JPH0790599B2 - How to coat the inner surface of the pipe - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to pipes for corrosive liquids and gases such as acids and alkalis, and pipes made of metal or ceramics used for pipes required to have functions such as non-adhesion, insulation and low friction. Alternatively, it relates to a method of coating a fluorine resin on the inner surface of a synthetic resin pipe.

[0002]

2. Description of the Related Art When a pipe made of metal such as iron or aluminum is used as a pipe for corrosive liquid such as acid or alkali, the inner wall surface of the pipe is excellent in heat resistance, non-adhesiveness and chemical resistance. It is used after being coated with resin. As a method of coating the inner wall surface of the pipe with a resin, a method of applying a resin powder coating material or a dispersion coating material in which a resin powder is dispersed in a solvent to the inner wall surface of the pipe and then baking the coating material is generally used.

There is also a method of inserting a resin tube having a thickness of 2 to 3 mm into a pipe. Further, as a corrosion-resistant application and other applications, for a large-diameter pipe having a diameter of 500 mm or more, there is also a method in which resin sheets are attached to each other with an adhesive and the seams between the sheets are welded. Furthermore, there is also a method in which an appropriate amount of resin powder or granules is put into a pipe, both ends of the pipe are closed by an appropriate method, and the resin in the pipe is welded to the wall surface of the pipe by heating and rotating from the outer surface. This method can be applied to a pipe having a small diameter, but a pipe having a diameter of 25 mm or less cannot often obtain a uniform coating due to the resin dropping during rotation.

[0004]

However, the method of applying the paint to the inner surface of the pipe has poor workability and the working method is limited. Furthermore, when the spray method is used for coating the inner surface of a thin pipe with an inner diameter of about 25 mm or less, there is no spray nozzle suitable for such a small diameter, and it is necessary to atomize the coating liquid during spraying. In order to atomize the coating liquid ejected or blown from the mouth, a minimum distance of 10 to 15 mm is required. Therefore, it is difficult to select the nozzle position for a pipe with an inner diameter of 25 mm or less, The current situation is that it does not turn into a uniform coating. Also,
If an attempt is made to apply while moving the nozzle for atomization of the coating liquid, the nozzle may come into contact with the coating surface that has not been sufficiently cured and stain the coating film.

Further, in the method of pouring a liquid substance on the inner surface of the pipe, only a thin film is formed, and further, the liquid substance does not uniformly adhere to the inner surface of the pipe, so that the original function of the coating film is sufficiently exhibited. Often not.
The method of press-fitting a resin tube has good workability and can obtain a uniform coating surface, but since it is difficult to press-fit a pipe having an inner diameter of 50 mm or less or a long pipe having an inner diameter of 50 mm or more, The scope of application was limited. .

The present invention has been made in view of the above circumstances, and an object thereof is to coat the inner surface of the pipe uniformly regardless of the length and diameter of the pipe and to improve workability. It is to provide a coating method for the inner surface of a pipe.

[0007]

The method for coating the inner surface of a pipe according to the present invention has an outer diameter smaller than the inner diameter of the pipe.
And, and one the other in the closed end inserts fluororesin tube is the open end into the pipe insertion step; said Ju
Fluorine-based material that constitutes the tube from the open end of the tube
By blowing air at a temperature below the melting point of the resin,
Expansion step of expanding the diameter of the tube in the pipe ;
Pipe heating that heats the pipe above the melting point of the tube
Heating step; and contact between the inner wall surface of the pipe heated in the pipe heating step and the tube expanded in the expansion step.
While in the tube molten Ri, characterized in that it comprises a fusion Chakukotei that Ru fusing the tube to the pipe wall.

[0008]

Since the coating method of the present invention is a method of inserting a tube having an outer diameter smaller than the inner diameter of the pipe into the pipe, no coating work or the like is required, and the workability is good, and even for a long or thin pipe. Applicable. Further, since the diameter of the inserted tube is expanded by blowing air and the tube is fused to the inner wall surface of the pipe, a uniform smooth surface can be obtained.

Further, the heating for bringing the tube into a molten state does not directly heat the tube from the inside of the tube but heats the tube through a heated pipe, so that the fluororesin forming the tube is heated. The temperature restriction of melting or lower than the decomposition temperature above the softening melting point is slightly relaxed, and the temperature control is simplified. That is, since the tube is heated from the outer surface by coming into contact with the heated pipe, it is rather preferable from the viewpoint of fusion even if it is overheated to about the melting point of the fluororesin,
Even if it is overheated to near the decomposition point, if the temperature above the decomposition point is not maintained for a certain time, only the outer surface of the tube will be overheated, so it will not cause deformation or uneven thickness of the tube. It does not affect the uniformity and smoothness of the inner surface.

[0010]

The method of the present invention will be described below. As the pipe to which the method of the present invention can be applied, material, length,
The inner diameter is not particularly limited, but a pipe made of metal, ceramics, or thermosetting resin is generally used.

The constituent material of the tube has excellent characteristics such as chemical resistance, non-adhesiveness, heat resistance, weather resistance, electrical characteristics, low friction coefficient and self-lubricating property, and can be formed into a tubular shape.
It is a fluororesin that is a thermoplastic resin that can be fused by heating. Examples of the fluorine-based resin include tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer (ETFE), poly Tetrafluoroethylene (TFE) etc. are mentioned.

