JPS5929654B2 - Strip temperature control method in continuous heat treatment furnace - Google Patents

Description

[Detailed Description of the Invention] This invention &'! This invention relates to a method for controlling the temperature of a strip in a continuous heat treatment furnace that continuously processes strips such as steel plate strips.

As a heat treatment furnace that continuously processes steel plate strips,
A generally known method is to divide the furnace into a plurality of control zones and to control the temperature of each of the control zones, thereby indirectly controlling the temperature of the steel sheet at the exit side of the furnace.

The steel plate temperature is monitored by the operator, who changes the furnace temperature set value for each control zone as necessary, and this work often relies on the operator's intuition and experience.

In order to automate and increase the accuracy of such work, as shown in Fig. 1, which is a block diagram of a steel plate temperature measuring device in a continuous heat treatment furnace, the actual value of the steel plate temperature at the exit side of the furnace 1 is measured using a steel plate thermometer. 2, and the deviation between the actual steel plate temperature value and the target steel plate temperature value from the thermometer 2 is measured via a PID type steel plate temperature control device 3 that performs a control operation that combines proportional, integral, and differential operations, and further , a method of cascading the output to the furnace temperature control device 4 provided for each control zone was attempted.

However, the path length of the steel strip from the inlet side of the furnace (or the inlet side of each control zone) to the outlet side of the furnace is very long, and therefore the furnace temperature of each control zone is controlled based on the furnace temperature set value. As a result, a considerable amount of dead time occurs before this appears as the actual steel plate temperature value on the furnace exit side, making it difficult to control the steel plate temperature to a predetermined temperature (target temperature).

Therefore, the inventors of the present invention aimed to solve the above-mentioned problems (as a result of research, the line speed of the steel plate strip,
Since a heat transfer model can be estimated in advance to estimate the temperature of the steel plate on the exit side of the furnace based on the thickness, width, and temperature inside the furnace unique to each control zone, this heat transfer model and the By correcting the furnace temperature set value for each control zone based on the actual value of the furnace temperature and the actual value of the steel plate temperature on the exit side of the furnace, it is possible to overcome the control difficulties caused by the aforementioned dead time. They obtained the knowledge that the steel plate temperature can be controlled to a target predetermined temperature.

This invention has been made based on the above knowledge, and provides a strip temperature control method in which the deviation between the actual value and the target value of the strip temperature on the furnace exit side is fed back to the furnace temperature control device as the furnace temperature set value. For each time, sample the actual values of the furnace temperature and the strip temperature on the exit side of the furnace, and based on the heat transfer model of the furnace and the sample values,
The present invention is characterized in that a setting value of the furnace temperature control device is corrected.

The present invention will be explained below by way of examples with reference to the drawings.

FIG. 2 is a block diagram of a steel plate temperature control device in a continuous heat treatment furnace to which the present invention is applied.

As shown in the figure, 5 is a furnace, 6 is a steel plate thermometer that measures the steel plate temperature on the outlet side of the furnace 5, and 7 is a furnace temperature control device for each control zone, which is configured by dividing the furnace 5 into a plurality of parts. The actual steel plate temperature value from the steel plate thermometer 6 and the actual furnace temperature value of each control zone from the furnace temperature control device 7 are sampled at predetermined time intervals by a sampling device 8 and are measured by the furnace temperature control device. Steel plate temperature control device 9 for setting the furnace temperature set value of 1
On the other hand, the steel plate temperature control device 9 receives external information such as the line speed of the steel plate strip in the furnace, the thickness and width of the strip, etc., for estimating a heat transfer model to be described later. 10 is entered.

Then, in the steel plate temperature control device 9, a heat transfer model is estimated from the external information 10, and based on this heat transfer model and the sample value from the sampling device 8, the furnace temperature is sent to the furnace temperature control device 7. The set value is corrected so that the deviation between the actual value and the target value of the temperature of the steel plate on the exit side of the furnace is minimized.

Next, the heat transfer model, the method of correcting the furnace temperature set value for each control zone, and the sample time interval ΔT will be explained.

■ Heat transfer model The heat transfer model is based on the steel plate temperature T on the exit side of the furnace.

This is for estimating, specifically, 2h(Tz-T)+26a(Tz'-T')T =ρ・Cp-t-V・−・・・・・・(1)X [However, , ρ: steel plate density Cp: steel plate specific heat t: steel plate thickness V Ni line speed ε: emissivity between the furnace and the steel plate σ: convective heat transfer coefficient between the furnace and the steel plate σ: Stefan Boltzmann constant Tz: control band Temperature inside the furnace at each time Given the temperature Ti, the steel plate temperature T at the exit side of the furnace is determined by numerically integrating it from the entrance side of the furnace to the exit side of the furnace along the direction of the strip path.

is found. However, Cp shall be changed according to T.

Here, the conditions for adapting the heat transfer model to an actual furnace by changing ε or h as a parameter will be explained.

In other words, first, the method for selecting parameters for adjusting the heat transfer model is to determine whether the heat transfer between the furnace and the steel plate is mainly due to radiation or convection, and select only one of the major ones. and the other is set as O.

Specifically, ε is selected as a parameter when radiation heat transfer is considered to be the main factor, such as in a radiant tube heating furnace, and when convective heat transfer is considered to be the main factor, such as in a gas W cooling furnace. In this case, h is selected as a parameter.

Furthermore, for the selected main parameters, the most appropriate values are determined in advance by back calculation from equation (1) based on the results of many sets of each variable.

