JP4734091B2 - Hot dipping method and hot dipping equipment - Google Patents

Description

  The present invention relates to a hot dipping method and hot dipping equipment for hot dipping a steel strip.

  The hot dip galvanizing step of the steel strip is performed, for example, by heating the steel strip to a predetermined temperature on the transport path of the steel strip and immersing the steel strip in the molten zinc in the hot dip zinc tank. The transport path just before the molten zinc tank is provided with a snout that surrounds the steel strip in a cylindrical shape to prevent oxidation of the steel strip during transport.

  By the way, in the above hot dip galvanizing process, the molten zinc in the molten zinc tank evaporates and the evaporated material solidifies and deposits on the inner wall of the snout, and then the deposited material falls from the snout, Contamination of the belt was a problem. In view of this, a technique has been proposed in which an electric heater is provided in the snout, the snout is heated to a high temperature of −100 ° C. or higher of the hot dip zinc plating bath, and the amount of evaporated substance in the snout is suppressed (see Patent Document 1). ).

JP-A-11-286762

  However, when the snout is heated using the electric heater as described above, it is necessary to attach the electric heater to the snout itself. In addition, a new temperature control device for controlling the electric heater is required. This increases the size and complexity of the hot dip galvanizing equipment and increases the cost of the equipment. In addition, since the electric heater is heated by power feeding, the amount of electricity consumed increases and the running cost of the hot dip galvanizing process also increases.

  The present invention has been made in view of such points, and raises the temperature of an enclosure such as a snout at a low cost with a simpler mechanism so that a molten metal evaporant such as molten zinc is deposited on the enclosure. The purpose is to suppress this.

  In order to achieve the above object, the present invention is a method of heating a steel strip and then allowing the steel strip to enter a molten metal and hot-plating the steel strip. Energized, energizing the encircling body surrounding the steel strip immediately before entering the molten metal, energizing the current flowing through the steel strip during the heating, heating the enveloping body by Joule heat by the energization, The enclosure is heated to a temperature higher than the molten metal temperature of −100 ° C.

  According to the present invention, since the enclosure is heated to a predetermined high temperature using the energy used when the steel strip is heated, there is no need to separately provide an electric heater on the enclosure as in the prior art. With a simple mechanism and low cost, it is possible to suppress the deposition of the evaporated material from the molten metal on the enclosure. The “steel strip immediately before entering the molten metal” is a portion within 5 mm at the longest from the liquid surface of the molten metal.

  The enclosure may be immersed in the molten metal, and the enclosure may be heated to the temperature by Joule heat generated by the energization and conduction heat from the molten metal.

  According to another aspect of the present invention, there is provided an apparatus for heating a steel strip and then allowing the steel strip to enter a molten metal and hot-plating the steel strip. An apparatus, a conductive enclosure surrounding the steel strip immediately before entering the molten metal, and a molten metal tank for storing the molten metal in this order from the upstream side on the conveying path of the steel strip, The enclosure is energized by a current flowing through the steel strip by the energization heating device, and the enclosure can be heated by Joule heat generated by the energization, and the enclosure is the energization heating device during the hot dip plating process of the steel strip. It may be formed so that the temperature is raised to a temperature higher than −100 ° C. of the temperature of the molten metal by energization.

  According to the present invention, since the enclosure can be heated to a predetermined high temperature by using the electric current of the energization heating device for heating the steel strip, there is no need to separately provide an electric heater on the enclosure as in the prior art. With a simple mechanism and low cost, it is possible to suppress the deposition of the evaporated material from the molten metal on the enclosure.

  The envelope has a downstream end immersed in the molten metal in the molten metal tank, and the upstream end of the envelope has a steel strip positioned upstream of the energization heating device. A connection line that electrically connects between the steel strip, the molten metal in the molten metal tank, and the energization circuit energized by the energization heating device by the enclosure and the connection line. It may be formed.

  A steel strip between the energization heating device and the enclosure is surrounded by another enclosure along the conveyance path, and an insulator is provided at a connection portion between the enclosure and the other enclosure. It may be interposed.

The material of the conductive enclosure surrounding the steel strip immediately before entering the molten metal may be austenitic stainless steel.

