epoxy madness
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
epoxy madness
Today we pressed our first skis. We have run into a lot of problems along the way, but all of our layup went well....except the epoxy. We are using QCM EHV-0050 resin and QCM ECA-315 hardener. We heated the resin up by putting the whole container in some warm water (fresh off the stove, pretty hot.) We mixed up 500 grams of resin with 100 grams of hardener for each ski, but after approximately 5 minutes, the epoxy cured within seconds. One second it was totally liquid, the next it was completely hardened. It turned an orange/brown color and got so hot it melted our gloves, brushes, plastic containers and pretty much anything in its path. Interestingly enough, it didnt heat up once spread out (the skis didnt heat up). If anyone knows anything about this particular resin-hardener combo I would greatly appreciate your insight. I am pretty sure that we heated the resin up too much and mixed too large of a batch. I am also unclear about the mix ratio. QCM recomended this epoxy for ski/snowboard building because it is very stong and cures fast at room temperature. Unfortunatley QCM also told us to mix a 4:1ratio (and also sent us 1 gal. resin and 1 qt. hardener) but the product information sheets say to use a 5:1 ratio. What will varying the ratios change? Thanks for your help.
A couple of things:
1.) I would heat the epoxy in a water bath with hot tap water. Water off the stove may be too hot.
2.) Your batches are too big. The epoxy reaction is exothermic, meaning it generates heat as it cures. Big batches in a container will generate a lot of heat and cause it to cure really fast, which generates more heat. Spreading it out does not allow the epoxy to build up as much heat. We are using a slower resin combo, but we only mix 200gms in one container. You may need to make even smaller batches if your epoxy is really fast to begin with.
QCMs website says 5:1 ratio, but I would call them and double check. Also, the harder/ resin amounts almost never match up, so you'll usually end up with more of one than the other. It's hard to predict what will happen if you vary the ratio. Most of the time, it just won't cure.
-kelvin
1.) I would heat the epoxy in a water bath with hot tap water. Water off the stove may be too hot.
2.) Your batches are too big. The epoxy reaction is exothermic, meaning it generates heat as it cures. Big batches in a container will generate a lot of heat and cause it to cure really fast, which generates more heat. Spreading it out does not allow the epoxy to build up as much heat. We are using a slower resin combo, but we only mix 200gms in one container. You may need to make even smaller batches if your epoxy is really fast to begin with.
QCMs website says 5:1 ratio, but I would call them and double check. Also, the harder/ resin amounts almost never match up, so you'll usually end up with more of one than the other. It's hard to predict what will happen if you vary the ratio. Most of the time, it just won't cure.
-kelvin
The first time is always the worst. But here is some help.
I use the same resin (ehv-0050) and hardener (eca-315) and I have found that it works great. I think your problem was that you warmed the epoxy and hardener up too much. I mix mine at room temperature (about 68 F) and I get about 15 to 20 minutes working time before it starts to gel. Then, it cures in about 3 hours with heat (about 100 F) in the press. Without heat, it takes around 6-8 hours at room temperature to cure to where it is workable.
The rapid heating you experienced is pretty common with epoxy. It hits critical mass, then like a nuclear reactor, kaboom. Once my dad was epoxying on a warm day and the epoxy started curing in about 1 minute, then it caught the plastic mixing container on fire and was solid within a couple minutes. With my setup, I use fiberglass as tip spacers, and this makes for a lot of epoxy at the tip and tail of the ski. When the epoxy squeezes out of the tips, it forms large pools that get really hot like you experienced.
I just finished up my third pair of skis using this epoxy setup and have had really good luck to date, so if you have any more questions about it, feel free to ask.
I use the same resin (ehv-0050) and hardener (eca-315) and I have found that it works great. I think your problem was that you warmed the epoxy and hardener up too much. I mix mine at room temperature (about 68 F) and I get about 15 to 20 minutes working time before it starts to gel. Then, it cures in about 3 hours with heat (about 100 F) in the press. Without heat, it takes around 6-8 hours at room temperature to cure to where it is workable.
The rapid heating you experienced is pretty common with epoxy. It hits critical mass, then like a nuclear reactor, kaboom. Once my dad was epoxying on a warm day and the epoxy started curing in about 1 minute, then it caught the plastic mixing container on fire and was solid within a couple minutes. With my setup, I use fiberglass as tip spacers, and this makes for a lot of epoxy at the tip and tail of the ski. When the epoxy squeezes out of the tips, it forms large pools that get really hot like you experienced.
I just finished up my third pair of skis using this epoxy setup and have had really good luck to date, so if you have any more questions about it, feel free to ask.
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Head Monkey
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Whoa! Be careful there… when epoxy overheats like that and starts eating itself it can generate some very toxic fumes.
Do _not_ heat your epoxy in the pot. The manufacturer of any epoxy will tell you what the pot life is at a certain “room temperature” and a certain volume. Usually about 77F and something around 100g. Mix your epoxy and hold the pot close to that temp. Don’t artificially heat or cool it. Once you have your skis laid up, then press them, and _then_ apply heat. Adding heat to any epoxy will always make it cure faster, but of course you don’t want it to cure until you’ve got it where you want it. I usually mix 600g of resin with 150g of hardener at a temp of around 68-70F. I keep it all in one pot and layup a snowboard and get it under pressure in about 25 min. I usually end up with about a half inch left in the bottom of my mixing cup (a 1qt cup) which finally hardens after about 40 min. This is for an epoxy with a “pot life” of “25 min, 105g @ 77F”. If I left all 750g of mixed epoxy in the pot at 68-70F then I’d expect it to catch on fire in under 20min. Your mileage will vary, of course, depending on the specific epoxy you use. The main point is to remember that cure rate is a function of volume, external heat, and epoxy formulation. You can prevent any epoxy from curing or make any epoxy cure amazingly fast (or catch on fire) by varying any of those enough. The key is to stay close to what the manufacturer recommends for your formulation so you achieve a final product with good physical properties.
Do _not_ heat your epoxy in the pot. The manufacturer of any epoxy will tell you what the pot life is at a certain “room temperature” and a certain volume. Usually about 77F and something around 100g. Mix your epoxy and hold the pot close to that temp. Don’t artificially heat or cool it. Once you have your skis laid up, then press them, and _then_ apply heat. Adding heat to any epoxy will always make it cure faster, but of course you don’t want it to cure until you’ve got it where you want it. I usually mix 600g of resin with 150g of hardener at a temp of around 68-70F. I keep it all in one pot and layup a snowboard and get it under pressure in about 25 min. I usually end up with about a half inch left in the bottom of my mixing cup (a 1qt cup) which finally hardens after about 40 min. This is for an epoxy with a “pot life” of “25 min, 105g @ 77F”. If I left all 750g of mixed epoxy in the pot at 68-70F then I’d expect it to catch on fire in under 20min. Your mileage will vary, of course, depending on the specific epoxy you use. The main point is to remember that cure rate is a function of volume, external heat, and epoxy formulation. You can prevent any epoxy from curing or make any epoxy cure amazingly fast (or catch on fire) by varying any of those enough. The key is to stay close to what the manufacturer recommends for your formulation so you achieve a final product with good physical properties.
Everything I know about snowboard building, almost: MonkeyWiki, a guide to snowboard construction
Free open source ski and snowboard CADCAM: MonkeyCAM, snoCAD-X
Free open source ski and snowboard CADCAM: MonkeyCAM, snoCAD-X