JPS649811B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a flexible synthetic resin double pipe used as a conduit for passing electric wires.

In recent years, wiring for electrical equipment in buildings, factories, etc. is generally housed in conduits. The wiring method is to connect conduit pipes of a specified length in advance and lay the pipes, embed them in the concrete of the floor, wall, ceiling, etc. of a building or factory, and then pull the wires in. Generally, iron pipes are often used for this electric conduit, which has advantages such as high strength and rigidity. However, on the other hand, there are problems in handling due to its large weight, there are many connection points because it is a fixed length item, which requires a lot of effort, it involves bending work, and it is highly corrosive. Furthermore, it has many problems such as inconveniences due to magnetism. Therefore, in recent years, hard synthetic resin pipes such as hard vinyl chloride pipes have come to be used instead of iron pipes.

As shown in Fig. 1, the flexible synthetic resin double pipe conventionally used as this type of conduit has a synthetic resin inner pipe 1' with corrugated surfaces on both sides, and a smooth outer surface on the outer surface of the inner pipe 1'. It was manufactured by covering the outer tube 2' with synthetic resin. However, when manufactured in this way, the outer surface of the outer tube 2' is smooth, so when the flexible synthetic resin double tube is bent, the outer tube 2' is stretched and bent so that it becomes thinner at the part on the outside of the bend. In the inner part, the outer tube 2' is bent so as to form wrinkles, making it difficult to bend and requiring a large amount of force to bend, resulting in poor workability and the disadvantage that the bending angle cannot be made large.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a flexible synthetic resin double pipe that can easily produce a flexible synthetic resin double pipe with good flexibility. To provide a manufacturing method.

The present invention will be specifically explained below using examples.
Reference numeral 1 denotes an inner tube made of a hard synthetic resin such as polyethylene, polypropylene, hard vinyl chloride, etc., and is formed in a wavy shape in which peaks 1a and troughs 1b are alternately continuous in the longitudinal direction. An outer tube 2 is made of a soft synthetic resin such as soft vinyl chloride or rubber, and is coated on the outer surface of the inner tube 1. This outer tube 2 has approximately the same wall thickness over its entire length in the longitudinal direction, and is locally recessed in a portion corresponding to the valley portion 1b of the inner tube 1.
A portion corresponding to the top of the mountain portion 1a is in contact with the inner tube 1. In this way, the inner tube 1 and the outer tube 2 form a flexible synthetic resin double tube.

The flexible synthetic resin double pipe thus formed is manufactured as follows. Reference numeral 4 is an extrusion molding machine for forming the inner tube, and as shown in FIG. 4, synthetic resin is continuously extruded into a tube shape from between an outer mold 4a and an inner mold 4b to form the inner tube 1. . This extrusion molding machine 4
A corrugating device 5 is disposed in front of the inner tube 1, and peaks 1a and troughs 1b are alternately formed on the inner tube 1. This corrugation device 5 has a pair of endless bands 5b arranged above and below, each of which is formed by connecting a plurality of corrugation molds 5a in an endless belt shape. It is formed with a recess 5c. The extruded inner tube 1 is introduced between the upper and lower endless bands 5b, and air is supplied from the air supply tube 5d to bring the outer surface of the inner tube 1 into close contact with the inner surface of the corrugated mold 5a. It is waved to 1. At this time, instead of using the air supply pipe 5d, a suction pipe may be communicated with each recess 5c to draw a vacuum from the suction pipe, and the inner pipe 1 may be brought into close contact with the recess 5c for corrugation. Reference numeral 6 is a crosshead type extrusion molding machine for forming an outer tube, and the outer tube 2 is continuously extruded from between an outer die 6a and an inner die 6b, and the outer tube 2 is continuously extruded from between an outer die 6a and an inner die 6b. An inner tube introduction hole 6c is provided on the circumferential side. An annular suction path 7 is formed in the inner wall of the inner tube introduction hole 6c, and the air near the discharge port 6d between the inner mold 6b and the outer mold 6a is evacuated from the suction port 8 through the suction path 7. I'm starting to do that. The inner tube 12 is continuously supplied to the inner tube introduction hole 6c of the extrusion molding machine 6 for forming the outer tube, and covers the outer tube 2 that is continuously extruded from the discharge port 6d. The inner tube 1 may be cured and may be continuously fed on the same line as the extrusion molding machine 4 for forming the inner tube, or it may be produced in a separate process. When the outer tube 2 is covered with the inner tube 1, the air between the inner tube 1 and the outer tube 2 is evacuated from the suction path 7, and the outer tube 2 has a uniform wall thickness over the entire length in the longitudinal direction and has a valley. A portion corresponding to portion 1b has a concave shape. Here, for comparison, we will discuss the case without evacuation. When the distance from the discharge port 6d to the outlet end of the inner tube introduction hole 6c, that is, the land length L, is short, the outer surface of the outer tube 2 becomes smooth and the inner surface also forms the trough of the inner tube 1, as shown in FIG. 6a. It is hardly embedded in 1b. Also, when the land length L is long, the outer surface of the outer tube 2 is almost smooth (however, there is a slight spontaneous sink mark in the part corresponding to the trough 1b), and the inner surface is embedded in the trough 1b of the inner tube 1. . Therefore, only by evacuation can the wall thickness of the outer tube 2 be approximately equal over the entire length in the longitudinal direction and the valley portion 1b
A concave flexible synthetic resin double tube is manufactured.

