1. Mixing the components
Add 100 parts of SILBIONE RTV 4524 A to 100 parts of SILBIONE RTV 4524 B.
The two components may be intimately mixed either by hand or using a low-speed electric or pneumatic mixer to minimize the introduction of air into the mixture.
After mixing parts A & B it is recommended to degas the product to eliminate the air introduced in the mixture; if the material is processed using an automatic dosing machine, each of the two parts has been previously degassed and air is not introduced during the mixing.
SILBIONE RTV 4524 A & B is degassed under a 30 to 50 mbar vacuum.
When the vacuum is applied the product expands 3-4 times its initial volume and bubbles form on the surface. Once bubbles disappear, the mixture collapses back to its initial volume. To complete degassing simply wait several minutes before releasing the vacuum, the product will then be ready to use.
Releasing the vacuum once or twice during the operation will improve and facilitate gas removal.
A container with a high diameter/height ratio will ease the operation as well.
Pour the degassed material slowly in a steady stream from one edge of the mould box so that the material flows evenly over the model minimizing the entrapment of air bubble under the flowing rubber.
SILBIONE RTV 4524 A & B cures at room temperature (23°C) regardless the thickness of the parts. Polymerisation occurs without formation of heat.
Room temperature curing assures the lowest possible shrinkage, if accelerated cure is desired, mild heat should be preferred. To minimize shrinkage cure the elastomer at maximum temperature of 60°C for 1-2hour, higher temperatures will cause higher shrinkage.
Conversely at lower temperature polymerization is much slower, at 20°C some hours may be necessary to complete cross-linking.
Be aware that contact with certain materials can inhibit the curing of this RTV:
- Natural rubbers vulcanized with sulphur.
- Polycondensation RTV catalysed with metal salts.
- PVC stabilizing agents.
- Amine cured epoxies.
- Sulphur containing clays.
If doubts exist it's recommendable to run a quick test with a small quantity of material in order to assess compatibility. Take duly note that cross contamination due to not well cleaned tools or devices is frequently the main causes of inhibition. The best way is to use only dedicated gear when processing polyaddition RTVs.