RU2254182C2 - Method for hot rolling of thin strip and mini-mill for performing the same - Google Patents

Abstract

FIELD: processes and apparatuses for hot rolling of thin strip from blanks in mini-mills having finish group of stands with furnace coilers.

SUBSTANCE: method comprises steps of reversing rolling of slab in rough stand till intermediate thickness; transferring strip of intermediate thickness to finish rolling two-stand group and simultaneously performing last rolling pass in rough stand and first finish pass in two-stand rolling group; performing reversing finish rolling of strip in finish two-stand rolling group to final thickness and coiling-uncoiling strip of intermediate thickness on coilers in furnaces mounted in front and after finish two-stand rolling group. Reversing rough rolling of slab is realized in parallel with reversing finish rolling of strip made of previous slab at timing cycles of reversing rough rolling and reversing finish rolling in such a way that last rough pass and first finish pass are realized simultaneously at operation of rough stand and finish two-stand rolling group in continuous operation mode. Finish reversing rolling of strip till final thickness is realized for three passes through two-stand rolling group at two times coiling of strip of intermediate thickness on coilers in furnaces. Mini-mill for making thin hot rolled strip includes heating furnace, transporting and working roller tables, apparatuses for hydraulic descaling, rough reversing stand, finish rolling group of two reversing stands, coilers in furnaces mounted in front and after finish rolling group, shears, coiler for ready strip, equipment for transporting strip coils for storage. Distance between rough stand and first stand of finish rolling group is selected according to condition that it exceeds length of piece rolled in last but one odd rough pass but it is less than length of piece rolled in last rough pass.

EFFECT: shortened time period for making strip due to favorable temperature parameters and improved operational characteristics of mill.

2 cl, 3 dwg, 4 tbl, 1 ex

Description

The invention relates to methods for hot rolling a thin strip of blanks on mini-mills containing the finishing group with furnace winders.

A known method for the production of hot rolled strips on a mini-mill (see PCT patent No. WO 95/13149, 21 V 1/00 from 05/18/95, US patent No. 5414923, 21 V 1/00, 13/22 from 16.05 .95 g.). A mini-mill that implements this method contains:

- a furnace for heating continuously cast slabs;

- transport and work roller tables;

- vertical stand;

- a device for descaling;

- reversible rolling stand, in front of and behind which coilers are installed in furnaces (Stekkel mill);

- a coiler for winding a hot strip;

- equipment for transporting rolls to the warehouse.

The production method under consideration consists of a series of operations.

Initially, slabs with a thickness of 140-150 mm after heating in a furnace and removal of scale are sent to a reversing stand. Rolling in it is carried out according to the following scheme:

- rolling the slab to the tackle with a thickness of 20-25 mm without winding on the furnace winders;

- rolling to a final thickness with simultaneous winding-unwinding of the tackle on the coilers in the furnaces behind and in front of the cage.

Then the rolled strip is sent for winding into a roll and transported to a warehouse.

The above production method has the following disadvantages:

- the inability to produce strips with a thickness of less than 2 mm due to temperature and speed conditions of rolling in one stand;

- low quality of the resulting strips due to the combination of rough and finish rolling in one stand;

- low mill productivity due to the length of the rolling cycle;

- the need for frequent change of rolls.

Some disadvantages of the previous analogue method are deprived of the method for producing a strip on a mini-mill described in the prospectus of SMS (prospectus of SMS Advanced hot strip Steckel nulls for special steel).

The mini-mill includes:

- a furnace for heating continuously cast slabs;

- transport and work roller tables;

- universal reverse roughing stand;

- devices for descaling;

- scissors for cutting the front and rear ends of the tackle;

- reversible finishing stand, before and behind which coilers are installed in furnaces (Stekkel mill);

- a winder for winding a hot strip;

- equipment for transporting rolls to the warehouse.

According to this method, roughing and finishing rolling are carried out sequentially in a roughing and finishing stand, while in the roughing stand, the rolling is crimped during the reverse rolling to a thickness of 20-25 mm and then transferred to the finishing stand for reverse rolling with winding-unwinding on furnace winders.

