JPH06226854A - Welding of plastic pipes - Google Patents

Abstract

PURPOSE:To provide a welding method preventing a molten bead from protruding from the inner surface of a welded part and suitable for the welding of plastic pipes mainly composed of a thermoplastic resin having heat resistance. CONSTITUTION:In a method for welding plastic pipes 2, 3 by heating and melting the pipe end surfaces 2a, 3a of plastic pipes 2, 3 arranged on both sides of a heating member 1 using the heating member 1 so as to be able to advance and retreat on the axial line and immediately abutting both pipe end surfaces 2a, 3a to bond them, cores 4, 5 are fitted to the end portions 2b, 3b of the both plastic pipes and the pipe end surfaces 2a, 3a are heated and melted in a state not being in contact with the heating member 1. Thereafter, the heating member 1 is separated from both plastic pipes 2, 3 and both pipe end surfaces 2a, 3a are immediately abutted each other and, after the completion of welding and bonding, cores 4, 5 are taken out of the integrated plastic pipe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for fusing plastic pipes, which is preferably used in the semiconductor industry, food industry, pharmaceutical industry, biotech industry, chemical industry, etc. TECHNICAL FIELD The present invention relates to a method for fusing a plastic pipe suitable for fusing a plastic pipe made of a thermoplastic resin having properties.

[0002]

2. Description of the Related Art Conventionally, plastic pipes made of polyethylene, polybutene, polytetrafluoroethylene (hereinafter PTFE), polyvinylidene fluoride (hereinafter PVDF), polyphenylene sulfide (hereinafter PPS), etc. have been difficult to melt because they are difficult to bond with an adhesive. The joining method by wearing is generally performed. In the fusion bonding method, a method in which the end surface of the plastic tube is brought into contact with a heating body to be heated and melted by heat conduction, and then both end surfaces of the tubes are butted and joined to each other is mainly used.

In order to improve the releasability of the plastic tube after heating and melting from the heating body, the surface of the heating body is usually coated with PTFE or the like, but a plastic made of a heat resistant resin such as PPS or PEEK. In the case of a pipe, if the heating and melting are repeated several times, the mold releasability deteriorates, and there arises a problem that a part of the end face of the plastic pipe is taken by the heating body.
As a result, problems such as insufficient fusion of both plastic pipes and increased useless work such as cleaning of the surface of the heating element and re-surface coating treatment with PTFE occur.

In order to solve these problems, recently, there is no suitable surface treatment agent to replace PTFE, so that the end surface of the plastic tube to be fused is heated and melted by heat radiation in a non-contact state with the heating body. It has been adopted, and an example thereof is disclosed in Japanese Patent Laid-Open No. 4-229231.

[0005]

However, in the method of fusing a plastic pipe disclosed in the above publication, the molten bead 13 generated by the molten resin protruding to the inner surface of the pipe of the fused portion is projected (see FIG. 5). ), The flow of the fluid in the pipe is deteriorated by the molten bead, or problems such as deterioration of the fluid purity occur due to generation of various bacteria such as bacteria and deposition of contaminants on the protruding bead portion.

The present invention has been made in view of the problems of the prior art as described above, and an object thereof is to efficiently perform a fusion work and to prevent the molten bead from protruding to the inner surface of the pipe of the fusion zone. It is an object of the present invention to provide a method for fusing a plastic pipe which makes the inner surface smooth.

[0007]

The structure of the present invention will be described with reference to FIGS. 1 to 3 corresponding to the embodiment thereof. The heating member 1 is arranged on both sides so as to be movable back and forth with the same axis. After the pipe end faces 2a, 3a of the plastic pipes 2, 3 thus melted are heated and melted by the heating body 1, the both pipe end faces 2 are immediately
plastic pipe 2 for joining a and 3a by butting
3, the cores 4 and 5 are fitted to the ends 2b and 3b of the two plastic pipes 2 and 3, and the pipe end faces 2a and 3a are heated and melted in a non-contact state with the heating body 1. After that, the heating body 1 is separated from both the plastic pipes 2 and 3, the both pipe end surfaces 2a and 3a are immediately butted, and the cores 4 and 5 are taken out from the inside of the integrated plastic pipe 10 after completion of fusion bonding. It is characterized by that. Other inventions are defined in claims 2 and 3 of the claims.
As described in.

The plastic pipe used in the present invention is made of an olefin resin such as polyethylene, polypropylene or polybutene, a fluororesin such as PTFE or PVDF, or a material such as PPS or PEEK resin which cannot be strongly bonded by an adhesive. However, the shape is not limited to a straight pipe, and includes joints such as cheese and elbow, a tubular portion at the valve end, and the like.

