RU2301123C1 - Method of preparation of rolling mill work rolls - Google Patents

Abstract

FIELD: metallurgy; rolling.

SUBSTANCE: invention can be used for preparation of work rolls of hot and cold rolling mills. Proposed method of preparation of work rolls of rolling mill includes forming barrels to shape made to contour defined by polynomial up to fifth degree y(x) = a₅x⁵ + a₄x⁴ + a₃x³ + a₂x³ + a₁x where x is coordinate along axis of roll with beginning in middle of barrel. Redressing of rolls is carried out in state it is heated in process of rolling, on NC roll-grinding machines and then roll is loaded into stand. Prior to dressing, temperature of surface is measured along length of roll barrel in three points minimum, and values of coefficients a₂ and a₄ in polynominal of roll profile at dressing are reduced, respectively, by △a₂ =(1-k)2αD△t_c/L² and △a₄ = k8αD△t_c/L⁴ where D and L are diameter and length of roll barrel; α is linear thermal expansion coefficient of roll material: △t_c is difference of surface temperature in middle and half sum of temperatures at ends of roll barrel; k = 0 at dressing of roll to polynominal of third degree and k = -0.65 at dressing of roll to polynominal of fifth degree.

EFFECT: increased service life of rolls and accuracy of adjustment of rolled strip profile.

2 tbl, 2 dwg

Description

The invention relates to rolling production and can be used in the preparation of work rolls of hot and cold rolling mills.

There is a knot of rolls of a rolling stand of a sheet mill with axial counter-directional movement of the upper and lower rolls, the profile of which is made along a contour defined by a polynomial to the 5th degree (see RF patent No. 2146973, MKI B21B 1/22, 13/02, 2000 ) The values of the coefficients of the polynomial are determined from the geometric parameters of the rolls and a given range of adjustable profile of the rolled strip. This technical solution allows you to adjust the profile and flatness of the rolled strip due to the axial movement of the rolls, controlled by an automatic system.

A disadvantage of the known device is the need to maintain a large fleet of rolls so that the rolls after they are rolled out of the stands for about one day are cooled in the warehouse to ambient temperature before grinding and subsequent filling in the mill stand. In addition, due to the fact that the rolls undergo 40-70 complete heating-cooling cycles during their operation, significant residual stresses accumulate in the body of their material, which reduce the resistance of the roll. The requirement for complete cooling of the roll is caused by the fact that after it is rolled out of the cage, the distribution along the length of the mass-average over the cross-section of the temperature of the roll is always uneven - Fig. 1. In the process of cooling the roll, this temperature distribution along the length changes, and after it the distribution of the thermal expansion of the roll along the length also changes, therefore, the profile of the roll. After resurfacing of the hot roll, this non-stationary process begins to distort the profiling performed on the roll grinding machine. Figure 2 shows a typical contour of the upper forming barrel of the lower roll of the 8th stand of the mill 2000 of OJSC NLMK equipped with an axial sliding system, made according to a polynomial of the 3rd degree on a roll that has not cooled down after rolling, and the profile of the same roll when filling in the crate 5 hours after grinding. It can be seen that the roll profiling changes significantly during cooling. The system for managing the profile and flatness of strips (SUPP), having information only about a given roll profile, which was executed on a roll grinding machine, controls the profile of the strip using axial shift of the rolls with low accuracy, because the actual roll profile has changed during cooling. During further rolling of the control system for thermal models, it calculates the roll heating from the rolled metal and its profile change. But since in the calculations the profile obtained on the roll grinding machine with a uniform temperature distribution along the length of the roll is taken as the initial roll profile, the error in adjusting the strip profile is not compensated.

A known method of preparing the rolling rolls for operation, in which the average temperature of the roll barrel after dumping from the cage, followed by cooling in a bath with running water for 25-30 minutes, and the water temperature is maintained at 27-30 ° C below the initial temperature of the roll barrel ( see USSR AS No. 923653, class B21B 27/06, 1982). Intensive water cooling of the roll reduces the uneven distribution of temperature along the length of the roll.

The disadvantages of this method are the availability of expensive equipment for controlled water cooling of the rolls, reduced durability of the rolls due to additional thermal loads of the working layer of the roll during forced cooling with water, lack of information about the initial (in front of the bath) and the final thermal profile of the roll, which does not allow manufacturing on a roll grinding the machine requires the required SUPP roll profile and when rolling adjust the strip profile with sufficient accuracy.

