Major issues welding last night

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OK, I am a total rookie and new to welding, but have been having pretty good luck... until last night.I was trying to MIG up my bumper supports 1-3/4" .120 wall welded tube.I was getting HORRIBLE welds.  Very porous... material was bubbling up even after I passed by it....  when i grinded them down the bubbles were hollow.I tried changing everything.  wire speed, voltage, gas flow, etc.  Weld would look fine  when doing it.. and sounded fine... but once you stopped and looked, it was a fricking mess!  It was almost like the air pressure from getting hot inside the tube was making it bubble out???  Best setting on my Hobart 180 still seemed to be Voltage at 3 and wirespeed at between 50-60.  These settings worked great before too.I have no idea why this was happening and it was real frustrating.  There was three of us welding and it happened to every one of us!  It was almost like the gas wasnt working.  So we tried to push the nozzle out to cover the electrode more... seemed like it helped a tad... but then I started getting the problem again.I will try to snap pics later... but it seemed like the material was contaminated some how.   I cleaned the outside of the tubes and inside at notches with acetone... couldnt get the inside part in the middle of the tube cuz it was already on the truck and couldnt reach inside.what normally causes porosity and bubbling???  I'm ****ed cuz the welds are horrid looking on my what was nice bumper...Last edited by FasterNU; 04-06-2007 at 04:36 PM.
Reply:is your gas normally supposed to be at 15-20 cubic feet per hour??  That's what i was told somewhere... but that's low on my dial... dial reads liters per hour and cubic feet per hour (i think)
Reply:i'm also worried about the cotton rags I am using to clean with.  they seem to leave a lot of cotton/lint behind.  What do you use to clean the material with... maybe those blue paper towells would be better???
Reply:Were you outside? Sounds like you were losing your gas coverage. I typically run 25 to 35 CFH. When you pull the trigger can you hear the gas flowing out of the nozzle end? Pics will tell a lot as well._________________Chris
Reply:Bad gas rarely leads to quality work... Got pic's?ThermalArc 185MillerMatic 180 w/ AutosetVictor Cutskill Oxy/AcetyleneThermal Dynamics Cutmaster 38and spite!
Reply:Were these the last welds on the tube?  If it was, you need a pressure relief.  Otherwise you have a gas problem.  Porisoty is from lack of gas coverage.  15 cfh should be fine,  too little and it doesn't do its job, too much and it makes a mess too.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:I'm pretty sure i know what your talking about...does it bubble up when your welding joint of old metal?we run in to this problem when welding on old big trucks where you can't totally get at all the dirt. and the weld bubbles  as it tries to pull the crap out. also pre heat the old metal to get the water out of it!
Reply:I agree with David R. I think what you're getting is 'gassing out' from the inside. It happens when you are trying to close a tube or even with tight fit ups. Denser cooler air inside the tube expanding at a fairly high ratio as well as the oils and other contaminants inside. This breathing in and breathing out can cycle as fast as the tube can heat and cool. Add to this any heavy oily vapor rising with the heat and there ya go. To counter this you can heat a significant section of the tubing to get the expansion out of the way, drill a vent hole for the bulk of the welding, use small tacks over a period of time to sneak up on it, things of this nature.  Getting all of the oily residue away from the inside of the area to be welded is very important.
Reply:If your not sure you have gas flow, stick the gun in the dirt on the floor and pull the trigger. If it blows the dust , you got gas. You can also put it in a pan of water, or maybe your coffee cup, and look for the bubbles.
Reply:what gas?  I use CO2, and under certain conditions, my regulator freezes off and quits.  Does it weld good, then go funky?
Reply:I had a similar problem which lead me to find this site. My welder was working great one minute than bang, porosity. Went through allot of testing and found out that the gun liner or part of the gun Assembly was drawing in air causing my porosity problem. A new gun fixed me up. Since their was allot of testing and in different areas, plus allot of good input from people on this site I have posted the link below to my porosity problem and all the input I received. Read through it and try some of the things I tried and see if it helps.  Good Luck and hope you find the problem as mine drove me crazy for awhile.http://www.weldingweb.com/vbb/showthread.php?t=8579Miller DVI2Lincoln Precision Tig 225Thermodynamics Cutmaster 38Everything else needed.
