JPH11221622A - Bending method in hot bender and hot bender - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of controlling a higher precise wall thinning rate about small radius bending by a hot bender such as a high frequency bender. SOLUTION: An annular heating part wherein bending is generated is divided into plural areas in its circumferential direction, and a temperature distribution about these respective areas is formed. For this purpose, an angular position βof a neutral axis about bending is obtained using not only deformation resistance correlating with a heating temperature but also the variation of thickness, a thrust and a compressing force as an important matter. And th division of the area (three divisions of e.g. -90 deg. to θ2 , θ2 to θ3 and θ3 to +90 deg.) is executed in the β position so that the temperature distribution for maintaining the neutral axis is obtd., and the temperatures T1 , T2 , T3 in these respective areas are set. By this method, the neutral axis is supposed with high precision. Consequently, bending with higher precision is efficiently executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a required thickness reduction ratio which is particularly problematic when a pipe is bent by a hot bender such as a high frequency bender with a small radius such as 3DR or less. Bending method and bender for controlling within range.

[0002]

2. Description of the Related Art Some techniques have already been proposed for a bending method intended to control a wall thinning rate when a small radius bending is performed by a high frequency bender which performs heating with an AC signal (alternating signal) of several hundred Hz to several thousand Hz. Are known. For example, JP
The representative methods are described in JP-A-3-135871, JP-A-55-144332 and JP-A-5-277571. Hereinafter, each of these methods will be sequentially described.

[0003] FIG. 17 is an explanatory diagram relating to this bending method disclosed in JP-A-53-135871. The pipe 82 to be processed needs to be locally heated by applying a bending force by a bending mechanism (not shown) while making the pipe 82 to be processed a narrow width annular by the heating coil 83 and applying a bending force by a bending mechanism (not shown). The bending process of a bend shape is performed. At this time, cooling water 85 is injected from the cooling jacket 84 provided on the entrance side of the heating coil 83 to the vicinity of the heating portion, thereby cooling the outside of the bend, that is, the portion having the largest bend radius on the back side. The aim is to reduce the wall thinning rate.
This method can reduce the wall thinning rate, but cannot set its target value accurately, and still has the problems that the wall thickness increasing rate becomes excessive. Although this is a structure common to general high-frequency benders, the heating coil 83 is formed of a single-turn conductor formed by processing a copper plate material into a ring shape, and the inside thereof is hollow, and there is a hollow inside. Cooling water is full. The cooling water 86 is used to quickly cool the heating section having a predetermined bend.

[0004] Bending method disclosed in JP-A-55-144332: FIG. 18 is an explanatory view of this method. Two cooling nozzles 88 at the entrance side of the heating coil (not shown),
Water is injected by 89 to cool the pipe 82. This cooling is performed with an appropriate width on each symmetrical part slightly shifted to the ventral side from the center point on the dorsal side. As a result, the neutral axis relating to bending deformation is biased to the back side, and the wall thinning rate can be reduced. However, the relationship between the degree of cooling and the position of the neutral axis, that is, the displacement of the angle is not considered. Therefore, in order to set a bending condition that gives a target wall thinning rate, it is necessary to rely on trial and error by trial bending.

FIG. 19 is an explanatory view of the bending method disclosed in Japanese Patent Application Laid-Open No. 5-277571, in which the cross section of the pipe at the heating portion is omitted for symmetrical halves. In this method, the annular heating portion is divided into a plurality of sections in the circumferential direction, and these sections have different temperatures to give a temperature distribution in the circumferential direction. The example in the figure is θ _A to θ
_2, and set the third area of theta ₂ through? ₃ And theta ₃ through? _B. And the temperatures T ₁ , T ₂ , T ₃ in each of these areas are:
These temperatures and the deformation resistance stresses σ ₁ , σ ₂ , σ _{3 of} each area and the true bending deformation neutral position (the position of the neutral axis expressed as an angle)
From the relational expression with θ _nu , the target thinning rate is obtained,
The temperature distribution is set based on the obtained temperatures T ₁ , T ₂ , and T ₃ . Therefore, according to this method, the relationship between the temperature distribution and the neutral axis can be inferred by calculation, and therefore, the accuracy of the wall thinning rate control can be improved as compared with the above methods. However, when actually tested by this method, there are many cases where there is a considerable error between the calculated thinning rate and the actually measured thinning rate. That is, although the relationship between the temperature distribution and the neutral axis can be estimated by calculation, the accuracy is not sufficient.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has been described in detail with respect to a small radius bending by a hot bender such as a high frequency bender. The purpose is to provide methods and vendors that allow control.

[0007]

SUMMARY OF THE INVENTION According to the present invention, an annular heating section having a predetermined width is formed by heating a pipe to be bent which is sent out with a predetermined thrust by a feeding mechanism by a heating means from the outer periphery thereof. A bending method in a hot bender configured to perform a bending process of a predetermined shape by continuously repeating generation of bending in the annular heating unit by a bending force applied by a bending mechanism; The neutral axis is determined from the balance of the forces at thickness, thrust, compressive force, and deformation resistance as requirements, and the temperature distribution in the circumferential direction of the annular heating section is given so as to maintain this neutral axis, thereby reducing bending. A bending method characterized by controlling a wall ratio is disclosed.

