RU2235611C1 - Method for hot rolling of wide strips in mill including continuous subgroup of rough rolling stands - Google Patents

Abstract

FIELD: manufacture of hot rolled strips in wide strip rolling mills.

SUBSTANCE: method comprises steps of rolling hot slab in rough group of stands; transporting rolled piece on intermediate roller table including transportation of rolled piece under screening unit; rolling blank in finish group of rolling stands; cooling it on delivery roller table and coiling rolled piece; performing rolling in finish group of stands at constant speed and providing quasi-constant temperature of rolled piece along it at inlet of finish group of stands due to rolling in rough group of stands with acceleration and due to screening rolled piece.

EFFECT: stable rolling mode in finish group of rolling stands, uniform factors of mechanical properties along length of ready strip, lowered electric energy consumption.

2 dwg, 6 ex

Description

 The invention relates to ferrous metallurgy, and more specifically to methods for hot rolling of strips on broadband mills.

A known method of broadband hot rolling in a mill containing a continuous subgroup of roughing stands, including rolling a hot slab in a roughing group of stands, including accelerating in the last stands of the roughing group, transferring the rolling along an intermediate roller table, rolling in finishing stands with acceleration, cooling to the discharge roller table and the winding of finished strips into a roll [see, for example, GG Fomin et al. “Mechanization and automation of wideband hot rolling mills”. Publishing house "Metallurgy", 1979, p. 23].

The main disadvantage of this method is its low efficiency in solving the problem of improving the temperature regime of rolling in the finishing group of stands: increasing the temperature of the rear end of the tack due to rolling with acceleration in a continuous draft subgroup can reach no more than 40 ° C, which is clearly not enough to implement the rolling process in finishing stands to produce a high-quality finished strip.

A method is known shirokopolosovoy hot rolling mill comprising a continuous subgroup of 3 ^x roughing stands, comprising rolling the hot slab in the roughing stands, the transmission tackle on the intermediate roller conveyor with its shielding in the process of this transmission, rolling in the finishing stands, cooling out table and winding of finished strips into a roll (see, for example, the Technological instruction “Hot rolling of strips in a hot rolling mill 2000”, TI-101-GL.10-374-90, Magnitogorsk, 1995, Appendix 3).

In the aggregate of essential features, this known method of broadband hot rolling is the closest to the proposed, therefore, adopted as a prototype.

The main disadvantage of this method is the insufficient (at the level of 60 ... 80%) degree of decrease in the “temperature wedge” in the shielding process, which does not allow rolling to be carried out in the finishing group of stands with constant speed. In turn, this leads to the need to perform finish rolling with reduced acceleration, which reduces the productivity of the process.

The proposed method of broadband hot rolling is free from this drawback of the known rolling method. Through its implementation, the entire rolling mode is stabilized in the finishing group of stands, which allows:

- reduce the longitudinal and transverse thickness difference of the finished strips, especially with a thickness of less than 2.5 mm;

- roll wider thin strips;

- to ensure uniformity of indicators of mechanical properties along the length of the finished strip;

- reduce energy consumption in finishing stands due to the rejection of their acceleration, as well as rolling hotter metal;

- for a number of standard sizes of strips, especially thin ones, by cutting the tackle in half on flying scissors, use 100% under heating furnaces and halve the loss of metal with trim on flying scissors.

The noted technical results are achieved in the method of hot-strip rolling in a mill containing a continuous subgroup of roughing stands, including rolling a hot slab in a roughing stand group, transferring the tackle to an intermediate roller table with its screening during this transfer, rolling in the finishing group of the stands, cooling on the discharge side the rolling table and the winding of finished strips into a roll due to the fact that they carry out rolling in the finishing group at a constant speed, while by rolling with acceleration in a continuous subgroup of roughing stands with subsequent screening of the tack on the intermediate roller table provides a quasi-constant temperature of the tack along its length at the entrance to the finishing stand group.

The proposed method is illustrated by a schematic drawing of the technological line of the mill containing a continuous subgroup of roughing stands on which the method is carried out, and known data on the leveling ability in temperature of the finishing group of stands.

