Abstract:
An arc metallurgic furnace slagging door having an upper panel and a lower panel substantially vertically aligned with the upper panel, the panels being placed in front of a tunnel giving access to a furnace melting pot and in front of the slagging door for closing the tunnel. The upper panel is outwardly inclined with respect to the tunnel, and movable between a closed position and an open position which permits remarks and interventions to be conducted on molten metal. The lower panel is movable independently with respect to the upper panel between closing, cleaning and slagging positions.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     The present application is a National Stage Application of PCT International Application No. PCT/EP2010/05143 (filed on Feb. 5, 2010), under 35 U.S.C. 371, which claims priority to Italian Patent Application No. MI2009A000227 (filed on Feb. 19, 2009), which are each hereby incorporated by reference in their respective entireties. 
     FIELD OF THE INVENTION 
     The present invention relates to an arc metallurgic furnace provided with a slagging door, comprising, according to an embodiment, a lower movable panel serving as a slag remover and as a scrap pusher and a top movable panel, which can be opened to carry out remarks and interventions on molten metal, and related control apparatus of the slagging door. 
     BACKGROUND OF THE INVENTION 
     A steel production cycle is known, complying with the secondary steel making method, which uses iron scrap for regenerating it and obtaining new steel. The core of the secondary steel making is the Electric Arc Furnace (EAF), wherein the scrap is molten. 
     A common electric arc furnace basically comprises a stack, composed by a melting pot for collecting the molten steel, a covering roof which can be opened, three electrodes, which lower through the roof and a fume plant. In the arc furnace, a slagging door is provided, typically located on the vertical wall of the furnace stack in communication with the interior of the furnace through a tunnel. Such a slagging door is used to periodically remove the slag, as well as for other activities, such as loading additives, collecting samples, measuring the temperature, inserting ports and oxygen injectors, and also for inspecting the interior of the furnace. 
     A furnace according to the prior art is disclosed in WO 2006/016201 A. 
     The present invention is directed both to optimizing the slag removal operation, which tends to build up in the tunnel, if any, or at the slagging door threshold, as well as to the separation of slag splashes, which are projected on the closing panel of the slagging door, and to pushing the scrap building up at the tunnel so to allow an easy access and the vision of the interior of the furnace. 
     Slag removal systems are already known, made of horizontally-moving pushing elements or horizontally rocking arms, whose efficiency is insufficient, though, as well as vertically moving closing panels of the slagging door, on which, however, the slag separation action is poor. 
     Therefore, it is the object of the present invention to provide an apparatus, which carries out the slag removal, the threshold cleaning and the scrap pushing actions, as well as the slag separation from the top closing panel of the slagging door, eliminating all the drawbacks of the prior art and optimizing said operations. 
     SUMMARY OF THE INVENTION 
     According to an example, such an object and such tasks are achieved in an electric arc furnace, which has a cooled slagging door, formed by a lower movable slagging panel and a top movable panel, also cooled, apt to enable several cleaning and control operations of the molten metal, addition of additives and oxygen and other operations requiring access to the melting pot. 
     In particular, such a top panel is slightly outwardly inclined and suitable to move itself toward outside the furnace and upward, while keeping substantially such an inclination in respect to the furnace wall. The top panel slides along an inclined guide, under the action of any suitable actuator, which acts on the bearing carrier of the panel. The movement can be simply obtained by means of hydraulic cylinders or by means of a chain, which slides on gear rings. The chains and the gear rings are connected by a drive shaft, which make movement integral and synchronous. The top panel movement outward and upward causes the separation of the slag, which are splashed thereon during the metal melting, due to the action of a scraper. 
