For shielded metal arc welding, there are two basic types of electrode coatings. These are the lime type indicated by the suffix 15 and the titanium type designated by the suffix 16.
The lime type electrodes are used only with direct current electrode positive (reverse polarity).
The titanium-coated electrode with the suffix 16 can be used with alternating current and with direct current electrode positive.
Both coatings are of the low-hydrogen type and both are used in all positions.
However, the type 16 is smoother, has more welder appeal, and operates better in the flat position.
The lime type electrodes are more crack resistant and are slightly better for out-of-position welding.
The width of weaving should be limited to two and-one-half (2.5) times the diameter of the electrode core wire.
Covered electrodes for shielded metal arc welding must be stored at normal room temperatures in dry area. These electrode coatings, of low hydrogen type, are susceptible to moisture pickup.
Once the electrode box has been opened, the electrodes should be kept in a dry box until used.
The gas tungsten arc welding process is widely used for thinner sections of stainless steel. The 2% tungsten is recommended and the electrode should be ground to a taper.
The gas metal arcwelding process is widely used for thicker materials since it is a faster welding process.
Argon is normally used for gas shielding; however, argon-helium mixtures are sometimes used for automatic applications.
The spray transfer mode is used for flat position welding and this requires the use of argon for shielding with 2% or 5% oxygen or special mixtures.
The oxygen helps in producing better wetting action on the edges of the weld.
The short-circuiting transfer can also be used on thinner materials. In this case CO2 shielding or the 25% CO2 plus 75% argon mixture is used.
The argon-oxygen mixture can also be used with small-diameter electrode wires.
With extra low-carbon electrode wires and CO2 shielding the amount of carbon pickup will increase slightly. This should be related to the service life of the weldment
If corrosion resistance is a major factor, the CO2 gas or the CO2-argon mixture should not be used.
For all welding operations, the weld area should be cleaned and free from all foreign materials, oil, paint, dirt, etc. The welding arc should be as short as possible when using any of the art processes.
