JP2885461B2 - Manufacturing method of composite pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention is used for water supply, hot water supply, drainage, exhaust, or the like, and a method for producing a composite pipe in which the inner peripheral surface of a metal pipe is coated with a synthetic resin. About.

(Prior Art) In recent years, a composite pipe having an inner peripheral surface of a metal pipe coated with a synthetic resin has been used as a discharge agent for hot water supply, hot water heating, and the like. FIG. 3 shows a cross-sectional view of a general apparatus for manufacturing such a composite pipe. The strip-shaped metal plate is conveyed while being continuously formed into a U-shape, and further formed into a tubular shape. A metal plate welding device 31 for welding the respective side edges of the metal plate 32a is installed above the side edges of the circular metal plate 32a. Then, the metal plate 32a is
Are welded to each other to form a metal tube 32c. Metal plate 32a
On the outside of the outside, there is an outer mold 3 for forming the metal plate 32a into a tubular shape.
7 are arranged. Inside the metal plate 32a, the metal plate 32a
A cylindrical inner mold 38 extending in the transport direction is inserted. A cylindrical core 34 having a predetermined gap with the inner mold 38 is inserted in the inner side 38 concentrically with the metal plate 32a. Core 34
Are supported by the inner mold 38 by the bridge 36. Core 34
Is formed integrally with the tip core portion 33 located downstream of the welded portion 32b of the metal tube 32c in the metal plate transport direction. The tip core portion 33 includes a tapered portion 33a having a tapered surface whose diameter gradually increases toward the downstream side in the metal plate transport direction, and is integrated with the core 34 via the tapered portion 33a. The outer diameter of the distal end of the distal core portion 33 is slightly smaller than the inner diameter of the metal tube 32c. A predetermined gap formed between the inner die 38 and the core 34 serves as a flow path 39 for the molten resin. The molten resin is fed through the flow passage 39, and is further extruded radially along the tapered surface of the distal end core portion 33. The molten resin has a predetermined thickness by a gap defined by the outer peripheral surface of the tip core portion 33 and the inner peripheral surface of the metal tube 32c, and covers the inner peripheral surface of the metal tube 32c to form the inner layer 35.

(Problem to be Solved by the Invention) In the inner layer 35 of the composite pipe manufactured as described above, a bridge-shaped groove (hereinafter, referred to as a bridge line) generated by passing through the bridge 36 remains. . Generally, in order to eliminate the bridge line, the clearance between the metal tube 32c and the distal core portion 33 is reduced by increasing the outer diameter of the distal core portion 33, thereby narrowing down the resin.

However, if the metal used has low tensile strength,
A crack is generated in the metal tube 32c due to an increase in the pressure of the resin caused by the drawing. Also, when the melt viscosity of the resin used is high and the flowability is poor, the flow resistance increases and the resin pressure increases, so the clearance between the metal tube 32c and the tip core portion 33 cannot be reduced so much, and the narrowing effect is reduced. Insufficient and the bridge line remains. If the composite pipe with the remaining bridge line is used for a hot water supply pipe or a drain pipe, there is a problem that a liquid or gas such as water flowing inside leaks to the outside of the composite pipe through the bridge line.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to reduce the size of a bridge line by regulating the outside of a metal tube with an outer mold when coating the inner peripheral surface of the metal tube with a synthetic resin. It is an object of the present invention to provide a method of manufacturing a composite pipe that can be performed and that does not cause cracks in a metal pipe even when an internal pressure due to a resin is applied.

(Means for Solving the Problems) A method for manufacturing a composite pipe according to the present invention is a method for manufacturing a composite pipe in which an inner peripheral surface of a metal pipe is coated with a synthetic resin, and sequentially forms a metal plate into a circular tube. Then, a step of bonding the respective side edges of the metal plate to each other to produce a metal tube, and applying a molten resin to the inner peripheral surface of the metal tube while regulating the outside of the manufactured metal tube with an outer mold. Covering the inner peripheral surface of the metal tube with the resin by radially extruding, thereby achieving the above object.

(Examples) Hereinafter, the present invention will be described based on examples.

In the manufacturing method of the present invention, first, a strip-shaped metal plate is sequentially curved into a U-shaped cross section by a U-shaped metal or a U-shaped forming machine. The U-shaped metal plate is conveyed and sequentially formed into a tubular shape, and is formed into a perfectly circular cross section in a state where the side edges are attached to each other or in an overlapping state. And each side edge part of a metal plate is welded by a welding machine, and a metal pipe is manufactured. The molten resin is fed into the inside of the tubular metal plate with the production of the metal tube, and the molten resin is extruded radially to coat the inner peripheral surface of the metal tube with the resin. The step of radially extruding the molten resin is performed in a state where the outside of the metal tube is regulated to a circular tube.

FIG. 1 is a sectional view of an apparatus according to an embodiment of the present invention. In the figure, a metal plate 12a formed into a tubular shape is welded at a welded portion 12b to form a metal tube 12c, and an inner peripheral surface of the metal tube 12c is coated with a resin to form an inner layer 15 made of the resin. .

