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Block Mold - Injection Type | Page 4

Block Mold Injection 22

Figure 22

 

Rubber bands are used to hold the mold box together while it is being assembled.

Block Mold Injection 23

Figure 23

 

The base of the mold box, as well as all vertical seams are sealed using a hot glue gun.

Block Mold Injection 24

Figure 24

   

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.


Block Mold Injection 25

Figure 25

 

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.

Block Mold Injection  26

Figure 26

 

When the silicone rubber has cured, the mold box is removed to reveal the completed two part silicone mold.


Block Mold Injection 27

Figure 27

 

The mold halves are spread apart and the original model is removed.

Block Mold Injection 28

Figure 28

 

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.


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