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How to get pinhole free and ready to paint phenolic part

How to get pinhole free and ready to paint phenolic part

How to get pinhole free and ready to paint phenolic part

I experience a lot of problems with surface pinholes while using Phenolic resin for hand layup (resole). As a result, the surface has to be sanded down, primed, sanded down again, primed again and then painted.

I was wondering if using an in-mould primer or a surfacing film would give me a pin hole free surface ready to be painted and help me get rid of the whole tedious process.

or whether using novalak could improve this. Even single vacuum bagging doesn't help with the situation, anyone has experience with DVB to get a better quality phenolic laminate and how? would a dwell help in the curing cycle?

Looking to take advantage of anyones experience.

I was hoping I could get some useful information from the book "Phenolic Liquid Resin Hand Lay-UP Techniques" by John A Wills but unfortunately can not find any copy of it now.

RE: How to get pinhole free and ready to paint phenolic part

Phenolic resin outgasses during cure and will be very difficult to get a good finish. In the past I even tried degassing the resin at low pressures to boil off as much as I could with no luck. Your best bet would be to change resins if possible. I hope this helps.

Rob Stupplebeen

RE: How to get pinhole free and ready to paint phenolic part

Phenolics are condensation cure and the water + volatiles produced needs to be carefully managed. Application of pressure can help, however, people have resorted to hydroclave to get the extreme pressures required for low porosity during cure, and I think this could be beyond the scope required for your parts (if they are hand laminated).
There are several open source NASA papers with the DVB process explained in detail, however, you will probably need to tailor the process to your resin system. It is basically to do with reducing vacuum bag compaction pressure during the initial stages of cure to allow volatiles to escape and then going to full vacuum to get good compaction pressure.
I agree that a change in resin system could be a good option if possible.

RE: How to get pinhole free and ready to paint phenolic part

I have a copy of John Wills's book. But the only method he describes in there for a pinhole free surface is the use of a surface paste.
In particular he mentions Georgia Pacific GP 5020/GP 4835 surface paste system. From the book "" The GP-5020/GP-4835 paste system produces smooth, void free surfaces for wet layup and RTM panels."" I have a data sheet for this material it is copyrighted 1995 so I do not know if this material is still in production.I could not find it on GP's list.

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