JPH093673A - Pickling device and pickling method for thin steel sheet - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a pickling apparatus and method for a thin steel sheet capable of shortening the pickling time and downsizing the equipment. [Structure] A steel plate heating unit for heating a steel plate, a pickling tank unit in which the steel plate is immersed, and an acid solution circulation tank unit for controlling the concentration and temperature of the acid solution are provided, and the steel plate is continuously descaled. A high-speed pickling device for thin steel plates, wherein the steel plate heating unit measures the temperature of the heated steel plate with a steel plate heating device provided between the bridle roll and the pickling tank on the pickling tank entry side. Has a thermometer for preventing bending of the waist, and the pickling tank part is a sink roll for controlling the immersion time of the steel plate, and an acid solution, scale, and other insoluble matter from the bottom of the pickling tank part. And a circulation tank part is provided in the lower part of the pickling tank part, and the upper pickling solution is used to adjust and control the concentration and temperature of the pickling solution in the upper pickling tank. It has a heat exchanger that circulates and supplies it to the tank and recovers the exhaust heat transferred from the steel sheet to the acid solution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pickling apparatus and a pickling method for thin steel sheets.

[0002]

2. Description of the Related Art For example, as shown in FIG. 3, in a conventional dipping-type hydrochloric acid pickling equipment, a hot-rolled steel sheet 1 is cooled to room temperature and then sent out from a payoff reel 2 of an entry-side equipment. , The welder 3, the looper 4, the bridle device 5, and the scale breaker 6 for 5 to 6 tanks (total length of about 10
(0 m), it is dipped in the hydrochloric acid tanks 7, 8 and finally wound up by the tension reel 9.

In the immersion traveling process in the hydrochloric acid tank, the scale of the surface layer of the steel plate is removed by a chemical reaction with hydrochloric acid, and then the steel plate 1 is fed to the next process or becomes a product. Each of the pickling tanks 7 and 8 has a depth of 500 to 1000 mm and a length of 10 to 20 m. As for the hydrochloric acid conditions in the pickling tanks 7 and 8, it is known that the higher the concentration and the higher the temperature, the more the descaling property improves. However, due to practical restrictions such as equipment or cost, these are not limited. It cannot be raised to a very high level, and the hydrochloric acid concentration is generally 4.0 to 15.0.
The weight% and the temperature are about 80 to 90 ° C.

In recent years, techniques for shortening the time of pickling treatment or shortening the length of pickling tank have been actively developed with the aim of improving productivity and restraining capital investment. A pickling method (Japanese Patent Laid-Open No. 56-160825) that promotes permeation of the acid solution by installing a breaker to cause cracks in the scale of the surface layer and a method of generating a jet flow in the pickling tank (Japanese Patent Laid-Open No. 62-62825). No. 196387), or a turbulence promoter for installing a shield plate to promote the metabolism of the acid solution in the vicinity of the steel plate (Japanese Patent Application Laid-Open No. Hei 4)
No. 59982), or a pickling method of promoting a chemical reaction between scale and hydrochloric acid by heating a steel sheet to a reaction temperature with an acid solution (JP-A-59-20487, JP-A-4-297589). ) Etc. have been proposed.

[0005]

However, the conventional immersion type hydrochloric acid pickling equipment requires a large installation space and enormous construction cost even with only the pickling tank section. Further, in terms of operation and quality, there is a problem that the temperature and concentration of the acid solution in a long pickling tank cannot be sufficiently controlled, and good steel sheet surface properties cannot be stably ensured. There is.

Further, the scale breaking method, which is carried out as a pickling method, cannot exert a sufficient effect because there is a risk of plate breakage in the vicinity of the welded part of the steel plate, resulting in uneven surface finish in the longitudinal direction. In addition, the effect of shortening the pickling time is small, and the line length is at the conventional level.

Further, in the jet system, although the effect of shortening the line length can be expected, it is offset by the increase in cost due to the addition of the acid resistant pump and piping, and the running cost also rises due to the increase in pump power cost. There is.

The present invention has been made to solve the above-mentioned problems, and it is possible to reduce the installation space and the cost of equipment construction, and at the same time, to produce a thin steel sheet having a good pickling finish. The purpose is to obtain a pickling equipment that can be stably manufactured.

