JPS5815202B2 - Coiling temperature control method for hot-rolled steel sheets - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for controlling the winding temperature of a hot rolled steel sheet.

By the way, post-rolling temperature control in a hot strip rolling mill, especially coiling temperature control that controls the strip temperature at a predetermined value during coiler winding, is known to be due to the coiling temperature depending on the mechanical strength and processing of the strip. However, since the cooling of high-temperature steel plates running at high speed is a problem, various influencing factors are interrelated and it is not easy to control them.

With the introduction of computer control to rolling lines, the winding temperature has also come to be controlled by computers, but no satisfactory control model or control method has been found.

Here, a conventional control method will be explained with reference to FIG.

The figure shows the area around the hot run table.In the figure, IU,
2U, -, NU represent each bank of the upper cooling device of the strip cooling device, 1L, 2L.

..., NL represent each bank of the lower cooling device.

Further, 11 is the final stand of the finishing rolling mill, 12 is the coiler for the strip 10 after rolling, and 13 is the final stand 11.
This is a motor for driving.

Furthermore, one of the signal detection devices necessary for winding temperature control is
01 is a plate thickness measuring device for measuring the thickness of the strip 10, 102 is a finishing thermometer for measuring the finishing temperature of the strip 10, and 103 is a winding device for measuring the temperature at the winding portion of the strip 10. Thermometer 104 indicates a roll tachometer connected to motor 13 to measure the speed of final stand 11.

However, the oldest control method is manual control by rolling workers.

In this method, the winding temperature of the winding thermometer 103 is checked with an indicator and the cooling bank is turned on and off based on the difference from the target value, but there is a control delay due to the transfer distance between the cooling bank and the thermometer. It is difficult to avoid this, and there is a drawback that the determination of the initial setting number of banks must depend on the accumulation of experience.

Based on such a state, we proceed to dynamic control of the cooling bank by changing the setting bank based on the value of the finishing thermometer 102 and changing the rolling speed, but reaching this point is extremely difficult with human processing power. .

For this reason, the functions performed by workers have been replaced by control devices, and these have also been replaced by computers.

In this case, the function is the properties of the rolled strip (
Setting the initial required number of cooling banks, which can be determined from the moving speed (temperature, dimensions, heat capacity) and moving speed, the amount of change in cooling water amount in response to changes in finishing temperature, and the change in cooling water amount in response to changes in strip transition speed in response to acceleration/deceleration of the rolling mill. By knowing the amount in some way, the cooling bank is turned on and off.

Increasing the rolling speed and increasing the acceleration rate and deceleration rate accordingly in order to increase the production volume in hot rolling deteriorates the accuracy of temperature control by the method described above.

It has also been pointed out that conventional control methods are based on heat transfer theory, but have problems in actual application, and do not sufficiently take into account constraints in actual operation.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for correcting these drawbacks and controlling the winding temperature with sufficient accuracy.

This invention will be explained below.

By the way, as is well known, the transfer of heat in an object such as a metal strip whose thickness is extremely small relative to its length and width is expressed by a one-dimensional heat conduction equation such as the following equation.

Here, T=T(x, t) is the point x1 of the strip, k
is thermal conductivity and Cρ is heat capacity.

However, the X coordinate is in the thickness direction of the strip, and the bottom surface is 0 and the top surface is the plate thickness.

To find out the temperature during strip cooling, you can solve equation (1), but this requires initial conditions and boundary conditions.

In a case like this example, the initial condition is T (x, 0) = TF−……………………………………
...(2) That is, it is constant regardless of X, and this is the temperature at the exit of the finishing rolling mill, that is, the finishing temperature TF.

Boundary conditions vary depending on cooling conditions.

First, cooling by radiation is most important in areas that are not in contact with cooling water, and temperature drops due to other causes can be ignored.

In this case, on the surface of the strip, on the bottom side, and on the top surface It is.

In addition, the temperature drop due to Newtonian cooling is dominant in the portions in contact with the cooling water, and is lower on the lower surface and lower on the upper surface.

Here, σ is the Stefan-Boltzmann constant, ε is the emissivity, TA is the ambient temperature, λL is the heat transfer coefficient at the bottom surface,
λU is the heat transfer coefficient at the upper surface, and Tw is the cooling water temperature.

