RU2732451C2 - Method of compensating thickness deviation of rolled strip at reversing cold rolling mill - Google Patents

Abstract

FIELD: metal rolling.SUBSTANCE: invention relates to rolling production and can be used in cold rolling of strips from various types of steel. Method includes generating a signal supplied to a position controller of a hydraulic pressing device (HPD) of mill rolls in accordance with a given rolling parameters of the HPD position, measurement of the strip movement speed at the mill outlet, taking into account of which the HPD position correction signal is generated, which is supplied to the said controller in addition to the signal corresponding to the specified rolling parameters, wherein correction signal is formed taking into account material of rolled strip, stiffness module of strip, stiffness module of rolling stand and speed of strip at stand outlet by preset mathematical expression.EFFECT: use of the invention increases accuracy of compensating deviation of thickness of rolled strip.1 cl, 6 dwg

Description

The invention relates to rolling production and can be used for cold rolling of steel strips on reversing mills. When rolling the strip, the specified thickness of the metal at the exit of the stand is maintained using an automatic thickness control system (CAPT). The most difficult, from the point of view of controlling the thickness, are the portions of the strip where the rolling speed changes. With increasing speed, the coefficient of friction in the deformation zone decreases, which leads to a decrease in the thickness of the rolled metal. When the speed decreases, the strip thickness at the exit of the stand increases accordingly. They are trying to solve this problem in two ways: by changing the parameters of the thickness regulators depending on the speed, or by additional influence on the position of the hydraulic pressure device (HPD), taking into account the absolute rolling speed. In the first case, it is difficult to compensate for the changing parameters of the controlled object, and therefore there are always deviations of the actual rolled thickness at the mill exit due to the inevitable delay. In the second case, it is necessary to correctly calculate the correction for the position of the hydraulic pressure device as a function of speed, taking into account the changing rolling conditions.

There is a known method of compensating the value of the roll gap depending on the value of the rolling speed by the empirical method (see patent RU 2492946 C1, В21В 1/26, 2013), where it is proposed to correct the value of the roll gap according to the formula

S = S ₀ + k⋅10 ^-3 ⋅V,

where S ₀ - roll gap set at the filling speed, mm;

k = 3.5 ÷ 5.5 - proportionality coefficient, depending on the degree of work hardening of the strip;

V is the peripheral speed of the rolls, m / s.

The lower value of the coefficient k refers to strips with a work hardening of less than 55%, and a larger value to strips with a work hardening of more than 75%. The author of the patent offers an approximate selection of the coefficient k depending on the strip work hardening.

In our opinion, this formula does not take into account a wide range of rolled steel grades - from soft carbon steels to hard electrical steels. In addition, the linear function of speed does not fully provide the required correction of the roll gap, and the gap itself is not accurate due to the lack of the possibility of measuring it.

In order to eliminate the above disadvantages, the authors decided to study the nature of the relationship between a small increase in the speed of the strip at the exit of the stand and the corresponding increase in the deviation of the thickness of the rolled strip with a constant rolling force, i.e. Δh / ΔV ₁ at F = const, at different speeds of the strip at the exit of the stand V ₁ . The studies were carried out on a reversible cold rolling mill on various materials - carbon, dynamo and transformer steels - and on all passes. The data were summarized in tables, which were then used to obtain graphical dependences Δh / ΔV ₁ = ƒ (V ₁ ). Figure 1 shows two curves: measured and calculated. Measured is plotted according to tabular data for dynamo steel; curves for other assortments differ only in scale. The resulting dependence most closely matches the formula

y = a * e ^{-k * x} ,

or, if you enter your arguments,

According to this formula, the calculated curve in figure 1 is built, where a = 0.4; k = 0.01.

In this formula, "a" and "k" are scaling factors. Having slightly transformed the formula, we get:

By integrating this formula, we find the deviation of the rolled strip thickness from the specified one at different rolling speeds:

where C is some constant. Since it can be of any value, it is convenient to take C * k / a = 1, and then

In our case, based on the experimentally obtained curves, a = 0.4 and k = 0.01. Function graph

shown in figure 2 (the thickness of the rolled strip is measured in microns, the speed of the strip at the exit of the stand - in m / min).

In order to use this function as a correction for the position regulator of the GNU, we introduce the coefficient A = a / k and take into account the ratio of the stiffness of the "stand - strip" system. In this case, the GNU position correction formula will look like this:

where C _m is the stiffness modulus of the strip, kN / mm;

C _g - stand stiffness modulus, kN / mm;

V ₁ - strip speed at the stand exit, m / min;

A is the scaling correction factor for various materials: for carbon steel A = 30, for dynamo steel A = 40, for transformer steel A = 120, μm.

The stiffness modulus of the stand C _g is understood as the rolling force causing its elastic linear deformation by 1 mm in the direction of the action of this force.

This function was implemented in the control system of the reversing mill in the NLMK Dynamo Steel Shop based on the SIMATIC FM-458 programmable controller.

The general functional control diagram is shown in figure 3, where:

1 - reversible stand;

2 - unwinder (input reel);

3 - output reel;

4 - strip speed meter at the entrance of the stand;

5 - strip speed meter at the stand exit;

6 - gauge of the deviation of the strip thickness at the inlet of the stand;

7 - gauge of deviation of the strip thickness at the exit of the stand;

8 - hydraulic pressure device;

9 - regulator of the position of the pressure device;

10 - adder;

11 - automatic thickness control system;

12 - total effort regulator;

13 - block for forming the setting of the position of the GNU at the initial effort;

14 - system for calculating the correction of the position of the GNU, depending on the speed of the strip at the exit of the stand.

