JPS62230430A - Method and device for bending metal pipe - Google Patents

Abstract

PURPOSE:To correctly and easily perform a small radius bending without using the deformation preventing means of a core metal and guide body, by making the heating temp. at the pipe inner face side a higher temp. than that of the innerface side at the bending inner peripheral side and by making the heating temp. and heating width at the bending outer peripheral side lower and narrower than those of the bending inner peripheral side. CONSTITUTION:A pipe 11 is advanced by starting a heating and cooling after setting a high frequency inductor 22 at the prescribed position inside the pipe 11 and a cooling ring 28 at the prescribed position outside the pipe 11, by holding the tip of the metal pipe 11 to be bent with the clamp jig 16 of a bending arm 12. Since the high frequency inductor 22 is heated so that the pipe outer face side become lower than the pipe inner face side on the pipe wall at the bending inner peripheral side of the pipe 11 an irregular deformation can be avoided. At the bending outer peripheral side the heating temp. is kept lower and the heating width is made narrower within the allowable range compared to the inner peripheral side, so the pipe wall becomes difficult to be deformed, the thickness reduction amount is reduced, the flattening is reduced as well and the bend pipe having smooth thickness increasing part is obtainable.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and apparatus for continuously bending straight pipes such as steel pipes, and in particular to bending with a small bending radius (hereinafter referred to as 11).
This invention relates to a bending method and apparatus suitable for bending.

[Conventional technology]

Conventionally, among various types of piping, elbows are often used especially for parts with small bending radii. When using an elbow, there will naturally be more joints when assembling the piping, and the accuracy of the joints will be reduced.

In order to obtain a highly reliable joint in terms of welding posture direction, etc., advanced technology is required, and there are many disadvantages in terms of construction time and cost.

To solve this problem, it may be possible to directly bend a part of the straight pipe itself with a straight bending radius and omit the joint required in the case of an elbow.

By the way, conventionally, as shown in FIG. 3, a metal tube l is inserted into an annular heating device 2 such as a high-frequency inductor equipped with a means for injecting a cooling liquid 3, and its tip is centered around a fulcrum 0. The metal tube 1 is held by the arm clamp 5 on the bending arm 4, which rotates as the metal tube 4 moves forward, while the heating device 2 heats the metal tube 1 in a narrow annular shape. A method is known in which the bending deformation portion is fixed by causing the bending deformation to occur and immediately cooling the portion with cooling fluid 3.

Therefore, it is conceivable to form the above-mentioned small radius bent portion by this method.

[Problem that the invention seeks to solve]

However, in this method of bending and deforming the tube by applying a bending moment, as shown in FIG.

Portions of the same length in the straight pipe section A +, B r, C
After +3 bending deformation, it becomes Ag, Bz, Cz, tensile stress acts on the outer circumference of bend 1, thinning occurs, compressive stress acts on the inner circumference of bend 1, thickening occurs, and the overall shape is flat. become

Such thickening, thinning, and flattening increase as the bending radius becomes smaller. Furthermore, in order to prevent thinning on the outer periphery of bending, it is possible to apply compressive force to the pipe during bending, or to keep the temperature on the outer periphery of bending lower than that on the inner periphery so that it does not stretch much. , the amount of compression on the inner circumferential side of the bend increases accordingly. As a result of the above, irregular deformations commonly known as bulges, wrinkles, and bellows (hereinafter referred to as "irregular deformations") tend to occur on the inner circumferential side of bending. The bending radius is.

It is said that the limit is 1.5 to 2D (D is the outer diameter of the tube), and there is a problem in that some means must be taken to achieve a small R target such as that used for elbows.

As a method for solving this problem, the present applicant has previously proposed Japanese Patent Application Laid-Open No. 49-59067. The method disclosed in this patent application is a method in which a core metal and a guide body are provided inside and outside the tube, and heating is performed from the inner peripheral surface of the tube while changing the temperature distribution on the inner circumferential side of the tube and the outer circumferential side of the bent tube. In this method, a core bar and a guide body are installed oppositely inside and outside the pipe.