The enclosure of the conductive surrounding the steel strip immediately before entering into said molten metal, the centering rolls are provided for pressing the strip to the linear axial of the enclosure of the passage through which the steel strip It may be. The centering roll is a roll that supports the steel strip from the lower surface so that the steel strip is positioned on the axis of the passage in the conductive enclosure surrounding the steel strip immediately before entering the molten metal. And it may be comprised by the other roll which hold | suppresses the steel strip which passes on the said axis | shaft from the upper surface.

The other roll and the one roll are arranged in this order from the upstream side along the path of the conductive enclosure surrounding the steel strip immediately before entering the molten metal, and sandwich the steel strip. You may face diagonally.

A part of the wall portion of the conductive enclosure surrounding the periphery of the steel strip immediately before entering the molten metal may protrude outward so as to bypass the one roll and the other roll. Further, the protruding portion of the upper wall portion of the conductive enclosure surrounding the steel strip and a lower wall portion immediately before entering into said molten metal, at positions displaced from each other on the passage of the enclosure It may be formed.

The centering roll may be attached to a conductive enclosure surrounding the steel strip immediately before entering the molten metal with an insulator interposed.

  The steel strip may be alloyed after hot dipping.

  According to the present invention, since the enclosure can be heated using the electric power of the energization heating device, the hot dip plating equipment can be reduced in size and cost.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 is an explanatory diagram showing an outline of the configuration of a hot dip galvanizing facility 1 according to the present embodiment.

  For example, the hot dip galvanizing equipment 1 has a transport path A through which the steel strip H is transported in one direction. In the conveying path A, for example, an electric heating device 10 for heating the steel strip H, a snout 11 as an enclosure, a molten zinc bath 12 in which molten zinc B is stored, and the steel strip H after hot dip galvanizing are alloyed. An alloying processing apparatus 13 for performing the chemical conversion treatment is disposed in order from the upstream side.

  The electric heating device 10 includes, for example, a ring-shaped iron core 20 surrounding the steel strip H on the conveyance path A, a primary coil 21 wound around the iron core 20, and an AC power supply 22 that supplies power to the primary coil 21. ing.

  In the conveying path A of the energization heating device 10, a conductive roll 30, a seal roll 31, and a turn roll 32 that are in contact with the steel strip H are provided in order from the upstream side. The iron core 20 of the electric heating device 10 is disposed between the seal roll 31 and the turn roll 32.

  On the downstream side of the tar roll 32 in the conveyance path A, a conductive snout 11 having a tip end (lower end) immersed in the molten zinc B in the molten zinc tank 12 is provided. Details of the configuration of the snout 11 will be described later. A bus bar 33 as an electrical connection line is connected between the rear end portion (upper end portion) of the snout 11 and the conductive roll 30. Thereby, the secondary coil 34 (electric conduction circuit) which winds the iron core 20 is formed by the conductive roll 30, the steel strip H on the conveyance path A, the molten zinc B in the molten zinc tank 12, the snout 11 and the bus bar 33. By applying a voltage to the primary coil 21 and causing a current to flow from the AC power source 22, power can be induced on the secondary coil 34 side and a high current can be passed through the steel strip H. With this current, the steel strip H can generate Joule heat, and the steel strip H can be heated to a predetermined temperature. By this energization heating device 10, heating by a transformer effect type energization heating method is realized.

  For example, the space from the seal roll 31 to the snout 11 in the conveyance path A is covered with a casing 40 as another enclosure. The casing 40 is formed in a rectangular tube shape along the conveyance path A, for example. The casing 40 is made of, for example, nonmagnetic stainless steel. By this casing 40, the heated steel strip H can be maintained in a predetermined inert atmosphere.

