MXPA98003494A

MXPA98003494A - An inducc oven

Info

Publication number: MXPA98003494A
Application number: MXPA/A/1998/003494A
Authority: MX
Inventors: H Mortimer John; A Peysakhovich Vitaly; J Box Benno
Original assignee: Inductotherm Corp
Priority date: 1997-05-01
Filing date: 1998-04-30
Publication date: 1999-04-06

Abstract

An induction furnace apparatus and a method for reducing the magnetic field produced by the operation of the furnace are described: the induction furnace includes a refractory vessel, an induction coil and an outer shell having a layer of metallic material and magnetically permeable; the metallic and magnetically permeable material comprises a plurality of elements having a shape and figure chosen to maximize the packing density of the elements along the layer, the outer shell further includes an upper part, a base and a side wall disposed around the refractory vessel so that the permeable metallic and magnetic material is formed between the refractory container and the outer shell, the invention provides a method for placing a metallic and magnetically permeable material with or without a non-conductive matrix, the cast materials can be configured in inserts or incorporated in the upper part, the base and the p The lateral shell is the outer shell, the invention includes inserts comprising metallic and magnetically permeable material located in a space formed between the refractory vessel and the outer shell.

Description

A PE INPUCGIQN OVEN FIELD OF THE INVENTION The present invention pertains to the design of an induction furnace. The invention provides an induction furnace having a surrounding layer of metallic material and magnetically permeable for the reduction of magnetic fields generated by the operation of an induction furnace.

BACKGROUND OF THE INVENTION An induction furnace uses electromagnetic energy to induce electric currents that flow within a load of metal or metal alloy. The electrical resistance of the metal produces heat as a natural consequence of the induced currents flowing in the metal. The combination of electrical power and applied frequency can be chosen to create sufficient heat within the metal, causing it to melt. The molten metal can then be cast in mol is or be used in another way to produce a wide variety of metal products. The basic elements of an induction furnace include an electromagnetic induction coil, a vessel having a coating of refractory material, and an infrastructure for supporting the induction coil and the vessel. The induction coil comprises an electrical conductor of sufficient size and current capacity to produce the magnitude of magnetic flux necessary to induce large currents in the metal load. The magnetic flux represents the force lines of a magnetic field. The magnetic field emanates from the furnace and surrounds the adjacent work area occupied by operating personnel and equipment. There is a need to reduce the magnetic fields produced by the operation of the induction furnaces. Although the health consequences that result from exposure to unknown magnetic fields, it is considered prudent to provide a design and method for the reduction of the magnetic field. However, it is well known that EMI (electromagnetic interference) can cause faults or the destruction of electronic equipment resulting from exposure to magnetic fields of energy. Therefore, there is a need to protect operating personnel and equipment from exposure to the magnetic field caused by the operation of an induction furnace.

