RU2254944C1 - Strip steel cold rolling method - Google Patents

Abstract

FIELD: rolled stock production, namely processes of cold rolling of strips in continuous rolling mills.

SUBSTANCE: method comprises steps of successively reducing metal in stands of continuous rolling mill at applying tension of predetermined values in intervals between stands. According to invention in mean zone of inter-stand intervals, additional vertical efforts are applied to strip by smooth bending of its cross section in zone symmetrical relative to lengthwise axis of strip, having width (0.60 - 0.67)B and maximum camber in mean part along width (of said zone) Δh = 0.5(1.04 - 1.06)^n-1 x l√ς_y, mm, where B and ς_y respectively width of rolled strip and its initial yield strength, MPa ; l - length of interval between stands, m; n - number of interval between stands along rolling process direction.

EFFECT: lowered cross thickness difference of strip, more uniform wear along roll barrel.

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Description

The present invention relates to the processing of metals by pressure and can be used in the production of cold rolled strip steel.

Such steel is usually produced in continuous cold rolling mills containing from three to six stands, by successively reducing the thickness of the strips, and hot rolled steel is used as a billet. The modern technology of cold rolling of strips is described in sufficient detail, for example, in the book of V.F. Zotov and V.I. Elin “Cold rolling of metal”, M., Metallurgy, 1988, pp. 165-173. Rolling on modern continuous mills is carried out with the mandatory application to the tension strip in the inter-stand spaces, as well as in front of the first and last mill stands, which reduces the pressure of the metal on the rolls and the total energy consumption.

A known method of cold rolling, in which the value of the interstand tension is controlled by changing the number of revolutions of the work rolls, and the constancy of the roll gaps is provided by changing the thickness of the oil film in the liquid friction bearings of the support rolls (see Japanese Pat. Cl. B 21 V 37/00, publ. 06/20/75). There is also a method of continuous cold rolling, which consists in the fact that after a certain degree of deformation, depending on the current ratio of the O / O values, the strip is straightened by bending and stretching (see AS USSR No. 1380813 class B 21 V 1/36 , published in BI No. 10, 1988).

A disadvantage of the known methods is the transverse different thickness of the rolled strips, as well as increased wear of the middle length of the barrels of the work rolls.

Indeed, the initial hot-rolled strip billet has, as a rule, a lenticular cross-section (see, for example, the book by S. P. Efimenko and V. P. Slednev “Roller of sheet rolling mills”, M., Metallurgy, 1980, p. 52-54 ), which is maintained during the cold rolling process. As a result of this, the specific (per unit cross-sectional area of the strip) tension in the middle part along the strip width is less than at the edges, which leads to increased specific pressures in this section.

The consequence of this phenomenon is the uneven wear of the rolls (it is more on the middle part of the length of their barrels) and the possibility of waviness on the edges of the rolled strip or even their rupture.

The closest analogue to the claimed object is a method (technology) of cold rolling on a continuous mill, described in the book under the editorship of P.I. Polukhina “Technology of metal forming processes”, M., Metallurgy, 1988, p.226-231.

This technology consists in successive compression of metal in the stands of a continuous mill with application of tension in the inter-cage spaces and is characterized by varying the total compression depending on the final strip thickness and the specific tension in the range of 20 ... 30% of the yield strength (of) of the strip metal.

A disadvantage of this technology is also the transverse thickness variation of the rolled strips and uneven wear of the roll barrels.

The technical task of the invention is to improve the flatness of strip (sheet) products and reduce the uneven wear of the rolls of cold rolling mills.

To solve this problem, in the method of cold rolling of strip steel, which consists in sequentially compressing the metal in the cages of a continuous mill with the application of tension of a given value in the inter-stand spaces, in the middle of these spaces additional vertical forces are applied to the strip by smoothly bending its cross section in a section symmetrical to the longitudinal the axis of the strip and the width (0.60 ... 0.67) B with a maximum deflection arrow in the middle of the width of this section equal to:

where B and σ _t - respectively, the width of the rolled strip in mm and its initial yield strength in MPa;

l is the length of the inter-cleft gap, m;

n is the number of the gap during rolling.

The given dependence is obtained as a result of processing experimental data and is empirical.

