SU990351A1 - Method of hot rolling of strip on wide-strip mill - Google Patents

Description

one

The invention relates to the production of hot-rolled strips on wide-strip mills in the steel industry.

There is a known method of hot rolling of stripes on continuous mills, in which a multi-stage reduction of the thickness of the roll is carried out, and in each stand of the finishing group, except the last, a roll is rolled with a variable cross-section along its length increasing to the front end 1.

A disadvantage of the known method of hot rolling of strips is to stimulate a temperature difference along the length of the rolls and the finished strip during the finishing rolling process.

It is known that the temperature of the finishing rolling, and especially the end of the finishing rolling, is a determining factor in obtaining quality stripes in terms of structure, mechanical properties, thickness variations and planetary density. Stabilization of the finishing rolling efforts along the length of the roll is the basis of the known method and affects the quality indicators of the strips, and if only their flatness and thickness variation.

The disadvantages of this method of hot rolling of strips should also include the need to produce a tackle in the last rough pass — with a variable cross-section along its length increasing to the front end. The latter requires a revision of the design of the pressure mechanism of the corresponding cage of the draft group, calculating it on the effort of pressing the roll out directly in the process of deformation.

The closest to the invention with the technical essence and the achieved result is the tool of hot rolling of strips on a wide-strip mill, which includes getting a tackle with a variable cross-section along its length increasing to the rear end and finishing rolling 2 in the last pass of rough rolling.

However, to obtain high-quality hot-rolled strips, it is necessary to ensure the smallest temperature difference of the finish rolling end along the length of the finished strip. The latter is practically excluded in the known method, since in order to ensure the smallest difference in this temperature, it is necessary to obtain a rolled strip in the last pass with a significant change in the cross section along its length (with a large wedge shape). With an increase in the specific gravity of rolled tackles (rolls of finished strips), and this is the general trend of the wide-strip hot process, the required change in cross-section along the rolled strip (its wedge shape) becomes so significant that the finishing rolling process in the first pass as by energy-power parameters , and at the angles of capture it definitely becomes no longer real. In order to reduce the drive overload and the design of the first finishing stand, it is recommended that in the last pass of rough rolling a roll with a front end thickness is less than the thickness of the calculated equal tire thickness. However, the effectiveness of this recommendation is limited to rolling the rolls (roll n .ai.J riDnwi U; 71 h / Rows) of low specific weight and with the growth of the latter the task of maintaining the finishing process of the wedge-shaped rolling in the first pass becomes insoluble. In the known rolling method, the problem of increasing the productivity of a wide-strip hot rolling mill is not solved, and this is also its disadvantage. Possibilities of the known method of hot rolling of strips on a broadband mill; gy; 7y; e ™ g; g4 ;; rGo "dGs ™." oT "Gk g length while simultaneously increasing the productivity of the mill is limited. The aim of the invention is to improve the quality of the strips by reducing the temperature difference of the end of finish rolling along their length, as well as increasing the productivity of the mill. This goal is achieved by the fact that according to the method of hot rolling of strips on a wide-strip mill, including receiving in the last pass of rough rolling, a rolling with variable cross-section along its length, increasing to the rear lff iJii f 1m t1i / T lt 1 ry hfrmotchul / end, and its rolling, roll is rolled with a variable cross-section along its length, with an increase to the rear end in at least two passes of finish rolling, while the speed of rolling in the passes changes in proportion to the increase in the cross-section of the roll in the first pass. In this case, the roll is rolled with a variable section along its length in each pass of the finishing rolling, except for the last. Moreover, the rolling speed in the passages with a constant cross section along the length of the roll increases in direct proportion to the increase in the cross section of the roll in the first pass, keeping it constant in the rest of the passes. In addition, the rolling speed in the passages with variable cross section along the length of the roll is reduced inversely with the increase in the cross section of the roll in the first pass, keeping it constant in the rest of the passes. The implementation of this method of hot rolling of strips on a wide-strip mill reduces the temperature drop of the finish rolling end along the length of hot rolled strips in comparison with the known method, opens up the possibility of a steady finishing pass, as well as in each pass and in all passes °° rolling roll with variable cross-section ™ supports the same stable rolling force. In aggregate, this provides an increase in the quality of hot-rolled strips in structure, mechanical properties, flatness, and heterogeneity. The productivity of the hot rolling mill strip mill at - ™ ° is increased, .. "the rollers of the bands on the broadband mill are carried out by the following equipment. At the hot rolling mill, the heated slabs are first subjected to rough rolling several passes before obtaining a rolled strip, which is then subjected to finishing, The tallah is increased to produce a tackle with a variable cross-section along its length, increasing towards the rear end. At the same time, in order to expand the possibility of adjusting the subsequent rolling purity, a tackle with a front end thickness less than the thickness of the calculated equal thickness rolled strip is obtained. The resulting wedge-shaped tackle is fed to the finishing rolling stage, which is carried out in several passes and arranged according to the principle of continuous rolling. In the process of finishing rolling, at least in the first two, and at most in. „..... each pass, except the last, starting from the moment of arrival of the metal into the work rolls, the latter is adjustable unwinding, thus rolling the roll with variable section along its length, extending to its rear end. High-speed finish rolling is organized in two ways. According to the first one, the rolling speed in the first finishing pass is taken as a basis and is kept constant during the passage of the whole roll. Constantly, the rolling speed is also generally maintained in all the finishing passes, in which the roll is rolled with a variable cross-section along its length.