Reply:Have you tried welding a different material.  If the porosity goes away then it is the metal, otherwise keep checking.However, I have to go with DavidR on this. You can also drill your holes were they will be hidden in other tubing.
Reply:maybe I missed this somewhere but do you have your polarity set right?
Reply:Originally Posted by David RWere these the last welds on the tube?  If it was, you need a pressure relief.  Otherwise you have a gas problem.  Porisoty is from lack of gas coverage.  15 cfh should be fine,  too little and it doesn't do its job, too much and it makes a mess too.David
Reply:The original question was "Were these the last welds on the tube? ".  Waiting for an answer from faster than you.  DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Originally Posted by David RThe original question was "Were these the last welds on the tube? ".  Waiting for an answer from faster than you.  David
Reply:you are welding bumper supports. did you grind the factory paint off. i know my mm 251 and the tb 302 don't weld paint very well. the underside of the car is likely painted black and you can clean it with acetone but you need to grind down to the shiny steel on the underside. check the steel, then check the gas coverage, then check the overpressure coming from inside the tube if your closing it off. if that fails, have someone hold your gun liner while your welding. my liner in my sp175 has a sweet spot that the wire jumps out the gun sporadically, especially when doing an overhead weld and the gun has a wicked down angle. i usually have to hold the cable with my foot when overhead welding. but thats just MHO.james"Retreat hell, were just fighting in the other direction"Miller Trailblazer 302, Extreme 12 VS, Dimension 400, Spectrum 375, HF 251D-1, Milermatic 251 w/ spoolgun  Hypertherm 1000Lincoln sp 1702000 F-450 to haul it
Reply:ok, sorry for the delays.  Polarity was correct.  This was occuring on all new tubing that was cleaned with acetone on the outside and as far inside as my fingers could reach with the rag.... This was indeed towards the end of sealing the tubes.  The joints were pretty tight as well.However, after more welding this weekend, I think it was a more of a coincidence it was happening towards the end of the weld when sealing the section of a tube.. or I was just seeing a combined effect of my two issues. I say this for 3x reasons:1.  I tried to weld some tubes later with open ends and was still getting porosity... lots of tiny bubbles.(got 1x big bubble and lots of small ones on each seam seal)2.  After moving the nozzle tip out to cover the electrode more and turning up the gas a bit to around 20 cfh... the problem seemed to go away.  No more tiny bubbles. 3.  I turned off the gas to see what a weld would look like without it... tons of tiny bubbles like when I had the isssueAlso, I did seal off some more tubes and didnt seem to get the big bubbles this weekend.... I'm wondering if the way I welded it this time(didnt allow time to cool before sealing) helped stop the internal pressure issue??Unfortunately I dont think I got a pic of the bad welds as I was too busy trying to figure it out.  I'll check my camera though
Reply:Oh, so how the hell do you guys heat the metal first... i dont have any torches or anything.... and I dont think I want to look like I'm working in a salon by breaking out a hair dryer or heat gun. hahaha
Reply:I have a "weedburner" torch.  It runs off a gas grill tank.  They are from $20.00 and up.  It will turn steel red in time.  LOTS O HEAT for cheap.Glad you found the problem.  It can be frustrating.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Hmmm I'll have to check into something like that...Here is the resulting bumper FWIW:
Reply:Are the inside of the tubes clean? If not then the heat from the weld can draw the crap into the puddle and cause porosity as well. Pressure build up inside... possible but I doubt it. Use a flapper wheel or a high speed carbide bit to clean the inside of the tube.15 - 20 CFH should be enough on the MIG as well.Good luck.
Reply:OK, here's some pictures of the bad weld.. this one was probably the worst.  now that i look close too... seems a lil undercut as well maybe?
Reply:I'd shoot those pigeons if they done that to me.Now, I didn't read everything said above, so this is probably a repeat, but hell it's not rocket science!Porosity is caused by lack of shielding or contamination.Lack of shielding can come from contaminated gas, wrong gas, leaks in the system drawing in air, drafts blowing gas away, not enough gas, too much gas, nozzle to far away, nozzle clogged up with spatter, arc length too long, wrong voltage/wire feed giving erratic/violent arc, and lots more things I can't think of right now.Contamination can include air, water, oils, oxides, etc.  Contamination can be on the base metal, in the joint, inside the tube, on the wire, in the gas.Slap so more paint on it, it might not fall off.Can you tell, I've had a ****er of day so far?