RU2414974C1 - Method of sheet hot rolling at reversing mill - Google Patents

Abstract

FIELD: process engineering. ^ SUBSTANCE: proposed method comprises multipass reduction between rolls with setting of roll-to-roll clearance before each pass processing from billet after-pass thickness and rolling force. Increase in accuracy of produced sheet thickness without increasing the number of finishing passes at minor reduction is ensured by defining roll-to-roll clearance by the following formula: S0=H1-Pp/G, where H1 is strip thickness after rolling; G is modulus of stand stiffness; Pp is designed rolling force. Note here that to calculate metal strain resistance Pp is defined proceeding from the moment of rolling during previous pass defined as the product of roll main drive motor mechanical factor and actual current of motor armature. ^ EFFECT: precise thickness, reduced number of hot rolling passes at reversing mills. ^ 2 ex

Description

The invention relates to rolling production and can be used for hot rolling of plate steel on reversible rolling mills.

A known method of hot rolling of sheets on a reversing mill, including multi-pass compression of the workpiece between the work rolls. The set compression ratio per passage is determined by the roll gap, which is set before each pass, and when the sheet thickness reaches 1-1.5 mm higher than the nominal value, one or two passes are carried out without changing the roll gap [1].

The disadvantages of this method are as follows. The force arising during rolling leads to elastic deformation of the stand and an increase in the pre-set inter-roll gap S ₀ . Therefore, the operator is forced to initially set the roll gap S ₀ smaller than the thickness of the roll N after the passage. The amount of elastic deformation of the stand depends on many factors (stand rigidity, diameter of work rolls, strength characteristics of rolled steel, sheet width, etc.) and is determined intuitively by the operator based on practical experience. At the same time, if in roughing and intermediate passages the accuracy of setting the roll gap is not so important, then errors in its installation in the pre-finishing and finishing passes lead to product rejection due to the exit of the finished sheet thickness beyond the tolerance field, which increases the cost of plate production. In addition, the fear of not getting into the specified thickness forces the operator to unjustifiably increase the number of finishing passes with small reductions and loss of productivity, which, however, also does not guarantee the receipt of the given thickness of the finished sheet.

The closest analogue to the present invention is a method of hot rolling of sheets on a reversing mill, including multi-pass compression of the workpiece between the work rolls with the setting of the roll gap, based on the thickness of the sheet after the passage and the rolling force, determined by the formula:

where H ₁ is the thickness of the strip after the passage, mm;

G - stand rigidity modulus, MN / mm;

P is the calculated value of the rolling force, determined using the stiffness index of the workpiece, MN [2].

The disadvantages of this method are that the dependence of the stiffness on the thickness of the workpiece is non-linear, therefore, the predicted value of the stiffness obtained using a directly proportional dependence is inaccurate. Since these dependences are empirical, with changes in the chemical composition of steel, roll diameter, temperature of rolling, rolling speed, etc., the accuracy of the sheets in thickness decreases. In addition, when hot sheet reversing rolling, there is an increase in the width of the workpieces, which is not taken into account in the known method. This leads to an inaccurate determination of the predicted value of the rolling force P _p , a decrease in the accuracy of the sheets in thickness, does not allow to reduce the required number of passes.

The technical problem solved by the invention is to increase the accuracy of the sheets by thickness and reduce the total number of passes.

To solve the technical problem in the known method of hot rolling of sheets on a reversing mill, including multi-pass compression of the workpiece between the work rolls with installation before each pass of the roll gap, based on the thickness of the workpiece after the passage and the rolling force, according to the invention, the armature current of the main drive motor is measured in the previous pass work rolls, and the rolling force P _p in the subsequent pass is determined by the formula:

, МН,

, MH,

- сопротивление металла деформации, МПа;Where

- resistance to metal deformation, MPa;

- усилие прокатки в предыдущем проходе, МН;

- rolling force in the previous pass, MN;

B ₀ , B ₁ - the width of the workpiece in the previous and subsequent passes, respectively, m;

R is the radius of the work roll, m;

ΔH ₀ , ΔH ₁ - absolute compression of the workpiece in the previous and subsequent passes, respectively, m;

M _and - the rolling moment in the previous pass, defined as the product of the mechanical coefficient C of the electric motor of the main drive of the work rolls and the current value of the current of its armature I _I , MNm;

ψ = 0.5 is the coefficient of the shoulder of the rolling force.

The invention consists in the following. Since the temperature of the workpiece during rolling of thick sheets on a reversing mill in two adjacent passes varies insignificantly, the resistance of the metal to deformation during the next pass can be taken to be the same as in the previous pass. Therefore, when previous pass produce measurement of actual values of the armature current I _I of the main drive motor, which is determined based on the first rolling moment M, _and then the true value of the rolling force and the calculated P _and deformation resistance of the metal σ.

