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:
The 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.
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
kelv@kdweston.biz
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