Irregular deformation mainly on the inner circumferential side of the bend is effectively prevented.

However, on the other hand, there is a lot of decay and wear, and the amount of heat transfer is also large, making it difficult to set the heating temperature, often making the deformation itself unstable, and therefore causing variations in quality. The problem remained that the system itself had a fairly complex configuration. Therefore, it is desirable to make a small radius target without using a core bar or a guide body.

The present invention was made based on these demands.

An object of the present invention is to provide a method and an 'A position that can accurately and easily set a small R target without using a means such as a core bar or a guide body that comes into contact with a metal tube and prevents unnecessary deformation. shall be.

[Means and effects for solving the problems] The present inventors:
The first findings were obtained by studying the characteristics and mechanism of irregular deformation that occurs on the inner circumferential side of the second bend when bending is performed using the conventional method shown in FIG. below.

The reason for this will be explained with reference to FIG. The heated zone of the metal tube l expands radially outwards due to thermal expansion.

Also, when starting the bending process, a forward force is applied to the pipe l,
In addition, as the bending arm moves, a compressive force in the tube axis direction acts on the tube 1, particularly on the inner circumferential side of the tube, and the easily deformable heating section is compressively deformed. Considering that the volume remains unchanged due to compressive deformation, it is natural that if the zero circumferential length expanded in other directions, that is, the circumferential direction and the thickness direction, becomes longer, the radius will increase proportionally. Therefore 1
At the beginning of bending, thermal expansion and compressive force cause the tube wall to bulge outward in the radial direction, ie, so-called barreling deformation, and therefore, the tube wall at the inner circumferential portion IA of bending also naturally bulges outward in the radial direction (
In other words, it bulges out (in the 0 direction of the bending center 9). On the other hand 7
Considering the progress of bending, the bulge in the direction of the bending center 0 results in shortening the bending arc and increasing the amount of compression in the axial direction of the two tubes. However, since the axial direction of the pipe has already been compressed due to bending, the amount of compression cannot be increased any further, and the pipe wall at the inner peripheral part of the bend is forced to move toward the center of the pipe, that is, the center of 2 bends is 0. It tries to expand in the opposite direction. In this way, on the inner circumferential side of the second bend, the tube, which was mainly deformed outward at the beginning of the bend, is dominated by a force that deforms the tube inward from the moment it is bent, but during this transitional period, the load condition becomes extremely unstable. Therefore, if there is some kind of trigger, the tube will turn over and the tube wall will be pushed inward. Accordingly, the stress state suddenly changes, the meat PJ fluctuation is suddenly accelerated, the heating situation becomes unstable, the pulsation of the tube wall is excited, and as a result, the above-mentioned irregular deformation occurs.

As a result of studies by the present inventors, it has been found that in order to prevent such irregular deformation, the heating width of the portion heated by the heating device and the cooling device to a temperature that allows undesired processing is extremely important. This heating width is too wide.

It is easy to cause buckling, denting, and unevenness, and if it is too narrow, it is easy to induce irregular deformation due to sudden and discontinuous deformation.
0° C. or higher), it has been found that the best value is usually about twice the thickness of the part concerned. Of course, the allowable range varies slightly depending on the bending radius of the heating surface 5, wall thickness, feeding speed, coefficient of thermal expansion, m property, etc., so it is necessary to set it appropriately in accordance with the actual situation. Therefore, in the present invention, the heating width on the inner circumferential side of the bend is set to an optimum width that does not cause irregular deformation when increasing the thickness.

Furthermore, in order to prevent irregular deformation, the outward bulge of the tube at the beginning of one bend should be suppressed as much as possible, and the tube wall should thicken inward as early as possible to reduce unstable loading conditions. I think it would be a good idea to do so. Therefore, 1. In the method of the present invention, 2.
The heating temperature on the bent inner tube wall is set so that the outer surface of the tube is lower than the inner surface of the tube. With such a temperature distribution, the rigidity of the outer surface of the tube is higher than that of the inner surface of the tube, and bulge toward the outer surface of the tube is suppressed.

