JP2524281B2 - Small R pipe bending method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to 3D
The present invention relates to a method for continuously bending a bend pipe with a bending radius R equal to or less than R, and particularly to a small R pipe bending method capable of accurately controlling the thickness reduction on the back side .

[0002]

2. Description of the Related Art In a method of bending a small R pipe having a diameter of 3DR or less, a number of techniques have been developed and a patent has been filed for a method of preventing wall thickness reduction on the back side, for example, Japanese Patent Publication No. 51-10834. As shown in the patent publication, compression bending with back pressure applied, first of all, equipment cost is expensive, and it is very difficult to control and bend while reducing the wall thickness while balancing the back pressure and the pressing force, It is not suitable for manufacturing with a simple machine, thus increasing the cost.

Further, as disclosed in Japanese Patent Publication No. 58-2727, in a method of cooling a band having an appropriate width at an appropriate distance on both circumferential sides from an outermost position (back side), an accurate reduction is required. It is difficult to set a target for meat ratio. (Because it does not satisfy the mechanical condition theoretically, there are many differences between the value obtained by the formula of the wall thinning rate shown in the patent gazette and the actually measured value.)

[0004] Japanese Patent Publication No. 2-53127 and Japanese Patent Publication No.
As described in JP-A-35609, in the method of lowering the processing temperature on the back side of the bent portion and increasing the processing temperature on the ventral side of the bent portion, an accurate relationship between the wall thickness reduction rate and the temperature distribution is used. Is not clear, and the processing accuracy is unclear.

[0005] As described above, in the conventional technique of high-frequency local heating bending, in the case of providing a temperature distribution in the circumferential direction and performing bending control on the back side, an accurate wall thickness reduction and temperature distribution (each deformation). However, a dynamic relationship with the resistance stress) is not required, and therefore, the relationship between the control method of the temperature distribution and the processing accuracy of the wall thinning rate has not been clarified. In addition, since an accurate tube thickness cannot be selected, there have been problems such as the necessity of using a thicker tube and the wall thickness falling below an allowable value and being defective.

[0006]

Accordingly, the present inventor has conducted intensive studies on how to accurately control the wall thinning rate on the back side of the bent portion, and found that the wall thinning rate was at the true bending deformation neutral position of the pipe. We found that it changed with movement. The present invention has been made by paying attention to this point. In manufacturing a bent tube of 3DR or less, it is possible to set an accurate wall-thinning rate, and it is possible to accurately select a wall thickness of a raw tube, and to reduce a wall thickness. It is an object of the present invention to provide a small R pipe bending method which does not cause a failure by dividing an allowable value.

[0007]

One of the small R pipe bending methods of the present invention for solving the above-mentioned problems is to heat the outer circumference of a straight pipe in a ring with a very narrow width in an annular manner to form a tube and a coil. Relatively moving, simultaneously gripping a part of the straight pipe, imparting a bending moment to the straight pipe around the pivot axis of the pivotable bending arm, and bending the bent pipe with a bending radius of 3DR or less. In doing so, a temperature distribution is set by dividing the temperature of the portion of the straight pipe to be subjected to high-frequency heating in an annular shape in the circumferential direction in advance, and an angle of a circumferential dividing point of the temperature distribution is set, and the temperature distribution is set. than the angle of circumferential dividing point of the deformation resistance stresses and temperature distribution in the divided position of, determine the true bending deformation neutral position theta _nu using the following equation (1), back from the true bending deformation neutral position theta _nu Side
Calculate the thinning rate, and then determine whether the thinning rate is the intended value
And if the intended value, the temperature distribution and
Adopt the division angle, and if the value is not intended, it is intended
The true bending deformation neutral position θ _{nu at} which the wall thinning rate becomes the same as above
Use the temperature distribution at that time and the division angle
Then, based on the temperature distribution adopted and its division angle,
At the bent side of the annular heating part of the tube, the coil is partially
Increase the magnetic flux density by approaching or partially
Increase the magnetic flux density by attaching a ferrite core
And the cooling nozzle behind the bend of the annular heating section of the pipe
Close or partially narrow the tube heating section
Or lower the magnetic flux density by moving the coil partially away from the tube
Then, after the temperature is lowered, the straight pipe is bent into a bend pipe. θ _nu = {− σ1 (θ2−θ1) − ‥‥‥‥‥ −σi−1 (θi−θi−1) + σi (θi + θi + 1) + σi + 1 (θi + 2−θi + 1) + ‥‥‥ + σn (θn + 1−θn)} / (2 σi) (1) where σi = 1, n: deformation resistance stress at a specific temperature (kgf / mm ² ) θi = 1, n + 1: angle (radian) at the circumferential division point shown in FIG.

