4wings.com Hovercraft development 47751 Michigan ave., Port Isabel - 78578 - Texas, US Tel.: (956)943 5150


Hovercraft development
47751 Michigan ave. , Port Isabel, TX, 78578
Tel:(956) 943-5150


The mythos and what it can really do for us!

What is Kevlar?

Kevlar is a long-chain synthetic polyamid, whose particular architecture qualifies it as an "aramid". Aramid's are close cousins to Nomex, it is used in structural honeycomb cores, and in fireproof garments worn by race car drivers and rescue personnel.
Bottom line - Kevlar is tough, abrasion and puncture resistant.

What is the Mythos ?

Let's get rid of some missleading aspects ! "Ballistic-grade" Kevlar ( Kevlar-29 ) is very different from "structural-grade" Kevlar ( Kevlar-49 ). Kevlar-29 is not a laminate - but multi-layer soft "blankets" of Kevlar plies sewn together - known as "soft armor" - and then mechanically fastened to the "what so ever " work piece - not very useful in our Hovercraft ! So if some Hovercraft's / Boats  have Kevlar components and get advertised as bulletproof - just walk away  - it is just a mythos - but not the fact .
Sorry if I killed somebody's advertising slogan .

Design and Application !

A big advantage is Kevlar's specific gravity of 1.5 in relation to E-glass with about 2.4 that allows you to produce a lighter work piece - on the other hand  - there is the problem that E-glass will sink easier in the resin than Kevlar and it is most important to apply extra care while wetting out and getting rid of excess resin - either by hand with squeegee's or with the application of Peel Ply!

But the first step is still to cut dry Kevlar !What is easy on E-glass - since you break the fibers more than cutting them is hard on Kevlar - Sharp tools are critical to successfully cutting Kevlar.Don't use the same tool for cutting Kevlar and E-glass since the E-glass will quickly kill the tool edge reducing its effectiveness in cutting the Kevlar fibers. If you have troubles cutting the fabric with your shears or get a very fuzzy edge - you can try to apply 3M blue masking tape on both sides of the cloth - lay it on a piece of hardwood , use a metal ruler and cut with a razor blade through the tape and the cloth - normally you will achieve good results for about 2 feet before you have to change the razor blade.

Resins which are very suitable for E-glass applications might not work well with Kevlar - you need lower viscosity epoxy resins to get the most out of your work piece. It is recommended to use Epoxies with viscosity's under 300 centipoints - in relation "general - purpose" styrenated laminating resins are 800 centipoints or above ! Keep in mind that the biggest downside of Kevlar is its compression  strength ( about 30% less than plain old E-glass) - but in the lift - thrust duct it would give great safety. Watch out for the cloth floating on your resin ( especially in corners or edges where you laminate in a L or U shape ) the resin will have the tendency to seep down and lift the Kevlar cloth on these locations ... if possible avoid a solid cloth and lay one at the bottom and when cured a second strip over the edge from the top down to reduce resin pockets.

Safety - Although Kevlar dust and fibers won't make  you itch like E-glass does, inhaling yellow fuzz simply isn't a smart idea. Wear suitable respiratory protection and a good fitting set of safety glasses or goggles. Even your nose and lungs won't know if you're laminating Kevlar or last weeks newspaper, a good respirator and adequate shop air-exchange rates  obviously are recommended during cutting, wet-layup and finishing  work!

Grinding - Sanding of the work piece is some headache since grits much coarser than 180 really "fuzz up " Kevlar - which is no big deal in case of a repair since the fibers mingle nicely with the patch and increase adhesion - just for the finishing up, you have to sand with 180 - 200 grit to reduce fuzing and last not least make a finish with ScotchBrite. Better even is if your Kevlar cloth is still covered by a thin layer of Fiberglass cloth as such you won't sand into it.

Cutting, boring and machining  is the best way to call 1-800-4-KEVLAR and ask for DuPont's product literature - and make use of the recommendations for tool vendors since it would take me 6 month to get all their links here together! Just for the moment to satisfy you : Basic rule of thumb  for almost all cutting, machining, and boring operations on Kevlar laminates is high speed, low feed!
Backing up the area which  is machined is important to avoid delamination. As well as keeping a eye on the workpiece temperature - Resins change their physical propperties above 180 F.

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Related external Links

Epoxy resins,

Scissors and Shears for Kevlar and Composites

Kevlar @ Jamestown Distributors which are real folks serving us for a long time with products we actually need - Thanks Guy's