JPS6130677A - Surface treatment of metal - Google Patents

Abstract

PURPOSE:To form a film having superior corrosion resistance, heat resistance and toughness by galvanizing an iron base, chromating it, coating the resulting chromate film with a heat resistant paint having a specified composition contg. Al powder, and baking the paint. CONSTITUTION:The surface of an iron base 1 is galvanized to form a Zn film 2 for preventing corrosion, and a chromate film 3 is formed on the film 2 by chromating as an under layer for giving a fine appearance and improving the adhesion. The chromate film 3 is coated with a heat resistant paint consisting of 10-15wt% Al powder, silicone resin, alkyd resin and an aromatic solvent, and the paint is baked to form a paint film 4. Since the chromate film 3 is protected with the paint film 4 contg. Al, the corrosion resistance, heat resistance and toughness are remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a surface treatment method for preventing corrosion of metal, particularly steel parts (eg, bolts, nuts, and other screws).

Conventional technology The most common anticorrosion treatment for steel parts is zinc plating, which has a large rust prevention effect and is inexpensive. In order to improve corrosion resistance, give the zinc plating a beautiful appearance, and improve adhesion as a paint base, most zinc plating is now subjected to chromate treatment.

Chromate treatment is a method of chemically depositing a film of zinc chromate on top of the galvanized film.The film is a gel-like hydrate, which is softer than metal and easily scratches. be. However, if the scratches are shallow, the reoxidation power of the chromate film has the ability to protect the galvanized film, but there are limits to this, and when external forces are applied to chromate-treated steel parts during use, In many cases, the chromate film on the surface is destroyed and a sufficient rust prevention effect cannot be expected.

Furthermore, chromate films also have problems in terms of heat resistance and water resistance. For example, if the temperature exceeds 350°C, it becomes powdery and easily falls off, and if it is continuously exposed to a temperature of 130＠C or above, the anticorrosion ability against the galvanized film disappears. Furthermore, when immersed in hot water or water for a long time, the chromate film swells and collapses, resulting in a loss of corrosion resistance.

Problems to be Solved by the Invention In order to solve the above-mentioned drawbacks of the chromate film, it is known to protect the chromate film by coating it with a coating, but in this case, what kind of film is most effective? The question is whether there is.

The inventor of the present invention conducted extensive research and conducted numerous tests with the aim of obtaining a film that has excellent corrosion resistance, heat resistance, and strong IF/l resistance to external forces. Similarly, among the metals that protect zinc and chromium by their tendency to ionize, we focused on the fact that aluminum is the most effective in terms of workability and cost, and have completed the present invention.

A means for solving the problem, that is, the present invention is to apply zinc plating to an iron base, perform chromate treatment, and then bake and apply a heat-resistant paint containing aluminum powder to the chromate film, thereby forming the aluminum-containing paint film. This is a metal surface treatment method characterized by coating a metal with a chromate film.

According to the present invention, the heat-resistant paint is preferably a paint composed of aluminum powder, silicone resin, alkyd resin, and aromatic solvent, and it is effective to use aluminum powder in a range of 10% to 15% by weight. be.

Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings. The drawing shows an enlarged sectional view of a steel part whose surface has been treated by the method of the present invention, in which 1 is an iron base, 2 is a zinc plating film, 3 is a chromate film, and 4 is a coating film containing aluminum.

As is clear from the above structure, the thin and soft chromate film 3 is combined with the tough and heat-resistant aluminum coating 4.
It is resistant to external force and heat because it is protected by
Even if the chromate film 3 is torn by an external force and a scratch is created that reaches the galvanized film 2, the ionization tendency of aluminum in the coating film 4 is greater than that of zinc, so the galvanized film 2 and the underlying iron base 1 are securely protected. protection and effectively prevent the occurrence of rust.

Comparative Example Sample 1: Galvanized (approximately 10 μm thick) and chromate-treated self-tapping screw Sample 2: Galvanized (approximately 10 μm thick) and chromate-treated using the method of the invention, followed by heat-resistant paint with the following ingredients: Tapping screws are painted (2009/2゜A) for baking.Coating thickness approx. 20μ Composition list Aluminum powder 13% (weight ratio) Silicone resin
3.5% (I) alkyd resin 13
．． 8% (I) Aromatic solvent 69.7% (I
) Salt spray test conducted on the above samples 1 and 2,
The results of the hydrochloric acid resistance test and alkali resistance test are as follows.

+11 After 432 hours of salt water spray g test and JIS Z2371 application test, sample 1 had significant corrosion of the iron base and red rust had occurred over the entire surface, but sample 2 had only a slight white corrosion and no red rust. It was not recognized at all.

(2) Hydrochloric acid resistance test The sample was immersed in a 5% hydrochloric acid solution for 24 hours. In Sample 1, the iron base was severely corroded, with spotty corrosion marks occurring over the entire surface, but in Sample 2, there was no change at all.

(3) Alkali resistance test The sample was immersed in a 3% hydroxide solution for 72 hours. In sample 1, no corrosion of the iron base was observed, but the plating film had completely peeled off and the iron base was exposed. On the other hand, in Sample 2, the coating film was slightly damaged by the alkali and slightly discolored, but the underlying plating film was completely in its original state.

Effects of the Invention As described above, according to the present invention, the iron substrate 1 is protected by the three-layer film consisting of the galvanized film 2, the chromate film 3, and the coating film 4 containing aluminum, so that it is protected against external forces and heat. It also has strong features.

Therefore, the method of the present invention is extremely effective for surface treatment of self-tapping screws and drill screws, which generate heat due to large frictional resistance when screwed in and are often exposed to wind and rain during use.

[Brief explanation of the drawing]

The drawing is an enlarged sectional view of a main part of a steel component whose surface has been treated by the method of the present invention. 1... Iron base 2... Zinc plating film 3... Chromate film 4... Coating film containing aluminum Patent applicant Hoshiko Giken Sagi Co., Ltd.

Claims (1)

[Claims] 1. After galvanizing an iron base and subjecting it to chromate treatment, the chromate film is coated with a heat-resistant paint containing aluminum powder by baking, and the chromate film is covered with a paint film containing aluminum. A metal surface treatment method characterized by: 2. The metal surface treatment method according to claim 1, wherein the heat-resistant paint contains 10 to 15% by weight of aluminum powder.