JPS61154713A - Descaling method of strip steel - Google Patents

Abstract

PURPOSE:To remove an oxidized film with good efficiency by subjecting the strip steel with oxidized film to rolling reduction by the roller with the roll which covers its surface with the elastic body having lower elastic coefficients than a steel on one part and with steel made roll on the other part. CONSTITUTION:A roller is composed of the roll which covers its surface by the elastic body having lower elastic coefficients than those of steel of one part, for instance by rubber roll 2 and by steel made roll 1 of the other part. And when the strip steel 3 which is before acid cleaning is passed between rolls 1, 2 with pressurizing state, strip steel 3 is bent to the steel made roll 1 side and cracks are caused on the oxidized film and removed. The acid cleaning is further performed in succession if necessary.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for removing scale from steel strip.

(Prior Art) The oxide film, so-called scale, on a steel strip becomes thicker as the winding temperature increases, making it difficult to descale with acid, resulting in an increase in pickling time, ie, a decrease in productivity. As a countermeasure against this problem, it is common practice to create cracks in the scale to improve pickling properties. Conventionally, leveler type scale breakers, which repeatedly bend the steel strip, and
Skin pass rolling, which creates cracks during rolling, has been put into practical use. However, the conventional method has the following drawbacks: In the skin bath rolling method, in order to introduce strain into the scale, the steel strip itself must be rolled by the same amount as the strain on the scale. However, it not only requires extra deformation energy, but also requires a strong stand to withstand the large rolling load, which has the disadvantage of requiring expensive equipment.

The leveler type scale breaker is a method that bends the steel strip with rolls to give the necessary strain to the scale, and there is no need for the steel strip itself to fully deform, so it is advantageous in terms of energy, but it is also non-tensionless. Or, if the tension is as low as that required for threading, the steel strip will not easily fit into the roll, and the roll radius (
R), i.e.,
The curvature of the steel strip is much smaller than the roll curvature, and the bending strain ε
has the disadvantage that it cannot increase up to the calculation formula % formula % (1) of the steel strip thickness (1) and the roll diameter (D = 2R).

Additionally, if you try to bend the steel strip strongly using a small-diameter roll under low tension, a bending phenomenon often occurs in which the bending strain becomes discontinuous, which not only does not improve pickling properties, but also causes deterioration of the material quality of the steel strip. It has the following.

To compensate for the drawbacks of the conventional scale breaker, there is also a tension leveler type scale breaker equipped with a prydle roll for applying tension to the exit side of a part of the leveler, as disclosed in Japanese Patent Application Laid-Open No. 58-209415. However, in order to apply a large tension with this tension leveler, a large number of pre-drill rolls for applying tension are required, which not only increases equipment costs but also requires a large area of equipment, making it difficult to use existing equipment. J of modification of pickling membrane q11
It also has the disadvantage of being a constraint on the j, i combination.

(Purpose of the Invention) In order to eliminate these drawbacks, the present inventors have developed a pair of roll machines consisting of a roll whose surface is covered with rubber on one side and a steel roll on the other, and this roll machine alone. Alternatively, they found a way to effectively apply strain to the scale by rolling down the steel strip using multiple roll machines with alternating combinations of rubber and steel, and then pickling as necessary. It is something.

(Structure and operation of the invention) The invention will be explained below using figures.

In FIG. 1, when the steel strip 3 before pickling is passed under pressure between the steel roll 1 and an elastic body with a lower elastic modulus than steel, such as the rubber roll 2, the 9V5 strip is on the side of the steel roll. It bends and cracks appear in the scale.

This method of applying bending strain to the scale does not require high tension like a tension leveler, and even without tension, it is possible to easily apply the strain necessary for descaling by adapting the steel strip to a small roll. In addition, the bending occurs near the bottom of the roll, so it has the advantage that it can be installed as long as there is enough room for the stand to fit.
In addition, since the bending occurs only in an extremely narrow area of the contact area between the roll and the steel strip, the bending phenomenon that occurs with ordinary levelers does not occur.

The energy required to bend the steel strip can be supplied from the tension of threading by driving the roll machine or by not driving the roll machine. The latter method of replenishing bending energy using strip tension requires a higher tension than the former, but in the present invention, only the strip bending energy needs to be supplied, so the tension is much lower than that of a tension leveler. In addition, unlike skin pass rolling, the entire steel strip is not stretched, but only the steel strip is bent, so a strong rolling load is not required, so a simple stand is sufficient. It is characterized by a significant reduction in equipment costs.

The principle behind how steel strips are bent with this roll machine is that both rolls have different elastic modulus, so when rolling pressure is applied, the roll with the smaller elastic modulus becomes larger. The steel strip deforms, and the width of contact with the steel strip differs greatly between the front and back surfaces of the steel strip, generating a bending moment, causing the steel strip to bend toward the roll with a higher elastic modulus, in this case the steel roll.

Up to this point, the invention has been described in detail using the terms rubber roll and steel roll, but in principle, it is sufficient if there is a large difference in the elastic modulus of both rolls. Practically, instead of the steel roll, a roll whose surface is made of any suitable acid-resistant metal or a hard material such as ceramic may be used. That is, the roll made of an elastic material having a lower elastic modulus than steel may be a roll whose surface is made of rubber, synthetic resin, or an organic material such as urethane rubber or polypropylene. If the roll is made of acid-resistant material, this roll machine can be installed even in a pickling tank, and since f[1 cracks are added to the scale of the steel strip in acid, pickling efficiency can be expected to improve considerably.

