Insulation between motor laminations?

[TimNJ]

Greetings,

I have an old radial arm saw that I’m rebuilding. I’ve cleaned it up, put new bearings in the motor and now want to paint it. The motor has exposed laminations on the body, presumably to save space or something.

As far as I know, there’s usually insulation between laminations, perhaps in the form of “backlack” or other varnish-y type material. Is this insulation also applied to the edges of each lamination? If I were to sand or wire wheel off the existing paint, do I run the risk of removing insulation and causing some lamination to lamination shorts? My thought is that the distance between laminations is already set by the thickness of the insulation between lamination, so I wouldn’t be shorting any together unless i applied severe pressure, enough to deform the laminations “into each other”.

Any thoughts?

Thanks,
Tim

[moffy]

Sanding or wire wheeling will produce metal swarf which can go anywhere, not really desirable.

[TimNJ]

I mean, it’s just the stator by itself right now, fairly easy to clean.

[TimNJ]

Unless by “anywhere”, you mean on a more microscopic level as it applies to my original question.

[strawberry]

must electrically insulate windings(so that vibration and dirt). other thing is esthetics

[Grandchuck]

Laminations are insulated to lessen induced currents and hence core losses.

[TimNJ]

If I may revive my own thread please...

I'm removing the old paint on this thing. I noticed that varnish was applied on the bottom of the junction box with the capacitor-start relay. (No continuity across the surface of the varnished area with an LCR meter.) In the attached photo, note the amber color coating on the left, and the darkened color over the laminations. This is the varnish.

Because the rest of this motor was so rusted and covered with flaking paint, I cannot tell whether varnish was also applied the rest of the stator/housing. (i.e. I don't think the paint was applied over top of a layer of varnish?)

But, I really do not know. From an electrical perspective, in there any reason to varnish the outside of the stator housing (on the edge of the laminations)? From my perspective, the laminations are already separated by some distance and varnishing the edges should not do much of anything, unless what ever paint I end up using is mildly conductive or something?

I just don't know why they would varnish the bottom of that junction box, because the other inside walls of the box are not varnished, so it's not to protect from a loose wire shorting to the housing or something. 

[coppercone2]

all that shit rusts like crazy I recommend painting it with varnish


usually they dip the thing in varnish. the procedure is usually to dip it and lift it from the varnish at some distance per second to get a nice coat. and use a vacuum and or pressure to get as much as possible in there

theoretically you should verify with those paint thickness gauges that spin for viscosity


the most clean way is probobly to mount it and dip it via clamping on the box and then drying it, that way you have excess varnish but you also don't have varnish covered towels and cleaning to do. (manufacturing engineer determined its OK to drop box in  varnish because why not )

Getting rid of excess varnish however is probobly a good idea for quality, because its more stuff to flake off and make a mess. but its mass production on heavy metal.........their not gonna mask and clean it up unless someone complains alot

if you ever see anything stupid with paint, its because towels and solvent is expensive, and letting it dry is cheap.


is there a engineering reason for apartment building outlets having 5000 layers of paint on them?

[Doctorandus_P]

Insulation between layers of lamination does not have to be very good. There is no need to worry at all about insulation for painting the outside. If you look at the round thing on the bottom, you see that a bunch of the laminations are even welded to each other. This is also a common practice in transformers. It probably reduces efficiency a bit (I don't know how much) but apparently it's acceptable.

[TimNJ]

Insulation between layers of lamination does not have to be very good. There is no need to worry at all about insulation for painting the outside. If you look at the round thing on the bottom, you see that a bunch of the laminations are even welded to each other. This is also a common practice in transformers. It probably reduces efficiency a bit (I don't know how much) but apparently it's acceptable.

Thank you. I also figured it must not matter that much based on the welds. Just didn't want to make a bone-headed move.

I measure a few 10's of kiloohm across the stator core, from one end to the other, so obviously they are not perfectly isolated, as you mention. I guess the resistance of the inter-lamination isolation just needs to be sufficient to reduce eddy current losses *enough*. Maybe the technology has improved since the 50's, better insulation, lower losses...I am not sure.