JP5000116B2 - Soaking furnace operation method in steel strip continuous treatment equipment - Google Patents

Description

This invention also relates to the soaking furnace operation how the continuous annealing facility or a continuous hot-dip plating equipment.

  In a soaking furnace such as a continuous annealing furnace for steel strips or continuous hot dipping plating equipment, steel strips are produced while changing the treatment temperature in a wide temperature range according to the heat treatment cycle of the steel strip. The steel strip temperature in the soaking furnace is changed by changing the steel strip temperature at the inlet of the soaking furnace by adjusting the heating or cooling conditions of the soaking furnace and by changing the soaking furnace temperature.

  The steel strip temperature at the inlet of the soaking furnace can usually be changed in a short time, and the furnace temperature of the soaking furnace can also be changed in a relatively short time. However, the steel strip transport roll in the soaking furnace has a large roll thickness and a large heat capacity from the viewpoint of heat resistance, and therefore the temperature change is slow. For this reason, when the heat treatment cycle is changed, a temperature difference is temporarily generated between the steel strip, the soaking furnace, and the transport rolls.

  For example, when trying to raise the steel strip temperature in the soaking furnace, the steel strip at the inlet of the soaking furnace is first heated to the predetermined temperature after the change, and then the temperature in the soaking furnace is raised. Thereafter, since the transport roll is heated by contact heat transfer from the heated steel strip, the temperature rise is delayed from the temperature rise of the steel strip. Furthermore, the roll center is in contact with the steel strip, but the unrolled roll end is heated by radiation from the furnace body, heat transfer from the furnace atmosphere gas, or heat conduction from the roll center. The heating rate is very slow. That is, in the steel strip temperature rising process in the soaking furnace, the temperature of each part is steel strip temperature> furnace temperature> roll center temperature> roll end temperature, and these temperature differences are inevitable. Even in the temperature reduction process of the steel strip in the soaking furnace, the steel strip temperature <the temperature in the furnace <the temperature at the center of the roll <the temperature at the end of the roll, and a temperature difference occurs.

In the soaking furnace, a. The steel strip temperature at the outlet of the soaking furnace does not reach the specified temperature due to heat transfer between the steel strip and roll b. The problem was that the steel strip meandered or squeezed due to the thermal crown of the roll. In particular, in a facility for processing various types of steel strips including high-strength steel strips, the heat treatment cycle is frequently changed. Therefore, the above problem has a serious effect on product quality and productivity.
Patent Document 1 discloses an invention of cooling or heating from the inside of a roll as a crown control method for a hearth roll. Patent Document 2 discloses an invention in which a hearth roll is placed in a roll chamber and a gas having the same temperature as that of the strip is blown into the roll chamber to prevent thermal deformation of the roll. Neither of them takes into account the control of the temperature of the steel strip, so that the response to the change in temperature was not accelerated, particularly when the heat treatment cycle was changed.

Conventionally, the following techniques have been used as means for solving the problems caused by the temperature difference.
1. Reduce the temperature increase or decrease rate of the steel strip to keep the temperature difference from causing problems. In this method, meandering and throttling do not occur by suppressing the temperature difference. However, it takes a long time to raise and lower the temperature of the steel strip, resulting in a problem that productivity and quality are lowered.
2. The atmosphere gas in the soaking furnace is adjusted to a temperature equal to the steel strip temperature, the temperature difference between the roll and the steel strip is reduced, and the thermal crown of the roll is prevented. In this method, the temperature difference between the roll center and the roll end is slightly reduced, and the meandering and drawing are slightly improved. However, since the temperature difference between the roll having a large thermal inertia and the steel strip does not disappear at the time of the heat cycle transition, it takes a long time to raise and lower the steel strip, and the productivity and quality are lowered.
3. An induction heating device is provided inside the transport roll. In this method, the temperature difference between the roll and the steel strip is eliminated, but the equipment cost becomes enormous, and the heat resistance of the induction heating device is as low as about 450 ° C., so the production type is limited.
JP-A-7-145424 Japanese Patent Publication No. 6-19120

