Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Mon, 09 Jun 2003 16:32:04 -0400
Message-ID: <redirect-2409001@logan.com>
From: Newlan2dl@aol.com
Subject: Re: [LML] Re: Tool time-void content
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Hi Steve and others:

You bring up a good point Steve about void content.  It is very critical, however burping out air with a mat roller does improve the results significantly.  Yes, there are still air bubbles attached to the fibers but they are smaller and the void content is reduced.  Here is just as an example of how in one instance (remember that if you change one variable in composites, you change everything) results from unidirectional toughened pre-preg compared with an auto clave vs. a vacuum bag.  The vacuum bag laminate had a 1-2% void content (lab sample) vs. essentially 0% in the autoclave.  The autoclaved parts were 25-30% stronger.  Open layup can be very close to a bagged part at best but don't count on it.  And it does require some practice to get reliable bagged parts. 

So if you really want the best parts you can get, start bagging!  Pumps are available through Grainger.  You shouldn't need a lot of air flow, just high sustained pressure.  A 1/2 HP motor for large projects or a 1/4 HP for small parts should be fine using a standard carbon vane pump.  These should achieve a sustained rate of at least 26" of Hg.  You may also want to consider a valve a guage to reduce this for thin laminates which can be over-vacuumed.

Dan Newland