Fully levitated melting processes can only be carried out with small amounts of material, so that an industrial application has not yet occurred. Semi-levitation melting processes have the disadvantage that that portion of the material used that has come into contact with the platform has to be discarded. Furthermore, casting in molds is difficult. As a result, a full suspension melting process for the production of cast bodies has so far not been economically feasible.

Aufgabetask

Es ist somit eine Aufgabe der vorliegenden Erfindung, ein Verfahren bereit zu stellen, das einen wirtschaftlichen Einsatz des Schwebeschmelzens unter Vermeidung des für das Halbschwebeschmelzverfahren und Kalttiegelverfahren typischen Materialverlusts und unter Erzielung sämtlicher Vorteile der Schwebeschmelztechnologie ermöglicht. Insbesondere sollte das Verfahren einen hohen Durchsatz ermöglichen und ohne Einsatz einer unterstützenden Plattform eine ausreichende Menge an Material schmelzen können, um eine wirtschaftliche Herstellung von Gusskörpern in sehr hoher Qualität zu ermöglichen.It is therefore an object of the present invention to provide a method which enables the economic use of levitation melting while avoiding the loss of material typical of the semi-levitation melting process and cold crucible process and while achieving all Advantages of levitation melting technology made possible. In particular, the method should enable a high throughput and be able to melt a sufficient amount of material without the use of a supporting platform in order to enable the economical production of castings of very high quality.

Beschreibung der ErfindungDescription of the invention

Die Aufgabe wird durch das erfindungsgemäße Verfahren gelöst. Erfindungsgemäß ist ein Verfahren zur Herstellung von Gusskörpern aus einem leitfähigen Material, umfassend die folgenden Schritte:

  • Einbringen einer Charge des leitfähigen Materials in den Einflussbereich wenigstens eines elektromagnetischen Wechselfelds (Schmelzbereich), so dass die Charge in einem Schwebezustand gehalten wird,
  • Schmelzen der Charge,
  • Positionieren einer Gussform in einem Füllbereich unterhalb der schwebenden Charge,
  • Abguss der gesamten Charge in die Gussform,
  • Entnahme des erstarrten Gusskörpers aus der Gussform,
wobei das Volumen der geschmolzenen Charge ausreichend ist, um die Gussform in einem für die Herstellung eines Gusskörpers ausreichenden Maße zu füllen ("Füllvolumen") und die Gussform im Moment des Befüllens in eine Translationsbewegung parallel zur Abgussrichtung der Charge versetzt wird. Nach demThe object is achieved by the method according to the invention. According to the invention, a method for producing cast bodies from a conductive material, comprising the following steps:
  • Introducing a charge of the conductive material into the area of influence of at least one electromagnetic alternating field (melting range) so that the charge is kept in a suspended state,
  • Melting the batch,
  • Positioning a casting mold in a filling area below the floating batch,
  • Casting the entire batch into the mold,
  • Removal of the solidified cast body from the casting mold,
wherein the volume of the molten charge is sufficient to fill the casting mold to an extent sufficient for the production of a casting ("filling volume") and the casting mold is set in a translational movement parallel to the direction of casting of the charge at the moment of filling. After this

Befüllen der Gussform wird diese abkühlen gelassen oder mit Kühlmittel abgekühlt, so dass das Material in der Form erstarrt. Danach kann der Gusskörper aus der Form entnommen werden. Der Abguss kann in einem Fallenlassen der Charge bestehen, insbesondere durch Abschaltung des elektromagnetischen Wechselfeldes; oder der Abguss kann durch ein elektromagnetisches Wechselfeld verlangsamt werden, z.B. durch die Verwendung einer Spule.When the casting mold is filled, it is allowed to cool or is cooled with coolant so that the material solidifies in the mold. The cast body can then be removed from the mold. The casting can consist of dropping the charge, in particular by switching off the electromagnetic alternating field; or the casting can be slowed down by an alternating electromagnetic field, e.g. by using a coil.

In einer Ausführungsform umfasst das Verfahren den Schritt des Bewegens der befüllten Gussform aus dem Füllbereich nach dem Abguss aber vor der Entnahme des erstarrten Gusskörpers. Diese Ausführungsform wird besonders vorteilhaft beim Einsatz verlorener Formen eingesetzt, da somit der Füllbereich für eine weitere verlorene Form freigegeben wird. In einer anderen Ausführungsform, insbesondere bei Einsatz einer Permanentform, kann die Entnahme des Gusskörpers im Füllbereich erfolgen.In one embodiment, the method comprises the step of moving the filled casting mold out of the filling area after casting but before removing the solidified cast body. This embodiment is used particularly advantageously when using lost molds, since the filling area is thus released for another lost mold. In another embodiment, in particular when using a permanent mold, the cast body can be removed in the filling area.

Die Entnahme des erstarrten Gusskörpers kann auf unterschiedliche Arten erfolgen. In einer Ausführungsform wird die Gussform bei der Entnahme des Gusskörpers zerstört. Man spricht von einer "verlorenen Form". In einer anderen Ausführungsform kann die Gussform als Permanentform, insbesondere als Permanentkokille ausgeführt sein. Permanentkokillen bestehen vorzugsweise aus einem metallischen Material. Sie sind für einfachere Bauteile geeignet.The solidified cast body can be removed in different ways. In one embodiment, the casting mold is destroyed when the casting is removed. One speaks of a "lost form". In another embodiment, the casting mold can be designed as a permanent mold, in particular as a permanent mold. Permanent molds are preferably made of a metallic material. They are suitable for simpler components.

Eine Permanentform weist vorzugsweise zwei oder mehr Formelemente auf, die voneinander getrennt werden können, um den Gusskörper zu entformen. Beim Entformen aus Permanentformen können ein oder mehrere Ausstoßer zum Einsatz kommen.A permanent mold preferably has two or more mold elements that can be separated from one another in order to demold the cast body. When demolding from permanent molds, one or more ejectors can be used.

Unter einem "leitfähigen Material" wird erfindungsgemäß ein Material verstanden, das eine geeignete Leitfähigkeit aufweist, um das Material induktiv zu erhitzen und in der Schwebe zu halten.According to the invention, a “conductive material” is understood to mean a material which has a suitable conductivity in order to inductively heat the material and to keep it in suspension.

Unter einem "Schwebezustand" wird erfindungsgemäß ein Zustand des vollständigen Schwebens verstanden, so dass die behandelte Charge keinerlei Kontakt zu einem Tiegel oder einer Plattform oder dergleichen hat.According to the invention, a “state of suspension” is understood to mean a state of complete suspension, so that the batch being treated has no contact whatsoever with a crucible or a platform or the like.

