MMA welding Flashcards
Describe the function of a transformer in arc welding
A step-down transformer is used to change the mains voltage from 220V to a suitable level (80-100V) for welding. This will provide the high current needed for welding. This type of transformer has more turns on the primary coil than the secondary coil and will induce alternating current (AC) at a lower voltage.
Draw: a physical step-down transformer with source and load directions
Describe the function of a Bridge Rectifier in arc welding
The rectifier changes alternating current (AC) to direct current (DC). It consists of four diodes which allow two of the diodes to conduct on each half-cycle of the AC supply.
Describe the function of a capacitor in arc welding
The capacitor is employed to provide a smooth supply of low voltage DC.
Draw: the effect a capacitor has on the AC and DC current
Describe the circuit diagram shown under the following points:
(i)Component names;
(ii)Method of operation;
(iii)Applications
a step-down transformer and a bridge rectifier
Components names –Transformer on the left –Bridge rectifier on the right
Method of operation –explained above
Applications –to produce a smooth, low voltage, high current D.C. supply
State three functions of the electrode (flux) coating
Helps to start the arc
Burns to give off a gas which prevents oxidation
Helps the formation of slag on the weld
Additional alloy material can be part of the coating to improve strength.
State two functions of the slag produced
Slag helps impurities float to the top of the weld
Slag creates an insulating layer to help the weld cool down slowly. This makes the weld tougher and less brittle.
Describe three safety features that minimise electrical hazards associated with MMA Welding
- MMA welding machines are protected from electrical surges.
- Welding stations need to be free from dampness.
- Cables and electrode holders are covered with plastic insulators.
- Welding machines are earthed.
- Power supplied can be adjusted to an appropriate level.
