How to Inject
Silicone Molds
· Often castings of an object are made by
injecting material into a mold. The mold may be made up of two or more pieces,
which are closed before injection begins. The main benefits of this process are
reduced seam lines in the product as well as allowing you to use only as much
casting material as you need with little waste. When injecting material into a
closed silicone mold, it is essential to take several steps to insure that the
casting comes out right. If your mold was designed for this purpose with the
holes already in place, begin at Step 6.
1
Determine
the best injection point in your mold. Ideally, this should be a place that is
not easily seen on the cast, such as the back or bottom. Mark the point with a
marker.
2
Determine
the highest points in the cast. Mark these with the marker.
3
Drill a
hole in the silicone at the injection point. The drill bit should be the same
diameter as the tip of the syringe. Use an extremely sharp drill bit to prevent
the rubber from grabbing onto the bit. It's a good idea to have a friend hold
the mold in place just in case the bit grabs the silicone; otherwise the entire
mold will spin and could cause injuries.
4
Drill
small holes in the highest points. Use the smallest bit you have for these as
they are simply to allow air to escape as you inject the casting material.
5
Mark the
holes in the mold shell and drill it out as well.
6
Apply a
thin coat of silicone mold release or hand soap to the entire inner mold
surface with a paintbrush. Allow it to dry and buff out the excess with a paper
towel.
7
Close the
mold and strap or clamp it shut tightly.
8
Mix the
casting material according to its instructions.
9
Pour the
casting material into the syringe.
10
Insert
the tip of the syringe into the injection hole and inject the casting material.
11
Allow the
casting material to run out of the air release holes for a few seconds before
plugging each one with a bit of clay. This allows any air bubbles in the
casting material to escape the mold.
12
Once the
mold is filled, remove the syringe and plug the injection hole with clay.
13
Allow the
casting material to cure and dry.
14
Remove
the cast from the mold.
15
Remove
the knobs left by the holes with a razor blade and sandpaper if needed.
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