Date: Thu, 11 Jul 1996 00:27:05 -0400 From: Jim Hocut Subject: COZY: Re: Postcure Mark Morris wrote: >3. I went in to this thinking postcure was an option ... but a review of >this years archive of messages has me concerned. I noticed a comment >that all "structural" components should be post-cured (I forget who >said it). Other than the arm rests and a few such items, what isn't >"structural?" Will a white aircraft in Florida need to be postcured? and Marc Z. replied: >While most everything is "structural", not everything is highly stressed. >Definitely post-cure the wings, main spar and canard. This will probably lead to another interesting discussion. Someone asked Burt Rutan in one of his forums at OSH last year about post-curing. He basically said that yes, it's a good idea, HOWEVER, look at the hundreds of airplanes on the flight line that have been flying for 10, 15, and even 20 years that were never post-cured. Myself, I'm not losing any sleep over it, but I'll probably eventually get around to post-curing the items Marc mentioned if I can figure out a fairly painless way of doing it. Remember to support anything being post-cured very well so that they can't sag during the process. Jim Hocut jhocut@mindspring.com From: Marc J. Zeitlin Subject: COZY: Re: Postcure (fwd) Date: Thu, 11 Jul 96 9:34:22 EDT Jim Hocut wrote; >Burt Rutan... said that yes, it's a good idea, HOWEVER, look at the hundreds of >airplanes on the flight line that have been flying for 10, 15, and even 20 >years that were never post-cured. >... I'll probably eventually get around to post-curing the items Marc >mentioned if I can figure out a fairly painless way of doing it. Remember >to support anything being post-cured very well so that they can't sag during >the process. Yes, I had forgotten that Burt had said that - I was there too. I guess I was recalling the Q2 plans, which claimed it was MANDATORY to postcure the wings. Maybe, since the original Q2 had the wheels at the tips of the canard so the canard was stressed highly 99.999% of it's life (sitting on the ground) it was a lot more important than it is for the standard canard configuration. Burt did mention, however, that there are some droopy wings out there, which MAY be attributable to not post-curing. Anyway, I post-cured the Q2 wings by painting them black with water color paint, and leaving them out in the sun on a hot summer day. I blocked them up carefully with foam so they had no stress on them. I measured the surface temperature, and they got up to ~140 - 150 deg F. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Marc J. Zeitlin Subject: COZY: Postcure (fwd) Date: Thu, 11 Jul 96 12:01:06 EDT Bob Misterka wrote; > 1. What did you use to measure surface temp.? Hoo, boy. 1983 brain cells, do your thing. I have only the slightest clue. I might have just taped a thermometer to the surface, or I might have used the little temperature sensitive flexible tape thermometers that ex-Alexander Airplane used to sell specifically for post cure temperature measurement. Or something else..... > 2. I suspect you would have to post cure both the top and bottom > surfaces, by exposing one side and then flipping the wing, canard, > etc. over and doing the other side. Correct? Correct. I painted both sides, left each side out in the sun until the temperature had stabilized + a couple of hours, and then flipped them. On a cloudless, sunny day, I did both wings in about 6 hours. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Thu, 11 Jul 96 11:52:50 EST From: MISTER@neesnet.com Subject: COZY: Postcure >Mark Zeitlin wrote: >"I measured the surface temperature, and they got up to ~140 - 150 > deg F." Mark, 1. What did you use to measure surface temp.? 2. I suspect you would have to post cure both the top and bottom surfaces, by exposing one side and then flipping the wing, canard, etc. over and doing the other side. Correct? Bob Misterka N342RM Date: Thu, 11 Jul 1996 16:31:45 -0400 From: CheckPilot@aol.com Subject: Re: COZY: Re: Postcure In a message dated 96-07-11 00:30:31 EDT, you write: > Myself, I'm not losing any sleep over it, >but I'll probably eventually get around to post-curing the items Marc >mentioned if I can figure out a fairly painless way of doing it. I remember reading somewhere that somebody suggested just wrapping