JPS6281217A - Straightening method for hot steel plate - Google Patents

Abstract

PURPOSE:To increase the flatness of a product by straightening after performing the temp. control in the plate width direction or as it is based on the measuring result of the temp. distribution in the plate width direction of the hot steel plate measured at the inlet side of a roll straightening machine. CONSTITUTION:The temp. distribution in the plate width direction of a hot steel plate 10 is measured by a thermometer 18. The thermal stress due to the temp. difference is operated based on the temp. distribution in the plate width direction by arithmetic unit 22. Then the thermal stress and the critical buckling stress in the longitudinal direction of the hot steel plate 10 are compared and in case of the thermal stress being smaller than the critical buckling stress the straightening is performed by a roll straightening machine 12 as it is. In case of the thermal stress being larger than the critical buckling stress the low temp. part of the hot steel plate 10 is heated by a heating device 20 and the straightening is performed after making the thermal stress smaller than the critical buckling stress. In this way, the flatness is increased.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for straightening a hot steel plate, and more particularly to an improvement in a method for straightening a hot steel plate by using a roll straightener.

[Conventional technology]

Conventionally, straightening of a hot steel plate is generally carried out using a roll straightening machine shown in FIG. 6 or a tension leveler shown in FIG. 7. As shown in FIG. 6, the roll straightening machine passes a material 2 such as a hot-worked steel plate between a large number of parallel rolls 1 arranged in a zigzag pattern and alternately passes the material 2 in opposite directions. By applying bending, the rolls are flattened or straightened, and the rolls are arranged in a straight line up and down, cutting into each other on the inlet side of the material to be straightened, and opening toward the outlet side. There is. The straightening machine using the tension leveler has a structure in which a bending unit 5 consisting of a group of parallel rolls 4 is inserted between a tension loading unit 3, as shown in FIG. This method involves repeatedly applying bending while applying tension to correct it. In addition, in the straightening method using the tension leveler, as disclosed in JP-A-54-142166, when the cape point differs in the width direction of the steel plate, a temperature difference is given to the steel plate to make the yield point uniform. A method has been proposed to correct this problem.

[Problems to be solved by the invention]

However, as shown in FIG. 8, after hot rolling, the temperature of the steel plate generally decreases sharply at the ends in the width direction of the steel plate. When this steel plate is flattened using a roll straightening machine, compressive stress is generated in the low temperature portion (end portion in the width direction) after the steel plate is cooled, as shown in FIG. When this compressive stress exceeds the buckling stress, the steel plate undergoes buckling deformation and distortion occurs again. This phenomenon is particularly noticeable in thin steel plates. In addition, in the straightening method using a tension leveler proposed in the above-mentioned Japanese Patent Application Laid-Open No. 54-142166, a temperature difference is given to the steel plate to make the yield point uniform, but if this temperature difference is small, problems may arise. However, if the temperature difference is as large as several tens of degrees Celsius, thermal stress will be generated in the steel plate due to the temperature difference after straightening cooling, resulting in so-called edge elongation, where the ends of the sheet elongate in the width direction, or elongation at the center of the sheet width direction. There are problems in that there is a possibility of shape defects such as stretch, or the occurrence of camber due to thermal stress when cutting the steel plate into strips.

[Purpose of the invention] The present invention was made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a method for straightening a hot copper plate that can prevent the occurrence of cooling distortion after straightening and cooling. [Means to solve the problem]

The present invention provides a hot steel plate straightening method for straightening a hot steel plate using a roll straightening machine, as shown in FIG. Measure the temperature distribution, find the temperature difference between the high temperature part and the low temperature part of the measured temperature distribution in the width direction of the board, and if this temperature difference is such that it does not cause cooling distortion after straightening cooling, straighten it as is. , when the temperature difference is a temperature difference that causes cooling distortion after corrective cooling, the temperature difference is a lagoon 1 that does not cause cooling distortion after corrective cooling.
The above object has been achieved by controlling the temperature of the hot steel sheet in the width direction so that the temperature is 1'1 or less, and then straightening the sheet.

