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Old 04-21-2008, 09:38 AM
oldred oldred is offline
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Quote:
Originally Posted by lowROLLERchevy
ive had problems from the pressure being to high. one of our "new guys" at work opened the bottle with the flow adjustment on the regulator. that lil ball in the glass site gauge bounced off the top with a solid thud ...

i didn't realize this till i had started to lay a bead in one of those "impossible to get to with a grinder" type spots

IIRC to much flow will suck air into the shielding glass from around the edge of the nozzle, diluting the shielding gas and causing porosity, just like the venturi in a carb sucks fuel into the air stream

a properly setup mig welder should be able to lay a porosity free bead even with a light breeze blowing across the work piece. if the smallest movement of air causes porosity examine the entire sheilding gas system for problems, THEN play with the pressure / flow settings

Agreed 100% and you have made some very good points. The flow meter you described works better for Mig/Tig welding than the pressure gauge type because it measures the actual flow regardless of pressure. That little incident with the ball hitting the top of the scale tube is not an uncommon occurrence and has been one of my pet gripes for years and sometimes it can even pop the safety plug in the top of the tube which will ruin the meter, you can not buy replacement parts. This happens when someone turns up the meter when the tank gets low on pressure and either forgets it or leaves the empty tank to be changed by someone else who is not aware it has been turned up. For the life of me I can not understand why anyone would do this but I have seen it happen countless times over the years. Doing this is just plain STUPID but people do it anyway! When a tank runs out of pressure it is EMPTY and no matter how much adjusting they do on the meter it is going to STAY EMPTY but they do it anyway! When I ran my shop I lost several Oxygen gauges and flow meters because of guys doing this and for as long as I ran the place that was the only thing I ever had to let an employee go for but one guy would do it every time he ran out of gas! Turning up the flow to the levels you would get with a wide open gauge would indeed cause porosity for the very reasons you mention and that is why I said that too much flow within reason would not hurt anything. An example of what I was talking about would be using 20 PSI (on a pressure type) when 15 PSI is all that MAY be needed, the extra 5 PSI would not hurt a thing but it would waste gas. The point you made about the air contaminating the shielding gas flow is a good one because that is probably 90% of most Mig/Tig problems. It is a common myth that turning up the flow is necessary to solve problems with a draft ruining the weld and indeed you can even find this recommendation in lots of welding books but in fact it rarely helps much. The common misconception is that the draft "blows away" the shielding gas when actually this is not the case since it would take a LOT of wind to do that. What actually happens is that the gas will become contaminated by the air when exposed to a draft and even though the gas still surrounds the weld area it can no longer protect it so the solution is to remove the draft, turning up the flow simply uses more gas which will still be contaminated. Other problems related to this can be things like a dirty or distorted nozzle which can cause a turbulent gas flow that will cause air to become mixed with the shielding gas or a leaking seal at the back of the nozzle (this can happen with either the slip on or screw on type) which will let air siphon into the gas flow. The dirty/distorted nozzle or leaking nozzle to gun seal are common problems often mistaken for draft problems and because of the siphon effect turning up the gas flow can actually make the problem worse.
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