JP2005171293A - Preliminary pickling method and device for steel strip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the pickling rate in continuous pickling by allowing the parts from which scale is hard to be removed in the vicinities of the outward-inward coiling parts and both end parts in the sheet to be subjected to preliminary pickling before pickling. <P>SOLUTION: The preliminary pickling method for a steel strip is characterized in that, before a steel strip is pickled in a pickling line, the steel strip is dipped into a pickling liquid from the pickling line in a coiled state, wherein pickling waste acid from the pickling line is used for the preliminary pickling. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to pickling for removing oxidized scale generated on the surface of a thin steel plate such as a hot-rolled steel plate, and more particularly to a preliminary pickling method for pickling and an apparatus therefor.

  A steel strip (thin steel plate) is manufactured by subjecting a steel piece to a hot rolling process, and an oxide film, that is, an oxide scale, is generated on the surface of the steel strip by hot rolling. When cold rolling or press forming is performed on a hot-rolled steel strip having an oxide scale, the oxide scale is pushed into the steel strip and causes surface defects.

  For this reason, a descaling step is usually provided for the purpose of removing oxide scale after the hot rolling step.

  As a descaling method, a continuous pickling method in which a steel strip is continuously immersed in a pickling bath such as hydrochloric acid or sulfuric acid is widely used.

  In the conventional continuous pickling method, for example, as shown in FIG. 1, a steel strip 1 is fed from a steel strip coil manufactured by hot rolling by a payoff reel 2, and a welding machine 3 is attached to the rear end of the preceding steel strip. The tip of the steel strip to be welded is welded, and the welded steel strip is continuously dipped in the pickling tanks 7 and 8 comprising 5 to 6 tanks via the looper 5, the bride roll 5 and the scale breaker 6. And take up with the tension reel 9. When the steel strip travels in the pickling tank, the scale of the steel strip surface layer is descaled by a chemical reaction with an acid such as hydrochloric acid. As the acid solution in the pickling tank, hydrochloric acid is generally used, and it is known that the higher the concentration and the higher the temperature, the better the descalability, but there are restrictions on actual operations such as equipment and cost. Therefore, it cannot be increased without limitation, and a hydrochloric acid concentration of 4.0 to 15.0% by mass and a temperature of 80 to 90 ° C. are common.

  In such continuous pickling, various techniques for shortening the pickling time and obtaining a steel strip having a good pickling finish have been proposed for the purpose of improving productivity. For example, by installing an induction heating device in the previous stage of the pickling tank, heating the steel sheet charged into the pickling tank to a temperature range above the boiling point of the acid solution, and performing descaling, the pickling tank part There is a high-speed pickling method capable of shortening the installation space and reducing the pickling time (see, for example, Patent Document 1). Moreover, before dipping into the pickling tank in the pickling process of the thin steel plate, pickling method for improving the passing speed of the pickling tank by applying hydrochloric acid to both ends of the plate by dropping or spraying at a high temperature of 80 ° C. or higher. (See, for example, Patent Document 2).

  In addition, the pickling method for cracking the oxide scale before pickling, the pickling method for adding ultrasonic vibration and magnetic vibration to the steel plate immersed in the pickling tank, and the flow of the pickling bath can be changed by a nozzle etc. There are pickling methods for improving the contact state between the steel strip and the pickling solution.

  On the other hand, a wire rod with a different product shape from a steel strip (thin steel plate), a strip steel coil is immersed in a pickling tank and batch pickling is performed to descale the oxide film formed on the wire rod and strip surface. There is a pickling method.

  For example, when pickling a wire, the wire coil is immersed in a pickling tank filled with acid such as hydrochloric acid or sulfuric acid, and after the scale attached to the wire is removed by the acid, the wire coil is pulled from the pickling tank. Deep-fried, washed, neutralized, and lubricated. However, the pickling tank is exposed to the atmosphere, and acid fumes are generated during pickling. For the purpose of repairing this fume without diffusing it into the air, a shield room is provided that is large enough to cover the upper edges of both sides of the pickling tank and high enough to lift the pickled item. There is a pickling device provided with a suction device for reducing the pressure of the water (for example, see Patent Document 3).

