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Tom,
Bonding in these windows can be tricky. We have had a number of bad installations come through our shop for repair. The main cause is usually poor window prep. Sanding the bonding surface with 80 grit by hand is our proven technique. Using 9360 Hysol will help too but if you have any shine left on that bonding flange it will tend to release too easily. Try cross hatching (sanding in opposite directions) when prepping, it will help to remove the shiny streaks quickly.
While helping with the Columbia 300 development we had to prove to the FAA we had a repeatable method of prepping the windows. Sometimes we used a water break test to evaluate how well a surface was prepped. Using a fine mist spay bottle and distilled water you can spray the prepped surface and if the water beads up at all you aren't done sanding. This will also indicate the surface may be a contaminated with an oil or something. If the water flows out the bond will be good. Obviously you must allow the water to dry before applying adhesive. This method works well on composite surfaces in question too.
Other tips while installing windows include:
-Be sure to wet out both surfaces very well with hysol before applying the majority of the adhesive that will fill any gap. The "wet out" is critical to proper adhesion. Be aware though, if a surface is wet out and left to sit for more than 10 minutes you must agitate it again with your wet out tool before sticking the parts together. A very thin oxidization film can form on the surface of the wet Hysol and can act as a sort of release.
-Don't pre-load the window in place. If you have to apply lots of force in any area of the window to make it fit, something is wrong. Even if the bond holds and looks fine this can still lead to a failed window over time. We usually see crazing (tiny cracks) develop near the area of stress in the window.
-Don't squeeze out all of your adhesive. If you push so hard on your window that you can see (looking through the window at the bond) areas of composite because the adhesive is thin, this isn't as good. It's best to have this adhesive be at least .010" thick to do its job.
Matthew Collier
Fibercraft Inc.
541-419-5634
www.fibercraft.us
On Sun, Nov 20, 2011 at 6:48 AM, Tom <Tom@wellswoodturning.com> wrote:
I installed two windows in my ES with Hysol 9394. I followed the
instructions
explicitly and after cure (14 days)there were no air gaps or voids in the
bond
area. As I was removing the clamps after cure that held the window in place
I
noticed small areas near where I pushed on the fasteners debonded. By
pushing
on the fiberglass around the window from the inside I could see the Hysol
debond
from the plexi glass. I ended up removing both windows by debonding them
using
this method.
I had been using Hysol 9394 as that at one point in time was the Hysol being
sold by Lancair. After reviewing the spec sheets of Hysol 9360 vs 9394 the
major difference noted was the peel strength of the 9394 (5 Lb/in) vs the
9360
(50 Lb/in) per the data sheets. I did a crude test using 9394 and 9360
bonding
a piece of prexiglass to a piece of fiberglass and allowing it to cure for
14
days. I found that the plexiglass could be removed from both simply by
flexing
the fiberglass although the 9360 seemed to be slightly better bond.
So...before
I bond these windows in again I would like to be sure of what to use. Has
anyone else experienced this phenomenon?
The supplier of the Lancair windows uses MIL-S-8802 to bond windows to
aluminum
and indicated they thought some builders had used it to bond windows to
fiberglass. They also indicated they used Weld-on 40 to bond fiberglass to
the
edge of the windows with good results.
Any insight on this would be greatly appreciated.
Blue Skies,
Tom
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