     The lower panel forming the real slagging door, in turn, carries out a composite oscillatory movement along the horizontal axes, as a dredging element, in order to penetrate inside the furnace, settle on the slag and then move back, thereby dragging said slag outwards. Such dredging movements iterate until the slag is completely removed. According to a preferred embodiment, the dredging movement can be inverted, in order to carry out, instead, a push into the furnace, to clear materials obstructing the threshold, such as scrap. The lower panel of the slagging door is operated, through an unequal-armed parallelogram, by another hydraulic actuator. The hydraulic actuators can comprise one or more hydraulic cylinders or hydraulic motors with or without a brake, as needed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will be more evident from the description of some embodiments, provided below only as a way of example, and not limitative, with reference to the following accompanying figures, wherein: 
         FIGS. 1A-1H  show in a side elevation and in cross-section a mere exemplary embodiment of a closing and opening apparatus of an arc metallurgic furnace slagging door in several steps of separating the slag splashed on the dual lower panel of the slagging door and removing the slag from the furnace; 
         FIG. 2  shows an elevational front view of said closing apparatus of the slagging door; 
         FIGS. 3 and 4  show a side and a cross-sectional elevational views, respectively, of the chain and gear ring drive for operating the panels and the lever parallelogram, which operates the dual lower slagging panel; 
         FIGS. 5A-5B  show in a side elevation and in cross-section a further exemplary embodiment of a closing and opening apparatus of an arc metallurgic furnace slagging door in various steps of movement; 
         FIG. 6  shows in a perspective view a metallurgic furnace comprising a slagging door according to a further exemplary embodiment of the invention; 
         FIG. 7  shows in a side elevation and in cross-section the closing and opening apparatus of the arc metallurgic furnace slagging door according to a further embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The electric arc furnace comprises, in a way known per se and therefore not illustrated, a stack formed by a rocking melting pot on a horizontal axis, coated by a refractory material and adapt to contain molten steel, a roof which can be opened, adapt to cover the melting pot and to allow loading a steel scrap mass, a plurality of electrodes adapt to melt the steel scrap mass, and means for placing the melting pot on a base. 
     In referring to  FIGS. 1A-1H , a plurality of cooling pipe panels is denoted by  12 , which cover the furnace stack liner. In the front part of the furnace, a short molten metal tapping tunnel  14  is provided, covered by cooling pipes. Such a short tapping tunnel  14 , according to an embodiment of the present invention, during the melting process is closed in the lower part, by a slagging door split, according to the invention, in a lower panel  16  and in a top panel  18 , both formed by cooled elements, for example a plurality of water circulation cooling pipes. The top panel  18  forms the control and adjusting panel of the characteristics of the molten mass, whereas the lower panel  16  has the function of removing the slag, pushing the scrap and, of course, it cooperates for closing the tapping tunnel. Such top and lower panels are mounted on a frame  20 , which supports an inclined guide  22 . 
     The top panel  18  is mounted on a carrier  20 , which slides on guides  22 . The carrier  20  is moved by an actuator, which, in an purely exemplary embodiment, can comprise two equal side rising and lowering systems, each formed by a chain  21 , which slides on gear rings  23  and  25 , and which is connected, on one side, to a lever  27  articulated on the cylinder  29 , and, on the other side, on the carrier  20  ( FIG. 4 ). The gear rings are connected by a drive shaft, which makes their movements integral and synchronous. The drive shaft is preferably actuated by a unit comprising a motor and a gear reducer. According to a further embodiment, the carrier  20  is operated by one or more cylinders connected to the carrier  20  itself ( FIG. 7 ). The top panel  18  can pass from a closing position ( FIG. 1A ) to an opening position ( FIG. 1B ), being able to assume also intermediate positions. 
     When the top panel  18 , supported by the carrier  20 , passes from the closing to the opening positions, the inclined translation movements upwards and outwards in respect to the inner wall of the furnace cause the slag to separate therefrom, splashed thereon during the melting operation, as a result of the scraper  24  dragging in the vicinity of the plane  18  surface, whereby the top panel  18  is cleared from the slag eventually deposited. 
     The lower panel  16  can comprise a single copper wall, eventually ceramic-coated. According to a particular exemplary, but not limitative, embodiment, illustrated in the accompanying drawings, the lower panel  16  is, in this case, formed by an outer wall  16 A and an inner wall  16 B, facing and separated to each other by a coil  16 C of water cooling pipe. Both walls  16 A and  16 B are made of metal, preferably copper, eventually with a ceramic coating. The inner face of the panel  16 , of course, has to be able to withstand the contact with the slag and prevent the slag from adhering. The lower part of the panel  16  is provided with metal elements, preferably made of steel, having the function of cleaning, since they will act on the slag for the removal thereof and it is susceptible of carrying out a movement for pushing and moving away the slag, which remain on the slagging door plane. 
