JP4600354B2 - Metal band shape correction method - Google Patents

Description

The present invention relates to a straightening how for improving the shape such as flatness of metal strip, including steel strip, particularly a metal strip having oxide scale on the surface, such as steel sheet after hot rolling, about the straightening how to extend the metal strip by skin pass mill and tension leveler.

  In metal products such as steel plates, the shape such as flatness is extremely important in terms of quality. Here, inferior flatness means that the metal strip product has a local wavy form such as (a) ear extension and (b) belly extension as shown in FIG. In FIG. 2, 1 indicates a metal band.

  As a method for correcting the shape of such a metal strip product, facilities such as a skin pass mill (also referred to as a temper rolling mill) 101 (see FIG. 3) and a tension leveler (also simply referred to as a leveler) 201 (see FIG. 4) are used. There is a method to correct the shape by giving a small strain. In FIG. 3, 102 and 103 are work rolls, in FIG. 4, 202 and 203 are extension rolls, and 204 is a straightening roll.

  Patent Document 1 discloses a correction method in which a skin pass mill and a leveler are arranged in series, and further, bridle rolls for applying tension are arranged upstream and downstream. Patent Document 2 discloses a method for calculating a set value such as intermesh and tension for obtaining a desired elongation rate (elongation strain) in a tension leveler.

  On the other hand, when a large tension is applied with a tension leveler when correcting a metal strip having oxidized scale on the surface such as a steel sheet after hot rolling, the scale is bitten into the steel sheet surface during roll bending, and scratches are generated. It has been known from experience that surface defects such as

By the way, as an index indicating the degree of the shape defect of the metal band, what is called steepness is used in the case of ear stretch or belly stretch. As shown in FIG. 5, when the metal band 1 shown in FIG. 2 is viewed from the side, the steepness λ is L, and the wave height in the plate thickness direction due to ear extension or belly extension is d, and the wave height is d. If
λ = d ÷ L × 100 (%) (1)
It is expressed.

JP 58-116931 A JP 63-101021 A

  As mentioned above, the importance of straightening the shape of metal strip products is increasing, but when straightening with a tension leveler, the scale is bitten into the surface of the steel sheet during roll bending, and the surface of scratches, etc. There is a problem that a defect may be caused.

  In the inventions of Patent Document 1 and Patent Document 2, generation of surface scratches due to scale biting as described above is not taken into consideration at all, and even if a desired elongation rate is obtained and the shape is corrected, surface defects are not generated. There is a problem that it may occur.

The present invention relates to a straightening how for improving the shape such as flatness and warpage of the metal strip, including steel strip, a metal strip having a particularly oxide scale on the surface, such as steel sheet after hot rolling and to provide a straightening how capable of straightening without generating surface defects caused by biting scale against.

In order to achieve this object, the present invention provides a metal band shape correction method for correcting the flatness and warpage of a metal band using a skin pass mill and a tension leveler as a shape correction means. In addition, the plate speed is detected on the entrance side and the exit side of the tension leveler, the elongation rate of the skin pass mill and the tension leveler is measured, and each is determined in advance according to the material conditions such as the material and thickness of the plate material The desired elongation ratio εS in the skin pass mill and the desired elongation ratio εL in the tension leveler are determined in accordance with the relationship between the elongation level in the tension leveler and the number of surface defects generated by biting of the oxide scale. From the upper limit β and the elongation rate α required to correct the metal band, the following relational expression
εL = β
εS = α-β
The metal is characterized in that at least one of a threading plate tension, a skin pass mill reduction amount, and a tension leveler pressing amount is adjusted in order to secure the calculated elongation rate εS and elongation rate εL. This is a belt shape correction method.

  According to the present invention, it is possible to correct a shape without causing surface defects such as scale biting even on a metal strip having an oxide scale on the surface such as a steel sheet after hot rolling.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment of the present invention)
The principle of shape correction with a skin pass mill and a tension leveler is to correct the flatness by applying a small elongation strain to a metal band with poor flatness. At that time, since the flatness defect of the metal strip is caused by the difference in elongation in the longitudinal direction, it is necessary to give an elongation rate equal to or greater than the difference in elongation.

