Hi Dave!
You are correct about the two different types of suffix numbers, but tey also represent two different flux compositions as well which are crucial in determining which of the two would be better suited for out of position welding... For instance...
-15 electrodes operate optimally with DC current, reverse polarity (DCEP). The flux coating contains substantial quantities of limestone and fluorspar and produces a globular transfer and large, hot-appearing arc weld puddle. the slag is quick freezing and the freezing line can be seen directly behind the arc. The fast freezing characteristic facilitates operation in the vertical and overhead positions favorably when compared to -16, or AC-DC covered electrodes.
For this reason DC lime electrodes as they are sometimes also called, are often preferred in pipe welding... The bead profile is convex, and is best for highly restrained root passes and for maximum impact strength at cryogenic temperatures.
- 16 electrodes operate on either AC, or DCEP, otherwise known as DC Reverse polarity... The coating contains dominant amounts of rutile (Titania), medium amounts of limestone and limited amounts of fluorspar... Arc Transfer is spray-like, arc stability excellent and spatter loss low... All size diameters strike and re-strike easily, and this electrode has a higher deposition rate which is better suited for the flat and horizontal positions. The weld beads are smooth, uniform and of excellent appearance (flat to slightly convex).
These electrodes can also be used in all positions, but can be harder for the welder to control out of position than with a DC Limestone electrode especially in groove welds and achieving adequate penetration in fillet welds that are out of position also.
Respectfully,
Henry
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