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Advanced composites possess
a characteristic called the glass transition point, Tg. If the
product is subjected to temperatures past the Tg, they will most
likely fail. Delamination, warping, vastly reduced properties
and other problems can occur at these temperatures. Strength,
rigidity and basically all normal physical properties are greatly
affected by temperatures higher than the parts Tg. Even if the
part hasn't reached the Tg temperature, typically a parts properties
start to drop off before that Tg temperature is reach. So it
has a larger affect than one might think even at lower than Tg
temperatures. |
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Even though Dream
has always used epoxy, it is not enough to fabricate them at
room temperature. Room temperature cured epoxies ($17-$65 per
gallon) have a maximum Tg of about 120-140F. These are resins
that are not designed for an elevated temperature cure cycle.
Cooking low temp resins DOES NOT allow them to have an increased
Tg point. It merely ruins the resin. |
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Dream uses epoxy because it has higher properties
than other resins. The particular epoxy that Dream uses also
is slightly higher in performance than average epoxy. It is more
expensive, ~$100/gallon, but we feel the performance gain is
worth the very mild increase in material costs. |
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Dream conducted tests
on a black surfaced material. The surface temperature went to
164F in direct sunlight even though the ambient temperature was
only 70F. 100-120F ambient temperatures, like Arizona and New
Mexico summers, will easily push the surface temperatures of
black/dark materials to over 200F. Therefore the use of products
that were made with conventional room temperature epoxy or resins
(vinyl-ester or polyester) in direct sunlight, even on very mild
days, passes the Tg of the resin systems. This is the reason
all home built aircraft that use non-elevated cure cycle resins
are painted white or a very light color. It is also the same
reason Dream only used room temperature resins for a very short
testing period. |
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Since that time parts,
including secondary bonded areas, are cooked in a computer controlled
oven ($45,000+), among other pieces of equipment.
The interior
usable space of the oven is roughly 6'x12'x6' (LWH) or 432 cubic
feet. The oven can easily handle 1m telescope structures.
Dream
currently uses a high temp epoxy that can be cooked as high as
350F, if the application requires such properties. |
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Dream is always striving to make its products last
longer and hold up in more
conditions. Daytime use of even clear-coated carbon fiber telescopes
(charcoal black in color) will now be able to withstand the high
surface temperatures associated with such exposure. This is also
due to the multiple coats of UV protectants applied to the composite
surfaces. |
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To learn more about advanced
composites, click here. |
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