JP2003130277A - Method for determining acceptability of frictionally fused connection part of pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine the acceptability of the connection part of a thermoplastic resin pipe by a rotatingly and frictionally fused connection method by non-destructive measurement such as the measurement of a change rate of the outer diameter of the receiving port of a joint before and after a connection and the roundness of the receiving port of the joint after the connection without relying upon a destructive test. SOLUTION: The thermoplastic resin pipe 1 and the thermoplastic resin joint 2 are directly fused to each other or connected through a thermoplastic resin collar 3 by the relative rotational friction of a contact surface. The outside diameters of the receiving port of the joint before and after the connection of the connection part are compared with each other, or the roundness of the receiving port of the joint after the connection is measured to determine whether the connection is acceptable or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for judging the quality of a thermoplastic resin pipe joint formed by a rotary friction welding method.

[0002]

2. Description of the Related Art It is known to use a rotary friction welding method for joining a thermoplastic resin tube, particularly a thermoplastic resin tube which is difficult to be joined with an adhesive, for example, a polyethylene tube (see, for example, Special Table See Japanese Patent Publication No. 8-504922). In this rotary friction fusion welding method, the thermoplastic resin pipe end is directly inserted into the receiving end of the thermoplastic resin joint with a predetermined fitting tolerance, or
Alternatively, insert a thermoplastic resin collar with a predetermined fitting tolerance into the clearance between the outer surface of the pipe end inserted into the joint receiving opening with a predetermined clearance and the inner surface of the receiving opening, and rotate the joint or the collar to form the joint receiving opening. Fusing the resin at the contact interface with the pipe end, or the resin at the contact interface between the joint receiving port and the collar and the contact interface between the collar and the pipe end with frictional heat, for a predetermined time
This rotational friction is continued, and after that, the molten resin is cooled and solidified to complete the joining.

An internal pressure test is usually used to judge the quality of the pipe joint, and conventionally, the quality of the joint is also judged by the internal pressure test for the above-mentioned rotary friction welding. .

[0004]

However, the internal pressure test is a destructive test, and it is required to judge the quality of the above-mentioned joint by a non-destructive test.

Now, considering the joining process of the above-mentioned rotary friction fusion welding method, the resin melted by the rotary friction causes surface pressure due to thermal expansion, and this surface pressure causes hoop stress at the joint receiving port. While receiving and expanding the diameter, the molten resin flows out from the bonding interface into the space adjacent to the interface. Then, after the frictional rotation is stopped, the molten resin at the joining interface is cooled and solidified and contracted, and the outer diameter of the joint receiving port is also contracted along with the solidified and contracted. Considering the surface pressure, assuming that there is no outflow of the molten resin from the bonding interface, the surface pressure is uniformly determined by the coefficient of thermal expansion of the molten resin. However, in reality, molten resin flows out from the bonding interface, and the larger the outflow amount, the lower the surface pressure. In the above, if the resin melting is insufficient, a predetermined bonding strength cannot be obtained, resulting in poor bonding. In this case, the amount of the molten resin flowing out is small, and the outer diameter shrinkage rate of the joint receiving port is small. On the other hand, if the resin is excessively melted, as opposed to being insufficiently melted, the surface pressure becomes low and the fusion strength becomes low, resulting in poor bonding. In this case, the outflow amount of the molten resin is large and the reduction rate of the outer diameter of the joint receiving port is large. Therefore, when the quality of the joint is judged by the rotary friction fusion welding method, the lower limit of the outer diameter change rate of the joint port, which is considered to be defective due to insufficient melting of resin, is X, and the joint to be defective due to excessive melting of resin. If the upper limit of the change rate of the outer diameter of the receiving port is Y, the range of X to Y can be determined to be good.

[0006] Thermoplastic resin joints are usually manufactured by injection molding, but due to unavoidable non-uniform cooling and non-uniform crystal shrinkage, even if there is a difference in degree, the elliptical shape of the joint port is not possible. Inevitable. Therefore, in the above-mentioned rotary friction fusion welding method, when the joint receiving port is elliptical, the thickness of the molten resin layer at the joint interface becomes non-uniform in the circumferential direction. The surface pressure becomes non-uniform, resulting in uneven fusion strength, resulting in poor bonding. Therefore, after rotational friction fusion welding,
That is, the quality of the joining can be determined also from the roundness of the joint receiving port after the molten resin at the joining interface is cooled and solidified.

As described above, the inventor of the present invention determines the quality of the joining of the joined portion by the rotary friction fusion welding method, the change rate of the outer diameter of the joint receiving port before and after the welding, and the perfect circle of the coupling receiving port after the welding. It was confirmed experimentally that it can be judged from the degree.