Accordingly, in the finishing passages in which the roll is rolled with a constant cross section along its length, the speed of rolling increases as the roll progresses directly proportional to the increase. the cross section in the first finishing pass. Thanks to the latter, along with a decrease in the temperature difference — along the length of the finished strip, the mill's productivity is increased. This variant of the speed mode is realized in mills in which at least one - two last finishing stands, which take away the live rolls and winders of the finished strips, are designed for finishing rolling with acceleration. I

According to the second variant of the high-speed rolling mode, the rolling speed in the last finishing pass is taken as a basis and is kept constant during the whole roll. Constantly, the rate of rolling is also generally maintained in all finishing passes, in which the roll is rolled with a constant cross section along its length. Accordingly, in the finishing passes, in which the roll is rolled with a variable cross-section along its length, the rolling speed as the roll passes is reduced inversely with the increase in the cross-section of the roll in the first pass. This version of the speed limit is realized on the walls, the finishing groups of which are not designed for ramming. Thus, in both versions of the speed mode, the corresponding change in the speed of finishing rolling in the passages of charts is easily determined from the known law of constant second metal consumption during continuous rolling.

Blrdar redistribution of work on the plastic deformation of a wedge-shaped tackle at least two, and at most all passes of the finishing rolling, except the last, reduce the power parameters in the first pass. By adjusting the clearance between the work rolls, a stable rolling force is maintained along the length of the stock in each pass of the finishing roll of a stock, with a variable cross section, as well as the same force of rolling in all these passages. The noted selections of the distribution of rolling reductions and efforts additionally provide an improvement in the quality of hot rolled stripes according to the flatness and thickness difference.

Due to the transfer of part of the work on plastic deformation of a wedge-shaped rolled strip to the second and further clean rolling passes, except the last, reduce as the roll rolls, heat loss by the working in the interstand gaps and further increases the heating of the metal due to plastic deformation, respectively, in the second and further finish rolling , except the last, lower it in the first pass. In this way, the temperature drop of the end of the continuous rolling along the length of the finished hot rolled strip is reduced. The latter is ensured by the improvement of the quality of hot-rolled strips in terms of structure and mechanical properties.

Example I. On a wide-strip hot rolling mill, with a specific gravity of 15.5 t / m of width, the production of hot-rolled strips with a thickness of 2.0 mm is organized. On the last pass of the rough rolling, a 60 m long rolled strip with a variable cross section along its length is obtained, so that the forward rolling along the rolling edge of the rolled strip has a thickness of 30 mm and its rear end is 36 mm, i.e. 6 mm greater than the calculated thickness. equal thickness 30 mm tackle. To obtain

such a roll in the process of rough rolling as the rolling of the last rough cell passes the gap between the rolls

increase.

The said tackle is fed to a finishing group consisting of seven stands, where it is rolled into a strip of 2.0 mm thickness, equal thickness throughout its entire length. The last two stands of the finishing group, the withdrawing roller conveyor and the mill winder are designed for accelerated rolling.

The finish rolling process is carried out as follows.

