From: "Hunter GA (Gary) at MSXSCC" Subject: COZY: POST CURING EPOXY Date: Fri, 15 Jan 1999 07:03:01 -0600 Terry Lamp - wrote: > Thanks for all of the advise you offer this forum. I read your posts, and > believe your are very knowledgeable about glass and epoxy. > > If I may ask you a couple of questions about post curing. > Thank you and YES, ask away.... > How hot and how long? > 140-150F for as long as possible within reason. Slowly heat the part over a period of about 4 hrs. Then hold it at temperature for no less than 4 hrs. and as much as 12-24 hrs. After the first 4 hrs at 140F, and if you have the capability to accurately control the temperature, it would be good to slowly increase the temperature to 170F for another 4 hrs. and then slowly cool it down in the oven. Don't just open the door and yank the parts out. They will be a little susceptible to distortion at 170F (depending on the resin you use). More so from uneven cooling and coefficient of thermal expansion factors than from being too hot. Remember, the foam core cannot cool as quickly as the skins and it's expansion coefficient is far greater. Thus, we want to EVENLY heat and cool slowly. If you look around, you should be able to find a automotive paint shop that has a heated paint booth you can rent on a weekend. Put a couple of box fans inside with the airplane to help circulate the air for even heating rates. Load everything up Saturday morning, cook all day, and cool all night, unload Sunday morning. > Should the part be held in the perfect alignment or flatness or what ever > for the post cure period? > YES. Although the post cure schedule outlined above is slow and gentle with intention to prevent distortion, every little bit of precaution to keep things straight is cheap insurance for the same. > Does it matter at what point in time after the initial cure that you post > cure? > NO. > If it had been say, 6 months for instance. And say we are talking about > the > wing, should it be placed back in the jigs to post cure? > After one week - YES, 6 months, NO - it isn't necessary to go to that extreme for supporting the wings. Simply position them leading edge down on a flat surface and support the winglet so the wing waterline is vertical. Same for the canard. Fuselage inverted on two level saw horses would be nice. If it is already on the gear and the floor is level, it will be level. Cowlings should be in place on the plane if possible. If not, stand them up on the floor with the forward edges down. > Sorry for all of the questions, but I have been saving up. > > I hope I'm not imposing. > Not at all. These are great questions, and as such I have copied this reply to the Canard Aviators and Cozy Mailing Lists for all to read. Hope you don't mind. Gary Hunter EAA Technical Counselor Incidentally, the EAA doesn't "officially" recognize what I do here on the internet. If any of you have the desire, please send a note to the EAA Technical Counselor Program - Ben Owen recently retired and do not know who his replacement is yet. From: "Hunter GA (Gary) at MSXSCC" Subject: COZY: RE: post curing epoxy Date: Wed, 20 Jan 1999 08:27:23 -0600 S123at@aol.com wrote: > WHAT'S THE REASON FOR POST CURING? > Post Curing or the heating of the composite article after the initial cure at ambient temperature conditions - is to further the curing process beyond what it is capable of achieving without it. Epoxies do not cure completely under ambient temperature conditions alone. For some applications, this is OK. And for the most part, depending on the conditions when we build are airplanes, it is OK not to post cure your airplane too. Post Curing will increase certain performance properties of the epoxy resin. Most notably will be the resins chemical resistance (fuel resistance in our case) and the glass transition temperature (heat or desert sun resistance). To a lesser degree, there will be improvements and/or changes in some physical strength characteristics. Generally, absolute values for tensile, flex, compression, and impact properties will improve. In some resins, the tensile strength may go up slightly, while the strain to failure will go down - slightly. Similarly with flex and compression. This is not terribly significant and is more than compensated for in the design safety factors used in composite aircraft (a fair amount of overkill in my opinion). Two things the design engineers cannot design in a safety factor for is chemical & heat resistance. The fuel tanks will gain the most benefit from a post cure. Physical strength characteristics of composite laminates are not absolute and are very dynamic with temperature. They diminish as the temperature approaches the resin's glass transition temperature. On a hot summer day, if your wings are anything but the purest of whites in color, the skin and subsequently, the spars will warm up considerably. Without a post cure, some of the resins we use barely have enough heat resistance to withstand the extreme summer day conditions in the desert. Theoretically, but not probable, a quick departure into turbulent conditions may result in buckling of the upper wing skins or worse if your wings are not white. Yes, the composite will post cure itself by being baked in the summer sun much the same as it would in an oven. One small difference - only the top side is getting baked and you stand a extremely small chance of warpage do to differential shrinkage, and blah blah blah. The point is, controlled Post Curing is a plus in every way. But not mandatory. > SHOULD YOU TAKE OUT AS MUCH METAL AS POSSIBLE (CONTROL SYSTEM, FORWARD > BRAKES ECT.) > NO > THE CONTROL SURFACES WILL TRY TO LEVEL. > WHAT ? > CAN YOU LEAVE IT ALL TOGETHER? > Everything but the wings. Date: Wed, 20 Jan 1999 20:47:57 -0600 From: James Russell Subject: Re: COZY: RE: post curing epoxy Hunter GA (Gary) at MSXSCC wrote: > S123at@aol.com wrote: > > > WHAT'S THE REASON FOR POST CURING? > > > Post Curing or the heating of the composite article after the initial cure Hi all: The only time I've been to OSH (1996), Rutan said they pull coupons from the prototype set of outer wing panels (for VariViggen) every so often and the physicals have gone up 5% since fabrication (ca. 1975?). The parts are left outside for long-term test @ Mojave. This really heartened me as I was in the final stages of picking the Cozy to build. I am going to install a skin temp gage ala the Extra (mainly for info). Regards, James From: "John Slade" Subject: COZY: post curing issues for all epoxy systems - from MGS technical representative Date: Thu, 15 Apr 1999 09:40:41 -0400 Fellow builders: The following correspondance took place between myself and Johannes of GS( meunier@mgs-online.com ) over the last few days. It contains a lot of information which might be helpful for others. I know we have a lot of stuff in the archives about epoxies, but most of this discussion is not covered, at least not in the same way. I have extracted a couple of quotes from the text below.... >"It is a fact that after a room temperature cure a Tg will be around the >120-140°F NO MATTER WHAT [epoxy] SYSTEM YOU TAKE [use]." >"the chemistry has its rules and all epoxies follow the same cure >cinetics and they are the same no matter if there´s an MGS label on the drum or >one of our competitors." I have advised Johannes how to join the maillist so he can get involved directly in future. John Slade #757 ---------------------------------------------------------------------------- --------------------------------------------------- Hello Johannes, I am using your MGS L335 resin system on my Cozy MkIV project. So far I like working with the epoxy and the results seem excellent. At the Cozy dinner at EAA Sun & Fun last night a presentor from Shell warned builders against using MGS resin without doing a post cure. What is your advice about the need for a formal post cure of each part and, if needed, how should it be done? Regards, John Slade ---------------------------------------------------------------------------- ------------------------------------------------------ Hello John, even though there are a few so called room curing epoxy systems available, I´d rather see every epoxy system to be post cured at elevated temperatures. The reason is as follows: One of the properties in which epoxy systems are different is the maximum possible Glass transition temperature (Tg). The Tg describes (among other properties) the amount of cross linking in the molecular structure of the epoxy and can be taken as a reference for the heat resistance of the cured epoxy resin (in practice, airplanes are designed to withstand structural stress while exposed to temperatures staying approx. 