JPS602172B2 - Bead crimping device for plastic-coated steel pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bead crimping layer when plastic coating is applied to a welded steel pipe.

Plastic-coated steel pipes are an extremely effective means of preventing corrosion of steel pipes, and their use is increasing in situations where maintenance is relatively difficult, such as underground burial and petroleum transport.
Such plastic-coated steel pipes are generally coated with plastic using an extruder, and if the target steel pipe is seamless, there is no problem, but welded steel pipes with seams In this case, as shown in FIG. 1, a phenomenon occurs in which the steel pipe and the coating layer do not come into close contact with each other at the foot of the bead.

One way to counter this problem is to fill the bead side with an adhesive or other adhesive to repair the extreme depressions above the neck if the undercoat material is adhesive.

On the other hand, if the undercoat material is a thermosetting adhesive, the heating required for curing may cause the viscosity of the adhesive to decrease dramatically before curing, causing dripping or even if there is no dripping or if it is an adhesive. In cases where the surface is coated with plastic without heating, as in the case of the plastic coating, the disadvantage is that the plastic coating increases the thickness of the plastic coating, reducing the impact strength. A solution has also been proposed that uses a hollow roll to press the bead and fill the void, but this method causes the roll itself to expand and deform abnormally due to internal fluid pressure, making it difficult to adjust the shape to fit the bead. Not only that, but there were also other inconveniences such as the need for a complicated cooling device to prevent roll overheating. The present inventors have proposed a method for manufacturing plastic-coated steel pipes using a cylindrical extrusion die that does not cause bridge thickness in the plastic coating film thickness at the bead portion and does not form voids between the plastic coating film and the steel pipe. As a result of considering specific measures, we decided to install a ring-shaped water cooling device connected to the extrusion die to cool the plastic-coated steel pipe, and to provide sufficient elasticity to press the base of the steel pipe bead during the water cooling period. We have arrived at a bead crimping device for plastic-coated steel pipes equipped with body rolls.

In the present invention, pressing the plastic-coated steel pipe with the solid elastic roll is performed while the plastic-coated steel pipe is water-cooled.

The purpose is not only to eliminate or reduce the adhesion of the plastic surface and prevent partial transfer of the plastic to the elastic roll, but also to prevent stripes during operation of the elastic roll. This makes it possible to omit the installation of a new cooling device for the rolls.

The surface of the plastic coated on the steel pipe has solidified as it cools, but the inside is molten and still deformable, so when it is pressed by an elastic roll, it will not stick to the roll. Although it is not, it is possible to fit it well at the foot of the bead.

The elastic roll used for this purpose is most commonly a heat-resistant synthetic rubber roll.

This roll needs to be non-hollow for the reasons mentioned above, and good results are likely to be obtained if the roll has a rubber hardness of approximately 25 to 50. If the value is outside this range, for example, less than 25, the elastic roll will be too soft and deformation of the roll will be large, making it impossible to completely press the foot of the bead.On the other hand, if it is more than 50, no deformation of the roll will occur. Similarly, the force will not reach the base of the bead. The shape of the elastic roll is not particularly limited and may be any shape as long as it can sandwich the bead and press the bottom portions on both sides of the bead, but generally the shape shown in Figure 2 is The one shown in FIG. 4 is used.

In the case of FIG. 2, an elastic roll 6 is shown in which a concave portion 5 corresponding to a bead is formed in a roll matched to the outer diameter of a steel pipe.

In this case, it cannot be used for pipes with different protrusions, but since the recess 5 is fixed for pipes of the same diameter, there is no need to adjust the interval. Further, FIG. 3 shows a similar effect obtained by combining two rollers 7.
In this case, by adjusting the fixing device for fixing the roller 7, it can be used for pipes of different diameters. Of course, it is also possible to use a system in which the roller 7 shown in FIG. 3 is made smaller and directly presses the foot of the bead.
Incidentally, FIG. 4 shows an example of a roll in which when processing plastic-coated steel pipes of different diameters, it is possible to simply shift the channel without changing the roll.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a bead in a plastic-coated steel pipe and the gap formed at its base, Figs. 2 and 3 are explanatory diagrams showing the pressing of the bead base by an elastic roll, and Fig. 4. is a conceptual diagram of a multiple roll. 1...Bead, 2...Gap, 3...Steel pipe, 4...
・Plastic coating film, 6...roll, 7...loaf. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In an apparatus for manufacturing plastic-coated steel pipes using a cylindrical extrusion die, a ring-shaped water cooling device for cooling the plastic-coated steel pipe is connected to the extrusion die, and the foot of the bead of the steel pipe is pressed during the water cooling period. A bead crimping device for plastic-coated steel pipes, which is characterized by having a fully elastic roll for crimping.