The disadvantages of this method of rolling strip on a mini-mill are as follows:

- the inability to produce strips with a thickness of less than 2 mm due to adverse temperature and speed conditions of rolling due to the large distance between the roughing and finishing stands and the long finishing cycle in one stand;

- low mill productivity due to the long finish rolling cycle;

- large capital investments in the construction of the mill due to the increased length of its production line due to the need to place both a roughing stand and an intermediate roller table with scissors for receiving rolled material obtained after rough passes. The production of a thin strip (about 1 mm thick) is realized by the method of hot rolling of a strip on a two-stand reversing mill (US patent No. 5752403 A, B 21 B 41/00, dated June 25, 1996), containing:

- a furnace for heating continuously cast slabs;

- transport and work roller tables;

- reversible rolling two-stand group with a vertical stand; coilers in ovens are installed in front of and behind the rental group;

- equipment for winding strip and cleaning rolls in a warehouse.

In accordance with the patent, slabs with a thickness of up to 250 mm after heating in a furnace are fed into a reversible rolling two-stand group.

First, a slab is subjected to a series of passes through a two-stand group until the thickness of the intermediate strip reaches about 20-25 mm without winding onto furnace winders (rough rolling).

Next, rolling to a final strip thickness is carried out in the same rolling group with simultaneous winding-unwinding of the intermediate-thickness tackle onto winders in furnaces behind and before the double-stand rolling group.

The number of passes is determined by the thickness of the initial workpiece and the size of the finished strip.

The rolled strip is sent to the winding and transported to the warehouse.

The rolling method according to the above scheme has the following disadvantages:

- rolling in a double-stand rolling group of both a thick slab and a thin strip leads to a deterioration in the quality of the finished product, the irrational use of auxiliary equipment;

- the combination of draft and finishing passes in the same stands limits the productivity of the mill;

- increased reduction in the stands during rough rolling leads to rapid wear of the rolls, which leads to a frequent change of rolls in the rolling stands and reduces the productivity of the mill.

Closest to the proposed method is a method of hot rolling of strips on a mini-mill described in US patent No. 4497191, MKI B 21 V 41/02 from 02/15/85. This method is selected for the prototype.

Mini-mill that implements this method contains the following equipment:

- oven for heating slabs;

- transport and work roller tables;

- universal reverse roughing stand;

- reversible two-stand finishing rolling group, before and behind which winders are installed in furnaces;

- flying scissors behind the finishing rolling group and before the coiler in the furnace;

- a winder for winding a hot strip;

- equipment for transporting rolls to the warehouse.

According to this rolling method, roughing and finishing rolling are carried out separately in a roughing stand and a double stand rolling group.

In this case, the roughing stand is as close as possible to the finishing stand with the condition of placing a furnace winder between them.

Rough rolling is carried out on condition that the roll is fed into the open rolls of the finishing stands.

At the last draft pass, rolling is carried out simultaneously in the roughing and finishing stands. After that, the strip is wound onto a coiler in an oven.

Finishing rolling of the strip to the required thickness is carried out in a two-stand continuous reversing group with a strip unwinding on winders in furnaces installed in front of and behind the group of stands.

Trimming the ends of the strip on the finishing passes is carried out with flying scissors.

This method of rolling the strip on a mini-mill makes it possible to obtain a thin strip with the maximum reduction of the technological line of the mill, which reduces the heat loss of the strip during transportation.

The separation of the processes of roughing and finishing rolling in different stands, when the finish rolling is carried out on finishing stands, leads to an increase in the quality of the finished strip.

However, this method has a drawback - low performance mini-mill, because due to the placement of the peel during rough passes in the area of the finishing stands (their rolls are open), the finishing group of stands is idle, and the time of the production technological cycle is increased (see FIG. 3).

The basis of the invention is the task of creating a method of rolling strip, providing high performance mini-mill.

