RU2047662C1 - Method for heating rolls of steel in hood-type furnaces - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: method involves controlling fuel supply according to stand temperature, with fuel flow rate being successively set for each of equal time intervals determined by conditions of automatic control system stability. Fuel flow rate is determined by stand temperature measured during previous time interval by design values of stand temperature, heating rate and acceleration for predetermined time interval according to formula recited in Specification, with initial heating rate for first heating time interval being within the range of 0.05-0.07 C. EFFECT: increased efficiency and high quality of steel. 1 tbl

Description

 The invention relates to metallurgy, in particular to the heating of strip steel in coils in bell furnaces.

 A known method of heating steel coils in bell-type furnaces, in which the fuel supply is controlled by the set temperature of the stand by supplying the maximum fuel consumption until the set temperature is reached, then the fuel consumption is gradually reduced while maintaining the set temperature in accordance with the task.

A disadvantage of the known method (prior art) is a high rate of temperature rise in the heating period, the temperature difference of the thickness of the coil reaches 200-250 ° ^C. To eliminate such temperature difference requires prolonged exposure, which leads to increased fuel consumption during heating and low quality metal due to overheating.

 The aim of the invention is to reduce fuel consumption and increase the yield of metal.

T

+ T_ст[I]

где T_ст[I] T_ст[I-1]+

Δτ

+

Δτ

+ 2S

n

1/град S

1/град t_T=

a коэффициент теплоотдачи, Вт/м² х град;
F поверхность нагрева, м²; Т постоянная времени, с;
К_п коэффициент потерь, Вт/град; q теплота сгорания топлива, Дж/м³;
К_д коэффициент выхода продуктов сгорания, Qc потери тепла, Вт;
К_р коэффициент регенерации тепла;
С_д теплоемкость продуктов сгорания, Дж/м³ град;
а начальная скорость нагрева для первого интервала времени нагрева выбирается в пределах 0,05-0,07 град/с.This goal is achieved by the fact that in the method of heating steel coils in bell-type furnaces, including controlling the fuel supply by the temperature of the bench, the fuel consumption is alternately set for separate identical time intervals determined by the stability conditions of the automatic control system and is determined by the temperature measured at the previous time step the bench with the calculated value of the bench temperature, speed and heating acceleration at a given time step according to the formula
B

T

+ T _article [I]

where T _article [I] T _article [I-1] +

Δτ

+

Δτ

+ 2S

n

1 / deg S

1 / deg t _T =

a heat transfer coefficient, W / m ² x deg;
F heating surface, m ² ; T is the time constant, s;
To _p loss coefficient, W / deg; q calorific value, J / m ³ ;
K _{d the} coefficient of output of the products of combustion, Qc heat loss, W;
K _p heat recovery coefficient;
C _{d the} heat capacity of the combustion products, J / m ³ deg;
and the initial heating rate for the first interval of the heating time is selected in the range of 0.05-0.07 deg / s.

 The calculation of the first and second derivatives is based on the numerical values of the input variables for each elementary interval.

 The proposed method and the prototype have the following identical essential features. Both are designed to heat steel coils in bell-type furnaces, in which the fuel supply is regulated by the set temperature of the stand by supplying fuel until the set temperature is reached.

T

+ T_ст[I]

,
где T_ст[I] T_ст[I-1]+

Δτ;

+

Δτ

=

+ 2S

n

1/град S

1/град t_T=

a коэффициент теплоотдачи, Вт/ м² x град;
F поверхность нагрева, м²; Т постоянная времени, с;
К_п коэффициент потерь, Вт/град; q теплота сгорания топлива, Дж/куб. м;
К_д коэффициент выхода продуктов сгорания; Q_c потери тепла, Вт;
К_р коэффициент регенерации тепла;
С_д теплоемкость продуктов сгорания, Дж/м³ град;
а начальная скорость нагрева для первого интервала времени нагрева выбирается в пределах 0,05-0,07 град/с.A significant difference is that in the method of heating steel coils in bell-type furnaces, fuel consumption is alternately set for individual identical time intervals determined by the stability conditions of the automatic control system. Another difference is that the amount of fuel for the specified interval is determined by the temperature of the stand measured at the previous step in time, the calculated values of the temperature of the stand, the speed and acceleration of heating at a given time step according to the formula
B

