Cold Curing

[macleodm3]

In preparation for laying up the insde of the right side fuselage (ch 5), I prepared some micro fillets for some of the corners that created air bubbles during the layup of the other (left) half. It was around 70F outside, so I forgot to turn on the shop heat before I went to bed. It hit 48F that night outside.

 

The next evening, after a full day of a shop temp of around 75 deg., the epoxy had not yet cured (MGS 335 w/ 50/50 slow and fast). The micro was almost hard, but you could still dig a fingernail into it. I turned the heat on to 75F, and gave it another 24 hours to cure.

 

The next evening, after another full 24 hour 75F (or warmer during day), there was no change, micro was still too soft to sand.

 

I took my professional grade heat gun (stolen from the bathroom), and got every square inch of uncured micro warm, but not hot. I'd say with High Heat and Fan on low, all the micro saw at least 1 minute from the hairdryer.

 

Last night, after work, I went out and the micro had restarted its cure, and was now hard as rock! It worked! It may have cured without my heat treatment, but I believe this got the curing reaction kickstarted.

 

I've never had any epoxy remain uncured for more than 24 hr, and this stuff took three days. If I wasn't taking my family on vacation this weekend, the second side big layup would be tomorrow am... but it'll have to wait.

[TMann]

Get yourself an electric blanket.

(good tip I got from chaisingmars)

 

Just make sure you get it back on the bed before your wife turns in.

[macleodm3]

For those not bagging or not using plastic peel-ply, how do you keep the blanket from becoming a structural part of the airplane?

[TMann]

For those not bagging or not using plastic peel-ply, how do you keep the blanket from becoming a structural part of the airplane?

Throw a piece of poly over your work after you put down your peel ply. You can reuse it over and over

[Jon Matcho]

Rig up a makeshift "tent" around your part and have a small space heater blow in there for 24 hours. Take care not to burn your shop down though.

[macleodm3]

Two very good ideas that I've seen other builders use. BUT, they only work if you turn them on. I'm glad to know that with a little heat, the reaction gets going again if accidently left out in the cold.

[macleodm3]

I had such a hard time with peel ply on the first fuselage inside layup, I'm only going to peel-ply areas where the bulkheads will be. Too many wrinkles in the peel ply with one big piece. The tent might be a great way for me to cure... its most likely cheaper than heating the whole shop all night.

[Big Steve]

Once you get the fuselage finished you can put parts in it and then throw plastic over it with a small heater works pretty good and a lot better than going out all night long every couple of hours to put wood in the stove. STEVE

[Phil Kriley]

I made a hot box big enough for the entire fuselage. I used 6 pieces of 4'x8' styrofoam, 2 inches thick. I cut 2 of the pieces in half and glued 3 pieces to the ends of 3 of the full sheets so that I had 3 pieces 4'x12'. These pieces make the sides and top of the box. I cut another piece in half to make the ends. I cut a hole in one end piece so that my Stanley heater would blow into the box.

 

The box is held together with 1/8" dowel rod "nails". This makes it easy to take apart for storage. I'm able to run up the internal temperature to 115 degrees.

 

The only time I had a layup take 3 days to cure was before I had a hot box, and I let the parts cure in my 65 degree basement - AND I had not used any fast hardener.

[jpolenek]

Here are some photos of the enclosures I made to cure parts for my last project. They were made of polyethylene (vapour barrier or garbage bags) and duct tape, with hair dryers providing the heat. Very easy to set up. The small one was for a bulkhead, made of 2 garbage bags, and it used one hair dryer. The large one was for a fuselage side, made of 6 mil polyethylene, and it used 2 hair dryers. With the garage temperature well below 60 degrees fahrenheit, the temperature inside the enclosure was over 100F. Worked great!

 

Joe Polenek

[Cozy1200]

... and it used one hair dryer.

 

Simply & effective, I like it. How long did you leave the hairdryers on? I would think a hairdryer would burn up after a while.

[jpolenek]

Simply & effective, I like it. How long did you leave the hairdryers on? I would think a hairdryer would burn up after a while.

It won't burn up. Most hair dryers have an internal switch that shuts it off if it overheats. (Try it out by placing your hand over the intake.) Once it cools down, it will switch on again. The trick to keeping it from switching off is to keep the filter clear of dust, and to keep the air moving through it. This means that if air goes into the enclosure, it has to come out somewhere. An enclosure like this will probably have enough leakage to facilitate this air flow no matter how air-tight you try to make it. If you do make it really air tight, just poke some holes to let some air escape.

 

One thing that will make it overheat is ducting the hot air from the enclosure back into the inlet of the hair dryer in an attempt to make it hotter. I tried this once on a small enclosure and it did shut itself off. However, with some experimenting, I balanced the amount of return air without triggering the shut-off, which maximized the enclosure temperature.

 

As for timing, I left it running all night without any issues. Knife trimming is a bit of a pain since you would have to open up the enclosure to get at the edges and then re-seal it. I just let it all cure and trimmed with a Dremel tool later. If you do decide to go in and knife trim, plan to do it WAY earlier than you would with a room-temperature cure. The extra heat really accelerates things.

 

Joe Polenek

[chasingmars]

\Knife trimming is a bit of a pain since you would have to open up the enclosure to get at the edges and then re-seal it. I just let it all cure and trimmed with a Dremel tool later.

I haven't knife trimmed since the day after I got my Fein, which I think was in chapter four. If you don't have a Fein with a HSS bit, you are missing the most labour saving tool for building this airplane out there, in my opinion. And far less risk of accidentally chopping off a finger using sharp blades on unevenly cured beta laminate that you didn't *quite* time right. Quite aside from it being impossible to knife trim a bagged part.