Here, the configuration of the snout 11 will be described in detail. As shown in FIG. 2, the snout 11 is formed in a substantially rectangular tube shape as a whole, and has a square frame cross-sectional shape. The snout 11 enters the slanted angle direction of about 30 ° with respect to the molten zinc tank 12 obliquely. Snout 11 is formed by, for example, specific electric resistance ^{7 × 10 -7 Ω · m~8 ×} 10 nonmagnetic having conductivity at about ^-7 Omega · m austenitic stainless steel. The snout 11 has a length of about 1.7 m, for example. In consideration of the range to which the evaporated substance of molten zinc adheres, a length of about 1.7 m is sufficient for the snout 11. The thickness of the wall portion of the snout 11 is formed to be, for example, about 30 mm to 50 mm thicker than the wall portion of the casing 40. In addition, the perimeter of the wall of the snout 11 surrounding the steel strip H (the perimeter of the frame shape of the snout 11 when the snout 11 is cut in a cross section perpendicular to the traveling direction of the steel strip H) is , About 3500-5500 mm. With this configuration, the snout 11 is set to the overall electrical resistance e.g. 4 × ^{10 -6} Ω~8 × about ^{10 -6} Omega. As a result, by passing a current through the snout 11 by the energization heating device 10, Joule heat is generated in the snout 11, and the snout 11 can be heated to a predetermined high temperature.

  Further, the lower end portion of the snout 11 is immersed in the hot molten zinc B in the molten zinc bath 12. The temperature of the snout 11 can also be increased by the conduction heat from the molten zinc B. Therefore, in the present embodiment, the snout 11 is provided with an appropriate electric resistance value and thermal conductivity, and Joule heat generated by the current flowing through the snout 11 and heat transfer from the molten zinc are used. Can heat itself. In addition, since the thickness of the wall part of the snout 11 is 30-50 mm as mentioned above, it is advantageous in transmitting the conduction heat from molten zinc. The wall thickness of the snout 11 is 30 to 50 mm over the entire length of the snout 11 in order to improve the heat transfer effect, but even if only the portion immersed in the molten zinc is 30 to 50 mm. Good.

  By the way, since an alternating current flows through the snout 11, a magnetic field is formed in the passage of the snout 11. As shown in FIG. 3, the magnetic field G generated from the upper and lower walls 11 a and 11 b of the snout 11 is canceled and becomes zero on the linear axis C viewed from the side surface of the passage S of the snout 11. This axis C is a linear axis passing through the middle of the passage S regardless of the shape of the wall portion of the snout 11 as shown in FIG. In other words, the axis C is a linear axis that passes through the center in the vertical direction of the passage S in a flat wall portion other than projecting portions 11d and 11e described later of the wall portion of the snout 11. Therefore, if the steel strip H through which current flows is not located on the axis C in the passage S of the snout 11, Lorentz force in the normal direction N acts on the steel strip H and induces vibration of the steel strip H. Is done.

  In order to prevent this, as shown in FIG. 4, two centering rolls 50 and 51 for positioning the steel strip H on the axis C of the passage S in the snout 11 are provided in the snout 11. The centering rolls 50 and 51 are sequentially spaced from the upstream side of the transport path A. The centering rolls 50 and 51 are provided diagonally opposite the upper and lower surfaces of the inclined steel strip H. The centering roll 51 on the downstream side supports the steel strip H from below so that the steel strip H passes over the axis C of the passage S in the snout 11. Thereby, the steel strip H is tensioned from the centering roll 51. The upstream centering roll 50 presses the steel strip H supported on the axis C of the passage S in the snout 11 from above by the centering roll 51.

  The upper and lower wall portions 11a and 11b of the snout 11 have portions with the centering rolls 50 and 51 protruding outward so as to bypass the centering rolls 50 and 51.

  The protruding portions 11d and 11e of the snout 11 on the outside of the wall portions 11a and 11b are formed at positions shifted from each other on the passage S of the snout 11 according to the positions of the centering rolls 50 and 51. As described above, when the positions of the projecting portions 11d and 11e are shifted from each other on the passage S, the vertical width of the passage S of the snout 11 is changed only by a portion where the centering rolls 50 and 51 are located. The center of the direction is shifted to the protruding portions 11d and 11e. As a result, the position where the magnetic field G becomes zero shifts from the axis C only in the position where the centering rolls 50 and 51 are present, and the steel strip H has a normal direction N where each centering roll 50 and 51 is present. Lorentz force works. Therefore, in a portion where the centering rolls 50 and 51 are present, the steel strip H is always pressed against the centering rolls 50 and 51, and this also suppresses the vibration of the steel strip H due to the magnetic field G.

