SU1641546A1 - Method for control of flash-butt resistance welding - Google Patents

Abstract

The invention relates to welding and can be used to connect large cross section pipes in various fields of engineering. The purpose of the invention is to stabilize the quality of welded joints. In the process of melting at a low speed of approach, two parameters are controlled: the allowance for melting and the average speed of approach of parts. When they reach the specified values, the correction is turned off, after which the power in the spark gap is monitored, and at a stable value for half a second, the approach speed is increased. 2 Il. SL

Description

The invention relates to welding and can be used in flash butt welding by melting parts of a large developed section, for example, pipes.

The purpose of the invention is to increase the stability of the properties of welded joints by providing repetitive from cycle to cycle heating of parts and eliminating short circuits in the welding circuit with increasing convergence speed.

On league. Figure 1 shows a plot of the heating temperature of the parts versus the allowance for flashing at parts approaching speeds of 0.11 and 0.25 mm / s (4, 10, 15, 0 mm - the distance of the thermocouple from the surface of melting); on pin 2a, the voltage recorded on the motor that controls the follow spool, obtained by setting the welding machine without welded parts (U h is the specified voltage in the process of moving parts together at low speed); on league. 26 - recording of the actual voltage on the engine controlling the next slide valve when welding pipes (Li is the level of voltage reduction on the engine compared to the set; A is the moment of correction off; on Lig. 2c is recording the power in the spark gap at pipe welding.

The essence of the present invention is as follows.

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The process of welding large-section parts is carried out on modes characterized by the maximum thermal cycle in the parts being welded, which is determined by the quasistationary thermal state.

For rational programming of the welding process, it is necessary to know the moment of obtaining a quasi-stationary thermal field with the maximum possible heating of the parts. Experiments show that heating during reflow is most accurately determined by the allowance for reflow. In this case, a quasi-stationary thermal state, for example, when welding pipes, sheets with a thickness of 10-30 mm, occurs after a reflow of 30 mm of the allowance (Fig. 1). The temperature fields in the reflowable parts at a convergence rate of 0.1-0.25 mm / s (it is these speeds that provide the maximum thermal cycle) are almost identical (figure 1). A decrease in speed of less than 0.1 mm / s reduces the stability of melting and affects the heating uniformity over the section of the part, and an increase of more than 0.25 mm / s increases the gradient of the temperature field, i.e. the amount of heat accumulated in the part is reduced.

When setting up the welding program in time, which is produced without the parts being rolled, i.e. without current in the welding circuit and without a signal in the correction circuit, on the motor that controls the next slide valve, is set to the voltage Uj (Fig 2a), which is proportional to

according to the speed of approaching parts. In the absence of a signal in the correction circuit and, accordingly, a constant value of Uj in time, the allowance S for reflow is uniquely determined 40

Example. Implementation of flash butt welding by fusing pipes φ 14-1420 mm. Pipes of such diameter are used in the construction of pipelines of critical purpose, therefore, when welding such pipes, high and stable quality of connections is especially necessary. Pipe welding

The ratio is (U) to. When welded - 45 $ 219 20 mm on a K584 machine, the actual voltage U, (Fig, 26), according to the program,

on the engine that drives the barely fusing in the first stage with the speedy

This valve is smaller than U by 0.2 mm / s. After switching on the program, it depends on many variable factors and controls the value of the flashing allowance and the average speed of approach. If during the melting of a 30 mm allowance, the average approach velocity is within 0.11-0.25 mm / s, a command is issued to disable the correction. After the correction is turned off, the power level in the welding circuit is monitored and, if it is at a stable level, a command to increase the speed is issued for 0.5 s. Possible va-

for example, the quality of stripping parts, the state of the current-carrying shoe of the welding machine, voltage fluctuations in the network, etc., and is therefore variable and unpredictable from welding to welding. Oscillations U result in a change in the value of S from welding to welding. Accordingly, the heating of parts also fluctuates, and only towards

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decrease, since U is always less than b when the approach speed corrector is working. Thus, in order to obtain a repetitive from cycle to a heating cycle of parts, it is necessary to provide a predetermined flush allowance and an average speed of approach of the part during the flashing time at low speed.

