JPH11229162A - Surface treatment method of metal spray coating for corrosion protection - Google Patents

Abstract

(57) [Summary] [Problem] Aluminum-silicon-manganese (Al-4Si-)
It is an object of the present invention to easily and inexpensively perform corrosion protection of a metal sprayed coating made of a 15Mn) alloy under a neutral environment. SOLUTION: The base surface of the ductile cast iron tube is made of aluminum.
A sprayed metal film made of a silicon-manganese alloy is formed, and a black aluminum oxide layer is formed on the surface by spraying hot salt water or spraying steam on the surface of the sprayed metal film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method in which a sprayed metal film made of an aluminum-silicon-manganese alloy is used as a corrosion-resistant film for a ductile cast iron pipe.

[0002]

2. Description of the Related Art Since a cast iron pipe is generally buried underground, an external corrosion-resistant coating is indispensable. This outer corrosion protection coating
It is necessary to have not only chemical resistance but also physical strength to withstand impact and friction such as backfilled earth and sand.

As a corrosion-resistant coating satisfying such conditions,
2. Description of the Related Art A metal spray coating for injecting and welding a molten metal to the outer periphery of a cast iron pipe is known.
It has been conventionally known that a -15Mn alloy material is excellent in corrosion resistance, material availability, and thermal sprayability.

[0004] In particular, this alloy exhibits an extremely high anticorrosion effect in an environment where chloride ions are present, and is therefore suitable as an external anticorrosion coating for buried pipes in soils containing salts.

[0005]

However, the above-mentioned sprayed metal film made of the Al-4Si-15Mn alloy is
In a neutral environment such as fresh water groundwater, there is a problem that white spot rust may be generated due to the aluminum component contained in the above alloy.

[0006] This white rust is considered to be due to electrical factors in the ground containing neutral water, and such rust does not occur in an environment containing chlorine, for example, in salt water. In order to prevent the occurrence of such rust, the applicant of the present invention has made the above-mentioned aluminum
A method has been proposed in which a second metal coating made of a metal having a sacrificial anode effect on the metal constituting the coating is spray-formed on a metal spray coating made of an alloy of silicon-manganese (Al-4Si-15Mn).

[0007] However, this method has a problem in that the metal spray coating must be spray-formed twice, and the production is troublesome. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and white spot rust is generated in a neutral environment such as fresh water of a metal sprayed coating of an aluminum-silicon-manganese (Al-4Si-15Mn) alloy. It is an object to provide a simple processing method for preventing occurrence.

[0008]

In order to achieve this object, according to the invention of claim 1, aluminum-silicon-manganese (Al-4Si-15M)
n) A sprayed metal film made of an alloy is formed, and hot salt water is sprayed on the surface of the sprayed metal film to form a black aluminum oxide layer on the surface.

Here, the warm salt water refers to salt water at 50 ° C. or higher, and the salt concentration is set to about 3% to 8% based on seawater. According to this method, an oxide film having excellent corrosion resistance, so-called black rust, is formed on a sprayed metal film made of an aluminum-silicon-manganese (Al-4Si-15Mn) alloy having excellent salt water resistance. An excellent corrosion-resistant layer can be formed.

[0010] According to a second aspect of the present invention, steam is blown instead of spraying the hot salt water in the first aspect. A similar oxide film can be formed by spraying with steam. It is to be noted that the steam does not need to be very hot, and the upper limit is about 200 ° C. at 100 ° C. or higher.

[0011]

Next, an embodiment of the present invention will be described. As shown in FIG. 1, an aluminum-silicon-manganese (Al-4Si-15Mn) alloy was used as a metal material of the sprayed metal film, and a metal sprayed film 2 was formed on a base surface of a ductile cast iron pipe 1.

Next, the ductile cast iron tube 1 is heated at 60 ° C.
Warm saline having a concentration of 5% was uniformly sprayed to form a black oxide film 3 on the surface of the metal sprayed film 2. The black oxide film 3 began to appear from the time when the spraying of the salt water was continued for 60 minutes, and the spraying of the salt water was continued for 200 minutes until the black oxide film 3 was entirely covered with the black oxide film made of aluminum oxide.

[0013] Instead of spraying with the above-mentioned warm salt water, steam at about 110 ° C was sprayed to form a black oxide film made of aluminum oxide. In this case, the black oxide film 3 made of aluminum oxide began to appear 10 minutes after the start of the steam spraying, and the time required until the entire surface was covered was 60 minutes.

Next, these painted ductile cast iron tubes 1
One was immersed in a fresh water tank, and the other was subjected to a corrosion resistance test by spraying with salt water. The results are as shown in Table 1. In all the test specimens, no point rust of aluminum or generation of red rust from the ductile cast iron pipe body was observed even after 180 days.

[0015]

[Table 1]

[0016]

As described above, according to the present invention, an extremely excellent corrosion-resistant oxide film is formed on a metal sprayed film exhibiting extremely tough corrosion resistance in an environment containing chlorine such as salt water. The generation of white spot rust in water can be effectively prevented.

In addition, since hot salt water or steam blowing at a non-high temperature is used as a method for forming an oxide film, the method is easy to carry out and can be carried out at low cost.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part of a corrosion-resistant layer of a ductile cast iron pipe obtained by a method of the present invention.

[Explanation of symbols]

 1. Ductile cast iron pipe 2. Metal spray coating 3. Oxide coating

Claims (2)

[Claims] 1. The method according to claim 1, wherein the surface of the base material of the ductile cast iron pipe is made of aluminum.
A surface treatment method for a metal spray coating for corrosion prevention, comprising: forming a spray metal coating made of a silicon-manganese alloy; and spraying hot salt water on the surface of the spray metal coating to form a black aluminum oxide layer on the surface. 2. A method for surface treatment of a metal spray coating for corrosion prevention, comprising forming a black aluminum oxide layer on the surface of the metal spray coating by spraying steam instead of spraying the warm salt water of claim 1.