Further, according to the present invention, an annular heating portion having a narrow width is formed on a pipe to be bent which is sent out with a predetermined thrust by a sending-out mechanism by heating means from the outer periphery thereof, and is added by a bending mechanism. In a bending method in a hot bender configured to perform a bending process of a predetermined shape by continuously repeating the generation of a bend in the annular heating portion by a bending force, the annular heating portion is moved in a circumferential direction thereof. It shall be divided into a plurality of sections, and a temperature distribution shall be formed for each of these sections, and the thickness, thrust, compressive force and deformation resistance in each of the sections from the balance of the forces in the annular heating section, and the neutral axis shall be Bending method characterized by controlling the wall thinning rate of a bent portion by giving a zone division and a temperature distribution so as to maintain the neutral axis. Is disclosed.

Further, the present invention provides a feeding mechanism for feeding a pipe to be bent by a predetermined thrust, a heating means for forming an annular heating portion having a predetermined width by heating from the outer periphery thereof, and a heating device for forming the annular heating portion on the annular heating portion by a bending force. A bending mechanism that causes bending, and in a hot bender that performs bending processing of a predetermined shape, the annular heating is performed so as to maintain a neutral axis determined as a requirement of thickness, thrust, compression force and deformation resistance. A hot bender characterized by comprising control means for controlling the temperature distribution in the circumferential direction of the section is disclosed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic concept of the present invention will be described first. The above-described conventional method of estimating the wall thinning rate computationally (the method disclosed in Japanese Patent Application Laid-Open No. 5-277571) is effective in principle to increase the accuracy of the wall thinning rate control. However, as mentioned above, conventional methods, when tested on them, do not actually provide much more stable control. Therefore, the inventors of the present application have repeatedly studied the cause. As a result, the displacement of the neutral axis involves not only the deformation resistance, which is an element for obtaining the neutral axis by the conventional method, but also the thickness change and thrust in each area and the compressive force in the case of compressive bending. It was also found that these contributions were not negligible.

[0011] The present invention has been obtained by such research, and determines not only the deformation resistance correlated with the heating temperature but also the thickness change, the thrust and the compression force, and maintains the neutral axis. The feature is that the area is divided and the temperature of each area is set so as to have a temperature distribution.

More specifically, the bending method according to the present invention comprises:
A pipe having a narrow width is formed on the pipe to be bent, which is sent out with a predetermined thrust by the sending mechanism, by heating from the outer periphery of the pipe by a heating means, and the bending force applied by the bending mechanism is applied to the annular heating section. This is a method used for a hot bender adapted to perform a bending process of a predetermined shape by continuously repeating generation of a bend, and the annular heating unit is divided into a plurality of sections in a circumferential direction thereof. In addition, a temperature distribution is formed for each of these sections, and a neutral axis is obtained from the balance of the forces in the annular heating section on the basis of the thickness, thrust, compressive force, and deformation resistance in each section as requirements. It is characterized in that the wall thickness reduction of the bent portion is controlled by giving the division of the area and the temperature distribution to keep.

[0013] As described above, the position of the neutral axis is determined based on not only the deformation resistance but also the thickness change, the thrust and the compressive force, so that the calculation of the wall thinning rate correlated with the position of the neutral axis. The estimation can be performed with extremely high accuracy, and at the same time, the division condition of the temperature area that gives this thinning rate and the way of the temperature distribution in the area set thereby can be obtained with high accuracy and calculation. As a result, it is possible to accurately determine the processing conditions according to the required bending specifications by simulation by calculation, and it is possible to more efficiently perform bending with higher accuracy.

When bending a pipe using, for example, a high-frequency bender using the bending method according to the present invention, it is important to determine the number of divisions of the area in the annular heating section. It can be said that the greater the number of divisions, the higher the control accuracy can be. However, considering the ease of controlling the temperature of each area and the complexity of calculating the neutral axis, the number of divisions is appropriate if three divisions are appropriate. Here, the pipe to be processed is a line segment connecting the center point on the ventral side (the position where the bending radius is the smallest on the ventral side) and the center point on the back side (the position on the back side where the bending radius is the largest). Is symmetrical with respect to. Therefore, when the division number of the area is, for example, three divisions, it is counted with respect to one of the symmetry.

