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The coating of this type of electrode consist of calcium fluoride
plus calcium and other
alkaline carbonates. The coating is mostly thick. These substances
make to slag more
viscose and fast freezing, thus unabling overhead and overhead and
vertical position applications.
Basic electrodes are baked at 400-500 ºC during production. As the
coating is hygroscopic
these electrodes should be stored in dry place. Before usage, basic
electrodes should
be redried for 30 minutes at a minimum of 250 ºC.
This type of electrodes is preferred when welding medium and thick
steel plates that
require high strength, high welding quality and high crack resistance.
Basic electrode are
mainly used in the heavy machinery and equipments industries, such
as ship building,
boiler and pressure vessels, and steel constructions subjected to
dynamic loads.
Main applications for basic electrodes:
- Welding of unalloyed or low alloyed steels with unknown composition,
- Welding of steels with a high content of carbon, sulphur, phosphorus
and nitrogen,
- Welding of steels having different carbon contents,
- Welding of thick-sections,
- Welding of machinery, equipment and structures that work under
temperatures below 0 ºC,
- Welding of structures where high strength is required against
dynamic
stresses,
- Welding of rigid constructions.
In this type of electrode, the transfer of the filler metal form
the arc to weld pool is in the
form of medium sized drops; the slag colour changes from brown to
black and is less easily cleaned
than the slag of other electrodes.
When welding, basic electrodes are generally connected to the positive
pole with DC. Some types
of basic electrodes can also be used with AC.
During the welding operation, rutile and acid coated electrodes,
should be held at a 45º angle
with respect to the surface of the work piece. For basic electrodes
this angle should be 85-90º.
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