JP2005220432A - Plate temperature cooling control method in cooling zone of continuous steel plate heat treatment equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plate temperature cooling control method in a cooling zone capable of suppressing insufficient cooling or supercooling of a steel plate traveling through the cooling zone of a continuous heat treatment equipment. <P>SOLUTION: In the plate temperature cooling control method to perform feed-forward control of the number of rotations of a cooling blower 4 by interlocking the plate passing schedule with information on the target plate temperature on the cooling zone inlet side, the target plate temperature on the cooling zone outlet side, the plate thickness, the plate width and the plate passing speed during the actual operation, and information on the welding point tracking, the plate thickness measured by a plate thickness meter 10 is taken in before the steel plate 1 is introduced in the cooling zone 2, the mean actual plate thickness is calculated for each divided section of the coil, and the mean actual plate thickness is used for the operation of the number of rotation of the blower for the plate temperature control during the feed-forward operation when the steel plate 1 is cooled by the cooling blower 4 in the cooling zone 2 of the continuous heat treatment equipment of the steel plate. The heat balance of the cooling zone 2 such as the cooling heat-removal amount of the steel plate 1, the furnace body heat radiation amount, and the heat exchange in a heat exchanger 6 is calculated, and the constant resolution of the number of rotations of the blower which must be stabilized when the temperature is converged to the plate temperature on the target output side is operated in advance to form the command value of the number of rotations of the blower. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a plate temperature cooling control method in a cooling zone of a continuous heat treatment facility for steel plates.

  Continuously heat-treating a steel plate by running a continuous heat treatment facility equipped with a heating zone, a cooling zone, and the like is performed. Among them, the control of the plate temperature in the cooling zone is disclosed in, for example, Patent Document 1 and Patent Document 2.

  In Patent Document 1, when changing the plate thickness of a steel plate, the rate of change of the cooling load is calculated from the rate of change of the plate thickness, and feedforward control is performed. Moreover, in patent document 2, the stable passage discriminating device sorts out the stable pass plate control data from the pass plate record data, and uses it for the correction of the feedforward control.

  FIG. 5 is a system diagram for cooling control of a conventional steel sheet. In FIG. 5, a cooling wind box 3 for cooling the traveling steel plate 1 is disposed in a cooling zone 2 for cooling the steel plate 1, and cooling gas is injected from the cooling wind box 3 by the cooling blower 4. The injected gas is discharged to the duct 5, cooled by the heat exchanger 6 in the middle of the duct, and circulated to the cooling zone 2 by the cooling blower 4. A cooling zone exit side plate thermometer 7 is arranged on the exit side of the cooling zone 2 and a cooling zone entrance side plate thermometer 8 is arranged on the entry side to detect the plate temperature.

The cooling control of the plate temperature is performed by changing the rotation speed of the cooling blower 4. The blower rotation speed is changed by feedforward control based on the deviation between the target plate temperature and the actual plate temperature in the cooling zone and the process computer 9, welding point tracking information (plate passing speed, welding point position), and plate passing schedule information (steel type). , Nominal plate thickness, plate width, plate passing speed, cooling zone inlet side temperature, cooling zone outlet side target temperature), plate thickness control model, nominal plate thickness, plate width, target plate temperature, line speed change amount Using the change rate as a parameter, feedforward control is performed in which the blower rotational speed calculator 9 calculates the amount of change in the blower rotational speed.
JP-A-6-212281 JP 2000-239748 A

  In steel plate temperature control, the target plate temperature and plate passing speed are changed when passing through welding points where steel plates with different nominal plate thickness, heat treatment temperature, and plate passing speed are continuously passed through the cooling zone. When this is done, feedforward control is performed to calculate the amount of change in the blower rotational speed using parameters such as nominal plate thickness, plate width, target plate temperature, line speed change amount and change rate as parameters. And the plate | board thickness value used for plate | board temperature control is a nominal plate | board thickness which the process computer recognizes as a plate-feeding schedule. As described above, in conventional feedforward, a model that calculates the amount of change in the blower rotation speed from the amount of change in nominal plate thickness, plate width, target plate temperature, and plate feed speed is common, and the actual plate temperature is the target. It is not based on the calculation of the equilibrium heat balance of the entire cooling zone in the steady state in thermal equilibrium when it converges to the plate temperature.

  Further, in general, the time until the change of the blower rotation speed is reflected in the change of the steel plate temperature is only the rotation speed change time and the duct length until the cooling gas reaches the steel plate in the cooling zone, and the response is fast.

However, considering the layout of the cooling windbox, that is, the length of the cooling zone and the distance to the outlet side thermometer, after confirming the actual plate temperature in which the change in the rotational speed command is reflected in the plate temperature change, Since the blower rotation speed change timing is set so that the rotation speed command can be calculated, although the response is fast, the blower rotation speed setting change timing is longer, and it takes several minutes to converge to the target plate temperature. It may be necessary (see the conventional example in FIG. 4).

