JPH0557349A - Method for restraining camber at the time of stripe-cutting thick steel plate - Google Patents

Abstract

PURPOSE:To restrain the development of camber at the time of stripe-cutting by executing heating and cooling with partial heating and cooling means based on the measured data of temp. distributing with a hot leveler. CONSTITUTION:The thick steel completing the finishing roll is passed through a thermometer 10 to measure temp. distribution in the width direction. This temp. measured result is transferred to width divided water cooling nozzles 14 with feedforward. A computer stores temp. distribution in the width direction and ON/OFF operation of the cooling nozzle 14 is controlled so that the lowest temp. becomes the temp. at the position in the other width direction. Successively, cooling effect with the water cooling nozzle 14 is measured with a thermometer 20 for width direction and feedback is executed to the cooling result. The thermometer 20 for width direction transmits the measured result for the whole width of thick steel plate to edge heaters through the computer. The edge heater executes adjustment of opening degree in the width direction based on data of the thermometer 20 in the width direction. Further, command of heating quantity under consideration of discharging heat till applying the hot leveler based on the temp. lowering quantity at both edges, is received from the computer and both edges are heated up.

Description

Description: TECHNICAL FIELD The present invention relates to a method for suppressing stripping camber of thick steel plates, that is, a method for suppressing stripping camber that occurs when cutting strips of thick steel plate. ..

(Prior Art) One of the uses of thick steel plates is long-distance materials for shipbuilding, steel frames, and bridges. The thick steel plates used for these are cut into strips from the state of wide plates, and the narrow plates obtained are processed into boxes and channels by means such as welding.

 In other words, long-distance materials for shipbuilding, or building materials such as bridges and steel frames, use narrow and long materials with a width of 300 to 600 mm and a width of 10 to 20 m. On the other hand, thick steel plates manufactured by blast furnace makers are It is a wide material with a thickness of 4 mm or more and a width of 2000 to 3000 mm. Therefore, such wide strips are usually cut into strips of narrow strips using a series of gas torches. It is a so-called strip.

 The problem here is the lateral bending that occurs in each cut and cut material, and this is simply called a camber or cut camber.

 For example, in the case of narrow and long products such as the above-mentioned long construction materials for shipbuilding and bridges, when cutting out from a wide plate material by gas cutting, a large slitting camber, for example a camber of about 50 mm at 10 m length is generated. In some cases, correction by pressing etc. after cutting was necessary.

Such additional processing increases manufacturing costs and impedes efficient production.

 The occurrence of such a strip camber decreases the dimensional accuracy of the final product such as a box or channel, and therefore it is desirable to suppress it even if it cannot be completely removed due to its nature.

 Although various factors are involved in the occurrence of the strip camber, it has been known that it is necessary to control the residual stress of the steel sheet at least to suppress it.

 However, the methods that have been put to practical use up to now are to temper steel plates online prior to stripping, or to release residual stress through a cold leveler, also offline, for example. It was the current situation that each occurrence would be corrected by a press etc.

It was also a cost issue.

(Problems to be Solved by the Invention) An object of the present invention is to provide a simple and inexpensive method for solving the problems in the prior art and suppressing the occurrence of camber at the time of cutting.

(Means for Solving the Problem) In order to achieve the above-mentioned object, the present inventor has conducted extensive studies, and as a result, after uniformizing the temperature distribution in the strip width direction by local heating / cooling means in the same rolling line, We have found that straightening with a hot leveler effectively suppresses the occurrence of stripping camber during subsequent stripping.

 Furthermore, as a means of such uniform temperature on-line, an edge heater that can heat up only the side edges of the steel sheet is adopted as a local heating means, while a widthwise split water cooling nozzle is used as a local cooling means. It was found that it is better to improve the controllability by using the width direction thermometers at three locations immediately before and after the edge heater and immediately before the water cooling device.

 Certainly, some proposals have already been made from the perspective of controlling the residual stress of steel sheets.

