Is it possible to suck out too much resin during infusion?

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#1

Hi Composite Experts,

When I am doing a vacuum infusion I have heard people say things such as “I leave my vacuum pump on for 12 hours”.

Well, In order to be absolutely certain I am holding a full vacuum I also leave my pump on.

What I do is clamp my resin feed line so no more resin can enter my infusion. BUT, I notice that all of the extra resin will go into my catchpot. This leads me to my question. Is it possible that by leaving the vacuum pump on, that I can de-saturate my layup and make it less saturated?

My part is purely structural and not cosmetic so I don’t care about the way it looks. I am mostly concerned of reaching the perfect resin to fabric ratio. Any tips or comments on sucking out extra resin?

#2

Yes, it is. Usually happens if the vacuum line is touching the part or too close to it. A general rule is keep the vacuum line atleast 25-50mm away from the edge of the laminate and use a piece of peel ply to bridge the gap. The peel ply is permable enough to pull air and good vacuum on the part, but not permable enough to pull out too much resin. Additionally there is a product called “MTI hose” which his only permable to air (impossible to suck in resin), you can also try this.

#3

I’ve heard about the MTI hose. It sounds like an awesome product, except what if I have “too much resin” in my laminate. Won’t the MTI hose leave all of the resin inside of my infusion, so that I’ll have to do some precise calculations in order to not have excess resin inside of my laminate.

#4

You also seem to be clamping the resin line too late. If you are waiting for dry spots to fill due to race tracking, then you need to re-orientate how your resin/vent lines are. As HoJo mentioned, if your mold is big enough, you can clamp your resin as the part hits Edge Of Part (EOP), and leave a layer of peelply as a “delay line” to suck out excess resin.

But normally, NO. Resin can not get sucked out too much. If it does, that means that you have a leak, OR your flow is so fast, it’s not saturating the fibers enough, and after clamping, the resin slowly gets sucked into your tows, and it looks like your part is resin starved.
The point of VARTM is that you are pulling out all the air. Resin will then enter all those vacuumed voids. If you keep pulling vacuum and there are no voids left, the resin has no where to go. It can go out your vent line, but you will never achieve a resin starved part. There are limits to how much can be sucked out (~55% FVF), and that is fine with industry for parts. It’s HARD to get a “ideal” FVF with vartm anyway, without additional steps.

Good paper: http://depts.washington.edu/amtas/events/jams_10/pap10-Heider.pdf

#5

Ahhh, okay. So assuming I have a good vacuum with no leaks, and I am having a lot of resin enter my catchpot this is “OK”. I won’t be “sucking out” too much resin. Once it hits the catch pot it (or before, if I use a peel ply stop) then it is okay for me to clamp the inlet line.

I guess, an analogy is that the cloth becomes “wet like a t-shirt”. Once it is wet, you can’t get it more wet, but you can get it less wet by sucking out the excess water/resin; but you can never make it dry…

#6

It is not correct that you can not suck out too much resin. If you clamp you resin feed and leave the vacuum open the vacuum is stil working on the laminate. A brake zone with peelply will slow down sucking out resin, but it will not stop it.
Depending on pot life, temperature, viscosity, part size… you will suck out more or less resin.
Also your laminate will not be homogenious because you will suck out most resin near the brake zone and not from the middle.
Also if you have even small voids / micro voids in your laminate the vacuum will expand them and that will push resin out.
If you have a low viscosity resin with a long pot life you can suck out that much resin that you will have pinholes, voids and a VF up to 70% wich is much to dry.
If you work with a closed system like MTI hose or the VAP process in the article riff posted your vacuum will not affect the part because once the part is filled no resin can pass the membrane so that the full ambient pressure is working on the part wich makes sure that you have a homogenious laminate without pinholes and voids.
Of course you can oversaturate your laminate because you can not suck out the excess resin, but if you do not infuse to much you also save resin.
Just place your resin pot about 1m below your part so that you create a light pressure difference which helps you to controll your VF.

#7

I’ve noticed dry spots near the hose on a few of my parts that more and more resin kept on getting sucked into the hose during the infusion process. The parts that resin doesn’t flood the hose usually come out better than those infusions that do suck up too much.

However sometimes I even notice dry spots directly where I infuse along with the resin near the vacuum. Anybody have any idea why that is? I usually don’t get dry spots in between those two areas. But every now and then I do.

#8

I usually just clamp off the feed once it’s wetted out to my liking and then leave vac on. I don’t use a catch pot, on my small parts, i usually just make a resin trap which is basically a bag tube with some fiberglass to carry vacuum. The resin moves so slowly after passing the break before the witness line that it only travels some inches through my resin trap. You can always do test panels and try the various methods and see which one contains the amount of resin your shooting for. Structural parts are better with lower resin content, within reason.

#9

If the bag has a good seal no need to leave the pump running.
Chris
www.carbonfibreworks.co.uk

#10

agreed, my garage projects usually don’t seal perfectly… :frowning: I hate ruined parts cause of crappy vac integrity!