T

+ T _article [I]

,
where T _article [I] T _article [I-1] +

Δτ;

+

Δτ

=

+ 2S

n

1 / deg S

1 / deg t _T =

a heat transfer coefficient, W / m ² x deg;
F heating surface, m ² ; T is the time constant, s;
To _p loss coefficient, W / deg; q calorific value, J / cu. m;
K _{d the} coefficient of output of the products of combustion; Q _c heat loss, W;
K _p heat recovery coefficient;
C _{d the} heat capacity of the combustion products, J / m ³ deg;
and the initial heating rate for the first interval of the heating time is selected in the range of 0.05-0.07 deg / s.

 The set of essential features of the proposed method and prototype allows to eliminate the temperature difference and prolonged exposure, which leads to increased fuel consumption during heating and low quality of the metal due to overheating and leads to a reduction in fuel consumption and increased yield of metal.

PRI me R. Metal of 0.8 kp grade in rolls weighing 37.0 tons, 0.5 mm thick and 700 mm wide was loaded into a bell furnace in a stack of three rolls and, at the calculated values of the coefficients, the heating period was divided into intervals of Δτ = 1 / 100τ _back . In our case, the _backside was 50 hours. Then, the initial heating rate was set to 0.05 deg / s (at which the size of the recrystallization grain corresponds to the required mechanical properties of steel 0.8 kp) and the fuel supply modes were calculated for each interval of 50/100 = 0 5 hours according to the formula (1). At the end of the calculation, a check was made to achieve the set value of the stand temperature according to the formula τ _s τ _calc .

L = T _st -T _st , if / L / <e, where e is the specified accuracy of 5-10 ^o C, then the calculation is complete. Otherwise, the initial value of the heating rate was changed, depending on the sign of L, by a value of (0.001-0.01) and the calculation is repeated until it falls within the specified interval + e.

As a result of the calculation, we obtained the trajectory of the optimal change in the set temperature of the stand (T _st ) and the minimum fuel consumption for each calculated heating interval, i.e. mode providing optimal control of fuel consumption with the maximum temperature difference across the thickness of the roll is not more than 50 ^{° C,} and therefore, metal quality and the yield for the same heating time.

 The results of heating the metal of the experimental batch were monitored by thermocouples installed at various points both along the height of the cage and along the section of the rolls. The choice of installation location is due to preliminary studies of extreme temperatures. Thermocouple readings were recorded with an automatic potentiometer. Metal samples for mechanical tests and microstructure studies were selected according to the scheme adopted at KarMK and in compliance with established GOSTs. Technical and economic indicators of 70 pilot industrial heating are shown in the table in comparison with the prototype.

Claims (1)

METHOD OF HEATING STEEL ROLLS IN CAPPER FURNACES, including regulation of fuel supply by bench temperature T _{c t} , characterized in that fuel consumption is set for each of the equal time intervals determined by the stability conditions of the automatic control system and is determined by the temperature measured in the previous time interval bench, according to the calculated values of the bench temperature, speed and heating acceleration for a given time interval according to the formula

a heat transfer coefficient, W / m ² · deg;
F heating surface, m ² ;
T time constant, s;
To _p the loss coefficient, W / deg,
q calorific value of fuel J / m ³ ;
K _{d the} coefficient of output of the products of combustion;
Q _with heat loss, W;
K _p heat recovery coefficient;
C _{d the} heat capacity of the combustion products, J / m ³ · deg.  and the initial heating rate for the first interval of the heating time is selected within 0.05 0.07 deg / s.

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