SU963753A1 - Liquid bridge condition pickup for electric arc welding with short circuits of arc gap - Google Patents

Description

This invention relates to the field of welding technology.

A liquid jumper state sensor is known, which is a threshold element that is triggered when the voltage on the jumper reaches a predetermined value of threshold voltage 1.

Although the voltage drop on the jumper reflects the change in its dimensions, however, as a result of the instability of the welding process, the voltage drop curve on it changes from cycle to cycle. Therefore, at a constant value of the threshold voltage, the time interval from the moment the sensor triggers (the moment the switching commences) to the moment of the supposed explosion of the jumper can significantly change during the welding process from cycle to cycle.

In this case, after the triggering, the self-destruction time of the jumper may be longer than the current switching interval, and the jumper will fail at a high current, i.e. switching will be premature. If the jumper is destroyed quickly and its destruction time is shorter than the current decrease time, the switching will be carried out too late and also with

bhhmshom current. In both cases, the destruction of the jumper occurs at more current, which leads to a significant metal spatter (4-5%) and deterioration of the welding quality.

Thus, the known sensor does not allow normal commutation in all welding cycles when the jumper is destroyed during operation.

10 only a small auxiliary current is flowing through it, i.e. without an explosion.

The closest to the technical essence of the invention is the sensor of the state of the liquid jumper included in the device for electric arc welding with short-circuit 2J

The sensor of the state of the liquid jumper contains parallel connected

20 differentiating and integrating. the circuits whose inputs are connected to the arc gap, and to the input of the threshold element. In d.tchik, the sum of the differentiated 25 and the integrated voltages on the jumper with the threshold voltage is compared. However, as a result of the instability of the welding process, the degradation of the transfer may occur prematurely or

30 too late, i.e. with a large Totce arc, which leads to a significant spatter of the electrode metal (4-5%). The aim of the invention is to reduce the splashing of the metal by determining the start time. switching the current through the jumper depending on the shape of the voltage curve on the jumper in the last stage of the short circuit. The goal is achieved. By the fact that the generator of a linearly varying voltage, two comparison circuits and two voltage dividers, are introduced into the sensor of the state of a short-circuit liquid arc jumper containing a threshold element and a differentiated circuit connected parallel to another gap. The input of each voltage divider is connected to the input of a differentiating circuit, the output of which is connected to the first inputs of the comparison circuits. The second inputs of the comparison circuits are connected to the corresponding outputs of the voltage dividers, the outputs to the generator inputs of a linearly varying voltage, the output of which is connected to the input of the threshold element. The transmission coefficient of the first voltage divider is equal to where Up - the voltage on the jumper 3Up is the time derivative of the voltage on the jumper, and the transmission coefficient of the second voltage divider is equal to. FIG. 1 is a block diagram of a liquid jumper state sensor; in fig. 2 shows timing charts explaining the operation of the liquid jumper state sensor. The sensor of the state of the liquid jumper contains a voltage divider 1 with a transmission coefficient K ,, differentiating circuit 2, a voltage divider 3 with a transmission coefficient K2 of comparison circuit 4 and 5, a generator of linearly varying voltage, and a threshold element 7. The inputs of the divisors 1 and 3 and differentiating circuit 2 are connected to the arc gap. The outputs of dividers 1 and 3 are connected to one of the inputs of each of the comparison circuits 4 and 5, the output of the differentiating circuit 2 is connected to the other input. The outputs of the comparison circuits 4 and 5 are connected to the inputs of a linearly varying voltage generator b connected to the input threshold element 7 Voltage divider 1 Designed to divide the voltage on the jumper UE by 1s times (where the voltage divider 3 is intended to divide the voltage on the jumper Up 2 ((. times to get the starting moment of the generator 6 linearly varying voltage re married they are linearly falling voltage in the middle of the time interval from the moment of time to the moment of the proposed explosion of jumper 0. The comparison circuits 4 and 5 serve to compare the voltage from the output of dividers 1 and 3 with the derivative voltage on the jumper of the differential circuit output 2. Threshold element 7 is defined The instant of the beginning of the commutation of the current through the jumper on the equality of the linearly falling voltage from the generator b with the specified threshold voltage 1M. Unopass works as follows. Let us consider two cycles of sensor operation. On the time diagrams, the voltage curves for the 1st cycle are shown by solid lines, and for the 2nd cycle, by dotted lines. To compare timing diagrams for the 1st and 2nd sensor cycles, these diagrams are combined in FIG. 2 along the time axis. The voltage on the jumper Up goes to the inputs of dividers 1 and 3 and to the input of differentiating circuit 2 from the output of which is derived from the voltage Up goes to one of the inputs of the comparison circuits 4 and 5. From the output of the divider 1, a voltage equal to K-, Up is supplied to the other input of the comparison circuit 4. dTxewa 4 comparisons compares the derivative of the voltage on the jumper with the voltage K-i Up. While these voltages are not equal to each other, there is no signal at the output of the comparison circuit 4. If these voltages are equal, at the time t-t (for the 1st sensor operation cycle) or (for the 2nd sensor operation cycle), the output of the comparison circuit 4 appears in the form of a voltage jump. In this case, the following equality holds: - L II 1 n, - transfer coefficient t, voltage divider 1 (constant value). The output signal of the comparison circuit 4 goes to one of the inputs of the generator b and starts it to the linearly increasing voltage mode at time t (for the 1st sensor operation cycle) or at t (for the 2nd cycle). From the output of the divider 3, a voltage equal to the other input of the comparison circuit 5 is supplied. The comparison circuit 5 compares the voltage derivative on the jumper with the voltage KgU. While these voltages are not equal to each other, there is no signal at the output of the comparison circuit 5. If these stresses are equal at time t2. (for the 1st cycle) or t2 {for the 2nd cycle) a output in the form of a surge voltage appears at the output of the comparison circuit 5. In this case, the following equality holds;

 . 2b,

-gr-tj

P

ib

where -t- is the transmission coefficient

2 divider 4 (constant value),

The time point tg is in the middle of the time interval between the time point t-,. and the moment O (the moment of the proposed explosion of the passage of the wire) for the 1st cycle. For the 2nd cycle, tJj is in the middle of the time interval between tJ and the moment n 0.

The signal from the output of the comparison circuit 5 is fed to another input of the generator 6 and starts it to the linearly falling voltage mode with the same time constant as the linearly rising voltage mode at time t2 (for the 1st cycle) or in t2 (for the 2nd cycle).

Signals from the output of the generator b are fed to the input of the threshold element 7, where it is compared with the predetermined threshold voltage Unop. By comparing these voltages, the output pulse of the threshold element 7 is a voltage pulse whose forward phase differs for the 1st and 2nd sensor operation cycles, but its falling edge coincides for the 1st and 2nd cycles, as well as for any other operation cycles. The trailing edge of the signal and determines the time instant t is the instant of the beginning of the current switching through the jumper.

Thus, for different sensor operation cycles, which are characterized by voltage curves on a jumper of different shapes, the time interval from the start of switching tj to the moment O of the supposed explosion of the jumper will be constant.

This allows for the normal switching of current through the jumper and the jumper will be destroyed due to the surface tension forces.

with a small amount of auxiliary current. The blast energy of the jumper is minimal. As a result, the sputtering of the electrode metal will be significantly reduced to 2-2.5%

(Ie ... 2. times compared with the prototype sensor). At the same time, labor costs for cleaning parts from electrode metal splashes are also reduced.

Claims (2)

1. USSR author's certificate 484055, cl. At 23 K 9/00, 07.07.73. 2. USSR author's certificate 551134, cl. At 23 K 9/00, 17.07,75 (prototype).