Shrinking a model is a common request from users of mold making and casting materials. The challenge is to shrink a model uniformly and with a high degree of predictability. The procedure should also be repeatable. Overview; A user can shrink a silicone rubber mold 18% - 22% by mixing NOVOCS silicone solvent with the silicone.
1 - It is possible and extremely easy to reduce the size of an original without any special equipment. Comparison of original sized model measuring 3” (7.6 cm), a casting out of a mold reduced in size to yield a casting that is 2 3/8” (6 cm) and a casting out of a mold reduced to yield a casting that is 1.9” ( 4.8 cm).
2 - A decorative rosette will be used for this demonstration.
3 - The rosette master model measures 3” (7.6 cm) in diameter.
4 - A small base is used to mount the model.
5 - A hot glue gun is used to secure the rosette master to the base.
6 - A plastic cup is cut and used to contain the liquid silicone.
7 - Mold Star® 16 will be used in this project because of its quick setup and demold times.
8 - NOVOCS® is a silicone solvent that does not contain VOC’s.
9 - Mold Star® Parts A and B are dispensed in equal amounts.
10 - 2 parts of NOVOCS® are dispensed.
11 - Proportions; 1A:1B:2 parts NOVOCS®
12 - All components are mixed thoroughly for 3 minutes.
13 - Viscosity of the mixture will be very low.
14 - Silicone is poured over the model.
15 - Silicone is allowed to cure for 2 hours.
16 - Plastic cup is removed from around the mold.
17 - Rubber mold is carefully peeled away from the model. Rubber is very weak at this point and has low tear strength.
18 - Mold is allowed to shrink for up to 10 days. Mold is ready for casting and will yield castings that at least 20% in size vs. the original.
19 - Comparison of original sized model measuring 3” (7.6 cm), a casting out of a mold reduced in size to yield a casting that is 2 3/8” (6 cm) and a casting out of a mold reduced to yield a casting that is 1.9” ( 4.8 cm).