Resin infusion and resin content 1

[sorenfdk]

Hi everybody!

I know that it's possible to achieve a very low resin content when using resin infusion. In fact, someone once told me that he would have a hard time getting a higher resin content than 40% when using infusion.

My question is this: Is this low resin content regardless of the type of reinforcement? Will CSM and UD have the same low content?

You might ask "Who would use resin infusion when working with CSM?" My answer: "Boatbuilders!"

If you have any typical numbers, please share!

Best regards,
Søren Flening

 

[Compositepro]

The bulk of the fiber reinforcement is the main factor that determines resin content. One way to view fibers under a vacuum back is as a spring in a cylinder with a piston on top. As you evacuate air from the cylinder the piston (vacuum bag)compresses the spring (fabric). By controlling the resin pressure or vacuum level you can control fiber volume within a range that is determined by how "spongy" or "springy" is the fiber reinforcement. Normally at the begining of infusion the resin is at ambient pressure and the uninfused fibers are at full vacuum. The fiber volume will be low at the injection point and high at the flow front. Often the injection port is closed when the flow front reaches the vacuum port. This cuts-off any more resin from entering the bag and then resin will flow from low fiber volume areas to higher fiber volume areas until resin pressure is equal in all areas under under the bag (if the resin does not gel first). A controlled vacuum can also be applied to the inlet port or vent port. It can get very complicated. The vapor pressure of the resin is also a factor. Highest fiber volume is when all of the bag pressure is used for fiber compaction. But at that point the resin pressure is zero (full vacuum) and most resins will boil due to volatile components.

 

[sorenfdk]

Thanks for your answer, but how does this translate into numbers?
Ideally, I would like some numbers for the resin (or fiber) content of CSM, WR and UD when using resin infusion. It's only for preliminary design work, so they don't have to be 100% exact - typical numbers will do.

Best regards,
Søren Flening

 

[Compositepro]

Almost all the infusion work that I am familiar with is with woven fabric. Normally you can get 50 to 65% fiber volume depending on weave style and fabric lot. Plain weave will not pack as tightly as satin weaves. 55% is typical. With uni-fabric its possible to get over 70% fiber volume using vacuum infusion, but not easily. When the fiber is packed that tightly it is very difficult to infuse. Chopped strand mat will give 30% to 50% fiber volume. As a point of interest - carbon paper which is sort of like CSM but the fiber is dispersed down to idividual filaments requires at least 85% resin content (21% F.V.)to make a void free laminate using 85 psig autoclave pressure.

 

[sorenfdk]

Thanks - That was just the answer I was looking for!

Best regards,
Søren Flening

 

[amorrison]

A consideration . . .

If the mold is "tall" when the resin is introduced there is the static fluid height pressureization effect that should be considered ie. the vacuum pressure at the bottom of the filled bag will be less than at the top resulting in a higher resin percentage at the bottom.

pressure from static head at the bottom

= specific weight X height

If s.g. =0.8 (good first assumption)
then = 0.8(specific weight of h2o)x height
= 0.8(9810kN/m^3)x height in meters

 

[rowen01960]

An additional consideration ...

FV can and is "tailored" with the use of rigid/semirigid IML tools thereby controlling the infusible volume... the volume can be controlled modified with a vacumm sealing chambers on removable "hard" stops. You are only limited by budget and imagination.

robert