That is, when the temperature of the soaking furnace is changed, the temperature difference in the soaking furnace, the steel strip, the center of the roll, and the end of the roll are caused, and in order to eliminate this temperature difference. There was a problem that productivity was lowered because it took a long time, and a problem that quality such as meandering and squeezing was lowered due to this temperature difference.
This invention solves the said problem, and makes it a subject to provide the soaking furnace operating method and soaking furnace in the continuous processing equipment of the steel strip which can aim at the improvement of product quality and productivity.

(1) The soaking furnace operating method in the steel strip continuous treatment facility of the present invention is a soaking furnace operating method in a steel strip continuous treatment facility in which the steel strip is continuously processed while being transported by a transport roll. Heating or cooling in the steel strip heating furnace or cooling furnace adjacent to the soaking furnace inlet while uniformly heating or cooling the entire width toward the temperature of the soaking furnace after changing the transport roll during steel strip transport The steel strip is uniformly heated or cooled over the entire width so as to be equal to the roll temperature of the steel, and the conveying roll is heated or cooled by spraying a heating gas or a cooling gas over the entire width of the outer circumferential surface or inner circumferential surface of the hollow conveying roll. The heating or cooling speed is 4.7 to 10 ° C./min.

(2) The heating gas or the cooling gas is a gas obtained by heating or cooling the atmospheric gas in the furnace by the atmospheric gas heating apparatus or the atmospheric gas cooling apparatus outside the furnace. Furnace operation method.

(3) The soaking furnace operating method in the steel strip continuous processing facility according to (1) or (2), wherein the steel strip is heated with an induction heater in the steel strip heating furnace.

According to this invention,
A. The steel strip temperature at the outlet of the soaking furnace can be heated or cooled to the target temperature in a short time (for example, about 10 minutes compared to about 1.5 to 4 hours in the past). Small variation in steel strip temperature at the soaking furnace outlet c. The meandering and drawing of the steel strip disappears. It is possible to suppress an increase in equipment cost (for example, about 50% reduction compared to the case where a heating device is provided inside the transport roll), and to improve product quality and productivity. it can.

  FIG. 1 shows an example of a continuous annealing facility in which the present invention is implemented, and is a schematic view of a furnace body. The furnace body 1 includes a heating furnace 2, a primary soaking furnace 4, a secondary soaking furnace 5, a primary cooling furnace 6, a reheating furnace 7, a resoaking furnace 8, and a secondary cooling furnace 9. The entrance side of the furnace body 1 is connected to the entrance facility via an entrance looper. The entry-side equipment consists of a pay-out reel, a welding machine, a cleaning device (all not shown) and others. On the exit side of the furnace body 1, a final cooling facility or a hot dipping bath, an alloying furnace, a temper rolling mill, an exit side looper, a flaw inspection device, a take-up reel, etc. (all not shown) are provided. .

  A case where the present invention is carried out in the reheating furnace will be described as an example. FIG. 2 is a schematic view of the reheating furnace 8 (hereinafter simply referred to as a soaking furnace) and its attached equipment. In the following description, the same devices as those shown in FIGS. 1 and 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the soaking furnace 8, a plurality of upper transport rolls 12 and a steering roll 14 are disposed near the top of the furnace, and a plurality of lower transport rolls 13 are disposed near the bottom of the furnace. A bridle roll 16 is disposed in the primary cooling furnace outlet roll chamber 37 of the primary cooling furnace 6, and an upper transport roll 18 is disposed in the upper roll chamber 10 of the secondary cooling furnace 9. The steel strip S is wound around the bridle roll 16, the upper transport roll 12, the lower transport roll 13, the steering roll 14 and the upper transport roll 18 in order and transported.

