Sub Arc on Girters

[OSUWE2010]

I am running into a problem and need some help. We are trying to use a single wire SAW tractor with L-61, 5/32" wire, Lincolnweld 980 Flux to weld up some 1.5"-2" thick girters. The settings we are running with now are roughly 34 volts, 700 amps, and about 16-18 inches a minute. We've ran a few test runs and are getting cracking right down center of the weld, nearly running the entire length of the weld. At first I thought it was a cool down issue or even a pre-heat issue but now I'm thinking it might be the wire or even the Flux. Does anyone have any suggestions or ideas what we can do? Any comments or ideas are greatly appreciated right now..

 

[Duwe6]

You have good wire & good flux, so that's not your problem.

Center-bead cracking is a result on insufficient preheat and/or too small a weld bead on a restrained joint.

Do you have preheat torches mounted on your welding head? If no, put some on. There should be one torch set about 1.5-ft ahead of the puddle, and a second about 6-8 inches ahead. They should run on propane/natural gas plus compressed air.

This thick of steel needs to be 150-200°F immediatly before the puddle. Take your preheat measurements about 2-inches ahead of the arc. Willing to bet $100 that your welding operator is trying to weld this item 'cold', as proper preheat is a pain in the hindquarters and takes extra torches.

If that is insufficient, try 300°F preheat or slowing down the travel speed [thus increasing the weld size].

 

[metengr]

I agree with the above advice. Preheat is essential for base material of this thickness. Centerline weld bead cracks are related to either excessive shrinkage stresses caused by large thermal gradients or weld bead deposited/depth of weld joint.


You really need to add supplemental heat applied in the form of either resistance heating blankets or preheat torches manipulated manually.

 

[Guest102023]

Look into the depth-to-width ratio of the bead - too high will cause CL cracking. Surface concavity may be concurently observed.

700A is possibly a bit on the high side for the wire diameter (and it is primarily amperage that gives penetration).