Electric arc furnace

The present invention relates to an electric arc furnace, containing a furnace shell, an electrode, a furnace shell moving mechanism that supports the furnace shell so as to be movable on an installation surface, and a first insulation that electrically insulates between the furnace shell and the furnace shell moving mechanism.

FIELD OF THE INVENTION

The present invention relates to an electric arc furnace and, in particular, relates to an electric arc furnace in which metal is melted while moving a furnace shell.

BACKGROUND ART OF THE INVENTION

In an arc furnace as a kind of electric arc furnace for melting metal material, a so-called hot spot and cold spot are formed within an inner space of a furnace shell containing the metal material. The hot spot places close to electrodes and at which the metal material is likely to be melted. The cold spot places distant from the electrodes and at which the metal material is not likely to be melted. In the cold spot, there arise a problem that it takes a long period of time to melt the metal material and thus melting of the metal material proceeds uniformly as a whole. In order to solve this problem, Patent Literature 1 proposes a process in which a furnace shell is rotationally displaced around an axis line extending in an up-down direction with respect to electrodes, thereby exchanging between the cold spot and the hot spot. In such the electric arc furnace, thermal nonuniformity within the furnace can be eliminated and an amount of wasteful power consumption can be reduced by rotationally displacing the furnace shell, without consuming power for a pump at an extra water-cooled part like in a shaft furnace and without additionally supplying burner combustion energy or the like for a composition appropriating processing of exhaust gas.

SUMMARY OF THE INVENTION

In the arc furnace, a great current flows in the electrode inserted into the furnace shell in order to melt the metal material. Due to the current flowing in the electrode, a current may also flow in the furnace shell. In particular, in a case where the current flowing in the electrode is alternate current, an induction current constantly flows in a surface of the furnace shell. In order to perform rotation displacement of the furnace shell, a furnace shell moving mechanism having a movable part such as a bearing is employed. If a leak current flowing through the metal material within the furnace shell or the induction current flowing through the surface of the furnace shell flows in this kind of movable part, such the current may damage the movable part and impair a function of the movable part. For example, in a state that an electrode are inserted into the furnace shell and supplied with current, if a leak current flowing through the metal material within the furnace shell or an induction current generated in the furnace shell flows in a member such as the bearing of the furnace shell moving mechanism and generates spark, even when the furnace shell moving mechanism is in a static state, constitutional members of the furnace shell moving mechanism may be damaged, and hence succeeding smooth movement of the furnace shell may be interfered.

Therefore, an object of the present invention is to provide an electric arc furnace having a furnace shell being moved, which can prevent current from flowing in a furnace shell moving mechanism for moving the furnace shell.

In order to solve the above problem, the present invention provides an electric arc furnace containing:a furnace shell;an electrode;a furnace shell moving mechanism that supports the furnace shell so as to be movable on an installation surface; anda first insulation member that electrically insulates between the furnace shell and the furnace shell moving mechanism.

Here, it is preferable that the furnace shell moving mechanism includes a first part that is fixed with respect to the installation surface and a second part that is fixed to the furnace shell and is movable with respect to the first part, and that the first part is electrically connected to the second part.

In this case, it is preferable that the electric arc furnace further contains a connecting wire that electrically connects between the first part and the second part of the furnace shell moving mechanism, in which the connecting wire has a length capable of following an entire movable range of the second part.

The furnace shell and the furnace shell moving mechanism are preferably independently grounded.

In addition, it is preferable that the electric arc furnace further contains:a furnace roof that covers an opening of the furnace shell;a furnace roof moving mechanism that moves the furnace roof with respect to the furnace shell; anda second insulation member that electrically insulates between the furnace roof moving mechanism and the furnace shell. In this case, the furnace shell and the furnace roof moving mechanism are preferably independently grounded.

In the electric arc furnace according to the present invention, an insulation member (first insulation member) is provided between the furnace shell and the furnace shell moving mechanism. Therefore, even in a case where current flows in the furnace shell due to current flowing in an electrode, the current flowing in the furnace shell is prevented from flowing in the furnace shell moving mechanism from the furnace shell. As a result, the furnace shell moving mechanism is prevented from being damaged by the current.

