Date: Tue, 25 Feb 1997 11:19:39 -0500 From: Jim Hocut Subject: COZY: Kevlar/Resin ? OK, maybe if I hurry I can get in the first airplane related question on the new improved Unofficial Cozy Builders Mailing List (will I get a prize?). After some of the discussion re. hockey pucks, steel plates, kevlar, etc. I went ahead and bought some kevlar to do some testing on my own. Impressive stuff, it EATS SCISSORS !!! Anyway, after I was finally able to get enough cut to do some layups, I'm not really impressed with my results, the peel strength doesn't seem real great. I used 2427, and it just didn't seem to wet out real well (and besides that I had a hard time telling if it was properly wet out while doing the layup). I suspect that this may not be the greatest resin system for use with kevlar. Any suggestions on a good resin system to use with kevlar? Anybody know of a good instructional book or other reference material with these kind of "how to" details? Thanks, Jim Hocut jhocut@mindspring.com by InfoAve.Net (PMDF V5.1-5 #17060) with SMTP id <01IFU20NQW6Q96PD20@InfoAve.Net> for cozy_builders@hpwarhw.an.hp.com; Tue, 25 Feb 1997 13:27:16 EST Date: Tue, 25 Feb 1997 13:27:09 -0500 From: Jeff S Russell Subject: Re: COZY: Kevlar/Resin ? Organization: AEROCAD INC. <33131A5C.3C18@yadtel.Net> Jim Hocut wrote: > Any suggestions on a good resin system to use with kevlar? Anybody know > of a good instructional book or other reference material with these kind of > "how to" details? Jim, kevlar is a BEAST to wet out as you now know. I have found it always better if the use of colored resin systems in the aid of telling when one has totally wet the cloth out. Kevlar is yellow and it goes from light yellow to a little darker yellow, Not clear like glass does. This is where color can help. If peel is still a problem? Water could be your problem? Glass, kevlar, foam and resin can hold water in storage. Check there first before changing resin system. The EZ resin will not have water problems because of the styrene that is added in it. We still use the 2427 system, but only because it was given to us as samples. We can only us it under vacuum bagging with no problems because of our high humid climate we work in. Thanks, guys and Marc for letting me stay!!!! -- AeroCad Inc. Jeff Russell 1445 Crater Lane Yadkinville, NC. 27055 phone/ call first for fax 910-961-2238 NEW E-mail: JRAEROCAD@yadtel.net web site: http://www.binary.net/aerocad Date: Tue, 25 Feb 1997 11:27:11 -0800 From: berkut@loop.com Subject: Re: COZY: Kevlar/Resin ? >Jim Hocut wrote: > >> Any suggestions on a good resin system to use with kevlar? Anybody know >> of a good instructional book or other reference material with these kind of >> "how to" details? We stick the kevlar in a toaster oven at about 200 degrees for an hour or so before applying it to drive off the moisture. We put it down hot and it wets out VERY quickly. -- Czech Sikhs! Richard Riley "Heavier than air flying machines are impossible." Lord Kelvin, President, Royal Society, c 1895 See the Berkut at http://www.berkut.com Date: Tue, 25 Feb 1997 16:14:34 -0500 From: Rick Roberts <102503.1561@compuserve.com> Subject: Re:COZY: Kevlar/Resin ? Greetings everyone, I have used a bunch of kevlar on the King Kozy, (mostly as a matter of fact). Lessons learned: 1) It is a real bear to cut. There are some special grinds you can put on scissors that really helps but you have to keep them sharp! Also serrating the edges with a diamond file keeps the kevlar from slipping. 2) I have used a lot of the material that Spruce sells as KS400, it is a unidirectional Kelvar that is about 3/8" kevlar with 1/8" of s-glass between bundles of kevlar. It really helps improve the compression strength of kevlar (which isn't very good) and also provides a indicator when it is wetted out. Its pretty cool. The company that made this material 4-5 years ago when I got it really had some quality control problems in their process of making the unidirectional material, (lots of areas that aren't held together well etc.) hopefully they have fixed their problems. 3) For Bidirectional Kevlar, I like the 285 weave that Spruce and DMC sell. It wets out pretty well. My kevlar (and graphite) laminates always looks better under a microscope than the glass laminates that I do. I usually have been using the original Saf-t-poxy (Unsosaf-t-poxy) on my lay-ups, I usually warm the resin and hardener under a heat lamp for 10-20 minutes before using so that it is pretty thin. (It also cures faster and harder (I believe, no Tg's to substanciate)) 4) Kevlar is fairly hydroscopic (sucks up water, it case I spelled it wrong), however the effects on hand laid up and room temp cure parts isn't that bad. The big problem we found in the defense industry was that if you built parts out of wet kevlar, graphite, glass, or resin the elevated cure cycle would cause a tremendous amount of porosity in the laminate, and that was bad. The problem Boeing had on engine structs with Kevlar panels was similar. The water would wick into the frayed edges (see comments on trimming) and expand and contract in the heat of the engine until the panel basically self destructed. Throw in a little acoustic vibration .... result bad problem. It won't hurt to dry the kevlar first, but if you use the KS-400 don't get it so hot it melts the glue that hold it together. 5) Trimming Kevlar laminates is probably the most challenging part. If you use saws or knives, the material laughs at you and it responds by shreding into very rough edges. (Caused both by the toughness of the kevlar and the relatively poor interlaminar strength of the kevlar laminates. The most effective method of cutting is by using a diamond cut-off wheel at 20,000 rpm. Then paint the edges with resin and allow to cure for several days and then touch any loose pieces with a sharp file or better yet a fine sandpaper disc on a high speed grinder. Always cut away from the edge in order to shear the material off. Its the only way it will fail. I usually wait up to a month for the resin to really get hard. If you notice, and it becomes more obvious with kevlar, the resin continues to harden for several months. So if you don't need to trim right away, don't. The longer you wait the cleaner the resin matrix will come off. If you trim immediately (24 hours or so) the resin with burn easier and will ball up on the diamond wheel. Well, there it is a brief (?) description of 15 years of Kevlar experience. It a little more challenging but not a problem. Any body want to know about graphite? Okay a teaser ($$$$$$$). Rick Roberts