JP3296241B2 - Chromate treatment method for galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for chromate treatment of a galvanized steel sheet, and more particularly to a reactive chromate treatment method for a galvanized steel sheet.

[0002]

2. Description of the Related Art It is widely practiced to apply a chromate treatment to a steel sheet such as a plated steel sheet to improve corrosion resistance, paintability and the like. For chromate treatment, arrange the treatment tank in the horizontal direction,
In many cases, the processing is performed using a horizontal processing tank in which a steel sheet travels in a horizontal direction in the processing tank. As a chromate treatment with excellent corrosion resistance, use a chromate treatment solution containing nitrate ions or fluorine ions to promote the reaction, spray the chromate treatment solution on the steel plate, and react with the steel plate and the chromate treatment solution to cause a large amount of chromium adhesion There is a reaction type chromate treatment for forming a chromate film.

A reaction type chromate treatment method using a horizontal treatment tank is disclosed in Japanese Utility Model Publication No. 1-14683 and Japanese Patent Publication No.
No. 4430, and the like.

FIG. 4 shows a horizontal processing tank 3 described in Japanese Utility Model Publication No. 1-14683. The chromate treatment solution is
The reactive processing liquid, which is pressurized by the pump 5 from the processing liquid tank 4 and disposed at the upper and lower portions of the steel sheet 1, is supplied to a number of spray devices 6 for spraying the steel sheet, and the chromate processing liquid is directed toward the upper and lower surfaces of the steel sheet 1. Spray and perform chromate treatment.
The unreacted chromate treatment liquid on the steel plate is squeezed out by the squeezing roll 12 on the outlet side of the treatment tank 3 and returns to the treatment liquid tank 4 again via the tray 9.

[0005] In the reaction type chromate treatment, the treatment unevenness is liable to occur, and the amount of chromium adhering is liable to fluctuate due to changes in operating conditions. The degree is affected by the type of plating of the steel sheet to be treated, the composition of the plating layer, the composition of the treatment solution, and the like.

[0006] Fluctuations in the amount of chromium deposited and unevenness in treatment not only affect various qualities of the steel sheet after chromate treatment, such as corrosion resistance and paintability, but also change the color tone in appearance and impair the commercial value. Is preferably as small as possible.

The treatment liquid is sprayed onto the steel sheet using a spray nozzle. In order to prevent the occurrence of processing unevenness, spray headers are arranged in multiple stages in the traveling direction of the steel sheet and opposed to the steel sheet in the longitudinal direction of each spray header. A large number of spray nozzles for spraying the processing liquid on the side to be processed are attached at predetermined intervals.

[0008] In the reactive chromate treatment, the amount of chromium deposited changes as the treatment time changes. In the case of performing a chromate treatment in a continuous steel plate processing equipment, the line speed cannot always be kept constant, so the number of spray headers arranged in multiple stages is adjusted according to the line speed.

As shown in FIG. 5, a horizontal processing tank is usually used to prevent the processing liquid blown out from a large number of spray nozzles 8 attached in the longitudinal direction of the spray header 7 (in the width direction of the steel plate) from scattering outside the tank. Removable lid 1 on top of tank 3
0 is a box-shaped structure. The lower surface of the lid is inclined from the center to the end of the steel plate, so that the processing liquid attached to the lower surface of the lid flows outward along the lower surface of the steel plate in the width direction of the steel plate, and adheres to the lower surface of the lid. The shape is such that the treatment liquid does not drop on the upper surface of the steel plate to cause the treatment unevenness.

The following technique is disclosed for preventing the occurrence of processing unevenness. (1) In the processing tank shown in FIG. 5 described above, the processing liquid blown out from the spray nozzle of the lower spray header disposed outside the end in the width direction of the steel sheet goes over the steel sheet,
Based on the finding that the processing liquid that hits the lower surface of the lid of the processing tank is dropped on the upper surface of the steel plate to cause processing unevenness, Japanese Patent Application Laid-Open No. Hei 6-277585 discloses that, as shown in FIG. cover the lower spray header 7 spray nozzles 8 of the _B located outside the end portion, in accordance with the steel plate width running, by providing a shielding member 11 of the adjustable retractable by a winding mechanism (not shown) The treatment liquid blown out from the lower spray nozzle is prevented from flowing above the steel plate 1 (Prior Art 1).

