JPS6012244A - Working method for increasing wall thickness of cylindrical body - Google Patents

Abstract

PURPOSE:To work a cylindrical body to increase the wall thickness thereof while suppressing the increase in the hardness of a working member and assuring the ductility thereof by attaching a heater for heat treatment to the rear part of a device for spraying a coolant and subjecting the material to the wall thickness increase and heat treatment at the same time. CONSTITUTION:A cylindrical body 1 consisting of a carbon steel or the like is fixed by a chucking device 3 and a fixing device 7 for said body. A local heater 6 and a heater 8 for heat treatment are operated and at the same time a coolant is sprayed from the ejection ports 5 of a device 4 for the coolant. The device 6 and the device 4 as well as the device 8 are run at the same speed V. When the temp. of the body 1 attains an equil. state, a pressurizing device 2 for increasing wall thickness is operated to extrude the body 1 at a specified swaging speed V. The equil. temp. of the part to be heated by the device 6 is kept at the temp. at which the strength of the material decreases as much as necessary for increasing the wall thickness. The equil. temp. of the part to be heated by the device 8 is kept lower than the temp. of the increased thickness part and higher than the temp. at which strength is high and martensite transformation is initiated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for increasing the wall thickness of cylindrical bodies such as pipes and rods by localized heating and cooling, which eliminates the need for post-processing heat treatment.

FIG. 1 is an explanatory view showing a conventional processing device for increasing the wall thickness of a cylindrical body by local heating and cooling.
The local heating device 06 is activated, and the IIC is set so that the coolant is sprayed from the injection port 05 of the coolant spraying device 04. Then, the local heating device 06 and the coolant dispersing device o4 were run at the same speed V, and the processed part of the cylinder 01a was locally heated and immediately cooled, so that the temperature of the heated part of the cylinder reached an equilibrium state. Later, through a series of operations of activating the pressure device 02 for thickening processing and pushing the cylindrical body o1 at a constant shrugging speed V, the cylindrical body o1 increases in thickness and diameter, and the thickness of the cylindrical body 01 increases. It can be processed.

However, when the wall thickness of the cylindrical body O1 is increased using the conventional processing method, the processed part is rapidly cooled from a high temperature.
If the structure is close to that of steel, the hardness will increase and the ductility will decrease. Therefore, when performing cold working such as bending to increase wall thickness, it is necessary to heat treat only this portion to reduce hardness and restore ductility.

The present invention has been proposed to improve the drawbacks of the conventional processing methods described above, and its gist is to install a heating device for heat treatment at the rear of the coolant spraying device, and to This is a method for increasing the wall thickness of a cylindrical body using a local heating and cooling method, in which heat treatment is performed at the same time as the thickness increasing process, and the purpose is to suppress an increase in the hardness of the workpiece and ensure ductility.

Below, the wall thickness increasing processing method according to the present invention will be explained in Figures 2 to 5.
A detailed explanation will be given based on the embodiment shown in the figures.

Figure 2 is a graph showing the relationship between the tensile strength and temperature of carbon steel. According to n, the temperature range where plastic deformation actually occurs due to wall thickness increasing processing is probably 800°C or higher. As expected, in the processing method according to the present invention, it is desirable that the high-temperature region be as narrow as possible, and that the regions on both sides of the high-temperature region quickly reduce the temperature and have sufficient strength. Therefore, cooling is performed immediately while heating, but at this time the hardness of the processed portion increases and the ductility decreases.

On the other hand, according to Figure 2, the tensile strength is 400 to 700°C.
If the temperature on both sides of the high-temperature region is about 500° C., it is considered that the strength necessary for the processing method according to the present invention is obtained.

In addition, the cause of the increase in hardness and decrease in ductility is 5M410C
As shown in Figure 3, which shows the CT curve and the cooling curve during wall thickness increasing processing, the phase changes to martensite due to rapid cooling, so it is necessary to control the cooling rate during shrug processing to avoid the martensitic transformation region. Or, even if it is unavoidable, it is expected that an increase in hardness and a decrease in ductility can be avoided by cooling at a cooling rate that reduces the proportion of martensitic structure.

Based on the above, regardless of the martensitic transformation region, it is necessary to cool rapidly to a temperature that maintains sufficient strength necessary for wall thickness increasing processing, and then slowly cool the nage processed part to increase hardness and ductility. This means that we have found that the decline can be avoided.

FIG. 4 is an explanatory diagram showing a wall thickness increasing processing apparatus according to the present invention. In this apparatus, the cylindrical body l is fixed by a catching device 3 and a fixing device 7 for the cylindrical body l, and a local heating device 6 and When the heating device 8 for heat treatment is activated, the coolant is sprayed from the injection port 5 of the coolant spraying device 4. Then, the local heating device 6, cooling and agent dispersion device 4, and heat treatment heating device 8 are run at the same speed V, and when the temperature of the heated portion of the cylindrical body l reaches an equilibrium state, pressure is applied for thickening processing. The device 2 is activated to push out the cylindrical body l at a constant shrugging speed V.

At this time, the equilibrium temperature of the heated part by the local heating device 6 and the material strength are set to be sufficiently low (e.g., 800° C. in the example shown in FIG. 2) such as # required for increasing the wall thickness, and The equilibrium temperature of the heated part is lower than the temperature of the thickened part, has high strength, and is higher than the martensitic transformation start temperature (for example, 500°C in the examples shown in Figures 2 and 3). degree).

Through the above operations, the cylindrical body 1 increases in thickness and diameter, and at the same time, the thermal cycle curve during machining to increase the thickness of the cylindrical body 1 is shown in Figure 5. Become. That is, the cylindrical body 1 is heated to the thickening processing temperature by the local heating device 6), immediately cooled by the coolant injected by the coolant injection port 5 of the coolant spraying device 4, and then heat-treated again. (by heating device 8) in a heat treatment temperature trench, and then air cooled. Therefore, the cooling curve of the processing section (as shown in Fig. 3), the structure has less martensite,
This suppresses the increase in hardness of the processed part and ensures ductility.

As described above in detail with reference to the embodiment shown in the drawings, according to the method for increasing the wall thickness of a cylindrical body according to the present invention, a heating device for heat treatment is installed at the rear of the coolant spraying device. established,
Since the heat treatment is performed simultaneously with the thickness increasing process, it is possible to suppress the increase in hardness of the material of the processed part and ensure ductility. Further, there are effects such as no need for a heat treatment process after the wall thickness increasing process.

Note that the processing method according to the present invention is not limited to cylindrical bodies, and can be similarly applied to other bodies such as tubular bodies and round rod bodies.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of a conventional wall thickness increasing processing device, Figure 2 is a graph showing the relationship between tensile strength of carbon steel and temperature, and Figure 3 is an OCT curve of 5M41 and a cooling curve during wall thickness increasing processing. 4 is an explanatory diagram of the wall thickness increasing processing apparatus according to the present invention, and FIG. 5 is a graph showing a thermal cycle curve during wall thickness increasing processing. In the drawings, 1 is a cylindrical body, 2 is a pressurizing device for thickening, 3 is a catching device, 4 is a coolant spraying device, 6 is a local heating device, 7 is a fixing device, and 8 is a heating device for heat treatment.

Claims (1)

[Claims] By attaching a heating device for heat treatment to the rear of the coolant dispersion device, the thickness of the cylindrical body can be increased by local heating and cooling, which is characterized in that it is configured to perform heat treatment at the same time as the thickness increasing process of the cylindrical body. Thickness increasing processing method.