JPH0585343B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to fusion joining (hereinafter abbreviated as welding) of plastic pipes suitably used in the semiconductor industry, food industry, pharmaceutical industry, biotech industry, chemical industry, etc. It's about how to do it, and for more information,
This invention relates to a method for welding plastic pipes in which no molten bead protrudes from the inner surface of the pipe welding part and the inner surface is finished smooth.

[Prior art]

Conventionally, plastic pipes made of polyethylene, polybutene, polytetrafluoroethylene (hereinafter referred to as PTFE), polyvinylidene fluoride (hereinafter referred to as PVDF), etc. are difficult to join with adhesives, so they are welded using a heating heater or the like. An example of this welding method is a method in which the end surfaces of plastic tubes to be welded are simultaneously melted using a heating heater, the heating heater is then removed, and the molten end surfaces of the tubes are butted against each other to join.

However, in the above joining method, the molten resin protrudes from the inner surface of the welded portion of the pipe, resulting in a large molten bead. Since the molten bead protrudes from the inner surface of the tube, it impairs the flow of fluid within the tube, and bacteria and other germs may grow in the protruding portion.
This has caused problems such as the accumulation of contaminants and a reduction in the purity of the fluid.

Various methods have been proposed to solve these problems, but the main one is
-272130 and Japanese Patent Application Laid-Open No. 1-110127.

[Problem to be solved by the invention]

However, in the method disclosed in Japanese Patent Application Laid-open No. 61-272130, after joining the plastic tubes,
This method removes the molten bead protruding from the inner circumferential surface of the pipe weld. It is said that the molten bead has a large effect on the bonding strength, and removing it poses a risk of reducing the bonding strength. Also, JP-A-1
In the method disclosed in Japanese Patent No. 110127, the inner surface of the welded portion of the plastic tube is indeed smooth, but the welding takes time and there is a problem in terms of work efficiency.

The present invention was made in view of the problems of the prior art as described above, and its purpose is to be able to weld in a short time, to make the inner surface of the welded part smooth without generating molten beads, Another object of the present invention is to provide a method for joining plastic tubes that forms a joint having no voids or cracks.

[Means to solve the problem]

As a result of extensive research based on the above-mentioned problems of the prior art, the present inventors have discovered that when plastic tubes are welded together, a pressing body is placed on the inner surface of the welded part, and the pressing body is composed of divided pieces. If you keep it,
After welding is completed, no molten bead is generated on the inner surface of the tube.
It has been discovered that the pressing body can be easily taken out of the plastic tube piece by piece and that the welding work can be carried out in a short time, leading to the present invention.

That is, the configuration of the present invention as a means for solving the above problems is described in the first embodiment corresponding to the embodiment.
To explain based on the drawings and FIG. 2, a pair of weldable plastic tubes 1 and 2 are attached to the outer periphery of one end of a cylindrical pressing body 3 consisting of a plurality of divided pieces 3a, 3b, and 3c.
One tube 1 is fitted, and the other tube 2 is fitted to the outer periphery of the other end of the pressing body 3 with an axial gap 4 between the two tubes 1 and 2. After heating and melting the opposing tube end surfaces 5 and 6 with a heating heater 7,
Both pipe ends 5 and 6 are butted and joined, and after completion of joining, the divided pieces 3a, 3b, 3 are inserted from inside both pipes 1 and 2.
This method is characterized by a method of joining plastic tubes that consists of taking out the c.

[Effect]

Since the present invention has the above-mentioned configuration, when welding the tube end surfaces 5 and 6 of the plastic tubes 1 and 2, the cylindrical pressing body 3 is arranged on the inner surface of the welded part, so that when welding, The resulting molten bead is prevented from protruding onto the inner surface of the tube, and a smooth inner circumferential surface of the tube can be obtained. Moreover, after the welding of both plastic tubes 1 and 2 is completed, the pressing body 3 is separated into divided pieces 3a, 3b, 3.
C, it can be easily pulled out from inside the pipe by fixing a string 8 or the like to each divided piece in advance. Incidentally, the pressing body 3
If it is an undivided, integrally molded product, it will be tightly fixed within the pipe, making it extremely difficult to remove it from the pipe after welding is complete.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show a first embodiment of the present invention, and FIG. 1 shows a state in which the end face of a plastic tube is simultaneously heated and melted by a heater,
FIG. 2 is a perspective view of the cylindrical pressing body.