The following is a more specific description of such a three-division system. -90 ° the center point of the ventral, as + 90 ° to the center point of the back side, -90 ° through? _2, theta ₂ ~
The areas of θ ₃ and θ ₃ to + 90 ° and the temperatures of these areas are set in one symmetric region with a symmetric line connecting the ventral center point and the dorsal center point therebetween, and the other symmetric region It is assumed that each area and each temperature are set so as to be symmetrical to this. First, the required position of the neutral axis is obtained from the following equation (Equation 3) with respect to the required wall thinning rate D by the angle β.
Next, θ ₂ and θ ₃ and the temperatures T ₁ , T ₂ ,
Setting a provisional value for T ₃ , obtaining the angle β _x of the neutral axis by the following equation (Equation 4) with respect to this value, and comparing the β _x with the angle β of the neutral axis are represented by β _x Is repeated until β and β coincide with each other, and θ ₂ , θ _{3 and} T ₁ , T ₂ , and T ₃ in the case of coincidence are set as control setting values.

(Equation 3)

(Equation 4)

However, in each equation, n = ρ ₀ / 2r
([Rho ₀ is the bending radius, r is the radius to the center thickness of the processing target of the pipe), S ₁ is the deformation resistance in the region -90 ° ~θ _2, S ₂ is the deformation resistance in the area θ ₂ ~θ _3, S ₃ is the area θ
Deformation resistance at ₃ to + 90 °, t ₁ is the area −90 ° to β
(beta <theta case ₂₎ or _{-90 ° ~θ 2 (θ 2 <} β ≦ θ
Pipe thickness at ₃ cases), t ₂ is the area β~θ ₂ (β
<For theta ₂₎ or theta case _{2 ~β (θ 2 <β ≦} θ 3)
Pipe thickness at, t ₃ is zone _{θ 2 ~θ 3 (β <θ} 2
) Or the thickness of the pipe in β to θ ₃ (when θ ₂ <β ≦ θ ₃ ), t ₄ is the thickness of the pipe in the area θ ₃ to + 90 °, and K _p is a multiple of the compressive force to the thrust.

The derivation of the above equation (Equation 4) will be described below. FIG. 1 shows the relationship between the temperature section and the angle β of the neutral axis in the case of three divisions in the bending cross section at the time of bending, by the angle β.
Is smaller than the temperature zone θ ₂ (β ≦ θ ₂ ). However, only one symmetric region (−90 ° to 90 °) is shown, and the other symmetric region is omitted. -90 ° ~
theta _2, the temperature of each zone is divided into three theta ₂ through? ₃ and theta ₃ to 90 ° and _{T 1, T 2, T 3} , S 1 the deformation resistance that correlates to these temperatures, S _2, and S _3. The thickness of the pipe in the bend section, as also divided requirements neutral _{axis, -90 ° ~β, β~θ 2,} θ 2 ~θ 3 and theta ₃ to 9
It is assumed to be different in each area of 0 °, and the respective average thicknesses are t ₁ , t ₂ , t ₃ , and t ₄ (not shown in the figure).

FIGS. 2A and 2B show the relationship between the axial load F and the moment M in the bending cross section, respectively. FIG.
(A) is a case of bending by a rotating arm type hot bender, in which a pipe 11 to be processed is sent out from the left side to the right side in the axial direction with an axial load F, and the pipe 11
The turning arm 14 gripping the tip of the turning means turns around the turning center 15 to perform a bending process with a bending radius ρ ₀ . R ₁ , R ₂ and R ₃ in the figure are support rollers for supporting the feeding of the pipe 11. The hatched portion 12 of the moment M is a locally heated local softening zone. A force F corresponding to the axial load F acts on the turning center 15 from the right to the left, and a bending moment M is generated in the locally softened region 12.

On the other hand, FIG. 2B shows a case of bending using a hot bending bender of a pressing and bending roller type. The pipe 11 to be processed is sent out from the left side to the right side in the axial direction with an axial load F, and the pressing is performed. The load F corresponding to the axial load F of the bending roller 10
Is given from the right to the left while moving along a predetermined trajectory, thereby performing a bending process with a bending radius ρ _{0 about} the bending center 13. Thereby, a bending moment M is generated in the locally softened region 12.

FIG. 3 shows the relationship between the bending cross section and the deformation resistance, stress distribution and strain distribution therein. (A) is a bending cross section similar to FIG. In addition to the neutral axis (angle β) considering the thickness change, thrust, compression force and deformation resistance, the neutral axis (angle β _dt ) due to the thickness change and deformation resistance when the axial load F = 0 is shown. is there. (B) shows deformation resistance. In this example, since the area between θ _{2 and} θ ₃ is cooled to a cold working temperature, the deformation resistance S ₂ is remarkably increased. (C) shows the stress distribution when the axial load F = 0, and the neutral axis is at the position of the angle β _dt . M ₀ is the bending moment when the axial load F = 0. (D) is the axial load F = 2F ₃
And the neutral axis is at the position of the angle β. M is a bending moment when the axial load F is acting. (E) shows a strain distribution. The tension side is reduced in thickness,
The compression side increases in thickness.

Assuming the above relationship, first, β ≦
for the case of theta _2, determining the angle β of the neutral axis from the balance of the total force. The relationship between the axial load F and the bending moment M ₀ is given by Equation (Equation 5) and Equation (Equation 6).

