JPH0617147A - Continuous heat treatment for steel strip - Google Patents

Abstract

PURPOSE:To cool a steel strip down to the desired temp. at the time when the sheet passing amount of the steel strip and the desired temp. are changed in continuous heat treatment for the steel strip. CONSTITUTION:When the sheet passing amount of a steel strip 3 and/or the desired sheet temp. of the steel strip 3 is changed, the values before and after the change are compared. On the basis of the comparison, the forced cooling for the steel strip in a cooling zone 4 is stopped and the inside of the cooling zone 4 is heated by an electrical means 12 or a radiant tube to rise the temp. of the steel strip 3 to the desired temp., or, the inside of the cooling zone 4 is heated by an electrical means 12 or a radiant tube and also the steel strip 3 is cooled down to the desired temp. by the forced cooling for the steel strip 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous heat treatment method for steel strip.

[0002]

2. Description of the Related Art In continuous heat treatment of steel strips, it is possible to set a heat pattern for each material in advance, change the furnace temperature, and set the annealing temperature of steel strips of different steel types to a target annealing temperature in a short time. It is disclosed in Japanese Patent Laid-Open No. 2-205634.

Generally, in continuous heat treatment equipment for steel strips, continuous hot-dip galvanizing equipment, etc., the capacity of the furnace for heating and soaking at the maximum strip thickness, the maximum strip width and the maximum strip-passing speed of steel strips and for reliable annealing. Is equipped with. In addition, even in a furnace that performs heating, soaking, followed by slow cooling, rapid cooling, etc., the capacity of the furnace that can reliably perform cooling with the maximum plate thickness, maximum plate width, and maximum plate passing speed as in the case of heating and soaking. Is equipped with.

In the cooling in this cooling furnace, a steel strip is passed through a cooling zone filled with a non-oxidizing atmosphere gas, and at that time, a cooling gas is sprayed onto the passing steel strip to perform forced cooling. Cool the steel strip to the target plate temperature.

[0005]

However, when the passing amount of the steel strip is reduced, for example, when the plate thickness and / or the width size of the steel strip is reduced, the sensible heat by heating and soaking of the steel strip is obtained. Is reduced due to the size reduction, the temperature in the furnace is lowered, and the steel strip is overcooled even if the forced cooling in the cooling zone is stopped. Also, when the strip running speed decreases due to equipment troubles, etc., the staying time in the cooling zone becomes longer due to the decrease in the strip running speed, and similarly, heating of the steel strip and sensible heat due to soaking eventually decrease, Even if the forced cooling is stopped because the temperature inside the furnace decreases, the steel strip will be overcooled. When the target plate temperature changes due to changes in the material of the steel strip, especially when the target plate temperature rises, the sensible heat due to heating and soaking is the same, so the furnace temperature is constant, but the plate temperature decrease width is small. Therefore, even if the forced cooling is stopped, the steel strip is overcooled.

That is, since it is a cooling zone, it has no heating mechanism and waits for the temperature inside the zone to rise due to the amount of heat carried into the steel strip, during which the steel strip continues to be cooled above the target temperature. Will end up. As a result, in such a continuous treatment, the steel strip is overcooled in the cooling zone when the size of the steel strip is reduced, and the material is damaged. There are some drawbacks.

An object of the present invention is to prevent overcooling of the steel strip in the cooling zone when the size of the steel strip is changed, the strip running speed is changed, or when the target strip temperature rises. Is.

[0008]

The gist of the present invention is as follows.

In the continuous heat treatment method for a steel strip to be heated, soaked and cooled, when the strip running amount of the steel strip and / or the target strip temperature of the steel strip changes, the forced cooling of the steel strip in the cooling zone is stopped. At the same time, the continuous heat treatment method for a steel strip is characterized in that the inside of the cooling strip is heated by an electric means or a radiant tube to raise the temperature of the steel strip to a target temperature.

In a continuous heat treatment method for a steel strip to be heated, soaked and cooled, an electric means or a radiant tube is used in the cooling zone when the amount of steel strip passed and / or the target strip temperature of the steel strip changes. A continuous heat treatment method for a steel strip, which comprises heating and cooling the steel strip to a target temperature by forced cooling.

