Silicone rubbers can be widely used for mold making.
Perhaps their most important feature is that they do not adhere (stick) to most of the materials therefore they are excellent for casting of products and prototypes.
They are available in transparent appearance which allows the casting process to be controlled visually. In other cases, also the color version can be used.
The following main considerations should be taken into account when selecting silicone rubbers.
- Hardness (Shore A)
- Break elongation
- Biocompatibility for medical application or food industry
- Thermal resistance for casting of low temperature alloy
The two-component RTV (room temperature vulcanisation) silicone rubbers can be distinguished as
- Polyaddition silicone rubbers
- Polycondensation silicone rubbers
The main features of condensation silicones
- Low tear resistance
- Mostly not translucent 1-2% shrinkage after fully being cured
- Usually 1 day curing time
- Vacuuming is not allowed, so it is difficult to make a bubble-free mould
Addition cure silicones
- High tear resistance
- Translucent version is the most widespread design but easy to color
- Practically 0% volume shrinkage
- Various curing times, which can be increased and decreased with additives and/or thermal treatment
- Can be freed from air bubbles by vacuum