JPH08318323A - Hot tube bending method and device therefor - Google Patents

Abstract

PURPOSE: To improve the strength of a bent tube by bending the tube while cooling a front part adjacent to a heating zone from inner and outer surfaces to narrow the softened zone of starting and ending parts of the bending. CONSTITUTION: The metallic tube 20 to be bent is connected to a short tube 20' with a flange 43 by welding 44. An inner surface cooling device 29 is inserted into the metallic tube 20 and the tip part of the metallic tube 20 is held by a clamp at the tip parts of a bending arm 24. The metallic tube 20 is advanced along guide rolls 26 while heating the tube 20 by a heating coil 27. The metallic tube 20 is bent by rotating the bending arm 24. The movement of the heating coil 27 at the time of starting and ending the bending is measured and the inner surface cooling device 29 in the metallic tube 20 is moved so as to be synchronized with the movement of the heating coil 27. Further, the front part adjoined to the heating zone is cooled from the inner and the outer surfaces by the inner surface cooling device 29 and an outer surface cooling ring 28. By this method, quenching from the inner and the outer surfaces can be stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention heats a metal tube made of high-strength steel used for piping for natural gas transportation, oil transportation, etc. by a high frequency heating method, and bends it while cooling its inner and outer surfaces. The present invention relates to a hot pipe bending method and a hot pipe bending apparatus.

[0002]

2. Description of the Related Art Conventionally, a metal tube is heated by a high frequency heating method, and bending is performed while cooling the inner and outer surfaces thereof.
As shown in Fig. 3, the tip of the metal tube 1 is held by the clamp 3 of the rotatable bending arm 2, and the bent end of the metal tube 1 is pressed from the outside while heating it in a circular shape with a heating coil 4 in a narrow width. The metal tube 1 is advanced along the guide rolls 5 to gradually move the heating zone in the longitudinal direction of the metal tube 1, and by the inner surface cooling ring 8 fixed to the fixed end 6 via the cooling tube 7. By cooling the end adjacent to the heating zone from the inside, and by cooling the end adjacent to the heating zone from the outside by the outer surface cooling ring 9 slightly ahead of the heating coil 4, the metal tube 1 is rotated by the bending arm 2. Bend. By doing so, the metal tube 1 can be efficiently subjected to solution treatment, and at the same time, a compressive residual stress can be uniformly and effectively generated on the inner surface of the tube (as a prior art document, Japanese Patent Publication No. 57-49292). ).

By the way, when the rear end of the metal pipe 1 to be bent is closed as shown in FIG. 9, a pusher 10 is connected to the rear end of the metal pipe 1 and a hydraulic cylinder 11 is connected to the pusher 10 to form a metal pipe. 1 is loaded with a processing force W in the direction of the arrow by a hydraulic cylinder 11 on the same axis (Japanese Patent Publication No. 2-61335 is a prior art document). In this case, since the metal tube 1 is allowed to move straight without being biased, the bending process by the rotation of the bending arm 2 is smoothly performed.

However, since the rear end of the metal tube 1 is closed, the end adjacent to the heating zone heated by the heating coil 4 can be cooled from the outside by the outer surface cooling ring 9 slightly ahead of the heating coil 4. However, I can not cool from the inside,
The advantage of the method of bending while cooling the inner and outer surfaces of the other side adjacent to the heating zone cannot be utilized.

In particular, when hot-bending a metal tube made of high-strength steel to a wall thickness of 15 mm or more, the quenching effect by the cooling water is low only by cooling the outer surface, and a strength commensurate with the high-strength steel is obtained. It was impossible. For this reason, the inventor of the present invention arranges the inner surface cooling device 12 in the metal tube 1 to be bent as shown in FIG. 10, and fixes the inner surface cooling device 12 at a fixed position with the wire or the chain 13 led out to the telescopic cylinder. A constant tension is applied to the wire or chain 13 by means of 15 to cool the end adjacent to the heating zone heated by the heating coil 4 from the outside by the outer surface cooling ring 9 integrated with the heating coil 4 and from the inside to the inner surface cooling device 12 We have developed a hot tube bending machine that cools by using.

However, in this hot pipe bending apparatus,
Wire or chain 13 during hot bending of the metal tube 1
Due to expansion and contraction, and due to the magnitude of friction with the pipe inner wall of the guide roll 14 of the inner surface cooling device 12, it is difficult to always keep the outer surface cooling position and the inner surface cooling position from the heating coil 4 constant, and The heating temperature becomes unstable, and quenching from the inner and outer surfaces becomes unstable. In particular, in the case of hot pipe bending of a metal pipe made of high-strength steel with a wall thickness of 15 mm or more, sufficient pulling is required unless the cooling positions of the inner and outer surfaces can be accurately controlled at the beginning of bending, during bending, and at the end of bending. Strength and hardness cannot be obtained.

