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?
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?
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
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
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
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
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
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
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.
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.
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
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
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.
A layered approach may be difficult or impractical, but I find it interesting. Is the consensus that this is done to create a gradient of dielectric constant? What is the advantage of this gradient? Is it to gradually bring the potential down? I'm just thinking out loud here so feel free to shoot.
I'm using a polyurethane based two component paint which is of course not engineered for insulation properties, but it more or less gets the job done. I'd rather have something designed for the task.
I'm using a polyurethane based two component paint which is of course not engineered for insulation properties, but it more or less gets the job done. I'd rather have something designed for the task.
That would be the theory, but I'm unconvinced of the efficacy. Often, a multilayer system is done just for adhesion purposes (topcoat/bondcoat). Problem with the gradient approach is that the difference in conductivity between the metal and the first layer is something like 10 orders of magnitude, whereas the difference between the insulating layers might be two or three.
Hello all,
I've learned some good stuff about materials' insulating properties reading this thread. As a former spray painter experienced with 2-part polyurethanes especially, I would add that one's spraying technique makes a huge difference in helping or mitigating a paint's tendency to run away from sharp edges, such as those around the hole perforations on sheet metal stators. In order to build up the coating thickness over a sharp edge, the first several coats should be misted on quite dry, allowing each coat to setup for 30 minutes or more between mist coats so that solvents in successive coats do not liquify the prior mist coats (or resulting capillary action will pull the paint away from the edge). After several mist coats are applied, allow the coating to setup for at least 60 minutes (it will look rough but you will smooth it out with later coats). The pot life of the 2-part poly will be spent by now so you will need to clean your paint gun and mix a fresh batch of paint to complete the job. Spray successive coats "just wet" with 15 minutes setup time between coats until the desired buildup is achieved. Hope this helps!
Charlie
I've learned some good stuff about materials' insulating properties reading this thread. As a former spray painter experienced with 2-part polyurethanes especially, I would add that one's spraying technique makes a huge difference in helping or mitigating a paint's tendency to run away from sharp edges, such as those around the hole perforations on sheet metal stators. In order to build up the coating thickness over a sharp edge, the first several coats should be misted on quite dry, allowing each coat to setup for 30 minutes or more between mist coats so that solvents in successive coats do not liquify the prior mist coats (or resulting capillary action will pull the paint away from the edge). After several mist coats are applied, allow the coating to setup for at least 60 minutes (it will look rough but you will smooth it out with later coats). The pot life of the 2-part poly will be spent by now so you will need to clean your paint gun and mix a fresh batch of paint to complete the job. Spray successive coats "just wet" with 15 minutes setup time between coats until the desired buildup is achieved. Hope this helps!
Charlie
Powder coating has a proven track record with ESL's and I think it would indeed be preferable-- certainly it would provide a harder, tougher coating with zero entrapped volatiles. Polyurethane isn't cheap either but if you don't have access to powder coating or the cost is prohibitive and you're opting for a sprayed paint coating, it's best to apply the first few coats "dry" for the reasons stated previously. That is; set the fan kinda wide and the fluid flow kinda low such that the the tiny aerosol droplets in the spray strike the surface so sparsely that they do not merge to form a continuous wet coating (if the coating is wet the paint will run away from the sharp edges around the holes). I would apply at least (4) dry-sprayed "tack coats" to serve as a foundation for holding the subsequent wet coats in place over the sharp edges, as needed to buildup the film thickness. Normally you would hold the gun perpendicular to the surface but, since you will be spraying a perforated surface and you want the aerosol droplets to adhere to the edges of the holes, you will need to apply the tack coats with the gun oriented at + or -45 degrees to the panel. Let's say you apply the 1st tack coat moving lengthwise on the panel with the gun angled at +45 degrees, then apply the second coat lengthwise also but reverse the gun angle to -45 degrees so that you hit the other side of the holes. Then apply a 3rd coat moving widthwise on the panel at +45 degrees, followed by a 4th coat moving widthwise also but with the gun angle reversed to -45 degrees-- that way the spray hits all the hole edges from 4 directions for maximum coverage.