Starting from the moment the front end of the roll arrives in the first-fifth finishing stands, in each of them the gap between the rolls is gradually increased, so that the first stand is changed from 14.5 mm at

the passage of the front end to 16.9 mm with the passage of the rear end of the roll, in the second stand, respectively, from 7.3 to 8.6 mm, in the third stand - from 5.1 to 6.0 mm,

in the fourth stand, from 3.8 to 4.3 mm, and in the fifth stand, from 2.8 to 3.2 mm. In the sixth finishing stand, the gap between the rollers is kept constant and equal to 2.3 mm, and the seventh stand is also constant and equal to 2.0 mm. The rolling speed at the exit of the first adhesive

they are set at 1.39 m / s, from the second stand - 2.75 m / s, from the third stand - 3.9 m / s, from the fourth stand - 5.25 m / s, from the fifth stand - 7, 2 m / s and in all these cells they keep constant during the whole roll.

The rolling speed at the exit of the sixth stand is increased from 8.6 m / s when passing the front end of the roll to 10.35 m / s when passing its rear end ,, in the seventh stand - from 9.9 to 11.9 m / s, respectively,

The latter provide increased productivity of the mill by 9 ,.

The final result is the finish rolling end temperature at the front end of the strip of 814 ° C, at its rear end of 802 ° C and the temperature difference of this temperature is 12 °.

When rolling a calculated equal thickness rolled strip 30 mm thick and 66 m long, rolled from the slab of the same weight in the roughing group of stands, and then in the finishing mode 30 - 25.5 - 26.5 - 18-13 / per strip of thickness 2, 0 mm with a rolling speed of 9.9 m / s at the front end of the strip had 814 ° C, at its rear end - 750 ° C and the temperature difference of 64 °.

Example 2. On a hot-rolling broadband mill, similarly to example 1, a slit-shaped tackle with a front end thickness of 30 mm and a rear end of 36 mm is obtained from the slab of the specific gravity of 15.5 t / m of width on the last pass of rough rolling.

This tackle is fed to the finishing group of stands consisting of seven stands not designed for accelerated rolling, where at a constant rolling speed in the last seventh stand 9.9 m / s is rolled into a 2 mm thick strip, uniform throughout its length.

In the process of finishing rolling, starting from the moment the front end of the roll reaches the first - fifth stands in each of them, the gap between the rolls is adjustable, so that at the time the roll out of these stands its thickness is respectively 2.5; 2.0; 0.75; 0.5 and 0.25 mm greater than the thickness of the calculated equal thickness roll. The rate at which the metal enters these cages at the time of rolling the rear end of the respective is reduced to 1.07; 1.93; 3.1; 4.3; 6.0 m / s.

As a result, the temperature of the finish rolling end at the front end of the strip is 814 ° C, at its rear end 750 ° C and the temperature difference of this temperature along the length of the strip is 64 °, which is 31% less compared to rolling an equally thick rolled strip.

Thus, if in the known rolling method, compared to rolling the calculated equal thickness tackle, the temperature drop on the finish rolling end over the length of the finished strip is reduced by 17%, in the proposed method - by 81%, i.e., the proposed method in terms of reducing the temperature drop along the length the finished strip is more efficient than the known 4.75 times. The proposed method is also more effective in part

Increase mill productivity by 9.2%.

Claims (4)

1. The method of hot rolling of strips on a broadband mill, providing for the production in the last stand of a rough rolling roll with a variable cross-section along its length, with an increase to the rear end, and its finishing rolling, characterized in that, in order to improve the quality of the strips by lowering the temperature difference of the finish rolling end along their length, the roll is rolled with a variable cross-section along its length, increasing to the rear end, at least in two passes of hard rolling, with In this way, the rolling speed in the passages is changed in proportion to the increase in the cross section of the roll in the first pass. 2. A method according to claim 1, characterized in that the roll is rolled with a variable section along its length in each pass of the finishing rolling, except for the last. 3. Method according to paragraphs. 1 and 2, characterized in that, in order to increase production. of the mill, increase the speed of rolling in the passages with a constant cross section along the length of the roll directly proportional to the increase in the cross section of the roll in the first pass, keeping it constant B the rest of the passes. 4. Method according to paragraphs. 1 and 2, characterized in that the rolling speed in the passages with variable cross section along the length of the roll is reduced in inverse proportion to the increase in the cross section of the roll in the first pass, keeping it constant in the rest of the passes. Sources of information taken into account during the examination 1. USSR Author's Certificate No. 498046, cl. B 21 B 1/26, 1974. 0 2. Patent. Japan No. 47-B 29 3, cl. 12 C 211, 2, 1972.