JPS5928415B2 - Metal pipe bending method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for bending metal pipes such as steel pipes, and an apparatus for carrying out the method.

Specifically, the rear end is supported by a piston that presses in the axial direction, and the tip is held by the guide fitting of the arm that rotates while maintaining a predetermined radius with back pressure.Bend the metal pipe around the circumference of the starting point. In a method of bending a part to a predetermined curvature while locally heating it with high frequency, a twisting device equipped with a chuck mechanism is secured to the rear end of a pipe supported by a piston, and the device reduces the pressing force by the piston. In parallel with the plastic deformation in the axial direction of the pipe due to the compressive force caused by the back pressure of the induction fitting, the heating area of the bending start part is twisted so as to apply a processing force that causes plastic deformation in the circumferential direction. This method is characterized by bending by applying pressure and force to facilitate the generation of bending moments due to multiaxial stress, and in particular, it is a hot bending method that uses high-frequency heating and an induction method using an arm. The purpose of this invention is to make the pipe work even more effectively, to save labor due to the miniaturization of equipment and equipment, and to prevent thinning and flattening of the bent portion of the pipe as much as possible. In the hot bending method using high-frequency heating, a heating device using an annular high-frequency heating coil placed around the pipe locally heats the circumference of the pipe at the beginning of bending to the plastic deformation temperature. Based on this, the heating area is propelled in the axial direction and the pipe is bent by rotation using a guide fitting of an arm that grips the tip. This causes a thinning phenomenon in which the wall thickness inevitably becomes thinner, and as a result, the cross section of the bent portion becomes flattened, which poses problems from the viewpoint of pressure resistance and corrosion resistance.

For this purpose, by applying back pressure to the rotating arm side in response to the pressing force of the piston that propels the pipe, compressive force is applied to the bent part due to heating, thereby applying a bending moment and preventing the occurrence of wall thinning. I'm trying to prevent it.

However, as an actual result, for example, the outer diameter is 11.4~
11.5~, when bending a general steel pipe with a wall thickness of about 6.0X, the piston pressing force for propelling the pipe. Approximately 25,000Kf1 Compression force due to back pressure・Approx. 2000
Since it requires a huge pressure of 0Kf, it is inevitable that the processing equipment will become larger and the equipment cost will be enormous.However, the thinning rate is still large at over 7% and the flatness rate is 12%, so it is a promising condition. The reality is that the problem has not yet been resolved.

In addition, we use an uneven-walled pipe consisting of a thicker part and a thinner part, in which surplus wall thickness is formed on one side in advance to account for the reduction in wall thickness due to bending, and the thicker part is bent to become the outer wall. It has also been proposed to process the pipe by setting it in the same manner as described above. However, in the production of this special pipe with uneven wall thickness, it is difficult to select the excess wall thickness, which is also a factor in the rise in the price of the processed product.

Therefore, as a result of intensive research, the present inventors found that in the plastic working of metal materials in the hot bending method, the stress perpendicular to the axis is greater than the uniaxial stress generated only by compressive force in the axial direction. We focused on the fact that plastic deformation is made easier by the multiaxial stress generated by applying processing forces in different directions, such as applying processing forces in different directions. Bending is performed by forming a multiaxial stress field that applies torsional force in the circumferential direction in addition to compressive force.

This enables plastic deformation with extremely small pressures compared to the conventional strong pushing and compressive forces.As a result, we have succeeded in downsizing and labor-saving processing equipment, and have also succeeded in reducing multi-axial stress without the need for excessive force. This processing method facilitates plastic deformation and has been successful in preventing thinning and flattening of the bent pipe portion.

An embodiment of the present invention will be described below with reference to the drawings.

Figures 1 to 3 sequentially show processing states by the bending method of the present invention, in which 1 is a metal pipe of a predetermined length to be bent, and 2 is a support for the rear end of the pipe. This is the piston of the hydraulic cylinder 3 which acts to press the cylinder in the axial direction, and 2a indicates the piston head.

