"stick"/SMA - root fusion / penetration, lap and T-joint fillet welds

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

It seems to me that you have a good handle on the concepts. From the description of your problem I suspect you are trying to put down too large a first pass on your fillet. As you say the objective is to put a weld right into the corner. With Rutile electrodes you can "dial " in the right heat if you put some passes on a flat plate using a drag technique. When the flux lifts up off the cooling bead like a fingernail you know you are in the zone. Finishing off an electrode and seeing that it is red indeed tells you the heat is to high. The flux also is a pain to remove when it bakes on. A classic problems is the standard fillet / groove weld test one has to do for structural welding. The first pass in the corner calls for a 5/16 fillet (8mm) maximum and of course welders put in a full size weld. The requirement calls for a maximum value and these people who don't read carefully fail because they get lack of fusion at the root. They were too concerned size when it was not important. Just cranking up the heat is not the solution with SMAW. It sorta works for cellulose but for the other rods. I am impressed with your understanding. Seems to me that you are soaking it up effectively. I heard a teacher state: "The good ones learn in spite of us , not because of us." It sounds like you are in that category. Randy