From the initial stage of bending, the tube wall bulges mainly on the inner surface of the tube due to thickening, and thereafter deforms stably and smoothly, avoiding irregular deformation.

On the other hand, on the outer circumferential side of the first bend, the heating temperature is kept lower within an allowable range than on the inner circumferential side of the fifth bend in order to reduce the amount of thinning. When the heating temperature is lowered, the tube wall becomes less deformed (and does not stretch much even when tensile stress due to the bending moment acting on the tube is applied, which helps to reduce the amount of thinning.
Since compressive stress does not act on the inner bending side, it is not necessary to make this heating width the same as the optimum heating width on the inner bending side.On the contrary, the heating width on the outer bending side should be the same as the inner bending side. , the deformable area is too long.

It was found that the flatness of the tube increases. Therefore, in the method of the present invention, the heating width on the outer periphery of bending is shortened within the range that allows bending, thereby preventing flattening of the tube.

As described above, the method of the present invention is characterized in that the heating temperature on the inner surface of the tube is set higher on the inner circumference side of the bend than on the outer side, and the heating temperature and heating width on the outer circumference side of the bend are made lower and narrower than on the inner circumference side of the bend. This prevents thinning and flattening on the outer circumference side of the 0 bend and prevents irregular deformation on the inner circumference side of the 9 bend.
This allows for small radius bending.

In addition, if the thinning of the bent product is particularly severely restricted, the moving speed of the bent portion of the metal tube may be reduced by applying a brake on the rotation of the bending arm in the straight pipe portion that is not bent. A bending method is known that prevents thinning by regulating the moving speed to be lower than the moving speed of the material. In this case, the thickness increase on the inner circumferential side of the bending becomes even larger, which tends to cause irregular deformation such as wrinkles due to compression.The present invention is also applicable to this bending method, and the present invention is applicable. This makes it possible to prevent irregular deformation and obtain a bent pipe with less wall thinning. Note that as a method of regulating the moving speed of the bent part 1, it is possible to apply a braking torque to the bending arm 2, or to control the turning speed of the bending arm so that the moving speed of the bent part 2 is a predetermined value. It is also possible to restrict the movement speed of the bent part to a constant value by moving the straight part of the pipe before bending forward at a constant speed. Even if this occurs, the amount of deformation is regulated, so pulsation does not occur and irregular deformation can be prevented.

Furthermore, in general, when bending with a small radius, if the bending radius is changed all at once at the beginning and end of one bend, compression in the axial direction occurs rapidly, making it impossible to smoothly change the wall thickness.

Since this may cause irregular deformation, the bending radius should be changed gently at the beginning and end of bending. So-called blur bending is performed. The present invention is applicable to this case as well, and by applying the present invention, it becomes possible to easily obtain a bent tube with a particularly small bending radius and a good shape.

The apparatus of the present invention for carrying out the above-mentioned method of the present invention includes: a drive device for moving the metal tube to be bent in the axial direction;

a heating device disposed inside the metal tube to locally heat the metal tube in an annular shape; and a heating device disposed outside the metal tube.

A cooling device that cools the metal tube in an annular shape by injecting a cooling medium onto the outer surface of the metal tube, a bending arm that can rotate by gripping the metal tube, and a bending arm that controls the rotation of the bending arm to bend the metal tube. and a rotation restriction device that makes the moving speed of the section smaller than the moving speed of the straight pipe section that cannot be bent.

The heating device has a characteristic of heating the bent inner circumferential side of the tube to a higher temperature than the bent outer circumferential side, and the heating device and the cooling device are each movable independently with respect to the metal tube, The apparatus is also characterized in that at least one of the bending parts is capable of changing an angle relative to the metal pipe.

As described above, by arranging the heating device inside the tube and the cooling device outside the tube, it becomes possible to heat the inner surface of the tube to a higher temperature than the outer surface of the tube on the tube wall on the inner peripheral side of the second bend. Further, by making it possible to change the angle of at least one of the heating device and the cooling device with respect to the metal tube, the heating widths on the inner circumferential side of one bend and on the outer circumferential side of one bend can be adjusted independently. This results in 9 bends on the inner circumference side.

