Patent Publication Number: US-3875322-A

Title: Electric induction furnace hearth for containing metal melt

Description:
United States Patent [191 Sundberg 5] Apr. 1, 1975 ELECTRIC INDUCTION FURNACE I 2,652,44l 9/1953 Gynt et al l3/26 HEART FOR CONTAINING METAL MELT 2.7] 1.436 6/l955 Jones et al. l3/26 [75] Inventor: Yngve Sundberg, Vasteras, Sweden FOREIGN PATENTS OR APPLICATIONS Assigneel Aumamla Svenska Elektriska l.208,45l l/l966 Germany 13/26 Aktlelmlaget Vasteras Sweden Primary Examiner-J. D. Miller [22] Filed: Jan. 21, 1974 Assistant E.taminerFred E. Bell Attorney. Agent, or Firm-Kenyon &amp; Kenyon Reilly [21] Appl. No.. 434,886 can &amp; Chapin [30] Foreign Application Priority Data [57] ABSTRACT I Jan. 31. 1973 Sweden 73013! [2 An electric induction furnace hearth for containing a metal melt is formed by refractory side and substan- [52] U.S. Cl. 13/27, 13/26 tially flat bottom walls, and at least one substantially [5|] Int. Cl. H05b 5/12 flat electric induction coil means positioned at least [58] Field of Search 13/26, 27 partially under this bottom wall and with the latter structurally connected with this coil means and at [56] References Cited least partially supported thereby against the weight of UNITED STATES PATENTS l0/l927 Gerth l3/27 the melt when the latter is contained in the hearth.  
 7 Claims, 5 Drawing Figures STE-3.3221  
 R-JENTEDAFR H975 SLIET 1 BF 2 ELECTRIC INDUCTION FURNACE I-IEARTH FOR CONTAINING METAL MELT BACKGROUND OF THE INVENTION One way to reduce metal oxides, such as iron ore, is by feeding the oxides in the form of particles to the surface of a carbonaceous metal melt heated by an electric induction coil means which may comprise one or more coils powered by alternating current of suitable frequency, such as from 50 to 60 cycles per second. The oxides are reduced on the surface of the melt. Therefore, it is desirable to proportion the hearth so that the melt extends over a large horizontal area while having a comparatively small vertical extent or depth. Conventional electric induction heating metallurgical furnace designs are not compatible with this requirement.  
 SUMMARY OF THE INVENTION The object of the present invention is to provide a furnace construction more compatible with the above requirement for an extended area of melt surface, particularly required for the melt reduction of oxides but possibly being desirable for other metallurgical practices. To achieve this object, the present invention provides an electric induction furnace hearth having the extended horizontal dimensions and restricted vertical dimensions. This hearth is formed by refractory vertical side walls and a substantially flat bottom wall, keeping in mind that structural considerations may require the latter to have a shallow concavity shape.  
  A flat electric induction coil is positioned underthis bottom wall and the latter is structurally connected with this coil so as to be supported by the coil, wholly or partially, against the weight of the melt when the latter is contained in the hearth. A plurality of such flat coils may be used in this way to support the bottom of the hearth.  
  The hearth may be of elongated shape with round or semicircular ends formed by appropriately contoured side and flat bottom walls. The side wall may be supported by being structurally connected with a correspondingly contoured electric induction coil or coils.  
  Electric induction coils must of necessity have turns or convolutions made of thick-walled electrically conductive tubing, usually made of copper. The tubing may be rectangular in cross section to obtain a tight pitch or turns ratio. It follows that an electric induction coil suitable for a rectangular electric furnace application inherently is structurally strong. By making such coil means a structural part of the furnace hearth the latters refractory lining component may be reduced in thickness to effect a more efficient or tighter coupling between the coil means and the metal melt, thus obtaining increased efficiency. Even when the hearth has a substantially flat bottom of extended horizontal area for the reason explained hereinbefore, the hearth bottom wall may be made adequately resistant to the weight of the melt.  
  The induction coil or coils may be made as a single flat layer of convolutions which may be asymmetrically pitched or otherwise interrelated to electromotively induce one or more upward bulges in the melt surface and which rise above floating slag resulting from the melt reduction of oxides. In this way a naked melt surface or surfaces can be exposed to metal oxides fed to a carbonaceous melt in the furnace for the practice of the melt reduction technique.  
 kit  
  The connection between the refractory hearth lining and the induction coil or coils may be effected during the construction of the hearth by tamping the refractory directly against the coil or coils to produce an integrated hearth construction.  
  Alternatively, the refractory may be tamped against refractory bricks supported by non-magnetic metal webs or bars of small thickness which are interspaced and positioned in planes at right angles to the hearth lining and which, in turn, are supported by the induction coil or coils. The webs should be sufficiently thinned to have thicknesses considerably less than the penetration depth for induced currents in the material from which they are made. Such material may be austenitic stainless steel. This type of construction permits the inherent strength of the coil or coils to be used to support the hearth construction while, at the same time, permitting the coil or coils to be made as removable components permitting them to be serviced without destruction of the hearths refractory lining. In this case this lining is tamped against the bricks.  
 BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated entirely schematically by the accompanying drawings in which:  
  FIG. 1 is a vertical section of a hearth incorporating the principles of the invention;  
  FIG. 2 is a cross section taken on the line A-A in FIG. 1;  
  FIG. 3 diagrammatically shows the energization of the coils of the coil means;  
  FIG. 4 represents a cross section of a hearth using asymmetrical coil means; and  
  FIG. 5 in cross section shows a portion of the new hearth using the brick and web construction previously referred to.  
 DETAILED DESCRIPTION OF THE INVENTION FIGS. 1 and 2 show an electric induction furnace hearth having a horizontal flat bottom 1 peripherally surrounded by an upstanding vertical side wall 2. The bottom wall I may be slightly conical or concave for constructional reasons. The horizontal contour is elongated, the hearth having straight interspaced parallel sides 2a and round or semicircular ends 2b. The relative internal dimensions may be such that the length is from four to ten times the width, although the hearth may be completely circular. for example, for relatively small production rate applications. The electric induction coil means is shown in the form of a flat, singlelayer coil 3 in contact with and supporting the outside of the side wall 2. This coil extends around the rounded or semicircular ends 2b and along the straight sides In. this coil extending vertically. Two horizontal flat, single-layer coils 4 and 5 are positioned in contact with the outside of the hearth s wall 1. It can be seen that the entire outside of the hearth is supported by the induction coils. The hearths walls are formed by any suitable material having the refractory properties required to confine molten metal and which may be tamped to form, against the induction coils. Thus, the hearth is in effect an integrated construction including the refractory and the coils which, due to their shape, have very substantial mechanical strength as previously described. The coils are shown as being formed by rectangular tubing which may be made of copper. An external iron core is provided by laminations of electric steel formed as bars and extending at 6 throughout the width of the hearth and at 7 for the height of the hearth. These are in contact with the outsides of the coils and provide further support for containing the weight of the melt. It is to be understood that the coil convolutions are electrically insulated from each other in the usual manner.  
  With this construction the hearth may have an extended horizontal area for supporting a melt of relatively shallow depth but having a surface area that is great as compared to this depth, thus making the hearth particularly useful when incorporated into a furnace construction for the practice of the melt reduction technique. As indicated by FIG. 1, the melt shown at 8. has eddy currents induced in it in the fashion indicated by the arrows 9 in FIG. 1. This is due to the fact that these currents are induced in the melt not only by the flat bottom coils 4 and but also by the upstanding vertical coil 3. With the coils energized by current having a frequency within the 50 60 cycles per second range. the desired upward bulge 8a in loop form, generally following the contour of the hearth. results. This effect is further enhanced by varying the turns ratio or convolution interspacing ofthe coils as indicated by the spacing 4a in FIG. 1. By varying the turns ratio of the coils and the manner in which the currents are phased in the respective coils. various melt surface bulge contours can be obtained, which is of advantage particularly in practicing the melt reduction technique. In addition to the inductive stirring providing the bulge contours, the melt is. of course, inductively heated.  
  FIG. 3 serves to show that the well-known doublefrequency principle may be used to stir the melt in planes perpendicular to the longitudinal axis of the hearth. Various lines connect the coils through suitable switches with the two frequencies LF 1 and LF 2, and with a normal frequency NF. FIG. 4 serves to illustrate how a flat bottom horizontal coil 9 with a small convolution pitch or turns ratio produces a high melt surface bulge 10 while the other horizontally extended coil ll with a large turns distribution, or wider convolution interspacing, produces a relatively lower but more extended bulge or elevation 12.  
  In FIG. 5 a portion of the flat bottom is shown in modified form. In this case the flat induction coil 13 supports the hearths refractory lining (not shown) via a series of interspaced webs 14 arranged in vertical planes and made of nonmagnetic metal. such as austenitic stainless steel, these webs extending transversely with respect to the hearth and supporting refractory bricks 15. The hearths refractory lining material is tamped against these bricks. With this construction the coil or coils 13 are not literally integrated with the hearths lining and they may, therefore, be made as removable elements permitting them to be serviced without destruction of the furnace lining, the latter being retained by the metal webs 14 which may be structurally interconnected and mounted.  
 What is claimed is:  
  1. An electric induction furnace hearth for containing a metal melt and formed by refractory side and substantially flat bottom walls, and at least one substantially flat electric induction coil means positioned at least partially under said bottom wall with the latter structurally connected therewith and at least partially supported thereby against the weight of said melt when the latter is contained in said hearth.  
  2. The furnace of claim 1 in which said hearth has a rounded end which includes said side wall, and said coil means includes a rounded coil portion around said end.  
  3. The furnace of claim 2 in which said side and bottom walls are formed in direct contact with said coil means.  
  4. The furnace of claim 2 in which refractory bricks connect at least said bottom wall with said coil means.  
  5. The furnace of claim 4 in which interspaced nonmagnetic webs in vertical planes are interposed between said bricks and said coil means.  
  6. The furnace of claim 2 in which said coil means includes a coil having an asymmetrical convolutions pitch.  
  7. The furnace of claim 2 in which said coil means includes rounded coil portions around both said side and bottom walls.  
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