15-20°C below the actual Tg). As a rule of thumb, the Tg rises with the post curing temperature and exceeds this temperature for maximum 20-25°C. Which means: After a room temperature cure (25°C /77°F) you´ll end up with a Tg of approx. 50°C/120°F. It also means that the shear modulus of the epoxy will drop, when exposed to temperatures higher than 40°C / 105°F. A post cure cycle, for example at 50°C /120°F will raise the Tg up to approx. 75°C / 165°F, depending on post cure time. A typical post cure cycle for example is a 15hours 50C/120F post cure cycle. The maximum possible Tg with the L335 is approx. 185°F All this is especially true for structural parts of airplanes such as spars, wing shells, and so on. It is less critical for bonding, because a low shear modulus is often advantageous for bonds due to its ability to cut stress peaks. Furthermore, when parts are exposed to higher temperatures, they normally post cure themselves. L335 has an excellent initial cure at room temperature. It can be demoulded, worked (trimming, grinding, ...) bonded and even after room teperature cure it shows already good mechanical properties. However, the german aviation authority requires a heat treatment for every structural part and for repairs on airplanes and we recommend it too, you simply get the best properties from the material. All this is not only true for MGS resins, but for all epoxy resins. The chemistry of these materials follows the same rules all over the world. If somebody tries to sell you a totally room temperature curing resin system, he is either in the urgent need of making fast sales, or he provides a resin system which only capable of a low Tg of (<120°F), wich would in my opinion limit your airplane to some 100°F structural temperature. I guess you would not feel too comfortable with this. Companies often advertise their systems with so high Tgs, but they don´t tell you that you have to post cure at high temperatures to obtain such a high Tg. We go the other way round. We first ask how high will the strutural temperature be on the produced part? Then we recommend a suitable resin system, which gives customers a Tg high enough for their purpose, but one they can achieve with their possibilities. A 120F post cure can be done by a homebuilder at home, but not a 200F post cure. Which again means that a system with a max Tg of 200F is NOT a suitable system for a typical homebuilder. The L335 has totally completed the requirements of the RHV, thus including strength tests at hot wet conditions (54°C/130°F), fatigue tests, a.s.o. and is being used for the design of sailplanes, motorgliders, ultralights, homebuilts and other devices. It features excellent working properites and good physiological compatibility. Post curing is an important item, but its only one of a whole bunch of things that should be considered when deciding for a resin system. I hope this could answer your question. If I can be of any further assistance, please don´t hesitate to contact me. It might sometimes take a little longer for me to answer, because I am often abroad, visiting customers or so. Have a lot of sun&fun (I´d rather be there too!) Regards, Johannes ---------------------------------------------------------------------------- ------------------------------------------------------ Hello Johannes, Thanks for the quick and informative reply. Between the lines it seems that you are saying that MGS is as good as any of the epoxies available in this area. A "tg" of 120f seems very low. I think other resins quote a higher figure. I am told that, even when painted white, the internal temperature of a part can rise to 140f when exposed to 90f sun on the ramp. (20 degrees above the temerature where you say the shear modulus will drop) Many composite aircraft survive these conditions daily without having had a post cure. I saw hundreds at Sun & Fun. Are they ok because they used a resin which gives a higher tg without post cure, or did they post cure naturally with time and gradual exposure to heat? Obviously I do not wish to park my airplane in Arizona one day and return next day to see the wings dragging on the ground! Is this possible, or are we only talking about severe stuctural stress when airborne (when the temp will not be high). My next question relates to a practical way to obtain a post cure. I live in South Florida. The daytime temperature here is often 90F plus. I have already build the fuselage tub of my Cozy. Some parts cured in 80 - 90 f temperatures. Some parts cured overnight in 60 - 70 f temperatures, but were later exposed to 90f degree temps the following day. The advice I have so far on this issue is "Don't worry. It will cure on the ramp when its finished." I think you are advising more proactive steps to obtain post cure whether builders use MGS or any other resin. If I put the fuselage (and other parts I make in the future) in the sun under a black plastic sheet I should be able to raise its temperature quite a bit, possibly to 120f for a period of 6 hours or so. 1. if the temperature of the part rises to, say 150f will my fuselage begin to sag? 2. will three short (5-6 hour) exposures to such heat have the same effect as one long (15 hour) one? 3. is more time better. i.e. should I expose it to the sun for 6 days instead of 3? Do you have any other practical suggestions for post cure method given that my fuselage is now too big to take easily to an enclosed space. What about those builders who live in colder climates and dont have the outside temperatures that I do. Should I send you some cured material for tg testing? If so, what should I send and where to, and how will I know that this is a representative sample given the different conditions under which cure took place for different parts. I'd like your permission to post your input to the Cozy maillist as I feel it is relevant to all. Regards, John Slade ---------------------------------------------------------------------------- ---------------------------------------------------------- John, unfortunately it seems to be normal that measured results are often very different from what companie advertise that their resin systems are able to. However, the chemistry has its rules and all epoxies follow the same cure cinetics and they are the same no matter if there´s an MGS label on the drum or one of our competitors. It is a fact that after a room temperature cure a Tg will be around the 120-140°F NO MATTER WHAT SYSTEM YOU TAKE. Of course different epoxy systems feature different properties such as: -The MAXIMUM Tg that a system can reach is different (But only after COMPLETE curing, this always requiring a heat treatment at a temperature close to the max Tg). Companies often state that their system state a high Tg, but they don´t tell you that if you want a Tg of for example 210°F, you have to post cure at a temperature of min.170°F (refer to the faxdiagram). -Working properties such as mixed viscosity, pot life, and so on is different -pysiological properties often are significantly different (in terms of allergies, skin rushes). This is an item we really care about, I don´t want people to become sick when they work with our products - And of course the mechanical properties are different -other differences The Tg is something important for research on systems and on work related to Q.A. procedures in the lab and it is one of a lot of material properties. But it is not the only criterium. It seems to me that it is often abused for marketing reason: everyone´s epoxy system has the highest Tg. Unfortunately you have to be quite into the theme to understand what the Tg tells you and what you can tell from a measured curve (a lot of those companies I guess don´t even have devices to measure a Tg). How should the average homebuilder know what the whole thing is about? So they think: the higher the better and a higher number is always better than a lower number. You could as well sell the resin at a higher price: a more expensive resin MUST be better than a cheaper one. For me, this is a different way of cheating, but this is only my personal opinion. To your questions. I will fax you a diagramm for L335 and L285, which shows the raise of Tg over the time for different post cure temperatures. When you see the diagramm, keep in mind that this means the structural temperature