SU41608A1 - Electric welding device - Google Patents

Description

The present invention relates to devices for spot electric welding, which are of particular importance for welding metals that drastically change their properties during overheating (for example, stainless steel, duralumin, etc.).

The main requirement for a spot welder is the need to accurately meter the amount of energy delivered to each point being welded.

It is known that, depending on both the grade of the metal and its thickness, a well-defined amount of energy is required for high-quality welding. The latter mainly depends on the size of the current to be welded and on the duration of its passage.

The oldest and most common method of controlling the duration of the welding current is to connect a welding switch of a mechanical switch to the primary circuit, which, after clamping the parts between the electrodes of the apparatus, closes the current, and then, after the necessary time delay, it opens. However, a mechanical switch is a device quite incomplete, and the time delay given to them can vary within a few hundred percent.

At present, it is already known to use for closing and opening the welding current of thyratrons, usually included in the secondary winding of a serial transformer. To control the duration of the period of operation and the intervals between the individual periods of operation of the thyratrons, the inclusion of a direct current source and an ohmic resistance through which rectangular current pulses are sent to the grid circuit is used. Since the thyratron is practically inertia-free, it makes it possible to produce with very high precision the shortest time limits.

Thanks to the use of thyratrons, it also becomes possible to successfully carry out welding with a discontinuous seam, i.e., such a welding, in which the objects to be welded all the time move between the rollers of the welding machine, and the current is supplied only by individual pulses; This method of welding has a number of advantages compared to simple seam welding.

The present invention relates to the aforementioned devices and consists in applying, in addition to the main, auxiliary thyratrons, which serve to send square current pulses in the circuit of the nets of the main thyratrons.

In the drawing of FIG. 1, the device schematic and FIG. 2-form current in the grid circuit.

- AC network, 2-welding transformer, the secondary winding of which is connected to the electrodes 5.

In the primary circuit of the welding transformer, a so-called seria-type transformer 4 is included, the secondary (high-voltage) winding of which is connected to the anodes of the thyratrons 5 w. 6. While these thyratrons are locked, the secondary winding of the serial transformer is open, and the last one represents a large inductive resistance. Therefore, relatively small power is supplied to the welding transformer.

When the thyratrons 5 and 6 are working, the secondary winding of the serial transformer is short-circuited. In this case, the resistance of the serial transformer becomes negligible, and considerable power is supplied to the welding transformer.

The operation time of the thyratrons 5 and 6 is regulated by the change in the grid voltage.

Normally, the grids of these thyratrons using a DC source 7 are given a large negative voltage so that the thyratrons are locked.

Consistently with the battery 7 is active resistance 8; when the current from the battery 9 is flowing through the latter, closing through the small thyratron 10, a voltage drop is produced at said resistance, compensating for the voltage of the DC source 7, due to which the thyratrons 5 and 6 are ignited.

Resistivity resistors 11 and 12 are used exclusively to limit the grid current of thratron 5 and no effect on the operation of the circuit.

The passage of current through resistance 5 is controlled as follows. Plus, the battery 9 is connected to the midpoint of the resistances 8 and / 3 connected together, which are connected to the anodes of the auxiliary thyratrons 10 and 14.

With the help of direct current sources 75 and 1c, the nets of the thyratrons 10 and 14 are given a negative bias sufficient to prevent

To ignite the thyratrons at a given anode battery 9 voltage. The thyratrons can be ignited by applying a positive pulse to their grids using transformers 17, 18.

When any of the thyratrons 10 and 14 is in operation, the capacitor 19 is charged to a voltage equal to the potential difference across the corresponding resistance 8 or 13.

The polarity at the capacitor clamps is determined by which of the W or 14 thyratrons is currently operating.

If, for example, the thyratron 14 is working, and the thyratron 10 is locked, on the left side of the capacitor 19 there will be a plus, and on the right-side the minus.

The current of the battery 9 will not be flowing through the resistance of 13 and the main thyratrons 5 and 5 will be locked.

