JP2543891Y2 - Electric fusion joint of plastic tube - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric fusion joint for joining plastic pipes such as polyethylene pipes and polybutene pipes.

[0002]

2. Description of the Related Art Polyolefins such as polyethylene and polybutene have poor adhesiveness. Therefore, when joining these plastic tubes, fusion welding is performed. One of the types of joints for fusing and joining the above plastic pipes is EF
There is an electro-fusion type joint called F (electrofusion fitting).

There are various types of electrofusion type joints. For example, Japanese Unexamined Patent Publication No. 2-130129 discloses the type shown in FIGS. FIG. 6 is a partial cross-sectional view showing a state where a plastic pipe is fused to the joint of FIG. In FIGS. 5 and 6, a heating wire 4 is wound and embedded near the fusion bonding portion (inner surface) 3 of the socket 1, and a gasket is provided at an end of the fusion bonding portion 3 on the center side. An arc-shaped groove 6 for mounting 30 is formed in the circumferential direction of the joint. 2 indicates a plastic tube.

At the time of joining, a gasket 30 is
Then, the plastic tube 2 is inserted, and the heating wire 4 is supplied from the terminal 5 to melt the joint portion 3 of the socket and the outer surface of the plastic tube 2 to join them.

FIG. 7 is a view showing a joint provided with a branch portion. 31 is a branch part. In this joint, a groove 6 having an arc-shaped cross section along the circumferential direction of the branch portion 31 is formed at an end on the center side of the fusion bonding portion 3.

In the above electrofusion joint, the groove 6 is provided for the purpose of mounting the gasket 30 and for improving the following problems. When the socket 1 and the plastic tube 2 are joined without providing the groove 6, a right-angled corner portion is formed at the joint portion by the fused portion of the socket 1 and the end face of the plastic tube 2. In addition, an unfused portion occurs at the joining end, and a slit portion (gap) is formed in the unfused portion. When an internal pressure or an axial force is applied during use, stress concentration occurs in a corner portion or a slit portion, and cracks may start to be generated from this portion. Therefore, by providing the groove 6 at the joint end, the corner portion as described above is prevented from being formed, and the stress concentration is reduced.

[0007]

However, in the above-described conventional electrofusion joint, stress concentration is greatly reduced, but there remains a problem to be solved.

The groove provided in the joint is a groove having a shape suitable for mounting a gasket, and is simply formed in an arc shape (semicircle shape) with respect to a plastic pipe to be joined. By forming the groove, a portion having a shape similar to a corner portion is newly formed. With such a shape, the degree of stress concentration at the fusion joint is reduced by the formation of the groove, but due to the newly formed shape similar to the corner part, the stress concentration at the fusion joint is reduced. Will still cause stress concentration. Therefore, there is still room for improvement as a countermeasure for reducing the stress concentration generated at the fusion bonding end.

Also, the groove formed along the center end and the
Also, since the distance of the heating wire wired on the center side is not determined, if it is separated by a certain distance or more, a portion that does not melt occurs. As a result, stress concentration occurs at the interface between the melted and bonded portion and the unmelted and unbonded portion. In fact, in an object having such a portion, the stress concentration coefficient fluctuates in a range of 1.2 to 3.5, and uniform performance cannot be secured.

Therefore, in the above-mentioned conventional joint, a gasket is mounted on the assumption that the sealing property of the fusion-bonded portion is reduced due to stress concentration.

When the gasket is mounted, a new problem arises in that the structure of the joint becomes complicated and the handling when joining the plastic pipe becomes complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electro-fusion type joint which only needs to provide a groove and does not need to mount a gasket.

[0013]

In order to achieve the above object, the invention according to claim 1 is to provide an arcuate shape along the center end of a fusion joint with a plastic pipe to be connected.
Groove is provided, and the fusion-bonded portion formed by the groove is formed.
The cross-sectional shape of the center-side end in the tube axis direction is a wedge-shaped
Have .

According to a second aspect of the present invention, an arc-shaped groove is provided along an end on the center side of the fusion bonding portion .
Of the central end of the fusion joint formed
Surface shape forms the wedge-shaped, folded the wedge angle type Ri acute der below 60 degrees, and reaches the perpendicular of fusion bonding surface of the heating wire arc of the groove is wired to the most central side Without
The distance to the heating wire is at least twice the diameter of the heating wire, and the distance between the heating wire and the wedge-shaped tip is within three times the diameter of the heating wire.

When the groove is formed as described above, a corner portion serving as a stress concentration point cannot be formed, and the stress concentration at the fusion bonding portion is significantly reduced. In addition, the most
The distance between the drawn heating wire and the tip of the wedge-shaped
If it is in the enclosure, the slit will not be formed
Is further reduced .

