JPS6213216A - Compression bending method for metal pipe - Google Patents

Abstract

PURPOSE:To form a bent pipe having a gently varied wall thickness by increasing a torque applied to a bending arm gradually in the initial bending and decreasing the torque gradually in the terminal bending. CONSTITUTION:As for a gradation bending for na pipe, a torque applied to an arm 4, a bending arm, is increased gradually from a state in which a bending radius is larger than a prescribed one to a state in which a bending radius equals to the prescribed one and the torque is decreased gradually in the terminal bending. To give such a torque, prescribed tension is given to the arm 4 based on a variation curve programed to a controller 13 previously and by use of a compression wheel 8 and a driving device 10. Therefore, forming of an excessive wall thickness in both the initial bending and terminal bending is prevented, so that a bent pipe having a gradually varied wall thickness is formed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention heats a metal tube annularly and locally, and applies a bending moment to the metal tube while moving the heating section in the longitudinal direction of the metal tube. Regarding methods of continuous bending, in particular, gradation bending is performed in which the bending radius is gradually changed at the beginning and end of bending in order to produce smooth curved pipes by smoothing the change in wall thickness of the pipe. , relates to a compression bending method that simultaneously applies compressive force to a pipe to increase its thickness.

[Conventional technology]

As a method of bending a metal tube (hereinafter simply referred to as a tube), as shown in FIG. 4, while heating the tube 1 annularly with a heater 6 (for example, a high-frequency inductor).

The tube 1 is advanced by the driving device 5, the heating section of the tube 1 is moved in the longitudinal direction of the tube, and the portion immediately after that is cooled by the cooling device provided in the heater 6, and at the same time, a bending moment is applied to the tube 1 by the arm 4. There is a known method of applying and continuously bending. In this method, 1 usually the heater 6 is connected to the arm 4.
The pipe is placed stationary on a straight line constant.

By the way, when the tube 1 is bent with a constant bending radius, there is a phenomenon in which the wall thickness of the tube changes rapidly between the beginning and the end of the bending. This phenomenon is particularly noticeable when the bending radius is small. As a method to prevent this sudden change in wall thickness, 1. At the beginning of bending, the bending radius is gradually reduced from a large value to a predetermined bending radius, and 2. At the end of bending, the bending radius is gradually expanded while performing the bending. (hereinafter referred to as blur bending) has been proposed (see JP-A-53-76158 and JP-A-56-45220). In these publications, in order to change the bending radius, the unbent portion ( By gradually tilting the right part of the heater 6 in Fig. 6,
Alternatively, a method is adopted in which the heater 6 is moved from the A1 position to the A position (beginning of bending) and then from the A position to the A position (end of bending).

In addition, in order to prevent the wall thickness from decreasing at the bending outer periphery of the bending part 9, there is also a method of applying a constant torque to the arm 4 around the pivot axis 3 and applying compressive force in the axial direction to the tube 1 to increase the wall thickness. Are known. The conventional torque applying device used here consists of a compression wheel 8. which is rotatable about a pivot shaft 3 together with an arm 4 as shown in FIG. It is composed of a wire 9 whose one end is fixed to the outer periphery of the compression wheel 8 and a drive device 10 that applies tension to the wire 9. Therefore, a constant torque is always applied to arm 4.

A constant compressive force can be applied to the tube 1 via the arm.

[Problem that the invention seeks to solve]

However, when performing the above-mentioned blur bending, when compression bending was performed using the compression wheel 8, although the bending radius was gradually changed at the beginning and end of the second bend, the fourth
As shown in the figure, a problem occurred in that the wall thickness suddenly changed.

The present invention aims to solve this problem, and aims to provide a compression bending method that prevents sudden changes in wall thickness at the beginning and end of bending.

[Means for solving problems]

In order to solve the above-mentioned problems, the present inventors have conducted intensive studies and found that the compressive force required to increase the wall thickness to a certain degree varies depending on the bending radius of the pipe, and when the bending radius is large, it may be small. The present invention was made based on this knowledge, and when the bending radius is gradually reduced from a large value to a predetermined bending radius at the start of one bending, at the same time, the bending arm, that is, the arm 4 is Gradually increase the applied torque from a certain small value.

