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Old Aug 22, 2012, 08:19 AM
Jack
USA, ME, Ellsworth
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Thanks again!

I have the feeling here that we are closing in on resolving one of the more troublesome areas in motor rewinding, the re-insulating of stators.

Wonderful stuff!

Jack
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Old Aug 22, 2012, 10:21 AM
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The local HF had yellow powder coat in stock. According to it's directions 400*F is what it takes to melt. I'm going to run a test using some scrap parts to get some practice before using a potentially good stator. The first thing that came to mind is the stator will need to be level before applying the powder.
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Old Aug 22, 2012, 10:54 AM
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Originally Posted by KKUSA View Post
As far as temperature, it varies depending on the powder, mainly due to particle size, and what sort of finish you want. Usually we heat to about 200c , which is well below the annealing temp of the stator material, and allows for a nice even flow.
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Originally Posted by zeroback
According to it's directions 400*F is what it takes to melt.
200 C =392 F

Annealing occurs above about 740 F though tempering begins to occur around 400 F.

So seems like shooting for as close to 200 C / 400 F as possible giving adequate working time is best.
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Old Aug 22, 2012, 01:51 PM
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Quote:
Originally Posted by zeroback View Post
The local HF had yellow powder coat in stock. According to it's directions 400*F is what it takes to melt. I'm going to run a test using some scrap parts to get some practice before using a potentially good stator. The first thing that came to mind is the stator will need to be level before applying the powder.
Not all powder coat is created equal. The Hf stuff is usually polyester based--not epoxy. The good stuff does a good job of protecting the wires from the sharp edges of the laminations--the other stuff is just made to look nice--I one fooled with the consumer grade powder coating materials---but after using the real stuff there is no comparison.

Steve
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Old Aug 23, 2012, 09:03 AM
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Harbor Freight Powder Coat: test 1

It would be marvelous to have access to super duty powder coat but the Harbor Freight PC is a significant improvement over nail polish, crazy glue, JB weld and hours spent applying Kapton tape.
I set my toaster oven to 400*F after twenty minutes of heating I sprinkled the powder with my finger tips. It melted right on down . A better method will be needed to evenly disperse the powder. It tended to gather in little little piles that got to about 1/32 high and then melted. Looking closely at the edges it is visible were the sprinkled powder hit the tapered edges of the test bearing. It melted right to the metal and did not run down the side of it. The directions mention .004" max thickness per coat to avoid runs and sags. Although in in this experiment it piled up and did not display a tendency to sag or run. In fact it did not flow out to level. Hence the need to create a way to sprinkle it in a uniform manner.
After cooling down I poked at it with knife and tapped on it with a little hammer, it is hard and it did stick.
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Old Aug 23, 2012, 09:40 AM
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I can tell you that we (where I work) check to see that the coating is about .009 thick. Corner coverage is paramount. Also, check for resoftening at expected stator temperatures. Keep going, you may be on to something that anybody can do!

If you need scrap laminations to play with I may be able to help.
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Old Aug 23, 2012, 09:41 AM
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What about dipping the hot part in powder, as KKUSA suggested?
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Old Aug 23, 2012, 10:06 AM
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I have a feeling that dipping may not work as well as sprinkling. I had a feeling surface tension would play a roll in this endeavor. In the pics it is evident the that powder was acting like a drop of water and collecting in the middle creating "The Magic Radius" that dulls the sharp edge of the stator. I'm going to try dipping and am open to all suggestion. Dipping may force the powder around the edges of the stator face, creating an unwanted bump. I don't know but am going to find out. I can see this stuff is going to be fun to play with, custom colored stators to match the air frame. For the pilot who has everything
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Old Aug 23, 2012, 10:10 AM
Jack
USA, ME, Ellsworth
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Quote:
Originally Posted by zeroback View Post
It would be marvelous to have access to super duty powder coat but the Harbor Freight PC is a significant improvement over nail polish, crazy glue, JB weld and hours spent applying Kapton tape.
I set my toaster oven to 400*F after twenty minutes of heating I sprinkled the powder with my finger tips. It melted right on down . A better method will be needed to evenly disperse the powder. It tended to gather in little little piles that got to about 1/32 high and then melted. Looking closely at the edges it is visible were the sprinkled powder hit the tapered edges of the test bearing. It melted right to the metal and did not run down the side of it. The directions mention .004" max thickness per coat to avoid runs and sags. Although in in this experiment it piled up and did not display a tendency to sag or run. In fact it did not flow out to level. Hence the need to create a way to sprinkle it in a uniform manner.
After cooling down I poked at it with knife and tapped on it with a little hammer, it is hard and it did stick.
Man! That's looking good! Do you know, is that the polyester powder as opposed to the epoxy type that Steve mentioned?