[0011]

In the present invention, in order to solve the above-mentioned problems, the inside of the cooling zone is electrically heated or changed when the size of the steel strip is changed, the strip running speed is changed, or when the target strip temperature rises. Raising the temperature by heating the radiant tube prevents supercooling of the steel strip in the cooling zone. Further, the steel strip is heated by electric heating or radiant tube heating, and the steel strip is adjusted to a target temperature by forced cooling. Since the temperature of the steel strip can be precisely adjusted by forced cooling, the inside of the cooling zone is heated above the cooling target temperature by electric heating or radiant tube heating, and the target temperature is precisely set by forced cooling.

As the cooling zone, a slow cooling zone and a rapid cooling zone may be provided in series. In this case, it is preferable to prevent supercooling on both sides by electric heating or radiant tube heating.

Such a continuous heat treatment method for steel strip can be advantageously applied to, for example, the operation of a pretreatment furnace of a continuous hot-dip galvanizing line, the operation of continuous annealing equipment for steel strip, and the like.

[0014]

[Embodiment 1] As shown in FIG. 1, the plate thickness, the plate width, and the material of the steel strip are stored in the storage device 1 in the order of processing for each coil having an average single weight of 20 tons. Cooling zone 4 of steel strip 3 which has detected the welding point and has been unwound from the next steel strip coil
An advance notice of the passing amount is introduced into the calculation mechanism 6 via the tracking device 5.

On the other hand, the plate thickness, the plate width, the material and the plate passing speed of the steel strip 3 currently being cooled are introduced from the storage device 1 into the calculating mechanism 6 to calculate the plate passing amount per unit time, Next, the thickness of the steel strip 3 to be cooled after finishing heating and soaking,
The strip width, the material, and the strip running speed are introduced into the computing mechanism 6, the strip running amount per predicted unit time is calculated from the actual strip running speed of the current steel strip, and the two are compared. The arithmetic expression is Equation 1.

[0016]

[ _Formula 1] TH _pr = TH _ma2 x (TH _n0 / TH _ma1 ) TH _n0 = DS x TH x WA x LS where TH _pr : Predicted strip amount of the next steel strip TH _ma2 : Specified strip of the next steel strip Amount TH _ma1 : _Specified strip _running amount of the current steel strip TH _n0 : Actual strip _running amount of the current steel strip DS: Strip density TH: Strip thickness WA: Strip width LS: Line speed

In addition, the target temperature of the steel strip 3 currently being cooled is introduced from the storage device 1 into the calculation mechanism 6, and
Next, when the target temperature of the steel strip 3 to be cooled after heating and soaking is also introduced into the calculation mechanism 6 and the target plate temperature changes,
Compare both.

In this way, when the steel strip of the next coil passes through the cooling zone 4 when the stripping amount and the target strip temperature of the two coils change, the target strip temperature of the next steel strip is within the cooling zone 4. When it is determined that the supercooling will occur, it is necessary to raise the temperature of the cooling zone 4 by electric heating. Therefore, the furnace temperature setting timing calculating mechanism 7 and the furnace temperature setting value calculating mechanism 8 are instructed respectively to stop the forced cooling and to turn on the electric power. The heating start timing and the furnace temperature set value are introduced into the furnace temperature adjusting device 10 via the furnace temperature setting mechanism 9. In the furnace temperature adjusting device 10, the result of measuring the current furnace temperature by the thermometer 11 is introduced, the heating amount based on the furnace temperature set value is determined, the electric power amount is calculated, the heater 12 is energized, and the cooling zone 4 is cooled. Is heated to the furnace temperature set value, the forced cooler 13 is stopped, and the blowing of the cooling gas from the nozzle 14 to the steel strip 3 is stopped. The furnace temperature set value is calculated by Equation 2.

[0019]

[Formula 2] TF = TS + C ₁ {TH (QS _ot −QS _it )}
/ (2 · HS) where TF: Reactor temperature TS: Target strip temperature C ₁ : Adjustment parameter TH: Predicted strip amount of the next steel strip QS _ot : Heat capacity of inlet strip temperature QS _it : Heat capacity of outlet strip temperature HS: Heat transfer coefficient

Further, in the calculation mechanism 6, the steel strip size, material,
If it is judged from the strip passing speed that the next steel strip is passed through the cooling zone 4 by electric cooling together with electric heating, the furnace temperature setting timing calculation mechanism 7, the furnace temperature set value calculation mechanism 8 and the furnace temperature setting are similarly set. The furnace temperature control device 10 is instructed via the mechanism 9, and the heater 12 is similarly energized to heat the cooling zone 4 and operate the forced cooler 13 to take out a part of the atmospheric gas in the cooling zone 4. Then, it is circulated and cooled by the cooler 13, sprayed from the nozzle 14 to the steel strip 3, and cooled to the set temperature.

