mogles

My Feedback: (7)

I would greatly appreciate if I could get some info from those who purchased the video. He is using PRO set 125/226 resin and hardner. I found the specs but I am concern on the temperature he is keeping/using the resin. Based on the website info, at around 95 degrees I can only get 10 to 13 minutes of work. Anyone is using the same technique and material?

Thanks in advance.

Mel Francis

Is 95 degrees the ambient temperature in your building?

Most epoxy systems work best at 65-70 degrees, ambient.

This time of year, early December in Colorado, it should be fairly easy to reduce your surrounding temperatures, thus increasing useful pot life.

Or am I completely misinterpreting something here?

mogles

My Feedback: (7)

Thanks for your reply. I am only trying to follow Phil's procedure. In the video he keeps his resin (the PRO SET 125/226) at about 95 degrees temperature more or less at all times. Even during the mixing process. You can tell that the resin is much more fluid during his demo. However, I do not understand why since the specs on the PRO SET website sais at 85 degrees you will have 15 minutes pot time. Judging by the video, he has tons of time to complete the wing. Perhpas someone has this info as I do not want to trial and error since someone I am sure has done it.

Thanks much.

Mel Francis

Yes, I was misinterpreting your situation.

STORAGE of the resin at 95 degrees.......

I've worked with hot epoxy resin at those temperatures and the working time is very short.

You must work with smaller batches, get them on quick, and the heat won't have a chance to build up, stuck in the pot. You'll still have good working time on the part surface, in a thin layer. It's good to have a helper on larger jobs, who can keep rolling and dabbing while you mix another batch and then spread it on.

You want to empty the pot and then work the resin, since any time spent holding a mixture of resin, while your other hand dabs the surface, just allows the chemical reaction to speed up.

Hope this helps.

davidfee

I have not used that particular epoxy but, if you mix it up and then quickly spread it out into a thin film (such as a wing skin laminate) then you will have much longer to work. Possibly as much as an hour. Left in the pot it will kick off very quickly but, in a thin film there is much more surface area and so a greatly reduced occurence of "exotherm."

Mikey D

Hi There
When mixing your resin are you in a cup or a plate? I cant speak for everyone, but I have used warmed epoxy in the past on a plate spread out this will extend your pot life quite a bit as compared to a cup.

Mikey D

mogles

My Feedback: (7)

Absolutely. I use a plate since the procedure is much more elegant and clean to spread the epoxy with a roller. However, as far as I know when the two compounds are mixed together (epoxy and hardener) they produce heat due to the chemical reaction which in terms the solution will start so solidify. If I add heat to the mixture, i then force the chemical reaction to take place sooner therefore shortening the life of the pot mixture. I guess I should try this for myself.

Thanks to everyone.

Soar Head

My Feedback: (5)

Are you sure he's using the 226 hardener? That is the faster curing hardener. he could easily have used one of the long cure hardeners which would give very long cure times.

The 237 hardener gives 240 min cure time.

I'm referencing from the CST site

http://www.cstsales.com/Material_Data/prosetdata.htm

mogles

My Feedback: (7)

I could swear that is what Phil is saying on the tape, which puzzles me. I agree with you. I even checked the PRO set site where it gives specific heat degree instruction template.

Soar Head

My Feedback: (5)

If you're "fairly" new at vacuum bagging, I'd go with the longest curing one I can get. All it takes is extra time to cure. And you don't have to be in a hurry before your partially completed work solidifies into an expensive unusable mess.

The only downside to long curing epoxy is, well, the long cure. I buy other epoxies for shorter curing time. I buy the longest cure I can get for bagging. I have found that I am not that fast, and can use the time.

Give it the full cure time specified before pulling it out of the bag. I've found the nice shine from the mylars can be temporary, if I pull it off before a full, hard cure.

daven

My Feedback: (1)

I just watched the video over the weekend, and was very impressed. I'm trying to figure out how to apply his techniques to Q500 racing planes while keeping things light.

