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Bazukaz 25th January 2006 10:20 AM

Stator coating
 
Hi, i have found one company which does powder coating. They can coat in polyester and epoxypolyester coatings. Are these coatings suitable ? How thick should it be ?


Regards ,
Lukas

Calvin 25th January 2006 02:01 PM

Insulation
 
Hi Lukas,

the thickness of the coating depends on two factors.
first: the voltage-levels You will have to isolate and
second: the dielectric breakdown voltage of the material itself

1. You have to keep in mind that You have to insulate peak-to-peak-voltage values, while normally voltages are given as rms-values (app. Factor 3). Additionally the brakdown-voltages are measured at very low frequencies (DC-50-60-400Hz). Things are different at higher frequencies. The breakdown voltages sink with rising frequencies. So calculate with just half of the given values! Too, calculate with a headroom factor of 2, because of aging reasons. The more the material is stressed the quicker it ages, which means that the brakdown voltages come down.
Even with low-voltage-designs with small d/s-spacing like MLs expect the insulation to be around 0.5mm thick


A lot of Polymers will show breakdown-strengths around 20kV/mm up to more than 100kV/mm. The center is around 40kV/mm. The higher the value the thinner the coating can be. Surf the Net for www.kundert.ch to find value-tables or look at the data sheets of the powder.

There will be several problems You should discuss with Your coater.
Tell him that You plan to coat thin perforated metal sheets and .....donīt be surprised when he bucks off ;-)
Tell him You need coating-thicknesses of app. 0.5mm or more and ....donīt be surprised when he bucks off :-)
Tell him You need the coating surface in perfect condition and the powder melted 100% and .....donīt be surprised..... :-) :-)
Tell him You liked it best coated in a fluidized bed manner and.....donīt be sur........... ;) :xeye: :D

jauu
Calvin



ahhh, by the way: the thicker the coating needs to be the higher the dielectric constant of the material should be to not to loose too much efficiency :clown:

moray james 25th January 2006 05:10 PM

one more thing
 
When powder coating perf metal you must be concerned with how the powder coat material behaves when it is thermoset. most coating materials will creep back away from sharp edges. Problem is that those sharp edges are where your high voltage wants to go to to jump off of the stator. So the edges are exactly where the film thickness of your powder coating matter most. You want to make sure that when you assemble your stators that you orient the perf panels such that the sharp edge (the punch out side) is the side facing away from the diaphragm. (perf metal is punched and the holes will have smoother edges on the punch in side and sharper edges on the punch out side)
The powder coating that has the least amount of creep at edges is Nylon and that makes it the best choice for ESL panels made from perf metal.
There are a lot of things to consider when choosing to go with perf metal. Many that are not so obvious. That is why fabricating stators with insulated wire is to me so attractive. More work perhaps but the results are reliable and dependable. For one off projects (most diy) insulated wire is the safest most dependable means of making an ESL stator panel in my opinion. Regards Moray James.

Bazukaz 25th January 2006 06:06 PM

Thanks for support,

I think that wire stators are better , but in my country i could not find a mechanically rigid plastic grid. I have tried painting stators , but even thick layer of paint didn't resist 3 kV testing.

Calvin 25th January 2006 06:24 PM

Plastic grid is not needed
 
Hi,

You donīt need a plastic grid necessarily!

jauu
CAlvin

Bazukaz 25th January 2006 08:13 PM

How do i do without a plastic grid ? The wires should be stationary fixed to a flat and rigid surface , what else could be used ?

moray james 25th January 2006 09:44 PM

well...
 
There are any number of ideas that could be used. You need to reference the wires in the stator to some rigid cross pieces at intervals that keep the whole thing solid. This could be done with cross struts of pastic or wood (sealed to prevent moisture absorption). You can search aound the ESL circuit for all kinds of ideas. You can also have a look at the Dutch ESL builder site for examples of fine craftsmanship.
The plastic floursent ceiling light louvres commonly known as "egg grate" are your best bet as they can be purchased all over and are inexpensive. They are available in 2X4 foot panels in either 1/2 or 3/8 inch thickness and are also available in standard Styrene or in Acrylic. Take a look at an old Acoustat panel and you will see how they were built. The Acoustat's are robust work well and last a long time. This form of construction is not all that different from the Janszen tweeters.
It has been my experience that even with simple construction methods there are usually lots of "tricks" to learn (read problems to be solved). The K.I.S.S. principle is one that will save you a lot of grief in the long run. That said if you are up to inovating and creating something new and wonderful go for it and you can show us how you did it when they are done. Best regards Moray James.

Bazukaz 25th January 2006 10:19 PM

I think wood is not a good choice , because it can change its shape depending on moisture , drying , etc.

In what kind of shops floursent ceiling light louvres are usually sold?
I have never seen it.

Regards ,
Lukas

moray james 26th January 2006 01:35 AM

check this out
 
You are right about wood but if done properly it can be made to work and do a good job but yes not my first choice either. I only wanted to offer up possibilities. Depending upon resources and available materials there is no good reason that anyone cannot build up a set of working panels with what they have at hand.
As I suggested go search the dozens of design projects at the ESL circuit. There are all kinds of great ideas to be found there.
You can have a look at this site to see what eggcrate light louvre is. Regards Moray James.

http://www.americanlouver.com/speclouvers.html#egg

Calvin 26th January 2006 08:06 AM

2 Attachment(s)
Hi,

have a look at the Audiostatic panels. They use a quite fragile but thick frame of insulating material. Square metal rods are glued horizontally onto this frame and to these metal rods the insulated wires are connected to. Thats imo one of the easiest ways to get a good safe stator with little stray capacitance and tight tolerances. But as You might see on the pics You have to use relatively thick single stranded wire that has to be straigthened. Such a design is very low in material-cost, but high in working hours :xeye:

jauu
Calvin


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