Post cure increase tg, increase élastic élongation and reduce Young modulus ended to a better elastic strengh. For RR i do 12h at 45°C. You can accélérate epoxy set with increase temp but on foam need good Seal before. For this i go Max 30°C.
Thanks Lemat
All true and I am in complete agreement.
The primary reason for a temp controlled cure on a lam is so that consecutive operations are not done on something that is changing all the time, in which case you would have a process that is not in control. Any process that is not in control has unpredictable results. The benefits on either a lam or hotcoat such as a more rapid cure (therefore reducing contamination time), cooking out blush, faster time to sanding, etc. just come along with it.
Few of us are true experts with epoxy resins, so to insure consistent high quality results we must follow a defined set of process steps. I would choose to use the same process steps that are used for high-end composites, since these are used in demanding environments which need consistent results. About 5 years ago, I worked with a prominent shaper/builder and we tested every US epoxy brand available, with / without heat cure, sanding, washing on full boards. This by no means made me an expert, but it did validate the process steps.
Per the aerospace composite people I’ve talked with, the critical part of heat cure is how the temp is cycled so that the EPS blank is not distorted or delams happen. With a full-on environmental chamber you can go to very high temps, kick it down rapidly then repeat over and over without stressing the board. With a dumb hotbox, the best we can hope for is to hit a target temp and hold it there for a while. The insurance for EPS distortion is to not go to very high temps and have an opening in the skin to vent (finbox holes) for delam’s. The temps that Greg and Lemat stated are fine, but you can go lower for a longer time or use more and shorter cycles at those temps. The important thing to remember is where you measure the temp. I’ve used a laser thermometer (Harbor Freight) to read actual skin temp then correlate with the hotbox air temp (or duration the heater was on). In my own experience, a skin temp of 35C for 8-10 hours will yield at least 90% of full cure using RR.
Yes my set up is a dumb hot box made of the insulation board that is used for HVAC ducts. Foil on the outside. I bought a cool temp controller on Amazon for about $25. Pic below. And use a heat lamp as the heat source. I watch it pretty close but the temp controller makes it easy. You just set the temp and it maintains within a set range, turning the lamp on and off as needed. I just time it with my watch.
Of course, other than mimicking the somewhat what is done by the aerospace boys, I have no way to test the goodness of my method. Faith is a wonderful thing.
Thanks for the insights here. This explains a lot of my epoxy hassles like a rosetta stone.
I’ll be using a shared space… Fire risk has to be convincingly reduced…
Greg Tate.
Why are smart people so stupid? Instead of glassing in a room at aprox 65-75 degrees and waiting for the resin to cure… you are going to build a fire hazard???
Really??? No… dont do it. No No No No !
When your hat box heats up and lights up your house. It’s going to be a radical fire. Your whole life is going down the crapper.
Over a crap shoot with Lamat and Pete.
Count me out. I hAVE WAY TOO MUCH TRAINING WITH RAD CHEMICALS.
Just say NO to CRAPPY HOME MADE hot box.
Perhaps no need to throw the baby out with the bath water. Use fire retardant foam insulation, seal the box very well so not much oxygen source and/or put some rusting iron in there to reduce oxygen further. Then put a wax triggered sprinkler over the top… All of this with the heat cycle switcher which regulates heat anyway
For sure you are right no crap home made hot box. Mine use composant made for this application.
Thanks, Ray,
Hilarious. I appreciate your concern for my safety. But I’m OK. I have a smoke/fire alarm on the box and the box is non flammable hvac board.
But post curing has not been without incident.
I left the heat on intending to cut it off at 11 PM when I was going to bed. I didn’t realize it at the time but our dog was sleeping on the box for a little extra warmth, and managed to pop the heat lamp bulb with a loud pop. He was startled and raced out the garage back door but got his tail stuck in the doggy door and severed it. THe wife and I made a midnight trip to the Vet emergency room and $1500 later we came home to a bloody mess. The wife was a little PO’d and after a few words, I was exiled to the park bench down the street. It’s late and I don’t have much battery left so I have to make this quick. The good thing is that it is a clear cool night and the stars are nice to see. But there is a smelly old woman with a loaded shopping cart trying to snuggle up to me and get a bite of the donut I found under the bench. She says if I’ll watch her cart and creat a little diversion for the cashier, she will steal some coffee from the 7/11. What can go wrong with this?
But I’m happy to report no fires in the box.
All the best and thanks for your concern
That’s a whopper! I’ll bet you dogtails to donuts that was the best cup of coffee you ever had!
To ray’s comments about Resin Research; No problems with RR for me in like conditions. Lowel
Call me an idiot Florida boy, but my hot-box is the back of my pickup truck (which has a topper). Only done it once so far, but it was easy and made me feel better to have it post-cured. It went like this:
- Glassed and fill-coated board.
- Drilled a hole in the middle of a couple fin locations for vent (they were going to be proboxes).
- In the morning, place rocker bed (EPS offcut) and board in “hot box”. I threw a piece of wide craft paper over the board just to keep the sun off it (my truck top - I mean hot box - has windows). Close it up and walk away.
- As the sun rose, regularly checked the temp of the board as well as internal temps in the hot box with a cheapy IR thermometer. I forget the exact numbers, but it slowly reached and held a steady 130-ish degrees F. After 2 or 3 hours at that temp, I opened it up and let it cool down before pulling the board out.
I’ve also thought it would be easy and safe to build a box out of whatever material, paint it black and use the sun to heat it up.
In order to keep it from over-heating, get a basic temp controller like what Greg has, and use it to kick on a fan that could pull fresh air into the box if it gets too warm.
If you have sun when you need it’s best system.
A hot box can be almost anything; outdoors, indoors, solar, whatever just keep in mind the serious fire hazard as Ray says. The main thing is to cure above 100F even for only a few of hours. It does make a difference, I can hear it with the sound when the bottom slaps the water. This along with washing off the blush and light prep sanding will reduce or eliminate the problems that people are posting all the time. Judging by the number of posts and how long this has been going on, not everybody has the same results with epoxy including same brands. There is more to it than instructions on a bottle or a single printed sheet, and I hope that this discussion will motivate people to look further into the subject.
Spot on , Pete. It really is not that hard. Just a few simple procedures, as you have noted, to give great results. When I find a few minutes, I might start a thread to summarize these few things so they are in an easy to find place for future ref.
All the best