JPH0155907B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a flanged inner-coated metal tube. Conventionally, the inner surface of metal pipes such as steel pipes has been coated with polyethylene to give them properties such as corrosion resistance and chemical resistance.
Coating with synthetic resin such as vinyl chloride resin is practiced, for example, the so-called lining method in which the inner surface of a metal pipe is lined with synthetic resin such as hard vinyl chloride pipe with an adhesive, and both ends of a preheated metal pipe are coated with synthetic resin such as vinyl chloride resin. There is a so-called powder coating method in which the inner surface of the metal tube is coated with resin by holding the metal tube in a joint and feeding a mixture of resin powder and gas into the metal tube. When joining metal pipes whose inner surfaces are coated with resin, the general method is to attach a metal flange to the end of the pipe, butt the flanges together via elastic packing, and connect them with bolts and nuts. The joint surfaces of the flanges must also be coated with synthetic resin. Therefore, in the case of the above-mentioned lining method, for example, as described in Japanese Utility Model Publication No. 51-51043, a flanged short pipe made of synthetic resin with a brim provided at one end of the straight pipe part is inserted into the synthetic resin lined pipe and bonded. The inner surface of the metal flange is coated. However, when products manufactured by this method are used in fields that require severe conditions such as chemical resistance and heat resistance, there is a problem that corrosion resistance cannot be guaranteed for a long period of time. be. On the other hand, in the case of the powder coating method, a resin coating layer is formed in a single coating process on the inner surface and flange surface of a flanged metal tube with a flange attached to the tube end in advance using an appropriate holder. However, in this case, depending on the shape and dimensions of the holder, the flow of the resin powder and gas mixture near the flange surface may be suddenly disrupted, causing the thickness of the coating layer on the flange surface and the pipe end to decrease. The disadvantage is that the thickness of the coating layer on the flange surface and the end of the tube becomes extremely thick or non-uniform due to thinning or, conversely, a pool of resin powder near the flange surface. Further, since the thickness of the coating layer on the flange surface is non-uniform, a step is formed on the flange surface, which causes a disadvantage that the sealing performance of the connection portion is deteriorated. In addition, if the thickness of the coating layer becomes extremely thick, it can be scraped off to a specified thickness using a grinder, etc., but normally, as the thickness of the coating layer increases, pinholes occur in the coating layer. As the number of pinholes increases significantly, even if the flange surface appears smooth, microscopically many pinholes are crushed, creating an uneven surface, which still causes the problem that reliable sealing performance cannot be obtained. remain. Furthermore, at piping sites, resin-coated metal pipes with flanges of various lengths are often required, but in this case, long inner-surface resin-coated metal pipes are cut to the specified length. It is efficient to weld the flange and form a resin coating layer on the tube end. In view of the above circumstances, the present invention provides a flanged inner-coated metal tube in which a smooth and uniformly thick polyphenylene sulfide resin (hereinafter abbreviated as PPS resin) powder coating layer is formed on the flange surface and inner surface of the tube. The purpose of this work is to provide a manufacturing method. What is the PPS resin powder used in the present invention?

