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Back purge.
- Thread starter Bsmith
- Start date
In an ideal world you should install a 'Y' piece on the outlet side of the argon regulator and use two flowmeters, one for the torch and one for the purge line.
Argon is heavier than air, so the purge inlet needs to be at the lowest part of the pipe and the purge outlet at the highest point. Ordinary masking tape can be used to seal the ends of the pipe, poke a hole in the bottom seal large enough to install the purge line and seal around it with some more tape. Poke another smaller hole in the top seal to vent the air which is displaced by the argon entering from the bottom. If welding an open butt, this should also be taped over, arrange the tape so that it can be peeled open starting at the lowest part of the butt as you weld. Estimate how much argon will be required to fill the pipe and add about 10%, using the flowmeter, purge the pipe. Avoid filling at too high a rate as it stirs up the trapped air inside the pipe and causes it to mix with the argon rather than purge. Once you are satisfied that the pipe is filled with pure argon, turn the flow rate down to a slow trickle to prevent any air returning. For thin walled pipe keep the purge running until you have completed the weld to prevent the inside from coking.
For butt welds in plate, use aluminium foil taped to the back of the butt, allow a gap between the foil and the butt to contain the argon, arrange the purge as before, in at the lowest point, vent at the highest.
Argon is heavier than air, so the purge inlet needs to be at the lowest part of the pipe and the purge outlet at the highest point. Ordinary masking tape can be used to seal the ends of the pipe, poke a hole in the bottom seal large enough to install the purge line and seal around it with some more tape. Poke another smaller hole in the top seal to vent the air which is displaced by the argon entering from the bottom. If welding an open butt, this should also be taped over, arrange the tape so that it can be peeled open starting at the lowest part of the butt as you weld. Estimate how much argon will be required to fill the pipe and add about 10%, using the flowmeter, purge the pipe. Avoid filling at too high a rate as it stirs up the trapped air inside the pipe and causes it to mix with the argon rather than purge. Once you are satisfied that the pipe is filled with pure argon, turn the flow rate down to a slow trickle to prevent any air returning. For thin walled pipe keep the purge running until you have completed the weld to prevent the inside from coking.
For butt welds in plate, use aluminium foil taped to the back of the butt, allow a gap between the foil and the butt to contain the argon, arrange the purge as before, in at the lowest point, vent at the highest.