Here, in the case where the furnace shell moving mechanism includes a first part that is fixed with respect to the installation surface and a second part that is fixed to the furnace shell and is movable with respect to the first part and the first part is electrically connected to the second part, the first part and the second part become equipotential. Thus, even if current flows in the furnace shell moving mechanism due to dielectric breakdown or the like of the first insulation member which electrically insulates between the furnace shell and the furnace shell moving mechanism, such a phenomenon unlikely occurs that current flows over a wide area within the furnace shell moving mechanism. As a result, the furnace shell moving mechanism can be prevented with high accuracy from being damaged seriously.

In this case, if a connecting wire for electrically connecting between the first part and the second part of the furnace shell moving mechanism is provided and has a length capable of following the entire movable range of the second part, the connecting wire is prevented from being damaged and applied with an excessive force even when the second part is moved with respect to the first part.

Further, in the case where the furnace shell and the furnace shell moving mechanism are independently grounded, the current flowing in the furnace shell can be more firmly prevented from flowing in the furnace shell moving mechanism.

Furthermore, in the case where the electric arc furnace further includes a furnace roof that covers the opening of the furnace shell, a furnace roof moving mechanism that moves the furnace roof with respect to the furnace shell, and an second insulation member that electrically insulates between the furnace roof moving mechanism and the furnace shell, the current flowing in the furnace shell can also be prevented from flowing in the furnace roof moving mechanism. Accordingly, a member constituting the furnace roof moving mechanism can also be prevented from being damaged due to the current.

In this case, if the furnace shell and the furnace roof moving mechanism are independently grounded, the current flowing in the furnace shell can be more firmly prevented from flowing in the furnace roof moving mechanism.

DETAILED DESCRIPTION OF THE INVENTION

Explanation will be made with reference to the drawings as to an electric arc furnace according to an embodiment of the present invention.

(Configuration of Electric Arc Furnace)

FIG. 1toFIG. 4Billustrate an electric arc furnace1according the embodiment of the present invention. The electric arc furnace1is installed on a platform90. The electric arc furnace1has, as a main body part, an electric arc furnace (arc furnace) similar to that described in Patent Literature 1, and includes a furnace shell10, a furnace roof20and electrodes25. In addition, the electric arc furnace1includes a furnace shell moving mechanism30and a furnace roof holding unit40having a furnace roof moving mechanism43. Further, the electric arc furnace1also includes a furnace shell insulation member (first insulation member)51and a furnace roof insulation member (second insulation member)52as insulation members, and a furnace shell ground wire61, a furnace shell moving mechanism ground wire62and a furnace roof moving mechanism ground wire63.

The furnace shell10is formed as an almost circular cylindrical bottomed vessel having an opening at its top part. The furnace shell10is formed by a material provided with a steel shell at an outer side of refractory made of a metal oxide.

The furnace roof20is formed as an almost disc-shape and is capable of closing the opening of the furnace shell10. The furnace roof20is held by the furnace roof holding unit40and performs an up/down movement and a rotation movement above the furnace shell10, thereby moving between a state of closing the opening of the furnace shell10and a state of opening the opening. Although the furnace roof20is also formed by a material similar to that of the furnace shell10, insulator is exposed at respective portions of the furnace roof near parts where the electrodes25described later penetrate the furnace roof. Thus, electric insulation is kept between the furnace roof and the electrodes25.

In the present embodiment, three electrodes25(only two electrodes are illustrated inFIG. 1) penetrate the furnace roof20from an upper side toward an inner space of the furnace shell10. The three electrodes25are arranged to form an almost equilateral triangle around a center axis of the furnace shell10. When a metal material such as iron scrap material is contained in the furnace shell10and the three electrodes25are supplied with current such as three-phase alternate current to perform discharge, the metal material can be molten. The electrodes25are electrically insulated from each of the furnace shell10and the furnace roof20.

