Sticking Tungsten

[mickeric]

Hi Guys ----This is a bit of a challenge ---sorry!!!

I bought a new combined stick and Tig. welder (thought to be a Chinese clone) I had it for one month. Used it twice and it blew up. I also have a 20 year old 90 amp AC “ buzz box “. The outer case had seen better day, but it is impossible to wear the dam thing out.

To cut my losses I decided to insert the “buzz box” working, into the new case. Adding four 150 amp diodes I converted it, to make it DC. I am really pleased how it welds, stick electrode positive. The output voltage (no load) is 68v I do not know that amperage because I only have a 10 amp multimeter.

This left me with a negative gas/ Tig terminal that I can attach the Tig touch to.

The downside of my conversion is that I now can’t control the amperage. The other problem is that when I try to scratch start, the tungsten just stick to the work piece and I can’t get an arch started. Ufff!!!!!

My questions are ----- does anyone know of a SIMPLE circuit design, to control the amperage, and why does the tungsten stick to the work piece.

 

[ChrisJohnsSculpture]

The tungsten sticks because it basically welds itself to the work. Most dedicated TIG machines have some sort of starting circuitry either 'lift start' where the electronics detect the short circuit when you touch the tungsten down and then automatically increase the current as you lift the tungsten off the surface. More sophisticated is HF start which produces a high frequency current which is able to start an arc with an air gap between the tungsten and the work. If you forget to attach the earth clamp you can see the little lightening bolts between the tungsten and the work without the main arc.

On solution to the starting problem is to use a chunk of graphite (an old motor brush is ideal) to start the arc and then transfer it across to the work without breaking the arc. This should stop the tungsten from sticking and reduce the risk of the tip breaking off.

 

[Robotstar5]

Most dedicated TIG machines have some sort of starting circuitry either 'lift start' where the electronics detect the short circuit when you touch the tungsten down and then automatically increase the current as you lift the tungsten off the surface. More sophisticated is HF start which produces a high frequency current which is able to start an arc with an air gap between the tungsten and the work.

You forgot "scratch start" but all types need some form of "electronikery" to work

I think the off work starting piece is called a shoe?

 

[hotrodder]

Electricity is witchcraft but scratch starting i can cope with although it's not the easiest technique to explain... first hit from googling 'scratch start tig' is this which isn't the greatest view but enough to get an idea, http://www.youtube.com/watch?v=XH9LMN4Tsyw Basically the cup was rested on the work and the torch 'tipped' up so that the tungsten barely touched down. As this happens you lift the torch to establish your arc length and off you go. Takes some practice and getting it wrong will dink the tungsten and leave 'tungsten inclusions' in the weld. That's where the starting block/shoe comes in.

Another way that won't guarentee you don't dink the tungsten/make a mess but at least means that if/when it happens you don't leave tungsten inclusions (not a big deal if welding furniture/a car exhaust etc) is to use the filler wire. Even harder to describe but basically you 'bridge' the gap by sliding the wire between the work and the tungsten to initiate the arc. It needs a deft touch and more practice than the first method

That vid also showed snapping the torch away briefly to break the arc. Doing so typically leaves a crater/pin hole which isn't a big deal at a stop/start but can be on the final stop/tie in. Sometimes 'run off' tabs can be used which is just a piece of metal tacked/clamped at the end of the run so you're not stopping on the work itself. Run on tabs can also be used, obviously neither are convenient to use all the time. Another way, say for a butt weld on tube, is to speed up as you make the tie in i.e. as you move faster the weldpool cools and then freezes. You can then snap the torch away without leaving a pinhole

 

[mickeric]

Thanks guy's I appreciate your efforts.

Mick