JP2000239871A - Cleaning method for steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive method which is capable of rapidly and surely cleaning steel. SOLUTION: In a cleaning method for steel in which steel is immersed in a cleaning solution to remove foreign matters adhered to its surface, gates 2a, 2b each provided with an inclined surface in which the distance from a pass line is gradually reduced in the advancing direction of the steel are arranged facing each other, and the steel is continuously passed through the inclined surfaces of the gates on both sides. Nozzles 4a, 4b for spraying cleaning solution are provided on the inclined surfaces, and preferably the cleaning solutions 5a, 5b are sprayed from the nozzles against the continuously traveling steel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for cleaning steel materials such as hot-rolled steel sheets, cold-rolled steel sheets, surface-treated steel sheets, and wire rods. More specifically, the present invention relates to an efficient cleaning technique applied to pickling, degreasing, cleaning and the like of steel materials.

[0002]

2. Description of the Related Art The oxide scale of steel is removed by pickling. As the pickling solution, an aqueous solution containing 5 to 10% by weight of hydrochloric acid or sulfuric acid or 10 to 20% by weight of phosphoric acid is generally used. An inhibitor is added to the pickling solution in order to prevent the surface of the steel material from being roughened due to peracid cleaning. The scale that is difficult to remove is subjected to electrolytic pickling.
This is intended to improve the pickling efficiency by utilizing stirring of the pickling solution, scale peeling, reduction action, etc. by hydrogen or oxygen generated by electrolysis.

[0003] If fats and oils, iron powder, dust and the like are adhered to the steel material, non-plating, poor coating, indentation flaws, etc. will occur in the next step, resulting in poor product quality and yield. In order to prevent this, a cleaning treatment of the steel material surface is performed as a pretreatment thereof. As the method, generally, an alkaline cleaning method using an alkaline cleaning liquid such as sodium hydroxide, sodium silicate, and sodium phosphate is used. A surfactant is added to the cleaning liquid to reduce the interfacial tension to improve the wettability of the adhered substance, and to promote the penetration, emulsification and dispersion of the cleaning liquid to increase the cleaning efficiency. A chelating agent is also added for the purpose of suppressing generation of deposits such as insoluble scum such as metal soap and metal ion hydrated oxides and carbonates, and preventing electrodeposition of metal ions on the material to be cleaned.

When it is difficult to remove the deposits, brushing or electrolytic cleaning is used together. Electrolytic cleaning, which is often used in finish cleaning, involves passing a steel material between electrode grids in an alkaline cleaning solution with high electrical conductivity, making it extremely clean using the action of microbubbles such as hydrogen and oxygen generated during electrolysis. It is a method to obtain a good surface. These pickled and washed steel materials are further washed away with a solution remaining on the surface of the steel materials using hot water or the like, drained, and dried.

[0005] In recent years, with the increasing demands for higher functionality, higher quality, and higher productivity of various steel materials, importance has been placed on the completeness and higher efficiency of the above-described cleaning work. However, in the method of immersing a steel material in a cleaning solution for cleaning, if the cleaning operation speed is increased, the cleaning becomes insufficient. Therefore, it is difficult to achieve both the quality improvement and the productivity improvement in the current process. In addition, as a method of improving the cleaning efficiency, methods such as strengthening the brushing, increasing the concentration of the cleaning solution, and frequently renewing the solution can be considered. However, these methods increase the cleaning cost and are not always satisfactory by these methods. There is a problem that a proper cleaning result is not always obtained.

[0006] As a method of improving the cleaning work, Japanese Patent Laid-Open No. 8-4 / 1994
JP-A-1667, JP-A-8-53785, JP-A-8-174402 and the like disclose a method of spraying a cleaning liquid or hot water onto steel at a high pressure. Also,
JP-A-9-195075, JP-A-9-23450
No. 7 discloses a method of injecting a cleaning liquid at high pressure into a steel material in the cleaning liquid. Further, Japanese Patent Laid-Open No. 4-3
Japanese Patent Application Laid-Open No. 41590 discloses a method of improving the pickling efficiency by applying strong ultrasonic waves to the surface of a steel sheet via a laminar high-pressure pickling solution column. A method is disclosed in which the steel sheet is wound around a plurality of deflector rolls to impart deformation to the steel sheet, an acid solution is injected into the wound portion, and the steel sheet is heated by an induction heating device to increase the pickling rate.

