<VV> Re: Puge Gas and Carbon Steel Tig Weldiing Advice

[Garth Stapon]

Craig:

Good idea on purging the aluminum tube.  This is a common practice on stainless and aluminum tubing, but is not typically required when welding carbon steel. ( I recommend a purge gas be used with chrome moly tube)

The gas flow requirement for purging is not that great - say 5 cfh max.  - so if you have a lot to do, it might be worth it to look at a separate argon flow meter, otherwise you can put a Y connector in the gas line, tape the end of the tube & purge for 2.5 times the internal volume of the tube.(If you calculate that the internal volume of the tube is 1 cubic foot, you would introduce a very slow purge - 5 cubic foot /hour gas flow for approximately 30 minutes prior to welding). If you are in a rush, you can purge for less time at a higher flow, but maximum quality will be achieved with a longer low flow purge cycle.  (I saved one client $ 800 K a year in part rejects with a change in their purge cycle time). When possible, keep the purge gas on during welding.

Pure argon is the preferred purge gas on aluminum and carbon steel.  On 300 series stainless (non magnetic) use argon / 2% - Hydrogen is best for 300 series stainless tube.  When it comes to successful purging, patience is a virtue. Lower gas flows and longer purge times are more effective.

For Tig welding steel, use DCSP (Direct current Straight Polarity - electrode negative), high frequency on start. Use 2% - 3/32 diameter thoriated tungsten.  Sharpen the tungsten to a 60 degree point with a dedicated grinding wheel as you can introduce contaminants from materials that have been previously ground on the wheel.   Hold the tungsten toward the ground when sharpening on the wheel as it is brittle and can break driving pieces into your hand.  Do not over heat the tungsten during grinding.  Be patient and cool it in water several times until you get a good 60 degree angle.

You metion that you have a foot pedal.  This is good.  For other members, if you do not have one, invest in one.  

Set your argon shielding gas flow at 20 cfh.  Set the panel control at 100 amps as you should not need more than this current level for most applications.  This will also give you more precise control with the foot pedal.  Sit on a stool and work on a bench when welding if possible. If this is not possible, put something next to the work so that you can rest your wrist on in order to maintain a consistent torch to work distance (a block of wood is good).  For bench work, I like to have my elbow on the table when possible. This helps to prevent dipping the tungsten into the molten weld pool. If you touch the molten pool with the tungsten, stop and regrind the tungsten. Use the high frequency circuit to start the welding cycle.  It is not necessary to touch the work piece with the tungsten when high frequency is available. Be patient with the current control and ramp up the current slowly.  The weld pool should be as small as possible to prevent atmospheric contamination. If the weld pool gets too large, reduce operating current. Match the filler metal to the base metal you are working with and make sure that every things is a clean as possible (grinding down to clean base metal is a good thing).  Attach the ground clamp directly to the work piece when possible.

Hold the torch as vertical as possible (90 degrees is good) and try to keep the filler metal in the shielded area.  The shield gas is heavier than air so holding it straight up will give better shielding properties.  If this is not possible due to joint configuration, increase gas flow to 25 cfh and maintain the torch to work distance as tight as possible.  If you exceed 1/2 inch, quality will drop exponentially. The process does not work well with torch to work distances that exceed 1 inch.  As a rule of thumb, as torch to work distances increase, it will be necessary to increase shielding gas flow. The tungsten should be as close to the cup as possible.  Tungsten stick out is typically determined by joint configuration, but less stick out is better. (This is always a fine line as having the tungsten stick out more improves visibility.  There are transparent cups that are available which improve visibility. Use a shade 12 lens in the helmet. Buy a high quality fine glove - sheep's skin is good as this will make it easier to manipulate the filler metal.

The toughest part is feeding filler metal into the molten pool as you weld.  This process is also good for straight fusion as well, so if you can get the base metal fit up close, tack multiple times - say every 3 inches and then weld without adding filler. (Not many people realize that this process can be done without adding filler).  If the base metal is contaminated, filler is helpful as it has cleansing agents that helps to improve quality, although when compared with other processes, it's tolerance to base metal contamination can be rated as poor at best.

Hope this helps.

Time to go see my 14 year old son play some hockey in the tournament final.

You can take the boy out of the Canada but hockey is a way of life.....

(Actually, CT is a bit of a hockey hot bed......)

Regards, Garth

LATE POWER GLIDE SEDANS (AND HOCKEY) RULE
----- Original Message ----- 
  From: NicolCS at aol.com 
  To: virtualvairs at corvair.org ; stapon1 at earthlink.net 
  Sent: Sunday, March 06, 2005 1:41 PM
  Subject: Aluminum Tig Weldiing Advice


  Thank You, Garth!  I just want to take a minute to publicly thank you for posting these welding tips.  Most of us poke around a bit with welding and your time and effort is much appreciated.  Where else would we find the straight scoop if it weren't for guys like you taking the time to post?  Re Frank's question about successful TIG welding Al tube.  Would it help to back-gas, given that it's tubing and the backside of any gaps is exposed to air?
  Also, what's the right set-up for using TIG on mild steel (gas, electrode, polarity, HF)?  I see all these Hot-rod and Motorcycle construction shows on TV where they seem to be nonchalantly welding steel with TIG but when I try it, I can't seem to get it to work.  I have a 310 amp, squarewave ESAB with remote pedal and water cooled torch.
  Craig Nicol (TIG, MIG, O/A)