Abstract:
A scrap charging apparatus for an electric arc furnace uses a skip hoist to supply scrap to a holding bunker having diverging end walls extending between converging side walls. The containment space for the scrap is increased by this wall arrangement and provides an impetus in the bunker for scrap flow to an underlying scrap delivery chute. The scrap delivery chute is formed by an elongated scrap carrying trough having a greater width than the exit width of the scrap holding bunker for delivering scrap to a charging opining for an electric arc furnace A superstructure supporting the scrap holding bunker at an elevated and lateral spaced location from the electric arc furnace. A ram controlled by a drive incrementally advances scrap along the scrap delivery chute for introducing successive preselected volumes of scrap to a charging opining for an electric arc furnace.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention related to patent application Ser. No. 09/737,440 filed Dec. 13, 2000 entitled Electric furnace of steel making; and patent application Ser. No. 09/738,095 filed Dec. 16, 2000 entitled Revamping of a basic Oxygen furnace installation to provide an electric furnace facility. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a scrap charging apparatus for an electric furnace used in a steel making process and more particularly, to such an apparatus embodying a construction and an arrangement of component parts to minimize the requirement of floor space in a steel making and passage of the scrap into a furnace in an incremental fashion to maintain flat bath operation by the furnace. 
     2. Description of the Prior Art 
     The charging of scrap into an electric furnace, particularly in an electric arc furnace, may be carried out by the use of sequential use of conveyors delivering the scrap from a remote storage area to the furnace. The scrap is allowed to fall through the top of the furnace after removal of the furnace roof and electrodes from the furnace interior. Many tons of scrap will be charged and impact with the refractory lining of the furnace cannot be avoided requiring repair to the damage refractory. The conveyors require a continuous presence along a usually extensive course of travel by the scrap. Conveyors must be of a heavy duty construction to rapidly transport the scrap need for a service charge and also to withstand the intense heat flowing from the top of the furnace. The use of a large liquid metal heel at the end of tapping of the furnace to promote flat bath furnace operation would be undesirable because splashing of the liquid metal as the scrap impacts with the liquid metal. Well drastically shortening the life of the furnace side walls, therefor it is usual to reestablish a liquid metal bath by melting scrap by using heat provided by the operation of the electrodes. As the scrap melts about the electrodes, cold spots form outwardly from the electrodes from which eventually cave in and instances fall against the electrodes causing electrode damage. 
     Accordingly, it is an object of the present invention to provide a scrap charge for an electric steel making furnace to charge scrap in a generally horizontal direction form a bunker to the furnace. 
     It is another object of the present invention to provide a skip hoist system to load a scrap charging bunker for reducing the requirement of floor space about an electric steel making furnace. 
     It is a further object of the present invention to provide a scrap storage bunker including diverging end wall communicating with an underlying scrap charging chutes having walls that enlarge the cross sectional are in the chute in the direction to an electric steel making furnace to maintain un impeded flow of scrap by the even increasing size of the scrap conducting space. 
     It is a further object of the present invention to provide a generally horizontal scrap charging chute communicating with a retractable fluid cold chute extending into the interior of an electric steel making furnace to establish a scrap fall space with a bath of liquid steel remaining the furnace after tapping. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention there is provided a scrap charging apparatus for an electric arc furnace, the apparatus including the combination of a scrap holding bunker having diverging end walls extending between converging side walls, the scrap burden along boundaries formed by the diverging end walls providing an impetus in the bunker for scrap flow to an underlying scrap delivery chute, the scrap delivery chute defining an elongated scrap carrying trough having a greater width than the exit width of the scrap holding bunker for delivering scrap to a charging opining for an electric arc furnace, a superstructure supporting the scrap holding bunker at an elevated and lateral spaced location from an electric arc furnace, a ram controlled by a drive to incrementally advance scrap along the scrap delivery chute for introducing successive preselected volumes of scrap to a charging opining for an electric arc furnace, and a conveyor for supplying scrap to the scrap holding bunker. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The present invention will be more fully understood when the following description is read in light of the accompanying drawings in which: 
     FIG. 1 is a front elevational view of an electric arc furnace installation embodying the features of a scrap charger according to the preferred embodiment of the present invention; 