[0009]

A pickling apparatus for a thin steel sheet according to the present invention controls a steel sheet heating section for heating a steel sheet, a pickling tank section in which the steel sheet is immersed, and a concentration and temperature of an acid solution. A pickling device for a thin steel plate, which comprises a pickling solution circulation tank part and continuously descales a steel plate, wherein the steel plate heating part comprises a bridle roll and a pickling tank on the pickling tank part side. A steel plate heating device provided between, a thermometer for measuring the temperature of the heated steel plate, and a waist bending prevention roll, and, the pickling tank portion, a sink roll for steel plate immersion time control and And means for discharging the acid solution, scale, and other insolubles from the lower part of the pickling tank part, the circulation tank part being provided in the lower part of the pickling tank part, and the upper pickling tank. The acid solution is circulated and supplied to the upper pickling tank to adjust and control the concentration and temperature of the acid solution in the steel. Characterized in that it has a heat exchanger for recovering waste heat having transferred to the acid solution from.

Further, a steel type, a steel plate temperature, a sink roll position, and an acid solution condition are input as detection data or initial setting data, and a calculation unit for calculating a steel plate heating temperature and a steel plate immersion time based on these input data, and the calculated steel plate. Control the heating operation of the steel plate heating unit based on the heating temperature to heat the steel plate to a temperature range where the nucleate boiling state of the acid solution is obtained during steel plate immersion, and control the sink roll operation based on the obtained steel plate immersion time to control the steel plate. And a controller for adjusting the immersion depth.

The thin steel sheet pickling method according to the present invention comprises a steel sheet heating section for heating a steel sheet and a pickling tank section in which the steel sheet is immersed, and the steel sheet is immersed in an acid solution for continuous descaling. A method for pickling a thin steel sheet to be treated, wherein the steel sheet is heated to a temperature range where the acid solution is in a nucleate boiling state when the steel sheet is immersed in the steel sheet heating section, and the steel sheet is immersed in the acid solution immediately after heating. To do.

The method of pickling thin steel sheet according to the present invention is
A steel plate heating unit for heating a steel plate, a pickling tank unit in which the steel plate is immersed, and an acid solution circulation tank unit for controlling the concentration and temperature of the acid solution, and a thin steel plate for continuously descaling the steel plate. A pickling device, wherein the steel plate heating unit is a steel plate heating device provided between the bridle roll and the pickling tank on the pickling tank portion-entry side, and for measuring the temperature of the heated steel plate. It has a thermometer and a waist bend preventing roll, and the pickling tank part is
A sink roll for steel plate immersion time control, and means for discharging the acid solution, scale, and other insolubles from the lower part of the pickling tank section, the circulation tank section, Heat exchange that is provided in the lower part and circulates and supplies the acid solution to the upper pickling tank to adjust and control the concentration and temperature of the acid solution in the upper pickling tank, and recovers the exhaust heat transferred from the steel plate to the acid solution. When a steel sheet is pickled using a steel sheet pickling apparatus having a vessel, a hydrochloric acid solution containing an inhibitor and having a concentration of 4.0 to 8.0% by weight is used at a rate of 60 to 150 kg per ton of steel sheet. Circulating and supplying to the pickling tank, the steel plate heating temperature is 100 to 3
It is characterized in that the steel plate is immersed in a hydrochloric acid solution at a temperature of 00 ° C. so that the steel plate penetration angle as an acute angle formed by the liquid surface of the acid solution and the steel plate is in the range of 30 to 60 °.

The acid solution is an inhibitor (pickling inhibitor).
In the case of a hydrochloric acid solution containing
It is desirable to heat to the temperature range of 150 to 300 ° C
It is more preferable to heat to the temperature range of. If the steel sheet is immersed in an acid solution immediately after being heated to such a temperature range, a nucleate boiling state is obtained near the surface of the steel sheet, and many fine cracks are generated in the scale, so that the steel sheet has good surface properties. Particularly, when the steel sheet is heated to a temperature range of 200 to 250 ° C., ideal surface properties of the steel sheet can be obtained.

Further, it is desirable that the steel plate penetration angle is in the range of 30 to 60 °. This is because the descaling state becomes poor both when the penetration angle of the steel sheet with respect to the acid solution in the pickling tank is below 30 ° and above 60 °.

