JPS6320695B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bead crimping device for applying plastic coating 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 oil transportation.

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 often occurs in which the steel pipe and the coating layer do not come into close contact at the base of the bead.

One way to counter this problem is to fill the bead side with an adhesive or other adhesive to repair the appearance of the extreme recesses, if the undercoat material is an 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. When 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 and reduces 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 disadvantages such as the need for a complicated cooling device to prevent roll overheating.

Another possible solution is to use an elastic roll to press the base of the bead to fill the void.One method is to first install a ring-shaped water-cooled pipe connected to the extrusion die to cool the plastic-coated steel pipe. We have proposed a bead crimping device for plastic-coated steel pipes, which is equipped with a full elastic roll for pressing the base of the steel pipe bead during water cooling (Japanese Patent Application No. 183623/1983). but,
This device has a ring-shaped water cooling device for cooling the plastic-coated steel pipe between the point at which the molten resin extruded from the extrusion die lands on the surface of the steel pipe and the press roll, so the molten resin lands at each point. The disadvantage is that the distance between the bead and the pressing point becomes long, making it impossible to completely extract the air caught in the side of the bead during coating, and therefore it may not always be possible to expect complete adhesion at the base of the bead. .

In manufacturing plastic-coated steel pipes using a cylindrical extrusion die, the present inventors have discovered that there is no unevenness in the thickness of the plastic coating at the bead, and no voids are formed under the coating beside the bead of the steel pipe. As a result of further studies to obtain a coating device, the present invention was achieved.

That is, the present invention provides an apparatus for manufacturing plastic-coated steel pipes using a cylindrical extrusion die, in which a solid elastic roll that presses the foot of a steel pipe bead in proximity to the extrusion die is connected to a water cooling device. The present invention relates to a plastic coating device for steel pipes, which is characterized by the following.

The solid elastic roll used in the present invention has, for example, the form shown in FIG. 2, and is most commonly made of heat-resistant synthetic rubber.

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, if it is 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 larger than 50, the roll will not deform. Similarly, the force will not reach the base of the bead.

In addition, by preparing an appropriate number of roll materials and shapes depending on the size of the steel pipe and the shape and size of the bead, and adjusting the load applied when pressing the rolls, the film thickness around the bead can be made uniform. It was recognized that it is possible to change the

FIG. 3 shows an embodiment of the structure of the present invention, in which a steel pipe 3 with the bead 1 facing upward is shown.
is placed on the plastic coating line while being supported by support rollers 8, and the plastic 4 is coated on the surface of the steel pipe 3 from the cylindrical extrusion die 6, and then a part of the bead of the steel pipe 3 is pressed by the elastic roll 5, Thereafter, the plastic 4 or the plastic 4 and the steel pipe 3 are cooled down to a certain temperature by passing through a ring-shaped water cooling device 7 (for example, to the extent that the plastic surface no longer deforms when it comes into contact with other substances), and then It is cooled by a conventional cooling means 9 to a temperature at which it can be transported at a factory or temporarily stored. Note that 10 is a device for adjusting the pressing force of the pressure roll 5, and uses an air cylinder or the like, for example.

By adopting such a configuration, compared to conventional plastic coating methods or equipment,
It is therefore possible to obtain a coating device that is capable of coating a high quality seamless steel pipe with plastic without impairing the uniformity of the film thickness around the bead and without any voids next to the bead.

The present invention will be further explained below with reference to Examples.

Example: After applying an epoxy thermosetting primer to a welded steel pipe with an outer diameter of 609.6 mmφ, a thickness of 8 mm, a length of 9 m, and a bead shape of 18 mm in width and 1.2 mm in height and heat curing, MI = 0.2 g. /10min, high-density polyethylene of d=0.950 was heated and melted and extruded from a cylindrical die to form a coating with a thickness of 2.5 mm. During this coating work, the bead of the steel pipe was held on the top surface.

In Fig. 2, the pressure roll is a=10mm, b
A material made of heat-resistant silicone rubber with a hardness of 30±5 and having dimensions of = 22 mm, c = 100 mm, d = 3 mm, and e = 100 mm was used.

Move this pressure roll 100mm from the landing position of the covering material.
The press rolls were placed apart and pressed so that the grooves of the press rolls matched with the steel pipe bead portions while controlling the roll pressure load within the range of 10 kg±2 kg. Note that the press rolls are supported so as to be rotatable by shear force generated by adhesion with the coating as the steel pipe advances.

On the other hand, a water cooling ring was installed at a position approximately 600 mm away from the pressure roll, and the plastic-coated steel pipe was cooled by water cooling.

After treating a steel pipe coated with extrusion using the above-mentioned apparatus, the coating around the bead was peeled off and the voids beside the bead were investigated. As a result, there were no voids present.

In addition, when the coating film thickness around the bead was measured, it was confirmed that a substantially uniform thickness was obtained as shown in FIG.

Comparative Example Coating was carried out under the same conditions as in the example, except that the same size steel pipe and the same pressure roll as in the example were used, and the pressure roll was installed at a distance of 700 mm from the coating landing position, and a water cooling ring was placed between them. I went to

When we peeled off the coating around the bead of the coated steel pipe and observed the voids caused by remaining air bubbles, we found that a void with a maximum size of approximately 2 mm wide x 20 mm long was formed at the side of the bead, albeit discontinuously. I was able to observe it.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the bead in a plastic-coated steel pipe and the gap formed at the base of the bead, Figure 2 is a front view of the elastic roll for extrusion, and Figure 3 is a front view of the elastic roll for extrusion.
The figure is a perspective view showing an embodiment of the coating apparatus according to the present invention, and FIG. 4 is a graph showing the displacement behavior of the plastic coating film thickness. 1...Bead, 2...Gap, 3...Steel pipe, 4...
...Plastic coating film, 5...Elastic roll, 6
... Cylindrical extrusion die, 7 ... Ring-shaped water cooling device.

Claims (1)

[Claims] 1. An apparatus for manufacturing plastic-coated steel pipes using a cylindrical extrusion die, characterized in that a solid elastic roll that presses the foot of the steel pipe bead in proximity to the extrusion die is connected to a water cooling device. Plastic coating equipment for steel pipes.