JP2003170504A - Pressure welding method and device for thermoplastic resin pipe - Google Patents

Abstract

(57) [Summary] A conventional pressure welding method in which end faces of resin pipes are opposed to each other, a tubular joint is arranged therebetween, and this is rotated and fused and joined to each other by frictional heat at that time. If the optimum heat generation rate is not realized for each process, the quality of the bonded portion is reduced due to excessive heat generation, and the work efficiency is reduced due to oxidation or insufficient heat generation. SOLUTION: By controlling the rotational speed of a tubular joint to an optimum value for each process, a heating speed of a joint due to frictional heat is maintained at an optimum value for each process, thereby achieving both high quality and high working efficiency of the joint. Can be realized simultaneously.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a thermoplastic resin pipe,
In particular, the present invention relates to a method for pressure-welding a thermoplastic resin tube and a pressure-welding apparatus for fusing a polyethylene tube or a polybutene tube by friction welding.

[0002]

2. Description of the Related Art FIG. 5 is a side view of a partial cross section of a conventional pressure welding apparatus for resin pipes disclosed in Japanese Patent Laid-Open No. 4-39028. In FIG. 5, the polyethylene pipes 1 and 2 are fusion-bonded via a tubular joint 3 arranged between the end faces thereof. That is, the polyethylene pipes 1 and 2 are fixed to the pipe fixtures 5 and 6 connected to the hydraulic pulling mechanisms 16 and 17, and their end faces face each other. The tubular joint 3 is held by a joint holder 10 and is rotatably arranged between the end faces of the polyethylene pipes 1 and 2 by a rotary drive mechanism 14. When the end faces of the polyethylene pipes 1 and 2 and the tubular joint 3 are in contact with each other, the tubular joint 3 is rotated, and when the contact surfaces of the polyethylene pipes 1 and 2 and the tubular joint 3 reach the melting point due to frictional heat. The end faces of the polyethylene pipes 1 and 2 and the tubular joint 3 are tightened by the hydraulic pulling mechanisms 16 and 17, and these are fused and integrated.

[0003]

When fusing resin pipes using frictional heat, the optimum heat generation rate differs in each step of the joining work. If the heat generation rate is too high, the resin temperature Oxidation due to excessive rise and insufficient melting time lead to insufficient removal of oxide film and dirt, resulting in deterioration of the quality of the melted portion. When the heat generation rate is too small, work efficiency decreases. In the conventional pressure welding method and apparatus for resin pipes as described above, the method of controlling the heat generation rate in each step is not clear, and all of these phenomena cannot be prevented. An object of the present invention is to provide a pressure welding method and a pressure welding apparatus for a resin pipe, which enables control of an optimum heat generation rate for each process and can simultaneously realize both high quality and high work efficiency of a welding portion.

[0004]

SUMMARY OF THE INVENTION A method for pressure-welding a thermoplastic resin pipe according to the present invention is one in which two thermoplastic resin pipes are contacted with their opposite end faces in contact with each other. In the pressure welding method in which frictional heat is generated and fused by rotating around the axis, both resin tubes are pulled in the axial direction at a predetermined relative speed, and the rotation speed of one resin tube is set to a predetermined value. To start the melting of the contact part, and one resin pipe is rotated at a predetermined rotation speed while pulling both resin pipes in the axial direction at a predetermined relative speed. And a melting continuation step for continuing the melting of No. 3, and the number of rotations in the melting start step is set higher than the number of rotations in the melting continuation step.

According to a second aspect of the present invention, there is provided a method for pressure-welding and joining a thermoplastic resin pipe, wherein two thermoplastic resin pipes are axially attached to each other in a state where their opposing end surfaces are in contact with each other. In a pressure welding method in which frictional heat is generated and fusion-bonded by rotating about the center, one resin pipe is rotated at a predetermined rotation speed while pulling both resin pipes in the axial direction at a predetermined relative speed. The melting range by continuing to melt the joint part by pulling both resin pipes in the axial direction at a relative speed lower than the melting continuation process and rotating one resin pipe at a predetermined rotation speed. And a melting range expanding step of expanding the melting range, and the number of rotations in the melting range expanding step is set to be higher than that in the melting continuing step.

