John, as you know, I love seeing this stuff. I would also like to see if you could provide a list of the "elements" you use. By this I mean the type of powder coating, paint, epoxy, etc.
Thanks. The powder coating I use is from two different companies. The brown colored one is made by 3M and I no longer have the number. After months and months of trying to get the stuff, someone right here on Slotblog got me some through work. It's normally only available in industrial quantities and not sold through regular retail sources that I've ever seen...and I really looked. I traded most of the container I got for some made by another manufacturer that is in the blue color. Both are similar, although they have slightly different working characteristics and finished properties. ***Like all epoxy products, whether in powder or liquid form, they do have a finite shelf life, and I keep them in a small refrigerator in the hope of extending their life as long as possible because I don't know that I'll be able to replace them when they're either gone or no longer work. ***If anyone is reading this and has a source, let me know. Epoxy and other (usually polyester) powder coatings are widely used now, so it's possible another source is out there. These powder coatings used for armatures are a high temperature epoxy type and are used in industry for coating rotors, stators and other electrical/motor components for insulating them. More commonly available powder coatings can be had from places like this one:
Columbia makes some really neat powders, and one of theirs is widely used in the firearms industry. Many of them should be fine for armatures even though they weren't developed for them because you're just looking for a tough, heat resistant coating that doesn't conduct electricity. The only problem here is that these powders were developed for electrostatic spray application. The electrostatic method requires extra measures in preparation of the armature as well as a way to capture extra powder that doesn't bond to the armature ("overspray") such as a type of mini-"booth" or some such thing. Electrostatic powder coating is capable of a thinner and very even finished product coating, but is more cumbersome for the reasons above and others, and requires a special gun for application. The guns that Columbia sells are very expensive and really meant for industry. Eastwood, sells inexpensive ($60) electrostatic guns that should work fine with Columbia's powders. I had one that I experimented with, but ultimately went with a different method of application. By the way, Eastwood sells powders as well and in a dizzying array of colors and finishes, but they're polyester powders and not as tough or heat resistant as the epoxy stuff:
I use a method of powder coating called "fluid be" application. If you use powders formulated for electrostatic application in a fluid bed, you'll get a very thick and heavy coating, at least with the powders I've tried, and this is not very suitable for armatures where you don't want to waste space or add useless extra mass. Fluid Bed application is really about preheating the part (*armature stack in our case) to around 375-400F (a cheap toaster oven works well), and then dipping the part into the powder which is contained in a "bed" with air (supplied by a cheap aquarium pump) rising up from the bottom through a membrane into the powder. Under these conditions, the powder looks like and behaves like a boiling liquid. Because of the "boiling" type movement of the powder, as well as preheating the part, the powder will get into the "nooks and crannies" and then stick instantly to the part. To make sure the part is well-coated on the insides, you give it a couple of "twists" or "spins" as you're dipping it. After dipping, the part goes back into the oven for "post curing"... fifteen or twenty minutes is plenty, as the arm will be subjected to more heat when curing the epoxy and even just running if the arm is "warm" wind With any method of powder coating, places you don't want the powder to stick to MUST be masked because, once coated, the powder is pretty darned difficult to remove. For masking that won't be ruined by the oven temperatures, teflon products in either tubing or tape work really well. I use this stuff from Eastwood in the 3/4" width and one roll will last you for years:
Looking around YouTube, I found several videos on fluid bed powder coating (anglers use the same method for applying tough, brightly colored coatings to fishing lures). This one even has the same air pump I use, but even smaller ones can work well. Whatever material you use for a "membrane" to separate the air coming into the fluid bed from the powder has a big effect on how well your fluid be will work. Generally speaking though, you really only need to see the powder "lift" up like a half inch or more and behave like a boiling liquid without so much air that the stuff starts getting all over the place and/or the powder coating isn't solid enough to provide good insulation against shorts. Building your own fluid bed is super EZ:
So, getting the right kind of powder can be tough, but some of the Columbia material should be fine...although it is meant for electrostatic application. Maybe you can get it to work well with some experimenting, and their coatings in general should be fine for less extreme winds. They do have ceramic type coatings, but application and even more so, curing becomes an issue. Powder coating is a whole area to investigate on it's own, but you CAN do it with some basic "scratchbuilding" type ingenuity. It isn't rocket science.
For the epoxy used to "pot" the armatures after winding. You want a lo-viscosity material that will penetrate the armature coils that will also have high heat tolerance. ***The commonly used magnet wire for armatures has no more than a 200-220C tolerant coating (around 400F), so anything beyond that with the epoxy is probably overkill in most cases. ***If an armature gets to 400F, other things are likely to be going wrong with the rest of the motor. That's not to say that even more heat-resistant epoxy wouldn't be a good thing, just probably not necessary in most cases. After being lo-viscosity and high heat-resistant, other properties you want in an epoxy is a relatively easy cure schedule and of course a fairly clear finished appearance. The epoxy I use is called "Duralco 4461" and is made by a company called "Cotronics". It's available in a one pint "sample kit" that has both the resin and the catalyst ("hardener"). If you keep the stuff cool, it can last you MUCH longer than the 6 month shelf life spec...much much longer. That's a good thing because even the "sample kit" is about $100. You might be able to ease that pain by finding someone to split the kit with. Then you could get some cheap plastic bottles, separate the material in half, pack it very carefully (the P.O. and other shippers have rules you need to follow) and send it off. Anyway, here's the link to Cotronics' "Duralco 4461":
You can also look at their "4460". This has even better heat-resistance (up to 600F under service), but requires more in the way of heat for curing. Either one will "speed-cure" and at least gel enough to not run all over the place under heat, but you DO have to be careful not to over-apply and watch the armature while it's starting to gel because getting it off after curing is impossible.
No regular "hardware store" type epoxy will work well. Even JB Weld, which has a good enough heat tolerance for many arms, is waaaaaay too thick to penetrate the coils and is of course not clear (their best formula anyway).
***That's all I have on the subject. I've posted all this at least several times before, so I hope someone will bookmark this so I don't have to post it again!