RU2036030C1 - Method for producing steel strip or sheet and a facility to implement it - Google Patents

Abstract

FIELD: continuous steel casting and rolling steel strip. SUBSTANCE: inductive heating through device is provided at least after the first compressing stage in the facility for radial continuous casting of flat ingot. The facility is joint to multi-stand rolling mill to produce strip. Similar heating facilities may be provided also and after intermediate compressing stages. EFFECT: high productivity. 5 cl, 3 dwg

Description

 The invention relates to a method for the continuous production of steel strip or steel sheets from slabs made by continuous casting, with the direction of the metal in an arc with a horizontal direction of exit.

 In the metallurgical industry, whether due to a general trend or in order to overcome the crisis experienced by users of obsolete equipment in previous years, there is an urgent need to reduce production and capital costs while improving production and increasing flexibility with respect to manufactured units of measurement, those. rolls of strip or steel sheets. By modernizing existing steel mills or by designing and implementing new steel mills, using new technological concepts and devices, they strive to increase productivity and economy while improving product quality, as well as greater freedom of action in the area of product size at which the final product must be produced with optimal range of uses.

 One of the new technologies, the development of which is currently being accelerated, taking into account the current requirements for steel production, relates to the processing stages between steel melting and winding a steel tape in the form of rolls or stacking sheets and includes the casting of thin flat billets close to the final thickness dimensions which can then only be processed into the desired end product in just a few subsequent passes or pressure processing operations. This has led to noteworthy improvements in the continuous casting technique, especially taking into account the design of the molds or the corresponding immersion nozzle, as well as to the improvements in the design of rolling stands and lines in order to achieve the desired deformation as soon as possible.

Known installations for the manufacture of tape steel, in which the continuous casting method produces thin flat billets with a thickness of about 50 mm, compared with traditional flat billets with a thickness of 150 to 320 mm. At the same time, these thin flat billets go through various rolling (processing) operations one after another, the end product is tape steel only a few millimeters thick. It was proposed to roll the casting product immediately after intermediate heating in a furnace, for example, in a tandem rolling mill with six stands. As the casting speed may be slightly higher than 5 m / min, the last stand of the rolling line are too low rolling speed to be able to maintain the required final rolling temperature of at least about 865 ^o C. e. Tape between one rolling phase and the one following it experiences too much cooling for a reason identical to the casting speed of the insignificant speed of entry into the rolling mill. Therefore, this decision was rejected, since even with the help of heat-shielding devices and heated rolls, the problem could not be solved economically, since the consequence would be a significant increase in capital and production costs.

Another solution involves cutting the tape in front of the heating furnace, in which heat treatment (temperature equalization) of the tape is then carried out over the entire cross section. This may be, for example, a gas heated furnace roller with which accounted regardless of the casting speed at the outlet of the furnace can be installed tape temperature of about 1100 ^C, i.e. optimum temperature for the subsequent rolling process [1] The tape is cut into pieces of standard length, which, for example, for a certain roll weight can be 50 m, which requires an appropriate furnace length of about 150 m, if the necessary buffer action is taken into account.

 Due to the separation of the rolling line from the direct casting process, thin flat billets or preliminary strips can be rolled at higher speeds, so you can not be afraid of a temperature drop below the minimum temperature that is acceptable for the final rolling stage. At the same time, from the excessive length of the furnace, which is approximately three times the length of a piece of tape, in addition to a significant increase in capital costs for the installation, there also arises an excessive occupied area on which many steel-making workshops cannot be built.

 In addition, the dimensions of the installation and thereby the furnace limit the length of the processed pieces of tape following each other and thereby the final weight of the bundle, which again limits the field of activity when used, taking into account the manufacture of rolls of maximum diameter. Accordingly, in an installation of this type, it is not possible to use even finer flat workpieces at the outlet. This is possible with the help of technological improvement of the continuous casting method. Assuming an outlet thickness of 25 cm, as has already been hypothetically done, instead of 50 mm, to realize the same final weight of the bundle, the tape would have to be cut into sections about 100 m long, for which a length of the order of about 300 m, which cannot be practically and economically realized.

 The aim of the invention is to create an appropriate installation, with which you can produce a continuous tape from a flat product exiting from a continuous casting installation with the direction of the metal in an arc.

 In particular, it is necessary to abandon the separation of the product between the casting process and at least the first rolling process, and the first pass of the workpiece during continuous casting of metal in the first rolling stand is carried out at the speed with which the rolled strip leaves the arc section of the continuous casting installation. Thus, the method can be implemented on the production line with almost unlimited flexibility, so that it becomes possible to produce rolled strips of any weight and any length or sheets without changing the dimensional parameters of the installation, since the separation of the rolling tape is carried out at least after the first rolling pass or after performing all technological operations directly in front of the winding or stacking device.

