Abstract
The invention relates to a levitation melting process and an apparatus for producing castings comprising a ring-shaped element of a conductive material for introducing the casting of a molten batch into a casting mould. In the process, the ring-shaped element is introduced into the region of the alternating electromagnetic field between the induction coils in order to cast the molten batch, thereby initiating a targeted run-off of the melt into the casting mould by influencing the induced magnetic field.
Claims
1. A method for producing cast bodies from an electrically conductive material by a levitation melting method, wherein alternating electromagnetic fields levitate a batch, the alternating electromagnetic fields being generated with at least one pair of opposing induction coils with a core of a ferromagnetic material, comprising: introducing a batch of a starting material into a sphere of influence of at least one alternating electromagnetic field so that the batch is kept in a levitating state; melting the batch; positioning a casting mold in a filling area below the levitating batch; casting the entire batch into the casting mold by introducing a ring-shaped element of an electrically conductive material into the region of the electromagnetic alternating field between the induction coils; removing a solidified cast body from the casting mold.
2. The method according to claim 1, wherein the electrically conductive material of the ring-shaped element contains one or more elements selected from the group consisting of: silver, copper, gold, aluminium, rhodium, tungsten, zinc, iron, platinum and tin.
3. The method according to claim 1, wherein the ring-shaped element tapers conically on a side first introduced into the alternating electromagnetic field region.
4. The method according to claim 1, wherein the ring-shaped element is a part of the casting mold.
5. The method according to claim 1, wherein the electromagnetic fields are generated with at least two pairs of induction coils.
6. The method according to any of claim 1, wherein the ring-shaped element is hollow-walled forming a cavity, and this cavity is filled with a phase change material.
7. The method according to claim 6, wherein the ring-shaped element rests on a cooled bearing surface during the melting process.
8. The method according to claim 7, wherein the ring-shaped element is raised by the casting mold for introduction into the region of the alternating electromagnetic field between the induction coils.
9. An apparatus for levitation melting an electrically conductive material, comprising at least one pair of opposing induction coils with a core of a ferromagnetic material for levitating a batch by means of alternating electromagnetic fields and a ring-shaped member of electrically conductive material insertable in the region of the alternating electromagnetic field between the induction coils.
10. The apparatus according to claim 9, wherein the electrically conductive material of the ring-shaped element contains one or more elements from the group consisting of: silver, copper, gold, aluminium, rhodium, tungsten, zinc, iron, platinum and tin.
11. The apparatus according to claim 9, wherein the ring-shaped element tapers conically on a side first introduced into the region of the alternating electromagnetic field.
12. The apparatus according to claim 9, wherein the electromagnetic fields are generated with at least two pairs of induction coils.
13. The apparatus according to claim 9, wherein the ring-shaped element is hollow-walled forming a cavity, and this cavity is filled with a phase change material.
14. The apparatus according to claim 13, wherein the ring-shaped element rests on a cooled bearing surface during the melting process.
15. A ring-shaped element consisting of an electrically conductive material and forming part of a casting mold in a levitation melting process for casting a batch into the casting mold by introducing into the region between induction coils that generate an alternating electromagnetic field levitating the batch.
Description
BRIEF DESCRIPTION OF THE FIGURES
(1) FIG. 1 is a lateral cross-sectional view of a casting mould below a melting area with ferromagnetic elements, coils, a ring-shaped element and a batch of conductive material.
(2) FIG. 2 is a lateral cross-sectional view of a variant of FIG. 1 in which the ring-shaped element is part of the casting mould.
(3) FIGS. 3a to 3c are a lateral cross-sectional view of a variant with a ring-shaped element with conical tapering in the course of the casting process.
(4) FIGS. 4a to 4d are a lateral cross-sectional view of a variant with a ring-shaped element with phase change material in the course of the casting process.
DESCRIPTION OF THE FIGURES
(5) The figures show preferred embodiments. They are for illustrative purposes only.
(6) FIG. 1 shows a batch (1) of conductive material which is in the influence region of alternating electromagnetic fields (melting area) generated by the coils (3). Below the batch (1) there is an empty casting mould (2) which is held in the filling area by a holder (5). The casting mould (2) has a funnel-shaped filling section (6). The holder (5) is suitable for lifting the casting mould (2) from a feeding position to a casting position, which is symbolized by the drawn arrow. A ferromagnetic element (4) is arranged in the core of the coils (3). The axes of the pair of coils (3) are horizontally aligned, wherein each two opposing coils (3) are forming a pair. Between the batch (1) and the funnel-shaped filling section (6) of the casting mould (2), the ring-shaped element (7) is arranged below the pair of coils (3). As symbolized by the arrow, it is vertically movable.
(7) The batch (1) is melted while levitating in the process according to the invention and cast into the casting mould (2) after the melt has occurred. For casting, the ring-shaped element (7) is slowly lifted into the region of the magnetic field between the coils (3). As a result, the melt passes slowly and in a controlled manner through the ring-shaped element (7) into the casting mould (2) without contaminating the coils (3) or their cores and the inside of the ring-shaped element (7) or spraying inside the funnel-shaped filling portion (6) of the casting mould (2).
