JP6135876B2 - Steel plate heating method and heating apparatus - Google Patents

Description

  The present invention relates to a method for heating a steel plate and a heating apparatus, and more particularly, to a method for heating a steel plate and a heating apparatus effective for preventing a drawing that tends to occur when the steel plate is rapidly heated.

  In continuous annealing equipment and continuous hot dip galvanizing equipment, steel plates that are continuously passed through are introduced into a furnace maintained at a high temperature, from heat conduction from the furnace atmosphere, from radiant tubes and furnace walls, etc. Heating from room temperature to high temperature is performed by indirect heating with radiant heat. However, with such an indirect heating method, it is difficult to obtain a large heating rate of 10 ° C./sec or more when the plate thickness is 1 mm. On the other hand, in terms of productivity and product characteristics, it may be required to heat more rapidly than the indirect heating method.

  Therefore, as a technology that meets the above requirements, a method has been developed in which a large current is passed through a steel plate or a direct heating is performed by installing an induction coil and causing an induced current to flow through the steel plate. For example, in Patent Document 1, a low-frequency current is passed between two points in the conveyance direction of a steel strip, and high-frequency induction heating is performed at a part between the two points to galvanize a steel sheet after hot dip galvanization. A technique for rapid heating from the bath temperature to the alloying treatment temperature is disclosed. Patent Document 2 discloses a technique for obtaining a unidirectional electrical steel sheet having a high magnetic flux density by energizing and heating between rolls in a temperature raising process of decarburization annealing and rapidly heating at 80 ° C./sec or more. ing.

  However, as a problem in the case of such rapid heating, there is a problem that the steel plate after rapid heating is likely to cause “drawing”. For example, in Patent Document 3, streaky wrinkles called “squeezing” occur after the steel sheet heated by the energizing heating device passes through the energizing roll on the downstream side in the sheet passing direction, and to prevent this throttling. Immediately before the downstream energizing roll, the squeezing prevention roll divided into two in the width direction is pressed against the steel sheet from either one of the upper and lower surfaces with an appropriate opening angle with respect to the steel sheet traveling direction, and the wrinkle is moved in the sheet width direction. It is described that it is effective to extend it.

JP 05-156420 A Japanese Patent Laid-Open No. 07-041860 Japanese Patent Laid-Open No. 08-277425

  Regarding the cause of the above-mentioned “drawing”, in Patent Document 3, the steel plates between the current-carrying rolls arranged upstream and downstream are rapidly heated by current heating and try to expand in the plate width direction. It is explained that wrinkles occur because the thermal expansion is constrained by the energizing roll, and this wrinkled portion is pressed and plastically deformed when passing through a pinch portion such as an energizing roll, resulting in a streak-like ridge Has been. According to the above description, it is considered that the occurrence of squeezing can be prevented by an induction heating method that does not use an energizing roll.

  Certainly, the induction heating without an energizing roll greatly reduces the occurrence of the above-mentioned squeezing. However, according to the inventors' investigation, it was confirmed that even in induction heating without a roll that restrains the free expansion of the steel sheet, a plurality of small vertical wrinkles are generated and drawing is caused as in the case of current heating. ing. There is a possibility that this diaphragm can be solved by applying the technique disclosed in Patent Document 3. However, if an anti-squeeze roll is installed immediately after the induction heating coil, wrinkles may occur due to the steel sheet coming into contact with the anti-squeeze roll. In addition, since the squeezing prevention roll has an action of restraining the slip in the direction in which the steel sheet expands, there is a problem that when the heating temperature is changed in various ways, it cannot cope with the change in thermal expansion associated therewith. It is also difficult to secure the space necessary for installation. Even if it can be installed, the throttling prevention roll of Patent Document 3 has many problems in terms of equipment costs and maintenance because of the complicated equipment.

  The present invention has been made in view of the above-mentioned problems of the prior art, and the purpose thereof is to effectively prevent a restriction that occurs regardless of the presence or absence of a roll that restrains the steel sheet when rapidly heating the steel sheet. In addition to proposing a heating method for a steel sheet, it is an object to provide a heating device used for the method.

  In order to solve the above-described problems, the inventors have made extensive studies on a method for preventing wrinkles caused by thermal expansion in the plate width direction due to rapid heating from developing into a throttle. As a result, in order not to develop a plurality of small vertical wrinkles generated due to the rapid heating into a drawing, it is effective to make the plurality of small vertical wrinkles into one large wrinkle, For that purpose, the sheet width center part of the steel plate in the sheet passing plate is heated in advance to generate one wrinkle, and then the heating region is expanded in the width direction so that the one wrinkle extends to the sheet width end part. The present inventors have found that it is only necessary to expand and have developed the present invention.