Now, if we solve equation (1) under the conditions of equations (2) to (6) above, we can find out the temperature at any point (including the surface) inside the IJ tube at any time. , this cannot be solved in a simple form.

Therefore, in general, a method is used in which equation (11) is solved approximately with the condition that there is no temperature gradient in the thickness direction.

Here, the strip of temperature To and thickness of the plate is maintained for time t,
The temperature T when subjected to cooling is , in the case of radiation cooling, and , in the case of Newtonian cooling.

However, λ is λU when only the top surface is cooled, λL when only the bottom surface is cooled, and λU+λL when both sides are cooled.
Substitute.

When using the above-mentioned force and equation (8), when the plate thickness is relatively small, it agrees well with reality, but when the plate thickness is small, the maximum temperature and minimum temperature (surface) in the thickness direction This is because the difference is relatively small and the above assumptions are approximately satisfied.

However, as the plate thickness increases, the temperature difference within the strip increases, causing an error between equations (7) and (8) and the actual temperature.

In order to reduce such errors, this invention uses a method of determining the emissivity ε in the force equation and the heat transfer coefficient λ in equation (8) from actual temperature measurement data, and at the same time For a strip of (1
) The above-mentioned parameters are determined by comparing the solution of the equation (7) or (8) with the numerical solution.

Therefore, temperature control according to the present invention is performed as follows.

Divide the hot run table into small intervals at equal intervals in advance.

1, 2, 3 in Figure 1. …. Preferably, this subsection is equal to the length of a unit bank of cooling spray, as indicated by N.

First, the radiation drop from the finishing thermometer 102 to the winding thermometer 103 can be determined using equation (7).

Generally, when a certain point of the strip is directly below the finishing thermometer 102, the temperature TF, the strip running speed V ((obtained from the final stand roll circumferential speed and its advance rate), and the plate thickness are measured using the plate thickness measuring device 101. Then, if we calculate the time t for the point to reach the winding thermometer 103 from the acceleration/deceleration rate at that time, the temperature drop amount TR due to radiation only is obtained from equation (7), and this temperature drop amount TR can be calculated by dividing into the above-mentioned subdivisions. Assign to each interval.

Here, since the radiation temperature drop in each small section is not the same, a coefficient γi is introduced to form the following form.

Here, ΔTRi is the radiation temperature drop in the first section, N is the number of sections between the finishing thermometer 102 and the winding thermometer 103, and the coefficient γi depends on the distance from the finishing thermometer 102, that is, the number of sections i. , for example, is expressed as:

γ1−ai+b …………………………………(11
) However, a and b are constants.

Now, the central idea of the winding temperature control according to the present invention is as follows.

Previously, the hot run table was divided into N small sections (sections), and the control function is operated every time the strip moves to one section.

In FIG. 2, 51 indicates a calculation control device, and data 52A from the initial data input device 52 or the sensor 10
Based on the data 101A from 1 to 104, the temperature drop of the strip for each cooling bank is determined by equation (8) while taking into account the radiation temperature drop of equation 00), and as described below, this is determined as the predetermined winding temperature. Increase the cooling bank until it is equal to or within the acceptable range.

Incidentally, each hot-rolled coil has a cooling pattern required by its use.

In other words, even if the coiling temperature is the same, there are differences in the crystal structure and particle size of the strip after cooling when the cooling device is different, such as when the strip is water-cooled at the front of the cooling device and when it is water-cooled at the rear. Because of this, the mechanical properties and appearance of the finished coil will be slightly different.

Therefore, it is necessary to use specific cooling patterns when specifically required.

Generally, the cooling banks are used in order from the front end (closer to the rolling mill), and this pattern will be described here.

First, as mentioned above, from equations (9) and 00), △TRi
Calculate.

Next, the outlet side temperature of each bank after cooling is calculated in order from the first bank according to the following formula.

Here, ti is the time for passing through the first section, and can be calculated based on the strip speed at that time.

This equation (12) can be used even if there is no water injection in i-bank for some reason. If λ-0 is used, then Ti=Ti-t-ΔTRi...
13), which represents the temperature drop due to radiation only, so in the case of no water injection, formula a3) can be used as is by setting λ=0.

