JPH0138854B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for energizing a curved pipe.

For example, when a curved pipe such as a hollow stabilizer is heated by supplying electricity to it, the side closer to the center of the curve (the inside of the curve) has a shorter electrical conduction distance and is relatively thicker, causing the curve to bend. The side farther from the center (outside of the curve) tends to be hotter. If the desired temperature is exceeded, problems such as coarsening of crystal grains tend to occur, and in the case of hardened products, the amount of nonmetallic inclusions that precipitate at grain boundaries increases, reducing the bonding strength between crystals. The problem of brittleness arises because it becomes weaker.

Furthermore, as disclosed in Japanese Patent Application Laid-open No. 47-42510, there is a method in which air is blown onto the inside of the curve of the curved tube to be heat treated, and an auxiliary heating device is provided on the outside of the curve.

However, in the case of this prior art, the cooling effect is low because only air is used for cooling, and when the air flow rate is increased to compensate for this, cooling is performed to the side far from the center of the curve (the outside of the curve), which lowers the temperature on the outside. I'll lower it. For this reason, it is necessary to provide the heating device outside the curved tube, but this increases energy loss and complicates the device.

The present invention was made in view of the above circumstances,
The object thereof is to provide a method for heating a curved pipe with electricity, which can heat the curved portion to a uniform temperature without requiring an auxiliary heating device.

Hereinafter, the present invention will be explained with reference to the drawings. In FIGS. 1 and 2, a curved pipe 1 is integrally equipped with straight parts 2, 2 and a curved part 3 located between these parts, and electrodes 4 attached to the straight parts 2, 2, By applying an appropriate potential difference from a power supply section 5 between the two electrodes 4 to 4, the electric current is applied and heated. In this case, the side 6 of the curved portion 3 closer to the center of curvature is cooled by spraying the gas-liquid mixed fluid 8 from the nozzle 7 .

This mixed fluid may consist of air and water, and other suitable gases and liquids may be used if necessary. The gas-liquid mixing ratio may be appropriately set so as to obtain a cooling rate suitable for the material of the curved pipe 1.

In addition, the injection pattern of the mixed fluid is preferably configured such that the major axis is an ellipse or an oval shape along the longitudinal direction of the curved pipe 1, and the outer diameter of the curved pipe 1 is The direction and pressure of the injection are appropriately set depending on the shape of the curved portion 3 and the like. In other words, when heating the curved pipe 1 with electricity, the temperature on the side far from the center of the curve (the outside of the curve) will be much lower than the inside, and if the outside is cooled, the outside will not reach the specified temperature and will be hardened. Since there is a risk of shortage, it is preferable to prevent the mixed fluid from reaching the outside of the curve.

The reason why the spray pattern is elliptical or oval is as follows.

When we actually measured the temperature distribution in the curved section when the curved tube was heated with electricity, we found that the temperature was highest at the center of the curve and gradually decreased toward both sides, as shown in Figure 5. . In order to make this temperature distribution uniform, an elliptical or elliptical injection pattern as described above is effective.

Even if only air were blown into the curved pipe, the air would not remain in the blown part but would escape by going around the pipe wall, so it would only be possible to cool a roughly circular area. On the other hand, in the case of a gas-liquid mixed fluid, the liquid content in this fluid adheres to the area to be sprayed and cools it, so by adjusting the nozzle shape or spray direction, it is possible to create an elliptical or elliptical shape. The range can also be cooled.

FIG. 4 shows the cooling effect of the above configuration. In the figure, the horizontal axis represents time, and the vertical axis represents temperature. t indicates the time when energization and spraying were stopped. Moreover, the characteristics A and B shown by solid lines are curved portion 3
The temperatures at the side 6 near the center of curvature and the side 9 far from the center of curvature are shown, and the characteristics A' and B' measured at the same positions without spraying are shown by broken lines.
The material of the test bent pipe is STKM15A, and the outer diameter is 22.2.
mm, thickness 2.6 mm, and the elapsed time from the starting point to the above time t was 15 seconds.

As can be seen from Figure 4, the temperature difference between both sides 6 and 9, which was approximately 400℃ when no spraying was performed, is
By spraying, the temperature was significantly reduced to approximately 80℃. Further, the temperature on the side (outside) 9 far from the center of curvature does not vary greatly depending on whether spraying is performed or not. This is due to the use of a spray-like gas-liquid mixed fluid for cooling.For example, air alone has poor cooling ability, and to compensate for this, increasing the flow speed will cause the air to reach the far side (outside) from the center of the curve. This is not desirable because it causes cooling.

As described above, when heating a curved tube with electricity, the gas-liquid mixed fluid is sprayed on the side of the curved portion near the center of the curve in an elliptical or oblong shape along the longitudinal direction of the curved tube. Since cooling is performed by blowing air in this way, each part can be heated more easily and almost evenly than when only air is blown, and there is no need to provide an auxiliary heating device on the outside of the curved pipe. Therefore, not only can crystal coarsening and brittle defects caused by partial heating be effectively prevented, but also energy loss is small and the structure of the device required for heating is simplified.

Furthermore, since the cooling medium is in the form of a spray, there is no need to provide a special device for cooling the part to be cooled while moving along with the movement of the part to be cooled due to thermal expansion during heating of the curved pipe. The device is therefore simple, inexpensive, and easy to operate and maintain.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG.
The figure is a sectional view taken along the - line in Figure 1, Figure 3 is an explanatory diagram illustrating the injection pattern, Figure 4 is a diagram showing a comparison of temperature characteristics, and Figure 5 is the temperature distribution state of the curved part. FIG. 1... Bent tube, 3... Curved part, 4... Electrode, 5...
...Power source section, 6... Side near the center of curvature, 7... Nozzle, 8... Gas-liquid mixed fluid.

Claims (1)

[Claims] 1. When heating a curved pipe by energizing it, a spray of gas-liquid mixed fluid is applied to the side of the curved portion near the center of the curve in an elliptical or oblong shape along the longitudinal direction of the curved pipe. A method for heating curved pipes by energization, which is characterized by cooling the pipes by spraying them in a similar manner.