The proposed method is characterized by the following technological operations: compression of a flat product after solidification of the metal in the first stage of compression at temperatures above 1100 ^about ; induction re-heating up to a temperature of about ¹¹⁰⁰ C at a best possible temperature equalization over the cross-section of the flat product; compression of the flat product in at least one next compression step at rolling speeds in accordance with a corresponding decrease in the thickness of the tape after passing through the rolls.

In an improvement of the method, it is proposed to wind the tape between the first and subsequent compression steps. It is possible to wind the rolled strip according to the weight of the roll after compression of the flat product, or after cutting the rolled strip after compression of the flat product, to stack them in packages of steel sheets of a predetermined length, if necessary after cooling and melting. Thus, the flat product first passes in the first rolling mill with the speed at which the product exits the continuous casting machine with the direction of the metal in an arc, and passes successive stages of rolling, respectively, with speeds that correspond to reduction in separate passes. The strip thus rolled is then either wound and, after the desired weight of the roll is reached, is cut off, or the tape is cut into pieces of the desired length and stacked in the form of sheets. An important aspect of the present invention is the induction reheating flat product after descaling to temperatures of about 1100 ^{° C} with the best possible temperature equalization, because in this way can advantageously counteract supercooling tape.

In another improved embodiment of the invention, it is proposed to provide one or more stages of induction intermediate heating of the flat product between these stages of compression. Through this intermediate heat as possible to counteract too strong cooling of the rolled strip, so that the required rolling temperature can be set constant so that the temperature in the last stage does not drop below the limit value of 860 ° ^C.

 The installation for implementing the method in accordance with the invention is characterized by the following parts in the specified sequence: a mold for the continuous casting of flat products followed by a pulling stand in the form of an arc; the first device (stand) for crimping the flat product of the pulling stand and / or immediately after it; a device for induction heating and temperature equalization along the cross section of a flat product; at least another rolling stand and a cutting device.

 A cutting device may be located behind the first crimping device and between the first crimping device and the next crimping device, a device for winding and unwinding a flat product in front of which the cutting device is located can be provided. A device for winding and unwinding a flat product is located behind the device for individual heating and before the subsequent crimping device.

 Alternatively, behind this installation there is either a cutting device for rolled tape and at least a rolling machine for winding a tape, or a cutting device for rolled tape, a cooling device, a straightening machine and a device for stacking cut sheets.

 In an improved embodiment of the invention, the installation further comprises at least one device for inductive intermediate heating between subsequent rolling stands.

 Advantageously, each of these devices is equipped with separately controlled heating stages.

 Devices are provided for sequential control of individual heating stages of furnaces immediately after the passage of the initial rolling strip.

 In FIG. 1 shows a diagram of the proposed installation; in FIG. 2 temperature characteristic of a steel tape; in FIG. 3 the same option.

 At the exit from the continuous casting mold 1, a flat product 2 is formed. The transporting flat product (product 2) guided in traditional pulling rollers passes from the initial vertical direction through the arc section formed by the pulling rollers to the horizontal position. After hardening, namely, in the end zone of the arc section, the flat product passes the first crimp step 3, in which its thickness is brought, for example, to a maximum of 25 mm. Stage 3 may consist of one or more rolling devices in the form of quarto stands.

 To maintain the temperature, further downstream of the descaler, a furnace 5 is provided, which is equipped with an induction heater. In this furnace 5, temperature equalization is carried out simultaneously over the entire cross section of the flat product 2, so that this product reaches the next stand 6 with a sufficient rolling temperature.

 Too slow the speed of the first pass, corresponding to the speed of exit from the arc section, should have led to a significant decrease in temperature, so that in the second rolling stand 7 of the next crimping step, a temperature insufficient for compression is obtained, so that, if necessary, another intermediate heating can be provided in as a second induction furnace 8 between the rolling stand 6 and the rolling stand 7, which may be shorter than the furnace 5. However, the second induction furnace is only necessary then and, when the furnace 5 is insufficient, during the compression along the entire other rolling stand 6, 7 and 9 of the other crimping step to set the corresponding temperature difference, namely, so that when passing into the last rolling stand 9, the temperature is within sufficient limits. When leaving the last rolling stand 9, the designated steppe as a tape 2 'flat product 2 has the desired thickness.

 The method ends either by winding the rolled tape 2 'on a rolling machine 10 with cutting on scissors 11 after reaching the desired roll weight, or cutting the tape 2' into pieces of the desired length and then stacking it on stacking device 12 (Fig. 2).

 Without the need for additional cutting devices, the installation for cutting the tape to the beginning of the working cycle can also be used to cut (not shown in the drawings) the initial rolled strip, which is cut after passing through the disconnected induction furnace 5 and the split rolls of the crimping device (6,7 and 9), as well as a possibly provided and also switched off intermediate heating device 8. Corresponding installation devices are provided with which le passage of the original rolled strip rolls again set to the required clearance for crimping normal rolling. In addition, the heating devices (furnace 5) consist of zones independent from each other, so that, based on the state of the switched-off furnace, the zones of the furnace passed through the corresponding source product are subsequently switched on for heating.

