Welding is a process of jointing two metallic pieces with the help of third metal called as electrode. In welding the metallic piece to be soldered are melted and filled up the gap. It is done at a high temperature.
Types of electric welding. The heat is developed electrically in case of welding so it is known as electric welding. It is of the following types:
(i) Resistance welding.
(ii) Arc welding.
Resistance welding. Resistance welding is a process in which heat is developed by passing current through the points to be welded. It is again classified as:
l. Butt welding.
2. Spot welding.
3. Seam welding.
In case of butt welding it is done for joining rods, wires and tubes etc. A heavy current at low voltage is send across the joint. The spot welding, is used for joining the thin metal sheets. The metal sheets to be joined are placed ore over the other between a pair of pointed copper electrode and heavv current at low voltage is passed through the joint. Seam welding is used where a continuous point is required between two overlapping metal sheets. In this case also low voltage heavy current intermittently is passed through the spot.
Arc welding. The process of welding two metal pieces by striking an electric arc is known as arc welding. It is again subdivided as
l. Carbon arc welding
2. Metal arc welding
3, Atomic hydrogen arc welding
4. Helium or argon arc welding.
In carbon arc welding this method is suitable on d.c. carbon rod is used are soldering. The voltage for arc varies from 35 to 50 V with 200 to 1000 A. In metal arc welding the metal electrode is used which itself feeds additional material to fill up the gap. In case of hydrogen or atomic arc welding — the arc is struck between the tungsten electrode and hydrogen gas is passed through the arc. In case of helium or argon arc welding, the arc is struck between the tungsten electrodes and in an atmosphere of inert gas like argon or helium.
