JP2009263701A - Method for heating material to be heated - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous rolling facility which can correct a temperature distribution in a longitudinal direction of a slab that has been heated under such conditions as to deviate from an original heating condition in a heating furnace, to an appropriate temperature distribution, and roll the slab under the optimum heating condition, and to provide a method for heating the material to be heated by using the continuous rolling facility. <P>SOLUTION: The method for heating the material to be heated by using a continuous heating furnace which can selectively switch the heating condition for the material to be heated between a uniform heating condition and a gradient heating condition, and an induction heating device arranged right in front of a finish rolling mill includes heating the material which has been heated by the continuous heating furnace in the period of switching the heating condition of the continuous heating furnace between the uniform heating condition and the gradient heating condition, by the induction heating device so as to compensate an amount of the insufficient heating which has been generated along the longitudinal direction in the switching period. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for heating a material to be heated for heating to a predetermined temperature when a slab or the like is hot-rolled.

  A continuous heating furnace is used to heat slabs, billets, blooms and the like after casting to a temperature suitable for hot rolling. Such a continuous heating furnace is generally composed of a pre-tropical zone, a heating zone, and a soaking zone, and a heated material such as a slab is successively moved through the pre-tropical zone, the heating zone, and the soaking zone in order to be heated. The material can be heated uniformly to a predetermined temperature.

Recently, not only the material to be heated, such as a slab, is heated uniformly, but it is also heated so as to have a temperature gradient between the front end portion and the rear end portion of the slab.
For example, when manufacturing a thin rolled sheet, the time from the start of finish rolling of the slab tip to the start of finish rolling of the slab rear end becomes longer, during which the temperature drop at the slab rear end In some cases, the deformation resistance is increased, the shape is deteriorated due to load fluctuation, or the temperature is lower than a predetermined lower limit of the finishing rolling temperature. In such a case, in anticipation of the amount of temperature decrease, if inclined heating is performed to make the temperature at the rear end of the slab higher than the temperature at the front end, the load fluctuation at the rear end of the slab can be reduced, or a predetermined finish can be achieved. It becomes possible to perform rolling within the rolling temperature range.

  In addition, in order to improve productivity, after the slab tip is caught in the finish rolling mill, hot rolling may be performed at a gradually increased speed. The temperature increases at the rear end of the slab (rolled steel plate) after rolling, and scale wrinkles may occur or the upper limit of the finish rolling temperature may be exceeded. In such a case, in anticipation of an increase in the finish delivery temperature, if reverse gradient heating is performed to lower the temperature at the rear end of the slab to be lower than the temperature at the front end, the finish rolling exit temperature at the rear end of the slab is predetermined. This makes it possible to achieve both high quality and improved productivity of the rolled steel sheet.

  As a conventional heating furnace, for example, a heating furnace shown in FIG. This heating furnace has a plurality of pairs of regenerative combustion devices that alternately burn on both sides in the furnace length direction, a continuous combustion device in the width direction in the middle of the furnace length direction of the heating furnace, and the combustion amount of the continuous combustion device By adjusting the temperature, the temperature in the furnace width direction of the slab is uniformly or arbitrarily controlled.

Moreover, the heating furnace currently disclosed by patent document 2 arrange | positions the several pairs heat storage type combustion apparatus which carries out alternating combustion to the furnace length direction both sides, and sets the combustion time of the heat storage type combustion apparatus of one side to the heat storage of the other side. The slab is heated in an inclined manner by making it longer or shorter than the combustion time of the combustion chamber.
Japanese Patent Application Laid-Open No. 11-323431 JP 9-53115 A

  However, in the heating furnace described in Patent Document 1, the roof burners that are continuous combustion apparatuses capable of adjusting the combustion amount are arranged in a row along the furnace width direction of the heating zone, and further downstream of the roof burner, A regenerative heating device is mainly used for heating the slab uniformly in the heating furnace width direction (longitudinal direction of the material to be heated). For this reason, it becomes difficult to have a gradient in the furnace temperature of the heating zone, and even if the gradient heating or the reverse gradient heating is performed, the slab is uniform along the furnace width direction by the regenerative combustion device installed in the soaking zone of the latter stage There was a problem that it was difficult to increase the temperature gradient of the slab.

  Furthermore, in the heating furnace described in Patent Document 2, even if the combustion amount of the regenerative heating apparatus for originally heating the slab uniformly in the width direction of the heating furnace is changed within a controllable range, the slab has a large temperature. It was difficult to create a gradient.

  In order to reliably perform the gradient heating and create a temperature difference between the front end portion and the rear end portion of the material to be heated, it is necessary to provide an inclined heating zone in a certain region on the extraction side of the heating furnace.

  By the way, in an actual operation, a uniform heating material that requires uniform heating and a gradient heating material that requires gradient heating are continuously charged into a heating furnace. For this reason, according to the kind of to-be-heated material, it is necessary to change the heating condition of a heating furnace from a uniform heating condition to a gradient heating condition, or to change from a gradient heating condition to a uniform heating condition.

