JPS60180623A - Method and device for bending metallic pipe - Google Patents

Abstract

PURPOSE:To minimize the working thickness-reduction at the back side of a bending part by lowering the working temperature of the back side of a bending part and elevating the working temperature of the belly side at the time of high frequency bending work. CONSTITUTION:In the bending work of a metallic pipe by high frequency heating, the temperature of the back side of a bending part is regulated to <=1,000 deg.C in case of stainless steel and to <=500 deg.C in case of carbon steel. Further, the temperature of the belly part of the bending part is regulated to >=1,000 deg.C in case of stainless steel and to >=700 deg.C in case of carbon steel. These temperature differences are easily attained by using a high-frequency heating coil having a taper formed by making the coil width at the back side of a bending part wider and the coil width at the belly part narrower.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method and apparatus for bending a metal tube. In particular, when bending metal tubes using high-frequency heating,
The present invention relates to a method for bending a metal tube that prevents deformation of the bent portion during processing, particularly a decrease in wall thickness on the back side of the bent portion, and a metal tube bending device related thereto.

[Background of the invention]

In conventional high-frequency induction heating bending, the high-frequency heating coil that heats the bent part is a circular coil whose shape is the same on the dorsal and ventral sides of the bent part, so the high-frequency heating area covers the dorsal and ventral sides of the bent part. It becomes almost uniform. Therefore, the yield point, tensile strength, and elongation of the metal tube due to external loads in this high-frequency heating region are almost uniform. Therefore, when a bending moment is applied to the high-frequency induction heating area by fixing one end of the pipe to be processed to an arm and pushing the pipe out using a pushing device at the other end, the bending moment that occurs will occur on the dorsal and ventral sides of the bent part. Because they are the same, the same amount of plastic deformation is induced on the dorsal and ventral sides of the bent part, and the amount of thickness increased on the ventral side of the bent part tends to decrease by an amount equivalent to the thickness increase on the dorsal side of the bent part. be.

This tendency is caused by shortening the length of the arm that draws a certain arc,
When the bending half-layer is set small, the increase in thickness on the side of the bending layer and the decrease in thickness on the side with the bending part become particularly large. Of these, the amount of thinning on the side with the bent part is large, which means that when using a bent pipe, in order to maintain the specified wall thickness required for the design, the amount of thinning to compensate for this thinning amount is increased. This has to be dealt with by adding an additional layer to the thickness of the metal tube before bending, which is a disadvantage in the use of bent tubes. In order to eliminate this disadvantage, it is generally a good practice to apply compressive force due to the pushing force and the braking force applied by the arm to the pipe to be bent to reduce the decrease in wall thickness on the side where the bending part is attached.

In this method, in order to apply braking force to the arm axis,
It is necessary to install a brake generator. This increases the manufacturing cost of the bending device, which is unfavorable in terms of equipment investment. Further, by applying this braking force to the central axis of the arm, a large thread moment is applied to the shaft, so there is a drawback that the central axis of the arm needs to be made thicker than necessary.

On the other hand, instead of these bending methods that apply compressive force to the pipe to be bent, in the hot working region of about 900C, the yield point and tensile strength decrease and the elongation increases. In the warm working area, the yield point and tensile strength are higher and the elongation is lower than in the hot working area. As a method of increasing the deformation resistance on the side of the bent part and reducing thickness loss by lowering the temperature, the heated part is cooled by spraying water on the high frequency heating part on the side of the bent part during bending. However, the bending temperature of the bending part side in the moment applying part is set higher than the hot working area, thereby increasing the yield point and tensile strength of the back side of the workpiece part, and keeping the elongation low. Methods are being taken to limit the amount of thinning. In this method, in addition to a cooling ring provided on the arm clamp side of the high-frequency heating ring, a nozzle for cooling the pole part is provided on the pushing device side of the high-frequency heating ring, and the pole part on the side with the bent part is locally heated with a width of approximately 60111 snO. It is effective to increase the deformation resistance and reduce the amount of thinning on the bent side by increasing the yield point and tensile strength on the bent side, but the high frequency heating coil and normal cooling ring setting In addition, it is necessary to set a nozzle for local cooling, which increases pre-processing setup time, causes unevenness in the bent pipe material due to setting errors in local nozzles, and causes the cooling water to cover the lower surface of the pipe due to gravity. There is a possibility that non-uniformity may occur in the material of the bending part due to continuous flow.Also, since the cooling water is controlled mechanically by adjusting the pulp opening, it is always uniform due to water pressure fluctuations. In addition, because the high-frequency bending method always processes items with the same diameter and does not always bend continuously, the coil must be removed and set, so it is always the same diameter. Since it is not possible to set the high-frequency heating coil, the cooling ring, and the local cooling ring at each location, fine adjustment of these three coils and the cooling ring is required.
The disadvantage is that it requires a skilled person.

