JPH04333323A - Hot bending device for metal tube - Google Patents

Abstract

PURPOSE:To prevent the development of wrinkle and bulge due to buckling developed at the time of bending to a metal tube and to obtain a hot ending device, which can reduce thinned thickness rate at back side of the tube. CONSTITUTION:The tube 1 passing through between guide rollers, is passed through a heating coil 4 set to the outer periphery at the bending part and an annular magnetic shield material 5 set to both sides of this coil 4, and the prescribed position in the tube is fixed with an arm. Then, by supplying high frequency current in the heating coil 4, the tube 1 is heated, and at the time of becoming the prescribed temp., load is given to one end of the tube 1 with a hydraulic cylinder 3 to execute the necessary bending work. The heating coil 4 is cooled with water in the inner part thereof and a part of the water is injected to the outer surface of tube 1 through an injection nozzle 8. At both sides of the heating coil 4, copper tubes 5 cooling the liner part with the flowing water, are set while insulating with the heating coil as the magnetic shield material. Then, by making distance between the heating coil 4 and the tube 1 at the back side of tube 1 larger than that at the front side of tube, eddy current density in the tube material at the back side is made to low, and heating temp. is made to low.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot bending apparatus for metal tubes using high-frequency induction heating.

0002

2. Description of the Related Art FIG. 6 shows an example of the shape and arrangement of heating coils in the conventional bending process of tubes by high-frequency induction heating. In the figure, 1 is a metal tube whose one end is clamped to a rotating arm (not shown), 4 is a heating coil placed around the outer periphery of the bent portion of the metal tube 1, and 8 is a metal tube placed on the inner diameter side of the heating coil 4. A water injection nozzle is used to inject cooling water 9 from the nozzle 8 toward the outer surface of the metal tube 1 for cooling. Note 3
indicates a hydraulic cylinder that applies a pushing force to one end of the tube 1.

[0003] The metal tube 1 is locally heated by high-frequency induction heating to apply a bending moment to the tube, thereby continuously bending the tube.

0004

By the way, in the conventional example shown in FIG. 6, the range heated by the heating coil 4, for example, the range heated to 800° C. or higher when the maximum heating temperature is 1000° C. and as shown in FIG. 4 (conventional method),
For example, since the thickness is three times or more than the plate thickness of the tube material 1 and the heating width is wide, the bending inner diameter side (hereinafter referred to as the ventral side) where compressive stress is generated during bending will buckle.

In order to narrow the heating width, spray nozzles 8 for cooling water 9 are installed at both ends of the inner diameter surface of the heating coil 4 to cool the outer surface of the tube 1, as shown in FIG. Currently, there is a limit to narrowing the heating width using only water cooling from the surface.

[0006] Also, "wrinkles" and "bumps" during pipe bending
Another problem is the phenomenon of thinning. In the example of FIG. 6, the shape and arrangement position of the heating coil 4 are the same on the ventral side of the bend and the outer diameter side of the bend (hereinafter referred to as the dorsal side), so the ventral side and the dorsal side are heated to the same temperature. That is, the deformation resistance of the tube material is the same on the ventral side and the dorsal side, and when the tube is bent, the thickness increases on the ventral side, but the thickness decreases by a corresponding amount on the dorsal side. If the amount of thinning increases, the strength required in the design cannot be secured, and the amount of thinning increases as the bending radius becomes smaller.
Therefore, there is a problem in that it is difficult to perform a bending process in which the bending radius is less than about twice the outer diameter of the tube.

The present invention solves the above problems of the prior art, narrows the heating width on the ventral side of the tube, and prevents the occurrence of "wrinkles" or "bumps" due to buckling during bending.
By heating the dorsal side to a lower temperature than the ventral side, the purpose is to reduce the amount of plastic deformation on the dorsal side, that is, to reduce the amount of thinning on the dorsal side.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the hot bending apparatus for metal tubes of the present invention includes a heating coil arranged around the outer periphery of the bending portion of the metal tube, and a high-frequency current applied to the heating coil. In a hot bending device that bends a tube while heating it, magnetic shielding materials are installed on both sides of the heating coil, and the distance between the inner diameter side of the bending and the heating coil is
The heating coil is characterized in that the heating coil is arranged so as to be narrower than the distance between the outer diameter side of the bend and the coil.

[0009]

[Operation] The above-described hot bending apparatus for metal tubes of the present invention has the following features:
In order to narrow the heating width on the ventral side of the bend, in addition to cooling the tube surface by spraying water, magnetic shielding material made of a material with high conductivity is installed on both sides of the heating coil, and the shielding material is This reduces the width of eddy currents generated in the tube.

As can be seen from the buckling theory formula, it is generally known that the critical buckling stress when compressive stress is applied is inversely proportional to the square of the heating width, if other conditions are constant. . In other words, during bending, in the length direction of the pipe,
By reducing the length (heating width) of the region with low deformation resistance, buckling becomes less likely to occur.

[0011] Furthermore, by changing the heating temperature on the ventral side and the dorsal side,
That is, in order to heat the ventral side to a higher temperature than the dorsal side, the distance between the heating coil and the ventral side of the tube is made smaller than the distance between the heating coil and the dorsal side of the tube. As a result, the ventral side is preferentially deformed (thickened) by the moment generated during bending, and when the same amount of deformation is applied, the amount of deformation on the dorsal side is smaller, and therefore the amount of thinning on the dorsal side is reduced. .

