Hello ,
I have an idea which i want to share with you for criticism.
If i dont have an autoclave and i just vacuum bag my prepreg
then would i get the same result with an autoclaves part if
i vacuum baged my part and then apply physical pressure of 3,
6 - until there it is easy but i can get i think up to 10 bar
with a piece of silicon or hard plastic that would be surounding
my part and get inflated from a plug which would be outside of the oven.
So my part would have negative pressure and also positive pressure from outside.
How does this sound to you ?
Thats a process that is done in the industry, also like building tools that can be closed and pressurized.
So if i use this method i dont need an autoclave right?
And the parts are the same quality as autoclaved ones?
How do you want to get 10 or even 3 bar pressure with a silicone or plastic?
Silicone can be used to exert huge pressure if you use its CTE to your advantage. Silicones expand a lot when heated, not sure of an exact figure in terms of psi but it’s easily enough to break your tool if you don’t build it strong enough. I also know it’s enough pressure to use regular pre-pregs and get pinhole free results, so it works in that regard.
It’s limited by the part/tool design though, obviously you would need to be able to remove the silicone after the part has cured.
what about making your own autoclave using an older compresser cylinder and welding on a flange that can be quick released ? i mean you only need to go to 5-6 bar ?
Haha, compressed oxygen and heat… Don’t do it near your loved ones!
lol mother-in-law included ?
An autoclave isn’t that complicated or dangerous when done right… Compressed air to start diesel engines is about 30 bar. Divers fill cylinders to 200 bar. so 5-6 bar at 120 degrees celcius? I don’t know a lot of people who would xxxx that up.
Anyway, a guy here in NL made his own. I would like a safety valve to dump excess pressure, and a valve which must be opened before the door can be opened, on a tested pressure tank. Other than that, if the tank can handle the pressure and heat, and you got some braincells, then it should’t be too hard to keep it safe.
The problem of prepreg is that, even if you find the way to correctly pressurize your piece, you will have to find a way also to heat it to 120°C, without damaging anything. By doing like you said, there would be a problem due to air expansion if you heat it. So the only way to be able working on prepregs is to construct an own autoclave, even a home made one.
My guess is to use an old cylinder to do it to make a home made pressure chamber: You simply cut it and then add a flange on which to bolt a lid to it. Then, if you have access to a compressor or compressed air, you can use it to fill the chamber, maybe also using vacuum bagging if you already have a vacuum pump, to reach the pressure you need without much effort. Now, for heating it you may use a heating resistance to put inside the chamber, but you must find a way to monitor both temperature and pressure (and, so, to intervene to lower pressure when it will rise too much), just because if you simply pressurize air and then heat it, there will be an explosion of the chamber due to air expansion!)
So, it’s quite complicated, and that’s why prepreg is mainly used in industrial applications, not in home made stuff.