REMOVABLE LINERS FOR INDUCTIVE FURNACES

Abstract: A liner (6) for an induction furnace (12) is capable of being removed intact or rotated. Removal allows the liner (6) to be refurbished or replaced with a different liner. Rotation allows asymmetrical wear on the liner (6) to be evened out by periodic rotation. The liner (6) is preferably made of a composite material of inductively transparent fibers and inductively transparent inorganic cements.

Description: REMOVABLE LINERS FOR INDUCTIVE FURNACES TECHNICAL FIELD This invention relates to the art of induction furnaces. In particular, the invention relates to removable and rotatable liners for induction furnaces. BACKGROUND Induction furnaces are well known and generally include a cylindrical induction coil lined with a refractory material, a power supply, and apparatus for tilting the furnace to discharge molten metal. The lining is a refractory material that is applied directly to the induction coil in one or more layers. A problem facing prior art induction furnaces is rapid deterioration of the refractory lining. The lining deteriorates by chemical reaction between the hot lining and air as the molten metal is poured out, by chemical attack from the slag or metal, or by physical damage during removal of the slag. The degradation due to air exposure is typically greatest in the region at the top of the lining and opposite the pour spout. Replacement of a refractory lining may require as long as several days because the refractory lining must be cooled and dug out of the furnace, typically, with a jackhammer, and then the new refractory lining must be installed and allowed to cure. One method addressing the problem of replacing a lining is contained in US 5,416,795 (Kaniuk). According to that suggestion a crucible assembly is provided comprising a crucible and crucible support. The crucible support is cast around the crucible to form the crucible assembly. The crucible assembly is capable of being removed from the induction coil, and a replacement unit may be installed. This system, however, does not permit reuse or refurbishment of the assembly, and it is discarded after its removal from the furnace. Inductively transparent ladles for manufacture of metals are also known. For example, US patents 4,921 ,222 and 5,039,345 (Mott) teach inductively transparent ladles made of inductively transparent glass fibers and inductively transparent inorganic cement forming a matrix for the fibers. These ladles are stand-alone structures that require no additional support and include elements such as trunions for allowing the ladles to be transported when full of molten metal and tilted for pouring the metal. SUMMARY OF THE INVENTION In accordance with the invention, a removable, inductively-transparent Iiner is provided for an induction furnace of the type that includes an induction coil located above a furnace bottom. The novel Iiner of the invention may be used for virtually any type of induction furnace, including furnaces used for processing iron, copper, stainless steel, carbon steel, or aluminum. The inductively transparent Iiner of the invention is preferably designed to fit within the induction coil of an existing furnace in such a manner that it may be moved with respect to the coil without harm to the Iiner. Thus, the outside dimensions of the Iiner are preferably slightly smaller than the inner dimensions of the coil whereby engagement between the Iiner and the coil is minimal. The Iiner is strong enough to support molten metal only when the Iiner is in the furnace but is not strong enough to transport molten metal by itself. Thus, when the Iiner is positioned in the furnace and engaging the bottom of the furnace, the Iiner will safely contain the molten metal without significant support from the coil structure. On the other hand, the Iiner s not strong enough to be removed safely from the furnace with a load of molten metal. This structure allows the Iiner to have only nominal or no contact with the sides of the furnace, i.e., the coil structure, and thereby to be released from the coil intact or rotated with respect to the coil for continued operation. The Iiner is secured to the furnace framework by known mechanical means, such as brackets, for normal operation and to allow it to be easily released from the framework by removal of the brackets. Replacement liners may be constructed at a separate location, for example, by the winding technique shown in the noted Mott patents. When it is desired to install a new Iiner, the previous one is simply released, and the new one installed. Installation of a new Iiner may be desirable when the refractory lining in a first one is spent or when it is desired to use the furnace to melt a different metal or alloy that requires a different refractory or to avoid contamination. In either instance, installation of a new Iiner will be a simple matter. Additionally, the Iiner itself may be refurbished by removing the spent refractory lining and then installing a new one. This would be done away from the furnace causing no furnace downtime. Periodic rotation of the Iiner allows wear or degradation of the refractory lining caused, for example by pouring or by oxidation of exposed areas, to be evened out. By thus spreading the degradation over the circumference of the refractory lining, the lifetime of the refractory lining is easily substantially increased. The amount and frequency of the rotation will be a function of specific circumstances. The inductively transparent Iiner is preferably made of a material including glass fibers and inorganic cements as taught in the noted Mott patents, to provide the necessary strength. The disclosure of these patents is hereby incorporated by reference. In the preferred embodiment, the material consists of the fibers and the cement to provide transparency to virtually all electromagnetic energy used in induction furnaces including frequencies above about 200 Hz. Also, a known refractory lining is provided to protect the Iiner and to insulate it from the temperatures of the molten metal. Alternatively, a pre-cast crucible is provided in lieu of the refractory lining. This crucible would be installed into the Iiner in a known manner with a backup refractory material placed between the Iiner and the crucible. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a vertical cross section of a known induction furnace having a removable inductively transparent Iiner in accordance with the invention therein. Figure 2 is a vertical cross section of a known induction furnace with a tilting mechanism and having an inductively transparent Iiner in accordance with the invention therein. Figure 3 shows an induction furnace as in figure 2 in the position where the metal is being poured. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to figure 1 , an inductive furnace includes a coil 2 that is connected to a power supply (not shown) for generating electromagnetic fields as known in the art. The spaces between the coils are filled with a grout 4 for holding the coil elements in place. In accordance with the invention, a removable Iiner 6 is formed of a composite comprising substantially continuous glass fibers and inorganic cement. The Iiner includes a lower cavity portion 8 for receiving materials for producing metals or metal alloys and a lip 10 for engaging a support 12. The Iiner may be secured to the support in any of several known ways. A refractory lining 14 is applied to the interior of the Iiner to protect the Iiner, the Iiner providing the majority of the structural strength required by the refractory lining to support the molten metal . It is noted in this connection, however, that the Iiner is not designed to be a stand-alone structure and requires the support of the bottom 9 of the furnace. Moreover, the Iiner is not designed to be carried with a full load of molten metal. Thus, the wall thickness of the liner may be substantially less than that of a ladle. The Iiner is capable of carrying frozen metal, however, because the walls as well as the bottom of the Iiner would support the metal. Because the Iiner has strength adequate to support the refractory and the metal without contact with the coil, it may be desired to provide a small gap 20 between the liner and the coil. Further, it may be desired to force air through this gap with a fan 22 to provide cooling. Figure 2 shows a furnace having a hydraulic tilting mechanism 16, which engages the support 12 for tilting the furnace and Iiner about a pivot 18 for discharging the molten metals by pouring. The furnace is shown in a normal operating orientation in figure 2, and figure 3 illustrates the furnace in an orientation where the metal is discharged by pouring. It will be appreciated that the portion of the refractory lining not covered by metal is exposed to the air and is subject to chemical degradation during pouring. In use, the Iiner 6 may be easily replaced by releasing the Iiner from the support 12 and lifting it away from the coil. There are many known devices for holding the Iiner to the support, such as mechanical brackets and these may be removed to allow the Iiner to be lifted out of the coil. The liner may then be replaced by a new Iiner, a refurbished Iiner, or by a different Iiner previously used for a different metal. Thus, the same furnace may be used for producing several kinds of metals without contamination among the metals. In accordance with another aspect of the invention, the Iiner is rotated periodically by releasing the securing brackets, rotating the lining, and securing the brackets. This changes the location on the Iiner where the metal is poured out of the Iiner and changes the portions of the Iiner that are exposed to the atmosphere and the molten metal during pouring. This process spreads the wear on the refractory lining caused by pouring evenly about the interior of the refractory lining and thereby extends the life of the lining. Modifications within the scope of the appended claims will be apparent to those of skill in the art.

