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A:
Virtually
any type of powder filler can be used in Smooth-On urethane
resins. Some examples of powder fillers:
-
Urefil™ 3
Crushed Ceramic • Play Sand
-
Urefil™
5 Woodgrain Simulater
• Micro Balloons
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Urefil™
7 General Purpose (also flame retarder) • Cab O Sil
-
Calcium
Carbonate • Metal Powders
-
Granite
Powder
You can
attain different resin effects depending on the type and
amount of filler that you add. For example, you can attain a
realistic marble effect by adding calcium carbonate and
pigment to our Smooth-Cast 300 resin. You can make
Smooth-Cast 320 plastic look just like wood by adding Urefil 5
filler. By adding metal powder to Smooth-Cast 325 resin, your
castings can have the look of bronze, copper, brass or other
metals.
Many
fillers cost a lot less than liquid plastics on a per lb./kg.
basis. As a result, the more filler you add, the lower your
cost per casting.
There are,
however, factors that will affect how well a filler works for
you and steps you can take
1.
Light vs. Heavy fillers – Lightweight fillers will have a tendency to float in the
resin and rise to the opening of your mold whereas heavy
fillers will have a tendency to sink in the resin and fall to
the mold surface. It is important to thoroughly mix the
filler into resin to minimize this effect. Otherwise,
castings may cure with areas of all resin and no filler and
vice versa. This will create a weak or brittle casting.
2.
Small vs. Large Particle Size -- Fillers of all sizes can be
used to create various effects, however, keep in mind that the
larger the particle size the weaker (brittle) the cured
plastic will become. The reason for this is that there will
be less urethane resin holding each individual particle
together. Smaller particle sizes generally yield a more
durable part.
3.
Fillers, in general, tend to contain and/or absorb moisture.
If filler does contain moisture, it will cause polyurethane
resin to bubble or foam. Eliminating moisture content in
fillers is accomplished by placing the filler flat on a metal
plate or cookie baking sheet in an oven and “baking” it for a
minimum of 2 hours at 150 F / 60 C. After “baking”, allow
filler to cool to room temperature and use promptly. If the
filler is allowed to sit for extended periods, it may again
absorb moisture.
4.
Pre-mix filler thoroughly with Part B of the resin
before adding Part A. Adding filler to resin that has both
components already mixed (Part A + Part B) will limit your
ability to
thoroughly mix the resin
5.
How Much Filler can I add to the urethane resin?
– This will depend on the particle size of the filler.
Smaller particle size fillers like cab-o-sil have a large
surface area and will absorb resin very quickly. The amount of filler that you add to your resin mix (A+B) is
up to you. Examples of filler “loading”
BY VOLUME
are as follows:
Liquid Plastic
Part B + |
Filler, Mix Well |
Add Part A,
Mix Well & Cast |
THIN MIX |
|
1 Part |
˝ Part |
1 Part |
|
|
1 Part |
1 Part |
1 Part |
|
1 Part |
2 Parts |
1 Part |
|
1 Part |
3 Parts |
1 Part |
|
1 Part |
4 Parts |
1 Part |
 THICKER |
Other Things You Need To Know
·
Increased viscosity – The viscosity of the resin/filler mix will increase in
proportion to the amount of filler added. The thicker the
resin and filler mix, the greater the chance for bubble
entrapment.
·
Increased Working Time & Cure Time –
pot life and demold time may be lengthened in proportion to
the amount of filler added.
·
The
finished look of the casting will change with the amount of
filler added.
·
Physical properties of the cured plastic may be diminished
in proportion to the amount of filler added.
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Smooth-On