Flexible mould making silicones

2nd April 2017

Techsil Ltd

Peter Smith

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Flexible moulding is a very popular go-to system across many industries when faced with a part reproduction application. It is more cost effective than 3D Printing for small runs and a great alternative to solid mould processes such a liquid injection moulding or resin transfer moulding.

UK-based distributor Techsil has launched flexible mould making grades from Momentive Performance Materials. These new products will join the popular RTV664, an addition cure silicone system that can be used in compliance with US FDA food grade regulations. Momentive’s comprehensive mould making range includes 21 addition and 8 condensation cure silicones for prototyping applications and making moulds for complex precision parts.

TSE3478T is a 2-part addition cure silicone; this oil bleed system is easy to degas, has a handy 10:1 mix ratio and works to standard cure conditions. The product cures to a translucent rubber with a tensile strength of 6.0MPa, hardness of 40 (Type A), 380% elongation and extremely low shrinkage.1

TSE3480T is a 2-part addition cure silicone; a non-oil bleed system that offers improved mould life. As with TSE3478T, this system has a handy 10:1 mix ratio and works to standard cure conditions. The product cures to a translucent rubber with a tensile strength of 6.0MPa, hardness of 37 (Type A), 380% elongation and extremely low shrinkage.1

RTV664 is a 2-part addition cure silicone; it is a non-oil bleed system with a high cured shore hardness and can be used in compliance with US FDA regulations. This product has a shorter work life and demould time at room temperature than the new materials, but which cannot be further shortened with the addition of heat. RTV664 cures to a 62 Shore A, light blue rubber with very good tensile strength (6.4 MPa), 245% elongation and very low linear shrinkage.1

RTV7888-20 is a 2-part condensation cure silicone; this non-oil bleed system is best suited for soft mould making. Again, it has a handy 10:1 mix ratio and works to standard cure conditions; however unlike TSE3478T & TSE3480T, RTV7888-20’s work life and demould time cannot be shortened with heat. The product cures to a soft 20 Shore A light pink rubber with a tensile strength of 3.4MPa, 350% elongation and low shrinkage.1

Momentive flexible moulding silicones offer excellent transfer of pattern detail, a moderate to long mould life and extremely high casting temperature restrictions. These are features and benefits that are not typically seen in other flexible mould materials such as latex, polysulfide, and PVC – which generally do not tolerate exotherms higher than 65°C and have very short mould life.

Although the relative material cost of silicone for flexible mould making is high compared to latex and PVC, the increased economic costs of silicone can be offset by its performance attributes required for fine detail castings and productivity.