JPH04370494A - Connection method for polyethylene pipe for supply water - Google Patents

Abstract

PURPOSE:To perfectly weld a polyethylene pipe, especially suitable for a pipeline for supply water to a polyethylene pipe coupling without fail. CONSTITUTION:A low density polyethylene pipe 2 for supply water is inserted in the inner surface of a high density polyethylene pipe coupling 1 for supply water. Further, a core tool 3 adhered on the inner surface of a pipe is engaged throughout the length of a weld part. Through energization of a heating wire 4 embedded in the weld surface of the pipe coupling, slight surplus welding is effected. Thermal expansion generated by heating is constrained between a high strength of the outer surface side and the core tool on the inner surface side and converted into reaction which strongly presses a contact surface. Thus, a dense and complete weld part is provided. Fine management of a work is eliminated. A piping work at a site is carried out without an individual difference and failure.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the joining of polyethylene pipes for water supply.

0002

2. Description of the Related Art Polyethylene pipes are lightweight, have high corrosion resistance, and have sufficient flexibility, so they have come to be widely used for water pipes and the like. Polyethylene pipes had problems with weather resistance, which is a characteristic of general synthetic resins, but this has almost been resolved by adding 2 to 3% carbon black, allowing them to be placed in the open before construction, during temporary piping, or on the roof of a house. It has been recognized that it can withstand direct sunlight in water heaters, etc., and its use is increasing. This polyethylene pipe for water supply has a density of 0.915~
The raw material is low-density polyethylene in the range of 0.940 g/cm3, especially linear low-density polyethylene (hereinafter "
It is displayed according to its common name, ``LLDPE''. ) is applied.

[0003]Next, conventional pipe fittings for general polyethylene pipes include those made of metal (gunmetal), as well as so-called electrofusion (hereinafter referred to as "electrofusion welding") type polyethylene pipe fittings made from polyethylene material. has also been proposed. This method attempts to weld the inner circumferential surface of the joint and the outer circumferential surface of the polyethylene pipe in contact with this surface by heat generation by energization of a heating wire after inserting the polyethylene pipe into the pipe joint. In this case, the polyethylene material softens and melts when the temperature rises, but it also undergoes thermal expansion during this time, so when the inner surface of the pipe joint is heated by the heating wire, thermal expansion begins from this area first, and the pipe joint, which is in a free state, begins to expand. tries to expand toward the outer peripheral surface. For this reason, when the contact surface between the inner circumferential surface of the pipe joint and the outer circumferential surface of the pipe is severely reduced compared to when it was fitted, a gap may be formed and strong welding may not be possible. Jitsukai 1986
As shown in Figure 2, the invention of No. 146091 is an improvement in which a glass base material layer 101 is covered on the outer peripheral surface of the pipe joint 1a to suppress this thermal expansion so that sufficient pressure can be maintained on the bonding surface. It is.

0004

[Problems to be Solved by the Invention] The above-mentioned prior art can be evaluated as effective in solving the problem when connecting a general polyethylene pipe and a polyethylene pipe joint. But in this case,
As an example of making a pipe joint, glass cloth is impregnated with epoxy resin, pre-progress made by semi-curing the impregnated epoxy resin is made into a cylindrical shape and inserted into an outer mold, and the inner mold with a coil wound thereon is set inside the outer mold. However, although the procedure for injection molding polyethylene between both molds is mentioned, it cannot be denied that such a rather complicated procedure has a non-negligible effect on productivity and cost. Furthermore, if we focus on the specific field of water supply pipes, when pipes are buried underground, they are subject to stress due to vibrations caused by earthquakes, ground vibrations caused by heavy vehicles passing by, subsidence, and other external forces. At times, the problem always concentrates on the pipe joint, so when the material is the same as the pipe, we are faced with a new problem: trouble tends to occur first from this joint. In order to solve this problem, it is most rational to make pipe fittings from polyethylene, which has a higher strength than polyethylene pipes for water supply, but it is best to make pipe joints from polyethylene, which has a strength different from that of polyethylene pipes. When welding is attempted, the deformation caused by thermal expansion concentrates on the polyethylene water pipe, which has a low density, and bulges on the inner surface of the pipe, making it impossible to maintain the correct cross-sectional area of the flow path. There are strong concerns that this will be a hindrance. In order to maintain proper electrofusion welding, it is necessary to control the various conditions during energization, but if the conditions change even slightly, the welding condition may suddenly be affected and the function as a pipe fitting may be lost, so please be careful when working. This is a major issue. For example, in order to examine the various conditions during energization and the results,
As shown in (a) and (b), the LLDPE pipe 2b is
There is a record of inserting it into the pipe joint 1b of the DPE and energizing it while changing the load time. In other words, as shown in figure (a), the potentiometer V,
Both ends of the electrical wiring, in which the battery B is connected in parallel and the ammeter A is connected in series, are connected to the heating wire 4b of the pipe joint. thermocouple T1
was fixed in contact with the outer peripheral surface of the pipe joint, thermocouple T2 was fixed in contact with the contact surface between the pipe joint and the pipe, and thermocouple T3 was fixed in contact with the inner peripheral surface of the polyethylene pipe, and connected to thermometer T, which was then energized. Table 1 shows the energization conditions, maximum temperature, and appearance characteristics.

[0005]

[Table 1] As can be seen from this table, the temperature near the contact surface is 170℃
When the tube rises above this level, a bulge 102 is generated on the inner surface of the tube as shown in FIG. Of course, if the temperature rise is too low, the electrofusion welding will be incomplete and water will leak from this part, or it will be easily pulled out by external force, causing more fatal problems.