  Further, there is a pickling treatment apparatus for wire that allows the pickling solution to easily permeate into the contact portion between the winding portions of the wire coil (see, for example, Patent Document 4).

  However, since the wire coil has a gap between the windings, surface descaling is achieved by immersing the wire coil in the pickling solution, but the steel strip coil has no gap as much as the wire coil between the plates. Similar to the wire coil, the method of immersing the steel strip coil in the pickling solution cannot perform sufficient descaling.

JP-A-7-197282 JP-A-6-128774 Japanese Patent Publication No. 48-30213 Japanese Patent Laid-Open No. 8-302491

  In conventional continuous pickling, in order to improve the pickling capacity, various efforts such as adding a pickling tank and extending the line length, introducing jet pickling and ultrasonic pickling equipment, high temperature coil pickling, etc. However, none of them has a sufficient effect on the amount of capital investment.

  The present inventor found that there is a difficult descaling portion that cannot be easily descaled by continuous pickling of the steel strip coil, in the vicinity of the outer coil inner winding portion and both ends of the plate, and the presence of this difficult descaling portion is an acid. It was found that the improvement of the washing speed was hindered.

  Therefore, the present invention aims to improve the pickling speed of continuous pickling by pre-pickling the steel strip coil outer inner winding portion and the hard-to-retract scale portion in the vicinity of both ends of the plate before pickling. is there.

  When a hot-rolled steel strip is used as a material for continuous annealing, it is advantageous to coarsely precipitate Ti, Nb, C, N, etc. at the hot-rolling stage in order to promote crystal grain growth during annealing. In many cases, winding is used. However, when high-temperature winding is performed, the thickness of the scale becomes thick, and further, during coil cooling, a portion in which air in the air-cooled material is in contact with oxygen in the air and water in the water-cooled material is increased. A portion where the scale thickness increases is generated. The inventor found that the portion where the scale thickness was increased became a difficult-to-scaling part, and in pickling, the difficult-to-scaling part governed the plate-feeding speed, so that the overall plate-passing speed was reduced to reduce the acidity of continuous pickling It was found that the washing speed was hindered.

  Therefore, the present inventor started pickling based on the idea that the continuous pickling speed can be drastically improved if the difficult-to-descale portion of the steel strip coil can be removed by preliminary pickling before continuous pickling. High-temperature hot-rolled coils that have already completed the hot-rolling process at the work-in place are stored for several hours to several tens of hours, so the storage time at the work-in place is effectively used for preliminary pickling and discharged by continuous pickling. The present invention has been completed by discovering that the refractory scale of the steel strip coil can be removed by preliminary pickling in advance by effectively utilizing the waste liquid to be used for preliminary pickling.

  The gist of the present invention is as follows.

  (1) A method for pre-pickling a steel strip, wherein the steel strip is immersed in a coiled state in a pickling solution from the pickling line before the steel strip is pickled in the pickling line.

  (2) The steel strip preliminary pickling method according to (1) above, wherein the coil is a hot-rolled coil.

  (3) The pickling method for steel strip according to (1) above, wherein the pickling solution from the pickling line is pickled waste acid.

  (4) The pre-pickling method for steel strip according to the above (1) or (2), wherein the pre-pickling solution which is a pickling waste solution is a hydrochloric acid solution having a concentration of 4% or less.

  (5) The pre-pickling method for a steel strip according to (4), wherein the pre-pickling solution contains 0.5% or more of a corrosion inhibitor.

  (6) Any of (1) to (5) above, wherein the temperature and concentration of the preliminary pickling solution are measured, and the immersion time of the coil in the preliminary pickling solution is adjusted based on the measured values. The pre-pickling method for steel strips as described in 1.

