JPH048535A - Joining of plastic pipes - Google Patents

Abstract

PURPOSE:To ensure easy extraction of a printed product in the form of each divided pieces from a plastic pipe after completion of welding the pressed product, and a short-time welding and the smoothness of an inner surface without the generation of weld beads on the internal surface of the welded part by arranging the pressed product on the internal surface of the welded part and constituting the pressed product with the divided pieces. CONSTITUTION:One of a pair of weldable plastic pipes 1, 2 is allowed to be engaged with the periphery of the one end of a cylindrical pressed product 3 consisting of divided pieces 3a, 3b, 3c, while the other pipe 2 is allowed to be engaged with the periphery of the other end of the pressed product 3 with a clearance 4 between the both pipes in an axial direction. After the opposite tubular end surface 5, 6 of the both pipes 1, 2 are thermally fused using a heater 7, the both pipe ends 5, 6 are butted with each other. If the joining process is completed, the divided pieces 3a, 3b, 3c are extracted from the interior of the both pipes 1, 2. As the cylindrical pressed product 3 is arranged on the internal surface of the welded part, protrusion of weld beads generated during welding to the internal surface of the pipe is prevented. Thus the finished internal surface is smooth. In addition, the divided pieces 3a, 3b, 3c can be pulled out of the interior of the pipe by attaching a string to the divided pieces previously.

Description

[Detailed Description of the Invention] C. Industrial Field of Application] The present invention relates to the fusion joining (hereinafter abbreviated as welding) of plastic pipes suitably used in the semiconductor industry, food industry, pharmaceutical industry, biotech industry, chemical industry, etc. ), and more specifically, the present invention relates to a method for welding plastic pipes in which no molten bead protrudes from the inner surface of the pipe welded portion and the inner surface is 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 t1 heating heater or the like. To give an example of this welding method, the end surfaces of the plastic pipes to be welded are simultaneously melted with a heater,
There is a method in which the heater is then removed and the molten end surfaces of the tubes are butted against each other and joined.

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 pipe, it may impede the flow of fluid within the pipe, causing bacteria and other germs to grow in the protruding part, contaminants to accumulate, or impairing the purity of the fluid. This caused problems such as lowering the performance.

Various methods have been proposed to solve these problems, but the main method is disclosed in Japanese Patent Application Laid-Open No. 61-27213.
This method is disclosed in Japanese Patent No. 0 and Japanese Patent Application Laid-open No. 1-110127.

[Problem to be solved by the invention]

However, the method disclosed in Japanese Unexamined Patent Publication No. 61-272130 is a method in which after joining plastic pipes, the molten bead protruding from the inner peripheral surface of the welded part of the pipes is removed. 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. Furthermore, in the method disclosed in Japanese Patent Application Laid-Open No. 1110127, although the inner surface of the welded portion of the plastic tube is indeed smooth, there is a problem in terms of work efficiency because the welding requires opening at times.

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 pipes that forms a joint having no voids or cracks.

[Means to solve the problem]

As a result of intensive research based on the problems of the above-mentioned conventional technology, the authors of this project have found that when welding plastic pipes together,
If the pressing body is arranged on the inner surface of the welding part and the pressing body is made up of divided pieces, melt beads will not be generated on the inner surface of the pipe, and after welding is completed, the pressing body can be separated into plastic parts for each divided piece. The inventors have discovered that it can be easily taken out from inside the pipe and that the welding work can be performed 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 will be explained based on FIGS. 1 and 2 corresponding to the embodiment.
c) One of the pair of weldable plastic pipes (1) and (2) is attached to the outer periphery of one end of the cylindrical pressing body (3).
), and the other tube (2) is placed on the outer periphery of the other end of the pressing body (3) so that there is an axial gap (4) between the one tube (1) and the other tube (2).
are provided and fitted, and the opposing end surfaces of both tubes (1) and (2) (
5) (6) is heated and melted with a heating heater (7), and then the two tube ends (5) and (6) are butted and joined, and after the joining is completed, the divided piece (3a) is inserted from inside both tubes (1) and (2). )(3b)
(3c) A method for joining plastic pipes is characterized by taking out the plastic pipes.

[For production]

Since the present invention has the above-described configuration, when welding the tube end surfaces 5 and 6 of the plastic tubes 1 and 2, the cylindrical pressing body 3 is placed on the inner surface of the welded part.
The molten bead generated during welding 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 the plastic tubes 1 and 2 is completed, the pressing body 3 is separated into the divided pieces 3a and 3.
Since it is composed of B3C, 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, if the pressing body 3 is an undivided integrally molded product, it will be tightly fixed in the pipe, making it extremely difficult to remove it from the pipe after welding is completed.

〔Example〕

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

FIG. 1 and FIG. 2 show a first embodiment of the present invention.
The figure shows a state in which the end face of the plastic tube is simultaneously heated and melted by a heating heater, and 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, and PTFE.

It is a plastic tube made of fluororesin such as 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, and the like.

Reference numeral 3 denotes a cylindrical or cylindrical pressing body having a circular outer circumferential surface made of metal into which the plastic tubes 1.2 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 body 3 is arranged on the inner surface of the welded portion of the plastic tubes 1 and 2, and prevents a molten bead generated 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 welding of the plastic pipe 1.2 is completed, in order to take out the pressing body 3 from inside the pipe, use the divided pieces 3a, 3b, 3c.
All you have to do is attach a string 8, wire, etc. to it and pull it. When one divided piece, for example 3a, is taken out, the remaining divided piece 3
b and 3c are loosened and can be easily removed. 7 is a heater that heats and melts the tube end surface 5.6 of the plastic tube. The heater 7 may be any device that can uniformly heat and melt the tube end surface 56.