According to a third aspect of the present invention, there is provided a method for pressure-welding a thermoplastic resin pipe, wherein two thermoplastic resin pipes are axially contacted with their opposite end faces abutting each other. In a pressure welding method in which frictional heat is generated by fusing the resin tubes to fuse them together, the rotational speed of one of the resin pipes reaches a predetermined value while pulling both resin pipes in the axial direction at a predetermined relative speed. Melting process to start the melting of the contact part and to melt the joint part by pulling both resin pipes at a predetermined relative speed in the axial direction and rotating one resin pipe at a predetermined rotation speed. And the melting continuation process that expands the melting range by pulling both resin pipes in the axial direction at a lower relative speed than the melting continuation process and rotating one resin pipe at a specified rotation speed. Process and The rotational speed at the start step higher than the rotational speed in the melt continuous process, and characterized by setting the rotational speed at melting range expansion step higher than the rotational speed in the melt continuous process.

Further, the method for press-contacting a thermoplastic resin pipe according to claim 4 of the present invention is the same as that of claim 2 or 3,
It is characterized in that the number of rotations in the melting range expanding step is set so that the temperature of the resin pipe joint is equal to or higher than the melting point of the thermoplastic resin pipe and equal to or lower than the oxidation start point.

Further, the method of press-contacting a thermoplastic resin pipe according to a fifth aspect of the present invention is the same as that of the first to fourth aspects.
If the ambient temperature is higher than the reference value set in advance by experiment, set the rotation speed in the melting continuation process or the melting range expansion process to a lower value, and increase it if the ambient temperature is lower than the above reference value. It is characterized by setting to.

According to a sixth aspect of the present invention, there is provided a pressure welding apparatus for joining thermoplastic resin pipes, which comprises two thermoplastic resin pipes to be joined together.
With these end faces facing each other, it is possible to draw at a predetermined relative speed, and the pipe support means for supporting the facing end faces so that they can be in close contact with each other by relative movement, and supported by this pipe support means, and , The rotation driving means for rotating one resin tube around its axis in a state where the opposite end surfaces are in close contact with each other, and the number of rotations of the resin tube to a predetermined value for each step constituting the pressure welding process of the resin tube. And a rotational speed control means capable of adjusting the rotation speed.

The present invention is not limited to directly joining two resin pipes, but a tubular joint made of a thermoplastic resin is interposed between the two resin pipes, and the end faces of the tubular joint are provided on both sides. The resin pipes may be joined by rotating the tubular joint in a state of abutting against the opposite end faces of the resin pipe and simultaneously melting both end portions of the tubular joint.

Further, the present invention is not limited to the case where the first thermoplastic resin pipe and the second thermoplastic resin pipe are made of the same material, but the first thermoplastic resin pipe and the second thermoplastic resin pipe are made of the same material. The material may be different from that of the thermoplastic resin tube.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the following, a tubular joint made of a thermoplastic resin is interposed between two resin pipes, and the end faces of the tubular joints are brought into contact with the opposite end faces of the resin pipes on both sides. The present invention will be described in detail by taking the case of rotating the tubular joint as an example.

As shown in FIG. 1, the present pressure welding device is
A fixed clamp 5 for holding the resin pipes 1 and 2 to be joined, a movable clamp 6, a tubular joint 3 is held between the end faces of the resin pipes 1 and 2 to be joined, and this tubular joint is provided around the axis of the resin pipe. From the tubular joint holding portion 4 for rotating the tubular joint holding portion, the movable bed 20 for rotatably holding the tubular joint holding portion, and the pipe feeding mechanism 9 for moving the resin pipe 2 held by the movable clamp 6 in the axial direction thereof. The tube support means, the rotary drive means mounted on the moving bed for rotating the tubular joint holding portion, and the rotational speed of the resin pipe to a predetermined value for each step constituting the pressure welding process of the resin pipe. And a rotational speed control means that can be adjusted.

The fixed clamp 5 and the movable clamp 6
Holds the resin pipes 1 and 2 to be joined by detachably clamping them, and the movable clamp 6 is guided by the slide shaft 21 and is movable in the axial direction of the resin pipes. The fixed clamp 5 and the movable clamp 6 can hold the resin pipes 1 and 2 to be joined so that the end surfaces thereof concentrically face each other.

The movable bed 20 includes the slide shaft 2
It can be moved in the direction of the resin pipe to be joined by being guided by 1. The tubular joint holding portion 4 has a ring shape having a through hole for penetrating the resin pipe, and the moving bed 2 is formed by a bearing.
It is rotatably supported at 0.

