JPH0242552B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a resin coating layer on the entire or partial inner surface of metal pipes using powdered resin (hereinafter referred to as powder).

BACKGROUND ART Conventionally, metal pipes have been widely used, the inner surface of which is coated with an anticorrosive coating layer of bituminous paint or synthetic resin for the purpose of anticorrosion. Among these, in metal tubes that are welded and joined on-site, the coating layer is thermally affected by welding heat, so an uncoated portion is provided in advance on the inner surface of the tube end. Therefore, after welding and joining at the site, it is necessary to form a coating layer on the uncoated portion of the joint surface. Further, during use of the metal tube, the coating layer may partially deteriorate or peel off, and it is necessary to form a coating layer on this portion for repair.

Conventionally, a method of applying a bituminous paint was used to form a coating layer on the limited portion of the inner surface of the pipe, but if the pre-formed coating layer was made of synthetic resin, the existing method This results in the formation of a coating layer that is different from the coating layer, resulting in incomplete fusion and the corrosion resistance of each coating layer being different, posing a problem in terms of anticorrosion performance.

As a method to solve this problem, a method was developed in which a powder of the same material as the existing coating layer was heat-fused to the uncoated area to form a coating layer, and a patent application was filed (Japanese Patent Laid-Open No. 115668/1983). There is. The coating layer forming step according to the method disclosed in this patent application is performed by the following procedure.

(1) Prepare the welded and uncoated parts by polishing, etc.

(2) Heat the area to be coated using a heating device from outside the tube.

(3) Inserting and setting the coating device into the pipe to form a space surrounding the part to be coated, and filling or scattering the powder into the space.

Note that the tube may be heated after it is filled with powder.

(4) After the powder filled or spread in the space comes into contact with the inner surface of the tube and an appropriate amount is heated and fused, the excess powder is collected with a collection hose.

(5) After taking the coating device out of the tube, reheat it with a heating device to completely fuse it.

(6) After complete fusion, let it cool or cool it with water from the outside.
The coating layer forming process is thus completed.

This method can be applied to welded joints, areas where the coating layer has peeled off, etc.
Although this is an excellent method for forming a coating layer using powder of the same material, it has been found that there are still some problems. That is, in the method disclosed in JP-A No. 56-115668, the powder is introduced into the space formed by the inner surface of the tube and the coating device using a pressure feeding method, and then filled or dispersed. On the upper side of the surface, the powder comes into contact only momentarily, resulting in a partially patchy coating, and on the lower side, the accumulated powder is layered, increasing the thickness of the coating layer, making it difficult to form a coating layer with a uniform thickness. In the filling method, air is released through an air vent with a filter while filling the powder into the space.
The air may not escape reliably and may remain as an air pocket on the upper side of the space, and the remaining air may not be sufficiently filled with powder, resulting in a complete coating layer on the inner surface of the tube facing this part. could not be expected to form, and it was still difficult to form a coating layer with a uniform thickness.

Furthermore, the following problem occurred when collecting excess powder after heat-sealing the powder. That is,
After the powder is heated and fused to the desired thickness, the heating of the tube is stopped, and while it is left to cool naturally, the excess powder filled in the tube is sucked by a suction blower, and air is taken in from the nozzle leading to the outside of the device, stirred, and collected. However, the agitating air that is taken in only by suction has a large flow resistance when it is filled with powder that is pressurized by pressure feeding.
It takes time to recover the flaws in order to easily recover the powder, and even though the tube wall temperature gradually decreases during powder recovery, it still exceeds the melting temperature of the powder at the beginning, so even when the powder is recovered, it still exceeds the melting temperature of the powder. Powder fusion progresses on a portion of the inner surface of the tube, and the thickness of the coating layer becomes increasingly uneven. In addition, since the heating part during natural cooling has a soft coating layer that is above its softening point, the suction agitation air may impact the surface and create unevenness, or the coating layer may be damaged due to accidents such as contact when taking out the device. There is a fear.

It is an object of the present invention to advantageously solve the above-mentioned problems and to provide a method capable of forming a uniform coating layer on the inner surface of metal pipes using powdered resin.

That is, the first invention of the present application is to fill the space facing the portion of the inner surface of the tube with powdered resin, and heat-fuse the powdered resin connected to the inner surface of the tube to coat the inner surface of the tube. The method for forming a layer is characterized in that the space is filled with powdered resin after or while the air in the space is removed by suction, thereby causing air pockets in the space. This is a method for forming an inner surface coating of metal pipes, which enables uniform filling of powdered resin and forms a coating layer with a uniform thickness. Here, a normal pressure feeding method may be used for transferring and filling the powdered resin, or a suction method using negative pressure within the space may be used.

