Induction crucible furnace with magnetic-flux guide

Abstract

The invention relates to an induction crucible furnace and to a magnetic return element for an induction crucible furnace. The induction crucible furnace has a corresponding coil and a plurality of magnetic return elements, which are designed in the form of individual units arranged on the outer lateral surface of the coil with peripheral spacing. In order to guide the magnetic flux produced by the coil, the magnetic return elements each have an assembly consisting of a plurality of elongate individual elements of magnetically permeable material that are electrically insulated from each other and extend parallel to the furnace axis. Said individual elements consist at least partially of bars, which are electrically insulated from each other and the longitudinal axes of which extend parallel to the furnace axis. In this way, both eddy currents that hit the assembly from the radial direction and eddy currents that hit the assembly with a transverse component are minimized.

Claims

1. A crucible induction furnace comprising: a crucible that is cylindrical, refractory, and centered on a furnace axis, a coil extending cylindrically around the crucible, a plurality of magnetic-flux guides formed as individual units spaced angularly around an outer surface of the coil and each including an array of elongated individual elements of magnetically permeable material that are electrically insulated with respect to one another, that extend parallel to the furnace axis, and that guide a magnetic flux generated by the coil, the individual elements each consisting at least partly of rods electrically insulated with respect to one another and having longitudinal axes extending parallel to the furnace axis, each array including at least two rods radially and at least two rods angularly of the coil, and fastener fixing the array on the outer surface of the coil.

2. The crucible induction furnace according to claim 1, wherein the at least two rods have a different cross-sectional shape.

3. The crucible induction furnace according to claim 1, wherein each array consists completely of rods electrically insulated with respect to one another.

4. The crucible induction furnace according to claim 1, wherein each array consists partly of sheets and partly of rods.

5. The crucible induction furnace according to claim 4, wherein each array has a central region consisting of sheets and two lateral outer regions consisting of rods.

6. The crucible induction furnace according to claim 1, wherein the means formed as a support and that the array is pressed, glued or cast into the support.

7. The crucible induction furnace according to claim 1, wherein the rods are rectangular in cross-section.

8. The crucible induction furnace according to claim 1, wherein the rods are round in cross-section.

9. The crucible induction furnace according to claim 1, wherein each array side surfaces, the furnace further comprising: a respective cooler at each of the side surfaces.

10. The crucible induction furnace according to claim 1, wherein the elongate individual elements of each array electrically insulated with respect to one another and extending parallel to the furnace axis are so constructed that rods are provided only in the upper and/or lower region of the respective element while portions with larger cross-section are thereadjacent.

11. A crucible induction furnace comprising: a crucible that is cylindrical, refractory, and centered on a furnace axis, a coil extending cylindrically around the crucible, and a plurality of magnetic-flux guides formed as individual units spaced angularly around an outer surface of the coil and each including an array of elongated individual elements of magnetically permeable material that are electrically insulated with respect to one another, that extend parallel to the furnace axis, and that guide a magnetic flux generated by the coil, the individual elements consisting at least partly of rods electrically insulated with respect to one another and having longitudinal axes extending parallel to the furnace axis, each array consisting partly of sheets and partly of rods and including at least two of the rods not only radially but also angularly of the coil, the rods and sheets being cast with a synthetic resin to form a complete pack.

12. A crucible induction furnace comprising: a crucible that is cylindrical, refractory, and centered on a furnace axis, a coil extending cylindrically around the crucible, and a plurality of magnetic-flux guides formed as individual units spaced angularly around an outer surface of the coil and each including an array of elongated individual elements of magnetically permeable material that are electrically insulated with respect to one another, that extend parallel to the furnace axis, and that guide a magnetic flux generated by the coil, the individual elements consisting at least partly of rods electrically insulated with respect to one another and having longitudinal axes extending parallel to the furnace axis, each array including at least two rods not only radially but also angularly of the coil, the elongate individual elements of each array electrically insulated with respect to one another and extending parallel to the furnace axis being so constructed that rods are provided only in the upper and/or lower region of the respective element while portions with larger cross-section are thereadjacent, each array having elongated individual elements comprising in the upper and/or lower region rods formed by slots extending parallel to the furnace axis.