3 and 4 are a longitudinal cross-sectional view and a perspective view of a fixing pin and a pressing body in FIG. 3, respectively, showing other aspects 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 has a cylindrical body 11
Four protrusions each having a rectangular cross section are provided on the outer circumferential side surface thereof in parallel to its axis. Among the protrusions, the protrusions 12 and 13 provided diametrically opposite each other are set in length so as to be in contact with the inner circumferential surface of the plastic tube to be inserted. or,
A protrusion 14315, which is similarly provided opposite the protrusions 12 and 13 at a position moved by 90 degrees, is lower than the protrusion 12.13, and is a semi-cylindrical divided piece 16.15 forming a pressing body.
It is slidably and loosely fitted into grooves 18 and 19 provided on the inner peripheral side of 17. The inner diameter of the divided pieces 16.17 is set larger than the diameter of the cylindrical main body 11, and a space 22.23 is provided between them. The axial side surfaces of both ends of the divided pieces 16.17 are in contact with the protrusions 12.13, and the outer periphery thereof is configured to form the same circle when combined with the tips of the protrusions 12 and 13. has been done. Furthermore, notches 2021 are provided at the corners of the side surfaces of both ends of the divided pieces 16.17.
is provided.

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 split piece 16.1
Since the split pieces 7 are separated from the inner circumferential surface of the plastic tube, the divided pieces 16 and 17 can also be easily pulled out of the tube, thereby further improving the efficiency of the plastic tube joining operation.

Below, an example of an actual method of joining PVDF pipes based on FIGS. 1 and 2 will be shown.

First, a PVDF tube 1 with a diameter of 53 mm is inserted into one end of the stainless steel pressing body 3, which is a three-part piece with a length of 40+ nm, and then the other PVDF tube 2 with the same diameter is inserted into the other end of the pressing body 3. The tube was inserted into the PVDF tube 1 leaving a gap of 12 mm between the end surface 5 and the end surface 5 of the PVDF tube 1. A plate-shaped heater 7 having a half-circular concave portion heated to 300±10° C. is attached to the gap, and the end surfaces 5 and 6 of the Pv leaf tube are simultaneously heated and melted for 10 to 15 seconds, and then Immediately after removing the heater 7, both PVDF tubes 1.2 are pressed against each other and the tube end faces 5.
6 were butted and joined. After this state was maintained for 30 to 60 seconds and allowed to cool, the strings 8 attached to the divided pieces of the pressing body 3 were pulled, and the divided pieces 3a3b and 3c were each taken out of the joined PVDF tube.

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

Similarly, for a polyethylene pipe with a diameter of 5Qmm,
Welding was performed using a heater heated to 240±10°C. The obtained polyethylene jointed pipe had the same finish as above and had no problems in terms of strength. [Effects of the Invention] As explained above, the following effects can be obtained in the method for joining plastic pipes of the present invention. .

1. Since no molten beads protrude from the inner surface of the welded part of the plastic tube, a smooth inner surface can be obtained. Therefore, the fluid in the pipe flows smoothly, and problems such as the generation of bacteria and other germs, the accumulation of contaminants, and a decrease in the purity of pure water do not occur.

2. Welding work can be 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 Description of the Drawings] Figure 1 is a longitudinal 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, and Figure 2 is a perspective view of the cylindrical pressing body in Figure 1. 3 is a vertical sectional view showing another aspect corresponding to FIG. 1, FIG. 4 is an exploded perspective view of the fixing pin and pressing body in FIG. 3, and FIG. 5 is an exploded perspective view of the fixing pin and pressing body, etc. It is a cross-sectional view showing a combination aspect. In the figure, 1 and 2...Plastic tube, 3...Press body, 3a, 3b, 3C...Divided piece, 4...Gap, 5.6...Pipe end surface, 7
... Heater 8 ... String, 10 ...
Fixing pin, 13.14, 15... protrusion, 19... groove, 23... space. 11...Inner columnar body, 16.17...Divided piece, 20.21...Notch part,

Claims (1)

[Claims] 1. A pair of weldable plastic pipes (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 attached to the outer periphery of the other end of the pressing body (3) with an axial gap (4) between the one tube (1) and the other tube (2). After fitting and heating and melting the opposing tube end surfaces (5) and (6) of both tubes (1) and (2) with a heating heater (7), both tube ends (5) and (6) are heated and melted.
) and join them, and after joining is completed, both pipes (1) (2
) A method for joining plastic pipes, characterized in that the divided pieces (3a), (3b), and (3c) are taken out from inside. 2. A string or wire (8) for removal is attached to each of the divided pieces (3a), (3b), and (3c). The method for joining plastic pipes according to claim 1. 3. Claim 1 in which the pressing body (3) comprises a plurality of divided pieces (3a), (3b), and (3c) divided along the circumferential direction thereof.
The method for joining plastic pipes described in . 4. The method for 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), and (14) that protrude in the radial direction and engage with the cylindrical body (11).
) (15). The method for joining plastic pipes according to claim 4.