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Catalyst Ratios:
Editor''s Note: Below, we
conclude the discussion of
resin catalyst ratios that began
on page 6 of our first issue.
Selected graphs are repeated
for ease of reference.
L
earning how fast a
given resin gels is
only part of understanding
how to use it in
boatbuilding. Right after
the catalyzed material has
reached the rubbery "B"
stage, it is no longer liquid
but has little, if any,
mechanical strength. Demold
a part during the B
stage, and it is guaranteed
to lose its shape. Only
over a span of hours after
gel does the resin begin
to harden.
The Barcol Hardness
days in an effort to preserve
precious mold contours.
That''s wise, because the
aforementioned green
phase, when the resin hasn''t
reached adequate hardness,
can persist for hours or
clays, depending on resin
chemistry, catalyst and
promote r levels, and
ambient temperatures.
What''s interesting, however,
is that the resin keeps curing—and
getting harder—
for months and, in some
cases, even years. Your local
tech rep can help you select
catalyst systems to speed
hardness development and
increase mold productivity.
Print-through, the transfer
Tester is the industry''s
standard instrument for
assessing the degree to
which the resin has
cured. This device simply
carries out an accurate "poke test,"
ramming a precisely tapered needle
down into the part and measuring the
amount of penetration. Note that the
product data sheet (PDS) accompanying
every resin commonly gives two
Barcol readings: one for a mat-reinforced
laminate and one for a 1/8"-thick,
unfilled casting.
The latter figure is a result of the soCarelessness
in measuring catalyst and blending it with resin
can lead to big problems, including print-through, component
distortion, and blistering.
when they''re still "green" and wobbly,
or to slow production by leaving parts
in the tooling longer than necessary.
Buy a Barcol tester, and eliminate
costly guesswork. It will run about
$370 and is available from regional
suppliers, who can be contacted through
the manufacturer, Barber Coleman
Co., telephone: 815-877-0241.
called "lid test," where a puddle of
resin is poured into a plastic coffee-can
lid (conveniently about 1/8" deep).
Running lid tests, as well as checking
gel times (see last issue''s discussion),
will allow a builder to test the hardness
development of his resin. Get nervous
if your results don''t match the numbers
on the PDS. The Navy and the Coast
Guard want Barcol readings of at least
40 before the part is demolded, and
they insist on Barcols of 45 to 50 for
finished parts.
Military standards aside, it doesn''t
make sense to risk popping parts
6 PROFESSIONAL BOATBUILDER
Hardness Development and
Print-Through
Resin continues to get harder after
it gels. Quality-conscious boatbuilders
let parts sit in the tooling for a few
About the author: In addition to
being Professional BoatBuilder''s technical
editor, Bruce Pfund is a consultant
to material manufacturers and
fabricators in the areas of process
control, testing, and vacuum bagging.
He has 25 years of experience with
marine composites and boatbuilding.
of reinforcing-fabric and
core patterns to the outer
hull surface, often occurs in
parts that are well beyond
the green phase. In fact, it
is most likely to appear
after the boat has been used
in sunny weather for a period of time.
Dark-colored laminates are particularly
vulnerable, because they get
the most solar heating. In terms of
expansion coefficient, there''s a tremendous
difference between fiberglass
filaments and most resins. It''s on
the order of 50:1, so the print-through
phenomenon isn''t all that surprising.
The importance of catalyst ratios
in print-through shouldn''t come as
a surprise, either. Laminates that are
undercured or undercatalyzed, as well
as those that are slow curing because
of low catalyst levels, will be more easily
distorted by thermal stresses when
exposed to sunlight. No builder should
think of this as a problem that will go
away after a few weeks. Lots of boats
that looked great in Maine for a few
seasons have developed horrible
complexions after their first visits to
Florida. Slight undercatalyzation can
haunt a part for months, perhaps even
years.
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