13. The crucible induction furnace according to claim 12, wherein the rods extend angularly of the crucible furnace or radially of the same.

14. The crucible induction furnace according to claim 12, wherein the array includes radially arranged sheets comprising in the upper and/or lower region rods formed by angularly extending slots.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In the following the invention is described by means of embodiments in connection with the drawing in detail. Of the drawing

(2) FIG. 1 is a horizontal section through a part of a prior-art crucible induction furnace wherein a magnetic-flux guide of the furnace is shown;

(3) FIG. 2 is a view like FIG. 1 of a first embodiment of the invention;

(4) FIG. 3 is a view like FIG. 1 a second embodiment of the invention;

(5) FIG. 4 is a vertical section through a part of another embodiment of a crucible induction furnace with a magnetic-flux guide;

(6) FIG. 5 is an enlarged view of the upper part of the magnetic-flux guide of FIG. 4; and

(7) FIG. 6 is a schematic front view of the magnetic-flux guide of FIGS. 4 and 5.

SPECIFIC DESCRIPTION OF THE INVENTION

(8) FIG. 1 is a horizontal section through a part of a coil 1 that surrounds a crucible (not shown) of a prior-art crucible induction furnace. Individual magnetic-flux guides are angularly spaced around the circumference of the coil 1. These magnetic-flux guides 2 are formed as individual units angularly spaced around the outer surface of the coil 1. These units form an array of a plurality of elongate individual elements of magnetically permeable material electrically insulated with respect to one another and extending parallel to the furnace axes for guiding the magnetic flux generated by the coil 1. The embodiment of the prior art shown in FIG. 1 is an array of a plurality of thin electric sheets electrically insulated with respect to one another and parallel to one another. These electric sheets extend substantially radially from the furnace coil 1. This array 3 of electric sheets is located within a support 5 surrounding all the sides of the array 3, also the upper side and the lower side. The array 3 of electric sheets is pressed into the support 5.

(9) A water cooler 4 is arranged on the one side surface of the support and serves for the compensation of corresponding eddy currents resulting from those field lines impinging from an azimuthal direction, i.e. with a cross component, onto the electric sheets and causing an additional heating of the sheets.

(10) FIG. 2 shows a corresponding embodiment according to which the magnetic-flux guide 2 is designed according to the invention. Also in this case the magnetic-flux guide 2 is in contact with the outer surface of the furnace coil 1 and consists principally of an array 3 of individual elements. Of these individual elements only the central part is formed from thin electric sheets while the two lateral outer regions 6 consist of rods electrically insulated with respect to one another and having longitudinal axes extending parallel to the furnace axis. By this, eddy currents are reduced that are based on field lines impinging onto the array from an azimuthal direction. Also in this embodiment the array is surrounded by a support 5 with which a water cooler 4 is laterally associated. One can also not provide this water cooler on account of the outer regions of the array that are formed by the rods electrically insulated with respect to one another.

(11) FIG. 3 shows a corresponding embodiment of a magnetic-flux guide according to which the complete array 3 is formed of rods 7 electrically insulated with respect to one another and having longitudinal axes extending parallel to the furnace axis.

(12) With this embodiment the rods 7 are cast with a synthetic resin to form an insert that is fixed within the support 5.

(13) The FIGS. 4 to 6 show another embodiment of a crucible induction furnace with a magnetic-flux guide. In the vertical section of FIG. 4 a part of a crucible furnace 10 with induction coil 1 is schematically shown. A magnetic-flux guide 2 is on the induction coil 1. In this embodiment the magnetic-flux guide comprises an array 3 of sheets radially extending parallel to one another. These sheets are subdivided at their upper end and at their lower end into individual rods 7 by slots 11 extending angularly of the crucible furnace 10. As with the preceding embodiments these rods are electrically insulated with respect to one another.

(14) In the embodiment that is shown here a sheet is subdivided by slits 11 into four rods 7 arranged side by side at the upper end and at the lower end. These rods 7 are provided at a location where the greatest eddy currents occur.

(15) FIG. 6 is a schematic front view of the magnetic-flux guide 2 with an array 3 of individual elements that include sheets arranged parallel to one another and radially and that are subdivided into rods 7 at the upper and lower end, respectively.