где Δt_F1 - изменение температуры подката на входе в чистовую группу, Δt_кп - обусловленное этим изменением колебание температуры конца прокатки (фиг.1).Figure 1 shows a diagram of a production line of a continuous broadband hot rolling mill (NSHPS cp), containing in the draft group a continuous subgroup of the last three stands; in FIG. 2 - change (journal "Steel", 1976, No. 11, p. 1012, Fig. 2) of the smoothing coefficient η depending on the number of finishing stands F _i and the thickness of the rolled strip h in mm. Here

where Δt _F1 is the change in temperature of the tackle at the entrance to the finishing group, Δt _kp is the fluctuation of the temperature of the end of rolling caused by this change (Fig. 1).

NSHPS production line (Fig. 1) contains heating (heating) furnaces 1, a roughing group of stands 2 with a continuous subgroup of the last three stands 3, an intermediate roller table 4 with a shielding unit 5, a finishing group of stands 6, an outlet roller table 7 and a winder 8. An integral part of the finishing group the stand is the interstand cooling system (ICE) 9.

The method of broadband hot rolling is as follows.

The hot slab heated / heated in the furnaces 1 is discharged from the furnace and fed into the roughing group of stands 2, where it is subsequently deformed to the thickness of the tack, which enters the intermediate roller table 4. During deformation in the roughing group by stands 2, in its continuous subgroup 3, rolling is carried out with acceleration, i.e. increase the rolling speed from the front to the rear end as they pass through the rolling stands of this subgroup. The implementation of rolling with acceleration is provided due to the fact that the drive stands of the continuous subgroup 3 is carried out from DC motors.

Thanks to accelerated rolling in a continuous continuous subgroup of stands, a temperature difference is obtained along the length of the tack: a lower temperature at the front end of the tack and a higher temperature at its rear end.

In this state, the tackle is passed through an intermediate roller table 4 to the finishing group of stands 6 containing seven stands F ₁ ... F ₇ . During this transfer, the tackle passes under the shielding unit 5. Finding the tackle under this unit reduces cooling of the rear end of the tackle, thereby increasing the temperature of the rear end of the tackle in comparison with its front end when the metal enters stand F _{1 of the} finishing group of stand 6. Specified increase the temperature of the rear end of the tackle in comparison with its front end is summed up with the already noted increase in the temperature of the rear end of the tackle in comparison with its front end, leveling including the increase e at 5 ... 8 ° C the temperature of the front end of the tackle due to passage under the shielding installation.

Ultimately, they provide a quasi-constant temperature distribution along the length of the tackle at the moment of its entry into the first stand F _{1 of the} finishing group of stands 6. Moreover, by the quasiconstant temperature distribution along the length of the tackle we mean the permissible difference in temperatures of the back and front ends of the tackle at the time of its entry into the stand F ₁ (Δt _F1 in figure 1) (“technologically necessary stability of the temperature of the roll” according to Yu.V. Konovalov and others. “Calculation of the parameters of sheet rolling”, Reference, Moscow: Metallurgy, 1986, p. 223) by the amount which the first one is smoothed out as the finishing group passes through stand 6 due to its leveling ability (Fig. 2) to the values of the end temperature recorded by the end temperature sensor at the exit of stand F ₇ as the permissible distribution of the end temperature (Δt _kp in Fig. 1) the length of the finished strip

[According to the technological instruction for hot rolling of strips in the corresponding mill].

When rolling the thinnest strips (1.2 ... 1.5 mm thick), the tackle is cut in half before flying to the F ₁ stand (using the original full length slabs), thereby creating a “temperature wedge” for each tack on the entrance to the stand F _{1 is} reduced by half, and the rest uses the already described techniques of the proposed rolling method.

These provisions are taken as the basis and rolling in the finishing group of stands 6 is carried out at a constant speed. In this case, to eliminate the decrease in the productivity of the rolling process due to the refusal of rolling with acceleration in the finishing group of stands 6, the overall level of the rolling speed in the finishing group of stands 6 is increased, and the possible elevated temperatures of the end of rolling are eliminated either by lowering the heating / heating temperature of the slabs, or by applying interstand cooling. Moreover, MCOs are mainly used in the third (F ₃ -F ₄ ) - sixth (F ₆ -F ₇ ) intercellular spaces of the finishing group of stands 6, which maximally use the effect of increasing the temperature of the rear end of the tackle at the entrance to stand F ₁ to reduce the load on stand F ₁ -F ₃ finishing group 6 (or to increase the reduction in these stands).

After leaving the stand F _{7, the} strip is transported along the discharge roller table 7 with forced cooling and wound into a roll on coilers 8.