[0007]

SUMMARY OF THE INVENTION Therefore, according to the present invention, when a metal tube whose tube pushing side is closed is pushed by a tube pushing device arranged on the same axis line to perform hot tube bending, an outer surface from a heating coil is formed. Hot pipe bending method and hot pipe capable of keeping the cooling position and the inner surface cooling position always constant, stabilizing the heating temperature of the heating zone, and stabilizing the quenching from the inner and outer surfaces It is intended to provide a bending device.

[0008]

One of the hot pipe bending methods of the present invention for solving the above problems is a pipe pushing device in which a metal pipe whose pipe pushing side is closed is arranged on the same axis. In the hot tube bending process by pressing, the movement of the heating coil at the beginning and end of bending is measured, and the inner surface cooling device arranged in the metal pipe is moved in synchronization with the movement of the heating coil, It is characterized in that the metal tube is heated by the heating coil, and the tip end adjacent to the heating zone is bent while being cooled from the inner and outer surfaces by the inner surface cooling device and the outer surface cooling ring.

Another one of the hot-tube bending methods of the present invention is to perform hot-tube bending by pressing a metal tube whose tube pushing side is closed by a tube pushing device arranged on the same axis. The movement of the heating coil at the beginning and end of bending is measured, the inner surface cooling device arranged in the metal pipe is moved so as to be synchronized with the movement of the heating coil, and during the bending process, the inner surface cooling device with respect to the heating coil is moved. It is characterized in that a metal coil is heated by a heating coil while keeping a constant distance, and bending is carried out while cooling a tip end adjacent to the heating zone from the inner and outer surfaces by an inner surface cooling device and an outer surface cooling ring.

One of the hot pipe bending devices of the present invention is a pipe pushing device connected to the closed rear end of a metal pipe to be bent and arranged on the same axis as the metal pipe, and a metal to be bent. A rotatable bending arm having a clamp for gripping the tip of the pipe, a guide roll for guiding the metal pipe to be bent in the axial direction, and a bent portion of the metal pipe in front of the guide roll with a narrow width from the outside. A heating coil for annular heating and an outer surface cooling ring for cooling the end adjacent to the heating zone integrally with the heating coil, and fixed by a chain or wire that is movably provided in the metal tube in the axial direction and led out of the metal tube In a hot pipe bending apparatus including an inner surface cooling device in which a wire or a chain is loaded with a certain tension by a telescopic cylinder, a coil movement control engine is attached to the heating coil. Attached a servo motor to the front of the inner surface cooling device, measure the moving amount of the heating coil at the beginning and end of bending of the metal tube with a coil movement control encoder, and based on the measured value, It is characterized in that the front part of the inner surface cooling device is moved synchronously with the heating coil by a servomotor.

Another one of the hot pipe bending apparatus of the present invention is the hot tube bending apparatus configured as described above, further comprising a pusher movement control encoder attached to the pusher of the tube pushing device, Attach a separate chain or wire inside the metal pipe to the inner surface cooling device, and install an encoder for measuring the movement amount of the inner surface cooling device at the fixed part at the rear end of the inner surface cooling device to measure the amount of expansion or contraction of the chain or wire during bending of the metal pipe. Measured by the encoder for moving amount measurement,
When there is a difference between the pipe pushing amount measured by the pusher movement control encoder and the pipe pushing amount, the inner cooling device is moved by the servo motor to keep the distance from the heating coil constant.

The inner surface cooling device in the above two hot pipe bending devices has a cooling ring for injecting cooling water at the tip, and immediately after that, an air injection ring for pushing out the cooling water flowing backward in the metal pipe to the forward direction. It is preferable that the moving device connected to the rear guide block is a telescopic cylinder, and these pipes are led to the outside in the vicinity of the closed portion of the metal pipe by the cable bearer method.

[0013]

According to one of the hot pipe bending methods of the present invention, the movement of the heating coil at the beginning and end of bending of the metal tube is measured, and the inside of the metal tube is synchronized with the movement of the heating coil. Since the arranged inner surface cooling device is moved to perform hot tube bending, the outer surface cooling position from the heating coil and the inner surface cooling position can be kept constant at all times, and the heating temperature in the heating zone can be stabilized. It is also possible to stabilize quenching from the inside and outside.

