Abstract:
A holding furnace for holding a molten metal includes a housing having an interior chamber for holding the molten metal. An insulating board structure is placed into the chamber along at least a side portion of the housing. The insulating board structure contains heat within the housing for maintaining the metal in a molten state. A heater assembly is provided in a side of the furnace. The heater assembly is installed in the side of the furnace with a structural arrangement that protects against leakage of molten metal from the furnace interior to the furnace exterior.

Description:
FIELD OF THE INVENTION 
       [0001]    The disclosure relates generally to board lined furnaces, and more particularly to side immersion heating elements disposed in sealing relation to the board lined furnaces. 
       BACKGROUND OF THE INVENTION 
       [0002]    Holding furnaces are reservoirs for holding and maintaining molten material in its molten state. There are generally two types of holding furnaces: castable lined holding furnaces and board lined holding furnaces. Within these groups, there are many types and grades of non-wetting castable refractory and non-wetting insulating refractory available. A board lined furnace, for example, may be lined with calcium silicate boards or blocks, but it may also be lined with many other different materials that are interchangeable with the calcium silicate. The calcium silicate board lined holding furnaces, however, are generally considered to be more energy efficient than the traditional castable lined holding furnaces. 
       SUMMARY OF THE INVENTION 
       [0003]    At least one embodiment of the invention is a holding furnace for holding a molten metal. The furnace comprises a housing having an interior chamber for holding the molten metal and an opening into the chamber. An insulating board structure is disposed within the chamber in overlying relation to at least a side portion of the housing. The insulating board structure is constructed and arranged to contain heat within the housing for maintaining the metal in a molten state. A heater assembly extends through a side opening of the housing and through a side opening in the insulating board structure into the chamber. The heater assembly is constructed and arranged to be immersed in the molten metal and to transfer heat thereto. A sealing device is disposed in sealing relation to the housing and to the insulating board structure and arranged in the side openings in the housing and the insulating board structure, the sealing device being configured to support the heater assembly. 
         [0004]    Other embodiments provide a holding furnace for holding a molten metal. The furnace comprises a housing having an interior chamber for holding the molten metal and an opening into the chamber. An insulating board structure is disposed within the chamber in overlying relation to at least a side portion of the housing. The insulating board structure is constructed and arranged to contain heat within the housing for maintaining the metal in a molten state. A heater assembly extends through a side opening of the housing and through a side opening in the insulating board structure into the chamber. The heater assembly is constructed and arranged to be immersed in the molten metal and to transfer heat thereto. A sealing means is disposed in sealing relation to the housing and to the insulating board structure and arranged in the side openings in the housing and the insulating board structure, the sealing means being configured to support the heater assembly. 
         [0005]    Still other embodiments comprise a method of heating a board lined furnace. The method comprises heating an interior of the furnace with a heater assembly provided through a side wall of the furnace, and retaining the heat in the interior of the furnace by lining the interior of the furnace with an insulating board structure. 
         [0006]    Yet other embodiments comprise a sealing device for sealing an opening provided in a side wall of a board lined holding furnace having a fluid sealing surface having a stepped portion configured to inhibit fluid flow along an exterior surface of the sealing device and configured to be disposed in fluid sealing relation to a housing of the furnace; and a supporting portion having another stepped portion configured to inhibit fluid flow along an interior surface of the sealing device, the supporting portion being configured to support a furnace heater arranged therein. 
         [0007]    There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
         [0008]    In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
         [0009]    As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a cross-sectional view of a board lined furnace with a heater assembly installed in a side portion according to an embodiment of the invention. 
           [0011]      FIG. 2  is a fragmentary top view of the board lined furnace shown in  FIG. 1  indicating structure to accommodate three heating elements in a side portion thereof according to an embodiment of the invention. 
           [0012]      FIG. 3  is a cross-sectional view along line A-A of the board lined furnace shown in  FIG. 2  showing openings in a side portion thereof for accommodating three heating elements according to an embodiment of the invention. 
           [0013]      FIG. 4  shows a cross-sectional view of an inner board assembly of the insulating board structure and a containment box of the example board lined furnace shown in  FIG. 1 . 
           [0014]      FIG. 5  shows a cross-sectional view of an outer board assembly of the insulating board structure of the board lined furnace shown in  FIG. 1  according to an embodiment of the invention. 