Further, it is desirable to circulate and supply a hydrochloric acid solution having a concentration of 4.0 to 8.0% by weight to the pickling tank section at a rate of 60 to 150 kg per ton of steel sheet. In the region where the supply amount of the hydrochloric acid solution per ton of steel plate is less than 60 kg, the descaling of the steel plate becomes insufficient, and in the region where the supply amount of the acid solution exceeds 150 kg, the descaling effect is saturated and becomes excessive supply. is there. A hydrochloric acid solution is preferably used as the acid solution for descaling. In this case, the hydrochloric acid concentration of the solution is in the range of 4.0 to 8.0% by weight. The lower limit of the hydrochloric acid concentration is 4.0% by weight because the descaling of the steel sheet is insufficient, and the upper limit of 8.0% by weight is that the base material of the steel sheet is corroded and the surface property is Because it will be damaged.
Further, it is desirable that the temperature of the acid solution is usually controlled in the range of 80 to 90 ° C.

[0016]

When a high-temperature object is immersed in a liquid, three-step boiling phenomenon appears depending on the temperature difference between the two. First, the nucleate boiling state appears in the relatively low temperature region of the first stage. In the nucleate boiling state, bubbles are generated from the entire surface of the object, and heat and mass are actively transferred between the surface and the liquid phase. Next, in the temperature range of the second stage, which is higher than this, the state transitions to the transition boiling state. In the transition boiling state, bubbles are continuously generated from most of the surface of the object and partially covered by the vapor film, and heat and mass transfer between the surface and the liquid phase becomes slower than during nucleate boiling. . In the higher temperature third stage temperature range, the film transitions to the film boiling state. In the film boiling state, the entire surface of the object is covered with the vapor film, which hinders the transfer of heat and mass, and becomes even dull.

In the pickling apparatus and the pickling method for a thin steel sheet according to the present invention, the steel sheet is preheated to a temperature range in which the acid solution is in a nucleate boiling state when the steel sheet is immersed in the steel sheet heating section, and the steel sheet is pickled immediately after heating. Since it is immersed in the liquid, a nucleate boiling state with rapid heat transfer and mass transfer appears near the steel plate. In this nucleate boiling state, the acid solution contacting the surface of the steel sheet is rapidly renewed in a short time, so that the descaling reaction is promoted in combination with the rapid heating.

Further, not only the preheating temperature of the steel sheet is controlled, but also the immersion depth and the penetration angle of the steel sheet are controlled, so that it is possible to flexibly cope with the descaling time change for each steel type and each generated scale amount. can do.
In addition, even if the temperature of the acid solution in the pickling tank is not uniform, there is a margin for the adjustment amount and control amount in the lower circulation tank, so it is possible to take detailed measures and stabilize the good pickling finish. Can be maintained at. What has been described above avoids a partial overheated state of the steel sheet, and substantially prevents the deformation (plate shape collapse) such as corrugation at both widthwise end portions of the steel sheet and bulging of the central portion. .

Further, it is particularly preferable that the steel plate heating temperature is in the range of 100 to 300 ° C. when immersed in an acid solution (hydrochloric acid solution) for the following reason. First, the boiling phenomenon cannot be obtained unless the boiling point is higher than the boiling point of the acid solution.

Secondly, when the heating temperature of the steel sheet is 300 ° C. or lower, the boiling phenomenon is in the nucleate boiling region, so that the generation of fine cracks on the surface layer scale is induced and the metabolism of the acid solution is promoted. This is because when the steel plate heating temperature exceeds 300 ° C., the transition from the transition boiling region to the film boiling region is caused, the generation of fine cracks is prevented, and the promotion of metabolism is slowed down (descaling property is deteriorated).

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The thin steel sheet 1 hot-rolled in a rolling mill is wound into a coil and cooled to room temperature, and then transported to an immersion type hydrochloric acid pickling equipment.

