It says in the technical datasheet of Easy Composistes out-of-autoclave Prepreg XPREG XC110, that for curing the "minimum vacuum pressure is 10mbar". This is a pretty low value. There are many vacuum pumps that can only achieve 50mbar, for example.

So my question basically is: why so low? To reduce the probability for pinholes? Because the relative gain in pressure when going from a 50mbar vacuum pump to a 10mbar vacuum pump is very small when you compare it to the outside pressure of a thousand mbar (well: 960mbar where I live).

The reason for such a low vacuum is, being out of autoclave, you are only relying on the atmospheric pressure pressing on the bag (due to being under vacuum) where as under autoclave conditions, you could have several times that pressure forcing the pre-preg onto to mould. This means every bit of pressure counts in terms of helping ensure the resin flows to the surface and you avoid pinholes or voids on the laminate surface.Reducing the level of vacuum means more chance of pinholes.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

So using a vacuum pump that achieves 1mbar is strictly superior to using one with 10mbar?

Yes if your pump is capable of 1mbar of absolute pressure, then it is closer to absolute vacuum than a 10mbar capable pump and thus a better level of vacuum is achieved.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Okay so lets assume I had an autoclave capable of generating an overpressure of 10bar (a whopping ten thousand mbar). Additionally the prepreg in its mould is vacuumed but now the difference between the mould pressure of 10mbar or 50mbar is even smaller: when the autoclave pressure is 10,000mbar, reducing the pressure in the mould from 50mbar to 10mbar results in a pressure increase of just 0.004 percent. So just from a pressure standpoint this gain is marginally. Is it still worth it to go for the 10mbar vacuum pump over the 50mbar pump in order get out that extra bit of air and thus decrease pinhole probability?

So in short: when using a 10,000mbar autoclave, does it matter if the pressure in the mould is 10mbar instead of 50mbar?

You don't need to use an autoclave with this pre-preg system, although you can if you wish.

Overall pressure is the relevant factor, it doesn't matter if it comes from a vacuum pump, platen press or an autoclave.  A vacuum bagged laminate inside a 10 bar autoclave will have way more overall force applied against it than the difference between say a 10mbar pump and a 50mbar pump.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

So what is the minimum overall pressure that is required for XC110? Or formulated in a different way: at what height would one need an autoclave with positive pressure?
Your vacuum pumps reach an internal pressure of just 0.03mbar. But at a height of 900 meters above sea levels the outside pressure drops from a little over 1,000mbar to roughly 900mbar. At 500 meters outside pressure is around 950mbar.

Thanks.