This problem is solved due to the technical result, which consists in combining in time rolling in a roughing stand and finishing rolling in a continuous two-stand group.

In order to achieve the above result, in the method of hot rolling a thin strip, including reverse rolling the slab in the roughing stand to an intermediate thickness, transferring the strip of intermediate thickness to the finishing two-stand rolling group while performing the last pass in the roughing stand and the first finish pass in the double stand rolling group, reverse finishing rolling of the strip in the finishing two-stand rolling group to a final thickness with the winding-unwinding of the strip of intermediate thickness on winders in the furnaces installed in front of and behind the finishing double-stand rolling group, according to the invention, the reverse rough rolling of the slab is carried out in parallel with the reverse finishing rolling of the strip obtained from the previous slab, with the coordination of the cycles of reverse rough rolling and reverse finishing rolling so that the last rough and first finishing pass carried out simultaneously during the work of the roughing stand and the finishing two-stand rolling group according to the principle of a continuous group of stands, while the finishing roar dis- tinguish rolling the strip to the final thickness is carried out in three passes through dvuhkletevuyu roll group at two coiling of the intermediate strip thickness at the coiler furnaces.

In addition, to achieve the above technical result, in a mini-mill for the production of a thin hot-rolled strip, including a heating furnace, transport and working roller tables, a device for descaling, a roughing stand, a finishing rolling group consisting of two reversing stands, a coiler in furnaces, installed in front of and behind the finishing rolling group, scissors, a winder for winding the finished strip into a roll, equipment for transporting the roll to a warehouse, according to the invention, the distance between the rough mill and the first stand of the finishing group is selected from the condition that it is longer than the length of roll, resulting in odd penultimate roughing pass, but less than the length of roll, resulting in the final roughing pass.

As a result of a comparative analysis of the proposed method for hot rolling a thin strip with a prototype, it was found that they have the following common features:

- reverse rough rolling of slabs in a roughing stand to an intermediate thickness;

- transfer of a strip of intermediate thickness to the finishing two-stand rolling group while performing the last draft and first finishing passes;

- reverse finishing rolling in a finishing two-stand rolling group to a final thickness;

- winding-unwinding strips of intermediate thickness during finish rolling on coilers in furnaces installed in front of and behind the finishing rolling group;

and distinguishing features:

- reverse rough rolling of the slab is carried out in parallel with the reverse finishing rolling of the strip obtained from the previous slab;

- the reverse rolling cycle in the roughing stand is coordinated with the reverse finishing rolling cycle in such a way that the last roughing and the first finishing passes are performed simultaneously when the roughing stand and the finishing two-stand rolling group work on the principle of a continuous group;

- finishing reverse rolling of the strip to the final thickness is carried out for three passes through a two-stand group with two windings of a strip of intermediate thickness on winders in furnaces;

- transport and work roller tables;

- a device for descaling;

- rough reverse stand;

- finishing rolling group, consisting of two reversing stands;

- winders in furnaces installed in front of and behind a clean rolling group;

- scissors;

- a winder for winding the finished strip into a roll;

- equipment for transporting rolls to a warehouse;

and distinguishing features:

- the distance between the roughing stand and the first stand of the finishing rolling group is selected on the condition that it is greater than the length of the roll obtained in the penultimate odd draft pass, but less than the length of the roll obtained in the last draft pass.

Thus, the proposed mini-mill for producing a thin hot-rolled strip has new connections between the machines.

Between the distinguishing features and the achieved technical result there is a causal relationship.

Due to the provision in the method of rolling a thin strip of reverse rolling of a slab in a roughing stand in parallel with reversible finishing rolling in a two-stand group of a strip obtained from the previous slab, it became possible to shorten the rolling cycle of the slab (see figure 2), which led to an increase in production volumes by camp and to increase its productivity in general.