Although only a part of the immersion type hydrochloric acid pickling line is shown in FIG. 1, in this immersion type hydrochloric acid pickling line, a payoff reel (not shown) on the upstream side and a tension reel (not shown) on the downstream side are provided. It is continuously fed up to
Is immersed in the pickling tank 16. A large number of conveying rolls (not shown) are arranged below the pass line so that the steel plate 1 can be conveyed at high speed. A bridle roll 12, an induction heating device 13, and a thermometer 15 are provided in this order between the pickling tank 16 and the payoff reel.
The upper pickling tank 16 has a pipe 25 and a pump 25 in the lower circulation tank 21.
And a circulation circuit for the acid solution is formed. The circulation tank 21 has a function of facilitating the control of the temperature and the concentration of the acid solution by extracting the acid solution and the in-tank precipitate from the lower portion of the upper pickling tank 16, and the heat exchange for recovering the exhaust heat in the tank. Bowl 1
9 is equipped. Water at almost room temperature is supplied to the tube side of the heat exchanger 19. The supplied water exchanges heat with the acid solution on the shell side to become warm water, which is the washing tank 2
0.

As a heating device constituting the steel plate heating section,
An induction heating device with short equipment length and excellent temperature controllability is desirable. For example, the coil length is preferably equal to or several times the plate width. The induction coil 13b of such an induction heating device 13 is the steel plate 1 on the pass line.
It is provided so as to surround and is connected to the AC power supply 13a. The coil power supply 13a is connected to the control unit 40 so that the amount of power supplied to the coil 13b is controlled. The steel sheet 1 is instantly heated to a temperature range of 100 to 400 ° C. by the induction heating of the coil 13b.

In the induction heating device 13, the edge portion is overheated (target temperature ± 10 ° C.) for uniform heating,
Generally, in the case of a coiled thin steel sheet, the scale thickness of the edge portion is thicker than that of the central portion, so that a desirable result is obtained. The induction heating device 13 also performs feedback control of temperature information obtained from a steel plate thermometer (not shown) provided on the outlet side to perform uniform heating and input / output control according to line deceleration. Heating device 13 and pickling tank 16
When the distance L from the sheet is long (L ≧ 0.5 m), it is necessary to install a waist bend prevention roll 22 having a roll diameter of 0.32 m or more to prevent the steel plate 1 from bending (buckling, which is a product defect of a thin steel plate). There is.

A radiation type thermometer 15 is provided immediately before the entrance side of the pickling tank 16 and above the pass line so that the temperature of the steel sheet 1 during passage can be continuously detected without contact. ing. The thermometer 15 is connected to the input side of the calculation unit 30. A position sensor (not shown), a concentration sensor (not shown), and a liquid temperature sensor (not shown) are also connected to the input side of the arithmetic unit 30, and a sync roll position detection signal and a hydrochloric acid condition data signal are supplied. Is entered. On the other hand, the output side of the arithmetic unit 30 is connected to the input side of the control unit 40, and various data signals are input to the control unit 40.

Immediately downstream of the thermometer 15, a pickling tank 16 and a water washing tank 20 are provided side by side in this order. In the pickling tank 16, the concentration of 4 to 4 adjusted to a liquid temperature of 80 to 90 ° C.
It contains an 8 wt% hydrochloric acid solution. This hydrochloric acid solution contains an inhibitor as a pickling inhibitor. A sink roll 17 and a fixed roll 18 are immersed in the hydrochloric acid solution. The sink roll 17 is a lifting cylinder (not shown)
It is supported by and can be immersed in or pulled from a hydrochloric acid solution. Thereby, the immersion length of steel plate 1 and the penetration angle θ are controlled.

The lower circulation tank 21 is the upper pickling tank 1
The acid solution and the in-tank precipitate are constantly extracted from the bottom of the tank 6 and accepted, and the temperature and concentration of the acid solution supplied to the upper pickling tank 16 are finely controlled by the control unit 40 and the arithmetic unit 30. That is, L. Calculation unit 3 based on the input data of S, steel type, hydrochloric acid condition, sink roll position, and steel plate temperature
0 calculates the optimum operating condition and sends it to the control unit 40. Based on this, the control unit 40 controls to supply the hydrochloric acid solution having a concentration of 4.0 to 8.0% by weight to the pickling tank unit 16 at a rate of 60 to 150 kg per ton of steel plate. A new acid solution is supplied to the pickling tank section 16 from another supply source (not shown) together with the acid solution circulated and recovered from the circulation tank 21.

The heat exchanger 19 is provided in the lower circulation tank 21 so that the water flowing through the internal passage of the heat exchanger 19 and the hydrochloric acid solution in the lower circulation tank 21 are heat-exchanged. ing. The hot water that has undergone heat exchange is sent to the washing tank 20. A thermometer for measuring liquid temperature (not shown)
And a concentration meter (not shown) are provided at appropriate places in the upper pickling tank 16 and the lower circulation tank 21, respectively, so that the temperature and the concentration of the hydrochloric acid solution can be detected.