Another one of the small R pipe bending methods of the present invention is as follows.
The outer circumference of the straight pipe is heated in an annular shape with a very narrow width in an annular manner, and the pipe and the coil are relatively moved. In applying a bending moment to a straight pipe and bending a bent pipe with a bending radius of 3DR or less, a target thinning rate on the back side is set in advance, and a true bending is performed based on the set thinning rate. The deformation neutral position θ _nu is determined, then the temperature of the portion of the straight pipe to be heated in a high-frequency manner is divided into several parts in the circumferential direction to set a temperature distribution, and the temperature of each of the divided portions is set to a predetermined temperature. , Then the true bending deformation neutral position θ _nu , the number of divisions of the temperature distribution,
The temperature of each part obtained by dividing, obtains the angle of the circumferential dividing point of the temperature distribution, after which the number of divisions of the temperature distribution, the temperature of each portion divided, based on the angle of the circumferential dividing point of the temperature distribution,
At the bent side of the annular heating part of the tube, the coil is partially
Increase the magnetic flux density by approaching or partially
Increase the magnetic flux density by attaching a ferrite core
And the cooling nozzle behind the bend of the annular heating section of the pipe
Close or partially narrow the tube heating section
Or lower the magnetic flux density by moving the coil partially away from the tube
Then, after the temperature is lowered, the straight pipe is bent into a bend pipe.

The two small R pipe bending methods of the present invention are as follows:
In any case, in bending a straight pipe into a bend pipe with a bending radius R of 3DR or less, the bending conditions are determined in advance, and the pipe is bent under the determined bending conditions to accurately control the thickness of the back side. The bending condition of the former small R pipe bending method is based on the following formulas (2) to (20) using the deformation resistance stress at the dividing position of the temperature distribution divided in the circumferential direction and the small area. The relationship between the circumferential division of the temperature distribution and the true bending neutral is obtained by solving the mechanical equilibrium condition of the force and the bending moment, and the relational expression (21) between the true bending neutral and the bend thinning is obtained. ) To the equation (24), the thinning rate of the small R bent pipe is correctly grasped. Therefore, based on the obtained bending conditions , that is, the temperature distribution and its division angle, the pipe ring
On the ventral side of the bent part of the shape heating section, use known means,
Increase the magnetic flux density by partially bringing the
Has a magnetic flux density by attaching a ferrite core partially to the coil.
Or raise the temperature, bending the annular heating section of the tube
On the back side, the cooling nozzle is
Close the heating section of the tube
The heat flux by lowering the magnetic flux density by partially moving the
By lowering the degree and bending the small R pipe,
Accurate wall thickness control can be performed. The balance of power from FIG.

[0010]

(Equation 2)

[0011] Here, each value is obtained by the following expression using the stress in FIGS.

[0012]

(Equation 3)

The temperature distribution is calculated from θ1 = θA = −π / 2 to θn.
+ 1 = θB = π / 2 is divided into n sections (FIGS. 1 and 3). Assuming that the temperature in that section is constant, the deformation resistance stress σ (θ) can also be treated as constant.

[0014]

(Equation 4)

[0015]

(Equation 5)

These are represented by θ1 to θ2, θ2 to θ3, and θ3 to θ.
Where the sum obtained by solving the integral equation by dividing the semicircle by n as 4,... Becomes zero (Equation 16), there is a deformation neutral position θ _nu of the bending deformation of the bend pipe. The inside of the bending radius from the deformation neutral position is a compressive stress, and the outside is a tensile stress.

[0017]

(Equation 6)

For example, for simplicity of explanation, as shown in FIG. 2, when n division is divided into three and θ _{n u} is solved, the equation (1)
Equation (20) is obtained from 8).

[0019]

(Equation 7)

Further, the deformation neutral position θ _nu and the _thickness reduction rate φ%
Relationship with is derived by the equation (21) (24).

