Vacuum Infusion of Lightweight Materials

Groper's right. I would skim coat it first, having looked at your website.

It will be very unpredictable.

 

Do not reduce the vacuum too much after infusion as you may not have enough resin to fill the now less compresed laminate stack, 80 - 85% works for me. You can minimise your mixed in air but the only way to eliminate dissolved gass is to de gass at full vacuum.

 

I have to say, even though I learned how to do half my build from Andrew (thank you), I have never had any problems with off gassing of resin.

Maybe different types of resins behave differently in that respect?

 

Catbuilder, yes i beleive you have had off gassing problems... that rear beam stiffener you did, you had zero leaks and a high vacuum which are conducive to outgassing of dissolved gasses in the resin and materials stack. I beleive this is what happened on that particular part you had issues with

I have infused all my panels so far at a fly turd off absolute vacuum (-101.3kpa) nearly every panel has some minor surface blemishing somewhere... the only place it can come from is dissolved gasses in the resin, gasses released during reaction or remaining air/gasses/liquids in the dry stack thats still escaping before i let the resin in... these expand under the reduced pressure and show up after the infusion has been clamped off...

 

Nope. That wasn't off gassing. That was from a pump failure when I didn't change the oil enough times. It lost the capacity to move the required volume and the infusion slowed down.

Noticing this, I changed pumps and let air in from the vac line while doing so. That's what causes the beam to have some air entrapment.

 

Once the vacuum is established, there is no volume for the pump to move... this is why you can infuse massive panels with very small CFM pumps. Its the vacuum pressure not the pump CFM thats important. So if the infusion slowed down beyond what is normal as things progressed, the pressure must have dropped, did you notice this on the pressure gauge?

All im saying is, ive read mulitple reports and studies on vacuum infusion, and many of them address the formation of voids (for muliple reasons) despite having no leaks in the setup. AndrewK mentioned an example that he did, whereby he did a perfect test panel on a pane of glass to see both sides of the infusion and during the resin flow everything looked perfect. After clamping the resin line, the perfect laminate began to form tiny bubbles in it for no apparent reason... The gas has to come from something inside the bag... it can be in the materials, reactions occuring between chemicals in the stack, water vapour, you name it... like is said, EVERY single panel i have done has imperfections - nothing major, just minor cosmetic stuff and slight translucent fibre whitening in places etc... im going to try reducing the vacuum pressure after clamping off the resin line to see if i can eliminate this as id like to strive for perfection if possible. I have been advised that this may or may not help depending on who you talk to - i can only try it for myself...

 

Heres a pic of what im talking about... i beleive most of the trapped gas is coming from the resin as i do not degas the resin first and cant see a practical way of doing it when your mixing up 20kgs or more for a large infusion without a purpose built degassing setup.

This is a close up pic of part of one of my beams, a 1/2in wide strip of peel ply has been torn back about 5 inches to give an idea of size. Notice the streaks of whitening between the uni fibre tows and also the small air pockets between the peel ply and laminate? Notice the air pockets occured where the laminate changed thickness from a single 1150gsm triax to where the additional 2 layers of 1000gsm UNI tape begins? The entrapped gas tends to collect in places like this...

 

Huh? Why are you arguing fact?

I have never had resin off gassing. Never made a panel that came out like the one you pictured.

Also, why are you arguing vacuum pumps? Were you here? Do you understand *why* I switched pumps? The pump stopped working because I didn't change the oil enough. The infusion progress stopped due to that. The pump could no longer move the required cfm to pull the resin at an appropriate rate. A stopped infusion risked the resin kicking before I could finish. Why argue this stuff with me?

Attached, is a picture of the infusion I did on Friday.

See any off gassing issues?

 

Not arguing mate, just probing possibilities as often things dont always happen for the reasons we think they do...

Consider this... in a perfect world with perfect resin, with ZERO dissolved gasses in both the resin AND the stack... in theory you could pull an absolute vacuum, shut off the vac pump and close the isolation valve, then open the resin line and begin infusing the part without the pump EVER having to run whilst the entire part infuses until its finsihed... the vacuum already in the bag would take care of everything...

I beleive the reason you cannot do this in the real world, (besides not being able to achieve a TRUE absolute vacuum) is because there is always dissolved gasses in the resin and laminate stack which expand under the reduced pressure and need to be constantly removed as the infusion progresses. All we can do to alleviate this, besides degassing, is provide a pathway for these gasses to escape rather than become trapped... i could show you parts of my beam that look just like your photo CB, i chose to show you a small part with the blemish... have you never experienced a blemish like in my photo?

 

Catbuilder; all resins suitable for infusion will be the same they will reach an equilibrium at 1 atm, when the pressure is reduced to 0 atm dissolved gases will be liberated untill a new equilibrium is reached.
Disolved gas issues are minor compared to mixed in air, pacsail's problem would have been mostly due to mixed in air.
Your laminates have not suffered this as the plastic over the top infusion media provides a very low path of resistance compared to the reinfocement. So any mixed in air is transported out through the mesh, later on any off gasing that takes place during the gel time rises up into the mesh.

Pacsail's tests show how effective over the top mesh is in transporting this air out. The scrim back block core is also least forgiving with mixed in air.

 

My experience is that resins come with a nice amount of air or other gasses dissolved in it. Even when not mixing, you can pull gas out of epoxy or polyester resin. Mixing surprisingly accounts for only a small amount of air, which is mixed in at relatively large bubbles, which escape more easily.

another factor is water. Experiment with some 5% water, mixed into epoxy resin. Most resin allows this to be mixed in even without getting cloudy. But watch the reaction when hardener is added. (nice experiment). Water is in everything. Fabrics, core materials, etc. Sometimes I see the vacuum meter drop to 20 mbar quickly, then stall. After a certain amount of time it suddenly drops further. At 20 mbar the water enclosed started to boil off.

And keep in mind that foams might take some time reaching a new quilibrium when under vacuum. Same for Soric, which takes at least 20 minutes. Only after that a drop test is possible.

 

Thanks, I'll run a test on the mold, about one foot wide across the middle, where it is about 10 feet across. What is bog?

 

bog, is slang for resin thickened up with powder modifiers such as micro balloons, cabosil etc your fibreglass supplier will have these powders and if you wish to "bog" your core to fill up the cracks and eliminate the racetacks, ask them which one will yeild the lightest weight - probably a micro balloon or lightweight fairing type powder which will also be easy to sand so you can get teh core a bit fairer and take out some of the "blockiness" etc...