Unter einem "Füllvolumen" einer Gussform wird ein Volumen verstanden, das die Gussform in einem Maße füllt, das für die Herstellung eines oder mehrerer vollständiger, mit der Gussform zu formenden Gusskörper ausreichend ist. Dies muss nicht notwendigerweise einer kompletten Füllung der Gussform entsprechen; auch muss es nicht einem minimal für die Herstellung eines Gusskörpers notwendigen Volumen entsprechen. Entscheidend ist, dass es nicht erforderlich ist, die Gussform über das Füllvolumen hinaus zu füllen. Insbesondere kann eine Gussform im Rahmen dieser Erfindung Kanäle oder Einfüllabschnitte aufweisen, deren Füllung nicht notwendig ist, um vollständige Gusskörper herzustellen, sondern die lediglich dazu dienen, die Schmelze in die Gussform zu füllen bzw. darin zu verteilen. Erfindungsgemäß wird die Gussform insbesondere nicht über das Volumen der geschmolzenen Charge hinaus befüllt.A “filling volume” of a casting mold is understood to mean a volume that fills the casting mold to an extent that is sufficient for the production of one or more complete cast bodies to be formed with the casting mold. This does not necessarily have to correspond to a complete filling of the casting mold; nor does it have to correspond to a minimum volume necessary for the production of a cast body. It is crucial that it is not necessary to fill the mold beyond the filling volume. In particular, within the scope of this invention, a casting mold can have channels or filler sections, the filling of which is not necessary in order to produce complete cast bodies, but which merely serve to fill the melt into the casting mold or to distribute it therein. According to the invention, the casting mold is in particular not filled beyond the volume of the molten charge.

Die erfindungsgemäß eingesetzten Gussformen weisen Kavitäten auf, die der Form der herzustellenden Gusskörper entsprechen. Es sind auch solche Gussformen im Rahmen dieser Erfindung verwendbar, die mehr als eine solche Kavität aufweisen und somit zur gleichzeitigen Herstellung von mehreren Gusskörpern geeignet sind. In einer Ausführungsform weisen die erfindungsgemäß verwendeten Gussformen genau eine Kavität zur Herstellung von genau einem Gusskörper auf. In einer Ausführungsform weist die Gussform einen Einfüllabschnitt auf, der einen größeren Durchmesser aufweist, als der zu füllende Hohlraum der Gussform. Ein solcher Einfüllabschnitt kann insbesondere trichterförmig ausgestaltet sein. Er dient dazu, den Eintritt der geschmolzenen Charge in die Gussform zu erleichtern.The casting molds used according to the invention have cavities which correspond to the shape of the cast bodies to be produced. In the context of this invention, it is also possible to use casting molds which have more than one such cavity and are therefore suitable for the simultaneous production of several cast bodies. In one embodiment, the casting molds used according to the invention have precisely one cavity for producing precisely one cast body. In one embodiment, the casting mold has a filling section which has a larger diameter than the cavity of the casting mold to be filled. Such a filling section can in particular be designed in the shape of a funnel. Its purpose is to facilitate entry of the molten charge into the casting mold.

Die Gussform besteht vorzugsweise aus einem keramischen, insbesondere oxidkeramischen, Material, wie insbesondere Al2O3, ZrO2, Y2O3 oder Mischungen daraus. Dieses Formenmaterial hat sich in der Praxis bewährt und ist besonders für verlorene Formen vorteilhaft. Erfindungsgemäß ebenfalls einsetzbare Permanentformen können aus einem metallischen Material, also einem Metall oder einer Metalllegierung, gefertigt sein.The casting mold preferably consists of a ceramic, in particular oxide-ceramic, material, such as in particular Al 2 O 3 , ZrO 2 , Y 2 O 3 or mixtures thereof. This mold material has proven itself in practice and is particularly advantageous for lost forms. Permanent forms that can also be used according to the invention can be made of a metallic material, that is to say a metal or a metal alloy.

Erfindungsgemäß kann nach dem Bewegen einer befüllten Gussform aus dem Füllbereich, oder ganz oder teilweise gleichzeitig mit dem Bewegen, der mit der Charge befüllten Gussform aus dem Füllbereich eine weitere leere Gussform in den Füllbereich hinein bewegt wird. Alternativ, insbesondere im Falle von Permanentformen, kann der Gusskörper noch in dem Füllbereich aus der Gussform entnommen werden, ohne dass die Gussform aus dem Füllbereich bewegt werden müsste. Ferner kann nach dem Abguss der Charge eine weitere Charge des leitfähigen Materials in den Einflussbereich des elektromagnetischen Wechselfeldes eingebracht werden. Die weitere Charge kann gleichermaßen geschmolzen und in die weitere Gussform abgegossen werden. Dieser Vorgang lässt sich beliebig oft wiederholen, zumal kein Tiegel benötigt wird, der einer Abnutzung unterworfen wäre. Das erfindungsgemäße Verfahren lässt sich derartig getaktet durchführen, dass jeder Charge leitfähigen Materials genau eine Gussform zugeordnet ist. Die Gussform ist mit einer Charge ausreichend befüllt und kann aus dem Füllbereich bewegt werden, um Platz für die nächste Gussform zum Empfang der nächsten Charge zu schaffen. Auf diese Weise wird ein besonders effizientes Verfahren ermöglicht, das selbst bei der relativ begrenzten Kapazität des Schwebeschmelzverfahrens einen hohen Durchsatz ermöglicht.According to the invention, after moving a filled casting mold out of the filling area, or completely or partially simultaneously with moving the casting mold filled with the charge out of the filling area, another empty casting mold is moved into the filling area. Alternatively, in particular in the case of permanent molds, the cast body can still be removed from the casting mold in the filling area without the casting mold having to be moved out of the filling area. Furthermore, after the batch has been cast, another batch of the conductive material can be introduced into the area of influence of the electromagnetic alternating field. The next batch can also be melted and poured into the further casting mold. This process can be repeated any number of times, especially since no crucible is required that would be subject to wear and tear. The method according to the invention can be carried out in such a clocked manner that exactly one casting mold is assigned to each batch of conductive material. The mold is sufficiently filled with one batch and can be moved out of the filling area to make space for the next mold to receive the next batch. In this way, a particularly efficient process is made possible, which enables a high throughput even with the relatively limited capacity of the levitation melting process.

