ESL powder coating?

[markusA]

I've finally taken the plunge...
Parts have been ordered and soon I'll start tinkering with my first set of ESL's.

I've read some previous posts and I'm trying to figure out the powdercoating bit.
300-500um seem like a good place to start and I found a local shop that can do 250-450um without much difficulties.

Is there anyting specific I should look for?
What thickness is "best"?

The stators are often recommended to have 40-50% open area.
Using Rv3-4 stators (51%) and a 300um coating will give you roughly 32.65% open area.
Rv5-6 (63%) is special order = VERY expensive -> 48.8% open area after coating. (300um)
Rv4-6 (43%) -> 29% open area after coating. (300um)

keeping with recommendations I should opt for the Rv5-6 perf metal but it would be insainly expensive and I'm curious how much the pattern would affect the efficiency of the panels?

Rv3-4 with 170um coating would give me 40% open area and be much much cheaper.

What would you do?

[Calvin]

Hi,

between what one claims and what one can actually do there are sometimes whole worlds. I have way so often heard from coaters in before, that it wouldn´t be any difficult....but in the end none of them could do the job properly.
250µ-400µm powder coating on punched metal sheet with an opening of app. 50% is not at all trivial. In fact it requires at least double- maybe even triple-coating, because a single layer of electrostatic spray coating is good only for 100-150µm based on Nylon/Rilsan, which is asumably the best powder material for our application. Since the powder layer needs to completely melt to achieve a pinhole free surface, a second or even third layer is difficult to apply.
Fluidized bed coating theoretically allows for sufficient layer thickness in one go, but the metal sheet cools down too quick for the powder to melt fully. It probabely requires some additional heat treatment process.
I doubt that a coater would be so lucky to find the right process parameters with the first try.
The way of least problems is possibly to have one good and thick layer spray coated with pure Nylon and add multiple layers of wet coating, with the first one thin and in the desired color and the following layers adding thick clear top-coats.
Rv3/4 is a good one. Punched metal sheets are best for stators with small d/s values, which in turn asks for small holes.

jauu
Calvin

[markusA]

He offered to measure the thickness if I needed to be sure.
It's a big industrial coater with very large capacity.
They are used to coating perf metal.
Multiple layers was doable without much trouble.
All acording to the person with whom I spoke.

I like Rv3-4 as well. (Cheap and easy to get + good open area ratio)
If the powder coater holds true to his word and sucessfully adds a 300um coating it'll result in 32.65% open area, is that ok?
Or should I go for a 170um coating to get the recommended 40% open area?
All assuming he can do it.
If he can't do it I think you are very much correct it's a good alterative way of doing it.

[SY]

Originally Posted by Calvin

...Nylon/Rilsan, which is asumably the best powder material for our application.

Why would that be the case? A thermoplastic will never have the low viscosity of an epoxy or polyester, so will not flow or level as well to give a thin and very even coating.

FWIW, I worked with a derivative of Kynar which had astounding adhesion to metal as a powder coating. This material was also made by Arkema. Kynar has much lower moisture regain than nylon, as well as superior insulating properties. It is, sadly, quite expensive.

[chinsettawong]

Hi MarkusG,

I wouldn't worry too much about the open area. It's better that you can have a good thick layer of powder coating.

Wachara C.

[markusA]

I'm sure it'll sound ok either way but I'd rather do it right the first if possible.

[bentl]

Ask the to put on a coat of white or clear powder first as it should be less conductive

I coated my stators all black and that is not enough to insulate the stators

Good luvk on your project

[Calvin]

Hi,

Kynar, as You suggested SY, would indeed be a alternative by it´s electrical properties. One can test this by using Kynar insulated wire-wrap wire for stator construction (and its silver plated copper wire-----so it must sound well *lol*).
I see two pros for Nylon/Rilsan. One is the rather lowish surface- and bulk-resistivity which reduces the tendency of charge buildup on the stator, reduces overload recovery time and which -in combination with it´s epsilon value- allows for a good efficiency.
The second is the low value of radius for equal coating thickness which allows for a slightly thicker layer at the whole edges.

jauu
Calvin

btw. pure Nylon is white in color

[bolserst]

Originally Posted by Calvin

Hi,

Kynar, as You suggested SY, would indeed be a alternative by it´s electrical properties. One can test this by using Kynar insulated wire-wrap wire for stator construction (and its silver plated copper wire-----so it must sound well *lol*).
I see two pros for Nylon/Rilsan. One is the rather lowish surface- and bulk-resistivity which reduces the tendency of charge buildup on the stator, reduces overload recovery time and which -in combination with it´s epsilon value- allows for a good efficiency.

Hi Calvin,

Can you share some specifics for bulk resistivity and dielectric constant for the Nylon/Rilsan mix you feel has advantages?


For comparison, here are values I found on the web for Kynar and PVC.

Kynar electrical properties:
Kynar bulk resistivity: 1.0e14 - 2.0e14 (ohms-cm) (dependent on Kynar type)
Kynar dielectric constant: 7.3 - 9.5 (depending on signal frequency and Kynar type)

PVC electrical properties:
PVC bulk resistivity: 1.0e13 - 1.0e15 (ohms-cm) (dependent on PVC type)
PVC dielectric constant: 3.5 - 8.0 (dependent on signal frequency and PVC type)

[markusA]

Please explain the mechanics at work here?
Resistivity being the inverse of conductivity should be as high as possible in an insulator?
Why would a low value be positive?

The dielectric constant should be low though to avoid charge build-up as much as possible? (If I'm remembering my physics right?)
Since it's also frequency dependant I'm curious as to how this will affect things in the audio band?

A low radius value sounds like a good thing for coating holes with small radius such as ours.

Thinking one step further...
Double the resistivity would allow for half the thickness of the coating with preserved insulation. With less dielectric it's also possible that this would lessen the charge buildup as well?
What am I missing here?

Since we're getting all scienfic here...
What's our target number?
Resistivity being thickness dependant, what's the minimum acceptable resistivity in the coating?

To make things even more technical.
What is lethal current?
I have a vague memory of hearing 15mA?
Let's assume 1mA?
And while we're at it, let's assume 3200V voltage.
R=U/I -> To avoid electricution the resistance should be 3.2e6.
Assuming the body resistance is negligeble compared to the dielectric.
Working with PVC @ 1.0e13 ohm/cm.
3.2e-9m would give us enough resistance for it not to be lethal.
That is 0.0032mm.
Please tell me if I'm missing something?