  (7) A pre-pickling solution tank, a rinsing water tank and a pre-pickling tank supplied with pickling waste liquid from the pickling line, and a pre-pickling solution and rinsing water tank from the pre-pickling solution tank A pre-pickling apparatus for steel strip, comprising a supply pipe for supplying rinsing water from the pre-pickling tank.

  (8) The steel strip preliminary pickling apparatus according to (7) above, further comprising a fume recovery device that recovers fumes generated from the preliminary pickling tank in the preliminary pickling step using a fume aggregating device.

  (9) The thermometer which measures the temperature of the pickling liquid in a preliminary pickling tank, and the concentration meter which measures the density | concentration of a pickling liquid are provided, The said (7) or (8) characterized by the above-mentioned Pre-pickling equipment for steel strip.

  During winding of the hot-rolled coil and subsequent cooling, difficult-to-scaling portions occur at both ends of the coil and at the top (front end) and bottom (rear end) of the coil, impeding the plate passing speed of the continuous pickling process. However, it is possible to drastically improve the sheeting speed of the pickling process, that is, the pickling speed by removing the difficult-to-scaling portion generated in the hot rolled coil prior to the pickling process by preliminary pickling. . And the capital investment for pickling capability improvement, such as the extension of a pickling tank and extending a line length, becomes unnecessary by improving a pickling speed.

  In the preliminary pickling, the low concentration (less than 4%) hydrochloric acid, which is the waste liquid of continuous pickling, can be used effectively, and the time that the hot-rolled coil is allowed to cool for several hours to several tens of hours in the in-process storage area is pre-pickled. It can be used effectively in time.

  Furthermore, the preliminary pickling can be effectively performed using the heat stored in the hot coil, and the temperature of the hot coil can be quickly cooled to a temperature of 130 ° C. or less suitable for continuous pickling.

  Hereinafter, the present invention will be described in detail.

  The hot-rolled steel strip in the hot rolling process is often wound at a high temperature. That is, since the material for continuous annealing promotes the growth of crystal grains during annealing, it is advantageous to deposit Ti, Nb, C, N, etc. in the hot rolling stage, so that high temperature winding is performed.

  When high-temperature winding is performed, the thickness of an oxide film (called a so-called scale) formed on the surface of the steel strip increases.

  FIG. 2 is a diagram illustrating the relationship between the hot rolling coiling temperature and the scale amount.

  The steel strip after the hot finish rolling is completed is cooled by water cooling or air cooling to a predetermined winding temperature and wound. Although the growth of the scale thickness varies depending on the cooling method, as shown in FIG. 2, the scale amount increases as the hot rolling coiling temperature increases. As an influence of the cooling method, the scale thickness becomes thicker in the air hollow cooling than in the water cooling. This phenomenon is considered that the scale thickness grows due to the steel strip reacting with oxygen in the atmosphere during cooling. On the other hand, in the case of water cooling, the scale thickness grows by reaction with oxygen in the water, but because there is less oxygen in the water than in the atmosphere, the scale thickness growth is lower in the water cooling in the temperature range of 630 ° C. or higher. . However, in a temperature range lower than 630 ° C., the water-cooled material has a larger scale thickness than the air-cooled material.

  It has been found that, by any of the cooling methods, the high-temperature winding material has a thick scale, and in particular, a portion where the scale thickness increases is generated in the coil width direction.

  FIG. 3 is a diagram showing the scale growth of the hot-rolled plate profile and the winding coil. FIG. 3 (a) is a schematic view showing the overlap of the hot-rolled coil profile having a plate crown. It is.

  As shown in FIG. 3A, for example, in a hot rolled sheet 10 having a plate width of 1500 mm, a body crown portion 11 having a width of about 150 mm and an edge drop portion 12 having a width of about 20 mm are inevitably formed at both ends.