BRIEF DESCRIPTION OF THE INVENTION The present invention is an induction furnace apparatus and a method for reducing magnetic fields produced by an induction coil during operation of the furnace. The induction furnace comprises a refractory vessel having an induction coil and an outer shell having a layer of metallic material and magnetically permeable to reduce the magnetic fields generated by the induction coil. The outer shell has components that include an upper part, a base and a side wall, which are arranged around the container and enclose it substantially. The components are located near the container and can form a space between the container and the outer shell. The upper part, the base and the side wall have a layer of metallic and magnetically permeable material close to the magnetic fields produced by the induction coil. In a preferred embodiment of the invention, the metallic and magnetically permeable material is manufactured in shapes that are cast and encapsulated in a non-conductive insulating or refractory material. The cast forms are each located along one side or are incorporated in the upper part, base and side walls of the outer shell. The base is used to support the components of the outer shell, the induction coil and the refractory vessel. The metallic and magnetically permeable material includes, but is not limited to. discrete elements that have a uniform or random size and shape. The material is located in or near the outer shell and works to reduce the intensity of the external magnetic field to the outer shell. This is achieved by retaining, absorbing, dissipating and deriving to the ground the energy of the magnetic field within the structure of the furnace. In a preferred embodiment of the invention, the metallic and magnetically permeable material is cast into the upper part, the bar and the side wall. In another preferred embodiment, the metallic and magnetically permeable material is cast into inserts that are located near the interior surfaces of the upper part, the base and the side wall. In yet another preferred embodiment. the metallic and magnetically permeable material is cast in the upper part and the baße. and an insert is located near the interior surface of the side wall. The inserts are made by casting the metallic and magnetically permeable material in a non-conductive matrix. In addition, the metallic and magnetically permeable material that is cast in the upper part, the base and the side wall can be encapsulated with a non-conductive matrix. The components of the outer shell, including the metallic and magnetically permeable material, are preferably made by casting. However, it is understood that the components of the invention can be formed by any commercially available process. During fabrication, a non-conductive matrix can be applied to the components, before, during or after they are formed. In addition, the components of the invention may have either a metallic or magnetically permeable material, or both, in a ratio necessary to achieve the reduction required in externally generated magnetic fields. In a preferred embodiment of the invention, the insert of the side wall is substantially cylindrical and adapts to the interior space formed by the outer shell and the induction coil. However, it is understood that the furnace, the outer shell and the insert of the side wall can be configured in any shape. The inserts may also be located outside the induction coil as necessary to reduce the intensity of magnetic flux entering the metallic and magnetically permeable material. The discrete elements of the metallic and magnetically permeable material are arranged in such a way that a maximum packing density is produced. In a preferred embodiment, the discrete elements of the metallic and magnetically permeable material have a substantially spherical shape and are of a uniform size. However, the size of the discrete elements can also be random. The discrete elements are arranged to maximize their packing density within the components or inserts of the outer shell. The preferred arrangement for the spherical discrete elements eß a narrow hexagonal packing. The packing density is further increased by the application of vibration and pressure during manufacture. The ratio of spherical elements to insulating material is adjusted according to the composition of the selected material and the amount of magnetic field reduction required. For example, the silicone insulating material will have a preferred ratio of 8054 of spherical elements to 2054 of silicone. The refractory insulating materials will have a preferred ratio of 7054 of spherical elements to 305i of refractory insulating materials. These percentages reflect packing densities that are preferred and that also provide satisfactory structural integrity of the discrete elements after vibration. It is preferred, but it is not essential. that metallic and magnetically permeable materials have a low sil- cone content. The size of the discrete elements is also an important factor in reducing the intensity of the magnetic field strength generated by the induction furnace. Typically, the force of the magnetic field is inversely proportional to the size and permeability of the element. For example, the reduction of the strength of the magnetic field can be achieved by increasing the diameter and / or the permeability of the discrete elements of spherical shape. further, the permeability can be further increased by selecting materials that have high permeability. Spherical-shaped elements are preferred because they tend to produce the greatest reduction in magnetic field strength. In addition, discrete elements that have a uniform size are preferred because they tend to produce the most efficient element packing arrangements. Although elements that are non-uniform in size and shape may be used, they may not produce the most efficient element packing arrangements. However, in another embodiment of the invention, large spheres are mixed with smaller spheres. This is done to increase the packing density of the larger elements which should result in a greater total permeability within the components or insert of the outer shell.

DESCRIPTION PE LQ? PIPUJQ? For the purpose of illustrating the invention, forms that are currently preferred are shown in the drawings; being understood, however, that this invention is not limited to the precise dispositions and instrumentalities shown. Figure 1 is a vertical longitudinal section of an induction furnace according to a mode of the invention, illustrating the container, the induction coil, the space, the insert, the outer shell, the base and the top from the oven. Figure 2 is an exposed isometric view of the embodiment in Figure 1. Figure 3 is a partial longitudinal section of the embodiment illustrated in Figure 1. showing the outer wall, the insert, the space, the induction coil and the container. Figure 4 illustrates a preferred arrangement of discrete elements of metallic and magnetically permeable material in a hexagonal narrow packed symmetry. Figure 5 is a vertical longitudinal section of the embodiment shown in Figure 1, showing magnetic fl ange lines produced by the coil. Figure 6 is a graphical illustration showing the relationship between the magnetically permeable material and the size of the discrete element.