In addition to the features of the first invention, the second invention of the present application provides that, after heating and fusing a desired amount of granular resin to the inner surface of a metal tube, the metal tube is rapidly cooled to form a coating layer of a desired amount or more. It is also characterized by stopping the
This prevents the powdered resin from being partially heated and fused to the inner surface of the tube when collecting surplus resin, and also prevents the formed coating layer from becoming uneven or damaged, resulting in a coating with a more uniform thickness. This is a method for forming an inner surface coating of metal tubes in which a layer can be formed.

Hereinafter, the present invention will be described in further detail with reference to embodiments shown in the drawings.

FIG. 1 shows a coating device 1 used for carrying out the method of the present invention.
and heating device 2, these devices 1 and 2 are set in a predetermined position for forming a coating layer on the uncoated portion 5 near the end welded joint 4 of the metal tubes 3 and 3. Shown by condition. In addition, code 6
is a resin coating layer previously applied to the inner surface of the metal tube 3 at a factory.

The coating device 1 includes a hollow cylindrical core 11, the core 1
a closing plate 12 fixed to one end of the core 11 and a closing plate 13 fixed to the other end of the core 11 via a rectifying plate 14;
A hollow rubber seal ring 15 that can be inflated with compressed air is attached to the outer periphery of each of the closing plates 12 and 13. These occlusion plates 12,
13 and the core 11 form a powder filling space 16 surrounding the portion of the inner surface of the tube to be coated. Note that the gap between the core 11 and the inner surface of the metal tube 3 is
In order to reduce the volume of the space 16 and shorten the powder supply and filling time and the discharge and collection time, it is preferable to uniformly fill the powder as much as possible. One of the closing plates 13 (the one on the right in the drawing) has a central tube section 13A and a conical section 13B following it, and between the conical section 13B and the end of the core 11,
A conical powder supply/discharge passage 17 communicating with the space 16 is formed. A plurality of rectifying plates 1 are provided in the passage 17.
4 are installed in parallel in the axial direction. The conical passage 17 and the rectifying plate 14 therein are suitable for uniformly supplying the powder from the tube section 13A to the space section 16, and conversely for uniformly sucking the powder in the space section 16 into the tube section 13A. be. The pipe portion 13A is connected to a powder tank 31 of a powder supply and recovery device 30 shown in FIG. 2 through a powder supply and discharge hose 18.

A suction port 19 with a filter is provided near the end of the core 11 on the opposite side from the passage 17, and the suction port 19 is connected to the suction side of a turbo blower 32 shown in FIG. 2 via a suction hose 20. has been done. Although one suction port 19 is provided in the illustrated embodiment, the number is not limited to one, and a plurality of suction ports 19 may be provided in the circumferential direction. A large number of nozzles 21 are provided on the cylindrical surface of the core 11, and the tip of a compressed air introduction hose 23 connected to a compressor 33 shown in FIG. 2 is inserted into the core 11. The nozzle 21 blows out compressed air during powder recovery, stirs and rotates the powder in the space 16, and blows it in the direction of the passage 17, thereby speeding up the recovery of the powder. When recovering the powder, the mixed fluid of powder and compressed air that is being stirred and rotated in the space 16 flows into the passage 17 and is rectified into an axial flow by the rectifier plate 14, so that the fluid can be passed through the supply/discharge hose without any hindrance. It flows within 18.

Conveying wheels 2 are provided at both ends of the coating device 1, respectively.
4 and 25 are attached, thereby allowing the coating device 1 to travel within the metal tube 3 to a predetermined position.

In FIG. 2, the powder supply and recovery device 30 includes a powder tank 31 containing powder of the same material as the existing coating layer 6, a turbo blower 32, a compressor 33, etc., and the powder in the powder tank 31 is pumped with compressed air. The powder in the space 16 can be collected into the powder tank by the suction force of the turbo blower 32. Since these can be used as known ones, detailed explanation will be omitted.

Referring again to FIG. 1, the heating device 2 heats the portion of the metal tube where the coating layer is to be formed to a temperature higher than the melting temperature of the powder, and in the illustrated embodiment an induction heating coil is used. Note that devices other than induction heating, such as an electric heater or a gas burner, may be used.

Next, a method for forming a coating layer using the above-mentioned apparatus will be explained. As shown in FIG. 1, a coating device 1 is connected to a metal tube 3
and the heating device 2 is attached to the outside of the coating layer forming section. Next, the heating device 2 is activated to heat the inner surface of the tube to a temperature higher than the melting temperature of the powder to be coated, and then the powder is supplied to the space 16. In this case, while operating the turbo blower 32 and removing the air in the space 16 by suctioning or removing it through the suction port 19 and the suction hose 20, the powder in the powder tank 31 is removed by the hose 1.
8. Supply and fill the space 16 through the passage 17. The amount of air sucked by the turbo blower 32 is selected so that the inside of the pipe becomes negative pressure. Thus,
Powder is filled uniformly and quickly without air pockets forming in the space 16. Note that when powder filling is performed while removing the air in the space 16 by suction, depending on the particle size and shape of the powder, it is not necessary to constantly perform the suction operation during the powder filling operation. at least for a period of time
It is also possible to simply apply suction to create a negative pressure inside the tube.