[0007]

However, according to the study of the present inventors, the methods described in JP-A-8-41667, JP-A-8-53785, JP-A-8-174402 and the like are disclosed. However, although the cleaning efficiency was increased as compared with the immersion method, the productivity improvement margin was still insufficient.

The methods disclosed in Japanese Patent Application Laid-Open Nos. 9-195075 and 9-234507 utilize cavitation generated by a high-speed jet in a solution. However, in this method, cavitation occurs only in the vicinity of the injection nozzle, and there is a problem in that the nozzle may need to be close to the steel plate to obtain a desired effect, so that there is an increased possibility that the steel material contacts the nozzle. In the method disclosed in JP-A-4-341590 or JP-A-9-78273,
There is a problem that the ultrasonic generator and the induction heating device are expensive and cannot be easily applied.

An object of the present invention is to solve these problems,
It is an object of the present invention to provide an inexpensive method for quickly and reliably cleaning steel materials.

[0010]

Means for Solving the Problems The surface of a steel material is treated with a cleaning liquid such as an acid solution or an alkaline solution (hereinafter, also simply referred to as "cleaning liquid") by using an oxide scale, oil and fat, iron powder, dust, etc. Wet the kimono) or dissolve a part of it, penetrate the cleaning liquid into the inside of the deposit and the interface between the deposit and the steel, and weaken the adhesion to the steel to remove the deposit Being clean. Therefore, if the penetration of the cleaning liquid into the deposit and the diffusion of the dissolved deposit into the cleaning liquid are promoted, the cleaning efficiency is improved.

The present inventors have conducted detailed studies on the mechanism of cleaning the surface of a steel material when the steel material is immersed in a cleaning solution for cleaning in order to improve the cleaning efficiency of the steel material. As a result, the following findings were obtained. .

On the surface of the steel material in the cleaning solution, there is generated a concentration boundary layer in which the concentration of an acid, an alkali, or the like is low, and the concentration of the attached matter dissolved is high. When the concentration boundary layer develops on the surface of the steel material, the cleaning solution penetrates the adhering substance, and the dissolving speed of the adhering substance decreases, so that the cleaning efficiency decreases.
Therefore, in order to enhance the cleaning effect by the immersion cleaning method, it is necessary to destroy the above-mentioned concentration boundary layer and maintain good penetration of the cleaning liquid into the deposit and diffusion of the deposit into the cleaning liquid.

[0013] In the vicinity of the surface of the continuously running steel immersed in the cleaning liquid, there is an entrained flow region in which the speed difference from the steel becomes smaller as approaching the surface of the running steel. The entrained flow contributes to the formation of the concentration boundary layer, and the turbulence is generated close to the surface of the steel material to destroy the concentration boundary layer on the surface of the steel material. In order to easily and inexpensively generate turbulence on the surface of the steel material, it is preferable to provide a turbulence promoter (hereinafter, simply referred to as a "weir") which is close to the surface of the steel material and hinders the flow of the liquid.

The surface of the weir facing the steel material pass line (hereinafter, also simply referred to as "weir bottom surface") is preferably an inclined surface whose distance from the pass line gradually decreases in the steel material advancing direction. By providing such a slope on the bottom surface of the weir, the flow path of the accompanying flow generated on the surface of the continuously running steel material becomes narrow near the outlet of the weir, and the pressure of the liquid near the outlet of the weir increases.

[0015] On both sides of a steel material pass line (hereinafter, also simply referred to as "pass line"), such a weir is provided at a target position with the pass line interposed therebetween. By applying pressure, the steel material can be held at an intermediate position between the dam bottoms on both sides of the pass line. Therefore, even if the interval between the weir outlets is narrowed, the steel material can be continuously run without contacting any of the weirs. That is, by making the bottom surface of the weir such a shape, it is possible to narrow the interval between the outlets of the weirs on both sides and generate a sufficient turbulent flow behind the weir.

By spraying the cleaning liquid from the bottom surface of the weir toward the surface of the steel material, the destruction of the concentration boundary layer is promoted and the turbulence behind the weir is caused by the effect of the collision of the jet stream on the steel material surface and the increase of the liquid outflow velocity on the weir side. A flow generation accelerating effect is obtained, and the cleaning efficiency can be further improved.

The present invention has been completed on the basis of these findings, and the gist of the invention lies in the following methods (1) and (2) for cleaning steel materials.

