RU2486974C1 - Method of asymmetric rolling of thick sheet front ends at reversing mill - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy, particularly, to production of rolled stock at thick-sheet one-stand hot-rolling mills with working rolls furnished with individual drives. Rolls running at equal peripheral velocity cause vertical flexure of breakdown bar front end due to geometrical, frictional and/or temperature asymmetry over deformation source height. To reduce vertical flexure of breakdown bar front end, factor of kinematic asymmetry, that is, working roll velocity mismatch is used. For this, roll working velocity mismatch is set to ΔV=0.1-2.0% at ε>ε_crit while at ε<ε_crit it is set to ΔV=2.01-15.0% at breakdown bar front end, its length not exceeding 1500 mm for its flexure toward the roll revolving at high velocity.

EFFECT: higher efficiency.

4 tbl, 4 dwg, 1 ex

Description

The invention relates to the field of metallurgy, and more particularly to the production of rolled metal on single-plate plate reversible hot rolling mills with an individual drive of work rolls.

When plate rolling in rolls rotating with the same peripheral speeds, there is a vertical bending of the front end of the roll due to the presence of geometric, frictional and / or temperature asymmetry along the height of the deformation zone. Increased vertical bending of the front end of the roll leads to "drilling" of the roll in the rollers of the discharge roller table and / or preliminary dressing machine. To reduce the vertical bending of the front end of the roll during plate rolling, the kinematic asymmetry factor is used - the mismatch of the speeds of the work rolls.

There is a method of asymmetric rolling in stands with an individual drive of work rolls (see USSR author's certificate for invention No. 1659139, IPC B21B 1/22, B21B 37/00, publ. 06/30/1991), according to which giving the specified curvature and direction of bending to the front end the roll is achieved due to the preliminary loading of the rolls with moments equal to the moments during the steady rolling process. In the known method, the process of trapping metal by rolls and deformation of the front end of the roll proceeds under conditions as close as possible to steady conditions, which eliminates fluctuations in the speed asymmetry of the work rolls and stabilizes the shape of the front end of the roll.

The disadvantages of this method include the fact that it does not take into account the influence of the deformation-thermal parameters of rolling, namely, relative compression and temperature, on the value of the speed asymmetry of the work rolls.

There is also known a method of asymmetric rolling of sheets (see USSR author's certificate for the invention No. 1560338, IPC B21B 1/38, publ. 04/30/1990), according to which the front end of the roll is captured by rolls having the same peripheral speed, and the moment of entering the mismatch task peripheral speeds of the work rolls are set directly proportional to the size of the end trim and inversely proportional to the peripheral speed of the work rolls at the time of capture.

The disadvantage of this method is that it does not allow you to control the curvature and direction of the bend of the front end of the roll during asymmetric rolling.

, то при прокатке передний конец раската изгибается в сторону валка, вращающегося с меньшей окружной скоростью. С увеличением степени деформации $$\left(\mathrm{2,2}<\frac{2\sqrt{\left(H-h\right)R}}{H+h}<\mathrm{5,5}\right)$$

передний конец раската изгибается в сторону валка, вращающегося с большей окружной скоростью. При дальнейшем увеличении степени деформации $$\left(\frac{2\sqrt{\left(H-h\right)R}}{H+h}>\mathrm{5,5}\right)$$

при прокатке передний конец раската снова изгибается в сторону валка, вращающегося с меньшей окружной скоростью. Уменьшение изгиба переднего конца полосы при выходе из валков достигается за счет того, что валок, на котором скорость выхода металла из очага деформации меньше, смещают в направлении прокатки на величину 5, а затем устанавливают степень деформации (см. авторское свидетельство СССР на изобретение №1212636, МПК В21В 1/22, опубл. 23.02.1986).The closest in technical essence is the method of asymmetric rolling of strips, including heating the workpiece and compressing it with different rotation speeds, while the task of the strip into the rollers determines the difference in speeds of the work rolls (mismatch of the speeds of the work rolls), the direction and curvature of the bend of the front end of the strip. If the degree of deformation is small $$\left(0<\frac{2\sqrt{\left(H-h\right)R}}{H+h}<2.2\right)$$

, when rolling, the front end of the roll bends towards the roll, rotating at a lower peripheral speed. With an increase in the degree of deformation $$\left(2.2<\frac{2\sqrt{\left(H-h\right)R}}{H+h}<5.5\right)$$

the front end of the roll bends towards the roll, rotating at a higher peripheral speed. With a further increase in the degree of deformation $$\left(\frac{2\sqrt{\left(H-h\right)R}}{H+h}>5.5\right)$$

when rolling, the front end of the roll bends again towards the roll, rotating at a lower peripheral speed. The decrease in the bending of the front end of the strip at the exit from the rolls is achieved due to the fact that the roll at which the metal exit speed from the deformation zone is less is shifted in the direction of rolling by 5 and then the degree of deformation is set (see USSR copyright certificate for invention No. 1212636 IPC В21В 1/22, publ. 02.23.1986).