  As shown in FIG. 3, a plurality of roll temperature detectors (thermocouples) 81 are attached to the inner peripheral surfaces of the transport rolls 12, 13, and 14 along the roll axis direction. A temperature detection signal from the roll temperature detector 81 is output to a control device 80 described later via a slip ring 82.

  The soaking furnace 8 is provided with an atmospheric gas circulation blower 20. The atmospheric gas circulation blower 20 has an intake side communicating with the furnace, and a circulation gas main pipe 22 connected to the exhaust side. An atmospheric gas cooling device 50 and an atmospheric gas heating device 60 are sequentially attached to the circulation gas main pipe 22, and a cooling bypass pipe 24, a cooling bypass valve 25 for bypassing the atmospheric gas cooling device 50, and atmospheric gas heating A heating bypass pipe 27 and a heating bypass valve 28 for bypassing the device 60 are connected.

  First to fifth branch pipes 31 to 35 are connected to the downstream side of the atmospheric gas heating device 60. The first to fifth branch pipes 31 to 35 approach the vicinity of each roll outside the furnace, the tips of the first, second and third branch pipes 31 to 33 are in the soaking furnace 8, and the tip of the fourth branch pipe 34 is In the primary cooling furnace outlet side bridle roll chamber 37, the tip of the fifth branch pipe 35 is located in the secondary cooling furnace upper transport roll chamber 10, respectively. First to fifth gas flow rate adjusting valves 41 to 45 are attached to the first to fifth branch pipes 31 to 35, respectively.

  The atmospheric gas cooling device 50 is provided with a gas cooling temperature adjustment valve 55 and a gas cooling heat exchanger 51. A cooling device outlet side gas temperature detector (thermocouple) 86 and a cooling outlet side shutoff valve 57 are attached to the outlet of the gas cooling heat exchanger 51. The gas cooling heat exchanger 51 includes a cooling pipe 53 to which cooling water is supplied from a cooling water pump 52.

  The atmospheric gas heating device 60 is provided with a heat exchanger 61 for gas heating. A gas heating temperature adjusting valve 67 is attached to the inlet of the gas heating heat exchanger 61, and a heating outlet side shutoff valve 68 and a heating device outlet side gas temperature detector (thermocouple) 87 are respectively attached to the outlet. The gas heating heat exchanger 61 includes a fuel gas combustion device 62, and the fuel gas supplied to the fuel gas combustion device 62 is burned by the combustor 63. Combustion air is supplied from the combustion air blower 64, and the combustion gas passes through the heating pipe 65 and the atmosphere gas is heated by the gas heating heat exchanger 61.

  A gas spray nozzle 71 is disposed immediately below the upper transport roll 12 and the steering roll 14, and a gas spray nozzle 72 is disposed directly above the lower transport roll 13. The gas spray nozzles 71 and 72 are slit nozzles. These gas spray nozzles 71 and 72 protrude from the header 73 as shown in FIGS. 3 and 4 and face the bottom and top portions of the outer peripheral surfaces of the transport rolls 12 and 13 and the steering roll 14, respectively. It extends over the entire length. The header 73 is connected to the first and second branch pipes 31 and 32, respectively.

  The gas spray nozzles 71 and 72 may be disposed inside the transport rolls 12 and 13 and the steering roll 14 as shown in FIGS. In this case, the gas spray nozzles 71 and 72 face the bottoms of the inner peripheral surfaces of the transport rolls 12 and 13 and the steering roll 14.

  As with the transport rolls 12, 13 and the steering roll 14, a gas spray nozzle 75 is applied to the bridle roll 16 of the primary cooling furnace outlet roll chamber 37, and a gas spray is applied to the upper transport roll 18 of the secondary cooling furnace upper roll chamber 10. The attachment nozzles 77 are respectively arranged. A plurality of headers (not shown) are connected to the third branch pipe 33, and a plurality of in-furnace gas ejection nozzles 74 are provided in each header along the furnace width direction. The furnace atmosphere temperature is adjusted by the gas ejected from the furnace gas ejection nozzle 74.