(1) A method for cleaning a steel material in which foreign substances adhering to the surface are removed by immersion in a cleaning solution, wherein the distance between the steel material pass line and the pass line in the cleaning solution gradually decreases in the direction in which the steel material advances. A method for cleaning steel, characterized in that weirs having inclined surfaces are provided opposite to each other, and the steel material is allowed to run continuously by passing between the inclined surfaces of the weirs on both sides.

(2) The nozzle according to (1), wherein a nozzle for jetting a cleaning liquid is provided on the inclined surface, and the nozzle jets the cleaning liquid onto the steel material which is continuously running. The method for cleaning a steel material according to item 1.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiment of the present invention will be described below in detail by taking a case where a cleaning object is a steel plate as an example. The case of a wire is the same as the case of a steel material such as a steel plate, except that the weir is disposed at a point-symmetric position.

FIG. 1 is a sectional view conceptually showing the positional relationship between the steel plate 1 in the cleaning liquid and the weirs 2a and 2b according to the embodiment of the present invention. As shown in FIG. 1, weirs 2 a having, on the upper and lower sides of a steel plate 1 running on a pass line, bottom surfaces 3 a and 3 b formed of slopes having an inclination angle θ with respect to the pass line, and having a thickness t. And a weir 2b.

The distance between the steel plate 1 and the bottom of the weir is large on the entrance side of the weir and small on the exit side. The minimum distance between the weir side and the steel sheet surface is h. As shown in FIG.
The vehicle is continuously driven through the middle between the bottom surfaces of both weirs.

FIG. 3 is a graph conceptually showing the change of the pressure exerted by the cleaning liquid on the steel sheet 1 along the running direction of the steel sheet on the upper surface of the pass line. Cleaning liquid near the steel plate surface includes
A wake flow F accompanying the traveling steel material is generated, but the pressure of the cleaning liquid brought as the wake flow F is increased due to a decrease in the distance between the steel plate 1 and the bottom surface 3a from the entrance side to the exit side of the weir 2a. It gets higher toward the exit side. A similar pressure change occurs in the cleaning liquid on the lower side of the pass line. Steel plate 1
Since the pressure having such a distribution acts on the upper and lower surfaces of the steel plate 1, the steel plate 1 is held at an intermediate position between the weirs on both sides. Therefore, even if the interval h at the outlet of the weir is reduced, the steel sheet can be continuously run at a high speed without contacting the weir.

At the outlet of the weir, since the flow path of the accompanying flow rapidly expands, a vortex is generated behind the weir, and the pressure on the steel plate surface fluctuates remarkably. This rapid pressure change promotes the penetration of the cleaning liquid into the deposit and the diffusion of the deposit into the cleaning liquid, thereby improving the cleaning efficiency.

FIG. 4 is a sectional view showing the dimensions of a model used by the present inventor to investigate the effect of the size and shape of the weir on the pressure fluctuation of the cleaning liquid. The average flow velocity of the water in the portion where there is no weir is considered as the steel sheet passing speed, and the weir bottom surface 3a and the lower wall G when the water flows at various flow rates through the flow path provided with the weirs of various dimensions.
The pressure increment (ΔP ₁ ) occurring between the _two and the maximum pressure fluctuation width behind the weir (ΔP ₂ ) were measured. The pressure was measured by an electronic manometer using a 0.5 mm diameter pressure measurement hole (both not shown) provided at regular intervals on the lower wall G.

[0026] Of the obtained measurement values, [Delta] P ₁ is the average when weir no dynamic pressure pV ^2/2 (where, [rho: liquid density, V: average flow velocity) as a reference value, obtained at each measurement conditions The case where the increment of the measured value with respect to the reference value is 0.5% or more of the reference value is ○, the case where it is 0.1% or more and less than 0.5% is Δ, and the case where it is less than 0.1% is ×. Was evaluated.

FIG. 5 shows a weir bottom inclination angle θ with respect to ΔP ₁ .
(°), the thickness t (mm) of the weir, and the shortest distance h between the weir and the steel plate
6 is a graph showing the effect of the ratio h / t to (mm). FIG.
As can be seen from FIG. 7, ΔP ₁ increases when the inclination angle θ of the bottom surface of the weir is less than 50 ° and the installation position of the weir is 1.
This is the case where the relationship of 6 or less is satisfied.

Although θ may be 0 °, if ΔP ₁ is too small, it is difficult to hold the steel plate between the weirs, so it is preferable that θ is 3 ° or more.

The inclination angle θ of the bottom surface of the weir is preferably 35 ° or less, h / t is preferably 1.4 or less, and more preferably, these values are (35h / t + 1.6θ) ≦ 1.6 ×
A condition range that satisfies the relationship of 35 is good.

