Expert: Steve Olson Date: 6/5/2008 Subject: bowing in phenolic composites
Question Dear Steve olson,
I am trying to produce a cabin using phenolic-E-glass. I produced some of the article. But I am not able to control the bowing effect which affects the panel dimension. My laminate construction is Surface tissue/CSM300/Biax600/parabeam 5mm/biax600/csm300
with phenolic resin. Though I use parabeam to control the bowing, still the panels are out of control. After laminating I introduce the panels to the oven at 80deg at 6 hours. My panels are flat and dimensions are 0.5mX2m to 1.5m to 2.5m. Please help me to solve this problem.
Thanks in advance,
Regards,
Vinoth
Answer Hi Vinoth,
Phenolic, must need fire resistance? I will assume then that you are heating this up to cure the phenolic instead of going with a catalized system as The phenol-formaldihyde only needs heat fro reaction.
There are several issues that can cause bowing of composite parts:
1. Tooling Coeff of Thermal Expansion mismatch
2. Balanced Lamination, probably not an issue as I can see
3. Symmetric Lamination, plies mirrored around the centerline
4. Temperature uniformity
The Minor issues first:
It looks like you tried to make the lamination symmetric, was it fully mirrored around the core?
The tooling, was it made from fiberglass with quai-isotropic lamination. This is the suggested approach.
The large issue with cored parts in Marine:
Temperature Uniformity seems to be the most inherent problem in this type of structure with Marine grade materials.
There is a couple of approaches:
Make sure the laminate is actually symmetric. Then you can build the part in 2 steps with facesheets and secondary bonding, or in one step with a fiberglass blanket on the part to help the temperature uniformity. Assuming it is heated under a bag you might want to use a blanket on top to keep everything uniform AND/OR you can go with a very slow heating rate.
So there's a few things to look at and a few simple ways to minimze the issues.
