JPH09276794A - Inner lining method of ductile pipe - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: When the inner surface of a cast iron pipe is lined with a powder coating material, the polishing treatment of the inner surface of the pipe is omitted. The purpose is to heat-treat and lining the inner surface with a powder coating excellent in water hygiene. SOLUTION: After the inner surface of the cast iron pipe is subjected to the surface treatment, the mortar is supplied to the inner surface while rotating the pipe, the cement mortar is hardened as a uniform layer by centrifugal force, and then the hardened cement mortar layer surface is polished. , Rotate the tube again to supply the powder coating to the inner surface of the tube to create a uniform layer by centrifugal force, then insert an infrared heater inside the tube to heat only the powder coating layer and melt or cure it by heat. Let

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for lining an inner surface of a ductile pipe.

[0002]

2. Description of the Related Art Conventionally, when lining the inner surface of a large-diameter ductile pipe with a powder coating, the inner surface of the ductile pipe is polished to prevent the occurrence of paint film pinholes, and then the pipe is heated to the melting temperature of the powder coating. While rotating, the powder coating is supplied to the inner surface of the ductile pipe to melt the powder coating, and the coating is uniformly distributed by centrifugal force to perform coating.

[0003]

[Problems of the prior art] By the way, the inner surface of the ductile pipe has "wrinkles" peculiar to casting, and in order to prevent pinholes in the lining layer, it is necessary to polish the inner surface of the ductile pipe to be sufficiently smooth as described above. There is. However, the larger the diameter of the pipe, the more time and labor it takes to polish the inner surface, which is disadvantageous for mass production.

On the other hand, when the inner surface of the ductile pipe is mortar-lined, the above-mentioned "wrinkles" are covered with the mortar lining layer, so that the inner surface polishing can be omitted. However, for example, when coating epoxy resin powder coating with excellent water hygiene on the mortar lining layer, it is necessary to heat the mortar lining pipe up to around 200 ° C, which is the melting temperature of the powder coating. As a result, the mortar lining layer is affected, resulting in a decrease in strength, cracks and the like, and there is a disadvantage that the meaning of providing a lining layer with a sharp corner is lost.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present invention is capable of omitting the polishing treatment of the inner surface of a pipe when lining with a powder coating, and further, without lowering the strength of the mortar lining or generating cracks, It was made for the purpose of lining the inner surface with a powder coating excellent in water hygiene.

[0006]

According to the powder coating composition of claim 1, after the inner surface of the cast iron pipe is ground, the mortar is supplied to the inner surface while rotating the pipe and a uniform layer is formed by centrifugal force. After that, after polishing the surface of the cement mortar layer that has hardened, the tube is rotated again to supply the powder coating to the inner surface of the tube to form a uniform layer by centrifugal force,
Next, an infrared heater is inserted into the tube to heat only the powder coating layer to melt and cure it or heat it.

As the powder coating material, epoxy resin, polyethylene resin, polyester resin, etc. can be applied.

[0008]

In the inner surface lining method of the ductile pipe according to the first aspect of the present invention, since the cast iron pipe having the mortar lining on the inner surface is used, the polishing treatment of "wrinkles" peculiar to the inner surface of the cast iron pipe is completely unnecessary. Further, since only the layer surface of the powder coating material supplied onto the mortar lining layer is heated by the infrared heater, heat is difficult to be transferred to the mortar lining layer, and therefore the strength of the mortar lining layer is reduced by heat and cracks are generated. Is prevented.

When an epoxy resin is used as the powder coating material, the epoxy resin is more excellent in terms of water hygiene, so that the reliability of the obtained ductile pipe with respect to the water quality can be improved, and the epoxy resin can be adhered to the mortar lining layer. As a result, a tough lining layer can be formed.

[0010]

Next, an embodiment of the present invention will be described. FIG. 1 is a cross-sectional view when carrying out the method of the present invention, and FIG. 2 is a vertical cross-sectional view.

[Example 1] After the inner surface of a cast iron pipe 1 having an inner diameter of 1,000 mm was pretreated, cement mortar 2 was supplied to the inner surface while rotating the pipe 1 to form a uniform layer having a thickness of 10 mm by centrifugal force. After the cement mortar layer 2 which has been hardened and then hardened is polished to remove latance, the pipe is rotated again and the powder coating 3 made of polyethylene resin is supplied to the inner surface of the pipe to form a uniform layer by centrifugal force. Then, the infrared heater 4 was inserted inside the tube to heat and melt only the powder coating layer 3 to form the surface coating layer 3. Then, the tube was cooled, and the inner surface lining of the ductile tube was completed.

