In 1980, Silmid began trading as a supplier of silicone products into the aviation market. Since then, our portfolio has extended to a number of other chemistries, but silicones still make up a large part of our business.
Our current silicones portfolio includes products from key brands such as Dowsil, Xiameter, Momentive and Novagard.
One Part or Two Part?
1 part silicones are standalone products that cure with no additional support. This is through Room Temperature Vulcanisation (RTV), meaning the product will begin to harden when exposed to temperatures of around 20°C. These products benefit from ease of use, as they require no mixing.
However, when depth is an issue, a 2 part product can be used. These products cure with the help of a catalyst or curing agent, meaning the cure spreads evenly throughout the silicone resulting in an even cure. This is often referred to as encapsulating or potting.
Acetoxy Cure or Neutral Cure?
With 1 part silicones, there are different cure systems available, categorised by the chemical given off during the curing process.
Acetoxy silicones give off acetic acid when they cure. This results in an unpleasant vinegar like smell, but can also lead to issues with the substrate depending on the material used. They are still heavily used due to cost effectiveness.
Neutral cure silicones do not give off any odour, but more importantly do not produce any corrosive chemicals during the cure that can damage components or the substrate. This is especially important in electrical applications. Neutral cure silicones can be further broken down into oxime cure (giving off Methyl Ethyl Ketoxime) and Alkoxy (giving off alcohol).
The difference between flowing (self-levelling) and non-flowing silicones is determined by their viscosity. Lower viscosity products tend to have better flow properties and are useful in hard to reach applications. Non flowable silicones are thicker, but are ideal for vertical applications where you do not want the silicone to run.