On the output side of the control unit 40, in addition to the coil power supply 13a of the heating device 13, a drive power supply for an elevating cylinder (not shown) of the sink roll 17 and a thermometer for liquid temperature measurement (not shown), respectively. It is connected.

Next, the case where the steel sheet is continuously pickled in the above-mentioned immersion type hydrochloric acid pickling line will be described.
Steel plate 1 manufactured in the hot rolling process and cooled to room temperature
Arrives at the bridle roll 12 via an entrance facility (not shown). The steel plate 1 is 1 by the induction heating device 13.
After being heated to a predetermined temperature in the range of 00 to 300 ° C,
After passing over the small-diameter transport roll 22 for preventing the waist from breaking, it reaches the pickling tank 16. In the pickling tank 16 (20 to 30 m), a vertically movable sink roll 17 is installed, and the lower circulation tank 21 receives the supply of the acid solution controlled to a predetermined liquid temperature and a predetermined concentration. It also has a control function to make the pickling finish uniform and stable for each line speed. The warm water recovered by the heat exchanger 19 in the circulation tank 21 is guided to the next washing tank 20.

When the heated steel plate 1 is dipped in the acid solution, the acid solution in contact with the steel plate 1 is in a nucleate boiling state. In the nucleate boiling state, innumerable bubbles are generated from the entire surface of the steel sheet 1, rapid heat transfer and mass transfer occur between the acid solution and the steel sheet 1, and the descaling reaction is sufficiently promoted.

The above-mentioned problems regarding the shortening of the pickling treatment time and the downsizing of the equipment are as follows: In the immersion hydrochloric acid pickling equipment, the steel sheet heating device 13, between the bridle roll 12 and the pickling tank 16 on the inlet side, A pickling method in which a steel plate heating unit including a steel plate thermometer 15 and a waist bending preventing roll 22 is provided to heat the steel plate within a temperature range of 100 to 300 ° C. at a boiling point of the acid liquid or higher, and then immersed in the acid liquid. (Hereinafter, it will be referred to as a high-temperature charging pickling method).

Next, referring to Table 1, the results of investigations on the crack occurrence state and descaling when the steel sheet temperature was variously changed were carried out, and Examples 1 to 5 and Comparative Examples 1 and 2, the conventional method, and the scale brake were examined. The explanation will be made in comparison with each of the Longing methods.

In Examples 1 to 5, the steel plate heating temperature was 1
It corresponds to the case of setting to 00 ° C, 150 ° C, 200 ° C, 250 ° C, 300 ° C. Comparative Examples 1 and 2 correspond to the case where the steel plate heating temperatures are set to 350 ° C. and 400 ° C., respectively. The conventional method corresponds to the case where the steel plate temperature is set to 30 ° C. (no heating) and 80 ° C. (low temperature heating), respectively. The scale breaking method corresponds to the case where the steel plate temperature is set to 30 ° C. (without heating). The scale breaking method is based on the methods described in JP-A-56-160825, JP-A-62-196387, and JP-A-4-59982.

The above-mentioned cases were examined with respect to the occurrence of cracks on the scale and the effect of shortening the pickling treatment time. In the table, double circles show the results with many fine cracks, single circles show the results with many cracks, triangles show the results with few cracks, and cross marks show the results with only a few large cracks. . As is clear from the table, good results could be obtained when the steel plate heating temperature was in the range of 150 to 300 ° C, and the best results could be obtained in the temperature range of 200 to 250 ° C.

Regarding the effect of shortening the pickling treatment time, the results of each method were examined with the conventional method at a steel plate temperature of 30 ° C. as a reference of 100%. 50% in Example 1, 3 in Example 2
3%, 20% in Example 3, 18% in Example 4, 20% in Example 5, 40% in Comparative Example 1, 4 in Comparative Example 2.
The results were 2%, 85% by the conventional method (80 ° C. low temperature heating) and 90% by the scale breaking method.

By the way, Japanese Patent Laid-Open No. 4-297589 discloses a method of heating the steel sheet to an acid solution temperature (80 ° C.) by induction heating and pickling. However, in the method of heating a steel sheet to about 80 ° C. with such an induction heating device and pickling, the effect of shortening the pickling time is 85% (15% of the standard total required time is shorter than the pickling technique described above. Shortened) and less.

