JPH03136828A - Double pipe manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a resonant silencer made of synthetic resin, etc., in which an outer tube is constructed such that a cavity of a predetermined shape is formed on the outer circumferential surface of the inner tube. The present invention relates to a method of manufacturing a double-walled tube in which a double tube is integrally formed, and relates to a technique for forming an outer tube from a parison by blow molding.

(Prior Art) As a prior art, the one described in Japanese Patent Application Laid-Open No. 60-95120 is known.

In this technology, an inner tube with a small hole is placed upright on a slide core that can move up and down, and an annular parison is supplied to the outside of this inner tube, and the slide core is raised to enter the crosshead. After pressing the tube to maintain airtightness at both ends of the inner tube, the mold is closed, and compressed air is injected from the small hole side of the inner tube to integrally weld the inner tube and the box formed from the annular parison. In this way, plastic double tubes are manufactured.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional technology, the inner tube is held in a substantially vertical direction and the annular parison is inserted outside of the inner tube. It requires a process to move the inner tube into the parison, and in addition to making the slide core that holds the inner tube movable up and down, it is also necessary to provide an air flow passage inside the slide core, making the work complicated and requiring complicated treatment. I had to prepare the ingredients.

In addition, since the inner tube is designed to fit over the entire length of the reslide core, it is only possible to use a substantially straight inner tube that matches the outer surface shape of the slide core, and the central axis is multidimensional. There is a drawback that a bent tube cannot be used as an inner tube.

Furthermore, the length of the inner tube is also limited by the length of the slide core, and it has been possible to manufacture only a double tube with a relatively short total length of the inner tube.

The present invention improves the conventional technology, shortens the work process, eliminates the need for a complicated mechanism as a jig for holding the inner tube, and uses a multi-dimensionally bent tube body as the inner tube. The present invention provides a method for manufacturing a double-walled tube that can use a long tube.

(Means for solving the problem) The first means for solving the above problem is to use a double pipe manufacturing method: (a) inserting the inner pipe between opposing molds for forming the outer pipe; (a step of holding the inner tube in a substantially horizontal direction, middle) A step of discharging a pair of sheet-shaped parisons from a nozzle between the molds, and letting them hang down to a predetermined length on both sides of the inner tube at least near the center between the molds, ( c) A step of clamping the mold and enclosing a parison between the molds of the inner tube (at least around the center); A step of blow-molding the outer tube fixed to the inner tube by introducing air into the parison through the communication portion is adopted.

In addition, in the second method, the steps (a) to (c) are the same, but instead of (e), the mold is inserted into the parison from a through hole drilled in the mold. The method employs a step of blow molding the outer wall fixed to the inner tube by introducing air through the parison wall.

(Function) In the present invention, the inner tube held approximately horizontally between the molds is not moved when the molds are clamped, and blow molding is performed in the position where it was initially held. In addition to omitting the step of moving the tube to a predetermined position, there is no need for complicated jigs such as slide cores.

Further, a tube body such as a slide core that is not restricted by the external shape of the jig can be used as the inner tube.

(Example) FIG. 11 shows a double pipe manufactured by the method of the present invention,
This double tube 1 is composed of a straight inner tube 2 and an outer tube 5 surrounding the central part of the inner tube 2 between the molds, and there is a cavity between the inner tube 2 and the outer tube 5. 6 is formed and
A communicating vibe section 3 that is open to the outside is integrally erected near the center of the inner tube 2 between the molds, and a cavity 6 is communicated with the inside of the inner tube 2 .

FIGS. 12 and 13 also show another double pipe 31.41 produced by the method of the invention, this double pipe 31.
41 is different from the double tube I only in that the inner tubes 32 and 42 are three-dimensionally bent tubes whose central axes are changed two-dimensionally or three-dimensionally, and the other configurations are as follows. It is similar.

Both the inner and outer tubes of these double tubes 1, 31, 41 are made of known synthetic resin materials such as polyethylene and polypropylene, and are used as resonance type mufflers.

Hereinafter, the manufacturing method will be explained using the illustrated double pipe 1 as an example.

1 to 5, reference numeral 11.12 denotes a pair of opposing molds, and this mold 11.12 has a cavity 13 for forming an outer tube 5 and an inner tube 2 on both sides of the cavity 13.
A concave portion 14,15 for accommodating the mold is continuously formed, and an acute protrusion 16 is formed along the circumferential direction in a portion that comes into contact with the periphery of the inner tube 2 when the mold is clamped.

A nozzle 17 is located above between the pair of molds 11 and 12.
A pair of sheet parisons 18 and 19 having predetermined numbers 11 are discharged from the nozzle 17 in parallel to each other and hang down.

In such an apparatus, first, the inner tube 2 having the communicating pipe portion 3 formed in advance is held between the molds 11 and 12 in a substantially horizontal direction.

The inner tube 2 is held by placing its both ends on support stands 20 and 21 provided outside the mold, but other jigs may be used as appropriate as long as they can hold the inner tube horizontally.

It goes without saying that when manufacturing the double tubes 31 and 41 shown in FIGS. 12 and 13, the inner tubes 32 and 42 having a three-dimensionally bent shape are used.

Then from the nozzle 17 a pair of sheet parisons 18.1
9 to both the left and right sides of the inner tube 2, and let it hang down around the center between the molds of the inner tube 2, and then pour it into the molds 11 and 12.
the inner tube 2 and the sheet parison 18.
The sheet parisons 18 and 19 surround the inner tube 2 near the center between the molds.