Further, another one of the hot pipe bending methods according to the present invention is to measure the movement of the heating coil at the beginning and end of the bending of the metal tube so as to synchronize with the movement of the heating coil. Move the inner cooling device arranged in the metal tube,
In addition, since the hot tube bending process is performed by keeping the distance from the heating coil of the inner cooling device to a constant value during the bending process, it is possible to always keep the outer cooling position and the inner cooling position from the heating coil constant and to match them. Therefore, the heating temperature of the heating zone can be stabilized, the quenching from the inner and outer surfaces is stable, and the softening regions at the bending work start portion and the bending work end portion are narrowed.

Therefore, according to one of the hot-tube bending apparatus of the present invention configured as described above, one of the hot-tube bending methods of the present invention can be carried out smoothly, reliably and efficiently. It is possible to obtain a bent tube with little variation in strength. Further, according to another one of the hot tube bending apparatus of the present invention configured as described above, another one of the hot tube bending method of the present invention can be smoothly, surely and efficiently performed. Therefore, it is possible to obtain a bending tube having high strength and a small variation in strength, and a narrow softening region at the bending work start portion and the bending work end portion. In particular, in the case where the inner surface cooling device in the above two hot pipe bending devices is configured as described above, the cooling water sprayed on the inner surface of the pipe is pushed backward by the jet of air because the cooling water flows back on the inner surface of the pipe. Therefore, the cooling water does not reach the heating zone, and the temperature of the heating zone does not change. Therefore, quenching is performed well.

[0016]

EXAMPLES Examples of the hot tube bending method and hot tube bending apparatus of the present invention will be described. First, one embodiment of a hot pipe bending apparatus will be described with reference to FIG. 1. A flanged short pipe 20 'is welded to a rear end of a metal pipe 20 to be bent, and the flanged short pipe 20' is flanged. A closed pipe 20 ″ with a flange is connected to a flange, a pusher 22 moving along a guide 21 is connected to a closed end of the closed pipe 20 ″, and a hydraulic cylinder 23 is connected to the pusher 22 so that the pusher 22 has the same axis as the metal pipe 1. A pipe pushing device is provided on the line. The tip of the metal tube 20 to be bent is held by a clamp 25 at the tip of a rotatable bending arm 24. A guide roll 26 for guiding the metal pipe 20 in the axial direction is provided on the intermediate outer peripheral side of the metal pipe 20 to be bent. A heating coil 27 is provided in front of the guide roll 26 to heat the bent portion of the metal tube 20 in an annular shape with a narrow width from the outside. The heating coil 27 integrally with the heating coil 27 is adjacent to the heating zone of the metal tube 20. An outer surface cooling ring 28 for cooling with cooling water is provided. An inner surface cooling device 29 is supported by the closed pipe 20 ″ so as to be movable in the axial direction. This inner surface cooling device 29 is a chain (or wire) led out from the closed pipe 20 ″ to the outside.
The chain (or wire) 30 is fixed by a telescopic cylinder 37 described later.
Is under a certain load.

In the case of the present embodiment, the inner surface cooling device 29 is provided with a cooling ring 31 for injecting cooling water at the tip, and immediately after that, an air injection ring 32 for pushing out the cooling water flowing back in the metal tube 20 to the forward direction. The cooling water pipe 33 and the air pipe 34 are provided in a cable bear system as shown in FIG. 2 and led out to the outside in the vicinity of the closed portion of the closed pipe 20 ″, and the base portion of the cooling ring 31 is shown in FIG. As shown in the figure, it is connected to a guide block 36 with a guide roller 35 so as to be movable back and forth, and a telescopic cylinder 37 fixed to the inner surface of the closed end of the closed tube 20 ″ is connected to the rear end surface of the guide block 36 as a moving device. Has been done.

A coil movement control encoder 38 is attached to the heating coil 27, and a servo motor 39 is attached to the base of the cooling ring 31 in the inner surface cooling device 29 by being screwed with the guide block 36, so that the metal The movement amount of the heating coil 27 at the beginning and end of bending of the pipe 20 is measured by the coil movement control encoder 38, and based on the measured amount, the cooling ring 31 and the air jet ring 32 of the inner surface cooling device 29 are servomotors. Three
It is configured so as to move synchronously with the heating coil 27 by 9.

