Heating resins in Microwave

[GrantC]

Anyone here know what possible risks there are heating resins in a microwave if done carefully of course? I have a friend that heats epoxy in the microwave and says it is fine to do this. But I thought I'd ask here. What about polyester or vinylester as well?

[Danielsan]

What would be the use of it? I hope this is not for mass production, could need a big micro wave. I hope you get no sparks as this occasionally can occur in a micro wave, the hot styrene vapors may say boom, or am I wrong?

[GrantC]

parts made using RTM/RTM lite process, helps control viscosity of resin and affects cure times.

[Danielsan]

There are some special low viscosity resins for RTM, I find it rather tricky to put it in MW. For how long does he put it in the MW?

[Ssor]

What ever happened to the need for ventilation? Aside from the fire/explosive hazard, heating the resin will raise the vapor pressure. If the resin is too cold to mix properly then the work place is probably too cold to cure the system. All that aside a hot water bath would allow much better control of the temperatures. I often find that a tube of caulk is too cold to gun but running hot water over it for a few minutes warms it adequately. Would I put it in a microwave oven? Not in this lifetime!

[captword]

if your friend is doing this to heat epoxy up on a cold winter day to get it to kick quicker. I have the safer answer. A friend who was helping me restore a 43 hatteras came up with this. We built a box our of scrap sheet pvc permaplank. Has a hinged lid that drops down, and you can slide out the epoxy pomps when mixing. Inside the box we put an exterior light fixture, with a 50 watt bulb. The hinged door stops an quarter inch short of the top for ventulation, but prevents rain from entering the box. Like the lightbulb in the pump house. Working in the boatyard in the winter it was needed and helped greatly. I do not like to leave it on overnight. Don't want to loose a job or boat to fire. I have found out that if you turn it on when you first get there in the mourning that by the time you gennerally need it, the epoxy is warm and ready.

[PAR]

I've used this technique for small patches to increase penetration and to warm cold epoxy. 10 seconds in my microwave is enough to bring 50 degree resin to 80 degrees or 70 to 110 or 120 degrees. Sure it'll kick fast if you're using something that will, but even at these temperatures West System 209 will have a good 20-30 minutes pot life if spread out thin. I usually get more time then this. I use epoxy in August here in Florida. You learn how to control reactions or smoke lots of goo.

Good bonds in difficult materials like oily woods can be tricky, but a good trick is to work with warmed epoxy and warmed parts to be glued. They must be put in a place where they will be in a cooling state when the epoxy goes on. The trick is to warm the pieces to say 120 and then place it in a much cooler environment. Bring the warmed epoxy to it and lather it up. The contracting air, moisture, lumber and oils in the piece literally suck the very thin epoxy it like no one's business. Much better penetration and bond, but don't trust me log on to the West System web site and ask them, this is where I learned about it. I usually warm the piece and place it in the cool area for several minutes to insure the temperature is dropping when the sticky stuff gets applied.

On larger batches, I use the warm water under the flat tray trick, but it's the same deal. I've not blown up my microwave yet (it was her's until I got caught) and have tested to destruction many pieces done this way and compared them to room temperature laminates. The warm stuff always wins. There's no advantage if using this trick on nonporous materials. Try it on a piece of end grain balsa and see the difference in penetration you get, you'll be doing it too.

[GrantC]

The reason I asked that I was at an RTM seminar a couple of years ago and the speaker talked about heating the epoxy so that the viscosity dropped drastically, where at room temp it might be 250cps, at 110 or so it is 125cps. I just never thought to ask what most were using to heat things up. Then a friend that I know said he uses a microwave. And also I just saw this Quicktime clip: http://www.astsurf.com/mixing.html it is a guy who developed and was/is trying to market polyurethane resin to the surfboard/sailboard/kiteboard market. I guess the polyurethane has excellent pyhsical properties but is bad for doing artwork/graphics so it is not being taken to by the makers. But a prerequsite is to heat the polyurethane in the microwave.

[cyclops]

Has anybody done a strength test on MICROWAVE mixes ? Do you use a thermometer? How do you get repeat results?

[GrantC]

No you don't use a thermometer, you use an Infrared Temperature Gun. This is an great tool when doing composites or fiberglassing of any kind. If your doing a layup of any kind you should know the temps of the tooling, resin, surrounding air temp, etc. This is how you get the best results when you know what is going on, because the curing process is all about temperature.

[PAR]

Bingo, GrantC . . . I got one at an auto parts store.

[cyclops]

I need one of those when I do engine work. Life is going to become pleasant with one. THANKS.

[PAR]

It beats the hell out of squeezing the upper radiator hose to check pump flow or if the thermostat is opening. Also good for checking duct temperatures and other things in A/C work . . .

[Herman]

I have a client who uses the microwave regularly to heat up resin. He mixes resin with aerosil to a syrup consistancy, mixes in some pigment, then heats it up in the microwave. Viscosity drops radically. He uses a cheap paint gun to gelcoat his molds with this mixture. If he wants a semi-transparent effect, he sloshes some acetone in the paint gun reservoir, shakes the paint gun, then continues painting. Metallic? Throw in some metal flakes. Poor paint gun...

End of story is that it really does work. But I must admit he is a kind of an artist...

[yokebutt]

Sure, I often put small parts that need a buildup of epoxy for clearcoat in a cardboard box, heat to 120-140 deg. F with a space heater, then add epoxy every 1/2 to 1 hour that's been microwaved for a couple of seconds per oz.

Use disposable foam brushes.

Happy spooging,
Yokebutt