JPH06218817A - Manufacture of composite pipe - Google Patents

Abstract

PURPOSE:To enable a composite pipe, wherein an inner circumferential surface of a metal pipe is lined with a non-foamed resin layer via a foamed resin layer, to be manufactured in the stable condition of interfacial bonding and in the uniform thickness of the foamed resin layer. CONSTITUTION:In a method of manufacturing a composite pipe by inserting a two-layer pipe 1, wherein a foamed resin layer 12 is provided on a non-foamed resin layer 11, into a metal pipe 3 and bonding the interfaces of both the pipes to each other with bonding agents 2, 13, the hardness of the outer surface of the foamed resin layer 12 is set in the range of R60 to R120 in the Rockwell hardness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a composite pipe used for producing an inner surface resin-lined metal pipe having an inner peripheral surface covered with a resin layer.

[0002]

2. Description of the Related Art As a water supply pipe, a hot water supply pipe, or a drain pipe, a composite pipe in which an inner peripheral surface of a metal pipe is lined with a resin layer for corrosion protection is often used.

This composite pipe is exposed to a severe heat cycle due to cold water, hot water, etc. depending on the conditions of use, and in this case, a remarkable difference in thermal expansion coefficient between the resin and the metal. Therefore, a large thermal stress is unavoidably generated at the interface between the resin layer and the metal tube, and there is a concern that interface peeling occurs.

In the above resin layer, the permeation of water particles due to diffusion is unavoidable due to the molecular structure, and under the above-mentioned interfacial peeling, peeling occurs with the progress of water permeation to the peeling interface. There is a risk that the release resin layer will be projected into the tube and eventually the tube will be blocked.

Therefore, the present applicant has previously proposed, in order to solve such a problem, to lining a resin layer (non-foaming) on the inner peripheral surface of the metal tube through a foaming resin layer (Actual Publication 55). -35147).

In this composite tube, the thermal expansion coefficient of the foamed resin layer is about the same as that of the non-foamed resin layer, which is considerably larger than that of the metal tube, but the Young's modulus of the foamed resin layer is non-foamed resin. It is considerably smaller than the Young's modulus of the layer.

However, the thermal stress is generated because the expansion or contraction due to the thermal expansion or the thermal contraction is restricted, and is naturally proportional to the Young's modulus of the material. And the thermal stress acting on the interface between the foamed resin layer and the non-foamed resin layer directly lining the metal tube can be sufficiently lower than the thermal stress acting on the interface,
Interfacial peeling can be well prevented (the thermal expansion coefficients of the foamed resin layer and the non-foamed resin layer are almost the same at the interface, and there is no problem of interfacial peeling).

Conventionally, as a method for producing a composite pipe in which a non-foamed resin layer is lined on the inner peripheral surface of a metal pipe with a foamed resin layer, a resin pipe having an outer diameter smaller than the inner diameter of the metal pipe is provided in the metal pipe. Then, a two-component foaming resin liquid (for example, urethane foaming liquid) is injected into the gap between the two, and a method of foaming and hardening this by heating, a foaming resin liquid is applied to the inner peripheral surface of the metal tube, Next, a method is known in which a resin tube is inserted and the foamable resin liquid coating layer is heated to foam and cure.

[0009]

However, in these methods, the two-component foamable resin liquid flows to the bottom side of the tube before foaming and curing, and it is difficult to form a foamed resin layer having a uniform thickness. is there.

Therefore, the present inventors have attempted to insert a two-layer pipe in which a non-foamed resin pipe is covered with a foamed layer to a uniform thickness by extrusion or the like into a metal pipe via an adhesive. . However, in a composite pipe obtained by this method, when subjected to a heat cycle test by alternate passage of cold water and hot water, delamination of the interface between the metal pipe and the foamed resin layer occurs relatively easily, and the composite pipe is disassembled. When observing the peeling point,
The foamed resin layer was cracked from the outer surface to the inside.

From this observation result, it can be seen from the observation result that the cracks are generated while the double-layer pipe is inserted into the metal pipe or before the double-layer pipe is inserted into the outer surface of the foamed resin layer. It is presumed that cracks were developed under the stress. Therefore, when the hardness of the outer surface of the foamed resin layer was increased (R60 to R120 in Rockwell hardness), the above interface peeling could be effectively reduced.

