JPS58280A - Manufacturing method of thermoplastic synthetic resin inner-coated steel pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the S-adic method for inner-coated steel pipes, such as water supply pipes, whose inner surfaces are coated with thermoplastic synthetic resin such as polyethylene.

The powder heat fusion method has been known as one of the methods for coating the inner surface of steel pipes with thermoplastic synthetic resin, and within this fusion method, there are four revolution molding methods, flow conveying methods, pipe filling methods, etc. Many methods are known. All of these methods have in common that the tube is heated to about 200 DEG C. to 310 DEG C., and a powdered thermoplastic synthetic resin is melted by its heat capacity to form a resin coating on the inner surface of the tube.

In the powder heat fusion method described above, after forming a resin coating on the inner surface of the tube, the steel tube is cooled with water or allowed to cool in the air to return it to room temperature. A cooling process using water cooling is used to improve the appearance (gloss of the paint film, unevenness, etc.). In this case, cooling methods using water cooling include a method in which the outer surface of the tube is cooled by a shower of cooling water, and a method in which the tube is placed in water and cooled from both the inside and outside.

However, when using such a cooling method, whether the shower type or submerged type, the resin coating on the inner surface of the steel pipe in the center part looks good,
The problem often arises that the resin coating formed on the inner surface of the tube at both ends (varies depending on the diameter, but generally the portions domestically and internationally from the tube end) exhibits poor appearance with uneven surfaces, etc. there were. The cause of this poor appearance of the inner coating film on the tube end was thought to be due to uneven cooling of the tube end during cooling.
In the past, it was impossible to think of an appropriate countermeasure for this kind of problem, and the problem was solved by methods such as applying cooling water.

The present inventors further analyzed and pursued the cause of the poor appearance of the tube inner surface coating film at the tube end portion as described above, and came to the following conclusion. In other words, poor appearance of the inner surface coating film at the end of the pipe often occurs particularly when a steel pipe formed on the inner surface of the pipe is cooled with water while the resin coating film is melted at a temperature higher than the melting point. According to the experimental results, when a tube whose inner surface resin coating is formed at a temperature higher than the melting point is water-cooled as described above, the underwater injection method causes uneven flow inside the tube near the tube end. In addition, in the case of one type of shank, non-uniform water intrusion into the pipe near the end of the pipe occurs. Because of this, non-uniform water enters the resin coating that melts at a temperature higher than the melting point in that part. A distributed state of cooling occurs, resulting in areas that partially solidify earlier or areas that partially solidify later (
It has been found that this results in the formation of an uneven surface (adhesion of bubbles, etc.).

The present invention was conceived based on the results of the above analysis, and after completing the process of forming a resin coating film on the inner surface of the tube and starting the water cooling process (Step 11), appropriate By performing a cooling treatment, the good appearance of the resin coating on the inner surface of the tube at the tube end can be maintained.
The purpose of this invention is to provide a method for manufacturing a steel pipe with a resin-coated inner surface.

The feature of the present invention is that the inner surface of a steel pipe heated to a predetermined temperature is coated with a thermoplastic synthetic resin, and in cooling the steel pipe as the next processing step, first the vicinity of both ends of the steel pipe are forcedly air cooled. At K, the temperature of the coating film on the inner surface near both ends of the tube was lowered to below the melting point of the thermoplastic synthetic resin to solidify the coating film, and then the outer periphery of the steel tube was cooled with water over its entire length.

Powder lining of resin on the inner surface of the tube is generally performed by pre-treating the raw tube with pickling K, chemical conversion treatment, and primer coating, and then applying polyethylene resin powder coating while heated to λgo''c1! degrees. In the present invention, in the next step, both ends of the pipe are subjected to air cooling treatment.For example, S, G, P (carbon steel pipe for piping)/SM, S.

What happens when the coating resin conditions etc. are changed for each steel pipe of ROM and ROM! For examples from to (3), the above-mentioned air cooling treatment was applied to the range of the tube end 3173 to set several temperature conditions around the melting point of the resin, and then the evaluation of the coating film appearance was shown when water cooling treatment was performed. This is shown in Table 1 below.