[Effect]

It has been confirmed that when the thermal stress σt exceeds the critical buckling stress σcr, the steel plate buckles and distortion occurs after the cold section. Therefore, in the present invention, 11
Measure the distribution, find the temperature difference between the high temperature part and the low temperature part of the measured temperature distribution in the width direction of the plate, and if this temperature difference is the temperature difference that causes cooling distortion after corrective cooling, this temperature difference is The hot steel sheet is straightened by controlling the temperature in the sheet width direction so that the temperature difference is below that which does not cause cooling distortion after straightening and cooling. Therefore, by reducing the temperature difference in the width direction of the hot steel plate, the thermal stress σt after cooling can be made equal to or less than the critical buckling stress σcr, thereby preventing the occurrence of distortion.

【Example】

Hereinafter, with reference to the drawings, a hot steel plate straightening facility for carrying out the method of the present invention will be described in detail. This equipment, as shown in Figures 2 to 5,
l■ In hot steel plate straightening equipment for straightening a steel plate 10 using a roll straightening machine 12, a roll straightening ff112 equipped with a large number of parallel rolls 14 arranged in a zigzag pattern, and a roll straightening machine 112 on the entry side of the roll straightening machine 12 A scanning thermometer 18 is disposed on the conveying table 16 and scans in the width direction of the hot steel plate 10 to measure the temperature value li in the width direction of the hot steel plate 1o.
A plurality of heating devices 20 are disposed in the width direction of the hot steel sheet 10 between the thermometer 18 and the roll straightening machine 12.
and the temperature valve i in the plate width direction measured by the thermometer 18 [
Based on this, the temperature difference between the high-temperature part and the low-temperature part is determined, the thermal stress due to the temperature difference is calculated, and the thermal stress in the longitudinal direction of the hot-worked steel plate 10 and the longitudinal direction of the hot-worked steel plate 10 are calculated. The apparatus is further provided with an arithmetic device 22 which compares the thermal stress with the critical buckling stress in the direction and outputs a heating control signal to the heating device 20 as described in 11 above when the thermal stress is larger than the critical buckling stress. The heating device 20 is constituted by an induction heating device, and as shown in FIG. 3, a plurality of heating devices 1'iil! It is possible to heat any part of the hot steel sheet 10 in the sheet width direction. The operation of the above equipment will be explained below. First, the temperature distribution in the width direction of the hot steel plate 10 is measured using the temperature resistance 18. Next, the calculation device 22 calculates the temperature difference between the high temperature portion and the low temperature portion of the temperature distribution based on the temperature distribution in the board width direction, and calculates the thermal stress due to this temperature difference. Next, the thermal stress in the longitudinal direction of the hot steel plate 10 and the hot steel plate 10
The thermal stress is compared with the critical buckling stress in the longitudinal direction, and if the thermal stress is smaller than the critical buckling stress, the roll straightening machine 12 is
We will correct the situation accordingly. That is, after straightening and cooling, if the temperature difference does not cause thermal distortion, straightening is performed as is. In addition, the thermal stress in the longitudinal direction of the hot steel plate 10 is
If the stress is greater than the critical buckling stress in the longitudinal direction, the heating device 20 heats the low-temperature portion of the hot steel plate 10. This heating is performed until the humidity reaches such a level that the thermal stress in the longitudinal direction of the hot steel plate 10 is smaller than the critical buckling stress in the longitudinal direction. In the case of an induction heating device for wooden equipment, the rise wetting mark Δ per unit time of the hot steel plate 10 is as follows:
It can be determined from the following relationship. ΔT-5ao-η-Q/(C-p-v-t-a>
・・・・・・・・・(1) Here, Q is the input power (kW), and C is the specific heat of the steel plate (kw).
cal/ke・'C) 1. O is the specific gravity of the steel plate (kg/
1n3), V is the sheet threading speed (em/s > , t is the sheet thickness (
mw+), a is the width (ding) of the induction heating device, and η is the efficiency. Based on the temperature increase ΔT of the hot steel plate 10 obtained from the above formula, the low temperature portion of the hot steel plate 10 is heated so that the temperature difference is equal to or lower than the temperature difference that does not cause cooling distortion after straightening cooling. Therefore, according to the above equipment, the temperature difference ΔT of the hot steel plate 10
By reducing the thermal stress σ after cooling to less than the critical buckling stress σC, it is possible to prevent the occurrence of distortion.Next, the results of implementing the above equipment will be explained. Hot work steel plate 10 with a thickness of 4.5 mm and a temperature distribution that allows
As a result of passing the steel sheet through the heating device 20 at a speed of 45 m/sin and then straightening it, one straightened hot steel sheet 10 having a temperature distribution as shown in FIG. 5 was obtained. When this hot steel plate 10 was cooled to room temperature, no ear waves were generated in this steel plate 10. Critical buckling stress σcr at this time
The ratio between the temperature and the thermal stress σ°C was σt/σcr−0.04. On the other hand, if the present invention is not carried out, that is, the hot steel sheet 10 having the humidity distribution as shown in FIG. 4 is rolled as is) n positive II! [When the steel plate 12 is straightened and cooled to room temperature by 1 comb, the straightened steel plate 12 generates ear waves, and the steepness of the distortion is λ (λ - H (wave crest height) / P (wave crest height)). The pitch of the mountain)) was 0.2%. In addition, in the above-mentioned equipment, one thermometer 18 is used to scan the hot steel plate 10 in the width direction of the hot steel plate 1o.
However, the present invention is not limited to this, and for example, assuming that a plurality of thermometers are installed in the width direction of the hot steel sheet 10, The temperature distribution in the width direction of the hot steel sheet 10 may be measured using a plurality of these hygrometers. In addition, in the illustrated embodiment, the temperature difference in the hot steel plate 10 is heated by the heating device 20, and the temperature is controlled so that the temperature difference becomes equal to or less than the temperature difference that does not cause cooling distortion after straightening cooling. However, the present invention is not limited to this, and depending on the operating conditions, the temperature may be controlled by cooling the high-temperature portion so that the temperature difference after straightening cooling does not cause cooling distortion. [Effects of R-light 1 As explained above, according to the present invention, there is an excellent effect that a flat steel plate can be obtained without generating distortion even when cooled after straightening.

