Learned about an HF welder today

I learned something interesting today, that is probably common knowledge to most welders. I have a friend that welds, mostly on marine equipment. He came to me wanting a switch installed on his tig torch to help him tig some anodized aluminum. He has an HF251-D1 high frequncy unit and a Trailblazer

Now, in order to figure this thing out I wanted to see it operate, So the welder went on to show me and it would not work. He could not get any high frequency arc. He said it worked fine last night, Ok, "so what did you change"? He had added about 70 feet of cable, OK, so let's take that cable out. So now the HF works fine, It turns out the cable was wound up making an inductor that would not allow the HF to operate properly. Once the cable was straighted out it worked fine. So.. the HF unit uses a spark gap to create HF and you can't coil the wire and use an HF unit. I thought it was interesting. Mikek

Years ago when I was working on the MinuterMan 2 missile sites we had a dozen or more big diesel 400+ amp welders up on the ridge of the 'Launch Control Center' hole. There was mucho feet of very heavy cable (over 100') coming down to the 'eggshells' that were the inside forms for the launch control capsules. The excess cable was coiled up at the welders in about 4' diameter circles. When a welder struck an arc (1/8" 7018) those coils would jump from the magnetic force generated.

I have seen that many times offshore. I also saw a rather knowledgeable weldor wrap the cables around the workpiece, which was quite large to combat a problem with arc blow that he was having. They do really jump quite a bit, don't they?

Steve

Cable on the input or output? If on the input you could probably slap a suitable capacitor across it (at the welder) and get it to work.

Best regards, Spehro Pefhany

And the FCC is going nuts wit all of the gruesome RFI complaints. Spark gap transmitters are almost 100 percent illegal now. "Almost"? if that was the only to transmit an SOS in a life-and death situation, then it is "just" barely acceptable (but do not do that again).

I think that it happens when only one cable out of the pair is wound. If they form a pair, they would cancel each other out, I think.

Bullshit!

Hobbyists operate tesla coils and it is legal as long as you don't get too many neighbours complaining. They also operate in museums and at shows. Also some medical electrosurgery units that are still in use today use a spark gap.

I once saw a dc welder(bullet shaped vertical thing with motor and generator vertically) the leads were wrapped round the whole thing and someone started welding, the whole thing blew up and made a hole in the roof of the shed,

While carbon-arcing the leads can really dance around. Running 1200 amps DC to a pigtailed carbon gun (600 A per lead) not only produces quite a light-show but is also an interesting lesson in electromagnetism. The leads can jump up to two feet horizontally, about eight inches vertically, depending on the tension of course.

I've often wondered- what would happen to someone working right next to a coil of lead used in an operation like that if they had a pace-maker or insulin pump? How well shielded are those things?

There must be a way to measure that electromagnetic moment. Results would be interesting.

Of course, the results would probably be in Gauss or some such, which is beyond me.

The instriuctions on those things say to stay away from welding leads.

We had a RF spot welder that had 2" bare !!! - braided and soft wire.

We bolted them down using hose clamps. We had a prof that removed one from the bolt and it thrashed all over the region it could.

The 600A in one lead goes to the work and then back into the other lead. SO 600A is max. don't double or add link currents.

Field would be in Kilo-Gauss likely.

Mart> >> While carbon-arcing the leads can really dance around. Running 1200

I'm not familiar with carbon guns -- but if you've got a total of two leads to it, you've got 1200 on each of them. If I'm misunderstanding (and I've already said I'm not familiar with those guns), and there are two power and two ground leads, then I apologize.

And in any case, 600A or 1200A? What on earth do you use that sort of current for?

At the local welding shop, they have a stick electrode on the counter. It's about 2' long, and the metal is at least 3/4" diameter. The counter man said it took 1200A to run it. I told him I wouldn't want to be anywhere near that operation.

Pete Keillor

Most of our older grid-banks will top out at 345 amps per unit, there being six units per bank. All share a common ground. Hook two pairs of units together with pigtails, (giving you four units outputting to two leads). Or use two big "single-man" power sources rated at 650 amps each. plug in your pig-tailed carbon gun to the other ends, add 90 PSI air, a 3/4 or 1 inch stick of carbon, and you can remove lots of metal in a big hurry. Lightning bolts and loud noises, ensue.

Used for backgouging thick materials (2+ inch HY-80 is one such) for full penetration welds.

I've used pigtailed carbon guns in training, but only twice on real jobs. Usually I CAC at around 350 to 650 A with a single lead carbon gun, typically using 5/16 or 3/8 inch carbon.

Very common practice in naval shipyards.

You have to have pretty strong wrists for that sort of stuff, right?

Pardon my ignorance. My experience extends to hobby MIGing and some autobody, and some bare dregs of OA. Correct me if I'm wrong, but I'm going to infer that 'backgouging ' for full penetration welding means that you're blasting away the back side of the weld. Removing both the parent metal and the filler at the root of the weld in order to fill in and create overlapping penetration from both sides. Now obviously its easier to use one machine on site. So if you're stick welding, its presumably easier to use a carbon rod, but I'm curious if this is too industrial for most Plasma cutters? Do they work in a gouging application, or are they only suited for blasting _through_ plate (and not at an angle to the work).

Just a curious novice. _Mark

Try this:

Hah! Definitely biased towards plasma. Expensive equipment required, multiple consumables needed for the torch, and often a limited reach from the machine.

It wouldn't surprise me if CAC is indeed less expensive in the long run.

Only real expense is the carbons themselves.

The higher the amperage and greater the airflow, the less chance of carbon inclusion. As with all welding and cutting operations, practice makes perfect. I and many others have turned out weld-ready backgouges with practically no grinding required.