JPS5814486B2 - How to control a heating furnace - Google Patents

Description

[Detailed Description of the Invention] When steel billets are continuously heated in a heating furnace, it is common practice to provide a suitable skid rail on the hearth of the furnace to ensure smooth movement of the steel billets within the furnace. ing.

Since the above-mentioned skid rail is cooled by passing cooling water inside, the part of the steel billet that comes into contact with the rail has a significant temperature difference compared to other parts, so a low-temperature area called a skid mark is formed on the back side of the steel billet. occurs in

This remains until after the steel billet is extracted from the heating furnace, causing plate thickness variations during the subsequent rolling operation of the heated material, and adversely affecting the quality of the product.

The present invention relates to a method for controlling a heating furnace having a skid rail for controlling plate thickness variations during rolling of a heated material due to skid marks in rolling a steel plate so as to fall within a predetermined range.

If the width of plate thickness variation due to this skid mark is within the allowable range of the product, it will not pose any problem in practice.

However, in the past, it was difficult to quantitatively grasp the amount of skid marks, so measures such as increasing the furnace temperature set value and extending the soaking time were taken as measures to reduce skid marks during actual heating furnace operation. However, these problems inevitably led to increases in fuel consumption and costs.

The present invention is based on the knowledge that there is a large correlation between plate thickness fluctuations caused by skid marks and the furnace temperature setting value in the heating furnace for steel billets. The first feature is that the plate thickness variation is controlled by the furnace set temperature of the heating furnace, and further, by controlling the furnace set temperature, The second feature is that the plate thickness variation is controlled to a predetermined value within the permissible basic unit limit.

Next, the control method of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is an explanatory diagram of the hot strip mill line layout in which the present invention is implemented.

In the figure, the steel billet 6 extracted from the four-zone heating furnace 1 enters directly into the first finishing standard rolling mill from the left side of the figure.

The illustrated rolling mill 3 is a first stand of a finishing rolling mill, and is provided with measuring devices for rolling load and gauge pressure.

This is set for ease of measurement, and these may be set at the final finishing stand.

As soon as the steel billet 6 is bitten by the rolling mill, the load detector 4
The lowering position detector 5 periodically collects detected values, for example, every 0.1 seconds, and the detected values are stored in the computer 7.

Collection of these detected values continues until rolling is completed.

The calculation device 7 calculates the furnace temperature set value and outputs the result to the furnace temperature control device 2.

FIG. 2 is a block diagram showing the process of calculating the furnace temperature set value performed by the arithmetic unit 7.

In the figure, A is (
1) is a block diagram for calculating the gauge meter thickness h using equation 1.

:M is the mill steel property coefficient.

Here, h is the calculation of the gauge meter thickness, but in a mill that does not change the rolling reduction during rolling, it is also possible to observe only P instead of h in equation (1) and use it as the same observed value as h. .

That is, in a mill where the rolling position does not change during rolling, it is sufficient to observe only the rolling load.

Hereinafter, similar processing is performed by replacing P→h.

B is a block diagram for determining the absolute value Δhi of the difference between adjacent extreme values in the variation of h calculated from equation (1).

FIG. 3 shows an example of the variation in h when a slab is hot rolled into a strip.

Since the temperature of the hot-rolled material is higher at the top than at the bottom, h is on the rise.

In the illustrated example, the portion corresponding to the skid mark shows an extremely thick value of h.

In B, the absolute value of the difference between extreme values △h,, △h2, △h3, △h
Find 4, △h,, △h6.

C is a block that determines whether the calculations of A and H have been completed over the entire length of the hot-rolled material.

Next, Δh is calculated in block D according to the following equation.

n: (number of extreme values) -1 The value of Δh indicates the plate thickness deviation due to skind marks.

E is a block that determines whether or not to change the furnace temperature set value based on the Δh value.

Setting values for this determination are determined in consideration of plate thickness, plate width, steel type, extraction temperature, finishing temperature, etc.

F is a block that calculates the changed furnace temperature set value.

G is a smoothing arithmetic unit.

If the furnace temperature set value is changed using the value obtained by F as it is, a so-called hunting phenomenon occurs in which the furnace temperature set value changes from one steel billet to another.

In order to avoid this, a smoothing calculation is performed to average out the fluctuations in the furnace temperature set value, taking into account the previously calculated values of the steel slab.

Next, Examples of the method of the present invention are shown in Table 1, and the effects of the method of the present invention will be explained.

This is an example of controlling the temperature of the fourth heating zone of the soaking furnace using the method of the present invention to reduce plate thickness variation.

Although this example uses a method of changing only the furnace temperature setting value of the outermost heating zone, the effect of the present method can also be achieved by changing other heating zone temperature settings or changing the soaking time. can get.

Note that the gauge meter thickness variation in this example is the value of the first finishing standard of the rolling mill.

Also, the slab dimensions are 250 mm thick x 1000 mm wide x 8320 mm.
The length and finished dimensions are 10mm thick x 1000mm wide.

The gauge meter thickness variation in example a is 420μ, which is thicker than the predetermined value, so as a result of calculation using the method of the present invention, as in example b, by increasing the fourth heating zone furnace set temperature by 60°C, the gauge meter thickness can be adjusted to the predetermined value. The value decreased to 210μ.

On the other hand, Example C is an example of the above-mentioned conventional countermeasure, and when the fourth heating furnace set temperature was set high, the gauge meter thickness decreased to 155 μm, which was within the predetermined value.

However, this means that the furnace temperature is set higher than necessary, which clearly means disadvantageous operation from the viewpoint of fuel consumption. According to the method of the present invention, both the gauge meter thickness variation and the furnace installation temperature are adjusted appropriately. It shows that it is controlled by

In addition, when considering strip width fluctuations due to rolling mills that are not equipped with an AGC device or skid marks, it is sufficient to calculate only the rolling load, that is, S in equation (1) is
Then, calculate the value of h.

The present method can also be implemented in heating furnace control for controlling gauge meter thickness variation in the final pass or a predetermined pass of a reversible rolling mill such as a plate mill to a predetermined value or less.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of an example of the arrangement of a hot strip mill line in which the present invention is implemented, and FIG. 2 is a block diagram showing the calculation process for determining the furnace temperature set value of the present invention. FIG. 3 shows an example of variation in gauge meter thickness h. 1...Heating furnace, 2...Fuel control device, 3...Rolling mill, 4
...Rolling load detector, 5... Rolling position detector, 6... Rolled material, 7... Arithmetic device, A... Gauge meter thickness calculation block, B... △hi calculation block, C... Collection value Complete completion judgment block, D... Gauge meter thickness deviation (△h)
Calculation block, E... Furnace temperature change judgment block, F
...Furnace temperature set value change block, G...7 smoothing calculation block.

Claims (1)

[Claims] 1. Continuously or periodically measure the rolling load or gauge meter thickness during rolling of the rolled material heated by a heating furnace equipped with skid rails, and determine the adjacent extreme values and minimum values in the variation of the rolling load or gauge meter thickness. 1. A method for controlling a heating furnace, characterized in that the temperature inside the heating furnace is controlled so that the average value of the absolute values of the differences is determined and the average value falls within a predetermined range.