If, on the grid of the thyratron 10, a positive pulse and a thyratron horizon are supplied by the transformer / 7, then the capacitor will be attached minus to the anode, and a plus to the cathode of the thyratron due to which the latter goes out. The current of the battery 9 will flow in this case over the resistance 8, and the main thyratrons 5 and 5 will work. The capacitor 19 is then recharged; on the right side there will be a plus, and on the left there will be a minus.

If then a positive pulse is applied to the grid of the thyratron 14, it will again light up, and the thyratron 10 will be locked by the discharge of the capacitor 19. The main thyratrons 5 to 6 will be locked again.

Thus, the duration of operation of the thyratron 70 determines the continuity of the welding current supply. The operation of the thyratron 14 determines the intervals between the individual feeds of this current.

The operation time of thyratrons 10 and 14 is controlled by a relaxation circuit consisting of two cold cathode ion diodes 20 and 21, constant capacitors 22 and 23, and high-resistance impedances 24 and 25.

The work of the relaxation scheme is as follows. If any of the thyratrons 10 or L4

The aiitept voltage between the anode and cathode is equal to the voltage of battery 9.

If, for example, the thyratron 10 is extinguished, then the capacitor 22 begins to charge through the resistance 24; as soon as the potential difference across it reaches the ignition threshold of the ion diode 20, the latter is immediately discharged through the primary winding of the transformer 17. At the same time, a positive pulse is applied to the grid of the thyratron 10 and it comes on. Thyratron 14 will be locked, therefore, between its cathode and anode, the full voltage of battery 9 will appear, and capacitor 23 will begin to charge through resistance.

When the voltage on the capacitor 23 reaches the ignition threshold of the ion diode 21, the latter is discharged through the primary winding of the transformer 18 and thus ignites the thyratron 14, the thyratron 10 goes out and the capacitor starts to charge, etc.

Thus, the charging time of the capacitor 23 controls the duration of the operation of the thyratron 10, i.e., the duration of the welding current on (in short, the welding time).

The charging time of the capacitor 22 regulates the duration of the burning of the thyratron 14, i.e. the duration of the interval between individual pulses of the welding current (in short, the interval time).

The duration of the charge of the capacitors 22 and 23 is determined by the capacitance of the latter, the magnitude of the active resistances 24 and 25 through which they are charged, as well as the ratio between the ignition voltage of the neon lamps and the voltage of the battery 9.

The final formula for the duration of the charge capacitor is as follows

V,

 (1- CR

 SI

Where

Vg is the voltage of battery 9;

Vz is the ignition voltage of neon lamps 20 to 21.

For stable operation of the circuit, it is necessary that the values of the threshold for ignition and voltage of battery 9 remain constant all the time. In addition, it follows from the formula that the smaller the ratio of these values, the less their change will be responded to by the value T.

Therefore, it is advisable to choose

, l Vg.

With 1 / g of close K Vg, it is difficult to obtain a stable operation of the circuit.

By adjusting the resistance values 24 and 25, as well as the capacitance of the capacitors 22 and 2S, you can set any desired welding time and interval time.

FIG. 2 shows schematically the current passing curve through resistance 6; the periods T on this curve correspond to the welding time, that is, the operating time of the thyratrons 5 vi 6.

Periods t correspond to the break time.

Therefore, all the time until welding is done, the tiratron 14 is working, and the tiratron 10 is locked.

Through the secondary winding of the transformer 17 when closing the contacts 28 on the welding machine, contacts 28 can be sent a current pulse from the battery 29.

This pulse is sent after the part being welded is clamped between the electrodes 3 by pressing the 5ft pedal.

Such a current pulse causes the appearance of a positive voltage on the secondary winding of the transformer 17 and, thus, ignites the thyratron 10.

After the thyratron 10 is ignited, the welding current begins to flow, but at the same time the capacitor 23 starts charging. When the voltage on its plates reaches the ignition threshold value Vz, the ion diode 21 is ignited and a current pulse passes through the winding of the transformer 18. the thyratron 14 ignites and locks the thyratron 10.

When the pedal 30 is pressed again, the contacts 28 again provide closures and the welding current supply starts again.