Why is Extra Gas Needed for MIG Weld Starts?

We are often asked why certain devices such as restriction orifices mounted at the feeder to control flow do not work or why welders complain about their use.  The following are some answers:

Question: Why is some extra gas needed at the weld start?

Question:  What are the devices that cause lack of sufficient extra gas at the weld start?

Answer:  Any device that attempts to control flow at the wire feeder will not have sufficient "stored gas" that can be quickly delivered to the welding torch cable, torch nozzle or weld start area.  This can be a:

1. Flowmeter,

2. Orifice that is controlling gas flow,

3. Needle valve or

4. Regulator/ flowgauge (low or high pressure.)  Note, low pressure devices have added problems. (See Q&A About Automatic Flow Compensation)

Question:  We're using a flowmeter at the gas source (cylinder or pipeline.)  Do we have a lack of start gas problem?

Question: What happens if we don't quickly have sufficient extra gas at the weld start?

Question: Is that why when we have used orifices mounted at the wire  feeder to control shielding gas flow welders complained and sometimes drilled out the orifice?

Question:  Are there specific production instances where a switch to some extra gas at the start helped weld performance?

Answer:  Yes, the following example validates the need for some extra gas at the weld start.  A bar joist manufacturer was using flow control orifices mounted at the wire feeders.  Argon/CO₂ shielding gas is supplied in a pipeline through about 15 feet of gas delivery hose.  The flow control orifice established the flow at 45 CFH.  However the welders wanted higher flow rates with some even drilling out the orifice!  The welding engineer wanted to avoid wasting shielding gas. With this flow setting arrangement where control is mounted at the feeder next to the gas solenoid  there is insufficient extra gas provided at the weld start.  This lack of extra gas prevents  to purging the weld start  area of moisture laden air.  

A test was made to check weld performance and potential shielding gas savings using two cylinders of shielding gas on two adjacent welders instead of their pipeline gas supply.  One was set with their standard flow control orifice system and a regulator providing a pressure that matched their pipeline, 50 psi.  The other with a regulator/flowmeter (also of a 50 psi design) using a 15  foot GSS without their flow control orifice.  Both steady state flows were set at 45 CFH.  Since welders stand side by side, it was easy to observe the weld start quality!   Instantly the welder using the GSS noticed  improved  starting.  After about an hour with observably better results the  welding engineer suggested we lower the shielding gas flow on the  welder with the GSS to 35 CFH!  The same improved weld start quality was observed and the welder was "happy."  In fact even though we lowered the steady-state flow to 35 CFH there was still about the same controlled amount of extra gas available at the start (that stored in the GSS hose when welding stopped.) The higher start gas flow rate established by the surge flow orifice in the GSS maintained the higher flow at the start.   This higher start flow rate quickly flooded and purged the weld start area of moisture laden air.  It was this air that was casing excess spatter and lack of shielding on all their other welders! After about 4 hours of observation it was obvious the spatter at the weld start was less with the GSS.  We also measured a reduced use of shielding gas of 25%.   After several months of testing to check this one system during windy days etc, this shop now has GSS's installed on all 50 welders!   

Bottom Line - - "Some extra gas flow at the start is very beneficial."  In addition, after about a year of use their gas supplier called to see if their business had turned down since they were using about 30% less gas- it had not!

Question: But we use a flow control orifice just to limit start surge flow and still control the steady flow with a flowmeter at the gas source.  Is that a problem?

Answer:  That will eliminate the problem of excess gas surge but depending on the orifice size may not supply sufficient extra gas.  We have found most commercially available orifices are actually not large enough to optimize start surge flow rate.  In addition you may be doing that since you perceive your saving gas.  You can hear the reduction that occurs in initial gas surge, right?  Yes the surge flow is reduced and you can here the difference.  However if you put a pressure gauge in your gas delivery hose you will see it still reaches the pipeline pressure (or with cylinder gas supply the regulator pressure) when welding stops!  The pressure will reduce to what is needed to flow the required amount of gas when welding starts (usually about 4 or 5 psi.)   Where does that extra gas go?  It is wasted almost as if you did not have the orifice in place!  It just takes longer to be expelled at the rate set by the orifice!  You may save some gas, may 10 to 15% of the waste.  Our GSS saves about 80% of the gas waste!  It pays for itself in a matter of weeks and includes, as part of its patented design, a surge flow limiting orifice at the feeder/welder end.  Check it out

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