JPH07232379A - Welding of tubular member - Google Patents

Abstract

PURPOSE:To minimize the bead formed to an inner peripheral surface and to obtain high welding strength. CONSTITUTION:In welding a pair of tubular members by heating the end surfaces 20 to be welded thereof by a heater to melt them and mutually pressing the molten end surfaces, each of the end surfaces 20 is processed into a shape consisting of a flat annular outside part 22 and a flat annular inside part 24 prior to welding the end surfaces 20. The inside and outside parts 22, 24 become right-angled with respect to the center axial line of the tubular members 12 and the outside parts 22 are arranged at the position outside the inside parts 24 with respect to the center axial line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of welding end faces of a pair of tubular members made of a thermoplastic resin by abutting them together.

[0002]

2. Description of the Related Art Conventionally, tubular members made of various synthetic resins have been used for various purposes. For example, tubular members molded from general-purpose thermoplastic resins such as polyvinyl chloride and polypropylene are widely used as water pipes for houses, factories, etc., and pipes for chemicals. Also,
A tubular member made of a thermoplastic resin having excellent heat resistance and solvent resistance such as polyetheretherketone and polyphenylene sulfide is used as a pipe for ultrapure water in the production of electronic devices such as LSI.

When piping is actually performed using such a tubular member made of a thermoplastic synthetic resin, it is necessary to join the tubular members to each other or the tubular member and the tubular ends of the devices. As a method for joining the tubular members, a welding method is known in which the end faces of the tubular members facing each other are heated and melted by a heating body, and then the melted end faces are pressed against each other to be joined. Further, in this welding method, there are a contact type in which an end face to be welded is directly brought into contact with a heating body and melted, and a non-contact type in which a gap is provided between the end face to be welded and the heating body and the end face is not melted. There is a contact type.

[0004]

In the welding method as described above, the molten resin is extruded inward and outward in the radial direction by the pressure at the time of welding, and the inner peripheral surface and the outer peripheral surface of the welded portion between the tubular members. Additionally, protrusions commonly referred to as "beads" may be formed.

When the beads are formed on the inner peripheral surface of the pipe, it causes the pressure loss of the fluid flowing therethrough. Further, before and after this bead, the flow of the fluid is settled or disturbed, so that microorganisms and fine particles may be accumulated there. In particular, in the case of piping for ultrapure water, it goes without saying that piping having beads that can be a reservoir for microorganisms and the like is not suitable for use.

Therefore, in the prior art, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent Laid-Open No. 4-71731, there has been proposed a method in which a core is arranged inside the welded portion between the tubular members and brought into close contact with the inner peripheral surface thereof. However, this method has not been put into practical use because it is difficult to hold the core by the non-contact welding method.

Further, in Japanese Patent Laid-Open Nos. 1-110128 and 2-106325, the inner peripheral edge of the end face to be welded is cut into a taper shape, and a cross section is obtained when the end faces of the tubular members are butted against each other. Has been proposed in which a space of approximately isosceles triangle, that is, a so-called V-shaped groove is formed. When such a V-shaped groove is formed, when the pair of tubular members are pressed against each other to weld them, the molten resin in the welded portion is pushed out by the pressing force, and the tubular member that defines the groove is formed. Proceed inward in the radial direction along the tapered surface to fill the groove. Therefore, if the size of the groove is set appropriately, the bead will only fill this groove and the amount of protrusion from the inner surface of the pipe will be
It is smaller than when the groove is not formed.

However, it is difficult to form a groove having an appropriate size. In addition, when welding is actually performed by completely filling the groove with molten resin or beads, a relatively large bead protrudes from the inner peripheral surface of the pipe despite forming the groove. . On the other hand, when the tubular member is pressed at a low pressure to reduce the bead protrusion amount,
The groove is not filled with the molten resin, and as a result, a recess is formed on the inner peripheral surface of the pipe. Such recesses serve as a reservoir for microorganisms and the like. In addition, a notch effect is produced by this recess. That is, when stress is applied to the pipe, the stress concentrates in this recess, so that the mechanical strength of the pipe is reduced and it cannot be put to practical use.

Therefore, an object of the present invention is to provide a welding method which can bring about a small bead and obtain a high welding strength.