  The time required for changing the heating condition is, for example, several tens of minutes in order to change from the uniform heating condition in which the temperature in the furnace width direction is constant to the inclined heating condition in which the temperature difference in the furnace width direction is 60 ° C. It may take. If the material to be heated and the material to be heated to be inclined are inserted into the heating furnace with an interval, each material to be heated can be heated according to the necessary heating conditions, but the productivity is not actually reduced. Therefore, the material to be heated and the material to be heated to be heated in many cases are continuously charged, and the material to be heated is heated under a condition deviating from the original heating condition for several tens of minutes while changing the heating condition. As a result, a part out of the condition, for example, a part of the rolled steel sheet, a part having a temperature lower than the target finish rolling end temperature is generated, and the required material cannot be obtained and rolled. There was a problem that the yield of the steel sheet was lowered.

  The present invention has been made in view of the above circumstances, and corrects the temperature distribution in the longitudinal direction of the slab to an appropriate temperature distribution for a slab heated in a heating furnace under conditions deviating from the original heating conditions. From the above, it is an object of the present invention to provide a continuous rolling line that can be rolled under optimum heating conditions and a method for heating a material to be heated using the continuous rolling line.

In order to achieve the above object, the present invention employs the following configuration.
In the heating method of the heated material of the present invention, the heated material is inserted so that the longitudinal direction of the heated material is orthogonal to the conveying direction of the conveying path provided in the heating furnace, and the heated material is used as the conveying path. A heating zone that is heated while being conveyed along a heating zone that can selectively switch the heating condition in the width direction of the furnace to uniform heating or inclined heating between the middle of the conveying path and the extraction section A heating method of a material to be heated using a continuous heating furnace and an induction heating device arranged immediately before a finishing rolling mill, wherein heating conditions of the switchable heating zone of the continuous heating furnace are uniform heating The material to be heated is compensated for the heating shortage generated along the longitudinal direction of the material to be heated by the continuous heating furnace during the switching period for switching between the inclined heating and the heating material. Heating is performed by an induction heating device.

  In the method for heating a material to be heated according to the present invention, the material to be heated heated by the continuous heating furnace is roughly rolled by a roughing mill installed at a subsequent stage of the continuous heating furnace. And the induction heating device disposed immediately before the finishing mill, the temperature distribution in the longitudinal direction of the heated material is measured, the measured temperature distribution profile of the heated material, and the target temperature distribution profile, It is preferable that the underheating amount is calculated along the longitudinal direction of the heated material by comparing the heated material with the induction heating device so as to compensate for the measured underheating amount. .

  Furthermore, in the heating method of the material to be heated according to the present invention, the continuous heating furnace includes a plurality of alternating combustions disposed on both sides of the conveying path of the material to be heated and disposed between the charging portion and the extraction portion. A heat storage combustion device and an upper side of the conveyance path, which are continuously arranged from the middle of the conveyance path to the extraction unit, and are arranged in a plurality of regions divided along the furnace width direction. And a plurality of continuous combustion devices capable of controlling the combustion amount for each region, wherein the continuous heating furnace is configured to adjust the combustion amount of the plurality of continuous combustion devices. It is preferable that the heating condition for the material to be heated can be selectively switched to uniform heating or gradient heating by controlling the temperature distribution in the furnace width direction.

  Furthermore, in the heating method of the heated material of the present invention, the timing for switching the heating condition of the heating zone of the continuous heating furnace between uniform heating and inclined heating is controlled so that the heated material is not overheated. It is preferable to do.

  According to the present invention, the temperature distribution in the longitudinal direction of the slab is applied to the material to be heated, which is heated under conditions deviating from the original heating conditions by the continuous heating furnace during the switching period between uniform heating and gradient heating. After correcting to an appropriate temperature distribution, rolling can be performed under optimum heating conditions, and a rolled steel sheet having excellent quality can be manufactured.

Hereinafter, a method for heating a material to be heated, which is an embodiment of the present invention, will be described with reference to the drawings. The drawings shown below are for explaining the configuration of equipment for carrying out the heating method of the material to be heated according to the present embodiment, and the size, thickness, dimensions, etc. of each part shown in the drawings are actual. It may be different from the dimensional relationship of the continuous rolling line.
FIG. 1 is a schematic view showing a continuous rolling line provided with heating equipment suitably used in the embodiment of the present invention, and FIG. 2 shows a continuous heating furnace provided in the continuous hot rolling line of FIG. It is a perspective schematic diagram shown. FIG. 3 is a schematic side view of the continuous heating furnace, and FIG. 4 is a schematic plan view of the continuous heating furnace. FIG. 5 is a schematic cross-sectional view corresponding to the line AA ′ of FIG.