(2) In Japanese Patent Publication No. 5-34430, a large number of spray booths are arranged, and when the line speed is reduced, the spraying of the preceding spray booth is stopped, thereby preventing a change in the amount of coating film to be processed. It is described that the occurrence of processing irregularities in the form of drops on the lower surface of the steel sheet when the spray is stopped is prevented (Prior Art 2).

[0012]

In recent years, various types of electrogalvanized steel sheets have been developed. These steel sheets are often manufactured by using the same manufacturing equipment as ordinary electrogalvanized steel sheets and exchanging a plating solution in a plating bath.

When the plating solution is exchanged, the production is stopped and the plating tank is cleaned during the exchange of the plating solution so that the plating solution before the change is not mixed into the plating solution after the change as an impurity. I have. However, even after careful cleaning, a part of the plating solution before the change is mixed into the plating solution after the change as contamination.

For example, when zinc-nickel alloy plating is changed to zinc plating, Ni ions in the plating solution before the change are mixed as impurities into the zinc plating solution after the change.

When Ni ions are mixed in the zinc plating solution, spot-like processing unevenness is liable to occur significantly on the upper surface of the steel sheet during the chromate treatment.

That is, the Ni concentration in the zinc plating solution is 5
At 0 ppm or less, no processing unevenness occurs during the chromate treatment as shown in FIG. Ni concentration is 50pp
If the amount is more than m and less than 100 ppm, light spot-like uneven processing 2 occurs as shown in (b), and if the Ni concentration exceeds 100 ppm, severe spot-like uneven processing 2 occurs as shown in (c). Become.

In the prior art 1, if the Ni concentration in the galvanizing solution exceeds 50 ppm, it is impossible to prevent the above-mentioned processing unevenness occurring on the upper surface of the steel sheet. Further, in the prior art 2, the processing unevenness occurring on the upper surface of the steel sheet is not taken into consideration, and the processing unevenness also occurs on the upper surface of the steel sheet similarly to the prior art 1.

Therefore, when the plating solution is changed from zinc-nickel alloy plating to zinc plating, and chromate treatment is performed after zinc plating, in order to prevent the occurrence of processing unevenness,
The Ni ion concentration in the zinc plating solution after replacement is 50 ppm
It is necessary to reduce it below. In order to reduce the Ni concentration to 50 ppm or less, a long cleaning operation of the plating tank is required, which significantly impairs productivity.

The present invention has been made in view of such circumstances. For example, zinc plating containing a small amount of Ni ions in a plating solution found when the plating solution is changed from zinc-nickel alloy plating to zinc plating. It is an object of the present invention to provide a chromate treatment method that can reduce treatment unevenness on the upper surface of a steel sheet, even in the case of reaction type chromate treatment in which treatment unevenness is likely to occur, such as in the case of reaction type chromate treatment after galvanizing with a solution. .

[0020]

Means for Solving the Problems The present inventors have found that during the above-mentioned reactive chromate treatment in which the above-mentioned process unevenness is likely to occur,
The cause of the spot-like process unevenness generated on the upper surface of the steel plate was investigated in detail. As a result, the processing liquid sprayed on the upper surface of the steel plate due to the occurrence of this processing unevenness collides with the steel plate and scatters,
The treatment liquid scattered in the direction opposite to the steel sheet advancing direction is caused by adhering to the steel sheet, and the spraying direction of the processing liquid is inclined by 15 to 60 degrees from the direction perpendicular to the steel sheet to the advancing direction of the steel sheet, so that the spotted shape Has been found to be able to prevent processing unevenness.

The present invention is based on this finding, and is characterized in that, when a chromate treatment is performed by spraying a reaction type chromate treatment liquid from a spray nozzle onto a steel sheet traveling in the horizontal direction, a spray disposed above the steel sheet is used. Prevents processing unevenness characterized by inclining the spraying direction of the reactive chromate treatment solution sprayed from the nozzle onto the steel sheet by 15 to 60 degrees in the direction of travel of the steel sheet from the direction perpendicular to the surface of the steel sheet.
This is a method for chromate treatment of galvanized steel sheets that can be stopped .

