Vacuum levels doubts ....

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#1

I will soon be doing my first large part infusion, a 33 feet boat hull, we will use vinylester infusion resin and have a big doubt in regards to the best way to do it, so far, and as far as I know, the best advise has been in order to avoid a too dry part has been to infuse at maximum vacuum levels and when part was infused reduce the vacuum level to 90% (or 27 inches of Hg), this can easily be done in small parts with only one resin inlet, and when vacuum is reduced to 90% the stack decompress a bit absorbing some extra resin into the stack making it a bit more resin rich and better looking.

My doubt arise as how this could be done in the case of a sequential strategy in a boat hull because then at the end of the infusion all the closed resin inlet tubes would have to be reopened for the extra resin to enter the stack and maybe this could cause uneven thicknesses, on the other hand if the hull is infused at a constant vacuum level of 90% since the beginning, the thicknesses are more likely to be equal BUT maybe as not all gasses have been removed ( there are still 10% of them )there is more tendency to getting some bubbles in the laminate, so what should be done to achieve best results? simply infuse at constant 90% vacuum and be done with it ?? or infuse at 98.5% and forget about the laminate being slightly dryer than if done at 90% ???

Please help me solve this “existencial” doubt … :confused:

#2

That’s a big pull, 33’! I’m researching doing just the interior of my hull at 31-1/2’. I’ve gotten a lot of help over on the boatdesign.net forums (sorry if this is a breach of protocol). With larger projects like this you have, according to my research, is divide the project up into smaller zones that you infuse in sequence. I was considering doing this.

http://www.compositescentral.com/showthread.php?t=9499

As it turns out that’s not he best way but the approach is still sound. There’s a ton of vids on Youtube of boat hulls being infused. Go over them a few times you’ll start to see the logic in the process. I’ll be redoing my infusion strategy soon.

Good luck with your project.

Rick

#3

I replied in your indicated thread, and I find quite interesting your concept …

In regards to our project you can take a look at it here if you wish, you may like it …
http://www.thehulltruth.com/boating-outdoor-photos/372020-raptor-project.html

#4

Never reduce the Vac level for a infusion! You need a vaclevel of less than 20mbar absolute! Even for a big boat hull.
If you wish a more resin rich laminate you can get that also with a high vacuum level. It just depends on the amount of resin you infuse.
It is also very important that your bag is tight, at these big parts I always make a double bag for vacuum integrity.
If you leave the resin inlet open for a longer time even after infusion has been finished you will get a VF of about 35-40% if you wish.
Easiest way is to work with MTI hose, so you can not suck out resin and it is easier to get a lowe VF. And because of the closed system the laminate will self leveling after infusion is completed.

#5

Hi DD, thank you for your help, by the way I will soon be ordering from you some 25 more DD clamps, they worked delightfully and we do not like working with anything else …

So in regards to slightly incresing the percentage of resin of our laminates, you suggest that instead of reducing vac levels to lets say 150mb abs, it will equally work to simply keep the resin inlet open for longer time ??

#6

Thank’s for the flowers :slight_smile:
Never reduce the Vaclevel, this will only cause more problems. You dont want more air in the laminate, you want more resin.
So how should it help you to have more air in the system to get more resin in it :wink:
Maybee I should make holidays at the canary islands :smiley:

#7

Definitely about the holidays, we have very nice winters here, as you know Gran Canaria is very popular as a holiday destination, and no flowers, your clamps have been very good, very safe, well made stuff.
Back to composites, we have two PVR 40 m3/h which produce a steady 20 mb abs, but we also have a “refrigerators technician” double stage 9 m3/h pump that can produce a vacuum as low as 4 mb abs, and we are thinking about connecting it to our vacuum manifold to use it to produce a deeper vacuum when the two large pumps have reached their maximum level of aprox 20 mb maybe this additional smaller pump will help in reducing the vacuum level inside the bag to maybe 7 - 8 mb or ideally if the bag could have a completely 100% perfect seal it should reach the maximum of the pump wich is 4 mb … maybe it is not worth the effort, but the pump is already in our shop …

We are going to follow your advise and use a double film aproach to ensure the complete seal. thanks for that;)