JPS5935667B2 - Metal pipe inner surface coating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for powder coating the inner surface of a metal tube.

In the case of metal pipes used for water, sewage and seawater transportation,
The inner surface is coated to prevent corrosion.

Powder coating has traditionally been used to coat the inside of metal tubes, but the method involved pumping a mixture of thermosetting and thermoplastic powder coatings and air through one end of the preheated metal tube, and then applying the mixture to the other end. Alternatively, the pressure inside the metal tube is set to negative and the paint is fed into the tube from one end using the pressure in the fluidizing tank or the difference between the atmospheric pressure and the paint is sucked and collected from the other end. However, with the above method, when painting long straight pipes, it tends to cause differences in the coating film thickness in the pipe axis direction, and it is necessary to improve the paint passing speed, time, and shape of the attachments at both ends of the pipe. A difficult problem arose.

Furthermore, since the paint is fed from one end of the tube, it is not possible to paint at right angles to the surface to be painted, which is the basis of painting, and defects such as pinholes are likely to occur. This tendency is particularly strong for materials with rough inner surfaces such as centrifugal cast iron pipes, and even if the powder paint is charged with static electricity of 30,000 to 90,000 V, it cannot follow the irregularities on the inner surface of the pipe and the pins become pinned. A hole is created. Furthermore, the paint sent into the pipe or the paint sucked out is not entirely coated on the inner surface of the pipe, and a considerable amount reaches the collection booth, but depending on the preheating temperature of the pipe, the paint may gel. Also, with fast-curing paints, there is a problem in that a part of the paint is semi-cured, causing a streak-like phenomenon. The present invention improves the coating efficiency by applying the paint at a certain angle to the surface to be painted, prevents defects in the paint film such as pinholes, and achieves industrially efficient coating. The purpose is to provide a coating device that can coat a film.

In order to achieve this object, the present invention provides two systems that are rotatably supported around the axis, movable relative to each other in the axial direction of the preheated coated metal tube, and that have a cooling water chamber formed inside. A lance with a heavy pipe structure is provided, and an insulating feed pipe capable of feeding powder paint and equipped with a high voltage application electrode at the tip is inserted into the lance. A baffle plate at the tip facing the tip of the feed pipe, and a cone located outside the baffle plate, coaxial with the feed pipe, widening at the tip, and having an angle of 30 to 60 degrees with the axial direction. The nozzle has a shaped guide surface and is electrically connected to the electrode.

Hereinafter, one embodiment of the present invention will be described based on the drawings.
In FIG. 1, reference numeral 1 denotes a metal tube to be painted, which is rotatably supported on a trolley 3 movable on rails 2. As shown in FIG.

Reference numeral 4 denotes a lance with a nozzle 5 attached to its tip, which is cantilevered by appropriate means (not shown) at its base so as to be located approximately on the same axis as the pipe to be painted 1. .

Reference numeral 6 denotes a powder pump, which is connected to the powder pump and feeds the powder paint toward the nozzle 5 through a feed pipe 7 whose tip end is inserted into the lance 4.

Reference numeral 8 denotes a high voltage generator, and the high voltage generated thereby is applied to an electrode disposed at the tip of the feed pipe T via a high voltage cable 9 passing through the lance 4.

Reference numeral 10 denotes a recovery booth, which is disposed facing the end surface of the tube to be painted 1 on the opposite side to the side where the lance 4 is disposed, and moves together with the cart 3.

Details of the lance 4 and the nozzle 5 at its tip will be explained with reference to FIG.

The lance 4 has a double tube structure in which a cooling water chamber 11 is formed, and a protective tube 12 made of an insulating plastic material is inserted inside the double tube structure. The feed pipe 7 made of an insulating plastic material is inserted into the inside of the protection tube 12, and the high voltage cable 9 is inserted between the protection tube 12 and the feed pipe T. 13
is an electrode attached to the tip of the feed pipe T, to which the high voltage cable 9 is connected.

A cap 15 is arranged to surround the tip and outer circumference of the electrode 13, and is attached to the protective tube 12 via an adapter 14 made of insulating plastic.