of your parts during the heat treatment, not of the surrounding. When you expose the parts to 120F warm air, it takes some time until the part has reached a temperature close to the surrounding. Still the diagramm makes some things clearer (by the way, all the info is also on the internet on our webpage www.mgs-online.com in our technical info). Airplanes have been built in the past without being post cured, even standard gliders that have been sold in hundreds and none of them (to the best of my knowledge) ever had a structural failure due to a Tg too low. What they say is true: an airplane post cures itself as it is exposed to higher temperatures. Secondly: temperaturewise the worst case indeed is the airplane standing on the ramp over a dark concrete surface somwhere in arizone (or in a burning hangar ). BUT: An airplane is normally designed to withstand some 2,6 - 5g (depending on applicable design rules) under worst case conditions with a safety of 1,725, not included the safety factor in the material (they don´t calculate with failiure values, but with approved material values or A/B values), at least this is the design philosophy in Germany. Which means that the STRESS on an airplane on the ground is low and the safety is enough to prevent failure like buckling or bending. This part is experience and no one will take a guarantee for it and still I´d rather see every epoxy structure to be post cured before it goes flying. We had an incident a couple of years ago where a glider stood in a burning hangar. It had (at least partly) been exposed there to temperatures of approx 200°C (390°F!) and the geloat already had turned brown when the fire was extingushed. The question came up whether the airplane (the resin was L285 / Hardener 287) was to be scrapped or overholed. Investigation showed that the airplane was not damaged and the material still had its full properties (and a real good Tg...). I would not recommed this as a common way to post cure, but it is a good example in terms of heat resistance and Tg. Post curing: You mentioned the first way: built your airplane, put it on the ramp somwhere on a hot day in summer and it will post cure itself. This has worked in the past, however, there are other disadvantages. Post cure means an ongoing in the chemical reaction (cross linking ) within the molecular structure of the epoxy. Although the shrinkage of epoxies is extremely low (normally <0,5%) you often see a printthrough of the internal sturctures on the surface (typical is: bulkheads in the fuselage, spar caps, ribs, foam cores, bonds on the wing). You can minimize this by post curing before you do your paint shop. This has no technical effect, but an optical and we are all the same: everybody would like his ship to be the most beautiful in Oshkosh... Exposure to heat - post curing: 1.The best way is a post cure oven, autoclave or whatever, unfortunately not everybody has such devices in is backyard. 2.But: every village has its automotive body shop and a lot of these shops have a spray booth that you can heat up to 120-140F. If a car fits in, you airplane will fit in too. You better find a spray booth anyway, for the paint shop on the airplane. Just remember to support your wing not only on the root and tip, but also somewhere in between. Then RAMP UP the temperature. Start for example with 2h/100°F and increase the temperature for example 20-40°F in 2hours. The oven won´t probabely go higher than 140°F but this is perfect (the Katana for example is post cured at 140°F and they look real good). Keep the temperature for 8-10h and the post cure is done. Do it BEFORE you paint the aircraft to minimize the printthrough. As you can see, holding the part at 5h at the stated temperatures gives you approx. 90% of the Tg you can obtain at a certain post cure temperature. Professional manufactureres normally post cure 10 - 15h. 3.Build a plastic tent around you parts and place them on a dark surface in the sunlight. It heats up itself and the tent prevents the wind to cool the parts. Or better (works in every workshop and for field repairs: Again the tent, but blow in with an elecric heater. DON`T LEAVE IT ALONE! They can start burning and they always do it when you leave them alone (Murphy´s law). Several times at same temperature: It is better to keep the temperature at the post curing temperature for a longer time span than several times for a shorter period of time. What happens inside the epoxy, again, is a chemical reaction. You need some energy to restart this reaction, which is given by a great temperatre difference. After some 5h as you can see on the diagram, the Tg is already so close to its maximum, that it would take a higher temperature to restart the reaction. You normally get better results if you keep it going once it has started. I can offer you to send over a sampe of the material you used. It should be cured resin, either neat or a reinfoced piece with a high resin content. A few grams is enough to cut a sample from. (a sample weighs approx. 20mg). On the other hand I have to ask people to understand that I can only measure those samples in our lab in my spare time, the lab equipment is primarily for Quality control and research purpose. Still the offer stands, If you feel it is necessary send a sample over and I´ll measure it. Could you be so kind to provide your fax number, I will then fax over a diagram with the Tg rise as promised. I fyou feel that our conversation is helpful for other homebuilders you are welcome to input it into the Cozy mail list. I guess this is on the internet, could you come up with their adress (link or something)? If I can be of any furhter assistance you are welcome to contact me. Regards, Johannes -----------------------------END----------------------------- From: "John Slade" Subject: Re: COZY: Epoxy brand compatibility Date: Sun, 2 May 1999 22:41:37 -0400 Gary, >This is based upon the manufacturer's product technical bulletins. i.e. what the manufacturers CLAIM in their marketing materials. Have any independant tests been done? I'd really like to see some real data on this subject. >MGS themselves prescribe a post cure for their products. I understand that the German aviation authority requires a heat treatment for every structural part and for all repairs on fiberglass airplanes without regard for the epoxy system in use. MGS tell me that they recommend post curing because "you simply get the best properties from the material. All this is not only true for MGS resins, but for all epoxy resins". I think this was backed up by Nat Puffer's recent post. In fact, Nat's data showed that MGS was significantly better both at room temperature and after post cure. >a friend of mine was telling me .... structural failures in these aircraft >could be simply overstress or design related, and the fact they may have >been built from MGS resin a pure coincidence. Come on Gary! Third hand rumor and innuendo is not good information and, in my opinion, is not appropriate for public posting. >However, considering the above, the requirement of a post cure, and given >the flawless tract record of the Safe-T-Poxy system (now EZ-Poxy) I am >curious as to why anyone would even consider using anything else. I haven't used it, but my understanding is that EZ-Poxy stinks and people are getting allergies from it despite using protective measures. Alternatively, MGS is strongly recommended by the designer of the Cozy. It claims low allergy ingredients and better curing properties. It also has low viscosity, good humidity performance and a controllable setup time. On this basis, I too am curious as to why anyone would even consider using anything else. I'm doubly curious now. Do you happen to know which company which makes the ingredients for EZ-Poxy? Regards, John Slade Cozy #757 N386JS Reserved Progress at: http://kgarden.com/cozy Of course, that's just my opinion. I could be wrong! Date: Mon, 03 May 1999 06:08:40 -0400 From: Jeff Russell Subject: Re: COZY: Epoxy brand compatibility John Slade wrote: > >Don't forget that you need to post cure the MGS system. > Are you suggesting that MGS requires a post cure while other epoxy systems > don't? If so, what do you base this on? This is what it says on the MSDS. Some of the other systems must not need the post cure to get the results needed for the strength that they tested for. Some say MUST and some say (for best results) -- Jeff Russell/AeroCad Inc. E-mail: Jeff@aerocad.com 2954 Curtis King Blvd. Ft. Pierce, FL. 34946 Shop# 