The pipe feeding mechanism 9 is provided with a screw shaft 22 as a driving means, and the screw shaft 22 is mounted in a female screw hole penetrating the movable clamp 6. By rotating the screw shaft 22, the movable clamp 6 moves in the axial direction.

The movable bed 20 has a through hole for inserting a resin pipe, and is free to move while being guided by the slide shaft 21 so as to be freely movable. When pushed by the end surface of the pipe 2, the tubular joint 3 moves in the axial direction of the resin pipe.

FIG. 2 shows the rotation driving means. The rotation driving means includes a drive motor 8, a gear 7 installed on the output shaft of the drive motor, and a gear 41 provided on the outer circumference of the tubular joint holding portion 4, and is mounted on the moving bed 20. The gear 7 meshes with the gear 41, and the drive motor 8 rotationally drives the tubular joint holding portion 4 and the tubular joint 3 via these gears.

Although the power transmission by the gear group has been described here, the power transmission mechanism may be of another type or may have a gear shifting function.

The rotation speed control means may be any as long as it can change the rotation speed of the tubular joint 3 according to the command. It may be one that controls the rotation speed of the drive motor, or a combination of a transmission and a contralo of the transmission that are interposed between the drive motor and the tubular joint. When controlling the rotation speed of the drive motor, the drive motor is preferably an inverter-driven induction motor or an AC servomotor.

The control of the pulling speed in the axial direction is performed by a servo motor using an encoder. The pressure contact pressure is controlled by controlling the torque of the servo motor. However, it is also possible to use the hydraulic servo by pulling in the axial direction with a hydraulic cylinder or the like and detecting the relative speed with a displacement gauge or the like. At this time, the pressure contact pressure is controlled by a pressure sensor such as a load cell.

The clamp forming the pipe supporting means is
It is not necessary that one is a fixed type and the other is a movable type, and both may be movable types as long as they can be pulled in the axial direction at a predetermined relative speed.

The pressure welding method of the present invention using this pressure welding apparatus will be described below. This pressure welding method is 5
It consists of two processes.

The first step is the resin pipes 1 and 2 and the tubular joint 3.
Is a step of arranging at a predetermined position. First, the resin pipe 1 is fixed to the fixed clamp 5. Next, the tubular joint 3 is fixed to the tubular joint holding portion 4, and then the movable bed 20 is slid so that the end surface of the resin pipe 1 and the end surface of the tubular joint 3 are in contact with each other. Then, the resin pipe 2 is fixed to the movable clamp 6 so as to come into contact with the tubular joint 3. Each end to be joined may be at right angles to the axial center to the extent that it is cut by a pipe cutter, and it is not necessary to cut the end again. In addition, it is not necessary to clean the end portion with a solvent such as acetone. The length of the tubular joint is determined so that the two pressure-welded joints do not interfere thermally and physically with the contact width of the tubular joint holder 4 with the tubular joint, and the length of the joint holder is 5 mm on each side. It only needs to have a certain length.

The second step is a melting start step in which melting of the resin pipe contact portion is started by rotating the tubular joint about the axis and raising and maintaining the rotation speed up to a predetermined number. The switch of the controller is turned on, and the tubular joint holding portion 4 holding the tubular joint 3 is rotated by the drive motor 8 with the gear 41. At the same time, the pipe feed mechanism 9 feeds the movable clamp 6 at a low speed to pull the resin pipe 2 toward the resin pipe 1 while sandwiching the tubular joint 3. The starting torque can be reduced by reducing the axial feed rate (relative pulling speed of the resin pipe) of the movable clamp 6 to reduce the friction between the end faces of the tubular joint and the resin pipe, and the tubular joint can be reasonably reduced. The rotation speed of can be increased. Movable clamp 6
The axial feed rate is increased after the rotational speed of the tubular joint reaches a predetermined value. As the contact between the tubular joint and the end surface of the resin pipe becomes stronger, frictional heat is generated in the contact portion between the rotating tubular joint 3 and the resin pipes 1 and 2, and melting is started.