Thanks to the installation of the roughing stand in the mini-mill for producing a thin strip at a distance from the first finishing stand, longer than the roll obtained in the penultimate odd rough pass, but shorter than the length of the roll obtained in the last rough pass, it became possible to carry out parallel rolling in the reversing stand and finishing rolling in a two-stand group with winding of a strip on winders in furnaces (all passes except the last draft and the first finishing, which are carried out according to the principle of continuous groups s in all stands simultaneously), and this led to a reduction in the total time (cycle) of rolling the slab, which ensured an increase in the productivity of the mill.

Thus, the use of the proposed method and mini-mill for the production of thin hot-rolled strips provides an increase in the productivity of this process.

An exception to the above set of distinctive features of at least one of them does not provide a solution to the problem - to obtain a high-performance method for rolling a thin strip on a mini-mill.

The claimed technical solution is unknown from the prior art, therefore, it is new.

The proposed solution has an inventive step, because the method and mini-mill for producing a thin hot-rolled strip, discussed above, for a specialist are not obvious from the prior art.

The claimed technical solution is industrially applicable, because its technical and technological performance is not difficult. By this decision, a preliminary design of a mini-mill for the production of thin hot-rolled strips at the Yenakiyevo Metallurgical Plant was completed.

Thus, the proposed technical solution may be given legal protection, as it is new, has an inventive step and is industrially applicable, which meets all the criteria of the invention.

The invention is illustrated by drawings, which depict:

figure 1 - line mini-mill for the production of thin hot rolled strips;

figure 2 is a sequence diagram of the mini-mill according to the proposed method of hot rolling of a thin strip;

figure 3 is a sequence diagram of the mini-mill according to the known method of hot rolling of a thin strip (US patent No. 4497191).

The mini-mill for hot rolling of thin strip 1 (Fig. 1) consists of a heating furnace, a device for descaling (not shown in Fig. 1), transport and working roller tables 2; draft reverse stand 3; finishing rolling group consisting of two reversing stands 4, 5; winders 6 in the furnace 7 installed in front of the finishing rolling group; winders 8 in the furnace 9 installed behind the finishing rolling group; scissors 10, 11 for trimming the ends of the strip; winders for winding the finished strip into a roll (not shown in figure 1); equipment for transporting rolls to a warehouse (not shown in FIG. 1).

The distance L between the draft reversing stand 3 and the first finishing reversing stand 4 is selected so that it is longer than the length of the roll obtained in the penultimate rough odd pass, but less than the length of the roll received in the last draft pass.

As an example, we consider the technological process of rolling a slab of low carbon steel with dimensions of 250 × 1500 × 11000 mm, weighing 32.4 tons into a thin strip (thickness 2.0 mm, 1.5 mm, 1.2 mm and 1.0 mm). Process parameters for different strip thicknesses are given in tables No. 1-4; the sequence diagram of the mini-mill according to the proposed method for hot rolling of a thin strip is shown in figure 2 (for rolling a strip with a thickness of 1.0 mm).

Slab parameters: 250 × 1500 × 11000 mm. Weight 32.4 tons

Material: low carbon steel.

Strip parameters: 2.00 × 1500 mm.

Table number 1 Stand number Badge number Strip thickness mm Relative compression,% Strip length, m Rolling speed, m / s Rolling force, tf Rolling moment, tcm The temperature of the strip at the exit from the stand, ° C at the entrance to the crate at the exit of the crate 1 I 250.00 200.00 20,0 13.75 2.00 1896 330 1236 1 II 200.00 150.00 25.0 17.74 2.00 1986 324 1230 1 III 150.00 105.00 30,0 26.19 2,50 2254 343 1222 1 IV 105.00 70.00 33.3 39.29 2,50 2266 298 1211 1 V 70.00 40.00 42.9 68.75 3.00 / 0.50 2798 324 1191 2 I 40.00 20.00 50,0 137.5 1.00 / 1.50 / 1.00 2523 184 1086 3 20.00 10.00 50,0 275.0 2.00 / 3.00 / 2.00 2464 120 1080 3 II 10.00 5.50 45.0 500,0 1.16 / 2.91 / 1.16 2269 67 1020 2 5.50 3.20 41.8 859.4 2.00 / 5.00 / 2.00 2219 48 1009 2 III 3.20 2.40 25.0 1145.8 8.33 1437 19 939 3 2.40 2.00 16.7 1375.0 10.00 1021 10 905