The outer peripheral side can be individually set to a desired suitable heating width. The turning control device keeps the moving speed of the bent portion of the pipe lower than the moving speed of the unbent straight pipe portion (1) to keep the heated portion of the pipe compressed and (2) prevent thinning during bending. . Furthermore, by making the heating device and the cooling device movable relative to the metal tube, both can be moved synchronously at the start of one bend and at the end of bending.

By changing the bending deformation position with respect to the center of rotation of the bending arm, it is possible to perform blurred bending in which the bending radius gradually changes.

〔Example〕

A preferred embodiment of the present invention shown in one drawing will be described below.

FIG. 1 is a plan view showing a bending apparatus according to an embodiment of the present invention. In the figure, 11 is a tube to be bent, and its rear end (upper end in the drawing) is held by a tailstock (not shown) so that it can be moved forward in the axial direction. 12 is a bending arm for imparting a bending moment to the pipe 11, which includes a vertical arm post 13, an arm boss 14 rotatably held by this arm post 13, an arm main body 15 fixed to this arm boss 14, and this bending arm. It consists of a clamp jig 16 that is held by the arm body 15 and grips the pipe 11, a hydraulic cylinder 17 that opens and closes the clamp jig 16, and the like. A brake hydraulic system Tl l 9 is connected to the arm boss 14 via a wire. This brake hydraulic system ff119.

When the bending arm 6 is turned from the position shown by the solid line to the position shown by the two-dot chain line due to the advancement of the pipe 11, the turning speed of the bending arm 6 is regulated, and the pipe is compressed and held by the necessary amount to reduce the thickness of the outer circumference of the bending. The rate is regulated to a desired value. Reference numeral 20 denotes a guide roller that regulates the moving position of the tube 11.

22 is a high-frequency inductor disposed inside the tube 11 and heats the tube 11 locally in an annular manner; 23 is a lead wire of the high-frequency inductor 22; 24 is a cooling pipe; and 25 is a support that holds the high-frequency inductor 22. , 26 is support 1-. Support 2
An inductor moving device (not shown) for moving the support 26 in the axial direction is connected to the rear end of the support 6.
The high frequency inductor 22 is moved within the tube 11 in the axial direction of the tube 11.
It is possible to move. The high-frequency inductor 22 is arranged approximately parallel to a line OX passing through the rotation center 0 of the bending arm 6 and perpendicular to the straight pipe portion of the tube 11, and its heating characteristics are such that the inner circumference side of the bending of the tube 11 is on the outer circumference side of the bending. The temperature is set to be higher than that of the 28 is a cooling ring placed outside the tube 11. The cooling ring 28 cools the tube in an annular manner by injecting a cooling liquid onto the outer surface of the tube, and the injection lines of this cooling liquid are indicated by symbols a and b in the figure. As shown in FIG.
The vicinity of the bent outer periphery of is rotatably held by a support shaft 30 provided on the support body 29.

Sleeve 31 held near the bending inner circumference by support body 29
It is held on a shaft 32 that can be slid on. Therefore, the shaft 32
By sliding the i! on the sleeve 31 and fixing it at an appropriate position, the cooling ring 28 is rotated about the support shaft 30, and the cooling i! The angle of inclination of the pipe 1228 and the high frequency inductor 22 can be set arbitrarily. Furthermore, cooling ring 2
A driving device (not shown) for moving the support 29 along the straight pipe portion of the pipe 11 is connected to the support 29 holding the pipe 8.