 In FIG. 2 shows the temperature characteristic of a flat product until the strip (2) leaves the last rolling stand.

 The table shows the data of the dependence of thickness on speed with the corresponding tape width. The given values were achieved experimentally with a tape 1000 mm wide and 25 mm thick, with a speed of 0.08 m / s.

Thickness, mm 25 12.30 6.20 4.05 Speed, m / s 0.08 0.017 0.33 0.51
Process sprouted from ingot rolling a flat product 2 at the output stage of the first mold 3 at a temperature of ¹⁰⁷⁵ C, which is on the way to the purifier 4 descaled lowered to 1049 ° ^C provided in this system the pressure descaling water dramatically lowers the temperature to 969 ^C. and cools the workpiece to the furnace 5 further to 934 ^about C.

In the furnace or in an induction furnace electric heating device 5), the temperature again is increased to ^about 1134 C, the temperature equalization is carried out over the entire cross section of the flat product. Before reaching the last rolling stand 6 undergoes a reduction in temperature to 1104 ^C, which is due to contact with the rolls in the rolling stand when the output therefrom is ^about 1063 C. In the case described laminated tape is partially heated in the electric furnace further included 8 individual from 1020 to 1120 ^C. . Omitting the second roll 7 furnace temperature is 1090 ^{° C} and decreases at the outlet of the rolling stand to ^about 1053 C, while it at the outlet in the third and last roll stand 9 is lowered to 988 ^o C. This temperature is deemed Ven accurate as the temperature for the final pass rolling laminated belt 2 leaves the last rolling stand 9 at a temperature ^of 953 C and then continues to decrease with temperature is cut into pieces of a desired length and stacked or wound (FIG. 1).

 As for the speed characteristics, in the embodiment, the speed when exiting the first crimp stage 3 is 0.08 m / s or 4.8 m / min. This corresponds to the speed at the entrance to the rolling stand of another crimping step, where the thickness of the flat product is another 25 mm. The speed at the entrance to the rolling stand 7 is 10.2 m / min while compressing a flat product with a thickness of 25 to 12.3 mm The rolled product enters the last rolling stand with a speed of 19.8 m / min and a thickness of 6.2 mm and leaves the rolling stand with a final thickness of 4.05 mm and a speed of 30.6 m / min.

As follows from the above embodiment, which, in principle, can be transferred to other cross sections of the tape, preceding the first rolling stand of another crimping stage, heating and, if necessary, carried out between the first rolling stand and the second rolling stand, intermediate heating can be set so that heating the flat product or the rolled strip after the first pass is performed up to 1100 C and ^the temperature level is maintained so that the final temperature rolling in the final rolling stand is not lower limit value of 860 ° ^C.

 In the embodiment of FIG. In a modified example of embodiment, an intermediate winding and unwinding device 12 is used. In this case, the winding and unwinding device is installed behind the induction electric furnace 5. The system is supplemented by an descaling device with a cleaner 4. The winding and unwinding device 12 winds the flat material until the desired roll size is reached. After the wound roll is moved to the unwinding position (in Fig. 3 to the right), the flat material is fed for further processing to the crimping stage consisting of one or more rolling stands (6,7 and 9). If necessary, an additional induction electric furnace 8 can be installed between the rolling stands of another stage 8. The finished tape is formed, for example, on a folding device.

 All installation parameters can influence each other thanks to the appropriate setting of the casting speed, rolling speeds, and also reductions.

 The power required for induction heating does not go beyond 8 MW, which can be considered as a very economical energy consumption for a steel mill of appropriate sizes.

 In particular, the heating device provided in front of the rolling mill or between the rolling stands can be replaced by another, different from the indicated induction furnaces, for example, a laser oven, reflective furnaces, etc.

Claims (5)

1. A method of manufacturing a steel strip or sheets, including continuous casting with the direction of the metal in an arc and with a horizontal exit of a flat cast billet and subsequent combined compression in several steps in a group of sequentially installed rolling rolls, as well as intermediate induction heating in a stream with equalization of temperature over the cross section billets to a temperature of about 1100 ^o C, characterized in that the intermediate heating is carried out after the first stage of compression.  2. The method according to claim 1, characterized in that the intermediate heating is additionally carried out after the intermediate stages of compression.  3. Installation for the manufacture of steel strip or sheets, including a continuous casting machine with a curved crystallizer, combined with a group of rolling stands, an induction heating device and scissors, characterized in that the heating device is installed after the first stand of the group.  4. Installation according to claim 3, characterized in that it is equipped with additional induction heating devices installed behind the intermediate stands of the group.  5. Installation according to claims 3 and 4, characterized in that the induction heating devices are equipped with means for individually switching on and controlling.

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