Moulding and casting Info
Types of silicone:
Tin cure silicone
- Less expensive
- Less issues with curing inhibition
- Shorter life span that platinum cure
- Will dry out over time
- Can shrink
Platinum cure silicone
- More expensive
- Lives a lot longer
- Does not shrink as much
- More issues with curing inhibition
Tin cure silicone seems to be the type most used.
Silicones have different shore hardnesses. The A scale is for softer plastics while the D scale is for harder ones. Lower number = softer, Higher number = More rigid.
Bill Doran suggests that a 30 is okay for most general purposes.
Tin cure silicone tap plastics rtv (rtv= room temperature vulcanisation), durometer: 25/30
Mold max 30 Reynolds advanced materials
Mould star 20 T - Transparent, cures really fast
For brush on moulds:Rebound 25 (platinum cure)
Silicone comes in two parts, you have to mix these two parts in equal ratios. Once you have mixed these two parts, the silicone will usually have lots of bubbles in it. To help get rid of these bubbles you can use the “bombs away method” and pour your silicone from really high up. As that strand of material drops, the bubbles will pop out of it as it goes. This is the cheap method, however it is best to buy a de-gassing chamber
Casting Material - Urethane Resin
- Comes in two parts
- Is a plastic resin
- Urethane does not like moisture, make sure you put the lids back on the resin containers, the moisture in the air will fuck up your resin!
- The resins come in different colors, curing times, shelf lives and shore hardnesses.
Good brands of resins to use:
- Smooth Cast 300 - General Purpose, good starting resin - cures white
- Smooth Cast 65D This resin has a higher viscosity so it will stick better to surfaces, especially useful when rotocasting - cures white
- Smooth cast 325, cures transparent
Making the Mould
- The first step when making the mould is to create the clay barrier. This barrier should cover half of you object. Non sulphidic clays are good for making the barriers. Plastalina Clay is a good brand. Make sure the seam line is clean and at a 90degree angle from your object.
- Then make registration marks in your clay. Make them about ______ This distance from your object, this will ensure that the two halves of the mould will line up as close as possible.
- Now mix up your silicone. If you are worried about any of the fine detail on your object getting lost, you can brush on a layer of silicone onto your object, making sure your brush it into all the crevices and fine detail spots. Allow this layer to set.
- Turn over the mould and now get rid of all the clay to expose the other side of your object. Cover the first half of the silicone mould with mould release then pour silicone over the other half of the object.