TIG steel with AC?

[evfreek]

Hi. I just bought a welder on craigslist for a very reasonable price. It was not advertised as a TIG welder, but it came with an HF box, a TIG torch, thoriated 1/16" tungstens, and a reg/flowmeter. Unfortunately, it only produces AC.

Can this machine be used to weld steel? I looked at the Miller guidelines, and it said that 1/16" thoriated 2% can be used from 60-120 amps on AC, nearly as much as for DCEN. I tried putting down some beads on sheet metal with some filler rod. Looked like decent fusion/penetration, even though I was welding in the wrong direction (away from filler). Now that I read the Miller site, it is clear that a push technique has to be used.

The beads had some start-stop craters (no foot pedal and I had a hard time feeding the filler with a gloved hand). Made a funny noise. But it doesn't seem to say much of anywhere on the web that AC can be used on steel. Is there anything obviously wrong with this? :confused:

[HWooldridge]

DC allows more heat so is usually employed on steel, titanium, copper, etc. AC is used on oxide producing metals like aluminum because of the scrubbing action. So, AC is not the best choice but can be used on steel in a pinch. When I first bought my rig, I tried DCEP, DCEN and AC on steel (just for fun) and there are differences.

The funny noise is probably the high frequency.

[Timekiller]

Just a tip about filler metal and gloves...

I was using a tight fitting leather glove to move filler, which worked great, but it was then brought to my attention the safety issue with the gloves. If they caught fire, I would be in big trouble, and after recently seeing my friend get 3rd

[Glenn]

Timekiller
Go to the top of the Forum page and click on User CP
Click on Edit Profile
Go to the bottom of the page and enter your location.
Save.

It will add your location to your posts.

[welder19]

Glenn, can't you just make location a required fill box?

welder19

[eburgblue]

??????? Glenn..... your profile is not showing location..........??????? other than IforgeIron..... I don't get it......??????

[Glenn]

That is where I seem to spend most of my time

The location of IForgeIron is at the bottom of most of the site pages.

[Hillbillysmith]

You can use AC on steel, but DC+ is preferred. Stick and TIG machines use constant current and yo can use an AC stick welder, right?? The only difference with stick is the flux on the filler rods, but with TIG, there are no fluxes. If you're worried about penetration, weld up a joint, I'd do a lap joint, let it cool, and break it. Don't make the weld too big and only weld one side but after breaking it, look at the to plate and If there is a jagged line, which shows where you tied in at the root, then you pass the test. If there is a distinct straight line, where the weld didn't fuse properly to the root, you fail. Just practice until you pass. Do it again with a different joint, different position. If you have any Q's about the testing, just ask. If I don't know, I'll ask my instructor. He's a certified welding inspector in several area's.

But here's my best advise: GET A FOOT PEDAL!!! Or at least a rig with a finger rheostat so you can regulate the amperage.

[Dr Dean]

How about a picture of your new welder. If I had to guess it's probably a stick welder with a HF box added on. If that's the case most likley there won't be any way to add a foot pedal or fingertip control.

[evfreek]

Hi fellas. Thanks for the great advice. HWooldridge, I am glad that I can run on AC until I get a DC welder. I tried welding DCEP in welding class once, and the heat really builds up on the tungsten and balls it up pretty quickly. Also, the charts show that max amperage is pretty low for this reason. AC is confusing, though. I ran a couple of beads, and rounded my tungsten pretty good, but I must have accidentally touched it without realizing it.

Timekiller, thanks for the tip about Tillman gloves. The kind of glove seems to make a big difference in feeding the filler. I will go to the local welding store to pick up a pair. Don't need much of an excuse to go, since it is owned by a blacksmith and the boys there are great.

Hillbillysmith and Dr Dean, you are probably correct about the foot pedal. This welder is a cobbled together stick welder, and does not have a foot pedal. The only thing TIG about it is the torch and flowmeter, as well as the HF box. A foot pedal is not difficult. I have all the parts for one; just need to put it together. They work a lot like those cheap router speed controls, with a special hysterisys and balance circuit for the inductive load. I have a better torch (Weldcraft wp17) but it has no accessories, so it is idle.

The beads I made look good, if a bit wobbly. I even burned through once. The interesting thing is that if you burn through, it is much easier to fill the hole than it is with stick. Filling a hole in sheet metal with 6013 almost guarantees me a slag inclusion. When I set the current a little low, the bead rode too high, just like stick.

This is fun. I was a little leery about the per foot argon cost, but it is worth the ride. I'm on my second tank now .

[evfreek]

Hi. I just connected a DC welder to my HF box and TIG torch to see the difference. There is not much difference in the quality of the weld. It is more important, it appears, to select correct amperage. The arc is much quieter and smoother. It is also more focussed and predictable. I used DCEN (the standard polarity for TIG). Now I understand why the people in the welding class complained about the sound of AC arcs for welding aluminum.

[Jose Gomez]

High frequency is commonly used with DC tig to initiate the arc without having to touch the electrode to the base metal. This is common with tig welding because the high frequency is capable of jumping across the gap between the tungsten and the base metal, thereby eliminating the need for "Scratch starting" or initiating the arc by striking the electrode across the base metal like a match (which typically contaminates the electrode). with DC positive or negative the arc only has to be initiated once because the current is only flowing in one direction, so no significant diference in weld performance aside from a slightly more stable and focused arc will be noticed.
Where HF is essential is when welding with alternating current. With AC the direction of current flow reverses 60 times per second (60 hertz typicaly) which means that the arc ignites in the positive cycle, then extinguishes itself, and then re-ignites in the negative cycle. all of this happens 60 times a second, which is where HF comes into play. HF continuously bridges the gap between the electrode and the base metal thereby keeping a "pathway" open for the arc to remain lit while the welder is transitioning between the positive and negative cycles. this constant switching of flow direction is where the AC arc gets its signature BUZZZZZZ.

The reason that almost all tig welding in steel and stainless is done with Direct current electrode negative is that 70 percent of the heat generated by the arc is focused on the positive side of the circuit. this is why the electrode remains sharp when used with DC electrode - and it "balls up" or melts when used DC electrode+ or AC. When the electrode balls up the arc is much less focused and tends to wander more.

As for you argon consumption, im not sure what you have your flow rate set at, but you can run as low as 15 to 20 CFH, anything more is a waste.

Kind a long winded explination, but I hope it helps.

[evfreek]

Hi Jose. Thanks for the reply. I do notice the tungsten getting blunter early on AC. for steel. I just read that AC is often used for brazing with silicon bronze. It is probably a heat into the metal control issue. Perhpas the tungsten is getting blunt because of lack of fine motor control. Time will tell as that skill develops. Just need to practice more. Looking at the charts on the Miller web site, the current capacity of thoriated tungsten is only a little less for AC than it is for DCEN. Much less, though for DCEP. I notice that the heating rate is much more directional with DC. The puddle gets much more slow to establish for angles off 90 degrees.