DESCRIPTION OF THE INVENTION Referring to the drawings "wherein like numbers indicate similar elements, Figure 1 illustrates an induction furnace 10 embodying the present invention. The induction furnace 10 has a refractory container 12. an induction coil 14 and an outer shell 16 that substantially enclose the refractory vessel 12. The outer shell 16 comprises a layer of metallic and magnetically permeable material 20 between the outer shell 16 and the outer shell 16. induction coil 14. In a preferred embodiment »the outer shell 16 substantially encloses the refractory vessel 12 and the induction coil 14» and the outer shell 16 further comprises a refractory upper part 17 »an inner side wall ll and a base refractory 15. The inner side wall 11 may be made of a refractory material or of a material with a conductive or non-conductive material or of a metallic material. Induction furnaces are typically cylindrical in shape "as shown in Figure 1. However, the details of the support structure including the shape of the furnace are not crucial to the invention and may vary from one furnace to another. Therefore, it should be understood that the details shown in the figures are representative of a preferred embodiment only and that other modalities are possible including those that are square, oval or triangular. Referring to Figure 1 »in a preferred embodiment. the induction coil 14 is enclosed sub-substantially by the outer shell 16. an insert 18. the inner side wall 11, the refractory base 15. the refractory upper part 17 and the outer shell 16. The outer shell 16 refers to a structure Outer enclosing the oven 10. The insert 18 comprises metallic and magnetically permeable material 20. In addition, the refractory base 15 and the refractory upper part 17 include a layer of magnetically permeable material 20. The metallic and magnetically permeable material 20 serves to retain the electromagnetic flux generated by the induction coil 14 during the operation of the furnace 10. With reference to Figure 2. the metallic and magnetically permeable material 20 is cast into an insert 18. the inner side wall 11. the refractory base 15. the refractory upper part 17. and substantially surrounds the induction coil 14 and the refractory vessel 12. Induction coil 14 is provided It is placed around the refractory vessel 12. Optionally, a space 32 can be formed between the induction coil 14 and the outer shell 16. The base 15 supports the components of the furnace 10 including the outer shell 16 »the insert 18» the induction coil 14 and the refractory container 12. In a preferred embodiment, the outer shell 16 is made of a non-conductive refractory material such as »but not limited to. a preformed material such as NAD IIM, or a castable material such as FonduMR »manufactured by LaFarge Calcium Alum ate. Inc. Alternatively, the outer shell 16 may be made of a low resistivity metal such as copper or aluminum. The inner side wall 11 can be made of a metallic material to further reduce the magnetic field that is not contained by the insert 18. The purpose of the insert 18 and the inner side wall 11 is to contain the magnetic field generated by the coil induction 14 inside the oven 10. The outer shell 16 provides protection for the coil 14 and provides a means of attachment to the furnace 10 so that it can be tilted or retained and positioned on the floor if necessary. Referring to Figure 3A, the space 32 formed between the outer shell and the induction coil 14 is occupied by the insert 18. The space 32 can be occupied completely or partially by the insert 18 or the inner side wall 11. In a preferred embodiment »the insert 18 substantially fills the space 32. The insert 18 is made of metallic and magnetically permeable material 20. The material is held together with a non-conductive matrix such as epoxy, refractory or sil-con and is cast with a single unit or segment. Although not shown, the insert 18 may comprise a plurality of ring debris stacked one on top of the other to form a substantially cylindrical body. Referring to FIGS. 3B and 4, the metallic and magnetically permeable material 20 comprises a plurality of discrete elements 22 having a selected shape, size and permeability as required to reduce the magnetic field produced by the coil 14. In an embodiment preferred »the discrete elements 22 have a sub-spherical shape and size chosen to provide a maximum element packing density within a selected volume of space. In a preferred embodiment of the invention, the metallic and magnetically permeable material 20 is cast into the upper part 17, the base 15 and the inner side wall 11.

