JPH0733593B2 - How to prevent discoloration of steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention is a method of performing chemical cleaning or electrolytic cleaning while feeding a long steel material, followed by washing with water, in which the surface is activated by chemical cleaning or electrolytic cleaning. The present invention relates to a method for preventing discoloration of a steel material when washed with water.

[Conventional technology]

There are various types of long steel materials such as steel plates, and they are shipped as products in each process such as hot rolling, cold rolling, annealing, plating, and painting. In each process, for the purpose of cleaning the surface of the steel material, chemical cleaning such as acid cleaning and alkali cleaning and electrolytic cleaning are performed while feeding the steel material. After these cleanings, in order to remove impurities adhering to the steel surface, rinse with water such as industrial water or pure water (rinse)
To be done.

Since the surface of the steel material cleaned by washing with water is activated, corrosion easily occurs, and the product discolors due to rusting. The rusted and discolored steel material not only lowers the product value, but also causes adverse effects on the subsequent processes, such as defective plating. Rusted and discolored steel materials cause a large loss due to a reduction in product yield due to cutting of defective parts (the defective rate may reach several%) and an increase in the number of processes due to re-cleaning. Defective products mainly occur during low-speed operation or when the line is stopped. As measures against these problems, pickling using a looper and continuous annealing equipment called CAL and CAPL have been put into practical use, and the above obstacles have been alleviated.

However, it is not possible to cope with the situation in all cases, and for example, in the production of high-grade steel, discontinuous electrolytic cleaning is performed. In this case, welding is required to wash the next coil, and the line is usually stopped for 3 to 5 minutes, which may cause discoloration of the steel material.

FIG. 1 is a system diagram showing an example of the cleaning process. Steel material 1 such as a steel plate is first chemically cleaned in an alkaline cleaning tank 2, then electrolytically cleaned in an electrolytic cleaning tank 3 by electrodes 3a and 3b, and further in a scrubber part 4 a brush roll 4a and a backup roll.
After the surface is scrubbed by 4b, it is washed with water in the dip tank 5. Cleaning water 6 is continuously supplied to the dip tank 5 from a water supply pipe 7, and is continuously discharged from a conduit 9 by a pump 8 and showered by a scrubber portion 4. While the steel material 1 is passing through the dip tank 5, the steel material 1
The surface of is washed with the washing water 6 in the dip tank 5.

However, in the conventional cleaning process, when the cleaning of one coil is completed, the end of the coil needs to be welded to the next coil, so that the feeding of the steel material 1 is interrupted and the line is stopped. At this time, the supply of the cleaning water 6 is also interrupted at the same time, which causes a problem that the surface of the steel material 1 is likely to be discolored. In order to prevent discoloration of the steel material 1, the discoloration inhibitor may be sprayed in the scrubber part 4, the discoloration inhibitor may be added to the cleaning water 6, or a combination of these may be used. I could not prevent it.

[Problems to be Solved by the Invention]

In order to solve the above problems, the object of the present invention is to prevent discoloration of a steel material whose surface has been activated by chemical cleaning or electrolytic cleaning, and to propose a method for preventing discoloration of a steel material capable of improving product quality and product yield. It is to be.

[Means for Solving the Problems]

The present invention is a method of washing with water after chemical cleaning or electrolytic cleaning while feeding a long steel material, in which the steel material is passed through the cleaning water containing a discoloration inhibitor and washed with water, and the cleaning is performed when the steel material is stopped. This is a method for preventing discoloration of steel, which is characterized by stirring water.

The steel material to be cleaned in the present invention is a long steel material and includes a steel plate, a strip material, a wire material, and the like.

These steel materials are hot rolled, cold rolled, annealed, plated,
It is manufactured through each process such as painting, and in each process, chemical cleaning such as acid cleaning and alkali cleaning and electrolytic cleaning are performed while the steel is being sent out for the purpose of cleaning the surface of the steel. After these washings, in order to remove impurities adhering to the surface of the steel sheet, washing with water such as industrial water or pure water (rinsing) is performed.

In the present invention, in the above-mentioned water washing, while sending out the steel material, the steel material is passed through the wash water containing the anti-tarnish agent to wash the water, and when the delivery of the steel material is stopped, the wash water is agitated to stir the steel material. Prevent discoloration.

Explaining the cleaning process of FIG. 1, the steel material 1 is first chemically cleaned in an alkaline cleaning tank 2, then electrolytically cleaned in an electrolytic cleaning tank 3, and then the surface is scrubbed by a scrubber portion 4 and then washed in a dip tank 5. To be done. The dipping tank 5 is continuously supplied with cleaning water 6 to which a discoloration preventing agent is added from a water supply pipe 7, and is continuously discharged from a conduit 9 by a pump 8 and spray-washed with a scrubber portion 4.
While the steel material 1 is passing through the dip tank 5, the surface of the steel material 1 is washed with the washing water 6 by stirring by supplying the washing water 6 and contact with the washing water 6 by passing the steel material 1.

In the conventional method, the supply of the cleaning water 6 is interrupted when the line is stopped due to welding or the like, but in the present invention, the supply of the cleaning water 6 is interrupted even when the line is stopped due to welding or the like. The washing water 6 in the dip tank 5 is constantly stirred. The washing water 6 may be agitated mechanically with an agitator, or may be a combination of agitation with water supply and agitation with an agitator. In addition to stirring the washing water 6 when the line is stopped, the pump 8
A more preferable result is obtained by discharging the cleaning water 6 from the conduit 9 to continue the showering in the scrubber part 4 by using the pump 10 and discharging the cleaning water 6 from the conduit 11 by the pump 10 to continue the showering at the entrance and exit of the dip tank 5. Is obtained. In this case, the discoloration preventive agent can be replenished to the wash water 6 for showering. The discoloration preventive agent for washing with spray water and the discoloration preventive agent for washing water in the dip tank may be the same or different. Also dip tank 5
The showering at the entrance / exit may be performed with fresh water containing an anti-tarnish agent.

