JPH0348854B2 - - Google Patents

Abstract

PURPOSE:To obtain a piping system made of a plastic material, which does not necessitate a metal connector, is superior in corrosion resistance and reliable in adherence, by making socket welding by making use of specific supporting metal fittings of the inside diameter consisting of a main body made of a shape memory alloy, a heating unit and a stringlike matter and a supporting metal fittings of the outside diameter. CONSTITUTION:Fusion welding of an inner and outer pipes is done by applying an electric current to the following heating unit while a supporting metal fittings of the outside diameter is being tightened according to requirement after a heating unit 42, which is due to Joule heat, connected with an outer electric power source by a lead wire 44 is inserted into the inside of about a cylindrical main body 41 made of a shape memory alloy, supporting metal fittings 40 of the inside diameter constituted by providing a stringlike matter 43 whose one end is fixed to a main body 41 and the other end is taken outside is inserted into the inner pipe 6, a heating unit 3 which is due to the Joule heat is wound around the outside of the inner pipe 6, which is inserted into the outer pipe 7 further and a supporting metal fittings 30 of the outside diameter having a tightening device is mounted on the outside of the outer pipe. In addition to the above, the main body 41 of the supporting metal fittings of the inside diameter is made into a shape having a slit 41A on one position of the side of a cylinder, and having a basic shape so that a cross-sectional shape is shrinked in a whirl state at a temperature more than a predetermined one and lower than a softening point of a material.

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to a method for connecting thermoplastic pipes such as polyethylene, and more specifically, a method for connecting thermoplastic pipes by socket welding using a heating element generated by Joule heat. The present invention relates to a method for connecting plastic pipes that enables reliable adhesion by compressing the welded portion with an inner diameter support fitting and an outer diameter support fitting.

(b) Prior art Among thermoplastic plastics, polyethylene and other materials are chemically extremely stable, but there are no good adhesives, and the adhesive strength can only be a fraction of the base material strength. is the current situation.

Therefore, for connecting plastic pipes such as polyethylene which require strength, mechanical connection methods using connecting fittings or connection methods by heat fusion are commonly used.

Plastic pipes such as polyethylene are often supplied in long lengths wound around drums rather than in fixed lengths, and pipes with flanges are rarely supplied. Therefore, in the mechanical connection method, the connection fitting and the pipe body are fixed by the frictional force between them, by pushing the pipe ends apart,
It depends on which method, but it lacks certainty and
It is said to be unsuitable for connecting pipes with a diameter of 2B or larger.

Furthermore, plastic piping essentially shows its effectiveness in corrosive atmospheres, but when connecting fittings are exposed to corrosive atmospheres in mechanical connection methods, expensive corrosion-resistant materials must be used. The drawback is that you have to do it.

Furthermore, as a method for connecting plastic pipes such as polyethylene by heat fusion, a method is adopted in which a heating tool such as a trowel is used to heat and melt the adhesive surface, and then the pipes are brought into close contact and welded. This method is
Although it is used for both butt welding and socket welding, it requires delicate adjustments such as the melting state of the bonding surface and the pressing pressure, and when performing construction under strict control in the factory, it is difficult to Connection can be made, but if it is outdoors, such as at a piping construction site,
It is extremely difficult to obtain reliable adhesion under changing external conditions such as rain and humidity.

In addition to the above-mentioned methods for connecting plastic pipes such as polyethylene by heat fusion, there has been proposed a method that utilizes the heat generated when electricity is applied to metal wires or metal foils.

Hereinafter, conventionally proposed methods will be explained based on the drawings. In FIG. 1, the ends of plastic pipes 1A and 1B are almost butted together,
A spacer 2 is inserted inside, spanning both 1A and 1B. A heating wire 3 is wrapped around the outer surface of the pipes 1A, 1B, a plastic sheet 4 of the same quality as the pipe is attached to the outside, and a rubber tape 5 is further wrapped around the outer periphery. By energizing the heating wire 3, the pipe 1
A and 1B are butt welded.

However, using this method, piping sites, etc.
When making a connection in a place with a poor working environment, the wrapping tension of the rubber tape 5 may be insufficient, and the air present between the heating wire 3 and the pipes 1A, 1B will not be able to escape, resulting in a connection that lacks airtightness. It is often seen being done.