Next, when a speed change is detected by the speed detector 15, the plate thickness, the plate width, the material, and the strip running speed before the speed change of the steel strip 3 currently being cooled are stored in the storage device 1. The sheet passing amount per unit time is calculated by introducing it into the calculation mechanism 6, and then the sheet passing speed after the speed change is introduced and similarly the sheet passing amount per unit time is calculated. Then, when both are compared and it is determined that the current coil and the steel strip 3 will be supercooled during the passage in the cooling zone 4, it is necessary to raise the temperature of the cooling zone 4 by electric heating. The furnace temperature adjusting device 10 is instructed through the calculation mechanism 7, the furnace temperature set value calculation mechanism 8 and the furnace temperature setting mechanism 9, and similarly, the heater 12 is energized to heat the inside of the cooling zone 4 and the forced cooler 13 is set. Then, the blowing of the cooling gas from the nozzle 14 to the steel strip 3 is stopped.

When a speed change is detected by the speed detector 15, the arithmetic mechanism 6 similarly determines the passing amount per unit time from the steel strip size, the material, the passing speed before and after the speed change. When it is determined that both the electric heating and the forced cooling should be performed, the temperature of the furnace is set via the furnace temperature setting timing calculating mechanism 7, the furnace temperature set value calculating mechanism 8 and the furnace temperature setting mechanism 9. The controller 12 is instructed to similarly energize the heater 12, heat the inside of the cooling zone 4 and operate the forced cooler 13, take out a part of the atmospheric gas in the cooling zone 4, and circulate and cool it with the cooler 13. Then
The steel strip 3 is sprayed from the nozzle 14 and cooled to a set temperature.

[0023]

[Embodiment 2] As shown in FIG. 2, the steel sheet thickness, the sheet width, and the material of the steel strip are stored in the storage device 1 in order of processing for each coil having an average single weight of 20 tons. A welding point of No. 3 is detected, and a notice of the passing amount of the steel strip 3 unwound from the next steel strip coil to the cooling zone 4 is introduced to the arithmetic mechanism 6 via the tracking device 5.

On the other hand, the plate thickness, the plate width, the material, and the plate passing speed of the steel strip 3 currently being cooled are introduced from the storage device 1 into the calculating mechanism 6 to calculate the plate passing amount per unit time, Next, the thickness of the steel strip 3 to be cooled after finishing heating and soaking,
The strip width, the material, and the strip running speed are introduced into the computing mechanism 6, the strip running amount per predicted unit time is calculated from the actual strip running speed of the current steel strip, and the two are compared. The arithmetic expression is Equation 3.

[0025]

[ _Formula 3] TH _pr = TH _ma2 x (TH _n0 / TH _ma1 ) TH _n0 = DS x TH x WA x LS where TH _pr : Predicted strip amount of the next steel strip TH _ma2 : Specified strip of the next steel strip Amount TH _ma1 : _Specified strip _running amount of the current steel strip TH _n0 : Actual strip _running amount of the current steel strip DS: Strip density TH: Strip thickness WA: Strip width LS: Line speed

Further, the target temperature of the steel strip 3 currently being cooled is introduced from the storage device 1 into the arithmetic mechanism 6, and
Next, when the target temperature of the steel strip 3 to be cooled after heating and soaking is also introduced into the calculation mechanism 6 and the target plate temperature changes,
Compare both.

In this way, when the steel strip of the next coil passes through the cooling zone 4 and the stripping amount or the target strip temperature of both of them changes, the target strip temperature of the next steel strip is within the cooling zone 4. When it is determined that supercooling will occur, it is necessary to raise the temperature of the cooling zone 4 by means of the radiant tube 16, so the furnace temperature setting timing calculating mechanism 7 and the furnace temperature setting value calculating mechanism 8 are respectively instructed to stop forced cooling and The heating start timing by the radiant tube 16 and the furnace temperature set value are introduced into the furnace temperature adjusting device 10 via the furnace temperature setting mechanism 9. In the furnace temperature control device 10,
The result of measurement of the current furnace temperature by the thermometer 11 is introduced, the heating amount based on the furnace temperature set value is determined, the fuel flow rate flowing in the radiant tube 16 is calculated, and the fuel is flowed to set the furnace temperature in the cooling zone 4. After heating to the value, the forced cooler 13 is stopped, and the blowing of the cooling gas from the nozzle 14 to the steel strip 3 is stopped.
The furnace temperature set value is calculated by Equation 4.