The reason for limiting the present invention will be described with reference to FIG. As shown in FIG. 2A, when the spray angle of the processing liquid is perpendicular to the steel sheet surface, the processing liquid sprayed on the steel sheet upper surface hits the steel sheet 1, and then a part thereof rebounds and scatters. The treatment liquid scattered in the direction opposite to the traveling direction of the steel sheet indicated by A in the figure comes into contact with the steel sheet, and an initial reaction of a chromate reaction occurs. In the case of reactive chromate treatment in which processing unevenness is likely to occur, this initial reaction has a great effect on the subsequent chromate reaction. for that reason,
The chromate film structure at the place where the initial reaction has occurred is different from the chromate film structure at the normal place where the treatment liquid has not scattered. As a result, the appearances after the chromate treatment are different from each other, and the place where the treatment liquid scatters and the initial reaction occurs is recognized as treatment unevenness.

When the spraying direction of the processing liquid is inclined in the direction in which the steel sheet travels, the angle increases and the processing liquid scattered in the direction opposite to the steel sheet traveling direction decreases, and accordingly, spot-like processing unevenness decreases. I do.

As shown in FIG. 2 (b), when the spraying angle (α) is 15 degrees or more, the processing liquid that collides with the steel sheet 1 indicated by B in the figure and then bounces off and decreases,
There is no processing liquid scattered in the direction opposite to the traveling direction of the steel sheet, a uniform initial reaction occurs, and a good appearance without spot-like processing unevenness is obtained.

However, if the spray angle (α) exceeds 60 degrees, the collision pressure of the processing liquid on the steel sheet surface decreases,
The reaction rate of the chromate reaction decreases, and the required amount of chromium cannot be secured. As a result, the color tone difference between the front and back surfaces also increases. Therefore, the spray angle (α) is 1
It must be within the range of 5 to 60 degrees.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In carrying out the present invention, a chromate treatment equipment commonly used for performing chromate treatment by spraying a chromate treatment liquid from a spray nozzle onto a steel sheet traveling in a horizontal direction can be widely used. .
There is no limitation on the number of spraying stages of the processing liquid in the traveling direction of the steel sheet.
It may be one stage or two or more stages.

When the chromate treatment liquid is a reactive type chromate treatment liquid or when the amount of Cr attached is large (for example, C
The effect is greater when r adhesion amount is 20 mg / m ² or more). In the reactive chromate treatment, the chromate reaction is
Since the initial reaction is particularly important, it is essential that the spray angle of the spray nozzle for performing the first spraying be within the range defined by the present invention. If the spray angle of the second and subsequent spray nozzles is also within the range of the present invention, the effect of preventing processing unevenness is more excellent, but in the case of a processing liquid in which processing unevenness is unlikely to occur,
The spray angle for the second and subsequent stages may be a conventional method.

Although there is no particular limitation on the galvanized steel sheet to which the present invention is applied, a steel sheet galvanized with a zinc plating solution containing 50 ppm or more of Ni ions or a zinc plating solution to which an organic brightener is added, which is liable to cause uneven processing. It is suitable when one or both surfaces are subjected to a reactive chromate treatment.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a chromate treatment apparatus, a flat spray nozzle was used for a spray nozzle 4 and a 1/4 manufactured by Kyoritsu Alloy Co., Ltd.
Using KSS-06110 equivalent (discharge rate at 3 kgf / cm ² : 6 l / min, spray angle: 110 degrees), 13 spray nozzles are attached at a pitch of 160 mm in the longitudinal direction of the spray header. Were provided in four stages per zone, for a total of five zones.