Reference numeral 4 is a guide fitting that grips the tip of the pipe, and is attached to an arm 5 that is pivotally connected to a rotating fulcrum shaft 6, so that it rotates at a predetermined curvature while applying an adjusted back pressure against the pressure of the piston 2. It is configured.

r is a plurality of guide rollers that assist in propelling the pipe pressed by the piston, and 8 is a high-frequency heating device constituted by an annular high-frequency heating coil set at the pipe bending start portion immediately before the induction fitting. It is provided so as to surround the circumference of the bending start part, W shown over the circumference indicates a heating area, and 9 is a heating device 8.
This is a cooling device placed immediately after the heating to cool the bent portion by cooling water injection nozzles or the like. Reference numeral 10 denotes a twisting device equipped with a chuck mechanism that twists the pipe in the circumferential direction, which is secured to the rear end of the pipe.

This twisting device may be constructed integrally with the head portion 2a of the piston, or may be constructed separately and secured thereto. Either a mechanical mechanism is used, or a mechanism is used that is configured to tighten naturally according to rotation in the torsional direction.

P in the diagram represents the torsional force, Tl and t2 represent the new pipe torsion under the conditions shown in Figures 1 and 2, and K and K
l, K2 are pipes bent at angles θ1, θ21fC. These are the marking lines K and their trajectories Kl and K2 displayed on the pipe to show the state of the twist angle when the pipe is bent, where A and b indicate the twist direction of the pipe, and Ml and m2 indicate the bending angle θ1. and θ2
This figure shows the area where multiaxial stress acts in response to compressive force and torsional force at the time.

Therefore, when performing bending using the apparatus of the present invention having the above-described configuration, first the pipe 1 is set in the state shown in FIG. 1, that is, the pipe 1 is guided and propelled by the guide rollers 7, and
Both ends are fixed by supporting the piston 2 and gripping the guide fitting 4, and together with A, the twisting device 10 is secured to the rear end by a chuck mechanism.

Therefore, the high frequency heating device 8VC. The circumferential portion at the bending start point is locally heated to a plastic deformation temperature, and the piston 2 presses the pipe 1 in the axial direction.

At the same time, when a compressive force is applied while applying an adjusted back pressure to the induction fitting 4, a corresponding compressive stress is generated in the heated region w at the bending start part, and a bending pipe action is activated. In parallel with the pressing of the piston, a continuous torsion force P is applied by the action of the torsion device 10 so as to apply an additional force in the circumferential direction which adds to the compressive force in the axial direction.
This facilitates the generation of a bending moment due to multiaxial stress in which compressive stress in the axial direction and torsional stress in the circumferential direction act synergistically on the heated region portion W. In other words, the synergistic effect of these two stresses makes plastic deformation extremely easy at the bending start point, thereby suppressing wall thickness reduction and flattening, and also reducing the pressing force of the piston to the back pressure of the guide fitting. It has the characteristic that the bending process can be easily performed with a small pressure, which reduces the compressive force associated with the bending process. The twisting direction by the twisting device is the fourth
As shown in the figure, a certain direction of right or left rotation (A,
B) Continuously or reciprocating forward and backward directions (C in the same figure)
The torsional force can be applied by means of transmission with a drive mechanism such as a deceleration motor.

The tip of the pipe is held by an induction fitting and fixed so that it does not rotate, and the external force is applied to the heated area that can be plastically deformed.
Therefore, the twisting range of the pipe due to the action of the twisting device extends over the length t1 in the bending start state shown in FIG. 1, and extends over the length T2 during the process shown in FIG. It will work.

The state of the twisting force in the circumferential direction of the pipe is determined by twisting the pipe in the right direction as shown in the example diagram. When it is bent, it will be in the state of trajectory K1, and further V
When the bending process at the Ce2 angle is completed, the state becomes the trajectory K2.

