JPH10185080A - Method of inside surface corrosion prevention of cast iron pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lining layer excellent in corrosion-proof effect without making any previous heating on the inner surface of a cast iron pipe on which inner surface cement lining has been applied, by applying injection coating while fusing resinous powdery paint in the flame of a spraying gun. SOLUTION: After making foundation treatment on the inner surface of a cast iron pipe 1 with an inner diameter of approximately 1,000mm, cement mortar is supplied on the inner surface thereof while spinning the cast iron tube 1, it is hardened as an uniform layer of about 10mm thickness by means of centrifugal force, and this cement mortar layer 2 is placed in its surface grinding treatment to remove laitance. Epoxy resin powder paint as a resin powder paint 4 is supplied from the central hole of a spraying gun 3 at a rate of about 50g per minute while injecting combustion flame by LP gas at about pressure 10psi from the combustion gas emission annulus on the outer periphery and about pressure 60psi from an intermediate air emission annulus so as to carry out injecting painting. In this way, a coating film 5 owing to epoxy resin paint is formed on the surface of a cement mortar layer 2. Thereby resin powder painting can be achieved while preventing any thermal deterioration of the cement lining layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for protecting an inner surface of a cast iron pipe from corrosion.

[0002]

2. Description of the Related Art Generally, the inner surface of a cast iron pipe is provided with a lining which is excellent in water quality and hygiene, and has good corrosion resistance and appearance.

[0003] As the inner corrosion prevention lining of this cast iron pipe, there are cement mortar lining, epoxy resin powder coating, liquid epoxy resin coating and the like. Among the anticorrosion linings, the cement mortar lining has a problem in that the pH of water in the pipe increases due to the loance that is deposited on the surface during curing and hardening.

[0004] Further, in the case of a liquid epoxy resin, although there is no such a problem of an increase in PH and hygiene as described above, there is a problem that a solvent odor remains for a while, and thus discomfort is given to drinking water and the like.

[0005] On the other hand, epoxy resin powder coating has no problems in water quality such as an increase in PH and sanitation. However, when performing epoxy resin powder coating, a base treatment is indispensable to eliminate pinholes in the coating film and increase adhesion.

However, as the diameter of the cast iron pipe increases, wrinkles and irregularities unique to the casting are generated on the inner surface, and a great deal of labor and time are required to completely remove the wrinkles and irregularities in the polishing process. There was a possible problem.

In the case of cement lining, the above wrinkles and irregularities can be easily coated because the layer can be made relatively thick, and as a result, the inner surface of the pipe can be made a smooth surface. Therefore, if the lining layer made of the epoxy resin powder coating is provided on the surface-treated cement lining layer, the advantages and disadvantages of each other are compensated for, and it is considered that a composite lining layer having an excellent anticorrosion effect is provided.

[0008]

However, coating with an epoxy resin powder coating requires the substrate to be heated to a high temperature of 180 to 220 ° C., so that the cement lining layer is significantly degraded during preheating, There was a problem that cracks and peeling occurred, and the meaning of precious cement lining was lost.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to easily obtain a lining layer having an excellent anticorrosion effect by making use of the advantages of a cement lining and an epoxy resin powder coating and compensating for the disadvantages of both. It was done.

[0010]

That is, according to the present invention, there is provided a method for preventing corrosion of an inner surface of a cast iron pipe, wherein the inner surface of the cast iron pipe having an inner surface cement lining is coated with a resin powder coating in a flame of a thermal spray gun without preheating. And spray-coating while melting.

[0011]

In the present invention, the thickness of the cement lining may be such that wrinkles and irregularities peculiar to the surface of the cast iron pipe are concealed and the surface becomes uniform, and a thin enough concealment of these is sufficient. .

Therefore, the surface of the cast iron pipe is made smooth by the cement lining without polishing, and becomes a base surface on which the epoxy resin powder coating can be applied without generating pinholes or the like.

On the other hand, to apply the epoxy resin powder coating, it is necessary to heat the base, but without doing this,
The spray coating is performed while melting the epoxy resin powder coating in the flame of the thermal spray gun.

As shown in FIG. 3, the thermal spray gun is a spray nozzle comprising a center hole 3A for spraying the powder coating material 4, an air jet ring 3B and a combustion gas jet ring 3C concentrically surrounding the center hole 3A. A coating apparatus in which a powder coating material is injected from the center of an atmosphere of air and combustion gas flame, and is heated to a required melting temperature when it adheres to an object to be coated.

Accordingly, the resin powder coating is heated and melted at the time of injection by the coating apparatus even if the object is not heated, and adheres to the surface of the object to be coated. To form

Therefore, even if a cement lining layer which may be deteriorated by heating is provided, the inner surface of the receiving port can be coated with the powder coating without affecting the cement lining layer.

On the other hand, since the surface of the cement lining layer is coated with an epoxy resin powder coating, the influence on water quality such as an increase in PH is prevented. The resin powder coating may be a thermosetting resin powder coating such as an epoxy resin powder coating, or a thermoplastic resin powder coating such as a polyethylene resin powder coating or a fluorine resin powder coating. It is.

[0018]

Next, an embodiment of the present invention will be described. [Example 1] After an inner surface of a cast iron tube 1 having an inner diameter of 1,000 mm was subjected to a base treatment, cement mortar was supplied to the inner surface while rotating the tube 1, and hardened as a uniform layer having a thickness of about 10 mm by centrifugal force. Thereafter, the hardened cement mortar layer 2 was polished to remove the lancet.