Some consideration will be given to the obtained results. In the steel plate heating part, the steel plate heated in the range of 100 to 300 ° C. is immersed in the acid solution (liquid temperature 80 to 90 ° C.) and rapidly cooled, and the scale generated in the surface layer part is In addition to cracking due to thermal shock, peeling occurs due to the difference in thermal expansion from the base material. Although it fulfills the same role and action as the method by installing the scale breaker described above, in the case where the heating temperature of the steel sheet is in the range of 150 to 300 ° C., fine cracks occur in Examples 2 to 5 and the vicinity of the welding point. There is no restriction such as deceleration of line speed and deterioration of operability due to deterioration of descaling property, and there is no problem of uneven surface finish in the longitudinal direction.

It has been conventionally known that increasing the concentration and temperature of the acid solution is effective for improving the descaling property, but it is realized by the limitation of the apparatus or the cost. There isn't. However, in the high-temperature charging pickling method, by heating the steel plate temperature above the boiling point of the acid solution and immersing it in the acid solution, the concentration and temperature are increased only near the steel plate, making it ideal for descaling chemical reactions. It is possible to obtain the pickling conditions and effects which cannot be obtained by the conventional technique.

Next, the pickling apparatus of this embodiment will be described with reference to FIGS. 2 and 3. FIG. 2 is a graph showing the results of examining the response of each tank with the time constant (minutes) of the pickling tank on the vertical axis. The length of the pickling tank is 20 m, and the tank volume per one is 50 m ³ . As is clear from the figure, in the conventional pickling tank consisting of about 5 to 6 tanks, the response of hydrochloric acid concentration and temperature is slow, and detailed control / management is not possible, resulting in stable product quality. The supply was impossible. However, in the apparatus of the present embodiment, the use of the circulation tank resulted in a response within a few minutes, and the responsiveness was remarkably improved and the product quality could be stabilized.

In FIG. 3, the horizontal axis indicates the supply amount of hydrochloric acid per ton of treated steel sheet (kg / ton), and the descaling properties are A, B, and
It was evaluated by ranking C. In the figure, the white circles indicate the density 8.
The results of a 0 wt% hydrochloric acid solution (temperature 80 ° C.) are shown, and the open triangles show the results of a 4.0 wt% concentration hydrochloric acid solution (temperature 80 ° C.). As is clear from the figure, it was found that the optimum supply range of the hydrochloric acid solution was 60 to 160 (kg / ton). In the optimum range, all the hydrochloric acid solutions having a concentration of 8.0 wt% were ranked A, but the hydrochloric acid solutions having a concentration of 4.0 wt% were varied from rank B to rank A. .

Next, the relationship between the descaling property and the steel plate heating temperature will be described with reference to FIG. FIG. 4 is a graph showing the results of examining the relationship between the two with the horizontal axis representing the steel plate heating temperature and the vertical axis representing the descaling property. A steel plate was immersed in a hydrochloric acid solution having a concentration of 8% by weight at a temperature of 80 ° C. for the same immersion time and examined. Descalability is A, B, C, D,
The evaluation was made in 5 grades of E. As is clear from the figure, the evaluation of the descaling property was good in the temperature range of 100 to 300 ° C, and the evaluation of A or B was obtained particularly in the temperature range of 150 to 300 ° C.

In FIG. 5, the horizontal axis represents the penetration angle θ formed by the steel plate and the liquid surface immediately before immersion, and the descaling property was evaluated by ranking A, B, and C. In the figure, white circles indicate that excellent results were obtained on both sides of the steel sheet, black circles indicate that both sides of the steel sheet were inferior, and black triangles indicate that the top surface of the steel sheet was inferior. , The black squares show the results that the lower surface of the steel plate was inferior. As is clear from the figure,
It can be seen that the pickling property is affected by the penetration angle, and A is for all penetration angles θ in the range of 30-60 °.
The result of rank evaluation was obtained. The main cause of this is the effect of bubbles during boiling, and in order to avoid this effect, it is essential to define the penetration angle θ within the range of 30 to 60 °.

