Patent Application
20110319270
This application claims foreign priority under 35 U.S.C. §119(a)-(d) to Application No. DE 102010024883.5 filed on 24 Jun. 2010, entitled “An Apparatus for Melting Metal Pieces,” the entire contents of which are hereby incorporated by reference.
The invention relates to an apparatus for melting down metals in form of pieces and/or powders in a heat-resistant crucible which is enclosed by at least one coil arrangement generating a DC magnetic field which predominantly penetrates the crucible transversely to its central axis and which generates short-circuit currents at least in the metal pieces and/or the metal powders during rotation of the crucible around its central axis.
Apparatuses for melting metal are generally known. In the case of rotatably driven crucibles and stationary coil arrangements or in the case of the rotation of the coil arrangement and a stationary crucible (and also by rotating the crucible and the coil arrangement in opposite directions relative to one another), short-circuit currents are obtained (generated) in the metal pieces, which heat up the metal pieces. Heating up to and over the melting point will only be achieved in metals with a relatively low melting point (e.g., aluminum and certain aluminum alloys) due to the high melting heat only if appropriately high induction currents are generated in the metals. This cannot be achieved by a high rotational speed because the penetration depth of the magnetic field will decrease with rising rotational speed and, irrespective of this, the induced voltage and the short-circuit current caused by this voltage will be the lower the closer the respective metal piece is disposed to the central axis of the crucible. Consequently, a very strong magnetic field is required instead. That is why the coil arrangement must have a very high number of ampere turns, i.e. a winding with numerous windings with a large conductor cross-section and a respectively powerful direct current source. A considerable heat loss is therefore produced in the winding which needs to be dissipated by forced cooling, usually by using water-carrying copper pipes for the coil winding.
The invention is based on the object of providing an apparatus which allows melting down metal pieces and/or metal powders in a considerably more energy-saving manner in comparison with the above systems. In particular, the present invention is directed toward an apparatus for melting down metal pieces and/or metal powders, the apparatus including a heat-resistant crucible enclosed by at least one coil arrangement generating a DC magnetic field predominantly penetrating the crucible transversely to its central axis and inducing short-circuit currents during rotation of the crucible about its central axis, wherein the coil arrangement includes at least one superconducting winding in a cryostat; and a stamp arranged above the crucible, wherein the stamp is lowered onto metal pieces contained in the crucible, and wherein the stamp is rotatably driven in the same direction as the crucible.
Like reference numerals have been used to identify like elements throughout this disclosure.
The superconducting winding 3.1 of the coil arrangement 3 carries a direct current and generates a magnetic flux in the C-shaped yoke 2, which magnetic flux penetrates the crucible 1, which is indicated by arrows in
The floor of the crucible 1 may be coupled in a torsion-proof but separable manner with a shaft 4 guided in at least one upper bearing 5 and is driven in operation of the apparatus on its part by a powerful electric motor (not shown). Conventional driving and coupling apparatuses may be utilized.
In accordance with
As shown, the stamp 7 is arranged above the crucible 1, which can be lowered onto the metal pieces 6 in the crucible. This improves the electrical contact between the metal pieces and thus accelerates the melting process. The stamp 7 rotates in the same direction and preferably synchronously with the crucible, so that the angular speed with which the metal pieces move will not drop behind that of the crucible and the amount of the short-circuit currents generated in the metal pieces by induction will not decrease thereby.
As a result of the low coefficient of friction between the melt and the inside wall of the crucible and additionally as a result of the braking effect which is generated by the interaction of the magnetic fields of the short-circuit currents with the magnetic field of the coil arrangement, the melt has the tendency to fall behind the rotation of the crucible. A further important improvement of the apparatus is therefore achieved if the stamp is provided with driving fingers 7.1 on the bottom side. Particularly when the metal pieces have been molten down completely or at least partly, the driving fingers prevent the melt from falling behind or the liquid metal layer that is formed first on the inside wall of the crucible.
The shaft 8 can be lifted (indicated by arrows P) from the lowered position to a raised position (indicated via broken lines), in which the crucible 1 can be filled with the scrap metal 6 on the one hand and in which the crucible 1 with the metal melt can be lifted out upward between the pole pieces 2.1 and 2.2 on the other hand and can be displaced by means of known horizontal conveyors and tilting apparatuses to a location and can be poured out at such location where the metal melt is required.
The stamp 7 and its drive as well as the content of the crucible 1 are removed in
An arrangement of the C-shaped yoke 2 as in
As is schematically indicated in the top view according to
In comparison with a normally conducting winding, the superconducting winding supplies the required high magnetic flux density with a considerably lower energy input, because it is only necessary to apply the electric power for the operation of the cryostat after the production of the current by the superconducting winding. This electric power is only 5% of the electric power which needs to be applied for covering the ohmic losses of a normally conducting winding and for its cooling. This applies not only to melting down but also to a subsequent further heating to a predetermined temperature, e.g. the casting temperature.
While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
The stamp 7 can be made of a non-magnetic non-conducting material such as a ceramic material, for example. It may we advantageous especially in the case of very small metal pieces and especially in the case of metal powders that the stamp is made at least partly of a non-magnetic electrically conducting material. In this case, the stamp will also heat up by the eddy currents and will therefore support the heating of the metal pieces or the powder by direct thermal conduction (and partly also by thermal radiation).
