Moulding and Casting

Tuesday 4^th October

Unit: PROPERTIES &TRANSFORMATION

Demonstration: Moulding and Casting

Today we learnt how to make a mould and cast an object. To make a mould you need a 3D object and put a dowel on the end to make a clean mould and can also create a pouring hole. Andy glued the dowel onto thermo plastic:

·         5.10mm higher then, the highest point of the object.

Diagram of the box with
the object inside.

He then cut 4 walls using the thermo plastic (the box can be made of anything though). Using the plastic weld he bonded the walls to the base, then welded wall to wall, base to base etc... Check for gaps, and fill in with a hot glue gun.

Next he mixed up the mould rubber and hardener (10 to 1). The hardener is a green colour so you can tell when it’s mixed up. When mixing it will bring air into the mixture, which you can get rid of by putting it into the vacuum degassing machine. While in the machine you must wait until the dial go’s all the way to the left, you must also let the air back in slowly, roll the mixture till all the surface bubbles are gone. After he poured the mixture on the side of the box, not onto the object because this could cause bubbles. He gave it a wobble to make sure it was level, and wait for 4 hours (using fast cast) or 24 hours (slow cast).

Then he made up the cast mixture using A & B resin (1 to 1), shaking both bottles first and checked for the right pigment. For this cast he made up 100g (50g to 50g) and mixed them up well. He poured it into the mould about half way and gave it a shake to let the air escape, then continued to fill it to the top.

For a flat mould (like a medal) he poured a little casting mix onto it and pushed it into the nooks and crannies. After he filled the rest up and put some tape covered plastic on top and weighed it down with something, then wait for it to dry, clean up and paint.