hi mates;my first try produce prepreg carbon hard case.my aplication 3 ply 200 gr carbon,2 mm pvc core(mostly critical flat area).cure schedule of oven cure ramp rate 1 minutes to 2 degree impending (20-80 degree,30 minutes dwell time,80-120 60 minutes dwell time).and full vacuum 29.92 in-hg my home sea level.silicone bag works absolutely perfect, there was no bridging.When I remove the product from the mold I have seen some small pin hole and some area big hole.What do you think is reason for this Pinholes?
I’m sorry for the bad quality pictures
hi morepower,
If you meant what prepregs material I did use,its a prepreg which it made with huntsman prepreg resins(cure at 120C for an hour).The supplier is located in Turkey.And I have been using airex C70 pvc core material.And yes mostly pinholes are worse where is the core located.In the other hands,I have realized another issue that some of the resins were left on the mold when I removed the part from mold.I suspect from the resin weight.But I do not know do you agree?
Many prepregs have pinholes…they are not the perfect material. You can make sure that your prepreg is stored correctly (sealed bag with dessicant pack), and not out in the open. If you leave it out, it might pick up moisture. Leave the prepreg debulking for several hours before cure. Also, make sure you debulk every few layers.
What do you have between the preform and the bag? If NOTHING, then there is no way for the gas/air to escape. use a layer or 2 peelply, or perforated film, and peelply as a breather, to allow airflow out of the preform.
And obviously…are there leaks? Never had luck with that material here…we do not use it. It always had holes.
Thanks for the reply,I keep the prepreg roles into coolroom at -18 C degrees.I will keep in mind your advices.I have used perforated release film and 1 layer of 150 gr/m2 breather with this unsuccessful application.And to be honest, I am not quite sure there is not leaks issue.Which is the better perforated,non perforated or peelply as release film?
perforated…you need the VOCs and air to be pulled from the part, and into the breather when curing.
Well…sometimes…there are many ways manufacturers recommend getting air out of the preform. Check with them. I’ve done things like sealing the edges 1/4" from EOP with flashbreaker and solid film. Overlapping the film 3" in the middle fo the part…that way NO resin comes out, but air sitll can find a path.
OK… Try to cure at the lower end of the temperature range and let it dwell at the lowest temp for about 1 hour before ramping up to a slightly higher temperature. I never cure at the top end of the cure range as it does not let the resin flow for long enough.
The core will be slightly porous I guess pulling some resin from the surface. I do try and avoid using a core and will add more layers of a heavier weight material like a 650 gram carbon.
I never use perforated release now either. I had some pinhole issues with perforated release films. You may also want to play with the breather stack with peel ply under the first layer on the flange face and/or peel ply on the last layer too. Run peel ply into the breather cloth too… Anything to try and get air off the material… But sadly you may have to change pre-preg to one more like Cytec’s VTF261. There is one more material which will be available soon which works perfectly too… But you may have to swap material to be honest…
Here is a part I made this week and as you can see from the photo is is just out of the mould and has not been finished to hide any possible problems as you can still see the untrimmed flange and the rough flashing from the mould section joints…
You may get the material to work but it could take quite a lot of experimenting on smaller parts.