The same considerations also apply to the crucible 1. If it is not made of a ceramic material but of a non-magnetic electrically conducting material, the metal pieces are also indirectly heated by thermal conduction and by thermal radiation especially of the crucible wall in addition to their direct heating by the short-circuit currents, as also the melt accumulating on the floor of the crucible. In certain cases, it may be useful if at least the wall of the crucible consists over at least a part of its height of a non-conducting material. If this is the upper part of the crucible wall for example, it is ensured that the molten material in this upper part will be heated indirectly via the crucible and directly in the bottom part. The upper part ensures the incipient melting and the bottom part ensures the further heat-up.
The crucible can be provided on the inside with a heat-resistant or a refractory lining, as is known from foundry practice for the protection of the vessel walls and for the reduction of losses by thermal radiation. The lining can be lost or permanent.
A rotary drive that is easy to realize can be provided by connecting the floor of the crucible with the end of a drive shaft in a torsion-proof manner. The axis of the drive shaft can coincide with the vertical central axis of the crucible.
The torsion-proof connection between the floor of the crucible and the end of the drive shaft is preferably detachable, e.g. it is arranged as a claw coupling. The crucible can then be removed from the apparatus by means of a conventional hoist and can be transported to the place of use of the metal melt.
The drive shaft can also be arranged horizontally, for example, and can include a pinion gear at its end which meshes with a gear rim on the floor of the crucible. The crucible can alternatively be in engagement on its outside circumference with an apparatus which makes it rotate. The apparatus may include, for example, a gear rim disposed on the wall of the crucible and a driven pinion gear, or of drivers in engagement with a drive chain.
The coil arrangement preferably comprises a ferromagnetic yoke with oppositely disposed, mutually spaced pole pieces, between which the pole faces of the crucible are rotatably held in a contact-free manner. The material of the yoke and its dimensions are appropriately chosen in such a way that the yoke can be operated close to its magnetic saturation. The magnetic leakage losses can be kept at a low level in this way and as a result of the pole pieces. The cross-section of the yoke can be smaller in the region of the winding than in the other areas.
The yoke is preferably substantially C-shaped. The superconducting winding can then be arranged on the middle section of the C-yoke and thus remote from the crucible forming a strong heat source in order to avoid having to apply unnecessarily high cooling power for the cryostat of the winding. In addition, a shield which screens the radiation heat can be applied between the crucible and the cryostat.
With respect to the accessibility of the crucible and its rotational drive it is easiest if the yoke is arranged in a lying fashion in a horizontal plane.
The yoke can principally also be arranged to be upright in a vertical plane, namely such that the middle section of the yoke is disposed beneath the crucible and, if necessary, comprises an opening for the passage of the drive shaft. As in the horizontal arrangement, the crucible can also be removed in this upright arrangement of the yoke upwardly out of the apparatus after the melting down of the metal and can be further transported. In the case of a vertically arranged drive shaft, the coil arrangement can comprise one superconducting winding each on either side of the opening of the yoke for the passage of the drive shaft. For removing the crucible, the stamp can be moved upwardly to a sufficient extent for removing the crucible or/and can be pivoted away laterally.
A further development of the apparatus is that a further yoke with pole pieces is arranged in a rectangular plane containing the yoke, which pole pieces assume a portion of the free space between the pole pieces of the first yoke, and that also at least one coil arrangement with a normally conducting winding however is disposed on a limb of the further yoke and is connected to a current-controllable and preferably also frequency-controllable alternating current source. The normally conducting winding consequently generates a magnetic alternating field which, apart from the un-avoidable leakage flux, also predominantly penetrates the crucible transversely to its central axis, but orthogonally to the direction of the DC magnetic field. Especially in the case of small-size metal pieces, e.g. shredded scrap metal, the magnetic alternating field reduces the initial phase of the heating up to softening or incident melting of the metals. Subsequently, the further coil arrangement and its alternating current source can be switched off.
The apparatus in accordance with the invention can also be expanded for melting down metal pieces and/or metal powders in two separate crucibles. An E-shaped yoke is used instead of a C-shaped yoke. The superconducting coil arrangement is best positioned on it middle limb. The same crucible as in the case of the C-shaped yoke is disposed between the middle limb and the one outside limb of the E-shaped yoke. A further similar crucible with a rotational drive, a lowerable stamp, etc. is disposed between the middle limb and the further outside limb.
As an alternative to a further yoke with an AC-supplied coil arrangement or in addition thereto, the melting-down process can further be accelerated in such a way that a sacrificial plate made of the same metal is added to the crucible together the metal pieces and/or the metal powders.
Although the disclosed inventions are illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the scope of the inventions and within the scope and range of equivalents of the claims. In addition, various features from one of the embodiments may be incorporated into another of the embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure as set forth in the following claims.
It is to be understood that terms such as “left,” “right,” “top,” “bottom,” “front,” “rear,” “side,” “height,” “length,” “width,” “upper,” “lower,” “interior,” “exterior,” “inner,” “outer” and the like as may be used herein, merely describe points or portions of reference and do not limit the present invention to any particular orientation or configuration. Further, terms such as “first,” “second,” “third,” etc., merely identify one of a number of portions, components and/or points of reference as disclosed herein, and do not limit the present invention to any particular configuration or orientation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102010024883.5 | Jun 2010 | DE | national |
