Is there any relation to the surface finish in a mould and how many pin holes that can appear in out of autoclave pre-pregs?? Does a high gloss surface stop air from moving off the surface compared to a more satin surface? possibly breaking up the air more or allowing it off the surface. A sort of lamina flow situation so to speak.
with ooa prepregs heat is mostly the important part to regulate the flow of resin. With thick parts and moulds or other influences on heat distribution you need to take that in account. Dwells at certain intervals can give your resin more time to flow, and a steady controllable ramp is needed too. I Don’t know if the mould surface is a big influence, but with enough resin flow you shouldn’t have problems on any surface.
My experience is that a smooth surface is more difficult to get pinhole free than a textured surface (self adhesive teflon coated glass). No idea why. Will ask when I am at the prepreg factory.
Cool… I was asking because I did a part which was made from an alloy bracket. No mould just made straight off the bracket. It had a slight bead or light sand blast surface to it… Nothing course but enough to make the part very matt. I used up some backing material not the VTF Surface material and the part was flawless…
I have always had the same issues with vac only pre preg.
I can get a good surface moulding off metal moulds or PTFE sticky back but will mostly always get pinholes when moulding off a composite mould.
Would love to know any tricks to solve this, I think it may be a combination of the right release system and the right cook sequence/dwell etc but this takes a lot of time and many tests.
Using VTF works very well. It is not cheap but it is the best material for OOA parts at the moment. I just wondered if a different surface texture makes a difference in anyone elses experience.
http://www.umeco.com/~/media/Products/Datasheets/Structural/Epoxy%20surface%20plies-films/VTF261%20pdf.pdf
I’ve used the VTF261 series, and the z-preg, and the BPS240 without any problems from pinholes with a dwell at 60 and 80 degrees c with thin laminates. With thicker laminates and foamcores and thick mould parts the dwell time/ramp has to be slower. or you could place a temperature sensor against the mould surface to monitor your temperature exactly, that solved a lot of problems we where having once 
I do use a thermo couple on the part too… The oven temp goes up faster than the part so getting to 60 degrees and leaving it to dwell for 60 minutes may only really be 20 to 40 minute dwell depending on how long it takes for the mould temp to catch up so dwell time is from the mould temp not the oven temp anyway…
Sorry to dig this out. I’m using VTF. My surface LOOKS pinhole free when popped out of the mould.
But as soon as it gets clear coated, you can see pinholes spread evenly across the surface of the lacquer.
Sanding back, clear coating again, sanding back and a final coat of clear gets a perfect surface, but that’s hours of work that I would like to reduce.
No problem… I would hope there are ways to get a better finish from other Pre-pregs… But the ONLY time I had a perfect part with any material other than VTF was on an alloy bracket… I have seen some good finishes with other pre-pregs that dont hold up when you get fine dust over them… Dymag wheels was one and now they wet lay and it is better but still has pin holes… The suppliers of other so called OOA pre-pregs never claim it is as good as VTF but will say things like “we have customers who are happy…” or "we get good results using our materials and think you will be happy with the results… " ect… But none will give a lay up to work with and will only suggest that if you know how VFT if laid up to use that lay up…
I have checked my belly pan with some colloidal silica on the surface and the SHD version has great clarity bur has pinholes that are barely acceptable if the painter has to lacquer it… The PRF material is better for pinholes but worse for clarity and Hexcell’s Pre-preg is unfortunatly the worst of them all with pinholes that are the length of the weave and weft. It seems the only good OOA Pre-preg is VTF.
Carbon Cactus how long do you leave the parts in the vacuum bag to consolidate before you cook them? Do you bag them after you lay down the surface layer??