  When this hot-rolled sheet is wound around a coil, it is wound into an overlapping state as shown in FIG. In such a coil, there are a portion 13 where the edge drop overlaps and a portion 14 where the body crown overlaps at the end, and a gap is formed in this overlapping portion. As for the scale growth of the winding coil, the overlapping portion 13 of the edge drop is cooled at the outermost edge and the temperature is low, so that the scale growth after winding is suppressed, but the overlapping portion 14 of the body crown is The scale grows considerably after winding because it is kept warm and has a lot of oxygen supply.

  Further, the portion 15 where the flat portion overlaps is a central portion and is well kept by preheating, and thus becomes a high temperature portion. However, since there is no overlap and there is no air gap, scale growth is suppressed. . However, in the portion where the coil outer winding or inner winding is loose, the scale grows because the oxygen supply is large. There are cases where the coiling temperature is consciously increased in order to ensure the coil temperature of the coil Top (front end) and the Bottom (rear end), which increases the scale thickness. For this reason, a thick scale part exists in the both ends of a hot-rolled coil, and Top and Bottom.

  FIG. 4 is a diagram showing the state of the scale thickness in the width direction of the coil wound at a hot rolling coiling temperature of 650 ° C.

  As shown in FIG. 4, the scale thickness in the plate width direction of the hot-rolled coil (plate width 1500 mm) is generated in the entire plate width direction regardless of whether the cooling method is water cooling or air cooling. It was thick in an area of about 300 mm from the edge including the area corresponding to the overlapping part of the crown. Although this region has a large variation due to the cooling pattern or the like, a portion with a thick scale is a difficult-to-retract scale portion, which regulates the plate-feeding speed in pickling, and causes a decrease in the overall plate-passing speed.

  Similarly, there is a difficult-to-descend portion at the top and bottom in the longitudinal direction of the hot-rolled coil.

  FIG. 5 is a diagram showing a state of thickness in the longitudinal scale of the coil at a winding temperature of 650 ° C.

  Regardless of whether the cooling method is water cooling or air cooling, the scale thickness in the longitudinal direction of the hot-rolled coil (plate width 1500 mm) is that the coil top and bottom windings are gentle and that the temperature is secured from the center to ensure the temperature. There was an operation to increase the target temperature, and there was a difficult-to-descaled portion with a thick scale in the area of about 50 m of Top and Bottom.

  Next, how the difficult descaling part is difficult to descal by pickling will be described.

The scale amount generated when the hot-rolled steel sheet was cooled to 730 ° C. and 580 ° C. by water cooling or air cooling and wound around a coil was determined as an average value of scale amount (g / m ² ). A pickling test was performed on steel sheets with different scale amounts, and the pickling time (seconds) until the scale removal was completed was measured. The results are shown in FIG.

  FIG. 6 is a diagram showing the relationship between the scale thickness (scale amount average) and the pickling time.

As shown in FIG. 6, the pickling time (second) becomes longer as the scale amount average (g / m ² ) increases. This indicates that, in the pickling operation, if the length of the pickling tank and the pickling solution conditions are the same, a material having a large scale thickness cannot be descaled unless the plate passing speed is low.

  Therefore, the top part and bottom part of the coil, which is the part where the scale thickness in the coil longitudinal direction is thick, must be passed at a lower plate speed, and at the middle part in the longitudinal direction, it exists at both ends in the plate width direction. The thicker part of the scale that is forced to force the pickling plate at a lower speed.

  Therefore, in the present invention, the hard-to-descale portion of the steel sheet coil that causes a decrease in the plate speed of continuous pickling is removed (including reduction) by preliminary pickling before the continuous pickling.

  The hot-rolled coil that has finished the hot-rolling process is stored for several hours to several tens of hours for cooling in the work-in place before pickling, so the storage time in the work-in place is used for preliminary pickling. Thus, the preliminary pickling can be performed without affecting the pickling time, and the preliminary pickling effectively uses the low-concentration pickling solution, which is a waste liquid of continuous pickling, and is thick locally over time. Since it is possible to reduce the difficult-to-descal portion in advance, it is possible to improve the pickling speed. In addition, the preheat pickling can be effectively performed by the heat retained in the hot-rolled coil after the hot-rolling process is completed. It is also useful for cooling the coiled coil, and can be 130 ° C. or less suitable for the plate temperature of continuous pickling.

