RU2467813C1 - Method of longitudinal rolling of strips - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy and may be used in cold and hot rolling of steel strips at reversing and continuous mills. Proposed method comprises squeezing the billet by two rolls with application of rear and front pressure thereto. Speed of billet entry in said rolls is kept equal to roll peripheral speed whereat neutral angle in deformation center equals to angle of hip. Note here that billet entry speed is set by varying billet tension and/or reduction ratio by relationship

where T₁, T₀ is billet front and rear tension, respectively, kN; µ is friction factor; p is contact pressure in deformation center, N/mm, b is billet width, mm, ΔH is absolute reduction par one pass, mm.

EFFECT: higher durability of rolls and strip quality.

1 tbl, 2 ex

Description

The invention relates to metallurgy and can be used for longitudinal hot and cold rolling of steel strips on reversible and continuous mills.

A known method of rolling strips, including multi-pass compression of the workpiece between two work rolls on a single-strand reversing mill with the front and rear tension applied to the workpiece [1].

There is also known a method of cold rolling strips between pairs of rolls with the front and rear tension applied to the workpiece, according to which the front and rear tension values are set depending on the strip thickness and rolling speed [2].

The disadvantages of the known methods are that the surface of the rolls during the rolling process is exposed to variables in the direction of movement of the metal and the action of reverse tangential stresses. As a result, there is intense wear of the rolls and the formation of chips. This, in turn, degrades the quality of the stripes.

The closest analogue to the present invention is a method of longitudinal rolling of steel strips, including multi-pass compression of the workpiece between two rolls with the front and rear tension applied to it, while the specific tension is 0.5-0.8 of the yield strength of the workpiece, and the input speed of the workpiece in rolls due to the lag effect is less than the peripheral speed of the work rolls [3].

The disadvantage of this method is as follows. Each of the work rolls in the lagging zone of the deformation zone is subject to frictional influence from the side of the workpiece, which flows plastically against the direction of rolling, and in the advance zone, to frictional influence from the side of the workpiece, which flows plastically in the direction of rolling. Reversing (alternating) impact on the roll of shear stresses and contact slides from the workpiece in the lagging and leading zones leads to intensive frictional and fatigue wear of the rolls, which reduces their durability and the quality of the rolled strips.

The technical problem solved by the invention is to increase the resistance of the rolls and the quality of the strips.

To solve the technical problem in the known method of longitudinal rolling of strips, comprising compressing a workpiece between two rolls with front and rear tension applied thereto, according to the invention, the speed of the workpiece entering the rolls is kept equal to the peripheral speed of rolls rotation by changing the workpiece tension and / or the amount of compression. In an embodiment of the method, rolling is carried out with a difference between the front and rear tension of the workpiece, set by the ratio:

,

,

where T ₁ , T ₀ - front and rear tension of the workpiece, respectively;

µ is the coefficient of friction;

p is the contact pressure in the deformation zone;

b is the width of the workpiece;

ΔН - absolute compression of the workpiece per pass.

The invention consists in the following. When the speed of entry of the workpiece into the rolls is equal to the peripheral speed of rotation of the rolls, the neutral angle in the deformation zone γ becomes equal to the capture angle α. In this case, the lag zone disappears in the deformation zone, and the advance zone occupies its entire length. In such a single-zone deformation zone, the deformable workpiece slides along the surface of the rolls in only one direction — in the rolling direction. Due to the fact that the reverse sliding of the workpiece on the surface of the roll is eliminated, the path and work of friction are reduced, its frictional and fatigue wear is almost halved, resulting in an increase in the quality of the strips.

