JPS582727B2 - Metal tube bending method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for bending metal tubes.

A conventionally well-known method for bending metal tubes is a method in which the tube is bent while being heated by high-frequency induction heating.

This method involves heating a metal tube locally in an annular manner by high-frequency induction heating to a temperature that allows plastic deformation, and applying a bending moment to the heating section while moving the heating section relatively in the longitudinal direction of the tube. Immediately thereafter, a cooling operation is performed to continuously plastically deform the tube in the heated region, the method comprising:
This is generally carried out using an apparatus as shown in FIG.

That is, in FIG. 1, 1 is a metal tube to be bent, 2,
2, 3, and 3 are pairs of guide rolls, 4 is an annular high-frequency inductor placed close to the rolls 3 and 3, and is integrally provided with a cooling water jet nozzle. An arm 6 is provided on the arm to rotate around the center point of the bending radius R of the metal tube 1, and a clamp 7 is provided on the arm to hold the bent end of the metal tube 1. 7 is a clamp that holds the rear end of the metal tube 1. An example of a high frequency tube bending device is constituted by the supporting tailstock and the above items 1 to 7.

In this device, the metal tube 1 is passed between the guide rolls 2 and 2 and between the guide rolls 3 and 3, passed through the inductor 4, and its bent end is clamped and held by the clamp 6, and the metal tube 1 is tightened by an appropriate means. is locally heated in an annular manner by an inductor 4 while being propelled and moved continuously and in a straight line, and immediately after the heating, cooling water 8 is jetted out from a cooling water jetting nozzle provided integrally with the inductor 4,
The heating section is cooled to a predetermined temperature, and the metal tube 1 is continuously plastically deformed and bent in the heated region while applying a bending moment to the metal tube 1 through rotational guidance of the arm 5. With this device, metal pipe 1
According to the conventional method of bending the metal tube 1, it is possible to bend the metal tube 1 efficiently and with a high degree of precision. A so-called thinning phenomenon occurs, and the strength of the thinned portion naturally decreases, so if the thinned portion is large, it becomes unusable even after bending.

Therefore, methods for preventing wall thinning in the above method include a method of applying compressive force to the metal tube 1, a method of simply creating a difference in mixing between the bent outside T and the bent inside C of the tube 1 during heating, etc. has been proposed, but the former not only requires a large-scale device, but also has the disadvantage of requiring significantly greater strength than the previous device, resulting in higher equipment costs and higher processing costs. Although the latter can prevent thinning, on the other hand, it has the disadvantage that the flattening phenomenon appears significantly.

In view of the above-mentioned prior art, the inventors of the present invention have conducted extensive research into a metal tube bending method that can prevent wall thinning in a relatively simple manner and can also prevent flattening. During bending, thinning always occurs on the outside of the bend, but if a specific zone near the part that does not expand or contract on the outside of the bend during heating is cooled to a specific temperature, the cooled part will have a higher tensile strength than other parts. It has been learned that since it is extremely large, it can prevent thinning and also has the effect of preventing flattening.

That is, in FIG. 2, the thickness center radius of the metal tube 1 to be bent is r, the bending radius of the metal tube 1 is R, and the expansion and contraction becomes zero at the bending outside T of the tube 1 when bending is performed. The distance from the vertical axis of the part is a and the thinning rate of the outermost part is α
Then, from this formula, a=r(1-ct) ctR.

Therefore, if a is calculated from the required thickness reduction rate and this portion is made to have no expansion or contraction, the thickness reduction rate will fall within the required value.

In fact, if during heating, the zone in the vicinity of the part that includes the central axis of the tube 1 and is a distance a from the plane perpendicular to the bending plane is cooled,
As the tensile strength of the cooling zone increases, the expansion and contraction of that part becomes relatively small, and together with the force that propels the tube 1, the area between A and A on the outside bending T of the cooling zone becomes a tensile zone and the inside bending area. The area between A and A in C becomes a compression area, which prevents thinning of the outside T of the bending.Also, as shown in the figure, the surplus force in the direction perpendicular to the wall of the pipe moves in the A to A zone as shown by the arrow. It is also possible to prevent flattening, and it has been found that even if the bands A and A are slightly deviated from those shown in the figure, the same effect as above, especially the flattening prevention effect, can be obtained.