Some consideration will be given below to the obtained results. As a controlling factor of the immersion type pickling reaction, the metabolism of the acid solution near the steel plate is slowed down.In the conventional technology, the solution is diffused by providing a turbulent flow promoter such as a jet flow and a shielding plate to solve the problem. . The high-temperature charging pickling method also has the above-mentioned effects. By immersing the heated steel sheet in the acid solution, a boiling phenomenon (nucleate boiling region) accompanied by rapid heat transfer and mass transfer occurs near the steel sheet, and metabolism of the acid solution is promoted. As an effect, assuming that mass transfer can be replaced by heat transfer (heat transfer coefficient), it is estimated that there is about 10 times that due to the addition of a turbulent promoter.

According to the method of the above-mentioned embodiment, the effect of shortening the pickling time to a great extent can be obtained as compared with the conventional method, and the equipment can be made compact. In addition, by controlling the steel plate heating temperature (steel type) in the steel plate heating part and the line speed, dipping time, and hydrochloric acid conditions (temperature, concentration) in the pickling tank part, uniform and good thin steel plate can be stabilized. Can be manufactured in a simple manner.

Next, referring to Table 2, the effects will be described while comparing the embodiment of the present invention with the comparative example. In Table 2, the steel plate heating temperature was variously changed and the deformation and the meandering of the plate shape were evaluated. The comprehensive evaluation is determined in consideration of the evaluation of the plate shape collapse and the meandering. In the table, circles indicate good results, triangles indicate results that are not particularly problematic for practical use, and cross marks indicate results that are problematic for practical use.

Good results were obtained in the temperature range of the steel sheet heating temperature of 100 to 300 ° C., but at 350 ° C. and 400 ° C. in which the temperature range of 300 ° C. or higher was reached, the shape of the plate was distorted (local difference due to temperature difference, etc.). Distortion of plate shape due to buckling deformation)
Is too large to be put to practical use. In this way, the steel plate heating temperature (300 ° C or higher) and the acid liquid temperature (80 to 90
It has been found that when the temperature difference between the temperature and the temperature is 250 ° C. or more, the plate shape is collapsed due to a rapid temperature change and the sheet passing property is deteriorated. Further, when the steel sheet is heated to 100 ° C. or higher, waist bending (buckling which is a product defect of thin steel sheet) occurs,
As in the embodiment of FIG. 1, the path is vertical and the roll diameter is restricted (φ ≧ 0.32) to solve the problem.

By carrying out and adopting the above, it becomes possible to shorten the pickling time and make the equipment compact, and it is possible to manufacture a steel sheet having a good pickling finish and excellent surface properties. The technique of the present invention can be applied to a descaling method for all metal materials.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

According to the present invention, the induction heating device is installed in the preceding stage of the pickling tank, and the steel sheet charged into the pickling tank is heated to a temperature range not lower than the boiling point of the acid solution to perform descaling treatment. As a result, it is possible to significantly shorten the pickling time and the number of pickling tanks, and it is possible to significantly reduce the cost of equipment.

Further, by controlling the steel sheet heating temperature (steel type) in the steel sheet heating section and the line speed, immersion time, and hydrochloric acid conditions (temperature, concentration) in the pickling tank section, uniform and good thinness can be achieved. A steel plate can be manufactured stably.

In particular, it is possible by providing a sink roll in the pickling tank, controlling the immersion time of the steel sheet in the liquid by the sink roll, and controlling the acid solution concentration control and the steel plate temperature control.

Furthermore, a heat exchanger is provided in the pickling tank to prevent the temperature rise of the liquid due to the high temperature charging pickling method, and the recovered hot water is used as the rinse water on the outlet side to save energy. Can be planned.

[Brief description of drawings]

FIG. 1 is a schematic view showing a part of a pickling line in which a pickling apparatus for thin steel sheets according to an embodiment of the present invention is used.

FIG. 2 is a graph showing the results of responsiveness in each pickling tank.

FIG. 3 is a graph showing the results of evaluation of descaling property based on the required supply amount of acid solution.

FIG. 4 is a graph showing the results of examining the correlation between the steel plate heating temperature and the descaling property.

FIG. 5 is a graph showing the results of examining the correlation between the steel plate penetration angle and the descaling property.

FIG. 6 is a schematic view showing a conventional pickling apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Steel plate, 12 ... Bridle roll, 13 ... Induction heating device, 15 ... Thermometer, 16 ... Pickling tank, 17 ... Sink roll, 18 ... Fixed roll, 20 ... Rinse tank, 22 ... Waist-bending prevention roll, 30 ... Calculation Part, 40 ... Control part.