In another preferred embodiment the metallic and magnetically permeable material 20 is cast into inserts that are located near the interior surfaces of the upper part 17, the base 15 and the inner side wall 11. In yet another preferred embodiment, the metallic material and magnetically permeable 20 is cast into the upper part 17 and the base 15. and an insert 18 is located near the inner surface of the inner side wall 11. The inserts are made by casting the metallic and magnetically permeable material 20 in a non-conductive matrix . Further. the metal and magnetically permeable material 20 which is cast in the upper part 17 »the base 15 and the inner side wall 11 can be encapsulated with a non-conductive matrix. The components of the outer shell 16, including the metallic and magnetically permeable material 20, are preferably made by casting. However, it is understood that the components of the invention can be formed by any commercially available process. During fabrication, a non-conductive matrix can be applied to the components, before, during or after they are formed. In addition, the components of the invention may have materials that are either metallic or magnetically permeable, or both, in a ratio that is effective to reduce the externally generated magnetic fields. In a preferred embodiment, the insert 18 is formed by combining metallic and magnetically permeable spherical elements 22 with a non-conductive matrix such as an epoxy or refractory material which is then cast and cast in a mold. The upper part 17 and the base 15 are cast in layers in a mold. The layers forming the outer surfaces of the casting are allowed to cure before emptying a layer containing the spherical elements 22. The spherical elements 22 are combined with a refractory material and then mixed and cast on the upper part of the previous layer in the mold . The mold is then vibrated to compact and stack the spherical elements 22. Additional material is added during this process to achieve a desired thickness and packing of the spherical elements 22. A final layer of refractory material is poured over the top of the layer in the mold to achieve the final thickness of the upper part 17 and the base 15. The refractory material is then hardened in a drying oven in accordance with normal commercial practice. The refractory material used to form the insert 18. the upper part 17 and the base 15 is a material based on silicon such as refractory materials of calcium aluminate or CAC 801-1010 manufactured by EMS. Inc. The metallic and magnetically permeable eßféricoß elements 22 are made of injection-molded materials. The elements are treated with a silicone adhesive. typically a silicone polymer in solvent, and left to dry. The spherical elements are then combined with the silicone refractory material in proportions of approximately 8054 spherical elements to 2054 silicone. It is understood that any proportion of spherical elements to silicone can produce a reduction in magnetic field. Therefore, the proportion of spherical elements to silicone, or refractory material, depends on the reduction in magnetic field that is desired and can vary from 1 to 100 percent. The refractory silicone formulation is placed in a mold and packed by vibration and pressure. Additional material can be added when the spherical elements are compacted. Referring to Figure 4, an important feature of the magnetically permeable material 20 is the packing density of the spherical elements 22. The packing density depends on the encapsulating material in the ratios given above. These relationships allow the highest densities possible while retaining a useful resistance in the molded components. The disposition more efficient and more preferred is a narrow hexagonal packing which is illustrated in Figure 4. With reference to Figure 5 »when properly constructed the metallic and magnetically permeable spherical elements 22 contained in the insert 18. the upper part 17 and the bar 15 »will substantially retain the magnetic field produced by the furnace 10. The magnetic field is illustrated by the magnetic flux lines 100 which are generated by the current excitation in the induction coil 14. The magnetic flux lines 100 are attracted and contained substantially by the metallic and magnetically permeable material 20. The space 32 formed between the outer shell 16 and the induction coil 14 can vary in volume depending on the volume and shape of the furnace 10. The size of the insert is also determined by the amount of magnetic field reduction required and by the type of magnetically permeable material used to build and l insert. The relative permeability for a certain element size and material density is defined according to equation 1 »and the results thereof are shown in graphical form in figure 6. μ (d, p) = 3.5 + ln 10 • d-100 100"2.3 • P EQ (1) where »μ (d, £) = relative material permeability for a certain element size and material density = s Diameter of elements (in 2.54 microns) £ 5 = Density of compound (g / cm») The present invention can be incorporated into other specific forms without getting away from the spirit or essential attributes of it and. consequently, reference should be made to the appended claims "in lieu of the foregoing description" to indicate the scope of the invention.