Furthermore, since there is no way to later remove the spacer 2 inserted into the inner surface of the pipes 1A, 1B, when used in a corrosive atmosphere, an expensive corrosive material must be used for the spacer 2, and the maximum A disadvantage is that the spacer 2 left behind becomes a bottleneck in the pipe, increasing flow resistance and causing blockage in slurry pipes such as sewage pipes.

Conventionally, in order to eliminate the above-mentioned drawbacks, a method of connecting plastic pipes as shown in FIG. 2 has been proposed. This method is a socket welding method in which a heating wire is wound between the inner tube and the outer tube and the heat is used to weld them together, but the welding part is compressed to ensure a secure bond. be.
That is, in FIG. 2, inside the inner tube 6,
The inner diameter support fitting 20 is inserted, and the support plate 21 is supported by coming into close contact with the inner wall of the inner tube 6.

A heating wire 3 is wound around the outside of the inner tube 6,
An outer tube 7 having an inner diameter approximately equal to the outer diameter of the inner tube 6 after the heating wire 3 is wound thereon is attached. An outer diameter support fitting 30 is attached to the outside of the outer tube 7.
The inner wall of the outer tube 7 is in close contact with the outer wall of the outer tube 7.

One end of the inner diameter support fitting 20 is connected to the flexible tube 8, and inside the flexible tube are a pressure tube 9 and a drain tube 10.
is stored. The flexible tube 8 is taken out from the outer tube, and the pressurizing tube 9 and the drain tube 10 are connected to a hydraulic pump 11.

FIG. 3 is a front view including a cross section showing the structure of the inner diameter support fitting, and FIG. 4 is a left side view thereof. In FIGS. 3 and 4, the main body 22 is composed of a cylinder portion 22A, a cam storage portion 22B, and a guide portion 22C.
A camshaft 23 is housed inside the main body in which 2Ds are provided (in this embodiment, four camshafts are provided). The camshaft 23 consists of a piston 23A, a cam 23B, and a guide shaft 23C.

The piston 23A is connected to the cylinder portion 22 of the main body 22.
In A, the guide shaft 23C is connected to the guide portion 22C of the main body 22.
are slidably fitted to each other. Main body 2
A spring 24 is inserted into the guide portion 22C of No. 2, and the camshaft 23 is inserted into the main body 22 after the spring insertion and is fixed to the main body 22 by a lid 25.

A lid 25 is attached to the cylinder portion 22A of the main body 22. The lid 25 has a pressurized water passage 25A at the bottom and a drain passage 25B at the top.
They are connected to a pressure pipe 9 and a drain pipe 10, respectively. Further, a flexible tube 8 is fixed to the lid 25.

The support plate 21 includes a plate 21A, a support shaft 21B, a spring bearing 21C, and a cam contact portion 21D. Plate 21A
consists of four hollow cylinders each having an outer diameter approximately equal to the inner diameter of the inner tube 6 and having the shape of approximately a quarter of the circumference. The width of the plate is processed and formed to be approximately equal to the insertion depth of the inner tube 6 and the outer tube 7. A support shaft 21B is fixed approximately at the center of each of the four plates 21A, and the other end of the support shaft 21B is
It serves as a spring receiver 21C and a cam contact portion 21D.
In the support plate 21, the spring receiver 21C is slidably fitted into a hole bored in the boss 22 of the main body 22, and the cam contact portion is attached to the cam 23B of the camshaft 23 by the spring 26 and the spring retainer 27. 23D is fixed to the main body 22 in a pressed manner.

FIG. 5 is a front view showing the structure of the outer diameter support fitting 30, and FIG. 6 is a side sectional view thereof. In FIGS. 5 and 6, the outer diameter support fitting 30 is composed of two half fittings 31 each having a shape obtained by dividing a cylindrical shape into two whose inner diameter is approximately equal to the outer diameter of the outer tube.
It is tightened by bolts 32 and nuts 33 so as to be in close contact with the outer wall of the outer tube. Half metal fitting 31
The width of the support plate 21 is processed to be approximately equal to the width of the plate 21A of the support plate 21.

