Casting method

Abstract

A method for producing cast items in a casting method, wherein a charge of a conductive material is introduced into the sphere of influence of at least one alternating electromagnetic field, so that the charge is kept in a levitating state. The melt is poured into moulds in order to produce turbine blades, prostheses or turbocharger impellers.

Claims

1. A method for producing cast items of a conductive material, comprising the following steps: introducing a charge of the conductive material into a sphere of influence of at least one alternating electromagnetic field, so that the charge is kept in a levitating state, melting the charge, positioning a mould in a filling region below the levitating charge, pouring the entire charge into the mould and solidifying the charge into a cast item, removing the solidified cast item from the mould, wherein the volume of the molten charge is sufficient to fill the mould to a fill volume that is sufficient for the production of a cast item, and wherein at the moment of filling, the mould is moved in translation parallel to the direction of pouring of the charge.

2. The method according to claim 1, wherein the mould is removed from the filling region after pouring of the charge and prior to removal of the cast item.

3. The method according to claim 2, wherein another empty mould is moved into the filling region after the removal from the filling region of the mould filled with the charge, or entirely or partially simultaneously with the removal from the filling region of the mould filled with the charge.

4. The method according to claim 1, wherein the mould is preheated prior to filling.

5. The method according to claim 1, wherein the mould is rotated about a vertical axis during filling.

6. The method according to claim 5, wherein the rotation is carried out with a rotational speed of 10 to 1000 revolutions per minute.

7. The method according to claim 5, wherein the rotation is carried out with a rotational speed of 100 to 500 revolutions per minute.

8. The method according to claim 1, wherein both melting of the charge and filling of the mould are carried out under vacuum or under a protective gas or one of the noble gases or mixtures thereof.

9. The method according to claim 1, wherein, at the moment of filling, the mould is moved in translation in the direction of pouring of the charge.

10. The method according to claim 1, wherein a rotational and/or the translational movement is triggered by the pouring of the charge.

11. The method according to claim 1, wherein the conductive material comprises at least one metal from the following group: titanium, zirconium, vanadium, tantalum, tungsten, hafnium, niobium, rhenium, molybdenum, nickel, iron, or aluminium.

12. The method according to claim 11, wherein the at least one metal has a fraction of at least 50 wt. % of the conductive material.

13. The method according to claim 1, wherein the conductive material is titanium or a titanium alloy.

14. The method according to claim 1, wherein the conductive material is superheated, during melting, to a temperature at least 10 C. above the melting point of the material.

15. The method according to claim 1, wherein the casting mould is made of a metallic or ceramic material.

16. The method according to claim 15, wherein the casting mould is made of an oxide-ceramic material.

17. The method according to claim 1, wherein melting is carried out for a duration of 0.5 min to 20 min.

18. The method according to claim 1, wherein, in order to bring about the levitating state of the charge, use is made of at least two electromagnetic fields of different alternating current frequency.

19. The method according to claim 18, wherein, in the absence of a load, the at least two electromagnetic fields produced run horizontally.

20. The method according to claim 18, wherein, in the absence of a load, the at least two electromagnetic fields produced are arranged at right angles to one another.

21. The method according to claim 1, wherein, in order to concentrate the at least one electromagnetic field and stabilize the charge, at least one ferromagnetic element made of a ferromagnetic material having an amplitude permeability .sub.a>10, is arranged horizontally around the region in which the charge is melted.

22. The method according to claim 18, wherein the at least two electromagnetic fields are generated using at least two pairs of induction coils whose axes (A, B) are oriented horizontally.

23. The method according to claim 18, wherein in addition a coil having a vertical coil axis is arranged below the charge to be melted, in order to influence the pouring rate, wherein this coil generates an electromagnetic field of a third alternating current frequency.

24. The method according to claim 23, wherein the coil is a conical coil.

25. The method according to claim 1, wherein the mould is a permanent die having two or more mould elements, wherein the removal of the cast item from the permanent die involves the separation of the two or more mould elements.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a lateral view of a casting mould below a melting region with a ferromagnetic element, coils and a charge of conductive material.

(2) FIG. 2 is a view in section of the setup of FIG. 1.

(3) FIG. 3 is a perspective view in section of the setup of FIG. 1.

(4) FIG. 4 is a plan view of a coil arrangement that can be used according to the invention.

(5) FIG. 5 is a perspective view of a permanent mould in a filling region with a charge in the melting region.

(6) FIG. 6 is a view in section of a permanent mould in a filling region, also with a charge in the melting region.

(7) The figures show preferred embodiments. They serve merely for illustrative purposes.

(8) FIG. 1 shows a charge 1 of conductive material which is located in the sphere of influence of alternating electromagnetic fields (the melting region) that are generated with the aid of the coils 3. Below the charge 1 there is an empty mould 2 which is held in the filling region by a holder 5. The holder 5 is able to move the mould 2 in rotation and/or in translation, which is indicated by the arrows in the figure. A ferromagnetic element 4 is arranged around the sphere of influence of the coils 3. In the method according to the invention, the charge 1 is melted while levitating and, once molten, is poured into the mould 2. The mould 2 has a funnel-shaped filling section 7.

(9) FIG. 2 shows the same components as FIG. 1. FIG. 2 also shows the bar sections 6 which project in the direction of the melting region and around which the coils 3 are arranged. In this preferred embodiment, the bar 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 oriented horizontally and at right angles to one another, with each two opposite coils 3 forming a pair.

(10) FIG. 3 shows the same components as FIGS. 1 and 2, wherein FIG. 3 clearly shows the orthogonal arrangement of the bar sections 6 and the coil axes.

(11) FIG. 4 again shows the arrangement of the coils 3 within a ferromagnetic element 4. The ferromagnetic element 4 takes the form of an octagonal annular element. In each case two coils 3 on an axis A, B form a coil pair. The filling section 7 of a mould is visible below the coil arrangement. The coil axes A, B are arranged at right angles to one another.

(12) FIG. 5 shows an arrangement for carrying out a method according to the invention using a permanent mould as the mould 2. The permanent mould 2 is a permanent die having two mould elements 8, 9 which can be separated from one another for the purpose of de-moulding. An ejector 10 is guided through one of the mould elements 8 in order to support de-moulding. The permanent mould 2 is arranged on a holder 5, as was the case for the moulds in the form of lost moulds, so that the mould 2 can be made to move in rotation and/or in translation. De-moulding of the permanent mould 2 can take place in the filling region.

(13) FIG. 6 shows a view in section through an arrangement for carrying out the method according to the invention, using a permanent mould 2 having two mould elements 8, 9 and an ejector 10. The permanent mould 2 also has a funnel-shaped filling section 7.

LIST OF REFERENCE NUMERALS

(14) 1 Charge 2 Mould 3 Coil 4 Ferromagnetic element 5 Holder 6 Bar section 7 Filling section 8, 9 Mould elements 10 Ejector