     FIG. 2 is a plan view of the electric arc furnace installation shown in FIG. 1; 
     FIG. 3 is a side elevational view taken along lines III—III of FIG. 2; 
     FIG. 4 is a sectional view taken along lines IV—IV of FIG. 3; 
     FIG. 5 is a plan view taken along lines V—V of FIG. 3; 
     FIG. 6 is a sectional view taken along lines VI—VI of FIG. 5; 
     FIG. 7 is a sectional view taken along lines VII—VII of FIG. 3; 
     FIG. 8 is a schematic illustration of a hydraulic control circuit for the scrap charging rain; and 
     FIG. 9 is a elevational view taken along lines IX—IX of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     There is illustrated in FIGS. 1 and 2 a preferred form of an electric furnace facility for use with the scrap charging apparatus of the present invention. The furnace facility includes an electric arc furnace  10  formed by a lower furnace shell  12 , an upper furnace shell  14  and a furnace roof  16 . The furnace roof  16  includes roof panels formed by an array of side-by-side coolant pipes with the coolant passageways communicating with annular upper and lower water supply headers  20  and  22 , respectively, interconnected by radial distributing pipes to form a water circulating system communicating with service lines  24  containing water supply and return lines. The service lines  24  include flexible sections to avoid the need to disconnect the service lines when it is desired to lift the furnace roof alone or combined with the upper furnace shell a short distance, e.g., 24 inches, for servicing the lower furnace shell. The upper water supply header  20  encircles a triangular array of three apertures in a roof insert  30 . The apertures are dimensional and arranged to accept the phase A, B and C electrodes  32 ,  34  and  36  carried by electrode support arms  38 ,  40  and  42 , respectively. Each of the electrode support arms is independently positioned vertically by a support post  44  restrained by horizontally spaced guides  46  in a superstructure for vertical displacement by actuator  48  typical in the form of piston and cylinder assembly. The electrode support arms also support water cooled cables for transmission of electrical current from transformers in a transformer vault  50  to the respective phase A, B and C electrodes. 
     A fume duct  52  extends vertically from an annular opening in the furnace roof  16  between the upper and lower water supply headers  20  and  22  for exhausting the fume from the interior of the furnace to an enlarged and vertically spaced overlying duct  54  formed by water coolant piping cool the fume and to provide thermal protection. The duct  54  supplies the exhaust fume to an evaporator chamber and filter equipment, not shown, to recover pollutants. 
     Vertically extended legs, not shown, at annular spaced apart intervals form lateral roof restraints for maintaining a desired superimposed relation of the furnace roof  16  on the furnace upper shell  14 . The furnace upper shell includes superimposed convolutions of coolant pipe supplied with coolant from spaced apart supply headers that are interconnected by vertical distribution pipes to form a water circulating system communicating with service lines  56  containing water supply and return lines. Metal panels may be supported by the coolant pipe of the furnace roof and the coolant pipe of the furnace upper shell for confinement of the fume to the interiors of these furnace components. The service lines  56  include a flexible section to avoid the need to disconnect the service lines when it is desired to lift the furnace roof combined with the upper furnace shell a short distance, e.g., 24 inches, for servicing the lower shell. The convolutions of coolant pipe are arranged to form an annular shape to the upper furnace shell interrupted by a scrap charge opening  58  in one quadrant of the shell. A slag discharge opening is closed by moveable door  60  supported by the upper furnace shell and extending to a slag discharge trough in the lower furnace shell  12 . Slag passes from the furnace along the trough beyond a threshold formed by carbon rod insert  62  which is supported by suitable brackets on the lower furnace shell  12 . The scrap charge opening  58  is provided to introduce quantities of scrap at closely spaced apart time intervals throughout the major portion of the furnace operating cycle. 
     Scrap residing in a retractable chute  64  in a constant communication with the interior of the furnace of a scrap charger  66  serves as a media to prevent unwanted escape of the fume from the furnace into the scrap charger. 
     The upper furnace shell  14  includes a circular ring, not shown, forming a lower boundary to the shell except where a gap exists at the slag discharge opening. Apertures in the circular ring are provided at annular spaced locations to receive upstanding locator pins on annular segments at opposite lateral sides of the lower furnace shell  12 . These annular ring segments are discontinuous at the slag discharge trough and at a bottom crescent-shaped section protruding in an eccentric fashion from the annular configuration of the overlying upper furnace shell  14 . The crescent-shaped bottom section is enclosed by a correspondingly shaped crescent roof section  68 . The crescent-shaped roof is formed by a layer of coolant pipes. The crescent-shaped bottom section is used to provide eccentric furnace tapping and is combined with the construction and operation of the lower furnace shell to achieve the benefits of flat bath operation and slag free tapping. 