Example 2 The inner surface lining of a ductile pipe was prepared in the same manner as in Example 1 except that the powder coating material 3 made of polyethylene resin in Example 1 was used instead of the powder coating material 3 made of polyester resin. finished.

[Example 3] The inner surface of the ductile pipe was lined in the same manner as in Example 1 except that the powder coating material 3 made of polyethylene resin in Example 1 was replaced with the powder coating material 3 made of epoxy resin. finished.

[Comparative Example 1] Same inner diameter as in Example 1, 1,000 mm
The inner surface of the cast iron pipe 1 was polished by a grinder until the "wrinkles" peculiar to the cast iron pipe (P in the partially enlarged view of FIG. 1) disappeared. After that, the whole pipe is heated, the powder coating 3 made of polyethylene resin is supplied to form a uniform layer by centrifugal force, and the inner surface of the ductile pipe is lined by forming a surface coating layer directly on the inner surface of the pipe without forming a mortar layer. Finished.

[Comparative Example 2] Same inner diameter as in Example 1, 1,000 mm
After the inner surface of the cast iron pipe 1 is subjected to a surface treatment, the mortar 2 is supplied to the inner surface while rotating the pipe 1 and is hardened as a uniform layer having a thickness of 10 mm by centrifugal force, and then the hardened cement mortar layer 2 surface Was polished to remove latance. Then, the surface of the cement mortar layer 2 was seal-coated to complete the inner lining of the ductile pipe.

[Comparative Example 3] Same inner diameter as in Example 1 1,000 mm
After the inner surface of the cast iron pipe 1 is subjected to a surface treatment, the mortar 2 is supplied to the inner surface while rotating the pipe 1 and is hardened as a uniform layer having a thickness of 10 mm by centrifugal force, and then the hardened cement mortar layer 2 surface Was polished to remove latance. After that, the entire tube was heated, the powder coating material 3 made of polyethylene resin was supplied, and a uniform layer was formed by centrifugal force, whereby the inner surface lining of the ductile tube was completed.

Regarding Examples 1 to 3 and Comparative Examples 1 to 3,
When the adhesion strength of the lining layer, the influence on water quality and the required treatment time were compared, the results shown in Table 1 were obtained. The adhesive strength was measured by adhering a tensile terminal manufactured by Elcometer Co., Ltd. to the surface of the lining layer with an epoxy adhesive and pulling it with a testing machine. The influence on water quality was tested by filling each tube with tap water and allowing it to stand still, and measuring the amount of increase in pH after 24 hours.

[0018]

[Table 1]

As is clear from Table 1, in Comparative Example 3, the cement lining layer was affected by heat in the adhesive strength.
The coating film adhesion strength was low. Regarding the influence of water quality, in Comparative Example 2, a slight increase in pH due to the alkaline component was observed. Regarding the processing time for use, Comparative Example 1 was very long and not practical.

[0020]

As described above, according to the present invention, when a lining layer is formed on the inner surface of a cast iron pipe, the cement lining layer is provided on the inner surface of the cast iron pipe to hide "wrinkles" peculiar to the cast iron pipe, which is time-consuming. The step of polishing the inner surface of the cast iron pipe can be omitted, and the powder coating on the surface of the cement lining layer is heated and melted and cured by an infrared heater only to that layer, so it is a tough powder coating layer without damaging the cement lining layer. Can be provided. Therefore, a very reliable lining layer can be easily obtained. In particular, when an epoxy resin powder coating is used as the powder coating, the surface lining layer can be made excellent in terms of water hygiene, and the epoxy resin powder coating has high adhesiveness with the cement lining layer, Therefore, it becomes possible to easily obtain a lining layer having higher reliability.

[Brief description of drawings]

1 is a cross-sectional view when carrying out the method of the present invention.

FIG. 2 is a vertical cross-sectional view when carrying out the method of the present invention.

[Explanation of symbols]

 1 ... Cast iron pipe 2 ... Cement mortar 3 ... Powder coating 4 ... Infrared heater

Claims (1)

[Claims] 1. An inner surface of a cast iron pipe is subjected to an undercoating treatment, and while the pipe is being rotated, cement mortar is supplied to the inner surface of the cast iron pipe to be hardened as a uniform layer by centrifugal force, and then the surface of the hardened cement mortar layer is polished. After that, the tube is rotated again to supply the powder coating to the inner surface of the tube to form a uniform layer by centrifugal force, and then an infrared heater is inserted inside the tube to heat only the powder coating layer to melt and cure it. A method for lining an inner surface of a ductile pipe, characterized by hardening.