JPS5930143B2 - Continuous manufacturing method for external thermosetting resin-coated steel pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for coating the outer surface of a preheated steel pipe with a thermosetting resin using a continuous steel pipe coating apparatus comprising a coater and a plurality of skew rolls.

Many methods have been proposed and implemented in the past for coating the outer surface of steel pipes with thermosetting resins, such as powdered epoxy resins, but most of them involve preheating to a predetermined temperature using a coater equipped with a spray gun. This method involves transporting the pipe while rotating it and applying electrostatic spray coating.

The method of rotating and transporting the tube to the coater can be roughly divided into two types: a cart method in which both ends of the tube are held with chucks, and a skew roll method in which a skew roll stand is used.
The present invention relates to a skew roll method. When sprayed into the coater by an electrostatic spray gun,
The electrically charged thermosetting resin powder adheres to the tube surface with coulomba. The tube is heated to a predetermined temperature in advance, and the heat melts the thermosetting resin and initiates a crosslinking reaction. The strength of the coating formed on the tube surface increases as the crosslinking reaction progresses, and the time it takes to reach a usable state is called the gel time. By the way, in the case of the skew roll method, after being coated with thermosetting resin in a coater, the tube comes into contact with the skew roll (referred to as roll touch).

), if the coating does not have sufficient strength, the shearing force (frictional force) between the roll and the coating will damage the coating.
Therefore, in order to prevent damage to the film, the time from coating to roll touching is currently set to approximately twice the gelling time of the resin. Incidentally, the gel time varies depending on the resin, and ranges from about 10 seconds to about 1 minute (at 230° C.). Therefore, coating efficiency varies depending on the curing characteristics of the resin. Furthermore, when epoxy resin is melted on a heated tube, it absorbs heat, which lowers the temperature of the tube. Furthermore, the decrease in temperature is more significant as the wall thickness of the tube becomes thinner. However, when the environmental temperature decreases,
Gel time will be longer. Therefore, the coating efficiency may vary depending on the wall thickness of the pipe. As mentioned above, in the conventional ski roll method for coating thermosetting resins, the roll touch is performed after the resin has sufficiently gelled, so the coating efficiency varies depending on the curing characteristics of the resin, the wall thickness of the raw tube, etc. ing.

Therefore, despite the continuous production method using ski roll stands, the current production efficiency is not as high as expected. An object of the present invention is to prevent coating damage caused by the skie roll during roll touch in a method of coating the outer surface of a steel pipe with a thermosetting resin using the skie roll method, to shorten the time from coating to roll touch, and to improve production efficiency. The purpose of the present invention is to provide a continuous manufacturing method for thermosetting resin-coated steel pipes.

The continuous manufacturing method of a steel pipe coated with an external thermosetting resin according to the present invention is a method for coating a preheated steel pipe external surface with a thermosetting resin using a continuous steel pipe coating device comprising a coater and a plurality of ski rolls. A cooling device is installed just before the skie roll on the output side of the coater, (b) cools the surface of the thermosetting resin coating on which the crosslinking reaction of the steel pipe coming out of the coater has not progressed sufficiently, and (c) cools the thermosetting resin coating surface. Temporarily strengthen the coating surface and pass it through ski rolls,
(d) This method is characterized by coating the outer surface of the steel pipe with a thermosetting resin while continuing the crosslinking reaction by melting the coating again with the heat retained in the steel pipe after passing through the pipe.

As described above, when the powder thermosetting resin is attached to a steel pipe that has been heated to a predetermined temperature, it is melted by the heat and starts a crosslinking reaction. When the reaction reaches a certain level, the resin rapidly changes to a gel state and increases its strength. Therefore, in the conventional method, roll touching is performed after the resin has sufficiently gelled. The present inventors conducted tests on the paintability and curing properties of powdered epoxy resins, and on the reliability of coating films, and found the following. That is, when powdered epoxy resin was applied to an iron plate heated to a predetermined temperature and the coating was rapidly cooled in a sufficiently large water tank before it gelled, the coating retained considerable strength.

However, the crosslinking reaction of the film prepared by the above procedure stopped during water cooling and the film was in an uncured state, so that sufficient film properties could not be obtained. Then, after coating, only the surface of the coating was water-cooled for a few seconds, and it retained considerable strength for a short time after the water-cooling stopped.

