Laminating Wood Core (Ash) & Carbon Problems

pmg · Post by **pmg** » Sat Dec 01, 2012 9:19 am

Hello,

after lots of reading in this Forum its time for my first post :)

My problem:
A friend of mine and I have been building 2 pairs of skis so far, both with carbon on top.

Laminating, pressing and so on is no problem, everything works as it should (more about our equipment later).

But: The carbon and the ash wood core dont stick together well. With some force we were partly (not everywhere though) able to tear the carbon off the wood.
The carbon itself was completely filled with epoxy, but after tearing off the carbon it looked as if there was no epoxy at all.

What we are using:
- a vacuum press that creates a pressure difference of 700mbar
- epoxy that starts curing after 45 minutes at room temperature (epoxy L and hardener L from R&G)
- an ash core with a planed surface (very fine surface actually, comparable to a P400 sanding finish)
- biax carbon

How we were laminating:
- Setting up everything (epoxying and assembling all the stuff in the press) in the workshop, temperature at this time about 10°C
- Afterwards putting the press in the sauna and heating it up to 60°C for 3 hours
- waiting another 15 hours before seeing the result.

At this moment, im thinking about 2 things that could cause the bad lamination:
1) The surface of the ash wood core could have been too fine.
2) The temperature in our workshop was too low so the epoxy was not liquid enough to go into the wood. By the time it was heated up by the sauna all excess epoxy was already pressed away.

Did some of you experience the same problem and do you have ideas what could have caused it? (And of course how to solve this problem ;) )

Thanks for your help
Philipp

Richuk · Post by **Richuk** » Sat Dec 01, 2012 3:04 pm

You should expect Ash to break/splinter before it lets go (peel test). You can test whether there is an issue with the wood/plastic, using a few drops of water. If it sits on the surface ... you have an issue. Oil or something on the blades?

I'd be surprised if the problem is the wood ...

- Mixing the epoxy at 10C is not ideal (I would look here first)
- At 10C the resin will be quite viscous, so it is going to have trouble wetting out the fabric and saturating/penetrating the surface of the wood (oh you've said this already)
- Not sure what the effect heat would have on the problem. I'm guessing with ambient cure, the epoxy becomes more viscous/gels and then cures ... so again, little time to saturate the wood????

If you determine it is the epoxy and you want to stay with ambient cure, then there are a number of options. I think KAm started with the West System.

You could run a test at room temp? A couple of G-clamps to simulate the press.

Good luck - its all gets easier from here on in!

Jibber · Post by **Jibber** » Sun Dec 02, 2012 3:44 am

I worked once with the same resin in low temps (~15°C) and found the viscosity not good. With 20°C + it flows much better.

Cheers, Christoph

Jekul · Post by **Jekul** » Sun Dec 02, 2012 8:28 am

Your wood core needs to have a noticeable amount of roughness. I always use some 80grit sandpaper after running the wood through the planer to assure the surface is rough enough. The added bumps/valleys will provide significantly more surface area for the epoxy to bond to.

skidesmond · Post by **skidesmond** » Sun Dec 02, 2012 10:33 am

Could have been like Rich said, epoxy. I usually warm my epoxy up so it flows easier and wets out faster. Does take much, a heat lamp is what I use. Were the cores wiped down to remove dust? and the core should not be super smooth. I usually use the cores straight from the planer, but using some 80 grit like Jekul suggests does'n't hurt just wipe down to remove dust. Even a damp cloth will raise the grain and fibers a little. Make sure cores are dry before lay up, obviously.

vinman · Post by **vinman** » Sun Dec 02, 2012 10:34 pm

Jekul wrote:Your wood core needs to have a noticeable amount of roughness. I always use some 80grit sandpaper after running the wood through the planer to assure the surface is rough enough. The added bumps/valleys will provide significantly more surface area for the epoxy to bond to.

This is actually incorrect. I have a document I posted on here a while ago that outlines how a planed surface is actually superior to a sanded surface in terms of bonding. A planed surface preserves the open cell structure of the wood. A sanded surface destroys the cell structure and actually decreases bonding. I'll repost the document here when I find it.

edit: found it
http://www.cedengineering.com/upload/Ad ... terial.pdf

give that article a read. There is really some great info in there on surface prep and many other aspect of bonding wood that I never knew about. In fact I may need to re-read it, its been a while.