Next, a thermospray gun “6P-II type” manufactured by METECO is used as the thermal spray gun 3, and an epoxy resin powder coating as a resin powder coating 4 from the center hole 3 A of the spray gun 3 as shown in FIG. Was supplied at a rate of 50 g per minute, and spray coating was performed while blowing a combustion flame of LP gas at a pressure of 10 psi from a combustion gas injection ring 3C on the outer periphery and air at a pressure of 60 psi from an intermediate air injection ring 3B.

In the figure, 3D indicates a flame of the combustion gas. As a result of this coating, a coating film 5 of an epoxy resin paint was formed on the surface of the cement mortar layer 2. [Example 2] The inner surface of the cast iron pipe 1 was coated in the same manner as in Example 1 except that a thermoplastic polyethylene resin powder coating was used instead of the epoxy resin powder coating.

As a result of this coating, a coating film 5 of a polyethylene resin paint was formed on the surface of the cement mortar layer 2. [Example 3] The inner surface of the cast iron pipe 1 was coated in the same manner as in Example 1 except that a thermoplastic polyester resin powder coating was used instead of the epoxy resin powder coating.

As a result of this coating, a coating film 5 of a polyester resin paint was formed on the surface of the cement mortar layer 2. Comparative Example 1 The inner surface of a cast iron tube 1 having an inner diameter of 1,000 mm, which was the same as in Example 1, was polished with a grinder until the wrinkles and irregularities unique to the cast iron tube disappeared.

Thereafter, the entire tube is heated to 220 ° C., and an epoxy resin powder coating is supplied while rotating to form a uniform layer.
The inner surface lining was completed by providing a layer of powder resin paint directly on the inner surface of the tube without forming a mortar layer. [Comparative Example 2] After the inner surface of a cast iron tube having the same inner diameter of 1,000 mm as in Example 1 was ground-treated, cement mortar was supplied to the inner surface while rotating the tube and hardened as a uniform layer having a thickness of 10 mm by centrifugal force. Thereafter, the hardened cement mortar layer surface was polished to remove the loance.

Then, the surface of the cement mortar layer was seal-coated to complete the inner lining of the cast iron pipe. [Comparative Example 3] After the inner surface of the same cast iron pipe having an inner diameter of 1,000 mm as in Example 1 was ground-treated, cement mortar was supplied to the inner face while rotating the pipe and hardened as a uniform layer having a thickness of 10 mm by centrifugal force. Thereafter, the hardened cement mortar layer surface was polished to remove the loance.

Thereafter, the entire pipe was heated to 220 ° C., and a powder coating made of polyethylene resin was scattered and supplied to make an average layer by centrifugal force, and the inner lining of the cast iron pipe was completed.
The results of Table 1 were obtained by comparing the adhesion of the lining layer, the effect on water quality, and the required processing time for Examples 1 to 3 and Comparative Examples 1 to 3.

The adhesion was measured by attaching a tensile terminal manufactured by Elcometer Co., Ltd. to the surface of the lining layer with an epoxy diameter adhesive, and pulling it with a tester. The Erichsen value was measured in accordance with the test described in JIS G 5528, “Epoxy resin powder coating on the inner surface of ductile cast iron pipe”. The standard value is 3m
m.

The effect on the water quality was tested by filling each tube with tap water and allowing it to stand, and measuring the increase in PH after 24 hours.

[0028]

[Table 1] Adhesion strength Water quality effect Required treatment time Erichsen value Example 1 26 kgf / cm ² or more 0.1 or less 20 minutes 3.5 mm Example 2 Same as above Same as above Same as above Same as above Same as above Comparative example 1 30 kgf / cm ² or more Same as above 6 hours Same as above Comparative Example 2 Same as above 0.4 20 minutes Same as above Comparative Example 3 0.5 kgf / cm ² 0.6 Same as above 0.6 mm As is clear from Table 1, the adhesion strength was treated with a base treatment. Although slightly inferior to Comparative Example 1 in which the powdered resin coating was directly applied to the surface of the cast iron pipe, the other test values showed that each of the examples had almost the same coating performance as Comparative Example 1.

Regarding the required processing time, Comparative Example 1 requires a long processing time of 6 hours, and the coating of the present invention is practically excellent in view of the fact that the adhesion strength has almost no problem in practical use. Was confirmed.

The reason why the adhesive strength, the effect of water quality and the Erichsen value of Comparative Example 3 were very poor is considered to be that the cement mortar layer was thermally degraded by preheating.

[0031]

As described above, according to the present invention, wrinkles and irregularities formed on the inner surface of a cast iron pipe are covered with a cement lining without polishing the surface, and a resin powder coating is applied thereon without heating the cement lining layer. Spray coating while melting in the flame of the spray gun, it is possible to apply resin powder coating while preventing thermal deterioration of the cement lining layer,
Thus, a highly reliable anticorrosive layer having good water resistance can be provided by the base layer treatment of the cement lining layer and the shielding effect of the resin powder coating.

Since the epoxy resin powder coating has high adhesiveness to the cement lining layer as a powder coating, it can be used as a more reliable anticorrosion layer.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment.

FIG. 2 is an enlarged sectional view of a main part of the embodiment.

FIG. 3 is an explanatory sectional view of a thermal spray gun.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cast iron pipe 2 ... Cement mortar layer 3 ... Thermal spray gun 3A ... Center hole of thermal spray gun 3B ... Air ejection ring 3C ... Combustion gas ejection ring 3D ... Combustion gas flame 4 ... Resin powder paint 5 ... Coating

Claims (1)

[Claims] An internal corrosion protection method for a cast iron pipe, characterized in that a resin powder coating is melted in a flame of a thermal spray gun and spray-coated without preheating on an inner surface of the cast iron pipe having an inner surface cement-lined. Method.