The disadvantages of this method include the fact that it does not take into account the influence of the temperature of the metal at the entrance to the deformation zone on the direction of bending of the front end of the strip (roll).

The technical result of the invention is to increase the productivity of the rolling mill by reducing, or perhaps completely eliminating, the downtime of the mill due to "drilling" of the roll in the rollers of the discharge roller table and / or preliminary dressing machine.

The specified technical result is achieved by the fact that in the known method of asymmetric rolling of the front ends of thick sheets on reversing mills, including heating a continuously cast billet, compressing the billet with a mismatch of the speeds of the work rolls, according to the invention, on the front section of the roll with a length of not more than 1500 mm for bending it towards the roll rotating at a higher speed, the magnitude of the mismatch of the speeds of the work rolls is set depending on the relative compression per pass, thickness and temperature the one at the entrance to the deformation zone:

ΔV = 0.1-2.0,%, if ε> ε _crit , and

ΔV = 2.01-15.0,%, if ε <ε _crit , and

ε _crit = -0.001H ² + 0.4H + 10 ^-5 (T-800) ² +0.01 (T-800) +3.7,% at 8 <H≤32 mm;

ε _crit = -0.003Н ² + 0.64Н-0.0002 (Т-800) ² +0.1 (Т-800) -4,% at 32 <Н≤50 mm,

where ΔV is the value of the mismatch of the speeds of the work rolls,%;

ε _crit - critical compression value,%;

N is the thickness of the roll at the entrance to the deformation zone, mm;

T is the temperature of the roll at the entrance to the deformation zone, ° C;

Formulas for calculating the critical compression value are obtained for cases of rolling in rolls with a diameter of 1200 mm of rolls having a thickness in the range of 8-50 mm and a temperature in the range of 800-1050 ° C at the entrance to the deformation zone. The above dependences are empirical and obtained as a result of processing experimental data on the production of thick sheets at the hot rolling mill “5000” of OJSC “Magnitogorsk Iron and Steel Works”.

If during the compression of the roll, the mismatch of the speeds of the work rolls is set to a length exceeding 1500 mm, this will lead to unsatisfactory flatness of the roll due to periodic repetitions of the radius of curvature along the length of the section on which this mismatch will be established.

When ε> ε _crit and ΔV> 2.0%, ε <ε _crit and ΔV> 15.0%, the radius of curvature of the front end of the roll sharply decreases, there are dangers of winding the roll on the work roll and an emergency.

Vertical bending of the front end of the roll during asymmetric rolling occurs as a result of rotation of the input (AC) and output (DE) sections of the deformation zone (Fig. 1) relative to the line of roll centers (O ₁ O ₂ ). In a vertically asymmetric deformation zone there is a zone in which, on opposite sections of the contact arcs, the friction forces are directed in opposite directions and, therefore, create a torque applied to the zone. The corresponding mutual displacement of the opposite contact pressure diagrams generates a compensating moment and ensures the balance of the moment system acting on the focus. As a result, the roll at the entrance to the deformation zone and the exit from it is inclined to the horizontal at angles β ₀ and β ₁ (see Salganik V.M., Pesin AM Asymmetric sheet rolling: the development of theory, technology and new solutions. - M.: MISIS 1997, p. 192).

It was established that during hot rolling of thick sheets there is a so-called “critical” compression ε _crit , in which the mismatch of the speeds of the work rolls ΔV does not affect the vertical bending of the roll, a kind of “dead point”.

If the value of the relative compression ε for the passage exceeds the "critical", the bending of the front end of the roll occurs in the direction of the roll rotating with a higher peripheral speed (see figure 2). Then the magnitude of the mismatch of the speeds of the work rolls ΔV is set inversely proportional to the radius of curvature of the front section of the roll from the range of 0.1-2.0%, and the larger ΔV, the smaller the radius of curvature and, accordingly, the “steeper” the bend of the front end of the roll.

