I am currently doing a DIY project of making an extended swim platform for my boat.  The platform is fairly large measuring 8 feet x 4 feet (2.4 m x 1.2 m).  I am making a mold from a plug and then will make the actual 'part' from the mold.  The platform design is of moderate complexity, having a step-down section to it and 'pylons' on the sides. The total area of fiberglass is about 40 sq. ft. (3.8 sq m) due to the complexities of shape.  I plan on using VARTM in order to achieve good conformity of the fiberglass to the various shapes of the platform, and hopefully to apply the resin in one step vs. a more labor intensive process of hand layup.

I'll be using polyester resin to make the mold and vinyl ester to make the part.  One concern right now is finding ways to reduce the 'fill' time of the VARTM mold/bag considering that poly resin has a fairly short 'open' time as compared to VE or epoxy resin.  In order to get a reasonable thickness of laminate, I plan on using 3 layers of 1.5 oz chopped stand mat. Then I will add stiffeners and reinforcements as hand layup after the vacuum bagging is complete.   I figure that the faster I can get resin into the mold/bag and going through the flow media to all areas of the mold, then the more time the resin has to flow into and saturate the fiberglass.  My plan is to have lots of resin runners throughout the mold so that the resin does not have to travel very far.

One idea that I am considering is to pressurize the resin pot slightly, which is more typical of an RTM process, so that the resin is drawn through the tubing and into the runner system and flow media by both the vacuum from the bag and the pressure from the resin pot.  I have done some searching and have not found much in terms of trials and experimentation of actually putting pressure into the resin pot, rather than merely relying on vacuum.

My thinking is that with just vacuum to move the resin from the pot to the mold, you are limited to 1 atmosphere of pressure.  With both vacuum and pressure in the pot, you can go beyond 1 atmosphere of pressure.  (within reason of course).

I am wondering if anyone has thoughts, comments, or experience in using both vacuum and pressure to get the resin to move to where it needs to go faster than it normally would with just vacuum?  Thanks in advance for any comments/insight/adverse effects.

why polyester resin and not epoxy? because of the price? epoxy would solve your problems with the cure when you take a slow infusion resin. 
But if you choose polyester resin you should be ok with using a small amount of MEKP. Keep in mind that the polyester resin will boil under vacuum. 
0,6 bar should be the vacuum you are aiming for. 

About your pressure + vacuum, I think you'll have some problems. if you have -1 Bar vacuum and add +1 (or more) of pressure in your pot, you'll end up with 0 bar of pressure in your bag.
At least if I understood well what you are planning to do.



Matthieu Libeert
Founder MAT2 Composites X Sports
website: www.mat2composites.com

Poly tastes better

I figured with a delayed gel time that I can get from either MCP or TBC, then I don't need to pressurize the resin feed.  A bit of gravity would probably do the trick.

I'll keep an eye on the vacuum pressure.  Within the mold, the resin should 'feel' the pressure from the outside air pressing on the vacuum bag as it saturates the fiberglass.  I have done a couple of test infusions and no 'boiling/degassing' of resin. I was pulling about 25 in Hg (0.85 bar) of vacuum.    I could see that a rigid mold might have more of a boiling problem.

I'm still working out a few bagging seal issues on my swim platform plug, but hopefully will get the 'big infusion' done within the next 2 weeks.