  A scale (not shown) for grasping, for example, the position of the steel strip H or the positions of the centering rolls 50, 51 is formed on the side wall portion of the snout 11, and the centering roll 50 is in accordance with this scale. , 51 can be adjusted to a strict position, and the position of the steel strip H can be set accurately. Further, the centering rolls 50 and 51 are securely fixed at the adjusted positions in order to suppress shaking due to electromagnetic vibration.

  As shown in FIG. 5, for example, the shaft 55 of each rotating shaft of the centering rolls 50 and 51 is provided so as to penetrate the side wall of the snout 11. Both ends of the shaft 55 are supported by bearings 56. The bearing 56 is supported by, for example, a ring-shaped joint 57, and the joint 57 is attached to the attachment portion 59 of the snout 11 with an insulator 58 interposed therebetween. As described above, the centering rolls 50 and 51 are insulated from the snout 11, and the current of the snout 11 can be prevented from flowing to the centering rolls 50 and 51 side. The surface of the centering rolls 50 and 51 or the entire centering rolls 50 and 51 may be formed of an insulator. Thereby, the steel strip H and the centering rolls 50 and 51 can also be insulated.

  As shown in FIG. 4, a rectangular frame-shaped flange 11 c is formed on the end face of the upper end portion of the snout 11 along the end face shape of the snout 11. An end surface of the casing 40 is connected to the flange 11c with an insulator 60 interposed therebetween. This insulator 60 prevents a change in magnetic flux from occurring in the casing 40 due to the influence of the alternating current flowing through the snout 11, and prevents an eddy current from occurring in the casing 40, thereby preventing the casing 40 from melting due to an increase in temperature due to the eddy current. . For example, an electrode 61 is provided on the flange 11 c of the snout 11, and a bus bar 33 is connected to the electrode 61.

  As shown in FIG. 1, a roll 70 is disposed in the molten zinc tank 12. The distance between the roll 70 and the above-described centering roll 51 is set to about 400 mm, for example. With this roll 70, the steel strip H conveyed into the molten zinc tank 12 from diagonally above can be sent out with its direction changed upward. The alloying processing device 13 is provided with a heating furnace (not shown), and the steel strip H can be heated to alloy the plating layer.

  Next, the operation of the hot dip galvanizing equipment 1 configured as described above will be described together with the treatment process of the steel strip H.

  For example, before the hot dip galvanizing process of the steel strip H is started, the snout 11 is preheated by the heat of the hot dip zinc B at, for example, 450 ° C. in the hot dip zinc tank 12. When the hot dip galvanizing process is started, the steel strip H that has been annealed is transported along the transport path A. At this time, first, in the electric heating device 10, a current is passed through the primary coil 21 and a high current is induced in the secondary coil 34, and the steel strip H → molten zinc B → snout 11 → bus bar 33 → conductive roll 30 → steel strip. A current flows through the H energization circuit. The steel strip H is heated to, for example, about 450 ° C. equivalent to the molten zinc temperature by the Joule heat at this time. Further, the snout 11 is also heated to a temperature higher than −100 ° C. (350 ° C.) of the molten zinc temperature (for example, 450 ° C.) using this current. As a result, the snout 11 itself and the inside of the snout 11 become high temperature, and it is suppressed that the evaporated substance of the molten zinc B in the molten zinc tank 12 adheres to the snout 11.

  When the steel strip H passes through the snout 11, the steel strip H is positioned by the centering rolls 50 and 51, and passes through the center of the passage in the snout 11 when viewed from the side. The steel strip H that has passed through the snout 11 is immersed in the molten zinc B in the molten zinc bath 12, and the surface of the steel strip H is plated with the molten zinc B. Thereafter, the steel strip H is transported to the alloying treatment device 13 and subjected to alloying treatment.

  According to the above embodiment, since the snout 11 can be heated to a temperature close to the molten zinc temperature by using the high current of the electric heating device 10, there is no need to provide a separate electric heater as in the prior art. Larger and more complex plating equipment 1 can be prevented. In addition, since the electric energy of the electric heating device 10 can be used effectively, the cost can be greatly reduced.