     The preferred form of the electric arc furnace has a configuration of the refractory face surfaces in the lower furnace shell  12  for supporting a metal charge during refining of a steel heat and providing eccentric bottom tapping of the steel heat. As seen in plan view of FIG. 3, there is annular side wall section  70  in an area bounded by a diameter  72  with a radius R 1  struck from the center of the diameter  72 . As seen in the sectional views of FIG. 6, the annular vertical side wall section  70  is bounded by a spherically-dished floor wall section  74  defined by a radius R 2  struck form a point along a line defined by intersecting vertical plane  76  containing the center of the diameter  72 . Plane  76  is a plane of symmetry of the configuration to the lower furnace shell. A floor wall section  78  begins at a vertical plane containing diameter  72  and proceeds away from the spherically-dished floor wall section  74  by a linear downward-sloping contour along plane  76  with an ever increasing radius of curvature transverse to plane  76  forming a rolled developed plate floor wall configuration. The ever increasing radius of transverse curvature of the floor wall section  78  results in an ever increasing height to the vertical side wall  82  as can be seen in FIG.  6 . The vertical side wall sections  70  and  82  forms a vertical boundary to the liquid metal surface commonly called a hot metal line  84  at the start of tapping a heat. At the conclusion of the tapping of the steel heat, there is a liquid heel line  86  formed by the upper surface of the steel heat and represents a reduction to the liquid metal depth at the diameter  72  typically slightly less than one-half of the depth of the steel heat than at the start of tapping. At the site of the sectional view of FIG. 6, the vertical side wall  82  is of maximum height and merges with floor wall section  78  along plane  76  at the site of a tap hole assembly  88 . The furnace is operated in a manner to always maintain a liquid heel depth, at the end of tapping, overlying the tap hole of at least three times the diameter of the tap hole during the useful life the tap hole ceramic discs. Additionally, the size of the heel at the end of tapping is at least 70% of the tapped heat preferably 100% so that the introduction of scrap into the furnace may be accomplished in an incremental fashion using the thermal energy of the heel and the continuous operation of the electrodes for maintaining flat bath operation. At the conclusion of the tapping of a heat into an underlying ladle  90  supported by a transfer car one of two transfer stopper assemblies  92  and  94  is used to fill the tap hole with sand and promptly thereafter a tap hole gate, not shown, is positioned to close off the bottom of the tap hole assembly. An emergency tap hole closure assembly  96  is shown in FIG. 6 in the event the tap hole gate malfunctions. 
     Referring again to FIGS. 1 and 2, it can be seen that rails  98  extend along opposite sides for the rails of the transfer car for the ladle  90 . The rails  98  support a furnace transfer car  100  used to support the lower furnace shell and the upper furnace shell and roof in a superimposed relation. The furnace transfer car is moved along the rails  98  from furnace operating position  102  to a furnace exchange position  104  by a suitable winch assembly. The furnace remains statically positioned throughout repetitive furnace operating cycles at the furnace operating position  102 . The charging of scrap therefor is preferably accomplished by the introduction of scrap through the side wall of the upper furnace shell although the scrap charger of the present invention is equally useful to charge scrap into an electric arc furnace that tilts in opposite directions for slagging and tapping. In both cases tilting furnace arrangement and the static operating arrangement, charging maybe accomplished through the top of the furnace exposed by removal of the furnace roof The scrap charger  66  according to the preferred form of the present invention includes a scrap charging car  106  supported on rails  108  and carrying side-by-side scrap boxes  110 . As best shown in FIG. 9, each scrap box is mounted by pivot shaft  112  to the scrap charging car and a piston and cylinder assembly  114  mounted on the car and joined with the respective scrap boxes by a clevis mounting for tilting a scrap box to discharge scrap into a car  116  forming part of a skip hoist  118 . A winch  120  is provided drum portion cables connected to the skip hoist car  116  draws the car laden with scrap along a skip hoist frame  122  to a point where support rails  124  for the car curve downwardly and serve to discharge the scrap content into a scrap holding bunker  126 . The bunker is supported by a super structure  127  to extend to an elevation laterally spaced from the scrap charging opening  58  in the electric furnace. The volume of scrap in scrap holding bunker is contained by diverging end walls  128  and  130  extending between opposed side walls that  132  and  134  converge in the direction toward a bunker discharge opening  136 . The bunker side wall  128 ,  130 ,  132  and  134  support an overlying scrap guide section  138 . As shown in FIGS. 3 and 7, the converging side wall  132  and  134  each have pairs of upper and lower scrap shover rams  140  and  142 , respectively. Each scrap shover ram is guided by a guide trough  144  angularly positioned in the respective side walls of the bunker and advanced from a start position to a scrap engaging position where the ram juts from the guide trough in