Insulating coatings

[arend-jan]

I'd like to start a discussion on insulating coatings, in particular coatings suitable for the insulation of stators. What would be the ideal properties of such a coating? What are you using right now?

My preference would be something that can be sprayed with a paint spray gun, and it would be nice if it is available in different colours as well.

To kick it off:


* high voltage resistant, also on a long time scale
* high electric strength
* high dielectric constant (relative static permittivity)
* good adhesion to metals and plastics, fibreboard
* good coverage of sharp edges (e.g. not withdrawing from edges)
* spray-able
* custom colours, nice finish?

[SY]

With these constraints, you're pretty much limited to epoxy or polyurethane.

In a more exotic process (polymer thermal spray), one can use some engineering thermoplastics, but again, this is not a diy-friendly process.

[Lucius]

Shellac..Get dewaxed super blond shellac flakes & mix with alcohol to the viscosity you want. Pour into a bottle used to mist plant leaves...Shellac is user friendly.

[harry_at]

Hi,

maybe the ROYALAC product range is worth a look.

For example ROYALAC 129 is an impregnating air drying varnish based on synthetic resins. Can be applied with a gun.

Dielectric breakdown 0.02mm > 2500V. Colours: Gold, Yellow and Colourless.

ROYALDIAMOND

Harry

[Calvin]

Hi,

there are nearly no important infos about the royaldiamond stuff.
no resistance values, no epsilon, no creep and track values, just some rudimentary mechanical data. Even the test conditions for the breakdown voltages are unknown apart from using a flat piece of coated copper. So one cannot comment in any way postive or negative about the usability of the stuff.
A decent datasheet should look rather like this one:
Electrolube PUC

jauu
Calvin

[Calvin]

Hi,

When looking at highly arc resistive coatings e.g for magnet wire, You will see that those are always 2 to 3 layer coatings of different materials. Often a combination of polyamid, polamidimid and polyurethan. I´ve extensively searched to find out, why this special combination of polymers is advantageous, but have not found a explanation yet. I just found out that sheet metal stators coated with similar material combinations work better and more reliable than single coating stators do. Besides the multiple layer technique allows for any colour of the stators you wish. Just insure that the colourizing layer is not the bottom or top layer.
If You look at the datasheets of PA, PA-imid, PVC or PU they don´t differ much in epsilon, resistances, creep and track.
My assumption is, that PA is good for high thickness of layer build up at small radii of wire or sharp edges of the holes of metal sheets. But PA has a rather high percentage of residual water, which is a reason for the rather low resistance values and might be the reason to use PU as topcoat. Reduction of sensitivity to humidity? PU bonds quite well with PA and other materials. Its a very hard yet flexible coating which is often used under rugged conditions (stair cases, boats, etc).

Nano-technology could improve the parameters of insulators further. Doped with a low percentage-of-weight part of Aerosil (~20nm particle size) silicone resins and silicone rubber showed increased values of breakdown voltage and -times.

jauu
Calvin

[SY]

Why use the PA as a coating if you're going to need PUR (or polyurea) as a topcoat? Just put the PUR straight onto the metal- it's easy to get good adhesion. That said, an epoxy would still seem superior from a mechanical standpoint. Epoxy's big disadvantage is weathering (tends to chalk), but that's not an issue indoors.

Getting silicones to bond permanently is something of a challenge. The best ones for adhesion are the acetic cure, but those carry a lot of problems. The Pt-catalyzed resins do not adhere as well, as a rule.

On a manufacturing level, a good dark-horse candidate would be PVDF (Kynar). Arkema makes some bondcoat/topcoat systems that are expensive, but have great adhesion, excellent hardness, and good electrical properties.

[Calvin]

Hi,

well I´m no chemist or physist, but I try to understand as much as I can. And so I read a lot of papers regarding insualation issues over the years.
I understand that the mixture of multtiple materials in different layers improves certain parameters like arc resistance, similar to alloying improves mechanical parameters of metals.
I just haven´t found a paper that clearly states the reasons and which material combinations to choose. What are the mechanisms or parameters that lead to the higher arc resistance?
It seems that wire manufacturer always use multiple coat/multipe materials -PA based laquers as bottom coatings and PU as top coating- for their highest rated magnet wires.
It wouldn´t make much sense to use multiple materials instead of just a thicker layer of a single (doped) material if it didn´t result in superior properties.

jauu
Calvin

[jlsem]

Just be careful when mixing dielectric coatings. Sometimes a mix can increase the tendency to arc. You should stick to a single coating unless you are prepared to carry out tests on your own combination of dissimilar coatings.

John

[SY]

Bingo. For HV insulation, there's often layering to get a gradient of dielectric constant. These can be modeled after careful measurement, but for the diyer or small scale manufacturer, that's impractical. Unless you're trying to push the state-of-the-art for bias voltage and drive level, a single insulator layer is probably the best approach.