Weld porosity - gas flow issues?

[OllieG]

Hello, not a regular poster and have been enjoying good welding results with my Portamig…til now!

I'm welding thin mild steel car bodywork but I'm finding that my welds are bubbling and brittle. I'm pretty sure, although not certain, that the problem is from poor gas feed. I prep the metal really well so I'm sure the surface is clean and not contaminating the weld.

I find that I have to turn the pressure right up on the regulator at the bottle to get even vaguely decent welds - and even then they're not great. I can hear the gas flowing but it's not consistent and isn't really flowing strongly until I've had the trigger down for a few seconds..

Any clues what could be wrong? Do I need all new hoses and new torch as I can't locate any obvious leaks?

Thanks all, Ollie.

 

[Richard.]

Do you have these items available to borrow to do a bit of fault finding.
Try one thing at a time. Then see how/if it improves.
Reg, line, torch.
If none of the above helps then the problems in unit.

 

[Bill Edwards]

I'd start by removing the gas line from the regulator, winding it so the pressure is off and open the cylinder valve.

Then wind in the screw on the regulator to let gas out and see what you can hear - the more you wind it in the more gas you'll hear escaping. If everything is smooth without fluctuations then the problem sounds to be downstream. Keep working like that.
Worth investing in a pea shooter style flowmeter to go onto the regulator outlet, it'll allow you to set the right amount of gas flow for your work and let you see what is happening.

 

[OllieG]

Thanks for the quick replies guys.. I've just been doing more investigation. My gut feeling is that the problem is more to do with the hose plug, hose itself or the torch. When I hit the trigger, I can hear the gas flowing 'somewhere' so I'm confident the cylinder is OK and gas is making it beyond the regulator - the read-outs on the regulator seem to be fine too. I have a feeling the gas is getting to the hose plug but then not finding its way down the hose to the torch - so possibly leaking out at the plug. Is that possible?

Unfortunately I have only one setup so I can't chop and change parts to find the fault. If the problem is with the plug then would I need to replace the entire hose plug, hose & torch combo?

 

[Bill Edwards]

Well how about blocking off the torch nozzle - bung the shroud up with something - then pull the trigger with the wire feed turned of/rollers slackened so it doess't feed.

Then if you hear gas flowing you know it can't be coming out of the torch so is somewhere between the solenoid on the machine (assume it's electric) and the torch. Narrow it down like that.
Don't worry about what you may need to replace until you are certain where the problem lies!

 

[mike 109444]

Had/having similar problem with my 3mt torch (have had to switch to 4mt one for now) Believe that the hose inside the torch has been squashed/bent probable from folding back a bit when packing up (well the torch is 25+ years old!). Found after fitting new liner that it was worse. Was using a net curtain wire for a liner which is smaller in outer diameter than the normal liner. So with new liner the gas pipe is fill more and so any bends etc make for a restriction that forces the gas back through the euro plug and out at the wire feed motor. So try turn down to zero your wire feed speed then pull trigger and listen for gas at the feed motor area. You could try as a temp (cheep) fix to replace the liner with a curtain wire one.

 

[Jan]

As said; there could be a kink in the gas feed line that's occluding gas flow. Does your torch have a 2 stage trigger? By that I mean does it click and feed gas with the trigger half depressed and only weld if you pull it all the way back? If there's a problem with the gas microswitch it could be losing contact as you continue pulling on the trigger.
If the trigger is 2-stage you can roughly gauge the gas flow by withdrawing the wire back to the reel (just to be certain) and dipping the torch nozzle in a cup of water. Keep watching the bubbles while you, or an assistant, manipulates the lead to the torch and also what may happen as you squeeze the trigger harder. As long as the earth lead is kept well out of the way there's zero chance of zapping yourself.

 

[mr migwire]

check its not leaking at the torch side of the gas solanoid as it sounds like its getting through so far then escaping through a damaged pipe/joint.

 

[OllieG]

Thanks for all the tips guys…I'm going to go back and check all the hoses inside the machine, check connections and look for damage. I guess it could be the solenoid so I'll have a close look at that too.

The torch isn't a 2 stage trigger no… it's strange because sometimes the gas flows out of the shroud, albeit quite weakly, other times it doesn't at all. But I can hear the gas flowing somewhere when I pull the trigger..like it's leaking out either inside the machine or at the hose plug but not really making its way to the torch efficiently.