1. The temperature of the slab: 1250 ° C.

2. The temperature of the space in the furnace of the Steckel mill: 1000 ° C.

3. The temperature of the surface of the drum in the furnace of the Steckel mill: 900 ° C.

4. The distance between the roughing and the first finishing stands is 36 m.

5. To ensure simultaneous rolling of the strip in stands No. 1, 2 and 3 (combining the last draft and first finishing passes) in the fifth draft pass before entering the strip in stand No. 2, the rolling speed in the roughing stand No. 1 is reduced from 3.00 m / s up to 0.5 m / s.

6. Start of winding in furnaces - after the 1st finishing pass.

7. Rolling speeds in finishing passes are given taking into account the rolling speeds of the front and rear ends of the tack, different from the rolling speeds of the main part of the strip.

8. Forces and moments of rolling, as well as the temperature of the strip are given for the main part of the strip.

9. The rolling cycle is 440 s. The hourly capacity of the mill is 265 tons.

Slab parameters: 250 × 1500 × 11000 mm. Weight 32.4 tons

Material: low carbon steel.

Strip parameters: 1.50 × 1500 mm.

Table number 2 Cell number Badge number Strip thickness mm Relative compression,% Strip length, m Rolling speed m / s Rolling force, tf Rolling moment, tcm The temperature of the strip at the exit from the stand, ° C at the entrance to the crate at the exit of the crate 1 I 250.00 200.00 20,0 13.75 2.00 1896 330 1236 1 II 200.00 150.00 25.0 17.74 2.00 1986 324 1230 1 III 150.00 105.00 30,0 26.19 2,50 2254 343 1222 1 IV 105.00 70.00 33.3 39.29 2,50 2266 298 1211 1 V 70.00 40.00 42.9 68.75 3.00 / 0.40 2798 324 1191 2 I 40.00 20.00 50,0 137.5 0.80 / 1.40 / 0.80 2549 186 1077 3 20.00 8.00 60.0 343.8 2.00 / 3.50 / 2.00 3212 161 1088 3 II 8.00 4.00 50,0 687.5 1.10 / 4.40 / 1.10 2598 72 1032 2 4.00 2.20 45.0 1250.0 2.00 / 8.00 / 2.00 2463 48 1028 2 III 2.20 1.75 20.5 1571.0 9.43 1145 12 934 3 1.75 1,50 14.3 1833.0 11.00 906 8 891

1. The temperature of the slab: 1250 ° C.

2. The temperature of the space in the furnace of the Steckel mill: 1000 ° C.

3. The temperature of the surface of the drum in the furnace of the Steckel mill: 900 ° C.

4. The distance between the roughing and the first finishing stands is 36 m.

5. To ensure simultaneous rolling of the strip in stands No. 1, 2 and 3 (combination of the last draft and first finishing passes) in the fifth draft pass before the strip enters the stand. No. 2, the rolling speed in the roughing stand No. 1 is reduced from 3.00 m / s to 0.4 m / s.

6. Start of winding in furnaces - after the 1st finishing pass.

7. Rolling speeds in finishing passes are given taking into account the rolling speeds of the front and rear ends of the tack, different from the rolling speeds of the main part of the strip.

8. Forces and moments of rolling, as well as the temperature of the strip are given for the main part of the strip.

9. The rolling cycle is 510 s. The hourly capacity of the mill is 228 tons.

Slab parameters: 250 × 1500 × 11000 mm. Weight 32.4 tons

Material: low carbon steel.

Strip parameters: 1.20 × 1500 mm.

