Bond overcoats on magnetic wire - electrical heat sealing?

[DAlbertson]

I'm winding a set of coils from 37 AWG magnet wire with a single-thickness polyurethane/nylon combination insulation (NEMA MW29-C) and a bonding overcoat of Polyvinyl Butyral.

The bond overcoat can be made liquid with either Isopropyl Alcohol or heat. If heating, then a temperature of 110 C to 140 C is recommended to liquify the overcoat. Heating can be done in an oven, or by running a current through the magnet wire.

The coils have 24 layers of wire, and the application puts a maximum of 4 lb-force axially on the coil.

1. Can someone give me guidance as to the voltage and time duration to make a good bond, without damaging the insulation?

2. Would it be reasonable to wind without a bobbin ("free-standing coil") using only the bond overcoat to keep the coil together?

3. How does the quality of a Polyvinyl Butyral bond compare with vacuum infusion with varnish or epoxy?

Thank you very much!
David

 

[hacksaw]

the current rating is pretty small for #37 wire, use external heat

 

[DAlbertson]

Hacksaw,

Thank you for your comment! You're right, a tray of bobbins going through an oven might be the simpler solution anyway.

Any thoughs on the quality of bond produced by the polyvinyl butyral overcoat versus vacuum infusion with varnish or epoxy?

Thank you again,
David

 

[sreid]

1) Bond quality. Every Loud Speaker Voice Coil is Heat Bonded as far as I know.

2)I heat bonded [in an automated coil winder] by using a temperature controller with an IR temperature probe pointed at the coil. A relay put voltage on the coil and we let the Temperature Controller hold the temperature [relay Bang-Bang]for a few seconds then shut off for cool down.