Abstract:
An insulation application and replacement system method for use on electric induction heating coils used to heat billets in industrial applications. Re-lining induction coil heating devices with non-hazardous materials of the invention uses a multiple step process of removing existing hazardous installation materials and replacing with multiple layers of environmental and user safe glass cloth material treated with suspended refractory material in a carrier solution.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   This invention relates to electric induction heating coils for heating metal billets that provide “high” point of use temperature within a limited area. Such induction heating coils require that the conductive coil “winding” be surrounded with a water cooled corresponding coil and an insulation layer to keep the “winding” at the desired operational temperature. 
   2. Description of Prior Art 
   Prior art insulation applications heretofore use the best available high temperature resistant insulation materials having the physical properties required for relative thin layer shaped conforming applications, such as asbestos. As has been well documented, asbestos mineral fibers are hazardous when they become friable, inhaled or exposed to the human organism. Insulation lining of vessels is well known, see U.S. Pat. Nos. 4,241,843 and 4,313,400 as well as novel induction heating apparatus coils, see U.S. Pat. No. 6,730,893 which illustrates prior art induction heating coils in which a magnetic field is generated by the coil and passes through the object to be heated. Prior art induction coil isolation insulation is used to protect the inductive coil, (winding) from the high temperatures induced in the metal billet during the heating cycle and contact with a conductive liner. Aluminum billets which are typically extruded offer operational challenges due to the low conductivity values associated with non-ferrous metals. Given that asbestos insulating liners of the coil surface has been the standard, the required replacement with less performing material has been the only option such as glass cloth. Such replacement materials have a shortened effective operational life especially in the so-called “gap” formed by the typical stainless steal induction coil liner which cannot be continuous in this electro-magnetic environment. The gap in the stainless steel liner becomes a critical failure point of new replacement materials and thus, as noted, shortens the overall usefulness and service life of the insulation before replacement. Such insulation within the gap becomes burned, brittle and fractured during use and must be replaced or the liner will short out the coil and fail. 
   SUMMARY OF THE INVENTION 
   The present invention deals with the replacement of electrically non-conductive thermal resistant insulation lining of electro-magnetic induction heating coils used to reheat metal billets for processing. The method of the system uses refractory coating and embedded of the fiberglass glass cloth to form a continuous insulation barrier between the induction coil stainless steel liner and the surface of the induction coil itself. Multiple method steps define the relining or initial lining of the coil as well as ongoing service method steps for replacing critical gap sealant material used to increase the service life of the insulation in the coil. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an induction heating coil representation for illustration purposes; 
       FIG. 2  is an enlarged cross-sectional view of the critical non-conductive gap in the steel liner which requires special insulation application; 
       FIG. 3  is an enlarged cross-sectional view of an alternate form of the invention; 
       FIG. 4  is an enlarged top plan view of end strips; 
       FIG. 5  is a side elevational view of interengaged end strips; and 
       FIG. 6  is an enlarged side elevational view of the interengaged end strips. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1  of the drawings, an induction heating coil  10  can be seen for illustration purposes that is used in the industry for rapid selective heating of metal billets positioned within. The basic components of the induction coil  10  are an electric conductive coil  11  in communication with a source of electrical power surrounded on its outer side by a corresponding water cooling coil  12 . A stainless steel coil liner  13  extends the interior length of the induction coil  10  through which billets to be heated are transported. Such electro-magnetic induction heating coils are well known and widely used on the industry and further explanation is not required for the enabling disclosure of this invention which is directed to insulation liners (not shown) used to protect the coil  11  from high temperatures generated within the billet during induction heating typically 1000 degrees Fahrenheit. 
   Such insulation lining material heretofore was made from mineral asbestos due to its high temperature performance and useful life characteristics. Asbestos has been found to be hazardous to human health especially when it breaks down and becomes friable in which “micro-fibers” are released into the air or when it comes in contact with the human skin. This invention is therefore directed to a method and material application for replacing asbestos materials used as well as the insulation lining of new induction coil heating coils  10 . 
