Hello everyone
Now doing "stick" / SMA at college. Have inverter, and good outdoor process (?)
Want to ask about current to choose for fillet welds. Wondered whether high amps might be self-defeating in some circumstances. Can you "cook-out" your cellulose and reduce your pen. with too high amperage when using rutile-cellulose rods?
Firstly, background comment - having problems of melting right into the corner of the plate intersections for lap and T-joint. Nick-break test reveals the fault. Electrode angles OK (instructor checked). Suspect systematically setting off too soon and holding the condition all the way along of the melt bridging over the root :-( Next week will try making sure I have a good weld-pool.
To get pen., using rutile-cellulose rods for the root run. Use straight rutile for capping run. Can see pen. is very limited straight rutile.
Now pen. and current.
"penetration" is not the same thing for full-penetration butt and for fillet welds, is it? For full-penetration butt welds you mean you put in enough well-directed heat to melt all the way through the thickness of the plate. That means amps, no two ways about it? For fillet, you mean "I melted right down into the corner", with the subtext "I don't care how widely I melted, thereby having no consideration of plate thickness - I'll get all that in a capping run".
This gives the amps a different meaning, does it not? For fillet root-run, you only care that you concentrate the arc into the corner?
The point I was really going for.
The rutile-cellulose rods we are using to root-run for this 6mm (1/4") plate are 2.5mm (100thous) diameter. (We use 3.25mm staight rutile at
120A for capping - seems good). The recommended max amps is 95A. There is some root-running going on at 100A. At 100A (and even at
95A), the stub of the rod gets red-hot. So there won't be much cellulose left there... Or is this heat conduction back from the melting end of the rod? So current has lesser influence?
Was thinking of maybe dropping back to say 80A. Now, I might get questions asked... Is there an argument for keeping the amps lower for root-running a fillet weld with rutile-cellulose? So that you keep the cellulose and get the hotter stiffer arc to project into the corner?
Resistive heating of the rod. Resistive heating power P=I^2 R (current squared * resistance). So going from 95A to 80A, your resistive heating is now 70% of previous. Considering from 100A to
80A it's 64% of previous. Go from 100A (often seen to be used) to 70A and your resistive heating of the rod is less than 50% of previous. Am I onto something here? About burning-out the cellulose leaves you worse off than if you kept the current down and retained your cellulose?
BTW - I get no pen. prob. if I use a straight cellulosic (6011) to root-run at 70A, but the weld is rough and suggested need 100% grind. ("only" 70A - the hydrogen from cellulose getting into the arc something like doubles the voltage drop over the arc gap, so the power you are putting in is actually quite high, plus the arc is stiff and concentrated)
Offshot question - with basics, the flux doesn't degrade with heat(?) and you can come it at higher amps to get pen. by simply stuffing in enough heat to get fluidity at the root / plate intersection?
Richard Smith