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Finally I gave a try to the West Systems 105-A epoxy and 209 extra slow hardener - superawesome chemicals! It gave me over an hour to wind the coil, unwind it and rewind it back until epoxy mix started to enter the jelly state. Then I put the coil into oven to cure at ~60C. The epoxy get hard after 2 hr (I checked periodically), but I took coil out after 3hr. Seems to be totally ready. Now the bad news. Epoxy is so fucking good that it bonds even to the plastic. Those thick soft plastic rings on the sides I used to separate metal cage from epoxy had some scratches. They come out as chopped pieces. But scotch tape easily peels off. So the sides of the winding form must be covered with scotch. Better to have a separate thin scotch rings, as some minor sticking still occurs.
Some more info. I tried to unwind a layer from that coil - wire came out without insulation. So the West Systems epoxy, unlike the others, bonds to the wire' enamel harder, than the enamel to the wire! Soaking coil in the epoxy is very important for coilgun coils, because the wire experiences a very hard pressures and pulse vibrations, which damages wire' insulation and tends to unwind the coil, changing it's shape. In addition, the common issue is a barrel squeezed by wire. Strong epoxy holds the coil in shape and prevents the inside turns from gripping the barrel. So for coil winding, I would definitely recommend everyone the West System 105 epoxy and 209 extra slow hardener - it is better than any other epoxies I ever used. Thanks again to the Ash Small for aiming me at that product! :)
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
klugesmith wrote ...
3. @Ash: where did you get that 100 degree figure? That isn't very hot for most electronic materials and components. Glass-epoxy multilayer circuit boards are lead-free soldered at over 220 degrees C. What do you think IC packages are made of? A quick Internet search turns up this slow-curing potting compound rated for service at 275 degrees C.
I was specifically referring to the 'general purpose', high-strength epoxies being discussed here. The West System datasheet for 105/209 epoxy/hardener combination here: ]tds_105_209.pdf[/file]
Gives a 'heat deflection temperature' (ASTM D-648) of 117 Farenheit (~47 Celcius).
Heat deflection temperature and ASTM D-648 are described here:
Some epoxies are claimed to withstand ~180 Celcius, or so, maybe even higher, but not a lot higher. I imagine physical strength isn't a major issue in the applications you describe, and some softening/weakening can be tolerated, but 'general purpose' epoxies will generally fail at not far above 100 Celcius, They will certainly be a lot weaker if they don't actually fail.
I was once told by an 'epoxy boffin' that 'different chemistry' is required at above 200 Celsius, or so.
@Yan,
EDIT: The specifications for the 'MG Chemicals 832HT High Temperature Epoxy Encapsulating and Potting Compound ' product linked to above makes no mention of strength, and is quite lacking in any technical specifications, but then, it's designed for potting, not for strengthening/re-inforcing a coil-gun coil.
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Coil construction