FIG. 6 is a graph showing the effect of θ and h / t on ΔP ₂ . △ P ₂ likewise, the case where the maximum pressure fluctuation range is not less than 0.1% of the reference value (the average dynamic pressure ^{ρV 2/2) ○, 0.05} % or more, less than 0.1% The case was evaluated as Δ, and the case of less than 0.05% was evaluated as ×.
△ for the P _2, it is better h / t is small. It is preferably 1.2 or less, more preferably 0.5 or less. h
/ T is preferably 0.01 or more.

If h is excessively small, the steel sheet may come into contact with the weir during the passing and flaws may occur in the steel sheet.
m or more. More preferably, it is good to be 10 mm or more. The thickness t of the weir may be 500 mm or less, and the lower limit is preferably 20 mm or more.

By providing a weir under such conditions,
The penetration of the cleaning liquid into the interface between the deposit and the steel sheet and the diffusion of the dissolved deposit into the cleaning liquid are promoted, and the cleaning effect is improved.

FIG. 2 is a sectional view showing an example of a weir provided with a nozzle on the bottom surface of the weir according to the present invention. Known shapes such as a circular hole, an elliptical hole, or a slit-like hole in the width direction can be applied to the shape of the nozzle provided on the bottom of the weir, but a circular hole is preferable because the nozzle can be easily processed. When the nozzle shape is a circular hole, the nozzle pitch in the width direction is preferably set to 10 to 20 times the hole diameter. The injection pressure of the cleaning liquid is preferably set to be higher than the dynamic pressure based on the steel sheet speed in order to destroy the concentration boundary layer formed by the flow accompanying the steel sheet.
Therefore, the injection pressure of the cleaning liquid is preferably set to 0.02 MPa or more. More preferably, it is 0.1 MPa or more.

The method of the present invention is applicable to various washing steps for removing oxide scale, oils and fats, iron powder, dust and the like adhering to steel materials such as hot rolled steel sheets, cold rolled steel sheets, surface-treated steel sheets, and wire rods. Applicable.

The cleaning method of the present invention is to provide a weir on both sides of a pass line of a steel material immersed in a cleaning liquid as described above, and to enhance the cleaning effect by utilizing the pressure fluctuation generated thereby. Therefore, the method of the present invention can be applied to a known cleaning method such as pickling, alkali cleaning, electrolytic cleaning, hot water cleaning and the like, in which a steel material is immersed in a cleaning liquid and continuously run to perform cleaning.

The method of the present invention provides a good cleaning effect by providing one set of the above-described weirs on both sides of the pass line or two or more sets of the weirs continuously at appropriate intervals in the passing direction of the steel material. Is obtained. The method of the present invention need not be limited to the use of only weirs, but in addition to weirs, known electrolytic cleaning,
Washing in combination with electrolytic pickling, ultrasonic washing, or the like, or brushing, or other known mechanical washing promoting means is no problem. When used in combination with these other methods, there is an advantage that the cleaning operation can be performed more efficiently.

Depending on the purpose of cleaning, the type of cleaning solution may be a single acid solution such as known sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid or a mixed acid solution thereof, sodium hydroxide, sodium silicate,
It may be used by appropriately selecting from an alkaline solution such as sodium phosphate or warm water. Other conditions are not particularly limited, and may be based on known conditions. For example, the passing speed of the steel plate may be 20 to 400 m / min. Known steel immersion tanks such as a horizontal type and a vertical type can be used.

[0038]

EXAMPLE 1 FIG. 7 shows that weirs 2a and 2b are provided according to the present invention in a pickling tank 6 of a continuous pickling facility for removing a surface scale by immersing a hot-rolled steel sheet in a pickling solution. FIG. 3 is a cross-sectional view conceptually showing a situation in which the user is in a closed state. The hot-rolled steel sheet 1 is immersed in the acid solution 9 of the pickling tank 6 via the entry roll 7 of the pickling tank,
It is bent by the delivery roll 8 and is carried out of the pickling tank, washed with water,
It is led to a device such as neutralization (neither is shown). The distance L between the entrance roll 7 and the exit roll 8 is 32 m,
a, 2b are the entrance rolls 7 to 28 on both sides of the pass line.
Weirs of the same dimensions were provided at three locations, m, 29 m and 30 m. The size of the weir was changed variously for each test number. The acid solution used was a hydrochloric acid solution containing 8.5% by weight of hydrochloric acid and having a temperature of 80 ° C.