Next, the bending operation of the metal tube by the bending device will be explained. A metal tube 11 to be bent is passed between guide rollers 20 as shown in FIG. 1, its tip is held by a clamp jig 16 of a bending arm 12, and its front and rear ends are held by a tail stock. The high frequency inductor 22 is set at a predetermined position within the tube 11, for example, at a position slightly shifted from the straight line oX in the front and rear end directions, and the cooling ring 28 is set at a predetermined position outside the tube 11. As shown in an enlarged view in FIG. 2, the center position of the cooling ring 28 is such that the cooling wire a is injected near the heated part by the high-frequency inductor 22 on the outer circumference side of the bend of the tube 11, and In this case, the cooling line is set to be injected at a position slightly away from the heating section by the high-frequency inductor 22. tube 11
The spraying position of the cooling line for the 3rd bend determines the cooling position of the tube 11, or in other words, the heating width of the tube 11, so it is set to be optimal for both the outer circumference side and the inner circumference side of the third bend. . A portion 11a indicated by hatching in FIG.
llb indicates a heating range in which bending deformation is possible. After setting the high frequency inductor 22 and the cooling ring 2 accurately at the predetermined positions, heating by the high frequency inductor 22 and injection of coolant from the cooling ring 28 are started, and the braking force by the braking hydraulic device 19 is applied to the bending arm 12. In the activated state, the tube 11 is advanced.

As the tube 11 moves forward, the first bending arm 12 pivots around the pivot center O, imparting a bending moment to the tube 11.

Since the tube 11 is heated to a temperature at which it can be locally deformed into an annular shape by the high-frequency inductor 22, the heated portion lla
.
As step 1 progresses, bending is performed continuously.

Here, the high frequency inductor 22 heats the bent inner wall of the tube 11 so that the outer surface of the tube is lower than the inner surface of the tube. Therefore, the rigidity of the outer surface of the tube becomes higher than the rigidity of the inner surface of the tube, and when the tube wall increases in thickness due to the compressive force acting on the tube wall on the inner peripheral side of the tube, bulge toward the outer surface of the tube is suppressed.

From the initial stage of bending, the tube wall bulges mainly on the inner surface of the tube.

After that, it deforms stably and smoothly, avoiding irregular deformation. Moreover, since the position of the cooling wire at this time is set to a position that ensures the desired heating width, smooth deformation is performed from this point as well. On the other hand, on the outer circumference side of bend 1, the heating temperature is kept lower within the allowable range than on the inner circumference side of bend 3,
The heating width is narrowed. This makes it difficult for the tube wall to deform, reducing the amount of thinning and causing less flattening (thus, a bent tube with less thinning and a smooth thickened portion can be obtained).

In addition, in the above embodiment, the high frequency inductor 22 and the cooling ring 28
In the above example, the high frequency inductor 22 and the cooling ring 28 are moved along the pipe 11 at the start and end of bending. In other words, by changing the deformation position of the tube with respect to the turning center 0, it is also possible to perform blurred bending in which the bending radius changes continuously. By performing such blurred bending, bending with a smaller radius becomes possible. Furthermore, in the above embodiment, the cooling ring can be tilted, and the position of the cooling line can be adjusted to set the heating width to the optimum value on the inner and outer circumferential sides of the tube. The high frequency inductor placed may be made to be inclined with respect to the tube 11, and the heating width may be adjusted by the inclination of the high frequency inductor.

Further, in the above embodiment, the pipe 11 is moved forward and the bending process is performed by applying a bending moment using a bending arm that rotates around a fulcrum O fixed in a fixed position, but the method of the present invention is limited to this. Instead, the tube 11 is fixed in place and the high frequency guide 22. Cooling ring 281 bending arm 12
It is also applicable to a bending method in which the entire tube 11 is moved along the pipe 11.

EXAMPLE Using the bending apparatus shown in FIG. 1, bending was carried out under the following conditions, and the following results were obtained.

■Test tube material 5TP038 Diameter 216.3 mm Thickness Sch 40 ■Bending bending shuttle radius 2031- Bending angle 90' ■Bending conditions Bending speed 1.5 sm / See High frequency inductor and cooling ring position High frequency inductor Bending inner circumference Side -3 Dragon bending outer circumference side -31 ■ Cooling ring bending inner circumference side +5 as bending outer circumference side
-4 Dragon This numerical value was defined as + if the position of the front surface of each device was in the direction of advancement of the tube section with reference to the plane passing through the arm rotation center 0 and going perpendicular to the straight tube section, and - if it was in the opposite direction.