In einer Ausführungsform wird die Gussform vor dem Befüllen vorgeheizt. Eine vorgeheizte Gussform hat den Vorteil, dass die geschmolzene Charge bei Kontakt mit der Gussform nicht sofort erstarrt. Gerade bei feinen auszufüllenden Hohlräumen, wie sie beispielsweise bei Schaufelrädern für Turbolader vorkommen, ist es zweckmäßig, die Gussform auf eine Temperatur vorzuheizen, die es der geschmolzenen Charge erlaubt, sich in die feinen Hohlräume der Gussform zu verteilen, bevor das Material erstarrt. Es hat sich als vorteilhaft erwiesen, die Gussformen auf Temperaturen im Bereich von 400 bis 1.100 °C, insbesondere 500 bis 800 °C, vorzuheizen, bevor die Gussform mit der geschmolzenen Charge befüllt wird. Eine zu geringe Temperatur kann die Erstarrung unter Umständen nicht verhindern. Eine zu hohe Temperatur erhöht die Gefahr unerwünschter Reaktionen des Materials mit der Gussform. Es sind auch Ausführungsformen erfindungsgemäß, bei denen die Gussform nicht vorgeheizt wird. Solche Ausführungsformen sind insbesondere dann durchführbar, wenn die geschmolzene Charge auf eine ausreichend hohe Temperatur überhitzt werden kann und somit trotz nicht vorgeheizter Gussform nicht sofort erstarrt. Der Fachmann wird im Einzelfall abzuwägen haben, ob und auf welche Temperatur die Gussform vorzuheizen ist, wobei die Größe der Gussform und deren Hohlräume, die Schmelztemperatur des Materials, dessen Schmelzpunkt und Abhängigkeit der Viskosität von der Temperatur, das Material der Gussform und die Reaktivität des Materials eine Rolle spielen.In one embodiment, the casting mold is preheated before filling. A preheated casting mold has the advantage that the molten charge does not solidify immediately upon contact with the casting mold. In the case of fine cavities to be filled, such as those found in turbine blades for turbochargers, it is useful to preheat the casting mold to a temperature that allows the molten charge to spread into the fine cavities of the casting mold before the material solidifies. It has proven advantageous to preheat the casting molds to temperatures in the range from 400 to 1,100 ° C., in particular 500 to 800 ° C., before the casting mold is filled with the molten charge. If the temperature is too low, it may not be able to prevent solidification. Too high a temperature increases the risk of undesirable reactions between the material and the casting mold. There are also embodiments according to the invention in which the casting mold is not preheated. Such embodiments are particularly feasible if the molten charge can be overheated to a sufficiently high temperature and thus does not solidify immediately despite the casting mold not being preheated. The person skilled in the art will have to weigh up in each individual case whether and to what temperature the casting mold is to be preheated, taking into account the size of the casting mold and its cavities, the melting temperature of the material, its melting point and the dependence of the Viscosity depends on the temperature, the material of the mold and the reactivity of the material play a role.

Um die Verteilung der Schmelze in der Gussform zu beschleunigen, kann die Gussform während der Befüllung um eine vertikale Achse, insbesondere eine vertikale Symmetrieachse, rotiert werden. Dadurch wird die Schmelze in der Gussform gleichsam in die Hohlräume geschleudert. Gerade bei Material, dessen Schmelze bei sinkender Temperatur schnell an Viskosität zunimmt, ist es wichtig, dieses Material schnell in die Hohlräume der Gussform zu bringen, damit keine Erstarrung eintritt, bevor die Form ausreichend befüllt ist. Es ist zu berücksichtigen, dass sich die geschmolzene Charge bereits mit dem Abguss abzukühlen beginnt. Ein Material, das eine ausgeprägte Abhängigkeit der Viskosität von der Temperatur zeigt, ist Titan und Titanlegierungen, insbesondere TiAl, so dass besonders bei Titan und Titanlegierungen als leitfähigem Material die Gussform rotiert werden sollte. Neben der schnelleren Verteilung der geschmolzenen Charge in der Gussform werden durch die Rotation auch Turbulenzen vermieden, die sich extrem schädlich auf die Qualität der Gusskörper auswirken.In order to accelerate the distribution of the melt in the casting mold, the casting mold can be rotated about a vertical axis, in particular a vertical axis of symmetry, during filling. As a result, the melt in the casting mold is, as it were, thrown into the cavities. Particularly in the case of material whose melt rapidly increases in viscosity as the temperature drops, it is important to bring this material quickly into the cavities of the casting mold so that no solidification occurs before the mold is sufficiently filled. It must be taken into account that the melted batch begins to cool down as soon as it is poured. A material that shows a pronounced dependence of the viscosity on the temperature is titanium and titanium alloys, in particular TiAl, so that the casting mold should be rotated, particularly with titanium and titanium alloys as conductive material. In addition to the faster distribution of the molten charge in the casting mold, the rotation also prevents turbulence, which has an extremely harmful effect on the quality of the cast body.

Es hat sich als vorteilhaft erwiesen, die Rotation der Gussform mit einer Drehzahl von 10 bis 1.000, insbesondere von 100 bis 500 oder von 150 bis 350, Umdrehungen pro Minute durchzuführen. Die zu wählende Drehzahl hängt von dem Viskositätsverhalten der geschmolzenen Charge und der inneren Form der Gussform ab. Je schneller die Viskosität des Materials bei Abkühlung steigt, desto schneller muss es in die Hohlräume der Gussform geschleudert werden.It has proven to be advantageous to rotate the casting mold at a speed of 10 to 1,000, in particular 100 to 500 or 150 to 350, revolutions per minute. The speed to be selected depends on the viscosity behavior of the molten charge and the internal shape of the casting mold. The faster the viscosity of the material increases when it cools, the faster it has to be thrown into the cavities of the mold.

Erfindungsgemäß bevorzugt wird sowohl das Schmelzen des leitfähigen Materials als auch das Befüllen der Gussform unter Vakuum oder unter Schutzgas durchgeführt. Bevorzugte Schutzgase sind je nach zu schmelzendem Material Stickstoff, eines der Edelgase oder Mischungen davon. Besonders bevorzugt wird Argon oder Helium verwendet. Der Einsatz von Schutzgas bzw. Vakuum dient der Vermeidung unerwünschter Reaktionen des Materials mit Komponenten der Atmosphäre, insbesondere mit Sauerstoff. Bevorzugt wird das Schmelzen und/oder das Befüllen der Gussform in einem Vakuum durchgeführt, insbesondere bei einem Druck von höchstens 1000 Pa.According to the invention, both the melting of the conductive material and the filling of the casting mold are preferably carried out under vacuum or under protective gas. Preferred protective gases, depending on the material to be melted, are nitrogen, one of the noble gases or mixtures thereof. Argon or helium is particularly preferably used. The use of protective gas or vacuum serves to avoid undesirable reactions of the material with components of the atmosphere, in particular with oxygen. The melting and / or the filling of the casting mold is preferably carried out in a vacuum, in particular at a pressure of at most 1000 Pa.