Claims: I claim: 1. In an induction furnace having a furnace bottom, an induction coil located above said bottom, a Iiner in said induction coil for receiving metal, and means for tilting said Iiner for discharging said metal, the improvement wherein said Iiner is inductively transparent to electromagnetic energy for heating and stirring said metal, including frequencies above about 200 Hz and comprises an inductively transparent composite material of inductively transparent, substantially continuous fibers and inductively transparent inorganic cement binding said fibers together. 2. An induction furnace according to claim 1 wherein said Iiner has an outer surface that is adjacent said induction coil and spaced therefrom by an air gap. 3. An induction furnace according to claim 2 further comprising means for forcing air to flow in said gap. 4. An induction furnace according to claim 1 wherein said liner has an outer surface that is in contact with said induction coil. 5. Apparatus for containing metal in an induction furnace compπsing an inductively transparent liner having side walls and a bottom wall for resting on a bottom of said furnace and for being received within an induction coil of said furnace, wherein the physical strength of said side walls and said bottom wall is such that said Iiner is capable of containing molten metal only when said Iiner is in said furnace. 6., Apparatus according to claim 5 wherein said side and bottom walls are made of inductively transparent fibers and inductively transparent inorganic cement. 7. Apparatus according to claim 5 or 6 wherein said liner is capable of containing solid or frozen metal and being removed from said furnace. 8. Apparatus according to claim 5 or 6 wherein said Iiner is capable of being rotated with respect to said induction coil. 9. Apparatus according to claim 5 or 6 wherein said Iiner is capable of being removed intact from said furnace after use and reused. 10. Apparatus according to claim 5 or 6 further comprising a refractory lining covering an interior surface of said Iiner. 11. A process for refining metal in an induction furnace of the type comprising an induction coil, a furnace bottom, and means for removing metal from said furnace, said process comprising the steps of placing an inductively-transparent Iiner in said induction coil, placing said metal in said Iiner, applying electric current to said coil to heat said metal, removing said metal, and removing said Iiner from said furnace intact. 12. A process according to claim 11 further comprising the step of refurbishing said Iiner to provide a refurbished Iiner and installing said refurbished Iiner in an induction furnace. 13. A process according to claim 11 wherein said Iiner is made of inductively transparent fibers in a matrix of inductively transparent inorganic cement. 14. A process according to claim 11 wherein each of said Iiner includes a refractory lining. 15. A process according to claim 12 wherein said step of refurbishing comprises replacing said refractory lining. 16. A process according to claim 11 further comprising the step of replacing said Iiner in said coil in a rotational orientation distinct from an initial rotational orientation. 17. A process for refining metal in an induction furnace of the type comprising an induction coil, a Iiner, a furnace bottom, and means for removing metal from said furnace by tilting said furnace to pour said metal from said furnace at a pouring location on said Iiner, said process comprising the steps of placing an inductively-transparent Iiner in said induction coil, placing said metal in said liner, applying electric current to said coil to heat said metal, removing said metal by pouring said metal out of said Iiner at said pouring location, and rotating said Iiner with respect to said means for removing to provide a new pouring location on said Iiner. 18. A process according to claim 17 wherein said Iiner is made of inductively transparent fibers in a matrix of inductively transparent inorganic cement.

Inventors: STANLEY EARL K, STANLEY, EARL, K.
Applicants: ADVANCED METALS TECH CORP, ADVANCED METALS TECHNOLOGY CORP.
Application year: 1996
Main classification: H05B6
IPC codes: H05B6