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Do You Back Purge Your Tig Welds?

Posted by David Taylor on

Why is back purging so necessary you may ask?    

Read on & all your questions will be answered.

We've all heard of it, but what is back purging?

 You should all know by now that you purge your welds while welding with an inert gas ( Generally Argon for tig welding ) that is supplied through your tig torch and then floods your weld via a cup, this, however, is only shielding the front side of your weld what about the backside?

Back purging is the act of removing all undesirable gasses and vapours from the backside of your welding surface by replacing the atmosphere with Argon, leaving your weld contaminant-free making it clean, smooth & looking like the front side of the weld.

Back purging is used most when welding tube, tanks, cylinders and numerous other hollow objects. All though important for all metals it is most detrimental if you are not back purging when working with Stainless Steel, Duplex steels, Nickle, Titanium and Zirconium.

You may still be thinking in your head is this all necessary?

The answer is YES

It may just sound like this is a lot of extra work for no reason, but if you are already welding without back purging, you're doing half the job.

Take a look at the image below you can see where the weld has started to penetrate and react with the atmosphere leaving a rough burnt sugar-like build up on the inside of your weld. 

Bend Brothers non-back purged welds showing contaminated build up

The contamination is nasty in several ways, the first being when molten metal, i.e. your weld is coming in contact with vapours and gases from the atmosphere. This causes a reaction with the molten metal forming undesirable compounds within it which can then affect the corrosion resistance and be instrumental in creating cracks and other structural defects.

Secondly, if the job you are working on happens to have something flowing through it, imagine how much all the crappy build up on the inside will affect flow. The build-up causes massive amounts of turbulence something you do not want in any application, let alone in a performance-related part.

Back purging can be done quite basically and cost affectively even when using a single shielding gas bottle.

You would generally need a dual regulator and two separate gas lines from your Argon bottle.

One with a higher flow rate for your tig torch ( around 7-15 l/min tig welding cup and material depending) and one at a much lower flow rate for back purging ( say 5-7 l/min ) you would then need to plug or seal ether end of your job. One with your gas line entering and one with a vent; this can be achieved by either making or buying plugs.

You could even use aluminium foil to plug the ends; this isn't the better option but still entirely functional for those on a budget.

 Bend Brothers basic aluminium foil back purging

 

If you have any questions or feedback, I would love to see it in the comments.

But now I feel we should touch on the subject of tig welding Titanium.

Titanium holds a certain aura around it of being a difficult material to work with, It does not need to be like this as with the proper prep work, exceptional cleanliness, and required back purging it can be easier to work with then Aluminium (The main reason is you do not need an AC/DC Welder)

The hardest part of this is keeping it clean as even the slightest touch with an ungloved hand will leave oils. Another build upon the material this is.

However, something we here at Bend Brothers have made easy for you guys as all our products (except for our straight tube) come pre-cleaned & ready to weld straight from the packaging.

If you're planning on using Titanium here's a handy list of do's & don'ts.  

 

  • Wear Gloves when handling Titanium material especially while unpacking any Bend Brothers products 

  • Use a chemical cleaner like Acetone to clean down your job after test fitting or handling.

  • Wipe down your filler wire with a chemical cleaner before every use 

  • Make sure you have more then adequate shielding gas coverage with a large flooding cup like our TigWare Drop Proof flooding cup or any of the brilliant Mfurick cup range you could even consider a trailing gas shield similar to the one below if required. 

Tig Weld Trailing Gas Shield

  • Make sure you have a properly functioning back purge setup. 

  • Most of all pay attention to your weld colour pretty colours do not equal a correctly welded titanium joint see the handy weld colour chart Here.

 

 

 

If you have found any of this information useful or have enjoyed reading, please let us know as we appreciate your feedback!

Stay posted for more weld related blogs. 

 

 


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