  The reheating furnace 7 is provided with an induction heater 39 for heating the steel strip S being conveyed. Steel strip temperature detectors (radiation thermometers) 84 and 85 for measuring the temperature of the steel strip S being conveyed are arranged at the entrance of the soaking furnace.

  The soaking furnace 8 includes a control device 80 for controlling the temperature of the steel strip S and the transport rolls 12 and 13, the steering roll 14, the bridle roll 16, and the upper transport roll 18. The control device 80 controls the temperature and flow rate of the gas supplied to the gas spray nozzles 71, 72, 74, 75, 77 based on the measured temperatures of the steel strip S and the other rolls of the transport rolls 12, 13, the induction heater 39. Control the output of. It also controls the opening and closing of the gas cooling temperature adjusting valve 55, the gas heating temperature adjusting valve 67, and other adjusting valves and shut-off valves.

  Here, an operation method of the soaking furnace 8 configured as described above, particularly temperature control at the time of switching the heat treatment cycle will be described. In the continuous annealing equipment, the heat treatment temperature varies depending on the material and dimensions of the steel strip to be treated, the final product (cold-rolled steel plate or hot-dip steel plate), and the heat treatment cycle is switched. In the soaking furnace 8 of the present invention, when the heat treatment cycle is switched, the atmospheric gas is heated or cooled, and the temperature in the furnace, the steel strip, and each roll are gradually raised or lowered to a predetermined temperature.

  Now, the temperature in the furnace, the steel strip, and each roll is increased to a predetermined temperature. Usually, the atmospheric gas circulation blower 20 is operated, and the first to fifth gas flow rate adjusting valves 41 to 45 are opened at a certain opening degree. In this state, the gas cooling temperature adjustment valve 55, the cooling outlet side cutoff valve 57, and the heating gas bypass valve 28 of the atmospheric gas cooling device 50 are closed, and the cooling bypass valve 25, the gas heating temperature adjustment valve 67, and the heating outlet side cutoff valve 68 are closed. open. At the same time, the fuel gas is supplied to the fuel gas combustion device 62 of the atmospheric gas heating device 60, the combustion air blower 64 is driven to supply the combustion air, and the fuel gas is combusted in the fuel gas combustor 63. The high-temperature combustion gas passes through the heating pipe 65 and heats the atmospheric gas to obtain a heating gas having a predetermined temperature. The heated gas is ejected from the gas spray nozzles 71, 72, 75, 77 and the furnace gas ejection nozzle 74 through the circulation gas main pipe 22, the branch pipes 31 to 35, and the header 73.

  The heated gas from the gas spray nozzles 71 and 72 is sprayed over the entire width of the roll to the bottom of the outer peripheral surface of the upper transport roll 12 and the steering roll 14 and the top of the lower transport roll 13. Since the transport rolls 12 and 13 and the steering roll 14 are rotating, heated gas is blown over the entire outer peripheral surface. Similarly, the heated gas is blown from the gas blowing nozzle 75 to the bridle roll 16 of the primary cooling furnace outlet roll chamber 37 and from the gas blowing nozzle 77 to the upper transport roll 18 of the secondary cooling furnace upper roll chamber 10. It is done. Further, the heated gas is ejected from the in-furnace gas ejection nozzle 74 into the furnace. As described above, the heated gas is blown over the entire width of the roll and is also ejected into the furnace, so that the roll being transported by the steel strip is uniformly heated to the predetermined temperature over the entire width.

  Since each roll is directly heated by a high-temperature heating gas, it is heated at a high temperature rising rate of 10 ° C./min, for example. On the other hand, the steel strip S is heated or cooled so as to be equal to the roll temperature as shown in FIG. 7 in a heating furnace or a cooling furnace adjacent to the soaking furnace inlet in order to prevent a temperature difference with the roll.