561-460-8020 7:00am to 3:30pm Home# 561-344-6200 Website: http://www.Aerocad.com Composite workshop info: http://www.Sportair.com From: "John Slade" Subject: Re: COZY: Epoxy brand compatibility Date: Mon, 3 May 1999 09:31:21 -0400 Jeff, >Some say MUST and some say (for best results) It seems that "for best results" applies, in fact, to all epoxy systems. I think I'll build a black tent. Regards, John Slade From: "Ryan Amendala" Subject: COZY: Post Curing Date: Mon, 03 May 1999 11:14:19 PDT When is the best time to post cure the entire airframe? Before/After final fill? Before/After prime/paint? Does it even matter? Thanks Ryan _______________________________________________________________ Get Free Email and Do More On The Web. Visit http://www.msn.com From: "Nat Puffer" Subject: Re: COZY: Post Curing Date: Mon, 3 May 1999 17:14:28 -0500 Cozy builders, There seems to be a great deal of misinformation and misunderstanding about post-curing. The property affected by post curing is the "Heat deformation temperature". This is the temperature at which epoxy begins to soften and lose its mechanical properties. All room temperature curing epoxies (including EZ Poxy) have to be post cured to reach their maximum HDT. This DOES NOT mean that composite airplanes have to be post cured. The subject of post curing hardly was even discussed until recent years. In the meantime hundreds (maybe thousands) of Variezes, Long EZs, Defiants, Cozy 3s and Cozy 4s have been built and are flying without post curing. You depend upon Glass for the structural properties of your airplane. The epoxy is there to hold the glass fibers together. You do not depend on the strength of the epoxy, and as long as you paint your airplane white, like everyone else, forget about post curing. The only place where post curing is important is in the landing gear struts. Here you want the manufacturer to use the best possible epoxy with the highest possible HDT and make sure that manufacturer heat treats it to the maximum achieveable HDT. If you notice from my previous post, MGS 285 has a HDT of 150 deg. F after only a room temperature cure. This is better than RAE, Safe-t-Poxy, 2427, and EZ Poxy, and almost as good as these after an elevated post cure. There is less reason to post cure MGS 285 than any of the other approved epoxies. Even MGS 335 is better after only a room temperature cure than any other of the approved epoxies, except MGS 285. Nuff Sed. Nat ---------- > From: Ryan Amendala > To: cozy_builders@canard.com > Subject: COZY: Post Curing > Date: Monday, May 03, 1999 1:14 PM > > When is the best time to post cure the entire airframe? Before/After final > fill? Before/After prime/paint? Does it even matter? > > Thanks > > Ryan > > > _______________________________________________________________ > Get Free Email and Do More On The Web. Visit http://www.msn.com From: ZeroGCorp1@aol.com Date: Tue, 4 May 1999 09:02:22 EDT Subject: Re: COZY: Epoxies-post cure In a message dated 4/30/99 2:04:01 PM Central Daylight Time, cozy@extremezone.com writes: > Epoxy R.T.Cure Elevated Post cure > RAE 120 151 > Safe-t-Poxy 118 171 > 2427 117 162 > EZ Poxy 125 158-170 > PTM&W --- 202 > MGS 335 130 185 > MGS 285 150 240 After checking with some Material scientists that work in my building and Burt Rutan, it really appears that the most important criteria for epoxy matrix here is the deflection temperature and compatibility with the foam core material. ASTM D 648-82 sets out a standard for measuring deflection temperatures of plastics under flexural load and I can't see why we couldn't use this to measure the various epoxies above before/after post cure and after ambient long term cure. Since the polymerization and most importantly, polymer cross linking, is not completely finished during a room temperature cure, the elevated cure temperature simply encourages the reaction to go to completion much faster. I think what Nat and others have said is that during the normal time of building, testing, and flying the plane, it is exposed (incrementally) to higher temperatures. Every time the polymer is elevated in temperature, then it cures (cross links) a little more. If you look at the Gillham time-temperature-transformation (TTT) diagram, what one sees is the typical "S-curve" that shows why an epoxy cure should be carried out in steps for maximum Tg. Keep in mind that in fiber-reinforced plastics, the fibers carry most of the mechanical load and the polymeric matrix serves to transfer stresses to the load-bearing fibers and to protect them against damage. With a lower Tg, one is susceptible to *sudden* increases in temperature (like, perhaps, flying into an active volcano, or low over a forrest fire). With slow, constantly elevated temperatures like are seen in virtually all of our garages, the Max Tg should always stay ahead of ambient as Nat pointed out in an earlier post. I will continue looking into this as I am interested in this as much as anyone on the list. There is much more to learn here and it is an important subject for discussion. I may carry out ASTM 648-82 on the MGS 335, 285 and EZ epoxy as I have those here. Maybe if these go well I can solicit sample lots from other Manufacturers and do further testing, but I do have a plane to build!! If anyone has any other information to add, I really would like to explore this as it will always be a "hot" subject when new epoxies are introduced. Ray Cronise CZ#770 References: Sperling, L.H., Physical Polymer Science, Wiley Interscience, 1986, p.p. 272-290 Gillaham, J.K. in "The Role of Polymer Matrix in the Processing and Structural Properties of Composite Materials," J.C. Seferis and L. Nicholais, Eds. Plenum, 1983, pp. 127-145 From: "John Slade" Subject: Re: COZY: Epoxies-post cure Date: Tue, 4 May 1999 09:50:15 -0400 Hello Ray, I was delighted to see your post. Important decisions are being made based on manufacturer's claims. Many of us are committed to a particular epoxy system at this point, but I'd very much like to see some independant testing done. The results might just make all our airplanes safer. If you have the expertise and equipment needed - go to it, then we can all make informed decisons. But as you say, there is that small matter of an airplane to build. Regards, John Slade #757 From: "Hunter GA (Gary) at MSXSCC" Subject: COZY: Epoxy brand compatibility - the continuing saga Date: Tue, 4 May 1999 11:28:13 -0500 John, > >This is based upon the manufacturer's product technical bulletins. > > i.e. what the manufacturers CLAIM in their marketing materials. Have any > independant tests been done? I'd really like to see some real data > on this subject. > I agree. I deal in this world all the time. The costs associated with formulating and testing are horrendous. I know - I have been doing it for 25 years now. Only the larger formulators, and well funded / supplier supported formulators can afford to publish any test data at all. MGS provides above average data. But data isn't everything. Field testing fills in the blanks. You (we) are the field tester(s). > >MGS themselves prescribe a post cure for their products. > I understand that the German aviation authority requires a heat treatment > for every structural part and for all repairs on fiberglass airplanes > without > regard for the epoxy system in use. MGS tell me that they recommend post > curing because "you simply get the best properties from the material. All > this is not only true for MGS resins, but for all epoxy resins". I think > this was backed up by Nat Puffer's recent post. In fact, Nat's data > showed > that MGS was significantly better both at room temperature and after post > cure. > And WHY do you suppose the German Federal Aviation Authority requires heat treatment ??????? It is true - you do get the best properties from post curing all epoxy systems. I have been say that all along. > >a friend of mine was telling me .... structural failures in these > aircraft > >could be simply overstress or design related, and the fact they may have > >been built from MGS resin a pure coincidence. > Come on Gary! Third hand rumor and innuendo is not good information and, > in > my opinion, is not appropriate for public posting. > I'll take my licks here. You are right, that was a poor form of communicating - GOOD information. > >However, considering the above, the requirement of a post cure, and given > >the flawless tract record of the Safe-T-Poxy system (now EZ-Poxy) I am > >curious as to why anyone would even consider using