JPH02299782A - Manufacture of resistance welded tube - Google Patents

Abstract

PURPOSE:To suppress the quantity of a bead discharged and to improve machinability of the bead and to improve working efficiency by heating both side edge parts of an open pipe up to the temperature above the Curie point by a first heating power source. CONSTITUTION:An induced current is generated on the open pipe 1 inserted into a work coil 52 for heating by applying a current of prescribed frequency to the coil 52 by the first heating power source 51. The vicinities of both side edge parts 1a and 1a of the open pipe 1 are preheated up to the temperature above the Curie point by the induced current. The current is then applied to a work coil 62 for welding by a second heating source 61 and both side edge parts 1a and 1a are heated up to the temperature above the sufficient melting temperature. Both edges 1a and 1a are then subjected to butt welding between squeeze rolls 3 and 3 to obtain the title resistance welded tube. By this method, the quantity of the bead discharged is suppressed and machinability of the bead is improved and working efficiency is improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method of manufacturing an electric resistance welded tube.

[Conventional technology]

FIG. 6 is a schematic diagram showing a conventional method of manufacturing an electric resistance welded pipe.
As shown in the figure, this method involves passing the oven vibe 1 through a high-frequency induction heating coil 2a.
In this method, an electric resistance welded pipe is manufactured by heating and melting the edge portions 1a and 1a on both sides to a temperature at which they become molten, and then butt welding the edge portions 1a and 1a on both sides between squeeze rolls 3 and 3. be. When such a high-frequency induction heating coil 2a is energized, the current density at both edge portions 1a, la increases due to the proximity effect and skin effect, as shown in FIG. As a result, a current is induced to flow through a path along both edge portions 1a, Ia. At the junction point 4, the current density is high, and the molten steel flows under the influence of the electromagnetic force, so if the metal has a strong tendency to oxidize, a large amount of oxide is generated. There was a problem in that objects were caught between the edge portions 1a and Ia on both sides, resulting in welding defects such as penetrators.

In addition, molten steel scatters (flash) due to the flow of molten steel.
As a result, there is a problem in that indentation flaws occur on the surface of the open pipe 1 and also cause problems in operation.

As a method for preventing the occurrence of venetrators, a method has been used in which the butt welded portion is sealed with an inert gas to prevent oxidation of the molten steel. In addition, as a method for preventing the occurrence of the flash, the heating temperature is lower than before,
A device that reduces the amount of flash generated is used.

However, in the method for preventing penetrators as described above, it is necessary to install an inert gas sealing device, which poses a problem in that work efficiency is reduced. In addition, in the method of preventing the occurrence of flash, ``the heating temperature is lower than before, but this temperature approaches the temperature range where welding defects are likely to occur, making it difficult to perform stable welding.''There's a problem.

In order to solve these problems, for example, JP-A-56-168
An apparatus for manufacturing an electric resistance welded pipe using two high-frequency heating devices as disclosed in Japanese Patent No. 981 is used. this is,
The first heating device heats the material to near the melting temperature to provide preheating, and the apprentice 2 heating device heats the material to a temperature higher than the melting temperature to perform butt welding.

[Problem to be solved by the invention]

However, with the above-mentioned apparatus for manufacturing electric resistance welded pipes using two heating devices, although some modifications have been made, there is a risk that welding defects such as venetrators and flash may occur depending on the welding conditions.

Therefore, the inventors of the present invention repeatedly conducted various studies in order to find desirable welding conditions when manufacturing an electric resistance welded pipe using an apparatus equipped with two heating devices, and found the optimum values of the welding conditions. That is, the present invention applies preheating to a temperature above the Curie point to both edge portions of an open vibe using a first power heating device, and uniformly heats both edge portions to prevent welding defects such as venetrators and flash. Prevent the occurrence
- The purpose of the present invention is to provide a method for manufacturing an ERW pipe.

