JPH03153889A - Descaling method for hot rolled steel strip - Google Patents

Abstract

PURPOSE:To efficiently descale various kinds of hot rolled steel strips from ordinary steels up to stainless steels by subjecting the hot rolled steel strips added with rolling down at a prescribed draft to bending of a prescribed surface distortion factor, then applying ultrasonic waves on the steel strips in a pickling tank and pickling the steel strip. CONSTITUTION:Various kinds of the hot rolled steel strips 1 are subjected to the rolling down of 0.5 to 10% draft by a rolling mill 2 and are subjected to the bending of 0.2 to 5% surface distortion factor while the strips pass benders 41 and 42. The steel strips 1 subjected to the bending are guided into the pickling tank 52 and are pickled while ultrasonic oscillation is applied thereon by an ultrasonic oscillator 6 in the pickling liquid. Since the steel strips are bent by the bender 41 mounted in the pickling tank 51, the steel strips are tightly dipped and the larger dipping length of the steel strips 1 can be taken as compared to a catenary system. The pickling speed is, therefore, increased. The steel strips are subjected to three roll bending with the bender 42 provided between the tanks 51 and 52.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for descaling various hot rolled copper strips ranging from ordinary steel to stainless steel.

(Prior Art) Conventionally, the following pickling method has been adopted for descaling hot rolled steel strip.

■ A method in which the rope is continuously immersed in an acid solution.

■ A method of performing mechanical descaling as a pretreatment for acid immersion.

Specific examples of this method include creating cracks in the scale by rolling and bending, or polishing the surface of the copper strip with scale adhering to it by shit blasting, etc., and then immersing it in acid. In Japanese Unexamined Patent Publication No. 57-47519, the applicant has disclosed that after rolling a hot rolled steel strip at a reduction rate of 3 to IO%, a tension leveler is used to roll the hot rolled steel strip to zero.
．． We devised a method of applying tensile bending of 5 to 3.0% and removing scale in a pickling tank. Also, JP-A-62-2801
In Publication No. 9, after applying reduction, instead of bending and tension,
A method of adding simple bending was disclosed.

By performing mechanical descaling in this manner, the time required for descaling can be shortened.

■ A method that adds ultrasonic vibration during pickling.

Regarding this method, for example, the present applicant proposed a method in which a copper strip is subjected to strain processing and then pickled while applying ultrasonic vibration (Japanese Patent Laid-Open No. 61-279311).

As mentioned above, hot-rolled steel strips are descaled by pickling, but the acid solution used for pickling differs between ordinary steel and stainless steel; hydrochloric acid is usually used for the former, while for the latter. A mixture of nitric acid and butic acid (nitrate/future M) is used. In particular, when descaling stainless steel, which is a dragon pickling material, it is common to carry out shiraishite blasting and then immerse it in nitric acid. Therefore, at present, ordinary steel and stainless steel are treated with separate pickling processes.

(Problems to be Solved by the Invention) As mentioned above, in the pickling of hot rolled steel strips, the lines for ordinary steel and stainless steel are different. Growth was inevitable.

In addition, looking at the individual equipment used for pickling, shot blasting, which is generally used as a pre-treatment for pickling stainless steel, has high equipment costs and running costs.
In addition, a tension leveler used for performing the above-mentioned bending and tensioning process is also installed (there are problems such as the 11F becomes taller and requires a large equipment space.

The present invention provides a method for descaling hot rolled steel strip that can be used for common steel and stainless steel, and can reduce equipment costs and space occupied by the equipment, as well as improve descaling efficiency. The purpose is to

(Means for Solving the Problems) The gist of the present invention is to roll hot-rolled steel strips at a rolling reduction of 0.5 to 10.
% reduction is applied, and after the reduction the copper strip has a surface strain rate of 0.2~
A method for descaling a hot-rolled steel strip, which comprises bending the steel strip by 5% and then pickling it in a pickling tank while applying ultrasonic waves.

The above-mentioned hot rolled steel strip may be of any type of steel such as not only ordinary steel but also low alloy steel and stainless steel.

