EP2400816A1 - Device for melting pieces of metal - Google Patents

Abstract

The device has a coil assembly (3) including a superconductor winding (3.1) formed in a cryostat (3.2). A heatproof cup is surrounded by the coil assembly. The coil assembly produces a constant magnetic field passing transverse to a central axis of a crucible (1) and induces short circuit current along the central axis of the crucible during rotation of the crucible. A stamper is positioned above the crucible, which is lowered on the metal pieces in the crucible. The stamper is rotatably propelled in the direction of the crucible. The stamper is partly made of non-magnetic non-conductive material and non-magnetic electrically conductive material. An independent claim is also included for a method for operating a device for melting metal pieces and metal powders.

Description

The invention relates to a device for melting metals in the form of pieces and / or powders in a heat-resistant crucible, which is surrounded by at least one coil assembly which generates a DC magnetic field, which predominantly passes through the crucible transverse to the central axis and the rotation of the crucible generates short-circuit currents around its center axis at least in the metal pieces and / or the metal powders.

Such a device is known from US 4,761,527 A .
Fig. 19 known. In a rotary-driven crucible and stationary coil arrangement or rotation of the coil assembly and resting crucible (as well by opposing rotation of the crucible and the coil assembly) arise in the metal pieces short-circuit currents that heat the metal pieces. A warming up to and beyond the melting point succeeds because of the high heat of fusion even at relatively low melting metals such as aluminum and certain aluminum alloys only when correspondingly high induction currents are generated in the metals. By a high speed, this can not be achieved because the penetration depth of the magnetic field decreases with increasing speed and, regardless, the induced voltage and the short-circuit current caused by this, the smaller, the closer the metal piece in question is located at the central axis of the crucible. Consequently, a very strong magnetic field is required instead. Therefore, the coil assembly must have a high Amperewindungszahl, ie a winding with numerous turns with a large conductor cross section and a correspondingly powerful DC power source. In the winding therefore creates a significant heat loss, which must be dissipated by forced cooling, usually by using water-flowed copper pipes for the coil winding.

From the DE 10 2007 034 970 A It is known to rotate a billet in a DC magnetic field, which is generated by means of a superconducting coil in a cryostat.

From the DE 1 281 149 A For example, an induction furnace with a crucible for melting brass chips is known, over which a carbon top layer is located. Above the crucible is arranged a stirrer which moves up and down, but does not dip into the melt, but presses the brass chips into the carbon top layer and optionally performs a reciprocating motion in the range of ± 45 °.

From the US 2,912,552 It is known to inductively heat metal pieces in a stationary crucible. For this purpose, a direct-current, multi-pole ring magnet is driven in rotation via slip rings.

From the DE 196 52 171 A It is known, for growing crystals, to produce a melt in a crucible, which is heated by means of an electromagnetic alternating field which is generated by a coil surrounding the crucible and induces ring currents in the crucible.

The invention has for its object to provide a device of the type mentioned in the introduction, which allows a compared to this considerably energy-saving smelting of metal pieces and / or metal powders.

This object is achieved by the features of claim 1.

Compared to a normally conducting winding, the superconducting winding provides the required, high magnetic flux density with significantly lower energy input, because after generating the current through the superconducting winding practically only the electrical energy for the operation of the cryostat must be expended. This electrical energy is only about 5% of the electrical energy that must be expended to cover the ohmic losses of a normal-conducting winding and to its cooling. This applies not only to the melting but also to a subsequent further heating to a predetermined temperature, e.g. the casting temperature.

Above the crucible, a stamp is arranged, which can be lowered onto the metal pieces in the crucible. As a result, the electrical contact between the metal pieces is improved and thus the melting process is accelerated.

The plunger rotates in the same direction and preferably synchronously with the crucible, so that the angular velocity with which the metal pieces move, does not lag behind that of the crucible and thereby reduces the amount of short-circuit currents generated by induction in the metal pieces.

Because of the small coefficient of friction between the melt and the crucible inner wall, and in addition due to the braking effect that the interaction of the magnetic fields of the short circuit currents with the magnetic field of the coil assembly produces, the melt tends to lag behind the rotation of the crucible. A further significant improvement of the device is achieved when the stamp has driver side underside. Especially when the metal pieces are already completely or at least partially melted, the driving fingers counteract a retention of the melt or the liquid metal layer which first forms on the crucible inner wall.

The stamp may be made of non-magnetic, non-conductive material, e.g. made of ceramic.