In dem erfindungsgemäßen Verfahren wird die Gussform im Moment des Befüllens in eine Translationsbewegung parallel zur Abgussrichtung der Charge, insbesondere in Abgussrichtung, versetzt. Mit anderen Worten wird die Gussform, ausgelöst durch den Vorgang des Abgusses, nach oben oder unten bewegt. Dadurch wird die Füllgeschwindigkeit der Gussform gesteuert, also beschleunigt oder verlangsamt. Diese Maßnahme der Translation kann zusammen mit der oben beschriebenen Rotation durchgeführt werden. Beide Maßnahmen tragen zu einer optimalen Befüllung im Sinne einer möglichst vollständigen und schnellen, gleichzeitig aber turbulenzarmen Befüllung der Gussform bei, so dass die Qualität der erhaltenen Gusskörper verbessert wird. Eine Translation in Abgussrichtung erfolgt mit einer Geschwindigkeit, die geringer ist als die Fallgeschwindigkeit der geschmolzenen Charge. Die Beschleunigung der Gussform in Abgussrichtung sollte geringer sein als die Fallbeschleunigung der Charge. Durch den Einsatz der Translation allein oder zusammen mit der Rotation wird ferner ein Herausspritzen oder Überlaufen der geschmolzenen Charge vermieden, was andernfalls aufgrund des schnellen und vollständigen Befüllens der Gussform in einem Guss zu befürchten wäre.In the method according to the invention, the casting mold is set in a translational movement parallel to the pouring direction of the batch, in particular in the pouring direction, at the moment of filling. In other words, the casting mold, triggered by the casting process, is moved up or down. This controls the filling speed of the mold, i.e. accelerates or decelerates it. This translation measure can be carried out together with the rotation described above become. Both measures contribute to an optimal filling in the sense of a filling of the casting mold that is as complete and as rapid as possible, but at the same time with little turbulence, so that the quality of the cast bodies obtained is improved. A translation in the pouring direction takes place at a speed which is less than the falling speed of the molten charge. The acceleration of the mold in the pouring direction should be less than the acceleration due to gravity of the batch. By using the translation alone or together with the rotation, splashing out or overflowing of the molten charge is avoided, which would otherwise be feared due to the rapid and complete filling of the casting mold in one pour.

Es hat sich als ausreichend erwiesen, die Translation über eine Strecke von höchstens 4 m, insbesondere höchstens 3 m, höchstens 2 m und besonderes bevorzugt höchstens 1 m durchzuführen, ausgehend von der Ausgangslage der Gussform im Moment des Abgusses. Diese Strecke genügt, um die Vorteile der Translationsbewegung auf die Qualität der hergestellten Gusskörper zu erzielen, ohne dass die benötigte Vorrichtung zu sehr vergrößert wird. Die Translation wird vorzugsweise gestoppt, wenn die gesamte Charge in die Gussform eingetreten ist.It has proven to be sufficient to carry out the translation over a distance of at most 4 m, in particular at most 3 m, at most 2 m and particularly preferably at most 1 m, starting from the initial position of the casting mold at the moment of casting. This distance is sufficient to achieve the advantages of the translational movement on the quality of the cast bodies produced without the required device being enlarged too much. The translation is preferably stopped when the entire batch has entered the mold.

Die Rotations- und/oder die Translationsbewegung wird insbesondere durch den Abguss der Charge ausgelöst. Zu diesem Zweck können Sensoren vorgesehen sein, die den Abguss detektieren und ein Signal an eine Antriebseinheit senden, die Rotation und/oder Translation an der Gussform auslöst. Geeignete Sensoren können beispielsweise eine Veränderung bzw. Abschaltung des elektromagnetischen Wechselfeldes erfassen oder die Anwesenheit der geschmolzenen Charge in einem Übergangsbereich zwischen einem Schmelzbereich und der Gussform (z.B. mittels Lichtschranke). Es sind auch viele andere Sensoren denkbar, um ein entsprechendes Signal auszulösen.The rotational and / or translational movement is triggered in particular by the casting of the batch. For this purpose, sensors can be provided that detect the casting and send a signal to a drive unit that triggers rotation and / or translation on the casting mold. Suitable sensors can, for example, detect a change or shutdown of the electromagnetic alternating field or the presence of the molten charge in a transition area between a melting area and the casting mold (e.g. by means of a light barrier). Many other sensors are also conceivable in order to trigger a corresponding signal.

Das erfindungsgemäß eingesetzte leitfähige Material weist in einer bevorzugten Ausführungsform wenigstens ein hochschmelzendes Metall aus der folgenden Gruppe auf: Titan, Zirkonium, Vanadium, Tantal, Wolfram, Hafnium, Niob, Rhenium, Molybdän. Alternativ kann auch ein weniger hoch schmelzendes Metall wie Nickel, Eisen oder Aluminium eingesetzt werden. Als leitfähiges Material kann auch eine Mischung bzw. Legierung mit einem oder mehreren der vorgenannten Metalle eingesetzt werden. Vorzugsweise hat das Metall einen Anteil von wenigstens 50 Gew.-%, insbesondere wenigstens 60 Gew.-% oder wenigstens 70 Gew.-%, an dem leitfähigen Material. Es hat sich gezeigt, dass diese Metalle besonders von den Vorteilen der vorliegenden Erfindung profitieren. In einer besonders bevorzugten Ausführungsform ist das leitfähige Material Titan oder eine Titanlegierung, insbesondere TiAl oder TiAIV. Diese Metalle bzw. Legierungen können besonders vorteilhaft verarbeitet werden, da sie eine ausgeprägte Abhängigkeit der Viskosität von der Temperatur aufweisen und darüber hinaus besonders reaktiv, insbesondere im Hinblick auf die Materialien der Gussform, sind. Da das erfindungsgemäße Verfahren ein kontaktloses Schmelzen in der Schwebe mit einem extrem schnellen Befüllen der Gussform kombiniert, kann gerade für solche Metalle ein besonderer Vorteil realisiert werden. Mit dem erfindungsgemäßen Verfahren lassen sich Gusskörper herstellen, die eine besonders dünne oder sogar keinerlei Oxidschicht aus der Reaktion der Schmelze mit dem Material der Gussform aufweisen.In a preferred embodiment, the conductive material used according to the invention has at least one high-melting metal from the following group: titanium, zirconium, vanadium, tantalum, tungsten, hafnium, niobium, rhenium, molybdenum. Alternatively, a metal with a lower melting point such as nickel, iron or aluminum can be used. A mixture or alloy with one or more of the aforementioned metals can also be used as the conductive material. The metal preferably has a proportion of at least 50% by weight, in particular at least 60% by weight or at least 70% by weight, of the conductive material. It has been shown that these metals particularly benefit from the advantages of the present invention. In a particularly preferred embodiment, the conductive material is titanium or a titanium alloy, in particular TiAl or TiAlV. These metals or alloys can be processed particularly advantageously because they have a pronounced dependency the viscosity of the temperature and, moreover, are particularly reactive, in particular with regard to the materials of the casting mold. Since the method according to the invention combines contactless melting in suspension with extremely fast filling of the casting mold, a particular advantage can be realized for such metals in particular. With the method according to the invention, cast bodies can be produced which have a particularly thin or even no oxide layer from the reaction of the melt with the material of the casting mold.