           [0015]      FIG. 6  is a cross-sectional view along line B-B of the board lined furnace shown in  FIG. 2  according to an embodiment of the invention. 
           [0016]      FIG. 7  is a cross-sectional view of a sealing device of the board lined furnace shown in  FIG. 1  according to an embodiment of the invention. 
           [0017]      FIG. 8  is a side view of the sealing device shown in  FIG. 7  according to an embodiment of the invention. 
           [0018]      FIG. 9  is a cross-sectional view of the sealing device shown in  FIG. 7  with two plates coupled to the block according to an embodiment of the invention. 
           [0019]      FIG. 10  is a side view of the sealing device shown in  FIG. 9  according to an embodiment of the invention. 
           [0020]      FIG. 11  is a side view of the sealing device shown in  FIG. 9  with a heater assembly mounted thereto with temporary holding rails according to an embodiment of the invention. 
           [0021]      FIG. 12 . is a top view of the sealing device and heater assembly shown in  FIG. 11  according to an embodiment of the invention. 
           [0022]      FIG. 13  is a top view of a retaining plate according to an embodiment of the invention. 
           [0023]      FIG. 14  is a side view of the retaining plate shown in  FIG. 13  according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Some of the principles of the disclosure are embodied in a holding furnace  20  for holding molten metal. The furnace  20  generally comprises a housing  22  having an interior chamber  24 , a side opening  26  into the chamber  24 , an insulating board structure  28  disposed within the chamber  24 , a heater assembly  32  extending through the side opening  26  into the chamber  24 , and a sealing device  36  to seal the opening  26 . 
         [0025]    The invention will now be described with reference to the drawing figures, in which like numerals refer to like parts throughout.  FIG. 1  shows a cross-sectional view of a board lined furnace according to principles of the invention. The furnace  20  includes the housing  22  having a housing floor  40 , a side wall  42  and an insulating cover (not shown). The housing  22  may be constructed of a metallic material as, for example, steel or any other suitable material. The housing  22  includes the interior chamber  24  and side opening  26  which provides access to the chamber  24 . The interior chamber  24  is a reservoir for containing molten metal or metal that is to be melted into a molten condition. The insulating board structure  28  generally lines the interior of the chamber  24  and provides a furnace floor  44 . The insulating board structure  28  is preferably formed of calcium silicate, although any other suitable high temperature non-wetting insulating refractory material may be used. In the example embodiment, the board lined furnace  20  includes an insulating board structure  28  having an inner assembly of boards  46 , an outer assembly of boards  48 , and a board containment box  70 . The inner assembly of boards may be two layers of calcium silicate board that in part form an inner double box assembly, for example. The outer assembly of boards may be made from vermiculite, for example. Generally, the inner assembly of boards and the outer assembly of boards are fastened together with screws and have refractory sealed joints. The board containment box  70  is built between the inner double box assembly of the inner assembly of boards  46  and the housing  22  of the furnace  20 . The board containment box  70  is formed of calcium silicate or any other suitable non-wetting insulating refractory material. The board containment box  70  is constructed the same way as the inner double box assembly so that it will not leak molten metal if the molten metal should make it that far. 
         [0026]    The sealing device  36  is used to mount the heater assembly  32  in the side openings  26 ,  34  provided in the housing  22  and the insulating board structure  28 , respectively. The sealing device  36  shown  FIG. 1  is one example of a sealing means. The sealing device  36  may be constructed of a calcium silicate block or any other suitable high temperature non-wetting insulating refractory material, and is machined to fit into the side openings  26 ,  34 . The sealing device  36  is configured with a side opening  72 . 