The furnace shell10is supported by a platform (installation surface)90via the furnace shell moving mechanism30. As illustrated inFIG. 2, the furnace shell moving mechanism30includes a support frame31which is made of a metal and has top and bottom surfaces each having an almost annular shape. The furnace shell10is placed on an upper surface31aas the top surface of the support frame31via a furnace shell insulation member51of an almost annular-plate shape. A plurality of concave portions31cis provided in the upper surface31aof the support frame31. The furnace shell10is fixed on the support frame31due to the engagement of convex portions (not illustrated) formed at the furnace shell10with the respective concave portions31cas well as own weight of the furnace shell10. The furnace shell insulation member51electrically insulates between the furnace shell10and the support frame31. A gear member31bis formed along an inner circumferential surface of the support frame31. An insulation resin is filled between a bottom portion of the furnace shell10and the support frame31in a manner of burying the furnace shell insulation member51therebetween. Accordingly, respective gaps formed among the bottom portion of the furnace shell10, the furnace shell insulation member51and the support frame31are filled by the insulation resin.

The support frame31is supported by a bearing32.FIG. 3is a cross-sectional view illustrating a part of the furnace shell moving mechanism in the vicinity of the bearing32. The bearing32is attached to an attachment base34made of metal fixed on the platform90. The bearing32has configuration of a known swing bearing, and includes an outer wheel (first part)32aand an inner wheel (second part)32beach made of a metal, and rolling elements (not illustrated) arranged between the outer wheel32aand the inner wheel32b. The inner wheel32bis smoothly swingable with respect to the outer wheel32a. The outer wheel32ais fixed to the attachment base34and the inner wheel32bis fixed to the gear member31bof the support fame31. A bearing connecting wire33electrically connects between the support frame31and the attachment base34. The bearing connecting wire33has a sufficient length capable of following an entire swingable or rotatable range of the support frame31. Since the outer wheel32aof the bearing32is made in contact with the attachment base34and the inner wheel32bis made in contact with the support frame31, the outer wheel32aand the inner wheel32bare electrically connected to each other by the bearing connecting wire33.

A gear part35having two gears (first gear35aand second gear35b) meshed to each other is provided at the inner periphery side of the support frame31. AlthoughFIG. 2shows the only one gear part35, another gear part similar to the gear part35is provided at an opposite position of the inner periphery. The first gear35aconstituting the gear part35meshes with the gear member31bprovided at the inner circumferential surface of the support frame31. A rotation shaft of the second gear35bmeshed with the first gear35ais coupled to an output shaft of a hydraulic motor (not illustrated).

The support frame31can be made to swing on the bearing32by driving the hydraulic motor of the gear part35. As a result, the furnace shell10is made to rotate (swing) on the platform90. When the furnace shell10rotates, respective positions of the electrodes25along a plane of the platform90do not change. Thus, relative arrangement between the furnace shell10and the electrodes25changes according to the rotation of the furnace shell10. A stopper mechanism (not illustrated) for holding the support frame31in a state where the rotation of the support frame31is stopped may be suitably provided at the inner peripheral side of the support frame31.

The furnace roof holding unit40is provided at the common platform90on which the furnace shell10is installed via the furnace shell moving mechanism30. The furnace roof holding unit40supports the furnace roof20by a furnace roof support part41and performs an up/down movement and a rotation movement of the furnace roof20. The furnace roof holding unit40also has a function of holding and performing an up/down movement of the electrodes25by electrode support parts42. Therefore, the furnace roof holding unit40can adjust an up/down position of the electrodes25depending on a melting state or the like of the metal material within the furnace shell10. The up/down and rotation movements of the furnace roof20and the up/down movement of the electrodes25are driven by the furnace roof moving mechanism43provided with a bearing and a hydraulic cylinder. The furnace roof support part41and the electrode support part42are electrically insulated to each other. The furnace roof insulation member52is provided between the furnace roof support part41and the furnace roof moving mechanism43. Thus, the furnace roof moving mechanism43is electrically insulated from the furnace roof20and the furnace roof support part41. The furnace roof moving mechanism43side portion of the furnace roof holding unit partitioned by the furnace roof insulation member52is grounded by the furnace roof moving mechanism ground wire63.

The platform90, on which the electric arc furnace1is installed, is a stand made of a metal. The platform90is grounded by the furnace shell moving mechanism ground wire62. The attachment base34of the furnace shell moving mechanism30is fixed on the platform90in a contact manner. Thus, the bearing32of the furnace shell moving mechanism30is grounded by the furnace shell moving mechanism ground wire62at the outer wheel32aportion. The platform90may be provided with a tilting mechanism for tilting constitutional members of the electric arc furnace1such as the furnace shell10, to thereby facilitate a tapping of molten metal and a discharging of slag from the furnace shell10.