(Equation 5)

(Equation 6)

Here, _Sf is the deformation resistance, and Z is the section modulus. The section modulus, if the average thickness of at radius r of the circular pipe is t _f, assuming _{t f / 2r ≒ 0, Z} ≒ 0.
8 (2r) ² · t _f = 3.2 r ² t _f

Here, if n = ρ ₀ / 2r (= ρ ₀ / D), the equation (Equation 7) is obtained.

(Equation 7)

FIG. 4 shows the relationship between the temperature axis and the neutral axis due to the change in thickness and the neutral axis due to the axial load in the bending cross section. beta _t is the angle of the neutral axis due to the change in thickness, beta _f the angle of the neutral axis by the axial load (thrust), deformation resistance between the S _f is beta _t and beta _f, the t _f are beta _t and beta _f The average thickness between. S _f = S ₁ (see FIG. 1), t _f = (t ₁ + t ₂ + t
₃ + t ₄ ) / 4, the equation (Equation 7) becomes as follows.

(Equation 8)

[0025] Here, considering the case of adding a compressive force against the axial load F for bending compression, when a multiple clogging compression / thrust compressive force on the thrust and K _P, equation (8) It looks like this:

(Equation 9)

On the other hand, from the deformation resistance corresponding to the axial load, the change in thickness, and the heating temperature, the balance of the force is represented by the following equation (Equation 10).

(Equation 10)

By rearranging the equations (Equation 10) and the equation (Equation 9), an equation relating to the angle β of the neutral axis corresponding to the equation (Equation 4) is obtained.

[Equation 11]

In the bending method according to the present invention, the neutral axis is determined on the basis of the thickness, the thrust, the deformation resistance and the compression force as described above. For this reason, the angle β of the neutral axis determined is the angle β _t of the neutral axis due to the change in thickness, the angle β _f of the neutral axis due to thrust, the angle β _d of the neutral axis due to deformation resistance, and the angle β _{b of the} neutral axis due to compressive force. Can be represented by the synthesis of That is, the degree of contribution of each element to the neutral axis can be easily evaluated. This will be described below.

FIG. 5 shows the angle β _t of the neutral axis due to a change in thickness and the angle β of the neutral axis due to deformation resistance in the bending section.
_d , the angle β _f of the neutral axis due to the thrust, the angle β _b of the neutral axis due to the compressive force, and the relationship of the angle β of the neutral axis which is a composite of these. The relationship between these neutral axes and each neutral axis is represented by the following equations.

(Equation 12)

Β _t and β _d can be derived from the angle β _{dt of the} neutral axis due to the thickness change and the deformation resistance when the axial load F = 0. First, β _dt is the first term of the equation (Equation 11) and is represented by the following equation (Equation 13).

(Equation 13)

Β _t is the case where S ₁ = S ₂ = S ₃ in the equation (Equation 13), and is represented by the following equation (Equation 14).

[Equation 14]

Β _d is expressed by the following equation (Equation 15).

(Equation 15)

Β _f and β _b are included in the second term of the equation (Equation 11), and are respectively _expressed by the following equations (Equation 16) and (Equation 17).
It is represented by

(Equation 16)

[Equation 17]

Next, the derivation of the angle β of the neutral axis when θ ₂ <β ≦ θ ₃ will be described. Β in this case can also be obtained by the same concept as above, and the following equation (Equation 1)
8).

(Equation 18)

The angles of the neutral axes for synthesizing β are expressed by the following equations.

[Equation 19]

(Equation 20)

(Equation 21)

(Equation 22)

(Equation 23)

[0036] Here, in equation (20) from equation (18), t ₁ is the average thickness of up to -90 ° ~θ _2, t ₂ is theta ₂
The average thickness of up ~β, t ₃ is the average thickness of up β~θ _3, and t ₄ is the average thickness of up to theta ₃ to 90 °.

Β and the wall thinning rate determined as described above,
FIG. 6 shows the relationship between the wall thickness increase rate and the cold area processing rate.
It will be described based on. The distance a in the bending center direction between 0 ° and β in FIG. 6, the distance b in the bending center direction between β and θ _3, and the wall thinning rate D, the wall thickening rate C, and the cold work ratio K are as follows. Given by The cold working rate is applied when the bending temperature is lower than the crystal temperature of the metal, and is 725 ° C. or less in the case of carbon steel.

(Equation 24)

(Equation 25)

(Equation 26)

[Equation 27]

[Equation 28]

Here, from the above equation (26), the above equation (3) for obtaining the angle β of the neutral axis based on the wall thinning rate given as the required specification is obtained. Tables 1 and 2 where the above equations and matters related to their derivation are attached as FIG. 13 and FIG.
It is summarized in.

In the bending method of the present invention as described above,
There are three types of temperature distribution of the annular heating part in the pipe to be bent. One is high-low-from ventral to dorsal
Medium type. This type is applied to, for example, neutral axis bending described later. The other one is high from ventral to dorsal-
This type is a medium-low type, and is applied to, for example, SR effect bending and temperature difference bending described later. The remaining types have a uniform temperature distribution and are applied to isothermal compression bending and isothermal bending.