Used designations in the diagram (figure 3):

V ₀ - speed of the strip at the entrance of the stand, m / min;

V ₁ - strip speed at the stand exit, m / min;

F _back , F _fact - set and actual effort, kN;

h _1zad - the specified thickness of the rolled metal, mm;

Δh ₀ - deviation of the strip thickness at the entrance of the stand, μm;

Δh ₁ - deviation of the strip thickness at the exit of the stand, μm;

C _m - modulus of rigidity of the rolled metal, kN / mm;

C _g - modulus (coefficient) of stand stiffness, kN / mm

S _back , S _fact - set and actual position of the GNU, μm.

Maintaining a given output thickness of the rolled metal is carried out by changing the position of the hydraulic pressure device (8). The position regulator (9) of the GNU is fed through the adder (10), the correction with the CAPT (11), the setting of the position of the GNU at the initial force (13) and the correction of the position of the GNU (14), which is dependent on the speed of the strip at the exit of the stand.

Consider rolling transformer and carbon steels on a reversing mill without using and using the proposed method for correcting the position of the GNU depending on the speed.

A roll of hot-rolled pickled strip is installed on the decoiler (inlet coiler). The front end of the strip is fed into the stand and then fed to the output coiler. After that, the stand is brought down, the initial force is created by the GNU, and the process of rolling steel begins with a given, for a given pass, the value of the strip thickness at the mill exit. Upon completion of the rolling pass, the next pass is selected, and the rolling process is repeated, but in the opposite direction. Rolling passes are changed until the final target steel thickness is reached. The reduction values and the number of passes are determined by the rolling plan and depend on the steel grade, input and specified metal thicknesses. The rolling speed of interest to us is divided into three sections - acceleration, working speed and braking. During acceleration and deceleration, when the rolling conditions change, the adjustment of the position of the GNU, which depends on the speed of the strip at the exit of the stand, is actively involved, which makes it possible to stabilize the operating conditions for the CAPT regulators and thereby obtain a high quality control of the output rolled thickness. As a rule, the acceleration of the mill is carried out stepwise, therefore, for clarity, the figures show graphs of the braking processes at the end of the passes:

Figure 4 - rolling of transformer steel without correction of the position of the GNU depending on the speed of the strip at the exit of the stand. Decrease in rolling speed of transformer steel from 400 m / min to 0 m / min at the end of pass 3 is shown;

Figure 5 - rolling of transformer steel with a correction of the position of the GNU depending on the speed of the strip at the exit of the stand. Also shown is a decrease in the rolling speed of transformer steel from 400 m / min to 0 m / min at the end of pass 3;

figure 6 - rolling of carbon steel with the correction of the position of the GNU, depending on the speed of the strip at the exit of the stand. An example of braking of a reversing mill is shown when rolling carbon steel from 800 m / min to 0 m / min at the end of pass 4.

Comments to graphs (figures 4, 5, 6)

1. The criterion for assessing the quality of correction of the position of the GNU, depending on the value of the strip speed at the exit of the stand is the deviation of the strip thickness at the exit of the mill.

2. The graph of the implemented formula for correcting the position of the GNU depending on the speed of the strip at the exit of the stand is highlighted in red.

3. The graph of the speed of the strip at the exit of the stand is combined with the signal of the passage number (red).

4. The stiffness of the rolled strip can be judged by the value of the signal C _m / C _g (the ratio of strip stiffness to stand stiffness).

5. The rest of the graphs (rolling force, deviation of the strip thickness at the inlet of the stand, adjustments of the thickness adjusters in microns and change in the position of the GNU) are given for general information.

6. All corrections of the position of the HPU from the thickness regulators of the CAPT (by deviation and by the mass flow) and the correction of the position of the HPU, depending on the speed of the strip at the exit of the stand, have the direction of action: "+" - on unloading the stand, "-" - on loading.

7. The presented graphs show that in the braking section of the mill without correction of the position of the HPT, depending on the speed of the strip at the exit of the stand, there is a significant deviation of the thickness of the strip at the exit of the stand (figure 4), and in the braking areas with correction of the position of the HPU, depending on the speed of the strip at the exit of the stand, - the deviation of the thickness of the strip at the exit of the stand remains the same as at a stable rolling speed (Figures 5, 6).

Thus, the implementation of the correction of the position of the GNU on the value of the speed of the strip at the exit of the stand gave a good result: the deviation of the thickness of the strip at the exit of the stand both in statics and in dynamics is maintained at the same level at all passes of rolling and on any assortment.

Claims (8)

A method for compensating for deviations in the thickness of a rolled strip on a reversing cold rolling mill, including generating a signal sent to the position regulator of the hydraulic pressure device (HPD) of the mill rolls in accordance with the specified rolling parameters by the position of the HPC, measuring the strip speed at the exit of the rolling stand, taking into account which a signal is generated correction of the position of the GNU, which is fed to the said regulator in addition to the signal corresponding to the given rolling parameters, characterized in that the said correction signal is generated taking into account the material of the rolled strip, the value of which corresponds to the value of the correction of the position of the GNU, which is determined by the mathematical expression:

Where Hcorr is the calculated value of the GNU position correction, μm, A - scaling correction factor, which is equal to: for carbon steel A = 30, for dynamo steel A = 40, for transformer steel A = 120, μm Cm - modulus of stiffness of the rolled strip, kN / mm, Cg - stiffness modulus of the rolling stand, kN / mm, V ₁ - strip speed at the exit of the rolling stand, m / min, k - speed scaling factor, k = 0.01.

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