The object of the present invention is to provide a composite pipe in which a non-foamed resin layer is lined on the inner peripheral surface of a metal pipe with a foamed resin layer on the inner peripheral surface of the metal pipe in a stable interfacial adhesion state and with a uniform foamed resin It is an object of the present invention to provide a method for manufacturing a composite pipe that can be manufactured with a layer thickness.

[0013]

A method for manufacturing a composite pipe according to the present invention comprises inserting a two-layer pipe, in which a foamed resin layer is provided on a non-foamed resin layer, into a metal pipe and using an adhesive to bond the interface between the two pipes. In the method of manufacturing a composite pipe by bonding, the hardness of the outer surface of the foamed resin layer is set to Rockwell hardness R60 to R120.

[0014]

Since the hardness of the outer surface of the foamed resin layer of the outer layer of the two-layer pipe is increased, it is possible to prevent the outer surface of the foamed resin layer from being scratched until the two-layer pipe is inserted into the metal pipe. It is possible to avoid the occurrence of cracks due to the expansion of scratches under thermal stress, and it is possible to manufacture a composite pipe in which the interface state between the foamed resin layer and the metal pipe is stable.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A shows a two-layer pipe 1 used in the present invention, which has a foamed resin layer 12 on a non-foamed resin pipe 11,
The outer surface of the foamed resin layer has a Rockwell hardness of R60 to R
It is set to 120 (temperature 23 ° C.). In FIG. 1A, 13 indicates an adhesive.

The non-foamed resin pipe 11 includes, for example, vinyl chloride resin pipe, polyethylene pipe, polypropylene pipe,
Nylon tubes can be used. The foamed resin layer 12 includes
For example, a foamed vinyl chloride resin layer can be used, and in order to make its surface hardness high (R60 to R120), a thick skin layer is formed on the surface of the foamed resin layer, and a hard resin layer (for example, hard A method of applying a vinyl chloride resin layer) or making the entire foamed resin layer have high hardness can be used. When the entire foamed resin layer has high hardness, calcium carbonate, silica sand, metal powder, or the like may be mixed, or a hard resin (hard vinyl chloride resin) may be used as the resin itself.

An extrusion method is usually used to form the foamed resin layer 12, and the non-foamed resin tube 11 and the foamed resin layer 12 are used.
It is preferable to bond the interface with and with the adhesive 13. A liquid material is preferably used as the adhesive 13, and for example, a thermoplastic resin adhesive, a thermosetting resin adhesive, a rubber adhesive, or a composite adhesive thereof is used.

When a foamed hard vinyl chloride layer is used as the foamed resin layer 12 to make the entire foamed resin layer highly hard, a vinyl chloride pipe is used as the non-foamed resin pipe 11, and the vinyl chloride pipe and the foamed hard chloride are used. Adhesive 1 if coextruded with vinyl layer
3 can be omitted.

In order to manufacture a composite pipe by the method of the present invention, as shown in FIG.
The adhesive 2 is applied to the outer surface thereof, and then the metal pipe 3 is inserted, the diameter of the metal pipe 3 is reduced, and the interface between the two-layer pipe 1 and the metal pipe 3 is adhered by the adhesive 2 to form a composite pipe. obtain.

The metal tube 3 has a diameter of 50 mm to 1000 m.
m, preferably 50 mm to several hundred mm, length 1 m
Several tens of meters, preferably one to several meters are used,
As a material, an ordinary metal pipe, for example, a copper pipe, a stainless pipe, a steel pipe or the like is used.

A liquid material is preferably used for the adhesive 2 as in the case of the adhesive 13. For example, a thermoplastic resin adhesive, a thermosetting resin adhesive, a rubber adhesive, or these adhesives is used. A composite adhesive is used.

The composite pipe manufactured according to the present invention is used as a water supply pipe, a hot water supply pipe, a drain pipe, etc., and is exposed to a severe heat cycle depending on the use conditions. In this case, the coefficient of thermal expansion of the foamed resin layer 12 is considerably larger than that of the metal tube 3, and at the interface between the metal tube 3 and the foamed resin layer 12, the expansion or contraction of the foamed resin layer occurs. Although a large strain is generated by being constrained by a rigid metal tube, since the Young's modulus is small due to the cell structure, the thermal stress is relatively small. However, the outer surface of the foamed resin layer of the two-layer pipe comes into contact with the end of the metal pipe when the two-layer pipe is subjected to rolling impact, collision with another object, or during insertion of the two-layer pipe into the metal pipe. At this time, if there is a damage, even under the above-mentioned relatively small thermal stress, due to the low mechanical strength due to the cell structure, the damage spreads, grows into cracks, and becomes a metal pipe. The interface with the foamed resin layer is destroyed.

However, in the present invention, the hardness of the outer surface of the foamed resin layer of the outer layer of the two-layer pipe is R60 to R in Rockwell hardness.
Since the hardness is as high as 120, scratches on the outer surface of the foamed resin layer can be eliminated, and the interface state between the metal tube and the foamed resin layer can be stably maintained.

In the present invention, the reason why the hardness of the outer surface of the foamed resin layer is limited to Rockwell hardness R60 to R120 is as follows.
When R60 or less, it becomes difficult to prevent scratches on the outer surface of the foamed resin layer, and it is difficult to guarantee maintenance of a stable interface state between the metal tube and the foamed resin layer under thermal stress. When R120 or more, Young's modulus becomes too high, This is because the thermal stress generated in the foamed resin layer at the interface becomes large and the interface is easily peeled off.

According to the present invention, a two-layered pipe in which a foamed resin layer is provided on a non-foamed resin layer is inserted into a metal pipe, and the interface between the two pipes is bonded by an adhesive. It is possible to manufacture a composite pipe that can stably maintain the interface state between the metal pipe and the foamed resin layer even under thermal stress. This can be confirmed from the following test results.

Test Results An outer diameter of 23.3 mm obtained by extruding a foamed vinyl chloride resin layer having a Rockwell hardness of about R50 on a vinyl chloride resin tube.
Two double-layer tubes a were manufactured. Further, a single two-layer tube a was passed through a heating die to form a thick skin layer on the surface of the foamed vinyl chloride resin layer, and a two-layer tube b having a surface hardness of about R80 was manufactured.

The two-layer pipes a and b are hit with a hammer under the same conditions, and then the two-layer pipe a is coated with an epoxy adhesive and inserted into a steel pipe having an outer diameter of 34 mm and a wall thickness of 3.2 mm.
The diameter of this steel pipe is reduced to produce a composite pipe A, and the two-layer pipe b is applied with an epoxy adhesive and then inserted into a steel pipe having an outer diameter of 34 mm and a wall thickness of 3.2 mm. A composite pipe B was manufactured.

For each of the composite pipes A and B, 30
Hot water flow at 85 ℃ for 30 minutes, cold water flow at 20 ℃ for 30 minutes 1
When the heat cycle as a cycle was performed 5000 times and disassembled, and the damage state of the foamed vinyl chloride resin layer was examined, cracks were observed in the foamed vinyl chloride resin layer in the composite pipe A. No abnormality was observed in the foamed vinyl chloride resin layer of A.

[0029]

The method for producing a composite pipe of the present invention has the above-described structure, and the two-layer pipe in which the foamed resin layer is provided on the non-foamed resin pipe is inserted and adhered in the metal pipe. Since the outer surface of the foamed resin layer has a high hardness (R60 or more), it is possible to prevent damage to the outer surface of the foamed resin layer during transport or insertion of a two-layer pipe, and relatively low heat that is unavoidable under such damage. It is possible to satisfactorily eliminate the occurrence of cracks in the foam layer due to the expansion of scratches under stress. Further, since the hardness of the foamed resin layer is suppressed to R120 or less and the Young's modulus is reduced, the thermal stress acting on the foamed resin layer at the interface between the metal tube and the foamed resin layer can be sufficiently reduced. Therefore, even under the heat cycle, the fixed state of the resin pipe to the inner surface of the metal pipe can be stably maintained.

Of course, the thickness of the two-layer pipe can be made uniform, and the resin lining having a uniform thickness can be easily applied.

[Brief description of drawings]

1 (a) is a sectional view showing a double-layer pipe used in the present invention, and FIG. 1 (b) is a sectional view showing a composite pipe manufactured by the present invention.

[Explanation of symbols]

 1 Two-layer pipe 11 Non-foamed resin layer 12 Foamed resin layer 13 Adhesive 2 Adhesive 3 Metal pipe

Claims (1)

[Claims] 1. A method for producing a composite pipe by inserting a two-layer pipe in which a foamed resin layer is provided on a non-foamed resin layer into a metal pipe, and bonding the interfaces of both pipes with an adhesive to produce a composite pipe. A method for producing a composite pipe, wherein the outer surface hardness of the layer is Rockwell hardness R60 to R120.