Flammable PR in oven

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soligen

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Sterling Heights, Michigan
I see a lot of poeple use a toaster oven for PR, especially in cold weather. Many have also commented on the flamability of PR fumes.

My question is, with the red hot element in a toaster oven, at what point is it safe to put the PR in the oven? Is it safe at the "just starting to gel phase" or do I need to wait until it is set enough to remove from the mold?

I know a lot of people use the toaster oven, but I dont want to try it until I'm sure the process is safe.

Today, I warmed a couple broken paver stones in the oven and put them in a cooler, but I lost a lot of heat with all the opening and closing of the cooler during my casting session. Things are still gooey 3 hours after casting, so I think I need more heat.
 
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I just cast my first test pieces of PR. They were still tacky after 18 hours so I used my wood drier (a table top grill with a 100 watt light bulb inside under the grill) to season them out. I used 4 drops / oz. Enough? I do not know. There is no red hot elements to ignite any fumes.
If need be, I have an old variack (an autotransformer) to regulate the temp inside the grill.
Charles
 
soligen said:
I see a lot of poeple use a toaster oven for PR, especially in cold weather. Many have also commented on the flamability of PR fumes.

My question is, with the red hot element in a toaster oven, at what point is it safe to put the PR in the oven? Is it safe at the "just starting to gel phase" or do I need to wait until it is set enough to remove from the mold?

I know a lot of people use the toaster oven, but I dont want to try it until I'm sure the process is safe.

Today, I warmed a couple broken paver stones in the oven and put them in a cooler, but I lost a lot of heat with all the opening and closing of the cooler during my casting session. Things are still gooey 3 hours after casting, so I think I need more heat.
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I am not positive where it is safe but I don't usually put PR in the oven with the exception of the post cure if needed.

I always in cold weather preheat my PR in an Ultrasonic Jewelry cleaner with a heater. You can always just get really hot tap water and water bath the cup of PR prior to casting.

Preheat your mold. That makes the most difference.

So, between the prewarming the resin and preheating the mold you shouldn't have any problems. At least that is how I do it.
 
I'm not sure if a toaster oven is safe for this so I made a kiln from a cube shaped styrofoam ice chest and a fishtank heater . I lined the inside with aluminum foil (I used spray glue to glue it in place) laid it on it's side and made a hole in the middle of the bottom (now the back since it's on it's side) sized to tightly fit the fishtank heater . I just stuck the heater into the hole (friction fit , but some duct tape wouldn't hurt) and put a piece of corian down as a shelf to put my stuff on .
The fishtank heater can be adjusted to give any temperature up to about 150 degrees . I have mine set at 125 degrees which I find warms the resin and mold for a quick setup (the resin gels in about 5 minutes using 3 drops of MEKP) , and post cure the blanks without making them brittle . I can turn the blanks in about 2 hours including about a half hour to cool the blanks off .
 
Once I pour my resin into the molds I put the molds into the toaster oven but i never turn it on. I contain the heat generated by the resin that way and let that assist the curing process. I see no need to turn it on unless it's still tacky after becoming a solid (only then I do 150degrees for 30min cycles till non tacky.) Right now I'm using 4-5 drops of catalyst per 1oz of resin. I wil also preheat my silicone molds at 150 for usually 30 mins or until the resin starts to gel. Hope this is helpful and feel free to contact me with any questions! Don't forget to post your work!
 
I use silmar 41 and 3 drops per ounce. The molds go into the pressure pot and the pressure pot goes into my office in the winter because I insulated and heated it. Temp. stays at 65 degrees f. I try to pour in the morning and then take the molds out 24 hours later the next morning. As soon as they come out, they go into the toaster over set at 150 f for one hour to post cure. This takes care of any tackiness. In the summer I will pull the molds 12 hours after they go into the pressure pot and then one hour in the toaster oven. I preheat the pr in the toaster oven at 150 for 15 minutes, then carefully stir in the mekp. Never had a problem. Sounds to me like you are not giving the pr enough time to cure. Hope this helps.
 
I re-heated the bricks in the oven after the chicken was done baking (soaking up the residual heat from dinner cooking) Not sure it was enough heat. So now, 6 hours after my casting session the blanks vary from tacky to leaving gooeyness on my finger when I touch it.

I just rigged a 40W bulb into the cooler for some sustained heat. Will report tomarrow.
 
In the past I use an old warming tray with a ceramic tile or something similar when mixing the resin. I also had an acrylic box that I put the molds in and used a space heater blowing in the box. This worked great. It sounds like everyone has there own way of warming it up on a cold day. Just PLEASE don't bring it in the house and use your home oven!
Alice
 
Alice, I know better than to bring it in the house!!!

I'm happy to report the light bulb in the cooler seems to have done the trick. I was only on for about 2 hours (I was worried about leaving it on over night). When I went to bed they were a touch tacky, but when cooled (about 30F) they were hard. I'm right now bringing them up to room temp just to be sure they arn't gooey at room temp, but I'm pretty confident I'll be de-molding them tonight and can bring them into the shop.

I need 2 of these blanks for commisioned work where I blew up the originally intended blanks. Lesson learned - dont take a commission for a blank I have only one of.
 
soligen said:
(Alice, I know better than to bring it in the house!!!)
Dennis,
I wasn't directing it at you, but over the years there have been those who have actually put PR in the home oven and couldn't understand why their wife was upset
Alice
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