There was a thread some time back concerning Araldite 420 and whether it was any
good after the "expiry date" on the can. My Araldite has a listed expiry date
of April 21, 2006. The gist of the thread was that as long as the inert
materials
were not mixed and were stored properly, the Araldite should work fine.
Several people suggested testing the bond on scrap to determine if "old"
Araldite
would hold.
In order to test the adhesion integrity of Araldite 420 past expiry date on the
can, I set up a test as follows:
I cut two pieces of scrap F04 PVC foam approximately 3 inches wide and 10 inches
long. I coated both sides of each piece with micro slurry, then laid up two
pieces of bid at 45 degree bias on each side (similar to the construction of
the aft bulkhead). The two pieces (I will refer to each piece as a
mini-bulkhead)
were laid up on June 10 and 12, 2007. After more than a month of post-cure,
I mixed a batch of Araldite 420 from containers opened on July 25, 2007, and
mixed in flox per the manual direction. I used this mixture to bond the two
previously laid-up foam/glass mini-bulkhead pieces together with a 6 inch
lengthwise
overlap on each piece.
After nearly two weeks of post-cure, I clamped the glued-together sandwich to a
piece of half-inch plywood on my shop bench. The piece was clamped in such
a fashion that when weight was applied to the end most distant from the bench,
force would be applied so as to try to pull apart the bond between the two
pieces
(in other words, the test of the bond was in tension rather than compression).
The first test involved hanging 23 lbs of weight 2 inches from the outer end of
the piece (8 inches from the edge of the plywood on the shop bench). The bonded
sandwich deflected approximately an inch, with no sign of delamination or
failure of the bond. The second test upped the weight to 36 lbs. A slight
additional
deflection occurred, with no delamination or failure of the bond. Finally,
57 lbs. of weight was added. The piece deflected several inches and held.
A slight cracking noise was heard, then the piece failed, approximately a
quarter inch beyond the edge of the plywood away from the clamps. The piece
did not fail all the way through, but remained deflected in approximately a 40
degree bend. The fiberglass layers held the parts together, and when removed
---From the clamps, some flexing was required to break the part completely in
two.
The Araldite bond remained completely intact.
I then took the remaining piece and clamped it in a steel vise bolted to another
bench. I then pulled on the upper mini-bulkhead piece as hard as I could, and
was able to make the sandwich fail. Once again, the failure occurred just
beyond the point of clamping, and the failure was limited to a break in the
bid/foam
laid-up piece. The Araldite bond again remained completely intact.
I don't have the math or engineering skills to calculate the forces in the my
(admittedly)
informal test, but it was comforting to see that a properly laid up
fiberglass/foam sandwich will fail before the Araldite bond. As one poster
to the earlier thread questioned, is there a "life" to the other materials we
are using in our planes, such as fiberglass cloth? It seems that if anything
on my plane is going to break, the Araldite bond will be the last thing to go.
I feel pretty comfortable using my Araldite as is.
Any comments to this post would be appreciated, and if anyone would like digital
pictures, I could try to upload them.
Thanks,
George Powell
Visit - www.EuropaOwners.org
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