, эмпирически была определена разность переднего и заднего натяжений, при которой для заданных значений других технологических параметров обеспечивается выравнивание скорости входа заготовки в валки и окружной скорости валков. Причем еслиIt was experimentally established that it is possible to ensure the speed of entry of the workpiece into the rolls equal to their peripheral speed of rotation and the advance zone spread over the entire length of the deformation zone by selecting the ratio of the technological parameters of rolling, the most significant of which are the front and rear tension of the workpiece and the amount of compression. As a result of experimental rolling with measuring the rolling force, compression, strip tension, the speed of the strip entering the rolls and the peripheral speed of the rolls, as well as calculating the length of the deformation zone using the formula

, empirically determined the difference between the front and rear tension, at which for the given values of other technological parameters provides equalization of the speed of entry of the workpiece into the rolls and the peripheral speed of the rolls. And if

,

,

then, as experiments showed, the speed at which the workpiece entered the rolls became lower than the peripheral speed of rotation of the rolls, a lag zone remained in the deformation zone, metal reversed sliding along the surface of the rolls, their wear increased, and the quality of the strips deteriorated.

Otherwise when

,

,

due to the excess value of the rear tension T _{0, the} speed of the strip entry into the rolls decreases and the rolls slip relative to the workpiece, which is accompanied by heating and increased wear of the rolls, deterioration of the strip quality.

Method implementation examples

1. A billet in the form of a hot-rolled pickled strip with a cross section of 2.5 × 1200 mm made of steel grade 08Yu rolled into a roll is installed on the uncoiler of a single-cage quarto 1400 rolling mill. The front end of the billet is passed between the work rolls, and then mounted on a reel drum. Using the unwinder electric motor, the rear tension of the strip T ₀ = 20 kN is created, and with the help of the winder electric motor, the front tension of the strip T ₁ = 40 kN is created. To the rolls and rolled billet serves cutting fluid. By changing the roll gap of the work rolls rotating with the filling peripheral speed V _pv = 0.50 m / s, the required absolute reduction ΔH = 0.8 mm is set. Using a roller installed in front of the stand, measure the speed of entry of the workpiece into the work rolls V ₃ = 0.47 m / s.

Since the speed of the workpiece V _s = 0.47 m / s with the specified compression and tension of the workpiece is less than the peripheral speed of the work rolls V _pv = 0.50 m / s, then monotonically increase the front tension T ₁ . An increase in the front tension T _{1 is} accompanied by an increase in the speed of entry of the workpiece into the rolls V _s . When the front tension of the workpiece reaches a value of T ₁ = 130 kN, the speed at which the workpiece enters the rolls V ₃ becomes equal to the peripheral speed of the work rolls: V _s = V _pv = 0.50 m / s. Therefore, the increase in the front tension T _{1 is} stopped, the rolling mill, the winder and the unwinder are accelerated to an operating speed of V _pb = 10.0 m / s and the workpiece is rolled into a strip.

The equality of the speed of entry of the workpiece into the rolls and the peripheral speed of the work rolls provides a single-zone contact sliding mode of the metal on the surface of the rolls in the deformation zone. This leads to increased durability of the work rolls and the quality of the strips.

2. The single-quarto rolling mill quarto 800 with polished work rolls with a radius of R = 130 mm does not have a system for measuring the speed of entry of the workpiece into the rolls. Therefore, the optimal difference between the values of the front and rear tension is determined by the proposed empirical ratio:

.

.

The workpiece is a hot-rolled etched strip with a thickness of 2.0 and a width of b = 600 mm made of ultra-low-carbon steel grade 01YUT, wound into a roll, installed on the uncoiler of a quarto mill 800. Based on a given strip thickness of 1.5 mm, the absolute reduction value ΔH = 0.5 is determined mm and the length of the deformation _zone l _∂ :

.

.

For cold rolling in polished work rolls with technological lubricant, which is used as mineral oil Industrial 20, the friction coefficient is µ = 0.05.

The front end of the workpiece is passed through work rolls and secured to a coiler. Technological grease — Industrial oil — is supplied to the rolls and the workpiece. A roll gap is set to obtain a strip 1.5 mm thick, and the rolling force is measured at P = 940 kN = 940,000 N.

Then calculate the contact pressure p in the deformation zone:

To implement a single-zone sliding mode of the metal on the surface of the work rolls, the difference between the front and rear tension of the workpiece is calculated:

The back tension of the workpiece using the unwinder motor is set to T ₀ = 20 kN. In this case, the front tension will be: T ₁ = 147.5 kN + 20 kN = 167.5 kN.

