[Pavlo]

I was practicing some TIG late yesterday after all the real work had been done, and also changed my torch. I had real problems trying to weld some 16g low alloy (T45) steel tube. I put it down to not fully purging the air out the hose of the new torch. SO I ground it all back, and ran the gas through the torch with the hose all straightened out and the torch held high.

Then I started to strike the arc up well away from the weld, new tungsten, and still it started to oxidise, low current or high the same bad result.

My welding gas is Argon from BOC in the UK and it was low, down to 10 bar out of 200. So I am now wondering if there is some air in the bottle, and when it was fuller it wasn't a problem as the air will separate in the bottle and if the bottle has a siphon tube in the valve head it might explain what I was seeing.

It got to the stage where as soon as the ARC was initiated there was light spitting and electrode discoloration.

Does anyone have any recommendations for how low to run the gas from a bottle? Any stories of air in the gas?

Thanks

paul

I was using the following setup in case anyone asks.

WP9 torch
1/16 2% Thoriated electrode
#7 gas lense
0.5s pre gas
35A to 72A
ER70S-2 filler

[Pavlo]

Well after a little research I would have to conclude it was not enough purging of the new hose and torch assembly. Any air or oxygen would be homogenised in the argon it would seem. Plus a google of purging brought up Murex manual recommending a 15 minute purge of a new torch assembly.

[noddybrian]

OK - lets get some myths cleared - the cylinder contents will never separate & if your Tig welding it's 100% argon so there is nothing else in there- there are no syphon tubes in any BOC cylinder except liquid draw propane ( like forklift tanks ) !I run all BOC bottles completely out of gas before changing & have never had a problem either at home / my shop or any place I've worked - BOC are robbing bar stewards BUT I never heard of bad gas from them - I think reading posts here it's common in other countries where small hobby bottles are routinely filled by decanting or using air over gas pumps to charge from larger cylinder banks without proper procedure being followed ( Len could elaborate on this if it's not top secret ! ) I would have to say it's more likely you have a leak somewhere or the torch hose has some moisture or other contaminant in ( especially if it's an Ebay finest ! ) or as simply as there is a restriction / blockage in the torch like a bad collet / contaminated gas lens screen - this is far more likely - check by ear at the torch for consistent flow ( not just surge at start ) if familiar - ( mind hf on ear ! ) or buy a pea shooter gauge ( the most reliable foolproof check for gas )

peashooter-large.jpg (47.89 KiB) Viewed 3748 times

[MinnesotaDave]

+1 on the slip on gauges to check for proper flow.
I also check my mig with it.

[Braehill]

Pavlo,
First off I think you solved you own mystery with it being a new torch ( or any other new component in the gas system) and needing a purge prior to welding. I think 15 minutes is a bit much, but you can always run a few practice beads before welding something critical to confirm the gas is running pure.

As Brian said there's a procedure that should be followed while filling any cylinder. Cylinders are emptied followed by a vacuum being pulled on the cylinder then a small amount put back in the cylinder and evacuated again, up to 3 times before the cylinder is filled to it's final pressure. This uses the gas as a carrier for the moisture to be withdrawn during the vacuum stage.

Argon cylinders do not in fact have a dip tube, they are essentially a hollow tube. Cylinders can get moisture in them but it's rare, and if they have moisture present it will be more noticeable at lower pressures. This is because the moisture will make up a larger PPM (Parts per Million) of the remaining gas in the cylinder.

I look at the gas only when I know that all other variables have been ruled out. Loose connections, cracks in the lines, broken O-rings, bad collets to name a few can all lead to Atmosphere being siphoned into your gas stream. A simple bubble test can usually find these leaks as they will be present under pressure of the Argon.

I actually went against this advice and returned a cylinder the other day with about 400# in it because I had added a piece of stainless tubing to my system that had something in it from sitting around the shop. I later found dust in my flow meter that I have mounted on the 'out' port of my gas solenoid. A thorough check would have save me some gas and an early trip to the cylinder fill plant.

I personally think a preflow setting is a waist of wiring and a timer. If you have it on your welder go ahead and set it, but bumping the pedal gives me up to whatever time I have my postflow time set to start welding while gas is flowing. I'm still a little bit old school when it comes to any machine you are trying to make a living with, less add on non-essential controls means less to go bad, but that's just me.

Len

[noddybrian]

Thanks for adding your expertise Len - despite bad gas cropping up here routinely at least in the UK using BOC or Air Products it's the least likely cause of a problem - glad the OP sorted it - & I'm with you on the complexity of newer machines - especially ones that are all digital & scroll wheel - at least a set of knobs can be checked at a glance - besides after the bombs drop what's going to still work ! - everyone's going to be round trying to borrow that old 1ton welder of Daves !

[Pavlo]

I figured the gas wouldn't be contaminated as soon as I did a little more research on it in general. I will certainly see if I can get a second flow meter on the torch to compare with the one of the bottle. The torch has been hanging around for a long while since I purchased it from my local welding supplies place. It's a Starcraft item which essentially means it's made in China, but it looks well enough. The torch has a long 25ft hose and I think that's making the issue worse, just means it takes a long time to purge.