[TMann]

I haven't knife trimmed since the day after I got my Fein, which I think was in chapter four. If you don't have a Fein with a HSS bit, you are missing the most labour saving tool for building this airplane out there, in my opinion.

I second that! It is without a doubt the best tool investment I made.

It's also my favorite tool to demonstrate

I'll take a scrap of cured layup or an area where I'm trimming and cut through it with the saw blade attachment ........ then, with it still running pass the blade accross my palm.

Those eyebrows pop up so high, the almost disapear into their hairline

 

Really .... it is a very effective tool as well as a very safe tool.

I highly recommend it.

[macleodm3]

Get yourself an electric blanket.

Ok I like this idea so I've been shopping for this, but alas, technology has outwitted me again. All the electric blankets that I can find have either a 3 hour or a 10 hour auto-off feature that cannot be bypassed.

 

Geez! Who comes up with these products? My heating pad at home shuts off after one hour, and the coffee pot at work shuts off after 90 minutes. When will it end? lol

 

I'm going to start shopping at the flea market.

[Cozy Girrrl]

There are probably not enough safeguards in these appliances as it is.

One morning I am sitting at the salon table aboard my boat, my back toawards the galley when I notice some dancing and flickering light reflected on the ceiling, only then the smell of something burning, I turn around and see my week-old coffee maker in flames... and the circuit breaker still had not popped on the panel. I am paranoid about electric devices burning up and quite often run around the house unplugging everything before going away for a weekend, I like my home to still be there, uncharred when I return.

...Chrissi

[TMann]

All the electric blankets that I can find have either a 3 hour or a 10 hour auto-off feature that cannot be bypassed.

I would advise going with the auto-off 10 hour timer option.

The other viable option would be to get a couple of overhead quartz infrared heaters and put them on a timer. They will direct the heat to your work object and heat it vs. the air around it.

[Neverquit]

I've used a blanket with a 10 hour shutoff the past two weeks outside in 45-50 evenings to do my strakes. It worked so good I went out and bought another one. No more keeping the garage warm for me unless I'm in it.

[Jon Matcho]

I'm not saying this is a bad idea, but don't we want at least 24-hour cures? I wouldn't be satisfied with a 10-hour cure on a summer day.

 

And what about that one spot on the blanket where your toes are always cold?

[TMann]

I'm not saying this is a bad idea, but don't we want at least 24-hour cures? I wouldn't be satisfied with a 10-hour cure on a summer day.

at 9:59:59 hit reset.

[Ron Springer]

I bought a couple electric blankets at Walmart last year. I used to reset them prior to 10 hours because I thought I had to. Once I forgot and they did not shut off. Turns out that I got one of the only Sunbeam models without the auto-off feature. Here is the manual from Sunbeam that shows which models do and do not have auto-off (see page 2):

 

http://www.sunbeambedding.com/manuals/BeddingMan06-English.pdf

[macleodm3]

Two weeks ago I went digging through our blanket closet and found our queen size electric blanket and guess what... the controller was actually with the blanket and it is not automatic shutoff. It has real rocker switches for power and real thermostats. So I've now got the blanket.

 

I first used the blanket for floxing the upper and lower longerons to the sides. After initial 10 hour cure in heated workshop, I removed the large clamps and doubled the blanket over the longeron, and turned off the shop heat. Nice warm longerons for the next 24 hours or so.

 

I used the blanket again for floxing on LWX and LWY, worked Great!! Not wasting money on heating the entire shop once I go to bed.

 

Last night a did the 6 ply layup over the electrical channel conduit and the areas inside LWX and LWY. Had my first problem with the blanket when I checked the layup this morning.... too much heat. The extra heat slightly wrinkled up the plastic peel ply. The same wrinkles may have happened with Dacron peel ply (just like what happens with too much heat gun heat).

 

The layup looks good, except for ridges of epoxy which I can sand off (formed with the wrinkles of palstic). No air bubbles, no dry areas.

 

I had the electric blanket doubled over two times, so I had four layers of electric blanket, then a wool blanket, then a piece a 4mil poly on top. It was cold last night, but my layup cured somewhere over 100 deg. F.

 

Next time, I will also place the thermostat under the blanket so that it will control the curing temperature. As it is now, the thermostat only measures the temp in the shop (lets say 45 deg.) and therefore current to the blanket never stops.

[TMann]

I had the electric blanket doubled over two times, so I had four layers of electric blanket.........

Note of Caution here:

I had a neighbor that thoght they smelled something and went about investigating. They opened the door to one of the kid's bedrooms and the incoming rush of oxygen resulted in a flash fire.

When it was all over, the fire department determined that the cause was the electric blanket that was in a pile on the bed and left on while the kids were geting ready for school.

[macleodm3]

I am glad the kids weren't still in the room. Thanks for that information too.

 

I believe that keeping the thermostat with the blanket and also not doubling up as much will help prevent fires.

[TMann]

Yeah ........ it might be a good Idea to put a smoke alarm over your layup table just as an early warning. My basement shop (under the garage) is concrete on all six sides so a fire there would be reasonably contained. I have a smoke alarm in there but to tell you the truth, I don't know how much good it would do (not sure I would hear it.) When the door is shut, you could use it as a shooting range and the neghbors would be none the wiser.

 

I'm thinking the area will make a great home theater when the project is completed! (no more 'turn that thing down!')