By Rosta Spicl - 1/21/2020 2:21:03 PM
Dear all
Just working on the project based on carbon prepreg honeycomb structure. The procedure below is OK, the final rigidity is excelent, but there is a problem on visible surface goes to be non flat after vacuum bagging. See the procedure:
1. Hit the first layer, carbon prepreg 210gsm, 1 layer, vacuum bagging, autoclave 100°C@-0.98bar/+8bar. Perfect results, excelent flat visible surface, no pinholes, final thickness cca 0,25-0.28mm.
2. Apply the epoxy glue RG (5min.) for better adhesive properties, put on the nomex honeycomb OX4.8, thickness 3mm.
3. Apply the outer layers on honeycomb side, 3x carbon prepreg 210gsm.
4. Vacuum bagging, autoclave 100°C@-0.98bar, no overpressure.
Final structure is fine, but on the mold side - the visible side of structure, there are after vacuuming around all the surface where the honeycomb was applied..how to say that..hollows? The surface is not absolutely flat like in step 1, but deffected by inner honeycomb core. See the picture. Any ideas what's wrong?
I'm convinced, the problem is vacuuming. If I hit the outer and inner side of prepregs separately in autoclave and glue the sandwich together in vacuum, the defect is quite same, if the thickness of outer visible side is 0.7mm instead 0.25mm, the defect is quite same.
Many thanks for support.
Rosta
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By f1rob - 1/22/2020 10:55:39 PM
If you vent your job,
Whether it has 30/60/90 that job wont have more force on it you still have the pressure acting on the bag an the bag pushing the material
Normally you would vent at 15psi as that's essentially the same as the pull that's being exerted by the vac on the bag,no point letting the pressure going higher then venting
Most jobs you dont have to vent but if you want to stop core marking its essential
Either that or do 2 pre cured skins and then bond them
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