In the figure, 1 and 2 are olefin resins such as polyethylene, polypropylene, polybutene, etc.
It is a plastic tube made of fluororesin such as PTFE or PVDF. The plastic pipe in the present invention is not limited to a straight pipe, but also includes a bent pipe, a joint pipe, an end pipe such as a valve, etc.

Reference numeral 3 denotes a cylindrical or cylindrical pressing body having a circular outer peripheral surface made of metal into which the plastic tubes 1 and 2 are fitted from both sides. The material of the pressing body 3 is not limited to metal, but any usable material having heat resistance may be used. The pressing member 3 is arranged on the inner surface of the welded portion of the plastic tubes 1 and 2, and prevents a molten bead produced during welding from protruding onto the inner surface of the tube. Although the pressing body 3 is composed of three sector-shaped pieces 3a, 3b, and 3c along its circumferential direction, the structure of the pressing body 3 is not limited to this. Further, the length of the pressing body 3 in the axial direction is not particularly limited, but in consideration of work efficiency, it is better to set it to a short dimension.

After completing the welding of plastic tubes 1 and 2, press body 3
In order to take out the tube from inside the pipe, separate the divided piece 3 in advance.
It is sufficient to attach strings 8, wires, etc. to a, 3b, and 3c and pull them. 1 divided piece e.g. 3
When part a is taken out, the remaining divided pieces 3b and 3c become loose and can be taken out easily. A heater 7 heats and melts the end surfaces 5 and 6 of the plastic tube. The heater 7 is connected to the tube end surface 5,
Any device may be used as long as it can uniformly heat and melt 6.

3 and 4 are a longitudinal sectional view and a perspective view of a fixing pin and a pressing body in FIG. 3, respectively, showing another embodiment of the present invention. In this embodiment, a fixing pin 9 is further inserted inside the pressing body 3 shown in FIG. The fixing pin 9 serves to prevent the pressing body 3 from deforming, and may be tapered in the axial direction to facilitate removal after welding is completed.

FIG. 5 is a cross-sectional view showing another embodiment of the combination of the fixing pin and the pressing body. The fixing pin 10 is
Four protrusions each having a rectangular cross section are provided on the outer peripheral side surface of the cylindrical main body 11 in parallel to its axis. Among the protrusions, protrusions 1 provided opposite to each other in the diametrical direction
2 and 13 are set in length so as to be in contact with the inner peripheral surface of the plastic tube to be inserted. Also, protrusion 1
Protrusions 14 and 15, which are similarly provided opposite to each other at positions 90 degrees shifted from 2 and 13, are provided lower than the protrusions 12 and 13, and semi-cylindrical divided pieces 16 and 17 forming a pressing body. A groove 18 provided on the inner peripheral side of the
19, and is slidably fitted into the hole. Split piece 1
The inner diameters of 6 and 17 are set larger than the diameter of the cylindrical main body 11, and spaces 22 and 23 are provided between them. The axial side surfaces of both ends of the divided pieces 16 and 17 are in contact with the protrusions 12 and 13, respectively, and when the outer periphery is combined with the tips of the protrusions 12 and 13,
They are configured to form the same circle. Furthermore, notches 20 and 21 are provided at the corners of the side surfaces of both ends of the divided pieces 16 and 17.

By configuring the fixing pin and the pressing body as described above, the fixing pin 10 can be easily pulled out from inside the plastic tube, and after the fixing pin 10 is removed, the divided pieces 16 and 17 are attached to the inner peripheral surface of the plastic tube. Since the split pieces 16 and 17 can be easily pulled out of the pipe, the efficiency of joining the plastic pipes can be further improved.

Below, an example of the method of joining PVDF pipes based on FIGS. 1 and 2 is shown.

