eh...ac balance...?

[georgetheforge]

Hi guys,

i just started down the road of tig.... have done mig and gas for donkeys but never maganaged to get me greasy paws on a tig...untill now...

It's an inverter type, quite basic but apparently good... it's a cea i think... anyways the question is....

having sucessfully tigged 2mm mild steel, mangaging to set it up ok with pre and post slopes etc seemed to do a good job.... however what the hell does the ac balance knob do.....? am i being thick? probably....

 

[shenion]

When welding aluminum, the AC current has more heat in one half cycle (electrode -), on the opposite cycle, there is less heat but it has a cleaning action effectively lifting the aluminum oxide off the surface.

The AC balance allows you to control the duty cycle. A TIG with no balance will have 50% on each polarity. A common setting (and the fixed value for some non-adjustable TIGs) is 60%/40%. That reduces the cleaning cycle putting more heat in the metal and less in the tungsten while still have some cleaniing.

 

[georgetheforge]

ahhhh i guessed it was something to do with ali.... i've got some diamond plate to weld on next week 6 mm thick... any major tips or should i just bash on in there.... with simular setting to the mild steel ones....apart from the ac current and adjusting the balance knob....!!

any tips or is it basically the same apart from the heat absobsion...?

 

[shenion]

Have not used my TIG much. I do use it for aluminum (use MIG and stick more for steel.) I do find you need a lot of current to get going on aluminum then less as you get going.

My old beast has no slope or pulse modes. I found a footpedal necessary on aluminum.

 

[hotrodder]

Aluminium behaves quite differently to steel, stainless etc. The naturally occuring oxide layer melts at around 3 times the temp of Al and while the AC output can deal with a certain amount you'll get better results if it's removed before welding (STAINLESS steel brush, scotchbrite etc), especially if it's old material as the oxide layer thickens with time and is porous- source of dirt/other contaminants which will make life harder and/or result in porous welds

6mm Al... depending on the size of the piece looking at upwards of 180A, preheat will make life a lot easier (at the very least take any 'chill' off)

 

[georgetheforge]

yeah 6mm.... ideally i'd use somthing lighter but thats all we've got in to mess about on...

 

[Seano]

Aluminium behaves quite differently,The naturally occuring oxide layer melts at around 3 times the temp of Al and while the AC output can deal with a certain amount you'll get better results if it's removed before welding (STAINLESS steel brush, scotchbrite etc), especially if it's old material as the oxide layer thickens with time and is porous- source of dirt/other contaminants which will make life harder and/or result in porous welds

For what it is worth something I just learned recently with regard to cleaning off old oxide layers (especially on old Al casting) is to run your tig torch up and down the weld seam a few times using just the arc (so pull the torch way from the job a way's) and after each pass a quick run over with SS brush and it will soon come back to nice shiny material again, also on each hot pass you may see a lot of black cr&p in the form of black spots appearing on the surface, once rid of this you should produce a tidy weld....

Sean.

 

[hotrodder]

Yep, that trick works very well for metallurgically 'dirty' castings although i tend to run a burr over the area to remove the crud and a little more material afterwoods.