$121 Note O No problem at all O Good Δ There is no problem in practical use - but the appearance is rather bad - × Poor appearance jL
(Pipe length! 1.5m) (The central part of the pipe is all in good condition) As can be seen from Table 1, the end of one pipe was forced air cooled at a temperature equal to or lower than the melting point of the inner coating resin, and then water cooled. In this case, there are no conditions that would deteriorate the appearance of the inner surface coating at the tube end. That is, it can be seen that if the water cooling treatment is carried out with the temperature of the tube end portion lowered to a temperature lower than the melting point of the resin coating film, the appearance of the inner surface coating film will not be affected at all even at the tube end portion.

In this case, the problem is how long the air cooling area at the tube end should be, but regarding the thickness, based on the above experiment, the conditions for each coating resin in 1 to WK in Table 1 are as follows:
It can be calculated based on Table S, which shows the maximum length of the defective coating film appearance when applied to each pipe of /Jmm, ymm, and 10mm.

Table 2 As can be seen from Table 3, in any case under the resin coating conditions of Kl to ■, the range of tube end lθ to , in the case of 10 μm, a defective appearance of the coating film was detected in a range of about 100 μm. Based on this result, the appropriate standard for the length of the pipe end to be air cooled is the value calculated by the formula: air cooling zone length ≥ 1.3 x pipe inner diameter. If the length of the tube end air-cooling zone obtained for each diameter tube is air-cooled to below the melting point of the coating resin as described above, and then water-cooled over the entire length, the inner coated steel tube will have a good inner coating. It turns out that you can get .

Next, the present invention will be explained with reference to examples.

Example 1 Coating film resin under conditions I shown in Table IK above! ,! 101 of m
8, G, P K Approximately t with a lining temperature of 110℃
One coated with a film thickness of oo/A, and one coated with a film thickness of about 100. A piece of wood coated with a film thickness of LL was made, and as shown in Fig. 1, they were kept in a heat retention oven (1) at a temperature of /10'C for about 20 minutes, and then heated on both sides outside the oven. Tube end part/
108 to 113℃ via air injection device (λ)
The pipe was cooled with forced air so that the
j'CK Central part of the tube (excluding the end part) when air-cooled
The temperature was /l/''C.

The appearance of the resin coating on the inner surface of the steel pipe that had undergone the treatment process as described above was good, with no defects at all not only in the central part of the pipe but also in the inner end part of the pipe.

When the length of the air cooling zone at the end of the sample tube in the above example was set to 37) m, a slightly defective portion in appearance was finally detected in the vicinity of the tube end 100cm.

Example 2 The coating resin of the condition H shown in Table 1K was s, 5IIIx'
/3mm S, G, and P coated with a lining temperature of 100°C to a film thickness of about 100°C and one coated to a film thickness of about 100°F were manufactured, and heat retention was maintained at 110°C. Furnace (/l K e to) After keeping warm for a minute, remove from the furnace.
and set the range of both pipes 11iii section 7Qm to 100 to 703
The central part of the tube is forcedly air cooled to a temperature of 17°C. 't)
, water cooling was performed immediately. The appearance of the Sohata inner-tree coating was good at both ends of the tube and at the center of the tube.

4.1IIN's Simple 1Ill Some are line diagrams showing the order of each process of heat retention and tube end air cooling range length in inner resin-coated steel pipes.

In -, (1)... heat retention furnace, (2) - air cooling device, (2)...
Water cooling device.

Patent applicant: Nippon Kokan Co., Ltd. Oka Steel Pipe Galvanizing Co., Ltd. Inventor: Yoshiaki Fujiwara Same as Tadao Kimura Oka Nagai Ims Red Manabu Oka Kobayashi Oka Mori Oka Yoshi 2 Shigeru Oka Ito Former Nippon 22n 11

Claims (1)

[Scope of Claims] L The inner surface of a steel pipe heated to a predetermined temperature is coated with a thermoplastic synthetic resin, and in cooling the steel pipe as the next treatment step, first, the vicinity of both ends of the steel pipe is forcedly air-cooled. A steel pipe coated with a thermoplastic synthetic resin inner surface, characterized in that the temperature of the coating on the inner surface near both ends of the pipe is set to below the melting point of the thermoplastic synthetic resin to solidify the coating film, and then the outer periphery of the steel pipe is cooled with water over its entire length. manufacturing method. a. The range of the air cooling area for forced air cooling of the temperature of the coating film on the inner surface of the inner end of the pipe to below the melting point is determined by the length of the air cooling area ≧/, the inner diameter of the JX pipe.Claim 1. The method for manufacturing the thermoplastic synthetic resin inner-coated steel pipe described above.