anything else. > > I haven't used it, but my understanding is that EZ-Poxy stinks and people > are getting allergies from it despite using protective measures. > Alternatively, > MGS is strongly recommended by the designer of the Cozy. It claims low > allergy ingredients and better curing properties. It also has low > viscosity, good humidity performance and a controllable setup time. On > this > basis, I too am curious as to why anyone would even consider using > anything > else. > Yes, it "smells". The fact is - no resin or curing agent is non-allergenic. The fact is - anybody can develop an allergy to a substance that other people do not. I have been working with epoxies in Shell's laboratories for 25 years. I have become allergic to a specific curing agent with a molecular weight of 400. If I am in the same room as this un-opened container of curing agent, a rash breaks out on my face within hours. But, I am not allergic to the exact same compound with a molecular weight of only 230. There have been no other reported incidents allergic response to that compound - GO FIGURE. The fact is, each of us have to search around for what works for them. For some of us, no epoxies are safe and a Glasair is in their future. > I'm doubly curious now. Do you happen to know which company which makes > the > ingredients for EZ-Poxy? > Yes ! The lowest bidder. Are you inferring I have an ulterior motive ? MGS is as good as any of the resin systems available today for building your airplane. As I have said before, the roots of their system is an industrial fabrication scene where for the most part, environmental controls are better than what is available or found in a typical homebuilder's shop. The primary component in the MGS and the Aeropoxy 2427 hardener is a cycloaliphatic amine. It provides very high Tg's over 150C (302F). Nowhere in the industry is this type amine (in it's unmodified-modified form) used without deliberate heat curing. Although it will "react" with epoxy groups at 25C (77F) (laboratory conditions) it can do a bunch of nasty things along the way. It will react with CO2 in the atmosphere to form probably the worst "amine blush" of all amine families. It also has a strong propensity to "B-stage". A "B-stage" is where the resin and curing agent forms a vitrified solid that for all practical purposes appears to be a cured resin / curing agent matrix, but it is not. And without the assistance of a post cure, it will not continue to cure any further. The result is a brittle product that behaves a lot like peanut brittle - it yields poor peel strengths in fiber reinforced composites (hint). So, in the formulators bag of tricks, we add what I call "fu fu juice, and mummy dust" to this curing agent to tame these nasty traits. They are non-reactive ingredients like - benzyl alcohol, and nonyl phenol to accelerate the reaction rate sufficient enough to reduce the severity of these problems. NOW the reaction rate is too fast for most applications, and so we blend in a minor amount of a slower aliphatic amines (polyoxyalkylamines typically) that have interesting traits as well. They don't blush (good), or cure completely at 25C in small masses (bad) and produce relatively low Tg's - even fully cured (bad). However, the benzyl alcohol and nonyl phenol will accelerate that amine too. If you get the formulation just right, the result is a nice blend that seems provide all the necessary properties "in the laboratory" and the intended industrial fabrication scene where there are good environmental controls (temperature and humidity). BUT..... In the homebuilder's world, the temperature control is "typically" not that good. If it drops much below 20C (68F), the cycloaliphatic component of the curing agent doesn't benefit as much from the accelerators as it did at 25C and it begins act like it's nasty old self again. AND, it can "B-stage" leaving all the accelerator for the other type amine. In a fiber reinforced composite, you get a cured solid that appears to have all the physical characteristics you expect (including HDT - Natt). However, certain performance properties like "peel strength" (Aeropoxy 2427) and chemical resistance (fuel) may not ever develop. There are a lot circumstances surrounding this next scenario (temperature during initial cure, humidity level, CO2 level in the room, how long it has been since it was initially cured, etc) If the formulation isn't just right - a post cure may not reactivate the curing process and you cannot alleviate the poor peel strength or chemical resistance problems. This is a real danger. I have preached shop temperature controls from day one on this list, and on the canard aviators.com list. When the 2427 thing started, I knew immediately what was going on. I didn't say anything. I really didn't what to jump into this bag of worms - let the Aeropoxy people handle it and they did. The lack of understanding the chemistry involved (and understandably so) makes it a real challenge. My position being a supplier to ALL these resin formulators makes it particularly precarious one. Then MGS showed up on the scene, and knowing the similarities to the 2427 hardener I became more concerned. I began my preachings on temperature controls and post curing. Fortunately, (and unfortunately for you John) only one incident of what can happen has happened thus far. Knowing MGS was from Germany, I thought product support would be non-existent. I am happy to say, I was WRONG and thanks to the internet - MGS has done a stellar job supporting their product here in the USA. I know you many of you may be confused by all this gobbledygook. That is not my intent. I hope to clear much this up with a forum at AirVenture '99. Gary Date: Tue, 4 May 1999 12:12:05 -0500 (CDT) From: Tom Brusehaver Subject: Re: COZY: Epoxy brand compatibility - the continuing saga >primary component in the MGS and the Aeropoxy 2427 hardener is a >cycloaliphatic amine. It provides very high Tg's over 150C (302F). Do you mean Aeropoxy or 2427? Aeropoxy (PTM&W) makes 3660 and PR2032? Hexcel makes (made?) 2427? From: "Hunter GA (Gary) at MSXSCC" Subject: RE: COZY: Epoxy brand compatibility - the continuing saga Date: Tue, 4 May 1999 12:29:18 -0500 Tom wrote: > Do you mean Aeropoxy or 2427? > > Aeropoxy (PTM&W) makes 3660 and PR2032? > > Hexcel makes (made?) 2427? > > WOW - did I do that ???? I meant Hexcel 2427. Later I referenced Aeropoxy fixing the 2427 too. I meant HEXCEL again. Sorry PTM&W - I'll probably hear about this one from my boss. Thanks for pointing that out Tom. Gary From: ZeroGCorp1@aol.com Date: Tue, 4 May 1999 14:02:01 EDT Subject: Re: COZY: Epoxies-post cure In a message dated 5/4/99 9:49:32 AM, rjslade@bellsouth.net writes: >Many of us are committed to a particular epoxy >system at this point, but I'd very much like to see some independant testing >done. The results might just make all our airplanes safer. If you have >the expertise and equipment needed - go to it, then we can all make informed >decisons. Here is a bit more data....I picked up several fiber reinforced plastics handbooks at the library. I found this to be interesting: "..one of the most striking effects due to fibers in composites is the great increase in heat distortion temperature....for amorphous materials the increase in heat distortion temperature is more of an apparent increase than a real increase since the increase results from a decrease in creep rate due to the higher modulaus rather than from a true increase in the softening temperature or glass transition." There was also a chart (for randomly oriented glass fibers in a high density polyethylene) Glass Fiber 0% 10% 20% 30% ________________________________ Temp (F) 160 240 264 266 (HDT) Flexural Str. 3000 6410 9750 12,290 (PSI) Obviously we have a lot more strength due to continuous fibers and biaxial orientation in the various layups. MY feeling at the moment is that if you paint your plain white, and don't use it to fly over forrest fires, your probably never going to to see much difference in the epoxy performance. Most of these designs have some hefty safety factors build in...besides, one question I thought of this morning, is how much problem do folks have with cowlings and firewalls? afterall the parts adjacent to the engine, certainly see temperatures in excess of the surface of the wings and there are a lot of these things flying... >But as you say, there is that small matter of an airplane to build. I knew I would start getting sidetracked with the technology...never