Wednesday, September 23, 2009

Finally a few hours left for boatbuilding

It has been busy with a baby, a 6 year old school starter and extended working hours as well as finishing the rebuild of the house etc, but today, with the very competent help from Staale, and definitely useful in the handling of 7 m pieces of fabric, the lower port hull was laminated. I rebated and sanded the foam shortly after my latest post, but it has not been possible to find time for this lamination until this afternoon (after working 34 hours since Monday). This is the sanded hull with preparations also made for the vacuum bag visible above the sanded field and along the keel line:

We first wetted out the foam surface thoroughly, using 40% of the fabric weight for this area. I was very keen on making this lamination successful regardless of being able to pull a decent vacuum or not. Then the first fabric layer was applied, the "B" carbon equivalent. Here Staale is making sure everything is well wetted out from the initially applied batch of epoxy (using Svapox 110 epoxy/GL hardener):

Then the hybrid fabric, making the combined carbon weight "A" equivalent and adding 160 g/m² of aramid for wear resistance, was applied and additional epoxy spread to make sure the aramid was thoroughly but not excessively wetted out. Then the peel ply and Staale had to leave for kindergarten pick-up. I went on with the perforated release film, the bleeder and the bag. I was able to pull approx -0,95 Bar in a short time.
I have read from several people that one should not use this amount of vacuum as the laminate gets "dry" but I strongly disagree. The dry laminate does not come from a good vacuum but either from poor wet-out or the intrusion of air leading to evacuation of epoxy. What about autoclave? They use several bars and do indeed get good quality laminates. Here the laminate is exposed to approx 950 kg pressure/m²:

This amount of pressure leads to compression of the fibres and the initially rather dry looking hand lay out is actually proven to be excessively wetted out as excessive epoxy is squeezed trough the peel-ply, trough the small perforations of the release film and captured in the bleeder in a quite evenly distributed pattern as this picture shows:

The heater and the vacuum pump is running and I expect a near perfect laminate to be exposed tomorrow.


Anonymous said...

Hi Tor , looks great , I agree about the laminate not being too dry , the milspec ( military specification ) for a laminate like this is 36% resin content . Think that is only achievable with autoclaves . What you have done is eliminate all possible air from the laminate and air is the enemy . Cheers , Jim Buckland .

Fram said...

Hi Thor, you are right about the dry laminate. A good wet-out is key factor, and this is in conflict whith getting a good vacuum bag in time. So I was wondering why you don't use RI, as in this setup with partly hull laminate it is even more easy to do. Keep up the good work! Henny

Tor Rabe said...

There are several reasons why I choose to bag and not infuse these parts, main reason being too many problems in the past with leaking bags. When doing RI the bag has to be 100% tight, or at least 99% if the leak is in the right place (which is close to the exit). With thin and light foam this is definitely doable, but very hard and it is often not possible to identify the leak until the resin flows and a dry spot is revealing. When bagging after a thorough wet out, the result is good even without the bag, everything pulled is a 'bonus'

Second, the RI laminate is heavier than the bagged, this must come from the foam surface being totally filled, which will give a better bond, but as Farrier designs for hand laminating, stronger than necessary. I guess this is more prone when using very thin fabric as the content in the foam surface constitutes a much larger part of the total.

I am still a huge fan of RI but I don't use it as much as I did.

The mast will definitely be RI'ed as it will be made in a mould. And for flat panels the method is superior!

Fram said...

Vacuum bagging is much more straightforward than RI, but this also depends of experience. I just hate the mess of the wet lay-up. Regarding airtight quality this must be easier to achieve on the outside when there is an inside laminate also. A leak in the bag is not too difficult to repair and indeed the very small ones are only noticable during infusion. As a final escape there is always the solution of the by-pass, which works quite well. The amount of resin in the foam depends first on the type of foam. I'm always thinking that less resin here in comparison with RI is less quality. Anyhow, for sure the benefits of RI are getting better with the thickness of the laminate. For very light laminates RI might be questionable. Henny

Tor Rabe said...

I forgot one other reason: Staale was available. It would just be a big mess trying to vacuum bag this 7 m² double layer field single handed without RI.

A strange thing happend when I prepared the RI of the float exterior. I couldn't get a decent vacuum, and i couldn't find the leak. i then pulled air much quicker which lead to the neat total implosion of the float as the capacity of my opening to the outside world from the float interior was exceeded. I still haven't figured out how it could bee such a leak to the interior, everything was glassed on the inside...

Fram said...

OK. I re-read your post on float infusion. That must be a real monster of vacuum cleaner you used. I guess I was more lucky then ..... Can I borrow Staale some day ;-)