GMAW flow meter settings

[DaveO]

I was thinking about my IMIG setup and how I have to remove the inert gas hose from my machine for storage (no dedicated welding cart and no space to keep one), and realized when I first pull the trigger on the MIG gun the hose has not yet filled with shielding gas, so the first welds would be shielded with air. Figured I'd need to purge the hose properly next time, but didn't know for how long to hold the trigger prior to starting a weld.

I measured the ID of the hose at 8mm and the hose length at 202.5 cm (using metric to accomodate the Liter Per Minute flowmeter). The volume of a cylinder is Pi*r^2*H where H is the height of the cylinder, in this case the length of the hose. Pi*4mm^2*2025mm = 101,787.6 cubic mm, divide by 1,000,000 to convert to liters = .1017876 liters. Multiplying by 60 seconds means I'd have to set the flowmeter to 6.1 LPM and hold the trigger for 1 second to purge the hose, and add some time to purge the machine and gun. That 1-second line purge surprised me a little, I think I expected it would be more.

But my question is: do different GMAW operations require different shielding gas settings and if yes, why do various calculators (Everlast, Miller) not offer them? Is there a set-and-forget setting, or is it a matter of turning flow up or down until you reach an optimal setting?

[performance]

As far as the "purge" setting goes.
The gun really doesn't empty out. Argon and CO2 is heavier than air, so it will not completely evacuate for some time. I would also imagine that the nozzle shields the gas inside the tubing from any air currents that would siphon the gas out.

[DaveO]

Thanks- for the hose purge I was thinking of the set-up for the first weld of the day, when the hose had been removed from the machine. I"m planning a little project so I will try to recreate it in a practice scenario, good idea.