If the relative compression for the passage is less than “critical”, then the bend of the front end of the roll can be directed towards the roll, which rotates with both higher and lower peripheral speeds. It depends on the magnitude of the mismatch of the speeds of the work rolls - if it is insignificant (0.1-2.0%), the bend of the roll is directed towards the roll rotating at a lower speed, and if it is significant, i.e. is in the range of 2.01-15%, the bend of the roll is directed towards the roll rotating at a higher speed (see figure 3).

This ambiguous behavior of the front end of the roll is due to the varying degree of frictional asymmetry of the upper and lower arcs of the contact of the metal with the rolls. As a result of this, the velocity fields of the metal at the exit from the deformation zone are different. Moreover, in the case of a less intense mismatch of the speeds of the work rolls, the resulting velocity field is directed towards the roll rotating at a lower speed. In the case of a more intense mismatch of the speeds of the work rolls, the resulting velocity field is directed, on the contrary, towards the roll rotating at a higher speed.

An example implementation of the method.

A continuously cast billet with a cross section of 300 × 2600 mm made of 09G2S steel is heated in a methodical furnace to a temperature of 1200 ° C, then, on a single-chamber reversible plate mill with a diameter of 1200 mm work rolls, the billet is rolled back to a final thickness of 14 mm in accordance with the technological parameters (see table 1).

The mill is equipped with pyrometers for measuring the temperatures of the upper and lower surfaces of the roll during rolling. According to the readings of the pyrometers, before each passage, the temperature difference ΔТ between the upper and lower surface of the roll is determined (see Table 2). Moreover, if ΔT> 0, then the upper surface is colder, if ΔT <0, then the lower one.

In the presence of a temperature gradient, the bending of the roll during rolling occurs towards a colder surface and becomes significant when the temperature gradient is 10 or more ° C. According to Table 2, in the 13th pass, the temperature gradient is 10 ° C, and in 14-17 passes - 20 ° C.

We determine the value of the “critical” compression in the 13th pass according to the formula ε _{crit 13} = -0.003N ₁₃ ² + 0.64N ₁₃ -0.0002 (T ₁₃ -800) ² +0.1 (T ₁₃ -800) -4, because H ₁₃ = 35 mm and T ₁₃ = 896 ° C (see table 1):

ε _{crit 13} = -0.003 * 35 ² + 0.64 * 35-0,0002 (896-800) ² +0.1 (896-800) -4 = 22.5%

We determine the value of the “critical” compression for the 14-17th passes according to the formula ε _crit = -0.001N ² + 0.4N + 10 * ⁵ (T-800) ² +0.01 (T-800) +3.7, because H _14-17 ≤32 mm (see table 1), for example, for the 14th pass, H ₁₄ = 29 mm and T ₁₄ = 895 ° C:

ε _crit14 = -0.001 * 29 ² + 0.4 * 29 + 10 ^-5 (895-800) ² +0.01 (895-800) + 3.7 = 15.5%

A similar calculation is performed for 15-17 passes (see table 3).

To reduce vertical bending of the front end of the roll in the 13th pass, the value of the mismatch of the speeds of the work rolls in the front section of the roll with a length of not more than 1500 mm, according to the invention, is taken from the range of 2.01-15.0%, because ε ₁₃ <ε _{crit 13} (17.1% <22.5%). The temperature gradient is relatively small (ΔT = 10 ° С); therefore, the value of AV _{] 3 is} taken equal to 2.5%, i.e. to bend the front end of the roll down, the rotation speed of the lower roll in the 13th pass should be 2.5% higher than the upper for about 100 ms after the metal is captured by the rolls.

To reduce vertical bending of the front end of the roll in the 14-17th passage, the value of the mismatch of the speeds of the work rolls in the front section of the roll with a length of not more than 1500 mm, according to the invention, is taken from the range of 0.1-2.0%, because ε ₁₄ > ε _{crit 14} (17.2%> 15.5%), ε ₁₅ > ε _{crit 15} (16.7%> 13.7%), ε ₁₆ > ε _{crit 16} (15.0%> 12.0%) , ε ₁₇ > ε _{crit 17} (17.6%> 10.7%). Based on the experience of producing thick sheets, the value of the mismatch of the speeds of the work rolls ΔV is chosen directly proportional to ΔT and inversely proportional to the difference ε-ε _crit (see table 3).