  That is, the present invention is a method of heating a continuously conveyed steel plate, heating the plate width central portion of the steel plate in advance, and the isotherm of the steel plate at the time of heating is convex on the upstream side and the interval between the isotherms Is a heating method of a steel sheet, characterized in that they are equal.

  The convex shape in the heating method of the present invention is an arc shape or a V shape.

Further, the present invention provides a heating apparatus for heating a continuously conveyed steel sheet, in which the steel sheet heating means heats the sheet width central portion of the steel sheet in advance, and the isotherm of the steel sheet during heating protrudes upstream. It is a steel plate heating device characterized in that the shape and the interval of isothermal lines are arranged to be equal .

  The heating means for the steel sheet in the present invention is a solenoid induction heating coil whose shape projected on the steel sheet surface is convex on the upstream side.

  In the present invention, the convex shape is an arc shape or a V shape.

Further, the present invention is characterized in that a presser roll is disposed between the heating device and the downstream side plate roll.

  According to the present invention, it is possible to effectively prevent the drawing generated when the steel sheet is rapidly heated, so that it is possible to stably pass the steel sheet through a continuous annealing facility or the like, and the product of the steel sheet. Contributes greatly to improving the quality of shapes.

It is a schematic diagram explaining the planar shape of the heating apparatus using the conventional solenoid type induction heating coil, and the steel plate rapidly heated with the apparatus. It is a schematic diagram explaining the AA 'cross-sectional shape of the steel plate shown in FIG. It is a schematic diagram explaining the planar shape of the heating apparatus of this invention using the arc-shaped solenoid type induction heating coil, and the steel plate rapidly heated with the apparatus. It is a schematic diagram explaining the BB 'cross-sectional shape of the steel plate shown in FIG. It is an overhead view explaining the change of the steel plate shape by the difference in the method of heating. It is a schematic diagram explaining the other heating apparatus of this invention using the V-shaped solenoid type induction heating coil. It is a schematic diagram explaining the other example of the heating apparatus of this invention which has arrange | positioned the presser roll downstream from the heating apparatus shown in FIG. It is a figure explaining the other heating apparatus of this invention using the solenoid type induction heating apparatus. It is a figure explaining the other heating apparatus of this invention using a transverse type induction heating apparatus.

  In general, in equipment for continuously annealing a steel plate, in order to retain the steel plate in the furnace for a long time, a number of conveying rolls are arranged facing each other in the annealing furnace, and the steel plate is reciprocated between the opposed conveying rolls. In order to prevent the meandering of the steel plate passing through the furnace and secure a stable plate, the crown of the transport roll is convex and a predetermined amount of tension is applied to the steel plate. Therefore, the steel plate that passes through the furnace has a force to shrink in the width direction of the plate, so small vertical wrinkles are likely to occur. It is known to reach a diaphragm called.

  However, the diaphragm targeted by the present invention is considered to be a phenomenon different from the diaphragm described above. The reason for this is that the restriction targeted by the present invention is due to the restraint of thermal expansion when the steel sheet is rapidly heated. However, it is common in that a plurality of small vertical wrinkles are brought into contact with the roll and are crushed to reduce the width of the wrinkles, leading to a stop. Therefore, there is a possibility that the vertical wrinkles described above and the vertical wrinkles due to rapid heating are superimposed to cause a restriction.

  The inventors have repeatedly studied a measure for preventing a plurality of small vertical lines generated due to the rapid heating from being developed into a diaphragm. As a result, it is possible to prevent narrowing by making a plurality of small vertical wrinkles into one wrinkle having a large width, and for that purpose, the central part of the plate width of the steel plate in the plate is heated in advance. One wrinkle is generated at the center of the plate width, and then the heating region is expanded to find that one wrinkle is expanded to the end of the plate width, and the present invention has been developed.

  FIG. 1 is a schematic diagram showing a heating device using a conventional solenoid induction heating coil and a shape change of the steel plate when the steel plate is rapidly heated by the device, where 1 is a steel plate, 2 ′ is a transport roll, 3 is a solenoid type induction heating coil having a rectangular projection shape on a steel plate surface, and 4 is a direction in which an alternating induction current flows through the coil. Moreover, FIG. 2 is the figure which showed typically the AA 'cross-sectional shape of the steel plate shown in FIG. As shown in FIG. 1 and FIG. 2, the steel plate rapidly heated by the conventional rectangular heating coil tries to be thermally expanded uniformly in the plate width direction, but is restrained by the transport roll 2 ′ on the downstream side, A plurality of small vertical wrinkles 5 that are long in the steel plate traveling direction are generated (an example of two vertical wrinkles is shown in FIGS. 1 and 2).

