sensei

I replied to your statement that Leroy most likely mixed his resin wrong by adding too much hardener and that caused the runaway. That is the misinformed statement and while we are on the subject, adding the alcohol to thin the viscosity only retards the cure cycle and adding more that 10 to 15% can cause a non curing condition of the matrix, so yes, really!

speedracerntrixie

My Feedback: (29)

Before we get into a big debate, please remember we are here to help Leroy on this particuar project and maybe help others understand composites a little better. The material that Leroy used was incorrect for the job at hand. We have now advised him that he should get some laminating resin. For the most part. mixing in less or more hardener will cause an incomplete cure, thinning more then 10% will cause an incomplete cure. Obviously none of us at the hobby level have the measuring equipment to measure surface hardness and then compare to the resin systems spec sheet. The simple way is to run hot tap water onto the part is it looses it's ridgitity, then it's an incomplete cure. There are exceptions to the rule and Ed would be correct if it was a resin matrix that was formulated for different mix volumes. The Epon / Epicure mix that I use for small parts and repairs is one of them. I mix at 5-1 to laminate or lay up small parts when I need more pot life and when I am doing repairs or filling, I mix at 3-1. Both mixes with exotherm and run away if I do not pour them into a shallow container after mixing. If all else fails, use the correct system for the job and mix as per instructed on the package. Can't go wrong.



BTW ED nice work on the molds. I would love to have a billet mold of a 13X13 but the Q-500 fuse mold shows some forward thinking for sure. I would never have thought about putting the splitter plate on the bottom but seeing it makes perfect sense.

sensei

Well said!

Bob

Leroy Gardner

What I find intresting is the many opinions, it only goes to prove that there many products out there for doing some of the things we do at the hobby level. Some of this stuff costs alot of money that puts it's use out of reach for the average model maker so we have to find the products that are reasonable enough to make -say a plug and get a cowling off it. Being this is my first experience at this I found there are some challenges related to it. I'm not repairing a boat hull here which I have done, I'm just building a small fiberglass cowl and it's not the same thing. however it's done much the same way. Many of you are very talented and experienced at this and it's nice to have your help, just keep in mind when trying to help in this area some of us may not know what the heck your talking about.

Composits can be a challenge and all I can offer is to learn as much as you can before you start on a project as simple as building a cowling which isn't that simple. When I get this thing off the plug I will show it to you but I gota get it off first,ha ha, just no end to the excitement.

Mk23socom

My Feedback: (7)

Leroy, please make sure to share the results, good, bad, ugly, or otherwise here, I have been following this thread closely as I have been wanting to learn how to lay up my own parts in the future for a few special projects!!

wyowindworks

Just for clarification:

Epoxy resins (bonding or laminating) cure by poly-addition. The monomer molecules (resin) create molecular links with the hardener molecules to create cross-linked polymer chains/networks. The monomers can only link together through a hardener molecule. If you add too much or not enough hardener then the you end up with molecules that do not link together......a.k.a. lower than desired cross-link density. The extra unlinked molecules end-up creating spaces between the polymers network resulting in a pooly organized molecular lattice. This lowers the Tg (glass transition temp), HDT (heat deflection temperature), strength, and stiffness. The same things happens when you add a solvent to reduce the viscosity of an epoxy resin. If the solvent molecules do not evaporate out of the mix then they will just inhibit the molecular linking of the epoxy. With epoxies you want to accurately mix it according to the specified ratio to get the maximum properties out of the resin. You do not want to alter the mixing ratio to alter the pot life. Instead, you want to use a different hardener to alter the working time. Weighing the resin mix on an accurate scale (.01 grams) is the best way to accurately mix the resin. The mix ratio by weight is typically different than the mix ratio by volume due the differing densities between the resin and the hardener.

Polyester resin work completely differently. In this scenario the monomers in the resin directly link with other monomers. The catalyst (MEKP) is a polymerization initiator. Add more MEKP, within reason, and the reaction happens faster. Add less and the reaction is slower.

Both resins create heat as a bi-product of the polymerization. Both resins will react faster when heated. Lower the temperature and the pot life increases. Increase the temperature and the pot life shortens. In large masses of mixed resins the heat generated by the polymerization will cause the resin to cure faster. The faster is cures the more heat is developed. This cycle can drive the polymerization at a rate that cause the resin to become very hot, cure very quickly, and result in a poor performing final product (low link density, pooly developed molecular lattice, high shrinkage). Spreading the resin out in a larger diameter cup/pot/tray increases the surface area of the resin so it can dissipate the heat. This will extend the pot life.