One of the hot tube bending methods of the present invention, which is performed using the hot tube bending apparatus having the above-described structure, will be described. First, as shown in FIG. 1, the metal pipe 20 to be bent beforehand is connected to the short pipe 20 ′ with the flange 43 by welding 44. And the closed pipe 20 ″ including the inner surface cooling device 29
And the inner surface cooling device 29 is inserted into the metal pipe 20 from the side of the short pipe 20 'with the flange 43, and the closed pipe 20 "is fastened to the flange 43 of the short pipe 20' with the flange 43. At this time, The inner surface cooling device 29 is retracted to the closed pipe 20 ″ side. The metal pipe 20, the short pipe 20 ', and the closed pipe 20 "in which the inner surface cooling device 29 is incorporated are placed on a pipe pusher (not shown), and the tip end of the metal pipe 20 is bent by the bending arm 2
It is held by the clamp 25 at the tip of No. 4. Next, the inner surface cooling device 29 is advanced by the telescopic cylinder 37 connected to the guide block 36 as shown in FIG. 3 to be aligned with the outer surface cooling ring 28. Thus the metal tube 20
After the cooling positions of the inner and outer surfaces of the metal pipe 20 are aligned, the bent portion of the metal tube 20 is heated from outside by the heating coil 27 in a narrow annular shape, and the rear end of the closed pipe 20 ″ is driven by the hydraulic cylinder 23 of the pipe pushing device. Is pushed by the pusher 22 moving forward along the guide 21, the metal tube 20 is moved forward along the guide roll 26, the heating zone is gradually moved in the longitudinal direction of the metal tube 20, and the cooling ring 31 of the inner surface cooling device 29 is moved. 4 cools the tip of the metal tube 20 adjacent to the heating zone from the inside and cools the tip of the metal tube 20 adjacent to the heating zone from the outside by the outer surface cooling ring 28 integrated with the heating coil 27. Bending arm 24 as shown
Bend by rotating.

In this way, the metal pipe 2 whose pipe pushing side is closed
Hydraulic cylinder 2 of pipe pushing device with 0 on the same axis
In the hot pipe bending process by pressing to 3,
In particular, the amount of movement of the heating coil 27 at the beginning and end of bending is measured by the coil movement control encoder 38 attached to the heating coil 27, and the cooling ring 31 and the air jet ring 32 of the inner surface cooling device 29 are measured based on the measured amount. Is moved in synchronism with the heating coil 27 by the servo motor 39 to perform hot tube bending processing. Thus, the outer surface cooling position and the inner surface cooling position of the metal tube 20 from the heating coil 27 can be always kept constant, the temperature of the heating zone can be stabilized, and the quenching from the inner and outer surfaces is also stable.

Next, another embodiment of the hot pipe bending apparatus will be described with reference to FIG. 5. This embodiment is the same as the hot pipe bending apparatus of FIG. The pusher movement control encoder 40 is attached to the pusher 22.
Is engaged with a rack 41 provided on a guide 21 for rotation, and is rotated for measurement.
In the 0 ', a chain (or wire) 30' is separately stretched between the guide block 36 of the inner surface cooling device 29 and the holding plate 37 'of the telescopic cylinder 37, and the rear end fixing portion is for measuring the inner surface cooling device movement amount. An encoder 42 is provided, and during bending of the metal tube 20, the expansion / contraction amount of the chain (or wire) 30 ′ is measured by the inner surface cooling device movement amount measurement encoder 42, and is measured by the pusher movement control encoder 40. When there is a difference with the pipe pushing amount, the inner surface cooling device 29 is driven by the servo motor 39.
Is moved to keep the distance from the heating coil 27 constant.

Another hot tube bending method of the present invention, which is carried out using the hot tube bending apparatus having the above-described structure, will be described. In the hot tube bending process by pressing the hydraulic cylinder 23 of the tube pushing device in which the metal tube 20 whose tube pushing side is closed is arranged on the same axis, exactly as in one of the hot tube bending methods of the present invention described above. In addition, in the present invention, the movement amount of the heating coil 27 at the beginning and end of bending is particularly attached to the heating coil 27.
In accordance with the measured amount, the cooling ring 31 and the air jet ring 32 of the inner surface cooling device 29 are moved synchronously with the heating coil 27 by the servomotor 39, and during bending, the chain (or wire) 30 ' Encoder 42 for measuring the amount of expansion / contraction
Measured by the encoder 40 for pusher movement control
When there is a difference between the pipe pushing amount measured in step # 2, the servo motor 39 moves the cooling ring 31 and the air jet ring 32 of the inner surface cooling device 29 to keep the distance from the heating coil 27 constant. Bend.

