JPH0450094B2 - - Google Patents

Description

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

FIG. 1 is an explanatory diagram showing a conventional apparatus for increasing the wall thickness of a tube by local heating and cooling. At the same time, the injection port 0 of the coolant distribution device 04 is activated.
From 5 onwards, coolant is sprayed. Then, the local heating device 06 and the coolant dispersion device 04 are run at the same speed V, and the processed portion of the pipe 01 is locally heated and immediately cooled, and after the temperature of the heated portion of the pipe reaches an equilibrium state, Through a series of operations of activating the pressure device 02 for thickening processing and pushing the pipe 01 at a constant shrugging speed v, the pipe 01 increases in thickness and diameter,
It is possible to increase the wall thickness of the pipe 01.

However, when the wall thickness of the pipe 01 is increased using such conventional processing methods, the processed part is rapidly cooled from a high temperature, so the material structure of the processed part becomes a quenched structure or a structure close to it, resulting in an increase in hardness. This results in a decrease in ductility. Therefore, when performing cold working such as bending on a portion that has been processed 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 that a local heating device is attached to the front part of the cooling spraying device, and a local heating device is attached to the front part of the cooling spraying device. A heating device for heat treatment is attached to the tube, and heat treatment is performed at the same time as the wall thickness increasing process.This method uses a local heating and cooling method to increase the wall thickness of the pipe, with the aim of suppressing the increase in hardness of the workpiece and ensuring ductility. be.

Hereinafter, the wall thickness increasing processing method according to the present invention will be explained in detail based on the embodiments shown in FIGS. 2 to 5.

Figure 2 is a graph showing the relationship between the tensile strength and temperature of carbon steel. According to this graph, the temperature range where plastic deformation actually occurs due to wall thickness increasing processing is 800.
It is expected that the temperature will be above ℃. Further, 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 cool down in 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 40 to 700
℃, and both sides of the high temperature range
It is considered that a temperature of about 500° C. provides the strength necessary for the processing method according to the present invention.

In addition, the cause of the increase in hardness and decrease in ductility is
As shown in Figure 3, which shows the CCT curve (continuous cooling transformation curve) of SM (JIS G 3106 Type 1 B) and the cooling curve during processing to increase wall thickness, the phase change to martensite occurs due to rapid cooling. If the cooling rate is controlled during shrugging to avoid the martensitic transformation region, or even if it cannot be avoided, cooling at a cooling rate that reduces the proportion of the martensitic structure will increase the hardness and decrease the ductility. It is expected that this can be avoided. From the above, regardless of the martensitic transformation region, rapid cooling to a temperature that maintains sufficient strength required for wall thickness increasing processing, and then gradual cooling will increase the hardness of the processed part and reduce ductility. It has been discovered that this can be avoided.

FIG. 4 is an explanatory view showing the wall thickness increasing processing apparatus according to the present invention. While operating the heating device 8, the injection port 5 of the coolant distribution device 4
Coolant is now sprayed from the ground. Therefore, the portions of the tube 1 surrounded by the local heating device 6 and the heat treatment processing device 8 are heated, and these portions become heated portions. Then, the local heating device 6, the coolant spraying device 4, and the heating device 8 for heat treatment are run at the same speed V, and when the temperature of the heated portion of the tube 1 reaches an equilibrium state, the pressure device 2 for thickening process is activated to push out the tube 1 at a constant shrugging speed v. In other words, the parts to be heated are different parts in FIG. 4 corresponding to the local heating device 6 and the heating device 8 for heat treatment, but the part of the tube 1 heated by the local heating device 6 is cooled. After being cooled by spraying a cooling agent, for example, cooling water, with the coolant spraying device 4, it is heated again with the heating device 8 for heat treatment. From the above, although the heated parts are different parts in FIG. 4, since the pipe 1 and these heating devices 6 and 8 move relatively, it can be said that the same part becomes the heated part twice. . In addition, to check whether the heated part has reached an equilibrium state, it is necessary to conduct a test in advance and select processing conditions such as the electric output and running speed V of the heating devices 6 and 8 so that the processing can be performed appropriately. Therefore, there is no need to particularly check during actual processing.

On the other hand, during processing, the equilibrium temperature of the heated part by the local heating device 6 is the temperature at which the material strength is sufficiently low to increase the wall thickness (for example, in the example shown in FIG.
800°C), and the equilibrium temperature of the heated part by the heat treatment heating device 8 is lower than the temperature of the thickened part.
In addition, the strength is high, and the temperature is higher than the martensitic transformation start temperature (for example, about 500° C. in the examples shown in FIGS. 2 and 3). The time it takes for the temperature of the heated part to reach equilibrium depends on the output of the heating devices 6 and 8, but can be, for example, 10 to 15 seconds, and during this time the tube 1 is moved. The distance is
It can be about 25mm to 40mm.

Through the above operations, the thickness and diameter of the tube 1 are increased, and at the same time, the thermal cycle during processing of the tube 1 becomes as shown in the thermal cycle curve during processing to increase the wall thickness shown in FIG. Here, FIG. 5 shows a thermal cycle when heat treatment is performed at the same time as the thickening process in the present invention, and the curve shows the input to the heat utilization heating device 8 of FIG. 4 when only the thickening process is performed. The curve shows the heat cycle of the thickened part when the machine is operated with the power turned off, and the curve shows the heat cycle of the thickened part when thickened and heat treated. At this time, the input to the heating device 8 for heat treatment shown in FIG. 4 is adjusted to match the heat treatment conditions. That is, the tube 1 is heated to the thickening processing temperature by the local heating device 6, and immediately cooled by the coolant injected from the coolant injection port 5 of the coolant spraying device 4, and then heated again to the heat treatment temperature by the heat treatment heating device 8. It is heated to 100% and then air cooled. Therefore, the cooling curve of the processed part becomes like curve 2 in FIG. 3, and the structure contains less martensite, suppressing the increase in hardness of the processed part and ensuring ductility.

As described above in detail based on the embodiment shown in the drawings, according to the pipe wall thickness increasing processing method according to the present invention, a heating device for heat treatment is provided at the rear of the coolant distribution device, Heat treatment is performed at the same time as the thickness increasing process, making it possible to suppress the increase in hardness of the material of the processed part and ensure ductility. Also,
This has the advantage of eliminating the need for a heat treatment process after wall thickness increasing processing.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the conventional wall thickness increasing processing equipment, Figure 2 is a graph showing the relationship between the tensile strength of carbon steel and temperature, and Figure 3 is the CCT curve of SM41 and the cooling curve during wall thickness increasing processing. FIG. 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 drawing, 1 is a pipe, 2 is a pressurizing device for thickening processing, 3
4 is a catching device, 4 is a coolant distribution device, 6 is a local heating device, 7 is a fixing device, and 8 is a heating device for heat treatment.

Claims (1)

[Claims] 1. A local heating device 6 is attached to the front of the coolant distribution device 4, and a heating device 8 for heat treatment is attached to the rear of the coolant distribution device 4, so that the heat treatment is performed simultaneously with the process of increasing the wall thickness of the pipe. A method for increasing the wall thickness of pipes using a localized heating and cooling method.