Leroy Gardner

wyo guy it's hard not to get the impression you know what your talking about and I do get the drift of what your saying. I did not know about the hardening and or inproper hardening thow. I do know whats left in the cup gets very hard and has no sticky residue on top of it where as a tackie surface is on the cloth, maybe this is layup resin. Can says general purpose and it sands ok and its no longer tackie. My experience is finish resin cures without a tackie surface, I don't know the value difference between the two. Belive it or not I'm learning plenty doing this cowl. I know guys that wouldn't even attempt to do what I'm doing because they never had success with it in the past, my limited experience on boats is all I have' besides you guys' or it would probably be a total mess.

For you guys wishing to do this be assured there is plenty of help here, all you have to do is ask and the answers will come.

I thank all of you who help so many of us, glad we have ya.

wyowindworks

An epoxy resin can still get hard with an improper mix ratio.  It may not be at it's designed performance level though.....especially in respect to Tg and HDT.  When mixing epoxy surface coats for molds an accurate mix can make a big difference in how the mold releases.  If there are lots of open molecular sites on the mold surface, due to low cross-link density of the surface coat, then the fresh laminating resin used to make the parts will try and chemically link with the open sites on the mold surface.  Wax is unable to block this chemical reactivity and PVA will be a must for a very long time.....sometimes for the life of the mold.

Hobby epoxy bonding resins often have a 1:1 mix ratio.  Laminating resins do not....at least I haven't use one.

"Finishing Resin" in the composites industry refers to a polyester resin that contains a wax.  Polyester resin by itself has a air inhibited cure.  This means that the outside surface of the resin that is exposed to the air will remain tacky.  This is great if you are going to add more layers because it enables you to have chemical linking between the two applications.  The tacky surface is a problem if it's the last layer and you need to sand and/or add paint.  The solution is to add a special wax to the resin.  The wax floats to the surface and seals the curing resin from the air.  This allows the resin on the surface to cure nice and hard.  The wax needs to be removed before one would do any painting.  A polyester resin that comes with the waxed pre-mixed is called a finishing resin.  Why Pacer calls their epoxy laminating resin a finishing resin makes no sense.  In my opinion this has caused a lot of misunderstanding in the hobby world.  Some epoxies will experience amine blush if the humidity is high.  If you work in an environment  with higher humidity or high carbon dioxide levels then you want to use a non-blushing epoxy resin.  Blushing is not a problem in molding applications because the part surface is sealed from the air by the mold.

sensei

"

Finishing Resin" in the composites industry refers to a polyester resin that contains a wax. Polyester resin by itself has a air inhibited cure. This means that the outside surface of the resin that is exposed to the air will remain tacky. This is great if you are going to add more layers because it enables you to have chemical linking between the two applications. The tacky surface is a problem if it's the last layer and you need to sand and/or add paint. The solution is to add a special wax to the resin.

Nah, just spray PVA on the last layer, allow to cure and rinse... Like Speed said, how is all this helping Leroy in finishing his cowling?

Bob

SCALECRAFT

My Feedback: (13)

I don't use polyester, well until just now for the 1st test flight air frame of my 104 (never again). I'm having the sticky surface problem right now with the weather we have. I may try the PVA idea. I can see it would work.

Why use epoxy for one I'm gonna guinea pig for throws, CG, and numbers.

Steve

speedracerntrixie

My Feedback: (29)

I would guess that the Polyerster manufactured airplane is going to be a bit hevier. Would this not make some of your data a little off?

sensei

To be very honest, I stopped using polyester resins of any kind some 20 + years ago, if I am planning on a painted balsa wood airplane then I simply use Stits covering system on all open bay areas and all sheeted areas get 3/4 oz. glass cloth, and Deft Sanding Sealer, or Minwax Polycrilic, after a couple of coats and light scuffing I prime, sand, and paint. There is just no need for the use of finishing resins IMO.

If I am going to build epoxy hobby parts then my resin of choice is E-Z Poxy 10 and E-Z 23 or 24 hardener, but that is just me.

Bob

Leroy Gardner

Guy's this simple request for help to build a simple plug has gone way past that point. All this technical stuff is so far over the head of the casual user such as me and I'm sure many others that it becoms pointless. While I do believe it's important to get some basic (and I said basic) information before starting something like this simply because it's all thats needed to do your first one and that alone may be your learning experience to be added to in the future. We are not building Boeing aircraft parts here, just a few basic RC parts and useing the most basic components to get it done. I can say this because that is what I have done doing my cowl over a plug made in the most simple of ways and it is working for me and will work for you.