[0010]

In order to achieve the above object, the present invention melts the end faces to be welded of a pair of tubular members made of a thermoplastic resin by the heat of a heating body and presses them against each other. In the method for welding a tubular member to be welded, prior to the melting of the end surface of the tubular member, the end surface is a substantially flat annular inner portion perpendicular to the central axis of the tubular member, and the inner portion. Placed coaxially around the
A step of processing into a shape composed of a substantially flat annular outer portion which is arranged at a position outside the inner portion along the central axis and is perpendicular to the central axis; It has a feature.

It should be noted that in the present invention, the tubular member includes not only pipes and tubes, but also nozzles and pipe joints of devices such as valves and other shaped articles.

[0012]

According to the welding method of the present invention as described above, 1
There is almost no bead protruding from the inner peripheral surface of the welded portion of the pair of tubular members, and even if a bead is formed, the size thereof is extremely small.

Further, since the substantially flat inner portions which are parallel to each other are brought into contact with each other at the time of welding, no recess is formed on the inner peripheral surface of the welded tubular member.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the drawings.

The method for welding tubular members in the examples described below is a so-called non-contact method, and the applicable tubular members are fluororesins such as perfluoroalkoxy resin, and thermoplastics such as polyether ether ketone and polyphenylene sulfide. It is molded from a synthetic resin by extrusion molding or the like.

FIG. 1 shows a welding apparatus 10 applicable to the non-contact welding method according to the present invention. This welding device 10 is a known device, and has a pair of tubular members 12a, 12
Clamps 14 for holding b respectively on the coaxial line
a and 14b are provided. One clamp 14a is movably attached to the base 16 of the welding device 10 so that it can approach and retract with respect to the other clamp 14b.
The tubular member 12 is provided between the clamps 14a and 14b.
A heating body 18 for heating and melting the facing end surfaces 20a and 20b of the a and 12b is arranged, and can be retracted from the moving path of the tubular member 12a. As the heating body 18, a heating plate 19 made of brass and a rod heater (not shown) connected to the heating plate 19 are preferable, but the material of the heating plate 19 is not particularly limited. Instead, a metal such as aluminum, brass, iron, or copper may be used, and a surface treatment such as coating or surface finishing may be performed if necessary. Also, as the heater, a nichrome wire or the like cast in the heating plate 19 can be used instead of the rod heater.

Using the welding device 10 as described above, the same shape 1
When welding the pair of tubular members 12a and 12b, first, attach each tubular member 12a and 12b to the corresponding clamp 14.
It is held by a and 14b. Thereby, the tubular member 12
The a and 12b are arranged on a coaxial line, and the end faces 20a and 20b to be welded are arranged to face each other with a predetermined distance. Next, the heating element 18 is placed between the end faces 20a, 20b of the tubular members 12a, 12b, and the rod heater of the heating element 18 is energized. After heating for a predetermined time, the heating element 18 is moved to the retracted position, and the movable clamp 1 on one side is moved.
4a is brought closer to the other clamp 14b. Then, the tubular members 12a and 12b are welded by pressing the end faces 20a and 20b against each other with a predetermined pressure for a predetermined time.

The above is the conventional method. Therefore, the end faces 20 of the tubular members 12a and 12b are
When a and 20b are not processed at all, large beads are formed on the inner and outer peripheral surfaces of the tube. Therefore, in the welding method according to the present invention, the end surfaces 20a, 20b of the tubular members 12a, 12b are processed prior to the above-mentioned welding step in order to remove or minimize the beads on the inner peripheral surface of the tube. .

FIG. 2 is an enlarged sectional view showing the shape of the end surface of one tubular member to be welded. Although the same processing is performed on the other tubular member, for simplicity, only one tubular member will be described. As shown in FIG. 2, the end surface 20 of the tubular member 12 has a stepped shape, and has an annular outer portion 22 and an annular inner portion 24 coaxially arranged radially inside the outer portion 22. It consists of Both the outer portion 22 and the inner portion 24 are substantially flat surfaces and are perpendicular to the central axis of the tubular member 12. Also, the outer portion 22 is the inner portion 24.
More than a predetermined distance along the central axis. Further, the inner peripheral edge of the outer portion 22 and the inner portion 24
The boundary surface 26 formed between the outer peripheral edge and the outer peripheral edge is a cylindrical surface or a conical surface. Such an end face shape may be formed on the end face 20 of the tubular member 12 from the beginning,
Further, it may be formed by an appropriate cutting device or grinding device at the welding site.