  Moreover, since the snout 11 is immersed in the molten zinc B of the molten zinc tank 12, the temperature of the snout 11 can be raised using the conduction heat from the high temperature molten zinc B, and the burden of heating by Joule heat can be reduced. In addition, the snout 11 can be heated to a predetermined high temperature in a short time.

  Since the insulator 60 is interposed at the connection portion between the snout 11 and the casing 40, the magnetic flux change is not generated in the casing 40 due to the alternating current of the snout 11, and the eddy current does not cause the casing 40 to be heated. And can be prevented from melting. In addition, no electric leakage is caused from the snout 11 to the casing 40 side, and the electric power of the energization heating device 10 can be efficiently used for heating the snout 11.

  Since the snout 11 is made of austenitic stainless steel, the electrical energy can be efficiently converted to Joule heat. Moreover, the corrosion resistance with respect to the molten zinc B is excellent, and the snout 11 can be immersed in the hot molten zinc B over a long period of time. Furthermore, since the snout 11 is a non-magnetic material, it is possible to prevent an induced current from being generated in the snout 11 under the influence of a magnetic field from the steel strip H through which an alternating current flows. As a result, an appropriate current flows through the snout 11 and desired Joule heat can be generated.

  Since the centering rolls 50 and 51 for positioning the steel strip H are provided in the snout 11 so that the steel strip H passes through the center of the passage in the snout 11, the steel strip H deviates from the center and vibrates due to the Lorentz force. Can be prevented. As a result, since the steel strip H smoothly enters the molten zinc B and the liquid level of the molten zinc B is not greatly disturbed, the molten zinc B can be plated on the steel strip H without any spots.

  Since the centering roll 51 supports the lower surface of the steel strip H and the centering roll 50 presses the upper surface side of the steel strip H, the steel strip H is positioned from both sides of the steel strip H, and the center of the steel strip H Can be prevented more reliably.

  Since some of the wall portions 11a and 11b of the snout 11 protrude outward so as to bypass the centering rolls 50 and 51, it is necessary to increase the inner diameter of the entire snout 11 when the centering rolls 50 and 51 are provided in the snout 11. Therefore, the passage volume in the snout 11 can be reduced accordingly. Therefore, the temperature of the main body of the snout 11 can be reliably raised in a short time, and the evaporation of the molten zinc B can be effectively suppressed. Further, since the temperature in the atmosphere inside the snout 11 is hardly generated and convection is hardly generated, the evaporation from the molten zinc B can be suppressed also by this.

  Since the centering rolls 50 and 51 are attached to the snout 11 via the insulator 58, the current flowing through the snout 11 does not pass through the centering rolls 50 and 51, and the flow of electricity in the snout 11 is prevented. The heating of the snout 11 is not disturbed.

  The steel strip H that is subjected to alloying after plating is required to have a more uniform plating with no foreign matter mixed in than the steel strip that is not subjected to alloying. In the above embodiment, since the contaminants are prevented from falling from the snout 11 to the molten zinc B or the steel strip H by heating the snout 11, the steel strip H is subjected to the alloying process. Also, proper plating is performed.

  The preferred embodiment of the present invention has been described above with reference to the accompanying drawings, but the present invention is not limited to such an example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the spirit described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs. For example, in the above embodiment, the plating metal is zinc, but another metal may be used. Further, in the above embodiment, the present invention is applied to the steel strip H that is subjected to the alloying treatment after plating, but may be applied to the steel strip H that is not subjected to the alloying treatment. The electric heating device 10 uses the transformer effect type electric heating method, but may use another electric heating method such as a direct electric heating method or an induction heating method.

  The present invention is useful for suppressing deposition of molten metal evaporates on an enclosure at a low cost by using a simpler mechanism.

