A word of caution for those post-curing flying surfaces with blue foam
cores: stick to the upper temperature limit of 50C in the Europa Build
Manual quoted below. While the Gurit datasheets for Ampreg 20 and 21
also specify elevated post-cure of up to 80C, this may be used for other
parts but is too high a temperature for the blue foam.
Some years ago the operator of a commercial oven was being sued because
they had heated a Classic wing to 80C for 5 hours instead of the 50C for
8 hours that had been specified by the owner. The result was a wing
sagging over the supports, just like the cautionary tale of the Quickie
builder mentioned on Page 37-3 of the Manual.
Regards,
Mike
Dr Mike Gregory
Europa Club Safety Officer
01480 451655
07885 355765
-----Original Message-----
From: owner-europa-list-server@matronics.com
<owner-europa-list-server@matronics.com> On Behalf Of Kelvin Weston
Sent: 29 May 2020 15:35
Subject: Europa-List: Re: Post curing response
<mailto:kelv@kdweston.biz> kelv@kdweston.biz>
Gents
The Europa Build Manual calls for a post-cure, see Chapter 37, Page 2,
which states:
"The first thing that you need to do with your flying surfaces is
post-cure them at a temperature between 40 - 50C. This will improve
their strength and cook off any remaining volatiles and moisture within
the epoxy system.
Make a simple oven with foam blocks, timber or sheets and an electric
fan heater and cure your flying surfaces for 8-10 hours.
Do take care not to get them too hot and make sure that they are fully
supported."
The Ampreg 20 and 21 datasheets from Gurit shows an initial cure at a
minimum of 18C (ideally 24hrs at 21C) followed by an elevated post-cure
of 5 hours at 70 - 80C or 16 hours at 50C.
The datasheet also states:
=C3=A2=82=AC=C5=93The post-cure need not be carried out immediately
after laminating. It is possible to assemble several composite
components and post-cure the entire assembly together. It is
recommended, however, that elevated temperature curing should be
completed before any further painting / finishing operations.
Furthermore, care should be taken to adequately support the laminate if
it is to be post-cured after demoulding, and the laminate must be
allowed to cool before the support is removed.
When post-curing it is recommended to use a ramp rate of 10 degC/hour
when heating from ambient to the post-cure temperature, to ensure that
the thermal performance of the laminate stays ahead of the oven
temperature. Higher ramp rates may result in the resin softening and
distortion of the part.=C3=A2=82=AC=C2=9D
The resulting specs with standard hardener for Ampreg 20, 21 and 30 are
all very similar and result in a Tg of around:
58C - Room temperature cure (28 days at 21C) 73C - Elevated post cure
(16hrs at 50C)
The ultimate Tg for Ampreg 20 and 30 is stated as around 98C. Ampreg 21
was slightly lower at 91C
--------
Regards
Kelv Weston
Kit 497
<mailto:kelv@kdweston.biz> kelv@kdweston.biz
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