Implementation of the proposed method of broadband hot rolling allows you to:

1) have significant energy savings in the finishing group of stands due to the rejection of rolling metal with acceleration of the finishing group of stands;

2) additionally have energy savings in the finishing group of stands at the level of 10 ... 12% due to the rolling of hotter metal in the first finishing stands;

3) to reduce the longitudinal and transverse thicknesses of the strips and the dispersion of the mechanical properties along the length of the finished strips due to the stabilization of the temperature-strain conditions of rolling in all stands of the finishing group;

4) for orders for lightweight rolls (especially for thin strips) to halve the loss of trim on flying shears and continuous caster by using solid slabs and cutting the half in half on flying shears. To increase the degree of use of the furnace hearth, significantly increase the yield.

Example 1. A continuous broadband hot rolling mill 2000 has the parameters shown in FIG. 1 and described in the book by G. G. Fomin et al. Mechanization and Optimization of Broadband Hot Rolling Mills, pp. 37 ... 63. This mill contains a continuous subgroup of ^the last 3 stands in the roughing group of stands, allowing the rolling speed to vary within 2 ... 5 m / s, the finishing group of the mill has 7 quart stands (table 7 in this book, NSHPS, n. 2000 of the Cherepovets Metallurgical Plant) and MCO.

The intermediate roller conveyor of the mill is equipped with a heat-preserving (shielding) installation with a length of 52.8 m (for shielding from above) and shielding from the bottom for 100 m, which is carried out using inter-roller plates with containers filled with air scale (a detailed description of the shielding installation and its capabilities are described in the article VN Khloponin et al. Heat-saving installation for broadband hot rolling mills, Ferrous metals, February 2002, pp. 13 ... 18).

According to the technological instructions of CherMK for rolling at this mill: “Hot rolling of strips in sheet rolling shop No. 2. TI-105-P.GL.2-02-92, table 8.1, clause 10, the maximum deviation of the temperature of the end of rolling t _cp from the nominal value Δt _cp = + 15 ° C is allowed [note that for the very close to the layout NSPS MMK according to the noted technological instructions TI-101-GL.10-374-90, tab. 10, rolling temperature Δt _kp ± 10 ° С from the nominal value is allowed, i.e. temperature difference Δt _kp = 20 ° C].

At the mill considered by the NSPS 2000, a hot slab with a thickness of 250 mm, a width of 1500 mm and a length of 10250 mm in the rough group is rolled onto a tack 35 mm thick and 73.2 m long. Moreover, rolling in a continuous subgroup 3 is carried out with acceleration, changing the rolling speed from V = 2 m / s in the last roughing stand for the front end of the tack to 5 m / s for the rear end of the tack, realizing a constant acceleration value.

In the process of transferring the tackle through the intermediate roller table 4 with the specified heat-saving unit 5 and rolling it in finishing group 6 onto a finished hot-rolled strip 3.0 mm thick with a constant rolling speed in the last finishing stand F ₇ of 10 m / s at the entrance to the first the finishing stand F ₁ form a temperature wedge Δt _F1 = 5 ° C with a lower temperature for the rear end of the tackle.

According to figure 2, when rolling a strip with a thickness of 3.0 mm, the smoothing coefficient for the seven-stand finish group is about 2.8. Thus, the rolling process is implemented in the finishing group at a constant speed and have a constant temperature of the end of rolling t _CP along the length of the finished strip (temperature difference Δt _CP along the length of the finished strip is 1.7 ° C).

Example 2. Under the conditions indicated in example 1 on NShPS 2000 g. a strip 10 mm thick and 1835 mm wide is rolled from a slab 250 mm thick, 1835 mm wide and 10,000 mm long, while rolling in the finishing group of stands is carried out at a constant speed in the last finishing stand F ₇ of 3.2 m / s. In this case, at the entrance to the first finishing stand F ₁ form a temperature wedge Δt _F1 = 4 ° C with a lower temperature for the rear end of the tack, the length of which is 71.4 m

Take into account that when rolling a strip 10 mm thick for a seven-stand finishing group, the smoothing coefficient is about 1.5 (Fig. 2). Thus, the rolling process is implemented in the finishing group at a constant speed and have a constant temperature of the end of rolling along the length of the finished strip (temperature difference Δt _kp along the length of the finished strip is 2.7 ° C).