Although the present electric arc furnace1is provided with the three ground wires, that is, the furnace shell ground wire61, the furnace shell moving mechanism ground wire62and the furnace roof moving mechanism ground wire63, they are provided as independent ground wires. For example, these three ground wires61to63are connected to three ground electrodes buried into the ground at separate positions, respectively.

(Characteristics of Electric Arc Furnace)

As described above, in the electric arc furnace1according to the present embodiment, a positional relation between the furnace shell10and the electrodes25can be changed by rotating the furnace shell10with respect to the electrodes25by the furnace shell moving mechanism30. By changing the positional relation, uniformity of heating and melting of the metal material within the furnace shell10can be enhanced. That is, as the electrodes25are arranged in a triangle shape around the center axis of the furnace shell10having an almost cylindrical shape, a hot spot, which is close to the electrodes25and likely to be a high temperature, and a cold spot, which is distant from the electrodes25and unlikely to be a high temperature, are inevitably generated within the furnace shell10. However, by rotating the furnace shell10to change the positional relation between the furnace shell10and the electrodes25during the melting process of the metal material, respective positions of the hot spot and the cold spot can be also changed suitably, whereby the uniformity of heating and melting of the metal material can be attained. In terms of necessarily and sufficiently changing the respective positions of the hot spot and the cold spot, a rotatable angle of the furnace shell10is preferably in a range of substantially from 50° to 60° in the case where the number of electrodes is three.

In a case of performing an arc discharge, alternate current of several ten kA order flows to the electrodes25inserted into the furnace shell10. This current may flow in the furnace shell moving mechanism30or the furnace roof moving mechanism43as a leak current via the metal material within the furnace shell10, the furnace shell10, the furnace roof20, and the like. Further, an induction current in a range of from several amperes to several hundred amperes may flow in the steel shell at the surface of the furnace shell10. If such the leak current or the induction current flows from the furnace shell10into a movable part such as the bearing of the furnace shell moving mechanism30or the furnace roof moving mechanism43, a spark may be generated at the movable part even when the furnace shell moving mechanism30or the furnace roof moving mechanism43is in a static state. Thus, smooth movement of the movable part may be interfered, and further irreversible damage such as breakage of material constituting the movable part may be caused.

However, in the electric arc furnace1according to the present embodiment, the furnace shell insulation member51is provided between the furnace shell10and the furnace shell moving mechanism30, thereby electrically insulating between the furnace shell10and the furnace shell moving mechanism30. Further, in the furnace roof holding unit40, the furnace roof insulation member52is provided between the furnace roof support part41and the furnace roof moving mechanism43. Therefore, also the furnace roof moving mechanism43is electrically insulated from each of the furnace roof20and the furnace shell10which contacts at its steel shell with the furnace roof20in a closed state of the furnace roof20. According to this arrangement, if the induction current or the leak current flows in the furnace shell10, these current is prevented from flowing the furnace shell moving mechanism30and the furnace roof moving mechanism43. Insulation material constituting the furnace shell insulation member51and the furnace roof insulation member52may be, for example, JIS-H type insulator having a high heat resistance such as a laminate (silicon laminate material) formed by silicon resin and glass.

In the electric arc furnace1, further, the respective constituent elements are independently grounded. That is, the furnace shell10is grounded by the furnace shell ground wire61, the furnace shell moving mechanism30is grounded by the furnace shell moving mechanism ground wire62via the platform90, and the furnace roof moving mechanism43is grounded by the furnace roof moving mechanism ground wire63. Therefore, even if dielectric breakdown occurs in the furnace shell insulation member51or the furnace roof insulation member52due to, for example, a high voltage applied to both ends thereof, the leak current or the induction current flowing in the furnace shell10flows to earth potential via the furnace shell ground wire61and hence unlikely flows in the furnace shell moving mechanism30and the furnace roof moving mechanism43.

