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Jabiru J450 Constructors Manual
General>Composite standard procedures
Tuesday, April 6, 2010
15 of 343
Epoxy measuring and mixing
Quality assurance and record keeping
In Australia the SAAA require that a wet and dry bulb thermometer is kept in the room where
the lay-ups are done. A further requirement is that a sample of each mix is kept as a quality
assurance step. In your builders log you should record the wet and dry bulb temperatures, the
mix number (all samples to be numbered) and the batch numbers of the resin and hardener.
Samples of resin batches should be retained, dated and labelled according to the Task on
which the batch was used. Samples should be inspected after 24 hours to ensure correct
curing. The cured resin should be hard and “scratch-able”.
A good sampling device is a small plastic medicine measure cup: wipe the interior of the cup
with wax before each use to facilitate easy removal of the sample. Samples should not exceed
10mm in depth otherwise the heat generated during curing may affect the result.
Measuring epoxy
The Epoxy system used for the production of Jabiru Aircraft is LC3600, which is mixed in a
3:1 ratio, which means that 3 parts of resin are mixed with 1 part of hardener.
The best method for ensuring accurate measuring is to use a digital kitchen scale as described
in the section
General>Required tools and equipment
which is what we do in our factory.
Curing times
The LC3600 is a room temperature (24° Celsius minimum) curing epoxy so it requires no
elevated temperature curing unless you are working in a particularly cold climate or perhaps
during winter months. The recommended curing time depends upon temperature but a
minimum of 24 hours is good rule of thumb.
Mixing epoxy
When mixing the epoxy the mixture will initially appear 'cloudy' then as you mix the mixture
will become clearer but 'stringy', keep mixing and finally you'll be left with a clear mixture
with no sign of being 'stringy'.
Note
: The smaller the mix the larger the possibility for errors, so consider combining several
tasks and doing a larger mix wherever possible.
Mixing in flock
As a general rule, mix flock so you can take a sample with a mixing stick turn it over & it
does not dribble off. If it is a little too runny, add more fibre flock.
Mixing epoxy and milled cotton flock together creates an excellent filler which is used in
many places to form edges and fillets. The mixture is referred to as 'flock' but is often used as
a verb, for example: "flock the bracket into the position shown...”
Mixing 5-minute Araldite
5-minute Araldite is a fast curing epoxy and is very useful for bonding non-structural items
into place. If you find that your Araldite won‟t cure it is usually because 2 lots of the same
part were used instead of 1 each. We have all made that mistake at least once.
Mixing 5-min Araldite with cotton flock creates a good paste for 'bedding' parts into place.
Same rule applies as for mixing Epoxy.