porosity in start of mig weld?

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Hello GU-RUUs,      I'm hoping that in all the infinite wisdom present on this site, someone will know the cause of my recently acquired problem. I have a Lincoln power MIG C and just recently, I'm getting porosity for a 1/4" or so in the beginning of my welds. It started this week, after I got a fresh cylinder of 75/25. I increased the flow to 25, or 50 S c f h. The increased flow greatly reduced the frequency of the start porosity, but it still happens some. Also, the porosity in weld starts seem to be more prominent in the first weld of the batch, meaning when the welder has not operated for a while, 15 to 30 minutes, the first weld performed will have greater porosity than the immediate following ones. And always and only in the first 1/4" or less of the weld. I soaped all connections and found no leaks. I disassembled the gun and cleaned all. I can't find the cause. HELP!!Miller TrailBlazer 251Miller HF-250-1Miller MaxStar 150 STLHyperTherm PowerMax 380 plasmaLincoln PowerMig 180Millermatic 252Miller Diversion 180
Reply:never mind. After reviewing similar posts, I followed some given suggestions and inspected the gas to cord inlet and found a major leak. After disassembling, cleaning, and reassembling, the leak was no more. Didn't try a weld, but I'm sure the problem is cured.Miller TrailBlazer 251Miller HF-250-1Miller MaxStar 150 STLHyperTherm PowerMax 380 plasmaLincoln PowerMig 180Millermatic 252Miller Diversion 180
Reply:I agree, a leak in the line or reg could cause the problem you have described.   Usually I run a little bit of wire out of the gun before the first weld after not welding for awhile, it allows the torch to be purged from any air that might be in it from sitting awhile.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Once you fixed your next back down on your gas flow. You don't need that much.Tough as nails and damn near as smart
Reply:Originally Posted by tresiOnce you fixed your next back down on your gas flow. You don't need that much.
Reply:I have the EXACT same issue with my Lincoln 180C .When I bought the machine ( new ) I had bought a replacement Mig gun just so I could convert it over to Centerfire consumables . The gun felt much better but I ALWAYS struggledwith porosity issues . I just recently hooked up the factory Lincoln 100L gun and it welds a lot better . No porosity at all ( but it feels cheap ). However , I still suspect there is a small leak . When the tank is opened , and the lines purged and then the tank reclosed , it will bleed off the pressure within about 10 minutes . This just does not seem right . My tig machine will maintain  pressurized lines for days .
Reply:Yeah, you have a leak if it's bleeding down in 10 minutes.  Not likely to be the torch though, unless there's a gas valve in the torch.  More likely it's the gas valve inside the machine, the reg, the hose connections, or hose itself.   I would suspect the gas valve if the hose connections are all good.  The gas valve is what's responsible for keeping the pressure in the tank and line from going out the torch anytime the tank valve is open.  If there's a leak in the torch, you wouldn't see a bleed down at the regulator if the gas valve is closed unless the gas valve, or regulator, or hose/connections are also leaking.Last edited by DesertRider33; 03-22-2009 at 07:18 PM.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Originally Posted by Tigster200I have the EXACT same issue with my Lincoln 180C .When I bought the machine ( new ) I had bought a replacement Mig gun just so I could convert it over to Centerfire consumables . The gun felt much better but I ALWAYS struggledwith porosity issues . I just recently hooked up the factory Lincoln 100L gun and it welds a lot better . No porosity at all ( but it feels cheap ). However , I still suspect there is a small leak . When the tank is opened , and the lines purged and then the tank reclosed , it will bleed off the pressure within about 10 minutes . This just does not seem right . My tig machine will maintain  pressurized lines for days .
Reply:Well , part of my problem was the hose connection at the back of the machine . I had cranked it on pretty darn tight , but , last night I put soapy water on the connections and that one was leaking . I tried teflon tape on the threads and it did help quite a bit . It's not perfect , but , it's about 90% better than it was .The main source of my porosity issue is the replacement mig gun from Praxair . It uses Bernard Center Fire consumables and seems to be built much better than the factory Lincoln 100L gun .However , upon very close inspection last night , I discovered that the brass "tip" that plugs into the wire drive ( with the two O rings ) is not exactly the same length as the Lincoln part .It physically pushes in , but , it does not go in as far and the rear O ring just barely gets into the housing .  I am not sure if the gas ports in the machine are physically lining up with the ports in the brass gun fitting or if the O rings are not sealing . Regardless , it does not work correctly . I thought that I could just swap tips and liners and still use this gun ( as that's all that's wrong ) but the local Praxair dealer says no . This was a $150 learning experience I guess .
Reply:i have converted several mig guns to the bernard centrefire configuration including Lincoln. as long as the diffuser can be removed it is possible to install a centrefire diffuser. an adapter my be necessary. I have been told on two occasions hat this could not be done but i have them converted and they work great. Perhaps contact a bernard rep and get him on the band wagonWhipit
Reply:Originally Posted by DesertRider33Usually I run a little bit of wire out of the gun before the first weld after not welding for awhile, it allows the torch to be purged from any air that might be in it from sitting awhile.
Reply:Originally Posted by duaneb55I do the same thing DR33 but rather than run wire out, I flip the door up and disengage the drive rolls so it doesn't feed.  This also allows me to confirm the desired cfh rate before attempting to weld.  Lock the drive rolls back down w/o changing the tension and away ya go.
Reply:Originally Posted by Tigster200Well , part of my problem was the hose connection at the back of the machine . I had cranked it on pretty darn tight , but , last night I put soapy water on the connections and that one was leaking . I tried teflon tape on the threads and it did help quite a bit . It's not perfect , but , it's about 90% better than it was .The main source of my porosity issue is the replacement mig gun from Praxair . It uses Bernard Center Fire consumables and seems to be built much better than the factory Lincoln 100L gun .However , upon very close inspection last night , I discovered that the brass "tip" that plugs into the wire drive ( with the two O rings ) is not exactly the same length as the Lincoln part .It physically pushes in , but , it does not go in as far and the rear O ring just barely gets into the housing .  I am not sure if the gas ports in the machine are physically lining up with the ports in the brass gun fitting or if the O rings are not sealing . Regardless , it does not work correctly . I thought that I could just swap tips and liners and still use this gun ( as that's all that's wrong ) but the local Praxair dealer says no . This was a $150 learning experience I guess .
Reply:Originally Posted by DesertRider33That is a good idea.  I just turn down the feed speed if I am going to be wasting more than a few inches of wire with my trigger pressing.
Reply:haha i stuck some wire in the side of my head one day doing that. maybe thats whats wrong with me!only thing worse than an ugly woman is an ugly weld
Reply:LMAO  :bMM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Originally Posted by El_Lloydeohaha i stuck some wire in the side of my head one day doing that. maybe thats whats wrong with me!
Reply:Just for S&G's... it seems that for the first part of the weld that it's cold, even with stick.  I really haven't figured a way around it other than running really slow at the beginning of the weld and shoving the rod in, but sometimes it seems that you can wind up piling up extra metal.  I don't really know a way around it."Any day above ground is a good day"http://www.farmersamm.com/
Reply:UpdateBernard sent to my LWS , a new liner and brass connection that fits into the Lincoln drive block . It is a completely different design that what originally came with the Praxair gunand it fits perfectly . No charge .Porosity problems solved . All is good now . Thanks Bernard
Reply:Thanks for the follow up. 9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:Great!  Kudos to Bernard too!MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op