In einer vorteilhaften Ausführungsform der Erfindung wird das leitfähige Material beim Schmelzen auf eine Temperatur überhitzt, die wenigstens 10 °C, wenigstens 20 °C oder wenigstens 30 °C über dem Schmelzpunkt des Materials liegt. Durch die Überhitzung wird vermieden, dass das Material beim Kontakt mit der Gussform, deren Temperatur unterhalb der Schmelztemperatur liegt, augenblicklich erstarrt. Es wird erreicht, dass sich die Charge in der Gussform verteilen kann, bevor die Viskosität des Materials zu hoch wird. Es ist ein Vorteil des Schwebeschmelzens, dass kein Tiegel verwendet werden muss, der im Kontakt mit der Schmelze ist. So wird der hohe Materialverlust des Kalttiegelverfahrens genauso vermieden wie eine Kontamination der Schmelze durch Tiegelbestandteile. Ein weiterer Vorteil ist, dass die Schmelze verhältnismäßig hoch erhitzt werden kann, da ein Betrieb im Vakuum oder unter Schutzgas möglich ist und kein Kontakt zu reaktionsfähigen Materialien stattfindet. Dennoch können die meisten Materialien nicht beliebig überhitzt werden, da andernfalls eine heftige Reaktion mit der Gussform zu befürchten ist. Daher ist die Überhitzung vorzugsweise auf höchstens 300 °C, insbesondere höchstens 200 °C und besonders bevorzugt höchstens 100 °C über den Schmelzpunkt des leitfähigen Materials begrenzt.In an advantageous embodiment of the invention, the conductive material is superheated during melting to a temperature which is at least 10 ° C., at least 20 ° C. or at least 30 ° C. above the melting point of the material. Overheating prevents the material from solidifying instantly when it comes into contact with the casting mold, the temperature of which is below the melting temperature. The result is that the charge can be distributed in the mold before the viscosity of the material becomes too high. It is an advantage of levitation melting that there is no need to use a crucible that is in contact with the melt. This avoids the high loss of material in the cold crucible process as well as contamination of the melt with crucible components. Another advantage is that the melt can be heated to a relatively high level, since operation in a vacuum or under protective gas is possible and there is no contact with reactive materials. However, most materials cannot be overheated at will, since otherwise a violent reaction with the mold is to be feared. The overheating is therefore preferably limited to at most 300 ° C., in particular at most 200 ° C. and particularly preferably at most 100 ° C. above the melting point of the conductive material.

Das Schmelzen wird erfindungsgemäß bevorzugt für eine Dauer von 0,5 min bis 20 min, insbesondere 1 min bis 10 min, durchgeführt. Diese Schmelzdauern lassen sich in dem Schwebeschmelzverfahren gut realisieren, da ein sehr effizienter Wärmeeintrag in die Charge möglich ist und aufgrund der induzierten Wirbelströme eine sehr gute Temperaturverteilung innerhalb kürzester Zeit erfolgt. Nach Abschluss des Schmelzens erfolgt der Abguss der geschmolzenen Charge in die Gussform. Der Abguss kann in einem Fallenlassen der geschmolzenen Charge bestehen oder kontrolliert durch elektromagnetische Beeinflussung etwa mit einer (weiteren) für diesen Zweck geeigneten Spule erfolgen. Die befüllte Gussform wird fortbewegt und vorzugsweise durch eine neue, leere Gussform ersetzt, so dass im Abstand weniger Minuten Gussformen befüllt werden können. Eine Charge leitfähigen Materials kann erfindungsgemäß bevorzugt Massen von 50 g bis 2 kg, insbesondere 100 g bis 1 kg aufweisen. In einer Ausführungsform beträgt die Masse wenigstens 200 g. Diese Massen sind ausreichend, um Turbinenschaufeln, Turboladerräder oder Prothesen herzustellen. Es sind aber auch beliebige andere Formen denkbar, zumal sich mit dem Verfahren auch komplexe Formen mit feinen und verzweigten Hohlräumen herstellen lassen. Die Kombination von hoher Schmelztemperatur und dadurch geringer Viskosität, Vakuum bzw. Schutzgas zur Vermeidung von Reaktionen, Rotation zur schnellen Verteilung der Schmelze in der Gussform, Translation zur Einstellung einer optimalen Füllgeschwindigkeit und getaktete Befüllung der Gussformen in nur einem Füllschritt führen zu einem extrem vielseitigen Verfahren, das abhängig von dem zu schmelzenden Material und der eingesetzten Gussform optimiert werden kann.According to the invention, melting is preferably carried out for a period of 0.5 min to 20 min, in particular 1 min to 10 min. These melting times can be easily achieved in the levitation melting process, since a very efficient heat input into the charge is possible and, due to the induced eddy currents, a very good temperature distribution takes place within a very short time. After melting is complete, the molten batch is poured into the casting mold. The casting can consist of dropping the molten charge or it can be controlled by electromagnetic interference, for example with a (further) coil suitable for this purpose. The filled casting mold is moved and preferably replaced by a new, empty casting mold, so that casting molds can be filled every few minutes. According to the invention, a batch of conductive material can preferably have masses of 50 g to 2 kg, in particular 100 g to 1 kg. In one embodiment the mass is at least 200 g. These masses are sufficient to produce turbine blades, turbocharger wheels or prostheses. But there are also any other shapes conceivable, especially since the process can also be used to produce complex shapes with fine and branched cavities. The combination of high melting temperature and thus low viscosity, vacuum or protective gas to avoid reactions, rotation for rapid distribution of the melt in the casting mold, translation for setting an optimal filling speed and clocked filling of the casting molds in just one filling step lead to an extremely versatile process which can be optimized depending on the material to be melted and the casting mold used.