The present invention is characterized in that when the bending radius is gradually increased from a predetermined bending radius at the end of bending, the torque applied to the arm 4 is simultaneously gradually decreased.

〔Example〕

Preferred changes in the torque applied to the arm 4 in the present invention will be described below.

FIG. 6 shows a state in which the bending is performed while increasing the thickness. In FIG. 6, it is assumed that the tube l is now bent to a bending radius R larger than the effective length of the arm 4 while increasing the wall thickness by μ times. At this time, the reaction force acting on the pivot shaft 3 is Pl; the tension applied to the compression wheel 8 is P; the axial compression force applied to the tube 1 is P; the bending moment applied to the tube 1 is M.

In addition, in FIG. 8 and the following description.

: Compression wheel radius C: Bending center y: Distance between the bending position 1a of the pipe and the center of the pivot axis 3 in the direction perpendicular to the axis of the pipe 1.

From Fig. 6, the relationship between each force acting during bending and the bending moment is:

Ptomi PI +px ・−・−
・+11M= yPI + (yr)Pt
--------(2+ Strictly speaking, distance #y is different from the effective length of arm 4, but the difference is minute.

y′4L −・−・・−
(3) Therefore, (21, +31 formula, M= L P + + (L r) P!
(41) By the way, when the pipe is bent with a bending radius R without increasing its thickness, the compressive force applied to the pipe 1 is Po, and the bending moment applied to the pipe l at this time is Mo, then 1. The following formula holds true.

Pa='-
-・-・-(5)R Here, Mo is a constant determined by the physical properties of the tube 1, the section modulus, etc.

As mentioned above, due to the compressive force 21 and the bending moment M, μ
Because the bending process is being performed while increasing the thickness twice.

Assuming that the compressive force P at this time is m times Po.

P = m P O−・・・−(6) M ” 11
M o '----・
-(7) [11, (Substituting equations (5) to (7) into equation 41 and rearranging.

L R L　　　　　m-μ Lm-μ P, = P (1---') r　　　　　　m Rr L　　　　m-μ P, --P r　　　　　　　　m LM(1 R becomes.

This means that the forces P and P+ satisfy the above (8) to α field formula.

When the bending process is performed at P2, it means that the bending process is performed with a constant thickness increase rate. Note that the force P, P, is 1 or more.

Of P2, the force P applied to the pivot shaft 3 is a reaction force.

There is no need for control, and the compressive force P applied to the tube 1 is when the tube 1 is moved in the longitudinal direction to perform a predetermined bend.

Since it is automatically determined according to the physical properties 1 of the pipe 1, such as the bending radius, there is no need for any particular control.Therefore, the tension Pt applied to the compression wheel 8 is adjusted according to the bending radius R of 2 based on formula 01. Then, the bending process is performed at a substantially constant thickness increase rate. This tension P causes a torque centered on the pivot shaft 3 to be generated in the arm 4, and let this torque be T.

T-rP.

Therefore, in carrying out the present invention, it is preferable that the torque applied to the arm 4 is determined based on the 00 formula, that is, inversely proportional to the bending radius R. Although it is a theoretical value that is not considered at all, in actual bending processing, disturbances such as friction occur, so the α1.00 formula may be used with appropriate correction.

FIG. 5 is a block diagram schematically showing an example of an apparatus used to carry out the method of the present invention. In this figure, the same reference numerals are used for the same parts as in FIG. 8. The torque applying device that applies torque to the arm 4 includes a compression wheel 8 that can rotate integrally with the arm 4 and a drive device IO that applies tension Pt to the compression wheel 8 via a wire 9.
A hydraulic cylinder is used as 0.

Hydraulic pressure is supplied to the hydraulic cylinder 10 via an electromagnetic proportional valve 12 . The electromagnetic proportional valve 12 is a program control device 13
controlled by signals from A tension detector 14 such as a load cell is attached to the wire 9 at an appropriate position, and its output signal is fed back to the control device 13.

Although not shown in the drawings, the drive device 5 that moves the tube 1 in the longitudinal direction and the drive device (not shown) that moves the heater 6 along the tube 1 are also program-controlled by the control device 13. A predetermined blur bending is performed.

