Hello, I’m going to use a silicone plate to generate pressure on the laminate in a closed mold system (fiberglass epoxy). Which thickness should I use for silicone? the single mold will have a 2000g/sqm layup
When you say silicone plate does that mean it is a rigid plate and not a flexible bag like a re-useable vac bag?
I was thinking to silicone rubber for the low cost and it can be found everywhere… I just need expansion, it will be placed outside the vacuum bag
I think getting just the correct thickness of silicone versus the cavity size and laminate thickness is the real key part, and why people don’t talk much about the details of this process. Trade secrets I’m guessing.
I have been trying this in various applications and the results have been widely variable.
For example, with small silicone pieces in a cavity (2 sq cm or so) I have trouble getting much compaction. Just one additional layer of fabric makes a large difference. I have to preload the rubber so it barely fits in with the fabric.
But I also broke a 5cm thick epoxy/aluminum granule mold with a (roughly) 300x150x10mm piece of silicone rubber because so much pressure was generated. It broke in the 10mm thickness direction, which is somewhat surprising, but I understand that the rubber behaves somewhat like a fluid as it expands.
I don’t know how to do the math to calculate pressure, but in my tests, a 70mm long piece of the rtv silicone rubber I’m using (BJB 5045) grew 1.8mm from 21 degrees C to 154 degrees C.
We had a piece in the press at tons of pressure and it was lifting up the press… some enormous pressures are generated. One of the engineers did some calculations and the pressures are easily over 150 PSI. I guess it depends on how much silicone you end up using and how high you cure at. The amount of expansion varies with different various rubber as well. Some have much better cte than others.
You need more compaction than the vacuum? And why not clamp the plate down instead of using silicone?
I intend to clamp the two moulds and use the silicone to get more compaction… thanks to everyone guys