  The control device 80 adjusts the combustion gas supply amount by controlling a flow rate adjustment valve (not shown) of the fuel gas combustion device 62 based on the target roll temperature, the roll temperature measurement value, and the heating device outlet side gas temperature measurement value. Then, the combustion air blower 64 is controlled to adjust the amount of combustion air, or the opening of the gas heating temperature adjustment valve 67 is adjusted to control the gas heating temperature. The roll temperature is controlled by the gas heating temperature. Further, the control device 80 controls the steel strip temperature at the soaking furnace so that the steel strip temperature becomes equal to the roll temperature.

  Next, the case where the temperature in the furnace, the steel strip, and each roll is lowered to a predetermined temperature will be described. The gas cooling temperature adjustment valve 55, the cooling outlet side shutoff valve 57 and the heating bypass valve 28 of the atmospheric gas cooling device 50 are opened, and the cooling bypass valve 25, the gas heating temperature regulating valve 67 and the heating outlet side shutoff valve 68 are closed. At the same time, the cooling water pump 52 is driven to supply cooling water to the cooling pipe 53. The cooling water cools the atmospheric gas passing through the cooling pipe 53 to a cooling gas having a predetermined temperature. The cooling gas is ejected from the gas spray nozzles 71, 72, 75, 77 and the in-furnace gas ejection nozzle 74 through the circulation gas main pipe 22, the branch pipes 31 to 35, and the header 73.

  The cooling gas is ejected from each nozzle as in the case of heating to cool each roll and cool the inside of the furnace. Since each roll is directly cooled by a low-temperature cooling gas, it is cooled at a rapid temperature drop rate of 10 ° C./min, for example. On the other hand, the steel strip S is cooled in the primary cooling furnace 6 so as to be equal to the roll temperature in order to prevent a temperature difference from the roll.

  The control device 80 controls the gas cooling temperature by adjusting the opening of the gas cooling temperature adjustment valve 55 based on the target roll temperature, the roll temperature measurement value, and the cooling device outlet side gas temperature measurement value. The roll temperature is controlled by the gas cooling temperature. Further, the control device 80 controls the steel strip temperature at the soaking furnace so that the steel strip temperature becomes equal to the roll temperature.

Example 1
In the equipment shown in FIG. 2, the temperature transition at the time of switching the heat treatment cycle was tested. The steel plate is a cold-rolled steel plate, and the material is a transition from a 1470 MPa class high-tensile steel plate (HITEN) to a 590 MPa class work-induced transformation type high strength steel (TRIP high tensile steel), the plate thickness is 1.0 mm, and the plate width is 1700 mm. It is. The steel sheet is heated from 250 ° C. to 390 ° C. (temperature difference 140 ° C.), and the temperature is decreased from 390 ° C. to 250 ° C. The test results are shown in FIGS. 8 (a) and (b). In the prior art, this cycle transition took 6 hours, but as is apparent from FIG. 8, the thermal cycle could be switched within 30 minutes. Note that meandering, drawing, etc. did not occur during this test. Also, the material was as specified and homogeneous.

(Example 2)
In the equipment shown in FIG. 2, the temperature transition at the time of switching the heat treatment cycle was tested. The steel plate is a hot-dip plated steel plate, and the material is a transition from 590MP class high tensile steel to 590MP class TRIP high tensile steel, the plate thickness is 1.0 mm, and the plate width is 1700 mm. The steel sheet is heated from 415 ° C. to 570 ° C., and the temperature is decreased from 570 ° C. to 415 ° C. The test results are shown in FIGS. 9 (a) and 9 (b). In the prior art, this cycle transition took 6 hours, but as is apparent from FIG. 9, the thermal cycle could be switched within 30 minutes.
In addition, the conventional method takes about 150 minutes at 60 ° C., which is the maximum temperature difference in normal heat treatment cycle switching. However, in this method, switching is possible in 10 minutes or less, and if the time is as short as 10 minutes, Since steel strips of steel grades that are not sensitive to heat treatment cycles can be inserted and products can be manufactured even during switching times, product quality and productivity are greatly improved. Note that meandering, drawing, etc. did not occur during this test. Also, the material was as specified and homogeneous.