In addition, in high-frequency heating bending processing, depending on the processing accuracy of the cooling nozzle, there may be differences in the direction of cooling water blowing out and the amount of cooling water blowing out from each hole, which may cause an imbalance in the cooling range. It is obvious that α non-uniformity occurs, and there is also the drawback that the processing accuracy (manufacturing accuracy) of the nozzle may lead to non-uniformity in the finished state or material of the bent pipe. As a processing method that creates a temperature difference between the bent side and the curved part side, the center axes of the fractured surface-bent pipe, high-frequency heating ring, and cooling ring are shifted, and the high-frequency heating ring and the fractured surface are placed in the gap between the surface of the processed pipe. By making υ larger on the bending part side and smaller on the bending part layer side, the temperature on the bending part side can be decreased by decreasing the magnetic flux density on the bending part side and increasing the magnetic flux density on the bending part layer side. A method has been devised to lower the temperature of the ventral side and raise the temperature of the ventral side, but the work of setting the gap is important because the heating temperature varies greatly depending on the difference in the gap. It is not possible to start bending immediately after setting, but requires fine adjustment by a skilled person.Therefore, there is a drawback that the setup work before bending increases.

Furthermore, the usefulness of this method of providing a gear blade differs depending on the material, and although it is possible to easily create a temperature difference in stainless steel, it has the disadvantage that it is difficult to create a temperature difference in carbon steel. In addition, even if the material is the same, as long as a perfectly circular high-frequency heating coil is used, if the gap is set at a temperature that is convenient for suppressing thinning on the side with the bent part, the temperature will drop in the neutral part and the gap will be minimized on the ventral side. Therefore, there is a drawback that there is a limit on the difference in heating temperature, and this limits the conditions.

Furthermore, the bending method that creates these temperature differences requires a skilled person for nozzle adjustment and gap adjustment, and is a high-frequency heating bending method that is difficult to employ in today's world where the number of skilled people is decreasing.

[Purpose of the invention]

The present invention has been made in order to solve the problems of the conventional technology, and it is possible to lower the processing temperature on the bending part side and increase the processing temperature on the bending part layer side during high frequency bending. It is an object of the present invention to provide a method for bending a metal tube and an apparatus for the same, which minimizes side wall loss during processing.

[Summary of the invention]

The present invention lowers the dorsal side bending temperature of the bent portion to a lower temperature than the ventral side bending temperature, and reduces the temperature-dependent deformation resistance of the metal tube such that the bending portion layer side bottoms out and the bending portion side In the temperature difference bending method, we focused on the fact that the current density of the heating coil is proportional to the amount of heat generated at the bending part on the side of the pipe to be processed, and that the current density is inversely proportional to the cross-sectional area of the coil. By changing the coil so that the width is small and the cross-sectional area of the coil is minimized, and the coil width on the side with the bent part is increased to maximize the coil cross-sectional area, the current density on the side of the bent part is increased and the workpiece is processed. To provide a heating coil for high frequency bending that heats up the tube, lowers the current density on the bending part side, and lowers the temperature of the tube to be processed. and providing appropriate conditions for temperature difference.

[Embodiments of the invention]

In the present invention, as shown in FIG. 1, for a constant input current value (I), the coil cross-sectional area is changed from ventral side SI to dorsal side S2.
If the ratio is α, then if the dorsal cross-sectional area is 1, the ventral side will have a ratio of 1/α.

Here, if the current density is ψ, it is expressed by the following relational expression.

Therefore, on the bending layer side, formula (3) is used, and on the back side, formula (4) is used.
The formula becomes

Thus, ψ1: ventral current density ψ2: dorsal current density. From equations (1), (3), and (4), ψl ψ2=−...(5) α, and the dorsal current density (ψ2) varies depending on the ratio of the cross-sectional area of the dorsal and ventral Change.

FIG. 2 shows the change in circumferential current density of the heating coil. As shown in this figure, the current density is high on the bending layer side,
It can be seen that the current density is low on the bent side.

Further, the calorific value (Q) of the wrinkled pipe is proportional to the applied current density (ψ).

