JPH0585275B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing an electric resistance welded tube that uses heating using an energy beam as well as heating using electric resistance. [Prior Art] One of the methods for manufacturing a welded pipe by welding the joints at both ends of an open pipe is electric resistance welding. The electric resistance welding method is a method of welding by heating and melting the metal at the welded part by electromagnetic induction or direct current using a high-frequency current of several tens to hundreds of KHz, and is the most efficient method for manufacturing welded pipes. This method is mainly used for small diameter metal pipes. However, it has been pointed out that the electric resistance welding method has drawbacks such as the problem that minute defects occur in the welded portion, making it unsuitable for manufacturing high-grade metal pipes. This microdefect is thought to be caused by excessive electromagnetic force at the junction. In other words, a large electromagnetic force acts on the molten metal at the joint, causing the molten metal to be locally ejected from the joint, changing the shape of the joint and its vicinity, and causing uneven melting.As a result, the squeeze roll Coagulation becomes uneven when an upset is applied. It is thought that the non-uniform solidification of the abutment area during the addition of upsets is the cause of the micro defects. In order to solve the above-mentioned problems with the electric resistance welding method and obtain high-quality welded pipes, a welding method that uses both a high-frequency current and an energy beam as a heating source has been proposed (Japanese Unexamined Patent Publication No. 56-168981, Kaisho
59-202187). These welding methods involve heating the opposing ends of an open pipe by generating Joule heat so that the temperature at the joining point of the both ends reaches or is close to the melting temperature, and then In this method, an energy beam is projected onto the welding point so that the temperature of the welding point reaches the melting temperature before the welding point reaches the welding point where the welding point is butt-welded. [Problem to be solved by the invention] Although it is true that the improved technology described in the above-mentioned publication reduces the micro defects in the electric resistance welding method to some extent, it has not yet been able to sufficiently prevent their occurrence. . This is because the electromagnetic force caused by the magnetic field generated by the high-frequency heating current acts on the joint, albeit weakly, and discharges the molten metal generated at the joint, and as a result, the molten pool is not stably maintained. The present invention has been made in view of the above circumstances, and its purpose is to provide a method for manufacturing an electric resistance welded pipe that can sufficiently suppress the occurrence of micro defects, which have been a problem in the past. . [Means for Solving the Problems] In order to achieve the above object, the present invention heats opposite ends of an open pipe to be transferred with a high frequency current, and then further heats them with an energy beam. In the method for manufacturing an electric resistance welded pipe combined with an energy beam, the impeder is moved so that its downstream end in the open pipe transport direction is moved upstream in the open pipe transport direction by a distance l greater than or equal to the outer diameter D of the open pipe from the junction where the both ends join. It is characterized in that it is disposed toward the transfer direction of the open pipe so as to be located on the side, and the open pipe is joined. [Function] In the present invention as described above, first, the opposite ends of the open pipe are preheated with high frequency current, and then an energy beam is projected onto the junction, so that the downstream end of the impeder opens from the junction. Since the pipe is located upstream by a distance l that is greater than the outer diameter D of the pipe, the molten metal in the molten pool formed is welded without being discharged, resulting in an electric resistance welded pipe with almost no weld defects. Manufactured. [Example] Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the method for manufacturing an electric resistance welded pipe according to the present invention (hereinafter referred to as the "method of the present invention"), and FIG.
The figure is an explanatory diagram showing the mutual positional relationship of both ends of the open pipe OP. Pass roll FR only is shown) and is bent from a U-shaped cross section to an O-shaped cross section with both ends E and E facing each other, and has an outer diameter D whose outer circumference is the skeleton width dimension after bending. have this open pipe
After passing through the fin pass roll FR, as the OP moves toward the squeeze roll SR side arranged downstream, both ends E and E are made to approach each other asymptotically, and the joint point is
The squeeze roll SR is butt-welded at the welding point O _{2 between O 1 and the point O 3 corresponding to} the rolling position of the squeeze roll SR (hereinafter referred to as the "rolling point"), and the squeeze roll SR is pressed down while the pipe P is being rolled down. Then, it is transported in the direction of the white arrow for the finishing process. During this time, the open pipe OP moves inside the coil W in the coil axial direction in order to heat both ends E, E at a position downstream of the fine pass roll FR and upstream of the junction point _O1 . In addition, in order to improve the heating efficiency of the open pipe OP by the coil W, an impeder IP is installed at a position downstream of the coil W and separated by l on the upstream side of the junction point _O1 . The downstream ends, that is, the tips thereof, are arranged so as to coincide with each other and extend toward the upstream side.
