vinyl ester resin FRP

[Tmoose]

We had some large FRP enclosures made, for less than 40 psi working pressure.
The material is E-glass hand laid up using a commercial vinyl ester resin and vacuum bagging.

The enclosures would not pass a 2 psi leak test, and the supplier "repaired" them. They failed re-test. Then we had the finish coat media blasted off. There are some large cracks in the parentmaterial, lots of porosity, and some areas that are still acky. During the blasting large flakes and patches blew right off, as if no bonding had occured at all.

Various internet sources talk about vinyl esters being hard to make reliable secondary bonds, and being pretty sensitive to humidity and not reliably curing in thin coats.

We don't need the chemical resistance or higher temp tolerance of the vinyl ester. We'd probably use a commercial epoxy for the next ones.

Any advice?

Thanks,

Dan T

 

[berkshire]

Tmoose (Mechanical)
What as the method of wetting out the fiberglass,
Was the resin hand mixed, or was a saturating gun with a mixing head used?
Either way, if you still have tacky areas in the lay up after the finish coat is removed you are looking at a QA problem with the resin mix or the temperature it was cured at.
I would suggest looking for another supplier.
B.E.

 

[CompositeGeek]

I concur with Berkshire. If after fully cured you found tacky zones then you definitely have an issue with your resin system.

You don't say, but it appears your supplier(?) is doing a wet lay-up. If they are their bagging technique and wet lay up methods will be the primary cause for porosity and thereby possible leaks.

Cracks in the parent material could be the result of how the part is removed from the mold or subsequent handling, trimming operations. That depends on the tooling and the geometry of the part.

Finally, if cost is not an issue (rare) epoxy is more expensive (typically) than vinyl ester. But there are so many variations in resin systems that is not always true any more. However due to its short cure time at room temps, typically vinyl esters are more commanly used with chopped fiber applications. Epoxies are more commonly used with laminations. (again this is a "glittering generality" and not necessarily consistantly true.)

I suggest you contact a few resin dealers, CompositeOne, 3M, Scott Bader, Reichold, etc. (a search on the web is always fun) and ask them about the application for the resin you are using and get some feedback from them.

Good Luck!

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There are gremlins in the autoclave!

 

[PanelGuy]

My guess is it is a bad mix, a bad lay up and a bad cure. Vinyl esters are not that difficult to work with but can be quick and difficult to mix. How big of an enclosure? If everything would have cured right, sealing should have been just a matter of a light sand and overcoat with thinned resin or use a little toluene to thin some silicone caulk and do a rubber overcoat to seal.

It sounds like the part did not cure right and laid up dry, subsequently was weak and cracked when it came out of the mold and was covered up with body putty and painted to hide the problem. Sad really. I suggest you find a reliable boat builder in your area and try again.


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