The outer diameter of the tube is smaller than the inner diameter of the pipe to be applied.
It is preferably from 8 to 70%, particularly preferably from 95 to 90%. The thickness of the tube is not particularly limited, but is preferably about 0.02 to 1 mm. If it is too thin, it will be broken as a result of expanding the diameter. Therefore, it is necessary for the outer diameter of the tube to be equal to the inner diameter of the pipe so that it does not break even when expanded.

Such a tube is inserted into a pipe to be coated, the tube is expanded in diameter , and the pipe is heated to a temperature above the melting point of the tube. Expansion process to expand the tube until it can contact the inner wall surface of the pipe,
The order of the pipe heating step of heating the pipe to the melting point of the tube or higher (about 380 ° C. in PFA) is appropriately selected. That is, after the tube expansion heating, after heating Chu
Inflated Bed, or tube may be heated while expanding.

The tube may be expanded by any method as long as the diameter can be expanded isotropically in the circumferential direction. For example, a method of blowing air into the tube can be mentioned. Temperature during expansion, is appropriately selected according to the inflation method. For example, when expanding by blowing air into the tube, the temperature is below the melting point of the tube (about 300 ° C for PFA).
It is preferable to hold for about 20 to 30 minutes.

The method for heating the pipe is not particularly limited,
A method of heating the whole pipe by putting it in an oven (see FIG. 1), a method of moving a small heater in the axial direction of the pipe to sequentially heat from the end of the pipe (see FIG. 2), a method by dielectric heating, etc. Can be mentioned. When the pipe and the pipe are in contact with each other and the pipe is heated above the melting point of the tube, or when the expanded wall comes into contact with the inner wall surface of the pipe heated above the melting point of the tube, the outer surface of the tube It melts and fuses to the inner wall surface of the pipe.

After the tube is fused to the inner wall surface of the pipe and then the whole is cooled, a coating surface made of the constituent material of the tube is formed on the inner surface of the pipe. In the method of inserting the tube in this way, the coating work is not performed unlike in the case of paint, so that the workability is good, and it can be applied regardless of the length and inner diameter of the pipe. In addition, since the diameter is isotropically expanded and fused, a uniform and smooth coating surface can be obtained. [Specific Example] An N, N dimethylformamide solution (10%) of polyparabanic acid (PPA) was uniformly poured into an iron pipe having an inner diameter of 14 mm and a thickness of 2 mm, and dried at 280 ° C for 1 hour. In this pipe, as shown in FIG.
m, thickness 50 μm PFA with one closed end and the other open end
The tube 6 made of the material was inserted, and the heater 7 was set at one end of the pipe 5. The temperature of the heater 7 is set to 400 ° C., and air is blown from the open end of the tube 6 at an air pressure of 0.6 kg / cm ² at a speed of 500 mm / min and the heater 7
Was moved from one end of the pipe 5 to the other end.

On the inner wall surface of the pipe, a uniform and smooth coating surface without air entrapment was formed. The adhesion of the coating surface to the inner wall surface of the pipe was high.

[0018]

The coating method for the inner surface of the pipe of the present invention can be applied to various pipes regardless of the inner diameter and length of the pipe. Moreover, since the tube is expanded and fused by heating, a uniform and smooth coating surface can be formed. The method of the present invention also comprises heating the pipe,
Ju <br/> over blanking is heated to a molten state by the heated pipe and tube are in contact Runode, by hot fluid
The temperature control during heating is simpler than the direct heating of the tube, and the tube can be brought into a molten state so as to be fused to the inner wall surface of the pipe without affecting the smoothness of the inner surface of the tube.

Further, the method of the present invention has good workability because it does not perform coating work or the like. Furthermore, since the fluororesin tube is used in the method of the present invention, a pipe excellent in heat resistance, chemical resistance, electrical characteristics and the like can be obtained by the method of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining another embodiment of the present invention.

FIG. 3 is a schematic diagram for explaining another embodiment of the present invention.

[Explanation of symbols]

 1 pipe 2 tube 5 pipe 6 tube 10 pipe 11 tube 12 suction tube

 ─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-2-202432 (JP, A) JP-A-60-121380 (JP, A) JP-A-56-80422 (JP, A) JP-A-62-1 27135 (JP, A)

Claims (1)

[Claims] [Claim 1] have a smaller outer diameter than the inner diameter of the pipe,
And an inserting step of inserting a fluororesin tube , one of which is a closed end and the other of which is an open end, into the pipe; the tube is formed from the open end of the tube.
Blowing air at a temperature below the melting point of the fluororesin
The expansion engineering whose diameter increases the tube within the pipe
Extent; pi for heating the pipe above the melting point of the tube
Heating step; and contact between the inner wall surface of the pipe heated by the pipe heating step and the tube expanded in the expansion step.
Wherein with the tube into a molten state, coating methods of the pipe inner surface, characterized in that it comprises a fusion Chakukotei that Ru fusing the tube to the pipe wall by.