First, a PVDF pipe 1 with a diameter of 50 mm is fitted into one end of the stainless steel pressing body 3, which is made of a three-part piece with a length of 40 mm, and then the other PVDF pipe 2 of the same diameter is inserted from the other end of the pressing body 3. It was inserted leaving a gap of 12 mm with the end face 5 of the tube 1. A plate heater 7 having a half-circular arc-shaped recess heated to 300±10°C is attached to the gap, and the end faces 5 and 6 of the PVDF tube are simultaneously heated and melted for 10 to 15 seconds, and then, Immediately after the heater 7 was removed, the PVDF tubes 1 and 2 were pressed against each other and their end surfaces 5 and 6 were butted together to join them. After cooling while holding this state for 30 to 60 seconds, the strings 8 attached to the divided pieces of the pressing body 3 are pulled, and the divided pieces 3a, 3b, and 3c are joined.
It was taken out of the PVDF tube.

The inner peripheral surface of the welded part of the obtained PVDF jointed pipe was a smooth surface with no protruding beads, and the pressure strength and tensile strength of the PVDF jointed pipe were completely satisfactory in use. .

Similarly, polyethylene pipes with a diameter of 50 mm were welded using a heater heated to 240±10°C. The resulting polyethylene jointed pipe had the same finish as above and had no problems in terms of strength.

〔Effect of the invention〕

As explained above, in the method for joining plastic tubes of the present invention, the following effects can be obtained.

1. A smooth inner surface is obtained because no molten bead protrudes from the inner surface of the welded part of the plastic tube. Therefore, the flow of the fluid in the pipe becomes smooth, and problems such as the generation of germs such as bacteria, the accumulation of contaminants, and a decrease in the purity of pure water do not occur.

2 Welding work is completed in a short time, improving work efficiency.

3. It is possible to obtain a welded tube that can be suitably used for ultrapure water piping lines in the semiconductor industry and piping lines in the aforementioned industries.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional view of the main part showing the state in which the end face of a plastic tube is heated and melted in the method of the present invention, Fig. 2 is a perspective view of the cylindrical pressing body in Fig. 1, and Fig. FIG. 4 is an exploded perspective view of the fixing pin and pressing body in FIG. 3, and FIG. 5 is a cross-sectional view showing another combination of the fixing pin and pressing body. It is a diagram. In the figure, 1, 2...Plastic tube, 3...Press body, 3a, 3b, 3c...Divided piece, 4...Gap,
5, 6...tube end surface, 7...heater, 8...string,
9, 10...Fixing pin, 11...Inner columnar body, 1
2, 13, 14, 15... Projection, 16, 17... Divided piece, 18, 19... Groove, 20, 21... Notch, 2
2, 23...Space.

Claims (1)

[Scope of Claims] 1 One pipe 1 of a pair of weldable plastic pipes 1 and 2 is fitted to the outer periphery of one end of a cylindrical pressing body 3 consisting of a plurality of divided pieces 3a, 3b, and 3c, and the other A tube 2 is attached to the outer periphery of the other end of the pressing body 3.
The tubes 1 and 2 are fitted with an axial gap 4 between them, and the opposing end surfaces 5 and 6 of both tubes 1 and 2 are heated by a heater 7.
A method for joining plastic tubes, which comprises heating and melting the plastic tubes, then joining the two tube ends 5, 6 against each other, and taking out the divided pieces 3a, 3b, 3c from inside the tubes 1, 2 after the joining is completed. 2. A removal string or wire 8 is attached to each of the divided pieces 3a, 3b, and 3c. The method of joining plastic tubes according to claim 1. 3. Claim 1 in which the pressing body 3 comprises a plurality of divided pieces 3a, 3b, 3c divided along the circumferential direction thereof.
The method for joining plastic tubes described in . 4. The method of joining plastic tubes according to claim 1, wherein the pressing body 3 comprises a cylindrical body and a fixing pin 9 fitted into the body. 5 The fixing pin 10 has protrusions 12, 13, 14 that protrude in the radial direction and engage with the cylindrical body 11.
5. The method of joining plastic tubes according to claim 4, further comprising: 15.