JPS5850569B2 - Manufacturing method of plastic coated steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a plastic-coated steel pipe, in which the surface of the steel pipe is continuously coated with plastic using a T-die method, and then cooled so that the coated surface becomes smooth. The aim is to provide a method to encourage

Generally, when coating a steel pipe with plastic using the T-die method, the steel pipe is rotated by a skew roll or the like and progressed in the longitudinal direction of the pipe, and as shown in FIG. It is well known that the extruded plastic 2 is wound spirally around the outer peripheral surface of a steel pipe 3, and then cooled and solidified.

Conventionally, for this cooling, as shown in the figure, a plurality of slit nozzles or the like are arranged perpendicular to the longitudinal direction of the pipe to uniformly cool the entire pipe.

However, in this case, the plastic sheet 2 is generally wound in a spiral manner, partially overlapping.
Therefore, even if uniform cooling is performed as described above, the partially overlapping part of the plastic sheet 2, that is, the triple layered part B as shown in FIG. The degree of cooling will be different in part A of the multilayer.

Therefore, for example, high-density polyethylene has a particularly large shrinkage rate during solidification (usually high-density 0 polyethylene has a large molding shrinkage).

In a plastic sheet (designed with a shrinkage rate of 0~01000), the balance of shrinkage is lost near the boundary between portions B and A, and a recess C is formed at that location. For this reason, there was a risk that the corrosion resistance on the surface of the coated steel pipe would be unbalanced, leading to major quality problems.

Therefore, in the present invention, by preferentially cooling the partially overlapping portions of the plastic sheets, the A and B
The aim is to maintain a balance in the cooling state of these parts and to produce smooth plastic-coated steel pipes with no recesses.

Next, an embodiment of the present invention will be explained with reference to FIG. 2. First, in the figure, 3 is a steel pipe, and 2 is a plastic coating. It is similar to the conventional method that the wires are partially overlapped and continuously wound in a spiral shape.

However, in the present invention, during cooling that is performed subsequent to such coating, the partially overlapping portion B of the plastic sheet is removed.
A plurality of spray nozzle groups or slit nozzles 4 are installed in the pipe length direction at positions corresponding to (in this example, the steel pipe 3
(Since the nozzle 4 is installed only on the upper half circumference side, but it is not limited to this, since the is progressing while rotating), from this nozzle 4 to the partial overlap part B,
Coolant such as air or water is sprayed preferentially.

In this case, the nozzle 4 is installed at a position where it passes through the partial overlap part B of the plastic sheets, which is known empirically based on the width of the plastic sheets, the width of the overlap part of the sheets, the outer diameter of the steel pipe, the line speed, etc. A plurality of nozzles 4 are installed at a constant pitch, and the direction of the nozzles is made to coincide with the traveling direction of the overlapping portion B of the plastic sheets.

When the partially overlapping part B of the plastic sheet is cooled preferentially in this way, the partially overlapping part B is cooled with the coolant having the highest degree of cooling, and also with the cooling degree slightly lowered. Partial overlap part B due to the flow of the agent
The thinner portion A of the double layer is cooled, and the overall cooling condition can be almost balanced on the coated surface side, thereby ensuring the smoothness of the coated surface.

Next, in order to confirm the effectiveness of the present invention, the following experiment was conducted and compared with the conventional method.

[Conventional method]

A 40 OA steel pipe is rotated on a skew roll line and advanced in the pipe length direction (pipe feed rate 50 cIn7/m1n at a pitch of 150 mm).

This was heated to 130° C. with a burner, and high-density polyethylene heated and melted at 230° C. was extruded from an extruder die and wound around a tube with a thickness of 1.5 mW and a width of −350 threads.

After that, compressed air at a pressure of 4 kg/cd was passed through a slit nozzle (length = 1000 ms,
The coating was uniformly cooled by blowing out in a band shape from a width of 8 peaks.

As a result, as shown in FIG. 1, the film thickness of the portion C was 0.5 to 0.7 rnw thinner than that of the portion A.

[Method of the present invention]

Coating was carried out under the same conditions as the conventional method described above, and then six air cooling nozzles (about 8 mm in diameter) were placed around the upper half of the partially overlapped part B of the plastic sheet, and these nozzle groups were aligned with the coating pitch. A plurality of cladding tubes were attached at intervals of 150 mm in the longitudinal direction of the cladding tube, and compressed air was blown onto the cladding tubes 4 to cool them.

As a result, the recess C shown in FIG. 1 did not occur, and a smooth coated surface was obtained.

As is clear from the above experimental examples, according to the method of the present invention,
Since the partially overlapping part B of the plastic sheet and the thinner part A are cooled in a well-balanced manner, the coating surface becomes smooth, and various excellent effects such as improved corrosion resistance and other qualities can be obtained. be.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view for explaining a conventional plastic coating method, FIG. 2 is a partial cross-sectional perspective view for explaining a plastic coating method according to the present invention, and FIG. 3 is a line A-A in FIG. 2. It is a sectional view along a line. In the figure, 1 is a T die, 2 is a plastic sheet, 3 is a steel pipe,
4 indicates the nozzle.

Claims (1)

[Claims] 1 In a method for manufacturing a plastic-coated steel pipe in which the surface of a steel pipe is partially overlapped with a plastic sheet using a T-die method to continuously coat the surface of the steel pipe in a spiral shape, and then cooled, the partially overlapping portion of the plastic sheet is preferentially coated. A method for manufacturing a plastic-coated steel pipe, characterized by cooling the pipe to