Trapped air bubbles

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#1

Hi,
Have a look at the photograph.
It is a Carbon-Epoxy cylinder of 370.0 mm Diameter.
It is mfged by Closed die and Va-RTM process. The resin is injected form bottom to top.

Problem: We observed such pattern (Refer pics) on the some of the surface of the part. especially on the top side .

They are very small in size and are large in number.

FYI: I do 2 hours of degassing before impregnation also. It has successfully passed UT also. So i believe it is on the surface only

Can some one say why this is happening in spite of vacuum & degassing?

#2

you have degass resin and dry fabric for 2 hours, or only one of the two?
Can be also a too fast infusion, in my opinion, or an air infiltration at the end of infusion. but only a my opinion :slight_smile:

#3

I do dry fabric for 2 hours.Could just explain about the fast infusion.
Question: In spite of perfect leak free connections in mould, how Fast infusion will trap air ?

#4

what viscosity resin are you using? Are you using uni and wooven cloth? Are you using a flow media to infuse? Do you end the flow media short of the end of the laminate?

#5

Viscosity: around 3500 to 4500Cps
Fabric: Wooven
Process: Va-RTM, pressure of infusion is 15 bar.

#6

Thats a very high viscosity resin to be using for infuision. Usually infusion resins are between 100-600cps on average. Not sure your specs for resin system but I can recommend using Gurit Prime 20ULV, visocosity is 150cps at RT.

#7

Keep an eye on the injection pressure. RTM is something different from resin infusion. Very probably the resin is prescribed in the certification process.

What I would like to know is the amount of vacuum that you achieve, just before injection.

Also, if you lower the injection pressure to for instance 12 bar, do you get less bubbles? Or do you run into problems with geltime? If not, you can inject at for instance 10 bar, and raise the pressure when the resin is reaching the end of the mould.

Is the mould heated?