guessed it would be this fast. Ray Cronise CZ#770 Reference: Mechanical Properties of Polymers and Composites, Nielson, L., Marcel Dekker, Inc. 1974, p.p.341-43 & p.p. 475-76. From: "John Slade" Subject: Re: COZY: Epoxies-post cure Date: Tue, 4 May 1999 21:40:25 -0400 Ray, >if you paint your plain white Don't you mean "if you paint your plane plain white" :) >I knew I would start getting sidetracked with the technology...never guessed >it would be this fast. Beware. All this chemistry and physics is fancinating stuff...which isn't likely to affect us builders very much at all provided we just follow the leader. They might have a new epoxy out by the time you've done all the testing - then you'd have to start all over again! "Build it and it will fly" John Slade From: extensionsystems@mindspring.com Subject: COZY: Fw: Post Cure ??? Date: Thu, 6 May 1999 08:39:38 -0500 If I do opt for a post cure (I can get into a large powder coat oven) 1. what Temp do I take the parts to 2. how long do they stay. 3. do I have to jig them to keep from twisting, bending ect... I am a long way from this stage but with the subject on everyone mind I thought this would be a good time to ask. Thanks Brian From: "Hunter GA (Gary) at MSXSCC" Subject: RE: COZY: Fw: Post Cure ??? Date: Thu, 6 May 1999 10:12:11 -0500 > If I do opt for a post cure (I can get into a large powder coat oven) > Typically powder coating ovens are operated in excess of 350F and as high as 450F and as such it will have a rather powerful heat source. Although the temperature controller may have the capability to regulate at the low temperatures you need, it may not be all that accurate and have large swings between on off cycles. So, my advice with this type oven is to preheat it at the desired settings, but measure the actual temperature with a separate pyrometer to determine any inaccuracies and variations. My concern is that with such a powerful oven operating way below its normal operating range, there is a potential for it to have a too rapid heat up cycle that usually leads to set temperature overshoot. However, with proper planning, you can work around this. Just be careful and preheat the oven if it is starting out cold. > > 1. what Temp do I take the parts to > 140-150F > 2. how long do they stay. > At least 4 hrs - and up to 12 hrs. > 3. do I have to jig them to keep from twisting, bending ect... > If the fuselage is on the gear, it can stand alone. Otherwise support it on saw horses inverted and level. The wings should be positioned vertically with the leading edge down - raise them off the floor a bit with at least 4 wood blocks and support the winglets. Likewise for the canard. I wouldn't post cure the canopy in the oven however. Paint the canopy frame in black primer and bake it in the sun in your back yard for a couple days. > Gary Hunter Date: Thu, 06 May 1999 12:24:59 -0700 From: hrogers@slac.stanford.edu (Howard Rogers) Subject: RE: COZY: Fw: Post Cure ??? >Gary Hunter wrote: >> I >wouldn't post cure the canopy in the oven however. Paint the canopy frame >in black primer and bake it in the sun in your back yard for a couple days. >> Gary's comments on the powerful oven made perfect sense to me, but the above statement causes me some concern. I seem to remember that Burt Rutan did some skin surface temperature measurements of different colors, in the Mohave, (published in CP) to illustrate the reason we paint these birds white. The Black or Navy Blue surface got to some incredibly high temperatures (I seem to remember more than double Gary's reccomended post cure temps). If the canopy frame was black, and sitting outside, it would mainly be heated on its top surface, by radiation. This is quite different from an oven. I see here, the potential for a tremendous temperature gradient from top to bottom, as well as a severe over-temp at the surface. Along with issues of proper support and warping, it doesn't sound like a good solution, to me. The canopy is not a structural member. It gets the usual amount of "garage post cure", and I think that is adequate, with just about ANY epoxy system. Painting it black and putting it out in the sun seems very risky. -Howard Rogers Date: Fri, 07 May 1999 11:00:39 +0200 From: "Rego Burger" Subject: COZY: Post Cure Delete if not interested in the subject. Before you stick your 2500hrs of hard labour into an oven at high risk consider this. FOAM CORES have temperature limits too! 90% of heat treated / Post Cured glass products are SOLID glass. Foam can collapse and deform when heated. Post Cure heat treatment can be done at lower temp. for longer periods of time and achieve the same results. example only: To achieve a HDT of 90 deg C the idea is to heat it at this temp for 1 hr. Now the same result can be achieved by exposing the item to 45 deg C for 2 hrs. ( The exact formula, heat / time ratio is available from manufacturers and may not be linear ) So don't be eager to aim for too high a heat deflec. temp. you will ruin the core. This is why the folks suggest trying to treat an item that has room temp cured over 14 days is a futile exercise by comparison to the desired effect. ( 20 deg C x 14 x +/-6hrs is said to achieve HDT of 150 F for a system) The main gear is solid glass and can handle much higher heat than a foam core item and NEEDS to be treated to handle some high temps from brakes. The added strength maybe around 10-15% but this is a bi-product of the exercise. No one in their right mind will design a foam core airframe's ulimate strength based on this being achieved by POST CURE. The idea was to keep cost and complication down on production for us home - builders. The moulded stuff is another subject and is often treated. The cheapest way to warm items after layup is to immediately expose them to an elevate temp. once you have finished a layup, I did this on a few items I felt required this to my tastes. I used fan ( moving air ) heaters under a "plastic" sheet tunnel on the work bench. This gave the resin an elevated curing temperature ( +/- 30Deg C on a digital termo.) I set the heater on a timer to switch off after 4 hrs, while I entered dream land.) This could be described as elevated temp. cure as opposed to Post Cure but is more moderate on the core material than that hot oven later. The main benefit was the next morning it was CURED and ready for trimming which speeded up production time in the winter months. Rego Burger. Date: Fri, 07 May 1999 20:46:56 -0400 From: "Marc J. Zeitlin" Subject: Fwd: COZY: Post Cure Rego Burger wrote; >FOAM CORES have temperature limits too! I'll agree with this 100%. >Post Cure heat treatment can be done at lower temp. for longer periods >of time and achieve the same results. > >example only: >To achieve a HDT of 90 deg C the idea is to heat it at this temp for 1 >hr. Now the same result can be achieved by exposing the item to 45 deg C >for 2 hrs. ( The exact formula, heat / time ratio is available from >manufacturers and may not be linear ) While I agree with the idea that you have to protect the foam, the notion that you can achieve higher Heat Deflection Temperatures merely by leaving the epoxy at a lower temperature for a longer period of time is misleading at best. By this logic, I should be able to leave it at 22 C for 4 hours, or 11 C for 8 hours, and get the same results. This is not true (I understand that this is just an example, but it's not a good one). First of all, you'd have to measure temperature in Kelvin (an absolute scale), not in Centigrade (a relative scale), even if the ratios were linear, which they're certainly not. Secondly, it's clear that leaving the epoxy at 22 C (about room temp.) will do absolutely nothing in the way of post cure. As you say, the temperature/time ratios are given by the MFG's of the epoxies (and by Gary Hunter here a number of times - look in the archives). I would not be so cavalier about throwing around examples like this - it could really give people the wrong impression (which I know was not your intent). Your warning about getting the foam too hot is absolutely valid, as is the idea that the epoxy cure can have different rates at different temperatures. Let's leave it at that, using the MFG's recommendations for those times and temps. -- Marc J. Zeitlin mailto:marcz@ultranet.com http://www.ultranet.com/~marcz/ From: cdenk@ix.netcom.com Date: Fri, 7 May 1999 20:56:23 -0500 (CDT) Subject: Re: Fwd: COZY: Post Cure Never considered post cure. The only pieces that have had heat after layup with hair dryer