Now, the wall thickness of the tubular member 12, more specifically, the wall thickness of the end portion adjacent to the end face 20 to be welded is T,
The distance along the radial direction from the inner peripheral edge of the outer portion 22 to the inner peripheral surface of the tubular member 12 is t ₁ , and the outer portion 22 and the inner portion 24 are
When the distance along the axial direction between and is D, and the angle between the surface formed by the outer portion 22 and the generatrix of the boundary surface 26 is θ ₁ ,
It has been found from various experiments that each dimension preferably satisfies the following conditions.

First, for t ₁ , usually 0.1T ≦ t
₁ ≤ 0.8T, preferably 0.15T ≤ t ₁ ≤ 0.7
T, and more preferably 0.2T ≦ t ₁ ≦ 0.6T. When t ₁ is less than 0.1T, or
When it exceeds 0.8 T, the end face 20 is not processed, and when the welding is performed by the welding device 10, a large bead is formed on the inner peripheral surface of the pipe.

Further, D does not depend on the wall thickness T, as long as the welding conditions do not change significantly due to the change in the wall thickness T of the tubular member 12 to be welded, and usually 0.1 mm ≦ D ≦
1.5 mm, preferably 0.2 mm ≦ D ≦ 1.25 m
m, and more preferably 0.3 mm ≦ D ≦ 1.0 mm. When D is less than 0.1, it becomes the same as when the end face 20 is not processed, and a large bead is formed on the inner peripheral surface of the pipe. On the other hand, when D exceeds 1.5 mm, the difference between the distance from the heating element 18 to the outer portion 22 of the end surface 20 and the distance from the heating element 18 to the inner portion 24 of the end surface 20 becomes too large to be ignored. , The outer part 22 and the inner part 24 have significantly different melting behaviors,
The desired strength cannot be obtained after welding.

Further, θ ₁ is usually 45 ° ≦ θ ₁ ≦ 90
And preferably 45 ° ≦ θ ₁ ≦ 85 °. θ ₁ is 4
If the angle is less than 5 °, the area of the inner portion 24 becomes small, and as a result, a large bead is formed on the inner peripheral surface of the pipe. When θ ₁ exceeds 90 °, the angle formed between the generatrix of the boundary surface 26 and the outer portion 22 becomes an acute angle, and the inner peripheral edge of the outer portion 22 is positioned radially inward of the outer peripheral edge of the inner portion 24. . Therefore, during welding, when the inner peripheral edge of the outer portion 22 is crushed, the boundary surface 26 may cover the outer peripheral edge of the inner portion 24, and air bubbles may be enclosed therein. Such bubbles adversely affect the welding strength.

After processing the end faces of the pair of tubular members 12a, 12b to be welded so as to satisfy the above-mentioned conditions, the tubular members 12a, 12b are welded using the welding device 10 as described above.
When 12b is welded, almost no bead is generated on the inner peripheral surfaces of the welded portions of the tubular members 12a and 12b, and even if the bead is generated, the protruding amount thereof is extremely small. Further, in the welding method of this embodiment, the end surfaces 20a and 20b parallel to each other are used.
Since the inner portions 24 of the above contact each other, no recess is formed on the inner peripheral surface of the welded portion.

In the above embodiment, the inner portion 24 of the end face 20 is
Although the shape of is a flat surface, as shown in FIG. 3, the inner peripheral edge of the inner portion 24 may be chamfered in a tapered shape. Here, the tapered surface 28 and the inner portion 2
Other parts of 4 the distance along the radial direction to the inner peripheral surface of the tubular member 12 and t ₂ from the boundary line between the (main portion), a surface and a tapered shape is formed by the other part of the inner portion 24 Surface 2
The angle formed by the bus line of 8 is θ ₂ . This t ₂ depends on the above-mentioned t ₁ , and is usually 0.05t ₁ ≦ t ₂ ≦ 0.5t ₁ ,
It is preferable to set 0.1t ₁ ≤t ₂ ≤0.4t ₁ . Further, θ ₂ is usually 10 ° ≦ θ ₂ ≦ 75 °, preferably 20 ° ≦ θ ₂ ≦ 60 °, more preferably 30 °
It is preferable to set ≦ θ ₂ ≦ 45 °. They are,
This is the condition obtained experimentally.