         [0027]    In the example embodiment, the sealing device  36  may be constructed so that an exterior surface  50  thereof is configured to form a multiple step joint shared with the containment box  70  and the inner double box assembly of the inner assembly of boards  46  to seal out leaks when assembled in the furnace  20 . The exterior surface  50  of the sealing device  36  may be constructed with different sized diameter circular or square portions  52 ,  54 , respectively, forming the multiple step joint. However, there other step join configurations are possible in keeping with the principles of the invention. The multiple step joint impedes fluid flow and ensures that there is no straight passage for fluid, such as molten metal, to flow from inside the chamber  24  to the exterior of the furnace  20 . An interior portion of the sealing device is constructed with a short tapered cone  56  facing the interior chamber  24  of the furnace  20  and the molten metal therein. The tapered cone  56  allows for the entire heated section of the heater assembly  32  to come in contact with the molten metal. The rectangular box shown on the heater assembly  32  that is nearly even with the interior in the chamber  24  represents the heated section. An adjacent portion of the sealing device  36  is configured with a longer tapered cone  58 , which may taper at a different angle than the first tapered cone  56  and may be longer or shorter or the same length as the first tapered cone  56 . This second tapered cone  58  in this example embodiment is dimensioned to fit and receive the heater assembly  32 . As shown in the example embodiment, the second tapered cone  58  of the sealing block  36  matches and receives a tapered section  60  of the heater assembly  32 . There can be different taper angles and taper lengths used for different sizes of heater assemblies  32 , but the taper  58  in the sealing block  36  preferably matches the taper section  60  of the heater assembly  32  in order to obtain a good seal between them. 
         [0028]    Along a terminal end  62  of the sealing device  36 , the end furthest away from the chamber  24 , is another stepped or recessed portion  64  formed along an interior portion of the sealing device  36 . This recessed portion  64  of the sealing device  36  is designed to accommodate plates  66 ,  68  mounted thereto, for example, by welding. The plates may be steel plates or manufactured from any other suitable material. The plates  66 ,  68  aide in the assembly process to mount the sealing device  36  to the housing  22  of the furnace  20 . 
         [0029]    The heater assembly  32  is provided in the side opening  72  in the sealing device  36 , and side openings  26 ,  34  in the housing  22  and inner board assembly  28 , respectively. The heater assembly  32  consists of a heating element  74  and a protective casing  76 , for example, an immersion protection tube. The heating element may be an electric heating element or may be a gas fired heating element. It is not necessary that the protective casing  76  be tube-shaped. It may be any other suitable shape including square. 
         [0030]    The immersion protection tube  76  is formed of a refractory, for example, manufactured to be fully immersible in the molten metal bath while at the same time protecting the heating element  74 . The heater protection tube  76  is sealed in the refractory lining to keep the molten metal from leaking out of the furnace  20 . The heater protection tube  76  is thus provided with a tapered sealing cone  60  close to the open end facing toward the exterior of the furnace  20  that provides a stepped sealing joint. As noted above, the sealing device  36 , in this example embodiment, is a machined calcium silicate block, and the tapered sealing cone  58  matches the taper  60  of the immersion protection tube  76 . This structural arrangement allows the sealing device  36  to be screwed and/or glued to the insulating board structure  28 . Any gap that may exist between the sealing device  36  and the immersion protection tube  76  (i.e., the tapered joint between the sealing device  36  and the immersion protection tube  76 ), is sealed with a refractory fiber gasket or cone, for example, or sealed in any other suitable manner including with any other suitable sealing material. 
         [0031]    The heating element  74  is contained in the immersion protection tube  76 . The heating element  74  may have any length, and as shown in the example embodiment may have a length that extends through a majority of the immersion protection tube  76  to provide for a large heated area of the immersion protection tube  76  for heating the furnace  20 . Further, both the immersion protection tube  76  and the heater element  74  are provided with annular flanges  82 ,  84  ( FIG. 11 ), respectively, at a terminal end thereof to allow for mounting of the immersion protection tube  76  and heater element  74  to the sealing device  36  providing further protection against leaks. The heating element  74  may have a non-wetting refractory plug  86  ( FIG. 11 ) near the terminal end thereof that is designed to stop the molten metal in the case of tube  76  failure. It is to be understood that the heater assembly may have varying configurations, such as with or without a terminal plug, and that the configuration of the heater assembly shown in the example embodiment is not intended to be limiting in any way. 
         [0032]    In the example embodiment shown in  FIG. 1 , the heated section of the heating element  74  is marked by a box and with the words 10.5 KW HEATED ZONE. It is to be understood that a range of heater assemblies providing wattages other than the 10.5 kw example heater assembly may be used. The 10.5 kw stands for 10.5 kilowatts or 10,500 watts. The heated zone is the rectangular box shown on the tube that is nearly even with the inside furnace refractory face of the chamber  24  out to near the closed end of the immersion protection tube  76 . From the line where the heated zone begins to the outside terminals of the heating element  74  is what is referred to as the cold zone. Each heating element  74 , in the example embodiment, has 10.5 kw output. So if, for example, there were three heating elements  74  provided, the total heating capacity would be 31.5 kw total output to the furnace  20 . As shown in  FIGS. 2 and 3  by structures  78  and openings  80  of the furnace  20 , the furnace  20  could be modified to accommodate more than one heating element  74 , in this case three heating elements  74 , to increase the heating capacity of the furnace  20 . 