are some small parts that were fabricated after the plane was flying, put in wifes kitchen oven for fast cure. Also composite spinner bulkhead which was made with hi-temp epoxy was post cured. Date: Mon, 10 May 1999 10:16:58 +0200 From: "Rego Burger" Subject: Re: Fwd: COZY: Post Cure Thanks, It was more to encourage folks to read up before they stick their hard work into an oven without knowing what they are doing, if we don't expand our knowledge we don't grow. I'm still learning. My resin supplier told me to borther after 14 days was a waste of time....? I feel a relatively "unknown" subject like post cure should have a simple home page on it's own with advice for us lesser mortals. Naturally the specific details of what temps. to use will differ from system to system. Any volunteers? :-) Rego. From: "Will Chorley" Subject: COZY: HDT, "Glass Transition Temps" and all that stuff Date: Fri, 7 May 1999 21:14:39 -0500 Believe it or not, sometimes it is GOOD that our epoxy systems soften in elevated temperatures. I had the occasion recently where I wanted to build some curved parts. I layed up a piece of the old "Clark" foam, one ply BID both sides using MGS epoxy thinking I could bend it to shape after cure, however, after cure it was too stiff to bend to my requirements. A short application of my heat gun softened the epoxy to just the right consistency to bend the part to the desired shape, and holding it for a few minutes left me with just the curve I wanted! One other point of interest. I recently had the opportunity to fly a Diamond Katana aircraft. One of the items on the pre-flight check list is to peer between the seats at a small temperature indicator attached to the center section spar. If it's black (I think that's right!) you don't fly! I guess black means that the wings might acquire some unwanted additional dihedral in flight! Anyone thought of dabbing some heat sensitive paint at strategic points on our aircraft to see what temperatures they actually do reach - particularly those of us who live in hot places? Might be an interesting research project. Will From: cdenk@ix.netcom.com Date: Fri, 7 May 1999 21:38:53 -0500 (CDT) Subject: Re: COZY: HDT, "Glass Transition Temps" and all that stuff Was said Hope its not a structural part. When bent, the inside radius glass fibers were required to conform to a shorter circumference. This likely resulted in the fibers not being straight, but slightly buckled. In tension, the fibers would straighten or break. In compression the fibers are bent already, a defect that reduces the strength. The process that Rutan developed is to shape the foam, and then add the fabric with epoxy. Sheet foams usually can be bent by heating. Though the temperature range between being able to permently bend, and destroy is small, requires much care and more than a bit of experience. From: "Mike Caine" Subject: Re: COZY: Apology Date: Fri, 7 May 1999 20:23:17 -0400 Gary, I agree with Larry, your information is pure gold. PLEASE don't stop sharing it! I also had one specific question about your comments on post curing. >Post-Curing. - Nat is absolutely correct about the EZ airframe design >..... >Nevertheless, post curing helps to make up for those nights when the shop >temperature dropped too much, and the lay-up was still sticky in the >morning... I had been under the impression that lower temperature during cure simply delays the cure, but that the ultimate strength would "eventually" be reached as long as the temperature didn't get too low. Is this wrong? In other words, is the ultimate strength significantly affected by (moderate) variations in temperature during cure (for example, if the temperature in the shop dips (overnight) and then rises again during the 24-48 hour cure cycle)? Mike Caine From: ZeroGCorp1@aol.com Date: Fri, 7 May 1999 21:55:15 EDT Subject: Fwd: COZY: Apology Return-path: ZeroGCorp1@aol.com From: ZeroGCorp1@aol.com Full-name: ZeroGCorp1 Message-ID: <87ceb74e.2464f367@aol.com> Date: Fri, 7 May 1999 21:54:47 EDT Subject: Re: COZY: Apology To: mec@alum.mit.edu MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: AOL 4.0 for Windows 95 sub 13 In a message dated 5/7/99 7:56:59 PM Central Daylight Time, mec@alum.mit.edu writes: > I had been under the impression that lower temperature during cure simply > delays the cure, but that the ultimate strength would "eventually" be > reached as long as the temperature didn't get too low. Is this wrong? In > other words, is the ultimate strength significantly affected by (moderate) > variations in temperature during cure (for example, if the temperature in > the shop dips (overnight) and then rises again during the 24-48 hour cure > cycle)? I think the easiest way to think about this is that post cures protect from sudden temperature changes...we really can't use the HDT alone as simply adding the glass fiber significantly increases the effective HDT by impeding movement of the material. So the best way of approaching this is that knowing that with a post cure the material achieves its best strength over the widest (and fastest) temperature swings.... Keep your fibers straight, epoxy/catalyst ratios correct, and paint your plane white and you are 95% there... Ray Cronise btw, I too like the "techno-speak." if it gets too complicated for someone to follow, I suggest a followup e-mail asking an explanation. I wouldn't want to try to keep everything at an absolute common level, or no one has a chance to learn. I'm all for information, but it would be real nice if folks can quote references where ever practical. From ???@??? Fri Oct 08 05:57:16 1999 Return-Path: owner-cozy_builders@betaweb.com Received: from twc2.betaweb.com (majordomo@betaweb.com [206.43.209.18]) by acestes-fe0.ultra.net (8.8.8/ult/n20340/mtc.v2) with ESMTP id NAA17638 for ; Fri, 8 Oct 1999 13:26:50 -0400 (EDT) Received: (from majordomo@localhost) by twc2.betaweb.com (8.8.5/8.8.5) id MAA05502 for cozy_builders-list; Fri, 8 Oct 1999 12:32:12 -0400 X-Authentication-Warning: twc2.betaweb.com: majordomo set sender to owner-cozy_builders@betaweb.com using -f Received: from dpn.deere.com (services2.dpn.deere.com [192.43.70.141]) by twc2.betaweb.com (8.8.5/8.8.5) with SMTP id MAA05496 for ; Fri, 8 Oct 1999 12:32:06 -0400 Received: by dpn.deere.com; id LAA02894; Fri, 8 Oct 1999 11:28:32 -0500 Received: from deeretrn.dpn.deere.com(192.43.70.78) by services2.dpn.deere.com via smap (4.1) id xma002749; Fri, 8 Oct 99 11:27:42 -0500 Received: from e90corp1.dx.deere.com by deere (8.8.8+Sun/SMI-SVR4) id LAA06965; Fri, 8 Oct 1999 11:27:42 -0500 (CDT) Received: by e90corp1 with Internet Mail Service (5.5.2448.0) id <4DM2Q0GA>; Fri, 8 Oct 1999 11:27:41 -0500 Message-ID: From: Epplin John A To: cozy_builders@canard.com Subject: COZY: Epoxy post cure Date: Fri, 8 Oct 1999 11:27:06 -0500 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2448.0) Content-Type: text/plain Sender: owner-cozy_builders@betaweb.com Precedence: bulk Reply-To: Epplin John A X-UIDL: 918bdc53ce8e020625ba1c0ae675bfa6 For what it is worth, a gentleman named Muineer (not sure of spelling) was present at the Cozy dinner this year at OSH. He is the technical expert from MGS. I had the opportunity to collar him for quite a bit at this meeting. We discussed post cure in some detail. I also attended Gary Hunter's presentation. This was very informative. Things learned from these conversations: All the room temp cure epoxies we use will benefit from a post cure at 140 deg F. The MGS is specified with such a post cure, however it will produce essentially the same properties as others without post cure. The biggest benefit will be chemical resistance, more so than structural characteristics. My intentions are to cure the tanks by blowing heated air into them through the filler openings at 140 deg for 6 to 8 hours, monitoring the internal temp with a couple of probes stuffed in the tank as far as I can get them, one through the drain fitting. Other than that, I can heat my garage to 120 deg + easy enough I just might do that for a day next spring before the first flight. Hope this answers a question for someone. John Epplin Mk4 #467 From: "Russ Fisher" Subject: Re: COZY: SportAir Video on Composite Date: Thu, 7 Oct 1999 20:07:41 -0400 -----Original Message----- From: Denis Thomassin Denis, >In the EAA Sport Aviation magasin there was a series of article on composite >and in the last one they say >that AeroEpoxy do not near to be cure. I wonder what to believe. To cure or >not to cure that is the question... I