The present invention was made as a result of the above-mentioned research, and has a structure in which a metal tube to be bent is heated locally in an annular manner to a temperature that allows plastic deformation by high-frequency induction heating, and the heating section is placed along the length of the tube. Applying a bending moment to the heated part while relatively propelling it in the direction, and immediately cooling it,
In a metal tube bending method in which the tube is continuously plastically deformed in its heating region, the metal tube is placed at an appropriate distance on both sides in the circumferential direction from the outermost position of the portion of the metal tube to be bent during the heating. This feature is characterized in that only a band of an appropriate width is cooled to suppress expansion and contraction of that portion.

Thus, the present invention can be easily implemented by adding a device as shown in FIG. 3 to the illustrative device shown in FIG.

That is, in FIG. 3, reference numeral 11 denotes a mounting plate that is conveniently attached to the apparatus shown in FIG. is a nozzle provided at the tip of the guide W12, and the tips of the nozzles 14 and 140 are directed toward zones A and A of appropriate width at an appropriate distance on both sides in the circumferential direction from the outermost position in the heating area of the metal tube 1. The conduit 12.12 includes a strainer 15, a pressure regulating valve 16,
Flow rate adjustment valve 11, branch pipe 18 to valves 19, 19, flow meter 20. 20, the cooling fluid is sent to the nozzles 14,1
4, the cooling fluid is injected into the zone AtA.In order to change the attachment position of the conduits 12, 12, bolt holes 21 for attaching the supports 13 are provided in a row, and the metal tubes 1 The conduits 12, 12 shall be arranged at positions appropriate for the size of the pipes.

Further, the nozzles 14, 14 may be attached to the inductor 4 with the nozzles 14, 14 directed toward the zones A, 12, without using the attachment plate 11 as described above.

Furthermore, when water is used as the cooling fluid, it scatters and enters zone A.
, A. If there is a risk that parts other than A may still cool down, this must be prevented.

In such a case, an appropriate draining jig capable of forming an air curtain may be used to cool the container while adjusting the amount of water and air.

In carrying out the present invention, the widths of the zones A and A are adjusted depending on the material of the metal tube, and the temperature difference with the heating section is adjusted.

The present invention is as described above, and in the conventionally known bending process of a metal tube, a band of an appropriate width is formed at an appropriate distance on both sides in the circumferential direction from the outermost position of a portion of the metal tube to be bent during heating. By heating the metal tube while cooling it, the bending process is performed while maintaining the tensile strength of the zone greater than that of the heated portion, which not only prevents thinning on the outer side of the bent metal tube, but also prevents the wall surface of the tube from forming in the zone. As a result of the component force in the vertical direction acting on the steel pipe, it is possible to prevent the flattening phenomenon from occurring.In addition, in the case of steel pipes, the deformation resistance is stable and does not change at temperatures below 400°C compared to the high temperature parts. Since it is possible to adopt a method of keeping the width constant and narrowing the width to significantly lower the cooling temperature, the work is stable and the reproducibility is also good.

The following table shows the results of bending by the method of the present invention compared with those of the conventional method and the method of applying compressive force.

[Brief explanation of drawings]

Fig. 1 is a plan view of a conventional metal tube bending device, Fig. 2 is a diagram showing the parts to be cooled during heating of the metal tube in the method of the present invention, and Fig. 3 is a plan view of the device shown in Fig. 1. FIG. 4 is a front view of an example of implementing the present invention using the present invention. 1... Metal tube, 2, 2, 3, 3... Guide roll, 4... High frequency inductor, 5...
・Arm, 6... Clamp, 7... Tail stock, 11... Attachment plate, 12...
... Cooling fluid conduit, 14... Nozzle.

Claims (1)

[Scope of Claims] 1. A metal tube to be bent is heated in an annular manner to a temperature that can be locally plastically deformed by high-frequency induction heating, and the heating section is moved while being relatively propelled in the longitudinal direction of the tube. A metal tube bending method in which a bending moment is applied to the tube, followed by cooling immediately after, and the tube is continuously plastically deformed in the heating region. A method for bending a metal tube, characterized by cooling only a band of an appropriate width at an appropriate distance on both sides in the circumferential direction from the outermost position of the part to be bent, thereby suppressing elongation of the part. 2. The bending method according to claim 1, wherein the zone to be cooled includes a portion that does not expand or contract on the outside of the pipe during bending.