One way to apply bending is to use equipment equipped with two or more pickling tanks, first perform bending in one of the pickling tanks, and then add 3-roll pending bending between the pickling tanks. If adopted, it is more suitable for improving descaling efficiency.

FIG. 1 is a schematic explanatory diagram showing the configuration of an example of an apparatus for carrying out the present invention.

In the figure, 2 is a rolling mill that applies rolling to 1i141tl, 3 is installed on the entry and exit sides of the rolling mill 2, and 1li
1 is a priddle roll that applies the necessary tension to the band 1; 41 is a bending device installed in the pickling tank 51; 42 is a bending device installed between the pickling tanks 51 and 52; 6 is a pickling tank 52;
This is an ultrasonic transducer installed inside.

In this device, the steel strip 1 is subjected to a rolling reduction of 0.5 to 10% by rolling Ia2, and subjected to bending with a surface strain of 0.2 to 5% while passing through bending devices 41 and 42, Next, it is guided to a pickling tank 52 and pickled while being subjected to ultrasonic vibration in a pickling liquid by an ultrasonic vibrator 6. Since the bending process is applied by the bending device 41 installed in the pickling tank 51, the steel strip l becomes a tight dip, and the immersion length of the steel strip l can be increased compared to the catenary type, so that the pickling speed can be increased. becomes possible. A bending device installed between pickling tanks 51 and 52! 42, a 3-roll pending bending process is added.

An acid solution such as hydrochloric acid or sulfuric acid having a concentration commonly used is circulated in the pickling tanks 51 and 52.

Note that Fig. 1 shows an example in which one pickling tank is equipped with a bending device that performs bending in the pickling tank, and one pickling tank that applies ultrasonic vibration. However, two or more tanks may be provided in each tank.

In that case, the bending device that performs the bending process in the pickling tank may be installed in one tank or two or more tanks, and the ultrasonic vibration may be applied not only in one tank (it may also be carried out in two or more tanks). good.

When carrying out the present invention, it is necessary to take measures to prevent the bending device 41 (roll) installed in the pickling tank 51 from being eroded by acid, but the material of the roll may be neoprene or fluorine thread rubber.

In addition, as an acid-proof measure for the ultrasonic transducer, for example, as shown in FIG. A structure can be adopted in which a partition is partitioned by a partition plate 7, and ultrasonic vibrators 6 are attached to both sides of the partition to fill the industrial water 8.

(Function) Below, the function and effect of the method of the present invention and the reasons for limiting the rolling reduction rate and surface strain rate will be explained.

Figures 3 and 4 are cross-sectional views of the surface layer of the copper strip schematically showing the process of descaling by pickling. This is the case where the scale 9 is subjected to tensile strain.

In FIG. 3, the outer FezO forming the scale 9
5lO and the inner Pe in contact with the base material (Fe) of steel strip 1
There are no cracks in J*11 and FeO12 (Figure 3 (a))
, this scale 9 gradually dissolves in the pickling solution starting from the outer pe = 0.10 (Fig. 3 (t+), (c)) and is removed (Fig. 3 (d)).

On the other hand, in Fig. 4, FetOz is on the scale 9.
A crack 13 that penetrates 1O, Fe5Oall, and FeO12 is generated (Fig. 3 (a)), and the pickling liquid penetrates into this crack 13 and quickly pickles Fe along the interface between Fe012 and Fe of the substrate. (FIG. 4 (0)), and the dissolution rate at this time is about 4 times higher than that of scale 9.

Therefore, the entire scale 9 is peeled off from its base (FIG. 4(c)) and removed (FIG. 4(d)).

Next, in the method of the present invention, rolling is applied by a rolling mill in order to perform mechanical descaling and to form cranks (cracks) in the scale.

When the rolling reduction rate is less than 0.5%, this effect is not sufficient and the descaling time cannot be shortened.

On the other hand, even if the rolling reduction exceeds 10%, no improvement in the effect of shortening the descaling time is observed.