According to another experiment, the lower limit of temperature increase is 140
There is also a record that the temperature is 0.degree. C., so the range in which complete electrofusion welding can be achieved is quite limited. However, it is almost impossible to strictly control such limitations in practice when constructing water pipes near the ends. As long as it is not possible to unify the outside temperature and the values specific to each material to the same conditions, even if ideal construction conditions are found, it will not necessarily lead to a perfect joint, and there will still be functional concerns.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, it is an object of the present invention to provide a method for joining pipe joints that ensures complete electrofusion welding even under relatively rough control conditions.

[0008]

[Means for Solving the Problems] The method of joining polyethylene pipes for water supply according to the present invention has a density of 0.915 to 0.940.
g/cm3 water supply polyethylene pipe with a density of 0.930
~0.965 g/cm3 and a polyethylene material with a density higher than that of the inserted pipe and 2 to 3% carbon black is inserted into a water supply polyethylene pipe fitting, and the pipe is inserted into the above welding range of the water supply polyethylene pipe. The above-mentioned problem was solved by inserting a core metal fitting that tightly adheres to the inner surface of the tube, applying electricity, and welding it slightly excessively.

[0009]

[Operation] The density and distribution components of the pipes and pipe joints described above are specific conditions for the polyethylene material forming the water pipes. That is, as mentioned before, polyethylene pipes for water supply are made of linear low density polyethylene (LLDPE),
Its density is in the range of 0.915 to 0.940 g/cm3, and its tensile strength is about 9.8 to 14.7 N/mm2, while its density is in the range of 0.930 to 0.940 g/cm3.
If a pipe joint is made of medium-density polyethylene (hereinafter referred to as "MDPE") with a density of 0.950 to 0.965 g/cm3 (hereinafter referred to as "HDPE"), its tensile strength will be at least 17.7N
/mm2 or more (MDPE), or at least 19.6N
/mm2 or more (HDPE), even if an external force is applied to the pipe and stress is concentrated on the pipe joint, it can sufficiently withstand this and maintain the normal function of the pipe. Secondly, the pipe joints contain 2-3% carbon black, which improves the weather resistance of all parts, including the outer surface that is exposed to direct sunlight. No problems that would cause deterioration occur. In addition, since the density of this pipe joint is greater than that of conventional polyethylene pipe, this high density provides a property that strongly resists the intrusion of chlorine contained in tap water. Therefore, troubles that cause quality deterioration from the inner circumferential surface do not occur, and weather resistance and chlorine water resistance are simultaneously achieved. Furthermore, in order to improve the chlorine water resistance, HDPE that does not contain carbon black is used only in the water contact portion of the joint. So-called two-color molding may also be considered.

[0010] By the way, when such water pipes and pipe fittings are electro-welded, the core metal fittings are closely fitted inside the tube, so if a slightly excessive electrical load is applied, the inner surface of the tube will expand thermally. It attempts to bulge in response to the force, but is blocked and converts into a reaction force that presses strongly on the contact surface. Of course, unlike the conventional technology, the material strength of the pipe joint is high, so it is not possible to bulge the free outer peripheral surface of the joint, and in the end, extremely strong pressing force acts on the molten resin from both sides while restraining it, resulting in compact welding. form a section.

[0011]

[Embodiment] Fig. 1 shows an embodiment of the present invention, in which a pipe fitting 1 made of HDPE or at least MDPE mixed with 2 to 3% carbon black is connected to a polyethylene pipe 2 for water use made of LLDPE.
is inserted, and the core metal fitting 3 that is in close contact with the inner surface of the tube is fitted over a range corresponding to the joint surface. The core fitting 3 is suitably made of a metal tube, such as a corrosion-resistant alloy steel tube. A heating wire 4 such as a nichrome wire buried in the inner circumferential surface of the pipe joint 1 is heated with electricity. The energization conditions are determined by experiment, but for example, the joint surface is 170°C.
It is desirable to raise the temperature to a temperature higher than 150°C. If the temperature is lower than 150°C, there is a risk of insufficient welding and water leakage or separation. Considering the control limits for on-site work, it is considered safer to set standards on the relatively high temperature side.

0012

[Effects of the Invention] As described above, the present invention provides a polyethylene pipe joint for joining polyethylene pipes for water supply that has sufficient resistance to stress concentration due to external force and weather resistance to meet the specific conditions of water supply use. It has properties that are ideal for water pipes, such as by combining chlorine water resistance and chlorine water resistance, and by maintaining the necessary surface pressure when electricity is applied and generating heat to obtain a tight welding surface. Furthermore, it is possible to prevent thermal deformation when electrofusion welding pipes and pipe joints that have different densities, and to replace thermal expansion with compaction of the joint surfaces, resulting in a dense and complete welded part. In addition, this work does not require delicate work management and there is little difference in skill between individuals, which is very convenient for on-site piping.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a prior art.

[Fig. 3] (A) and (B) show the overall wiring diagram and wiring diagram of the main parts for the experiment.

FIG. 4 is a sectional view showing another conventional technique.

[Explanation of symbols]

1 Polyethylene pipe fittings for water supply 2 Polyethylene pipe for water supply 3 Core metal fittings 4 Heating wire

Claims (1)

[Claims] Claim 1: A method for joining polyethylene pipes in which a polyethylene pipe is inserted into the inner surface of a polyethylene pipe joint, and electric heating wires buried in the inner surface are energized and welded by electrofusion.
．． A water supply made by blending 915 to 0.940 g/cm3 water supply polyethylene pipe with 2 to 3% carbon black to a polyethylene material with a density of 0.950 to 0.965 g/cm3 and higher density than the insertion pipe. A polyethylene pipe for water supply, which is inserted into a polyethylene pipe joint for water supply, and is fitted with a core metal fitting that closely contacts the inner surface of the pipe over the welding range of the polyethylene pipe for water supply, and is energized to weld slightly excessively. Joining method.