[Means to solve the problem]

The method for manufacturing an electric resistance welded pipe according to the present invention includes sequentially heating and melting opposing edge portions of an open pipe using a first heating device and a second heating device, and then butt welding them using squeeze rolls. Accordingly, in the apparatus for manufacturing an electric resistance welded pipe, the temperature of both edge portions of the open pipe is heated to a temperature higher than the Curie point by the first heating device.

[Effect]

When the temperature of both edge portions of the open pipe becomes equal to or higher than the Curie point, the relative magnetic permeability of both edge portions decreases, so that the penetration depth of the current passed by the second heating device increases. As a result, concentration of the current at the corners of both edge portions is alleviated, and the both edge portions are uniformly heated.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments thereof.

FIG. 1 is a schematic diagram showing the configuration of an electric resistance welded tube manufacturing apparatus used when carrying out the method of the present invention. In the figure, reference numeral 3.3 denotes a squeeze roll, and the upstream side of the working path of the squeeze roll 3.3 is connected to a first heating power source 51 which is a high frequency electric power source (or medium frequency power source) of the first heating device 5. A heating work coil 52 is provided. Said squeeze roll 3,3
A second heating device 6 is provided between the heating work coil 52 and the heating work coil 52.
A welding work coil 62 connected to a second heating power source 61 which is a high frequency or medium frequency power source is provided. The oven vibrator l has the heating work coil 52.
and the squeeze roll 3 passing through the welding work coil 62.
, 3. An invader 7 made of a ferrite core or a silicon steel plate is inserted into the open pipe 1 to increase the heating effect and improve welding efficiency.

Next, a method for manufacturing an electric resistance welded tube using the electric resistance welded tube manufacturing apparatus configured as described above will be explained. The first heating power source 51 causes a current of a predetermined frequency to flow through the heating work coil 52, thereby generating an induced current in the open pipe l inserted through the heating work coil 52. This induced current preheats the vicinity of the edges 1a and 1a on both sides of the open pipe 1 to a temperature above the Curie point. Then the second
A current is passed through the welding work coil 62 by the heating power source 61, thereby heating the edge portions 1a and 1a on both sides to a temperature equal to or higher than the melting temperature. An electric resistance welded tube is obtained by butt welding parts 1a and 1a.

Next, the reason why the first heating device 5 heats the edge portions 1a and 1a of the open pipe 1 to a temperature higher than the Curie point will be explained.

Figure 2 shows both edges of open pipe 1 where conventional butt welding was performed! FIG. 5 is a schematic side view of a and la. In the figure, IO indicates the high-temperature deformation portion of the edge portions 1a and 1a on both sides. When the open pipe 1 is butt-welded using the conventional ERW pipe manufacturing method, the high-frequency heating induced current is concentrated at the corners of the edge portions 1a and Ia on both sides due to the skin effect, so the open pipe 1 is welded as shown in Fig. 2. The spread in the circumferential direction of the high-temperature deformation portion 10.10 of the pipe 1 is not uniform in distribution in the thickness direction, and the outer peripheral surface heat-affected width is the width of the high-temperature deformation portion 10.10 on the outer peripheral surface of the open pipe l. A
The inner circumferential surface heat affected width C, which is the width of the high temperature deformed portion 10.10 on the inner circumferential surface, is the width of the high temperature deformed portion 10.10 at the center in the thickness direction.
is wider than the central heat affected width B.

Generally, the current penetration depth δ is expressed by the following equation (1).

ρ: Specific resistance μ: Relative magnetic permeability f: Frequency It is known that the relative magnetic permeability μ in the above equation (1) changes depending on the temperature of the material. FIG. 3 is a graph showing the relationship between relative magnetic permeability and temperature, with relative magnetic permeability on the vertical axis and temperature on the horizontal axis, and the relationship between them is shown by a solid line. Further, P indicated by a broken line indicates the Curie point. As is clear from this figure, the relative magnetic permeability μ decreases as the temperature increases, and saturates at 1 when the temperature reaches the Curie point of 2 or higher. As a result, when the first heating device 5 heats both edge portions 1a, 1a of the open pipe 1 to a temperature equal to or higher than the Curie point 2, the relative magnetic permeability becomes 1 and the penetration depth δ increases.