  Here, the problem when the shape of a metal strip having an oxide scale on the surface such as a steel sheet after hot rolling is corrected with a tension leveler will be described with reference to FIG. As shown in FIG. 6 (a), the oxide scale is a film of a reaction product that is generated when a metal strip comes into contact with air in a high-temperature processing step such as hot rolling. A layer of oxide such as FeO is formed. In the figure, 1 indicates a metal band and 2 indicates an oxide scale. This oxide scale is generally hard and has a very low ductility compared to the inner layer metal material. Therefore, when an elongation strain for shape correction is applied, the oxide scale layer adheres in a finely divided state as shown in FIG. When a metal band having such an oxide scale layer is corrected with a tension leveler, the oxide scale 2 is placed inside the metal band 1 on the side in contact with the roll 205 by roll bending as shown in FIG. It tends to pierce and cause scratches on the surface of the metal strip.

FIG. 7 shows an example of experimentally determining the ease of occurrence of surface defects due to such a scale. Here, this example is a high-strength steel plate commonly called 600 MPa class high tensile steel, and is an example having a thickness of 2.0 mm and a width of 1500 mm. In the figure, the horizontal axis indicates the elongation ratio given to the metal strip by the tension leveler, and the vertical axis indicates the average number of defects per 1 m ^{2 of} surface area as an evaluation of surface defects due to biting of the oxide scale. From the figure, it can be seen that as the elongation rate increases, the surface defects due to oxide scale biting also increase. In particular, it can be seen that the surface defects suddenly increased when the elongation ratio exceeded 1.0%. Therefore, from the viewpoint of preventing surface defects, it is desirable to set an upper limit on the elongation rate added by the tension leveler. A preferred upper limit is 1% or less.

  As the elongation ratio increases, the surface defects due to the oxide scale biting also increase. As the elongation ratio increases, the oxide scale fragmentation as described in FIG. 6 increases. It is presumed that the number of oxide scales to be pierced toward the surface increases.

  In the present invention, as shown in FIG. 1, in the metal band straightening method for correcting the flatness and warpage of the metal band using the skin pass mill 101 and the tension leveler 201 as the shape correcting means, the entrance side and the exit side of the skin pass mill 101 are used. On the other hand, plate speed detecting means 301 are provided on the entry side and the exit side of the tension leveler 201 so that the elongation rates of the skin pass mill 101 and the tension leveler 201 can be individually measured. As the plate speed detecting means 301, for example, a contact-type plate speed meter can be used, but it is not limited to this.

  Then, the elongation rate in the skin pass mill 101 and the tension leveler 201 is determined in advance according to the material conditions such as the material and thickness of the sheet passing material. It is characterized by adjusting the amount or the pushing amount of the tension leveler.

As a specific procedure, when the elongation rate in the skin pass mill 101 is εS, the elongation rate in the tension leveler 201 is εL, the elongation rate necessary to correct the shape is α, and the surface defect due to the oxide scale biting. If the elongation rate of the tension leveler 201 for preventing is β,
εL = β (2)
εS + εL = α (3)
Than,
εS = α−β (4)
It becomes.

  Here, α may be a value larger than the elongation difference in the width direction of the metal strip, and may be determined based on the result of actual measurement of the flatness of the metal strip before shape correction. Since the degree of flatness is often known depending on the material conditions such as the material and thickness, α may be determined in advance according to the material conditions such as the material and thickness of the sheet passing material. Also, β can be determined by obtaining the relationship as shown in FIG. 7 in advance according to the material conditions such as the material and thickness of the sheet passing material.

  Since the elongation rate of each of the skin pass mill 101 and the tension leveler 201 can be calculated from the difference between the plate speeds detected by the plate speed detecting means 301 provided on the entry side and the exit side, the desired elongation rate should be ensured. The threading plate tension, the amount of reduction of the skin pass mill 101, or the amount of pressing of the tension leveler 201 may be adjusted.

  By adjusting the skin pass mill 101 and the tension leveler 201 in such a procedure, it is possible to obtain a good surface quality as well as a shape improvement effect.

  The Example which applied this invention to the shape correction in the skin pass mill 101 and tension leveler 201 installed in the front | former stage of the continuous pickling line as shown in FIG. The metal strip 1 to be passed is a hot rolled steel plate (hot rolled steel plate).