FIG. 1 is a graph showing the characteristics of an example of the bending process performed by the apparatus shown in FIG. In Fig. 1, the angle θf at the beginning of 1 bend
In between, the bending radius R decreases in a curved manner, after which bending is performed at a constant bending radius (effective length of the arm), and between the angle 05 at the end of the first bending, the bending radius R increases in a curved manner. are doing. Such a bending curve is obtained by the program controller 13 controlling the moving speed of the tube 1 and the moving speed of the heater 6. For this bending curve (change in bending radius R), (P from formula 81,01).

When P2 is determined, it becomes as shown in FIG. In other words, the angle θf at the beginning of 1 bending increases linearly from the smaller value of 1.
In the area where the bending radius is constant, it is maintained at a predetermined value, and decreases linearly between the angle 05 at the end of two bends. This tension P! A change curve of W is programmed in the control device 13 in advance, and W
The A motion device 10 controls the tension Pg according to a program as the bending progresses. In this way, bending is performed with a substantially constant thickness increase rate, and excessive wall thickness fluctuations at the beginning and end of one bend are prevented. FIG. 3 shows a bent tube that has been bent according to the characteristics shown in FIG. 1, and the wall thickness of one bent portion varies gently. On the other hand, FIG. 4 shows a bent pipe in which the tension P2 was kept constant over the entire range and the bending process was performed using the same bending curve as in FIG. 1.

This bent pipe clearly has bulges at both ends of the bend.

FIG. 2 is a characteristic diagram of another embodiment of the present invention. In this example, the bending radius R changes linearly between the bending start angle θf and the bending end angle 05. In this case, the tension P2 is increased and decreased in a curve based on the formula α. In this case as well, swelling of the wall thickness at both ends of the bent portion is prevented.

〔Effect of the invention〕

As explained above (1) In the present invention, when the bending radius is gradually decreased from a large value at the beginning of bending.

The torque applied to the bending arm (arm 4) is gradually increased from a small value, and conversely, when the bending radius is gradually increased at the end of the first bend, the torque applied to the second bending arm is gradually decreased. 1. Excessive thickness increase at the beginning and end of bending is prevented, and a gentle thickness change can be obtained. Thus, the two aspects of the present invention have the effect of making it possible to manufacture a thickened bent pipe with smooth wall thickness changes.

[Brief explanation of drawings]

FIG. 1 is a graph showing the characteristics of an embodiment of the method of the present invention. FIG. 2 is a graph showing the characteristics of another embodiment. FIG. 3 is a partially sectional side view showing a bent tube bent by the method shown in FIG. 1. FIG. 4 is a partial cross-sectional side view showing a bent tube that has been bent while maintaining a constant tension P2 applied to the compression wheel. FIG. 5 is a block diagram showing an example of a bending device used to carry out the method of the present invention. FIG. 6 is an explanatory diagram showing the relationship of forces acting during compression bending. FIG. 7 is a schematic plan view of a bending device for explaining the blur bending process. FIG. 8 is a schematic plan view of a bending device for explaining compression bending. 1...Pipe 3-Swivel axis 4...
- Arm (bending arm) 5 - Drive device 6 - Heater
8... Compression wheel 9-Wire 10
- Drive device 12 - - Electromagnetic proportional valve 13 - - Program control device Patent applicant Daiichi Koshuha Kogyo Co., Ltd. Representative Patent attorney Kyo Matsu 321 Figure 2

Claims (1)

[Claims] A heater that locally heats the metal tube to be bent in an annular manner is moved relatively in the longitudinal direction of the metal tube, and at the same time, a part of the metal tube is gripped and the pivot axis of the rotatable bending arm is adjusted. A method of continuously bending a metal tube by moving it relatively parallel to the metal tube to apply a bending moment to the metal tube, and at the beginning of bending, the bending radius is gradually reduced to a predetermined bending radius. In a bending method in which the bending radius is gradually increased from a predetermined bending radius at the end of bending, a compressive force in the axial direction is applied to the metal tube by applying a torque centered on the pivot axis to the bending arm, and The amount of torque is gradually increased from a small value at the beginning of bending to a predetermined value,
A method for compression bending a metal tube, characterized in that the predetermined value is gradually decreased at the end of bending.