everything in black plastic and setting it in the sun during the summer should heat it up quite a bit but I don't remember any numbers. Jack, was it in the newsletter a few years back???? (I loaned my newsletters out so I can't check myself). Jim Cozy III #455 Date: Wed, 17 Jul 1996 12:01:10 -0600 (MDT) From: Roy Grossinger Subject: COZY: Post Cure Last night I had just taken the vac bag off the Electrical covers for Chap 5. This was at the 5 hour point, I wanted the part cured so I could epoxy it in place. I heated my oven up to 165F and roasted the part for about 30 min. By this time I was done making the tapes for the sides and checked on the covers. (I figured if I messed up this part it was easy to make again) Is it okay to do this with other more important parts? A company I did some work for has a room sized environmental chamber which can be heated to any temperature below 230F. Can I do a post cure using this chamber if I keep the part supported, and if so what is the optimum temperature and for how long? Roy Date: Fri, 11 Oct 1996 15:54:01 +0200 From: Rego Burger Subject: COZY: POSTCURE This is another subject that can create a long debate. Chris van Hoof mentioned that it has an effect on the temp deflection. The theory is that if you cured an item at 80 deg F for two hrs your part would be able to withstand a heat source of 160 deg F for one hr. before doing silly things? All designers and builders I've spoken too so far reckon that they don't have an oven big enough to do this job to lab. specs. They use grey paint and sunshine etc. This in itself posses a warp risk. For wings I would reckon that you build a jig to hold the wing LE down and TE up to reduce this risk. Other designers and builders tell me that after two weeks at Room temp you will not get ANY benefit from post curing. They claim that the epoxy matures with age. With all this hazy info. one is left thinking that this is not an exact science. When mixed with opinion it tends to get one cringing. Manufacturers will tend to tell you over the phone what they perceive you want to hear to get a sale, then when you request things on paper the excuses are as varied as the # of stars. At one of our Universities attempts were made to get some figures on paper to boost a local suppliers claims. When I got hold of the "professor" who did the tests I managed to get him to confess that the samples got lost before the tests were done. The figures therefore are based on &*%$^#@! . My faith in that supplier has now been rated at (- infinity). Not all go to the lengths I do to get the Truth, so I'm a little worried when people can't put their money where their mouths are. Does anyone have an e-mail address of hexcell's lab. or tech. division. An salesman may be biased. 2427 is sold as having a "greater impact resistance" this sound great for those wishing to do barn storming. A data sheet with the physical specs. and so on would help a little to compair things with our market here please. West epoxies have the "BEST" impact resistance in the world, but they are used on boats and for finishing? I feel laminating resins need a moderate stiffness and adhesive qualities to make a structure reliable. If it is too stiff and brittle ( low elongation to break) it will crack easy. Anyone got the numbers for us all please? Rego Burger P.E. S.A. http://microfast.com/rego/ e-mail: burgerr@telkom.co.za Date: Fri, 11 Oct 1996 23:01:25 -0400 From: Nigel Field Subject: Re: COZY: POSTCURE At 03:54 PM 10/11/96 +0200, Rego wrote: > >Other designers and builders tell me that after two weeks at Room temp >you will not get ANY benefit from post curing. They claim that the epoxy >matures with age. With all this hazy info. one is left thinking that >this is not an exact science. When mixed with opinion it tends to get >one cringing. Manufacturers will tend to tell you over the phone what >they perceive you want to hear to get a sale, then when you request >things on paper the excuses are as varied as the # of stars. > Hi Rego, Yea, I can sure relate to that, found the same thing, most vendors of anything just seem to babble when you ask why or how or what. Seems to be a big gap between the engineering department and marketing. Anyway I have a bunch of Epoxy data but by far my most complete is a nice package put out by