am assuming that you are talking about POST-curing. Gary Hunter, an epoxy expert, stated at Oshkosh that ALL epoxy will benefit from post-curing. There are many airplanes flying that have not had any post-cure, but I personally am going to do it. See the archives for various techniques and suggestions on how to do this. Russ Fisher From: "Ryan Amendala" Subject: Re: COZY: SportAir Video on Composite Date: Fri, 08 Oct 1999 15:51:56 GMT All, I asked Gary this exact question about AeroPoxy and MGS. He said Post Cure (140degF) is not necessary but did say it has benefits. He did recommend post curing the fuel tanks when using Aeropoxy and MGS (if I recall correctly). There was also a slew of this type of thread a while back the the Canard aviators forum. What I took from it was: post cure not required, post cure tanks and if you have the capability to do the entire plane, why not. He did recommend finishing contours before post curing as "finishing systems" will shrink a little. Just my 2c Ryan ----Original Message Follows---- From: "Russ Fisher" Reply-To: "Russ Fisher" To: "Cozy Builders" Subject: Re: COZY: SportAir Video on Composite Date: Thu, 7 Oct 1999 20:07:41 -0400 -----Original Message----- From: Denis Thomassin Denis, >In the EAA Sport Aviation magasin there was a series of article on composite >and in the last one they say >that AeroEpoxy do not near to be cure. I wonder what to believe. To cure or >not to cure that is the question... I am assuming that you are talking about POST-curing. Gary Hunter, an epoxy expert, stated at Oshkosh that ALL epoxy will benefit from post-curing. There are many airplanes flying that have not had any post-cure, but I personally am going to do it. See the archives for various techniques and suggestions on how to do this. Russ Fisher ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com From: Ian Douglas Subject: RE: COZY: SportAir Video on Composite Date: Thu, 7 Oct 1999 22:23:10 -0400 Hi Denis, I am building in Ottawa and use Aeropoxy. There is no real need to do a high temp cure according to the guys at Aeropoxy. I normally try to get the workshop up to 90 - 100F during cure (back when I had a woodstove it was easy just through in 10 logs - we just moved to Orleans). This year I will have to heat with the furnace in the house ducted to the garage plus additional electric forced air and a base board unit (I do a large amount of my plane building during the winter months). Still in the process of sorting out from the move 'cause I went from a 40' x 20' workshop to a little 17' x 20' garage and now I seem to have lots of stuff and no room... Ian in Ottawa (building a 10' x 8' shed to store "non aeroplane" stuff) then back to chapter 22 and the control system... From: "Hunter, Gary GA SCC" Subject: RE: COZY: epoxy curing - cold temps. Date: Mon, 22 Nov 1999 06:17:25 -0600 Stuart Seigler wrote: > I have found that once you bring the temp back up to the correct > range, 70 -90ish for a reasonable amount of time, that the epoxy > cures correctly. > > Has Gary chimed in here on this issue? He is the expert! > > Stuart I was waiting for all others to contribute first.... Here is my reply to "that other email group" on the Subject: SHOP HEAT Graham is correct - optimum Tg is only achieved by "post curing" at higher than ambient temperatures Doing a layup at 40F ambient, with a surface temperature of 75F is OK too, PROVIDED the surface temperature STAYS at 75F for a least 24 hrs. If the surface temperature is allowed to cool to ambient (40F) immediately after the layup is completed, I seriously doubt the laminate will actually cure within the first 24 hrs. Instead it will only advance to a 'B-stage' - a vitrified solid state that gives all the appearance that it is cured, but in actuality it is something like hard taffy candy. Warming the laminate to optimum cure temperatures will re-start the curing reaction. Depending on what point in time during the B-stage, re-heating the laminate can make the resin re-liquefy (like melting the taffy candy) or at least soften to the consistency of chewing gum. As it cures it will eventually become a full fledged cured thermoset plastic. But, if the laminate is kept cold enough long enough, the chemical reaction may never restart upon warming - even at elevated temperatures. It can remain a brittle, low peel strength laminate forever (we have seen this before). In some cases, it may never harden at all, and stay a rubbery solid forever. More often than not, the laminates will eventually see enough warmth to allow the reaction to progress to a gel point at least. However, it will have a very low Tg until it sees additional heat. Probably around 100-105F. So if you ACCIDENTALLY, have a sudden cool spell after a layup, it would be prudent to NOT move the article until it warms up enough to allow the cure to advance to a reasonable gel stage. This may take a week or more. Then a post cure would be highly recommended. Folks, the cool season is upon us once again. Please, don't take any chances. IMHO - if you have an enclosed environment with some reasonable amount of insulation - buy a dual mode window air-conditioner for your shop. It will provide safe heat in the winter, and keep things cool and dry during the summer. A new one runs about $400 - used ones are cheaper. Having a comfortable environment to work in year round will speed up the completion of your project considerably. It is money well spent. Gary Hunter From: "Hunter, Gary GA SCC" Subject: COZY: RE: [c-a] POST CURING - was SHOP HEAT Date: Mon, 22 Nov 1999 08:25:00 -0600 Patrick wrote: .......one of my relatives, who operates an auto body repair shop, just installed a state of the art, > temperature controlled spray booth.... > ....The booth is computer controlled and can be programed to do about any thing. I think it is capable of 150 f degrees. > I could use it for two days (on a weekend). There might be other builders > out there who have access to similar facilties, but haven't thought about > using them for post cure..... > > My question to you is should I use this facility to post cure, and if so > how do I do it ? > > Patrick, YES !!! You are very fortunate to have such a nice paint booth to your avail. I have always advocated this type facility for post curing. Here are my suggestions on post curing. If possible - post cure after micro-filling and sanding, but before painting. I have seen many older composite airplanes, develop surface imperfections and fabric weave "print-thru" due to filler shrinkage from baking in the sun over the years. If you post cure the micro-fill too, the majority of the filler will have been pre-shrunk. Before, painting you can "re-work" the surfaces - thus reducing or even eliminating filler shrinkage related surface irregularities that can occur later on. You can be as far along as the high build surfacer/primer stage if you like. But be prepared to rework any areas that exhibit post cure shrinkage. There is no need to completely assemble the airplane - the wings can stand alone. Position the main wings leading edge down with support under the winglet so the main wing chord is perpendicular to - but off the floor. A wing cradle comes in real handy for this. Position the canard leaded edge down too. The fuselage should have the canopy and cowlings securely in place. Do not preheat the oven. Raise the temperature gradually to 140-150F over a period of 3-4 hours. The more gradual - the better. Once the oven is up to temperature, allow it stay there for at least 6 hours and up to 12 hours. This allows time for everything to become completely heat soaked. The cool down cycle should be very gradual over a period of 4-8 hours in the oven. Do not shock cool by pulling it out of the oven into a cold wintery day. The airplane temperature should be within 20F of the ambient temperature before removing from the oven. The whole process takes about a day. Place everything in the oven one morning - start the sequence - remove the next morning. Gary Hunter From: "Hunter, Gary GA SCC" Subject: COZY: POST CURING Date: Tue, 23 Nov 1999 06:22:30 -0600 > Great Idea. Is there any chance that the trailing edges could warp ? > Should > they be clamped with tubing or straight edge ? Gary > Warping of trailing edges is not likely to occur, IF you have good control over the temperature. For warpage to occur, the temperature must go well beyond the Tg of the resin. A slow increase in temperature to 140-150F maximum will not allow that to happen. Gary Hunter