  In FIG. 8, 701 is a metal band coil to be dispensed, 702 and 703 are bridle rolls for applying tension to the metal band 1, 704 and 705 are pickling tanks for pickling the metal band 1, and 706 is a winding Metal band coil. The skin pass mill 101 and the tension leveler 201 are installed in a section where the metal band 1 is tensioned by bridle rolls 702 and 703. A contact-type plate speed meter 301 is installed on the entrance / exit side of the skin pass mill 101 and the tension leveler 201.

  The test material for the experiment is a hot-rolled steel sheet of high strength steel and mild steel as shown in Table 1.

  The yield point of high strength steel is 600 MPa, and the yield point of mild steel is 250 MPa. Since both are steel plates after hot rolling, oxide scale is attached to the surface. In order to correct the shape of both high-strength steel plates and mild steel plates, an elongation rate of 1.5% or more is required. In addition, it has been found that high-strength steel sheets tend to cause surface defects due to biting of the oxide scale when the elongation level exceeds 1.0% with a tension leveler. Further, it has been found that, in a mild steel sheet, when the elongation rate exceeds 1.5% with a tension leveler, surface defects are likely to occur due to the inclusion of oxide scale.

  Table 1 shows invention examples and comparative examples.

  Invention Examples 1 and 2 are the shapes of the metal strip 1 using the skin pass mill 101 and the tension leveler 201 installed on the continuous pickling line shown in FIG. This is an example applied to correction. In Inventive Example 1, shape correction was performed by setting the elongation rate with the skin pass mill 101 to 1.0%, the elongation rate with the tension leveler 201 to 1.0%, and the total elongation rate to 2.0%. In Inventive Example 2, the shape correction was performed with the elongation rate at the skin pass mill 101 being 1.2%, the elongation rate at the tension leveler 201 being 0.5%, and the total elongation rate being 1.7%. The elongation rate in the skin pass mill 101 and the tension leveler 201 is calculated from the difference in the plate speed of the metal strip 1 measured by the plate speedometer 301, and is applied by the bridle rolls 702 and 703 so as to maintain the elongation rate. The passing plate tension, the reduction amount of the skin pass mill 101, or the pressing amount of the tension leveler 201 was set.

  Invention Examples 3 and 4 are examples in which a mild steel plate having a plate thickness of 2.5 mm and a plate width of 1200 mm is applied to shape correction of the metal strip 1 using the skin pass mill 101 and the tension leveler 201. In Invention Example 3, the shape correction was performed with an elongation rate of 0.5% in the skin pass mill 101, an elongation rate of 1.5% in the tension leveler 201, and a total elongation rate of 2.0%. In Invention Example 4, shape correction was performed with an elongation rate of 0.6% with a skin pass mill, an elongation rate of 1.0 with a tension leveler, and a total elongation rate of 1.6%. The elongation rate in the skin pass mill 101 and the tension leveler 201 is calculated from the difference in the plate passing speed of the metal strip as described above, and the plate passing tension, the reduction amount of the skin pass mill, or the tension leveler so as to maintain the above-described elongation rate. The indentation amount was set.

  Comparative Example 1 shows the shape of the metal strip 1 using a skin pass mill 101 and a tension leveler 201 for a high strength steel plate having a plate thickness of 2.0 mm and a plate width of 1500 mm, and for a mild steel plate having a plate thickness of 2.0 mm and a plate width of 1500 mm. This is an example applied to correction. In Comparative Example 1, shape correction was performed with a total elongation of 2.0%. At this time, the elongation rate in the skin pass mill 101 calculated from the difference in the sheet feeding speed of the metal strip was 0.8%, and the elongation rate in the tension leveler 201 was 1.2%.

  Comparative Example 2 is an example in which a mild steel plate having a plate thickness of 2.5 mm and a plate width of 1200 mm is applied to shape correction of the metal strip 1 using the skin pass mill 101 and the tension leveler 201. In Comparative Example 2, shape correction was performed with a total elongation rate of 2.0%. At this time, the elongation rate in the skin pass mill 101 calculated from the difference in the sheet feeding speed of the metal strip was 0.3%, and the elongation rate in the tension leveler 201 was 1.7%.