In view of the above, an object of the present invention is to judge the quality of a thermoplastic resin pipe joint by the rotary friction fusion welding method without using a destructive test, and to determine the rate of change in the outer diameter of the joint before and after joining and after joining. The non-destructive measurement, which is the measurement of the roundness and the like of the joint receiving end of, can be performed.

[0009]

According to a first aspect of the present invention, there is provided a method for determining the quality of a friction-fusion-bonded joint portion of a pipe, wherein a thermoplastic resin pipe and a thermoplastic resin joint are directly connected to each other or via a thermoplastic resin collar. It is characterized in that the quality of the joining is judged by comparing the outer diameters of the joint receiving ports before and after the joining of the joined portion fused by the relative rotational friction of the contact surfaces.

According to a second aspect of the present invention, a method for determining the quality of a friction-fusion-bonded joint portion of a pipe is a relative rotation of a contact surface between a thermoplastic resin pipe and a thermoplastic resin joint, directly or through a thermoplastic resin collar. It is characterized in that the roundness of the joint opening after the joining of the joined portion fused by friction is measured to judge the quality of the joining.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical cross-sectional view showing an example of a thermoplastic resin pipe joint portion which is a determination target of the present invention. In FIG. 1, 1 is a thermoplastic resin pipe, for example, a polyethylene pipe, 2 is a thermoplastic resin joint, for example, a polyethylene joint, and the pipe end is inserted into the joint receiving port 21 with a predetermined fitting tolerance, and the pipe 1 is The joint 2 is rotated, and the joint surface between the joint receiving inner surface and the pipe end outer surface is friction-welded. To rotate the joint 2 in this case, a driven gear is fixedly installed at the center of the outer surface of the joint, a joining device having a drive gear is arranged at a predetermined position, and the drive gear and the driven gear are meshed with each other to drive the drive gear. Is driven by the electric motor of the joining device.

FIG. 2 is a vertical cross-sectional view showing another example of the thermoplastic resin pipe joint which is the object of the determination of the present invention. In FIG. 2, 1 is a thermoplastic resin pipe such as a polyethylene pipe, and 2 is a thermoplastic resin joint such as a polyethylene joint, which has a space for receiving the collar described below. Three
Is a thermoplastic resin collar, for example, a polyethylene collar, and the collar 3 is inserted in the space between the outer surface of the pipe end after inserting the pipe end into the joint receiving port 21 and the inner surface of the joint receiving port. The joint 2 and the pipe 3 are made non-rotatable, and the collar 3 is rotated to frictionally bond the joint surface between the joint receiving inner surface and the collar outer surface and the joint surface between the collar inner surface and the pipe end outer surface. . To rotate the collar 3 in this case, a driven gear is fixedly mounted on the rear end of the collar, a joining device having a drive gear is arranged at a predetermined position, and the drive gear and the driven gear are meshed to drive the gear. This can be done by driving the gear with the electric motor of the joining device.

In the above-mentioned rotary friction fusion welding, as described above, surface pressure is generated due to thermal expansion of the molten resin at the joint interface, and when the resin melting amount becomes excessive, the molten resin flows out from the joint surface. The surface pressure becomes low, and the molten resin at the joint interface is cooled and solidified and contracted by stopping the rotational friction.

As the cause of the defective joint, the following items can be listed. (1) Insufficient melting of the resin at the bonding interface. In this case, the outflow of the molten resin from the bonding interface is very small, and the resin at the bonding interface is substantially changed from the solid phase to the liquid phase to the solid phase with the original weight. The thickness change of the resin layer at the interface is substantially zero. However, since the diameter of the joint receiving port is expanded, and even a slight amount is permanently deformed, the outer diameter of the joint receiving port after joining is slightly increased with respect to the original diameter. In the case of this (1), the change rate of the outer diameter of the joint receiving port before and after joining is extremely small. (2) Excessive melting of resin at the bonding interface. In this case, the outflow amount of the molten resin from the joining interface becomes excessive, a large amount of the resin at the matching interface is lost, and the thickness of the resin is reduced, so that the outer diameter of the joint receiving port after joining is considerably reduced. In the case of this (2), the change rate of the outer diameter of the joint receiving port before and after joining is considerably large.

If the rate of change of the outer diameter of the joint port before and after the welding by the rotary friction fusion welding method is between the rate of change of (1) and the rate of change of (2), it is judged as good welding. I made a polyethylene joint with a 30 mm outer diameter
The joint receiving outer diameter after joining which was confirmed to be good (confirmed by the internal pressure test) was 28 mm to 30 mm. Therefore, if the outer diameter of the joint receiving port after the rotary friction fusion welding is 0.93 to 1.0 times the outer diameter of the joint receiving port before the welding, it can be determined as a pass.