A continuous rolling line 101 shown in FIG. 1 continuously rolls a heated slab (material to be heated) sandwiched between rolls, thins it to a minimum of about 1 mm, and winds it up. A continuous heating furnace 1 capable of selectively switching the condition to uniform heating or inclined heating, and a slab installed on the downstream side of the continuous heating furnace 1 and rolled by a rough bar ( A rough rolling mill 11 to be heated), a finishing mill 21 which is installed downstream of the rough rolling mill 11 and continuously hot-rolls the rough bar to a predetermined thickness, and the finishing mill 21 It is schematically configured from an induction heating device 31 installed immediately before.
Note that the coarse bar is obtained by roughly rolling a slab, and in this embodiment, both the slab and the coarse bar may be referred to as materials to be heated.

  Further, the continuous rolling line 101 includes a thermometer 32 for measuring the temperature distribution in the longitudinal direction of the rough bar, a measuring means 33 connected to the thermometer 32, and a control means 34 connected to the measuring means 33. It has been. The thermometer 32 is installed between the rough rolling mill 11 and the induction heating device 31, and measures the temperature of the coarse bar behind the rough rolling mill 11. The control means 34 is connected to the induction heating device 31 so that the heating amount of the induction heating device 31 can be controlled by a control signal.

  Further, the continuous rolling line 101 is provided with a facility 41 for removing oxide scale generated on the slab surface in the continuous heating furnace 1 between the continuous heating furnace 1 and the rough rolling mill 11. Also, on the downstream side of the finish rolling mill 21, a cooling device 42 that cools the hot rolled steel sheet that has been hot finish rolled with cooling water, and a winder that winds the rolled steel sheet cooled by the cooling device 42 into a roll shape. 43.

As shown in FIGS. 2 to 5, the continuous heating furnace 1 includes a conveyance path 2 that sequentially conveys a slab (material to be heated) from the charging unit 1 </ b> A side to the extraction unit 1 </ b> B side, and a charging unit 1 </ b> A. A furnace chamber 3 provided along the conveyance path 2 up to the extraction unit 1B, a plurality of regenerative combustion devices 4 disposed on both sides in the conveyance direction of the conveyance path 2, and an extraction unit from the middle of the conveyance path 2 And a plurality of continuous combustion devices 5 arranged on the upper side of the conveying path 2.
In the continuous heating furnace 1, when a slab (material to be heated) is continuously conveyed from the insertion unit 1 </ b> A side to the extraction unit 1 </ b> B side by the conveyance path 2, first, the slab is predetermined by the regenerative combustion device 4. Heat uniformly to temperature. Next, the slab is inclined so that the temperature along the longitudinal direction of the slab has an inclination by independently controlling the combustion amount of the continuous combustion apparatus 5 divided into a plurality of areas in the width direction for each divided area. Heat or uniformly heat so that the temperature along the longitudinal direction of the slab is constant. The continuous heating furnace 1 according to the present embodiment can selectively uniformly heat or incline the slab by controlling the combustion amount of the continuous combustion device 5.

  And the slab heat-processed by the continuous heating furnace 1 is hot-rolled by the rough rolling mill 11 and the finishing mill 21 arrange | positioned in the back | latter stage of the continuous heating furnace 1. FIG.

The slab (material to be heated) is continuously transported by the transport path 2 provided in the continuous heating furnace 1. As the conveyance path 2, for example, a walking beam device capable of continuously conveying a slab is used.
The slab is transported along the transport path 2 in a posture in which the longitudinal direction is oriented in a direction substantially orthogonal to the transport direction. That is, the slab is transported in such a posture that its longitudinal direction is along the furnace width direction.

  Next, on both sides of the conveyance path 2, a plurality of regenerative combustion apparatuses 4 are disposed between the charging unit 1 </ b> A and the extraction unit 1 </ b> B. For example, an FDI type regenerative burner can be used as the heat storage combustion device 4. In the continuous heating furnace 1 shown in FIGS. 2 to 5, the burner port of the regenerative combustion apparatus 4 is disposed on the side wall surface 3 a of the furnace chamber 3, and the frame F blows out from the burner port along the furnace width direction. It has come to be. The regenerative combustion apparatus 4 is arranged side by side along the conveyance direction of the conveyance path 2 on the upper side and the lower side of the conveyance path 2. With this configuration, when the material to be heated is conveyed through the conveyance path 2, the material to be heated can be heated uniformly from the upper side and the lower side.

However, as shown in FIGS. 2 to 4, the regenerative combustion apparatus 4 is not disposed on the upper side of the conveyance path 2 near the extraction unit 1 </ b> B where the continuous combustion apparatus 5 is disposed. If the regenerative combustion apparatus 4 is disposed in the region where the continuous combustion apparatus 5 is disposed, the material to be heated is uniformly heated by the regenerative combustion apparatus 4 and it becomes difficult to perform gradient heating, which is not preferable.
On the other hand, a regenerative combustion device 4 is disposed below the conveyance path 2 near the extraction unit 1B in order to sufficiently heat the lower surface side of the material to be heated.