[Brief explanation of drawings]

Fig. 1 is a flowchart without showing the gist of the hot steel plate straightening method according to the present invention, and Fig. 2 is a side view, including a partial block diagram, showing hot steel plate straightening equipment to which the present invention method is applied. , Fig. 3 is a view taken along the m MFA in Fig. 2, Fig. 4 is a diagram showing the temperature distribution in the width direction of the hot steel plate before straightening in the same straightening equipment, and Fig. 5 is a diagram showing the temperature distribution in the width direction of the hot steel plate before straightening in the same straightening equipment. Fig. 6 is a side view showing the main parts of a conventional roll straightening machine; Fig. 7 is a side view showing the same conventional tension leveler; Figure 9 is the same (conventional diagram showing the temperature drop in the sheet width direction), and Figure 9 is the same (conventional diagram showing the stress distribution in the sheet width direction of a hot steel sheet after straightening cooling). 1o... Hot steel plate, 12... Roll straightening machine, 14... Straightening roll, 18... Thermometer, 20... Heating device, 22... Arithmetic device.

Claims (1)

[Claims] (1) In a hot steel plate straightening method in which a hot steel plate is straightened using a roll straightening machine, the temperature distribution in the sheet width direction of the hot steel plate on the entry side of the roll straightening machine is measured, and the measured sheet width is Find the temperature difference between the high temperature part and the low temperature part of the temperature distribution in the direction, and if this temperature difference is a temperature difference that does not cause cooling distortion after correction cooling, correct it as it is, and the temperature difference will cause cooling distortion after correction cooling. A method for straightening a hot-worked steel sheet, which comprises controlling the temperature in the width direction of the hot-worked steel sheet so that the temperature difference is below a temperature difference that does not cause cooling distortion after straightening and cooling. .