What is the difference between addition and condensation curing?
Two-part room-temperature-vulcanizing silicones (RTV-2) come in two systems. Both produce an elastic silicone rubber but differ in chemistry, processing and applications.
| Property | Addition-curing | Condensation-curing |
|---|---|---|
| Catalyst | Platinum | Tin (in the hardener) |
| By-products | none | small amounts of alcohol |
| Shrinkage | virtually none | low |
| Heat | strongly accelerates curing | accelerates only slightly |
| Sensitivity | can be inhibited by sulphur, amines, tin | insensitive |
| Mixing ratio | fixed, e.g. 1:1 or 9:1 | variable hardener amount (adjustable pot life) |
Addition-curing silicones
The first choice when dimensional accuracy, potting in closed housings or fast heat-accelerated processes are required – e.g. in electronics potting or precision mould making. Pot life can be extended with WACKER INHIBITOR PT 88.
Examples: ELASTOSIL RT 601 A/B, ELASTOSIL RT 604 A/B, ELASTOSIL M 4601 A/B, ELASTOSIL VARIO 15.
Condensation-curing silicones
Robust to process and tolerant of contamination, they are well suited to mould making, casting and potting where slight shrinkage does not matter. Pot life and cure can be adjusted by the choice and amount of hardener.
Examples: ELASTOSIL RT 426 with WACKER Härter T 40, ELASTOSIL M 4470 with WACKER Härter T 37, ELASTOSIL RT 563, ELASTOSIL RT 480; fast hardener: WACKER Härter T 47.
What about one-part silicones?
One-part silicones (RTV-1) such as ELASTOSIL E43 or ELASTOSIL N2199 cure with atmospheric moisture from the outside in. They are suited to bonding and sealing in thin layers, not to thick potting.
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