In order to carry out the bending method according to the present invention, a high frequency bender is usually used. As the high-frequency bender, any of a rotating arm type and a press bending roller type can be used. FIG. 7 schematically shows an example of a swing arm type high frequency bender.
Shown in This high frequency bender includes a pusher 7, a guide roller 8, a heating coil 9, a turning arm 14 that turns around a turning center 15 as a fulcrum, and an auxiliary cooling device 44.
In order to bend the pipe 11 to be processed by the high frequency bender, first, the tip of the pipe 11 is clamped by the turning arm 14. Then, in this state, the bent portion of the pipe 11 is heated annularly with a heating coil 9 in a narrow width of, for example, about several cm to form a locally softened region 12 that can be plastically deformed. The bending of the bending radius ρ ₀ is given to the local softening region 12 in combination with the turning operation of the arm 14, and the local softening region 12 is cooled immediately by injecting the cooling water 20. Thereafter, the same heating, bending operation, and cooling are repeated to perform bending to a predetermined bending angle.

Next, a heating coil and an auxiliary cooling device for setting the heating temperature and its distribution required in the bending method according to the present invention to the locally softened portion will be described. FIG. 8 shows FIG.
The relationship between the heating coil 9 and the auxiliary cooling device 44 in the high frequency bender is simply shown. The inside of the heating coil 9 is formed as a cavity 16, and the cooling water 20 filled therein is filled with the water injection hole 1.
Water is injected into the pipe 11 from 8 toward the outlet side of the heating coil 9 to cool the outlet side of the heating coil 9, that is, to rapidly cool the bent local softened portion. The heating coil 9
Is provided with a temperature sensor 21. The temperature sensors 21 are attached at a plurality of locations in the circumferential direction of the heating coil 9, measure the temperature at each location, and transmit the measured temperature to a control device (not shown). The control device controls the heating temperature of the heating coil 9 based on the temperature data, and performs control for setting each temperature in each section by cooling by the auxiliary cooling device 44 as shown in FIG. The auxiliary cooling device 44 includes a front cooling block 26, a middle cooling block 28, and a rear cooling block 30. The auxiliary cooling device 44 can be moved in the front-rear direction through the mounting portion 22 and the sliding rod 24 connected thereto. , Heating coil 9
It is attached to. Hereinafter, an example of properly using each cooling block in the auxiliary cooling device 44 will be described.

The rear cooling block 30 includes the auxiliary cooling device 4
The cooling water 42 is injected into the back side of the pipe 11 from the injection hole 36 toward the inlet side of the pipe 4. As shown in FIG. 9, the water injection range is, for example, 90 ° from the center point on the back side of the pipe 11, that is, the position on the back side where the bending radius is largest, to the ventral side.
Than the range of small angles theta _m and the angle theta _n also. In this example, θ _m = 50 ° and θ _n = 40 °, but these are changed according to the processing conditions.

The middle cooling block 28 includes the auxiliary cooling device 4
In the plane of 4, the cooling water 4
Fill with 0. As shown in FIG. 10, the water injection range is, for example, 90 ° to the ventral side from the central point on the dorsal side of the pipe 11 to cool the semicircle on the dorsal side. This range is also changed according to the processing conditions.

In the front cooling block 26, each of the cooling blocks 28 and 30 cools the entrance side and the surface of the auxiliary cooling device 44, thereby indirectly cooling the heating portion by the heating coil 9. Whereas the auxiliary cooling device 4
The cooling part 38 is directly cooled by injecting the cooling water 38 to the back side of the pipe 11 from the water injection hole 32 toward the outlet side of No. 4. For this reason, for example, 350
Mainly used when cooling to about ° C. As shown in FIG. 11, an example of the water injection range is a relatively narrow range centered on, for example, the position of the neutral axis at angles β and −β, and is an area between θ _{2 and} θ ₃ in FIG.

Here, the hot bending performed by applying the bending method according to the present invention depends on the temperature distribution condition and the presence or absence of compression.
For convenience, it can be divided into several bending types. Possible bending types include, for example, neutral axis bending in which the temperature of the neutral axis portion and its vicinity is set to a cold temperature (for example, 350 ° C.).
SR effect bending with a temperature distribution giving the SR effect (annealing effect), temperature difference bending giving a temperature distribution in a temperature range that does not cause the cold bending or SR effect, uniform temperature distribution with no temperature difference in each area There are isothermal compression bending in which compression is performed under conditions, temperature difference compression bending in which compression is performed in a temperature distribution condition within a temperature range that does not cause cold bending, and isothermal bending in which uniform temperature distribution is performed. Therefore, cooling (water injection) by each cooling block in the auxiliary cooling device 44 as described above,
It will be optimally used depending on the type of bending method.