However, the distance l is not smaller than the diameter D of the open pipe OP. Further, an energy beam launch source (not shown) is arranged facing the transfer path of the open pipe OP in order to project an energy beam to the junction point _O1 and its vicinity. Here, the coil W is for heating both end portions E and E, and its coil terminal is connected to a high frequency power source of tens to hundreds of kHz (not shown), and the skin effect and proximity effect Both ends E,
A high frequency current is induced in E. The high frequency current induced in both ends E, E is passed between both ends E, E via junction _O1 ,
As a result, both end portions E and E are heated. Here, the high frequency power source and the coil W are designed electrically and in a layout such that the both end portions E, E can be heated to the melting temperature or a temperature close to the melting temperature at the junction point _O1 . Therefore, the joint between both ends E and E is such that both ends are at or near the melting temperature and are in a solid state or molten but do not flow even when subjected to external force such as electromagnetic force. This will be carried out under a molten state that will not cause any damage. On the other hand, the energy beam is directed toward the junction and its vicinity. Here, the amount of energy beam projected is designed to heat both ends E and E at the welding point _O2 to a temperature higher than the melting temperature, which is sufficient for butt welding. There is. Therefore, the butt welding of the open pipe OP is performed under the condition that most of the molten metal between the opposite ends E and E at the welding point _O2 is pressed down by the squeeze roll SR and discharged to the outside. become. In this way, the open pipe OP is formed into a pipe P. Figure 3 shows the temperature distribution on the outer surface near the side end when the open pipe OP is stationary and heated in the above-mentioned device, and the horizontal axis represents the axial position of the open pipe. , and the temperature 5 seconds after heating is plotted on the vertical axis. Here, the A curve (the curve shown by the thin line in the figure) is the temperature distribution when the conventional separation dimension l from the junction point to the tip of the impeder IP is zero, and the B curve (the curve shown by the thick line in the figure) ) is l≧D(=
This is the temperature distribution when l = 34 mm, which fills the minimum amount of air (34 mm). In the figure, the higher the temperature of the outer surface near both ends E and E of the open pipe OP, the
This means that the magnetic field on the outer surface of the coil W provided for heating due to the high frequency current applied thereto is strong, and therefore the induced current and current density are also large. From this, it can be considered that the lower the current density in the figure, the smaller the electromagnetic force acting on that part, and the smaller the discharge of molten metal due to the electromagnetic force. As is clear from the figure, in the case of l=34 mm according to the present invention,
The temperature at the junction is low, and therefore the discharge of molten metal due to electromagnetic force is small, but if l = 0 mm, that is, if the impeder IP is positioned so that its tip coincides with the junction, the temperature at the junction will be low. The temperature is high, so it can be said that the discharge of molten metal due to electromagnetic force is large. Table 1 shows the materials to be joined, pipe manufacturing speed, laser output,
It shows the measurement results of the occurrence of welding defects when the high frequency output and impeder position (l) were varied.
Note that the laser used for the measurement was a multi-mode carbon dioxide laser. Comparative Examples Nos. 1 to 5 are cases in which an energy beam is projected after preheating with a coil W to near the melting point, and l<D. In these cases, weld defects are not sufficiently suppressed. Comparative Example No. 6 is a case where the high frequency output is increased and melting occurs before the welding point, and defects that are considered to be caused by fluctuations in the molten steel occur. Comparative Examples No. 7 to 9 are electric resistance welding that does not use an energy beam, and in Comparative Example No. 7 where l = D, cold welding defects (indicated by an x in the table) appear over the entire length. In Comparative Examples No. 8 and 9 where , l=0, a relatively large number of penetrators were generated. On the other hand, Example No. 1 which is an example of the present invention
-5, welding defects are completely suppressed. In addition, in Examples Nos. 4 and 5 and Comparative Example No. 9, shielding with nitrogen gas was performed in order to prevent oxidation of the molten metal.

【table】

〔Effect of the invention〕

As described above, in the electric resistance welded pipe manufacturing method according to the present invention, the impeder is disposed so that its downstream end is located upstream from the junction point by a distance l equal to or more than the outer diameter D of the open pipe. The present invention has excellent effects, such as being able to sufficiently suppress the occurrence of micro defects that have been previously known.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the method of the present invention, FIG. 2 is a schematic diagram of an open pipe OP, and FIG. 3 is a temperature distribution diagram. OP...Open pipe, FR...Fin pass roll, SR...Squeeze roll, E...Side end, W...Coil, IP...Impeder, _O1 ...Joint point, _O2 ...Welding point, _O3 ...Reducing point.

Claims (1)

[Claims] 1. A method for manufacturing an electric resistance welded pipe using an energy beam, in which opposite ends of an open pipe to be transferred are heated with a high-frequency current, and then further heated with an energy beam. In the transfer direction of the open pipe, the downstream end in the open pipe transfer direction is located upstream in the open pipe transfer direction by a distance l equal to or more than the outer diameter D of the open pipe from the junction where the both end portions join. A method of manufacturing an electric resistance welded pipe combined with an energy beam, characterized in that the open pipes are arranged facing each other and joined together.