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bridgewire, spot welded ?


dave321

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any ideas how this would be manufactured ?

it is the broken bridgewire of a fired item

 

much smaller than a standard fusehead strip

 

lead wires are 0.4mm

 

dave

post-9500-0-73083800-1354913137_thumb.jpg

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yes, i've got a wire wrapping tool on order

 

but the actual item does not seem to be wire wrapped

 

i've a pretty good idea how fusehead strips are manufactured

but a bit of nichrome across 2 small wires at the end, well, i cant visualise how its done

i'm guessing its automated someway, but as i say i cant think how

 

any more knowledgable people out there ?

 

dave

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Dave,

 

Some items are soldered. I know we used to solder thermocouples where the joint is heated up, fluxed, and then dipped in a small melt pot of silver solder. Maybe this is what you're after. I bought a bunch of chips from ODA to make my own e-matches and their method was to solder them as well.

 

Mark

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hm, interesting, looks a bit scrappy though, :P

 

wire wrapping has quite a high success rate on its own

, i guess maybe micro spot welding somehow would do the job of securing the connection

 

somone, somewhere somehow, are knocking these out commercially for an item thats on the market

...........probably the chinese for cheapness

 

dave

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I'd be thinking of a machine cutting off the copper leadwire leaving a formed end to suit retaining the bridge wire by crimping. Consider also that the lead wires will be enamelled and this must be removed at the fixing point but nowhere else
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In the late `90's I worked for a company that designed and built automated machinery to build initiators. The key to my company's success (at the time) was their automated bridgewire welder. They took an hermetcally sealed base as you see in the photos above, ran the length of bridgewire across it and spot-welded it to the base (as seen in the second photo). The machine used very precise adjustments utilizing micrometers for each leg of the welder, but the greatest secret was a drop of alcohol on the head before the weld was activated.

 

Without the alcohol to cool the operation,by evaporation, the bridgewire was burned out almost every time. I suppose that's how the bridgewire is welded to the copper leads in the example above. If you try to duplicate it, don't shunt the lead wires till after the welding operation.

 

WSM B)

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any ideas how this would be manufactured ?

it is the broken bridgewire of a fired item

much smaller than a standard fusehead strip

lead wires are 0.4mm

dave

 

Upon closer inspection of the orignal photograph, I suspect they wrap the bridgewire on the bare ends of the twisted lead wires and soldered the bridgewire onto them.

 

If you try to duplicate these, I suggest you use phosphoric acid as a flux. A miniscule amount of H3PO4 will wet the copper leads and the NiCr bridgewire with solder as you apply heat from the soldering iron. A fair amount of practice may be required to consistently get a good soldering job on these, but it is possible (I've managed it myself, years ago).

 

Good luck.

 

WSM B)

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I'd be thinking of a machine cutting off the copper leadwire leaving a formed end to suit retaining the bridge wire by crimping. Consider also that the lead wires will be enamelled and this must be removed at the fixing point but nowhere else

 

Several European companies seem to use a process where they flatten the copper leads, lay the bridgewire across them, fold and crimp those flattened leads over the bridgewire to seal it in place; all before dipping it into the pyrogen. They usually use a pre-formed insulative foundation to precisely hold the leads fixed in place, before setting the bridgewire.

 

The second sentence is correct, if you're using enameled magnet wire for leads, as the original photo seems to show.

 

There are myriad ways to accomplish the task of building an electric initiator. You should choose the one that works best for you.

 

WSM B)

Edited by WSM
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If you try to duplicate these, I suggest you use phosphoric acid as a flux. A miniscule amount of H3PO4 will wet the copper leads and the NiCr bridgewire with solder as you apply heat from the soldering iron. A fair amount of practice may be required to consistently get a good soldering job on these, but it is possible (I've managed it myself, years ago).

 

Good luck.

 

WSM B)

 

i'll give the phosphoric acid a try.

as i said earlier, wire wrapping alone is quite succesful so with a bit of solder

that should be the bees knees

 

surprisingly a normal fusehead is too large for the application in mind, and even when shortened

it is still a bit on the thick side :o

 

extra solder with wire wrapping sounds promising

 

dave

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i'll give the phosphoric acid a try.

as i said earlier, wire wrapping alone is quite succesful so with a bit of solder

that should be the bees knees

surprisingly a normal fusehead is too large for the application in mind, and even when shortened

it is still a bit on the thick side :o

extra solder with wire wrapping sounds promising

dave

 

Good luck with your research.

 

For specialty purposes, I've made e-matches small enough to replace Visco fuse in small class C items.

 

WSM

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  • 1 year later...

i'll give the phosphoric acid a try.

as i said earlier, wire wrapping alone is quite succesful so with a bit of solder

that should be the bees knees

 

surprisingly a normal fusehead is too large for the application in mind, and even when shortened

it is still a bit on the thick side :o

 

extra solder with wire wrapping sounds promising

 

dave

 

If you need it to fit in a tight place, remember that the idea that makes this work is the tiny resistance wire getting hot - there is no need for the lead wires to be close to the ignition point if the resistance wire is long enough. You could make a long "U" shape out of the resistance wire that is just over twice the width of the resistance wire and insert only that part into wherever you need ignition, leaving the lead wires entirely outside the device/etc. You might need to use a bit of binder near the straight parts of the "U" in order to prevent it from shorting, but that shouldn't be too difficult (tiny drop of wax, super glue, use a sliver of tape to insulate the legs from each other, etc).

Edited by Extrarius
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