Next, an example of the operation of the high-frequency bender to which the bending method according to the present invention is applied to the three-division method will be described with reference to the flowchart shown in FIG. Step 50
Then, as the data of the bending condition from the CAD data,
Read the bending radius, bending angle, wall thinning rate, etc. Then
Based on the read data, an optimum method is selected from the above-described bending method types while referring to a logic table (step 51). In step 52, a β value corresponding to the thinning rate required by the required specifications is set. This β value is calculated by the above equation (Equation 26) to Equation (Equation 3)
Can also be obtained from Next, at the temperature T _1, which is estimated to be optimal for the type of bending method selected in step 51,
Temporarily set T ₃ and temperature zones θ ₂ and θ ₃ (Step 5)
3). Then, in step 52, the set β and step 53
The neutral axis angle β calculated by the above equation (Equation 11) or Equation (Equation 18) using T _{1 to} T ₃ and θ ₂ and θ _{3 set} in the above.
_x is calculated (step 54). Note that the thicknesses t ₁ to t ₄ in Equation (Equation 11) and Equation (Equation 18) can be obtained by calculation from the required wall thinning rate and the wall thickness increasing rate obtained from the above β by Equation (Equation 27). Step compare 55 In this beta _x and the beta, to determine whether they are consistent. if,
If they do not match, the process returns to step 53, and T _{1 to} T ₃
, And recalculate by changing the set values for θ ₂ and θ ₃ .
If the set value and the calculated value match, the process proceeds to step 56.

In step 56, T _{1 to} T ₃ and θ ₂ , θ ₃ that give β _x coincident with β are determined as actual bending parameters. Then, these bending parameters are converted into NC language for actually controlling the device, and the data converted into NC language is stored as control data in a control table (step 57). In step 60, control of the high-frequency power supply, the heating coil, the auxiliary cooling device, the pusher, the turning arm, and the like is started based on the control data.

At the start of bending, as a preheating operation at the start of bending, the heating coil is moved over a range of about 6 ° to give a temperature gradient (step 61). During the bending process, while measuring the temperature with the temperature sensor 21 in FIG.
By controlling the heating coil and the auxiliary cooling device, the neutral axis is maintained at the angle β (step 62). In parallel with this,
By controlling the pusher and the turning arm, the bending is performed with a predetermined bending radius (step 63). During the bending process, a springback is detected at a necessary place, and if the required specification is exceeded, straightening control is performed (step 64).

In step 65, the bending angle is detected from the turning angle of the turning arm, and it is determined whether or not it has reached a predetermined angle, for example, 90 °. When the bending angle reaches a predetermined value,
At this time, the heating coil is moved over a range of about 6 ° in the same manner as at the start of bending to prevent the deformation at the bending end, so that the temperature gradient is moderated (step 66). . Then, in step 67, the operation of bending is completed.

Subsequently, after the heating coil is retracted, the processed pipe is unloaded by the unloading roller (step 6).
8). Finally, the processing data such as the temperature, bending angle, and bending radius displayed in real time on the status monitor is reflected in the control table, the logic table, the CAD data, and the like for the next and subsequent bending (step 69). ).

The above description of the operation has been made for the case where necessary calculations are performed each time. However, in addition to the above, for example, various various kinds of data sequentially accumulated based on the processing results obtained by applying the method according to the present invention. It is also possible to obtain the optimum processing conditions for the requested specifications from a list such as a table in which the data relating to the processing conditions are put together, and to perform the processing based on these. In some cases, it is also possible to perform all calculation simulations in advance with respect to various processing conditions and use the results in a list or the like.

[0052]

EXAMPLE FIGS. 15 and 16 show the results of the above-described bending method according to the present invention performed on a carbon steel pipe. The types of bending methods performed are neutral axis bending (indicated as neutral axis in the figure, symbol I) and SR effect bending (SR in the figure).
Effect and description, symbol II), temperature difference bending (temperature difference in the figure, symbol III), isothermal compression bending (compression in the figure, symbol IV), temperature difference compression bending ( Is described as pressure difference, symbol V) and isothermal bending (described as isothermal in the figure, symbol
VI). In addition, the evaluation listed in the figure indicates that if the required thinning rate is, for example, 12.5%, which is generally required, in relation to this thinning rate, the thinning that can be realized under each specific condition The degree of rate, the degree of cold working rate, and the required axial load capacity were evaluated. In other words, the quality of the evaluation is naturally different when the thinning rate is sufficient or when a smaller thickness is required.

Neutral axis bending (symbol I): cold bending (350 ° C.) in two areas near the neutral axis, and the working rate is 10%
(5% required for impact test). In the four examples listed in the table, the wall loss rate of -9.1% to -11.2% can be calculated. In these examples, the bend radius is 3
For r (bend DR = 1.5) and 4r (bend DR = 2),
In each case, the overall evaluation is indicated by a double circle mark, and in this double circle state, the overall evaluation is good.