Thereafter, an airtight lid 22 is attached to one end of the inner tube 2, and compressed gas is blown into the interior from the other end to inflate the sheet parison 18. The outer tube 5 is blow-molded by pressing it against the inner circumferential surface of the
The inner tube 2 and the outer tube 5 are integrally fixed, and a cavity 6 of a predetermined shape is formed between them.

At this time, the molds 11 and 12 are provided with through holes that communicate with the outside so that the air in the mold is discharged to the outside through the through holes during blow molding, or the air from the mold is discharged to the outside through the through holes. Suction may be applied to allow the outer tube to be accurately and easily formed into a predetermined shape. Further, as shown in FIG. 6, a plurality of concave portions 7 or convex portions 8 are continuously formed in the same direction at the junction of the inner tube 2 and the outer tube 5, so that the inner tube 2 and the outer tube Note that the recesses 7 or the protrusions 8 may be formed intermittently in the circumferential direction, or may be formed singly.

In addition, in order to prevent unnecessary sheet parison from being fused to parts of the inner tube 2 other than the joint with the outer tube 5, a release tape is attached or a release agent is applied to the parts. Good too.

FIG. 7 shows another embodiment of the method according to the invention, in which mold 11.1
The steps up to the process of clamping the sheet parison are the same as those in the previous embodiment, but the blow pin 24 is inserted through the through hole 23 drilled in the mold 12, penetrates the wall of the parison, and introduces compressed gas into the interior of the sheet parison. In this embodiment, the outer tube 5 is blow-molded.

In this case, it is preferable to close both ends of the inner tube 2 to keep the inside airtight.

In addition, in this embodiment, the air injection hole left by the blowbin on the molded outer tube may be filled and sealed with rubber or plastic material, and a communication part to the outside may be provided. A double pipe in which the cavity 6 becomes a closed space may be formed by using an inner pipe without the inner pipe.

Figures 8 to 10 show another embodiment of a double tube manufactured by the method of the present invention, and Figure 8 shows a sheet parison for forming an outer tube made of non-foamed thermoplastic resin and foamed thermoplastic resin. The outer tube 5 has a multilayer structure integrally formed with an outer layer 5a made of non-foaming resin and an inner layer 5b made of foamable resin. The communication pipe section 3'6 provided upright on the pipe 2 is bent at a substantially right angle to increase its length and thereby improve the sound deadening effect.

In the above-described embodiment, a pair of sheet parisons were used as the parison for forming the outer tube, but the annular parison discharged from the nozzle was cut in half along the axial direction to form two sheet parisons. A material formed into a parison may be used.

Furthermore, instead of erecting one or more communication pipe sections as a communication section of the inner tube to the outside, one or more through holes may be bored in the inner tube.

(Effects of the Invention) According to the present invention, there is no need to move the inner tube to a predetermined position between the molds during mold clamping, and the work of moving the inner tube can be omitted, thereby shortening the manufacturing cycle. can.

In addition, as a jig to support the inner tube, a simple jig that can hold the inner tube in a substantially horizontal direction is sufficient, and there is no need to prepare a complicated jig that can move up and down and has an air flow passage formed inside. There is no.

Furthermore, a multi-dimensionally bent complex-shaped tube or a long tube can be used as the inner tube, and various double tubes can be manufactured depending on the purpose.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a perspective view of a mold used in the present invention, and FIGS. 2 and 3 are front sectional views and side views showing a state in which the parison is suspended on both sides of the inner tube. cross section,
Figures 4 and 5 are front sectional views and side sectional views showing the blow molded state, Figure 6 is an enlarged sectional view showing how the inner tube and outer tube are connected, and Figure 7 is another embodiment. Figures 8 to 10 are cross-sectional views showing the structure of other embodiments of the double pipe, and Figure 11 is a perspective view of the double pipe whose inner pipe is approximately straight. 12 is a perspective view of a double pipe whose inner pipe is bent two-dimensionally, and FIG. 13 is a perspective view of a double pipe whose inner pipe is bent three-dimensionally. 1.31.41...Double pipe, 2.32.42...Inner pipe, 1.3'4...Communication pipe section, 5...Outer tube, 6...Cavity part, 11. 12...
Mold, 18.19... Sheet parison, 23... Through hole, 24... Blow pin. Figure 1

Claims (2)

[Claims] (1) A step of holding the inner tube in a substantially horizontal direction between opposing molds for forming the outer tube, and discharging a pair of sheet-like parisons from a nozzle between the molds at least at the center in the longitudinal direction of the inner tube. hanging down to a predetermined length on both sides near the inner tube; clamping the mold and surrounding at least the vicinity of the central portion in the longitudinal direction of the inner tube with the parison; forming the inner tube from inside the inner tube; A method for manufacturing a double-walled tube, comprising the step of blow-molding an outer tube fixed to the inner tube by introducing air into the parison through a communicating portion to the outside. (2) holding the inner tube in a substantially horizontal direction between opposing molds for forming the outer tube, discharging a pair of sheet-like parisons from a nozzle between the molds at least at the center in the longitudinal direction of the inner tube; hanging down to a predetermined length on both sides near the inner tube; clamping the mold and surrounding at least the vicinity of the central portion in the longitudinal direction of the inner tube with the parison; A method for manufacturing a double tube, comprising the steps of blow molding an outer tube fixed to the inner tube by introducing air into the parison by penetrating the wall of the parison.