Phenolic/Foam issue 4

[tapirg]

We are using HexPly HT93 135 C Curing phenolic matrix (HEXCEL), HT93-6k 2x2 TWILL PHENOLIC 285gsm 1200mm more precisely, in some of our new components combine with some strips of Rohacell foam IG51 and we are having some issues with the foam on those components (please see attached document to get more information)

We have checked and we are following the Rohacell supplier specifications for using that foam and we are still getting the same problems so my biggest concern is that the foam is absorbing moisture form the resin volatiles generated while curing the components, as I know that phenolic resins generates lots of vapour water when are being cured.

Have anyone heard about similar problems?
There is a recommended curing profile to allow the volatiles to escape more quickly/easily?
Our current cure profile is:

Ramp to 135C @ 3C Min
Dwell at 135C for 1Hour and 15 mins
Cool to 40C at 0.5C Min

30 PSI pressure at 2.5 PSI Min
Vacuum bag is Vented to atmosphere when pressure reach 15 PSI



Please let me know your thoughts and suggestions to solve the problem, I would also appreciate any information you could send me about phenolic laminates.

 

[Joshmo]

Tapirg,

From my experience I would recomend using alot more pressure during the cure to evacuate the higher level of volatiles associated with phenolic resin. I would say at least 60 psi would be necessary assuming that this much pressure doesn't damage the foam.

Josh

 

[Compositepro]

This is a type of problem I often work on as a consultant. You have air entrapment in your lay-up which combines with the water vapor released during cure to lift plies apart.

I would suggest that you do not vent vacuum or apply pressure until your part temperature reaches 100C. The Hexcel datasheet is really bad. It has several blatant errors and little useful information (like volatile content).

 

[wes616]

Also, how close an eye are you keeping on your humidity (not just in your layup area, but in your material storage). Rohacell sucks up moisture from the atmosphere. I believe that we have had problems at more than 15 or 20 % humidity. It's well worth the experiment in drying your core prior to use.

Wes C.
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[MikeHalloran]

Pre-existing moisture in your other materials may make a difference, but water also comes out of phenolic during cure because it's a direct reaction product.

I used to work with a wet layup process that included a long dwell at 71C just to give the reaction water a chance to ooze out of the phenolic as it transitioned through a sticky--> liquid--> gel stage. Without that dwell, the product developed pinholes and bubbles.



Mike Halloran
Pembroke Pines, FL, USA

 

[tapirg]

Thank you very much all for your Ideas

We are using a new perforated released film with more and bigger holes than the old one and we have also perforated with holes the pieces of foam to improve venting and this seem to be working as we haven’t had any scrap panels for the last week.

I will post again if the problem rises again.

Thanks to all once more.