JPH05293877A - Manufacture of corrugated tube - Google Patents

Abstract

PURPOSE:To provide the manufacturing method of a corrugated tube for which lowering of strength is not generated even if any difference in level is formed in a joint of respective molds. CONSTITUTION:A corrugated tube is manufactured by using a movable mold 8 in the continuous blow molding method. Crest sections 9a of a mold 9 provided with notches 11 on the edges on the parison side are used as a joint 12 and continuously disposed closely to form said molds 8. Projected sections 14 are formed on a corrugated tube 10 by the notch sections 11. The wall of the projected section 14 is formed thicker than those of other sections, and in the case any difference in level is generated at the joint 12, the difference in level of the corrugated tube is not made thinner in its wall thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrugated pipe manufacturing method, and more particularly to a corrugated pipe manufacturing method by continuous blow molding.

[0002]

2. Description of the Related Art In order to prevent deformation and crushing due to a force applied in a radial direction, corrugated corrugated pipes are widely used for electric wire conduits, drainage pipes and the like. This corrugated tube can be manufactured by spirally winding an extruded parison with a corrugated cross-section of one unit on a mandrel to produce a corrugated tube, or by using a moving metal having a cylindrical parison with irregularities. A method of applying an internal pressure while extruding and moving into a mold, or vacuuming the outside to press it against a mold due to a pressure difference to form a corrugated shape is usually used.

The former method has the advantage that a corrugated pipe with various corrugations can be obtained because the degree of freedom of the extrusion shape is large by changing the mold of one unit, but the seam for each unit is different. It has the drawback of being difficult to fuse.

On the other hand, the latter method is a continuous blow molding method, which has a small degree of freedom in shape but has a high manufacturing speed,
Commonly used.

The latter method, which is a continuous blow molding method for corrugated pipes using a moving mold, comprises a cylindrical parison extruded from an extruder and a plurality of molds having one or more corrugations. Then, it is molded by a molding device which is closely arranged. In this molding device, the valley portion of the die corresponding to the wave crests of the corrugated pipe is pulled by decompression, and the parison is decompressed and sucked when the die moves along with the movement of the parison in the die. As a result, the outer surface of the parison is formed into a corrugated shape.

In the method using a plurality of moving molds as described above, as shown in FIG. 4, the adjacent molds 2 are joined together at the joint 5 so as not to spoil the appearance of the formed corrugated pipe 4. In, it is necessary to arrange so that there are no steps or gaps. The corrugated pipe 4 as shown in FIG. 4 can be obtained by using the mold correctly arranged in this way.

That is, in FIG. 4, the adjacent dies 2 are arranged so that the inner surface ridges 2a thereof are substantially on the same plane, and therefore, the outer surfaces of the corrugated pipe corresponding to the joint 5 are arranged. Does not cause a step.

[0008]

However, in reality, due to the clearance of the machine or the like, a slight misalignment occurs between the adjacent dies 2, and as shown in FIG. It may occur. If the dies arranged in this way are used, steps 4a and 4b will occur on the inner surface and outer surface of the obtained corrugated tube 4. If there is a step on the inner surface and the outer surface of the corrugated pipe 4, the thickness of the portion 4c corresponding to the seam 5 is thin, and the tensile strength and the like are reduced. Therefore, it is necessary to increase the overall thickness in order to prevent the reduction in strength due to the step. Further, for example, it exerts a notch effect against impact or the like, gives an impression of being easily broken, and significantly lowers the commercial value.

Therefore, the present invention provides a method for manufacturing a corrugated pipe that does not cause a decrease in strength even when a step is formed at the joint between adjacent moving molds and does not affect the appearance. The purpose is to

[0010]

In order to solve the above-mentioned problems, the present invention extrudes a pair of molding devices in which a plurality of dies having one or more corrugations are continuously arranged in close contact with each other. In a method for manufacturing a corrugated pipe that is formed into a corrugated shape by moving it along a curved cylindrical parison, a notch is provided in a parison side edge portion of a joint of the plurality of molds, and a groove portion is formed between adjacent molds. By providing the corrugated pipe, the annular convex portion corresponding to the groove is provided in the outer surface valley portion of the corrugated pipe.

In the method of the present invention, a thermoplastic compound mainly composed of polyethylene, polypropylene, polyvinyl chloride or the like can be used as the parison which is a raw material of the corrugated pipe.

The seam of the mold provided with the notch is
The obtained corrugated pipe may be located at any of the mountain portion, the wall portion, and the valley portion. Since a convex portion is formed in the portion of the corrugated pipe corresponding to this cutout portion, adjacent molds may be connected to each other at the peak portion so that the convex portion is formed in the valley portion of the corrugated pipe. The appearance of the obtained corrugated pipe is preferable. In continuous blow molding, the extruded parison is spread to the valley of the mold and forms the peaks of the corrugated tube. Therefore, the corrugated pipe has a thin peak portion and a thick valley portion. Therefore, even if the convex portion is provided in the valley portion of the corrugated pipe, the influence on the wall thickness around the convex portion is small.

The height of the convex portion of the corrugated pipe formed by the notch portion is preferably about 1 to 2 mm.