Thus the metal tube 20 from the heating coil 27
The outer surface cooling position and the inner surface cooling position can always be kept constant, and the outer surface cooling position and the inner surface cooling position can be matched. Therefore, the heating temperature of the heating zone can be stabilized, and quenching from the inner and outer surfaces can be stabilized. The softened regions of the outside, the bending start portion and the bending end portion are narrowed. In another specific embodiment of this hot tube bending method, the outer diameter is 768.
mm, the thickness of 23 mm, the high-strength steel pipe API 5LX65 test material was used to fabricate a 3DR bent pipe under the processing conditions shown in Table 1 below.

[0024]

[Table 1]

As shown in the tensile test values and Vickers hardness in Table 2 below, the test numbers C-1 to C-4 in which the position of the inner surface cooling device 29 cannot be accurately controlled have variations in strength and are acceptable. Some did not satisfy the value,
Test numbers D-1 to D-4, in which the position of the inner surface cooling device 29 was accurately controlled by this method, had little variation in strength and satisfied the allowable value.

[0026]

[Table 2]

When the hardness of the heating start portion and the heating end portion of the test material of test number D-2 was measured, the results shown in the graphs of FIGS. 6 and 7 were obtained. As is clear from the graphs of FIGS. 6 and 7, it can be seen that the softened regions of the heating start portion and the heating end portion are narrowed and the strength is improved.

[0028]

As can be seen from the above description, according to one of the hot pipe bending methods of the present invention, the outer surface cooling position and the inner surface cooling position from the heating coil can be kept constant at all times. The heating temperature of the zone can be stabilized, and quenching from the inner and outer surfaces is also stable. Further, according to another one of the hot pipe bending methods of the present invention, since the outer surface cooling position and the inner surface cooling position from the heating coil can be always kept constant and matched, the temperature of the heating zone can be stabilized. As a result, the quenching from the inner and outer surfaces is stable, and the softening region at the bending process start part and the bending process end part can be narrowed, and the strength can be improved. Further, according to one of the hot tube bending apparatus of the present invention, one of the hot tube bending methods of the present invention can be smoothly and
It is possible to reliably and efficiently carry out the operation, and it is possible to obtain a bent tube with little variation in strength. Further, according to another one of the hot tube bending apparatus of the present invention, another one of the hot tube bending method of the present invention can be smoothly, reliably and efficiently carried out, and variation in strength is small. In addition, a softened region at the bending work start portion and the bending work end portion is narrow, and a bending pipe having high strength can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing one embodiment of a hot pipe bending apparatus of the present invention.

FIG. 2 is a diagram showing a cable bear type cooling water pipe and air pipe in the hot pipe bending apparatus of FIG.

FIG. 3 is a view showing a state where the inner surface cooling device is moved to a predetermined position in the hot pipe bending apparatus of FIG.

FIG. 4 is a view showing a state during hot tube bending of a metal tube in the hot tube bending apparatus of FIG.

FIG. 5 is a view showing another embodiment of the hot pipe bending apparatus of the present invention.

FIG. 6 is a graph showing the results of measuring the hardness of the heating start portion of the test material produced by another one of the hot pipe bending methods of the present invention.

FIG. 7 is a graph showing the results of measuring the hardness of the heating end portion of the test material produced by another one of the hot pipe bending methods of the present invention.

FIG. 8 is a diagram showing a general example of a conventional hot tube bending method.

FIG. 9 is a view showing a conventional hot pipe bending method when a rear end of a metal pipe to be bent is closed.

FIG. 10 is a schematic view of a hot pipe bending apparatus in which an inner surface cooling device is arranged in the metal pipe when the rear end of the metal pipe to be bent is closed.

[Explanation of symbols]

 20 Metal Pipe 20 'Short Pipe with Flange 20' Closure Pipe 21 Guide 22 Pusher 23 Hydraulic Cylinder 24 Bending Arm 25 Clamp 26 Guide Roll 27 Heating Coil 28 External Cooling Ring 29 Internal Cooling Device 30, 30 'Chain (or Wire) 31 Cooling Ring 32 Air jet ring 33 Cooling water pipe 34 Air pipe 35 Guide roller 36 Guide block 37 Telescopic cylinder 38 Coil movement control encoder 39 Servo motor 40 Pusher movement control encoder 41 Rack 42 Inner cooling device movement amount measurement encoder 43 Flange 44 welding