Especially with very small pieces of metal and v.a. However, in the case of metal powders, it may be advantageous if the stamp is at least partially made of a non-magnetic, electrically conductive material, because then the stamp is heated by eddy currents and therefore supports the heating of the metal pieces or the powder by direct heat conduction (and in part also by heat radiation).

The same considerations apply to the crucible. If it is not made of ceramic but of a non-magnetic, electrically conductive material, the metal pieces in addition to their direct heating by the short-circuit currents also indirectly by heat conduction and heated by the heat radiation, in particular the crucible wall, as well as the melting on the bottom of the crucible accumulating. In certain cases, however, it may be expedient if at least the wall of the crucible over at least part of its height consists of a non-conductive material. If this is, for example, the upper part of the crucible wall, this is achieved in that the melt in this is heated indirectly in the upper part of the crucible and in the lower part directly. The upper part then ensures the melting and the lower for further heating.

The crucible may have inside a refractory or refractory lining, as known from the foundry technology for the protection of the vessel walls and to reduce the losses due to heat radiation. The lining can be lost or permanent.

An easy-to-implement rotary drive is to connect the bottom of the crucible with the end of a drive shaft rotatably. The axis of the drive shaft may coincide with the vertical center axis of the crucible.

Preferably, the non-rotatable connection between the bottom of the crucible and the end of the drive shaft is releasable, e.g. designed as a dog clutch. The crucible can then be removed from the device by means of a conventional hoist and transported to the place of use of the molten metal.

The drive shaft can also be arranged horizontally, for example, and have at its end a pinion that meshes with a ring gear at the bottom of the crucible.

Alternatively, the crucible may be engaged on its outer periphery with a rotating device. The device may e.g. consist of a seated on the wall of the crucible and a sprocket driven pinion or drivers in engagement with a drive chain.

The coil arrangement preferably comprises a ferromagnetic yoke with opposing, mutually spaced pole pieces, between the pole faces of the crucible is rotatably mounted without contact. The material for the yoke and its dimensions are suitably chosen so that the yoke can be operated close to its magnetic saturation. As a result, and by the pole pieces, the magnetic leakage losses are kept low. The cross section of the yoke may be smaller in the region of the winding than in the remaining regions.

The yoke is preferably substantially C-shaped.

The superconducting winding may then be placed on the middle portion of the C-yoke, away from the high heat-generating crucible, so as not to impose unnecessarily high cooling power on the winding cryostat. In addition, a shielding the radiant heat of the crucible aperture can be attached between the crucible and the cryostat.

In view of the accessibility of the crucible and on its rotary drive, it is easiest if the yoke is arranged horizontally in a horizontal plane.

In principle, the yoke can also be arranged vertically in a vertical plane, in such a way that the middle section of the yoke is located below the crucible and, if necessary, has an opening for the passage of the drive shaft. As in the case of the horizontal arrangement, even with this upright arrangement of the yoke, the crucible can be taken out of the device after the metal has been melted upwards and transported further. In the case of a vertically arranged drive shaft, the coil arrangement can each comprise a superconducting winding on both sides of the opening of the yoke for the passage of the drive shaft. The stamp can either be driven sufficiently far up to remove the crucible and / or laterally swung away.

A development of the device consists in that in a yoke containing the rectangular plane another yoke with pole pieces is arranged, which occupy a portion of the free space between the pole pieces of the first yoke and that on a leg of the further yoke also at least one coil arrangement , However, sitting with a normal conducting winding, which is connected to a current and preferably also adjustable frequency AC power source. The normally conducting winding thus generates an alternating magnetic field which, apart from the unavoidable leakage flux, also predominantly passes through the crucible transverse to its central axis, but orthogonal to the direction of the direct magnetic field. Especially with small pieces of metal, eg shredded metal scrap, the alternating magnetic field shortens the initial phase of heating until softening or melting of the metals. Subsequently, the further coil arrangement or its AC power source can be switched off.

The device according to the invention can also be extended to melt metal pieces and / or metal powders in two separate crucibles. In place of a C-shaped yoke then enters an E-shaped yoke. The superconducting coil assembly is best positioned on its center leg. Between the middle leg and the one outer leg of the E yoke is the same crucible as in the case of the C-yoke, between the middle leg and the other outer leg another, similar crucible with rotary drive, lowerable punch, etc.

As an alternative to a further yoke with an AC-fed coil arrangement or in addition, the melting process can be accelerated by adding a sacrificial plate made of the same metal into the crucible together with the metal pieces and / or metal powders.