значение желаемой толщины заготовки (или листа) после прохода Н₁, величину Р_p и жесткость клети G (определяемой по паспортным данным реверсивного толстолистового стана).For a given value of the absolute compression in the subsequent pass ΔН ₁ calculate the rolling force P _p . After that, determine the exact value of the roll gap S ₀ , substituting in the well-known formula

the value of the desired thickness of the workpiece (or sheet) after the passage of H ₁ , the value of P _p and the rigidity of the stand G (determined by the passport data of the reversible plate mill).

The use of the actual value of the armature current of the electric motor of the main drive to determine the roll gap, as well as taking into account the width of the billet, increase the accuracy of the sheets in thickness and reduce the total number of passes.

Method implementation examples

The implementation of the proposed method will be considered on the example of a finishing reverse stand quarto 3600 rolling, having the following parameters:

- stand rigidity modulus G = 10.1 MN / mm;

- radius of the work rolls R = 500 mm;

- the mechanical coefficient of the electric motor of the main drive C = 0.393 MNm / kA.

A slab 200 mm thick made of grade 45 steel is heated in a methodical furnace to an austenitizing temperature T _a = 1250 ° C, rolled in a rough reversing stand duo 3600 in 7 passes into a workpiece 40 mm (0.04 m) thick, B = 2.7 wide m and at a temperature T _s = 1140 ° C is transferred to a finishing reversible stand quarto.

In the finishing reverse stand in the first pass, the strip is rolled with absolute compression ΔH ₀ = 12 mm (0.012 m) to a thickness of H ₀ = 28 mm. During rolling, the current of the main drive motor is fixed: I _i = 3.4 kA.

Based on the measured value of I, determine the moment of rolling:

M _and = C × I, _i = 0.393 × 3.4 = 1.336 MNm.

The value of the rolling moment calculates the rolling force P _and :

Based on the values of P _and calculate the metal resistance to deformation σ:

Since the drop in the temperature of the workpiece during the first pass was less than 10 ° C, it is assumed that the strain resistance σ did not change.

According to the condition of obtaining the sheet after the second pass with a thickness of H ₁ = 10 mm, the absolute compression of the workpiece in the second pass will be: ΔH ₁ = H ₀ -H ₁ = 28-10 = 18 mm (0.018 m).

The calculated value of the rolling force in the second pass is equal to:

The inter-roll gap S ₀ to ensure a given sheet thickness of 10 mm is:

Using an electromechanical push mechanism, an inter-roll gap S ₀ = 5.79 mm is installed and the workpiece is rolled into a sheet 10 mm thick.

The technical and economic advantages of the proposed rolling method are that due to a more accurate setting of the roll gap of the reversing stand, an increase in the accuracy of the rolled sheets in thickness is achieved. At the same time, the need to increase the number of finishing passes with small reductions and loss of productivity of the rolling mill is eliminated. Determination of the metal resistance to deformation from experimental data, based on the measured values of the force (or moment) of rolling, simultaneously provides consideration of both the actual chemical composition of the rolled steel and the temperature of the roll.

The calculation of the roll gap can be done automatically in the “on-line” mode by a computer of the automatic control system of a reversible hot rolling mill. Using the proposed method provides an increase in the profitability of the production of sheet steel on a reversing mill quarto by 12-14%.

Literature

1. RF patent No. 2343016, IPC B21B 1/22, 2009

2. Auto USSR No. 1186303, IPC В21В 37/00, 1985

Claims (1)

The method of hot rolling of sheets on a reversing mill, including multi-pass compression of the workpiece between the work rolls with the installation of a roll gap before each pass based on the thickness of the workpiece after the pass and the rolling force, characterized in that in the previous pass the armature current of the electric motor of the main drive of the work rolls is measured, and the force rolling R _p in a subsequent pass is determined by the formula

, MH,
Where

- resistance to metal deformation, MPa;

- rolling force in the previous pass, MN;
In _about , B ₁ - the width of the workpiece in the previous and subsequent passes, respectively, mm;
R is the radius of the work roll, mm;
ΔН _about , ΔH ₁ - absolute compression of the workpiece in the previous and subsequent passes, respectively, mm;
M _and - the rolling moment in the previous pass, defined as the product of the mechanical coefficient of the electric motor of the main drive of the work rolls and the current value of the current of its armature, MNm;
ψ = 0.5 is the coefficient of the shoulder rolling force.