Next, a method for connecting plastic pipes using the inner diameter support fitting 20, outer diameter support fitting 30, etc. having the structure described above will be described. First, when the valve (not shown) of the drain pipe 10 is opened, the cylinder portion 22A of the inner diameter support fitting 20 is not pressurized, and the camshaft 23 is moved to the third position by the force of the spring 24. The support plate 21 is pushed toward the right in the figure, and the support plate 21 is drawn toward the center of the inner diameter support fitting 20 by the action of the cam 23B and the spring 26. As a result, the outer diameter of the support plate 21 is considerably smaller than the inner diameter of the inner tube 6.

In this state, insert the inner diameter support fitting 20 into the inner pipe 6, close the valve of the drain pipe 10, and operate the water pressure pump 11.
The water is sent to the cylinder portion 22A of the main body 22 through the pressurized water passage 25A, and the camshaft 23 moves to the left in FIG. pushed outward from When the outer diameter of the support plate 21 becomes approximately equal to the inner diameter of the inner tube 6, the operation of the water pressure pump 11 is stopped, the heating wire 3 is wound around the outside of the inner tube 6, and the outer tube 7 is placed over the outside. After attaching the diameter support fitting 30, electricity is passed through the heating wire to heat it.

During heating, the water pressure pump 11 is operated as appropriate to push out the support plate 21, or the outer diameter support fitting 30 is tightened with the nut 33 to compress the heated portion. After heating for a predetermined time, the valve of the drain pipe 10 is opened to take out the inner diameter support fitting 20, and the outer diameter support fitting 30 is removed to complete the connection between the inner pipe 6 and the outer pipe 7.

In the conventional plastic connection method described above, the plastic is heated between the outer tube and the inner tube, so it is not affected by wind, rain, etc., and since the heating is done by Joule heat, there is no heat input. Since the pressure is constant and the heated part is compressed, air, gas, etc. can be expelled from the welded part, making it possible to achieve extremely reliable bonding.

However, the inner diameter support used in this method has a very complicated structure, so 1 1/2
The drawback was that it was difficult to apply to piping of B or lower.

(c) Purpose of the Invention The present invention solves the drawbacks of the conventional plastic connection method described above, and provides a plastic pipe connection that can be applied to pipes of 1 1/2 B or less, and that can be performed reliably and easily even outdoors. The purpose is to provide a method.

(d) Structure and operation of the invention The present invention provides that if metal is made to memorize a predetermined basic shape at a certain temperature, no matter how it is deformed at other temperatures, it will return to its original shape when the initial temperature is reached. Taking note of the fact that a shape memory alloy has been developed, the above objective is achieved by using this shape memory alloy for the inner diameter support fitting.

Embodiments of the present invention will be described below based on the drawings. FIG. 7 illustrates a method of connecting plastic pipes according to the present invention. In this method as well, the heating wire 3 is wound around the outside of the inner tube 6, and it is further inserted into the outer tube 7, and an outer diameter support fitting is attached to the outside of the outer tube 7, and an inner diameter support fitting is attached to the inside of the inner tube. There is no difference from the conventional example described above in that the heating wire is attached and the heating wire is heated and welded, but the structure of the inner diameter support fitting 40 is completely different from the conventional example. That is, in the figure, the inner diameter support fitting 40 includes a substantially cylindrical main body 41, a heating element 42 using Joule heat that is attached to the inside of the main body 41 and connected to an external power source through a conductive wire 44, and one end of which is connected to the main body 41. installed in
The other end consists of a string-like body 43 taken out to the outside.

FIG. 8 is a front sectional view of the main body 41, and FIG. 9 is a right side view thereof. In both figures, the main body 41 has a cylindrical shape with a cutout 41A at one location on the side surface, and is manufactured from a shape memory alloy.
This main body 41 is heated to a predetermined temperature θ which is higher than room temperature and lower than the softening point of the plastic material of the pipe.
℃ or higher, it has a basic spiral shape as shown by the two-dot chain line in FIG. 9, and is used after being transformed into the shape shown by the solid line at room temperature. At this time, the outer diameter dimension d should be approximately the same as the inner diameter dimension of the inner tube, or a dimension including a slight interference margin. When this main body 41 is heated and the temperature reaches θ°C or higher, it takes on its basic spiral shape, and its outer diameter becomes considerably smaller than the inner diameter of the inner tube, allowing it to move freely inside the inner tube. You can pass.

The outer diameter support fitting 30 of the plastic pipe connection method shown in this example is completely the same as the conventional one explained in FIGS. There is no difference from the conventional example shown in FIG.