response to operation of a piston and cylinder assembly  148 . The lower pairs of rams  142  in each side wall are interconnected by a plate  146  to increase the working area of the scrap shover rams. The flow of scrap in the bunker is monitored by a video camera  150 . The diverging end wall provides an impetus for scrap flow in the bunker to an underlying scrap delivery chute  152  which as shown in FIGS. 4,  5  and  7  have side walls  154  spaced apart at a distance which is greater than the width of the bunker discharge opening  136  of the bunker to promote scrap flow into the delivery chute. The chute is closed by an upwardly diverging top wall section  155  extending between diverging end wall  130  of the bunker and retractable chute  64 . The delivery chute further includes a downward diverging continuous floor wall  156  supported by spaced apart cradle supports  157 . The cradle support includes a transverse carrier beam  158  joined with post members  160  extending from the floor upwardly along the side walls  154  to a point where a cross beam  162  interconnects the post members  160  and provides a stable cradle support structure. The elevations of the transverse carrier beams  158  change at each support site along the length of the chute  152  thereby positioning the chute in a downwardly angled fashion so that gravity contributes to scrap flow along the chute. A top wall section  164  closes off the top of the chute between the diverging end wall  128  of the scrap holding bunker  128  to the remote end of the chute where an upstanding anchor  166  is provided with a clevis mounting for supporting the cylinder member of a piston and cylinder assembly  168 . The rod end of the piston and cylinder assembly  168  is mounted to a pusher block  170  and forming an end wall to a pusher ram  172  made up of side walls, top walls and floor walls surrounding the entire length of the piston and cylinder assembly  168 . The pusher ram is incrementally advanced along the scrap delivery chute  152  to advance a predetermined volume of scrap into the furnace. Scrap is charged into the furnace at closely space intervals commencing with the end of the tapping of a heat and extending to a short period, e.g., three minutes, before tapping of the next heat. The static placement of the furnace throughout consecutive operating cycles allows the retractable chute  64  to extend through the charging open  58 . The rod ends of piston and cylinder assemblies  174  are mounted on the retractable chute. The cylinder members of the piston and cylinder assemblies  174  are mounted on the top wall  155  and floor wall  156  of the chute. The piston and cylinder assemblies  174  are operated when it is desired to withdraw the chute  164  from the charging opening such as for moving the lower or upper and lower furnace shells to the furnace exchange position  104 . The piston and cylinder assemblies  174  position the retractable chute to project into the furnace by a distance sufficient so that the chute traverses the refractory forming the vertical wall in the lower furnace shell. The retractable chute is constructed from convolutions of coolant pipes joined together in an edge-to-edge relation. Coolant water is continually circulated through the pipes to prevent destruction while residing in the highly heated environment in the furnace. The extent to which the chute projects into the furnace is selected to assure scrap will fall directly into the liquid metal bath and not impact with the refractory of the side wall. Further, the volume of scrap introduced during each push cycle by the rain is predetermined to prevent damaging impact with electrodes  32 ,  34  and  36  and maintain flat bath operation by the furnace. 
     FIG. 8 schematically illustrates a control for the piston and cylinder assembly  168  and includes limit switches LS 1 , LS 2 , LS 3  . . . LSN placed at equally spaced intervals along the side wall  154  of the underlying scrap delivery chute  152  within boundaries formed by the diverging end wall  128  and  130  of the scrap storage bunker. A signal provided by the limit switches is delivered to an actuator  176  for a hydraulic control valve  178  supplied with pressurized hydraulic fluid from a reservoir  180  by a motor driven pump  182 . The distance separating the limit switches forms the incremental length “L” of an individual scrap charge. The length “L” is always less than the distance “X” corresponding to the linear length of the fall space between the end of the moveable chute in the furnace and the vertical wall of an electrode most adjacent the chute as shown in FIG.  3 . While the limit switches LS 1 , LS 2 , LS 3  . . . LSN have been selected for the purpose of detecting the advanced positions of the rams, other devices maybe used for this purpose without departing from the present invention. One such form of another device is a detector responsive to displacement of a linear scale by movement of the ram  170 . The rain has an elongated length sufficient to traverse the distance between the end walls  128  and  130  of the scrap holding bunker  126 . When the pusher block  170  passes beyond wall  130 , the ram is retracted to a start position residing below roof  157  to allow scrap to flow into the chute from the overlying bunker. In the unlikely event of a blockage to the downward migration of the scrap, one axis more of the piston and cylinder assemblies  148  are operated to cause the associated scrap shover rams to supply forces to the mass of the scrap and restart flow due to gravity. 
     While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.