The material of the core attached to the end of the plastic tube is not limited to metal, but may be heat resistant plastic (eg, PTFE). Also, its shape is
A cylindrical shape or a cylindrical shape is preferable, and further, when the fusion-bonding is completed, the work efficiency is further improved by dividing the tube into two or three in order to facilitate taking out.

[0010]

Since the present invention has the above-mentioned structure, since the pipe end faces 2a, 3a of the plastic pipes 2 and 3 are heated and melted by heat radiation in a non-contact state with the heating body 1, the heating body 1 The pipe end faces 2a, 3a are not attached to the pipe end, and the useless work described above is eliminated. Further, when the pipe end faces 2a, 3a are heated and melted and then abutted and fused with each other, since the cores 4 and 5 are fitted to the pipe end portions 2b, 3b, the molten bead 12 generated at the time of fusion is formed on the inner face of the pipe. It is prevented from protruding.

[0011]

Embodiments of the present invention will be described below with reference to the drawings, but it goes without saying that the present invention is not limited to the embodiments shown below.

FIG. 1 is a vertical cross-sectional view of a main part showing a state in which the end faces of a pair of plastic pipes are heated and melted in a non-contact state with a heating body. In the figure, reference numeral 1 is a heater 1.
It is a disk-shaped heating element with a built-in therein. 2 and 3 are
It is a plastic pipe made of PPS (hereinafter referred to as PPS pipe) which is fixed (not shown) to the device so that both axes can be moved back and forth in the same manner. The tube end surfaces 2a, 3a of the PPS tubes 2, 3 are arranged in a non-contact state with the heating body 1, that is, with the gaps 8, 9 provided.

The size of the gaps 8 and 9 in the axial direction depends on the melting point of the plastic tube to be fused, the surface temperature of the heating element 1 and the melting time, but is in the range of 0.1 to 2.0 mm. Good to set. More preferably 0.5-
It is better to set it to 1.5 mm. If the gaps 8 and 9 are smaller than 0.1 mm, the tube end faces 2a and 3a are melted and become blistered, and there is a risk of contact with the heating element 1. Also,
If it is larger than 2.0 mm, the thermal efficiency due to heat radiation is deteriorated and the melting time of the tube end faces 2a, 3a becomes long. There are various methods for setting the gap, but it is convenient to use a spacer having a constant thickness.

Numerals 4 and 5 are columnar cores made of PTFE mounted on the ends 2b and 3b of the PPS tubes 2 and 3, respectively. The side surfaces of the cores 4 and 5 facing the heating body 1 are made of PPS.
It is preferable that the tubes 2 and 3 are mounted so as to be flush with the tube end surfaces 2a and 3a, or to project to the heating body 1 side at a very high level. Since the cores 4 and 5 are fitted at the time of fusion-bonding the PPS pipes 2 and 3, the beads 12 generated at the time of fusion-bonding are prevented from protruding to the inner surface of the pipes (see FIG. 2).

Cores 4 and 5 are made up of three pieces, as shown in FIG. 3 (represented by 4). In order to facilitate removal from the fusion-bonded tube, it is convenient to provide each axial contact surface of the three-piece segment with a taper (see FIG. 4). Reference numerals 6 and 7 are PTFE cord-shaped members attached to the cores 4 and 5. The strings 6 and 7 are made of PTF
The material is not limited to E, but may be made of hemp, cotton, other synthetic resin, wire or the like.

After the fusion bonding of the PPS tubes 2 and 3 is completed, when the cores 4 and 5 are taken out from the integrated PPS tube 10, the divided pieces can be easily taken out by pulling the cord-like bodies 6 and 7. It suffices if the cord-like bodies 6 and 7 are attached to at least one divided piece, but it is better to attach them to each divided piece in consideration of work efficiency. Further, when the divided pieces of the cores 3 and 4 are taken out at a time, in order to allow the divided pieces to come out with a time lag, at least the lengthwise dimension of the divided pieces is different in the length of the cord. If set, it will be easy to take out each divided piece.

An experimental example of the fusion bonding method based on the above description will be shown below. First, the PTFE cores 4 and 5 consisting of three divided pieces with a length of 20 mm and a diameter of 27 mm are attached to the pipe end portions 2b and 3b of the PPS pipes 2 and 3 having an outer diameter of 32 mm and a wall thickness of 2.5 mm.
a and 3a were fitted to each other so that their end faces were flush with each other.

Next, between the PPS tubes 2 and 3 which are arranged with the same axis line and spaced apart (at a position where the heating body 1 is arranged later), the thickness of the heating body 1 in the axial direction of the pipe is 2 mm larger. A spacer (not shown) having a thickness was placed, and the PPS tubes 2 and 3 were moved in the axial direction to bring the end faces 2a and 3a into close contact with the spacer. After fixing the PPS tubes 2, 3 in place, the spacers were removed.