The essence of the claimed technical solution lies in the application to the medium-wide section of the rolled strip of additional tensile force (tension) from the action of a vertically directed force, which causes lateral bending of the middle part of the strip and its rise to a specific value Δh for a given mill and rolled metal.

As a result of this, the tension (including specific) of the middle of the strip increases with a corresponding decrease in the metal pressure by the middle part of the barrel of the work rolls, which leads to a decrease in their deflection in the vertical plane. This, in turn, firstly, reduces the transverse thickness difference of the strip and, secondly, makes the roll barrel wear more uniform along the length, i.e. rolling of the strip edges (with known negative consequences) is prevented by rolls in which the diameter in the middle of the barrel is smaller than along its edges.

The proposed method is implemented, for example, using a roller installed in the middle of each interstand space of a continuous cold rolling mill (on some mills in these spaces there are already roller tension meters - see Fig. 2 on p. 301 of the book by Y. S. Finkelshtein “Reference rolling and pipe production ”, M., Metallurgy, 1975). The barrel of the roller should have a curvilinear (for example, parabolic) generatrix, and the roller should be able to move vertically by a predetermined amount.

Experimental verification of the proposed method was carried out on a five-stand mill 1200 cold rolling of OJSC “Magnitogorsk Iron and Steel Works”. For this purpose, rollers with a parabolic barrel, the length of which was different, depending on the width of the rolled strips (this width was in the range of 700 ... 1000 mm), were installed between the II-III and III-IV stands of the mill.

The size of the inter-cleft gap of this camp: l = 4 mm; rolled metal with σ _t = 230 ... 350 MPa with an initial thickness of 2.2 ... 3.0 mm.

The best results (transverse thickness variation within 2% and the most uniform wear along the length of the roll barrels at the exit of rolled products of grade I on average 98.7%) were obtained when implementing the proposed method. Deviations from its recommended parameters worsened the quality indicators of the rolled strips and increased the uneven wear of the work rolls.

Transverse thickness variation and uneven wear of the rolls increased with decreasing Δh; with an increase in Δh, banding began to appear in the bands (waviness of the middle part of the strip in width). Similarly to the increase in Δh, the decrease in the barrel length l _{b of the} additional roller to (0.45 ... 0.59) V also influenced. For l _b > 0.67V, in order to obtain a positive effect, it was necessary to increase the inter-stand tension to unacceptable values: due to an increase in the roll speeds of subsequent stands, their slippage relative to the metal surface with the appearance of scratches and wear of the work rolls increased.

Control rolling using known technology gave the first grade yield up to 97.5%, and the transverse thickness difference was in the range of 4-5% with an increase in the unevenness of the wear of the rolls.

Thus, an experimental verification confirmed the acceptability of the technical solution found to achieve the goal and its advantages over a known object.

Technical and economic studies conducted in the Central Control Laboratory of OJSC MMK showed that the use of the proposed method in the production of cold-rolled thin-sheet steel will increase the yield of rolled products of first grade with increased flatness by approximately 1.0 ... 1.5% and will extend the working campaign rolls of the cold rolling mill by at least 20%.

Concrete example

Cold rolling of strips on a four-stand mill 2500 is carried out with the application of vertical force in all inter-stand spaces with l = 4 m.

When the width of the strips B = 2000 mm, the force is applied on a plot with a width of 0.64V = 0.64 · 2000 = 1280 mm using a barrel-shaped roller.

For bands with σ _t = 350 MPa, the Δh values in the individual inter-stand spaces of the mill should be:

between I-II stands -

between the II-III stands -

between III-IV stands -

Claims (1)

The method of cold rolling strip steel, which consists in sequentially compressing the metal in the cages of a continuous mill with the application of tension of a given value in the inter-clenched spaces, characterized in that in the middle of these spaces additional vertical forces are applied to the strip by smoothly bending its cross section in a section symmetrical to the longitudinal axis strip and width (0.60 ... 0.67) V with a maximum deflection arrow in the middle of the width of this section equal to

where B and σ _t - respectively, the width of the rolled strip, mm, and its initial yield strength, MPa; l is the length of the inter-cleft gap, m; n is the number of the gap during rolling.