In the flexible synthetic resin double tube manufactured as described above, the outer tube 2 has approximately the same thickness in the longitudinal direction and is recessed in the portion corresponding to the trough 1b, so the outer tube 2 can easily expand and contract. Good flexibility. Furthermore, since the outer tube 2 has a recess 2a on its outer surface, it can be easily and reliably connected to the joiner 3. In other words, Joyner 3
As shown in FIG. 3, there is a cylindrical jointer body 3a.
A partially cut-out annular locking ring 3b is installed inside the locking ring 3b, and a plurality of locking claws 3c are formed around the inner circumference of the locking ring 3b. The locking claws 3c are respectively locked in the recesses 2a of the outer tube 2 by simply inserting them through the opening at the end of the joiner main body 3a.

As described above, a synthetic resin inner tube that has been continuously corrugated in the longitudinal direction is guided in a hardened state to an extrusion molding machine for forming an outer tube, and the outer circumference of the inner tube is covered with a synthetic resin outer tube. At the same time, the space between the outer tube and the inner tube is suctioned and the outer tube is corrugated before it hardens, so just by applying a vacuum in the extruder, the outer tube can be made to have the same thickness in the longitudinal direction and the grooves can be created. The outer tube can be recessed in the corresponding part, and the outer tube can be coated with a structure in which the inner surface of the outer tube is in sliding contact with the top of the inner tube, and at the same time, it has a flexible structure with good flexibility. It is possible to manufacture flexible synthetic resin double pipes.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a conventional example, Fig. 2 is a cross-sectional view of an embodiment of a flexible synthetic resin double pipe obtained by the manufacturing method of the present invention, and Fig. 3 is a cross-sectional view of an embodiment of the flexible synthetic resin double pipe obtained by the manufacturing method of the present invention. 4 is a cross-sectional view of the state in which the inner tube is manufactured by the manufacturing method of the present invention, FIG. 5 is a cross-sectional view of the state in which the outer tube is covered with the same as above, and FIGS. 6 a and b are of the comparative example of the same as above. In the cross-sectional view, 1 is an inner tube and 2 is an outer tube.

Claims (1)

[Claims] 1. A synthetic resin inner tube that has been continuously corrugated in the longitudinal direction is guided in a hardened state to an extrusion molding machine for forming an outer tube, and a synthetic resin outer tube is coated on the outer periphery of the inner tube, and the outer tube is A method for producing a flexible synthetic resin double tube, characterized in that the outer tube is corrugated by suction between the inner tube and the outer tube before it hardens.