JPS6012110B2 - Cooling method in the manufacturing process of plastic-coated metal tubes - Google Patents

Description

[Detailed Description of the Invention] - This invention relates to cooling immediately after coating in the process of manufacturing a plastic-coated metal tube by spirally wrapping a thermoplastic plastic strip around the outer surface of a metal tube such as a steel tube, steel tube, or aluminum tube. Regarding the method.

BACKGROUND OF THE INVENTION Various methods have been known for coating pipelines used for transporting oil, gas, etc., particularly metal pipes buried underground, with thermoplastic plastics such as polyethylene. The method of coating the outer surface of a metal tube with thermoplastic such as polyethylene is to heat the metal tube to a coating temperature and then coat the outer surface with a primer layer (
A method is known in which a semi-molten thermoplastic plastic strip is coated with a pressure-sensitive adhesive (adhesive or adhesive layer) and then continuously extruded using an extruder to form a helical coating. In these known plastic coating methods, in order to ensure sufficient adhesion between the metal tube and the thermoplastic layer, it is generally necessary to preheat the metal tube to a temperature of 18 psi or higher, and the thermoplastic layer extruded from the extruder The extrusion temperature of the plastic strip also needs to be 200°C.

In order to manufacture plastic-coated metal tubes in this way, it is necessary to heat the metal tubes and thermoplastics to high temperatures, and in order to cool the metal tubes after coating, conveying rollers over a considerable distance are required immediately after coating. At the top, cooling water was dripped from above the coated metal pipe to cool it. However, this dripping cooling method has poor cooling efficiency, and it has been practically impossible to increase the coating speed beyond a certain limit for coating due to various problems. If the sheathing speed is increased beyond a certain limit, the moving speed of the sheathed metal pipe in the pipe direction will increase, and the cooling capacity within the cooling zone established between a certain distance will decrease, resulting in semi-molten heat. There are disadvantages in that the solidification of the plastic plastic becomes uneven, and after burial, cracks are likely to occur in the plastic coating layer, resulting in a plastic-coated metal tube with poor anti-corrosion performance. In addition, especially in the case of heavy metal tubes, the pressure on the conveyor rollers that rotate while supporting the metal tube becomes extremely high, so the thermoplastic plastic that has not yet solidified immediately after being coated with the semi-molten thermoplastic Because the layer is compressed between the metal tube and the conveyor roller and twisted by the conveyor roller, the plastic coating layer is permanently deformed, which not only deteriorates the appearance of the plastic-coated metal tube but also causes damage after burial. The drawback is that cracks occur in the plastic coating layer, resulting in significantly poor corrosion resistance. In addition, in this conventional method, the weight of the plastic-coated metal tube is entirely applied to the conveying rollers, so that the conveying rollers are subject to severe wear and the life of the conveying rollers is also short.

The object of the present invention is to provide a cooling method in the manufacturing process of plastic-coated metal tubes that eliminates the above-mentioned drawbacks.

That is, in the process of cooling the plastic-coated metal tube immediately after coating the outer surface of the metal tube with thermoplastic plastic, the present invention blows high-pressure water from below the metal tube immediately after coating the thermoplastic plastic. Put it on,
This is a cooling method in a manufacturing process of a plastic-coated metal tube, characterized by cooling the metal tube while reducing the load on a conveying roller that rotates the metal tube while supporting it.

Next, the method of the present invention will be explained in detail using the illustrated example. First, before the coating process, the outer surface of the metal tube is cleaned, heated to a predetermined temperature, and a primer is applied to the outer surface.

The metal tube whose surface has been treated in this manner is rotated by a conveyor roller and moved in all directions along the tube axis, and a semi-molten thermoplastic strip is pressed by a presser and is spirally wound around the outer surface of the metal tube to apply the coating. conduct. Thereafter, as shown in FIG.
20 ~ from the cooling box 3, 3', 3'' installed below the
The plastic-coated metal tube 1 is cooled by spraying high-pressure water at a rate of 30 kg/hour while supporting the plastic-coated metal tube 1 while reducing the load on the conveying loaves 2, 2', and 2'' which are rotated on the other hand.

Next, a cooling device used in the method of the present invention will be explained with reference to embodiments shown in FIGS. 1 to 3.

Fig. 1 is a front view showing an example of a cooling device used in the method of the present invention, Fig. 2 is a side view of Fig. 1, and Fig. 3a is a plan view showing an example of a cooling box used in the method of the present invention. Fig. 3b
is a front view of FIG. 3a, and FIG. 3c is a side view of FIG. 3b. The cooling device shown in Fig. 1 is placed immediately after the thermoplastic coating process, and immediately before the conveyor belt.
As shown in the figure, there are cooling boxes 3, 3', 3'' that cool the plastic-coated metal tube 1 by spraying high-pressure water from below, as shown in the figure. As shown in Fig. 3, each cooling box 3, 3', 3r has a certain space on its inner surface, a large number of injection nozzles 8 at the bottom, and cooling water at both ends. A soft sealing material 9 is provided to prevent the plastic coating from flowing out from both ends and to prevent the plastic coating layer from being damaged even if the plastic-coated steel pipe 1 comes into contact with the plastic coating.