Fig. 1:

eine teilweise im Schnitt gehaltene Seitenansicht einer ersten Ausführungsform,

Fig. 2:

eine perspektivische Darstellung dieser ersten Ausführungsform,

Fig. 3:

eine Aufsicht auf die erste Ausführungsform,

Fig. 4:

eine perspektivische Darstellung einer zweiten Ausführungsform,

Fig. 5:

eine perspektivische Darstellung einer dritten Ausführungsform,

Fig. 6:

eine Aufsicht auf die dritte Ausführungsform,

Fig. 7:

eine Aufsicht auf eine vierte Ausführungsform und

Fig. 8:

eine Aufsicht auf eine fünfte Ausführungsform.

The invention is explained below with reference to the drawing, which illustrates some embodiments of the device in a schematic simplification. It shows:

Fig. 1:

a partially sectioned side view of a first embodiment,

Fig. 2:

a perspective view of this first embodiment,

3:

a plan view of the first embodiment,

4:

a perspective view of a second embodiment,

Fig. 5:

a perspective view of a third embodiment,

Fig. 6:

a plan view of the third embodiment,

Fig. 7:

a plan view of a fourth embodiment and

Fig. 8:

a plan view of a fifth embodiment.

The FIGS. 1 to 3 illustrate a first embodiment of the device. It comprises a crucible 1 with refractory lining 1.1 between pole pieces 2.1 and 2.2 of a C-shaped yoke 2. On the center leg 2.3 sits a coil assembly 3 which comprises a superconducting winding 3.1 in a known per se, indicated by dashed lines 3.2 cryostat.

The superconducting winding 3.1 of the coil assembly 3 is flowed through DC and generates in the C-shaped yoke 2, a magnetic flux, the crucible 1 in the in FIG. 3 interspersed only schematically and disregarding the leakage flux. The yoke 2 is arranged horizontally in this example.

The bottom of the crucible 1 is rotatably but separable (not shown) coupled to a shaft 4, which is guided in at least one upper bearing 5 and in turn is driven by a non-illustrated, powerful electric motor during operation of the device. Suitable entrainment and coupling devices are known in the art.

In the crucible 1 is according to Fig. 1 Metal scrap 6 over a sacrificial plate 30, which is made of the same material as the metal scrap 6. In the crucible 1 dives a stamp 7 with several lower-side driving fingers as 7.1. The punch 7 and its driving finger 7.1 are made of a refractory or refractory material. The punch 7 can be rotated by a shaft 8 in the same direction to the shaft 4 and preferably at the same speed as the latter in rotation. In the drawn in solid lines, lowered position of the serves Stamp 7 for the compaction of the metal scrap 6 to produce the longest possible current paths. The driving fingers 7.1 avoid that the metal scrap 6 and later, after the melting, the molten metal remains behind the rotation of the crucible 1.

The shaft 8 is additionally raised according to the arrow P from the position in solid lines in a position indicated only by dashed lines, in the one hand, the crucible 1 can be equipped with the metal scrap 6 and in the other hand, the crucible 1 with the molten metal up between the Pole pieces 2.1 and 2.2 highlighted and eg can be spent by means of known horizontal conveyor and tilting devices to the place and poured out where the molten metal is needed.

In the FIGS. 2 and 3 as well as the other figures, for clarity, in particular the punch 7 and its drive and the contents of the crucible 1 are not shown.

In FIG. 4 is a second embodiment (without punch 7 and its drive) shown. In this embodiment, the C-shaped yoke 2 is different from Fig. 2 standing, so arranged in a vertical plane. Therefore, the center leg 2.3 has a passage opening 2.3.1 for the shaft 4 of the crucible 1. The coil assembly 3 is seated on one of the two free (lateral) legs of the C-shaped yoke 2. A division into two symmetrical coil arrangements (the second coil arrangement is indicated by dashed lines) is possible, but would not represent a significant improvement functionally, but increase the cost significantly.

An arrangement of the C-shaped yoke 2 as in Fig. 4 is especially useful when the device is supplemented by a second C-shaped yoke 9, which carries an AC-powered coil assembly 10. This third embodiment is in Fig. 5 shown, again only for reasons of clarity without the punch 7, etc. The C-shaped yokes 2 and 9 can also be arranged Vertungsvertauscht, that is, the yoke 2 as in Fig. 2 lying in a horizontal plane and the yoke 9 standing in a vertical plane, as the yoke 2 in Fig. 4 ,

As schematically in the supervision according to Fig. 6 indicated, enforce in this embodiment of the superconducting winding 3.1 in Fig. 5 generated direct magnetic flux (directional arrows) and generated by the normal conducting, AC-driven coil assembly 10, alternating magnetic flux (double arrows) the crucible 1 is substantially orthogonal, which accelerate especially the initial phase of heating the crucible contents and thus can be shortened in time.