  FIG. 7 is a diagram showing an outline of the preliminary pickling method and apparatus of the present invention.

  First, a predetermined number of coils 17 are hung on an empty pre-pickling tank 16 with a coil lifting tool, and a fume-preventing variable seal lid 18 is moved to the upper surface of the tank and attached to the supply line on the pre-pickling solution tank 19 side. The valve is opened and the pump 20 is activated to allow the acid solution to flow into the preliminary pickling tank 16. The preliminary pickling solution tank 19 is supplied with low-concentration waste acid solution (hydrochloric acid solution having a concentration of 4% or less) from the # 1 tank of the continuous pickling line. The pickling solution is sent to the acid recovery device by starting the pump 21.

  Further, in parallel with the inflow of the acid solution, a corrosion inhibitor (inhibitor) for preventing corrosion of the ground iron is supplied from the inhibitor tank 22 so as to be a predetermined amount, for example, 0.15 to 0.3% of the acid amount. As the corrosion inhibitor, a known one can be used, and as such an inhibitor, there are organic compounds having a shared electron pair in the structure, for example, 1 of primary, secondary, and tertiary amino groups. Inhibitors having a composition containing organic amines containing seeds or more are used, and in particular, corrosion inhibitors containing polyethyleneimine are widely used.

  When pickling is supplied to the preliminary pickling tank 16, the hot coil after hot rolling comes in contact with the pickling, and the acid solution evaporates and fumes are generated. Operate and collect fume. The remainder that could not be collected is exhausted 24.

  The acid solution is supplied up to the coil level, the pump 20 on the pickling supply side is stopped, and the valve is closed. However, the acid solution can be automatically supplied in response to the fluctuation of the solution level.

  In the preliminary pickling, the temperature and concentration of the pickling solution are measured by the pickling bath thermometer 25 and the pickling bath concentration meter 26, and the preliminary pickling time is determined by comparing the measured data with reference data. Pickle. Pickling is selected because the acid solution easily enters the difficult-to-retract scale parts on both ends of the coil and the difficult-to-retract scale parts on the top (front end) and bottom (rear end) of the coil that is loosely wound. In particular, this difficult-to-descale portion can be pickled. Pre-pickling does not require complete descaling.

  After the preliminary pickling is completed, the discharge valve on the discharge system side of the preliminary pickling tank 16 to the preliminary pickling solution tank is opened to return the pickling to the preliminary pickling liquid tank 19, and when completed, the valve is closed.

  Next, the valve on the supply side of the rinsing water tank 24 is opened and the pump 20 is activated to supply rinsing water to the preliminary pickling tank 16 for washing the coils.

  The rinsing water is supplied to the level of the coil, the pump on the rinsing water supply side is stopped, and the valve is closed.

  After a predetermined time, the discharge valve on the discharge system side to the rinse water tank of the preliminary pickling tank is opened to return the rinse water to the rinse water tank 24, and the valve is closed when completed.

  In order to suspend the preliminary pickling coil, the fume discharge system is stopped, the variable seal lid 18 is moved, the preliminary pickling tank is opened, and the coil is suspended by the coil lifting tool. The coil after preliminary pickling is supplied to a continuous pickling line and pickled.

  The fact that the cold time of the hot coil after hot rolling can be shortened by preliminary pickling will be described.

  FIG. 8 is a diagram showing the relationship between the cooling time of the hot coil and the coil temperature.

The relationship between the cooling time (Hr) and the coil temperature (° C.) when the 18 to 20-ton coil of 2.5 m thickness × 4 feet width was cooled from 560 ° C. was investigated. In FIG. 8, the cooling temperature curve of natural air cooling of the three-stage stacked middle coil naturally cooled in the atmosphere at 35 ° C. is indicated by a solid line, and the forced air cooling of the three-stage stacked middle coil that is forced air cooled by injecting air of 7 m ³ / min. The cooling temperature curve is shown by a dotted line.

