What is Coated Electrode?
The coated electrodes are the electrodes having a layer of flux which produces gases on decomposition that prevents the weld from contamination, slag, as well as it improves the arc stability and weld quality.
The electrode consists of straight solid metallic wire called core wire. This wire consists of a concentric coating of flux around it.
At one end of the electrode, around 25 to 50 mm of space is left uncoated, so that it can be easily gripped in a welding rod holder.
The size of the electrode is determined by the diameter of its core wire.
For different sizes of electrodes, different currents are recommended.
Welding electrode current chart is mentioned below.
|Electrode size (mm)||Welding current (Ampere)|
|For light work||For heavy work||For normal work|
|6.3 mm||220 A||320 A||260 A|
|5 mm||180 A||240 A||210 A|
|4 mm||140 A||180 A||165 A|
|3.15 /3.2 mm||90 A||130 A||110 A|
|2.5 mm||55 A||85 A||70 A|
|2 mm||40 A||60 A||60 A|
|1.6 mm||25 A||40 A||30 A|
The thickness of flux may vary according to different brands and class of electrodes.
This is usually expressed as a coating factor (C.F).
Coating factor (C.F) is a ratio of coating diameter to the core wire diameter.
C.F = D/d
D = diameter of flux
d = diameter of core wire or bare electrode
If the coating factor is between 1.2 to 1.35, then the electrode is said to be light coated.
If the coating factor is between 1.4 to 1.7, then the electrode is said to be medium coated.
If the coating factor is between 1.8 to 2.2, then the electrode is said to be heavy coated.
Types of electrode coatings
The arc welding electrodes can have different types of coating material depending upon the welding power source, material to be welded, etc.
6 types of electrode coatings are mentioned below.
Few important things about each of these electrode coatings are discussed below.
#1) Cellulose type
Cellulose type coatings contain around 30% of organic materials like wood floor, charcoal, cotton, cellulose, yarn, paper wrappings, gums as deoxidizers, liquid sodium as a binder silicate.
Electrodes containing cellulose type coating develop a strong plasma jet that gives good penetration.
The burning rate of this type of electrode is low and it forms a small amount of slag which is suitable for positional welding.
During the arc welding process, the cellulose decomposes and it forms the gas shield which protects the arc from the atmospheric oxygen and nitrogen.
Electrodes having cellulose type coating generally operate on a DC current.
For using these electrodes on both AC and DC current, the calcium and potassium compounds are added to the coating material along with potassium silicate as a binder.
#2) Rutile type
The rutile type coated electrodes contain about 50% titanium dioxide (TiO2).
The major constituents include rutile, china clay, sodium silicate, calcium and potassium compounds.
Because of these compounds, good arc stability is achieved during an arc welding process.
These electrodes can easily work with AC current at low voltage.
This type of electrodes produces viscous, heavy and compact slag and they are also suitable for welding in vertical and overhead position.
The slag is easily controllable, plus it produces low spatters. The penetration is also medium and the weld deposition rate is also high. Because of these reasons, the rutile type electrodes are used for general engineering.
#3) Acid type
Acid type electrodes contain the flux materials like iron, manganese compound, silica, potassium silicate.
The organic materials are absent in acid type flux coatings.
During the arc welding process, this coating produces a high amount of slag which is acidic in nature.
The coating of these electrodes contains deoxidizers that give sound weld deposition which have good mechanical properties.
#4) Acid rutile type
As the name suggests, these types of electrodes have properties of acid type as well as rutile type electrodes.
The slag formation in axis rutile type coated electrodes is similar to that of the acid type electrodes, but they have slightly more fluidity.
The mechanical properties of the weld obtained by these electrodes is similar to that of the acid type electrodes.
#5) Oxidizing type
The oxidizing type electrodes contain a coating of iron oxide and silicate with or without manganese oxides.
These types of electrodes form heavy slag during the arc welding process but the weld has low mechanical properties.
So this type of electrode has limited use (It is mainly used for sheet metal fabrication process).
#6) Basic type
Basic type of coating has a high amount of calcium carbonate and calcium fluoride.
Because of such composition, the slag formed during the welding process is basic in nature.
The weld obtained by this type of electrode has good mechanical properties and the weld contains low amounts of oxygen, hydrogen and nitrogen.