He definately seemed to have at least 45 minutes of working time.

phil barnes

I do indeed use Pro Set 125 resin and 226 hardener. Some of my layups take 45 minutes to do. I even occasionally do longer layups than that. You can't tell much from reading about a working time given by manufacturer's specs other than to compare one epoxy to another. Even then, it may only be useful in comparing one of that manufacturer's hardeners to another. I would not take the numbers on pot life to be meaningful as actual amounts of time and perhaps not even useful to compare one manufacturer's epoxy to another. There is some very specific procedure they use to come up with working time numbers and that procedure probably has little similarity to the way that we are likely to use the epoxy.

I keep the epoxy in a warming box but I don't leave the heater on all the time. I turn the heater on when I expect to be doing some layups. It might stay on for a few days if I am doing a large batch of wings but most of the time the epoxy is stored at room temperature. As soon as the epoxy is pumped out of the can onto a paper plate it begins to cool. By the time it is stirred and ready to spread, it is way cooler than 95 degrees. By the time it is rolled into the layup, it may be approaching room temperature. The pot life mentioned by manufacturers probably involves mixing the epoxy in a cup and letting it sit in the cup and exotherm.

After mixing the epoxy I immediately roll a lot of it, maybe most of it in some cases, onto the mylar. I don't leave the epoxy sitting on the plate in a deep puddle. Epoxy gets thick by either getting cold or by curing. There is always a balance between the two. I want the epoxy to be warm since warm liquids are thinner than cold liquids but I don't want the epoxy to cure too fast. My particular technique just sort of evolved into a system that works for me. I used to heat the epoxy even more than I do now. I had an ongoing problem with unpainted HL wings where there would be little "nits" of foreign material in the layup and I couldn't figure out where they were coming from. Finally, I realized that the epoxy on the plate was "skinning over" as it sat there. That is to say that a skin of partially cured epoxy would form on top of the puddle of epoxy and that is what became little "nits" of stuff in the layup. So I reduced the temperature in my warming box. Years ago when I first started warming epoxy to make it thinner I would just set the plate on top of the heater and stir the epoxy to mix it until it got warm enough to be a thin watery consistency. Then I would take the plate off the heater and set it on a scrap of foam on the bench. One day I decided to try just leaving the plate on the heater while I did the layup. You can probably guess what happened. After a few minutes the epoxy suddenly gelled on the plate. This is the result that you would expect from reading the working time specs but is not what happens when you take the epoxy away from the heat source after mixing it.

At the end of a long layup, the epoxy gets quite a bit thicker than it was at the beginning. This is due to a combination of getting cold and getting cured. The thicker epoxy is not such a problem after the fabrics are in place and the epoxy is evenly spread. You mostly want the epoxy to be thin so that the carbon and kevlar can be moved into position more easily and so that the epoxy can be quickly and easily distributed and evened out.

Epoxy generates heat as it cures. This heat then causes the epoxy to cure even faster. That is why "pot life" can be so short. Epoxy sitting in a "pot" or cup will cure very quickly. Almost all of the heat generated by curing (exothermic reaction) goes into the epoxy to heat the mass of epoxy and make it cure faster. A thin film of epoxy will also exotherm but almost all of the heat will be lost to the surroundings (The mylars, the work bench, the surrounding air) and not much of that heat will be retained in the epoxy to speed the cure. That is why we get much longer working times when mixing the epoxy on a paper plate and immediately spreading it into a thin film than what you might read in the manufacturer's specs.

I have never used the longer curing Pro Set hardeners. I need the wings to cure overnight so I can move on to bag the next batch. You need to work out your own system that works for you (or copy mine exactly). Some combination of hardeners and heat and technique will work best depending your own style. As long as you understand what is happening, you shouldn't have any trouble working it out.

If you would like to learn more about my technique or have other questions about the video, you might find some answers in the SALgliders YAHOO group where I spend most of my time. A search of the message archives or a look into the files section will answer many questions. I only joined this group because Bill Haymaker (the guy that shot the video) told me about this message thread. I may or may not end up watching this group for similar questions, but I always watch the SALgliders group.

http://groups.yahoo.com/group/SALglider/messages

Phil Barnes