An outer die 17 that regulates the outer peripheral surface of the metal plate 12a and forms a circular tube is provided in the transfer area of the metal plate 12a. Outer die 17
Has a notch at a position corresponding to the welded portion 12b. A metal plate welding device 11 for welding the respective side edges of the metal plate 12a at the welded portion 12b is installed in the notch. Inside the metal plate 12a formed in a tubular shape, a cylindrical inner mold 18 is inserted in the transport direction of the metal plate 12a.
Inside the inner die 18, a columnar core 14 is inserted concentrically with the metal plate 12 a having a perfect circular cross section so as to have a predetermined gap between the inner die 18. The core 14 is supported by the inner mold 18 by the bridge 16. A predetermined gap formed between the inner die 18 and the core 14 serves as a flow path 19 for the molten resin.
The core 14 is formed integrally with the tip core 13 located downstream of the weld 12b in the metal plate transport direction. The tip core portion 13 is a column having a tapered portion 13a having a tapered surface whose diameter gradually increases toward the downstream side in the metal plate transport direction. The tip core portion 13 is integrated with the core 14 via the tapered portion 13a. The outer diameter of the cylindrical portion of the tip core portion 13 is slightly smaller than the inner diameter of the metal tube 12c, and the clearance between the two corresponds to the thickness of the inner layer 15 made of resin that covers the inner peripheral surface of the metal tube.

In the apparatus having the above configuration, the metal plate 12a
Is formed into a tubular shape by the outer mold 7, and the metal plate welding device 11 welds the respective side edges of the metal plate 12a at the welding portion 12b to produce the metal pipe 12c. On the other hand, the molten resin
9 and is radially extruded along the tapered surface of the tip core portion 13 to cover the inner peripheral surface of the metal tube 12c.

When the molten resin is extruded radially along the tapered surface of the tip core portion 13, a pressure generated by narrowing down the resin is applied to the metal tube 12c. However, the outside of the metal tube 12c is covered with the outer mold 17. Therefore, the metal tube 12c does not expand due to the pressure of the resin,
There is no crack in 2c. Further, since the metal tube 12c is less likely to be torn due to the regulation of the outer mold 17, the clearance between the metal tube 12c and the tip core portion 13 can be made smaller than before. Therefore, generation of a bridge line can be suppressed.

Next, another embodiment of the present invention will be described with reference to FIG.

In the figure, an outer mold 27a for regulating the metal plate 12a into a tubular shape is provided outside the metal plate 12a. Outside the metal tube 12c, an outer mold 27b for regulating the metal tube 12c into a circular tube is provided. The outer mold 27b is movable in the radial direction of the metal tube 12c. By changing the clearance between the outer mold 27b and the metal tube 12c by moving the outer mold 27b in the radial direction, the metal tube 12c
The clearance between the tip and the tip core 13 can be changed. That is, the thickness of the inner layer 15 can be changed. Therefore, in the present embodiment, the thickness deviation of the inner layer 15 can be adjusted by adjusting the position of the outer mold 27b.

In the present invention, as the metal plate, aluminum,
Metals such as iron and copper, or alloys thereof are used. As a welding method used for the metal plate welding apparatus, there are ultrasonic welding, TIG welding and the like. Examples of the resin used for the inner layer 5 include thermoplastic resins such as vinyl chloride, polyethylene, polypropylene, polybutene, polyamide, and fluororesin, and mixtures thereof.

As a composite tube having a preferred configuration produced by the production method of the present invention, for example, a composite tube in which the inner peripheral surface of an aluminum tube is covered with an adhesive cross-linked polyethylene layer is exemplified.
Aluminum is lightweight and easy to handle. Since the inner peripheral surface of the aluminum tube is coated with a resin, the aluminum is prevented from being corroded by a liquid such as water flowing through the inside of the tube. Also, since the polyethylene of the resin layer can be directly and firmly bonded to the aluminum tube, water does not easily enter between the resin layer and the metal tube, causing blisters,
There is no peeling of the resin layer. Thus, a composite pipe having excellent durability can be obtained. Further, since the crosslinked polyethylene is excellent in heat resistance, the composite pipe can be used for a portion using high-temperature water.

(Effects of the Invention) As described above, according to the manufacturing method of the present invention, a uniform resin layer can be formed by eliminating a bridge line without causing a crack in a metal tube. In addition, by using a movable outer mold, uneven thickness of the resin layer can be prevented. Therefore, a composite tube having a good appearance and good water stopping properties can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an apparatus used for carrying out the manufacturing method of the present invention, FIG. 2 is a sectional view of an apparatus used for another embodiment of the manufacturing method of the present invention, and FIG. FIG. 4 is a cross-sectional view of an apparatus used for performing the manufacturing method of FIG. 12a, 32a ... metal plate, 12c, 32c ... metal tube, 15, 35 ... inner layer, 16, 36 ... bridge, 17, 27a, 27b, 37 ... outer mold,
18, 28, 38 …… Inner type.

Claims (1)

(57) [Claims] 1. A method for manufacturing a composite pipe in which an inner peripheral surface of a metal pipe is coated with a synthetic resin, wherein a metal plate is sequentially formed into a tubular shape, and respective side edges of the metal plate are joined to each other. And manufacturing a metal tube by extruding the molten resin radially onto the inner surface of the metal tube while regulating the outer surface of the manufactured metal tube with an outer mold. A method of producing a composite pipe, comprising: coating with a resin.