  Next, as shown in FIG. 2, the continuous combustion apparatus 5 is located on the upper side of the conveyance path 2 and is continuously arranged along the furnace length direction from the middle of the conveyance path 2 to the extraction unit 1B. ing. Here, “continuous arrangement” refers to a state in which a plurality of continuous combustion apparatuses 5 are arranged side by side with a predetermined interval. The continuous combustion device 5 is located above the conveyance path 2, and more specifically, the burner port of the continuous combustion device 5 is disposed on the ceiling surface 3 b of the furnace chamber 3. The ceiling surface 3b on which the continuous combustion device 5 is disposed is disposed closer to the conveyance path 2 than the other ceiling surface 3c. Moreover, the continuous combustion apparatus 5 is each arrange | positioned at the area | region divided | segmented equally into four along the furnace width direction, as shown in FIGS. As will be described later, the number of divisions is preferably three or more, and is not limited to four. These continuous combustion devices 5 can freely adjust the combustion amount, and can control the combustion amount for each of the regions 5A to 5D.

  The continuous combustion device 5 is a combustion device that blows out a flame continuously and burns it. The continuous combustion device 5 may be, for example, either a roof burner that blows the frame downward from the ceiling surface 3b of the furnace chamber 3 or an axial burner that blows the frame in the furnace length direction. A roof burner is good.

  The arrangement configuration of the continuous combustion device 5 will be described in more detail. The continuous combustion device 5 is arranged along the furnace length direction from the middle of the conveyance path 2 to the extraction unit 1B as shown in FIGS. Are arranged consecutively. The arrangement length along the furnace length direction of the continuous combustion apparatus 5 is preferably 15% to 80% or less with respect to the total furnace length of the heating furnace 1. That is, when the total furnace length of the heating furnace 1 is L, the length of the region where the continuous combustion apparatus 5 is disposed is preferably in the range of 0.15L to 0.80L.

  The proportion of the arrangement length along the furnace length direction of the continuous combustion apparatus 5 with respect to the total furnace length of the heating furnace 1 depends on the temperature difference in the longitudinal direction of the material to be applied and the furnace of the heating furnace 1. It is determined from the temperature difference of the chamber 3 or the like. The temperature difference in the longitudinal direction of the material to be heated is the temperature difference between the front end portion and the rear end portion in the longitudinal direction of the heated material after heating. The temperature difference in the furnace chamber 3 is a temperature difference between the highest temperature and the lowest temperature on the transfer path 2 when the combustion amount of the continuous heating device 5 is controlled along the furnace width direction. When determining the lower limit of the required arrangement length, the maximum temperature difference determined by the capacity of the combustion device and the durability of the refractory in the heating furnace is determined. In FIG. 6, the ratio of the arrangement length along the furnace length direction of the continuous combustion apparatus 5 to the total furnace length of the heating furnace 1 under the general heating conditions when hot rolling the slab as the material to be heated, The relationship with the longitudinal temperature difference of a to-be-heated material is shown with the graph. FIG. 6 shows a case where the slab extraction temperature is 1150 ° C. and the furnace wall temperature difference is about 100 ° C. The temperature difference in the longitudinal direction of the material to be heated may be about 30 ° C. from the past results. Under the conditions shown in FIG. 6, the ratio of the arrangement length along the longitudinal direction of the continuous combustion device 5 should be 15% or more. I understand that When the temperature difference in the furnace chamber 3 is smaller than 100 ° C., the ratio of the arrangement length may be increased. However, as the ratio of the arrangement length of the continuous combustion apparatus 5 increases, it becomes disadvantageous for energy saving. % Is the upper limit.

Moreover, the continuous combustion apparatus 5 is each arrange | positioned at several area | region 5A-5D divided | segmented along the furnace width direction, as shown in FIGS. In the present embodiment, an example in which the number of regions is four is shown, but the number of regions is preferably 3 or more, and more preferably 3 to 5.
The continuous combustion apparatus 5 can adjust the combustion amount for each of the regions 5A to 5D. For example, the continuous combustion device in the region 5A on one end side in the furnace width direction is burned with a certain rated combustion amount, and the continuous combustion device in the adjacent region 5B is burned with a smaller combustion amount than the region 5A, Similarly, the combustion amount can be gradually reduced in the regions 5C and 5D. Thereby, the furnace temperature of the furnace chamber 3 under the continuous combustion apparatus 5 can be inclined along the furnace width direction, and the temperature difference between the maximum temperature and the minimum temperature of the furnace temperature on the conveyance path 2. Can be made 30 ° C. or higher.

The amount of combustion for each of the regions 5A to 5D of the continuous combustion apparatus needs to be adjusted according to the target temperature distribution in the longitudinal direction of the material to be heated. For example, the target temperature distribution in the longitudinal direction of the heated material is such that the heating target temperature at the front end of the heated material is t ₁ ° C., and the heating target temperature at the rear end is t ₂ ° C. (for example, t ₁ > t ₂ ). It is assumed that the temperature distribution between the front end portion and the rear end portion changes at a predetermined rate along the longitudinal direction of the material to be heated. In this case, the combustion amount for each of the regions 5A to 5D of the continuous combustion apparatus has an arrangement length along the longitudinal direction of the continuous combustion apparatus 5 so that the temperature distribution after heating of the material to be heated matches the target temperature distribution. The ratio may be adjusted so that the temperature difference in the furnace chamber 3 is optimal.

