KR20120007756A - High frequency electric resistance welding method - Google Patents

Abstract

PURPOSE: A high-frequency electric resistance welding method is provided to improve welding quality by controlling the periodicity of a narrow gap. CONSTITUTION: A high-frequency electric resistance welding method is as follows. Welding power for welding a pipe forming material is set(S12). A power control reference and supplied first power for controlling the level of output power are inputted(S16). The supplied first power is measured(S22). An electric transformer, which receives the first power, computes output power that is second power(S24). A power control reference is changed by comparing the output power with set welding power(S40).

Description

High frequency electric resistance welding method {HIGH FREQUENCY ELECTRIC RESISTANCE WELDING METHOD}

The present invention relates to a high frequency electric resistance welding method. More specifically, the present invention relates to a high frequency electric resistance welding method capable of minimizing welding defects in the process of manufacturing steel pipes such as pipes.

In general, high frequency electric resistance welding used to produce steel pipes such as pipes is a method of generating resistance heat by supplying a high frequency current to a welded portion to melt and join a welded object.

Usually, the frequency of the current supplied for high frequency electric resistance welding is a high frequency of 300 to 1000 kHz. When two high-frequency currents are supplied by contacting two to-be-welded members, which function as electrodes, to form a short-circuit closed circuit centered on the contactor, the region to be welded near the closed circuit is formed by resistance heat. Melts. A steel pipe is manufactured by continuously pressing the molten portion with a pair of pressure rollers to form a welded seam.

Such high frequency electric resistance welding has been widely used to manufacture an electric seal pipe because of its high welding speed. In particular, high-frequency electric resistance welding is excellent in economics and excellent in welding quality, and is widely applied to parts requiring high quality of oil and gas oil pipes, oil well pipes, and mechanical structural steel pipes. Therefore, the sealing tube used for such an important application must be strictly controlled in the quality of the welded portion thereof.

In order to minimize the occurrence frequency of weld defects of steel pipe manufactured by high frequency electric resistance welding method, an automatic heat input control device is developed and used. This automatic heat input control device is used for welding which affects the welding quality. It detects key welding variables such as speed and the thickness of the welded object and automatically adjusts the welding heat input to maintain proper welding conditions.

However, since the automatic heat input control device uses a feedback signal according to the change in the oscillation frequency, the shape of the bead, the welding temperature, and the like, the response of the control is slow as about 1 second due to the time delay for signal processing.

Meanwhile, as a result of observing high frequency electric resistance welding process using a high speed camera, the welding defect is related to the periodicity of the narrow gap, and the periodic change of the narrow gap is hundreds to thousands of times per second. It was confirmed that it is repeated throughout.

Therefore, when the automatic heat input control device having a response of about 1 second is used, there is a problem that welding defects may occur up to several thousand times per second.

The present invention is to solve the problem to minimize the welding defects that may occur in the high-frequency electrical resistance welding process.

More specifically, it is an object of the present invention to provide a high frequency electric resistance welding method that can improve welding quality by minimizing welding defects by controlling welding power to control the periodicity of the narrow gap.

In the high frequency electric resistance welding method according to the present invention for solving this problem, the step of setting the welding power for welding the tube material, the level of the output power supplied to the two metallic contacts installed near the welding portion of the tube material Inputting a power control reference for adjusting the power supply and primary power to be supplied, measuring the primary power to be supplied, and calculating the output power which is the secondary power output by the transformer receiving the primary power And comparing the output power with the set welding power and changing the power control reference so that the output power is equal to the set welding power.

The primary power is a three-phase AC power of 60Hz frequency, the secondary power is characterized in that the DC pulse power.

The secondary power may be calculated by multiplying a secondary current calculated by multiplying a transformer current ratio of the transformer by a primary current of the primary power and a secondary voltage of the transformer output terminal.

The secondary voltage is characterized in that it is measured through signal isolation and decompression.

The power control reference is leveled to correspond to the level of the output power and is stored in advance.

The change of the power control reference is automatically performed in memory logic until the output power is equal to the set welding power.

According to the present invention, there is an effect that can minimize the welding defects that may occur in the high-frequency electrical resistance welding process.

More specifically, by controlling the welding power to control the periodicity of the narrow gap, the generation of welding defects is minimized and the welding quality is greatly improved.