  On the other hand, FIG. 3 is a schematic view showing the heating device of the present invention and the shape change of the steel plate when the steel plate is rapidly heated by the device, wherein 1 is a steel plate, 2 ′ is a transport roll, and 6 is a book. The solenoid-type induction heating coil whose projection shape on the steel plate surface according to the invention has an arc shape, 4 indicates the direction in which an alternating induction current flows through the coil. FIG. 4 is a diagram schematically showing a BB ′ cross-sectional shape of the steel plate shown in FIG. As shown in FIGS. 3 and 4, in the heating device of the present invention, the central portion of the plate width of the steel plate is preheated by the protruding portion of the arc-shaped heating coil. As a result, the rapidly heated steel plate does not generate a plurality of small vertical wrinkles as in the conventional heating device even when thermally expanded, and generates only one vertical wrinkle 5 having a large radius of curvature. Even if it comes into contact with the transport roll 2 ', it does not develop into a diaphragm.

  1 and 2 and one vertical wrinkle shown in FIGS. 3 and 4 are generated due to out-of-plane deformation of the thermal expansion of the steel sheet, and FIG. Is shown in an overhead view. The steel plate 101 is sent from left to right and heated near the center of the figure. In FIG. 5 (a), which is a conventional heating method, the isothermal line 102 at the initial stage of heating and the isothermal line 103 at the end of heating are both It is represented by a straight line. At this time, the steel sheet undergoes out-of-plane deformation (in this example, vertical deformation) due to thermal expansion, and is displaced in the vertical direction as indicated by 104. In this conventional example, five starting points 105 for the out-of-plane deformation in the vertical direction are used, but since the starting points for the out-of-plane deformation can be anywhere on the isotherm 102, the number is indefinite. However, once many wrinkles are generated, the number is often stabilized.

  On the other hand, in the heating method of the present invention, as shown in FIG. 5 (b), the isotherm in the initial stage of heating is curved because the center of the width precedes and becomes high temperature, and the deformation of out-of-plane deformation occurs. There is only one starting point in the center of the plate width direction. Therefore, one wrinkle (wide vertical wrinkle) is generated, and all the thermal expansion deformation is absorbed by the wrinkle and finally becomes a vertical wrinkle with one large curvature radius.

  In the present invention, the isotherm between the isotherm 102 at the initial stage of heating and the isotherm 103 at the completion of heating is all the isotherm from the start to the end of the heating, and the isotherm moves in parallel with the traveling direction of the plate. It is desirable to heat so that it matches when it is made. This is because when the density of the isotherm is increased in the traveling direction of the plate, the dense place is heated at a short distance and greatly expands, whereas the sparse place has a small thermal expansion. This is because wrinkles are concentrated in a place where isotherms are dense as shown in FIG.

  Here, the reason why the heating device of the present invention is an induction heating coil and the solenoid type is shown as an example in induction heating is that the solenoid type is advantageous in terms of heating speed, and the steel plate is sandwiched from above and below by the coil. In a simple transverse type heating coil, the AC magnetic field is orthogonal to the plate surface, and the induced current flows around the plate surface. This is because it is not possible to simply heat the center part in advance.

  FIG. 6 shows another embodiment of the heating device of the present invention. The projected shape on the steel plate surface in FIG. 3 is replaced with an arc-shaped induction heating coil, and the projected shape on the steel plate surface is V-shaped. This is an example in which a cylindrical induction heating coil 7 is used. Even with such a V-shaped induction heating coil, the central portion of the plate width can be heated in advance, so that the occurrence of throttling can be effectively suppressed.

  In order to form one large vertical wrinkle with the heating device of the present invention, it is preferable to heat the isotherm of the heated steel sheet so that the intervals are as equal as possible. It can be said that it is preferable to use the arc-shaped or the V-shaped induction heating coil shown in FIG.

  In addition, as described above, the heating method and the heating device according to the present invention are characterized by suppressing the generation of a plurality of small vertical wrinkles by heating the central portion of the plate width in advance, thereby generating one large wrinkle. However, if this wrinkle becomes too large, it becomes a so-called “C warp”, which may cause contact with other mechanical equipment other than the transport roll. Therefore, in order to prevent such a problem, it is preferable to dispose a pressing roll downstream of the induction heating coil and upstream of the downstream transport roll.

  FIG. 7 shows an example in which a pressing roll 9 is installed on the downstream side of the induction heating coil of the heating apparatus of the present invention shown in FIG. Since this presser roll does not require complicated incidental facilities such as the squeezing prevention roll disclosed in Patent Document 3, there is an advantage that the installation space is small and there are few problems in equipment cost and maintenance.

  The heating device of the present invention can be applied to both vertical and horizontal annealing facilities. Moreover, the heating apparatus of this invention should just be installed in the location which needs rapid heating, and may be installed in a furnace for heat insulation, temperature maintenance, or atmosphere control. Moreover, the heating device of the present invention may be installed singly, or may be installed in a plurality in series, or may be installed separately.

