JPH11106890A - Thermal spraying method for outside face of corrosion resistant tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent the generation of pinholes even if they are very small in the case metallic sprayed coating is formed on the outside face of a metallic tube by superhigh speed flame spraying. SOLUTION: In the method in which the outside face of a metallic tube is thermally sprayed with corrosion resistant alloy powder by a superhigh speed flame spraying device to form corrosion resistant metallic coating, at first, the outside face of a metallic tube is thermally sprayed by a superhigh speed flame spraying device to form corrosion resistant metallic coating, next, the feed of the corrosion resistant alloy powder to the superhigh speed flame spraying device is stopped, and the sprayed metallic coating is heated only by thermal spraying flame.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for spraying a corrosion-resistant pipe on an outer surface, and more particularly, to an improved method for forming a corrosion-resistant metal coating by spraying a corrosion-resistant alloy powder on a metal pipe surface such as a ductile cast iron pipe. About.

[0002]

2. Description of the Related Art Conventionally, in order to improve the corrosion resistance of the outer periphery of a cast iron pipe, a metal powder having excellent corrosion resistance is sprayed by ultra-high-speed flame spraying to form a metal film.

[0003] In this ultra-high-speed flame spraying, a metal film is formed by spraying metal particles melted by a jet flame using acetylene or propane and oxygen onto the surface of a metal plate. Can be selected,
For example, an extremely corrosion-resistant alloy such as an aluminum alloy can be used, which has an effect of obtaining excellent performance as an anticorrosion film of a ductile cast iron pipe buried underground.

[0004]

However, in the above-mentioned ultra-high-speed flame spraying, since metal particles are sprayed, there is a possibility that pinholes may be generated stochastically. There were problems that could be compromised.

For example, as described above, when an aluminum alloy is sprayed as a corrosion protection film on a ductile cast iron pipe, even if the pinholes are so small as to be invisible, the aluminum alloy has a lower ionization tendency than cast iron. Cast iron pipes are corroded at pinholes by underground stray currents,
There has been a problem that the corrosion may spread to the tube wall starting from this.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and has as its object to provide a method for spraying an outer corrosion-resistant tube which can effectively prevent the generation of even a very small pinhole. It was done.

[0007]

The method of spraying a corrosion-resistant outer surface of a tube according to the present invention is a method of spraying a corrosion-resistant alloy powder onto the outer surface of a metal tube with an ultra-high-speed flame spraying apparatus to form a corrosion-resistant metal coating. The corrosion-resistant alloy powder is sprayed on the outer surface of the metal tube with an ultra-high-speed flame spraying device to form a corrosion-resistant metal coating, and then the supply of the corrosion-resistant alloy powder to the ultra-high-speed flame spraying device is stopped. It is characterized by heating the film.

That is, once a metal coating is formed by thermal spraying, the coating is heated again only with thermal spray flame to fluidize the coating and eliminate pinholes.

[0009]

Next, an embodiment of the present invention will be described. On a side surface of a supporting device 2 for rotating the cast iron tube 1 around the tube axis, a carriage 4 on which an ultra-high-speed spray gun 3 was installed was installed.

Next, while rotating the cast iron tube 1, 81% of aluminum, 4% of silica,
% Of the Al-Si alloy powder was sprayed and the carriage 4 was moved from one end 1A to the other end 1B of the cast iron tube 1 to perform uniform metal spraying on the outer surface of the cast iron tube.

After the thermal spray reaches the other end 1B, the supply of the alloy powder to the thermal spray gun 3 is stopped, and only the thermal spray flame is ejected to move the thermal spray gun 3 from the other end toward the one end. .
The moving speed was a speed at which the metal coating forming the thermal spray coating on the surface of the cast iron pipe 1 was heated to a temperature of 600 to 700 ° C at which the metal coating began to melt and flow.

When the ultrahigh-speed spray gun 3 returns to the end 1A, the spraying is terminated. The corrosion resistance test was performed on the cast iron tube 1 on which the metal coating was formed as described above by spraying with salt water and immersing in tap water. The results shown in Table 1 were obtained.

[0013] In Table 1, the comparative example shows the case where the heat treatment by the thermal spraying flame was not performed. In Table 1, "white rust" is rust peculiar to an aluminum alloy, and it is empirically known that the rust is more likely to occur when immersed in tap water than when sprayed with salt water.

As is clear from Table 1, in the comparative example, white rust was generated after 60 days even after spraying with salt water, whereas in the embodiment of the present invention, such white rust was not generated. It did not occur for 60 days or more even in tap water immersion, which is liable to occur, and it was confirmed that corrosion resistance was superior to that of the comparative example.

[0015]

[Table 1]

[0016]

As described above, according to the present invention, when a metal film is formed by ultra-high-speed flame spraying, the metal film once formed is heated to a temperature at which it can be melted again by the spraying flame used for spraying. The generated pinholes disappear during this reheating, and a tough metal film without defects can be formed.

[Brief description of the drawings]

FIG. 1 is a plan view of an apparatus for performing the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cast iron tube 1A One end of cast iron tube 1B The other end of cast iron tube 2 Supporting device 3 Ultra high speed spray gun 4 Dolly

Claims (1)

[Claims] 1. A method for forming a corrosion-resistant metal coating by spraying an corrosion-resistant alloy powder on an outer surface of a metal tube with an ultra-high-speed flame spraying device, first spraying the corrosion-resistant alloy powder on the outer surface of the metal tube with an ultra-high-speed flame spraying device. Forming a corrosion-resistant metal film by heating the sprayed metal film, and then stopping the supply of the corrosion-resistant alloy powder to the ultra-high-speed flame spraying apparatus, and heating the sprayed metal film only by a spray flame.