The cooling water cooled to a constant temperature in the cooling tank 4 is pumped by the pump 5, and the injection pressure of the injection nozzle 8 of the cooling box 3, 3', 3'' is increased to 20~3''.
Water is supplied at a pressure raised to 0k9/ground. Also, the cooling water sprayed from the cooling boxes 3, 3', 3'' is released from the side of the seal plate 6 provided to prevent scattering, and the released cooling water is collected into a cooling tank 4. In this embodiment, in order to further improve the cooling effect, a shower pipe 7 is installed above the plastic-coated metal tube 1, as shown in FIG. In this embodiment, a cooling box is installed in front of the transport rotary roller 2, between the transport rollers 2 and 2', and between the transport rollers 2' and 2'', respectively. However, the reason why the cooling box 3 is installed immediately before the conveyance roller 2 is to cool the plastic-coated metal tube 1 because it is permanently deformed by the conveyance roller 2 before the tip of the plastic-coated metal tube 1 reaches the first conveyance roller 2. 80o
This is to lower the temperature of the plastic surface to a temperature below 80 mm (a temperature close to 0.8 mm) and to reduce the load on the conveying low footer 2, and between the conveying rollers 2 and 2' and between the conveying low footers 2' and 2. The reason why the cooling boxes 3' and 3'' are installed between the cooling boxes 3 and 3 is because the temperature of the plastic surface of the plastic coated metal tube 1 cooled by the cooling box 3 is below 8 pi○ (a temperature close to 8030). ), but the temperature inside is 150℃0 due to the heat of the metal tube.
This is to prevent double heat on the plastic surface, and to avoid deformation of the plastic layer if a large load is applied in this state.
This is to provide a cooling effect to prevent this deformation and to reduce the load on the conveyance roller.

In the method of the present invention, if the plastic surface temperature of the plastic-coated metal tube 1 can be cooled down to 8 pi or less by another cooling means before reaching the first conveying roller 2, a cooling box is placed immediately before the conveying roller 2. 3 may not be provided.

Regarding the shape and number of cooling boxes, it is sufficient to arrange a necessary number of cooling boxes that will not cause permanent deformation of the plastic coating layer even if the coating speed increases, but the area in which they are placed should be determined as appropriate depending on the situation. can be selected. Next, examples of the present invention will be described.

A semi-molten polyethylene strip was spirally wound around the outer surface of a steel pipe with an outer diameter of 600 mm and a length of 11.5 mm to form a coating layer of 4 mm thick, and then cooled by the method of the present invention and the conventional method. I did it.

The cooling conditions of the present invention at this time are that five cooling boxes each having a length of two skins as shown in the figure are installed in the transport direction in the 15 skin area of the cooling process, and the number of injection nozzles in one cooling box is 12.
0, the distance from the tip of the injection nozzle to the outer surface of the polyethylene-coated steel pipe is on the 50 side, and the injection pressure of the injection nozzle is 20~
Cooling was performed by adjusting the discharge pressure of the pump so that the pressure was 30k9/kg. As a result, in the case of the conventional drip cooling method, the maximum coating speed that could be uniformly cooled without causing permanent deformation was 6.5 m/min, but in the method of the present invention, the maximum coating speed was as high as low/min. I was able to improve it.

Furthermore, the polyethylene-coated steel pipes obtained by the method of the present invention had more uniform polyethylene physical properties and a more uniform overall coating thickness than those obtained by the conventional method. In addition, the method of the present invention had the effect that the wear of the conveyor roll was less than that of the conventional method. As described above, according to the method of the present invention, compared to the conventional method, it is possible to greatly improve the plastic coating speed without causing permanent deformation of the plastic coating layer, so productivity is greatly improved. In addition, a plastic-coated metal tube with a uniform coating thickness and a beautiful appearance can be obtained, and there are many effects such as less wear on the conveyor roller and an extension of the life of the conveyor roll shaft.

[Brief explanation of the drawing]

Fig. 1 is a front view showing an example of a cooling device used in the method of the present invention, Fig. 2 is a side view of Fig. 1, and Fig. 3a is a plan view showing an example of a cooling box used in the present invention. , FIG. 3b is a front view of FIG. 3a, and FIG. 3c is a side view of FIG. 3b. 1...Plastic coated metal tube, 2, 2', 2~...
・To conveyance lo-fu, 3, 3', 3...Cooling box, 4...Cooling tank, 5...Pump, 6
... Seal plate, 7 ... Shower pipe, 8
...Injection nozzle, 9...Sealing material. Figure 2. Figure 2. Figure 3 (〇

Claims (1)

[Claims] 1. In the process of cooling the plastic-coated metal tube immediately after coating the outer surface of the metal tube with thermoplastic plastic,
The plastic is characterized in that high-pressure water is sprayed onto the metal tube immediately after it has been coated with the thermoplastic plastic from below the metal tube to cool the metal tube while reducing the load on a conveying roller that rotates while supporting the metal tube. Cooling method in the manufacturing process of coated metal tubes.