Abstract:
A heating apparatus is disclosed, that may include a ceramic rod having at least one circumferential groove extending substantially circumferentially about a perimeter of the rod; and a coil located about the perimeter of the rod and having turns of the coil embedded with the grooves of the rod.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates in general to heating systems and methods and in particular to the use of heating elements that are resilient in the face of very high temperatures and the possibility of flux or other debris being deposited near or on the heating elements. 
         [0002]    On occasion, laboratory personnel using such devices will also add a halogen chemical compound, to facilitate the removal of the end-product. Upon heating the crucible, the lithium borate melts and dissolves the sample. This dissolution reaction is enhanced by the agitation of the crucible. After complete reaction, the resulting hot solution is poured into a plate-shaped mold and cooled, to produce a glassy disk that is then placed in an elemental analyzer. 
         [0003]    The temperature of the crucible-heating process can reach 1200 degrees Celsius, which poses tremendous challenges to the durability of the materials and parts used. At such high temperatures, most materials will likely burn, melt, rapidly oxidize in the presence of oxygen in the air and possibly chemically interact with the halogen gases released by the heating process. 
         [0004]    Thus, there is a need in the art for an apparatus that would durably support the crucibles and the molds and reliably heat the furnace chamber, to minimize repair operations by laboratory personnel in remote areas, while maintaining a clean environment in the furnace, and while avoiding contaminating the samples being processed. 
       Crucible Holders 
       [0005]    In existing systems, crucibles are typically held either using metallic clips (as in the case of gas fluxers from Corporation Scientifique Claisse, Canada), or placed in a shallow tube (as practiced in the electrical furnace by ModuTemp, Australia), or on horizontally running parallel ceramic rods (as offered by Katanax and Corporation Scientifique Claisse on their respective electric fluxers). In the last of the above-listed configurations, crucibles are held apart by small ceramic spacers (Katanax) or by a single scalloped metallic part (Corporation Scientifique Claisse). 
         [0006]    Crucible holders are typically designed to enable repair or replacement to be as easy and as fast as possible. The ease and speed of replacement are needed because flux tends to spill onto the holder, and cleaning must be performed quickly in a production setting to avoid costly downtime. 
       Mold Holders 
       [0007]    Molds can be secured with metallic clips (as offered on gas fluxers by Corporation Scientific Claisse, Canada), or the mold may rest on a metal plate with circular openings. Both the mold and the crucible holder may increase thermal expansion of their respective lengths in the range of 3 to 8 mm (millimeters). If compliance is not built into the surrounding parts to accept this expansion, the heat-exposed parts will be longitudinally compressed between their fastening points (located outside the furnace), and are likely to sag and fail. 
       Heating Elements 
       [0008]    The only heating elements that are known to reach temperatures suitable for resistive heating fusion machines are: SiC—Silicon carbide. One drawback of SiC is ageing. Due to heat exposure, each heating element&#39;s electrical characteristics will change over time, making it nearly impossible to replace a single element in a multi-element configuration. Doing so would strongly reduce the life expectancy of the heating elements that are not being replaced. 
         [0009]    MoSi2—molybdenum disilicide is another element commonly used for heating elements. The main challenge encountered when designing with MoSi2 is that it sags heavily at high temperature, and becomes very brittle upon cooling. The heating element is typically installed in a U-shaped free-hanging configuration. Molybdenum disilicide is known to potentially react with halogens, and degrade prematurely. 
       FECRAL—Iron-Chromium-Aluminum Metallic Alloy: 
       [0010]    The effects incurred at high temperatures cause the drawback of this alloy. At high temperatures, FeCrAl becomes soft, and coil-shaped elements will deform to the point that the turns of the helically wound resistive heating coil tend to approach one another, leading to element failure by localized overheating. This type of element can also experience surface reaction with halogen gases or flux spills, and then fail rapidly. 
         [0011]    Accordingly, there is a need in the art for improved configurations of heating elements and associated parts of resistive-heating furnaces. 
       SUMMARY OF THE INVENTION 
       [0012]    According to one aspect, the invention is direct to a heating apparatus that may include a ceramic rod having at least one circumferential groove extending substantially circumferentially about a perimeter of the rod; and a coil located about the perimeter of the rod and having turns of the coil embedded with the grooves of the rod. 
         [0013]    Other aspects, features, advantages, etc. will become apparent to one skilled in the art when the description of the preferred embodiments of the invention herein is taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    For the purposes of illustrating the various aspects of the invention, there are shown in the drawings forms that are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
           [0015]      FIG. 1  is a perspective view of a crucible holder in accordance with an embodiment of the present invention; 
           [0016]      FIG. 2  is a perspective view of a mold holder in accordance with an embodiment of the present invention; 
           [0017]      FIG. 3  is a perspective view of a heating element assembly in accordance with an embodiment of the present invention; 
           [0018]      FIG. 4  is an exploded perspective view of the heating element assembly of  FIG. 3 ; 
           [0019]      FIG. 5  is an exploded perspective view of a furnace having a housing and a removable heating block assembly; 
           [0020]      FIG. 6  is a perspective view of an alternative embodiment of a furnace with heating elements and a shield located so as to protect the heating elements in accordance with an embodiment of the invention; and 
           [0021]      FIG. 7  is an exploded view of the furnace of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    In the following description, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one having ordinary skill in the art that the invention may be practiced without these specific details. In some instances, well-known features may be omitted or simplified so as not to obscure the present invention. Furthermore, reference in the specification to phrases such as “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of phrases such as “in one embodiment” or “in an embodiment” in various places in the specification do not necessarily all refer to the same embodiment. 
