JP3085879B2 - Manufacturing method of external corrosion resistant tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an external corrosion-resistant tube.

[0002]

2. Description of the Related Art Cast iron tubes are generally manufactured using a centrifugal casting method. In the case of this centrifugal casting method, after the cast iron tube is drawn out of the mold after casting, it is charged into an annealing furnace, and is usually held at a temperature of about 800 to 1000 ° C. for 1 to 2 hours to perform annealing heat treatment. I am giving.

[0003] Oxide is generated on the outer peripheral surface of the cast iron pipe by this annealing heat treatment, and this oxide is removed by a shot blast treatment after the heat treatment. Then, a zinc-rich paint having good anticorrosion properties is applied to the ground generated by the shot blasting process, or zinc spraying is applied, and finally, an acrylic paint is finish-coated to obtain a product.

However, such shot blasting or paint coating does not improve productivity. Therefore, for example, Japanese Patent Application Laid-Open No. 3-150343
In order to prevent the formation of thick scale during the annealing heat treatment and to form an excellent anticorrosion film on the outer peripheral surface of the cast iron pipe, the patent publication discloses that aluminum is cast on the outer peripheral surface of the cast iron pipe before the annealing heat treatment after casting. Alternatively, it is described that an aluminum alloy film is applied by thermal spraying.

[0005]

However, if the thermal spraying of aluminum is performed as described above, the equipment for the thermal spraying becomes large.

Accordingly, the present invention is a further improvement of such a conventional technique so that an iron-aluminum alloy layer formed by applying an aluminum film to the outer peripheral surface of a cast iron pipe can be formed with simple equipment. The purpose is to.

[0007]

In order to achieve this object, the present invention provides a method of spraying aluminum-based metal powder onto the surface of a cast iron pipe having a temperature higher than the melting point of aluminum after casting. The metal powder is melted and the surface of the cast iron tube is coated with an aluminum layer, and then the cast iron tube coated with this aluminum layer is annealed to convert aluminum to the iron portion at the interface between the iron portion and the aluminum layer. In addition to forming an iron-aluminum alloy layer on the surface of the iron portion by diffusion and infiltration, a passivation film of aluminum oxide is formed on the surface of the alloy layer.

[0008] By dispersing the powder of aluminum-based metal on the surface of the cast iron pipe still having a temperature equal to or higher than the melting point of aluminum after casting, the heat of the cast iron pipe causes the aluminum-based metal to melt. Thus, a uniform aluminum layer is formed on the surface of the cast iron pipe. Then, by performing annealing heat treatment thereafter, aluminum diffuses into the iron base material to form an iron-aluminum alloy layer, and a passivation film of aluminum oxide is formed on the surface thereof.

[0009]

FIG. 2 shows a ductile cast iron pipe 1 immediately after being cast in a cylindrical mold in a centrifugal casting machine and immediately after being pulled out of the mold. The cast iron tube 1 is horizontally supported by a plurality of supporting rotating rollers 2 so as to be rotatable around an axis.
The cast iron tube 1 immediately after such casting is in a red-hot state,
It has a temperature of about 700 to 900 ° C. higher than the melting point of aluminum.

As shown in the drawing, a hopper 3 having a scatter slit of a predetermined size is installed above a cast iron pipe 1 supported by a supporting rotary roller 2. The hopper 3 stores aluminum-based metal powder.

The hopper 3 is caused to run in the axial direction of the pipe while rotating the cast iron pipe 1 around the axis by the supporting rotary roller 2, and the powder 4 of aluminum-based metal is dropped from the scatter slit to remove the cast iron pipe 1. Spray on the outer surface of.

Then, the powder 4 is uniformly dispersed over the entire circumference and the entire length of the cast iron pipe 1, and FIG.
As shown in (a), the powder 4 is melted by receiving the heat of the iron part 6 of the cast iron tube 1, so that the surface of the iron part 6 is uniformly melted as shown in FIG. Aluminum layer 7
Is formed.

