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Bextrene Cone Coatings

 
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speakerguru
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Joined: 18 Nov 2005
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Location: Green Hut, Tovil

PostPosted: Sat Dec 27, 2014 12:36 pm    Post subject: Bextrene Cone Coatings Reply with quote

Extracted from an old thread and posted here as a "sticky" for reference re damping coats.

Bextrene cones had one coat of AD7 (which did stick to bextrene) and 2 coats of AD18 (which had the required damping properties but did not stick to bextrene) on the back. The front had only one, more or less cosmetic coat of AD18. It clung on but did not really stick. You could peel it off and recoat if required. The stuff on the back did the real damping and could be controlled by weighing the coated cone as you applied it. The front coat became thinner and thinner as years went by but was never left off because "you had to see" that there was damping compound being used. AD18 had various other internal KEF AD numbers as different thinned versions were used.

Although AD18 was a type of PVA, trade name "Plastiflex", it was a bookbinding adhesive. It was not a regular white glue wood adhesive nor was it made by Evode or Bostik. I'm sorry I can't remember who made it or what it was replaced with when it eventually became unavailable.
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Cigfran
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PostPosted: Sat Jan 09, 2016 11:30 am    Post subject: Reply with quote

A bit more information about coatings:

The rear coating that does stick is Bostik 4141
The front coating is Plastiflex P1200 made by the Borden Chemical Co.
I do not know if either of these adhesives is still available. A bit of googling suggests not.

The front coating also has the function of making the central dustcap airtight and stuck. The dustcap was initially held in place with a bead of cyanoacrylate around the edge before painting with Plastiflex.

4141 can also be heat bonded once dry, on some bass units it was used like this to bond surround to diaphragm and surround to chassis.

Hope that helps!
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speakerguru
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PostPosted: Sat Jan 09, 2016 2:10 pm    Post subject: Reply with quote

Well done. Thanks for filling in the gaps. I'd forgotten Borden.
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