         [0023]      FIG. 1  is a perspective view of a crucible holder  100  useable in conjunction with an embodiment of the present invention. Crucible holder  100  may include heating element crucibles  110 , brackets  120 , and retaining beams  130 . Crucible holder  100  is one configuration of an assembly for securing crucibles  110  within a resistive-heated furnace (furnace not shown). 
         [0024]    In the embodiment of  FIG. 1 , metal (such as brackets  120 ) is used only at the ends of the holder central portion  130 , which tends to inhibit contamination of the metal. Most of holder  100  is made of high purity ceramic, which does not oxidize or peel, and which therefore has a very low thermal expansion coefficient. The end supports  140  are made of ceramic, which is much less prone to heat sagging than metals. 
         [0025]      FIG. 2  is a perspective view of a mold holder assembly  200  in accordance with an embodiment of the present invention. Mold holder assembly  200  may include molds  210  and spacers  220 , which may be made of ceramic. 
         [0026]    Consistent with the goal of making mold holder  200  resilient to heat, very little metal is present in mold holder  200 , thereby helping to avoid contamination, and to make for a more sag-proof assembly. End supports  230  are ceramic, and the holder central portion is freely suspended, thereby eliminating the concern for thermal expansion issues. In a preferred embodiment, brackets  240  are the only metal portion of mold holder  200 . Brackets  240  may be made of a Nickel/Chrome (80/20) alloy, that is 80% nickel and 20% chrome. However, other alloys, metals, and/or alloy compositions may be employed. 
         [0027]      FIG. 3  is a perspective view of a heating element assembly  300  in accordance with an embodiment of the present invention.  FIG. 4  is an exploded perspective view of the heating element  300  of  FIG. 3 . 
         [0028]    Heating element  300  may include ceramic rod  310 , coil  320 , and/or shield  330 . However, in some embodiments, shield  330  may not include shield  330 . Rod  310  preferably includes grooves around the perimeter thereof, which are preferably in a spiral pattern. Coil  320  is preferably configured as a single helical coil having turns that match the geometry of the spiral groove in rod  310 . However, the present invention is not limited the specific geometry of the spiral coil  320  and the grooves in rod  310  shown in  FIG. 4 , and other spiral/groove geometries may be practiced. FeCrAl is the preferred material for rod  310 . However, the invention is not limited to the use of this material. Coil  320  is preferably made of metal, and at that of a conductive metal. 
         [0029]    When coil  320  is assembled onto rod  310 , the turns of coil  320  become embedded within respective grooves around the exterior of rod  310 . Thus, the ridges in between the grooves of the exterior of rod  310  end up being located in between adjacent turns of the coil  320 . With this arrangement, the ridges restrain any possible movement of the turns of coil  320 , and thus keep adjacent turns of coil  320  properly spaced apart from one another during high temperature conditions within the furnace. Thus, even when high temperatures tend to create expansion forces within coil  320 , the ridges between the grooves on the exterior of rod  310  prevent the turns of coil  320  from approaching one another. Thus, the prior-art problem of excess localized heating arising from turns of coil  320  moving toward one another under high temperature conditions is prevented by the presence of grooves and ridges on rod  310 . 
         [0030]    After coil  320  has been assembled onto rod  310 , shield  330  may be slid over the combination of coil  320  and rod  310  to form heating element assembly  300 , as shown in  FIG. 3 . Shield  330  operates to protect the coil  320  and rod  310  from flux and/or other debris that may unintentionally spill onto the rods  310  during the heating process. Shield  330  may be made of quartz, sapphire, and/or other suitable material. 
         [0031]      FIG. 6  is a perspective view of an alternative embodiment of a furnace  500  with heating element  300  and a shield  630  located so as to protect the heating element  300 .  FIG. 7  is an exploded view of the furnace of  FIG. 6 . 
         [0032]    In the embodiment of  FIG. 6 , heating element  300  is in the form of a spiral that encircles crucible  110  several times. Shield  630  is preferably sheet of quartz, sapphire or other suitable material that is configured into the shape of a hollow cylinder, and placed radially outward from crucible  110  and radially inward of heating element  300 . Placement of shield  630  in this location operates to prevent flux and other debris, which is commonly present on the exterior of crucible  110  in production situations, from reaching and inflicting damage on heating element  300 . 
         [0033]      FIG. 5  is an exploded perspective view of a furnace  500  having a housing and a removable heating block assembly. Furnace  500  may include housing  510 , heating element assemblies  300 , and a module  502  including ceramic block  530  and panel  520 , which may be metallic. 
         [0034]    As shown in  FIG. 5 , the removal of module  520  provides a user with unobstructed access to heating element assemblies  300  located inside housing  510 , thereby making cleaning, removal, and replacement of heating element assemblies  300  much faster, safer and easier. Once operations such cleaning and/or replacement of the heating element assemblies  300  are complete, module  502  may be readily re-attached to housing  510  to properly seal furnace  500 . 
         [0035]    The disclosed embodiment overcomes problems in the prior art that arose when users needed to extract heating elements  300  through restricted openings in housing  510  under conditions providing limited access, poor visibility, and the possibility of damaging heating element assemblies  300  upon removing same from the housing  510 . 
         [0036]    Attention is now directed to benefits observed due to some of the inventive embodiments disclosed herein. Employing the removable module, the crucible holders can be removed and disassembled in under a minute, without the use of tools. Individual parts can then be replaced or cleaned easily. The materials used for heat shield  330  operate to minimize the risk of sample contamination, and reduce the likelihood of thermal expansion and sagging. Durability is greatly improved with the inventive embodiments. As for the heating elements, life expectancy was dramatically increased, in order to minimize costly downtime in laboratories. Flux spills and halogen vapors are much less of a problem with the inventive embodiments. 
         [0037]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.