     The lower panel  16  is capable of carrying out a composite movement, similar to the one carried out by a dredger, under the command of any hydraulic actuator, for example, a cylinder or a brake hydraulic motor. However, such an actuator is represented in the annexed drawings and it will be disclosed in the form of a central hydraulic cylinder  35  in an exemplary embodiment thereof. The panel  16  is supported by an articulation lever parallelogram comprising a bracket  30 , on which two levers are pivoted, spaced to each other and of different length  32  and  34 . The shorter lever  34  is pivoted on the slider  26 , to which also the longer lever  32  is pivoted. Shifting the slider  26 , along the upwards and outwards inclined guide  22 , causes the lower panel  16 , and consequently the parallelogram formed by the several levers, to assume several positions. In every position, the panel  16  can be moved independently from the top panel  18 , assuming closing, cleaning and slagging positions. When the lower panel  16  is subjected to a slag dredging movement, the top panel  18  remains still in the closing position. 
     The scraping operation can be horizontally carried out, both from left to right (removal of the slag) and from right to left (cleaning, i.e. pushing inwards the material to be moved into the melting pot). The actuators are protected by the heat radiation and powder, as they work in a protective closed environment. 
     The operation of the apparatus as a slag removing device will be now disclosed. 
     From the position in  FIG. 1A  (Operation  1 ) with a closed slagging door one passes to the one in  FIG. 1B  (Operation  2 ) with maximum opening of the slagging door, employing the main hydraulic actuator  29 , which implements a quick translation of the entire slagging door until the maximum opening. 
     The movement of the lower panel  16  is implemented according to a different axis from the top panel axis. During such an operation, the lower panel moves away from the stack wall and the underlying short tunnel, allowing an easy separation of slag, possibly, stuck on the tunnel, thereby enabling an easy opening of the slagging door ( FIG. 1C ) with the half-open slagging door (Operation  3 ), wherein the lower and top panels  16  and  18  are in an intermediate vertical position, with the lower panel  16  closing the top part of the slagging door. Such a movement is carried out by the main actuator, by operating, for example, the pair of cylinders  29  for moving the top panel, with the consequent partial opening of the entire slagging door, until a position required by the operator is reached. 
       FIG. 1D  shows a possible movement of the lower panel  16  (Operation  4 ) starting from the closing position. 
       FIG. 1E  (Operation  5 ) shows the lower panel  16  moving from the closing position to the opening position. This position is used only for removing skull. 
     In  FIGS. 1F and 1G  (Operations  6  and  7  of the cleaning cycle) the main actuator lowers the lower panels  16 , to start a cleaning operation, pushing forward ( FIG. 1F ) or backward ( FIG. 1G ) the cleaning lower panels  16 . This movement is carried out by the lower cylinder. Finally, after operations  6  and  7  have been repeated several times, or until the desired result of slag removal has been achieved, it returns to the starting position, represented in  FIG. 1H . Such a cycle can be implemented at different heights and positions. The command for carrying out the slag removal can be manually or automatically implemented. 
     By manually commanding, the operator drives the door, carrying out the slag scraping or dredging, causing the lower panel to remain in contact with the slag, in order to prevent it from hitting the frame, that is, preventing the single cylinder  35  from being extracted, when the sliding carrier, on which the linkage is mounted, is above a certain height. 
     An automatic cleaning cycle is adopted in order to avoid erroneous or dangerous operations and such a cycle is operable only after the top panel is completely open. It includes the following steps: 
     1—Approaching the lower panel  16 , until it contacts the slag, signalled by an encoder and by a pressure sensor; 
     2—Releasing said slagging panel  16 , when contacting the slag; 
     3—Removing said slagging, by actuating the single cylinder in retraction; 
     4—Slightly rising and completely extracting the single cylinder; 
     5—Releasing the slagging panel when contacting the slag; 
     6—Second removal of the slag, operating the dual cylinder in retraction; 
     7—Repeating steps 5, 6 and 7, until the slag has been completely removed, by moving to the closing position of the slagging door. 
