JPH04341587A - Method for continuously pickling steel strip - Google Patents

Abstract

PURPOSE:To reduce the pickling time or to make the equipment compact by increasing the pickling capacity of a pickling soln. at the time of pickling a hot-rolled steel strip. CONSTITUTION:When a steel strip 1 is continuously pickled and descaled, the strip 1 is heated by a preheater 6 to the temp. close to the b.p. of a pickling soln. 3 under atmospheric pressure. The pickling soln. in a pickling tank 2 is then heated, boiled and bubbled or high-temp. vapor or gas is blown into the tank 2 to generate bubbles in the pickling soln., and the strip is descaled. Consequently, an active pickling reaction is initiated immediately after the strip is introduced into the pickling tank, the boundary layer formed on the strip surface in pickling is broken by bubbling, and the pickling rate is drastically increased since the soln. is agitated under high temps.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for rapidly pickling and removing scale from metal materials, particularly steel strips, and is not limited to pickling hot rolled steel strips, but also pretreatment methods such as electroplating and electrolytic cleaning. This invention relates to a continuous pickling method applicable to

0002

2. Description of the Related Art An example of a conventional continuous pickling apparatus is shown in FIG. In Fig. 4, 1 is a steel strip, 2 is a pickling tank, 3 is a pickling liquid,
4a, 4b, 4c, 4d, 4e are guide rolls for steel strip 1
Information board will be posted. Briefly, after a steel strip 1 at room temperature is unwound from a payoff reel (not shown), an acid solution 3 in a pickling tank 2 is heated.
The scale that had formed on the surface of the steel strip while running while immersed in water is removed by pickling with acid solution 3, and the descaled steel strip 1 comes out of the pickling tank 2 and is supplied to a subsequent process (not shown). It is said that it will be done.

[0003] In the above-mentioned continuous pickling apparatus, the surface of the steel strip 1 must be in contact with the acid solution 3 for a certain period of time in order to achieve the purpose of removing scale. Regarding this, considering the heat and corrosion resistance of the pickling equipment or the running cost, we have been working at a temperature of about 80°C at a concentration of 10 to 15%.
Hydrochloric acid and sulfuric acid were commonly used.

[0004] For this reason, if the sheet threading speed is increased, the acid liquid tank must be made longer, which causes problems such as higher equipment costs, longer equipment space, and an increase in the amount of acid liquid to be treated. For this reason, there is an increasing need for equipment with high pickling capacity in order to make pickling equipment more compact and to handle pickling of materials that are difficult to pickle, such as stainless steel, whose production has recently increased. There is.

As a means of improving the pickling ability, for example, Japanese Patent Application Laid-open No. 60-61112 discloses that a scale breaker is used to apply tensile bending strain to the scale of the steel strip to create minute cracks, and then the narrowed pickling liquid path is A method has been proposed in which pickling is carried out by passing a steel strip through the steel strip and bringing it into contact with a pickling solution at high speed.

[0006] Furthermore, Japanese Patent Laid-Open No. 61-41783 discloses that strips are provided at narrow intervals in a pickling tank to serve as passageways for steel strips.
A method is disclosed in which a pickling liquid is supplied to the plate passageway and pickling is performed using a turbulent thin acid liquid layer. Although these methods have certain effects, they also have the following problems.

[0007]

[Problems to be Solved by the Invention] Steel strips produced on actual production lines, such as hot-rolled steel strips, are not necessarily flat due to so-called side waves or medium elongation. In addition, it is desirable to run the plate as fast as possible from the perspective of ensuring productivity, but vertical vibration of the plate is unavoidable during threading, and in narrow pickling passages, the steel strip may come into contact with the components of the passageway, resulting in scratches. There is a limit to high-speed sheet threading because it may cause damage to the sheet threading path. Furthermore, during pickling, an acid solution boundary layer may be formed on the surface of the steel strip, which may prevent the reaction rate from increasing.

On the other hand, by raising the temperature of the acid solution to a temperature higher than its boiling point, the bubbles generated during boiling, or by blowing high-temperature steam or gas into the pickling tank to generate bubbles, the acid solution boundary layer on the surface of the steel strip is created. It has been discovered that by increasing the reaction rate by destroying the pickling process, it is possible to shorten the pickling time and achieve high-speed descaling without being affected by the shape of the steel strip to be pickled. Furthermore, various studies were conducted to speed up this descaling process, and in order to maximize the effective reaction length in the pickling solution at a high temperature around the boiling point, the steel strip was placed at atmospheric pressure in front of the pickling tank. It was found that setting the temperature around the boiling point of the pickling solution is effective for descaling ability.

[0009] The present invention heats and boils the pickling liquid in the pickling tank to generate air bubbles, or blows high-temperature steam or gas into the pickling tank to generate air bubbles to remove scale in the pickling liquid. When washing and removing the steel strip, the steel strip is preheated to a temperature around the boiling point of the pickling solution under atmospheric pressure before being led into the pickling tank, thereby maximizing the effective reaction length in the pickling solution. The purpose of the present invention is to provide a method that can shorten the cleaning time and perform pickling with high productivity without being affected by the shape of the steel strip to be pickled.