SR effect bending (symbol II): 850 on the compression side
A quasi-SR effect is obtained by performing high-temperature bending at 950C to 950C and setting the tensile side to the SR temperature (620C in the case of carbon steel). Each example satisfies the thinning rate, but the cold working rate is 1
The overall rating is slightly good, with 2.1 to 13.6%. In other words, the cold working rate is unnecessarily high under the condition of the required thinning rate of 12.5%.

Temperature difference bending (symbol III): The recrystallization temperature (725 ° C. in the case of carbon steel) is set on the tensile side, and cold working or SR
Make a temperature difference in the temperature range where the effect is not obtained. For this reason, there is a limit to the temperature difference, and in the case of 1.5 DR bending (bending radius is 3r), the wall thickness reduction rate is 14.4%, and the overall evaluation is x (bad).

Isothermal compression bending (symbol IV): Compressive force magnification of 2
By setting it to ３3 times, even in the case of 1.5 DR bending, the wall thinning rate can be sufficiently satisfied. However, there is a disadvantage that the equipment becomes large because the axial load capacity is increased. Also, as the rate of increase in wall thickness increases, bumps occur on the bending compression side,
Flattening tends to occur. Therefore, assuming a target thinning rate of 12.5%, the overall evaluation is x (bad).

Temperature difference compression bending (symbol V): This method can minimize the wall thinning rate. Therefore, it is suitable especially when a small wall thinning rate is required, but may be the same as in isothermal compression bending. Assuming a target wall thinning rate of 12.5%, the overall evaluation is x (poor).

Isothermal bending (symbol VI): This method is the easiest to control, but it is applied to a bending less than 3DR unless the pipe is thickened under the assumption that the normally required target thinning rate is 12.5%. Can not. Therefore, the overall evaluation is x (bad).

In each of the above embodiments relating to each bending method type, a very good agreement is found between the calculated value of the wall thinning rate and the actually measured value. From this, it can be understood that the bending method according to the present invention is highly effective.

The example of division in the circumferential direction is representative of an example of three divisions or five divisions, but the number is not particularly limited. Also, there may be unequal division examples. Further, in addition to these discrete division examples, there may be a continuous temperature control method without division. Further, it goes without saying that the present invention can be applied to various members requiring wall thinning control other than the example of the pipe.

[0061]

As described above, according to the present invention, not only the deformation resistance according to the temperature but also the thickness change, the thrust and the compressive force are required to determine the angular position of the neutral shaft. A highly accurate neutral axis can be used as the basis for controlling the wall ratio. For this reason, it is possible to accurately predict the actual thinning rate according to the processing conditions, and to select the optimum bending method according to the required processing specifications and efficiently perform high-precision bending. it can. As a result, it is possible to contribute to a further improvement in quality in bending the pipe.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a relationship between a temperature zone and a neutral axis in a case of three divisions in a bending section.

FIG. 2 is an explanatory diagram showing a relationship between an axial load and a moment in a bending section.

FIG. 3 is an explanatory diagram showing a relationship between a bending cross section and deformation resistance, stress distribution, and strain distribution therein.

FIG. 4 is an explanatory diagram showing a relationship between a neutral axis and a shaft load due to a change in thickness and a temperature zone in a bending section;

FIG. 5 shows the angle of the neutral axis due to a change in thickness, the angle of the neutral axis due to deformation resistance, the angle of the neutral axis due to thrust, the angle of the neutral axis due to compressive force, and the angle of the neutral axis that is a combination of these angles. It is explanatory drawing which shows the relationship.

FIG. 6 is an explanatory diagram showing a relationship among a thinning rate, a thickening rate, and a cold section processing rate in a bent cross section.

FIG. 7 is a simplified plan view of a high-frequency bender that can be used in the bending method according to the present invention.

8 is a simplified cross-sectional view of a heating coil and an auxiliary cooling device in the high frequency bender of FIG.

FIG. 9 is an explanatory diagram of a cooling range on the inlet side of the auxiliary cooling device.

FIG. 10 is an explanatory diagram of a cooling range in the plane by the auxiliary cooling device.

FIG. 11 is an explanatory diagram of a cooling range on the outlet side of the auxiliary cooling device.

FIG. 12 is a flowchart illustrating an operation example of a high-frequency bender to which the bending method according to the present invention is applied.

FIG. 13 is a diagram showing a list of mathematical formulas and the like included in the bending method according to the present invention.

FIG. 14 is a diagram showing a list similar to FIG.

FIG. 15 is a table showing a list of data obtained by performing the bending method according to the present invention for various types.

FIG. 16 is a diagram showing a list similar to FIG. 16;

FIG. 17 is an explanatory view of one of the conventional bending methods.

FIG. 18 is an explanatory view of another conventional bending method.

FIG. 19 is an explanatory diagram of still another one of the conventional bending methods.