Vorzugsweise werden zur Herbeiführung des Schwebezustandes der Charge wenigstens zwei elektromagnetische Felder unterschiedlicher Wechselstromfrequenz verwendet. Im klassischen Schwebeschmelzverfahren wird mit einer oder mehreren konischen Spulen gearbeitet, um die benötigten elektromagnetischen Felder zu erzeugen. Auch so ein klassisches Schwebeschmelzverfahren mit konischen Spulen kann erfindungsgemäß eingesetzt werden. Es sind dann allerdings die Chargengrößen stark begrenzt, da im Bereich der Symmetrieachse nur die Oberflächenspannung der geschmolzenen Charge das Abfließen verhindert. Dieser Nachteil kann durch den Einsatz wenigstens zweier elektromagnetischer Felder unterschiedlicher Frequenz vermieden werden (vgl. Spitans et al., Magnetohydrodynamics Vol.51 (2015), No.1, pp.121-132 ). Die Magnetfelder sollten in Abwesenheit einer Ladung vorzugsweise horizontal und insbesondere rechtwinklig zueinander verlaufen. Auf diese Weise können verhältnismäßig große Massen eines leitfähigen Materials in einem Vollschwebeschmelzverfahren verarbeitet werden. Der Einsatz unterschiedlicher Frequenzen verhindert die Rotation der Probe, bevorzugt ist ein Frequenzunterschied von jeweils wenigstens 1 kHz.Preferably, at least two electromagnetic fields of different alternating current frequencies are used to bring the charge into suspension. In the classic levitation melting process, one or more conical coils are used to generate the required electromagnetic fields. Such a classic levitation melting process with conical coils can also be used according to the invention. However, the batch sizes are then very limited, since in the area of the axis of symmetry only the surface tension of the molten batch prevents it from flowing off. This disadvantage can be avoided by using at least two electromagnetic fields with different frequencies (cf. Spitans et al., Magnetohydrodynamics Vol. 51 (2015), No.1, pp.121-132 ). In the absence of a charge, the magnetic fields should preferably run horizontally and in particular at right angles to one another. In this way, relatively large masses of conductive material can be processed in a full suspension melting process. The use of different frequencies prevents the sample from rotating; a frequency difference of at least 1 kHz in each case is preferred.

In einer bevorzugten Ausführungsform des Verfahrens wird zur Konzentration des Magnetfeldes und Stabilisierung der Charge wenigstens ein ferromagnetisches Element horizontal um den Bereich angeordnet, in dem die Charge geschmolzen wird. Das ferromagnetische Element kann ringförmig um den Schmelzbereich angeordnet sein, wobei unter "ringförmig" nicht nur kreisrunde Elemente, sondern auch eckige, insbesondere vier- oder mehreckige Ringelemente verstanden werden. Das Element kann mehrere Stababschnitte aufweisen, die insbesondere horizontal in Richtung des Schmelzbereiches ragen. Das ferromagnetische Element besteht aus einem ferromagnetischen Material, vorzugsweise mit einer Amplitudenpermeabilität µa > 10, mehr bevorzugt µa > 50 und besonders bevorzugt µa > 100. Die Amplitudenpermeabilität bezieht sich insbesondere auf die Permeabilität in einem Temperaturbereich zwischen 25 °C und 100 °C und bei einer magnetischen Flussdichte zwischen 0 und 400 mT. Die Amplitudenpermeabilität beträgt insbesondere wenigstens ein Hundertstel, insbesondere wenigstens 10 Hundertstel oder 25 Hundertstel der Amplitudenpermeabilität von weichmagnetischem Ferrit (z.B. 3C92). Dem Fachmann sind geeignete Materialien bekannt.In a preferred embodiment of the method, in order to concentrate the magnetic field and stabilize the charge, at least one ferromagnetic element is arranged horizontally around the area in which the charge is melted. The ferromagnetic element can be arranged in a ring around the melting area, with "ring-shaped" not only being understood to mean circular elements, but also angular, in particular square or polygonal ring elements. The element can have several rod sections, which in particular protrude horizontally in the direction of the melting area. The ferromagnetic element consists of a ferromagnetic material, preferably with an amplitude permeability μ a > 10, more preferably μ a > 50 and particularly preferably μ a > 100. The amplitude permeability relates in particular to the permeability in a temperature range between 25 ° C and 100 ° C and at a magnetic flux density between 0 and 400 mT. The amplitude permeability is in particular at least one hundredth, in particular at least 10 hundredths or 25 hundredths of the amplitude permeability of soft magnetic ferrite (for example 3C92). Suitable materials are known to those skilled in the art.

In einer bevorzugten Ausführungsform werden die elektromagnetischen Felder von wenigstens zwei Paaren von Induktionsspulen erzeugt, deren Achsen horizontal ausgerichtet sind, die Leiter der Spulen sind also vorzugsweise jeweils auf einen horizontal ausgerichteten Spulenkörper gewickelt. Die Spulen können jeweils um einen in Richtung des Schmelzbereiches ragenden Stababschnitt des ferromagnetischen Elements angeordnet sein. Die Spulen können kühlmittelgekühlte Leiter aufweisen.In a preferred embodiment, the electromagnetic fields are generated by at least two pairs of induction coils, the axes of which are horizontally aligned, so the conductors of the coils are preferably each wound on a horizontally aligned coil former. The coils can each be arranged around a rod section of the ferromagnetic element protruding in the direction of the melting area. The coils can have coolant-cooled conductors.

In einer besonders bevorzugten Ausführungsform des Verfahrens wird zusätzlich eine Spule, insbesondere eine konische Spule, mit vertikaler Symmetrieachse unterhalb der zu schmelzenden Charge angeordnet, um die Abgussgeschwindigkeit zu beeinflussen. Diese Spule kann in einer bevorzugten Ausführungsform ein elektromagnetisches Feld einer dritten Wechselstromfrequenz erzeugen (vgl. Spitans et al., Numerical and experimental investigations of a large scale electromagnetic levitation melting of metals, Conference Paper 10th PAMIR International Conference - Fundamental and Applied MHD, June 20-24, 2016, Cagliari, Italy ). Diese Spule kann vorzugsweise ferner dazu dienen, das ferromagnetische Element vor dem Einfluss zu großer Hitze zu schützen. Zu diesem Zweck kann der Leiter dieser Spule von einem Kühlmittel durchströmt werden.In a particularly preferred embodiment of the method, a coil, in particular a conical coil, with a vertical axis of symmetry is additionally arranged below the charge to be melted in order to influence the casting speed. In a preferred embodiment, this coil can generate an electromagnetic field of a third alternating current frequency (cf. Spitans et al., Numerical and experimental investigations of a large scale electromagnetic levitation melting of metals, Conference Paper 10th PAMIR International Conference - Fundamental and Applied MHD, June 20-24, 2016, Cagliari, Italy ). This coil can preferably also serve to protect the ferromagnetic element from the influence of excessive heat. For this purpose a coolant can flow through the conductor of this coil.