Calorific value (Q) = current density (ψ) ... (6) Therefore,
As shown in FIG. 3, the distribution of heat generation #(Q) in the circumferential direction of the heating section is such that the amount of heat generated is high on the bent layer side and low on the side with the bent portion. Processing temperature (T) and calorific value (
Q) is in a proportional relationship.

Processing temperature (T) - calorific value (Q) (7) Fig. 4 shows the processing temperature distribution of the wrinkled pipe. The dashed line is
The solid line shows the case where there is no heat conduction within the wrinkled tube wall, and the solid line indicates the case where there is heat conduction within the wrinkled tube wall. By continuously changing the coil cross-sectional area in this way, it is possible to maintain the processing temperature of the tube to be processed high on the bending layer side and low on the bending layer side.

FIG. 5 shows the cross-sectional shape of the heating coil in the present invention, and FIG. 6 shows the dorsal side cross-sectional shape and the ventral side cross-sectional shape of the heating coil. When using coil materials of the same thickness, the temperature distribution shown in FIG. 4 can be obtained by making the coil width t2 on the side with the bending part wider than the coil width t1 on the side of the bending part layer.

FIG. 7 shows an example of the relationship between the stress difference Δσ between the back side and the ventral side of the bent portion and the thickness reduction suppression amount Δe of the deformation resistance at the processing temperature. It is clear from this that the greater the stress difference Δσ, the greater the amount of suppression of wall thinning. Furthermore, this stress difference Δσ depends on temperature, and FIG. 8 shows the temperature dependence of the deformation resistance value.

Examples of the method of applying a temperature difference according to the present invention are as follows for stainless steel pipes and carbon steel pipes.

For stainless steel, when the bending radius is twice the diameter, the heating temperature on the side with the bending part is tooot:' or more and the heating temperature on the layer side of the bending part is 800C or less to reduce the deformation resistance difference Δσ. = 7 kg/lea
``It is possible to obtain a thickness reduction prevention amount of 9 inches, and since the amount of thickness reduction in normal bending processing is around 20%, it is possible to improve the amount of thickness reduction to around ttS. Become.

For carbon steel, when the bending radius is twice the diameter, the heating temperature on the bending side is 700T:' or more, and the heating temperature on the bending layer side is 500C or less to reduce the difference in deformation resistance. Δσ=7Kf/flIl12,
It is possible to obtain a thickness reduction prevention amount of 9 inches, and as with stainless steel, the amount of thinning is usually around 20 inches during processing, so the amount of thinning can be improved to around 11 inches. becomes. In this way, both carbon steel and steel/stainless steel have approximately 2
By providing a temperature difference of 00C, it is possible to improve the amount of thinning, and the shape of the tapered high-frequency heating coil that satisfies this condition is as follows.

The high temperature side (ventral side) bending temperature (function of current value) is TI
If it is (I), then is the Teba high frequency heating Koino? The ratio α between the dorsal coil cross-sectional area (S2) and the ventral coil cross-sectional area (Sl) is expressed by equation (8).

T1(I) ,,, (9°TI(I)-ΔT where ΔT: temperature difference between dorsal side and ventral side Therefore, in the previous example, for stainless steel, α=
1.25...(10) For carbon steel, α=1.4 Kawa (11).

However, the shape of the tapered high-frequency heating coil in this embodiment in the case of stainless steel is as shown in FIG. 9, and the shape of the tapered high-frequency heating coil in this embodiment in the case of carbon steel is as shown in FIG. 1θ.

In addition, in the embodiment according to the present invention, a perfectly circular annular coil,
Since the coil is designed so that it becomes longer in the coil axis direction from the bending layer side to the back side, the bending layer side is heated to a high temperature.
The effect of lowering the temperature on the side where the bent part is attached is poor, so the conventional method of locally cooling the side where the bent part is attached, and the method of changing the gap between the coil and the processed pipe on the dorsal and ventral sides of the bent part, are not effective. Yosi,
It is possible to obtain the same effect as the method of lowering the temperature on the side with the bent part and increasing the temperature on the layer side of the bent part, and the wrinkling that is normally done by bending can be achieved by simply aligning the processed pipe and the axis of the high-frequency heating coil. It is possible to easily create a temperature difference between the dorsal side and the ventral side of the bent part, and by controlling the longitudinal waves supplied to the high-frequency heating coil, it is possible to easily and accurately control the temperature.
It has the feature that it is possible to adjust the roll and heating temperature.

Further, FIG. 11 shows a sequence of bending operations when this embodiment is used.