Example 3. Under the conditions indicated in example 1 on NSPS 2000 from a slab 250 mm thick, 1200 mm wide and 9400 mm long, strips 1.5 mm thick and 1200 mm wide are rolled. Moreover, in the finishing group of stands, rolling is carried out at a constant speed in the last finishing stand F ₇ equal to 10 m / s. In this case, at the entrance to the first finishing stand F ₁ form a temperature wedge Δt _F1 equal to 44 ° C for the length of the rolling 67100 mm Take into account that when rolling a strip with a thickness of 1.5 mm for a seven-stand finishing group, the smoothing coefficient is about 4.55 (Fig. 2). Therefore, they carry out the rolling process in the finishing group with the indicated constant speed and have the temperature difference along the length of the finished strip that fits into the requirements of the technological instruction at the level of Δt _kp = 9.8 ° C.

Example 4. Rolling a strip with a thickness of 1.5 mm is carried out under the conditions described in example 3, but the tackle on flying scissors is cut in half, eventually obtaining two strips. Thus, on the length of each tackle at the entrance to the finishing group they have a “temperature wedge” Δt _F1 = 22 ° C, which is equivalent to a practically uniform distribution of the temperature of the end of rolling along the length of each finished strip (temperature difference Δt _kp along the length of the finished strip is 4.9 ° FROM). Thus provide technologically necessary stability temperature peals. In addition, in comparison with rolling the same strips from the original slabs of the full length (i.e., 10,000 mm), they have a reduction in metal losses during the cutting of slabs in continuous casting machines, and halve the loss of metal with trim on flying NSHPS shears, fully used under a heating furnace and ultimately increase the yield.

Example 5. Rolling a strip with a thickness of 1.2 mm is carried out under the conditions described in example 3. Rolling technology involves cutting the tackle in half on flying scissors. As a result, for each tackle, a “temperature wedge” Δt _{F1 is} provided at the entrance to the first finishing stand at 35 ° C and the technologically necessary temperature stability between the tackles. When the rolling speed in the last stand F ₇ seven-stand finishing group of strips with a thickness of 1.2 mm, the smoothing coefficient is equal to about 5.2 (figure 2). Under these conditions, the difference in temperature of the end of rolling Δt _kp along the length of each finished strip is 6.7 ° C, which is quite acceptable according to the technological instruction in force at this mill (almost 2.2 times lower than the limit of 15 ° C established by the technological instruction) . In addition, they receive the economic effect of increasing the yield.

Example 6. With the parameters indicated in example 1 NShPS g.p. and under rolling conditions in a rough group of rolling stands, 73.2 m long, from a slab 250 mm thick, 1500 mm wide and 10250 mm long, strips 2.5 mm thick are rolled. Rolling in the finishing group of stands is carried out at a constant speed equal to 10 m / s for the last seventh stand F ₇ . Due to rolling in a continuous draft subgroup 3 with acceleration: increase the rolling speed from 2.0 m / s at the beginning of the rolling process to 5.0 m / s at its end, provide an increased temperature of the rear end of the rolling and subsequent screening of the rolling form at the entrance to the first stand F _{1 of the} finishing group “temperature wedge” Δt _F1 at the level of 3 ° С. The latter (taking into account the data of FIG. 2) under the indicated rolling conditions is equivalent to a uniform temperature distribution along the length of the tackle at the entrance to the finishing stand F ₁ and also its uniform distribution (t _CP ) along the length of the finished 2.5 mm strip. Under these conditions, with 100% guarantee, they provide uniform along the strip length indicators of mechanical properties, longitudinal and transverse strip thickness difference.

The materials in examples 1-6 were obtained by computer simulation using mathematical models described in the magazines Steel, 1990, No. 10, p. 40 ... 50 and Ferrous metals, February 2002, p. 13 ... 18. In all the considered examples of hot rolling of strips from slabs, the strips are uniformly cooled along their main length on the discharge roller 7, which ensures constant winding temperature along their length in accordance with the technological instruction and the formation of the specified parameters of the mechanical properties, after which they are rolled up on coilers 8.

Claims (1)

A method of broadband hot rolling in a mill containing a continuous subgroup of roughing stands, including rolling a hot slab in a roughing stand group, transferring the rolled wire through an intermediate roller table with its screening during this transfer, rolling in the finishing group of stands, cooling on the discharge roller table and winding the finished strips in a roll, characterized in that the rolling in the finishing group of stands is carried out at a constant speed, while by rolling with acceleration in a continuous subgroup of draft crates followed by screening of the intermediate roller conveyor mistimed provide quasi-permanent temperature rolled along its length at the entrance of the finishing group stands.

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