  Note that the control of the combustion amount is not limited to the case where the combustion amount is sequentially decreased from the region 5A to the region 5D as described above, and the combustion amount may be sequentially increased from the region 5A to the region 5D. Further, uniform heating may be performed with the same amount of combustion in the regions 5A to 5D.

  Further, the continuous combustion apparatus may be further divided into a plurality of regions along the furnace length direction, and the combustion amount in the furnace width direction may be adjusted for each region divided along the furnace length direction.

  The thermometer 32 is installed on the upstream side of the induction heating device 31 in order to measure the temperature distribution in the longitudinal direction of the coarse bar. The thermometer 32 is installed above the conveyance path of the coarse bar, continuously measures the temperature of the coarse bar moving under the thermometer 32, and sends the measurement data to the sequential measurement means 33.

  The measuring means 33 and the control means 34 are each constituted by an electronic computer provided with a calculation unit, a storage unit, and a signal input / output unit. The measuring means 33 and the control means 34 may be built in one electronic computer, and each means 33 and 34 may be divided into a plurality of electronic computers.

  The measuring means 33 creates a temperature distribution profile in the longitudinal direction of the coarse bar based on the measurement data of the coarse bar (material to be heated) sent from the thermometer 32. This temperature profile consists of multiple data such as the length of the coarse bar, each temperature at the leading and trailing edges of the coarse bar, and the temperature in each segment when the coarse bar is divided into a number of segments along the longitudinal direction. Composed.

  The storage unit of the measuring unit 33 stores a target rough bar temperature distribution profile. This target temperature distribution profile is the temperature at the finishing mill entry side necessary for the finish rolling temperature to become a predetermined temperature, and the thickness, rolling reduction, rolling time, and target finishing rolling temperature of the rolled material. Like the temperature distribution profile in the longitudinal direction of the coarse bar created based on the measurement data, such as rolling conditions, etc., the rolling condition is composed of a plurality of data such as the length of the coarse bar.

  Further, the measuring means 33 compares the temperature distribution profile in the longitudinal direction of the coarse bar with the target temperature distribution profile, and calculates the amount of insufficient heating generated along the longitudinal direction. Then, the calculated underheating amount data is sent to the control means 34.

  The control unit 34 is configured to control the heating amount of the induction heating device based on the data of the insufficient heating amount sent from the measuring unit 33.

  The induction heating device 31 may be a solenoid-type heating furnace in which a coarse bar passes along a central axis of a heating coil formed in a spiral shape, and an induction heating unit in which a heating coil is wound around a core is provided above and below the coarse bar. Although an upper and lower split type heating furnace arranged in the direction may be used, an upper and lower split type induction heating apparatus is preferable. The induction heating device 31 can finely control the heating amount for the coarse bar by controlling the energization amount of the heating coil. For example, the heating amount at the leading end of the coarse bar is minimized, Control that maximizes the amount of heating and gradually increases the amount of heating from the front end to the rear end is possible.

Next, the heating method of the to-be-heated material by the heating equipment of this embodiment is demonstrated.
In the continuous rolling line 101, after a plurality of uniformly heated slabs are subjected to a rolling process, the plurality of inclined slabs may be subjected to a rolling process. The reverse is also true. In the actual continuous rolling line 101, for example, immediately after a plurality of uniformly heated slabs are extracted from the continuous heating furnace 1, the heating condition of the continuous heating furnace 1 is changed from uniform heating to improve production efficiency. Switch to ramp heating. Then, the slab extracted from the continuous heating furnace after switching is handled as a slab heated by a gradient, and a production plan is made so that the slab heated by the gradient is continuously rolled following the slab heated uniformly. .

  In order to change the heating condition from the uniform heating to the side oblique heating in the continuous heating furnace 1, by continuously adjusting the combustion amount of the continuous combustion device 5 shown in FIGS. 2 to 5 for each of the regions 5A to 5D, The temperature in the furnace chamber 3 under the combustion chamber 5 is changed from a constant state (uniform heating) along the furnace width direction to a state inclined (tilted heating) along the furnace width direction. .

  FIG. 7 shows the behavior of the furnace temperature in the furnace chamber 3 below the continuous combustion apparatus 5 at this time. FIG. 7 is a graph showing the relationship between the switching elapsed time of the combustion amount in the furnace width direction of the continuous heating furnace and the furnace temperature difference in the furnace width direction of the continuous heating furnace. The elapsed time of switching of the combustion amount in the furnace width direction on the horizontal axis in FIG. 7 is the operating time of the continuous heating furnace when the time when the heating condition of the continuous heating furnace is switched from uniform heating to gradient heating is set to 0 minutes. . Moreover, the heating furnace width direction temperature difference which is the vertical axis in FIG. 7 is the temperature difference between the maximum temperature and the minimum temperature in the furnace width direction on the conveyance path 2.