A metal tube 4 to be bent is fixed at one end to an arm 2 that draws a constant arc and is rotatable in the rotation υ of the rotation axis l, and the other end is sifted by a pushing device 3 and further guided by a guide roller 6. is inserted into the tapered high-frequency heating coil 7 connected to the high-frequency power supply 5 without contacting it, and the area immediately below the high-frequency heating coil is heated by high-frequency induction heating while keeping the temperature of the dorsal side of the bent part low and the temperature of the ventral side of the bent part high. High-frequency heating is performed by blowing out cooling water through a cooling ring 8 provided on the arm side of the high-frequency induction heating coil 7.While heating is controlled, the tube to be processed 4 is pushed forward by a pushing device 3. The bending process is performed by applying a #i bending moment to the area.

〔Effect of the invention〕

In the present invention, the heating temperature on the side with the bent part is 80°C using stainless steel.
0C or less, 5001Z' or less for carbon steel, and the heating temperature on the bending part layer side is 1oooc or more for stainless steel, and 700C or more for carbon steel. By lowering the processing temperature on the layer side, the amount of thinning on the bent side can be reduced.
This temperature difference can be easily created by using a tapered high-frequency heating coil that has a wider coil width on the side with the bent portion and a narrower coil width on the side of the bent portion layer.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the cross-sectional area distribution of the high-frequency heating coil;
Figure 2 is a diagram showing the change in circumferential current density of the heating coil, Figure 3 is a diagram showing the circumferential calorific value (Q) distribution of the heating section, and Figure 4 is a diagram showing the circumferential heat generation (Q) distribution of the heating coil. A diagram showing the processing temperature distribution, FIG. 5 is a cross-sectional view of the heating coil measured during the main egg generation, and FIG. 6 is a longitudinal cross-sectional view showing the dorsal and ventral cross-sectional shapes of the heating coil. , Figure 7 shows the relationship between the stress difference Δσ on the back side and the ventral side of the bending part of the deformation resistance at the processing temperature and the amount of thickness reduction suppression Δe, and Figure 8 shows the temperature dependence of the deformation resistance value. 9 is a longitudinal sectional view showing an embodiment of the present invention in stainless steel, FIG. 10 is a longitudinal sectional view showing an embodiment of the invention in carbon steel, and FIG. 11 is a longitudinal sectional view showing an embodiment of the invention in carbon steel.
When this implementation sequence is used, ψ...Current density, T...Bending part side, N...Bending part neutral part, C...Bending part layer side,
Q...Power generation amount, T...Heating temperature, t2...Bending back coil width, Δσ...Stress difference, Δe...Thickening suppression amount, σγ...Deformation resistance, 1...・Rotating shaft, 2...Arm, 3...Pushing device, 4...Pipe to be bent, 5...
- High frequency power supply, 6... Guide row 2-17... Tapered high frequency heating coil, 8... Cooling ring. Agent Patent Attorney Akio Takahashi'$ 1 Figure NTNC CA/ 7 /V' C $ 3 CN 7 A/ C CN, 7 N ('$3727 Figure 〈→ '$7rI3 Figure 8, '& A ( 'O Y q diagram

Claims (1)

[Claims] 1. A metal tube to be bent is connected to a high-frequency power source, with one end fixed to an arm drawing a constant arc, and the other end connected to a device that pushes the vibrator forward by hydraulic pressure or chain drive. The area directly under the high-frequency heating coil is heated by high-frequency induction heating to the warm or hot processing area, and at the same time, it is cooled from the cooling ring attached to the arm side of the high-frequency heating coil. In this method, the material is blown out, the heating width is controlled, and at the same time a pushing device is used to push the shivive toward the arm side, applying a bending moment to a narrow high-frequency heating area and performing bending. 8
00C or less, 500U or less for carbon steel, and the temperature on the ventral side of the bent part is more than tooC for stainless steel, 700C for carbon steel.
As described above, there is provided a metal tube bending method characterized by suppressing a decrease in the dorsal wall thickness. 2. In claim 1, in order to set the temperature on the back side of the bending part to be lower than the temperature on the ventral side of the bending part, the heating width on the back side of the bending part and the heating width on the ventral side of the bending part is changed; Metal tube bending method 3, characterized by widening the heating width at the bending part and narrowing the heating width at the ventral side of the bending part. Furthermore, in order to narrow the heating width, the high-frequency heating coil width is widened on the back side of the bending part and narrowed on the ventral side of the bending part.