Resin infusion and resin content

[sorenfdk]

Originally Posted by Herman

I am only available on the METS 2004 on tuesday and thursday, by the way.

..and I'm there monday to wednesday. Monday and tuesday, I'm attending the HISWA Symposium, but if there are no delays, I'll try and catch you tuesday afternoon. If nothing else, then just to say thanks for your help!

[Not A Guest]

I don't do resin infusion or use CSM but ...

41% fiber content for UD
32% fiber content for BD

work well for me as design estimates. They work well for mixes of UD and BD.

[petereng]

Hi All,
I do a lot of infusion and testing these are accurate;
1) UD 25-28% by weight resin in glass
2) WR and CSM 30-35% resin by weight. I hope you find this helpful. Even if this is an old thread at least the info is here.

Peter S

[Herman]

What is the density of the resin used? Or in other words, what is the Vf (volume fraction) you are working with?

[petereng]

Hi Herman,
With glass the Vf is usually around 50%. So if resin density is 1100kg/m3 (cured resin could be 1050 to 1250 depends on if PE, VE or Epoxy and supplier)and glass is 2550kg/m3 (glass can be 2500 -2600 depending) then Rw=30% and Vf=50% density=1827kg/m3 and 1000gsm=0.78mm.
I usually use Rw=30% as the starting point even for CSM. Most of my customers are getting <35% defineatly for any cloth. Well stacked and consolidated UD I've built at Rw=25% using double stage vacuum pump and very good processing. This would be Vf=56% Cheers Peter S

[petereng]

Hi All,
I've just reread the forum and there is some comments there about glass Vf>70% for UD. Using non autoclave processes this is unreasonable and very unlikley. I want to say impossible but who knows these days? Glass at Vf=70% is Rw=16% this is very dry for most normal purposes and processes. I have not been able to make a UD stack under Rw=25% using std vacuum processing. But I have seen Boeing Research data in which they infused the laminate (Rw=30%) then put it into an autoclave and squashed it to 15% Rw. Now Boeing use very special, very low viscosity and very precise processes to do this. The limiting Vf for infusion is the 10tonne per square metre the atmosphere can squash the laminate stack at sea level. This is a mechanical spring problem. The initial vacuum acts as a press and squashes the laminate until its springback equals the air pressure. The better the vacuum the thinner the dry laminate, but obviously it is limited. Then water in the stack evaporates and pushes out on the bag until it steams off. Could be 1 or 2 hrs to do this. Then if you use a very good vacuum process so outgassing from the laminate and some consumables at the low pressure does not de-compress the bag, the laminate will get a little thinner as the resin acts as a lubricant. If when the resin front goes by and the laminate gets a bit thicker this points at a vacuum integrity problem. But if it goes to plan this will be the thinnest the laminate can be made. So if you measure the stacks thickness under vacuum this should be its infused thickness (or a little thinner). Once you know the thickness you can back calculate what the Vf and Rw will be from the cured resin density and the fibreglass density. Hope this helps. Plus its approxiamately the thickness that can you measure the dry stack with a venier gauged squeezed tight with fingers. You must use full vacuum that the pump is capable of and never change the vacuum level while the infusion is happening. Major error if you play with the pressure. The aim is to have a constant bag volume for the entire process.

Cheers Peter S

[Herman]

So true.

I believe glass at Vf=70% mathematically is the best you can get.

What helps is a couple of hours or a night under full vacuum. This will compact the laminate as much as possible, so less resin is used. I always recommend infusing at the lowest pressure that can be reached. Be careful at 20 mbar or around that value, though. This can be caused by water flashing off. Give the vacuum a bit of time to dry out all the water. Many times I see the needle drop to 20 mbar, then stall for minutes if not an hour or more, then dropping again. (until the pump reaches its limit)

[petereng]

Hi Herman,
The theoretical for close packed hexagonal circles is about 95% Vf I think. Been a while since I calculated that.Cheers Peter S

[petereng]

Hi Herman,
Just recalculated theoretical max Vf and its 91% using hexagonal close pack. Cheers Peter S