RU2343020C2 - Continuous mill for cold rolling of steel strips - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: continuous mill for cold rolling of steel strips with different carbon content in steel contains serially installed four-high cages, working rollers of which are arranged with preset microrelief of their barrels. Height of Ra microroughnesses of roller barrels surface in the last cage of mill is determined with carbon content [C] in roller steel, at that for rolling of steel with [C]≤0.1 wt %, value Ra is accepted within the range of 2.4…3.2 micrometer, and for steel with [C]>0.1 wt %, minimum value of Ra is 1.5 micrometer.

EFFECT: higher yield of strip steel rolling at cold rolling mills and better quality of rolled product surface.

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Description

The invention relates to equipment for metal forming and can be used in cold rolling of strip steel.

For rolling strip (sheet) steel with a different carbon content, usually continuous cold rolling mills are used, containing several sequentially located quarto stands (i.e. four-roll), in which work and backup rolls are installed. The types of mills used for cold rolling of strips, as well as the location of the stands of a quarto continuous mill, are given, for example, in the book by V. B. Bakhtinov “Rolling production”, M., “Metallurgy”, 1987, p.339-340 and fig. 162b .

In order to obtain the necessary microgeometry of cold-rolled metal, the mill rolls are subjected to appropriate processing (grinding of roll barrels and their notch) to obtain the necessary microgeometry of the surface, determined by the height of microroughness Ra (see, for example, Pat. RF No. 2252599, class. C21D 8/04, publ. in BI No. 19, 2005).

A continuous cold rolling mill is known, comprising working quarters of a quarto and an additional roller straightening device located after the second mill stand and containing preferably five rollers (see AS USSR No. 1026850 class B21B 1/2, published in BI No. 25, 1983 g.). The disadvantage of the mill is the uncertainty of the microrelief of the barrels of its work rolls, which makes it difficult to obtain high-quality strips with a given surface microgeometry.

The closest analogue to the claimed object is a continuous cold strip rolling mill described in A.S. USSR No. 1421432 class. B21B 1/38, publ. in BI No. 33, 1988

This mill consists of sequentially located quarto stands, the work rolls of which are made with a given microrelief of their barrels, and are characterized by the presence of five stands, while the roughness (microroughness) of the roll barrels in the first stand: Ra = 4.5 μm, in the second and third Ra = 0.8 μm, in the fourth - the lower work roll with Ra = 0.8 μm, and the upper with Ra = 2 ... 3 μm, and in the fifth stand - Ra = 4 μm. A disadvantage of the known mill is the constancy of Ra values for rolling steel strips with different carbon contents, which can lead to a decrease in yield.

An object of the present invention is to increase the yield of sheet metal by improving the quality of its surface.

To solve this problem, a continuous cold rolling mill of steel strips with different carbon contents in steel, consisting of sequentially arranged quarto stands, the work rolls of which are made with a given microrelief of their barrels, the height value Ra of the microroughness of the surface of the roll barrels of the last mill stand is determined by the carbon content [C ] in the rolled steel, while for rolling steel with [C] ≤0.1 vol.% the value of Ra is within 2.4 ... 3.2 μm, and for steel with [C]> 0.1 vol.% the minimum the value of Ra = 1.5 μm.

The essence of the proposed technical solution is to optimize the microrelief of the barrels of the work rolls of the last (finishing) mill stand, which largely determines the surface quality of the cold-rolled strips, and the Ra value of the microroughness of the roll barrels is different for rolling strips with different carbon steel contents.

The notch of the rolls of the stands of the cold rolling mill is necessary, first of all, in order to prevent “sticking” of the coils of the roll strip during its annealing. The tendency to “stick together” is due to the significant tension of the strip being wound into a roll. Moreover, the lower the surface hardness of the steel (and it depends on the carbon content in it: the higher it is, the higher the hardness), the more likely it is to “stick together” the strip coils tightly pressed against each other in the annealed roll.

Therefore, for softer strip steel (i.e., with a lower carbon content), a rougher roughness of its surface (and, accordingly, of the rolls, especially the finishing stand of the mill) is necessary.

The proposed continuous mill (its working stands) is schematically shown in figure 1, where the arrow is the direction of movement of the rolled strip.

The mill contains four quarto stands 1, each containing a pair of work 2 and backup rolls 3. Work rolls 4 of the last stand 5 of the mill are made with the proposed surface of their barrels, i.e. with a given value of microroughness Ra.

When the mill is operating, the initial value of Ra gradually decreases to critical, after which the work rolls are replaced with new ones. If at first the strips with the content of [C] ≤0.1% are rolled, then after the wear of the surface of the roll barrels of the last stand and the value Ra <2.4 μm, it is possible to start rolling the strips with [C]> 0.1 vol.%, Since the maximum permissible value of Ra is equal to 1.5 microns.

A pilot test of the claimed facility was carried out on a continuous four-stand cold rolling mill 2500 of OJSC Magnitogorsk Iron and Steel Works. For this purpose, when rolling strips with carbon content [C] = 0.06 ... 0.25%, the surface Ra of the barrels of the work rolls of the last (fourth) mill stand was varied (by appropriate treatment). The results of the experiments were evaluated by the yield of good quality rolled products after its annealing in rolls.

The best results (yield was 99.5 ... 99.8%) were obtained with the implementation of the proposed technical solution. When rolling strips with a content of [C] ≤0.1 vol% in the rolls of the last stand with Ra <2.4 μm, the yield was no more than 95.0% due to the aforementioned defect during annealing of the coils, and when rolling metal with [ C]> 0.1 vol.% At Ra <1.5 μm, the yield did not exceed 98.0%. It was also found that the maximum value of Ra = 3.2 μm is optimal from the point of view of the absence of contamination of the metal surface after rolling (which is unacceptable during its annealing), as well as obtaining the required Ra value of the finished sheets (it is determined, for example, in GOST 9045) .

A well-known object, selected as the closest analogue (see above), was not checked, since it is a five-cage rigid catalytic mill. Thus, the experiments confirmed the acceptability of the technical solution found to achieve the goal and its advantage over the famous mill.

According to the Central Laboratory of OJSC MMK, the use of the proposed mill in the production of cold-rolled strips at the plant will increase the yield of sheet metal by at least 99.5% with a corresponding increase in profit from its sale.

Concrete example

1. At a four-stand continuous quarto 2500 mill, strips with a content of [C] = 0.08% are rolled. Work rolls of the IV stand are made with barrels having Ra = 2.8 μm.

2. At the same mill, strips with [C] = 0.15 vol.% Are rolled. The barrels of the work rolls of the IV stand have a surface with Ra = 1.6 μm.

The finished cold-rolled sheet has Ra = 1.3 ... 1.5 and 0.7 ... 0.8 μm, respectively, which meets the requirements of GOST 9045.

Claims (1)

A continuous cold rolling mill of steel strips with different carbon content in steel, consisting of sequentially arranged quarto stands, the work rolls of which are made with a given microrelief of their barrels, characterized in that the height Ra of the microroughness of the surface of the roll barrels of the last mill stand is determined taking into account the carbon content [C ] in a rolled steel strip, and when rolling a strip with [C] ≤0.1 vol.% in steel, the value of Ra is 2.4-3.2 μm, and when rolling a strip with [C]> 0.1 vol.% in steel, the minimum value of Ra = 1.5 μm.