I know there are no leaks up to the Dinse adaptor as when I first fitted it the side hose barb for the gas was blocked with solder.

I have some oxygen sensing (for exhaust gas) equipment which I might see if I can rig up on the torch outlet and measure what's going on. Not sure how it will work but it I'm keen to try!

As for pre flow, I've got another tig without it, and using a trigger means that if you accidentally hit it before you're ready you can get some arcing without the gas, on cosmetic stuff it can be a pain, on thin stuff if can be a hole (like a radiator tube).

[Braehill]

Pavlo,
I think the flow meters that go on the end of the torch are fine to verify gas flow in general, but I find that at least the ones I have are not very accurate. I have access to some very accurate flow meters at work and they read at 20 scfh when the 'peashooter' reads about 12 scfh. Using it to set up a torch in my case would waste 8 scfh of Argon. I've checked my Harris, old Union Carbide and Radnor against the ones at work and they're all right on the money, so I trust my ear and the flow meter on my machine.

As a side note, my flow meter is now mounted on the 'out' port of my gas solenoid to eliminate that gas surge when you hit the pedal, works great.

Len

[RichardH]

As a side note, my flow meter is now mounted on the 'out' port of my gas solenoid to eliminate that gas surge when you hit the pedal, works great.

Cool! Glad to hear that works well. I'm still curious why it's not common practice for the flow meter to be on the back of the welder, where it's both closer to the weldor for adjusting / checking, and more effective. Or even integrated into the welder, since argon and CO2 gauges seem to be practically interchangeable.

Cheers,
Richard

[Pavlo]

Well I found the problem....

Cheap nasty gas lense. I thought I was putting in a CK 1/16 gas lense, but it was a cheap far eastern part I had knocking about. I tried my 3/32 CK part and hardware, problem gone. Then I found my 1/16 CK part still in the bag.

The difference is night and day when you look at them, the screen on the CK goes right out to the cup almost, minimal material on the brass body on the outside of the screen.

I did do some testing for leaks, but found none to speak of. If you seal the head of the torch with your fingers there is nothing, if you leave the back cap on then it leaks when there is some pressure buildup.

So there you go, thanks to those that pointed me in the right direction!

[noddybrian]

Glad you got it sorted - collapsed collets & bad gas screens are often the culprit - just creeps up on you - one time they work then one day problems & not obvious at first glance whats changed - collets being the worst in yview.

@Braehill.
I agree the accuracy is'nt always great on some pea shooters though they do vary - no reason they can't be accurate really - it's pretty much the same as a regular flowmeter - just not directly fixed - for people that got used to setting " by ear " they are not needed - but it's a great help to check what's coming out where it matters for those not experienced - especially as many people don't appreciate the difference between gauges which are effectively measuring pressure but calibrated as a nominal flow & actual flow - the fact the pea shooters are often not calibrated for any particular gas is off putting - but if you trust a given gauge - set a known flow then test with pea shooter & note the difference - bit like tire pressure gauges - most are consistent - but not necessarily accurate - unless marked against a quality one.

I've not moved my flow meter to the output side though it makes perfect sense - only thing is the metal part of the body & needle valve knob will be live when welding - you would need to bump the torch switch then set gas using post flow to avoid the hf biting - is this what you do or are power & gas separate on your machine ? - most here have mono cables terminated in3/8" BSP taking gas & power together.

[Braehill]

Mine a separate so it's not live with the power cable.


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[kiwi2wheels]

Glad you got it sorted - collapsed collets & bad gas screens are often the culprit - just creeps up on you - one time they work then one day problems & not obvious at first glance whats changed - collets being the worst in yview.

Could you please explain how problem with collapsed collets manifests itself and what to look for if it's not real obvious. I've been using a " communal welder " that gets zero care and attention , re the torch consumables, and sometimes a weld would look like dog doo ( stainless welds appeared as if there was marginal gas coverage ) I had fitted a new Weldcraft gas lens, new O ring on the back cap and picked the best of the collets that locked up easy and checked all the usual things.

I suggested they get the C&K Wedge Collets............. not interested. Thanks.

http://www.ckworldwide.com/wedge_collets.htm

[noddybrian]

It's not always obvious with collets - all I can say is when they're new & straight & copper colored you never have a problem - but once they've been overheated a few times they don't grip the tungsten as well & require more pressure on the back cap - this causes them to reduce slightly in length but swell out the diameter - you also notice the slit is not quite straight - having a slight twist to it - once this becomes pronounced then the gas flow between the collet & torch internally is restricted - it can do it to the point no gas comes out - I figure the gap is so small to start with it does'nt take much to restrict it - but take out a heat soaked / distorted collet - replace with a new one & watch the flow meter shoot up again- the wedge collet would be an ideal solution - alternative is buy your own torch parts & swap them out when using this shared welder - take them off & keep them safe when others are using it.

[kiwi2wheels]

Many thanks for that, never would have thought about that , but it makes good sense. And many of the import pattern WP20 style collets are marginal on tightening when new ..................Normally I do have my own torch and parts but in this instance, unfortunately no.

A set of wedge locks are on the shopping list ! Cheers.