  In Patent Document 1, when changing the plate thickness of the steel sheet, the change rate of the cooling load is calculated from the change rate and feedforward control is performed. However, the amount of change in the blower rotation speed with respect to the plate thickness change rate depends on the plate thickness range. Since it is not uniform, it is difficult for the predictive control based on the plate thickness changing efficiency to accurately match the target plate temperature from the leading edge of the succeeding material. In addition, the tip and tail ends of steel sheet coils tend to have larger errors within the plate thickness tolerance than the center of the coil. Make it difficult.

  The tolerance of the nominal thickness of the cold-rolled steel sheet specified by JIS depends on the nominal thickness and width, but is specified within a maximum error range of ± 5% to 15%. Further, the thickness tolerance of the hot-rolled steel sheet is larger than that of the cold-rolled steel sheet, and is defined within a maximum error range of about ± 7% to 15% even when viewed from a plate size that can be passed through a continuous annealing furnace. Normally, the plate temperature control uses the nominal plate thickness recognized in the plate passing schedule for the plate temperature control model. However, since the amount of heat to be removed from the steel plate is proportional to the plate thickness, the actual amount of heat removed from the steel plate to achieve a predetermined plate temperature is the removal of the steel plate with the nominal plate thickness recognized by the plate temperature control model. There will be a maximum error of ± 5 to 15% with respect to the amount of heat.

FIG. 3 is a graph showing the plate thickness and the cooling load, that is, the rotational speed of the cooling blower in a steady plate-passing state in which heat balance is achieved, that is, in an equilibrium state. Here, for simplification, the cooling zone inlet side plate temperature is constant, the plate passing speed is constant, and the plate width is constant. In FIG. 3, T ₁ and T ₂ are curves with a constant cooling zone outlet side plate temperature, and here, T ₁ <T ₂ , so that the rotational speed of the blower is larger in T ₁ . _T 1high, T 2high the steel sheet of each nominal thickness is the rotational speed of the cooling blower for cooling home use side plate temperature with each _T 1, _{T 2} in the case of maximum thickness within the allowable board thickness range specified in JIS It is a curve. T _1low and T _2low are the rotation speed curves of the cooling blower where the cooling _{zone outlet} side plate temperatures are respectively T ₁ and T ₂ when the thickness is minimum.

As an example, cooling control before and after the welding point is considered for a preceding material having a nominal thickness t ₁ and an actual thickness t _1a , and a succeeding material having a nominal thickness t ₂ and an actual thickness t _2a (t _1a <t ₁ , t _2a > t ₂ ). Cooling home use side plate temperature is no different in both T ₁ before and after the welding point. From the graph, the blower rotational speed must be changed from R _1a to R _2a , but since the plate temperature control model recognizes the nominal plate thicknesses t ₁ and t ₂ , the amount of change in the blower rotational speed Is the difference ΔR between R ₂ and R ₁ . Accordingly, R _1a + ΔR becomes a command value for the blower rotational speed calculated by feedforward control, and cooling is insufficient, so that the plate temperature is cooled only to T ₂ higher than T ₁ .

  On the contrary, in the welding point where the preceding material thicker than the nominal plate thickness and the subsequent material thinner than the nominal plate thickness are connected, the leading edge of the subsequent material is overcooled.

  Moreover, in patent document 2, although the data at the time of stable passage are selected with the stable state discriminator and the stable passage control data are used for feedforward correction, it is difficult to determine the stable state, At the initial stage of new construction, stable data is not collected and predictive control does not work well. In recent multi-product production, there are many changes in the heat cycle by changing the steel type, and there are various types of steel, plate thickness, plate width, plate passing speed, etc., and there is a problem that stable data cannot be accumulated easily.

  Therefore, the present invention provides a plate temperature cooling control method in a cooling zone that can suppress insufficient cooling or overcooling of a steel plate traveling in a cooling zone of a continuous heat treatment facility.

  In the cooling zone of the steel plate continuous heat treatment facility, the present invention is designed to cool the steel plate with a cooling blower, and the cooling plate inlet side target plate temperature, the cooling zone outlet side target plate temperature, the plate thickness, and the plate width in the actual operation. In the plate temperature cooling control method in the cooling zone of the continuous heat treatment equipment for the steel plate, the rotation speed of the cooling blower is feedforward controlled in conjunction with the information on the plate passing speed and the welding point tracking information. Takes the measured thickness value measured by the thickness gauge before being introduced, calculates the average actual thickness for each division of the number of coils, and calculates the average actual thickness in the feedforward calculation, the blower rotation speed calculation for the plate temperature control In addition, the heat balance calculation of the cooling zone, such as the amount of heat removed from the steel sheet, the amount of heat dissipated in the furnace, and the heat exchange in the heat exchanger, is performed, and the blower rotation speed that should be stabilized when it converges to the target outlet plate temperature Calculate the solution in advance Characterized by a rotation speed command value.