Kurzbeschreibunq der FigurenBrief description of the figures

  • Figur 1 ist eine Seitenansicht einer Gussform unterhalb eines Schmelzbereiches mit ferromagnetischem Element, Spulen und einer Charge leitfähigen Materials. Figure 1 Figure 13 is a side view of a mold below a melt area with ferromagnetic element, coils and a charge of conductive material.
  • Figur 2 ist eine Schnittansicht des Aufbaus gemäß Figur 1. Figure 2 FIG. 13 is a sectional view of the structure of FIG Figure 1 .
  • Figur 3 ist eine perspektivische Schnittansicht des Aufbaus gemäß Figur 1. Figure 3 FIG. 13 is a perspective sectional view of the structure of FIG Figure 1 .
  • Figur 4 zeigt eine erfindungsgemäß einsetzbare Spulenanordnung in Aufsicht. Figure 4 shows a coil arrangement that can be used according to the invention in plan view.
  • Figur 5 zeigt perspektivische Ansicht einer Permanentform in einem Füllbereich mit Charge im Schmelzbereich. Figure 5 shows a perspective view of a permanent form in a filling area with charge in the melting area.
  • Figur 6 zeigt eine Schnittansicht einer Permanentform in einem Füllbereich, ebenfalls mit Charge im Schmelzbereich. Figure 6 shows a sectional view of a permanent form in a filling area, also with a charge in the melting area.
FigurenbeschreibungFigure description

Die Figuren zeigen bevorzugte Ausführungsformen. Sie dienen allein der Veranschaulichung.

  • Figur 1 zeigt eine Charge 1 aus leitfähigem Material, die sich im Einflussbereich von elektromagnetischen Wechselfeldern befindet (Schmelzbereich), die mit Hilfe der Spulen 3 erzeugt werden. Unterhalb der Charge 1 befindet sich eine leere Gussform 2, die von einem Halter 5 im Füllbereich gehalten wird. Der Halter 5 ist geeignet, die Gussform 2 in Rotation und/oder Translation zu versetzen, was durch die eingezeichneten Pfeile symbolisiert wird. Um den Einflussbereich der Spulen 3 ist ein ferromagnetisches Element 4 angeordnet. Die Charge 1 wird in dem erfindungsgemäßen Verfahren schwebend geschmolzen und nach erfolgter Schmelze in die Gussform 2 abgegossen. Die Gussform 2 weist einen trichterförmigen Einfüllabschnitt 7 auf.
  • Figur 2 zeigt die gleichen Komponenten wie Figur 1. In Figur 2 sind auch die in Richtung des Schmelzbereichs ragenden Stababschnitte 6 zu erkennen, um die herum die Spulen 3 angeordnet sind. Die Stababschnitte 6 sind in dieser bevorzugten Ausführungsform Teile des ferromagnetischen Elements 4 und bilden die Kerne der Spulen 3. Die Achsen der Spulenpaare 3 sind horizontal und rechtwinklig zueinander ausgerichtet, wobei je zwei gegenüberliegende Spulen 3 ein Paar bilden.
  • Figur 3 zeigt die gleichen Komponenten wie die Figuren 1 und 2, wobei in Figur 3 die rechtwinklige Anordnung der Stababschnitte 6 und der Spulenachsen gut erkennbar ist.
  • Figur 4 zeigt nochmals die Anordnung der Spulen 3 innerhalb eines ferromagnetischen Elements 4. Das ferromagnetische Element 4 ist als achteckiges Ringelement ausgestaltet. Jeweils zwei auf einer Achse A, B liegende Spulen 3 bilden ein Spulenpaar. Unterhalb der Spulenanordnung ist der Einfüllabschnitt 7 einer Gussform erkennbar. Die Spulenachsen A, B sind rechtwinklig zueinander angeordnet.
  • Figur 5 zeigt eine Anordnung zur Durchführung eines erfindungsgemäßen Verfahrens mit einer Permanentform als Gussform 2. Die Permanentform 2 ist eine Permanentkokille mit zwei Formelementen 8, 9, die zum Zweck des Entformens voneinander getrennt werden können. Ein Ausstoßer 10 ist durch eines der Formelemente 8 geführt, um das Entformen unterstützen. Die Permanentform 2 ist wie die als verlorene Formen ausgeführten Gussformen auf einem Halter 5 angeordnet, so dass die Gussform 2 in eine Rotations- und/oder Translationsbewegung versetzt werden kann. Das Entformen der Permanentform 2 kann im Füllbereich stattfinden.
  • Figur 6 zeigt eine Schnittansicht einer Anordnung zur Durchführung des erfindungsgemäßen Verfahrens mit einer Permanentform 2 mit zwei Formelementen 8, 9 und Ausstoßer 10. Die Permanentform 2 weist auch einen trichterförmigen Einfüllabschnitt 7 auf.
The figures show preferred embodiments. They are used for illustration purposes only.
  • Figure 1 shows a charge 1 of conductive material that is in the area of influence of alternating electromagnetic fields (melting area) that are generated with the aid of the coils 3. Below the batch 1 there is an empty casting mold 2, which is held by a holder 5 in the filling area. The holder 5 is suitable for setting the casting mold 2 in rotation and / or translation, which is symbolized by the arrows shown. A ferromagnetic element 4 is arranged around the area of influence of the coils 3. In the method according to the invention, the batch 1 is suspended and poured into the casting mold 2 after the melt has been carried out. The casting mold 2 has a funnel-shaped filling section 7.
  • Figure 2 shows the same components as Figure 1 . In Figure 2 the rod sections 6 protruding in the direction of the melting area around which the coils 3 are arranged can also be seen. In this preferred embodiment, the rod sections 6 are parts of the ferromagnetic element 4 and form the cores of the coils 3. The axes of the coil pairs 3 are aligned horizontally and at right angles to one another, with two opposing coils 3 forming a pair.
  • Figure 3 shows the same components as that Figures 1 and 2 , where in Figure 3 the right-angled arrangement of the rod sections 6 and the coil axes can be clearly seen.
  • Figure 4 shows again the arrangement of the coils 3 within a ferromagnetic element 4. The ferromagnetic element 4 is designed as an octagonal ring element. In each case two coils 3 lying on an axis A, B form a coil pair. The filling section 7 of a casting mold can be seen below the coil arrangement. The coil axes A, B are arranged at right angles to one another.
  • Figure 5 shows an arrangement for carrying out a method according to the invention with a permanent mold as the casting mold 2. The permanent mold 2 is a permanent mold with two mold elements 8, 9, which can be separated from one another for the purpose of demolding. An ejector 10 is guided through one of the mold elements 8 in order to assist the demolding. The permanent mold 2, like the casting molds designed as lost molds, is arranged on a holder 5, so that the casting mold 2 can be set in a rotational and / or translational movement. The demolding of the permanent mold 2 can take place in the filling area.
  • Figure 6 shows a sectional view of an arrangement for carrying out the method according to the invention with a permanent mold 2 with two mold elements 8, 9 and an ejector 10. The permanent mold 2 also has a funnel-shaped filling section 7.