Next, how to set the rolling blade or roll gap of the roll machine of the present invention will be described.

When the cut plate 4a cut from the target steel strip is passed through it while closing the roll cap of the roll machine, the cut plate 4b after passing through the plate bends concavely toward the steel roll 1 side, as shown in Fig. 2. As shown in FIG. 3, the curvature increases as the number of rolling blades increases, and eventually saturates at a constant curvature determined by the diameter of the steel roll. Therefore, when this roll machine is operated at a rolling force equal to or higher than the rolling force at which the curvature after threading is saturated, the steel strip is always given a curvature determined by the diameter of the steel side roll. In this case, if the roll gap is set at a constant value so that the maximum thickness of the target steel strip can be bent sufficiently, even if the thickness of the steel strip changes to the thinner side, the roll load will rapidly decrease due to the elastic properties of rubber. There is no bending, sufficient bending strain is applied to the scale, and the operation is extremely simple.

The relationship between the curvature of the steel strip and the rolling blade is that since the steel strip is connected continuously, the part bent by the roll machine is unbent in the middle of the pass, and no noticeable bending is observed in the cut plate.
Because the bending principle in the roll machine is the same.

If the pressure is the same, it can be assumed that the bending is the same.

As shown in FIG. 4, the relationship between strain and pickling time is such that the larger the strain, the shorter the pickling time. When attempting to impart a strain of 5% or more, which has a remarkable effect on shortening the pickling time, to a hot rolled steel strip with a thickness of 3■■, from equation (1), D < Go m+s
Such a small diameter roll, which may be set to φ, causes a problem of deflection, so it is necessary to appropriately install a backup roll of a large diameter to prevent deflection in order to reduce the diameter.

Furthermore, even if the bending strain is not as large as 5%, the present invention has a larger bending strain than conventional scale breakers because the steel roll diameter itself is equal to the curvature at which the steel strip is actually bent by the roll. The diameter also has a large effect on improving pickling properties.

The diameter of the rubber roll does not have to be the same as the steel roll; it is preferable that the rubber roll has a larger diameter than the steel roll.
Since the steel strip is pressed against the steel roll by the deformation of the rubber,
In the case of a straight roll gap, the contact length between the rubber roll and the steel strip is larger on the larger diameter side, resulting in a larger bending moment, and the roll deflection is smaller on the larger diameter side. However, even in the case of a small diameter, it is sufficient to increase the pushing force of the roll a little to increase the amount of deformation of the rubber, and the deflection of the roll can also be taken into consideration when attaching a crown, so there is no need to specify anything in particular. do not have.

Next, in order to reduce the pickling time, the number of passes is 1.
This effect can be achieved by passing the sheet through the sheet once, but the descaling effect due to bending is worse on the tension side than on the compression side, so it is desirable to run the sheet twice with alternating combinations of rolls. An example of its application is shown in Figure 5. If the strain is passed more than 2 times, the effect reaches saturation because the strain is determined by the roll diameter and plate thickness, but if the number of passes is large (for example, 6 or more passes) with small diameter rolls, the pickling process will be easier in the later process. Even if you don't do this, most of the scale will be removed.

(Examples are shown next.) Table 1 Example sample material Two-low carbon ordinary steel hot rolled winding temperature near 30°C Plate thickness: 3.2 am, Plate width: 1000 am
Rubber-coated roll diameter: 250 armφ Urethane rubber thickness: 20+sm The pickling time in each method was evaluated based on relative ratios, with the pickling time of the hot-rolled steel strip as tooot.

Table 1 (Effects of the invention) Continuous annealing has become popular as a method for producing cold rolled steel strips, but in general J! ! The hot rolling winding temperature of 8 rolled steel strips for continuous annealing is much higher than the hot rolling winding temperature of the box annealing method, so as the number of continuously annealed steel strips increases, the pickling time increases and productivity decreases. This is a hindering factor.

If the present invention is applied to the conventional pickling line, it will be possible to greatly reduce the pickling time with simple equipment, and when there are many continuously annealed steel strips, productivity will be prevented from decreasing, and box-type annealing When there is a lot of steel strip, the effect of increasing production is brought about.

In addition, if a large number of roll machines of the present invention with small diameter steel rolls are arranged, pickling is hardly required in the post-process.
A descaling line can be constructed, and the effect of escaping the troublesome treatment of waste liquids such as waste acids can also be obtained.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of the roll machine used in the present invention, Figure 2 is a diagram showing the warping of the plate after the roll passes with different rolling blades, and Figure 3 is the relationship between the rolling blade and the plate curvature after passing. FIG. 4 is a diagram showing the relationship between surface strain of a plate and pickling time, and FIG. 5 is a diagram showing an example of the present invention using a multi-roll machine. 1...Steel tff-ru, 2...Rubber roll, 3...
・Steel strip, 4a4b...cut plate.

Claims (2)

[Claims] (1) The oxide film is removed by rolling down the steel strip with the oxide film using a roll machine with one roll covered with an elastic material with a lower elastic modulus than steel and the other steel roll. A method for removing scale from a steel strip, characterized by: (2) A steel strip with an oxide film is rolled down using a roll machine consisting of a roll whose surface is covered with an elastic material with a lower elastic modulus than steel on one side and a steel roll on the other, and then pickled. A method for removing scale from a steel strip, characterized by: