JP2015078393A - Corrosion prevention method of cast iron pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a stable corrosion prevention layer even on a part where it is easily left unpainted due to irregularity of ditches and protrusions such as on a surface of a cast iron pipe, and where lack of preparation process (blast process) is likely to occur.SOLUTION: Zinc metal with excellent corrosion prevention property is fused and blasted on a surface of the cast iron pipe, and then, the corrosion prevention layer is formed by spray paint overcoating of zinc rich paint. Thereby, making use of advantages of different two methods of spray coating and painting, the zinc corrosion prevention layer with excellent rust prevention property is stably formed.

Description

  The present invention relates to an anticorrosion method for cast iron pipes, and more particularly, to an anticorrosion method for preventing the occurrence of rust by providing an anticorrosion layer having a certain thickness on the surface of a cast iron pipe having uneven portions such as grooves and protrusions.

Conventionally, there has been a demand for a technique for forming an anticorrosion layer on the surface of a cast iron pipe so that it does not rust even when wet.
For example, when forming the anticorrosion layer (coating film) by painting the inner surface of the receiving port of a cast iron pipe, it is required to coat the inner surface of the receiving port including grooves and protrusions with a coating film having a uniform thickness.

The cast iron pipe is mainly used for a water pipe or the like, and as shown in FIG. 4, includes a cylindrical portion 31 having a uniform inner and outer diameter, and a receiving port 32 provided at one end thereof and swelled to the outside. Is painted for anticorrosion.
On the inner surface of the receiving port 32, a circumferential groove or a ridge for fitting a metal ring or rubber packing is formed in order to provide a retaining function and a water stopping function after piping. Further, a portion 35 that forms a back wall that connects the step between the inner surface of the receiving port 32 and the inner surface of the cylindrical portion 31 is referred to as a body portion.

For example, as shown in this drawing, the inner surface of the cast iron pipe is coated with the spray gun 1 from the end of the receiving port 32 in a state where the cast iron pipe 3 is rotated around the axis, and is exposed to the inner surface of the pipe. The liquid paint is sprayed from the downward coating nozzle 11 with the spray pattern 2 spreading in a conical shape.
In this way, while spraying the paint over the entire inner surface of the pipe, the spray gun 1 is moved along the axial direction of the pipe 3, and the spraying position is extended in the axial direction of the pipe, so that the vicinity of the body portion that becomes the coating boundary Paint until.

  By the way, zinc rich paint is known as a liquid paint to be applied to the inner surface of a receiving port of a cast iron pipe. Zinc Rich Paint is widely used as a zinc-based primer that contains a large amount of zinc powder as a pigment and has excellent rust-prevention power. Yes. (For example, see Patent Document 1)

  Conventionally, in order to prevent corrosion of metal pipes, a technique of spraying a metal with excellent corrosion resistance such as zinc or aluminum to form a sprayed coating on the surface of the metal pipe has been widely used. A thermal spraying method and a thermal spraying torch for forming a thermal spray coating on the inner surface of the receptacle have already been disclosed. (For example, see Patent Document 2)

Japanese Patent Laid-Open No. 11-253857 Japanese Patent Laid-Open No. 11-172407

  However, when the undercoating of a part with irregularities such as grooves and protrusions, such as the inner surface coating of a cast iron pipe, is performed by spraying zinc rich paint, the surface along the direction in which the paint is sprayed, that is, the spraying direction On the parallel surfaces (for example, the side walls 37 and 38 in FIG. 5), the amount of coating decreases, and omission (unpainted) tends to occur.

In addition, when spraying the inner surface of the receiving port at one end of the cast iron tube rotated at high speed around the axis, the paint blown out from the nozzle tends to flow from the center side of the tube toward the receiving end side. In addition, the surface of the side wall facing the receiving end of the tube (for example, the side wall 37 in FIG. 5) is particularly difficult to be coated with, and unpainted portions are likely to occur.
If the amount of paint sprayed is increased in order to prevent unpainted paint, the paint will not dry well, and the paint may sag on the side wall 38 of the groove or may accumulate on the bottom 39 of the groove.

  On the other hand, when spraying the surface of a cast iron pipe instead of painting, blasting is performed as a base treatment before spraying in order to improve the adhesion between the pipe surface and the sprayed coating. As shown in FIG. 5, since the steel grains for the surface cleaning are projected from the outside of the receiving end toward the inner surface of the receiving end, the surface facing the receiving end side (for example, the side wall 37 in FIG. 5) is sufficient. Although the surface is polished, the surface facing the center of the tube (for example, the side wall 38 in FIG. 5) becomes a blind spot of the projection and is hard to hit the steel grain, and deposits such as core sand remain on the substrate, and the thermal spray coating There was a risk of peeling off.

  Since the present invention is provided with uneven portions such as grooves and protrusions like the surface of a cast iron pipe, it is easy to leave uncoated areas, and even if there is a portion that is difficult to be subjected to a base treatment (blast treatment) before spraying. An object is to form a stable anticorrosion layer.