Table number 3 Stand number Badge number Strip thickness mm Relative compression,% Strip length, m Rolling speed, m / s Rolling force, tf Rolling moment, tcm The temperature of the strip at the exit from the stand, ° C at the entrance to the crate at the exit of the crate 1 I 250.00 200.00 20,0 13.75 2.00 1896 330 1236 1 II 200.00 150.00 25.0 17.74 2.00 1986 324 1230 1 III 150.00 105.00 30,0 26.19 2,50 2254 343 1222 1 IV 105.00 70.00 33.3 39.29 2,50 2266 298 1211 1 V 70.00 40.00 42.9 68.75 3.00 / 0.375 2798 324 1191 2 I 40.00 20.00 50,0 137.5 0.75 / 1.31 / 0.75 2559 186 1070 3 20.00 7.50 62.5 366.7 2.00 / 3.50 / 2.00 3437 173 1087 3 II 7.50 3.70 50.7 743.2 1.08 / 4.32 / 1.08 2659 72 1026 2 3.70 2.00 45.9 1375.0 2.00 / 8.00 / 2.00 2583 49 1024 2 IIII 2.00 1.45 27.5 1896.6 9.10 1714 twenty 927 3 1.45 1.20 17,2 2291.7 11.00 1207 eleven 879

1. The temperature of the slab: 1250 ° C.

2. The temperature of the space in the furnace of the Steckel mill: 1000 ° C.

3. The temperature of the surface of the drum in the furnace of the Steckel mill: 900 ° C.

4. The distance between the roughing and the first finishing stands is 36 m.

5. To ensure simultaneous rolling of the strip in stands No. 1, 2 and 3 (combining the last draft and first finishing passes) in the fifth draft pass before entering the strip in stand No. 2, the rolling speed in the roughing stand No. 1 is reduced from 3.00 m / s up to 0.375 m / s.

6. Start of winding in furnaces - after the 1st finishing pass.

7. Rolling speeds in finishing passes are given taking into account the rolling speeds of the front and rear ends of the tack, different from the rolling speeds of the main part of the strip.

8. Forces and moments of rolling, as well as the temperature of the strip are given for the main part of the strip.

9. The rolling cycle is 580 s. Hourly productivity of the mill - 201 tons.

Slab parameters: 250 × 1500 × 11000 mm. Weight 32.4 tons

Material: low carbon steel.

Strip parameters: 1.00 × 1500 mm.

Table number 4 Stand number Badge number Strip thickness, m Relative compression,% Strip length, m Rolling speed, m / s Rolling force, tf Rolling moment, tcm The temperature of the strip at the exit from the stand, ° C at the entrance to the crate at the exit of the crate 1 I 250.00 200.00 20,0 13.75 2.00 1896 330 1236 1 II 200.00 150.00 25.0 17.74 2.00 1916 324 1230 1 III 150.00 105.00 30,0 26.19 2,50 2254 343 1222 1 IV 105.00 70.00 33.3 39.29 2,50 2266 298 1211 1 V 70.00 40.00 42.9 68.75 3.00 / 0.375 2798 324 1191 2 I 40.00 20.00 50,0 137.5 0.75 / 1.31 / 0.75 2559 186 1070 3 20.00 7.50 62.5 366.7 2.00 / 3.50 / 2.00 3437 173 1087 3 II 7.50 3,50 53.3 785.7 1.03 / 4.14 / 1.03 2852 79 1026 2 3,50 1.80 48.6 1527.8 2.00 / 8.00 / 2.00 2807 54 1029 2 III 1.80 1.20 33.3 2291.7 9.17 2319 thirty 931 3 1.20 1.00 16.7 2750.0 11.00 1217 10 873

1. The temperature of the slab: 1250 ° C.

2. The temperature of the space in the furnace of the Steckel mill: 1000 ° C.

3. The temperature of the surface of the drum in the furnace of the Steckel mill: 900 ° C.

4. The distance between the roughing and the first finishing stands is 36 m.

5. To ensure simultaneous rolling of the strip in stands No. 1, 2 and 3 (combining the last draft and first finishing passes) in the fifth draft pass before entering the strip in stand No. 2, the rolling speed in the roughing stand No. 1 is reduced from 3.00 m / s up to 0.375 m / s.

