Insulating a custom conductor

[pkelecy]

I'm developing an actuator that uses an unusual conductor design, one that is machined from copper. I've fabricated several prototypes that look fine, but am now trying to sort out how best to insulate them.

The machining process leaves some burrs and sharp edges. So I'm thinking of first soaking the parts in an etching solution (ferric chloride?) to remove any burrs and sharp edges. After that, wash them off, dip in an insulation bath (polyamide), and bake.

Does this sound like a reasonable approach? If not, any suggestions? My main concern is with the insulating process. I would like to end up with a thin, uniform coating over the conductor, but am not sure dipping will provide that. Seems like gravity might cause the insulation to run down towards the bottom side of the conductor. Any thoughts?

Also, I wouldn't mind outsourcing this work to a vendor. If anyone knows of one that might be able to handle this, I would appreciate the reference.

Thanks for any help with this!

 

[itsmoked]

You can't just slide a piece of shrink tube over it and shrink it? "No messy chemicals" as they say on TV.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

If you post a sketch of the conductor I think answers would be more accurately focussed on solving your problem. Right now we are guessing what it is, which is likely to be a futile waste of time.


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If we learn from our mistakes I'm getting a great education!

 

[pkelecy]

Thanks for the responses.

For proprietary reasons I rather not post a picture of it, but perhaps I can give a better description.

The conductor is essentially a copper ribbon that has been profiled somewhat (i.e. has thickness and height variations). Because of that, as well as its long length, putting a piece a shrink tubing over it would be difficult and probably wouldn't work very well. Also, because the final winding consists of many such layers stacked against each other, the insulation needs to be thin to keep the fill factor reasonable. So a polyamide insulation (similar to that used on magnet wire) is probably what is needed, I think.

But thanks for the suggestion. Any others are welcomed!

 

[sreid]

You might be able to debur with a sand blast box.

For varnishes, see Dolph.

http://www.dolphs.com/

The trickle impregnation varnishes have low viscosity.

 

[ScottyUK]

Laminated busbar material is already available, although only in standard shapes. Would it be possible to machine your part from a commercially available section? If you are looking at a decent quantity then perhaps the manufacturers of laminated busbar would be interested in making it for you?


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If we learn from our mistakes I'm getting a great education!

 

[mcgyvr]

Electrical grade epoxy powdercoat
(I've used this before with great results

http://www.rohmhaas.com/wcm/products/product_detail.page?product=1121028)

 

[7anoter4]

First of all you need a wire drawing machine with a new diamond die and so the conductor surface will be smooth enough and no need for chemical treatment. May be a thermal treatment will be necessary for copper annealing.
Secondly, you need an extruder to heat the raw polyamid and to extrude the necessary insulation [heating the nylon resin to a melt temperature of 450°-550°F].You also need chill rolls for rapid cooling.
But, why polyamid? It is not a good electrical insulation never-the–less it has very good mechanical properties and is very hygroscopic that means if it is wet the insulation properties will be even lower. We used once the polyamid for D10- military field telephone- but, actually, the insulation was extruded polyethylene and the nylon was only the resistance jacket. Even polyamid extrusion may be a problem [and may be you'll need a preheating of the wire before].
Regards

 

[pkelecy]

Thanks for the additional suggestions.

One thing I didn't make very clear is that this winding is actually wrapped around on itself (similar to a roll of tape) rather than being individual conductor segments stacked to together. So a busbar manufacturer might find it challenging to make. However, we have the fabrication of the "raw' winding (or roll) worked out. Insulating is the main issue.

Powder coating sounds promising. Since it uses electrostatic forces to attract the powder (I believe), it should cover edges especially well (which is good). What I'm not sure about is the film thickness. I'd like to keep that between 0.5 to 1 mil, if possible. I don't know whether powder coating can do that, but will check with Rohmihaas.

I mentioned polyamide enamel earlier because that's commonly used in magnet wire, and it seems to adhere very well based on my experience. But I really don't know much about electrical insulations, and if there are better choices for this application, please let me know. This conductor is not round however, but rectangular in cross-section. So conventional die drawing techniques won't work in this case. One process that looks ideal is "MEDIS" developed by Mitsubishi. It uses electro-disposition to apply the insulation. It works especially well with rectangular conductors (in fact, I think it was designed for it) since the voltage applied to the conductor creates electrostatic field concentrations at the edges, which in turn cause the insulation layer to be thicker at those points (where it's really needed). Unfortunately, that process appears to be proprietary to Mitsubishi, and not generally available.

Anyway, thanks again for the suggestions. They've been helpful. Any others are appreciated.

 

[ScottyUK]

Polyamide or polyimide? Two very different materials! Polyimide is typically used for electrical insulation in severe environments: mechanically tough, resistant to most solvents, and good temperature performance for an organic material.


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If we learn from our mistakes I'm getting a great education!

 

[sreid]

MWS has flat wire products if that's of any use to you.

http://www.mwswire.com/ribbon.htm

They also have a nice table to the types of insulations they supply.