   Referring now to  FIGS. 1 &amp; 2  of the drawings, the stainless steel coil liner  13  can be seen (enlarged and simplified for illustration and understanding) having a required non-conductive elongated gap at  14 . The gap area  14  is a critical point of prior art liner failure as will be described in greater detail hereinafter. 
   The method steps of the invention require that the stainless steel liner  13  be removed by conventional means for access to the interior surface of the coil  11 . The stainless steel liner  13  is somewhat resilient and can therefore be compressed annularly slightly for removal and reinsertion. Any existing traditional lining material is removed presenting a clean inner surface  11 A of the conductive coil  11 . An insulating lining system  15  of the invention is then applied, first to the inner surface  11 A of the coil  11 . Sheets of fiberglass glass cloth  16  are positioned in place and coated or pre-coated with a high temperature refractory material  17  such as Noxtab brand manufactured by the Noc &amp; Sons Company of Cleveland, Ohio. The refractory coating material  17  is in a semi-liquid based suspension for application purposes and will penetrate the glass cloth  16  to form an integral bond thereto within the textured surface of the glass cloth  16 . As the refractory coating  17  dries, it becomes hard and takes on its high temperature resistance properties. Multiple layers of impregnated glass cloth  16  can be used depending on the application required. 
   Once the refractory coating material  17  has dried, in this application, the stainless steel coil liner  13  is reinserted using the normal installation techniques re-engaging the refractory surface  17  of the treated glass cloth  16 . The gap area  14  defined by the stainless liner  13  is required as a non-electrically conductive break in the liner in all applications, as noted. 
   Since the elongated exposed area of the insulation within the gap area  14  is subject to the direct harsh environment of the billet chamber formed by the coil  11  a second layer of refractory coating material  17  is applied directly into the gap area. It will be seen that over time the gap area  14  may become degraded and it will therefore be a simple matter to simply reapply the refractory coating material  17  into the gap area  14  when needed. It will also be seen that given the insulating properties of the refractory coated  17  glass cloth liner  16 , it will provide adequate protection even if the additional refractory coating material  17  is not applied to the gap area  14 , just a shortened lifespan than the full application method described hereinabove. 
   Referring now to  FIG. 3  of the drawings, an alternate form of the invention can be seen wherein coated grass glass cloth  18  is installed into the interior surface of the coil  11  and then a secondary strip glass cloth material  19  is saturated with the high temperature refractory coating material  17  and let dry. The secondary strip  19  is then positioned in place (gap area)  14  and held temporarily while the stainless steel liner  13  is reinstalled. Mounting and positioning engagement elements  19 A (grommets in pairs), best seen in  FIGS. 5 and 6  of the drawings on oppositely disposed ends of the strip  19  will allow for future removal and replacement by attaching a replacement strip  20  to the existing strip  19  and simply pulling it out inserting the new strip  20 . The cover strip of insulation material  19  is substantially wider than the actual gap area  14  assuring an effective cover application. 
   The exposed area of the strips  19  or  20  once installed defined by the gap area  14  can also be repaired and maintained by overlying a layer of applied refractory coating material  17  which will extend useful in-service life, if needed, before replacement. 
   Additionally, the gap area  14  is also subject to thermal cooling due to the open nature of the induction coil and the movement of billets (not shown) in and out in any application of the preferred embodiment set forth previously or the alternate form of the invention as described. 
   It will be evident from the above description that to prevent premature insulation failure that a multiple layer insulation application process is required in the coil application environment. By use of the preferred embodiment system and materials application with the glass cloth  16  coated with the refractory coating material  19  in combination with the secondary layer or coating of refractory material  17  independently directly into the gap area  14  thereafter, as needed, it will be substantially increasing the operational life of the so treated induction heating coil  11  between extended maintenance cycles. 
   It will thus be seen that a new and novel method and application for insulation of an induction heating coil has been illustrated and described and it will be evident to those skilled in the art that various changes and modifications may be made thereto without departing from the spirit of the invention.