A known method of preparing the work rolls of a broadband hot rolling mill with convex or concave profiling, in which, after the roll is rolled out of the cage, the surface temperature is measured along the length of the roll. Then, according to the dependences, including the surface temperature difference between the middle and the edges of the roll barrel, the weighted average strip width of the finished assembly lot, the time between transshipment and grinding of the roll, the physical and geometric parameters of the roll, the profile thermal corrections along the roll barrel length are calculated separately for sections corresponding to the weighted average bandwidth, and end sections. The machine profile for resurfacing a hot roll in each cross section is calculated either by summing the original profile with the calculated thermal correction for the convex forming barrel, or subtracting the thermal correction for the concave forming barrel of the roll (see AS USSR No. 1600001, class B21B 28/02 , 1990).

The disadvantage of this technical solution is the inability to use it for resurfacing hot rolls that regulate the strip profile using CVC (Continuously Variable Crown) technology due to the axial movement of the rolls and having an S-shaped profiling. In addition, such rolls are not unambiguously convex or concave; they are polished on a CNC roll grinding machine, into the computer of which it is necessary to enter the values of the coefficients of the polynomial coefficients of the curve of the grinded contour of the roll.

In the inventive method for the preparation of work rolls of a rolling mill, the problem of reducing the fleet of S-shaped work rolls, increasing the durability of the rolls and the accuracy of adjusting the profile of the rolled strip is solved. These problems are solved due to the fact that in the method of preparing work rolls of a rolling mill, including rolling the roll from the stand, measuring the surface temperature along the length of the roll barrel at least at three points, resurfacing in a state heated from rolling and subsequent filling into the roll stand, profiling of barrels which are made along the contour y (x), defined by a polynomial to the 5th degree:

и

соответственно,y (x) = a ₅ x ⁵ + a ₄ x ⁴ + a ₃ x ³ + a ₂ x ² + a ₁ x, the coefficients a ₂ and a ₄ in the polynomial of the roll profile during grinding are reduced by

and

respectively,

where x is the coordinate along the axis of the roll with the beginning in the middle of the barrel;

D and L are the diameter and length of the roll barrel;

α is the coefficient of linear thermal expansion of the material of the roll;

Δt _c is the difference in surface temperature in the middle and half the temperature at the edges of the roll barrel;

k = 0 when grinding the roll on a polynomial 3rd degree and k = -0.65 when grinding on a polynomial 5th degree.

The proposed method of preparing work rolls of a rolling mill is as follows.

After rolling the assembly lot of the strips, the S-shaped rolls of the rolling mill are thrown out of the crate. Due to the contact of the rolls with hot metal during rolling, the rolls after dumping have an elevated temperature - see Fig. 1. Despite this, rolls are immediately prepared for the next campaign. Before regrinding for profiling along a contour defined by a polynomial to the 5th degree, the surface temperature of the roll is measured, for example, by a contact thermocouple at three points: in the middle and at the edges of the barrel. The relative surface temperature, Δt _{c, is} calculated as the difference of the surface temperature in the middle and half the temperature at the edges of the roll barrel.

The distribution along the roll length of the relative surface temperature (the difference between the current surface temperature and the half-temperature at the edges of the roll barrel) can be described with sufficient accuracy by a polynomial to the 4th degree:

where Δt _c is the relative surface temperature of the middle of the roll barrel; k is the coefficient of influence on the approximation of the relative temperature of the surface of the roll of a member of the polynomial containing the coordinate of the roll "x" in the 4th degree.

The distribution along the length of the roll of the mass-average temperature cross section that defines the thermal contour of the roll is equidistant to the distribution of the relative surface temperature along the length of the roll - Fig. 1. Hence, the roll profiling contour, taking into account its thermal expansion, is equal to:

where y (x) = a ₅ x ⁵ + a ₄ x ⁴ + a ₃ x ³ + a ₂ x ² + a ₁ x is the given roll contour (polynomial to the 5th degree), k = 0 for the roll contour made for a polynomial of the 3rd degree, k = -0.65 for the contour of the roll made by a polynomial of the 5th degree (determined experimentally).

The transformations do not take into account the terms at the “x” coordinate with a zero degree, so they do not affect roll profiling.

Для валка, который шлифуется по полиному 5-й степени, величины коэффициентов а₂ и а₄ полинома заданного контура валка уменьшают на

и на

соответственно, (k=-0,65). Новые, скорректированные с учетом температуры коэффициенты а₂ и а₄ также вводят в компьютер вальцешлифовального станка.Thus, for regrinding the hot roll, all coefficients of the polynomial of a given contour are entered into the computer of the roll grinding machine, except for the coefficients a ₂ and a ₄ . For a roll, the contour of which is polished according to a polynomial of the 3rd degree, the coefficient coefficient _{2 of the} polynomial of the given roll contour is reduced by

For a roll that is polished by a polynomial of the 5th degree, the coefficients a ₂ and a _{4 of the} polynomial of a given contour of the roll are reduced by

and on

respectively (k = -0.65). New, temperature-corrected coefficients a ₂ and a _{4 are} also entered into the roller grinding machine computer.