  The uniform heating is performed under the condition that the combustion amount (fuel supply amount) in each of the regions 5A to 5D of the continuous heating device 5 is the same, and the furnace temperature is set to a constant temperature along the furnace width direction (furnace The condition in which the temperature difference in the width direction is 0 ° C.). On the other hand, the gradient heating conditions are such that the combustion amount (fuel supply amount) in each of the regions 5A to 5D of the continuous heating device 5 is individually controlled so that the temperature difference in the furnace width direction is, for example, 90 ° C. It is.

  As shown in FIG. 7, immediately after switching from uniform heating to gradient heating, the temperature difference in the furnace width direction increases from 0 ° C. to 40 ° C., but thereafter, the expansion width of the temperature difference in the furnace width direction becomes gentle and the furnace interior It can be seen that it takes 90 minutes for the temperature difference in the furnace width direction to reach 90 ° C.

Moreover, in FIG. 8, the relationship between the switching elapsed time of the furnace width direction combustion amount of a continuous heating furnace and the longitudinal direction temperature difference of a to-be-heated material is shown. The horizontal axis in FIG. 8 is the same as the horizontal axis in FIG. Moreover, the to-be-heated material longitudinal direction temperature difference of the vertical axis | shaft of FIG. 8 is a temperature difference of the longitudinal direction front-end | tip part and rear-end part of the to-be-heated material immediately after extracting from a continuous heating furnace. In the gradient heating, it is necessary to obtain a temperature difference of approximately 30 ° C. or more immediately after extraction from the continuous heating furnace.
As shown in FIG. 8, immediately after switching from uniform heating to gradient heating, the temperature difference in the longitudinal direction of the material to be heated gradually increases, and it takes about 25 minutes to reach 30 ° C., which is a standard for temperature deviation. I understand that. In this embodiment, the period from immediately after switching until 25 minutes has elapsed is the switching period.

  Thus, a switching period of about 25 minutes is required from uniform heating to gradient heating with a longitudinal temperature difference of 30 ° C. or more. During this switching period, the longitudinal temperature difference is less than 30 ° C. In other words, the slab, in other words, the slab with insufficient gradient heating is extracted from the continuous heating furnace and may be rolled as it is by a finishing mill.

  In the present embodiment, the slab (rough bar) with insufficient gradient heating is heated to compensate for the insufficient heating by the induction heating device 31 disposed immediately before the finish rolling mill 21. As shown in FIG. 9, induction heating is performed on a slab (coarse bar) having a longitudinal temperature difference of less than 30 ° C. heated by a continuous heating furnace during a switching period in which the combustion amount switching time is less than 25 minutes. The longitudinal temperature difference is compensated by heating by the apparatus. On the other hand, for slabs (coarse bars) having a longitudinal temperature difference of 30 ° C. or more heated by a continuous heating furnace that has reached a steady state after a combustion amount switching time of 25 minutes or longer, the induction heating device 31 Heating is not necessary.

A specific procedure will be described below with reference to FIGS.
First, a slab with insufficient gradient heating heated by a continuous heating furnace during the switching period is rolled by a roughing mill 11 to form a rough bar, and then installed between the roughing mill 11 and the induction heating device 31. The temperature of the coarse bar is measured by the thermometer 32 along the longitudinal direction of the coarse bar. The measured data is sent to the measuring means 33 and processed into a temperature profile along the longitudinal direction of the coarse bar in consideration of the amount of temperature decrease during the transfer from the temperature measurement position to the induction heating device 31. The coarse bar at this time is a continuous heating furnace with a temperature difference in the longitudinal direction of, for example, 10 ° C., and the temperature profile is as shown by the solid line in FIG. The temperature changes so that the temperature gradually decreases over the portion.
This temperature profile is created in the measuring means 33 based on the measurement data sent from the thermometer 32 to the measuring means 33.

  On the other hand, the target temperature profile (hereinafter referred to as the target temperature profile) is constant from the front end to the rear end in the longitudinal direction of the coarse bar, for example, when the finish rolling is constant speed rolling, as indicated by the dotted line in FIG. It becomes temperature. When accelerated rolling is performed in the middle of finish rolling, processing heat generated by accelerated rolling is taken into consideration, and the target temperature profile is as shown by the dotted line in FIG. These target temperature profiles are stored in advance in the storage unit of the measuring means.

  And in the calculating part of the measurement means 33, the measured temperature profile of the rough bar is compared with the target temperature profile, and the difference between both profiles is calculated. This difference, that is, the hatched portion in FIGS. 10 and 11, is an underheating amount generated along the longitudinal direction of the coarse bar (material to be heated).

  Next, the calculated underheating amount profile is sent to the control means 34. In the control means, the heating amount by the induction heating device 31 is determined based on the profile of the insufficient heating amount. For example, in the example shown in FIG. 10, heating from the front end to the vicinity of the center in the longitudinal direction is unnecessary, but the heating amount is gradually increased from the vicinity of the center in the longitudinal direction to the rear end so as to be equal to or higher than the target temperature.