0010

[Means for Solving the Problems] In order to continuously pickle the scale of a steel strip, the present invention heats the steel strip in a preheating device to a temperature around the boiling point of the pickling solution under atmospheric pressure.
After that, the pickling solution in the pickling tank is heated and boiled to generate bubbles, or high-temperature steam or gas is blown into the pickling tank to generate bubbles.The steel strip is introduced into the pickling solution to pickle the scale. This is a continuous pickling method for steel strips, which is characterized by removing.

The present invention will be explained in detail below based on one embodiment with reference to the drawings. In FIG. 1, reference numeral 1 indicates a steel strip to be descaled, and reference numeral 2 indicates a pickling tank 3, which is a pickling solution containing, for example, sulfuric acid or hydrochloric acid. Guide rolls 4a and 4b pass the steel strip 1 while immersing it in the pickling solution 3. Reference numeral 5 denotes a pickling liquid heating tube provided in the pickling tank 2, and in this embodiment, the pickling liquid is heated by passing high-temperature steam of, for example, over 100°C to boil it from the surface of the pickling liquid heating tube 5 or its vicinity. High-temperature pickling liquid bubbles are thrown onto the steel strip 1 which generates bubbles and passes above them. The pickling liquid heating pipes 5 are installed at intervals below the steel strip passage, or are installed over the entire surface.

[0012] Since the pickling liquid is boiled and air bubbles are thrown onto the steel strip 1, the boundary layer of the pickling liquid that forms on or near the steel strip surface is destroyed, and the pickling liquid is further stirred at a high temperature and the steel strip is heated. Reaction with scale is promoted and scale is removed in a short time. 6 is a preheating device, for example, induction heating,
Heating devices using electrical heating, gas heating, steam, and hot water spraying are applicable. These heating means heat the steel strip 1 on the inlet side of the pickling tank 2 to a temperature around the boiling point of the pickling solution under atmospheric pressure, maximizing the effective reaction length in the pickling tank and reducing the pickling time. It is possible to shorten the time and improve productivity. In addition, the present invention utilizes bubbles during boiling or bubbles caused by blowing gas to produce the stirring effect, so there is no need to pass the steel strip through a narrow threading space, and high-speed pickling is possible. It becomes possible. Furthermore, the acid concentration of the general pickling solution used for descaling is stable because the passivation effect of the steel strip is prevented from occurring over a wide range from pure iron to stainless steel at temperatures near the boiling point. Continuous pickling treatment becomes possible.

[0013]

[Example] Pickling of a hot-rolled chromium stainless steel strip is carried out by putting a pickling solution containing 15% H2SO4 into the pickling tank 2, and introducing steam into the pickling solution heating pipe 5. The pickling liquid 2 is boiled through the boiler, and the preheating device 6 is heated with steam (steam pressure 4 kg/
Pickling according to the present invention, in which the steel strip 1 was preheated with an effective heating length of 7 m using 140°C) and the temperature of the steel strip at the entrance of the pickling tank was 110°C, and the same pickling as a comparative example. A comparison was made with conventional pickling in which the washing liquid was heated to 90°C. As a result of this pickling, in the present invention, the threading speed was 75 m/min for complete descaling. On the other hand, in the comparative example, the plate passing speed was 30 m/min for complete descaling, and as shown in FIG. 2, the pickling treatment can be completed at 2.5 times the line speed in the present invention.

[0014]

Effects of the Invention As described in detail above, the present invention is capable of forming an oxidized layer and acid solution by heating and boiling the pickling solution to generate bubbles, or by blowing high-temperature steam or gas to generate bubbles for pickling. The reaction with the pickling process is accelerated and the pickling treatment time can be shortened. Furthermore, by preheating the steel strip to a temperature around the boiling point of the pickling solution under atmospheric pressure before leading it to the pickling tank, the pickling treatment time can be further shortened. In addition, the pickling properties of even difficult-to-pickleable steel strips are significantly improved compared to conventional methods. Due to these effects, the present invention allows the pickling equipment to be shortened and to save space.

[Brief explanation of drawings]

FIG. 1 shows a pickling device in an embodiment of the present invention.

FIG. 2 shows the performance improvement of the present invention over conventional pickling in one embodiment of the present invention.

FIG. 3 shows a conventional pickling device.

[Explanation of symbols]

1 Steel strip 2 Pickling tank 3 Pickling liquid 4 Guide roll 5 Pickling liquid heating tube 6 Preheating device

Claims (1)

[Claims] Claim 1: When continuously pickling scale on a steel strip, the steel strip is heated in a preheating device to a temperature around the boiling point of the pickling solution under atmospheric pressure, and then the acid in the pickling tank is heated. Steel characterized by the process of removing scale by pickling by introducing a steel strip into a pickling solution in which bubbles are generated by heating and boiling the washing solution, or by blowing high-temperature steam or gas into a pickling tank to generate bubbles. Continuous pickling method for strips.