The processing by the bending device opens the crank formed by the reduction and promotes the peeling off of the scale due to the effect shown in FIG. 4. However, if the surface strain rate is less than 0.2%, there will be no scale peeling effect, and if the surface strain rate exceeds 5%, the scale peeling effect will reach a saturated state, and the equipment cost will increase, making it inefficient. .

In the bending process, the bending process is performed in the middle of pickling as described above, that is, in FIG. After dissolving and removing Fezes, which is a hard-to-remove scale layer, in the washing tank 51), bending is applied to the Fe0 layer using the bending device 42, and pickling is performed again in the pickling tank 52 to perform efficient descaling. It is. In addition, by adding a three-roll pending bending process using the bending device 42, it is possible to bend not only from one direction, for example, from the front side of the scale layer, but also from the front side of the scale layer.
Bending from both sides of the front and (■) can increase the scale removal effect.

The addition of ultrasonic vibration has the effect of promoting the renewal of the pickling solution that has penetrated into the inside of the crank, further increases the dissolution rate of Fe at the interface between the scale and the copper strip, and prevents the peeling and falling off of the scale. Significantly reduces the time required.

The method of the present invention has the above-mentioned effects, and has a large scale removal effect, so there is no need to use nitric acid or butyric acid as an acid solution even when pickling stainless steel, which is a material that is difficult to pickle. Alternatively, it is possible to sufficiently descale with sulfuric acid. Therefore, various types of hot rolled steel strips, from ordinary steel to stainless steel, can be treated in the same pickling tank.

(Example) A method of descaling a hot rolled stainless steel strip (SO5430) with a thickness of 3.0 mm and a diameter of 10100 O+ by applying the method of the present invention by pickling, followed by conventional shot blasting and pickling. compared with.

In the method of the present invention, the rolling reduction ratio of the rolling mill is 5%, the plastic elongation (surface strain rate) due to bending is 3%, and the length of the pickling tank is 20%.
4 m tanks are arranged in series, bending is performed in the 3 pickling tanks from the upstream side, 3 roll pending bending is performed between the 3rd and 4th tanks, and the final pickling tank is Ultrasonic waves were applied in four tanks. As the acid solution, hydrochloric acid with an average concentration of 10% (bath temperature 85'C) was used for each type.

On the other hand, the pickling tank used in the conventional method has a length of 20 m x 4 layers (in series), similar to the method of the present invention, but shot blasting is applied before passing through the pickling tank, and no bending is performed in the pickling tank. ,
The steel strip was passed through a pickling tank in an unrestrained state (catenary type), and the # solution was 10% nitric/butyric acid for each type.

The comparison results between the method of the present invention and the conventional method are as follows, and the descaling efficiency of the method of the present invention is significantly higher than that of the conventional method.

Descaling time Inventive method: 50 sec Conventional method: 90 sec The pickling process of this example was also applicable to ordinary steel and low alloy steel.

(Effects of the Invention) The descaling method of the present invention can be used for both common steel and stainless steel, and the descaling efficiency is significantly improved. In addition, since there is no need for equipment such as shot blasting, tensile run, leveler, etc., equipment costs and space occupied by the equipment can be reduced, and the practical value is extremely large.

[Brief explanation of the drawing]

1 and 2 are schematic explanatory diagrams showing the configuration of an example of an apparatus for carrying out the method of the present invention. FIG. 1 is an overall view, and FIG. Longitudinal front view, (II
) is a longitudinal side view). Figures 3 and 4 are cross-sectional views of the surface layer of a copper strip schematically showing the process of descaling by pickling. This is the case when a tensile strain is applied to the

Claims (2)

[Claims] (1) A hot-rolled steel strip is subjected to a rolling reduction of 0.5 to 10%, and the rolled steel strip is subjected to a bending process with a surface strain of 0.2 to 5%, and then placed in a pickling tank. A method for descaling hot rolled steel strip, characterized by carrying out pickling while applying ultrasonic waves. (2) Using multiple pickling tanks, bending is performed in the upstream pickling tank, then 3-roll pending bending is performed between the pickling tanks, and then superposition is performed in the downstream pickling tank. The method for descaling a hot rolled steel strip according to claim 1, wherein the pickling is carried out while applying sound waves.