SU1662787A1 - Method for resistance flash butt welding - Google Patents

Abstract

The invention relates to resistance butt welding by smelting and can be used in welding parts with a large cross section. The purpose of the invention is to increase the productivity of welding machines and the efficiency of the process. The method includes reflowing at a given tolerance at a low initial velocity of movement and its subsequent increase before draft. Before settling, the stability of the melting is controlled. In the process of monitoring the stability of melting in the presence of a short circuit in the process of increasing the speed, its duration is measured. The duration of the short circuit is compared with the set value and, when the set value is exceeded, the parts are diluted before the short circuit is terminated. The fusion is then resumed at a low initial rate of approach. Once a stable melting process is achieved, they again increase the rate of approach and control. The method allows to avoid product rejection in case of short circuit in the final stage of melting. 2 Il.

Description

The invention relates to flash butt welding, and can be used in welding parts with a large cross section.

The aim of the invention is to increase the productivity of welding machines and the efficiency of the process.

FIG. Figure 1 shows the diagrams: changes in the speed of approaching VB of parts to be welded depending on the path of approaching L (1) and changes in the welding current St depending on the process time t (2); in fig. 2 is a structural block diagram of an apparatus for implementing a welding method. . The essence of the method is as follows.

According to the flash butt welding method at a low initial

the speed of movement and its subsequent increase before the draft in the process of increasing the speed control the stability of the melting and interrupt it in the presence of short circuits. In the presence of a short circuit c. In the process of increasing the velocity V, its duration AtK.3 is measured. compared to a predetermined value and, when the predetermined value is exceeded, the parts are diluted until the short circuit is terminated, then the reflow is resumed at a low initial velocity of approach, and when a stable process of melting is achieved, the approximation speed and control are again increased. Continuous monitoring of the stability of the melting is performed from the moment of the beginning of the melting at an increasing rate. At this stage of fusing, short circuits occur

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when the speed of approaching parts exceeds the melting speed of contact bridges. This is a consequence of insufficient heating, spasmodic speed changes due to malfunctions in the hydraulic system of the machine, etc. At the same time, contacts with low resistance are formed between the ends of the parts and their explosion-like destruction becomes impossible, as the approach speed continues to increase. power supply is limited. Therefore, after detecting a short circuit, its duration is measured and compared with a predetermined value. For example, if, when welding pipes from steel 20, the duration of a short circuit is more than 3 periods of the current frequency (0.06 s), which is unacceptable in the final stage of melting, then a command is given to dilute the parts to be welded (Fig. 1). When the parts to be welded are reversed, the short circuit is eliminated, but the flashing continuity is interrupted. The time from the moment the command to reverse is given to the resumption of the reflow after the termination of a short circuit is on average 0.3-0.8 s. At the same time, the metal at the ends cools down and is rapidly oxidized with the formation of solid films. The resumption of fusion with increasing speed inevitably leads to a short circuit. Therefore, after reversal, the reflow resumes at a low initial velocity (Fig. 1, curve 1).

When a stable process is achieved (Fig. 1, curve 2), the speed is repeatedly increased and the melting stability is monitored. The magnitude of the re-melting allowance at the initial low speed until a steady process is obtained is, as practice shows, 1.5-3.0 mm with a speed of the drive providing reverse and return to reflow in 1–2 s. Obtaining a sustainable process is estimated from electrical power fluctuations. In the case of repeated short circuits in the process of increasing the speed before sedimentation, according to the proposed method, it is repeated no more than 2 times. The repetition of short circuits more times in the process of increasing the speed indicates gross violations of the technological mode. In this case, the further continuation of the welding process is inexpedient, since the flush allowance is limited.

The method can be implemented using the automatic control and regulation scheme (Fig. 2) in the following sequence of operation of its elements.

After melting, the specified allowance (counted by the displacement sensor 1) with

LOW Initial SPEED / beg (fig. 1)

the programming device 2 generates a co- ,.

Mandu speed controller at the beginning of the melt with increasing speed. At the same time, permission is given to the refining stability control unit 3 and the short closure duration measurement unit 4 for monitoring the reflow stability control. The magnitude of the current in the contact zone is monitored by the current sensor 5, and the voltage value in the welding circuit is monitored by the sensor 6.

5 When the current rises to a level exceeding the short circuit current in the process of increasing the speed, the comparator K of block 3 switches to zero and enables the pulse counting of the counter CT of block 4. The pulses are generated using a zero detector (DN), each pulse corresponds to a current frequency period . If the short circuit duration is less than three frequency periods of the supply current, the signal at the input of the comparator K of block 3 takes a high level and the counter of block 4 of the unit zeroes the measured value. Thus, the presence of single bursts of current amplitude resulting from the explosion of contacts is not taken into account. If the duration of the short circuit has exceeded three periods (0.06 s), then from the output of the counter of block 4 to the input 7 of the programming device 2 a signal is received, at which

5, a command is issued to the feed rate controller to reverse the parts to be welded. When the current reaches a value below the short circuit level, the signal at the output of comparator K of unit 3 becomes equal to

0 unit and the output of block 4 switches to zero. The programmer 2 then issues a command to the speed controller to resume the reflow at a low initial speed (Fig. 1) and begins to count the additional reflow allowance at a low initial speed. After achieving a steady reflow, a command is issued to re-speed up. This command passes to the speed controller only if the process is stable, i.e. there are no significant fluctuations in power. At the same time, the signal at the output of the power control unit 8 for power fluctuations is equal to a logical unit. At the same time, a command is issued to allow the control to check blocks 3 and 4 and the control is repeated. The repetition of the speed increase and control is performed no more than two times. The number of repeats is recorded by the counters in the programming device.

2 and after repeating it twice, the welding process is interrupted. The power released at the junction is monitored by power sensor 9.

All units of the device are made according to known schemes. As a control unit for the stability of the melting of the 3, a comparator K 521 SAS was used. The unit for measuring the duration of a short circuit is made on the basis of a counter with a decoder on the microcircuit K564 IE9. A comparator with a horse was used as a power control unit. The power sensor is made on the K525 PS2 microcircuit. Movement sensor-type BE-178.

The method is implemented on a K584 machine for welding high-pressure pipes during the construction of trunk gas pipelines under conditions of underwater dry welding. Pipes welded with a diameter of 219 mm and a wall thickness of 12 mm made of steel X60.

Welding was carried out at the following technological parameters: 30 mm reflow allowance; initial reflow rate of 0.25 mm / s; final flash rate 2 mm / s; melting time with an increasing speed of 10 s; allowable duration short-circuit in the process of increasing the speed of 0.03 s; 12 mm draft allowance; upsetting speed 50 mm / s.

B

The application of the method allows to avoid the forced rejection of products in case of a short circuit in the final stage of melting, at the same time saving metal, energy and increasing machine productivity

Claims (1)

Invention Formula A flash butt flash welding method that includes reflowing at a predetermined tolerance at a low initial speed of movement and its subsequent increase before slump, while before slump, the stability of the flashing is monitored for short circuits, due to the fact that, in order to increase welding machine productivity and efficiency process, in the process of controlling the stability of the melting in the presence of a short circuit, its duration is measured, this duration is compared with the specified value and when exceeding 3 values of the items is diluted until no short circuit, and then is resumed at low initial melting speed convergence and reaches a stable process reflow again increase the speed of convergence and control. FIG. / Draft