Claims

NOVELTY PE THE INVENTION CLAIMS

1. - An induction furnace 10 having a refractory vessel 12 »an induction coil 14 and an outer shell 16 substantially enclosing the refractory vessel 12, comprising a layer of metallic and magnetically permeable material 20 between the outer shell and the coil induction.

2. The induction furnace according to claim 1, further characterized in that the outer shell has an upper part 17, a base 15 and a side wall 11 between it, and the outer shell contains the material metal and magnetically permeable 20.

3. The induction furnace according to claim 2. further characterized in that the side wall has a substantially cindical shape around the longitudinal axis of the refractory container »the upper part and the base having a disk shape substantially .

4. The induction furnace according to the rei indication 3, further characterized in that the metallic and magnetically permeable material comprises a plurality of elements 22 having a substantially spherical shape and a size that are chosen to maximize the packing density of the elements along the layer.

5. - The induction furnace according to claim 1, further characterized in that the metallic and magnetically permeable material forms an insert IB that is cast into a non-conductive matrix »the insert is located between the outer shell and the refractory container.

6. The induction furnace according to claim 3 »further characterized in that the insert has a substantially cylindrical shape about the longitudinal axis of the refractory container» and the metallic and magnetically permeable material comprises a plurality of elements having a substantially spherical shape and a size that is chosen to maximize the packing density of the elements within the insert.

7. The induction furnace according to claim 5. further characterized in that the non-conductive matrix comprises a material selected from silicone. epoxy and a refractory castable material.

8. The induction furnace according to the re-indication 1. further characterized in that said outer shell comprises a material selected from a low resistivity metal and a ceramic.

9. The induction furnace according to claim 1. further characterized in that the outer shell is a non-conductive material.

10. The induction furnace according to claim 8. further characterized in that said low resistivity metal includes a material selected from copper »aluminum and copper and aluminum alloys.

11. A method for reducing the external magnetic field produced by the operation of an induction furnace having an induction coil and a refractory vessel therein, said method comprising the step of encircling the induction coil and the vessel. with a layer of metallic material and magnetically permeable supported by a matrix.

12. The method according to claim 10 »further comprising the additional step of selecting said plurality of elements of the metallic material and magnetically permeable according to shape and size, choosing the shape and size to maximize the packing density of the elements supported by said matrix.

13. The method according to claim 11. further comprising the additional step of casting said metallic and magnetically permeable material with a substantial material non-conductive.

14. The method according to the rei indication 11, which further comprises the additional step of casting said metallic and magnetically permeable material with a semiconductor or non-conductive material.

15. An induction furnace having a refractory vessel, an induction coil and an outer shell substantially surrounding the refractory vessel; comprising: a layer of metallic and magnetically permeable material comprising a plurality of elements between the outer shell and the induction coil; the outer shell has a base, an upper part and a side wall each comprising the metallic material and magnetically permeable; further characterized in that the elements of the metallic and magnetically permeable material are disposed substantially in a narrow hexagonal packing for maximum density, and are cast in a shape having a non-conductive matrix.

16. An induction furnace having a refractory vessel, an induction coil and an outer shell substantially surrounding the refractory vessel; comprising: a layer of metallic material and magnetically permeable between the outer shell and the induction coil, the outer layer has a base, an upper part and a side wall »and an insert comprising metallic and magnetically permeable material and located in space 32 between the outer shell and the refractory container, further characterized in that the metallic and magnetically permeable material comprises a plurality of elements which are arranged in a narrow hexagonal packing for maximum density and which are cast in a form that has a non-conductive matrix.