When the line speed is 60 mpm and the size is 0.
7 mm x 1400 mm cold-rolled steel sheet is degreased by an ordinary method,
After pickling, zinc plating solution containing no Ni ions or 20
Using a zinc plating solution containing 0 ppm of Ni ions, electrogalvanizing with a plating amount of 20 g / m ² was performed, followed by washing with water and a chromic acid concentration of 10 g / l (Cr ³⁺ / Cr ⁶⁺ ratio =
3), Cl ion concentration: 3 g / l, NO ₃ ion concentration 1
Chromate treatment is performed by spraying a reactive chromate treatment liquid having a concentration of 0 g / l and an F ion concentration of 2 g / l at a temperature of 45 ° C. and a spray pressure of 1.0 kgf / cm ² using the above-described spray apparatus comprising 5 zones. The unreacted chromate treatment liquid was squeezed out with a squeezing roll and dried. For each of the zinc plating solution containing no Ni ions and the zinc plating solution containing Ni ions, when the spray angle (α) of the treatment solution shown in FIG.
The pH of the treatment liquid was adjusted so as to be mg / m ² . The target chromium deposition amount range was 40 ± 5 mg / m ² .

During the chromate treatment, the spraying angle (α) of the treatment liquid shown in FIG. 2B was changed in the range of 0 to 75 degrees, and the occurrence of processing unevenness on the upper surface of the steel sheet and the amount of chromium adhered were investigated. .

The appearance of the processing unevenness was determined by visually observing the appearance of the steel sheet after the processing and determining the degree of the processing unevenness as follows. （(Good): no processing unevenness as shown in FIG. 3 (a) Δ (slightly poor): one with light spot-like processing unevenness as shown in FIG. 3 (b) × (bad): figure As shown in FIG. 3 (c), those having severe spot-like unevenness in processing. The amount of attached chromium was measured by X-ray fluorescence analysis.

FIG. 1 shows the results of the investigation. As is clear from FIG. 1, the spraying angle (α) falls within the range of 15 to 6 within the range of the present invention.
When it is within the range of 0 degrees, no processing unevenness occurs, and the chromium adhesion amount is within the target range.

When the spraying angle (α) is less than the range of the present invention, the zinc plating solution containing Ni ions, which is liable to cause processing unevenness, caused severe processing unevenness after chromate treatment. When the spraying angle is 75 degrees exceeding the range of the present invention, the chromium adhesion amount is 35 mg, which is the lower limit of the target adhesion amount.
/ M ² could not be secured.

[0035]

According to the present invention, even in the case of the reactive chromate treatment in which the processing unevenness is liable to occur, the occurrence of the processing unevenness can be prevented and the yield is improved. In addition, since it is possible to prevent the occurrence of processing unevenness due to the contamination of impurities accompanying the exchange of the plating solution such as when the plating solution is changed from zinc-nickel alloy to zinc plating, the cleaning time for switching can be reduced, and the productivity can be reduced. It also contributes to improvement.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a spraying angle, an external appearance, and a Cr adhesion amount.

FIG. 2 is a diagram illustrating the operation of the present invention.

FIG. 3 is a diagram showing the appearance of processing unevenness and the appearance evaluation.

FIG. 4 is a view showing a horizontal processing tank.

FIG. 5 is a view showing a tank structure of a horizontal processing tank.

FIG. 6 is a diagram showing a processing unevenness prevention device according to Prior Art 1.

[Brief description of reference numerals]

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Processing unevenness 3 Processing tank 4 Processing liquid tank 5 Pump 6 Spray device 7, 7 _B spray header 8 Spray nozzle 9 Receiving tray 10 Cover 11 Shielding member 12 Squeezing roll

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-17279 (JP, A) JP-A-63-7385 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 22/00-22/86

Claims (1)

(57) [Claims] When spraying a reaction type chromate treatment liquid from a spray nozzle onto a galvanized steel sheet traveling in a horizontal direction to perform chromate treatment, the spray direction of the reaction type chromate treatment liquid sprayed onto the steel sheet from a spray nozzle disposed above the steel sheet is changed. Characterized in that the steel sheet is inclined at an angle of 15 to 60 degrees in a traveling direction of the steel sheet from a direction perpendicular to the steel sheet surface .
A chromate treatment method for galvanized steel sheets that can prevent lamination.