         [0033]    Providing an immersion heating element  74  and immersion protection tube  76  directly in the molten metal bath and in particular arranging them in a side wall  30  of the furnace  20  close to the furnace floor  44  so that they may be fully immersed in the molten metal bath is a very efficient means for heat transfer from the heating element  74  to the molten metal bath. This structural arrangement provides a higher power input through a much larger heating surface to be in contact with the molten metal providing very efficient heat transfer. Since the heater assembly  32  is inserted through a side wall  30  close to the furnace floor  44 , the normal variations in bath depth between charges of molten metal does not expose the heating element  74  and immersion protection tube  76  to air which is a poor conductor of heat. 
         [0034]    Having discussed the main components of the board lined holding furnace with a side immersion heating element, the assembly of the components will now be discussed. As shown in  FIG. 4 , an inner board assembly  46  is constructed with overlaying boards. Mounted to the side of the inner double box assembly of the inner board assembly  46  with screws and non-wetting refractory glue or with any other suitable fastening means, for example, is the board containment box  70 . The outer assembly of boards  48 , shown in  FIG. 5 , is arranged in the housing  22 . The inner board assembly  46  with the board containment box  70  mounted thereto is thereafter arranged in the outer board assembly  48  in the housing  22 , as shown in  FIG. 6 . 
         [0035]    Referring to  FIGS. 7 and 8 , the sealing device  36  has two thick metal plates  66 ,  68  seated in the recessed portion  64  in the terminal end of the sealing device  36 , as shown in  FIGS. 9 and 10 . The metal plates  66 ,  68  are shaped as annular rings or flanges and are welded together or secured together in any other suitable manner. The dimensions of the plates  66 ,  68  are chosen to allow room for additional packing of insulating refractory. The plates  66 ,  68  are mounted to the sealing device  36  with a fastening member, such as a screw. The sealing device  36  with plates  66 ,  68  already attached is then secured with temporary holding rails  88  (shown in  FIGS. 11 and 12 ), and inserted into side openings  26 ,  34  provided in the housing  22  and the insulating board structure  28 , respectively. The temporary holding rails  88  help to mount the sealing device  36  into the side openings  26 ,  34  of the housing  22  and insulating board structure  28 . The free ends of the holding rails  88  temporarily secure to the housing  22  to hold the sealing device  36  in the selected position. 
         [0036]    The joint between the flat on the sealing device  36  behind section  52  is glued to the back of the double inner box assembly of the inner assembly of boards  46  with a special non-wetting cement designed specifically for use with calcium silicate material. A non-wetting plastic refractory, which bonds well with the calcium silicate board and block, is then packed around the sealing device  36 , from inside the furnace  20  along the double inner box assembly of the inner assembly of boards  46 , and from outside the furnace  20  between the sealing device  36  and the containment box  70  to seal and hold in place the sealing device  36 . Then, the temporary holding rails  88  are removed. 
         [0037]    Next, the refractory fiber gasket is inserted into the sealing device  36 , and the immersion protection tube  76  is placed inside the refractory fiber gasket. Flange  82  of the immersion protection tube is then mounted and slowly tightened into place until the immersion protection tube  76  is supported and the refractory fiber gasket is compressed to approximately half its original thickness, providing a further barrier against leaks. The heating element  74  is inserted into the protection tube  76 , and flange  84  of the heating element  74  is mounted and slowly tightened until the heating element  74  is seated and supported. 
         [0038]    The final assembly is fastened in place with a retaining plate  90 , shown in  FIGS. 13 and 14 . The retaining plate is bolted on the housing  22  of the furnace  20  (as shown in  FIG. 1 ), and secured to the sealing device  36  having the metal plates  66 ,  68  attached thereto. 
         [0039]    Thus, with the arrangement provided, a board lined holding furnace is provided with immersion heating elements provided in a side thereof that is sealed against leaks. 
         [0040]    The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.