And based on the heating amount determined in the control means 34, the induction heating apparatus 31 is controlled and a rough bar is heated.
The coarse bar heated so that the longitudinal temperature difference is compensated by the induction heating device 31 is then further rolled by the finish rolling mill 21, cooled by the cooling device 42, and then rolled by the winder 43. It is wound up.

  The induction heating device 31 may be installed between the continuous heating furnace 1 and the roughing mill 11 in addition to the installation immediately before the finishing mill 21, but in the present embodiment, immediately before the finishing mill 21. It is good to install in. Since the material to be heated extracted from the continuous heating furnace 1 is in the form of a slab and has a relatively large thickness, it is difficult to raise the temperature sufficiently by the induction heating device 31. On the other hand, if it is installed immediately before the finishing mill 21, the material to be heated becomes a rough bar and the thickness is relatively small with respect to the slab, so that it can be sufficiently heated by the induction heating device 31.

  Further, the induction heating device 31 is most suitable as a heating means for heating the coarse bar. Since the induction heating device 31 has a higher heating speed and excellent response speed than other heating means, it is optimal as a means for heating a rough bar being rolled online. In addition, by controlling the amount of electric power applied to the heating coil, the heating conditions can be finely controlled, and therefore, it is suitable as a heating means for rough bars with insufficient gradient heating.

  As described above, according to the heating method of the material to be heated according to the present embodiment, the heating is insufficient with respect to the slab (coarse bar) heated during the switching period in which the heating condition is switched between uniform heating and inclined heating. Since the heating is performed by the induction heating device 31 so as to compensate the amount, the temperature profile in the longitudinal direction of the coarse bar can be corrected to the target temperature profile immediately before the finish rolling, and finish rolling in an appropriate state. It can be performed. Thereby, the rolled steel plate excellent in quality can be manufactured.

In the above embodiment, the case where the heating condition in the continuous heating furnace is switched from uniform heating to gradient heating has been described, but the present invention is not limited to this, and the heating condition in the continuous heating furnace is changed from gradient heating to uniform heating. It can also be applied to the case of switching.
Further, in the above-described embodiment, the gradient heating in which the temperature of the rear end portion of the slab is made higher than the temperature of the tip portion has been described, but the reverse gradient heating in which the temperature of the rear end portion of the slab is made lower than the temperature of the tip portion is also applied. it can.

  It should be noted that the switching of the heating conditions of the continuous heating furnace is preferably performed at a timing such that the slab during the switching period is not overheated. In other words, the switching timing from uniform heating to gradient heating to increase the temperature at the rear end of the slab is after the material to be heated is extracted from the continuous heating furnace, and the switching timing from gradient heating to uniform heating is Consider the transfer speed in the continuous heating furnace, the length of the inclined heating zone, and the time required for the transition from the inclined heating state to the uniform heating state so that the heating material is in a uniform heating state at the time of extraction. To decide. The switching timing from reverse gradient heating to uniform heating is after the reverse gradient heating material has been extracted from the continuous heating furnace, and the switching timing from reverse heating to reverse gradient heating, which lowers the temperature at the rear end of the slab. Necessary for the transfer speed in the continuous heating furnace, the length of the inclined heating zone, and the transition from the uniform heating state to the reverse inclined heating state so that the reverse inclined heating material is in the reverse inclined heating state when the reverse inclined heating material is extracted. Decide in consideration of time.

  In the continuous rolling line and the continuous heating furnace shown in FIGS. 1 to 5, a plurality of slabs having a length of 9 to 11 m, a width of 1020 to 1050 mm, and a thickness of 250 mm were heated and rolled as a material to be heated. The slab temperature when charging the continuous heating furnace was about 600 ° C., and the in-furnace time in the heating furnace was 150 minutes.

  The heating condition of the continuous heating furnace was switched from uniform heating in the middle to gradient heating in which a temperature difference of 60 ° C. was provided in the furnace width direction to heat the rear end of the slab to a high temperature. Immediately after the switching, the slab that should be heated by inclination was roughly rolled by a roughing mill into a rough bar having a length of 70 m, a width of 1000 mm, and a thickness of 33 mm. And on the entrance side of the induction heating device, the surface temperature was measured over the entire length of the coarse bar, and necessary heating was performed by the induction heating device based on the measurement result. The surface temperature of the coarse bar after heating was also measured on the exit side of the induction heating apparatus. The coarse bar after induction heating was rolled to a sheet thickness of 2.5 mm with a finish rolling mill, cooled with a cooling device, and then wound with a winding device to form a coil. For comparison, the slab extracted next was not subjected to induction heating, and was rolled under the same other rolling conditions as a coil.