In Fig. 7 schematically is a plan view of a fourth embodiment shown, which largely coincides with the first embodiment, with the proviso that in the region of the winding 3.1, the cross section of the yoke 2 is reduced in relation to the cross section of the other parts of the yoke. As a result, it is possible to reduce the reinduction voltage which is caused in the winding 3.1 by the time-varying magnetic fields of the short-circuit currents generated in the crucible and / or the crucible contents.

FIG. 8 shows quite schematically a fifth embodiment of the device, which makes it possible to heat the contents of two crucibles 21 and 22 at the same time, as long as both crucibles are simultaneously rotated. This embodiment comprises an E-shaped yoke 11, which to a certain extent has been created by joining two yokes 2 of the first embodiment, but carries the superconducting coil arrangement 3 on the center leg 11.1.

Claims (18)

Device for melting metal pieces (6) and / or metal powders in a heat-resistant crucible (1), which is surrounded by at least one coil arrangement (3) which generates a direct magnetic field which predominantly passes through the crucible (1) transversely to its central axis and the during rotation of the crucible (1) induces short circuit currents about its central axis, characterized in that the coil arrangement (3) comprises at least one superconducting winding (3.1) in a cryostat (3.2), and that above the crucible (1) a punch (7) is arranged, which is lowered on the metal pieces (6) in the crucible (1) and rotatably driven in the same direction to the crucible (1). Apparatus according to claim 1, characterized in that the punch (7) underside driving finger (7.1) has. Apparatus according to claim 1 or 2, characterized in that the punch (7) consists at least partially of a non-magnetic, non-conductive material. Device according to one of claims 1 or 2, characterized in that the punch (7) consists at least partially of a non-magnetic, electrically conductive material. Device according to one of claims 1 to 4, characterized in that at least the wall of the crucible (1) over at least part of its height consists of a non-magnetic, non-conductive material. Device according to one of claims 1 to 4, characterized in that at least the wall of the crucible (1) over at least part of its height consists of a non-magnetic, electrically conductive material. Device according to one of claims 1 to 6, characterized in that the crucible (1) on the inside has a heat-resistant or refractory lining (1.1). Device according to one of claims 1 to 7, characterized in that the bottom of the crucible (1) with the end of a drive shaft (4) is rotatably connected. Apparatus according to claim 8, characterized in that the rotationally fixed connection between the bottom of the crucible (1) and the end of the drive shaft (4) is releasable. Device according to one of claims 1 to 7, characterized in that the crucible (1) is on its outer periphery in engagement with a device which rotates it. Device according to one of claims 1 to 10, characterized in that the coil arrangement has a ferromagnetic yoke (2) with opposite, spaced apart pole pieces (2.1, 2.2), between the pole faces of the crucible (1) is arranged without contact. Apparatus according to claim 11, characterized in that the yoke (2) is substantially C-shaped. Apparatus according to claim 11 or 12, characterized in that the superconducting winding (3.1) on the central portion (2.3) of the C-shaped yoke (2) sits. Device according to one of claims 11 to 13, characterized in that the yoke (2) is arranged lying in a horizontal plane. Device according to one of claims 11 to 13, characterized in that the yoke (2) is arranged vertically in a vertical plane and that the central portion of the yoke (2.3) is located below the crucible (1) and an opening (2.3.1 ) for the passage of the drive shaft (4). Device according to one of claims 11 to 15, characterized in that in a plane perpendicular to the plane containing the yoke (2) another yoke (9) with pole pieces is arranged, which occupies part of the free space between the pole pieces (2.1, 2.2 ) of the first yoke (2) and that on one leg of the further yoke is at least one further, normally conducting winding (10) which is connected to a current and frequency controllable AC power source. Apparatus according to claim 11, characterized in that the yoke (11) is substantially E-shaped to receive another, similar crucible for melting metal pieces and / or metal powders. A method of operating a device according to any one of claims 1 to 17, characterized in that in addition to the metal pieces and / or metal powders, a sacrificial plate (30) of the same material in the crucible (1) is given.

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