The action of the method is illustrated in figure 4. When rolling strip 3 in rolls 1 and 2, the front end 4 bends upward due to the presence of a temperature gradient between the upper and lower surface of the roll (the top is colder). The mismatch of the speeds of the work rolls creates an anti-bend of the front end of the roll 5. In this case, the speed of the lower roll 2 is greater than the speed of the upper roll 1. The kinematic asymmetry factor - the mismatch of the speeds of the work rolls - compensates for the effect of another asymmetry factor - the temperature gradient across the thickness of the roll, as a result, the front end of the roll 6 at the exit from the deformation zone it does not have a vertical bend.

Options for the production of thick sheets, according to which, in accordance with the claimed method and according to the prototypes, rolling was carried out at the mill 5000 of OJSC MMK are presented in table 4.

Compliance with the technology of asymmetric rolling of the front ends of thick sheets on reversing mills in accordance with the proposed method ensures the absence of vertical bending of the front end of the roll (see figure 4) and, therefore, eliminates the possibility of "drilling" of the roll in the rollers of the discharge roller table and / or preliminary dressing machine .

Based on the foregoing, we can conclude that the claimed method is workable and eliminates the disadvantages that occur in the prototypes.

The inventive method can be widely used on plate reversing hot rolling mills with an individual drive of the work rolls, and therefore meets the patentability condition "industrial applicability".

Table 1 Deformation-thermal parameters of rolling Passage number The thickness of the roll at the entrance to the deformation zone N, mm Relative compression per pass ε,% Roll temperature T, ° С one 300 13.3 1058 2 260 16.9 1032 3 216 16.7 1028 four 180 16.7 1023 5 150 16.7 1020 6 125 16,0 1018 7 105 16,2 1016 8 88 15.9 905 9 74 16,2 904 10 62 19,4 903 eleven fifty 16,0 901 12 42 16.7 897 13 35 17.1 896 fourteen 29th 17,2 895 fifteen 24 16.7 888 16 twenty 15.0 868 17 17 17.6 847

table 2 Temperature gradient ΔT according to pyrometer readings. Passage number The thickness of the roll at the entrance to the deformation zone N, mm Temperature gradient between the upper and lower surface of the roll ΔT, ° C one 300 -5 2 260 -5 3 216 -5 four 180 -5 5 150 -5 6 125 -5 7 105 -5 8 88 0 9 74 0 10 62 0 eleven fifty 5 12 42 5 13 35 10 fourteen 29th twenty fifteen 24 twenty 16 twenty twenty 17 17 twenty

Table 3 The critical compression value ε _{crit the} value of the mismatch of the speeds of the work rolls ΔV Passage number The thickness of the roll at the entrance to the deformation zone N, mm Roll temperature T, ° С Relative compression per pass ε,% Critical compression ε _crit ,% The value of the mismatch of the speeds of the work rolls ΔV,% 13 35 896 17.1 22.5 2.5 fourteen 29th 895 17,2 15,5 1,2 fifteen 24 888 16.7 13.7 0.6 16 twenty 868 15.0 12.0 0.6 17 17 847 17.6 10.7 0.2

Claims (1)

The method of asymmetric rolling of the front ends of thick sheets on reversing mills, including heating a continuously cast billet, compressing a billet with rolls with different peripheral rotational speeds, while the mismatch of the speeds of the work rolls is determined before the task of rolling into rolls, characterized in that the front section of the roll is no more than 1500 mm for its bending towards the roll, rotating with a higher peripheral speed, the value of the mismatch of the speeds of the work rolls is set depending on the relative burn Atia for the passage, thickness and temperature of the roll at the entrance to the deformation zone:
ΔV = 0.1-2.0,%, if ε> ε _crit ,
ΔV = 2.01-15.0,%, if ε <ε _crit ,
moreover, ε _crit = -0.001H ² + 0.4H + 10 ^-5 (T-800) ² +0.01 (T-800) +3.7,%, at 8 <H≤32 mm,
ε _crit = -0.003Н ² + 0.64Н-0.0002 (Т-800) ² +0.1 (Т-800) -4,%, at 32 <Н≤50 mm,
where ΔV is the value of the mismatch of the speeds of the work rolls,%,
ε _crit - the value of the critical compression,%,
N - thickness of the roll at the entrance to the deformation zone, mm,
T - temperature roll at the entrance to the deformation zone, ° C.

Images