Magnetic Ground Clamp

dragoneggs · May 11, 2017

bdog said:
Yes. It some instances the magnet was great but in others it was constantly falling off anytime I accidentally brushed against the ground lead. I also fried a magnetic one but that was a rare deal. I welded for about three hours straight at high amperage on some 7/8" plate and the mag clamp got so hot it quit working. The knob on the top would not turn anymore and it wouldn't stick anymore. Mine were the tweco 200 amp units and I was welding at 150 amps when it failed. Don't get me wrong I am not bashing them they are great for some things and maybe having a quick connect to swap between a magnet and a clamp would be good. For all my welders I use the tweco GC-300. They have not let me down yet.

I get it... actually makes sense now that I think about it. Depending on the type of steel the magnetism can very greatly. Stainless is a prime example. I wasn't thinking other than the mild steel I play with.

aczlan · May 13, 2017

bdog said:
I also fried a magnetic one but that was a rare deal. I welded for about three hours straight at high amperage on some 7/8" plate and the mag clamp got so hot it quit working. The knob on the top would not turn anymore and it wouldn't stick anymore. Mine were the tweco 200 amp units and I was welding at 150 amps when it failed. Don't get me wrong I am not bashing them they are great for some things and maybe having a quick connect to swap between a magnet and a clamp would be good. For all my welders I use the tweco GC-300. They have not let me down yet.

Interesting. IIRC, some magnets can be de-magnetised by heat, perhaps that is what happened to you?

Aaron Z

BukitCase · May 13, 2017

AFAIK, ALL magnets can lose their magnetism if the temperature gets too high; that point is called the Curie temperature, and varies depending on the material. At least SOME, if not all, magnetic materials will, when heated and cooled, take on the magnetic properties of their environment when cooled back down. (If they didn't actually MELT in the process

) if they cool while NOT in proximity to another magnetic field, they will lose most (if not ALL) their magnetic properties.

Decades ago I was involved in a complicated experiment aimed at high speed duplicating of video tapes - we started with a standard ferric oxide recorded tape, ran it thru a transport that heated a Chromium Dioxide coated BLANK tape to a temp that was ABOVE it's Curie point, then pressed the two tapes together for a long enough distance that the CRO2 tape cooled BELOW its Curie point - at that time we had a mirror image of the recording, which would NOT work in a playback machine. Next, we used that CRO2 "backward copy" as a master and REPEATED the process, heating ONLY the "copy" so the CRO2 "master" didn't lose its information....

Ultimately the project failed, but NOT because the theory wasn't sound - at that time, CRO2 oxides were in their infancy, and VERY abrasive so those tapes would make short work of video heads. The owners ended up with a VERY expensive "boat anchor" - can you say "tax write-off ??!?

Anyway, because of this "curie point" if I end up going with a mag ground, it will be rated for about DOUBLE the amps I would ever use it for... Steve