Abstract:
An induction furnace includes a pair of induction coils with a pair of faraday rings disposed between the induction coils to substantially prevent mutual inductance between the first and second induction coils. The induction coils preferably have a different size circumference and may be coplanar. The prevention of mutual inductance provided by the faraday rings is particularly useful for a pusher furnace in which adjacent furnace sections are heated to different and rather specific temperatures.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Application Ser. No. 60/749,015 filed Dec. 7, 2005; the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates generally to induction furnaces. More particularly, the invention relates to induction furnaces which utilize a plurality of induction coils for heating adjacent sections of the furnace. Specifically, the invention relates to the use of inner and outer faraday rings disposed between adjacent induction coils to prevent mutual induction between the adjacent induction coils. 
     2. Background Information 
     Induction furnaces are well-known in the art and typically utilize one or more induction coils to heat the furnace via a susceptor or via direct inductive heating of the load within the furnace. Pusher furnaces or the like involve a plurality of sections which form an elongated passage through which the load is conveyed in order to most typically provide continuous heating of the load within heating sections of the furnace. Faraday rings are well known for reducing the mutual induction between the pair of adjacent induction coils. However, current known arrangements are not able to sufficiently eliminate the mutual inductance between the coils which is necessary to independently operate the induction coils for a variety of purposes. The present invention addresses this and other problems. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides an induction furnace comprising a first heating section including a first induction coil; a second heating section including a second induction coil adjacent the first induction coil and spaced therefrom; first and second faraday rings disposed between the first and second induction coils to help prevent mutual inductance between the first and second induction coils. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a diagrammatic side view of the induction furnace of the present invention showing the inner and outer faraday rings. 
         FIG. 2  is an enlarged fragmentary sectional view taken from the side of the furnace in  FIG. 1 . 
         FIG. 3  is a sectional view taken on line  3 - 3  of  FIG. 2 . 
         FIG. 4  is a fragmentary sectional view similar to  FIG. 2  diagrammatically showing the electromagnetic field produced by the induction coils and the effect of the faraday rings thereon. 
         FIG. 5  is similar to  FIG. 4  and shows a second embodiment of the induction furnace with the inner and outer faraday rings spaced differently than in the first embodiment. 
     
    
    
     Similar numbers refer to similar parts throughout the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of the induction furnace of the present invention is indicated generally at  10  in  FIGS. 1-2 ; and a second embodiment of the induction furnace is indicated generally at  100  in  FIG. 5 . Referring to  FIG. 1 , induction furnace  10  includes first and second sections  12  and  14  which are disposed laterally adjacent one another. First section  12  includes a first induction coil  16  and second section  14  includes a second induction coil  18 . First induction coil  16  has first and second ends  20  and  22  defining therebetween a longitudinal direction which is the same as the longitudinal direction of furnace  10 . Likewise, second coil  18  has first and second ends  24  and  26  defining therebetween a longitudinal direction which is the same as that of coil  16  and furnace  10 . First end  20  of coil  16  is an entry end and a second end  26  of coil  18  is an exit end. Second end  22  of first coil  16  is adjacent and spaced from first end  24  of second coil  18  and thus defines therebetween a space  28  in which are disposed inner faraday ring  30  and an outer faraday ring  34 , each formed of a metal. Induction coils  16  and  18  and faraday rings  30  and  34  are all formed about a longitudinal axis A which is substantially horizontal. Inner ring  30  and outer ring  34  generally lie along a common plane which is substantially perpendicular to axis A. 
     Referring to  FIG. 2 , furnace  10  further includes a conveying platform  36  such as slide rails extending in the longitudinal direction along which a plurality of loads  38  move in the direction of Arrows B in  FIG. 2  from entrance end  20  of coil  16  to exit end  26  of coil  18 . First section  12  includes a first susceptor  40  associated with first induction coil  16  and second section  14  includes a second susceptor  42  associated with second induction coil  18 . First section  12  further includes several insulation layers  44  of refractory material disposed between susceptor  40  and first induction coil  16 . Likewise, second section  14  further includes a plurality of insulation layers  46  of refractory materials disposed between susceptor  42  and second induction coil  18 . First susceptor  40  defines a first passage  48  and second susceptor  42  defines a second passage  50  aligned with passage  48 . As previously noted, sections  12  and  14  typically will abut one another so that passages  48  and  50  are a continuous longitudinally extending heating passage. Conveying platform  36  extends through first and second passages  48  and  50  in order to convey loads  38  therethrough. 
     Referring to  FIG. 3 , furnace  10  further includes a power source  52  in electrical communication with second induction coil  18 . First induction coil  16  is likewise in electrical communication with a power source (not shown) so that the power sources respectively power induction coils  16  and  18  separately. Inner and outer rings  30  and  34  are mounted to one another via a plurality of radially extending mounting structures  54 . 
