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Date: Fri, 16 Jul 1999 02:56:47 -0400
To: lancair.list@olsusa.com
From: Marvin Kaye <marvkaye@olsusa.com>
Subject: Back to Bonding
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Posted for Guy Buchanan <bnn@abac.com>:

>I liked that a bunch but then I started thinking about how I could squeeze
>more juice out until the layers were just barely wet to get a lighter
>result.

Your statement caught my attention. It is possible to squeeze out too much
resin. All cloth, (even unidirectional,) has a material bulk packing
factor.  That is, there is a finite thickness to the cloth, and a finite
fiber volume.  This is true regardless of the pressure applied during
de-bulk and cure.  (Obviously the thickness and fiber volume will vary
substantially, depending on the weave and cure pressure.) The thickest cure
occurs during contact lamination, wherein no cure pressure is used. The
cured ply occupies approximately the same volume as if you threw it down
dry on the table. If you add pressure during cure you can reduce the
thickness and increase the fiber volume somewhat. If you roll a contact
laminate hard during de-bulk, you run the risk of removing excess resin.
What happens is that you locally reduce the bulk packing factor, rolling
the resin ahead. Behind, the cloth re-inflates to the same bulk packing
factor as when it came of the roll. This sucks a bunch of air into the
laminate resulting in a very porous, weak, and soft laminate. You should be
trying to achieve an exact fiber / resin ratio, no more or no less.

For your 7781/vinylester combination you would use 55.5% fiber and 44.5%
resin by volume, or 72% fiber and 28% resin by weight. This gives a ply
thickness of .0085". More resin weakens the laminate, but not nearly as
much as too little resin. (Data from HANDBOOK OF COMPOSITES, by Lubin.)

Guy Buchanan 
BUCHANAN & NEWCOMER


[Guy... please shut off the HTML and remember the subject requirement.
"Re: lancair.list V1 #49" doesn't tell us about which post you're replying
to.  Thanks.

<Marv>         ]

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