My hat is off to those who understand that alot of technical jargon is of no help, thank you for the common sense approach for the beginner some have provided.

sensei

That is not by any means my idea, it has been used on polyester layups or gel coat surfaces as far back as I can remember, when I was in my late teens I spent a couple of years working at a place named Jurran Glider Service and Repair located at Mojave airport in California, We would hot wire cut foam sections that would make up 30' + full scale competition sailplane wing halves master models. Once they were all sectioned together we would use Shell Epon 815 resin and style 7500 cloth and perform a 6 ply layup, after cure and scuffing we would place two gallons of bondo with MEK paste added on the paint shaker for one minute, open, dump, spread, and spline sand over and over until it was ready for a complete heavy sprayed application of gel coat, once the gel coat was applied we would seal the entire surface with PVA so the surface would properly cure to our needs. Now without the PVA the surface would remain gummy after full cure inhibiting us from the final sanding, sealing and waxing processes needed prior to manufacturing the epoxy layup tools. Today is so different, we just create a cad model, toss the tooling board on one of the 3 axis routers, run the program seal the tooling board and we are ready to make out layup tooling, or we cut the lay up tool from the get go and start running production.

Bob

sensei

I am happy it all worked out for you Leroy, I am looking forward to the finish and test flight of your build.

Bob

wyowindworks

Thanks for comments, Leroy. I'm a person who likes to know the how and why so I can fully apply and trouble shoot a composites problem and improve my composites skills. Some just want to know the "what to do". I apologize for cluttering up your thread with info that you found unhelpful. Best wishes on your project. I hope that it comes out awesome.

Leroy Gardner

Please take no offence, my only intent was to suggest to get this down to entry level and make it more understandable to the novice. At this point I well know there is a technical side to the many types of composits and are used for different things for different reasons all of which I know nothing about and thats what I was trying to get across. Keep it as simple as possible just makes it easier for the new guy on the block.

I will get mine done because I just don't give up, right or wrong and I ask questions along the way and have already learned enough to know if I do it again I "will" do it another way. I like the desolved foam way Bob mentioned further up and that means another plug, yikes. Leroy

Leroy Gardner

Getting the glass on turned out not to be to bad you just have to cut things right and get them on in the right order, the last two layups went on very nice and didn't require alot of work getting it all smoothed out. Applied thin coat of bondo and sanded most off and it was looking pretty good. then the high build primer. Non the less I started to feel some excitement as the end was near. I had made the cowl plug 1" longer so I could cut it off and get a nice edge on the skirt which I did on the table saw. Now it was time to get the plug out and it proved to be easier than I thought. I had ran a feeler guage between the shell and plug and found the stickey film I was warned about but it wasn't stuck to the plug. My understanding is had I used PVA that wouldn't have happened. I cut several slits in the core and just broke it out in pieces leaving the epoxy film in there which I just peeled out and it wasn't stuck any place. I cleaned up the interior with acetone and it's nice and dry now.

Next came the openings for shaft, and air inlet and the head, had to do that before I could fit it to the plane. Some minor adjustments to lower front corners of side walls and it slid on with spinner clearance and fit like a glove. It really looks nice I think, hard to believe I made it the way I did and never had a big problem with any of it. I probably got away with some of the problems related with doing this because I skiped a couple steps but I had a feeling all along that I could get away with it an did. The information many of you has given me has made this alot easier to understand and the lessons learned will only aid me should I ever decide to do another one. I hope others will get something out of this also, it's not hard to do, just use the right products and do it right, you will save yourself the grief if you do.

Here is my proof, pretty cool stuff,Ya think, ? Leroy

Well internet Is acting up so will get pict's later

sidgates

My Feedback: (2)

I am pleased you are happy with your result. I have done extensive fiber glass molding work the past 3 years. I almost always learn something new from WyoWindWorks posts. I realize his comments may seem technical at times but they can save you from learning molding lesson the hard way.

Leroy Gardner

You said a mouthfull and don't even know it. I have done "extensive" fiberglass molding work for the past 3 yr's, problem is you forgot as well as others where you started, little or no knowledge in the beginning. You started with the basics and worked your way up. I have taught many men and some women the fine art of fabracation, welding and a host of other things all with a learning curve and it's no different with fiberglassing or anything else. The only difference is , the more technical it is the longer the learning curve is. I see it all over the Universe, big long technical answers to the most basic questions and ofter not even answering the original question instead it turnes into a format for others to argue and assert there point of view. Case in point, some of that was going on here and it's going on on other threads.

I don't put anyone down for what they know but when it gets to the point of being out of control I'm not afraid to say something to get back on track not to insult or offend anyone, maybe they will learn something too.

sidgates

My Feedback: (2)

I haven't forgotten where I started and I know exactly what I said above. I still wish I had the advantage of some of the "techincal" post above before I started. Over and Out