About more than the half of Basic Electrode composition, is
composed of basic/alkaline compounds. These basic compounds are mostly calcium
fluoride, magnesium carbonate and calcium carbonate. The basic electrode has
some advantageous features over a cellulosic electrode and gives clean and
quality weld outcomes with good metallurgical characteristics. Efficiency of these electrodes is made more increased with the addition of iron
powder. Described below, are the distinctive characteristics of a basic
electrode that make them special in certain applications.
1. Basic Slag Formation
The foremost advantage of this type electrode, is the
removal of impurities like sulphur and phosphorous that can impart unfavorable effects on the weldment. The constituents of electrode coating, react with
these impurities and produce a Basic Slag.
2. Formation of gases
Flux constituents of electrode coating when heated in arc,
give off carbon monoxide and carbon dioxide gases, which take part in gas
shielding.
3. Deoxidation
The constituents of basic coating also assists in the
reduction of oxygen and renders de-oxidation of weld metal. They are mostly the
ferro alloying elements such as ferro-titanium, ferro-manganese etc.
4. Low Moisture
Such type coatings don’t need any moisture content to
stabilize covering of electrode and hence less possibilities for hydrogen
cracking in weldment due to low moisture. The basic electrodes are baked or
held in heating ovens before use, to prevent any moisture pick up. See What is Hydrogen Induced Cracking and How to control it?
5. Viscous Slag
Although the basic slag is viscous and its removal is bit
difficult but on the other hand, it can be easily controllable and helps to
apply basic electrodes in all positions. Some basic electrode coatings are
available that can be applied in vertical down position.
6. High quality Weld
Coating constituents like alkaline compounds, flux
materials, deoxidants and binders all contribute to give clean and sound weld
with desired mechanical properties. In this way basic electrodes can be applied
in those applications where strict radiography and ultrasonic testing is
required for example pressure vessel, heat exchanger, boilers etc.
7. High Toughness at low temperature
Unlike cellulosic electrodes, high toughness is achieved
even at the low temperature and the weld deposit is free from impurities.
8. Low Hydrogen Level
In low alloy steels, hydrogen induced cracking is a major
concern which is primarily caused by high hydrogen level. Unlike cellulosic
electrodes, basic electrodes has low hydrogen level. Because of low hydrogen, they
can be used in those applications where hydrogen induced cracking (cold
cracking) must be averted.
9. Vacuum Packing
Basic coatings have low hydrogen level and must be baked
before use to avoid any moisture absorption. Baking and storage facilities must
be there, in order to avoid any moisture pick-up. Now a days, electrodes are
available in vacuum packing and can be used without baking. This helps to skip
the baking and storage responsibilities.
10. Metallic Powder Addition
With the addition of metallic powder in these electrodes,
greater efficiency and deposition rates are achieved without any adverse
outcome. Slag removal is bit difficult in case of normal basic electrodes
however with the use of metallic powder electrodes, slag removal is made easier.
Last comment
Basic electrodes don’t provide sound gas shielding, as
compared to other electrodes and atmospheric contamination may cause porosity
in the weldment. In order to prevent this, great skills are required for
electrode handling keeping the arc short.