 For example, in Japanese Unexamined Patent Publication No. 61-212422, a thick steel plate that has been cooled to a straightening temperature by water cooling after completion of rolling is temperature-compensated by an induction heating device in a thick plate rolling line, and the temperature of the steel plate is adjusted. After eliminating the variation, the hot leveler is used to straighten the hot surface to eliminate the variation in mechanical strength. Further, in Japanese Patent Laid-Open No. 166113/1985, a heating device is divided into a plurality of parts in a direction orthogonal to the conveying direction at regular intervals in the slab conveying direction, and a surface thermometer for measuring the temperature in the slab width direction. Is installed and the temperature distribution inside the slab is estimated by a computer, and the controlled heating is performed based on it. The purpose is to suppress the occurrence of crops at the front and rear ends of the slab.

 Moreover, from the viewpoint of making the temperature of the steel sheet in the width direction uniform, in the device disclosed in the above-mentioned JP-A-61-212422, the temperature detector is only on the inlet side of the heating furnace. The result of heating is not fed back, and a large number of full-width induction heating devices are required.

 Further, in JP-A-60-166113, a large number of induction heating devices divided in the width direction are required, and it is difficult to achieve the object of the present invention because a hot leveler is not provided.

 Here, the present invention was obtained by measuring the temperature distribution in the width direction of the plate at the time of hot leveler straightening after finish rolling of the plate, in order to prevent the stripping camber that occurs during the stripping of the plate. Based on the measured data, heating and / or cooling is performed by local heating / cooling means, and the temperature distribution in the width direction is made uniform and then corrected by a hot leveler. Is the law.

 According to the preferred embodiment of the present invention, the temperature uniformity in the width direction of the thick steel plate is achieved by observing the result of the measurement of the temperature distribution in the width direction so that the edge part of the plate that is supercooled is an edge as a local heating means. With the heater, temperature unevenness in the central part is achieved by partial water cooling using the widthwise divided water cooling nozzle as a local cooling means.

 Thus, according to the present invention, for example, when cutting a wide steel plate having a plate thickness of 4 mm or more, preferably 10 to 50 mm and a plate width of 2000 to 3000 mm into a 300 to 600 mm width, as described above, Only by processing, it is possible to suppress the formation of stripping chambers to a length of 10 mm and 16 mm or less, preferably less than 15 mm.

 Incidentally. The above "edge heater" is not limited to a specific structure as long as only the plate side edge is heated, but high frequency induction heating is preferable.

 The same applies to the local water-cooling means, which is generally composed of water-cooling nozzles divided in the width direction, but it may have, for example, a structure of a compressed air nozzle.

(Operation) Next, the present invention will be described in more detail with reference to the accompanying drawings.

 FIG. 1 is a schematic explanatory view showing the arrangement of devices for carrying out the method of the present invention.

 The illustrated device is a thermometer 10 that measures the temperature in the width direction of the thick steel plate exiting the finishing rolling mill, and a width-division type water-cooling nozzle 14 that adjusts the cooling amount based on the measurement data of this temperature distribution in the width direction. And another thermometer 20 provided downstream thereof, an edge heater 22, and a thermometer 30 for measuring the widthwise temperature distribution of the thick steel plate before being sent to the hot leveler.

 Next, the operation of uniformizing the temperature in the width direction according to the present invention will be described. In the present invention, however, flatness correction is required after finish rolling. Therefore, after completion of plate rolling or accelerated cooling, the hot leveler is first used. It is preferable to carry out leveling by carrying out reciprocal leveling twice with a hot leveler and performing the temperature homogenization treatment of the present invention immediately before the third pass leveling.

 The width-direction temperature uniformizing treatment according to the present invention comprises the following steps.

Step-1: Pass the thick steel plate that has finished finish rolling at 45 m / min through the thermometer 10 and measure the temperature distribution in the width direction.

Process-2: Send the temperature measurement result inside the plate by the thermometer 10 excluding 200 mm inward from both edges of the plate to the width division water cooling nozzle 14 by feed forward.

Process-3: The computer stores the temperature distribution in the width direction for each pitch of 50 mm, and turns on / off the water cooling nozzle so that the other width direction part of the lowest temperature is located. (Nozzles are divided into 50 mm pitches in the width direction) Step-4: The cooling result by the water cooling nozzle 14 is measured by the width direction thermometer 20 and the cooling result is fed back.