6. Start of winding in furnaces - after the 1st finishing pass.

7. Rolling speeds in finishing passes are given taking into account the rolling speeds of the front and rear ends of the tack, different from the rolling speeds of the main part of the strip.

8. Forces and moments of rolling, as well as the temperature of the strip are given for the main part of the strip.

9. The rolling cycle is 650 s. Hourly productivity of the mill - 179 tons.

The proposed method for producing a thin hot-rolled strip is implemented as follows (see figure 2).

The slab heated in the heating furnace is fed into the roughing stand 3, where for 5 passes (I, II, III, IV, V) it is rolled into an intermediate strip (tackle) 40 mm thick. The rolling speed in the first and second passes is 2 m / s, and in the third and fourth passes - 2.5 m / s.

Since the distance between the roughing stand 3 and the finishing stand 4 is less than the length of the tack obtained after the last rough pass, the last fifth rough pass is combined with rolling in the finishing stands 4, 5. In this case, the tack leaving the roughing stand 3 at a speed of 3.0 m / s, before the task in finishing stands 4, 5 it slows down to a speed of 0.375 ... 0.50 m / s (depending on the thickness of the finished strip) (see figure 2).

Finishing rolling is as follows.

Before the task of the strip 1 in the finishing stands 4, 5 there is a segment of the front end of the tackle on scissors 10.

After the first (I) finishing pass (passage through stands 4, 5), a strip 7.5 ... 10.0 mm thick is rolled up onto a coiler.

The filling of the strip into the coiler 8 takes place at a speed of the order of 2 m / s, which is the reason for the speed of entry of the rolled metal into the first stand (0.375 ... 0.50 m / s).

After the strip is “captured” by coiler 8, stands 4, 5 and coiler 8 are accelerated to the rolling speed, at this speed the main part of the strip is rolled (pass I), after which finishing stands 4, 5 and coiler 8 are decelerated to a speed of about 2 m / s . At this speed, the rear end of the strip rolls.

The strip rolled in the finishing stands 4, 5 stops in front of the coiler 8 in the zone of operation of the scissors 11. A segment of the rear end of the strip occurs.

Next, the strip is reversed and the second pass (II) through stands 4, 5. Herewith, along with the strip unwinding from the winder 8, it is wound onto the winder 6. The strip is fed into the winder 6 and the strip is rolled in the second pass at a speed of approximately 2 m / s. The main part of the strip is rolled at the required rolling speed.

The strip rolled in the finishing stands 5 and 4 stops in front of the coiler 6 in the area of operation of the scissors 10. A segment of the rear end of the strip occurs.

After this, the strip is reversed and it is finally rolled to the required thickness at the required technical speed (pass III).

It is possible to descale scale before each odd rough pass and before each final pass through stands 4, 5.

The rolling strip is cooled, and it is wound onto a roll on a coiler for winding the finished strip, after which the roll is tied, marked, weighed and transported to the finished product warehouse.

A characteristic feature of the work of the mini-mill on the proposed method of hot rolling of a thin strip is that the reverse rolling of the slab in the roughing stand 3 is carried out in parallel with the reverse rolling in the finishing two-stand rolling group of the strip obtained from the previous slab.

In Fig.2, the time of parallel rolling of the first and second slabs is highlighted by a shaded zone and is about 80 s.

The beginning of the rolling cycle in the roughing stand of the subsequent slab is coordinated in time with the end of the finishing cycle of the strip from the previous slab, so that the last rough pass (V - in figure 2) and the first finishing pass of the same slab are carried out together. In Fig.2, the joint rolling time is highlighted by a shaded zone and is 56 s.

This method of hot rolling became possible because the distance L (see FIG. 1) between the roughing stand 3 and the first stand 4 of the finishing rolling group was selected so that it is greater than the length of the roll obtained in the penultimate odd rough rolling pass (in this case is the III pass, and the length of the roll is 26.19 m), but less than the length of the roll obtained in the last draft rolling pass (in the case under consideration, this is the V pass and the length of the roll is 68.75 m).

