JPH0688333B2 - Manufacturing method of composite pipe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a plurality of tubes in which an inner tube is bonded and integrated with an outer tube through a foam layer, and in particular, an inner surface of a metal tube is formed of a synthetic resin tube. It is suitable as a method for producing a plurality of tubes lined with a foam layer.

(Prior Art) Conventionally, as a method for producing such a composite pipe, a foaming adhesive is applied to either one or both of the inner surface of the outer tube and the outer surface of the inner tube, and the inner tube is inserted into the outer tube. Although there is a method of foaming and hardening, there is a drawback that the gap between the inner and outer tubes is not constant in the circumferential direction. To eliminate this drawback,
In JP-A-59-49885, it is proposed that a plurality of continuous ridges are provided on the outer surface of the inner pipe in the axial direction of the pipe to make the gap between the inner and outer pipes uniform in the circumferential direction. Has been done.

(Problems to be Solved by the Invention) In the above method, in order to make the gap between the inner and outer tubes uniform in the circumferential direction, it is necessary to make the height of the ridge substantially coincide with the size of the gap. On the other hand, if a thin synthetic resin pipe can be used as the inner pipe in order to obtain a composite pipe having an inner surface corrosion resistance, the cost will be low. However, when this inner tube is inserted into the outer tube whose inner surface is coated with adhesive, the ridges of the inner tube come into contact with the adhesive layer on the inner surface of the outer tube, causing resistance, and Since a strong resistance is generated at the position where the agent layer is in strong contact, the thin inner tube is bent or deformed to cause runout, or is twisted and inserted into the outer tube. If you shake or twist when inserting the inner tube,
At the position where the ridge of the inner pipe hits strongly, the adhesive layer on the inner surface of the outer pipe will be scraped off by the ridge over the twisted width of the ridge. A nonexistent portion and a portion where the adhesive is abundant due to being scraped by the ridge are generated. When this is heated to foam and cure the adhesive layer, the scraped-off portion of the adhesive remains as voids.

In this way, if there is a gap between the inner pipe and the outer pipe of a plurality of pipes, water intrudes from the gap of the end face to corrode the inner surface of the outer pipe, or when hot water or warm waste water is flowed, the synthetic resin The inner tube is softened, and the closed void is volume-expanded, and the inner tube may expand inward to block the conduit.

(Means for Solving Problems) The present invention solves the above-mentioned drawbacks in the method of manufacturing a composite pipe using a synthetic resin pipe provided with continuous ridges as an inner pipe, and the synthetic resin pipe is a thin pipe. Even if there is, there is no gap between the outer tube and the inner tube when the adhesive layer is foamed and cured, providing a composite tube that does not corrode the outer tube or block the pipeline even when hot water is circulated. The purpose is to do.

For this reason, in the present invention, a synthetic resin pipe is used as the inner pipe, in which axially intermittent projections are provided on the outer surface at substantially equal intervals in the circumferential direction.

The intermittent ridge has a small cross-sectional area of each ridge, for example, a cross-section protruding in a triangular shape from the outer surface of the inner pipe, and its height is in the gap when the inner pipe and the outer pipe are concentrically arranged. It is preferable that they are made almost equal, and the axial length of this ridge is
It is 1.0 to 10 mm, preferably 1.0 to 5 mm, and the interval between the ridges in the axial direction is 10 to 100 mm, preferably 30 to 70 mm. Also, these intermittent ridges are 10 to 30 mm circumferentially on the outer surface of the inner pipe.
It is provided at regular intervals. The length of the ridge is preferably as short as possible if the distance between the ridge and the outer pipe can be maintained, and the axial and circumferential intervals of the ridge are longer if the outer pipe and the inner pipe can be held concentrically. It is preferable that it is within the above range, although it varies depending on the wall thickness of the inner tube.

The above-mentioned projections may be arranged on the outer surface of the inner pipe in such a manner that the projections are arranged side by side in the circumferential direction, in a staggered arrangement, or in a spiral arrangement. Such an inner tube may be manufactured by extruding a synthetic resin tube such as a vinyl chloride resin or polyethylene provided with continuous ridges, and removing unnecessary portions by secondary processing such as cutting. In addition, when performing extrusion molding, use an outer mold with a groove on the inner surface side and move this outer mold forward and backward in the extrusion direction to intermittently communicate the groove with the extrusion port, or rotate while moving forward and backward. For example, the ridge can be formed simultaneously with the extrusion molding.

In the present invention, the synthetic resin pipe having the intermittent ridges is used as the inner pipe, and a method similar to the conventional method for producing a composite pipe having a foam layer between the inner pipe and the outer pipe. The composite pipe may be manufactured by. That is, a foaming adhesive is added to the inner surface of an outer tube such as a metal tube, for example, a urethane-based, epoxy-based, polyester-based resin-forming composition to which a hydrocarbon such as Freon, hexane, heptane, or the like is added as a foaming agent. Then, the synthetic resin inner tube having the intermittent ridges is inserted into the outer tube from one end before the foamable adhesive layer is foamed and cured. After inserting the synthetic resin inner tube into the outer tube, hot water is applied from outside the outer tube to heat the adhesive layer to foam and cure it. The hot water is preferably heated from one end of the pipe to the other end, or from the middle part to both ends.