To accelerate the work, the polishing coefficients for all the specified roll roll contours and possible variants of the relative surface temperatures of the barrel middle Δt _c are introduced into the computer memory of the roll grinding machine in advance. Before grinding the hot roll, the grinder measures its surface temperature at three points, calculates the relative surface temperature of the barrel middle Δt _c , selects from the series of polynomials already entered into the machine computer memory the polynomial corresponding to the measured temperature Δt _c , and starts grinding the hot roll. A roll polished taking into account the temperature in a non-cooled state is installed in the cage for rolling a new strip campaign. Since the initial machine-tool S-shaped profile of the roll takes into account its residual thermal profile, the SUPP controls the strip profile during the rolling process due to the axial shift of the rolls with fairly high accuracy. In addition, due to the fact that the amplitude of cyclic fluctuations in the thermal state of the roll decreases and due to this, the value of residual stresses in the roll body decreases, the resistance of the working layer and the durability of the roll increase.

The proposed method for the preparation of work rolls of a rolling mill was tested in the preparation of work rolls in stands No. 8, 9, 10 of the 2000 hot rolling mill of NLMK, equipped with axial shift mechanisms for work rolls and an automatic strip profile control system. In accordance with the invention, after dumping from stands No. 8-10, the work rolls were prepared for regrinding - dismantled pillows with bearings, set the roll on a CNC roll grinding machine. Using a contact thermocouple, we measured the surface temperature of the rolls at three points: in the middle and along the edges of the barrel, calculated the relative surface temperature of the middle of the barrel Δt _c - table 1.

Table 1 Crate, roll position The surface temperature along the length of the roll barrel, ° C The relative surface temperature of the middle of the barrel Δt _c , ° C drive side service side the middle 8 cells., Top 36 thirty 52 19 8 cells, bottom thirty 34 51 19 9 cells, top 31 29th 47 17 9 cells, bottom 34 29th 41 9.5 10 cells, top 31 29th 49 19 10 cells, bottom 33 32 51 18.5

For the ranges of regulation of the roll gap profile, the polynomial coefficients of the 3rd degree (k = 0) of roll profiles, roll diameter D = 800 mm, barrel length -L = 2300 mm, coefficient of linear thermal expansion of the cast iron roll α = 1.15 · 10 ^{-5 1} / ° С and temperatures Δt _c , presented in table 1, calculated the coefficient polynomial coefficient a ₂ taking into account the temperature correction (Δa ₂ ) - table 2.

The coefficients of the polynomial of the 3rd degree were entered into the computer of the machine (Table 2) and the roll was polished along the contour of this polynomial. Thus, all rolls 8, 9 and 10 of the stands were polished. After 8-10 hours, the rolls were installed in the mill stands. When rolling with these rolls, the accuracy of tuning the control system to a given strip profile was 98.9%, the standard deviation of the actual strip profile from a given profile for this campaign was 10.9 μm, which is 10-40% lower than in campaigns with polished rolls excluding roll temperature.

The proposed method for preparing work rolls of a rolling mill allows to reduce the fleet of S-shaped work rolls necessary for work, to increase the accuracy of regulation of the profile of the rolled strip and the durability of the rolls.

Claims (1)

A method of preparing work rolls of a rolling mill, including rolling the roll from the stand, measuring the surface temperature along the length of the roll barrel at least at three points, resurfacing in a state heated from rolling and subsequent filling into the stand, characterized in that the resurfacing of the rolls, profiling of which barrels are made along the contour y (x) defined by a polynomial to the 5th degree: y (x) = a ₅ x ⁵ + a ₄ x ⁴ + a ₃ x ³ + a ₂ x ² + a ₁ x, produce along the contour defined by the indicated polynomial with coefficients a ₂ and a ₄ less than:

and

respectively, where x is the coordinate along the axis of the roll with the beginning in the middle of the barrel; D and L - diameter and length of the roll barrel; α is the coefficient of linear thermal expansion of the material of the roll; Δt _c is the difference in surface temperature in the middle and half the temperature at the edges of the roll barrel; k = 0 when grinding the roll along a contour defined by a polynomial of degree 3; k = -0.65 when grinding along a contour defined by a polynomial of the 5th degree.

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