As shown in FIG. 4, in the initial stage of the melting start step, the relative movement amount of the resin tube is almost zero, the pressure contact pressure is almost zero, and the temperature of the joint is almost not increased. After increasing the rotational speed of the tubular joint to a predetermined rotational speed, by increasing the axial feed rate, the contact between the tubular joint and the end surface of the resin pipe becomes stronger, and the pressure contact pressure rises temporarily, When the melting of the contact portion is started, the pressure contact pressure sharply decreases. On the other hand, the temperature of the resin contact portion rises to the melting point in a short time. In order to improve the work efficiency, the predetermined number of rotations in this step should be as high as possible.

The third step is a melting continuation step for continuing the melting of the tubular joint and the resin pipe end. The contact portion of the resin tube is a viscoelastic body, and the temperature rises above the melting point due to heat generation due to shear friction. Then, the resin whose viscosity is lowered by melting is continuously discharged from the pressure contact surface to the outer surface side and the inner surface side of the resin pipe. By continuing this process for a predetermined period,
Initially, the oxide film and dirt on the end face are completely discharged outside the tube. If the rotational speed of the tubular joint 3 is too high, the heat generation rate becomes fast, and the oxidation start temperature of the resin is reached before the oxide film and dirt are completely discharged to the outside of the pipe, resulting in smoke and odor, or at the joint part. Will cause a deterioration in quality. Therefore, the number of rotations of the tubular joint in the melting continuation step is, by the time the oxidation start point is reached,
The heat generation rate is set so that it takes sufficient time to completely discharge the oxide film and dirt out of the tube. Regarding the relative drawing speed of the resin pipe, the value increased in the latter stage of the previous process is maintained.

The fourth step is a melting range expanding step of suppressing the discharge of the resin from the pressure contact surface and expanding the range of the melting part and at the same time making it uniform. In this step, the relative drawing speed of the resin pipe is set to be low so that the pressure contact pressure becomes almost zero. Further, the rotational speed of the tubular joint is set so that the heat generation rate due to friction balances with the heat radiation rate and the temperature of the melting portion is maintained as high as possible at the melting point or higher and the oxidation start point or lower as much as possible.

Since it is difficult to measure the temperature of the welded portion during the actual pressure welding operation, the number of rotations is to be obtained in advance by an experiment. In this experiment, a small temperature measuring means such as a thermocouple is buried near the portion to be joined of the resin pipe.

The fifth step is a pressure-contact cooling step of fusing the tubular joint and the resin pipe sandwiching it. While stopping the rotation of the tubular joint 3 and applying a constant pressure contact pressure, the first and second
The end face of the thermoplastic resin pipe is pressure-welded to fuse the tubular joint and the thermoplastic resin pipe. In this process, the resin whose temperature has been raised above the melting point and whose molecular weight has been lowered is discharged to the outside of the tube because of its low viscosity. Since the cooling rate also depends on the rate at which the resin is discharged out of the pipe, in order to control the cooling rate so that a good joint can be obtained, the resin pipe is pushed under the restriction of the relative drawing speed. wear. The resin discharged outside the pipe is
Even after the rotation is stopped, they are integrated and form a bead with a smooth shape on the inner and outer surfaces of the pipe.

As shown in FIG. 4, the pressure contact pressure in the pressure contact cooling step is maintained at a constant value by torque control. The temperature of the joint portion is lowered by the rotation being stopped and the heat generation being eliminated, and the high temperature resin being extruded to the inner and outer surfaces of the pipe, and being cooled while being pressed. However, when pulling in the axial direction with a hydraulic cylinder, etc., the hydraulic pressure is measured with a pressure sensor such as a load cell and the hydraulic servo is used to maintain the constant pressure contact pressure during the pressure contact cooling process. It

When the ambient temperature is higher than a preset reference value, the heat dissipation rate is weakened, so that the time of the predetermined melting continuation process is shortened or the joint temperature in the melting range expansion process is increased. It may become. In that case, the number of rotations of the tubular joint may be set lower in order to reduce the heat generation rate. On the contrary, when the ambient temperature is lower than the preset reference value, the rotational speed of the tubular joint in the melting continuation step or the melting range expansion step may be set higher in order to increase the heat generation rate.

As described above, the tubular joint of the thermoplastic resin is interposed between the two resin pipes, and the tubular joint is rotated while the end faces of the tubular joint are brought into contact with the opposite end faces of the resin pipes on both sides. Although a case has been described as an example, the present invention is not limited to this, and it goes without saying that a case of directly joining two resin pipes without using a tubular joint is also included.

