|
|
Consumables Electrodes - They are low melting point electrodes made up of different metals and their alloys. When the arc between the electrode and job is struck, the end of the electrode starts melting and transfers to the job in the form of droplets. The electrode itself adds filler metal. Droplets transferring (from electrode end and through arc) to the workpiece deposit there most of the heat generated as resistance heating in the electrode and of the arc.
Because of this reason a consumable electrode welding system possesses higher thermal efficiency (about 85%) as compared to that of a nonconsumable electrode welding arrangement (about 55%). Consumable electrodes may be of the following types.
|
|
Bare electrodes
They consist of a metal or alloy wire without any flux coating on them.
Lightly coated electrodes
Electrodes with a coating factor* approximately 1.25 are termed as lightly coated electrodes.
Medium coated electrodes
They are the electrodes with a coating factor about 1.45.
Heavily coated electrodes
The coating factor is between 1.6 and 2.2 for heavily coated electrodes. Example: Citofine (A.O.). As compared to lightly coated electrodes, heavily coated ones find applications in severe conditions; they produce deeper penetrations and weld metal of high quality. In heavily coated electrodes, the core wire melts before the flux coating, giving rise to a cavity, hence producing arc constriction and arc heat concentration on the workpiece.
|
|
|
Because of unstable are, irregular metal transfer and atmospheric contamination, bare electrodes do not produce sound and satisfactory welds but still they find\ application where weld strength is not a primary consideration and it is difficult to carry post cleaning of the joint.
Covered Electrodes produce very well in heavy coated electrodes weld appearances, weld metal properties and defect free joints.
Certain electrodes give good results on DCRP and others work equally well on AC or DC, for example
(a) A WS E 6012, BS E 206, IS M 2Q6253 electrodes work well on both AC and DCSP.
(b) A WS E 6010, BS E 100, IS M 100264 are operated on DCRP only.
(c) AWS E 7018, BS E 601 JH, IS M 601389 JH are used on AC or DCRP.
|
Some of the welding electrodes e.g.,
A WS E 6013, 6010, BS E 316, E 614, IS M 616478 HJ, M 216251 weld well in all positions whereas others give best results only when welding is carried out in certain positions e.g. A WS E 6027, BS E 922 P, IS M 922 XXXP are better employed for welding in flat and horizontal positions only.
Covered electrodes may also be categorized as follows:
(a) Electrodes which have cellulose content impart deep penetration and increased electrode burn off rate. Welding may be carried out in all positions. Examples of electrodes having cellulose content:
A WS E 6010,6011,7010,7011, BS E 110, IS (814-1970) E 10022 A, M 100264.
|
| |
(b) Rutile (Titania) electrodes give a smooth and quiet arc, negligible spatter, and easily removable slag. The electrode will work on both AC and DC. Addition of other ingredients can make the slag fluid or viscous with the result that the electrode can be used for welding in different positions. Examples of such electrodes:
AWS E 6012, 6013, 7013, 8013 B2, BS E 317, IS M 317275, E 31432 C etc.
(c) Electrodes containing iron oxide produce fluid slag, good weld appearance and mechanical properties. Electrode can be operated on AC and DC both. Slag is easily detachable. These electrodes (because of slag fluidity) are generally employed for flat welding. Examples of electrodes:
E 6030, 7030, BS E 432, IS M 422275 etc.
(d) Electrodes with iron power content have stable arc and large metal deposition rates.
|
Examples of electrodes: AWS E 6016, 7016, BS E 616 H, IS M 616489 H, etc.
(e) Low hydrogen electrodes contain low moisture content, flourspar, limestone etc. They produce weld metal highly resistant to cracking and for maximum notch ductility. Such electrodes need some heating before use; they work in all positions and can be operated on AC and DCRP. Examples of electrodes:
A WS E 6016, 7016, BS E 616 H, IS M 616489 H, etc.
|
|