The width of the convex portion depends on the size of one unit of the waveform, but is preferably about 1 to 5 mm at the intermediate height.

Further, the shape of the tip of the convex portion is preferably rounded, but may be triangular pyramid in cross section or trapezoidal in cross section. Therefore, the notch portion of the mold may be provided according to the shape of the convex portion.

It should be noted that a notch may be provided in the inner surface mountain portion where no step is formed in the mold, and by doing so, a corrugated pipe having a uniform appearance can be obtained.

[0017]

In the method of the present invention, a moving mold having a notch at the joint of the mold is used. Therefore, a convex portion is formed in the portion corresponding to the cutout portion in the corrugated pipe to be manufactured, and the wall thickness is thicker than other portions. Even if a step is formed at the seam, the step causes The wall thickness does not decrease and the strength does not decrease.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings.

FIG. 1 shows a continuous blow molding apparatus using a moving mold for producing a corrugated pipe by the method of the present invention.

In FIG. 1, the die 16 of the extruder 15
The cylindrical parison 3 extruded from between the nipple 17 and the nipple 17 has a plurality of closely arranged molds 9 having two corrugations.
It goes inside and moves in the direction of arrow B together with the mold 9. A large number of molds 9 are arranged in a caterpillar shape to form the mold unit 8. The mold unit 8 moves a predetermined distance to shape the parison 3 into a corrugated shape, and then rotates in the direction of arrow A to separate from the corrugated tube 10 that has been molded. The die 9 has a semicircular cross section (a direction perpendicular to the paper surface) and covers a half of the circumference of the extruded parison 3 to form the upper half of the parison 3. to share the load. That is, although not shown, a mold unit having a structure similar to the mold unit 8 described above, which shares the molding of the lower half of the parison 3, is arranged below the parison 3.

The mold 9 has a ridge portion 9a and a valley portion 9b, respectively, and the valley portion 9b is provided with a pressure reducing port 7a. The decompression port 7a is connected to a decompression device (not shown) via the decompression path 7b. At the time of molding, the decompressor is operated to suck the parison 3 that moves together with the mold 9 from the decompression port 7a, thereby molding the parison 3 into a corrugated shape.

FIG. 2 shows a joint 12 of the movable mold shown in FIG.
FIG. Each mold 9 that constitutes the mold unit 8 is provided with a notch 11 at the edge of the seam 12 on the parison side. By entering the parison 3 into the cutout portion 11, a convex portion 14 is formed in the outer surface valley portion of the corrugated tube 10 that has been formed, and as a result, the buildup is positively performed.

FIG. 3 shows a case where a step is formed at the joint 12 of the mold 9. Corrugated tube 10 obtained in this case
The thickness does not become thin even in the portion corresponding to the seam 12.

By forming a notch in the non-seam 13 in the mold 9 to form a protrusion, uniformity in appearance can be obtained.

[0025]

As described above in detail, according to the manufacturing method of the present invention, the movable mold having the notch portion at the seam of the mold is used to cope with the seam of the mold of the corrugated pipe. Since a convex portion is formed on the part, even if a step is generated at the seam of the mold,
The wall thickness of the portion corresponding to the step of the corrugated pipe does not become thin. Therefore, it is not necessary to increase the wall thickness of the entire corrugated pipe in order to suppress the strength reduction of the corrugated pipe and to reinforce the wall thickness of the portion corresponding to the step.

[Brief description of drawings]

FIG. 1 is a view showing a cross section at the time of continuous blow molding by a moving mold used in the method of the present invention.

FIG. 2 is a view showing an enlarged portion of a seam of a mold used in the method of the present invention.

FIG. 3 is a view showing an enlarged portion of a seam of a mold used in the method of the present invention.

FIG. 4 is a view showing an enlarged portion of a seam of a mold used in a conventional manufacturing method.

FIG. 5 is a view showing an enlarged portion of a seam of a mold used in a conventional manufacturing method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Moving mold, 2 ... Mold, 2a ... Inner surface mountain part of the mold, 2b
… Inner valley of mold 3… Parison, 4… Corrugated tube, 4a… Upper step of corrugated tube 4b… Lower step of corrugated tube, 4c… Step part of corrugated tube 5… Between molds Seam, 6 ... Non-seam between molds, 7a
Decompression port 7b ... Decompression path, 8 ... Moving mold used in the method of the present invention 9 ... Mold, 9a ... Inner surface ridge portion of mold, 9b ... Inner surface valley portion of mold, 10 ... Corrugated pipe 11 ... Notch, 12 ... Seam between molds, 13 ... Non-seam between molds 14 ... Convex portion of corrugated pipe, 15 ... Extruder, 16 ... Die, 17 ... Nipple.

Claims (1)

[Claims] 1. A corrugation is formed by moving a pair of molding devices in which a plurality of molds having one unit or more of corrugation are arranged in close contact with each other continuously along an extruded cylindrical parison. In the method for manufacturing a corrugated pipe, a notch is provided in the parison side edge of the seam of the plurality of molds, and a groove is formed between adjacent molds, thereby corrugating an annular convex portion corresponding to this groove. A method for manufacturing a corrugated pipe, characterized in that the corrugated pipe is provided in the outer valley portion of the pipe.