@ Modification method of furnace temperature control value for each control zone Modification of furnace temperature control value for each control zone is performed based on the heat transfer model.

This correction method will be explained with reference to a diagram showing the relationship between furnace temperature and steel plate temperature shown in FIG.

As shown in the figure, the horizontal axis represents the steel plate temperature at the exit side of the furnace, and the vertical axis represents the furnace temperature, and the two curves A and B represent the actual (estimated) and two variables in the heat transfer model, respectively. It shows the relationship between

Here, the final objective is to find the point on curve A at the target value TR of the steel plate temperature, that is, the furnace temperature TzR, but since curve A is unknown in advance, the furnace temperature TzR is estimated from curve B based on the heat transfer model. do.

First, find the point on curve B at the current furnace temperature (furnace temperature actual value) Tz, that is, the steel plate temperature T1, and then calculate the difference between the steel plate temperature T1 and the steel plate temperature actual value Ts to the steel plate temperature target value TR. In addition, the estimated steel plate temperature T2 is determined.

Then, if the point on the curve B at the temperature T2, that is, the estimated furnace temperature set value T/ZR, is found, this set value T'zR
is the estimated value of the furnace temperature T z H based on the heat transfer model.

In this way, it is possible to reset (correct) the furnace temperature control device without using the integral operation of a PID type steel plate temperature control device, etc., and therefore the deviation between the actual value and target value of the steel plate temperature on the exit side of the furnace can be adjusted. A suitable furnace temperature setpoint is set.

In the above explanation, the furnace temperature for each control zone was treated as one variable, but in reality, it is a variable equal to the number of control zones.

Therefore, when calculating the estimated furnace temperature setting value T'zR corresponding to the point on the curve B at the estimated steel plate temperature T2,
There is a degree of freedom (number of control zones - 1), but in determining the furnace temperature for each control zone, the ratio of the set values of the furnace temperature control device for each control zone should be kept constant. For example, a method can be considered to predetermine the furnace temperature pattern, for example, by giving the material dimensions, material properties, steel plate temperature on the entrance side, target temperature of the steel plate on the exit side, line speed, and the ratio of the furnace temperature setting values for each control zone. Then, the absolute value of each control zone furnace temperature may be calculated, and each control zone furnace temperature may be set using the calculated value.

○ Sample time interval △T Sample time interval △T & ζ Almost equal to the control dead time from when the furnace temperature is controlled based on the furnace temperature set value for each control band until this appears as the actual steel plate temperature value on the furnace exit side. Bye.

Here, the method for calculating ΔT is, for example, based on the following formula.

That is, [where C: adjustment coefficient L: in-furnace strip path length V second line speed] Note that the adjustment coefficient C can be determined experimentally from operational data.

Next, examples will be explained.

FIG. 4 is a diagram showing →U of the steel plate temperature control results with the vertical axis representing the furnace temperature actual value as a control variable according to the present invention and time along the horizontal axis, and FIG. FIG. 2 is a diagram showing an example of a steel plate temperature control result by a PID type steel plate temperature control device (see FIG. 1) as a conventional example.

Note that the control amount due to disturbance, that is, the change in the actual furnace temperature value when no control is performed, is shown equally by the dotted line in both figures.

In the PID type steel plate temperature control device, resetting in response to changes in the control amount is a function of integral operation, so here we simply considered the case of only integral operation.

In FIG. 5, in consideration of appropriate attenuation of the controlled variable, the integration time R was determined as follows: R=1.2XΔT [where ΔT: sample time interval of the above-mentioned θ (dead time in control)].

Here, the natural period of the control loop that adds the integral controller to the process with dead time △T is generally 4 x △T, so
Changes in the control amount are approximately as shown in FIG.

As described above, the method of the present invention shown in FIG. 4 is superior to the conventional method shown in FIG. 5 in the following points.

That is, (1) the time required for the controlled variable to settle to the target value is short (within 2XΔT from the end of the change due to disturbance);

■ The controlled variable does not exceed the target value.

Although the above explanation has been made regarding a steel plate strip, it goes without saying that the present invention can be applied to a continuous heat treatment furnace for metal strips, wire rods, and other strips.

As explained above, in the present invention, the deviation between the actual value and the target value of the strip temperature on the furnace exit side can be eliminated without any time delay, and highly accurate strip temperature control can be performed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional steel plate temperature control device, Fig. 2 is a block diagram of a steel plate temperature control device in a continuous heat treatment furnace to which the present invention is applied, and Fig. 3 shows the relationship between the furnace temperature and the steel plate temperature at the exit side of the furnace. FIG. 4 is a diagram showing an example of control results according to the present invention, and FIG. 5 is a diagram showing an example of control results according to a conventional example. 1.5...furnace, 2,6...steel plate thermometer, 3.・、P
ID type steel plate temperature control device, 4, 7...Furnace temperature control device,
8... Sampling device, 9... Steel plate temperature control device, 10... External information.

Claims (1)

[Scope of Claims] 1. A strip temperature control method in which the deviation between the actual value and the target value of the strip temperature on the furnace exit side is fed back to the furnace temperature control device as a furnace temperature set value, comprising: Sample the actual values of the furnace temperature and the strip temperature on the exit side of the furnace, and based on the heat transfer model of the furnace and the sample values,
A method for controlling a strip temperature in a continuous heat treatment furnace, the method comprising: modifying the furnace temperature setting value.