An example of the continuous annealing equipment in which this invention is implemented is shown, and it is the schematic of a furnace main-body part. It is a furnace block diagram which shows typically the soaking furnace of the continuous annealing furnace shown in FIG. It is roll sectional drawing which shows typically an example of the conveyance roll and gas spray nozzle of the said soaking furnace. It is a side view of the conveyance roll of FIG. 3, and a gas spray nozzle. It is roll sectional drawing which shows the other example of a conveyance roll and a gas spray nozzle typically. It is a longitudinal cross-sectional view of the conveyance roll shown in FIG. It is a graph which shows the time change of steel strip temperature and conveyance roll temperature. It is a graph which shows the result of having simulated the time change of the heating gas temperature in a cold-rolled steel plate manufacturing process, the conveyance roll temperature, and the furnace temperature. It is a graph which shows the result of having simulated the time change of the heating gas temperature in a hot-dip-plated steel plate manufacturing process, a conveyance roll temperature, and the furnace temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Furnace main part of a continuous annealing furnace 2 Heating furnace 4 Primary soaking furnace 5 Secondary soaking furnace 6 Primary cooling furnace 7 Reheating furnace 8 Reheating furnace 9 Secondary cooling furnace 10 Secondary cooling furnace upper roll chamber 12, DESCRIPTION OF SYMBOLS 13, 18 Conveyance roll 14 Steering roll 16 Bridle roll 20 Atmospheric gas circulation blower 22 Circulation gas main pipe 24 Cooling bypass valve 25 Cooling bypass valve 27 Heating bypass pipe 28 Heating bypass valve 31-35 Branch pipe 37 Primary cooling furnace exit side roll chamber 39 Induction heaters 41 to 45 Gas flow rate adjustment valve 50 Atmospheric gas cooling device 51 Gas cooling heat exchanger 52 Cooling water pump 53 Cooling pipe 55 Gas cooling temperature adjustment valve 57 Cooling outlet side shutoff valve 60 Atmospheric gas heating device 61 For gas heating Heat exchanger 62 Fuel gas combustion device 63 Fuel gas combustor 64 Air blower for combustion 65 Heating pipe 67 Gas heating temperature Adjustment valve 68 Heating outlet side shut-off valve 71, 72, 75, 77 Gas spray nozzle 73 Nozzle header 74 In-furnace gas ejection nozzle 80 Control device 81 Roll temperature detector 82 Slip ring 84, 85 Steel strip temperature detector 86 Cooling device Outlet gas temperature detector 87 Heating device outlet gas temperature detector

Claims (3)

In a soaking furnace operating method in a steel strip continuous treatment facility that continuously treats steel strips while transporting them with transport rolls, when changing the heat treatment cycle, the transport rolls during transport of steel strips are changed to the temperature of the soaking furnace While heating or cooling uniformly over the entire width, the steel strip is heated or cooled uniformly over the entire width so as to be equal to the roll temperature during heating or cooling in the steel strip heating furnace or cooling furnace adjacent to the soaking furnace inlet. The heating roll or cooling gas is blown over the entire width or width of the outer circumferential surface or inner circumferential surface of the hollow conveyance roll to heat or cool the conveyance roll, and the heating or cooling speed is 4.7 to 10 ° C./min. The soaking furnace operating method in the steel strip continuous processing equipment. The soaking furnace operating method in the steel strip continuous processing facility according to claim 1, wherein the heating gas or the cooling gas is a gas obtained by heating or cooling the atmospheric gas in the furnace by an atmospheric gas heating device or an atmospheric gas cooling device outside the furnace. . The soaking furnace operating method in the steel strip continuous processing equipment according to claim 1 or 2, wherein the steel strip is heated by an induction heater in the steel strip heating furnace.

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