(8) FIG. 2 shows a design variant analogous to FIG. 1, in which the ring-shaped element (7) is part of the casting mould (2). In the variant shown, the ring-shaped element (7) is designed as a collar around the funnel-shaped filling section (6) of the casting mould (2). While the holder (5) in the variant of FIG. 1 remains in the position shown during casting and only the ring-shaped element (7) is moved by a mechanism which is not illustrated, here the entire casting mould (2) with the holder (5) is moved further upwards from the position shown for casting. This has the additional advantage that the distance between the melt and the funnel-shaped filling section (6) is reduced at the same time, thus minimizing the free-fall distance of the melt. This ensures that spraying can be safely ruled out.
(9) The FIG. 3 show a step-by-step casting process using a design variant with a ring-shaped element (7) with conical taper on the upper side. The drawing does not show the casting mould (2) arranged below the ring-shaped element (7).
(10) FIG. 3a shows the stage at the end of the melting process. The ring-shaped element (7) is located below the magnetic field of the coils (3). The melt levitates in the area above the coils (3). The drawn magnetic field lines run freely between the poles of ferromagnetic material (4) of the coils (3).
(11) FIG. 3b shows the situation at the beginning of the entry of the ring-shaped element (7) into the magnetic field of the coils (3). As can be seen, the magnetic field lines are increasingly deflected, especially in the region of the cone, and guided around the ring-shaped element (7) so that they do not penetrate the area inside the cone and the cylindrical part. In the drawing, the field lines running behind the ring-shaped element (7) are shown dashed. The density of the Lorentz force increases strongly along the inclination to the tips of the ring-shaped element (7) due to the magnetic field generated by the eddy currents in the ring-shaped element (7).
(12) FIG. 3c finally shows the situation at the beginning of the casting. In the centre of the ring-shaped element (7), the funnel effect generated by the deflected magnetic forces has formed the beginning of a melt jet. The first large drop of the melt of the batch (1) already protrudes into the opening of the cone, whereby the magnetic field at the tip of the cone ensures both the constriction of the levitating batch (1) at its underside and prevents contact. Accordingly, the volume of the melt in the coil area has already slightly decreased. In the drawing, the magnetic field lines running behind the ring-shaped element (7) and the melt drop are again shown dotted. The ring-shaped element (7) is now continuously and slowly pushed upwards until the entire melt of the batch (1) has run off into the casting mould (2).
(13) The FIG. 4 show a casting process using a design variant with a ring-shaped element (7) step-by-step with phase change material in the cavity wall and a cooled bearing surface.
(14) FIG. 4a shows the situation at the end of the melting process. The finished melt (1) levitates above the induction coils (3) with their cores of ferromagnetic material (4). The casting mould (2) with its funnel-shaped filling section (6) is provided below. For casting, the casting mould (2) is moved upwards as indicated by the arrow. In this example, the casting is initiated by a ring-shaped element (7) in cylindrical tube form, which is filled with a phase change material (8) in the hollow wall. During the melting phase it rests on the strongly cooled bearing surface (10). When the casting mould (2) is lifted, the filling section passes through the cooled bearing surface into the ring-shaped element (7) and lifts the ring-shaped element (7) by means of the collar (9). The ring-shaped member (7) and the cooled bearing surface (10) on which it rests are dimensioned in their inner diameter so as to surround the upper outer diameter of the filling section (6) with little clearance. The flange-like collar (9) protrudes inwards just enough to sit on the edge of the filling section (6) without covering the funnel surface.
(15) FIG. 4b shows the situation at the beginning of the casting process. The casting mould (2) with the ring-shaped element (7) turned over has been lifted into the coil field to below the levitating melt (1). To carry out the casting, they are now pushed a little further up until the melt (1) has run off into the casting mould (2). The ring-shaped element (7) heats up due to the radiant heat of the melt (1) and the alternating magnetic field. The increase in temperature can be reduced or delayed by the phase change of the phase change material (8) inside the ring-shaped element (7).
(16) FIG. 4c shows the casting mould (2) filled with the melt (1) after casting again in the direction of the arrow on the way down. It deposits the hot ring-shaped element (7) again on the cooled bearing surface (10), where it is cooled for the next melt batch with a renewed phase change of the phase change material (8).
(17) This state at the end of the casting process is shown in FIG. 4d. The casting mould (2) has been completely lowered through the cooled bearing surface (10) and can now be exchanged for a new empty mould. The ring-shaped element (7) rests again on the cooled bearing surface (10) as shown in FIG. 4a. When the new casting mould (2) is positioned, the next melting process can be started by introducing the next batch (1) into the magnetic field.
(18) FIG. 5 is a lateral cross-sectional view of an embodiment analogue to FIG. 1 now comprising two pairs of induction coils.
LIST OF REFERENCE NUMERALS
(19) 1 batch 2 casting mould 3 induction coil 4 ferromagnetic material 5 holder 6 filling section 7 ring-shaped element 8 phase change material 9 collar 10 cooled bearing surface