According to claim 1 of the present application, the outer diameter of the joint receiving port before and after the rotary friction fusion welding is measured with a gauge, and the outer diameter of the joint receiving port after the rotary friction fusion welding is measured before the welding. Those with 0.93 to 1.0 times the outer diameter of the mouth can be judged as acceptable.

Another cause of the defect of the joint portion by the above-mentioned rotary friction fusion welding method is (3) a remarkable oval shape of the joint port after the joint. In this case, the thickness of the molten resin layer at the joint interface between the inner surface of the joint receiving port and the outer surface of the pipe end or at the joint interface between the inner surface of the joint receiving port and the outer surface of the collar is uneven in the circumferential direction, and the surface pressure is also increased accordingly. Since unevenness occurs and the fusion bonding strength at the bonding interface becomes non-uniform in the circumferential direction, bonding failure occurs.

The elliptical shape of the joint receiving port occurs in the following cases. (A) The joint is manufactured by injection molding, and the cooling rate varies depending on the position of the joint, so that the thermal contraction strain or the crystal contraction strain deforms the joint port, so that the port becomes elliptical. (B) While the resin at the joint interface is in a molten state, the joint is unstable with respect to an external load, and vibration of the electric motor or the like during gear drive causes the joint to tilt. The joint may be rotated to make the joint socket oval. Further, when the resin at the bonding interface after the rotation is stopped is not completely solidified, an external load may act on the joint receiving port to flatten the joint receiving port.

From the above-mentioned defective joint form (3), it is determined that the joint is good after the molten resin at the joint interface is solidified, that is, when the roundness of the joint opening after the joint is within a predetermined range. As a result, an experiment was conducted on a polyethylene joint having an outside diameter of 30 mm as follows. Even if the joint opening after joining was elliptical, if the ratio of the major axis length to the minor axis length was 0.93 or less. Can be passed.

[Experimental Example] As shown in FIG. 3, a cross-linked polyethylene tube 1 of 13A was rotationally friction-welded to each of the receiving ports 21 of a polyethylene header 2 with three receiving ports 21 by using a polyethylene collar 3. After stopping the rotation of the collar, for about 90 seconds until the cooling is completed, each receptacle is sandwiched from a direction perpendicular to the header axis direction and a pressure of about 70 kg is applied to the receptacle to have a length of one side of 28.0 mm to 30 mm. 0.0 mm, other shaft side length 28
mm. The elliptical sample of 0 mm to 30.0 mm was used for 10
As a result of the internal pressure creep test at 95 ° C., all polyethylene pipes were broken and no water leakage from the joint was observed.

According to claim 2 of the present application, when the receiving port of the joint after the rotational friction welding is elliptical, the major axis length and the minor axis length of the ellipse are measured, and the minor axis is measured. If the ratio of length / major axis length is within 0.93, it can be passed.

[0022]

According to the first aspect of the present invention, the quality of the joint portion obtained by the rotary friction fusion welding method can be determined by comparing the outer diameters of the joint receiving ports before and after the welding. It is possible to determine the quality of the joint by the welding method by measuring the roundness of the joint port after the welding, and the non-destructive method for the quality of the joint by the rotary friction fusion welding method.

[Brief description of drawings]

FIG. 1 is a view showing an example of a joint portion determined according to the present invention.

FIG. 2 is a view showing another example of a joint portion determined according to the present invention.

FIG. 3 is a view showing a header in which pipes are joined by a rotary friction fusion welding method.

[Explanation of symbols]

1 Thermoplastic resin tube 2 Thermoplastic joint 21 mouth 3 Thermoplastic color

Claims (2)

[Claims] Claim: What is claimed is: 1. A thermoplastic resin pipe and a thermoplastic resin joint are directly or through a thermoplastic resin collar, and the outer diameter of a joint receiving port before and after joining of a welded portion by relative rotational friction of a contact surface is measured. A method for determining the quality of a friction-fusion-bonded portion of a pipe, which comprises comparing and determining the quality of welding. 2. A roundness of a joint receiving end after joining of a joint portion where a thermoplastic resin pipe and a thermoplastic resin joint are fused directly or through a thermoplastic resin collar by relative rotational friction of contact surfaces. A method for determining the quality of a friction-fusion-bonded joint portion of a pipe, characterized by measuring the temperature and determining the quality of the welding.