  In the present invention, since the average rotational plate thickness is used instead of the calculation based on the nominal plate thickness for the blower rotational speed calculation, the controllability of the feedforward control is improved and the deviation of the plate temperature immediately after the welding point is reduced. Also, the plate temperature converges faster in the plate temperature control transition period such as when the set plate temperature is changed or when the plate passing speed is changed.

  In the present invention, first, the output of an on-line sheet thickness meter installed on the entrance side of the annealing furnace of the continuous heat treatment equipment is always taken into the process computer, interlocked with the welding point tracking, the coil is virtually divided into several parts, The average actual plate thickness of the division is calculated. Sheet thickness measurement is not limited to the entrance side of the annealing furnace of the continuous heat treatment equipment, but the measured values of the thickness gauges installed on the cold-rolling line and the exit side of the hot-rolling line are the coil information. You may take in and control. Then, when entering the feedforward calculation, the average actual plate thickness obtained from the measured value of the plate thickness meter is used for the plate temperature control, not the nominal plate thickness conventionally used.

  Furthermore, the plate temperature converged to the target plate temperature and stabilized from the cooling load of the steel plate to be passed (cooling zone entry side plate temperature, cooling zone exit side plate temperature, average actual plate thickness, plate width, line speed). Perform heat balance calculations such as heat removal from the steel plate, furnace body heat dissipation, atmosphere heat dissipation, heat exchanger heat exchange, etc. during steady plate passing in advance, and the number of blower revolutions to be stabilized when it converges to the target outlet side plate temperature. A steady solution is calculated in advance, and the steady solution is used as a command value for the blower speed.

  In normal times, the blower speed is controlled by feedback control based on the deviation between the target and actual plate temperatures. However, when the heat cycle is changed by passing through the welding point, the thickness, width, and threading speed are changed, and the information that the target sheet temperature and threading speed have been changed by operation is entered, the sheet temperature control model performs feedforward calculation. Enter. When the feedforward calculation is entered, the above-mentioned parameters including the average actual plate thickness are read, and the solution of the blower rotational speed is calculated using the steady solution model. This steady solution is used as the blower rotational speed command value. Thereafter, the plate temperature is controlled by the foot-back control until the next event of entering the feedforward operation occurs.

  In addition, as shown in the graph of Fig. 3, the steady solution model takes into account the heat balance of the cooling zone, ie, the jet cooler and the heat balance of the heat exchanger, taking into account the heat dissipated in the cooling zone. A model that can find a solution to solve.

    FIG. 1 is a system diagram showing an embodiment to which the present invention is applied. A cooling wind box 3 for cooling the traveling steel plate 1 is disposed in the cooling zone 2 for cooling the steel plate 1, and a cooling gas is injected from the cooling wind box 3 by the cooling blower 4 and injected. The gas is discharged to the duct 5, cooled by the heat exchanger 6 in the middle of the duct, and circulated to the cooling zone 2 by the cooling blower 4. A cooling zone exit side plate thermometer 7 is arranged on the exit side of the cooling zone 2, and a cooling zone entrance side plate thermometer 8 is arranged on the entry side to detect the plate temperature. Before the steel plate 1 is introduced into the cooling zone 2, the plate thickness is measured by the plate thickness meter 10. In the present invention, not the nominal thickness but the average actual thickness obtained from the thickness measured by the thickness gauge 10 before the steel plate is introduced into the cooling zone is applied to the blower rotational speed calculation.

  The plate temperature is controlled by changing the rotation speed of the cooling blower. The blower speed is changed by feedforward control based on the deviation between the target plate temperature and the actual plate temperature in the cooling zone and the process computer, welding point tracking information (plate speed, welding point position), and plate schedule information (steel type, Actual plate thickness, plate width, plate speed, cooling zone inlet side temperature, cooling zone outlet side target temperature), and changes and changes in actual plate thickness, plate width, target plate temperature, line speed in the plate temperature control model Feedforward control is performed in which the blower rotational speed calculator 9 calculates the amount of change in the blower rotational speed using the rate and the like as parameters.

  FIG. 2 is a diagram showing a flow of plate temperature control according to the present invention. When the welding point passes, the mode for changing the plate passing speed or changing the target plate temperature is determined (step S1). If it is determined in this step S1 that the mode is normal, the process computer 9 performs a feedback calculation based on the deviation between the target plate temperature and the actual plate temperature (step S2). Based on the feedback calculation, the rotational speed of the blower is controlled by a blower rotational speed command (step S3).