The powder filled in the space 16 is sequentially melted and fused to the inner surface of the tube starting from the powder that comes into contact with the inner surface of the tube, thereby forming a coating layer. The thickness of this coating layer increases over time, so after the time required to form a coating layer of a desired thickness, if the heating device 2 is energized to maintain the temperature, immediately turn off the heating device 2. The operation is stopped, and the heated heating section is rapidly cooled from the outside surface of the tube by an appropriate cooling method, for example, water cooling. This ensures that the covering layer no longer grows and remains at the desired thickness. Note that heating of the metal tube 3 is not limited to before filling with powder, but may be performed after filling.

Next, the suction force of the turbo blower 32 is applied to the powder tank 31 to bring the inside of the tank 31 into a negative pressure state, and the excess powder in the space 16 is sucked into the tank 31 through the hose 18 and collected. At this time, by supplying compressed air from the compressor 33 into the core 11 and ejecting it from the many nozzles 21, the excess powder in the space 16 is agitated by this compressed air, and the air is supplied to the passage 17 and the hose 18. The powder is sent in using the pressure of compressed air, and the powder is discharged and collected extremely quickly. Note that although the air ejected from the nozzle 21 may impact the formed coating layer, since the coating layer has already been cooled to below its softening temperature, no unevenness will occur on the surface.

After the collection of powder is completed, the coating device 1 is taken out. Even in this case, the coating layer is not damaged by the coating device 1. After that, heating is performed again using the heating device 2 to a temperature higher than the melting temperature to form a complete fused coating layer,
Finally, the existing coating layer 6 is cooled by air cooling or water cooling from the outside, as shown in Figure 3.
A coating layer 26 made of the same material is formed which partially overlaps and is fixed to the surface.

In the above example, after the required thickness of the coating layer has been formed using the filling powder, the coating layer forming part is immediately quenched from the outside of the tube and the coating layer formation is stopped. Even if they are in contact, the coating layer does not grow, and even if the time difference between the start and end of discharge and collection of excess powder becomes large, there will be no difference in the thickness of the coating layer. in this way,
After forming the coating layer, rapid cooling is extremely effective in forming a coating layer with a uniform thickness. However, depending on the powder used, or when it is not necessary to form a very uniform coating layer over the entire coating, rapid cooling from the outside of the tube may not be necessary and it may be sufficient to simply allow the powder to cool. For example, a powder with a high melting point such as a soft resin requires a large amount of heat when forming a molten coating layer, and it also takes a long time for the coating layer to grow, so simply stopping the heating by the heating device 2 is sufficient. Subsequent growth of the coating layer does not occur much, and therefore, even if it takes time to discharge and collect the powder, the difference in film thickness does not become too large, and a coating layer with a relatively uniform thickness can be formed.

Next, FIG. 4 shows a modification of the coating apparatus 1 used for carrying out the method of the present invention. In the coating device 1 of FIG. 4, the seal bearing 4 of one of the closing plates 12 is
0 and the support body 41 attached to the other closing plate 13
A rotating core 43 is rotatably held by a sealed bearing 42, and a motor 44 is used to rotate the rotating core 43. The rotating core 43 has a suction port 19 and a nozzle 21 on its cylindrical surface. In addition, screw blades 45 are provided. In addition, the rotating core 43
A suction hose 20 and compressed air introduction hoses 23 and 46 are connected to the shaft end of the rotary joint through appropriate rotary joints. The suction hose 20 is connected to the suction port 19 via a pipe inside the core, and acts to suck air from the space 16 when filling the space 16 with powder. The introduction hose 23 supplies compressed air into the rotating core 43 when collecting excess powder,
It acts to blow out air from the nozzle 21. The inlet hose 46 connects to the hollow rubber seal ring 15 via a pipe in the core and a suitable rotary joint (not shown).
It is connected to the.

The coating device 1 shown in FIG. 4 having the above structure is also set in a tube in the same way as the one shown in FIG. . However, the two methods differ in the discharge and collection of excess powder. That is, in the coating device shown in FIG.
Rotating core 43 while sucking powder from 3A
is rotated, and most of the excess powder in the space 16 is sent into the tube part 13A side by the screw blade 45. At the same time, a small amount of powder remaining in the small gap between the tip of the screw blade and the surface of the coating layer, where the screw blade does not act, is sent to the pipe portion 13A side by air blown from the nozzle 21 and is discharged. Thus, with the apparatus shown in FIG. 4, excess powder can be discharged and recovered in an extremely short time. As mentioned above, this device has a short recovery time for surplus powder, so even if there is a slight time lag between discharge and recovery, there will be no difference in the thickness of the coating layer when using powder, or if there is a slight difference in the thickness of the coating layer. If this does not pose a problem, the rapid cooling step after the fusion formation of the coating layer can be omitted, which is very suitable.