Next, between the PPS pipes 2 and 3 fixed to the disk-shaped heating body 1 which is positioned rearward of the center of the PPS pipes 2 and 3 and is movable in the circumferential direction, and which is heated to 480 ° C. Was moved to the center, and fixed at positions where the gaps 8 and 9 between the tube end faces 2a and 3a and the heating body 1 were maintained at 1 mm, respectively. (The state of FIG. 1 is exaggerated for clarity.) 5
After holding this state for 0 seconds to sufficiently heat and melt both pipe end surfaces 2a and 3a, the heating body 1 is moved in the circumferential direction to set P
The PPS pipes 2 and 3 were moved away from the PS pipes 2 and 3 and immediately moved in the axial direction so that both pipe end faces 2a and 3a were butt-welded together.

The method for butting the PPS tubes 2 and 3 may be, for example, a method in which the PPS tube 2 is fixed and the PPS tube 3 is moved, and the method is not particularly limited. After allowing to cool for 120 seconds while maintaining the fusion-bonded state, the integrated joining pipe 10 is removed from the fixing device, and the PTFE cords 6 and 7 attached to the divided pieces of the cores 4 and 5 are pulled to separate the divided pieces. Each was taken out from the joint pipe 10. The obtained PPS
The fusion-bonded portion 11 of the joining pipe 10 was uniformly fused over the entire circumference, and the molten bead did not project on the inner surface of the fusion-bonded portion of the pipe, and the surface was smooth.

Both ends of the joint pipe 10 were sealed, and a hydraulic fracture test was carried out at 23 ° C. As a result, the joint was broken at a water pressure of 125 kgf / cm ² , but there was no abnormality at the fused portion. Further, both ends of the joint pipe 10 obtained in the same manner were clamped and fixed, and a tensile test was carried out at a rate of 10 mm / min at 23 ° C. in the axial direction of the pipe.
Although it broke under a load of 1405 kgf, there was no abnormality in the fused portion. As can be seen from the above both test results, both the pressure resistance and the tensile strength of the obtained PPS joint pipe 10 were completely satisfactory in use.

[0022]

As described above, according to the method of fusing a plastic pipe of the present invention, the following effects can be obtained. 1. Since the end surface of the plastic pipe is heated and melted by heat radiation in a non-contact state with respect to the heating body, the plastic does not adhere to the heating body after being melted and is not removed.
There is no need for a mold release treatment of coating the surface of the heating element with PTFE or the like. 2. The fused portion of the plastic tube can be fused uniformly over the entire circumference, and since the molten bead does not project on the inner surface of the fused portion of the tube, a smooth inner surface can be obtained. Therefore, the flow of the fluid in the pipe becomes smooth, the generation of bacteria such as bacteria and the accumulation of contaminants are prevented, and the fluid (for example, pure water) is prevented.
The problems such as a decrease in the purity of the are solved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a main part showing a state in which a pipe end surface of a plastic pipe is simultaneously heated and melted in a non-contact state by a heating body.

FIG. 2 is a vertical cross-sectional view of a main part showing the positions of a plastic pipe and a core after completion of fusion bonding.

FIG. 3 is a perspective view showing a state in which a core is fitted in a plastic pipe.

FIG. 4 is a perspective view showing an example of a core.

FIG. 5 is a vertical cross-sectional view of a fusion-bonded portion of a plastic pipe obtained by a conventional method after fusion-bonding is completed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating body, 1a ... Heater, 2, 3 ... Plastic tube, 2a, 3a ... Tube end surface, 2b, 3b ... Tube end part, 4, 5
... core, 6, 7 ... string-like body, 8, 9 ... gap, 10 ... joining pipe, 11 ... fusion-bonded part, 12, 13 ... molten bead.

Claims (3)

[Claims] 1. A plastic in which end faces of a plastic pipe arranged on both sides of a heating body so as to be able to move back and forth so as to have the same axis line are heated and melted by the heating body, and then both pipe end faces are immediately butted and joined. In the method of fusing the pipes, a core is fitted to the end portions of the both plastic pipes, and the end faces of the pipes are heated and melted in a non-contact state with the heating body, and then the heating bodies are separated from the plastic pipes. A method for fusing a plastic pipe, characterized in that both pipe end faces are abutted apart immediately and the core is taken out from the inside of the integrated plastic pipe after fusion bonding is completed. 2. The method for fusing a plastic pipe according to claim 1, wherein the gap between the heating element and the end face of the plastic pipe is 0.1 to 2.0 mm. 3. The method for fusing a plastic pipe according to claim 1, wherein the core is a divided piece.