     Analogously an automatic cycle of scrap pushing inside the furnace can be adopted, which comprises the following steps: 
     1—Positioning the lower panel  16  in the closing position maintaining the top panel  18  in the opening position or in a position close to the opening position; 
     2—Inserting the lower panel  16  inside the furnace pushing the eventually accumulated scrap; 
     3—Returning the lower panel  16  in the position of step  1 ; 
     4—Lowering the top panel  18  in the closing position or in a position close to the closing position; 
     5—Inserting the lower panel  16  inside the furnace pushing the eventually accumulated scrap; 
     6—Returning the lower panel  16  in the position of step  3 . 
     It is to be noted that the movement downward occurs as a result of gravity (even if a suitable drive hydraulic system may be provided), which allows the slagging door to be closed, also when part of the slag remains on the slagging door plane. The pair of cylinders  29  of the hydraulic drive actuator system of the top panel is actuated by a single proportional valve. The single cylinder, which drives the lower panel of the slagging door, is driven by a single proportional valve. 
     A further advantage of the present invention is represented by the possibility to control the slag leakage from the furnace, particularly during the production of a foamy slag, i.e. CO-bubble filled slag from the fine carbon oxidation, injected in a bath, simultaneously with an injection of oxygen, with a substantially horizontal furnace, acting on the opening degree of the lower panel  16 , in order to guarantee a controlled leakage of the slag, whereby the lower panel  16  acts as a sort of valve for controlling the leaking slag flow. 
     It is also to be noted that, setting up this apparatus requires the presence of a tunnel on the furnace wall. This tunnel will have a depth equal to the diameter of about 180 mm, which is about twice the diameter of a cooling pipe. 
     As previously said, the movement of the lower panel  16 , when directed from the interior towards the exterior of the furnace, can be advantageously used for removing slag eventually accumulated at the tunnel or the not completely molten scrap by pushing it inside the furnace into the melting pot. This aspect can be better understood referring to  FIGS. 5A-5B . In  FIG. 5A , both the lower panel  16  and the top panel  18  are in the closing position. By operating the hydraulic actuator  35  controlling it, it is possible to cause the lower panel  16  to move towards the interior of the furnace, i.e. from right to left in  FIG. 5A . As a consequence of this movement, the lower panel moves towards the interior of the furnace along the tunnel ( FIG. 5B ). The lower panel follows the same trajectory which it follows during the movement which has been described whit reference to the use as a slag remover device, i.e. similar to that of a dredger. In this manner, slag or scraps which eventually have remained at the tunnel, are pushed into the melting pot and can be molten therein. It is to be noted that the lower panel  16  is able to follow inside the furnace from the closing position a long distance path. Preferably, it can enter the furnace by 500-600 mm from the closing position. 
     According to an embodiment, the top panel  18  side rising and lowering systems are at least partially canned in casings  36 , for example made of sheet metal ( FIG. 6 ). Such a configuration avoids encrustations in the movement mechanisms of the top panel  18 , for example due to molten material splashes or due to the slag itself, and therefore jams in the movement thereof. Particularly, the areas in which the relative movement between the top panel  16  carrier  20  and the inclined guide  22  occurs, at which suitable bearings can be provided (which preferably are arranged only in the outer sides of the inclined guides  22 ), are arranged inside casings  36 ′, such that the zone in which the movement of the top panel occurs is not in contact with the outside, and so it is kept substantially without impurities. Preferably, the motor-gear reducer unit for the movement of the drive shaft which actuates the top panel  18  is housed inside a further casing. 
     According to a possible embodiment, also the cylinder  35  actuating the lower panel  16  is canned inside a further casing. 
     According to a possible embodiment of the invention, the lower panel  16  is rearly water-cooled. To this purpose, a cooling shield  37  can be provided which is associated to the lower panel. This cooling shield  37  can comprise loopholes suitable to allow dust or dirt eventually accumulated thereon to fall and to be eliminated. 
     It is evident that only some particular embodiments of the subject electric furnace of the present invention have been disclosed, to which those skilled in the art will be able to make all the necessary modifications to adapt it to particular applications, moreover without departing from the scope of protection of the present invention defined in the following claims.