Block Mold - Injection Type | Page 4
Rubber bands are used to hold the mold box together while it is being assembled.
The base of the mold box, as well as all vertical seams are sealed using a hot glue gun.
In preparation for the second silicone rubber pour, the inside of the mold box is coated with mold release. It is particularly important to cover the bottom half of the cured silicone mold as silicone will stick fast to silicone. So spray at least three light coats of mold release on all silicone rubber surfaces allowing each coat to dry before adding the next coat. Use light coats as the silicone will pick up all drip marks if the release is allowed to run.
The two-part silicone mold rubber is weighed out, combined, mixed and vacuumed just as was done with the first half of the mold making procedure. It is then poured, holding the container high above the mold and in a narrow stream to further aid the escape of any residual air bubbles. The pouring is always in one spot to allow the liquid mold rubber to envelop the model, further pushing out any trapped surface air. When the mold box is filled, the silicone is left undisturbed to cure.
When the silicone rubber has cured, the mold box is removed to reveal the completed two part silicone mold.
The mold halves are spread apart and the original model is removed.
Now it is time to survey the inner mold to determine where to place air holes (sprues) in all the high stops to eliminate air traps which will prevent the casting material to evenly fill the mold. A small hollow tube with one and sharpened is fitted to an electric drill and bored completely through he rubber so it come out the bottom of the mold.
Click below to continue: