JPH06213387A - Polyolefin pipe joint method and metal in-core for use in it - Google Patents

Abstract

PURPOSE:To establish a joining method for polyolefin pipe and provide an in-core of metal suitable for application of this method wherein the use of in-core (inner cylinder) is set as the condition due to the electrofusion pipe fitting, with which mounting of the pipe fitting to a pipe to be joined can be done easily, which is after joining free from undulation of the pipe inner surface, sagging of the molten substance of a fusion attachment layer into the pipe, etc., and which can present easily a flat and smooth inner surface of pipe joined. CONSTITUTION:An electrofusion pipe fitting 1 is equipped with a fusion attachment layer 2 made of thermoplastic polymers and including a heat emitting means and a base layer 3 which is made of a shape memory recovering resin having a shape holding property at the melting point of the thermoplastic polymer and which is formed in a single piece on the outside of the fusion attachment layer 2. The inside diameter of this electrofusion pipe fitting 1 is enlarged to over the outside diameter of a pipe to be joined 4 made of polyolefin, and an in-core 5 is installed in such a position as enclosing the gap in the joint part from the inside of the pipe joined 4. The in-core 5 for use with the joining method for polyolefin pipe 4 has a locating projection 6 in a flange form.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining a polyolefin pipe by an electrofusion pipe joint and a metal incore used for the method.

[0002]

2. Description of the Related Art As a method for joining polyolefin pipes typified by polyethylene, there is known a method using an electrofusion pipe joint provided with a fusion layer including a heating means. In this method, the pipes to be joined are inserted from both sides of the joint, the end portions of the pipes are melted together with the fusion layer of the joint by heat generating means, and these are fused together.

However, in general, when an attempt is made to join a thin-walled polyolefin pipe by an electrofusion pipe fitting, the inner surface of the pipe is corrugated or swelled, and the melted layer melts droop into the pipe, resulting in a narrow flow path. There is a problem that foreign matter is clogged and the pipe is likely to be blocked, and various proposals have been conventionally made to solve this problem.

For example, there is a proposal to regulate the shape of the pipe to be welded during heating and softening by providing a deep groove for receiving the pipe to be joined in addition to the opening at the end of the electrofusion pipe joint (special feature). Kaihei 2-253091
issue).

However, in this method, the structure of the joint is complicated and the manufacturing process is complicated, and the man-hours for mounting the joint on the pipes to be joined cannot be ignored. Moreover, although this proposal aims at avoiding the squeezing of the flow path in the pipe, since the deep groove for receiving the welded pipe is provided at the end of the joint, the opening area of the joint itself is smaller than that of the pipe. In comparison, the area corresponding to the wall thickness between the groove and the opening is narrowed, and the thick portion serves as a step between the pipe inner surface and the joint inner surface.

Therefore, there is no doubt as to whether or not the above-mentioned proposal can satisfactorily achieve the ultimate purpose of avoiding the squeezing of the flow path and the blockage of the pipe, even though the deformation of the pipe during heating and softening can be avoided. Not.

As a method of preventing deformation of the pipes to be joined at the time of joining, a shape memory alloy member that stores a secondary shape that substantially matches the inner shape of the pipe is installed inside the pipe to heat and soften the pipe. There is a proposal that sometimes the secondary shape of this member is used to prevent the deformation of the pipe, and after the joining is completed, the shape of the member is restored to the primary shape and the member is removed from the pipe (Japanese Patent Laid-Open No. Sho 6-96). 59-176018
issue).

However, in order to restore the shape-memory alloy member to its original shape, it is necessary to heat the shape-memory alloy member to a temperature higher than the transformation temperature. Therefore, it is difficult to put it into practical use in consideration of the heat resistance of the plastic pipe. Further, in this method, after the joining of the pipes is completed, the shape memory alloy member must be pulled out with a string and taken out. Therefore, it is doubtful whether or not this can be taken out smoothly in a long pipe or the like having a bent portion.

An overview of these conventional techniques has advantages and disadvantages, and it is considered that a technique that completely overcomes the problems described above has not yet appeared.

[0010]

In view of the above-mentioned problems of the prior art, the present invention is a method for joining a polyolefin pipe using an electrofusion pipe joint, in which the joint can be easily attached to the pipes to be joined before joining. In addition, there is no waviness on the inner surface of the pipe after welding and no fusion layer melt drips into the pipe, and it is possible to easily obtain a smooth joined pipe inner surface. It is an object to provide a method and a metal incore used for the method.

[0011]

In order to achieve the above object, in the method for joining polyolefin pipes according to the present invention, a fusion layer made of a thermoplastic polymer and including a heat generating means, and a melting point of the thermoplastic polymer are provided. In the electrofusion pipe joint provided with a shape memory recoverable resin having shape retention property and integrally formed on the outside of the fusion layer, the inner diameter of the pipe joint is equal to or larger than the outer diameter of the pipe to be joined. It is characterized by including each step of expanding the diameter and arranging the metal incore at a position covering the gap of the joint from the inside of the pipe to be joined.

The metal incore used in the above method is characterized in that it has a collar-shaped positioning protrusion.

This metal incore is formed by winding a metal plate in a cylindrical shape to form a partially opened tubular body, and a collar-shaped body formed of a thermoplastic polymer that is more easily melted than the pipes to be joined is used. It is also possible to reduce the diameter of the shape body and fit it into the outer periphery of the shape body and fix it to form a positioning projection.

[0014]

[Action]

(Pipe Joint) Pipes to be joined in the method for joining polyolefin pipes according to the present invention are mainly made of polyolefin such as polyethylene, polypropylene and polybutene, but have a thermoplastic property and are fused with the fusion layer of the joint. The material is not particularly limited as long as it is possible.

The fusion layer of the electrofusion pipe joint used in the joining method of the present invention is preferably made of the same thermoplastic polymer as the pipes to be joined from the viewpoint of matching the melting points. However, different types of thermoplastic polymers can be used if they can be fused.

Examples of such a thermoplastic polymer include high density polyethylene (PE), medium density PE, low density PE, ultra high molecular weight PE, ethylene-propylene copolymer, ethylene-butene-1 copolymer, Polypropylene (PP), polybutene-1, polypentene-1, poly4
-Methylpentene-1, ethylene-propylene rubber (E
PR), ethylene-propylene-diene terpolymer (EPDM), ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, ethylene-vinyl chloride copolymer, etc. as the main component Olefin-based polymer; vinyl halide-based polymer such as polyvinyl chloride (PVC); aromatic vinyl-based polymer such as polystyrene; chlorinated products of these polymers;
Various block copolymers composed of an aromatic vinyl compound typified by styrene and a conjugated diene such as isoprene or butadiene, specifically, S-I type, S-I-S
Type, S-B-S type, S-I-S-I-S type block copolymers, hydrides of these, hydrocarbon-based thermoplastic elastomers such as mixtures thereof; polybutadiene, polyisoprene, styrene- Examples include unvulcanized rubber such as butadiene copolymer, chloroprene rubber, and butyl rubber.

These thermoplastic polymers, thermoplastic elastomers and unvulcanized rubbers can be used by mixing them with the above-mentioned olefinic polymers at an arbitrary ratio. Among them, fusion with a polyolefin pipe is possible. From the viewpoint of properties, an olefin polymer is preferable, and a polyolefin composed of only an olefin monomer is particularly preferable.

The heat generating means included in the fusion layer may be either one in which a heating wire is embedded in the fusion layer or one in which conductive particles such as carbon black are mixed in the fusion layer. Considering the convenience of expanding the diameter of the pipe joint to be described later, a heating means in which conductive particles are mixed in the fusion layer is preferable, but even in the case of a heating means of a type in which a heating wire is embedded in the fusion layer, The heating wire is arranged so as to reciprocate in the longitudinal direction of the joint, and any type that does not constrain the joint in the circumferential direction can be used.

The conductive particles to be mixed in the fusion layer include, for example, carbon black, graphite particles, metal particles (copper,
Powders of iron, nickel, etc.), mixtures thereof, and the like can be mentioned. Among them, Ketjen Black, which has excellent conductivity, is preferable.

The content of these conductive particles may be appropriately selected within a range where uniform heating of the heating element is generated by energization, but usually 5 to 35% by weight based on the thermoplastic resin,
Preferably, the content is 10 to 30% by weight.

In general, a pipe joint needs to secure an appropriate clearance between the pipe to be joined and the pipe to be joined from the viewpoint of easiness of inserting the pipe to be joined into the joint. It is usually slightly larger than the outer diameter of. However, in the joining method of the present invention, this clearance is ensured by making the inner diameter of the joint during molding practically equal to the outer diameter of the pipes to be joined and forcibly expanding the diameter before use.

In this case, if the inner diameter of the joint before expansion is too small, the effect of tightening the pipes to be joined utilizing the shape memory recoverability of the base layer, which will be described later, becomes excessive, resulting in a flat inner surface of the pipe and the inner core. The connection may be compromised.
It is possible to make the inner diameter of the joint before expansion larger than the outer diameter of the pipe to be joined as long as such a problem does not occur, but normally the inner diameter of the joint before expansion is the outer diameter of the pipe to be joined. It is better to increase it by about 0.5 mm, preferably about 0.3 mm.

As the diameter expanding method, there are two methods of expanding the diameter from the both ends of the joint to a certain size and leaving the center portion as the inner diameter at the time of molding, and a method of uniformly expanding the diameter of the entire joint. There are methods, but both are possible (see FIGS. 1 and 2). If the joint is heated to an appropriate temperature above room temperature during diameter expansion, diameter expansion processing becomes easier.

Further, since the diameter expansion amount is thereafter reduced, it is possible to take a sufficiently large amount so that the pipes to be joined can be easily inserted into the joint. However, practically, it is sufficient to provide a diameter difference of about 3 mm to 5 mm between the outer surface of the pipe to be joined and the inner surface of the joint after the diameter expansion.

The bonding method of the present invention utilizes the shape memory recoverability of the synthetic resin forming the base layer. The shape-memory recoverability here means that the base layer has its shape-memory recovery temperature due to the heat generated by the heat-generating means for fusing the fusion layer and the pipe to be joined, regardless of the diameter expansion performed before heating the joint. When it reaches, it means to recover the shape and size before the diameter expansion. The shape memory recovery temperature is set to a temperature equal to or higher than the melting point of the fusion layer.

Examples of such a synthetic resin having shape memory recovery include thermosetting resins such as polynorbornene resins, polyurethane resins, epoxy resins and polyester resins.

The thermosetting resin is a reaction injection molding (RIM) in which two or more kinds of low-viscosity raw materials that react with each other to form a polymer rapidly are mixed and then supplied into a mold and cured in the mold. It can be manufactured by a reaction molding method such as a method. For example, a reaction solution containing a norbornene-based monomer and an activator and a reaction solution containing a norbornene-based monomer and a metathesis catalyst are mixed and supplied into a mold to perform bulk ring-opening polymerization to obtain a polynorbornene-based resin molded product. . In addition, a reaction liquid containing a polyol and an isocyanate is added to the RIM.
A polyurethane resin molded product is obtained by curing in a mold by the method. Among them, the molding of the polynorbornene-based resin by the reaction molding method has a remarkably low injection pressure as compared with the injection molding of the usual thermoplastic resin, so that there is an advantage that a lightweight and inexpensive mold can be used.

Due to the shape memory recoverability of the base layer thus realized, the inner diameter of the joint is reduced to the dimension before the expansion when the fusion layer is melted, and as a result, the thermal expansion during fusion is prevented. Then, the inner surface of the fusion layer presses the outer surface of the pipes to be joined, so that a close contact therebetween is achieved. (Incore) As described above, in the method for joining a polyolefin pipe according to the present invention, the shape memory recoverability of the base layer is used to achieve close contact between the inner surface of the fusion layer and the outer surface of the pipe to be joined. On the other hand, if no shape control is applied to the joints of the pipes to be joined, the thermal expansion of the fusion layer and the pipes at the time of melting both go to the inside of the pipes, causing swelling of the inner surface of the pipes and waviness of irregularities. easy.

In addition to this, when the fusion layer is overheated, a phenomenon may occur in which the melt hangs down from the gap at the pipe joint. All of these are not preferable because they cause an increase in the flow path resistance of the pipe after joining and blockage of the pipe line due to catching of foreign matter.

In order to avoid such an unfavorable phenomenon appearing on the inner surface of the pipe, in the method of the present invention, a metal incore, that is, a tubular body is arranged at a position covering the gap between the inside of the pipe to be joined and the joint. . The metal incore is generally preferable because it has sufficient rigidity even if it is thin, and since it has good heat conduction, it can keep the temperature at the joint portion where the incore is applied uniformly and prevent fusion defects.
The resin-made incore is not preferable because it has a large wall thickness and forms a step with the inner surface of the pipe.

The metal incore is preferably one that does not generate rust or the like even when it comes into contact with the fluid in the pipe. Examples of the material for the in-core include stainless steel, aluminum, copper, brass, alloys such as carbon steel, tin plate, etc. Among them, stainless steel is, of course, rust-proof, and a metal plate to be described later is wound. It is particularly preferable because it is excellent in restoring force required in the case of incore to be prepared.

Further, when the surface of the metal incore which comes into contact with the corrosive fluid is coated with a thermoplastic resin such as polyolefin of the same material as the pipe or a hot-melt adhesive containing these as the main components, the anticorrosive effect is obtained. It is preferable because the effect of preventing leakage due to fusion with the pipe can be expected. There is an optimum range for the coating thickness, which is 5μ
m to 50 μm is preferable. This is because if it is too thick, the heat during fusion bonding of the pipes tends to cause unevenness, and if it is thin, the metal is likely to be exposed.

In order to facilitate the insertion of the in-core into the pipe, it is necessary to provide a clearance between the inner surface of the pipe and the outer surface of the in-core. The clearance is equivalent to the diameter of 0.3 mm or less, preferably 0.1 mm or less. It is desirable to stop. If this clearance is too large, or if the thickness of the incore is too thick, it may cause a step between the inner surface of the pipe and the inner surface of the incore, and must be avoided.

In that sense, it is preferable that the thickness of the incore is thin, but if it is too thin, it cannot withstand the bulging pressure of the inner surface of the pipe and the purpose of using the incore cannot be achieved.
In the case of a steel in-core used for a pipe with a diameter of about 60 mm, which is frequently used, a wall thickness of about 0.5 mm is required.

The length of the in-core in the pipe axis direction is 0.5
20 mm from the length of the fusion layer of the joint in the case of mm in-core
It is desirable that the length is within mm, preferably about 10 mm and short. If it is too short, the effect of suppressing bulging on the inner surface of the pipe will be diminished, and the purpose of inserting the incore cannot be achieved.
Also, if it is too long, the end of the incore remains as a step without conforming to the inner surface of the pipe. When this length is appropriate, the inner surface of the pipe near the tip of the incore slightly bulges out, and the incore smoothly digs into the inner surface of the pipe without any steps, and is firmly fixed at that position (see Fig. 3). ).

The effect that the inner surface of the in-core and the inner surface of the pipe are smoothly connected without any step and the in-core is fixed in this manner, in combination with the proper thickness and length of the in-core, is the shape of the base layer described above. It is brought about by the compression effect of the joined pipe due to the memory recovery property. If the joint was originally made loosely to the pipes to be joined without taking advantage of shape memory recoverability, such a compression effect could not be expected and therefore the incore and pipe as described above would not be expected. A smooth connection and immobilization of the inner surface cannot be achieved.

By the way, in order for the inner surface of the pipe and the inner surface of the incore to be connected in the ideal state as described above, the relative positional relationship between the fusion layer and the incore is important, and It must be inserted in the pipe so that the incores are symmetrically positioned with the joint part in between. However, in the case of an opaque pipe, it is very difficult to confirm whether the incore is inserted in the correct position.

In order to solve this point, it is convenient to provide a flange-shaped positioning protrusion on the circumference of the central portion of the incore, as shown in FIG. This is because if the incore is pushed into the pipe until the projection hits the end of the pipe to be joined, the pipe is automatically inserted in the correct position.

As described above, the metal incore is formed by winding a metal plate to form a tubular body, and a flange-shaped body formed of a thermoplastic polymer that is more easily melted than the pipes to be joined is used. It is also possible to reduce the diameter of the shape body and fit it into the outer periphery of the shape body and fix it to form a positioning protrusion (see FIG. 5).

That is, 20 m from the length of the fusion layer of the joint.
One side (A side) shorter than m, preferably about 10 mm,
A metal plate (for example, a stainless steel plate having a thickness of about 1 mm) having another side (B side) having substantially the same length as the inner circumference of the pipes to be joined is prepared. This metal plate is wound in the direction of side B to form a tubular body having an outer diameter of about 1.2 times the inner diameter of the pipes to be joined. On the other hand, a resin collar-shaped body having an inner diameter smaller than the inner diameter of the pipe to be joined and an outer diameter larger than the inner diameter of the pipe to be joined and smaller than the outer diameter of the pipe is produced. As a material for the collar body, a resin that is more easily melted than the pipes to be joined is used. The tubular body is wound and contracted so that the outer diameter is smaller than the inner diameter of the pipe to be joined, and the tubular body is passed through the collar body, and the collar body is arranged so as to be located in the axial central portion of the tubular body. Incore

Since the in-core thus constructed has an outer diameter smaller than the inner diameter of the pipes to be joined, it is extremely easy to insert it into the pipes to be joined, and therefore the workability is good.

Further, in the process in which the fusion layer of the joint is heated to the melting temperature, the collar body is melted and the cylindrical body is unconstrained,
Since the outer diameter is to be restored to the initially given outer diameter, the tubular body adheres to the inner surface of the pipe to be joined. Since the thickness of the tubular body is thin, no step is formed between the tubular body and the inner surface of the pipe, as in the case of the metal incore described above.

[0043]

【Example】

Example 1 (joint) The fusion bonding layer 2 was made of polyethylene (density 0.92,
MFI 5.0) compounded with 30% by weight of conductive carbon black, inner diameter 60 mmφ, outer diameter 64 m
It was formed by extrusion molding into mφ and cutting this into a length of 120 mm. A current-carrying electrode consisting of two braided wires was heat-fused at equal intervals in parallel to the outer longitudinal direction of the fusion layer 2 also serving as a heating element, and the portion where the braided wire protruded from the fusion layer 2 was used as a terminal. .

The base layer 3 has the fusion layer 2 as a core.
A thermosetting norbornene resin with a thickness of 5 mm is applied to the outer circumference of the resin.
IM molding was performed to prepare an electrofusion pipe joint 1 integrated with the fusion layer 2. The pipe joint 1 was heated to 80 ° C., a metal rod having an outer diameter of 65 mmφ was press-fitted inside the pipe joint, and then the pipe was pulled out. As a result, the inner diameter of the joint 1 was about 65 mm.
The diameter was expanded to mmφ. (Incore) A stainless steel pipe having an outer diameter of 53 mmφ and a thickness of 1 mm is cut into a length of 100 mm, and the incore 5 is cut.
PE was extruded into a rod shape having a diameter of about 1 mm on the center circumference thereof, and the PE was wound in a ring shape and the end portion was heat-melted and fixed to form a flange-shaped positioning projection 6. (Pipe to be joined) Outside diameter 60mmφ, Inside diameter 53mmφ
The cross-linked PE pipe having the outer layer coated with the low-density PE having the same quality as that of the heating element by welding was used as the pipe 4 to be joined. Prepare two pieces of this pipe 4 cut into a length of about 50 cm, fit each of them until they hit the central protrusion 6 from both ends of the in-core 5, and fit the center line to the outside to attach the joint 1. did. (Heat fusion) When an AC voltage of 60 V is applied from the terminal of the joint 1, the temperature of the fusion layer 2 is about 220 ° C. after about 70 seconds.
And the diameter reduction of the joint 1 was started. Where the voltage is 3
After the voltage was dropped to 0 V to maintain the fusion layer 2 at about 200 ° C. and this state was maintained for 5 minutes, the power supply was stopped. The diameter of the joint 1 was completely reduced, and the pipe 4 and the joint 1 were fusion-bonded. (Results) When the joint 1 including the pipe connecting portion was left to cool, the joint 1 was observed to contract and tighten the pipe 4 from the outside. Seal both ends of the connected pipe 4, 20
A water pressure of kgf / cm ² was applied and the mixture was allowed to stand for 24 hours. During that time, there were no abnormalities such as water leakage and migration of the incore 5.

After completion of the water pressure test, the joint 1 and the pipe 4
When the inside is cut open and the inside is observed, the incore 5 shows the pipe 4
There was no step in the pipe 4 because it was embedded in the inner surface of the pipe. Example 2 (Comparative Example) The joint 1 and the pipe 4 were prepared under the same conditions as in Example 1 except that the incore 5 was not used, and heating, fusion bonding and joining were performed. When an alternating voltage of 60 V was applied for about 6 minutes, it was observed visually from the end of the pipe 4 that irregularities were formed on the inner surface of the pipe 4. Example 3 (in-core) From a stainless steel plate having a thickness of 0.7 mm, a plate of about 16.5 cm × about 10 cm was cut out, and 16.5 c was cut.
The side on the m side was rolled and rounded to form a tubular body 5 having an outer diameter of about 60 mm with a gap of about 2 cm between the ends. On the other hand, PE (density 0.92, MF12.0) is extruded into a 3.5 mm square prism, cut into a length of about 15 cm, and both ends are fused to form a collar-shaped body 6 with an inner diameter of about 4.8 cm. did.

The tubular body 5 was reduced in diameter and passed through the collar body 6, and the collar body 6 was fastened to the center of the tubular body 5 to form an in-core. Using this incore, the pipes 4 were joined under the same conditions as in Example 1 above. (Results) After the joining was completed, when the joined portion was observed, the in-core was expanded to a diameter substantially the same as the inner diameter of the pipe 4, and the end overlapped portion of the tubular body 5 before heating the joint disappeared.

[0047]

According to the method for joining polyolefin pipes of the present invention, a sufficient clearance can be secured by expanding the inner diameter of the electrofusion pipe joint before use, which is high at the time of forming the pipe joint. It is possible to realize high workability in the work of inserting the pipe to be joined into the pipe joint without requiring accuracy of the inner diameter.

Further, since the in-core is inserted into the pipes to be welded to cover the molten portion of the pipes to be welded from the inside, swelling and irregularities on the inner surface of the pipe during heating and melting, and the melt dripping from the gap at the end of the pipe. It is possible to obtain a smooth inner surface without any jamming.

Moreover, the shape-memory recoverability of the base layer is used to reduce the diameter of the once expanded pipe joint in the molten state of the fusion layer, and the effect of this is to tighten the pipe to be joined from the outside. The inner surface and the outer surface of the pipe to be joined will not come into close contact with each other, creating a gap that may cause leakage,
Moreover, the incore bites smoothly into the inner surface of the pipe without any step and is firmly fixed.

As a result, even if the control of the temperature and time during heating is not made as strict as before, leakage at the pipe joint,
The increase in flow path resistance, the risk of blockage, etc. can be minimized, and consistently high bonding quality can be obtained.

Further, by using the metal incore provided with the flange-shaped projection according to the present invention, the incore can be easily positioned at the correct position when the incore is inserted into the pipes to be joined. The excellent effect of the joining method according to the present invention can be effectively exhibited.

Furthermore, the in-core made by winding the metal plate is easy to make, and it is completed simply by passing the rolled metal plate through the ring on site. Moreover, since it is easy to insert into the pipe, workability is good, and the result of joining the pipes is comparable to that of a normal metal incore.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing an electrofusion pipe joint in which a diameter is expanded from both ends to a certain size, and a central portion is left as an inner diameter when molding.

FIG. 2 is a partial cross-sectional view showing an electrofusion pipe joint whose diameter is uniformly expanded over the entire length.

FIG. 3 is a partial cross-sectional view showing the electrofusion pipe joint, the pipe to be joined, and the incore in a state where the incore is inserted into the pipe to be joined and joined by the method for joining polyolefin pipes according to the present invention.

FIG. 4 is a perspective view showing an incore provided with a flange-like protrusion according to the present invention.

FIG. 5 is a perspective view showing an incore formed by winding a metal plate according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrofusion pipe joint 2 ... Fusion layer including a heating element 3 ... Base layer 4 ... Pipe to be joined 5 ... In-core (cylindrical body) 6 ... Collar-shaped positioning protrusion (collar-shaped body)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Kadoma 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) In-house Tsuneo Aoi 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (3)

[Claims] 1. A method for melt-bonding a pipe made of polyolefin, comprising a fusion layer made of a thermoplastic polymer and including heat generating means, and a shape memory recovering resin having shape retention at the melting point of the thermoplastic polymer. An electrofusion pipe joint including a base layer integrally formed on the outside of the fusion layer is used, the inner diameter of the joint is expanded to be equal to or larger than the outer diameter of the pipe to be joined, and the gap between the inside of the pipe to be joined and the joint is formed. A method for joining polyolefin pipes, comprising the steps of disposing a metal incore at a position covering the core. 2. A metal incore for joining a polyolefin pipe, which has a collar-shaped positioning protrusion. 3. A cylindrical body in which a metal plate is rolled into a cylindrical shape and a part of which is opened, and a collar-shaped body formed of a thermoplastic polymer which is more easily melted than the pipes to be joined is compressed into the tubular body. A metal incore for joining polyolefin pipes, characterized in that it has a diameter and is fitted into and fixed to the outer periphery thereof to form a positioning protrusion.