Electrostatic Precipitator to Contain Graphite Powder

  • #1
Hi all!

This is my first post here and I really hope you guys can help! I am currently in senior design at Purdue Fort Wayne in the MET department. I also own a company called Graphite Customs where we make graphite molds for glass blowers. When machining graphite, the powder is very abrasive so when it gets into the bearings or ball screws of the machine they tend to wear quickly. Graphite is also very conductive so if theres a build up on any of the machine electronics, they could short out. Our Idea is to make an electrostaic precipitator to charge the graphite and attract it to another plate, containing a much larger amount. The problem we are having is trying to figure out what amount of high voltage(10kV?) and where to buy an adjustable power supply to try different voltages. I attached our proposal so you can see a rough sketch and get a little better idea of what we are doing.

I would really appreciate any help or suggestions!

Thanks!
Casey
 

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  • #2
Bystander
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machining graphite, the powder is very abrasive
Graphite? Abrasive? What sort of additives/binders are in the "graphite" stock? That's the material tearing up the machinery, and that you want to control.
 
  • #3
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I supported the development of an electrostatic AC cleaner. We used a six watt, 10kv supply which we could turn down to 6 kv.
However, I can't see it working in this application due to build up of conductive residues.
You may wish to consider to consider a cyclonic separator.
 
  • #4
NascentOxygen
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I'll pass along an optimistic anecdote. From a past interest in negative ion generators, I recall reading that a magazine editor discovered that such a simple device sited atop the kitchen fridge soon saw the fridge's white enamel turn black with soot, cigarette ash, and other gunk it precipitated out (as an unexpected effect of the negative ions). Maybe that's something you could try—a $30 off-the-shelf "domestic" negative ion generator—as a test to see whether it's going to produce results.

Wayne Green, W2NSD :)
 
  • #5
jim hardy
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How do Xerox machines do it ?
 
  • #6
Graphite? Abrasive? What sort of additives/binders are in the "graphite" stock? That's the material tearing up the machinery, and that you want to control.
Bystander, I'm pretty sure graphite itself is quite abrasive and wears down bearings when there is a build up in the grease. Either way, it all needs to be contained.

I supported the development of an electrostatic AC cleaner. We used a six watt, 10kv supply which we could turn down to 6 kv.
However, I can't see it working in this application due to build up of conductive residues.
You may wish to consider to consider a cyclonic separator.
Mike, If you are talking about having too much graphite on the plate, we plan on writing a small program through an Arduino to turn off the power for a split second so the plate can clear by the vacuum and continue to collect. As for the separator, I currently have one but I can't get a large enough collection through just the vacuum. But the separator does work very well for what I can get!

Maybe that's something you could try—a $30 off-the-shelf "domestic" negative ion generator—as a test to see whether it's going to produce results.
Not a bad idea. From what little I've researched, it looks like pretty much the same process as a precipitator.


So I found this HV power supply on Ebay which seems like a pretty good deal and looks like it should work for what I'm doing. Any advice on what I'm looking at?
http://www.ebay.com/itm/Acopian-Adj...924?pt=LH_DefaultDomain_0&hash=item2a427a0b1c

As a mechanical student, this probably wasn't the best idea for a senior project but I thought it would be really cool if it worked. Thanks for the help! I'll keep you guys updated as we work through this project!
 
  • #7
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Bystander, I'm pretty sure graphite itself is quite abrasive and wears down bearings when there is a build up in the grease. Either way, it all needs to be contained.
http://en.wikipedia.org/wiki/Dry_lubricant
A general note on use of graphite as a lubricant.
As far as dust containment goes, is there room enough at the cutting tool to get in with a vacuum nozzle similar to woodworking shops?
 
  • #9
jim hardy
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Can't quite see the drawings

Are the machine tool bits metal? If so, during machining process your conductive graphite block will be at potential of the router bit and the chuck that's holding it , probably earthed.
..just curious about your hookup.

i'd think the voltage you need would be in proportion to the distance involved for it's not just volts that the particles "feel" but field strength, volts/meter

This paper looks interesting as an introduction to precipitators.....
http://nepis.epa.gov/Adobe/PDF/P1000G9Q.pdf
i've never worked with them.
 
  • #10
dlgoff
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I suspect that you won't be able to get all the dust with the 10kV and eventually this supply, with all its openings, will fail also.

If you don't need voltage variability, maybe a neon sign transformer would work.
 
  • #11
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There's an old saying:
"What some haven't had time to learn, others haven't had time to forget."

The dust will inevitably coat the insulated materials and start a conductive path. If enough power is available, it will scorch any flammable insulator, which will produce a conductive path to carry more current...

I've seen PCBs catch fire due to high voltages. I've also seen what soot trapped in a box with 230VAC does - it guts the entire box with the material it finds to burn. An ignition voltage in the presence of a flammable powder sounds very very bad.
 
  • #12
Alright, you guys have officially scared me out of doing it this way.


Are the machine tool bits metal? If so, during machining process your conductive graphite block will be at potential of the router bit and the chuck that's holding it , probably earthed.
There will be a metal bit into the graphite. Does that mean the voltage would short through the router?

New idea:
What if we put a precipitator between the current vortex separator and the vacuum to prevent very small particles from escaping the 2 micron fabric filter without getting a HEPA filter. Right now, if I touch the filter bag you can see a fine powder come off of it. Maybe that would eliminate it? It would act as a secondary separator for finer particles.

Then how are the charged plates cleaned when they are discharged without letting everything go right into the vacuum...
 
  • #15
NascentOxygen
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It goes without saying that basic electrostatic precipitators are not going to be maintenance-free. The best would be something totally encapsulated (e.g., in a cast aluminium box completely sealed with epoxy or special silicone) except for a part that each month (or week) can be taken outside and hosed out with water and detergent.

You just have to examine the gunk that eventually coats the HT transformer and lead in those big old TV sets to see how particulates settle out on high voltage circuitry. I marvel how they manage to keep working!
 
  • #16
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The sixties vintage TV's didn't always do so well. Burnt components and a goop called "corona dope" were normal for the day. But, they had one huge advantage over this endeavor - the gunk in the air wasn't a great conductor!

I think the idea of supplementing a filter has merit - because you can conceivably keep the high voltage away from the graphite stream.

If you were to inject ionized air into the vacuum line alongside the graphite, the two streams would mix and to some degree, the graphite would pick up a charge. Charged graphite would be drawn to nearby surfaces as it goes through the filter media.

Unfortunately, any charge would be promptly dissipated on contact and you would be dependent upon surface forces to keep the graphite in place.

I recall diamond miners would run their gravel over grease to get the diamonds to stick, so there are surface chemistries that even the pickiest of carbons are attracted to.
 

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