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Spark gap electrodes?

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hboy007

Sun Apr 18 2010, 11:03AM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
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Posts: 374

spark eroded tungsten electrodes... anyone concerned about tungsten oxide dust levels during indoor operation or am I just paranoid?
I think machined bolts of structural steel would be fine, or at least some screws and nuts made of low-alloy steel.

Arcstarter

Sun Apr 18 2010, 06:10PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

gatedbreakdown wrote ...

radiotech wrote ...

Also, do you think the spark energy will increase or decrease the torque loading of your rotary gap?

well the gap as Ive designed it, I dont think it will make any significant effects on torque, as long as the electrodes dont colide or something, this might have an impact if I were to use a gap with magnetized electrodes, or ring shaped mangets around the electrodes to provide perhaps magnetic quenching, however I dont see how that will effect the torque of the gap, since not all electrode materials are magnetic.

so I do not really understand what you said radiotech, can you explain further?

also, what year is that image from? finding something like that for 12 dollars seems a bit far fetched now days.
and one killowatt is unforchunatly too low of a rating.

Well, if you where to use a srsg, it takes a very little load to cause it to run out of sync. But you are using DC and a srsg, so it will not be a problem.

radiotech

Sun Apr 18 2010, 07:33PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

The image is from one of Hugo Gernsback's family companies- might be out of date a bit, about 96 years or so.

The discovery of the forces in an arc, (if you can hear it, there are forces), (and sparks seldom change momentum midway, or do they?) would be an usefull outcome, since most of our modern physics came out of spark research.

Coronafix

Mon Apr 19 2010, 01:43AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

I use brass threaded rod and have no problems with fast erosion. It is also cheap and easy to wind in and out.
I run them at about 4kW of power too.

Herr Zapp

Mon Apr 19 2010, 02:22AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

gbd -

For some reason I thought your design was a SRSG, but going back and reading your first post I see that you didn't actually specify what type of RSG this is. If you are using an appropriately sized DC motor to drive the flying electrode, there is probably no issue with having adequate torque to spin everything up to the desired speed. If you are planning to spin this thing up beyond 4k or 5k RPM, make sure that your hub is mechanically robust, well secured to the motor shaft, and accurately machined. When positioning the electrode in the hub, make sure that the final assembly is dynamically balanced, as evey a small imbalance can result in large radial loads at high RPM.

Regards,
Herr Zapp

dmg

Mon Apr 19 2010, 03:08AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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ah, my bad on that one, but yes, you are right, it is an ARSG, and the motor will be turning around 11,000RPM or so.
I will have a bolt on the very top of the shaft, that is screwed in to hold the flying electrode, and there will be either 2 nuts or two fastners for the electrode side to side of the gap.

Herr Zapp

Tue Apr 20 2010, 05:23AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

gbd -

Do you have any mechanical engineering experience, or access to a well-equipped machine shop (lathe, milling machine, etc)?

What material is your "hub" going to made out of, and how will it be attached to the motor shaft?

It's not clear what you mean by "there will be either 2 nuts or two fastners for the electrode side to side of the gap". Can you describe this deswign, or post a sketch?

The forces centrifugal generated at 11,000 RPM will instantly destroy a gap like this unless it is very robustly designed and precisely machined. Obviously, parts flying from a disintegrating rotor at high speed are hazardous to everyone anywhere near the gap.

Regards,
Herr Zapp

dmg

Tue Apr 20 2010, 05:48AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

Herr Zapp,

Unforchunatly, I do not have any experience in mechanical engineering, I am still in grade 10, however I do have access to a lathe shop, but however I will consider trying to find a shop and getting the parts proffesionally done by a CNC machine.

as for the shaft material, I was thinking of using some form of solid rod, high density polyethylene rod comes to mind, please forgive my crudely drawn diagram, but that is the general construction plan, as for securing the shaft to the motor, damn, I haven't really considered the forces involved, so I dont think shaping the armature to ---+--- and using epoxy to secure it will cut it. so if you know a better method to secure it onto a smooth bore armature, feel free to share it.

brown represents the wood cover that the motor will be hidding behind, since the gap is on top, the gray is the gap material.

Turkey9

Tue Apr 20 2010, 06:34AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

If you cut a circle of some thick plastic, Fiber reinforced polyester might do it (fibergalss), at least 3/8 in thick, that should work nicely. The hub would be the shaft. You could then over lay copper sheet to get the electrical path.

I doubt that makes any sense. The point is, if you have a circle spinning at 11,000RPM, it is easier to balance than just a shaft spinning around. It will also create less drag while spinning. The circle can be easily made by an appropriately sized hole saw and you will also get a nice center hole, perfectly concentric.

IntraWinding

Tue Apr 20 2010, 09:37AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Is Tungsten really the best stuff for spark gap electrodes? It's only resistant to very high temperatures in the absence of oxygen and it's not a particularly hard or conductive metal. Has there been a systematic study of material wear when sparked?

Alan

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