Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml@lancaironline.net
Date: Tue, 04 Nov 2003 15:13:21 -0500
Message-ID: <redirect-2709700@logan.com>
From: Newlan2dl@aol.com
Subject: Re: [LML] Re: Closing Surfaces With Epoxy/Flox Vs. Hysol?
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Ooops, forgot about the other stuff.

Hysol is a high bond strength adhesive.  Jeffco and West System are also epoxies but a general purpose epoxy and if you talk to some formulators, they categorize it under "wood bonding epoxy".  The fact is that they are OK materials but not truly aerospace bonding adhesives.  They are designed to be good at lamination and good at bonding but not do a super job at each.

Saying "epoxy" to a composite person is like saying "metal" to an airplane designer.  It means nothing.  Another example is some of the carbon fibers I've used.  So are priced at $20.00 per pound (like 33 million modulus, 500 ksi tensile "generic T300) and other is $3000 - $5000 per pound specialty fibers.  This stuff may be 120 million moduls and 900 ksi tensile and almost zero coefficient of thermal epansion.  And is that difficult to use!

There are something like 200 + epoxy formulators out there buying 2 major neat resin suppliers (Shell and Cieba Geigy), and 50 or so cross linker (hardner) manufacturers.  Every combination of this makes a different product.

For myself, I really like to use toughened epoxy at every structural application I do.  Toughening adds an elastomer to make a cured part more resistant to fracture, fatigue and give higher bond strength, (most notably in peel).  The trade off is generally lower heat distortion temperature, higher cost and lower modulus of elasticity.  But HDT and modulus are able to be raised so they're not an insurmountable obstacles.