Figures 10A, 10B and 10C are diagrams showing the procedure for connecting two plastic pipes 1A, 1B with a socket joint 12 by this exemplified method.
That is, first, the inner diameter supporting metal fitting 40 is attached to the pipe 1A, the heating wire 3 is wound around the outside of the pipe 1A, and then the heating wire 3 is inserted into the socket joint 12, and then the outer diameter supporting metal fitting 30 is attached to the outside thereof (see FIG. 2). At this time, the main body 41 is at room temperature and has a shape as shown by the solid line in FIG. The heating wire 3 is connected to a power source and heated for a predetermined period of time, and if necessary, the outer diameter support fitting is tightened to compress the welded portion (see figure 2). After heating, turn off the power to the heating wire 3, turn on the power to the heating element 42, and the main body 4 of the inner diameter support fitting
1 reaches a predetermined temperature (.theta..degree. C.) and assumes the basic spiral shape, so that the inner diameter support fitting can be easily taken out. Then, by the same procedure, pipe 1B
and the socket joint 12 (see figure C).

(e) Effects of the invention To summarize what has been stated above, the present invention has the following extremely excellent effects.

Since this connection method relies on melt bonding of plastic, it does not require metal joints and can provide a piping system with excellent corrosion resistance.

Even pipes made of polyethylene or the like that do not have good adhesives can be reliably bonded.

Since no spacers or the like are left in the piping, no bottlenecks are formed or clogging occurs.

Adhesion is extremely reliable as it compresses the welded area and expels air, gas, etc.

Since the heating is based on Joule heat, the amount of heat input is constant and the bonding is reliable.

Since welding is performed between the inner and outer tubes,
It is not significantly affected by rain, wind, outside temperature, etc.

Since the structure of the inner diameter support fitting is extremely simple, it can be sufficiently applied to small piping of 1 1/2 or less.

Since it is extremely easy to take out the inner diameter support fitting, it is also easy to connect extremely long pipes.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a conventional method of connecting plastic pipes, Fig. 2 is a diagram showing another conventional method of connecting plastic pipes, and Fig. 3 is the structure of the inner diameter support fitting. 4 is a left side view thereof, and FIG. 5 is a front view showing the structure of the outer diameter support fitting.
FIG. 6 is a side sectional view thereof, FIG. 7 is a diagram illustrating a method of connecting plastic pipes according to the present invention,
Figure 8 is a front sectional view showing the main body of the inner diameter support fitting, Figure 9 is a right side view thereof, and Figures 10 A to 10 C show the procedure for connecting plastic pipes with socket joints using this method. It is a diagram. 1A, 1B...Plastic pipe, 2...Spacer, 3...Heating wire, 4...Plastic sheet, 5...Rubber tape, 6...Inner tube, 7...Outer tube, 8...Flexible tube, 9 ... Pressure pipe, 10 ... Drain pipe, 11 ... Water pressure pump, 12 ... Socket joint, 20 ... Inner diameter support fitting, 21 ... Support plate, 2
2...Main body, 23...Camshaft, 24...Spring, 2
5...Lid, 26...Spring, 27...Spring retainer, 3
0... Outer diameter support metal fitting, 31... Half metal fitting, 32...
... Bolt, 33 ... Nut, 40 ... Inner diameter support fitting, 41 ... Main body, 42 ... Heating element, 43 ... String-shaped body, 44 ... Conductor.

Claims (1)

[Claims] 1. An inner diameter support fitting having the elements (a) to (c) described below is inserted inside the inner tube and attached to the inner tube, and a heating element using Joule heat such as a metal wire is attached to the outside of the inner tube. is wound and inserted inside the outer tube, and an outer diameter support fitting having a tightening means is attached to the outside of the outer tube, and then an electric current is passed through the heating element to tighten the outer diameter support fitting as necessary to tighten the inner and outer tubes. How to connect plastic pipes by melt-bonding. (a) At room temperature, it has a shape obtained by cutting one part of the side surface of a cylinder along a plane that includes the cylinder axis, and at a predetermined temperature that is higher than room temperature and lower than the softening point of the material of the plastic pipe ( θ℃)
In the above, (b) the body is made of a shape memory alloy and has a basic shape in which the cross-sectional shape cut on a plane perpendicular to the cylinder axis contracts in a spiral shape; (c) A string-like body that is attached to the main body and whose end is taken out to the outside.