Compare the rolling technology of the proposed method with the rolling technology in the method of the prototype. The operation diagram of the mini-mill according to the prototype is shown in Fig. 3 (rolling strip with the same parameters as in the proposed mini-mill is considered).

In the prototype, the roughing stand is as close as possible to the finishing rolling group, and the minimum of this distance is limited by the need to place between the roughing stand and the first stand of the finishing rolling group of the coiler in the furnace.

This mutual arrangement of the stands leads to the fact that in intermediate odd passes, the roll enters the area of the finishing stands, the rolls of which at this time must be kept diluted. This excludes parallel roughing and finishing rolling of adjacent peals, which determines the pause time in the finishing group (in figure 3, A1 is indicated), which in the case under consideration is 85 s.

The rolling cycle time is determined by the sum of the finish rolling time and the pause time in the finishing stands and for the prototype is 650 + 85 = 735 s.

In the proposed method, due to the optimal relative position of the roughing and finishing stands, the pause time in the finishing group is reduced to 5 s (A is indicated in FIG. 2), and the rolling cycle time according to the proposed method is 650 + 5 = 655 s.

Thus, the use of the proposed method and the mill in relation to the case under consideration in comparison with the prototype allows to increase the productivity of the mini-mill by more than 10%.

In general, the proposed method for hot rolling of thin strips has the following main advantages:

- provides the possibility of simultaneous finishing rolling and rough rolling, as a result of which the strip production cycle is determined only by the finish rolling time;

- the small distance between the roughing and finishing stands provides favorable temperature parameters of the rolling stock and reduces the length of the mill technological line;

- a slab and a roll of large thickness is not included in the equipment area of the finishing stands, which increases the operational characteristics of the mill;

- the optimal thickness of the rolled (40 mm) provides a high temperature of the end of the rough rolling;

- the increased rolling speed in the last draft pass and its reduction only at the very end of the pass (before the task in the finishing stands) provides a high temperature for the start of finishing rolling;

- finishing rolling is carried out in three passes through a double-stand finishing group with increased reductions and two windings in heating furnaces, which ensures the end of rolling in the region of austenitic temperatures, even for a strip with a thickness of about 1 mm. From all of the above, it is seen that the proposed method for the production of hot-rolled thin strips on a mini-mill is a high-performance process that provides high-quality products.

Claims (2)

1. A method of hot rolling a thin strip, including reversing the rolling of a slab in a roughing stand to an intermediate thickness, transferring a strip of intermediate thickness to a finishing two-stand rolling group while performing the last rolling pass in the roughing stand and the first finishing pass in a two-stand rolling group, reverse finishing rolling of the strip in the final two-stand rolling group to a final thickness with the winding-unwinding strip of intermediate thickness on coilers in furnaces installed in front of and behind finishing double-stand rolling group, characterized in that the reverse rough rolling of the slab is carried out in parallel with the reverse finishing rolling of the strip obtained from the previous slab, with the coordination of the cycles of reverse rough rolling and reverse finishing rolling so that the last rough and first finishing pass are carried out simultaneously during operation roughing stand and finishing two-stand rolling group according to the principle of a continuous group of stands, while the final reverse rolling of the strip to the end thickness is carried out for three passes through a two-stand rolling group with two windings of a strip of intermediate thickness on winders in furnaces. 2. A mini-mill for the production of thin hot-rolled strips, including a heating furnace, transport and working rollers, devices for descaling, a draft reversing stand, a finishing rolling group consisting of two reversing stands, winders in furnaces installed in front of and behind the finishing rolling group , scissors, a winder for winding the finished strip into a roll, equipment for transporting rolls to a warehouse, characterized in that the distance between the roughing stand and the first stand of the finishing rolling group is selected from the condition I, that it is longer than the length of the roll received in the penultimate odd draft pass, but less than the length of the roll received in the last draft pass.

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