[0021]

(Equation 8)

The bending condition of the latter small R tube bending method is calculated by the inverse calculation of the above method, that is, the integration of the above method (Equation 16).
Is obtained by completely solving That is, first, when the thickness reduction rate φ% is set, a true tune is calculated from the set thickness reduction rate φ.
Motomari neutral position theta _nu under deformation, then the temperature of the annular each moiety high frequency heating to a temperature of the portion set by the number divided in the circumferential direction and the division into the straight tube to a predetermined temperature,
Next, from the neutral position θ _nu of the true bending deformation, the number of divisions of the temperature distribution, and the temperature of each of the divided parts, the angle of the circumferential division point of the temperature distribution is calculated with respect to the temperature distribution two less than the number of divisions. Numerical analysis is performed by setting each angle range and moving the angle range in a range from −90 ° to + 90 ° so as to satisfy Expression (16).
The angle of the circumferential division point of the temperature distribution is determined. Based on the bending conditions obtained in this way, the number of divisions of the temperature distribution, the temperature of each divided part, and the angle of the circumferential division point of the temperature distribution , the annular shape of the pipe
On the ventral side of the heating section, use known means,
To increase the magnetic flux density by partially approaching the tube
Attach a ferrite core partially to the coil to reduce the magnetic flux density
Raise or raise the temperature and bend the annular heating section of the tube
On the back side, by known means, i.e. the cooling nozzle is partially
Close the pipe heating section or carp it
The magnetic flux density by moving the
By lowering the degree and bending the small R pipe,
Accurate wall thickness control can be performed.

[0023]

EXAMPLES Specific examples of the small R pipe bending method of the present invention will be described. First, the small R pipe bending method of claim 1
More, 12B, original schedule 40, STPG370
Example 1 shown in Table 1 was changed to a 2DR bent 90 ° bend pipe.
Treatment were processed adopted to 4 bending conditions, Rukoto have thinning ratio calculated from seeking modified neutral in the calculation as shown in the lower column of Table 1 and the measured thickness reduction ratio is matched very well Make sure
Was. The small R pipe bending method according to claim 1 is an embodiment in which n = 3, and the deformation resistance stress and the circumferential angle are shown in FIG.

[0024]

[Table 1]

Next, a raw pipe having the same size as that of the above embodiment is bent at the same 2DR bending angle of 90 ° by the small R pipe bending method according to claim 2 .
Examples 1 to 4 shown in Table 2 were used for processing into bend pipes.
It sets a target thinning ratio and dividing the processing temperature, as shown in, this
The angle of the circumferential dividing point of Rekara modified neutral position and the temperature distribution
After having determined, processing which is processed in the condition bending which was verify that the target thinning rate as shown in Table 2 and actual thinning rate after processing match very well. The above claim 1 and
In the small R pipe bending method 2, fine adjustment of temperature
While monitoring with a thermometer, move the coil
Adjusting the magnetic flux density by adjusting the distance between the coil and the pipe,
In addition, a mist of air and water is injected with a ring-shaped nozzle
This was done by cooling the hot part. As shown in FIG. 7, since the deformation resistance stress changes depending on the processing temperature, it is necessary to collect data for each material.

[0026]

[Table 2]

In the conventional small R pipe bending method, the tolerance of the wall thickness of the steel pipe is, for example, -12.5 in the case of a hot-finished seamless steel pipe of JIS G3454 carbon steel pipe for pressure piping.
%, Which is usually 5 to 5
Steel pipes reduced in thickness to 8% nominal wall thickness are common, and when this is bent as a raw pipe, the thickness reduction rate on the back side cannot be clearly controlled. Use, and in some cases the wall thickness
It could be bad.

[0028]

As described above, the small R pipe bending method of the present invention can precisely control the mechanical balance condition, so that the thickness reduction rate on the back side can be clearly controlled, and therefore, the accurate raw pipe wall thickness can be reduced. This eliminates the need to use a thicker tube as in the prior art, and eliminates the problem that the thickness is less than the allowable value.

[Brief description of the drawings]

FIG. 1 is a half cross section of a bend tube, where θA = θ1 is the ventral side and θB
= Θn + 1 represents the back side, and is a diagram showing the relationship between θ and deformation stress σ when divided into n.