[0034]

EXAMPLES Examples of the present invention will be described below. In each of the embodiments, a tubular joint made of a thermoplastic resin is interposed between two resin pipes, and the tubular joint is rotated in a state where the end faces of the tubular joint are in contact with the opposite end faces of the resin pipes on both sides. This is the case of joining resin pipes. Further, the clamp constituting the pipe supporting means has the same structure as that shown in FIG.
One is fixed and the other is movable. The rotary drive means is of a type in which the power of the drive motor is transmitted by a gear group, as in the configuration shown in FIG. The rotation speed control means,
The number of rotations of the drive motor is directly changed. A 150 A medium density polyethylene pipe is used as the resin pipe and the tubular joint, and the length of the tubular joint is 10 cm.

(Example 1) Pressure welding was performed at an ambient temperature of 23 ° C. First, in the melting start step, the axial feed rate of the movable clamp was set to 0.01 mm / sec, and the rotational speed of the tubular joint was increased to the maximum rotational speed of 1200 rpm. Then, set the axial feed rate of the movable clamp to 0.1.
The temperature was raised to mm / sec and the temperature of the resin tube contact portion was raised to the melting point. In the next melting continuation step, while keeping the axial feed rate of the movable clamp at 0.1 mm / sec, the rotation of the tubular joint was set to 700 rpm, and the temperature of the contact portion was the melting point.
The oxide film and dirt were completely discharged outside the tube while maintaining the temperature at 5 ° C or higher and 250 ° C or lower, which is the oxidation start point. Then
In the melting range expansion process, the axial feed rate of the movable clamp was 0.01 mm / sec, and the rotation of the tubular joint was 800 rp.
set to m. The time required up to this point was 60 seconds.
In the final pressure contact cooling step, rotation is stopped, the axial feed rate of the movable clamp is limited to 4 mm / sec or less, and the pressing torque of the drive motor is controlled to 60% of the rated value in order to keep the pressure contact pressure constant. It was possible to obtain a good joint. The pressure contact pressure at this time was 1.5 kg / cm ² .

(Example 2) Pressure welding was performed at an ambient temperature of -5 ° C. First, in the melting start step, the axial feed rate of the movable clamp was set to 0.01 mm / sec, and the rotational speed of the tubular joint was increased to the maximum rotational speed of 1200 rpm. Then, set the axial feed rate of the movable clamp to 0.1.
The temperature was raised to mm / sec and the temperature was raised to the melting point. In the next melting continuation process, the axial feed rate of the movable clamp is 0.1m.
Rotation speed of the tubular joint is 800 rpm while maintaining m / sec.
And the temperature of the contact portion was maintained at 135 ° C. or higher as the melting point and 250 ° C. or lower as the oxidation start point, while the oxide film and dirt were completely discharged outside the tube. Next, in the melting range expanding process, the axial feed rate of the movable clamp is 0.01 m.
The rotation speed of the tubular joint was set to 1000 rpm. The time required up to this point was 60 seconds. In the final pressure contact cooling step, rotation is stopped and the pressing torque is maintained at 60% of the rated value in order to keep the pressure contact pressure constant while limiting the axial feed rate of the movable clamp to 4 mm / sec or less. I was able to get a good joint. The pressure contact pressure at this time was 1.5 kg / cm ² .

As described above, even if the ambient temperature was changed, by adjusting the rotational speed of the tubular joint, good pressure welding was possible in the same amount of time.

[0038]

According to the above-described method and apparatus for pressure-bonding and joining a thermoplastic resin pipe of the present invention, the number of revolutions of the rotary drive means is controlled according to each process, so that the joint portion due to excessive heat generation is produced. It is possible to realize the pressure welding in an optimum time without causing the oxidization and the deterioration of the quality of the steel and the deterioration of the work efficiency due to the excessive heat generation. In addition, regardless of the ambient temperature, it is possible to obtain a highly reliable and good joint performance with the same joining time.

[Brief description of drawings]

FIG. 1 is a side view schematically showing a device configuration in an embodiment of a pressure welding device for a thermoplastic resin pipe according to the present invention.

FIG. 2 is a cross-sectional view showing a tubular joint holding mechanism and a rotary drive mechanism in an embodiment of a thermoplastic resin pipe pressure welding device according to the present invention.

FIG. 3 is a perspective view of a device in one embodiment of a pressure welding device for a thermoplastic resin pipe according to the present invention.