If the average rate of convergence is not; however, the reflow is continued, and the correction is turned off when the actual value of the average velocity corresponds to the preset.

When the correction is turned off (point A in Fig. 26, c), there is a slight increase in the speed of parts approaching (depending on & U). This can lead to an abrupt increase in power due to the increment in the average area of simultaneously existing contacts and transients in the welding circuit. In this connection, after switching off the correction, a command to increase the speed of approaching should be given only at a stable power level. It was established experimentally that a stable power level for 0.5 s is evidence of a steady process. An increase in time of more than 0.5 s results in a waste of time and energy, and a decrease in less than sec does not allow a reliable talk about a sustainable process.

Example. Implementation of flash butt welding by fusing pipes φ 14-1420 mm. Pipes of such diameter are used in the construction of pipelines of critical purpose, therefore, when welding such pipes, high and stable quality of connections is especially necessary. Pipe welding

5 $ 219 20 mm on the machine K584 produces 0.2 mm / s. After turning on the program

we control the amount of flashing allowance and the average speed of approach. If during the melting of a 30 mm allowance, the average approach velocity is within 0.11-0.25 mm / s, a command is issued to disable the correction. After the correction is turned off, the power level in the welding circuit is monitored and, if it is at a stable level, a command to increase the speed is issued for 0.5 s. Possible va-

When the average approach speed is less than 0.1 mm / s (above 0.25 mm / s, it cannot be, because when the corrector is working, the actual speed of approach is always less than the specified one).

In this case, the reflow process is continued, and the offset is turned off when the average velocity reaches a predetermined value within Q 0.10-0.25 mm / s. It was established that if after reflow of 30 mm the average speed was lower than the specified one (in our case it was less than O, 1 mm / s, then with continued reflow by 3-5 mm, the actual average speed reaches the specified value. This is due to with the greatest intensity, the corrector reduces the target convergence rate at the initial stage of flashing. As the ends are heated, the flashing process becomes more stable and with continued 3-5 mm flashing of oversize more than 30 mm with a predetermined approach velocity of 0.2 mm / s / 25 The predetermined speed of parts approaching when melting at low speed) the average speed of approaching reaches a predetermined

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nor - signal on the engine, control

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following spool, processed on a specific amplifier. Monitoring the stability of the power level is provided by a signal from the mode sensor of the comparator.

The application of the proposed method of controlling the process of resistance butt welding allows to reduce the scrap during welding by 4%.

Claims (1)

Invention Formula - A method of controlling the process of resistance butt welding by continuous flashing of parts, mainly tubes of developed cross-section, in which the time control is carried out according to a program that includes maintaining flashing at a low speed of parts approaching with its flashing current correction, turning off the correction and an increase in the rate of approaching the start of the precipitation, which is the fact that, in order to increase the stability of the properties of welded joints by providing repeated heating of parts Go value. Only in this case, the level of 30 in all cycles and the exclusion of short You can issue a command to disable the correction. If further melting (3-5 mm allowance) does not give the desired result, then the process is interrupted, as this indicates gross violations of the welding welding mode or a malfunction of the displacement drive. For the implementation of the method using known devices. For example, a signal from the displacement sensors can be used to count the value of the flashing allowance, to determine the average velocity value five short circuits in the welding circuit with increasing speed of approach, in the process of melting at low speed, the value of the melted allowance from the beginning of the program and the average speed of approach of parts is measured, compared with the set values and when the set values are reached with both parameters, the correction power. in the spark gap and at a stable power level, within half a second, a command is given to increase the speed of approach. 15 20 T5 3035 FIG. 1 U.B a col 5 M3 four Wrw Usbl 0.25mp / s Vc6fi 0.11 mp / s 40 Aonr, mi c Ui