FIG. 2 is a diagram illustrating a relationship between θ, deformation stress σ, and processing temperature T when a half circumference of a bend pipe is divided into three.

FIG. 3 is a view showing a bending cross section of a bend pipe, where ρ is a bending radius, and r is a thickness center radius of the pipe.

FIG. 4 is a side view showing a stress relationship at a pipe bending portion.

FIG. 5 is a cross-sectional view showing a stress relationship at a pipe bending portion.

FIG. 6 is a plan view of the high-frequency local heating tube bending device, showing the relationship between force and moment.

FIG. 7 is a graph showing the temperature dependence of the deformation resistance of SUS370 and STPG304.

(Equation 1)

Claims (2)

(57) [Claims] 1. An outer circumference of a straight pipe is heated in an annular manner with a very narrow width in an annular manner to relatively move a pipe and a coil, and at the same time, to grip a part of the straight pipe to turn a bending arm which can be turned. A bending moment is applied to the straight pipe about the axis, and a bending R of 3DR or less is applied.
In bending the bend pipe by using, in advance, the temperature of the portion of the straight pipe to be subjected to high-frequency heating is divided into several parts in the circumferential direction to set a temperature distribution, and the angle of the circumferential division point of the temperature distribution is set. set, than the angle of circumferential dividing point of the deformation resistance stresses and temperature distribution in the divided position of the temperature distribution, obtains a true bending deformation neutral position theta _nu using the following equation (1), in the true bend
From the deformation neutral position θ _nu , calculate the backside thinning rate, and then
Check whether this thinning rate is the intended value or not, and
In that case, the temperature distribution and its division angle are adopted as they are,
If the value is not intended, the true bending change will result in the intended thinning rate.
The shape neutral position θ _nu is obtained in the same manner as described above, and the temperature at that time is obtained.
Degree distribution and its division angle are adopted, and then the temperature part adopted
Based on the cloth and its division angle, the bent part of the annular heating part of the tube
On the side, increase the magnetic flux density by moving the coil partially close to the tube
Or partially attach the ferrite core to the coil
Increase the temperature by increasing the magnetic flux density, and the annular heating part of the tube
Behind the bent part of the pipe, the cooling nozzle is partially
Close the coil or partially cut the coil
After lowering the temperature by separating from the magnetic flux density,
A small R pipe bending method characterized by bending a straight pipe into a bent pipe. θ _nu = {− σ1 (θ2−θ1) − ‥‥‥‥‥ −σi−1 (θi−θi−1) + σi (θi + θi + 1) + σi + 1 (θi + 2−θi + 1) + ‥‥‥ + σn (θn + 1−θn)} / (2 σi) (1) where σi = 1, n: deformation resistance stress at a specific temperature (kgf / mm ² ) θi = 1, n + 1: angle (radian) at the circumferential division point shown in FIG. 2. A high-frequency heating of the outer circumference of a straight pipe in an annular shape with a very narrow width to relatively move the pipe and the coil, and at the same time, to grip a part of the straight pipe and to turn a bending arm which can be turned. A bending moment is applied to the straight pipe about the axis, and a bending R of 3DR or less is applied.
In bending into a bend pipe, a target thinning rate on the back side is set in advance, and a true bending deformation neutral position θ _nu is determined from the set thinning rate, and then the annular shape of the straight pipe is determined. The temperature of the part to be heated by high frequency is divided into several parts in the circumferential direction to set the temperature distribution, and the temperature of each divided part is set to a predetermined temperature. Then, the true bending deformation neutral position θ _nu , the temperature division number distribution, the temperature of each part obtained by dividing, obtains the angle of the circumferential dividing point of the temperature distribution, after which the number of divisions of the temperature distribution, the temperature of each portion divided, in the circumferential direction dividing point of the temperature distribution Based on the angle , the coil on the ventral side of the bend of the annular heating part of the tube
Partially close the tube to increase the magnetic flux density or
Attach a ferrite core partially to the coil to increase magnetic flux density
To raise the temperature to the back of the bend of the annular heating section of the pipe.
Now, let the cooling nozzle partially narrow the heating section of the tube
Move magnetic flux close or partially away from the tube
A small R pipe bending method comprising bending a straight pipe into a bend pipe after reducing the temperature by reducing the density .