Also shows a cooling temperature curves of the immersion water cooling in the case where the first coil immersed natural cooling during the hot coil to 60m 3 ⁽³⁰ ℃) water bath by a one-dot chain line.

  As shown in FIG. 8, in order to cool the hot coil to a temperature of 130 ° C. or less suitable for continuous pickling by natural air cooling or forced air cooling, it takes about 70 hours by natural air cooling and about 50 hours by forced air cooling. .

  However, when immersed in water, the hot coil can be brought to a temperature of 130 ° C. or less within a few hours. That is, if the hot coil is subjected to preliminary pickling, the hot coil is cooled with the preliminary pickling solution and cooled to a temperature suitable for continuous pickling in a short time. When pickling hot coils with continuous pickling equipment, pickling efficiency is improved, but there are problems in heat resistance of the steel plate and folding, and pickling at 130 ° C or lower, preferably 90 ° C or lower. In general, it is necessary to cool to 130 ° C. or lower before continuous pickling.

  FIG. 9 is a diagram showing the relationship between the concentration and temperature of hydrochloric acid in continuous pickling and the pickling time.

  In FIG. 9, the concentration of the hydrochloric acid solution containing 1% of the corrosion inhibitor (inhibitor) is adjusted to 0.5%, 1%, 2.5%, 5%, and the temperature of the hydrochloric acid solution is 50 ° C., respectively. Adjusting to 60 ° C, 70 ° C, 80 ° C, and 95 ° C, continuous pickling of the Al killed steel strip was performed. The result is shown in FIG.

  As shown in FIG. 9, it can be seen that the higher the concentration of hydrochloric acid and the higher the pickling temperature, the shorter the pickling time. However, regardless of the pickling temperature, the shortening of the pickling time is almost saturated when the hydrochloric acid concentration is about 4%. Therefore, even if the hydrochloric acid concentration is further increased, the pickling speed is not improved. Rather, the increased concentration of hydrochloric acid increases the corrosion of the equipment, necessitating the need for corrosion protection of the equipment.

  Therefore, it is preferable to perform pickling with a hydrochloric acid solution having a concentration of 4% or less, and the pickling waste solution from the pickling line is a hydrochloric acid solution having a concentration of 4% or less. The following hydrochloric acid solution was specified for use in preliminary pickling.

  Hereinafter, the present invention will be described in detail based on examples.

  The steel strip that has been hot-rolled at the rolling mill is taken up by a coil and stored in a work-in storage area.

  As shown in FIG. 7, a predetermined number (for example, 4 coils) of the hot coil in the work place is hung in the preliminary pickling tank. A plurality of preliminary pickling tanks may be used as necessary. About 1% hydrochloric acid waste liquid from the continuous pickling line is allowed to flow into the preliminary pickling tank until it reaches the level of the coil. In addition, an inhibitor corresponding to 0.8% of the amount of hydrochloric acid is added to the preliminary pickling tank. As the inhibitor, a trade name “Super Hibiron AS-20KS (Sugimura Chemical)”, which is mainly composed of a cationic amine derivative and a sulfur-containing organic compound, was used.

  Table 1 shows the conditions for the preliminary pickling.

  After the preliminary pickling, the pickling solution is discharged from the preliminary pickling tank, and the coil is cleaned by flowing the rinse water from the rinse water tank. After washing, drain the rinse water in the preliminary pickling tank.

  Subsequently, the coil after preliminary pickling is continuously pickled with 4% hydrochloric acid pickling solution.

  In the preliminary pickling and pickling tests, pickling was performed on hot rolled coils of three steel types: Al killed steel (steel grade A), Ti-added salk (steel grade B), Nb, and Ti-added IF steel (steel grade C). .