Using a winder electric motor, the front tension of the workpiece is created T ₁ = 167.5 kN and the entire workpiece is rolled at a speed of V _pv = 2 m / s. The speed of entry of the workpiece into the rolls is: V _s = V _pv = 2 m / s.

One-zone sliding of metal over the surface of the rolls in the deformation zone in the direction coinciding with the direction of rolling, reduces wear on the rolls, increases their durability and quality of the strips.

3. The same parameters of the mill and technological operations as in example 2, only for the initially set front tension T ₁ = 167500 N and rear tension T ₀ = 20000 N of the workpiece, determined on the basis of the permissible technological equipment of the mill quarto 800, calculate absolute compression, in which the speed of entry of the workpiece into the work rolls will be equal to their peripheral speed. From the proposed relation

следует:

should:

.

.

Solving the last equation with respect to ΔН we have:

That is, to ensure single-zone sliding of metal over the surface of work rolls in the deformation zone, it is necessary to maintain the absolute value of compression over the thickness of the workpiece equal to ΔН = 0.5 mm.

Using push mechanisms, the absolute compression of the strip ΔН of 0.5 mm is established and the workpiece is rolled into a strip. This ensures the fulfillment of the condition V _s = V _pb = 2 m / s and realizes single-zone metal sliding on the surfaces of the rolls in the deformation zone.

Implementation options of the proposed method and indicators of their effectiveness are presented in the table.

From the data presented in the table, it follows that when implementing the proposed method (option No. 2), an increase in roll resistance and strip quality is achieved. When the speed of entry of the workpiece V _s into the rolls is less than the peripheral speed of the rolls V _in (options No. 1 and No. 3), as well as the implementation of the known method [3] (option No. 4), there is a decrease in the resistance of the rolls and the quality of the strips, as a result of which the output of the strips 1 group of product finishes is reduced.

Modes of longitudinal rolling of strips and indicators of their effectiveness No. p / p Correlated. speeds V _s and V _p The ratio of rolling parameters Operating time per roll (km of rolled strips) The output of the strips with 1 group of surface finish,% one V _s <V _pv

120 96.3 2 V _s = V _pv

238 99.8 3 V _s <V _pv

132 97.8 four V _s <V _pv Not regulated [3] 118 96.1

The technical and economic advantages of the proposed method are that the alignment of the speed of entry of the workpiece into the rolls and the peripheral speed of the rolls by changing the tension of the workpiece and / or the amount of compression provides the formation of a single-zone deformation zone in which the deformable metal in the plastic state flows on the surfaces of the rolls only in direction of rolling. The exclusion of reverse metal flow in the deformation zone leads to a decrease in the wear of the rolls, to increase their resistance. The increase in roll resistance, in turn, provides an improvement in the quality of the rolled strips.

As the base object in assessing the effectiveness of the proposed method, the closest analogue was selected [3]. Using the proposed method will increase the profitability of strip production by an average of 12%.

Literature used in the preparation of the description of the invention

1. Japanese application No. 63171203, IPC B21B 1/28, 1988

2. Auto USSR No. 1079327, IPC B21B 37/06, 1984

3. Sheftel N.I. Production technology of rolled products. M .: Metallurgy, 1976, p. 457-459.

Claims (1)

A method for longitudinal rolling of strips, comprising compressing a workpiece with two rolls with front and rear tension applied to it, setting the speed of the workpiece entering the rolls with a neutral angle in the deformation zone equal to the grip angle, characterized in that the speed of the workpiece entering the rolls is set by changing blank tension and / or compression ratio in relation to:

where T ₁ , T ₀ - front and rear tension of the workpiece, respectively, kN;
µ is the coefficient of friction;
p is the contact pressure in the deformation zone, N / mm ² ;
b is the width of the workpiece, mm;
ΔH - absolute compression of the workpiece per passage, mm