Using the outer circumferential surface heat affected width A, central portion heat affected width B, and inner circumferential surface heat affected width C, the heat affected width ratio, which represents the uniformity of the heating state, is determined as shown in equation (2) below. The influence width ratio and the first
The relationship with the preheating temperature by the heating device is shown in FIG.

Figure 4 shows C with a wall thickness of 4.0 mm and an outer diameter of 54I11111.
O, 15%, Mn0 966% carbon steel preheating frequency 55k
This is a graph showing the relationship between the heat effect width ratio and the preheating temperature in the case of heating at llz, with the heat effect width ratio on the vertical axis and the preheating temperature on the horizontal axis. From FIG. 4, the heat effect width ratio approaches 1 and saturates to its maximum value when the preheating temperature reaches the Curie point 2 or more shown in FIG. 3. This is because, as described above, the relative magnetic permeability becomes 1, the penetration depth δ becomes large, and the thickness direction of both edge portions 1a, la of the open pipe 1 is heated almost uniformly. As a result, it is clear that when the preheating temperature is set to a temperature equal to or higher than the Curie point 2, both edge portions la, la of the open pipe 1 are heated uniformly.

Moreover, when the preheating temperature is set to a temperature equal to or higher than the Curie point 2, the welding quality becomes good.

FIG. 5 is a graph showing the correlation between the preheating temperature and welding temperature and the occurrence of flash when butt welding carbon steel with C=O, 15%, Mn=0.6%. In the figure, the horizontal axis shows the preheating temperature, which is the heating temperature by the first heating device 5, and the vertical axis shows the welding temperature finally given by the second heating device 6. The data is shown as a black circle, the data when no flash occurs and the bonding condition is good is shown as a white circle, and the data when no flash occurs and the bonding condition is poor is shown as an open triangle. . In the figure, H indicates a high quality region where flash does not occur and the bonding state is good. As is clear from the figure, the width of the range in which the product ffjl region can be obtained increases from near the Curie point P as the preheating temperature increases, and becomes approximately constant at the Curie point 2 or higher. From this, it is clear that when the preheating temperature is set to be higher than the Curie point, it becomes easier to obtain a high quality product.

〔Effect of the invention〕

As detailed above, in the method for manufacturing an electric resistance welded pipe according to the present invention, the first heating device preheats both edge portions of the open pipe 1 to a temperature higher than the Curie point, thereby uniformly heating both edge portions. By doing so, it is possible to suppress the generation of beads ejected due to upset, thereby improving bead cutting performance, improving work efficiency, and preventing welding defects such as penetrators and the occurrence of flash, etc. This invention has excellent advantages. be effective.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an ERW pipe manufacturing apparatus used to carry out the ERW pipe manufacturing method according to the present invention, and Fig. 2 shows the edges of both sides of an open pipe subjected to conventional butt welding. Schematic side view, Figure 3 is a graph showing the relationship between specific i3 magnetic coefficient and temperature, Figure 4 is a graph showing the relationship between heat influence width ratio and preheating temperature, and Figure 5 is a graph showing the relationship between butt welding. Graphs showing the relationship between preheating temperature and welding temperature and the presence or absence of flash, and FIGS. 6 and 7 are schematic diagrams showing a conventional method of manufacturing an electric resistance welded pipe. 1...Open pipe 3...Squeeze roll 5.
...First heating device 6...Second heating device patent Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent attorney Kawa Jin
Noboru No. 4 Flash Z 5 Figure

Claims (1)

[Claims] 1. Opposing both side edge portions of the open pipe are
In the method of manufacturing an electric resistance welded pipe by successively heating and melting with a heating device and a second heating device, and butt welding with a squeeze roll, the edges of both sides of the open pipe are A method for manufacturing an electric resistance welded tube, characterized by heating the tube to a temperature above the Curie point.