[Explanation of symbols]

Reference Signs List 7 Pusher (delivery mechanism) 9 Heating coil (heating means) 11 Pipe 12 Annular heating section 14 Revolving arm (bending mechanism) F Thrust β Angle of neutral axis θ Angle of boundary of area ₂ θ of boundary of area ₃

Continuing from the front page (72) Inventor Shiraishi Hachishu 3-2-2, Sachimachi, Hitachi, Ibaraki Prefecture Within Hitachi Engineering Services Co., Ltd. (72) Keisuke Tomino 3-2-2, Sachimachi, Hitachi, Ibaraki No. Within Hitachi Engineering Services Co., Ltd.

Claims (6)

[Claims] 1. An annular heating portion having a predetermined width is formed by heating a pipe to be bent, which is sent out by a sending mechanism with a predetermined thrust, from a periphery thereof by a heating means, and is formed by a bending force applied by a bending mechanism. In a bending method in a hot bender configured to perform a bending process of a predetermined shape by continuously repeating the generation of bending in the annular heating unit, the thickness from the balance of the force in the annular heating unit, Thrust,
It was found that the neutral axis was determined based on the compressive force and deformation resistance, and the wall thickness reduction rate of the bent part was controlled by giving the temperature distribution in the circumferential direction of the annular heating part so as to maintain this neutral axis. Characteristic bending method in hot bender. 2. A pipe having a narrow width is formed by heating a pipe to be bent, which is sent out with a predetermined thrust by a sending-out mechanism, from a periphery thereof by a heating means, and the bending force applied by the bending mechanism is used. In a bending method in a hot bender configured to perform a bending process of a predetermined shape by continuously repeating the generation of bending in the annular heating unit, the annular heating unit includes a plurality of sections in a circumferential direction thereof. And a temperature distribution is formed for each of these areas, and a neutral axis is obtained from the balance of the forces in the annular heating section, assuming the thickness, thrust, compression force and deformation resistance in each of the areas as requirements. The hot bender is characterized by controlling the wall thinning rate of the bent part by giving the area division and temperature distribution that maintain the neutral axis Under way. Wherein the center point of the ventral -90 °, as + 90 ° to the center point of the back _{side, -90 ° ~θ 2, θ 2} ~θ 3 and theta
The temperature of each zone of ₃ to + 90 ° and the temperature of each zone is set in one symmetric region sandwiching the symmetry line connecting the ventral center point and the dorsal center point, and The respective zones and the respective temperatures are set so as to be symmetrical. First, for the required thinning rate D, the required position of the neutral axis is obtained from the following equation (Equation 1) by the angle β, and then θ ₂ and It said sets the value of the temporary for the temperature T _1, T _2, T ₃ of each zone theta ₃ thereto, and determining the angle beta _x of the neutral axis by the following equation (equation 2) for this value, the this beta _x The comparison of the angle β of the neutral axis is repeated until β _x and β coincide, and θ ₂ , θ _{3 and} T ₁ , T
_{3. The} method for bending a hot bender according to claim ₂ , wherein T ₂ and T ₃ are set values for control. (Equation 1) (Equation 2) However, in each equation, n = ρ ₀ / 2r (ρ ₀ is the bending radius, r is the radius to the center of the thickness of the pipe to be machined), S ₁
The deformation resistance in the region -90 ° ~θ _2, S ₂ is the area theta ₂
Deformation resistance in through? _3, S ₃ are deformation resistance in the region _{θ 3 ~ + 90 °, t} 1 (in the case of β <θ ₂₎ area -90 ° ~β or _{-90 ° ~θ 2 (θ 2 <} β ≦ pipe thickness in the case of θ _3), t ₂ is the area β~θ ₂ (β <for theta ₂₎
Or _{θ 2 ~β (θ 2 <β} ≦ θ 3 of the case) pipe thickness at, t ₃ (in the case of beta <theta ₂₎ zone theta ₂ through? ₃ or _{β~θ 3 (θ 2 <β ≦} θ pipe thickness at ₃ cases), t ₄ the pipe thickness in the region θ ₃ ~ + 90 °, K
_p is a multiple of the compression force with respect to the thrust. 4. The angle β of the neutral axis is the angle β _t of the neutral axis due to thickness change, the angle β _f of the neutral axis due to thrust, the angle β _b of the neutral axis due to compressive force, and the angle β of the neutral axis due to deformation resistance. 4. The method for bending a hot bender according to claim 2, wherein the method is a combination of _d . 5. The temperature distribution of the annular heating section is set to high-low-medium or high-medium-low from the ventral side to the dorsal side.
The method for bending a hot bender according to any one of the preceding claims. 6. A feeding mechanism for feeding a pipe to be bent with a predetermined thrust, heating means for forming a ring-shaped heating portion having a predetermined width by heating from the outer periphery thereof, and bending of the ring-shaped heating portion by bending force. And a bending mechanism for causing
In a hot bender performing a bending process of a predetermined shape, a control for controlling a temperature distribution in a circumferential direction of the annular heating section so as to maintain a neutral axis obtained by taking thickness, thrust, compression force and deformation resistance as requirements. A hot bender comprising means.