Gougeon Bros Inc Ph (517) 694-7286 on their Pro-Set system which is used for aerospace applications. Its far too long for Email so will include some select portions. >From the introduction section: " For some resin hardner combinations, a room temp cure will be sufficient for many applications, while others require an elevated post cure. However with post curing _ALL_ Pro-set Laminating Epoxies develope 100% of their potential physical properties. Higher Heat Deflection Temps (HDT) are reached by post curing. Even moderate post curing develops higher fatigue resistance and tensile strength." end quote. Small sample from a large matrix of resin/hardner and cure schedules shows: "125 resin / 226 hardner (a popular mix for airplane construction) room temp 2 wks RT 15hrs+140F 8hrs RT 15hrs+180F 8hrs Hardness shore D 80 80 84 Comp. Yield psi 14,700 15,696 15,757 Tensile str psi 7,960 10,386 11,071 Tensile elongation% 3.9 3.7 5.0 Tensile Modulus psi 5.3E+05 4.5E+05 4.32E+05 Flexural Strength psi 12,760 19,086 19,077 Flexural modulus psi 5.3E+05 5.24E+05 4.95E+05 Heat defl. (HTD) deg F 122.9 139.9 172.2 Izod impact (ft lb/in) .43 .63 .49 end quote. I have not been able to obtain any test data on 2427 so cant compare to above. Perhaps who ever "approved" it could provide this data??? No conclusions offered here just some interesting data to add to the discussion. Nigel Field Date: Mon, 14 Oct 96 14:24:07 est From: "Larry Schuler" Subject: COZY: POSTCURE Rego Burger wrote: >This is another subject that can create a long debate. >snip> Ok, I'm game; but only because I like the idea of post cure to increase the perfomance of the witch's brew. Generally accepted that post cure improves the performance of the epoxys we use, but would also like to know the specific results. I'd test it myself, but I don't have the wherewithall to do proper testing; just subjective, which isn't good enough.... Just as an FYI, Nat indicated in the training section, that post cure at 140 degrees is a good thing; therefore is an "approved" activity. He didn't elaborate too much on technique though..... He also aproves of (and currently uses) 2427, which I use; but, has not provided any technical info on post cure results [or the basic resin for that matter]. Shouldn't expect that though, since he doesn't provide any stress analysis data on the completed airplane either.... just the general operational limits. I guess it's classified info or something. Check the archives for more on post cure. I have been looking for specs on 2427 [need it for some stress analysis work], but so far drawn a big fat blank. If I do get some "reliable" info; I will post it along with source ID. Larry Schuler MKIV-#500 Ch-6, step 1 (Still!) Date: Tue, 22 Oct 1996 17:40:19 -0400 From: HighPlane@aol.com Subject: COZY: Re: Postcuring--statute of limitations? Is there any statute of limitations on postcuring--that is, any period after which it's less effective? Or can I still post-cure parts I made six months ago? BTW, every time I'm in the sauna at the local YMCA, I try to figure out a way to wrap my canard in a towel and sneak it in with me. Anybody in the group got any experience with sauna-based post-curing?! Date: Wed, 23 Oct 1996 12:11:17 -0400 From: DevoCoach@aol.com Subject: Re: COZY: Re: Postcuring--statute of limitations? I asked Stan the same question because I had completed my wings two years earlier. He said epoxies don't reach full cure for approximately 8 years and recommended postcuring all structures. I checked my notes from the seminar last night and found that he recommended postcuring at temps as high as 150 degrees. He also noted blue foam melts at 170 degrees (be careful)! I also found a spec sheet for Aeropoxy that lists the Tg, if cured at room temp (they don't define room temp), at 175 degrees. Post curing at 150 degrees for 4 hours increases Tg to 190. Stan took exception to the 175 degrees because Tg is determined by cure temp (60 degrees - 100 degrees??) Anyway, if you are located up north, as I am, and dont have the luxury of doing layups in 90 degree weather (my garage is 52 degrees this morning!), postcuring is probably a very sound idea! FWIW, Stan actually builds a cardboard structure around his epoxy structures, inserts a heater, and used a meat thermometer to monitor temps. Jeff Mallia