The amount of the foaming adhesive applied to the inner surface of the outer pipe depends on the gap between the inner and outer pipes and the foaming ratio of the adhesive, but when foaming and filling the gap, it is still possible to have sufficient foaming reserve capacity. Do well. For this reason, the coating thickness is adjusted so that the volume of the gap can be suppressed to half or less of the volume when free foaming.

(Operation) In the present invention, since the synthetic resin pipe in which axially intermittent projections are provided on the outer surface at substantially equal intervals in the circumferential direction is used as the inner pipe, the inner pipe is covered with the foaming adhesive. When inserting into the outer pipe coated on the inner surface, the insertion resistance is smaller than that with continuous ridges, and even if a thin synthetic resin pipe is used as the inner pipe, it may bend due to the resistance during insertion. ,
It is less likely to be deformed or twisted, and the foamable adhesive layer is less likely to be scraped off on the side surface of the ridge. Therefore, the uneven distribution of the foamable adhesive layer between the inner and outer tubes after inserting the inner tube into the outer tube is reduced, and the gap between the inner and outer tubes can be filled without gap by the foaming of the adhesive layer.

Also, when the synthetic resin pipe is inserted into the outer pipe, even if it shakes or twists to some extent, the ridges are provided intermittently, so the adhesive layer is scraped off only where the ridges exist. Since the adhesive layer is not scratched between the ridges, uneven distribution of the adhesive layer can be reduced, and if unevenly distributed, voids are not formed due to foaming of the adhesive layer.

(Example) A steel pipe having an outer diameter of 110 mm, an inner diameter of 106 mm and a length of 5 m was used as an outer pipe, and a hard vinyl chloride pipe having an outer diameter of 104 mm, an inner diameter of 100 mm and a length of 5 m was used as an inner pipe. On the outer surface of the inner tube, the length of the ridge is 3 mm,
Sixteen intermittent ridges with an axial spacing of 50 mm and a triangular cross section with a height of 1 mm are formed in the circumferential direction at intervals of 20.4 mm.

Further, a semi-rigid urethane resin forming stock solution was used as the foaming adhesive. The composition of this stock solution is as follows in parts by weight.

Diol (0H value 28) 100 Ethylene glycol 15 Triethylenediamine 0.6 Silicon foam stabilizer 2.0 Water 2.0 Glue MDI (NCO index 105) 90 Pigment (special polyester resin mixed with 25% by weight of carbon black) 2.0 This stock solution is free to foam , Foamed about 10 times, and the closed cell ratio was 33%.

This foamable stock solution was applied on the inner surface of the metal outer tube to an average thickness of 0.35 mm. The coating was performed by inserting a jet nozzle into the metal tube and jetting the adhesive from the jet nozzle.
Immediately after application, a synthetic resin inner tube having intermittent ridges was inserted. The insertion was low in resistance, the inner tube was hardly shaken or twisted, and the insertion was smooth and easy. The gap between the inner tube and the outer tube was uniform in the circumferential direction. After inserting the inner tube into the outer tube in this way, hot water was applied to the outer surface of the outer tube from the central portion toward both ends to heat the foamable adhesive layer through the metal outer tube to foam and cure it.

The composite tube thus obtained has a synthetic resin inner tube strongly adhered with a uniform foam layer located in the center of the metal outer tube regardless of the cross section, and no voids are seen in the foam layer. There wasn't. Moreover, no bulge was observed on the inner surface even when hot water at 85 ° C. and water at 20 ° C. were alternately flowed repeatedly through this composite pipe.

(Effect of the invention) As described above, the present invention uses, as the inner pipe, the synthetic resin pipe in which the axially intermittent projections are provided at the circumferential direction at substantially equal intervals. Even when the synthetic resin pipe is inserted into the outer pipe coated with the foamable adhesive layer, the contact between the ridge and the adhesive layer is small, and therefore the insertion resistance is small, and even if the synthetic resin pipe is thin-walled. It is extremely unlikely to bend, deform, shake, or twist. Therefore, when the inner tube is inserted, the adhesive layer applied to the inner surface of the outer tube is less likely to be scraped off by the ridge,
Uneven distribution of the adhesive layer can be prevented. Further, even if the synthetic resin pipe is shaken or twisted to some extent due to the intermittent protrusions, only the side surface of the protrusions scrapes off the adhesive layer, and the area thereof is extremely small. Therefore, when the foamable adhesive layer foams, the foaming pressure does not fill the space between the inner and outer tubes without any space.

In this way, a composite pipe in which the gap between the inner and outer pipes is filled with foam and firmly bonded is obtained, so that water does not enter from the end face and the inner pipe inner surface is completely protected against corrosion, and the hot wastewater Even if it is used for repeated circulation of cold water, no bulge occurs on the inner surface.

Claims (2)

[Claims] 1. A method for producing a composite pipe, wherein an inner tube is inserted into an outer tube having an inner surface coated with a foaming adhesive, and the foaming adhesive is heated and foam-cured between the two tubes. A method for producing a plurality of pipes, characterized in that a synthetic resin pipe having axially intermittent projections provided at substantially equal intervals in the circumferential direction is used. [Claim 2] The length of each intermittent ridge in the axial direction is 1.
The method for producing a composite pipe according to claim 1, wherein the distance between the ridges is 10 to 100 mm, and the distance in the circumferential direction is 10 to 30 mm.