Thanks to Will for the detailed description.
Thought this article I stumbled across on Cruising World might add some
additional detail.
http://www.cruisingworld.com/how-to/systems/composite-construction-decoding-the-matrix
Mark
---------------------
Dr. Mark Bodnar
B.Sc., D.C., FCCOPR(C)
Bedford Chiropractic
---------------------
There is no cure for birth and death save to enjoy the interval.
- George Santayana
On 02/03/2014 6:05 PM, Will Harris wrote:
I'll take a shot at answering some of the questions in a general way:
The bits and pieces=
Gelcoat - gives a finished outer surface and makes the part easier to
get out of the mold
Fibers - The fibers are what give strength to the part. The engineers
have gotten very clever to matching the type, amount and orientation
of the fibers to realize the best strength to weight ratio
Resin- The resin is only there to hold the fibers in orientation.
Resin does not add strength on its own really.
Core- The core separates two thin skins. The skins can be a lot
lighter, and stiffer working together across a core.
A good laminate-
A good laminate comes from:
Good engineering. Really, this is the key. After it, it is just
execution. Getting the right fiber, orientation, resin, resin ratio,
Core and cure is probably 80% of the game. If you have a crappy
recipe, you get a crappy cookie.
Fibers - There are a few basic fibers used commonly in boatbuilding.
Glass, Carbon and Kevlar. There are all sorts of different types,
weaves and delivery systems with in each group. Kevlar is receding in
popularity.
Cores - There are 3 main cores - Balsa, foam, honeycomb. Basically,
they go in that order for both cost and performance. The core needs to
be strong enough to resist the sheer forces of the two skins trying to
go opposite directions. Most of the time when the Volvo boats have
big delam issues, it is because the core sheered. The right thickness
of core is important. Too thin, the boat will not be stiff. Too
thick, you add weight and $$ for nothing.
Resins - Polyester, Vinylester, Epoxy. Again, performance tracks
price! Poly is cheap. It is the most brittle too. Epoxy is awesome
stuff. One of its best properties is that it is the most flexible.
Sounds counter-intuitive but that is good. In poly, little
microscopic cracks form because it is brittle. This lets the fibers
move a little in relation to each other and the boat gets softer
overtime.
Vinylester is right between. We like it a lot because it shares many
of the good properties of epoxy, it easy to work with and is a bit
less expensive than epoxy. A bonus is that Polyester gelcoat sticks
to it just fine!
Resin to Fiber ratio - Too much resin in the laminate is a common
issue. It seems like you would just slather it in there, but you'd be
wrong. Each system has an ideal resin/fiber ratio. Too much resin
does two things; 1- Adds weight- remember, resin is not very strong.
2- makes the laminate weaker! Remember those micro-cracks. The are
cracks in the resin. We want the fibers nice and tight with just
enough resin to hold them in place.
Compaction- As discussed a second ago, we want the fibers nice and
squished together. Air voids are hard to eliminate, but must be
minimized. They weaken the laminate a ton.
Building Process - Wet lay-up, infusion, pre-preg. Again in
$$:performance. Assuming we are using female tooling. In wet layup,
the cloth is put in the mold dry and wet out and compacted with
rollers. Fast simple cheap. Your boats were made this way.
Infusion- In the infusion method, all the fiber, core etc are put in
the mold dry. Then we stick a vacuum bag on it with very
strategically placed resin inlets and exhausts. We draw the vacuum,
and get the laminate really firmly consolidated. Then, a metered
amount of catalyzed resin is introduced through the ports. Getting
the ports place right is really important to draw the proper resing
front through the part. When the correct amount of resin is injected,
the vacuum stays on until the part cures. This gives us really good
control over both the resin ratio and the consolidation.
Pre-preg - carbon comes from a laboratory with a heat setting epoxy
already in the fiber. This is placed in the mold, a vacuum applied
and it is cooked in a oven. First, the heat melts the glue and lets
it flow. Then the heat is kicked up a notch and that sets off the
cure cycle. There is a really specific protocol for ramp up, cure and
ramp down temps. If you really like spending, the oven can be an
autoclave with increases the pressure to about 6 ATM as opposed to the
1 possible with an ambient bag.
This is the highest performance option, but stupid spendy. Our little
30 footer could come out a the $330 - $400 K range. Ouch.
That is a short ( for an overview), but long ( for a mail list ) run
down of modern boat building. If you have specific questions; fire away.
Come to the Open House! We will be running infusion demonstrations,
and the smart guys will be able to explain anything to you. Plus, you
can heckle Andy and get a free lunch.
Will
_______________________________________________
This List is provided by the C&C Photo Album
http://www.cncphotoalbum.com
[email protected]