[0028]

[Formula 4] TF = TS + C ₁ {TH (QS _ot −QS _it )}
/ (2 · HS) However, TF: furnace temperature TS: target strip temperature C ₁ : adjustment parameter TH: predicted strip volume of the next steel strip QS _ot : heat capacity of inlet strip temperature QS _it : heat capacity of outlet strip temperature HS: Heat transfer coefficient

Further, in the calculation mechanism 6, the steel strip size, material,
If it is determined from the strip running speed that the next steel strip is striped through the cooling zone 4 by the radiant tube heating and the forced cooling, the furnace temperature setting timing calculating mechanism 7, the furnace temperature setting value calculating mechanism 8 and the furnace temperature are similarly set. The furnace temperature control device 10 is instructed via the setting mechanism 9, and similarly the radiant tube 16
The fuel is flown into the cooling zone 4 to heat the cooling zone 4 and the forced cooler 13 is operated.
And cool to the set temperature.

Next, when the speed change is detected by the speed detector 15, the plate thickness, the plate width, the material, and the passing speed before the speed change of the steel strip 3 currently being cooled are stored in the storage device 1. The sheet passing amount per unit time is calculated by introducing it into the calculation mechanism 6, and then the sheet passing speed after the speed change is introduced and similarly the sheet passing amount per unit time is calculated. When the steel strips 3 of the current coil are compared with each other and it is determined that the steel strip 3 will be supercooled during passage in the cooling zone 4, it is necessary to raise the temperature of the cooling zone 4 by the radiant tube 16. The furnace temperature adjusting device 10 is instructed via the timing calculation mechanism 7, the furnace temperature set value calculation mechanism 8 and the furnace temperature setting mechanism 9, and similarly, the fuel flowing to the radiant tube 16 is operated to heat the inside of the cooling zone 4. The forced cooler 13 is stopped, and the steel strip 3 is discharged from the nozzle 14.
Stop blowing cooling gas to.

When a speed change is detected by the speed detector 15, the arithmetic mechanism 6 similarly determines the amount of steel passing per unit time from the steel strip size, the material, and the plate passing speed before and after the speed change. When the calculation is performed and the two are compared, and it is determined that the heating is performed by the radiant tube and the forced cooling is performed, the furnace temperature setting timing calculation mechanism 7, the furnace temperature set value calculation mechanism 8, and the furnace temperature setting mechanism 9 are similarly used. The furnace temperature control device 10 is instructed to flow the fuel to the radiant tube 16 in the same manner to heat the cooling zone 4 and operate the forced cooler 13 to take out a part of the atmospheric gas in the cooling zone 4 and cool the cooler. It is circulated and cooled at 13, is sprayed from the nozzle 14 to the steel strip 3, and is cooled to a set temperature.

[0032]

According to the present invention, it is possible to perform an appropriate heat treatment on a target steel strip material. Further, when applied to a pretreatment facility of a continuous hot dip galvanizing facility, excellent effects such as improvement of material and prevention of plating failure can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an apparatus for carrying out the present invention.

FIG. 2 is an explanatory diagram showing another example of an apparatus for carrying out the present invention.

[Explanation of symbols]

 1 Storage Device 2 Detection Sensor 3 Steel Strip 4 Cooling Zone 5 Tracking Device 6 Calculation Mechanism 7 Reactor Temperature Setting Timing Calculation Mechanism 8 Reactor Temperature Set Value Calculation Mechanism 9 Reactor Temperature Setting Mechanism 10 Reactor Temperature Controller 11 Thermometer 12 Heater 13 Forced Cooling Vessel 14 nozzle 15 speed detector 16 radiant tube

Claims (2)

[Claims] 1. In a continuous heat treatment method for a steel strip to be heated, soaked and cooled, forced strip cooling in the cooling zone is carried out when the strip running amount of the steel strip and / or the target strip temperature of the steel strip changes. A continuous heat treatment method for a steel strip, which comprises stopping and heating the inside of the cooling strip by an electric means or a radiant tube to raise the temperature of the steel strip to a target temperature. 2. In a continuous heat treatment method for a steel strip to be heated, soaked and cooled, an electric means or a radiant inside the cooling zone is produced when the amount of steel strip passed and / or the target strip temperature of the steel strip changes. A continuous heat treatment method for a steel strip, which comprises heating the steel strip by a tube and cooling the steel strip to a target temperature by forcibly cooling the steel strip.