Gidday,
I've spent a bit of time talking to SP Systems about Amine Blush and mix
ratios. I'll talk about each in turn:
AMINE BLUSH
Quote: "Amine Blush which you mention in your letter we call Amine
Bi-Product but it is the same thing. The Amines in the epoxy hardener will
react with any moisture in the atmosphere as the epoxy cures. This will only
occur after the epoxy has started to gel and will continue until a
reasonable state of cure has been reached.
This bi-product feels greasy or sticky dependant on the system and the
amount of moisture in the atmosphere. The slower the hardener the longer the
epoxy has to react wiht the moisture. I WOULD SUGGEST THAT ALL THE AMPREG 20
HARDENER YOU ARE USING PRODUCES BI-PRODUCT TO A GREATER OR LESSER DEGREE BUT
THE SLOW HARDENER PRODUCES THAT UCH MORE SO IT IS MORE EASILY DETECTED
Without curing the epoxy under a vacuum or in a laboratory whth zero
humidity there are only two ways of overcoming the productionof bi-product.
1. Use a Peel Ply which a Nylon 66 woven material which is Silicon Free.
This is applied to the surface of the laminate and 'wetted out' whth the
epoxy system used.The laminate is then left to cure as normal. When the next
stage in the laminating /coating is to be carried out, the peel ply is
pulled from the surface. This leaves a perfectly prepared surface for
secondary bonding or coating as the bi-product which forms is removed on the
top surface of the peel ply.
2. The second is to wet sand the surface after the epoxy has cured, as the
bi-produce is water soluble, please note that dry sanding only clogs the
paper and smears the bi-product across the surface but does not remove it.
THIS BI-PRODUCT MUST BE REMOVED BEFORE THE NEXT COAT OR LAMINATE LAYER IS
APPLIED AS ADHESION TO THE PREVIOUS COATING/LAYER WILL BE GREATLY EFFECTED.
I later asked him about using vinegar to wash down the surface,prompted by
other e-mails where it has come up as an option. He explains:
"As to your question over why some people are using vinegar,the reason for
this is that if the bi-product is left for any length of time it bakes onto
the surface and can be very hard to remove. Then it is some time necessary
to a 50/50 mix of vinegar and water. The vinegar is a mild acid which in
conjunction with a 'scotch Brite' pad will remove even baked on material. If
the bi-product is not left for any time, it will not be necessary to use the
50/50 mix but only water.
Thats it! As a comment, there has been extensive dialogue about using Peel
Ply over the entire surface. The general consensus is DON'T DO IT!! Read
your Aircraft Spruce and Specialty Catalogue, read previous posted messages,
speak to Graham Singleton etc.So that only leaves the washdown option. You
may well ask why this isn't included in our manuals (or at least I don't
think it is). The a/c no doubt has it's composite design to achieve Ivan's
goals, and no doubt it does. At the same time,SP have suggested a treatment
to the surface prior to filling and painting. I know what I will be doing!
RESIN MIX RATIOS
My other topic Ratio mixing is prompted because I have purchased a set of
electronic scales accurate to 1/2 gram i.e. in 1 gram readout
increments.What follows is SP Systems response on the required accuracy of
mixes required by them. I should add that I made simultaneous enquiries to
Europa regarding mix ratios,whilst organising the purchase and shipment of
my wing and fuselage kits. Europa say a maximum of 5%! Does anyone remember
what I said once about "Believe nothing because a wise man said it" etc
etc.!!!!Don't stop asking questions! Anyway SP's next response follows to my
questioning about ratios:
"Your question about the accuracy of mix with Ampreg 20 has raised a debate
within our company. This is not the first time this qiestion has come to
light, but it has never been as fully explored in the past.
I am sorry to inform you that the current consensus is that the accuracy we
have been recommending to people in the past is not sufficiently strict, and
that it should be tightened to 1% of the total mix.This will mean that your
current scales are sufficient for 100 gram mixed but are not for 50 gram.
I am sorry that we can not recommend or guarantee that any of our products,
when mix ( with or without an error in measurement) can be used for a
specific application without carrying out trials under the same conditions.
Re Resin Pumps he says:
"I believe the other measuring device you mention is supplied by a company
in the US called J&B Products. If this is the case we have a sample which is
currently inder going trials, but as yet we do not gave a accuracy figure
which we could give you".
There is more talk to SP coming re postcuring. I have it on good authority
( an airlines fibreglass workshop staff), that postcuring needs to be done
in an exact way to maintain stability of the polymers, especially with
regard to how the piece is brought back to ambient i.e. the temperature drop
needs to be certainly controlled. This would suggest a more professional
method of oven design, but I'll reserve my judgement till I know more, and
I'll post it,hopefully more succinctly..
Regards
Tony Renshaw
Builder No.236
The Aussie Connection
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