Furthermore, as shown in FIG. 4, the tubular member 1
One or more, in the illustrated embodiment, two step surfaces 30, in the portion of the end surface 20 of the second portion adjacent to the inner peripheral edge of the inner portion 24,
32 may be ablated. These step surfaces 3
The area of 0, 32 is considerably smaller than the other parts of the inner part 24. Also, these step surfaces 30, 32
Is perpendicular to the central axis of the tubular member 12. Even when such stepped surfaces 30 and 32 are formed, the bead protrusion amount becomes extremely small.

Next, the results of experiments actually conducted under the above conditions will be described. First, a pipe made of polyphenylene sulfide (25A manufactured by Kureha Chemical Industry Co., Ltd., thickness: 2.4 mm) was used as a pair of tubular members to be welded, and the end faces thereof were processed into a shape as shown in FIG. On this occasion,
The above t ₁ is 1.2 mm, D is 0.3 mm, and θ ₁ is 75 °.
The end face was processed so that Then, using a non-contact type welding device having a heating body composed of a brass heating plate and a rod heater, the surface temperature of the heating plate is 470 ° C., the distance from the end face of each pipe to the opposing heating plate is 1 mm, and heating is performed. Welding was carried out for a time of 30 seconds, a pressure contact time of 120 seconds, and a pressure contact pressure of 600 kPa. As a result, the bead formed on the inner surface of the welded pipe protruded 0.5 mm from the inner peripheral surface, and had a substantially uniform shape in the circumferential direction. In addition, JIS K677
The welding strength determined according to No. 6 was 60 MPa.

Further, the same polyphenylene sulfide pipe as described above was processed for its end face into a shape as shown in FIG. 3, and an experiment was conducted under the same conditions as above. At this time, t ₁ is 1.2 mm, D is 0.3 mm, and θ ₁ is 75
°, t ₂ was 0.6 mm and θ ₂ was 45 °. In such a case, no bead protruding from the inner peripheral surface of the pipe is recognized,
The welding strength was 59 MPa.

Further, as a comparative example, the same polyphenylene sulfide pipe as described above was processed into an end face having a shape as shown in FIG. 5 so as to obtain a conventional V-shaped groove, and a similar experiment was conducted. went. In this case, the angle θ ₃ is 30 °
And t ₃ was 1 mm. In this experiment, the welding strength was 62 MPa, which was satisfactory, but the bead protrusion amount on the inner peripheral surface of the pipe was as large as 1.0 mm.

In the above embodiment, the welding device 10 as shown in FIG. 1 was used, but the present invention is not limited to the illustrated device as long as it can be applied to a non-contact welding method. For example, it is possible to use a heating body of an infrared heating system or the like instead of a heating body composed of a heating plate as a heating system. The welding method of the present invention can also be applied to the contact type.

[0031]

As described above, when a tubular member is welded according to the welding method of the present invention, a welding strength that can withstand practical use can be obtained, and almost no beads are formed on the inner peripheral surface of the welded tubular member. It is not formed, and even if it is formed, its size is extremely small. Therefore, the present invention can eliminate or reduce problems such as pressure loss of fluid due to beads and retention of microorganisms.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a non-contact welding apparatus that can be applied to a welding method according to the present invention.

FIG. 2 is a partial sectional view showing an enlarged shape of an end surface of a tubular member processed according to an embodiment of the present invention.

FIG. 3 is an enlarged partial sectional view showing a shape of an end face of a tubular member processed according to a second embodiment of the present invention.

FIG. 4 is an enlarged partial sectional view showing a shape of an end surface of a tubular member processed according to a third embodiment of the present invention.

FIG. 5 is an enlarged partial sectional view showing the shape of the end face of a tubular member processed in comparison with the present invention.

