Metal cutting - oxyfuel cutting, plasma cutting, machining, grinding, and other preparatory work.
converting arc to tig for hygiene welds on a beer keg
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geewhizz
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    Tue Oct 02, 2018 1:47 pm

Hi there, firstly thanks for all the info I've received from the people on the forum so far. You've been a great help getting my confidence up with my recently arc welding project using 2mm mild steel box section.

Now I need to utilise TIG for my new project as I'm using thin stainless (I'd guess 1.5-3mm) and I need a better finish to the weld. I'll be welding various 2-4" tri-clamp ferrules and pipes and thermowells onto a stainless beer keg. I'll also be welding one smaller keg inside another keg. Those particular welds would need to withstand a vacuum of about 1 bar under atmospheric pressure so I've got to make a pretty good job of it. :mrgreen:

Help required:
Mainly, I'd like to know if my current ARC welder would be up to the job to do these types of welds.
I have a Rehm 140 booster, heres a link https://www.rehm-online.de/en/schweissg ... r-140.html

I know I need a conversion kit so was thinking about this here - https://www.weldequip.com/tig-conversion.htm

I understand I'd need to back purge my work piece to get nice welds (hopefully the conversion kit above allows two lines out or would i need to organise an additional splitter? Also which rods would be best for the job?

Is there anything else that I need to know or purchase (aside from an argon cylinder) ? Also if anyone has any general tips what so ever I'd be hugely grateful to receive them.

Thanks for taking the time to read, Gee
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cj737
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    Thu Sep 29, 2016 8:59 am

Your machine will accept a TIG conversion kit. The kit you posted shows only a single outlet Regulator. For a quality back purge, you really want a dual outlet so you can adjust the flow for the torch and purge independently.

One caution I’d offer, the welder you have only offers Lift Arc for TIG. This is not preferred for stainless, especially thin stainless. You also really want a variable amp control foot pedal or torch switch, so consider adding that. You can weld with lift arc, but, for thin stainless in a food quality environment, it would not be “preferred”.

I’d use 316l filler, probably 1/16” or smaller. A large cup #8 or #12, and clean the material well first.
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Coldman
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I think the manufacturer is using the words "lift start" with poetic license. If it was lift start, there would be setable upslope on it, don't see any such controls. I think it is a dc stick machine that you can use for basic scratch start tig. Unless you are uber cool at tig, you're not going to be happy with the result on your staino project with that rig.
Time to bone up for better rig with high frequency start and a pedal.
Flat out like a lizard drinkin'
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tweake
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    Mon Dec 18, 2017 4:53 am
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a lot of welders now run lift start without any upslope etc.
i found to be a pain in the butt. i have a manual torch with lift start machine (muilti process) and it was a nitemare to use.
bought an ac/dc machine with hf and its a whole lot easier.

imho go get an HF start tig with good features like foot pedal, variable frequency etc. its just so much easier to learn with.
i find thin stainless the hardest for me to do. so get plenty of practice in before doing the project.
tweak it until it breaks
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geewhizz
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    Tue Oct 02, 2018 1:47 pm

Thank you all for your replies. I've been busy educating myself on the various functions of HF, scratch, lift, pulse, slope etc. I've also tried to get details from the manufactured of my machine regarding its poetic ;) 'lift' function. Still waiting on a response but as noted, it doesn't have any external controls for setting slope. Was wondering if this is something to do with the circuity that supposedly reduces power when sticking an electrode arc welding. From their website - " An equally important feature is the anti-stick function. It prevents the electrode from burning out due to accidental sticking. In this event the practical function automatically reduces the welding current" - Anyway I believe Rehm are a good manufacturer so hopefully they can clarify.

The cost of a machine that includes torch and pedal function from R-Tech in the UK (again seems reputable) isn't out the question. That would start about 400-500 GBP Unfortunately adding AC probably takes this out of my budget, certainly from R-tech anyways. Looking at the first two here... seems like the the extra £100 gets you - lower amp range (5 instead of 10), pulse width and frequency controls and pre gas flow. Also the slope up, slope down and post gas flow capability is extended (25 secs instead of 10secs)
https://www.r-techwelding.co.uk/welding ... ig-welder/

I guess the key thing I'd want to avoid is buying all the conversion components to find out I'd need to buy a new machine (as they seem to come with all the kit - foot pedal excluded but I'd probably have a go at making my own)

Again I'd welcome any thoughts from people in the know.


Many thanks,
Gee
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User avatar
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Serviceable welds can be made with scratch start but it takes lots of practice. In order to reduce crater cracking at the end of the bead, you need to increase the travel speed so that the pool tapers down to nothing then snap out. You need to get the gas flow back over the hot metal quickly. It won't be perfect, but you can get there.
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cj737
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    Thu Sep 29, 2016 8:59 am

All those features are nice for an experienced welder to do specific, code-restricted work. In your case, if you only used a Lift Arc capable welder, then Slope would be a great help, and a torch switch with amp control could satisfy. AC is up to you. You don't need it for carbon or stainless welding. Preflow is nice, but with a torch switch or gas pedal, you can accomplish the same thing.

Referring to your recital of "electrode anti-stick", that's referred to as DIG on Stick welding. It does change the current under certain conditions, but it is not applicable or usable for TIG.

One trick you can use with Lift Arc and thin stainless is to have a scrap piece of thicker stainless laying on the work, light up on the scrap, then quickly whip over to your weld area. This eliminates any arc starts on the thin pieces. As for coming to the end of the weld puddle, to avoid craters, leave the filler in the puddle and kill the arc. Then simply wiggle the filer and snap it off. You can grind that flat for appearance.

I guess the moral of the story is: where's theres a requirement, there's a way. Lots can be done with little since Welders have been welding for decades with machines of your range and getting their work done. Its up to you to develop the skills and techniques to get there. Or buy a machine with the features to overcome your skill curve. ;)
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Jody did some on this subject for scratch TIG and some hints and tips:

https://www.youtube.com/watch?v=-KS4TcXps5o

https://www.youtube.com/watch?v=28NRNYACv9I

And with the 'blade' foot switch in the welder cable to cut the arc on demand:

https://www.youtube.com/watch?v=CA3w9Wq5mh0

Bye, Arno.
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geewhizz
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    Tue Oct 02, 2018 1:47 pm

Thanks again for the advice, and also the links to welding videos, they're actually super helpful. After weighing up the advice and tips here, I recon I'll make do with my current welder and see how it goes. I like a challenge. Will try post some pics

Thanks again all !

G
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