Allow the tack coats to completely setup so that they won't re-melt when you come back with wet coats to build up thickness. I used clear polyurethane except added couple of coats of black about midway in the buildup. I would also spray a small test panel and measure it's thickness with a caliper or micrometer before and during spraying until you have at least 12 mils of film thickness on the stators. I found that 12 mils worked OK (about 18 months so far) on my hybrid ESL's, which use 2.5 KV bias voltage and 1/16" stator to diaphragm spacing. However, I did have to redo one panel right off the bat because I either didn't properly smooth over a sharp trim edge and/or I didn't get enough coating thickness on the trimmed edge--- I fired it up and it played wonderfully for about 30 seconds before it flashed over and shorted out the panel and also shut down my beloved Carver power amp (fortunately, just tripped the protection circuitry-- thanks Bob Carver). Anyway, I had a horrendous time stripping and re-coating the stators on that shorted panel-- I thought I would never get all those thousands of holes cleaned out. Lesson learned: Be sure to smooth over the stators' trimmed edges and spend as much attention on coating the edges as the rest of the stators and you won't have a problem.
Allow the tack coats to completely setup so that they won't re-melt when you come back with wet coats to build up thickness. I used clear polyurethane except added couple of coats of black about midway in the buildup. I would also spray a small test panel and measure it's thickness with a caliper or micrometer before and during spraying until you have at least 12 mils of film thickness on the stators. I found that 12 mils worked OK (about 18 months so far) on my hybrid ESL's, which use 2.5 KV bias voltage and 1/16" stator to diaphragm spacing. However, I did have to redo one panel right off the bat because I either didn't properly smooth over a sharp trim edge and/or I didn't get enough coating thickness on the trimmed edge--- I fired it up and it played wonderfully for about 30 seconds before it flashed over and shorted out the panel and also shut down my beloved Carver power amp (fortunately, just tripped the protection circuitry-- thanks Bob Carver). Anyway, I had a horrendous time stripping and re-coating the stators on that shorted panel-- I thought I would never get all those thousands of holes cleaned out. Lesson learned: Be sure to smooth over the stators' trimmed edges and spend as much attention on coating the edges as the rest of the stators and you won't have a problem.
Hi,
the second lessons You should have learned is: Test the stator, i.e. the coating before building.
An easy diy friendly test is to use a sheet of aluminium foil for kitchen use) and connect it and the stator to a Bias supply thats voltage can be varied.
Don´t forget to use a current limiting resistor, but rather a small one. You need some energy within the spark. When the spark is of sufficient energy content, it will first make some tickling noise and with increasing energy ´hammer´ a tiny spot into the foil, which allows You to easily find the weak spots in the coating.
Besides You can detect tiny spots within the coating (from dust or bubbles) which stem from the coating process and which You should sand even and recoat.
jauu
Calvin
the second lessons You should have learned is: Test the stator, i.e. the coating before building
.An easy diy friendly test is to use a sheet of aluminium foil for kitchen use) and connect it and the stator to a Bias supply thats voltage can be varied.
Don´t forget to use a current limiting resistor, but rather a small one. You need some energy within the spark. When the spark is of sufficient energy content, it will first make some tickling noise and with increasing energy ´hammer´ a tiny spot into the foil, which allows You to easily find the weak spots in the coating.
Besides You can detect tiny spots within the coating (from dust or bubbles) which stem from the coating process and which You should sand even and recoat.
jauu
Calvin
Hi,
of course You should keep in mind, that You operate quite open with potentially lethal voltages/currents. So watch carefully what you do.
Don´t wear anything metallic, eg. watches and keep one hand always in Your pocket and use as weak a Bias supply as possible and a limiting resistor that only allows for very few mA maximum current. A second person as safety supervisor is highly recommended.
jauu
Calvin
ps: When I retire from commercial ESLing I might just write my own book: "Taming the Diva!".
Somehow my investments should pay back, eeh?
of course You should keep in mind, that You operate quite open with potentially lethal voltages/currents. So watch carefully what you do.
Don´t wear anything metallic, eg. watches and keep one hand always in Your pocket and use as weak a Bias supply as possible and a limiting resistor that only allows for very few mA maximum current. A second person as safety supervisor is highly recommended.
jauu
Calvin
ps: When I retire from commercial ESLing I might just write my own book: "Taming the Diva!".
Somehow my investments should pay back, eeh?
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Some things that you can buy anywhere are coated with a pretty thick semisoft plastic coting, seemingly PVC. The items seems to be dipped in floating PVC.
I bought a PVC dipped bicycle shopping basket for testing and the results shows that this coating easily could withstand 8 kV@0.3mm thickness.
The basket consists mainly of a metal net with small holes and there's no PVC clogging up the holes.
I wonder how the dipping process is done, anyone heard of it?
I bought a PVC dipped bicycle shopping basket for testing and the results shows that this coating easily could withstand 8 kV@0.3mm thickness.
The basket consists mainly of a metal net with small holes and there's no PVC clogging up the holes.
I wonder how the dipping process is done, anyone heard of it?
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