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takashi Kurita, 2-5-13 Sanno, Ota-ku, Tokyo Stock company Benkan (72) Inventor Masakazu Ishikawa 2-5-13 Sano, Ota-ku, Tokyo Stock association Within Benkan

Claims (5)

[Claims] 1. In the hot pipe bending process, the movement of the heating coil at the beginning and end of bending is measured by pressing a metal pipe whose pipe pushing side is closed by a pipe pushing device arranged on the same axis. , The inner cooling device arranged in the metal pipe is moved in synchronism with the movement of the heating coil, the metal pipe is heated by the heating coil, and the inner side cooling device and the outer cooling ring are used to move the inner side cooling device to the inner side. A hot tube bending method characterized by bending while cooling from the outer surface. 2. In the hot pipe bending process, the movement of the heating coil at the beginning and end of bending is measured by pressing a metal tube whose tube pushing side is closed by a tube pushing device arranged on the same axis. , Moving the inner surface cooling device arranged in the metal pipe in synchronism with the movement of the heating coil, and heating the metal pipe by the heating coil with a constant distance to the heating coil of the inner surface cooling device during bending. A method for bending a hot tube, characterized in that the inner tube cooling device and the outer tube cooling ring are bent while cooling the tip end adjacent to the heating zone from the inner and outer surfaces. 3. A rotation equipped with a pipe pushing device connected to a closed rear end of a metal pipe to be bent and arranged on the same axis as the metal pipe, and a clamp for gripping a front end portion of the metal pipe to be bent. A flexible bending arm, a guide roll that guides the metal pipe to be bent in the axial direction, a heating coil that heats the bent portion of the metal pipe in a narrow annular shape from the outside in front of the guide roll, and the heating coil With an outer surface cooling ring that cools the end adjacent to the heating zone, and a chain or wire that is provided in the metal tube so as to be movable in the axial direction and is led out of the metal tube, and fixed to the wire or chain by a telescopic cylinder. In a hot pipe bending apparatus comprising an inner surface cooling device loaded with tension, an encoder for coil movement control is attached to the heating coil, and the inner surface cooling device is attached. Attach a servo motor to the front part of the, and measure the moving amount of the heating coil at the beginning and end of bending of the metal tube with the coil movement control encoder, and based on the measured value, servo the front part of the inner surface cooling device. A hot pipe bending apparatus characterized in that it is moved synchronously with a heating coil by a motor. 4. A rotation equipped with a pipe pushing device connected to the closed rear end of a metal pipe to be bent and arranged on the same axis as the metal pipe, and a clamp for gripping the tip of the metal pipe to be bent. A flexible bending arm, a guide roll that guides the metal pipe to be bent in the axial direction, a heating coil that heats the bent portion of the metal pipe in a narrow annular shape from the outside in front of the guide roll, and the heating coil With an outer surface cooling ring that cools the end adjacent to the heating zone, and a chain or wire that is provided in the metal tube so as to be movable in the axial direction and is led out of the metal tube, and fixed to the wire or chain by a telescopic cylinder. In a hot pipe bending apparatus comprising an inner surface cooling device loaded with tension, an encoder for coil movement control is attached to the heating coil, and the inner surface cooling device is attached. Attach a servo motor to the front part of the, and measure the moving amount of the heating coil at the beginning and end of bending of the metal tube with the coil movement control encoder, and based on the measured value, servo the front part of the inner surface cooling device. The motor is moved synchronously with the heating coil, the pusher movement control encoder is attached to the pusher of the pipe pushing device, a chain or wire is separately stretched in the metal pipe on the inner surface cooling device, and the inner surface cooling device is attached to the rear end fixing portion. An encoder for moving amount measurement is installed to measure the expansion / contraction amount of the chain or wire with the encoder for moving amount measurement of the inner surface cooling device during bending of the metal pipe, and between the amount of pipe pushing measured by the pusher control encoder. When there is a difference in temperature, the front part of the internal cooling device is moved by the servo motor to keep the distance from the heating coil constant. Hot tube bending device, characterized in that as. 5. The hot water pipe bending apparatus according to claim 3, wherein the inner surface cooling device has a cooling ring for injecting cooling water at the tip, and immediately after that, the cooling water flows backward in the metal pipe. It has an air blowout ring that pushes out to the front, these pipes are made into a cable bearer system and led out to the outside in the vicinity of the closed part of the metal pipe, and the moving device connected to the rear guide block is a telescopic cylinder A hot pipe bending device.