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Ian Brooks - n/a
27-Mar-06, 08:56 PM
Hello



Does anyone have experience of laminating KEVLAR cloth? (500gm/m^2)



If so I would appreciate any guidance or tips...



Ian

Michel - n/a
27-Mar-06, 09:59 PM
Hello Ian,

Using Kevlar is good for bottom hull, or anytime you need something light, and strong against shocks or scratches. The trouble with it is it refuses to follow curves easily, tends to act like a spring. I used it for surfboards , with epoxy resin. It would be easier to use it with polyester resin, due to quicker hardening. If you need to follow an angle like front hull, you may wrap the kevlar + resin with an alimentary film, as to maintain it glued to hull. The film doesn' t glue to resin , if it' s flat enough, you can remove it easily when resin is dried. The best use of kevlar is to reinforce flat parts of hull, or angles , where hull scratches ground.

It should need a very long time and a lot of skill to make a full kevlar hull. And it should be too souple, that' s why we use carbon mixed with kevlar as stiffener, for boards and canoes.

hoverbucks - n/a
28-Mar-06, 01:06 PM
When I worked with kevlar, I purchased the slow curing (tropical) hardener (2-3 days cure time). I would layup the layer of kevlar first, then apply a layer of glass cloth on top of it while it was still wet. The glass cloth does 3 things:

1. adds strength

2. holds the kevlar in place on all but the most drastic curves

3. Allows sanding when cured. Sanding a kevlar laminate alone will result in alot of fuzz because you end up sanding the matrix and not the cloth!

I'm not yet convinced that it is worth the trouble.

Ian Brooks - n/a
28-Mar-06, 07:03 PM
Hi



The kevlar is to be used for the propeller containment - I want something lighter than the 'regulation' 6 layers of 450 gm (13oz) CSM, which would come in around 16kg (35lb). It will be a single curvature wrapped around a 1.5m (59") propeller, on a simple former. This particular material is used for blade containment on aero gas turbines.



I plan on doing some experiments to determine the construction which is 'equivelent' to 6 layers 450gm csm, probably either:



1 layer 6oz cloth, 1 layer kevlar, 1 layer cloth

or

1 layer cloth, 1 kevlar, 1 CSM, 1 kevlar, 1 cloth

or

upwards of this.



Ian

Jamie Lewendon - n/a
28-Mar-06, 07:46 PM
You can lay up kevlar easily. Just treat it as another layer of glass. Make sure you sandwich it with a layer of csm on the inside and the outside, and use pigment in the resin. Kevlar will degrade in UV light (sunlight) if it is not covered. Also kevlar is quite thirsty on the resin.



jamie

Michel - n/a
28-Mar-06, 10:53 PM
I forgot,

I conform: do not try to sand if kevlar is used as outer layer, plushes ! And plushes become sponges.

If you use it as a duct close to propeller path, aerodynamic trick is : don' t sand it at all, let it a little bit rough, it' s better ( too long to explain here, but believe me ).

I think using a slow hardener is not so good. Hardening must been achieved in a precise time to insure strength quality, for any deviation in this time, you lower Kevlar quality.

In my opinion, I should use several kevlar layers on the inside to prevent gravels holes in the duct, and fiberglass layers on the outside for strength and better look, and colour.

skiericski - n/a
23-Apr-06, 09:28 PM
DON'T use polyester resin to lay up kevlar, it does not bond well enough to kevlar to properly transmit load to the fibers.

Michel - n/a
23-Apr-06, 10:06 PM
Yes and no,

Kevlar is best used with epoxy resin, BUT:

if your hull is in fiberglass + polyester resin, and you want to reinforce part of hull with kevlar material, you MUST use polyester resin, otherwise, the added layer has many chances ( or risks ) to stay on the first obstacle you' ll bump in. It will flake off at the first sun ray or schock.

team black - n/a
25-Apr-06, 09:43 PM
If you follow the advice above and bond CSM in an epoxy laminate, get CSM that is intended for epoxy. The PVA in ordinary CSM won't break down

Ian Brooks - n/a
26-Apr-06, 08:57 PM
Thanks for the advice everyone...



The purpose of the lamination is to provide some stiffness so that the structure will be self-supporting, it does not need to carry much load in normal circumstances. The primary purpose of the kevlar is to retain the debris from any prop failure, and the kevlar will be able to do that without relying on the polyester bond - indeed it is likely to perform better if the structure deforms grossly on impact.



So, having listened to the debate, I will laminate with polyester, then it will bond properly to the rest of the hull and be self-supporting whilst the integrity of the kevlar-polyester bond will not be critical.



Cheers

Ian

skiericski - n/a
27-Apr-06, 02:44 AM
If you're not expecting any structural contribution from the kevlar layer(s), then polyester resin will do an adequate job.



Epoxy will adhere better to fully cured polyester(or any other substrate for that matter) than polyester itself will. However you DON'T want to try the opposite, polyester resin or gelcoat won't adhere very well to cured epoxy.

Michel - n/a
27-Apr-06, 05:17 AM
Don' t forget to scratch the surface with big sand paper before applying a new layer.