It is a powdered compound containing a repeating unit of the formula, which may be partially oxidized or crosslinked. As a guideline for the molecular weight of the PPS resin, for example, if the MI value under a load condition of 320°C x 5 kg is 200 to 2000 g/10 minutes, a dense coating layer with an extremely smooth surface and no pinholes can be obtained. It will be done. A filler such as alumina powder may be added to the PPS resin powder used in the present invention. Hereinafter, the present invention will be explained based on FIGS. 1 to 4. 1 is a metal tube, and a coating layer 2 of PPS resin powder is formed on the inner surface of the tube by a known coating method. Next, flanges 3 are welded and attached to both ends of the metal tube 1 (it may be only one end). To prevent sparks from hitting the internal coating layer 2 during welding,
As shown in FIG. 2, it is preferable to perform masking 4 using an appropriate material. Further, in order to reduce the number of burnt parts 5, 5 of the coating layer 2 at both ends as much as possible, it is preferable to cool the vicinity of both ends. Next, as shown in FIG.
1 is exposed. When scraping off the burnt parts 5, 5, by forming a taper in the back direction on the boundary end faces 6, 6 as shown in Fig. 3, a smoother and better coating can be obtained during the subsequent coating on the flange surface in the next step. You get layers. The end of the metal tube 1 and the flange 3 are locally heated, and the flange surface 31 and the inner surfaces 11, 1 of the metal tube are heated.
1. Spray PPS resin powder using an electrostatic coating gun or the like to fuse it. At this time, it is best to perform this while rotating the entire metal tube. Continue heating and PPS
By crosslinking the resin, the flange surfaces 31, 31 and the inner surface 11 of the metal tube 1 shown in FIG.
A flanged inner-coated metal tube in which a smooth, tough, and uniformly thick PPS resin coating layer 7 is formed on the flange 11 is obtained. Incidentally, in order to improve the adhesion between the PPS resin coating layer and the metal surface, the flange surface and the exposed inner surface of the metal tube may be subjected to surface treatment with an appropriate primer. In addition, the above flange surface and the inner surface of the metal tube
The PPS resin powder may be sprayed at room temperature, and then the sprayed part may be heated to melt it. As described above, the method of the present invention involves welding and attaching a flange to the end of a metal tube having a PPS resin coating layer formed on the inner surface, and then removing the damaged portion of the coating layer from the tube end. The same as above is applied to the removed part and flange surface.
Since this is a method of spraying and painting PPS resin powder and then heating it to form a coating layer, a smooth and uniformly thick PPS resin powder coating layer is formed on the flange surface and the inner surface of the metal tube, and can be applied to any length. A flanged inner-coated metal tube can be obtained. Furthermore, resin-coated metal tubes of various lengths can be easily produced. Examples of the present invention will be described below. The inner surface is coated with PPS resin powder approximately 400μ thick.
A SGP100A pipe (length 2.75 m) was prepared, and 10KF flanges were welded and attached to both ends of this pipe. Welding was performed by masking to prevent sparks from hitting the resin coating layer on the inner surface, and by water cooling near the ends to reduce burnt parts of the resin coating layer. The resin coating layer up to about 50mm from the end surface was burnt, so this part of the coating layer was scraped off with a grinder and a file.
The scraped portion and the flange surface were blasted to remove rust and roughen the base, and then a primer was applied to provide a base treatment. Next, while rotating the metal tube at 30 rpm, the flange part and the scraped part of the PPS resin coating layer were locally heated to approximately 380°C using an aluminum casting heater, and PPS resin powder was sprayed onto the areas using an electrostatic coating gun. After fusion, the sprayed part was heated at 380°C for 30 minutes to crosslink the PPS resin, and then cooled with water to obtain a flanged inner-coated metal tube in which the flange surface and the inner surface of the metal tube were coated with PPS resin powder. Ta. The surface of the coating layer of the flanged inner-coated metal tube was excellent in smoothness, and the thickness distribution of the coating layer on the flange surface and in the vicinity of the flange was almost uniform as shown in FIG.

[Brief explanation of drawings]

1 to 4 are explanatory diagrams showing the manufacturing process of the method of the present invention, and FIG. 5 shows the thickness distribution of the coating layer on the flange surface and in the vicinity of the flange. 1... Metal tube, 2, 7... Coating layer, 3... Flange, 31... Flange surface, 4... Masking,
5...burnt part, 6... boundary end face.

Claims (1)

[Claims] 1. A flange is welded to the end of a metal tube on which a coating layer of polyphenylene sulfide resin is formed on the inner surface, and a portion of the coating layer of the flanged metal tube that is damaged due to welding is removed from the tube end. An inner-coated metal tube with a flange, characterized in that a metal surface is exposed, the exposed metal surface and the flange surface are sprayed with powder of the same resin as the coating layer, and then heated to form a coating layer. manufacturing method.