Mig welding Porosity

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Lately I've been having trouble with my Hobart 187, most of my welds end up with porosity, I've checked the cable and wire connections and everything looks tight, I have replaced the cup and tip w/o good results. It seems that this problem started when the CO2 tank got down to half full, after my first fill up... in other words; when the tank was full, there was no problem, now the gauge reads about half full and I have the porosity problem... even with the flow set at 25.I can hear the gas flow thru the tip when pressing the trigger, so I believe there is enough C25 gas mix coming thru the cup. I'm starting to lean toward a bad gas mix in the tank, it that even possible?I appreciate any help troubleshooting this problem. Thanks Joe
Reply:I don't see how it could be bad gas if it worked fine before...post up a pic. it could help....are you using co2 or a mix?....how have you prepared the steel?
Reply:There can be many reasons for porosity.  We need more input. As mentioned, metal prep. wind conditions, ect. It is also possible to have too much flow and cause turbulence which can induce air into the gas coverage area.  Did you increase amps or is the metal thinner. You could be drawing air from the backside of metal if the puddle is molten all the way thru. Are you sure you have a flow meter and not a pressure regulator? Did you change anything else about your welding process? Cup angle, travel speed, ect?SA200,Ranger8,Trailblazer251NT,MM250,Dayton225AC,T  D-XL75,SpoolMate3545SGA100C,HF-15-1  RFCS-14 When I stick it, it stays stuck!
Reply:I haven't mig welded in a few years but did a lot of before retiring. In my experience probably 98% of porosity problems are caused by shielding gas or metal contamination problems. Figuering out the correct flow rates on the particular shielding gas you are using and staying out of any air currents virtually eliminates any problems on that end. Usually cleaning any scale or oily residue off new metal and having ground it shiny made any porosity go away. Some metals that are reused after being in a contaminating environment simply will not accept mig welding no matter how clean and shiny you get them and you have to go to stick electrodes. I've never had a problem with a bottle of shielding gas, if it was good at the start it was still good until it was empty. It may turn out to be something else but those are the two areas I would address first if it were me.
Reply:CO2 is a gas compressed to a liquid.  The pressure will remain roughly the same, until the liquid is used up in the tank.  Then will drop rapidly.  Much like propane.My guess, there's enough for a burst when you squeeze the trigger, but not enough pressure to sustain any decent flow to keep the atmosphere from interfering with your weld.Just to clarify... you say CO2 at the beginning of your post, then change to C25... Which do you have again??
Reply:Start with the simple things:Remove your gas nozzle and clean out any spatter build-up so that you have a smooth flow of shielding gas.  Build-up can lead to turbulence leaving the nozzle, and introduce Atmospheric air into the weld zone.Checkover your diffuser to make sure all the holes for the shielding gas are open and not blocked by spatter.Check O-rings on diffuser (if any) for cuts or pieces missing.  Replace as needed.  - I take a small dab of nozzle dip and spread it on back end of diffuser below gas ports to 1) Help remove/install nozzle, and 2) Help seal to prevent gas loss.Re-intall the nozzle onto the diffuser, and seat firmly to seal back end onto diffuser.Pre-weld preparation is always important, but you will not see a difference if your nozzle is full of spatter build up, and you are not getting a constant, smooth flow of shielding gas into the weld zone.Just my $.02Later,Jason
Reply:What Jason said.Now check these spots peculiar to Hobarts.The gun MUST be seated all the way up to the back of the gun seat. Also check both O-rings on the gun. They can get pretty nicked up if you swap out guns or remove it often.
Reply:What DDA52 said jarred something in my memory. I have had the machine end of the gun lead pull away from the seat due to pulling on the gun, and allow atmosphere to enter around the sealing surfaces/o-rings. Just one more thing you might check.SA200,Ranger8,Trailblazer251NT,MM250,Dayton225AC,T  D-XL75,SpoolMate3545SGA100C,HF-15-1  RFCS-14 When I stick it, it stays stuck!
Reply:Thanks for the replys guysI went to the garage and fiddle with it some more...I believe the problem is IN the gun, there's a bad contact in there because in certain positions it wont fire and if I twist the gun cable it works fine...I need to disassemble the gun and investigate further...My tank contains C25, not CO2...sorry for confusing you, also the metal is cleaned from mill scale, and I have a pressure regulator which I keep the flow at around 20.I'll post pics of the project and the gun ( if I can figure out how to disassemble it)Thanks againJoe
Reply:Joe if you have your owners manual it will show you how to take the gun apart....if not go to the hobart site and you can down load it.
Reply:Thanks Mike
Reply:Sometimes you can run into contaminated / dirty wire. If the wire has picked up moisture or has rusted or come into contact with foreign objects like dust or dirt, that will defiantly give you porosity. Oxy
Reply:Heres a thread I posted the other day. Might help you out a little bit on turning your flowmeter up.http://weldingweb.com/vbb/showthread.php?t=21241As said by CHENRY:you cant weld on a thingamajig like that. are you even certified to do thingamajig welding ? I once saw an improperly welded thingamajig fail and eleventy twelvoteen things got ballywhacked. I dont think i would risk it.
Reply:Are you welding outside?Wind?  Any breeze will blow your gas away.Me!
Reply:Originally Posted by JoeDThanks for the replys guysI went to the garage and fiddle with it some more...I believe the problem is IN the gun, there's a bad contact in there because in certain positions it wont fire and if I twist the gun cable it works fine...I need to disassemble the gun and investigate further...My tank contains C25, not CO2...sorry for confusing you, also the metal is cleaned from mill scale, and I have a pressure regulator which I keep the flow at around 20.I'll post pics of the project and the gun ( if I can figure out how to disassemble it)Thanks againJoe
Reply:Joe, sounds like you found the problem. you might want to increase your flow to 30-35 cfh.Oldtimer, can you elaborate on this:Some metals that are reused after being in a contaminating environment simply will not accept mig welding no matter how clean and shiny you get them and you have to go to stick electrodesSlam, I'm not sure that i have ever encountered the problem referenced below. Is it a common problem if you have your flow set correctly?CO2 is a gas compressed to a liquid. The pressure will remain roughly the same, until the liquid is used up in the tank. Then will drop rapidly. Much like propane.My guess, there's enough for a burst when you squeeze the trigger, but not enough pressure to sustain any decent flow to keep the atmosphere from interfering with your weld.good catch Jason
Reply:Hey guys It has been awhile… I disassembled the gun and found the problem, as you can see the gas nipple came out of the hose, so I wasn’t always getting the gas when welding. Well, later I discovered that my 16 YO might have pulled the cart by the gun…kids!!!!!Anyways, here are a few pics of the repair, it should last awhile:Here's the porosity How I found the gun:Improv. clamp...(a cotter pin)Elect. tape:Here's a better bead; 1/2" rod on a 1 1/4" flat stock:And here's my project, a smoker/pig roaster...mostly from recycled materials (scrap yard)Guys, once again thanks for helping out.Joe
Reply:oooo that's nice ChuckASME Pressure Vessel welder