Welding contd.

Types of electrodes: bare, coated, consumable and non-consumable.
Consumable electrodes: Molen metal from the electrodes and base metal are mixed under the arc provides necessary joint.Electrode is serving the purpose of filler rod as wellas input for heat.
Non consumable electrodes: not consumed during welding.Separate filler rod is used if necessary to fill the gap.These are of carbon & graphite for DC welding.
Tungsten electrodes are used for DC & AC welding and have better control over the heat input because sources are separate.Used in carbon arc & TIG welding.
Bare electrodes are without coating of flux and flux is used separately as non-consumable electrodes.The striking of arc is difficult in such electrodes especially with AC supply.
Coated electrodes are coated with flux and called STICK electrodes.The problem is moisture picked-up by yhe flux and dissociates into oxygen and hydrogen and being absorbed by the liquid metaland released during solidification causing porosity and so advised to keep the electrodes in a dry place.

FLUX:During welding, when metal is heated in air, the oxygen from air combines the metal and forms oxides,which results poor quality, low strength weld and even some cases welding becomes impossible. To protect the weld pool from oxygen of ambient air,flux is used and does not allow the air to come in contact with fused metal.
Thus fluxes may be divided into the following categories.
Gas Forming: Components are organic matters such as starch,wood, pulp etc, which form gas layer, thus isolating the welding zone from the ambient air.
Slag Forming: The slag forming components are chinaclay, felspar, manganese and titanium ores etc and enhance slag formation.Slag covering the molten metal to come in contact with air.