Is there any advantage between scratch and lift type tig welders?, eg welding aluminium?
Answers:
OK so you want to know what the difference is between Scratch Type and Lift type tig welders?
Scratch type - are called scratch type as you must make the electrical circuit to enable the arc to start. The welder can only supply a running voltage to the tungsten electrode in the hand piece so once you scratch it, it starts. BUT there is a draw back to this - when preforming scratch starts when the arc starts there is a small amount of pollution that occurs as the surface of the material you are welding is vaporised, it's very small amount but it shortens the life of the electrode and in some cases when welding exotic alloys like Titanium and Inconel can cause dirt or debris inclusion in the start of the weld, as you can image these materials are used in areas where strenght is a requirement no one wants a dirty weld, it wouldn't pass inspection which would lead to part failure.
Lift Type: - A lift type TIG welder has a secondary circuit that supplies a very high frequency voltage to the tungsten electrode, you are able to hold the tip of the electrode about 2 mm away and upon depressing the foot switch the 'High Frequency Circuit' activates causing a small arc to jump from the tungsten electrode to the work (dependendant on polarity and workpiece material) this arc is only a few micro seconds in length and is controlled by the HF Circuit once trigged the welder then supplies the main welding voltage as a piggy back onto the HF circuit allowing you to weld at you preset amperage. The advantage? No contamination of the work piece or the elctrode, HF circuits can me used to do fancy things in TIG welders such as 'Crater Fill' where the main welding amperage is reduced then spiked to allow the filling of small holes or undercuts in welds.
The only draw back is really in price, getting a decent welder with an HF circuit usually means a lot of money but you get some other useful features such as water cooled nozzles for working all day!
Hope it helps, happy welding.
Tungsten Inert Gas (TIG) is about as pure a weld as you can lay. As far as aluminum, that is a nasty metal to try and weld unless it is sparkling clean and lying flat. I prefer MIG for aluminum because it's just faster and does about as well as can be expected unless you are into some really exotic alloys.
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