FIG. 1 is a photograph showing a change in a narrow gap appearing in a welding area during high frequency electric resistance welding.
2 is a view showing a correlation between welding defects, welding power, and narrow gap length.
3 is a view showing a high frequency electric resistance welding method according to an embodiment of the present invention.
4 is a view conceptually showing an example of a device configuration for performing a high frequency electric resistance welding method according to an embodiment of the present invention.
FIG. 5 is a diagram illustrating a power supply system for converting primary power of three phases into secondary power of a pulse of pulse through a transformer and supplying the primary power to a welding site according to an embodiment of the present invention.
6 is a photograph of a welding portion to which a high frequency electric resistance welding method according to an embodiment of the present invention is applied.
FIG. 7 is a view conceptually illustrating a welded portion of FIG. 6.
8 is a view for explaining a process of discharging the melt to the outside in accordance with the change in the Lorentz force according to the applied welding current and the magnetic field in an embodiment of the present invention.

Before describing an embodiment of the present invention, elements for determining welding quality according to high frequency electric resistance welding will be described.

FIG. 1 is a photograph showing a change in a narrow gap appearing in a welding area during high frequency electric resistance welding.

Referring to FIG. 1, it can be seen that the narrow gap G undergoes a four-step change process within one period.

The first stage (Stage 1) is the process of generating the narrow gap (G), the second stage (Stage 2) is the development and development process of the narrow gap (G), and the third stage (Stage 3) is the narrow process The short-circuit BR, that is, the generation of the bridge, which destroys the gap G, is generated, and the fourth stage (Stage 4) is the disappearance of the narrow gap G.

In order to examine the correlation between the periodicity of the narrow gap G and the weld defect, the length of the narrow gap G and the amount of the weld defect generated were measured while varying the welding heat input, that is, the welding power supplied to the weld portion. The results are shown graphically in FIG.

FIG. 2 shows the correlation between weld defects, welding power, and narrow gap length when the welding speed is 16 m / min, the welding frequency is 320 KHz, and the V-angle, which is an angle formed by the cracked surface of the tubular material, is 5 °. The figure which shows.

Referring to FIG. 2, it can be seen that when the welding power maintains a certain range, the length of the narrow gap also maintains a predetermined range corresponding to the welding power, and the welding quality in this case is good. On the other hand, when the welding power is out of this range, it can be seen that the welding quality is sharply degraded.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to provide a high frequency electric resistance welding method that can greatly improve welding quality by controlling welding power to control the periodicity of the narrow gap.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention;

3 is a view showing a high frequency electric resistance welding method according to an embodiment of the present invention, Figure 4 is a view conceptually showing an example of a device configuration for performing a high frequency electric resistance welding method according to an embodiment of the present invention FIG. 5 is a diagram illustrating a power supply system for converting three-phase primary current into a single-phase secondary current using a transformer and supplying the weld current to a welding site, and FIG. 6 is an embodiment of the present invention. 7 is a photograph of a welding portion to which a high frequency electric resistance welding method is applied, and FIG. 7 is a view conceptually illustrating a welding portion of FIG. 6.

3 to 7, the high frequency electric resistance welding method according to an exemplary embodiment of the present disclosure may include setting welding power (S12), inputting a power control reference and primary power to be supplied (S16), Measuring the primary power (S22), calculating the secondary current (S24), measuring the secondary voltage (S26), calculating the output power (S28) and the output power and the set welding power And comparing the power control reference so that the output power is equal to the set welding power in comparison (S30, S40).

First, in step S12, the welding power, the welding speed, and the welding frequency for welding the tube material are set. Welding power, welding speed, and welding frequency are values obtained through experiments and are pre-stored values that are optimized according to the material and thickness of the tube material.

Next, in step S14, a pair of squeeze rolls R1 and R2 are rotated to start supplying the tubular material.

Next, in step S16, the waveform of the power control reference and the primary current is selected to input the primary power. The power control reference is a value for adjusting the level of the output power, and is a value that is leveled to correspond to the level of the output power and stored in advance in the memory. In step S16 one of these values is selected, at which time the selected value becomes the initial power control reference. Primary power input in step S16 may be a three-phase AC power of 60Hz frequency.