Dr. Delam · Post by **Dr. Delam** » Sun Dec 02, 2012 11:04 pm

I kept searching for that article but you beat me to it. While I was searching, I did come across several random web articles that contradicted it though.

I am sticking with going straight from the planer. I have never had a bonding problem this way and no point in adding any more unnecessary labor.

Richuk · Post by **Richuk** » Mon Dec 03, 2012 4:43 am

The best link to provide when the properties of wood is in question is this: http://www.fpl.fs.fed.us/products/publi ... ending=yes. It provides a range of relevant information. I believe your article references this source.

The thing I have in the back of my mind when it comes to the planner, is the snowboard company that doesn't glue it's stringers together. They agitate the stringers (vibration), heat builds because of the friction and the resin in the wood is activated and forms a bond.

I wonder if it is possible i.e. the resin content of wood must vary according to species (per tree) ... that planner blades (non-commercial planners) hold a similar potential i.e. slightly too much friction due to improper depth of cut or slightly blunt blades ... Is this the contradiction Dr D?

I don't water test every ski core. I have done peel tests with Ash, so it shouldn't be the issue. Accounting for different cell structures within species, I wouldn't be too sure that certain species don't need to be roughened up, to compensate for other issues. Essentially, you have to do the test on the materials you are using and adjust accordingly.

... lunch is over

pmg · Post by **pmg** » Mon Dec 03, 2012 5:17 am

Hi,

thanks for all the answers. I will give temperature the first try: Will try to have everything at room temperature, especially the epoxy. I really think that it wasn't fluid enough to go into the wood cells.

Jekul · Post by **Jekul** » Mon Dec 03, 2012 8:56 am

Vinman -
I have to read 26 pages of material on wood bonding, no google widget or readers digets short-copy...!?

Thanks for reposting. Looks quite intersting, I'll give it a read.

vinman · Post by **vinman** » Mon Dec 03, 2012 11:11 am

You really should read it. But you won't need to read all of it.

It did make mention of improved bonding with use of 100 grit, but anything under that damages the cell structure.

Also good info on acidic woods and bonding such as oak.

Jekul · Post by **Jekul** » Mon Dec 03, 2012 6:25 pm

Very interesting article. Definitely more thought about bonding than I've put into it. I thought the bondability of the different species of woods was very interesting. I'll definitely refer back to this when choosing some of my woods in my skis.

Unfortunately the woods I'd want to use in my sidewalls have some of the poorest bond strength (I want closed cell woods for sidewalls = less bond strength)

jellyfish · Post by **jellyfish** » Wed Dec 05, 2012 5:15 am

Not familiar with your epoxy but if it's typically a room temp cure resin then I would guess it's the 60* temp cure that is causing the problems. Crystalization of the epoxy or out gassing of a not dry enough core lots of possibilities,

Also keep in mind that although vacuum pressing is an acceptable method there are some problems, you need to be meticulis with it when trying to stick it all together some of these problems are too much resin and it floats the layers remember resin is the glue too much and it has no strength by itself, however once in or part of the composite the glue works good, if you put a hard shell top sheet over the composite you have to be carefull trapping air and resin there is just not enough force to flatten out the fibers and push out air, too thick of resin and the fibers fill up get thick like rope unless you wick out this resin with a breather it stays inside and is trapped it makes a damped ride thinner laminates provide more life working the fiber resin bond . Think about if you are trying to glue two pieces of wood together too much glue and not not clamped tight enough the joint is week get it clamped tight at its strong now if you are able to clamp all the fibers together in a nice tight matrix it will be the strongest. Including the bond between wood and fiber.

Of course there is more to this whole process i hope it helps how you think about what is happening inside the bag.

Do some test panels drop your cure temp to 25* and 30* warm your resin try without a topsheet and use a breather on another, takes some time but you need to practice building and learn what's happening inside saves time and money in the end wish I had learned this way instead of the hard way,

Cheers Jim

Brazen · Post by **Brazen** » Wed Dec 05, 2012 9:36 am

Is ash an "oily" wood?

skidesmond · Post by **skidesmond** » Wed Dec 05, 2012 10:18 am

No it's not oily.

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Laminating Wood Core (Ash) & Carbon Problems

Laminating Wood Core (Ash) & Carbon Problems