In order to solve the above problems, the anticorrosion method of the present invention is an anticorrosion method for a cast iron pipe that prevents corrosion by forming an anticorrosion layer on the surface of the cast iron pipe, and melts a zinc-based metal having excellent rust prevention power. And then sprayed onto the surface of the cast iron pipe, and then coated with zinc rich paint to form a zinc-based anticorrosion layer on the surface of the cast iron pipe.
Thereby, since the zinc-type anticorrosion layer excellent in rust prevention power is formed taking advantage of two different anticorrosion methods such as thermal spraying and painting, a more stable rust prevention effect can be obtained.

Further, as a method for preventing corrosion of the cast iron pipe of the present invention, it is a method for preventing corrosion by forming an anticorrosion layer on the inner surface of the receiving end of the cast iron pipe to prevent corrosion, and melting a zinc-based metal having excellent rust prevention power. It is possible to adopt a configuration in which a zinc-based anticorrosion layer is formed on the inner surface of the receiving port of the cast iron pipe by spraying the inner surface of the receiving port by spraying from the outside of the receiving end toward the inner surface of the receiving port.
Thereby, the stable anticorrosion layer can be formed also on the side wall of the uneven | corrugated | grooved part in the receptacle inner surface of a cast iron pipe.
That is, a sprayed coating can be formed in advance on the side wall of the side wall facing the receiving end side where the zinc rich paint is difficult to adhere, thereby compensating for the paint leakage of the zinc rich paint.

  Furthermore, as a method for preventing corrosion of a cast iron pipe according to the present invention, it is possible to adopt a configuration in which a zinc rich paint is overcoated by spray coating.

  According to the anticorrosion method of the present invention, since it has uneven portions such as grooves and protrusions like the surface of a cast iron pipe, it is easy to leave unpainted areas, and furthermore, it is difficult to perform a base treatment (blast treatment) before spraying. Even if there is a portion, a stable anticorrosion layer can be formed.

It is a flow figure showing the whole process about cast iron pipe corrosion prevention concerning an embodiment of the present invention. It is explanatory drawing of a thermal spraying process. It is explanatory drawing of a thermal spray gun. It is explanatory drawing of a painting process. It is detail explanatory drawing of the opening part of a cast iron pipe.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same reference numerals are assigned to those common to the background art described above, and redundant description is omitted.

FIG. 1 is a flowchart showing the anticorrosion layer forming step of the cast iron pipe according to the embodiment of the present invention.
First, a cast iron pipe that has been cast and trimmed is finished to a predetermined shape by machining or the like. (Casting and processing process)
Subsequently, in order to remove foreign substances adhering to the surface of the cast iron pipe, such as foundry sand and oxide scale, steel particles are projected at a high speed to sharpen the substrate (cast surface). At this time, polishing is performed by projecting steel grains from the outside of the pipe to the inner surface of the receiving port. Thereafter, the steel grains remaining in the tube are removed. (Ground treatment process)

Next, using a spray gun, the molten zinc-based metal is sprayed from the outside of the tube toward the inner surface of the receiving port by the flow of compressed air. (Zinc spraying process)
Subsequently, the nozzle of the spray coating gun is inserted into the receiving port, and zinc rich paint is sprayed from the nozzle toward the inner surface of the receiving port together with the compressed air, and the zinc rich paint is sprayed over the entire circumference of the inner surface of the receiving port. (Zinc rich paint painting process)
After the zinc rich paint is dried, a predetermined resin coating is applied to the inner surface of the receiving port as a top coat. (Resin coating process)
This completes the anticorrosive layer on the inner surface of the cast iron pipe receptacle.

Next, the zinc spraying process will be described with reference to FIGS.
FIG. 2 is an explanatory view showing a state in which zinc spraying is performed on the inner surface of the receiving port of the cast iron pipe 3, and the cast iron pipe 3 is placed on the cylindrical roller 4 so that the axis is horizontal, and the roller It is rotating around the axis according to the rotation of 4.
The spray gun 5 is disposed at the tip of the receiving end 321 of the cast iron pipe 3 with the tip of the spray nozzle 511 facing the lower side of the inner surface of the receiving port, and the zinc-based metal melted from the nozzle 511 receives the inner surface of the receiving port. It is sprayed toward. The spray reaches the surfaces of the circumferential groove 33 and the protrusion 34.

FIG. 3 is a cross-sectional view of the tip structure of the spray gun 5 used in the spraying process, in which two wires 52, 52 made of zinc-based metal contact in a cap 51 at the tip of the spray gun, where an arc Occurs and the wires 52 and 52 melt.
The molten metal is atomized by the compressed air flowing in the cap, blown out from the nozzle 511 at the tip of the cap, and the molten metal atomized by the compressed air sprayed from the blowing hole 53 provided near the outer periphery of the cap. The spread of the blowout shape is restricted, and a neat conical spray pattern 54 is completed to some extent.