Reference numeral 16 denotes a baffle plate disposed on the cap 15 at appropriate intervals from the tip opening to the tip side, and radially blocks the powder paint that has passed through the feed pipe T, passed through the electrode 13, and the cap 15. deflect.

The nozzle 5 is fitted onto the cap 15 and is connected to the electrode 1.
3, and has a conical guide surface 17 on its inner circumferential surface that extends from the outer circumference of the gap between the cap 15 and the baffle plate 16 in a tapering shape. The angle formed by this conical guide surface 17 with respect to the tube axis is θ. In the above apparatus, the preheated pipe 1 to be coated is placed on the trolley 3 and rotated while the trolley 3 is moved toward the lance 4 side, and the powder coating is sprayed from the nozzle 5 onto the inner surface of the pipe 1 to be coated, and the entire length of the pipe is sprayed. It is painted over and over.

The powder paint is guided from the powder pump 6 through the feed pipe T to the nozzle 5, where the mixture of powder paint and air collides with the baffle plate 16 and flows along the conical guide surface 17 of the nozzle to the inner surface of the tube. It is ejected towards the. The baffle plate 16 has the function of deflecting the powder paint from the feed pipe T in the radial direction and sending it to the conical guide surface IT as described above, and restricts the discharge state of the powder paint so that it can be used all around the circumference. It works to discharge the liquid evenly. Since the tube 1 to be coated is preheated at this time, there is a risk that the powder coating may gel in the feed pipe 7. However, in the present invention, the lance 4 is provided with a cooling water chamber 11, and the interior thereof is heated. Since the temperature rise is prevented, there is no such risk. Furthermore, since the cantilevered lance 4 is used, the tube 1 to be coated and the nozzle 5 are in a non-contact state, so it goes without saying that the number of coatings can be set arbitrarily. If the angle θ of the conical guide surface IT is large, the paint will be ejected almost perpendicularly to the inner surface of the tube, so that unevenness on the inner surface of the tube can be coated neatly, and pinholes can be eliminated even in thin film coating. However, if the amount of paint ejected is increased, a spiral pattern is likely to occur in the paint film. On the other hand, if the angle θ is too small, the spiral pattern of the coating will disappear, but on the other hand, it will not be able to follow the unevenness of the inner surface of the tube, and pinholes will easily occur. Therefore, in order to prevent the occurrence of pinholes and efficiently obtain a clean coating film free of spiral patterns, tests were conducted on centrifugally cast tubes by changing the angle θ. Example 1 Tagtar cast iron straight pipe of 75 to 250 mmφ x 4 m1,
A coating test was conducted using an epoxy resin powder coating.

When the nozzle 5 shown in Fig. 2 was removed and tested, it was found that if the powder coating discharge rate was 150 gr/min or more, a spiral pattern was formed on the coating film regardless of the electrostatic applied voltage or the coating thickness. occured. Also, 75m77! φ~1001
In the case of a small-diameter straight pipe such as nmφ, a sufficient distance could not be secured between the cap 15 and the inner surface of the pipe, and dust combustion occurred due to the relationship between electrical sparks and dust concentration therebetween. Example 2 Tests were conducted in the same manner as in Example 1 while varying the angle θ of the nozzle 5.

However, the discharge rate of the powder coating material was varied from 200 to 1000 gr/min. The results are shown in the table below. From the above results, it can be seen that an angle θ of 30 to 60, particularly 30 to 40, is effective in preventing spiral patterns and reducing the coating thickness required to prevent pinholes.

Furthermore, we also investigated the presence or absence of high voltage loads, but no significant difference was found. Example 3 If the angle θ of the nozzle 5 is 30mm, it is 100m7! Lφ×
4m1 tag tar cast iron pipe with powder coating output of 1000
Coating tests were conducted at gr/min.