It is explanatory drawing which shows the outline of a structure of the hot dip galvanization equipment concerning this Embodiment. It is a perspective view of a snout. It is explanatory drawing which shows the magnetic field in a snout. It is explanatory drawing of the longitudinal cross-section which shows the outline of a structure of a snout. It is explanatory drawing of the cross section of the snout which shows the attachment mechanism of a centering roll.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hot-dip galvanization equipment 10 Electric heating apparatus 11 Snout 12 Hot-dip zinc tank 30 Conductive roll 33 Bus bar A Conveyance path B Hot-dip zinc H Steel strip

Claims (13)

A method in which a steel strip is heated and then the steel strip is allowed to enter a molten metal and the steel strip is hot dip plated.
The steel strip is heated by energizing the steel strip,
The enclosure surrounding the steel strip immediately before entering the molten metal is energized with a current flowing through the steel strip during the heating, and the enclosure is heated by Joule heat by the energization to melt the enclosure A hot dipping method characterized by heating to a temperature higher than −100 ° C. of the temperature of the metal. The enclosure is immersed in the molten metal;
2. The hot dipping method according to claim 1, wherein the enclosure is heated to the temperature by Joule heat generated by the energization and conduction heat from the molten metal. An apparatus that heats a steel strip and then causes the steel strip to enter a molten metal to hot dip the steel strip,
An electric heating device for energizing the steel strip to heat the steel strip;
A conductive enclosure surrounding the periphery of the steel strip immediately before entering the molten metal;
A molten metal tank for storing the molten metal, and in this order from the upstream side on the conveying path of the steel strip,
The enclosure is energized by a current flowing through the steel strip by the energization heating device, and the enclosure can be heated by Joule heat due to the energization,
The enclosure is formed so as to be heated to a temperature higher than a molten metal temperature of −100 ° C. by energization by the energization heating device at the time of hot dip plating of the steel strip. Hot dipping equipment. The envelope has a downstream end immersed in the molten metal in the molten metal tank,
A connection line for electrically connecting the steel strip located on the upstream side of the energization heating device is connected to the other end portion on the upstream side of the enclosure,
The melting circuit according to claim 3, wherein an energization circuit energized by the energization heating device is formed by a steel strip, the molten metal in the molten metal tank, the enclosure and the connection line. Plating equipment. The steel strip between the energization heating device and the enclosure is surrounded by another enclosure along the conveying path,
5. The hot dipping apparatus according to claim 3, wherein an insulator is interposed at a connection portion between the surrounding body and the other surrounding body. 6. The hot dipping apparatus according to any one of claims 3 to 5, wherein the material of the conductive enclosure surrounding the steel strip immediately before entering the molten metal is austenitic stainless steel. . The enclosure of the conductive surrounding the steel strip immediately before entering into said molten metal, the centering rolls are provided for pressing the strip to the linear axial of the enclosure of the passage through which the steel strip The hot dipping equipment according to any one of claims 3 to 6, wherein The centering roll is a roll that supports the steel strip from the lower surface so that the steel strip is positioned on the axis of the passage in the conductive enclosure surrounding the periphery of the steel strip immediately before entering the molten metal ; The hot dip plating equipment according to claim 7, wherein the hot dip plating equipment is constituted by another roll for pressing a steel strip passing on the shaft from the upper surface. The other roll and the one roll are arranged in this order from the upstream side along the path of the conductive enclosure surrounding the steel strip immediately before entering the molten metal, and sandwich the steel strip. The hot dipping apparatus according to claim 8, wherein the hot dipping apparatus is diagonally opposed. Part of the upper and lower walls of the conductive enclosure surrounding the periphery of the steel strip immediately before entering the molten metal protrudes outward so as to bypass the one roll and the other roll. 10. The hot dipping apparatus according to claim 8 or 9, characterized in that The projecting portion of the upper wall portion of the conductive enclosure surrounding the steel strip and a lower wall portion of the immediately before going into the molten metal is formed in a position shifted from each other on the passage of the enclosure The hot dipping equipment according to claim 10, wherein The centering roll is attached to an electrically conductive enclosure surrounding a steel strip immediately before entering the molten metal with an insulator interposed therebetween. The hot dipping equipment in any one. The hot-dip plating equipment according to any one of claims 3 to 12, wherein the steel strip is subjected to an alloying treatment after hot-dip plating.

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