JPS6013093A - Double galvanizing method for providing high corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a finished article of a double-galvanized steel sheet having high corrosion resistance and preventing the stripping of the secondary zinc layer by subjecting the surface of a worked article of a galvanized steel sheet to pretreatments including alkali activation and by carrying out galvanization and chromating. CONSTITUTION:A galvanized steel sheet is worked by roll forming, press forming and welding, and the worked article of the steel sheet is degreased with a degreasing agent for nonferrous metal without stripping the surface zinc layer. It is washed, activated in an alkali bath, and washed. The steel sheet is then galvanized in a galvanizing bath, washed, neutralized, washed, and chromated. Said activation is carried out by immersion in an about 5+ or -1% NaOH soln. at about 25-35 deg.C for about 30-5sec and washing with flowing water at ordinary temp. for about 10sec.

Description

[Detailed Description of the Invention] The present invention relates to a novel highly corrosion-resistant two-layer galvanizing method in which electrolytic galvanizing is directly applied to molded products made from galvanized steel sheets without peeling off the galvanized layer. Galvanized copper plate processed products obtained by roll forming and seam welding of galvanized steel sheets to form seam pipes or press forming into various brackets can be compared to automobile parts, such as galvanized sealed pipes and radiator pipes. , Tsuyu 12 pipes, etc. In particular, high corrosion resistance is required for export cars, etc., and in conventional products processed from galvanized steel sheets, rust occurs on the cut edges and exposed areas of the copper plate at welded parts, accelerating corrosion. Therefore, galvanized steel products are treated with chromate treatment to improve their corrosion resistance, but at present it is not possible to completely prevent rust from non-plated parts. Also, if you try to re-galvanize a galvanized steel product.

In the conventional galvanizing pre-treatment method, so-called hydrochloric acid activation treatment, a zinc film does not form on the single-layer galvanized layer, resulting in a peeling phenomenon, making it difficult to carry out.

The present invention utilizes roll forming, press forming, and
To provide a double-layer galvanized steel sheet product with high corrosion resistance, which is obtained by forming a secondary galvanized layer and a chromate film on a galvanized steel sheet product processed by welding etc. without peeling off the surface galvanized layer. This relates to a secondary galvanizing method, in which the surface of a galvanized steel sheet product is degreased, washed with water, further activated in an alkaline bath, plated in a galvanizing bath, washed with water, neutralized, washed with water, It is characterized by being subjected to chromate treatment.

The galvanized steel sheet products obtained by the highly corrosion-resistant double-layer galvanizing method of the present invention are produced by forming, welding, and other processes using galvanized copper sheets as raw materials as described above, and then subjecting them to conventional dezincing treatment. Since secondary galvanizing is applied directly without any additional coating, the thickness of the galvanizing layer is large, there is no bare metal exposed, and corrosion resistance is significantly improved.

What made this type of secondary galvanizing possible is the adoption of alkali activation in the pre-treatment for secondary galvanizing of processed products. Table 1 shows the pretreatment process in comparison with the conventional method.

As is clear from the comparison in Table 1, the present invention differs from the conventional method in that a degreasing agent for non-ferrous metals is used instead of a degreasing agent for ferrous substrates, that electrolytic degreasing is omitted, and that A particular feature of this method is that an alkali is used as the activating agent, and two-layer galvanizing can be performed by an alkali activation treatment.

After the water washing treatment shown in Table 1, electroplating is carried out in the same manner as in the conventional method, such as metal zinc (5 to 12 g/Ω) and caustic saw Table 1 (120±30 g/A), followed by water washing. .

Dry to make a product.

In addition, in conventional galvanizing baths, when the processed product is pipe-shaped, efforts are made to use an auxiliary electrolyte to uniformly plate the inside of the pipe, but in the case of a single method, most of the work has already been done. Since the zinc plating remains on the inner wall surface, there is no need to do so.The subsequent chromate treatment forms a chromate film on the surface of the galvanized surface, increasing the corrosion resistance of the pipe to 6~6.
This is a sevenfold improvement.

An example of a salt water spray n test as a corrosion resistance test is shown below.
It is as shown in Table 2.

As is clear from the comparison between Example 1 and Comparative Example 1 in Table 2, the pipes that were double-layered galvanized by the method of the present invention and further chromate-treated had an almost rust-free outer surface and an inner surface of the pipe. However, even if colored chromate was applied after secondary galvanizing using the conventional method, the corrosion resistance of the outer surface of the pipe was good, but no effect of surface treatment was observed on the inner surface. There was a lot of rust.

Table 2 The highly corrosion-resistant two-layer galvanizing method of the present invention is characterized by a pretreatment accompanied by alkali activation treatment, which enables two-layer plating of galvanized copper sheet products, which has never been attempted before. This resulted in an excellent product with extremely high corrosion resistance.

Claims (1)

[Claims] 1. Roll forming and press forming from a galvanized rust plate. The surface of galvanized steel products processed by welding etc. is degreased, washed with water, and then activated in an alkaline bath. After plating in a water washer and galvanized bath, washed with water, neutralized, washed with water, and subjected to chromate treatment. High corrosion resistance double layer galvanizing method for galvanized steel products.