At that time, we set up a collection booth 10 and measured the amount of collected paint using a dust collector that combines a cyclone and bag filter to investigate the paint application efficiency, and found that it was approximately 95% or more.
Moreover, the recovered paint did not gel, and could be reused in the same way as new paint. Also 75mmφ~400m77!
In the case of a relatively small diameter pipe such as φ, the coating efficiency could be maintained at 95% or more without applying a high voltage, and the pinhole resistance was also the same. For diameters larger than this, it is effective to attach a high voltage application electrode to the tip to improve coating efficiency. Note that in the above description, only the angle θ of the conical guide surface 17 of the nozzle 5 is focused, and other factors are not considered, but this point will be explained next.

(a) Rotational speed of the pipe to be coated 1 This rotational speed is determined from the relationship between the discharge amount, the coating amount, and the coating efficiency, and as long as it is at least the minimum rotational speed for uniformly coating the entire circumference. Often, even if the rotation speed is increased, the pitch interval of the spiral pattern becomes smaller, and this has nothing to do with the angle θ of the conical guide surface 17 for preventing the spiral pattern. The relative movement speed is also determined by the rotational speed of the tube 1 to be coated.

(c) Location of the electrode 13 In order to effectively charge the powder paint with static electricity, the entire discharge tip is made into an electrode.

That is, in the above embodiment, as shown in FIG.
As a result, the entire discharge tip can act as an electrode, so the exact position of the electrode 13 itself does not matter. The present invention can be implemented as shown in the above embodiments, and is capable of relative movement in the preheated metal tube to be coated in the tube axis direction, and has a cooling water chamber formed inside. A powder coating feed pipe is inserted into a lance with a heavy pipe structure, and a nozzle is provided at the tip of the feed pipe, so the paint discharged from the nozzle onto the inner surface of the metal pipe to be coated can be applied to the tube. The coating can be applied sequentially in the axial direction, and the entire inner surface of the tube can be coated uniformly and with high coating efficiency.

Furthermore, since the nozzle has a conical guide surface that is coaxial with the feed pipe and widens at the tip, by appropriately selecting the inclination angle, it is possible to paint without spiral patterns or pinholes. In addition, since a cooling water chamber is provided in the lance to prevent the internal temperature from rising, it is possible to effectively prevent the powder coating from gelling inside the feed pipe by preheating the pipe to be coated. . For example, with thermosetting resins, when the paint gels, the flowability of the paint deteriorates and the paint film cannot be formed, and the gel remains as foreign matter within the paint film, resulting in pinholes and foreign matter bite. Not only does this cause a problem in the painting section where the finish of the painted surface is poor, but also a blocking phenomenon occurs in the feed pipe, which creates resistance when the powder paint is conveyed by air pressure, making it difficult to supply the powder paint smoothly. However, according to the present invention, all of these problems can be solved. Furthermore, by setting the angle between the conical guide surface and the axial direction to 30 to 60 degrees, it is possible to prevent spiral patterns in the coating film and to reduce the minimum coating thickness required to prevent pinholes. .

[Brief explanation of the drawing]

FIG. 1 is a schematic front view showing the overall configuration of an embodiment of the present invention, and FIG. 2 is an enlarged longitudinal sectional front view of the main parts. 1...Metal pipe to be painted, 3...Dolly,
4...Lance, 5...Nozzle, 6...
...Powder pump, T...Feeding pipe,
8... High voltage generator, 9... High voltage cable, 10... Collection booth, 11...
...Cooling water chamber, 12...Protection tube, 13...
...Electrode, 14...Adapter, 15...
...Cap, 16...Baffle plate, 1T...
...Conical guide surface.

Claims (1)

[Claims] 1. A lance is provided with a double-tube structure that is rotatably supported around the axis and relatively movable in the axial direction of the preheated metal tube to be coated, and has a cooling water chamber formed inside. An insulating feed pipe capable of feeding powder paint and equipped with a high voltage application electrode at the tip is inserted into the lance, and the tip of the feed pipe is inserted into the lance. a baffle plate facing the electrode; and a conical guide surface located outside the baffle plate, coaxial with the feed pipe, expanding at the tip, and having an angle of 30 to 60° with respect to the axial direction. A metal pipe inner surface coating device characterized by having a nozzle electrically connected to the metal pipe.