There were a surprising (to me) burst of new lessons with SMA welding. This surprise was from the basis of my expectations given that I had passed SMA at City and Guilds before.
Was taught to keep a much shorter arc length, much more carefully controlled, than before. The effect solely due to this was
My run-rate as I tried starting welding was immediately picked-up on
as being much too slow. I was initially trying to run at a rate which
made the run-out about a third of the rod length. The actually
desired run-out length of a straight weld ("stringer-bead") for a
rutile ("6013") rod is one rod-length.
Furthermore, the run speed needed to be very consistent.
The effect of these two combined
The angles, "slope" (w.r.t. welding direction) and tilt (with respect to horizontal plane (???)) next came into focus in an onward wave of improvement. A slope near to vertical, at around 75degrees (15degrees off vertical), gives a very rounded bead. More slope, over at around 55degrees (35degrees from vertical) kicks up a ridge in the weld deposit and leaves "fishbone" or chevron-shaped solidification marks on the weld deposit. I was later to find an instance where a high slope could be used to good effect (the stringer-bead h-v lap).
In the horizontal-vertical (h-v) lap joint, if using three runs, the final bead, meeting the upper plate edge, can be made to give a flat area continuing the top plate surface, resisting beveling of the plate edge, by doing this run with a large slope of 50deg to 55deg.
Here it is:
Run a single-run fillet - T-fillet or lap - on 3mm plate steel using a
2.5mm diameter rutile (6013) welding rod at a current not exceeding
its recommended maximum current of 90Amps - getting complete fusion at
the root corner.
This is an exercise in control.
You could easily do this weld commercially using a 3.2mm 6013 electrode at its maximum current rating of 140A, dragging the electrode fast along the joint with contact of the flux outer periphery on the plate faces. This gives a short consistent arc which focuses into the weld root.
But that is not the point - the welding exercise described is purely about developing control of arc length, run rate, rod slope and tilt and position above the fillet corner.
Using a 2.5mm 6013 at 90A for a 3mm plate fillet, the problems encountered are:
Need short arc else
A big problem of getting the weld run underway without "cold" lack-of-fusion and slag inclusion defects was solved by striking the arc with the rod sticking over the end of the joint. The arc loops back to the plate and warms it while holding this position, while the filler metal melting from the rod falls into space. The welding rod end is then drawn above the joint and the weld starts properly with correct heat.