Manual Metal Arc Welding

In manual metal arc welding using coated stick electrodes, the coating assumes the function
of a protective gas shield on one hand and of forming a slag on the other, thereby protecting
the metal droplets transferred and the weld metal in turn against contact with atmospheric oxygen.
Further functions of the coating are de-oxidation of the weld metal, increasing the metal
recovery, offsetting burn-off and ensuring good flow behaviour.
In practical use there are three significant types of coating: rutile, basic and cellulose coated
stick electrodes as well as mixtures of these.
Rutile-coated stick electrode (R)
This type of coating is the one most commonly used in practice. The reason for this is found
in a series of advantages such as:
• Easier handling for the welder
• May be welded with direct and alternating current
• Good starting and re-starting properties
• Suitable for all welding positions – depending on the type and thickness of coating
• Good slag removal properties
• Not susceptible to moisture (only applies however to non-alloy and low-alloy types)
The disadvantages of rutile-coated stick electrodes are:
• Not suitable for thick-walled components (above 20-25 mm)
• Low notch toughness at temperatures below zero
• Higher hydrogen contents (20 ml/100 g weld metal)
• Not suitable for high-carbon steels (C <> 0.2 %).
Disadvantages are:
• Slightly more difficult handling for the welder
• In part only weldable with direct current
• Less favourable slag removal properties and rougher weld surface
• Certain amount of susceptibility to moisture absorption
3.3.1 Manual Metal Arc Welding with
Covered Electrodes
Selection Guide
3-35
Cellulose-coated stick electrode (C)
This type of coating was specially developed for vertical-down welding of large pipes. An arc
with high stability and intensity is generated due to the large proportion of cellulose in the coating.
This ensures pore-free welds and reliable root fusion even at high welding speeds and
larger electrode diameters.
The mechanical property values are comparable with those of the basic-coated stick electrodes.
However, due to the organic constituents in the coating the hydrogen content of the weld
metal is considerably higher (50 ml/100 g), therefore attention must be paid to good weldability
of the parent metals and the welding technology must be suitably matched (pre-heating).
Mixed types (RC, RB)
In addition to these three important basic types there is a large number of so-called “mixed
types” such as RC or RB coatings. The aim of these is to combine as many positive characteristics
as possible in one stick electrode.
Coated stick electrodes are universally suitable in practically all materials with good weldability.
The cost of equipment is relatively small although the economic profitability of this procedure

is deemed poor due to the low deposition rate.