  Moreover, FIG. 8 shows other embodiment of the heating apparatus of this invention which has the induction heating coil comprised with the electrically conductive plate. Since the essential requirement in the present invention is to heat the steel plate so that the center of the plate width reaches a high temperature in advance, the conductive copper shown in the overhead view in FIG. As shown in FIG. 8 (b), if the protruding portion 205 and the notch portion 206 are provided to the solenoid induction heating coil 202 made of a metal plate, the current flows smoothly. And can be heated. Further, if this principle is applied, the present invention can be implemented even with a conventional rectangular solenoid induction heating apparatus, for example, by adding conductors 204 and 205 as shown in FIG. 8C. Can do.

  In the description of the heating method and the heating apparatus of the present invention described above, an example of rapid heating using a solenoid type induction heating coil as the heating means has been described. However, as the rapid heating means, a transverse type is used. The present invention can also be implemented using an induction heating device. For example, as shown in FIG. 9 (a), a heating apparatus provided with a transverse induction heating coil 302 having an arc-shaped current path in the plate width direction, or a conventional apparatus as shown in FIG. 9 (b). Even in the case of the rectangular transverse coil 305, a heating device that can heat the plate width center in advance by changing the arrangement of the core material (iron core) 304 may be used.

  Furthermore, the heating device of the present invention may use any heating means as long as it can rapidly heat the sheet width center in advance, for example, burner heating, plasma heating, laser heating. Any heating means such as infrared heating may be used.

  A heating device having a solenoid type induction heating coil having a circular arc shape projected onto the steel plate surface, a solenoid opening cross section of width: 1500 mm × height: 140 mm, and length: 6000 mm is installed in the continuous annealing equipment, and the plate thickness : 0.3 mm x sheet width: 1300 mm of 3 mass% Si-containing cold-rolled steel sheet is transported at 100 m / min and rapidly heated from room temperature to 700 ° C at 100 ° C / sec or 200 ° C / sec to perform primary recrystallization annealing Thus, a grain-oriented electrical steel sheet was produced. As the arc-shaped solenoid type induction heating coil, two types having a length of the central protruding portion with respect to both width end portions of 50 mm and 100 mm were used. Moreover, the heating apparatus which provided the pressing roll shown in FIG. 7 was used for some steel plates.

  The defect rate of products generated due to the above-mentioned drawing due to rapid heating is expressed as a standard (1.0) when heating at 200 ° C./sec with a heating device having a conventional rectangular solenoid induction heating coil. It was shown in 1. From this result, it can be seen that by applying the heating device of the present invention, it is possible to significantly reduce defects caused by the diaphragm.

  Since the technology of the present invention can rapidly heat a steel sheet at 100 ° C./sec or more without causing a drawing, applying this to the heating of primary recrystallization annealing enables the directional electromagnetic with excellent magnetic properties. A steel plate can be advantageously produced.

1: Steel plate 2, 2 ': Conveying roll 3: Conventional rectangular solenoid induction heating coil 4: Direction of excitation current flow 5: Vertical wrinkles (diaphragm)
6: Arc-shaped solenoid induction heating coil 7: V-shaped solenoid induction heating coil 9: Presser roll 101, 201, 301: Steel plate 102: Isothermal line at the beginning of heating 103: Isothermal line at the end of heating 104: Surface External deformation (displacement in the vertical direction of the steel sheet)
105: Origin of out-of-plane deformation 202: Solenoid induction heating coil 203, 303: Coil current (alternating current, but shown with a one-way arrow)
204: Conductive plate added by modification 205: Protrusion 206: Notch 302: Transverse induction heating coil 304: Core material 305: Conventional transverse induction heating coil

Claims (6)

In the method of heating continuously conveyed steel plates, the center of the plate width of the steel plate is heated in advance so that the isotherm of the steel plate at the time of heating is convex on the upstream side and the intervals of the isotherms are equal. A method of heating a steel sheet, characterized in that The steel sheet heating method according to claim 1, wherein the convex shape is an arc shape or a V shape. In a heating device that heats a steel plate that is continuously conveyed, the heating means of the steel plate heats the plate width central portion of the steel plate in advance, and the isotherm of the steel plate during heating is convex on the upstream side and the interval between the isotherms A heating apparatus for a steel sheet, characterized in that they are arranged to be equal to each other. 4. The steel sheet heating apparatus according to claim 3, wherein the steel sheet heating means is a solenoid induction heating coil whose shape projected onto the steel sheet surface is convex upstream. The steel sheet heating apparatus according to claim 4, wherein the convex shape is an arc shape or a V shape. The steel sheet heating apparatus according to any one of claims 3 to 5, wherein a pressing roll is disposed between the heating apparatus and the downstream sheet passing roll.

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