[0016]

1 is a view showing one embodiment of the present invention, and FIG. 2 is a partial sectional view showing a state where a plastic pipe is joined to the joint of FIG. 1 and 2, the same components as those in FIGS. 5 and 6 are denoted by the same reference numerals, and description thereof will be omitted. The joint in this embodiment satisfies the following conditions.

The center-side end of the fusion joint is connected to this end.
It has a wedge-shaped structure formed by grooves provided along the pipe and having a cross-sectional shape in the tube axis direction at an acute angle (θ) of 60 degrees or less. The groove has an arc shape. However, the position where the groove 10 cuts into the fusion bonding portion 3 side most does not reach the vertical line N of the fusion bonding portion (joint inner surface) 3 passing through the heating wire 4a routed to the most central side. . The groove 10 is provided at a predetermined interval from the heating wire 4, and the interval L ₁ is at least twice the diameter of the heating wire 4 from any point of the groove 10. Groove 10 is provided from the portion of the heating wire 4a wired innermost at predetermined intervals, one side of the groove located the distance L ₂ within three times the diameter of the heating wire 4.

The angle θ of the wedge at the center side end of the fusion bonding portion is basically required to be an acute angle, but it is more preferable to set the angle θ to 60 degrees or less so as to avoid concentrated stress. Can be.

FIG. 3 shows another embodiment of the present invention, which is a joint provided with a branch portion. FIG. 4 is a partial cross-sectional view showing a state where a plastic tube is inserted into the joint of FIG. 3 and fused. In this joint, a branch portion 31 is provided at the end of the fusion bonding portion 3.
A groove 10 is formed along the circumferential direction. Also in the case of this joint, it is premised that the shape and the location of the groove 10 satisfy the above four conditions.

The operation when the above-described groove is provided will be described. When the groove 10 is cut into the heating wire 4 side, one side of the groove 10 (one side of the groove having an arc-shaped cross section) has an acute angle, and a core which becomes a stress concentration point is formed.
It does not become a knurl. The radius of curvature of the groove 10 is desirably as large as possible, and is at least about 8 mm to 10 mm.

[0021] When the distance L ₂ between one heating wire 4a wired in most most central to the side of the groove within three times the diameter of the heating wire 4, can not unfused portion, a stress concentration point No slit portion is formed.

Stress concentration occurs around the heating wire 4 (within a range of about 1.5 times the diameter of the heating wire 4).
If the distance L ₁ between 0 and heating wire 4 more than twice the diameter of the heating wire 4 is not affected.

As a result, the stress concentration coefficient at the fusion-joined end was 1.2 to 3.5 in the case of the conventional joint, whereas it was around 1.1 in the case of the joint of FIG. It was further reduced. Further, since the stress concentration coefficient becomes uniform, stable performance can always be ensured.

[0024]

[Effect of the Invention] In the electrofusion joint of the present invention, since the above-mentioned groove is formed, it becomes a stress concentration point.
No corner portion is formed, and the stress concentration at the fusion joint is significantly reduced. In addition, wiring the most central side
Heating wire from the wedge-shaped tip of the fusion joint
Since it is located at a distance, a slit is formed.
And the stress concentration at the fusion joint is further reduced.
It is . Further, the bonding force becomes uniform, and stable performance can be secured. Furthermore, it is not necessary to mount a gasket on the assumption that the fusion joint is damaged, the structure is simple, and handling at the time of joining is easy.

[Brief description of the drawings]

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

FIG. 2 is a partial sectional view showing a state where a plastic pipe is joined to the joint of FIG. 1;

FIG. 3 is a view showing another embodiment of the present invention.

FIG. 4 is a partial cross-sectional view showing a state in which a plastic tube is inserted into and fused to the joint of FIG. 3;

FIG. 5 is a diagram showing an example of a conventional electrofusion joint.

FIG. 6 is a partial cross-sectional view showing a state where a plastic tube is fused to the joint of FIG. 5;

FIG. 7 is a view showing another example of a conventional electrofusion joint.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Socket 2 Plastic tube 3 Fusion bonding part 4 Heating wire 4a Heating wire wired at the most central side 6, 10 groove

Claims (2)

(57) [Scope of request for utility model registration] 1. A fusion joint with a plastic tube to be connected
An arc-shaped groove is provided along the end on the center side of the
Therefore, the center end of the fusion-bonded portion formed
Electrical welding Fittings of plastic tube cross section, characterized in that it is at an acute angle of the wedge-shaped. 2. A fusion joint with a plastic tube to be connected.
An arc-shaped groove is provided along the end on the center side of the
Therefore, the center end of the fusion-bonded portion formed
Sectional shape without a wedge-shaped, folded the wedge angle type Ri acute der below 60 degrees, and reaches the perpendicular of fusion bonding surface of the heating wire arc of the groove is wired to the most central side The distance to the heating wire is at least twice the diameter of the heating wire, and the distance between the heating wire and the wedge-shaped tip is within three times the diameter of the heating wire. Electric fusion joint for plastic pipes.