In the figure, the supply direction of the cleaning water 6 and the delivery direction of the steel material 1 are described as countercurrent, but the supply of the cleaning water 6 is performed so that both sides of the steel material 1 are most effectively cleaned. For example, water may be supplied from a direction orthogonal to the delivery direction of the steel material 1.

As described above, in the present invention, even when the delivery of the steel material 1 is interrupted and the line is stopped, the discoloration of the steel material 1 can be prevented by stirring the cleaning water 6.

FIG. 1 shows a cleaning process of an electrolytic cleaning line for cold-rolled steel sheets, which comprises a cleaning process of pickling and rinsing hot coils,
It can also be applied to a cleaning process in which chemical cleaning or electrolytic cleaning is performed alone or in combination.

The discoloration inhibitor used in the present invention is not particularly limited as long as it is a water-soluble discoloration inhibitor which is usually used for steel material 1. For example, polyethylenepolyamines such as pentaethylenehexamine; alkanols such as monoethanolamine. Amines; Cyclic amines such as cyclohexylamine; Aliphatic dibasic acids such as dodecanedioic acid and adipic acid; Oxycarboxylic acids such as citric acid and gluconic acid; Aromatic organic acids such as p-t-butylbenzoic acid; Alternatively, a mixture of these can be used.

The amount of anti-tarnish agent added depends on the anti-tarnish agent used,
Usually, the discoloration inhibitor concentration in the wash water is preferably 50 mg / l to 5,000 mg / l. If it is less than 50 mg / l, the discoloration preventing effect is small, and if it exceeds 5,000 mg / l, it is economically disadvantageous.
The discoloration preventing agent is preferably added to the washing water in advance, but the discoloration preventing agent may be directly injected as it is or as a diluted solution.

The washing water 6 supplied to the dip tank 5 is usually 10 to 95 ° C, preferably 40 to 90 ° C.

Although the supply rate of the washing water 6 to the dip tank 5 depends on the size of the dip tank 5, the average residence time in the dip tank 5 is usually 60 minutes or less, preferably 30 minutes or less. When it exceeds 60 minutes, the flow velocity of the steel material 1 in the dip tank 5 becomes small, and not only the discoloration preventing effect becomes small, but also the cleaning water 6 becomes severely contaminated and the effect of cleaning the steel material 1 is lowered.

It is presumed that the mechanism of action of the present invention makes it easy to supply the discoloration preventive agent to the surface of the steel product by constantly stirring the wash water containing the discoloration preventive agent, and as a result, the discoloration preventive effect is enhanced. .

〔The invention's effect〕

According to the present invention, the steel material that has been subjected to chemical cleaning or electrolytic cleaning is washed with water while constantly stirring the cleaning water to which the discoloration inhibitor is added, so that the steel material whose surface has been activated by chemical cleaning or electrolytic cleaning. Can be prevented from discoloring, and product quality and product yield can be improved.

〔Example〕

 Examples of the present invention will be described below.

Examples 1 to 4 Cut cooling steel plate after electrolytic cleaning (SPCC / SB, 60 mm
X 100 mm x 0.8 mm thickness) was used as the test piece. The test piece was subjected to ultrasonic degreasing with toluene for 30 minutes, wiped off the dirt, further washed with water, immersed in methanol, dried with cool air by a dryer, and then cross-cut with a cutter. On the other hand, after adding the following rust preventive agent to tap water heated to 80 ° C., the above test piece was dipped, stirred with a magnetic stirrer and kept for 5 minutes while giving a flow rate. After 5 minutes, the test piece was taken out, immersed in methanol, and dried with cold air by a dryer.

The treated test piece was visually observed, and the occurrence of rust and discoloration was evaluated according to the following criteria.

◎… very excellent (no rusting or discoloration) ○… excellent (almost no rusting or discoloration) △… somewhat inferior (some rusting or discoloration) ×… inferior (rusting) , Discoloration is remarkable.) The results are shown in Table 1. The following rust preventives were used.

Rust inhibitor I: 95: 5 (weight ratio) mixture of pentaethylenehexamine and gluconic acid Rust inhibitor II: 80: 2 of monoethanolamine and dodecanedioic acid
0 (weight ratio) mixture Comparative Examples 1 to 4 The same procedure as in Examples was carried out except that the rust preventive agent was not added, the dipping method was changed, or the stirring was not performed. The results are shown in Table 1.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a steel material cleaning process. 1: Steel material, 2: Alkaline cleaning tank, 3: Electrolytic cleaning tank, 4: Scrubber part, 5: Dip tank, 6: Cleaning water, 7: Water supply pipe, 8, 10: Pump, 9, 11: Conduit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaharu Kohari 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd. Inside the Kaisha Sakai Works (72) Inventor Takayuki Kondo, 5 Ishizu Nishimachi, Sakai City, Osaka Nisshin Steel Co., Ltd. Inside the Kaisha Sakai Works (72) Inventor Eiji Danji 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd. Inside Kaisha Sakai Works (72) Hideki Muraoka, Nisshin Steel Co., Ltd., Nisshin Steel Co., Ltd. (72) Inventor Masayuki Kobayashi No. 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd. Inside the Kaisha Sakai Works

Claims (1)

[Claims] 1. A method of performing chemical cleaning or electrolytic cleaning while feeding a long steel material, followed by washing with water, in which the steel material is passed through cleaning water containing a discoloration inhibitor and rinsed, and at the time of stopping the steel material, A method for preventing discoloration of a steel material, which comprises stirring washing water.