In the electric arc furnace1, the bearing connecting wire33electrically connects between the outer wheel32aand the inner wheel32bof the bearing32of the furnace shell moving mechanism30. Therefore, the outer wheel32aand the inner wheel32bare kept to be equipotential. Further, not only the outer wheel32ais grounded by the furnace shell moving mechanism ground wire62via the platform90and the attachment base34but also the inner wheel32bis grounded. As a result, current is prevented from flowing between the outer wheel32aand the inner wheel32b. Accordingly, even if the leak current or the induction current flowing in the furnace shell10also flows in one of the outer wheel32aand the inner wheel32b, these current is prevented from flowing in the other of these wheels and generating spark in a wide area of the bearing32.

The bearing connecting wire33is simply illustrated as a wiring connecting between the support frame31and the attachment base34inFIG. 3. However, a concrete attachment method of the bearing connecting wire33may be any one so long as the outer wheel32aand the inner wheel32bof the bearing32are electrically connected to each other. An example of such the attachment method is illustrated inFIG. 4AandFIG. 4B. In this example, brackets31cmade conductive with a main body of the support frame31are each provided at an almost center portion of the support frame31in a height direction. Connection rods91made conductive with a main body of the platform90stand on the platform90, and respective bracket91ais provided at an upper end of the corresponding connection rod91so as to locate at substantially the same height as the corresponding frame-side brackets31c. Each of the connection rods91is provided at a substantially center angular position of a movable range of the inner wheel32bof the bearing32. One end of each of bearing connecting wires33is connected to the corresponding support frame-side bracket31c, and the other end thereof is connected to the corresponding connection-rod side bracket91a. Each of the bearing connecting wires33has a sufficient length capable of following the entire movable range of the inner wheel32bof the bearing32. The length of each of the bearing connecting wires33and the positions of the corresponding two brackets31cand91aare set in a manner that the each bearing connecting wire33locates above an obstacle (not illustrated) such as a necessary unit attached to a driving unit provided at the platform90for driving the bearing32, in the entire movable range of the inner wheel32b.

When the bearing connecting wire33is connected by utilizing the corresponding brackets31cand91a, conductivity between the outer wheel32aand the inner wheel32bof the bearing32can be ensured with high reliability. Further, when each of the bearing connecting wires33is made to have the length capable of following the entire rotatable range of the inner wheel32b, the each bearing connecting wire33can be prevented from being damaged or applied with an excessive external force over the entire rotatable range of the inner wheel32b, as illustrated by steady and dotted lines inFIG. 4A. In particular, as illustrated inFIG. 4B, if the length of each of the bearing connecting wires33is set slightly longer so that the each bearing connecting wire can maintain a bent state without being strained over the entire rotatable range of the inner wheel32b, the each bearing connecting wire33can be effectively prevented from being damaged or applied with an excessive external force.

Further, when each of the bearing connecting wires33is arranged above the plane of the platform90and also above the obstacle (not illustrated) such as the necessary unit attached to the driving unit provided at the platform90for driving the bearing32, the each bearing connecting wire33can avoid interfering with the obstacle when the inner wheel32bof the bearing32rotates. In a case where a member acting as the obstacle with respect to the bearing connecting wire33is provided in an area above the platform90where the bearing connecting wire33passes accompanying with the rotation of the inner wheel32b, when the bearing connecting wire33is not arranged to grovel along the plane of the platform90but arranged above the plane of the platform90, preferably, above the obstacle, the bearing connecting wire33can avoid interfering with the obstacle. Although the bearing connecting wire33preferably has the length capable of maintaining the bent state as described above, the length is desirably set within such a degree that the bent portion does not contact the obstacle. In the case that each of the connection rods91is provided at the substantially center angular position of the movable range of the inner wheel32b, the bent state of the corresponding bearing connecting wire33can be easily ensured over the entire movable range of the inner wheel32bwithout excessively elongating the corresponding bearing connecting wire33.

As described above, although the embodiment according to the present invention are explained in detail, the present invention is not limited to the above-described embodiment and may be changed and modified in various manners within a range not departing from the gist of the present invention. For example, the movement of the furnace shell is not limited to the rotation (swing) around the center axis of the furnace shell but may be any movement on the platform. Further, the furnace shell moving mechanism is not limited to one using the bearing but may be one using a roller, for example.

The present application is based on the Japanese patent applications No. 2014-225148 filed on Nov. 5, 2014 and No. 2015-146743 filed on Jul. 24, 2015, which contents are incorporated herein by reference.

DESCRIPTION OF REFERENCE NUMERALS