BezugszeichenlisteList of reference symbols

11
ChargeBatch
22
Gussformmold
33
SpuleKitchen sink
44th
ferromagnetisches Elementferromagnetic element
55
Halterholder
66th
StababschnittRod section
77th
EinfüllabschnittFilling section
8, 98, 9
FormelementeForm elements
1010
AusstoßerEjector

Claims (21)

  1. Method for producing cast items of a conductive material, comprising the following steps:
    - introducing a charge (1) of the conductive material into the sphere of influence of at least one alternating electromagnetic field, so that the charge is kept in a levitating state,
    - melting the charge (1),
    - positioning a mould (2) in a filling region below the levitating charge (1),
    - pouring the entire charge (1) into the mould (2),
    - removing the solidified cast item from the mould (2),
    characterized in that the volume of the molten charge (1) is sufficient to fill the mould (2) to an adequate degree for the production of a cast item, and at the moment of casting, the mould (2) is moved in translation parallel to the direction of pouring of the charge (1).
  2. Method according to Claim 1, wherein the filled mould (2) is removed from the filling region after pouring of the charge (1) and prior to removal of the cast item.
  3. Method according to Claim 2, wherein another empty mould (2) is moved into the filling region after the removal from the filling region of the filled mould (2), or entirely or partially simultaneously with the removal from the filling region of the mould (2) filled with the charge (1).
  4. Method according to one of Claims 1 to 3, wherein the mould (2) is preheated prior to filling.
  5. Method according to at least one of the preceding claims, wherein the mould (2) is rotated about a vertical axis during filling.
  6. Method according to Claim 5, wherein the rotation is carried out with a rotational speed of 10 to 1000, in particular 100 to 500, revolutions per minute.
  7. Method according to at least one of the preceding claims, wherein both melting of the charge (1) and filling of the mould (2) are carried out under vacuum, in particular at a pressure of at most 1000 Pa, or under a protective gas, in particular nitrogen, one of the noble gases or mixtures thereof.
  8. Method according to at least one of the preceding claims, wherein, at the moment of filling, the mould (2) is moved in translation in the direction of pouring.
  9. Method according to at least one of Claims 5 to 8, wherein the rotational and/or translational movement is triggered by the pouring of the charge (1).
  10. Method according to at least one of the preceding claims, wherein the conductive material contains at least one metal from the following group: titanium, zirconium, vanadium, tantalum, tungsten, hafnium, niobium, rhenium, molybdenum, nickel, iron, aluminium.
  11. Method according to Claim 10, wherein the metal has a fraction of at least 50 wt%, in particular at least 60 wt% or at least 70 wt%, of the conductive material.
  12. Method according to at least one of the preceding claims, wherein the conductive material is titanium or a titanium alloy, in particular TiAl or TiAIV.
  13. Method according to at least one of the preceding claims, wherein the conductive material is superheated, during melting, to a temperature at least 10°C, at least 20°C or at least 30°C above the melting point of the material.
  14. Method according to at least one of the preceding claims, wherein the casting mould (2) is made of a metallic or ceramic material, in particular an oxide-ceramic material.
  15. Method according to at least one of the preceding claims, wherein melting is carried out for a duration of 0.5 min to 20 min, in particular 1 min to 10 min.
  16. Method according to at least one of the preceding claims, wherein, in order to bring about the levitating state of the charge (1), use is made of at least two electromagnetic fields of different alternating current frequency.
  17. Method according to Claim 16, wherein, in the absence of a load, the magnetic fields produced run horizontally and/or are arranged at right angles to one another.
  18. Method according to at least one of the preceding claims, wherein, in order to concentrate the magnetic field and stabilize the charge (1), at least one ferromagnetic element (4) made of a ferromagnetic material, in particular having an amplitude permeability µa > 10, is arranged horizontally around the region in which the charge (1) is melted.
  19. Method according to one of Claims 16 to 18, wherein the electromagnetic fields are generated using at least two pairs of induction coils (3) whose axes (A, B) are oriented horizontally.
  20. Method according to at least one of Claims 16 to 19, wherein in addition a coil (3), in particular a conical coil, having a vertical coil axis is arranged below the charge (1) to be melted, in order to influence the pouring rate, wherein this coil generates an electromagnetic field of a third alternating current frequency.
  21. Method according to at least one of the preceding claims, wherein the mould (2) is a permanent die having two or more mould elements (8, 9), wherein the removal of the cast item from the permanent die involves the separation of the mould elements (8, 9).
EP18701010.3A 2017-01-17 2018-01-17 Casting method Active EP3570993B8 (en)

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DE102017100836.5A DE102017100836B4 (en) 2017-01-17 2017-01-17 Casting process
PCT/EP2018/051056 WO2018134219A1 (en) 2017-01-17 2018-01-17 Casting method

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CN109963668A (en) 2019-07-02
RU2738851C2 (en) 2020-12-17
JP6861823B2 (en) 2021-04-21
JP2020514064A (en) 2020-05-21
PT3570993T (en) 2020-11-04
TW201831247A (en) 2018-09-01
ES2827073T3 (en) 2021-05-19
SI3570993T1 (en) 2021-02-26
US20190366427A1 (en) 2019-12-05
KR102222041B1 (en) 2021-03-03
EP3570993A1 (en) 2019-11-27
WO2018134219A1 (en) 2018-07-26
TWI724269B (en) 2021-04-11
RU2019117213A (en) 2020-12-04
DE102017100836B4 (en) 2020-06-18
KR20190108105A (en) 2019-09-23
EP3570993B8 (en) 2020-11-18
CN109963668B (en) 2022-04-19
DE102017100836A1 (en) 2018-08-09
RU2019117213A3 (en) 2020-12-04
US10843259B2 (en) 2020-11-24

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