Next, the cast iron pipe 1 coated with the molten aluminum layer 7 is annealed in a normal annealing furnace.
Then, as shown in FIG. 3C, aluminum diffuses into the iron portion 6 and, at the same time, aluminum is oxidized on the surface portion to form aluminum oxide 8.

Finally, as shown in FIG. 2D, an iron-aluminum alloy layer 9 is formed on the outer peripheral surface of the iron portion 7 of the cast iron pipe 2 and the outer peripheral surface of the alloy layer 9 is formed on the outer peripheral surface of the alloy layer 9. A passivation film 10 of aluminum oxide is formed. Aluminum oxide powder 11 is formed on the surface of the passivation film 10, but the powder 11 is not integrated with the cast iron pipe 1.

Next, a specific example will be described. Caliber 100
After centrifugally casting a ductile iron pipe having a length of 4 m and a length of 4 m, the pipe was pulled out of the mold. When the pipe temperature reached 800 ° C., the pipe was rotated at a peripheral speed of 120 mm using the apparatus shown in FIG.
The tube was rotated around the axis at a speed of mm / sec. When the tube temperature reached 753 ° C., aluminum powder was sprayed from the hopper onto the outer surface of the tube. This aluminum powder has a particle size of 70 to 1
20 mesh, purity of 99.7% was used. The scatter slit of the hopper was 2 mm wide and 100 mm long. Then, while spraying 12.5 g of powder per second from the slit, the hopper was moved in the axial direction of the tube to spray the entire length of the tube in 25 seconds. That is, the feed speed of the hopper in the pipe axis direction was set to 160 mm / sec.

Thus, the aluminum powder sprayed on the surface of the cast iron pipe was melted, and a uniform molten aluminum layer was formed on the outer peripheral surface of the pipe. Next, the cast iron tube was heat-treated in a special annealing furnace called a rollover furnace, and ordinary ferritizing annealing was performed.

When the microstructure of the cross section in the thickness direction of the outer surface of the cast iron pipe after annealing was observed at a magnification of 200 times, a dense passive film having a thickness of about 10 μm was observed on the outermost surface. In addition, an aluminum diffusion layer having a thickness of about 120 μm, that is, an iron-aluminum alloy layer was observed underneath.

[0018]

As described above, according to the present invention, aluminum-based metal powder is sprinkled on the surface of a cast iron pipe that has a temperature equal to or higher than the melting point of aluminum after casting. Since it is melted and coated with an aluminum layer on the surface of the cast iron pipe, the aluminum layer can be formed only by spraying such an aluminum-based metal, and it does not require large-scale facilities such as aluminum thermal spraying, and is simple. An aluminum layer can be formed only with equipment.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a process of forming an iron-aluminum alloy layer according to the present invention.

FIG. 2 is a diagram illustrating a step of spraying aluminum-based metal powder according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cast iron pipe 4 Aluminum powder 6 Iron part 7 Molten aluminum layer 9 Iron-aluminum alloy layer 10 Passive film of aluminum oxide

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-103177 (JP, A) JP-A-3-150343 (JP, A) JP-A-7-18409 (JP, A) JP-A-4- 193966 (JP, A) JP-A-6-136510 (JP, A) JP-A-60-63364 (JP, A) JP-A-5-239615 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 10/50

Claims (1)

(57) [Claims] 1. An aluminum-based metal powder is sprayed on the surface of a cast iron pipe still having a temperature equal to or higher than the melting point of aluminum after casting, and the aluminum-based metal powder is melted to form an aluminum layer on the surface of the cast iron pipe. Then, the cast iron tube coated with the aluminum layer is annealed to diffuse aluminum into the iron portion at the interface between the iron portion and the aluminum layer, thereby forming an iron-aluminum alloy layer on the surface of the iron portion. Forming a passive film of aluminum oxide on the surface of the alloy layer.