And do you think that the coating you got is ready to take windings and would be tough survive the windings (not liable to be pulled through or displaced)?

As far as the heat, that will take some time to figure out, we just need to smoke a motor and see what happens!

Jack
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Old Aug 23, 2012, 10:32 AM
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Poking this with a sharp knife tip, compared to any epoxy I've used, this is harder. So far so good , it's feels tough. Will it hold up after I wind it with way to big a wire and have to remove it (3 times) and redo it? I'm going to find out.
Reading the label there is no indication of the chemical make up. It's made in India so I would assume it to be polyester. It dose indicate that if it gets hot enough to "decompose" that the fumes are toxic in California.
@Kenstate Thank you for the offer, that would be helpful, I have few misc parts to play with before going to a known good stator. The next step is to turn this bearing over and coat the other side to see what happens to the first side on a reheat. According to the instructions on the label additional coats can be applied. So I'm assuming that once hardened the stuff won't soften on reheat
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Old Aug 23, 2012, 11:16 AM
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Quote:
Originally Posted by zeroback View Post
I have a feeling that dipping may not work as well as sprinkling. I had a feeling surface tension would play a roll in this endeavor. In the pics it is evident the that powder was acting like a drop of water and collecting in the middle creating "The Magic Radius" that dulls the sharp edge of the stator. I'm going to try dipping and am open to all suggestion. Dipping may force the powder around the edges of the stator face, creating an unwanted bump. I don't know but am going to find out. I can see this stuff is going to be fun to play with, custom colored stators to match the air frame. For the pilot who has everything
Chamfer corners first. Dip. Leave inverted til hardened. The "bump" is beneficial to cover corner, but earlier chamfering reduces or eliminates its effective height.

A full coated stator (as in most RC motor stators) just carries the height through the flat part of the stator anyway. The "bump" is just longer.
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Old Aug 23, 2012, 10:30 PM
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Yea, thats lookin good. As with any coating process, make sure your part is clean and oil free.

You could put the hot stator on a dowel and coat the whole thing. The proper dowel would mask the ID surface, then just cut it away. That way you could do it in one shot.

Maybe I will remember tomorrow to get the name of the place we get our small quantity powder from. However, I do believe the HF stuff will be adequate with a bit of experimentation. It sure is cheap enough. That $5 pail will go a loooong way!!!
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Old Aug 24, 2012, 08:15 AM
Jack
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I was browsing street prices on eBay on powder, looks like $10 a pound for polyester power, plus shipping, is typical.

I didn't see an epoxy or obviously higher quality powder but I didn't spend much time there. You can buy an entire fulll bull powder coating system there if you want, but you have to have pretty deep pockets!

Jack
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Old Aug 25, 2012, 07:16 AM
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Had a few minutes to put a coat on the other side of the test part in between storm preparations. Well I had to test the genset which hasn't run since Wilma. I figured the toaster oven would be a good load test. Good news is when this stuff is kicked it dose not soften during reheat. I slapped some Kapton tape on to it to see if what I have on hand will hold up to 400*F. It worked fine but I can see that it will need to be pulled off before the liquid turns hard.
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Old Sep 01, 2012, 03:17 PM
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Originally Posted by zeroback View Post
Had a few minutes to put a coat on the other side of the test part in between storm preparations. Well I had to test the genset which hasn't run since Wilma. I figured the toaster oven would be a good load test. Good news is when this stuff is kicked it dose not soften during reheat. I slapped some Kapton tape on to it to see if what I have on hand will hold up to 400*F. It worked fine but I can see that it will need to be pulled off before the liquid turns hard.
Nice!!, Yea, definitely pull the tape before it cools. Just as it becomes "rubbery" is the best time to pull the tape.
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