In all of the above embodiments, a powder feeding method is used to supply and fill the space 16 with powder.
The powder supply method is not limited to the pressure feeding method, and other methods such as a suction method using negative pressure within the space 16 may be used. Furthermore, the apparatuses shown in FIGS. 1 and 4 can be used not only to form a coating layer on the uncoated portion of the inner surface of an in-situ welded joint of an internally coated metal tube, but also to repair a damaged portion of an existing coating layer.

Furthermore, the present invention is not limited to the case where the coating layer is formed only on a part of the inner surface of the tube as shown in the above embodiment;
It is also applicable when forming a coating layer on the entire inner surface of a tube. FIG. 5 shows an example in which a coating layer is formed on the entire inner surface of the curved pipe 50. In the same figure, first, the entire curved tube 50 is heated in a furnace or the like, and then a powder supply tube 51 is connected to one end of the curved tube 50, and a filter 5 is connected to the other end.
Connect the suction tube 52 with 3. After the air inside the curved tube 50 is suctioned and removed by the suction tube 52, or while being suctioned and removed, powder is supplied from the supply tube 51 to fill the curved tube 50, and the powder in contact with the inner surface is heated and fused. After forming the coating layer of a desired thickness, the curved tube 50 is rapidly cooled, the coating layer formation is stopped, and the excess powder inside is discharged by an appropriate method. As described above, an extremely uniform resin coating layer can be formed on the entire inner surface of the curved pipe 50. In addition, this curved pipe 5
For heating at zero, other means such as a burner or high-frequency induction heating may be used in addition to a heating furnace, or a suitable core may be placed in the curved tube 50 to reduce the powder filling space. This method is not limited to forming a coating layer on a curved pipe of the shape shown, but can also be applied to straight pipes, flanges, and those having mechanical joints.

As explained above, according to the first invention of the present application, when the powder is force-fed and filled into the space surrounding the portion of the inner surface of the tube where the coating layer is to be formed, air is removed by suction from the space. Therefore, air pockets which conventionally tend to occur on the filling upper side of the space are eliminated, and a coating layer of uniform thickness can be formed. Furthermore, according to the second invention of the present application, after a desired amount of powder is melted and fused to the inner surface of the tube, this portion is rapidly cooled to below the melting temperature of the powder, so that when collecting surplus powder, the powder is formed first. Even if a compressed air jet nozzle is used to discharge and collect excess powder, the ejected air will cause unevenness in the covering layer. Therefore, it is possible to form a smooth coating layer with a more uniform thickness.
As a result, not only can a uniform coating layer be formed on the entire inner surface of the tube, but also a coating layer of uniform thickness made of the same or similar material as the existing coating layer can be applied to a part of the inner surface of the cladding tube. It can be formed completely integrated with the end of the existing coating layer, and a coating layer with excellent corrosion resistance and electrical insulation can be formed.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an example of the coating device and heating device used in the method of the present invention, set in a predetermined position, and Fig. 2 is a section showing the coating device of Fig. 1 and the powder supply and recovery device combined therewith. 3 is a sectional view showing a coating layer formed by the method of the present invention; FIG. 4 is a sectional view similar to FIG. 1 showing a coating device different from that in FIG. 1;
The figure is a horizontal cross-sectional view showing a state in which a coating layer is formed on the entire inner surface of a curved pipe according to the method of the present invention. DESCRIPTION OF SYMBOLS 1... Coating device, 2... Heating device, 3... Metal tube, 4... Welded joint part, 5... Uncoated part, 6...
Existing coating layer, 16... Space, 18... Powder supply/discharge hose, 19... Suction port, 20... Suction hose, 30... Powder supply and recovery device, 32... Turbo blower.

Claims (1)

[Claims] 1. A coating layer is formed by filling the space facing the portion of the inner surface of the tube with powdered resin, and heating and fusing the powdered resin in contact with the inner surface of the tube to the inner surface of the tube. A method for forming an inner surface coating for metal pipes, characterized in that the space is filled with powdered resin after or while the air in the space is suctioned and removed. 2. A method for forming a coating layer by filling a space facing a portion of the inner surface of a tube with powdered resin and heating and fusing the powdered resin in contact with the inner surface of the tube to the inner surface of the tube, as described above. After suctioning or removing the air in the space, the space is filled with granular resin, and further, after heating and fusing a desired amount of granular resin to the inner surface of the metal tube, the metal tube is rapidly cooled. A method for forming an inner surface coating on metal pipes, characterized by stopping the formation of a coating layer in excess of a desired amount.