  Steel type A was 550 ° C., steel type B was 650 ° C., and steel type C was wound at 700 ° C. to form a hot rolled coil. The higher the winding temperature, the thicker the scale.

  The pickling speed in the case of continuous pickling without applying preliminary pickling to the hot rolled coil of each steel type and in the case of performing continuous pickling after applying preliminary pickling were determined. The results are shown in Table 2.

  In the continuous pickling, five tanks of pickling lines were used.

  In Table 2, the ratio was displayed with an average speed of 90 m / min of the pickling line before application of steel type A as 100%.

  As shown in Table 2, the pickling tank passage speed was improved by about 20% by applying preliminary pickling.

  Therefore, according to the present invention, the sheet passing speed can be improved, and thus the production amount can be increased.

It is a figure which shows the conventional continuous pickling method. It is a figure which shows the relationship between hot rolling coiling temperature and the amount of scales. FIGS. 3A and 3B are diagrams showing scale growth of a hot-rolled plate profile and a winding coil, in which FIG. 3A is a schematic view showing an overlap of hot-rolled coil profiles and FIG. It is a figure which shows the state of the width direction scale thickness of the coil wound up by hot rolling coiling temperature 650 degreeC. It is a figure which shows the longitudinal direction thickness state of a coil in the coiling temperature of 650 degreeC. It is a figure which shows the relationship between scale thickness (scale amount average) and pickling time. It is a figure which shows the outline | summary of the preliminary pickling method and its apparatus of this invention. It is a figure which shows the relationship between the cooling time of a hot coil, and coil temperature. It is a figure which shows the relationship between the hydrochloric acid concentration and temperature of continuous pickling, and pickling time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel strip 2 Pay-off reel 3 Welding machine 4 Looper 5 Bride roll 6 Scale breaker 7, 8 Pickling tank 9 Tension reel 10 Hot rolled plate 11 Body crown part 12 Edge drop part 13 Edge drop overlapping part 14 Body crown overlapping part DESCRIPTION OF SYMBOLS 15 The part where a flat part overlaps 16 Preliminary pickling tank 17 Coil 18 Variable seal lid | cover for fume prevention 19 Preliminary pickling solution tank 20, 21 Pump 22 Inhibitor tank 23 Fume coagulator 24 Tank for water for pickling 25 25 Pickling thermometer 26 Densitometer

Claims (9)

A pre-pickling method for a steel strip, wherein the steel strip is immersed in a coiled state in a pickling solution from the pickling line before the steel strip is pickled in the pickling line. The steel strip preliminary pickling method according to claim 1, wherein the coil is a hot rolled coil. The pickling method for steel strip according to claim 1, wherein the pickling solution from the pickling line is pickling waste acid. The pre-pickling method for steel strip according to claim 1 or 2, wherein the pre-pickling solution which is a pickling waste solution is a hydrochloric acid solution having a concentration of 4% or less. The pre-pickling method for steel strip according to claim 4, wherein the pre-pickling solution contains 0.5% or more of a corrosion inhibitor. The temperature and the concentration of the preliminary pickling solution are measured, and the immersion time of the coil in the preliminary pickling solution is adjusted based on the measured value. The steel strip according to any one of claims 1 to 5, Pre-pickling method. A pre-pickling solution tank, a rinsing water tank and a pre-pickling tank supplied with pickling waste liquid from the pickling line, and a pre-pickling solution from the pre-pickling solution tank and a rinsing from the rinsing water tank A steel strip preliminary pickling apparatus comprising a supply pipe for supplying water to a preliminary pickling tank. The pre-pickling device for steel strip according to claim 7, further comprising a fume collecting device for collecting fumes generated from the pre-pickling tank in the pre-pickling step by a fume aggregating device. The steel strip pre-pickling according to claim 7 or 8, further comprising a thermometer for measuring the temperature of the pickling solution in the pre-pickling tank and a concentration meter for measuring the concentration of the pickling solution. apparatus.

Images