Claims (6)

[Claims] 1. A steel plate heating unit for heating a steel plate, a pickling tank unit in which the steel plate is immersed, and an acid solution circulation tank unit for controlling the concentration and temperature of the acid solution, and the steel plate is continuously descaled. A pickling device for a thin steel plate to be processed, wherein the steel plate heating unit is a steel plate heating device provided between the bridle roll and the pickling tank on the side of the pickling tank, and the temperature of the heated steel plate. A thermometer for measuring, and a waist bending prevention roll, and, the pickling tank part, a sink roll for steel plate immersion time control, an acid solution from the bottom of the pickling tank part, scale, and other And a means for discharging insoluble matter, wherein the circulation tank section is provided in a lower portion of the pickling tank section, and the acid solution for adjusting and controlling the concentration and temperature of the acid solution in the upper pickling tank. Circulates and supplies it to the upper pickling tank, and has a heat exchanger to recover the exhaust heat transferred from the steel plate to the acid solution. A pickling device for thin steel sheets, which is characterized by: 2. Further, a steel type, a steel plate temperature, a sink roll position, and an acid solution condition are inputted as detection data or initial setting data, and a calculation unit for calculating a steel plate heating temperature and a steel plate immersion time based on these input data, The heating operation of the steel plate heating part is controlled based on the steel plate heating temperature, and the steel plate is heated to a temperature range in which the acid liquid contacting the steel plate during the steel plate immersion is in the nucleate boiling state before the steel plate is immersed in the steel plate. 2. A pickling apparatus for thin steel sheet according to claim 1, further comprising: a control unit that controls a sink roll operation based on the control unit to adjust the immersion depth of the steel sheet. 3. A pickling method for a thin steel sheet, comprising heating a steel sheet, immersing the heated steel sheet in an acid solution, and continuously performing descaling, wherein the acid solution in contact with the steel sheet during immersion is in a nucleate boiling state. A method for pickling a thin steel sheet, which comprises heating the steel sheet to a temperature range of 1% before being immersed in the acid solution, and immediately immersing the steel sheet in the acid solution. 4. The steel plate heating temperature is set in the range of 100 to 300 ° C., and when the steel plate is immersed in a hydrochloric acid solution containing an inhibitor, the steel plate penetration angle as an acute angle between the liquid surface and the steel plate is 30 to 60 °. It is set as the range.
A method for pickling a thin steel sheet as described above. 5. The thin steel sheet according to claim 4, wherein a hydrochloric acid solution having a concentration of 4.0 to 8.0% by weight is circulated and supplied to the pickling tank section at a rate of 60 to 150 kg per ton of steel sheet. Pickling method. 6. A steel plate heating unit for heating a steel plate, a pickling tank unit in which the steel plate is immersed, and an acid solution circulating tank unit for controlling the concentration and temperature of the acid solution, and continuously descaling the steel plate. A pickling device for a thin steel plate to be treated, wherein the steel plate heating unit is a steel plate heating device provided between the bridle roll and the pickling tank on the side of the pickling tank, and the temperature of the heated steel plate. A thermometer for measuring, and a waist bend preventing roll, and the pickling tank part, a sink roll for steel plate immersion time control,
Means for discharging the acid solution, scale, and other insolubles from the lower part of the pickling tank part, the circulation tank part is provided in the lower part of the pickling tank part, and in the upper pickling tank In order to regulate and control the concentration and temperature of the acid solution, the acid solution is circulated and supplied to the upper pickling tank, and a pickling device for thin steel sheets having a heat exchanger that recovers the exhaust heat transferred from the steel sheet to the acid solution When a steel sheet is subjected to pickling treatment using, a hydrochloric acid solution containing an inhibitor and having a concentration of 4.0 to 8.0% by weight is circulated and supplied to the pickling tank portion at a rate of 60 to 150 kg per ton of the steel sheet. The heating temperature is set in the range of 100 to 300 ° C., and the steel plate is immersed in the hydrochloric acid solution so that the steel plate penetration angle as an acute angle formed by the acid liquid surface and the steel plate is in the range of 30 to 60 °. Pickling method for thin steel sheet.