Chain welding

that's funny (was thinking about this last night). that's something i've always wondered about welded seam pipe. how come the electricity doesn't flow around the back instead of through the joint. i mean, obviously it works, but it would seem to me the juice would flow through the metal instead of through the weld.

As you increase the frequency the current is less willing to take the long path do to inductance.

Yes it's resistance welded. They did a segment on (I think) "How it's made" on chain. Interesting sequence of events!

You'd think that, but you'd be wrong.

I have an old DoAll saw equipped with a blade welder. If you try to weld pieces that do not complete a loop, it won't weld them. Sort of defies everything you think you know about electricity, doesn't it?

Harold

It is and why it works was explained by others. Saw a film where they made chains and it was *really* impressive. Not that kind of neglace chains, but

*real* chains. For ships anchors. It's a hard work to connect the links (it was some kind of carussell (SP?). The links were about 500mm long, diameter something like 100mm or more. Big presses and the welding machine ... I don't want to pay their electricity-bill! :-)

Nick

I also have a DoAll blade welder and often weld two short pieces of scrap blade together to dial in the settings. It is odd that your welder requires a full loop. These welders can be finicky. Mine once was making making great welds, and the next minute it wouldn't weld anything. After a lot of investigation I found that the moveable jaw was sticking.

I find it intriguing that this topic came up. I've been trying to figure out how to make welded links for things like chainmail, safety-mail (like the microlink gloves that prevent you from cutting yourself while filleting fish) and even necklaces.

I just found the following site that talks about Resistance welding...

The Wiki says that currents from 100 to 100K amps are used...

Hmmmm.... I wonder how hard it would be to design a Homebuilt power supply for a Resistance welding rig? Jaeger Seattle, WA "Dead wizards are not known to sleep soundly, nor to wake jovial"

On Wed, 02 Jan 2008 04:31:13 GMT, with neither quill nor qualm, "BillM" quickly quoth:

I couldn't find that so I kept looking until this popped up:

Larry, that was a great page to look at, thanks. (and probably not a great place to work at)

i

Jaeger

I wonder if it's because mine is very old---it was built in '43----perhaps with lower technology. I struggled like hell to make a good blade from two short pieces of new stock. Finally resorted to clamping the loose ends together and got instant success. Being a retired toolmaker, I completely rebuilt the clamping assembly on my welder. It looks as good as a new one---works perfectly aside from not welding pieces.

Harold

resistance

In the Black Country, traditionally by hammer welding, and often by women. Fred Dibnah covered it in one of his programs when he went round Britain showing lapsed technology after he was diagnosed with terminal cancer. ~Even huge anchor chains were hammer welded.

AWEM

I've seen lengths of anchor chain attached to wire rope for use to snag the arresting hook of an aircraft equipped to use it. Damn impressive chunks of steel. Dragging the chain down a runway after hitting the wire sure slows down an aircraft quick. Must be fun work in summer hauling the chains back and resetting the wire.

Wes

It isn't an all-or-nothing situation. Some current will go 'round the back way, but if the electrodes are close to the joint and the faces makes good contact, then most of the current will go thru the joint.

[ ... ]

I think that in *that* situation -- the welder is depending on the current through the back loop to trigger the solenoid which brings the ends of the blade into firm contact to make the weld. I've never bothered to actually trace out the circuitry for the stand-alone blade welder which I have, however.

Enjoy, DoN.

My unit is pretty primitive. The motion that brings the blade ends together is manual, a lever that is depressed. I'm mystified by this thing, DoN.

Harold

I have a pretty primitive blade welder too, but it welds hacksaw blades just fine. Doubt we'll ever get to the bottom of Harold's, glad his blade welder works!

Grant

My theory is that the current is to high without the loop. I know on my blade welder I can't weld to short a loop of large blade (say 24" of 3/4" blade). The loop definitely takes some of the power out of the weld but most of it still takes the shorter path.

Ah. This makes some sense. Until I learned to only set mine about halfway up the scale, it too used too much current and the welds didn't work worth beans. Generally they'd blow out pinholes and more generally they would break.

Grant