Step-5: The width direction thermometer 20 transfers the measurement result of the full width of the thick steel plate to the edge heater via the computer.

Step-6: The edge heater adjusts the width opening based on the data of the width direction thermometer 20. Furthermore, based on the temperature drop of 200mm on both edges, the computer receives the amount of heat to cool down until the hot leveler is implemented and heats up both edges.

Process-7: The heat-up result is measured by the width direction thermometer 30, and the measured value at that time is fed back.

 In the above example, the plate feed speed is set to 45 m / min, but it can be changed up to 150 m / min depending on the rolling pitch.

In that case, it is necessary to change the amount of cooling water or the electric power supplied to the edge heater for induction heating according to the speed.

 Next, the present invention will be described more specifically by way of its examples.

Example 1 In this example, using the apparatus shown in FIG. 1, a thick plate having a size of 32.times.2275.times.16000 mm was straightened by a 3-pass hot leveler without heating the side edges, and then cut.

 At that time, the temperature distribution immediately before the three passes in the strip width direction and the state of residual stress are as shown in Fig. 2 (a), and the occurrence of the stripping camber after stripping is shown in Fig. 2 (b). It is particularly remarkable at both ends as shown by the amount of overhang (mm).

 In this case, the temperature drop at the edge is significant, and along with this, the occurrence of the stripping camber is significant.

 Next, a thick plate with the same dimensions was heated on the side edges immediately before 3 passes, and then subjected to hot leveling and then slitting, and the occurrence of slitting camber was investigated. As shown in Fig. 3 (a) and (b). It can be seen that the number of street stripping cambers has decreased considerably.

 In this example, water cooling was performed only in the central portion. The heating of the edge was induction heating.

Example 2 In this example as well, in the same manner as in Example 1, a thick plate having a plate size of 20 × 3200 × 2000 mm was heated at the side edges and cooled at the center and was subjected to a hot leveler. As shown in Fig. 4 (a) and (b), respectively, the temperature distribution, residual stress distribution, and the situation of strip camber occurrence, the occurrence of strip camber is almost the same as at the plate center even at the plate edge. I was able to suppress it to a certain degree.

Example 3 In this example, Example 2 was repeated using a thick plate having a plate size of 50 × 2400 × 10000 mm. The results are shown in Fig. 5 (a) and (b). Substantially no temperature deviation in the width direction was observed, and the effect of suppressing the occurrence of strip camber is remarkable.

Conventional Example 1 In this example, the method disclosed in JP-A-61-212422 was implemented.

 The plate rolling was completed at 750 ° C and transferred to the hot leveler in 30 seconds. Side spray to prevent indentation was carried out, and hot leveler 3 pass was carried out.

 Figure 6 (a) shows the temperature distribution in the strip width direction at this time. This temperature distribution is that just before the third pass.

 A thick plate with a plate size of 32 × 2275 × 16000 mm was used, but the controllability is poor because only the temperature distribution before heating is measured, and it is considerably small to reduce the temperature fluctuation inside the induction coil. (Width 200 mm or less) must be placed, which is expensive in terms of equipment.

 The results are shown in FIGS. 6 (a) and 6 (b).

(Effects of the Invention) Since the present invention is configured as described above, even if a thick plate straightened by a hot leveler is cut into strips, almost no stripping camber occurs. It is possible to supply excellent structural materials such as bridges, which is extremely useful in industry.

[Brief description of drawings]

 FIG. 1 is a process chart for carrying out the present invention; FIG. 2 is (a), (b) to FIG. 5 (a), (b) are graphs showing the results of the examples; and FIG. (a) and (b) are graphs showing the results of the conventional example. 10: Thermometer 14: Water cooling nozzle 20: Thermometer 22: Edge heater 30: Thermometer

Claims (1)

[Claims] 1. A measurement data obtained by measuring the temperature distribution in the width direction of the plate at the time of straightening the hot leveler after finish rolling of the plate to prevent the stripping camber that occurs when cutting the plate. Based on the above, heating and / or cooling is performed by means of local heating / cooling means, and the temperature distribution in the width direction is made uniform and then corrected by a hot leveler. Law.