Thus, if the final used bank is k, the winding temperature Tcc at this time is Tcc=Tk-(N-k)ΔTR
kl………………(14) In other words, the radiation temperature drop in each section after bank k is △TR at the center of the radiation section.
to average.

Temperature Tcc of formula 04 is l Tcc with respect to target temperature Tc
−Te l≦δ ……………………… (151 is satisfied.

Here, δ is the permissible deviation of the winding temperature, and it is desirable that this deviation δ is smaller than the final permissible deviation.

Cooling banks usually have a main bank and a fine adjustment bank.
If only the main bank is used, no matter what value k is taken (if it does not satisfy Equation 151, the last one is corrected by the fine adjustment bank.

For example, the winding temperature when main bank k is used is Tck, (
k+1) Tck-Tc〉δ …………………………………(16
) and Tck+1−Tckuichiδ………………………………(1
7) Then use the main bank up to k and (Tck-Tc)
It is sufficient to cool down the temperature difference using a fine adjustment bank.

Of course, how many fine adjustment banks to use can be calculated in the same manner as described above.

The thus calculated required banks are controlled on-off by the valve control device 21.

By the method described above, it is possible to equalize the temperature of each section of the strip to the target temperature within ±δ.

According to this method, even if the target temperature changes in the longitudinal direction of the strip, it is possible to control the temperature to a predetermined value.

Of course, the timing of actual pulp opening and closing must be determined by considering the strip transition speed and valve delay time.

In other words, when bank B of the cooling device downstream of the strip A section (directly below the finishing thermometer) that is the subject of calculation receives a new injection on command (or water injection off command), the strip The water injection starts exactly when the A section moves to the position directly below (or directly above) the B bank (or the water injection that was being received until now is turned off).
The timing must be determined accordingly.

The determination of this timing is already known as disclosed in Japanese Patent Application Laid-open No. 49-118655, but
For example, it is done as follows.

The current velocity of the strip is Vo (m/s), the acceleration is α [m/s2], the distance from the finishing thermometer to the B bank is L (m), and the A section of the strip is from just below the finishing thermometer to the B bank. The time required to move to the bottom is T
(s), the strip speed after t(s) from the current time is Vo+αt [m/s], so the following equation holds true.

If we solve this for T becomes.

Here, the B bank valve operation delay time, that is, the time from when the ON command is given until the B bank cooling water reaches the strip (or from when the OFF command is given until the B bank cooling water reaches the strip) If TD (s) is the time required for the power to run out, then the ON command (or OFF command) can be issued after T-TD (s), which is shorter than the time T in Equation 9 by TD.

Thus, by controlling each bank on and off, a small section of the strip can receive water injection from all the calculated required banks in just the right amount while moving through the hot run table, and the winding temperature can be adjusted accordingly. can be controlled to the target.

Note that in the above description, an approximate method is used to calculate the cooling effect due to radiation among the amount of temperature drop, but it is also possible to calculate this more precisely.

That is, from the time required for each section of the strip to advance, the radiant temperature drop during this period is calculated each time using equation (7) and used in place of △Tki in equation (10), and further, equation (14) is calculated. Instead of (N-k)△TRk' in the equation, the radiation drop from the bank outlet to the winding thermometer is (
9) Calculate and use in the same way as formula.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an outline of a hot run table, and FIG. 2 is a diagram showing an outline of a hot run table to which the method of the present invention is applied. 10... Strip, 11... Final stand of finishing rolling mill, 12... Coiler, 13... Motor, 101... Plate thickness measuring device, 102... Finishing thermometer, 103... Winding thermometer, 21... Valve control device, 51... Calculation control device, 5
2...Initial data input device.

Claims (1)

[Claims] 1 Every time the rolled steel plate moves a predetermined distance on the hot run table, the exit side plate thickness and finishing temperature are measured using a plate thickness measuring device and finishing temperature meter installed on the rolling machine exit side, and the rolling The steel plate transfer speed is measured using a roll rotation speed meter installed on the final stand of the machine, and the number of banks of the cooling system required to obtain the specified coiling temperature is calculated based on the acceleration/deceleration rate of the rolling mill at that time. The hot rolling is characterized in that the pulp in the calculated banks is opened and closed at appropriate timings taking into account the operation delay time, so that all the required banks are injected with just enough water and the coiling temperature is controlled to the target value. Method for controlling coiling temperature of steel plate.