Using the equipment described above, C: 0.
High-carbon steel hot-rolled steel sheets having a thickness of 2.6 mm and a width of 923 to 1062 mm containing 5 to 0.6% and Mn: 0.8 to 1.3% are immersed in an acid solution at various passing speeds. And pickled. Visual observation of the surface of the steel plate after pickling, measuring the upper limit of the pickling speed at which the oxide scale on the surface can be sufficiently removed, and taking the improvement rate based on the pickling speed in the conventional method without a weir. investigated. Table 1 shows the obtained results.

[0040]

[Table 1]

As can be seen from Table 1, when the method of the present invention is used, the pickling speed is several meters higher than that of the conventional horizontal immersion pickling method.
数 m / min. Further, even when the passing speed was increased, the steel plate did not contact the weir, and no surface defects such as scratches occurred.

(Example 2) A weir having the same dimensions as those used in Example 1 except that jet holes having a diameter of 2.5 mm were provided at intervals of 30 mm in the width direction at the center in the thickness direction of the bottom surface of the weir. To
Three sets were provided in the same place as in Example 1. A hot-rolled steel sheet similar to that used in Example 1 was subjected to a pickling solution directed from a nozzle toward the steel sheet surface while the steel sheet was running, at a pressure of 0.6 to 4.0 M.
Continuous immersion pickling was performed in the same manner as in Example 1 except that the jet was jetted under the conditions of Pa and a jetting rate of 10 to 25 liters / min per nozzle, and pickling as compared with the conventional method using no weir. The speed improvement fee was investigated. Table 2 shows the obtained results.

[0043]

[Table 2]

As can be seen from Table 2, when the method of the present invention is used, the pickling rate is several to several times smaller than that of the conventional horizontal immersion pickling method.
Improved by several tens m / min. In addition, even during high-speed threading, the steel sheet did not contact the weir and no abrasion occurred.

[0045]

According to the method of the present invention, pickling and degreasing cleaning of a steel material can be performed quickly and reliably. The method of the present invention can be carried out by utilizing conventional cleaning equipment and can be easily modified at a low cost, and is extremely economical because it does not require consumables.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a concept of a positional relationship between a steel plate 1 in a cleaning liquid and dams 2a and 2b according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating an example of a weir having a nozzle provided on a bottom surface of the weir according to the present invention.

FIG. 3 is a graph conceptually showing a change in the pressure exerted by the cleaning liquid on the steel sheet 1 along the running direction of the steel sheet on the upper surface of the pass line.

FIG. 4 is a sectional view showing the dimensions of a model used by the present inventor to investigate the effect of the shape of the weir on the pressure fluctuation of the cleaning liquid.

FIG. 5 is a graph showing the effect of the ratio h / t of the weir bottom inclination angle θ (°), the thickness of the weir t (mm), and the shortest distance h (mm) between the weir and the steel plate on ΔP ₁ . .

FIG. 6 is a graph showing the influence of θ and h / t on ΔP ₂ .

FIG. 7 is a cross-sectional view conceptually showing a situation in which a weir is provided according to the present invention in a pickling tank of a continuous pickling facility for removing a surface scale by immersing a hot-rolled steel sheet in a pickling solution.

[Explanation of symbols]

1 ... steel plate, 2a and 2b ... weir, 3, 3a
··· 3b ··· Weir bottom, 4a and 4b ··· Nozzle, 5a and 5b ··· Cleaning liquid, 6 ··· Pickling tank, 7 ··· Inlet roll, 8 ··· Outgoing roll, 9
... Acid solution, F... Associate flow, G.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3B201 AA08 AB13 AB42 BB04 BB24 BB82 BB92 BB96 CB01 CC01 4K053 PA02 PA12 PA14 QA01 QA04 QA07 RA07 RA15 RA16 RA17 RA19 RA22 RA25 RA27 SA04 TA02 TA03 TA12 TA16 TA18 XA22 XA45 YA

Claims (2)

[Claims] 1. A method for cleaning a steel material in which foreign substances adhered to a surface of the steel material are removed by immersing the cleaning material in a cleaning liquid. A method of cleaning a steel material, wherein weirs having surfaces are provided facing each other, and the steel material is caused to run continuously by passing between inclined surfaces of the weirs on both sides. 2. The method for cleaning steel material according to claim 1, wherein a nozzle for cleaning liquid injection is provided on the inclined surface, and the cleaning liquid is injected from the nozzle to the steel material that is continuously running.