By EWE
Date 10-01-2001 20:23
I have been working with this problem in my profession.
I solved the problem by using a machine backing of the base material. (We weld pipes with a gable, pressure wessels.)
Before we used GTAW for the first rootbead and following beads consists of GMAW. By solving this problem we managed to reduce welding time 70%. (Only using GMAW, spray arc/root bead)
The problem from the beginning was to design the thickness of the machine backing. (It`s not a loose backing, the gable and pipe together forms a backing of about two mm in a V-shaped groove.)
After the designproblem was solved it was quite easy to fix the welding parameters.
If you want more info please send a new question.
Anders
EWE, European Welding Eng.
(We also weld a rootbead with spray arc and every welding procedure is approved by the Eurocode EN 288-3 and ASME sec 9.)
By -
Date 10-03-2001 18:24
As with most things, it takes practice to get anything right properly, so don't give up. As I am not a welder, I would not be able to perform the weld myself, but I can give you a pointer about the wire shooting through. The wire must not be on the leading edge of the puddle. It must be inside the puddle. Getting this right is very much a psychological thing. We typically "want" to push the arc ahead of the puddle.
Hope this helps, and happy practicing.
Niekie
By -
Date 10-03-2001 22:35
It's been my experience with SCT using .035 dia. wire to have a joint with a 1/8" root opening and knife edge (no land). Run the root bead downhill with the wire angled back into the puddle edge, literally the reverse as with SMAW.
As Nieke stated, keep your wire on the leading edge of the puddle. If you set back on the puddle as little as a 1/16", it's been my experience that you stand a great chance of incurring LOF (lack of fusion). If you set back on the puddle, the finished root bead will look great but be worthless. If you use this technique, you should try to go just fast enough to not pop the wire through. The faster your travel speed is the better/deeper your penetration will be up to the point of pop-through.
It's better to pop through once in a while then make a weld that doesn't have a fused root!