Next, in step S18, the supply of primary power is started. A process of supplying primary power will be described with reference to FIGS. 4 and 5. For example, when primary powers i1u, i1v, and i1w of three-phase alternating current are supplied to a transformer, a secondary current I2 of a DC pulse is output through a conversion and filtering process in the transformer. This secondary current I2 is supplied through a loop consisting of a metallic contact S1, a tubular material, and a metallic contact S2. The secondary voltage V2 is the potential difference between the contact S1 and the contact S2, and the output power which is the secondary power supplied to the welding site is the product of the secondary current I2 and the secondary voltage V2. This secondary power may be DC pulse power.

Next, in step S22, the primary current supplied is measured. Although not shown, the primary current may be measured using three AC current sensors.

Next, in step S24, the secondary current is calculated by multiplying the measured primary current by the transformer ratio of the transformer.

Next, in step S26, the secondary voltage between the two contacts S1 to which the secondary current is supplied and the contacts S2 is measured. Since the secondary voltage is a high voltage, it is measured after signal conversion using a pressure reduction circuit and an insulating element (not shown), for example.

Next, in step S28, the output power is calculated by multiplying the secondary current and the secondary voltage.

Next, in step S30, the output power is compared with the welding power set in step S12. As a result of the comparison in step S30 1) If the value of the output power is different from the value of the set welding power, it is switched to step S40, and 2) If the value of the output power is equal to the value of the set welding power, it is switched to step S50.

In step S50, the power control reference is changed so that the output power is equal to the set welding power.

As described above, the power control reference is a value for adjusting the level of the output power, and is a value leveled to correspond to the level of the output power and stored in advance in the memory. In step S50, the process of changing this value is automatically performed in the memory logic. If the power control reference is changed, the magnitude of the primary power supplied in step S18 is changed accordingly. When the magnitude of the primary power is changed, the output power is eventually changed through the above-described process. These processes are performed repeatedly until the output power is equal to the set welding power.

While the welding is performed by the output power equal to the size of the welding power set through the above processes, when the welding end signal is input through step S50, the welding is finished.

8 is a view for explaining a process of discharging the melt to the outside according to the change in the Lorentz force according to the welding current and the magnetic field applied in the present invention, the current density (J) and the magnetic flux density (B) It can be seen that the Lorentz force (P) expressed as a vector product of) maintains the narrow gap (G) by being in equilibrium with the surface tension of the melt.

According to the present invention as described in detail above, there is an effect that can minimize the welding defects that can occur in the high-frequency electrical resistance welding process.

More specifically, by controlling the welding power to control the periodicity of the narrow gap, the generation of welding defects is minimized and the welding quality is greatly improved.

Although the technical spirit of the present invention has been described above with reference to the accompanying drawings, the present invention has been described by way of example and is not intended to limit the present invention. In addition, it is obvious that any person skilled in the art may make various modifications and imitations without departing from the scope of the technical idea of the present invention.

i1u, i1v, i1w: primary current
I2: secondary current
Vo: secondary voltage
V: V-convergency point
W: welding point
G: narrow gap area
R1, R2: Squeeze roll
S1, S2: Contact

Claims (6)

In the high frequency electric resistance welding method,
Setting welding power for welding the tubular material;
Inputting a power control reference for adjusting the level of output power supplied to two metallic contacts installed near the welded portion of the tubular material and the primary power to be supplied;
Measuring the primary power supplied;
Calculating the output power which is the secondary power output by the transformer receiving the primary power;
And comparing the output power with the set welding power to change the power control reference such that the output power is equal to the set welding power. The method according to claim 1,
The primary power is a three-phase AC power of 60Hz frequency, the secondary power is characterized in that the DC pulse power, high frequency electrical resistance welding method. The method according to claim 1,
And the secondary power is calculated by multiplying the secondary current calculated by multiplying the transformer current ratio of the transformer by the primary current at the primary power and the secondary voltage of the transformer output stage. The method of claim 3,
And the secondary voltage is measured by signal isolation and pressure reduction. The method according to claim 1,
The power control reference is leveled so as to correspond to the level of the output power is stored, characterized in that the high frequency electrical resistance welding method. The method according to claim 1,
Wherein the alteration of the power control reference is automatically performed in memory logic until the output power is equal to the set welding power.

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