Next, the zinc rich paint painting process will be described with reference to FIG.
FIG. 4 is an explanatory view of a state in which zinc rich paint is spray-coated on the inner surface of the receiving port of the cast iron pipe 3, and the cast iron pipe 3 is placed on the cylindrical roller 4 ′ so that the axis is horizontal. This represents a state in which the roller 4 ′ rotates around the axis.
The nozzle piping of the air spray coating gun 1 is inserted into the receiving port from the outside of the receiving port end 321 of the tube, and is directed downward from the inner surface of the receiving port from the paint nozzle 11 attached to the tip of the pipe bent downward. Zinc rich paint is sprayed.
Zinc rich paint and compressed air supply pipes (12, 13) are connected to the painting gun 1, respectively. Inside the painting gun, the zinc rich paint and the compressed air are mixed. Rich paint erupts.
The coating gun 1 moves along the axial direction of the cast iron pipe 3 and sprays zinc rich paint with a conical spray pattern 2 over the entire circumference of the inner surface of the receiving port from the receiving end 321 to the body portion 35. Yes.

[Experimental example]
As an experimental example of the anticorrosion method of the cast iron pipe according to the present invention, on the inner surface of the ductile cast iron pipe (straight pipe / mortar lining pipe) having a nominal diameter of 100 mm and a length of 4 m, the anticorrosion method according to the present invention, An anticorrosion layer including a zinc-based primer layer was formed.

First, in order to perform the ground treatment of the inner surface of the receiving port, a steel shot sphere is projected at high speed from the outside of the tube (receiving port end) toward the inner surface of the receiving port, and shot blasting processing of the inner surface of the receiving port is performed Thereafter, the shot sphere was removed from the inner surface of the receiving port.
In the next zinc spraying process, two zinc wires (52) with a diameter of 2.3 mm are supplied to the arc spray gun (5) and melted from the outside of the pipe (receiving end) toward the lower side of the receiving face. Zinc was injected (see FIGS. 2 and 3).
The spray amount of thermal spraying was about 130 g / m ² . (Target film thickness 20μm)

In the subsequent zinc rich paint coating process, the tube that has been sprayed on the inner surface of the receiving port is preheated to about 80 ° C., and the heated tube (3) is rotated about its axis while an air spray gun ( Insert the nozzle (11) of 1) and atomize the water-based zinc rich paint (Kurimoto Coat WZ: Zinc Rich Paint Water-based Dainippon Paint Co., Ltd. (JIS K 5552 compliant product)) toward the inner surface of the pipe inlet Then, while spraying downward from the nozzle, the air spray gun (1) was moved in the tube axis direction, and water-based zinc rich paint was sprayed on the entire inner surface of the receiving port (see FIG. 4).
The coating amount of the aqueous zinc rich paint was set to about 150 g / m ² . (Target film thickness 20μm)

  After the water-based zinc-rich paint applied on the inner surface of the receptacle is dry, the target film thickness is 60 μm. Furthermore, Kurimoto Coat AC-1 (acrylic resin paint, solvent type, JWWA K 139 standard product manufactured by Nippon Paint Co., Ltd.) was applied with a target film thickness of 20 μm.

  After the paint dries, cut the tube receiving portion along the tube axis direction and observe the cut surface with a microscope to confirm the formation of the anticorrosion layer on the inner surface of the receiving tube. (37) and the side wall (38) facing the center of the pipe also have at least a primer layer of either a zinc sprayed coating or a zinc rich paint coating, and the entire surface of the inner surface of the receiving port is not interrupted by the zinc-based primer layer. It was confirmed that it was formed.

DESCRIPTION OF SYMBOLS 1 Air spray painting gun 11 Coating nozzle 12 Zinc rich paint supply piping 13 Compressed air piping 2 Zinc rich paint injection pattern 3 Cast iron pipe 31 Cylindrical part 32 Receiving port 321 Receiving end 33 Peripheral groove 34 Projection 35 Body part 37 Side wall ( (Facing the receiving end)
38 Side wall (towards the center of the tube)
39 Bottom surface 4, 4 ′ Roller 5 Thermal spray gun 51 Cap 511 Thermal spray nozzle 52 Wire material 53 Blowout hole 54 Thermal spray pattern

Claims (3)

  A corrosion prevention method for a cast iron pipe that prevents corrosion by forming a corrosion prevention layer on the surface of the cast iron pipe, melting the zinc-based metal and spraying it on the surface of the cast iron pipe, and then overcoating with zinc rich paint to the surface of the cast iron pipe An anticorrosion method for cast iron pipes in which a zinc-based anticorrosion layer is formed.   A corrosion prevention method for a cast iron pipe that prevents corrosion by forming an anticorrosion layer on the inner surface of the receiving end of the cast iron pipe, and melts and sprays zinc-based metal from the outside of the receiving end toward the inner surface of the receiving end. An anticorrosion method for a cast iron pipe, in which a rich paint is overcoated on the inner face of the receptacle to form a zinc-based anticorrosive layer on the inner face of the cast iron pipe.   A cast iron pipe corrosion prevention method that prevents corrosion by forming a corrosion prevention layer on the surface of the cast iron pipe, melting the zinc-based metal and spraying it on the surface of the cast iron pipe, and then overcoating with zinc rich paint by spray coating. An anticorrosion method for a cast iron pipe in which a zinc-based anticorrosion layer is formed on the surface of the pipe.