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MJTennison
Posts: 10
Joined: Sat Aug 04, 2012 4:59 pm
Location: Baltimore, MD

Post by MJTennison »

Hey Fellas,

It's been awhile since I've been on here, but after hitting another issue during wet layup, I figured I'd share my issues with the experts to troubleshoot. The issue is the top sheet/fiber layer de-laminated when I tried to remove from mold. The epoxy seemed brittle and the fiber didn't look completely wet out even though I used *what i calculated* the correct amount of epoxy (~24 fl oz).

Basic info:
-Construction: top sheet (UHMW), 19 oz triaxial, shaped poplar core w/ attached sidewalls with tip/tail spacers (UHMW), 19 oz triaxial, base layer (UHMW) with attached edges
-Epoxy: ECA0043, and ECA-408 hardener (4:1 ratio)
-Process: Vacuum bag (mdf female mold)
-Total qty of epoxy = 24 fl oz (does this jive with other people's calc's?)
-Layup cured w/ vacuum on for ~14 hrs, then I allowed to sit at for another day in the mold without removing
-I used carpet tape on the base layer to prevent movement during curing
-Room temperature cured (this I think is where the epoxy and I had a falling out)

Good news-
1. The overall process/assembly went pretty well, other than alignment of core to base layer. I used the method of super gluing 2 inserts on the base layer prior to layup, then during layup using an exacto on the first fiber sheet to cut out around those inserts for clearance. This sounded way easier than it turned out...anyone have any advice as to how to keep the fiber from fraying during this (or is that even an issue?)
2. MDF mold held up well, vacuum pulled almost 1 atm; I used peel ply, breather cloth, bag with mastik (spelling?) tape

Not so good news-
1. when I went to pull the assembly out of the mold, the top sheet and first layer of glass pulled up off of the poplar core without much resistance....no bueno! I have a few theories, and before I put together a formal design of experiments, I wanted to get some feedback first to make sure it's not something totally stupid I overlooked:
a. Ratio of resin/hardener was off: I measured by weight (~19.2 oz resin/ 4.8 oz hardener = 24 oz total).
b. Chosen harder/epoxy was not a good choice for room temp. curing.
c. I didn't allow enough time before trying to remove from the mold (epoxies are thermosets which rely on cross-linking...temperature and/or time are variables)

I will try to post some pictures of the process at a later time, but any insight/feedback is much appreciated.

Thanks!

Merritt
MJTennison
Posts: 10
Joined: Sat Aug 04, 2012 4:59 pm
Location: Baltimore, MD

Post by MJTennison »

I meant to mention this was a Snowboard layup.

Thanks,

-M
gozaimaas
Posts: 663
Joined: Fri Feb 10, 2012 4:17 am
Location: Nagano Japan

Post by gozaimaas »

Dont cut the glass, just work it around the insert. I use an old pen to pry the fibres apart enough for the insert to pop through.

As for the delam it sounds like it was dry between the core and the top glass layrr. Did you wet the core with epoxy or just lay the glass on and put epoxy on from the top?
MJTennison
Posts: 10
Joined: Sat Aug 04, 2012 4:59 pm
Location: Baltimore, MD

Post by MJTennison »

Thanks gozaimaas for the insight-

Yes I wet out the core before placing the top fiber layer. Maybe I didn't do a good enough job wetting it out completely though, that's possible for sure.

So when the topsheet/fiberglass started pulling away from core, I stopped and just left it in the mold. I figure if I leave it in there a couple more days and try to remove again, it will at least answer the question of whether or not I was premature to remove.

Next step is probably to run some more test swatches...
Richuk
Posts: 1146
Joined: Sun Jan 31, 2010 9:53 am
Location: The Duchy of Grand Fenwick

Post by Richuk »

It would help if you were writing a journal and posting pictures in support.

The most likely issue is the choice resin, it's expecting heat and pressure to be part of the equation. You need to gain a technical understand why heat and pressure are so important during the cure cycle and why you need to optimise the cure.

UHMWPE is difficult to bond, find out why and what steps the ski base manufacturers take to improve bonding and why they work. I think Crown have video's posted on you tube. Understanding how materials bond, what an adhesive seeks to achieve will help you isolate the issue with the core.

The results of this research should provide you with a sense of why you might be having issues. You may have minor issues with process controls. The steps you need to take will be clear from the research.
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