[Explanation of symbols]

10 ... Welding device, 12, 12a, 12b ... Tubular member, 1
4a, 14b ... Clamp, 16 ... Base, 18 ... Heating body, 20, 20a, 20b ... End face, 22 ... Outer part, 2
4 ... Inner part, 26 ... Boundary surface, 28 ... Tapered surface, 3
0, 32 ... stepped surface.

Claims (13)

[Claims] 1. A method for welding tubular members, wherein the end faces to be welded of a pair of tubular members made of a thermoplastic resin are melted by the heat of a heating body and are pressed against each other to weld the tubular members. Prior to melting, the end face,
A substantially flat annular inner portion that is perpendicular to the central axis of the tubular member, and is coaxially arranged on the outer periphery of the inner portion, and is arranged at a position outside the inner portion along the central axis. And a method for welding a tubular member, which comprises a step of processing into a shape consisting of a substantially flat annular outer portion that is perpendicular to the central axis. 2. The wall thickness of the end portion of the tubular member adjacent to the end surface is T, and the radial distance between the inner peripheral edge of the outer portion and the inner peripheral surface of the end portion is t ₁ . if you did this,
When 0.1T ≦ t ₁ ≦ 0.8T is satisfied and the distance between the outer portion and the inner portion along the central axis is D, 0.1 mm ≦ D ≦ 1.5 mm is satisfied, Further, when the angle formed by the generatrix of the annular boundary surface formed between the inner peripheral edge of the outer portion and the outer peripheral edge of the inner portion and the surface formed by the outer portion is θ ₁ , 45 ° ≦ θ ₁ ≤
The method for welding a tubular member according to claim 1, which satisfies 90 °. 3. The distance t ₁ between the inner peripheral edge of the outer portion and the inner peripheral surface of the end portion is 0.15T ≦ t ₁ ≦ 0.7T.
The method for welding a tubular member according to claim 2, wherein 4. The tubular member according to claim 2, wherein the distance t ₁ between the inner peripheral edge of the outer portion and the inner peripheral surface of the end portion satisfies 0.2T ≦ t ₁ ≦ 0.6T. Welding method. 5. The method for welding a tubular member according to claim 2, wherein a distance D between the outer portion and the inner portion satisfies 0.2 mm ≦ D ≦ 1.25 mm. 6. The method for welding a tubular member according to claim 2, wherein the distance D between the outer portion and the inner portion satisfies 0.3 mm ≦ D ≦ 1.0 mm. 7. The method for welding a tubular member according to claim 2, wherein an angle θ ₁ formed by a generatrix of the boundary surface and a surface formed by the outer portion satisfies 45 ° ≦ θ ₁ ≦ 85 °. 8. The method for welding a tubular member according to claim 1, further comprising a step of performing chamfering in a tapered shape on an inner peripheral edge portion of the inner portion. 9. The angle formed by the tapered surface formed by the chamfering step and the surface formed by the inner portion is θ.
_{When 2} is set, 10 ° ≦ θ ₂ ≦ 75 ° is satisfied, and the distance along the radial direction between the inner peripheral surface of the end portion of the tubular member adjacent to the end surface and the inner peripheral edge of the outer portion. If a and t _1, the distance along the radial direction between the inner peripheral surface of the outer peripheral edge and said end portion of said tapered surface has a t _2, 0.05 t
_The method for welding tubular members according to claim 8, wherein ₁ ≦ t ₂ ≦ 0.5t ₁ is satisfied. 10. The method for welding a tubular member according to claim 9, wherein an angle θ ₂ formed by the tapered surface and a surface formed by the inner portion satisfies 20 ° ≦ θ ₂ ≦ 60 °. 11. The method for welding a tubular member according to claim 9, wherein an angle θ ₂ formed by the tapered surface and a surface formed by the inner portion satisfies 30 ° ≦ θ ₂ ≦ 45 °. 12. The distance t ₂ between the outer peripheral edge of the tapered surface and the inner peripheral surface of the end portion is 0.1t ₁ ≦ t ₂ ≦
The method for welding tubular members according to claim 9, wherein 0.4t ₁ is satisfied. 13. The method for welding a tubular member according to claim 1, further comprising the step of forming at least one step surface on a portion adjacent to the inner peripheral edge of the inner portion.