  FIG. 12 shows the temperature measurement result on the induction heating apparatus outlet side, and FIG. 13 shows the measurement result of the finish rolling end temperature. By heating the insufficient heating on the rear end side of the coarse bar with an induction heating device, the target finish rolling temperature can be satisfied over the entire length of the coil. On the other hand, in the comparative material that was not subjected to induction heating, there was a portion that could not satisfy the finish rolling finishing temperature required after the rear end side 700 m of the coil.

  As is apparent from the present example, according to the heating method of the present invention, it is understood that the temperature of the coarse bar can be corrected by the induction heating device during the switching period of the heating condition of the inclined heating zone of the continuous heating furnace.

Drawing 1 is a mimetic diagram showing the continuous rolling equipment which is an embodiment of the present invention. FIG. 2 is a schematic perspective view showing a combustion heating furnace provided in the continuous rolling facility of FIG. FIG. 3 is a schematic side view of a combustion heating furnace provided in the continuous rolling facility of FIG. 4 is a schematic plan view of a combustion heating furnace provided in the continuous rolling facility of FIG. FIG. 5 is a schematic cross-sectional view corresponding to the line A-A ′ of FIG. 4. FIG. 6 is a graph showing the relationship between the ratio of the arrangement length of the continuous combustion apparatus to the total furnace length of the combustion heating furnace and the longitudinal temperature difference deviation of the material to be heated. FIG. 7 is a graph showing the relationship between the switching elapsed time of the combustion amount in the furnace width direction of the combustion heating furnace and the furnace temperature difference in the furnace width direction of the combustion heating furnace. FIG. 8 is a graph showing the relationship between the switching elapsed time of the combustion amount in the furnace width direction of the combustion heating furnace and the longitudinal temperature difference of the material to be heated. FIG. 9 is a graph showing the relationship between the switching time of the combustion amount in the furnace width direction of the combustion heating furnace and the temperature difference in the longitudinal direction of the material to be heated, and shows the relationship between the gradient heating switching period and the gradient heating steady period. It is a graph. FIG. 10 is a graph showing the relationship between the temperature distribution profile of the material to be heated and the target temperature distribution profile when the finish rolling is constant speed rolling. FIG. 11 is a graph showing the relationship between the temperature distribution profile of the material to be heated and the target temperature distribution profile when finish rolling is accelerated rolling. FIG. 12 is a graph showing the temperature measurement results on the exit side of the induction heating device of the coarse bar of Example 1 and Comparative Example 1. FIG. 13 is a graph showing measurement results of finish rolling end temperatures of Example 1 and Comparative Example 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Combustion heating furnace, 1A ... Charge part, 1B ... Extraction part, 2 ... Conveyance path, 4 ... Regenerative combustion apparatus, 5 ... Continuous combustion apparatus, 11 ... Rough rolling mill, 21 ... Finish rolling mill, 31 ... Induction heating furnace, 32 ... thermometer, 33 ... measuring means, 34 ... control means, 101 ... continuous rolling equipment

Claims (4)

A continuous heating furnace in which the material to be heated is inserted so that the longitudinal direction of the material to be heated is orthogonal to the conveying direction of the conveying path provided in the heating furnace, and the heated material is heated while being conveyed along the conveying path. And a continuous heating furnace provided with a heating zone in which the heating condition in the furnace width direction can be selectively switched to uniform heating or inclined heating in the middle of the conveying path to the extraction section, and immediately before the finishing mill A heating method of a material to be heated using an induction heating device arranged in
Along the longitudinal direction of the material to be heated heated by the continuous heating furnace during the switching period in which the heating condition of the switchable heating zone of the continuous heating furnace is switched between uniform heating and inclined heating. The heating material is heated by the induction heating device so as to compensate for the insufficient heating amount generated by heating. The induction heating apparatus disposed in front of the roughing mill and the finishing mill is roughly rolled by a roughing mill installed at a subsequent stage of the continuous heating furnace, to be heated by the continuous heating furnace. And measure the temperature distribution in the longitudinal direction of the material to be heated,
By comparing the measured temperature distribution profile of the heated material with the target temperature distribution profile, the underheating amount is calculated along the longitudinal direction of the heated material, and the measured underheating amount is calculated. The method for heating a material to be heated according to claim 1, wherein the material to be heated is heated by the induction heating device so as to compensate. The continuous heating furnace is on both sides of the conveying path of the material to be heated and is located on the upper side of the conveying path, and a plurality of regenerative combustion apparatuses for alternating combustion disposed between the charging section and the extracting section. A plurality of continuous arrangements from the middle of the conveying path to the extraction unit, and arranged in a plurality of regions divided along the furnace width direction, each of which can control the amount of combustion Comprising a continuous combustion device of
By adjusting the amount of combustion of the plurality of continuous combustion devices and controlling the temperature distribution in the furnace width direction in the continuous heating furnace, the heating condition for the material to be heated is selected to be uniform heating or gradient heating The method for heating a material to be heated according to claim 1, wherein the heating material is switchable automatically.   The timing for switching the heating condition of the heating zone of the continuous heating furnace between uniform heating and inclined heating is controlled so that the heated material is not overheated. The heating method of the to-be-heated material of description.

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