As can be understood from the state of the trajectory above, by simultaneously applying a synergistic axial compressive force and circumferential torsional force to the pipe, multiaxial stress is applied to the heated region at the beginning of bending. A field is formed, and the bending moment generated by this stress greatly facilitates plastic deformation, resulting in thinning of the bending outer wall of the bent pipe section of the multiaxial stress acting portion Ml, m2 and flattening of the cross section of the bent pipe section. Both are resolved with almost no occurrence.

Next, an experimental example conducted by the present inventors will be shown.

Experimental example 1: Heating a steel pipe with an outer diameter of 114.3% and a wall thickness of 6.0% at a temperature of 90
When bent into a bent pipe with a bending radius of 152.4% at 0°C, a steel pipe with an outer diameter of 304.8~ and a wall thickness of 8.2% was heated to a temperature of 90°C.
When applying a bending force to a curved pipe with a bending radius of 216.3~ at 0°C, as shown in the comparison table based on the above experimental examples, the present invention requires a torsional force. , in order to generate multiaxial stress, both the pushing force and compressive force of the pipe are 1/10 for ordinary steel pipes with an outer diameter of 114.3X.
VC is reduced and the thinning rate is 1/7.3.
V.C. Also, even if it is a large diameter steel pipe with an outer diameter of 304.8X, the pressing force and compressive force are 1/5, and the thinning rate and flatness rate are both 1/3. .7 respectively.

[Brief explanation of the drawing]

The drawings are one embodiment of the present invention, and FIGS. 1 to 3 are schematic diagrams sequentially showing processing states by the bending method, and FIG.
Each of the figures A, B, and C shows the twisting direction of the pipe. Main symbols: 1...Metal pipe, 2...Zeston, 4...Induction fitting, 8...High frequency heating device, 10...Chuck mechanism A twisting device equipped with P...Twisting force, W...Heating area portion.

Claims (1)

[Claims] 1. A metal pipe is bent, the rear end of which is supported by a piston that presses in the axial direction, and the tip of which is held by a guide fitting of an arm that rotates while maintaining a predetermined radius with back pressure. In a method of bending a circumferential part of a starting part to a predetermined curvature while locally heating it with high frequency, a twisting device equipped with a chuck mechanism is fixed to the rear end of a pipe supported by a piston, and the device In parallel with the plastic deformation in the axial direction of the pipe due to the pressing force by the piston and the compressive force due to the back pressure of the induction fitting, a processing force is applied that causes the heated region of the bending start part to undergo plastic deformation in the circumferential direction. A metal pipe bending method characterized by bending by applying a torsional force to facilitate the generation of bending moment due to multiaxial stress. 2. Bending is performed by continuously applying a torsional force in a certain direction to apply a working force that causes plastic deformation in the circumferential direction to the heated region of the bending start part. The metal pipe bending method described in item 1. 3. Bending is performed by alternately and continuously applying a torsional force that applies a processing force that causes plastic deformation in the circumferential direction to the heated region of the bending start part in a reciprocating forward and reverse direction. A method for bending a metal pipe according to claim 1. 4. A piston that supports the rear end of a metal pipe and presses it in the axial direction; a guide fitting attached to an arm that grips the tip of the pipe being pressed and rotates to a predetermined curvature while applying back pressure; In a hot bending device equipped with a high frequency heating device that locally heats a circumferential portion of a bending start part,
A metal pipe bending device characterized by a structure in which a twisting device equipped with a chuck mechanism that applies a twisting force in the circumferential direction to a heated region of the pipe is fixed to the rear end of the pipe. 5. The metal pipe bending device according to claim 4, wherein the twisting device provided to be secured to the rear end of the pipe is constructed integrally with the head portion of the piston. 6. The metal pipe bending device according to claim 4, wherein the twisting device provided to fasten to the rear end of the pipe is constructed separately from the head of the piston.