About the said invention example and the comparative example, the sample was extract | collected from the coil wound up by the exit side of the pickling line, and the shape and surface quality of the metal strip were evaluated. When the average steepness was within 0.5%, the shape when the plate-passing experiment was performed 10 times under each condition was evaluated as ◯ (good), and when it was larger than 0.5%, it was rated as x (bad). Regarding the surface quality, the surface of the metal band was visually observed, and if the surface defect due to the oxide scale biting was less than 1 per 1 m ^{2 of} surface area, it was judged as “good” (good), and when it was 1 or more, it was judged as “x” (bad).

  In Table 1, the shape of each of Invention Examples 1 to 4 and Comparative Examples 1 and 2 was good (good). This is because a stretch rate of 1.5% or more was given under any condition, and sufficient shape correction was achieved.

  On the other hand, the surface quality was ○ (good) in Examples 1 to 4 of the present invention, but x (bad) in Comparative Examples 1 and 2. This is because, in the examples of the high-strength steel sheets of Invention Examples 1 and 2, the elongation ratio at the tension leveler 201 is 1.0% or less of the elongation ratio at which surface defects due to the oxide scale biting are likely to occur in the high-strength steel sheets. Because there is. This is because in the examples of the mild steel sheets of Invention Examples 3 and 4, the elongation rate at the tension leveler 201 is 1.5% or less of the elongation rate at which surface defects due to the oxide scale biting are likely to occur in the mild steel plate. In the example of the high-strength steel plate of Comparative Example 1, the elongation rate at the tension leveler 201 exceeds 1.0% of the elongation rate at which surface defects due to oxide scale biting easily occur in the high-strength steel plate. . This is because, in the example of the mild steel plate of Comparative Example 2, the elongation rate at the tension leveler 201 exceeds 1.5% of the elongation rate at which surface defects due to oxide scale biting tend to occur in the mild steel plate.

  Based on the above results, the elongation rate of the skin pass mill and tension leveler was measured, and the elongation rate of the skin pass mill and tension leveler where surface defects did not occur was previously determined according to the material conditions such as the material and thickness of the thread plate. Metals with oxide scale on the surface such as steel sheet, especially after hot rolling, by setting the plate tension, skin pass mill reduction amount, or tension leveler indentation amount to ensure the desired elongation rate respectively It is possible to correct the shape of the band without causing surface defects such as biting of the scale.

The figure which shows an example of embodiment of this invention Diagram showing the shape of the metal strip product The figure which illustrates technology about shape correction of the metal belt using the conventional skin pass mill A diagram illustrating the technology related to shape correction of a metal strip using a conventional tension leveler A diagram illustrating the definition of steepness Diagram explaining generation of surface defects due to oxide scale biting The figure which shows the relationship between the elongation rate in the tension leveler in this invention, and the surface defect by oxide scale biting The figure which shows typically the continuous pickling line in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal strip 2 ... Oxide scale 101 ... Skin pass mill 201 ... Tension tension leveler 202, 203 ... Elongation roll 204 ... Correction roll 205 ... Roll 301 ... Plate speedometer (plate speed detection means)
701, 706 ... Metal strip coil 702, 703 ... Bridle roll

Claims (1)

In the metal band shape correction method of correcting the flatness of the metal band using a skin pass mill and a tension leveler,
The plate speed is detected on the entrance and exit sides of the skin pass mill and on the entrance and exit sides of the tension leveler, and the elongation rate of the skin pass mill and tension leveler is measured.
The desired elongation rate εS in the skin pass mill and the desired elongation rate εL in the tension leveler are determined in advance according to the material conditions such as the material and thickness of the threading plate material, and the elongation rate in the tension leveler and oxidation From the upper limit β of the elongation rate at the tension leveler determined from the relationship between the number of surface defects due to scale biting and the elongation rate α necessary to correct the metal band, the following relational expression
εL = β
εS = α-β
Calculated by
In order to ensure the calculated elongation rate εS and elongation rate εL , at least one of a threading plate tension, a skin pass mill reduction amount, and a tension leveler pressing amount is adjusted. Method.

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