FIG. 4 is a conceptual diagram showing changes over time of various parameters in the method for pressure-welding a thermoplastic resin pipe according to the present invention.
From top to bottom, (1) Relative pulling speed of resin pipe,
(2) shows the relative movement amount of the resin pipe, (3) shows the rotational speed of the tubular joint, (4) shows the pressure contact pressure, and (5) shows the joint temperature.

FIG. 5 is a side view of a partial cross section of a pressure welding device for a thermoplastic resin pipe according to the prior art.

[Explanation of symbols]

1 resin tube 2 resin tubes 3 tubular joint 4 Tubular joint holder 5 fixed clamp 6 movable clamp 7 gears 8 motor 9 Pipe feeding mechanism 20 moving beds

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroyuki Unishi             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F-term (reference) 3H019 GA06 GA12                 4F211 AD05 AD12 AG08 AH11 AR09                       TA01 TC08 TC11 TD07 TN20                       TQ01

Claims (6)

[Claims] 1. Two thermoplastic resin tubes are fused with each other by causing frictional heat to be generated by rotating one of the resin tubes around an axis in a state where the opposite end surfaces of the two thermoplastic resin tubes are in contact with each other. In the pressure welding method, while pulling both resin pipes at a predetermined relative speed in the axial direction, the rotation speed of one resin pipe is increased until it reaches a predetermined value, and a melting start step in which melting of the contact portion starts, Includes a melting continuation step that continues melting the joint by rotating one resin tube at a specified rotation speed while pulling both resin tubes in the axial direction at a specified relative speed. A method for pressure welding of thermoplastic resin pipes, characterized in that the number is set higher than the number of rotations in the continuous melting process. 2. The two thermoplastic resin pipes are caused to generate frictional heat by fusing them by rotating one of the resin pipes around an axis in a state where the opposite end surfaces of the two thermoplastic resin pipes are in contact with each other. In the pressure welding method, while continuously pulling both resin pipes at a predetermined relative speed in the axial direction, one of the resin pipes is rotated at a predetermined number of revolutions to continue melting the joint portion, and a melting continuation process. Including the melting range expanding step of expanding the melting range by rotating one of the resin tubes at a predetermined rotation speed while pulling both resin tubes in the axial direction at a lower relative speed, A method for pressure-welding a thermoplastic resin pipe, characterized in that the number of rotations is set higher than that in the continuous melting step. 3. A pressure welding method in which two thermoplastic resin pipes are fused to each other by generating frictional heat by rotating one of the resin pipes around an axis in a state where the opposite end faces are in contact with each other. In the joining method, while pulling both resin pipes at a predetermined relative speed in the axial direction, the number of rotations of one resin pipe is increased until it reaches a predetermined value, and a melting start step in which melting of the contact part starts, While continuing to draw both resin pipes at a relative speed in the axial direction, a melting continuation step of continuing melting of the joint portion by rotating one resin pipe at a predetermined rotation speed,
A melting range expanding step of expanding the melting range by rotating one resin tube at a predetermined rotation speed while pulling both resin tubes in the axial direction at a lower relative speed than the melting continuing step, and a melting starting step. Is set to be higher than the number of revolutions in the melting continuation step, and the number of revolutions in the melting range expansion step is set to be higher than the number of revolutions in the melting continuation step. 4. The thermoplastic resin according to claim 2 or 3, wherein the number of revolutions in the melting range expanding step is set so that the temperature of the resin pipe joint is equal to or higher than the melting point of the thermoplastic resin pipe and equal to or lower than the oxidation start point. Pressure welding method for pipes. 5. The number of rotations in the melting continuation step or the melting range expansion step is set to a lower value when the ambient temperature is higher than a reference value determined in advance by experiments, and when the ambient temperature is lower than the above reference value. The method for press-welding a thermoplastic resin pipe according to any one of claims 1 to 4, wherein the method is set to a higher value. 6. Two thermoplastic resin pipes to be joined can be attracted at a predetermined relative speed with their end faces facing each other, and the opposite end faces can be closely contacted by relative movement. And a rotary driving means for rotating one resin pipe around its axis while being supported by the pipe supporting means and in contact with each other and facing each other, and performing a pressure welding process for the resin pipe. And a rotational speed control means capable of adjusting the rotational speed of the resin pipe to a predetermined value for each step.