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a hot bending apparatus for tubes using high-frequency induction heating using an arm rotation method according to the present invention. In the figure, a metal tube 1 is moved between guide rollers 2, and then passed through an annular heating coil 4 and annular magnetic shielding materials 5 installed on both sides of the heating coil 4, and a predetermined position of the tube 1 is moved through an arm 6.
Fixed to. Thereafter, a high frequency current is supplied to the heating coil 4 to heat the tube 1, and when a predetermined position of the tube 1 reaches a predetermined temperature, a load is applied to one end of the tube 1 by the hydraulic cylinder 3, and the arm 6 is heated. rotates around the arm center 7, the bending of the pipe 1 progresses continuously, and when a predetermined bending angle is reached, the load on the hydraulic cylinder 3 is removed and the bending process is completed.

FIGS. 2(a) and 2(b) are enlarged views of the vicinity of the heating coil 4 in FIG. In order to narrow the heating width of the pipe 1 through the injection nozzle 8,
sprayed onto the outer surface of the In addition, on both sides of the heating coil 4, there are copper tubes (magnetic shielding material) 5 whose insides are cooled with running water.
is installed insulated from the heating coil 4. By making the distance between the heating coil 4 and the tube 1 larger on the dorsal side than on the ventral side, the eddy current density in the tube material on the dorsal side is reduced, and the heating temperature is lowered.

In addition, in the case of FIG. 2(a), the distance between the heating coil 4 and the tube 1 and the distance between the magnetic shield 5 and the tube 1 are approximately equal, but in FIG. This is a case where the magnetic shielding material 5 is placed closer to the tube 1 than the heating coil 4 to increase the magnetic shielding effect on the dorsal side and to increase the temperature difference between the ventral side and the dorsal side.
The relative position between the heating coil 4 and the magnetic shielding material 5 needs to be adjusted appropriately depending on the size or material of the tube 1. Therefore, in the present invention, the relative position between the heating coil 4 and the magnetic shielding material 5 is as shown in FIG. (b) Either case may be used, and there is no particular limitation.

FIG. 3 shows the heating coil 4 shown in FIG. 2(a).
and magnetic shielding material 5 (copper tube), frequency 1000H
When the magnetic shield 5 is installed when a high frequency current of z is supplied so that the maximum magnetic flux density generated in a stainless steel tube (SUS304TP) with a diameter of 216 mm and a thickness of 8.2 mm is the same (Figure 3 (a) ), the eddy current density distribution in the pipe material was determined by electromagnetic analysis, and when there is no magnetic shield 5 (
The figures are shown in comparison with the analytical values in Fig. 3(b)), and the eddy currents generated by installing the magnetic shield 5 concentrate near the coil, thereby increasing the heating width (as mentioned above, for example, the maximum heating When the temperature is 1000°C, the length of the region heated to 800°C or higher) becomes narrower. The ratio between the heating width of 800°C or more and the thickness of the pipe 1 is when bending is performed while supplying the high frequency current and moving the pipe of the above size and material at 0.8 mm/sec using the hydraulic cylinder 3. As shown in FIG. 4, 3. without the magnetic shield 5.
3, it is smaller than 2.8 due to the installation of the magnetic shield 5.

The relationship between the above heating conditions, the heating temperature depending on the size and material of the tube, and the distance (clearance) between the coil 4 and the tube 1 is as shown in FIG.
mm, 0.8m assuming dorsal clearance as 15mm
As a result of bending at a bending radius of 1.5 times the diameter of tube 1 at a speed of m/s, there were no "wrinkles" or "humps" on the ventral side due to buckling, and the thinning rate on the dorsal side was low. 10 to 12%, making it possible to bend with a smaller radius compared to a conventional bending device that does not have a magnetic shield 5 and heats the ventral and dorsal sides to the same temperature.

[0017]

[Effects of the Invention] As described above, according to the metal tube hot bending apparatus of the present invention, the heating width of the bent portion can be narrowed by installing magnetic shielding materials (magnetic shields) on both sides of the heating coil. This prevents the tube from buckling during bending, reduces the amount of thinning on the dorsal side by lowering the temperature on the dorsal side than the temperature on the ventral side, and also reduces the amount of wall thinning on the dorsal side. There are various features and effects that can be easily realized by changing the distance between the heating coil and the tube.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a bending apparatus according to an embodiment of the present invention.

[Fig. 2] Shows an enlarged view of the vicinity of the heating coil in the processing device in Fig. 1, where (a) shows the case where the distances between the heating coil and magnetic shielding material and the tube are almost equal, and (b) shows the case where there is a difference in the distance. FIG.

[Figure 3] Electromagnetic analysis results of eddy current density distribution generated in the pipe, (a) shows when a magnetic shield is installed, (b)
indicates the case without magnetic shielding.

FIG. 4 is a diagram comparing the heating width of the present invention and the conventional method.

FIG. 5 is a diagram showing the relationship between the heating peak temperature and the clearance between the coil and the tube according to the embodiment of the present invention.

FIG. 6 is a cross-sectional view of the vicinity of a heating coil in an example of a conventional tube bending method.

[Explanation of symbols]

1 pipe 2 Guide roller 3 Hydraulic cylinder 4 Heating coil 5 Magnetic shielding material 6 Arm 7 Arm rotation center 8 Water injection nozzle 9 Cooling water

Claims (1)

[Claims] 1. A hot bending apparatus in which a heating coil is arranged around the outer periphery of a bending portion of a metal tube, and a high frequency current is supplied to the heating coil to bend the tube while heating the tube. magnetic shielding material is installed on both sides of the metal, and the heating coil is arranged so that the distance between the inner diameter side of the bend and the heating coil is narrower than the distance between the outer diameter side of the bend and the coil. Hot pipe bending equipment.