After that, the heat retained by the iron plate melted the film again, causing it to gel. The film produced by the above procedure was tested for accuracy, and no difference was found between the film and the film that was not subjected to water cooling. The present invention was created based on the above facts, and immediately before contacting the skie roll, only the surface of the coating before gelation is rapidly cooled, temporarily strengthened, and then subjected to a roll pass. This is a continuous production method for externally coated steel pipes with thermosetting resin, characterized by coating the outer surface of the pipe with thermosetting resin by melting the coating again using the heat retained in the pipe and continuing the crosslinking reaction after the roll pass. .

The thermosetting resin used in the method of the present invention is mainly epoxy resin, but polyester resin, acrylic resin, etc. can also be used.

The simplest method for rapidly cooling the coating surface is to use water spray, but the method is not particularly limited to water spray.

Next, an embodiment of an apparatus for carrying out the method of the present invention is shown in FIG.

In the drawing, 1 is a coater, 2 is a pipe, 3 is a ski roll stand, and 4 is a spray nozzle of a cooling device used in the method of the present invention. be. A steel pipe 2 that has been heated to a required temperature in advance is sent in the direction of the arrow while being rotated by a ski roll of a ski roll stand 3.

At the coater 1, the thermosetting resin is electrostatically deposited on the tube surface and melted. Immediately before passing through the ski roll stand 3, the surface of the coated thermosetting resin is rapidly cooled by a spray nozzle 4 to temporarily maintain its strength.
Pass through ski euros without sustaining any damage.
After passing through the skie roll, the resin is melted again by the heat retained in the steel pipe, allowing the crosslinking reaction to continue and complete curing.
According to the method of the present invention, unlike conventional methods, there is no need to wait until the film is in a gel state before applying the roll, so it is possible to shorten the time from coating to applying the roll. Improved efficiency can be measured. The time until roll touch and the cooling conditions for the coating surface vary depending on the type of powder thermosetting resin, the weight of the raw tube, the wall thickness, the angle of the skie roll, the circumferential speed of the raw tube, etc. It is difficult to define the time and conditions. Below, powder epoxy resin A. An example using B will be described. The gel times of the resins used in the examples are shown in Table 1. Example 1 Powder thermosetting resin: Epoxy resin A Original tube: 600A111.1m7! L Base treatment: Sandblasting Sa2-f Preheating temperature: 23'C Pipe advancement speed: 4 m/min Pipe rotation speed: 12.5 rpm (peripheral speed 24 m/min) Cooling of coating surface: Cooling for 2 seconds using water spray Under the above conditions, the outer surface of the steel pipe was coated with epoxy resin by the method of the present invention.

The distance between the coater and ski roll stand was also varied, and the time required to touch the roll was varied. The results are shown in Table 2 together with the results obtained by the conventional method in which the coating surface was not cooled. In the method according to the present invention, the surface temperature was measured immediately after the roll pass and was approximately 120°C.

Also, regarding this resin, the time to roll touch is 20
As a result of examining whether or not the coating was damaged by changing the cooling time, it was found that coatings whose temperature immediately after the roll pass was 130° C. or lower were not damaged. Example 2 Powder thermosetting resin: Epoxy resin B Original tube: 600A115.9m77! Surface treatment: Sandblasting, Sa2-f Preheating temperature: 230°C Pipe advancement speed: 4 m/min Pipe rotation speed: 12.5 rpm (circumferential speed 24 m7/min) or higher, and the coating surface was cooled the same as in Example 1. A test was conducted under the same conditions as in Example 1.

The results are shown in Table 3. For the method according to the invention, the surface temperature immediately after the roll pass was about 120°C.

Also, regarding this resin, the time to roll touch is 35
As a result of examining the presence or absence of damage to the coating by changing the cooling time in seconds, no damage to the coating was observed in cases where the coating temperature was 140° C. or less immediately after the roll pass.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of an apparatus for carrying out the method of the invention. In the drawings, 1 is a coater, 2 is a pipe, 3 is a ski roll stand, and 4 is a soubre nozzle.

Claims (1)

[Claims] 1. In a method of coating a thermosetting resin on the outer surface of a preheated steel pipe with a continuous steel pipe coating device consisting of a coater and a plurality of skew rolls, (a) a cooling device is installed immediately before the skew rolls on the outlet side of the coater. (b) cools the surface of the thermosetting resin coating on which the crosslinking reaction of the steel pipe coming out of the coater has not progressed sufficiently, and (c) temporarily adds strength to the thermosetting resin coating surface to skew it. A steel pipe coated with an external thermosetting resin, characterized in that: (d) the outer surface of the steel pipe is coated with a thermosetting resin while passing through a roll, and (d) melting the coating again with the heat retained in the steel pipe after passing through and continuing a crosslinking reaction. continuous manufacturing method.