This personal mail is reposted to the group by request of the
reciever... This might be of general interest... It presents a technique for
impregnation of the glass before setting it to the surface...
Here is how I proceed for this kind of lamination technique:
- Use a big worktable, ideally as big as the surface of cloth that
you want to impregnate.
- Cover the table with a protective sheet, a layer of cotton felt
(typically the one used for vacum lamination, about 3 mm thick), and a black
protective polyethylen sheet. This last sheet must be relative thick
typically the thickness used for thick plastic covers (.12 or .15 mm
thickness) so that it doesn't buildup any ply. A black sheet of packing
paper and a thin transparent plastic does the job also. Tape this sheet on
the sides of your tables so that it won't move. Your worktable is now ready...
- For the lamination itself use a thin transparent polyethylen
sheet, this sheet must be able to accomodate some kind of plastic
deformation with little effort. The best I've found are protection sheets
slightly thinner than a standard plastic bag. Put a sheet on your worktable
and cut the glass cloth you need to use. Personally I don't try to
impregnate more than 2 layers of 300 g/m
2 or 3 layers of 180 g/m
2 at a
time. If needed also put the layer of peel ply. Once your layers are cut and
ready for impregnation, weight them. Prepare the resin and weight the
quantity you want to use to impregnate the glass and peel ply. Depending on
the resin and tissue, you can get down to less than 45% resin in the final
laminate, so at the begin use the same weight of resin and tissue and try to
decrease the amount of resin until bubbles can't be eliminated or all the
cloth can't impregnated.
- Pour your weighted resin on the prepared cloth and put another
polyethylen sheet over it. To impregnate the tissue squedge the resin
through the plastic sheet with a relative stiff squedger (stiffer than the
rubber ones used for hand lamination). The only thing to pay attention to is
not to damage the plastic sheet. Squedge both sides to eliminate the plys of
the plastic sheet, and until you see no bubbles on your laminate (that's why
you need a black background, it's far easier to see the bubbles). The less
resin you have used, the longer it will take until no bubbles can be seen
through you laminate. You can then position the laminate over the part to
cover and cut it at the good size (that's far easier to cut with the plastic...)
-Then eventually coat you foam surface with resin and micro to fill
the foam pores and finally peel gently the plastic sheet on the inside of
your laminate and place it on your surface. The external plastic allows you
to eliminate the bubbles between the foam and the laminate without any risk
to displace some fibers... etc. When you're satisfied, just peel the
plastic... et voila... you should get a perfect laminate garanteed with no
resin-rich pockets and as few bubbles as possible.
Some final recommandations:
- If you need to laminate more layers than it is possible to
impregnate in one time, you can put the supplemental layers one by one and
be careful to chase the bubbles between each layer... Or you can safely let
the first coats set (with a peel ply), and put the rest of the tissues
later... after removing the peel-ply and a slight sanding to get a flat
surface...
-Be sure to use clean polyethylen sheets with no wax or other
coatings present on the surface... for obvious reasons..
-As usual practice before trying it to your left (or right) Europa
wing... The key is in the quality of the plastic sheet...
-Use a resin with a slow hardener, it takes always more time than
expected... The slower I have goes up to 210' of working time... (R&G resin
system)
-If some bubbles persists, a few drops of resin will help to
eliminate them...
Hope it helps... And that these long explanations are clear enough...
Just try it before claiming it's a good method... I know of people
who never catch it...
I'm not yet building an Europa, but I'm mandated by the Swiss EAA to
check the structural calculations for the Swiss Certification as
homebuilt... That's why I keep lurking the mailing list... I've some
composite experience gained on some friend's planes, some gliders repairs,
some airplane models... and others...
I'm open to any sugestion to increase the efficency of this
method... I'm not named God...
Luc JOB Mat. sci. Eng. Swiss Federal Institute of Technology
'If nothing else works... change the standards'
1963 JODEL DR-1051 HB-EBM, wood, fabric, 2+2, <6 gph @ >125 KTAS...
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