     In accordance with the invention and with continued reference to  FIG. 3 , inner faraday ring  30  forms a continuous loop having a shape and outer faraday ring  34  forms a continuous loop having a shape which is substantially the same as the shape of inner faraday ring  30  except that it is larger. More particularly, each point along the continuous loop of outer ring  34  is spaced radially outwardly from a respective associated radial point of inner ring  30 . This is illustrated in  FIG. 3  with a first radius R 1  and second radius R 2  which extend from axis A. Radius R 1  intersects the inner surface of outer ring  34  at a point P 1  which is radially outwardly of point P 2 , which is the intersection of radius R 1  and the outer surface of inner ring  30 . Likewise and by way of further example, point P 3  on radius R 2  is disposed radially outwardly of point P 4  wherein points P 3  and P 4  are analogous to points P 1  and P 2  with regard to radius R 2 . Most preferably, the normal distance D 3  ( FIG. 3 ) between inner ring  30  and outer ring  34  is substantially the same all along the continuous loop. More particularly, in the lower right of  FIG. 3 , a tangent T 1  to the outer surface of inner ring  30  is shown with distance D 3  being perpendicular to tangent T 1 . Tangent T 1  is thus representative of any tangent along the outer surface of inner ring  30 . In the exemplary embodiment, inner ring  30  and outer ring  34  each have a shape which is generally rectangular with rounded corners. This is likewise true of susceptor  42  and coils  16  and  18 . However, the shape of these various structures may vary in accordance with the particular configuration of the furnace desired. 
     In accordance with the invention and with reference to  FIG. 4 , when the respective power sources are operated to power induction coils  16  and  18 , induction coil  16  produces a magnetic field F 1  and induction coil  18  produces a magnetic field F 2  respectively represented at the dashed flux lines in  FIG. 4 . As is well known in the art, induction coil  16  couples with susceptor  40  via magnetic field F 1  and induction coil  18  couples with susceptor  42  via magnetic field F 2  and respectively inductively heats susceptors  40  and  42  to transfer heat to loads  38 . Inner ring  30  limits the effect of magnetic field F 1  in the longitudinal direction toward second induction coil  18  as indicated by the altered magnetic flux lines at area A 1 . Similarly, inner ring  30  limits the longitudinal effect of magnetic field F 2  toward induction coil  16  as indicated at the altered magnetic flux lines of area A 2 . Inner ring  30  and susceptor  40  in combination prevent the portion of magnetic field F 1  radially inwardly of ring  30  from affecting induction coil  18 , as indicated at area A 3 . Likewise, inner ring  30  in combination with susceptor  42  prevent field F 2  from affecting induction coil  16  as indicated at area A 4 . However, inner ring  30  is not sufficient to eliminate or substantially eliminate the inductive effect of magnetic field F 1  on induction coil  18  and the effect of magnetic field F 2  on induction coil  16 . 
     In accordance with the invention, outer ring  34  prevents the portion of magnetic field F 1  which is radially outward of inner ring  30  from extending longitudinally toward second coil  18  to produce electromagnetic induction therein, as indicated at area A 5 . Likewise, outer ring  34  limits the longitudinal reach of magnetic field F 2  external to inner ring  30  toward induction coil  16  to prevent inductance therein caused by field F 2 . Without outer ring  34 , induction coils  16  and  18  would create magnetic fields which cause mutual inductance in one another and thus alter the amount of energy being absorbed by susceptors  40  and  42 . Such mutual inductance would also affect the respective power sources, such as power source  52  which are connected to induction coil  16  and  18 . Such mutual inductance prevents the ability to independently control induction coils  16  and  18  in order to provide the desired inductive heating respectively within sections  12  and  14  of furnace  10 . The use of outer faraday ring  34  eliminates or substantially eliminates the mutual inductance between coils  16  and  18  so that they are independently operable. This allows the independent control of coils  16  and  18  to provide the specific desired heating effect within each of sections  12  and  14 . This is especially useful when it is desired to create specific temperature zones, for example a first zone within section  12  and a second zone within section  14  having different temperatures or temperature ranges. This ability to closely control such temperature zones allows for the production of certain loads  38  which require close control of the temperatures within certain zones for specific periods of time as the loads pass through the different heating zones. 
     With reference to  FIG. 5 , induction furnace  100  is described. Furnace  100  is substantially the same as furnace  10  except that furnace  100  includes a second section  114  which is slightly altered to accommodate an inner ring  130  which is positioned differently with respect to outer ring  34  than in the first embodiment. Furnace  10  is shown primarily to indicate that the inner and outer faraday rings do not have to be substantially coplanar with one another. Thus, section  114  includes additional space between the end thereof and second coil  18  in which is disposed inner faraday ring  130 . More particularly, inner ring  130  is disposed intermediate outer faraday ring  34  and second induction coil  18  in the longitudinal direction. Although inner ring  130  is longitudinally offset from outer ring  34 , the effect is the same in the ability to prevent mutual inductance between induction coils  16  and  18 .  FIG. 5  has been marked with areas A 1   b , A 2   b , A 3   b , A 4   b , A 5   b  and A 6   b  which are analogous to areas A 1 -A 6  in  FIG. 4  and thus are not further detailed. 
     In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. 
     Moreover, the description and illustration of the invention is an example and the invention is not limited to the exact details shown or described.