  If it is determined in step S1 that the welding speed has passed and the mode for changing the plate speed or the target plate temperature is changed, the average actual plate thickness, the plate speed, obtained based on the actual measurement values measured by the thickness gauge, From the cooling zone inlet side temperature, the cooling zone outlet side target temperature, and the plate width, a feedforward calculation is performed using a plate temperature control model based on a steady solution (step S4). Based on the feedforward calculation, the rotational speed of the blower is controlled by a blower rotational speed command (step S5).

Next, the heat balance of the cooling zone will be described.
Q _C : Heat removal by forced convection with jet cooler spray Q _S : Heat dissipation from steel plate Q _L : Heat dissipation from cooling zone (including atmosphere heat dissipation)
W _S: amount of processing steel I _S 1: cooling zone steel sheet entry side sensible I _S 2: Cooling home use side of the steel sheet sensible B: steel Width Lf: cooling zone heat transfer effective furnace length alpha: Jet cooler heat transfer coefficient ΔTm: Logarithmic average temperature difference between steel plate and cooling gas N: Blower rotation speed
Q _S = Q _L + Q _C
Q _S = W _S × (I _S 1 -I _S 2)
Q _C = 2 × B × Lf × α × ΔTm
It becomes.
Ws = Ws (B, plate temperature, plate speed)
α = α (Blowing flow velocity, spraying distance, nozzle pitch, gas physical properties)
Q _L = Q _L (cooling zone furnace temperature, furnace zone heat transmissivity, furnace zone radiation area, amount of atmospheric gas)
And
N∝Vg∝α ⁿ
It becomes.

Next, the heat balance of the heat exchanger will be described.
Qhx1: Heat removal amount in heat exchanger Ahx: Heat transfer area of heat exchanger Khx: Heat flow rate of heat exchanger ΔTmhx: Logarithmic average temperature difference of gas-water Vg: Jet cooler Circulating gas amount ΔKg: Jet cooler Circulating gas Sensible heat difference between the inlet side and the outlet side Vw: cooling water amount ΔKw: heat exchanger of the cooling water sensible heat difference between the inlet side and the outlet side Qhx1 = Qc = Ahx × Khx × ΔTmhx = Vg × ΔKg = Vw × ΔKw
Based on the above, in a state where the heat balance of the cooling zone and the heat exchanger is balanced, the spraying flow rate at which the cooling zone outlet side target plate temperature can be achieved, that is, the blower rotational speed is calculated by convergence calculation.

  FIG. 4 is a graph showing the relationship between the time after passing the welding point and the plate temperature. The annealed steel plate is cooled to a predetermined plate temperature in the cooling zone, and the inlet side target temperature and the outlet side target plate temperature of the cooling zone are set by a process computer depending on the steel type, and are automatically controlled. As shown in FIG. 4, in the conventional control, for example, even if the target plate temperature does not change, when the plate thickness of the steel plate and the plate width change, the actual plate temperature is about 3 minutes. It sometimes took about 10 minutes for the target plate temperature to swing within the range of about ± 15 ° C. and converge to the target plate temperature of ± 5 ° C. When the present invention was applied to this, the target plate temperature could be within a range of about ± 5 ° C. from the first blower rotation speed setting. After this, the target plate temperature is converged by normal feedback control.

It is a system diagram showing an example to which the present invention is applied. It is a figure showing the flow of plate temperature control of this invention. It is a graph which shows the relationship between plate | board thickness and a blower rotation speed. It is a graph which shows the relationship between the time after welding point passage, and plate temperature. It is a system figure of the cooling control of the conventional steel plate.

Explanation of symbols

1: Steel plate 2: Cooling zone 3: Cooling wind box 4: Cooling blower 5: Duct 6: Heat exchanger 7: Cooling zone outlet side thermometer 8: Cooling zone inlet side thermometer 9: Process computer 10: Plate thickness gauge

Claims (1)

When cooling the steel plate with a cooling blower in the cooling zone of the continuous heat treatment equipment for the steel plate, the cooling plate inlet side target plate temperature, cooling zone outlet side target plate temperature, plate thickness, plate width, plate passing speed in the actual operation In the plate temperature cooling control method in the cooling zone of the continuous heat treatment equipment of the steel plate, which feedforward-controls the rotational speed of the cooling blower in conjunction with the information of the welding point tracking information,
Takes the measured thickness measured by the thickness gauge before the steel plate is introduced into the cooling zone, calculates the average actual thickness for each number of coils divided, and controls the average actual thickness at the time of feedforward calculation It should be used when calculating the heat balance of the cooling zone, such as the amount of heat removed from the steel plate, the amount of heat dissipated in the furnace, and the heat exchange in the heat exchanger, and should be stable when it converges to the target outlet side plate temperature. A plate temperature cooling control method in a cooling zone of a continuous heat treatment facility for a steel plate, wherein a steady solution of a blower rotational speed is calculated in advance and used as a blower rotational speed command value.

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