■Result wall thickness Before bending After bending Inner circumference of bending
8.2 19.3 Bend center part 8.2
10.2 Bending outer circumference 8.2 7.5 Diameter inside bending plane 217 208 Perpendicular plane 217 219 When the bent inner circumference side of the bent pipe obtained by bending was cut and the cross section was investigated, the cross section is shown in Fig. 5. It had a good cross section with no irregular deformation.

Comparative Example For comparison, a bending experiment was conducted using the conventional bending apparatus shown in FIG. 3, and the following results were obtained.

■Test pipe Same as above ■Bending radius Same as above ■Bending conditions Bending speed 1.5/Sec The high frequency inductor and cooling ring are of integral structure and are placed on the outside of the tube Location: Inner circumference of bend -41 Outer circumference of bend
-4m@ ■Result wall thickness Before bending After bending Inner circumference of bending
8.2 13-20 bend center part 8.2
9.9 Bending outer periphery 8.2 7.1 Diameter bending surface 217 201 to 209 same right angle surface
21? 220 When the bent pipe obtained by the bending process was cut at the inner peripheral side of the bend and its cross section was examined, it had the shape shown in FIG. 6, and large irregular deformations had occurred, especially at the bending start part A.

〔Effect of the invention〕

As explained above, the present invention provides a curved pipe with an excellent shape that can prevent excessive wall thinning, flattening, and irregular deformation when bending with a small radius, and can be applied to a variety of pipes.

The bent pipe produced by the present invention has the advantage of being of stable quality and being able to be produced economically, and can be suitably used in confined spaces such as chemical plants and power plants.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a bending device according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view showing the situation during bending by the device, and FIG. 3 is a typical conventional bending device. 2 is a plan view showing the processing device; FIG. 4 is an enlarged sectional view showing the situation during bending in the device; and FIG. FIG. 6 is a cross-sectional view of the inner circumferential side of a tube manufactured using a conventional bending device.

Claims (4)

[Claims] (1) Locally heating the metal tube to be bent into an annular shape,
In a method of bending the metal tube by applying a bending moment to the heating portion while moving the heating portion in the axial direction of the metal tube, and cooling the portion immediately after, the heating width of the heating portion may be adjusted to The inner circumferential side of the bend is made wider than the outer circumferential side of the bend, and the heating temperature of the heating section is set higher on the inner circumferential side of the bend than on the outer circumferential side of the bend, and further, the temperature of the tube wall on the inner circumference side of the bend in the heating section is set so that the inner surface A method for bending a metal tube, characterized by making the tube higher than the outer surface. (2) When applying a bending moment to the heating section to deform it, the moving speed of the bent portion of the metal tube is regulated to be lower than the moving speed of the unbent straight pipe portion. A method for bending a metal tube according to scope 1. (3) At the beginning of bending the metal pipe, the bending radius is gradually reduced from the straight pipe part, and at the end of the bending, on the contrary, the bending radius is gradually increased. Or the method for bending a metal tube according to item 2. (4) a drive device that moves the metal tube to be bent in the axial direction; a heating device that is placed inside the metal tube and locally heats the metal tube in an annular shape; and a heating device that is placed outside the metal tube. a cooling device that cools the metal tube in an annular shape by injecting a cooling medium onto the outer surface of the metal tube; a bending arm that can grip and rotate the metal tube; and a bending arm that restricts the rotation of the bending arm to bend the metal tube. a turning control device that makes the moving speed of the straight pipe portion smaller than the moving speed of the straight pipe portion that cannot be bent, and the heating device has a characteristic of heating the bent inner circumferential side of the pipe to a higher temperature than the bent outer circumferential side. A metal tube bending apparatus, wherein the heating device and the cooling device are each movable independently with respect to the metal tube, and at least one of them is capable of changing an angle with respect to the metal tube.