High freq issues

[motorcyclemac]

Greetings All,

I have a question about the high frequency from square wave tig welding. I know that there is always caution advised about HF affecting computers and such. I know that Miller and likely every other welder supplier suggesting that your table be grounded well to squelch HF from leaking into the surrounding area. My question is this: After doing a bunch of reworking in my shop to allow for my ammo reloading bench I wonder about using the TIG in the same building. The two processes reloading and welding are on the opposite ends of the shop but I wonder about the exposure of HF to primers and powder. Can HF cause vibration and or static discharge issues? Static around powder and primers wouldn't be good. Would you think that HF in the same building as loaded ammo should be cause for concern? There is quite a distance between where I weld vs where I reload...but Miller suggests that HF radiates up to 50 feet. I thought I would ask before I tried to see what happened. The powder and primers are stored in separate military 20mm ammo cans. Would that metal ammo can provide any shielding from HF discharge?

Cheers
Bill

[japcas]

[QUOTE=motorcyclemac]The powder and primers are stored in separate military 20mm ammo cans. Would that metal ammo can provide any shielding from HF discharge?

I don't know much about the high frequency but I'm pretty sure reloading powder shouldn't be stored in an ammo can like you are doing. Same for primers.

Ignited stored powder can raise pressure within the storage area, thus there are specific requirements for keeping powder on hand. The first of these is never to transfer any propellant from its original container, which is designed to burst or partially open at a very low pressure. Some containers will simply have their cap pushed off if the contents are ignited. This will then allow for all the gasses to be vented from the container. (keeping powder in the original container is also essential for the proper identification of the propellant). This information comes from reloadbench.com under powder storage.

I know this doesn't answer your question but I thought you should be aware of this. Even if the powder is still stored in it's original container inside the ammo can it shouldn't be stored this way.

[motorcyclemac]

japcas says: I don't know much about the high frequency but I'm pretty sure reloading powder shouldn't be stored in an ammo can like you are doing. Same for primers.


Thanks for the info. I was aware of the storage issue there. The ammo cans have had the latching devices removed so that the lids simply are held shut by gravity. In the event of combustion the lids would lift eliminating any pressure build up. I thought of that when I decided to store powder in that fashion. I put it in there...and looked at it....saying to myself "nice bomb". Shortly there after in a few minutes I had removed the latches allowing the lids to have free movement. I like the metal box only for keeping moisture away from the containers as well as stopping any vermin from potentially chewing the packaging.

Thanks
Bill

[J Tiers]

I would think that the liklihood of problems is low.

That said, I am mindful of the original radio reception, which was in the form of a spark gap reciever, resonant at the sending frequency. So there is a chance that just the right combination of shapes and distances could develop a substantial voltage from a welder, even at a distance.

If you have the powder in metal containers, and/or within a metal box, even a screen enclosure, that should block RF from getting at it.

Then if you don't weld when you re-load, all should be well if you clean up spills.

[Leigh]

Yeah... what JT said :D

Welding will not generate static electricity, not will any other active use of electricity. Static is generated on an insulator when the electrons have nowhere to go. If you have metal containers they will dissipate static and prevent it from building up.

As far as the distance RF can travel, it travels all the way around the world, and from the sun to the earth, so 50 feet is of no significance. However, the chance of intercepting any significant amount of that energy and converting it into a spark is between slim and none. The geometry of the components is completely wrong.

But, since I'm always one to err on the side of safety, it wouldn't hurt to put the volatile material inside a shielded storage area. The shielding can be as simple as chicken wire stapled onto some 2x4s, as long as it encircles the stored material. I envision stapling it to the walls, then making a small door from a 2x4 frame and a single diagonal for support to finish off the "storeroom". Then connect a wire from the chicken wire to the cold water pipes in the house to complete a good ground connection.

[Evan]

Store the powder in an old microwave. Make sure it isn't plugged in. :eek:

That will positively guarantee that it is inside an effective faraday cage that will completely shield it from any RF.
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[JRouche]

That will positively guarantee that it is inside an effective faraday cage that will completely shield it from any RF.
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Well, as long as the wave length is close :D Otherwise its just sitting in another can...

I think the primers are ok with the welder freq. and power. While in the military we had numerous transmitters putting out varying frequencies and power levels. We also had a wide range of ammunition, everywhere :D

We never had a round discharge from electromagnetic energy. We also never put a round directly in front of the 1MW continuous wave transmitter either, I think that would have cooked one off. JRouche

[Evan]

Well, as long as the wave length is close :D Otherwise its just sitting in another can...

Nope. If it will shield 2.4 ghz then it will shield anything below that and frequencies above it until you go above half the wavelength at 2.4 ghz.

[J Tiers]

Luckily, the energy input to touch off most forms of powder is higher than the requirement for carbureted vapors, etc.

So no radios around liquid fueling stations is good precaution (aside from coal loading, where it doesn't matter much).

I have actually never tried to set off any type of powder with a spark. I can assure you that there IS a spark that will light it, but exactly where that starts is unknown to me. Most electrical firing is direct heat via a heating wire, uses some less stable material like fulminate, etc, etc etc.

And most cased rounds should be pretty immune even to fairly distant RF heating, as brass etc is a decent conductor and would not heat much without heavy currents.

If you stick it directly in an induction coil you could obviously cook off the primer or the propellant with sufficient heat.

[motorcyclemac]

I was pretty sure that it would be ok. That said I still had a shadow of concern and not being geek enough in that area I though I would ask first.

Cheers
Bill