Manual welding with piece electrodes. Scheme, description

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Electric welding. Manual welding with piece electrodes. Encyclopedia of radio electronics and electrical engineering

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Until now, in production and in everyday life, manual stick electrode welding (MMA). And if direct current welding is mainly used in production, then in everyday life they prefer to use alternating current. This is due to the simplicity, low cost and reliability of transformer AC welding sources.

In manual welding in the current range from 60 to 300 A, the arc has a rigid static current-voltage characteristic. In this case, the average voltage of the welding arc in volts can be found by the formula:

where I_St. - welding current.

In practice, due to fluctuations in the length of the arc, the arc voltage can change up or down relative to the calculated value. To provide high quality welding the following conditions must be met.

Condition 1. When changing the length of the arc, changes in the welding current should be minimal.

Condition 2. The open circuit voltage of the welding source should be 1,8-2,5 times the arc voltage.

Condition 3. The short circuit current of the welding source must not exceed twice the welding current.

These conditions are met by a welding source with a steeply falling external current-voltage characteristic (CVC). The steeply falling characteristic can be obtained by connecting in series with the secondary winding of the welding transformer, active or reactance X_ф (Fig. 18.1).

MMA welding
Rice. 18.1. Scheme of formation of the external characteristic of the source

In this case, the open circuit voltage U_xx welding source is equal to the voltage on the secondary winding of the welding transformer. The short circuit current can be found by the formula:

By changing the X value_ф it is possible to change the short-circuit current and, consequently, the welding current I_St. (Fig. 18.2).

MMA welding
Rice. 18.2. Welding current control

Author: Koryakin-Chernyak S.L.

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