Toaster Oven Directions or FAQ's????

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sekach

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Dec 31, 2008
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Is there anywere that has some basic info on how to perform the basic curing of PR after casting with a toaster oven? I have been experimenting with casting over the last couple of months and I get the sticky surface all the time and usually wait almost 4-5 days before turning just to make sure everything is good and dry. However, I keep seeing posts on using a toaster oven and just popping in your blanks after they harden (a couple hours after casting). So can someone hook a brother up and point me in the right direction on basic how to use a toaster oven (i.e. temp, time, etc) after casting PR blanks?

Thanks....

Bob
 
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sekach

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I read the above link from last week, and numerous others from doing a search, but there wasn't as much info in that thread or others that I was looking for. I am looking for the basics, i.e. can you put freshly poured castings straight into the oven or should you wait? How long after pouring should you wait before putting the casting in the oven? The normal temps (135-150?)? What if you use rubber plugs, will they melt or do I just get to be surprised? Has anyone had any issues with items that were embedded into the castings (i.e. flowers, metallic objects, etc) that affected the end result? I can probably go on but it seems that we have so many casters out there that have always gone above and beyond when helping out the less experienced that I was assuming there was something already put together. Maybe there is a book at Borders/Barnes&Noble/Amazon someone could suggest?

Thanks for the input so far, much appreciated!

Bob
 
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Bob,

I think we need to step back and make sure we are speaking the same "language".

When you say "freshly poured" do you mean after it has cured? Or do you literally mean fresh liquid catalyzed resin poured into the mold?

I leave the castings in the pressure pot to cure for between 7 & 12 hours.

I take the cured castings straight from the pressure pot to the toaster for a post cure.

If you are concerned with the rubber plugs you have, and they do not list what they are made of and their technical specifications are unknown then you need to test them in your curing oven and make notes in your casting journal. Many rubber materials are vulcanized between 200F-250F, it depends on the particular chemistry.

The higher the heat in post curing PR the more shrinkage you will have.

I hope this answers some of your questions.
 

ldb2000

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Laurence Harbor, NJ, USA.
Bob , sorry to say that there are no tutorials or books or even allot of information out there because we are all just winging it on some of the things when it come to casting . The MEKP that you add causes a chemical reaction that generates heat to cure the resin , additional heat is NOT needed for casting but it does help cure the cast blanks faster .
How you heat the mold/blanks can be done several different ways , you can use a toaster oven , a heat lamp over the mold/blanks you can even put the mold/blanks in the noonday sun for a bit , these will all speed curing .
I use a Styrofoam ice chest laying on it's side with a fish tank heater installed through the bottom to heat the molds/blanks to about 100 degrees and post cure my blanks that way .
With a toaster oven set at it's lowest setting , keep it under 150 degrees , it will take less then an hour to post cure your blanks . You put the mold/blanks in the oven after the resin has gelled and started curing .
Hope this helps .
 

RAdams

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i built a box specificly for this job. it has a heat bulb in the top, and a tray that is adjustable.

I am considering making a vibrating table for inside the pressure pot. I think a slight vibration would help get the bubbles out.
 

OKLAHOMAN

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Charles, I bow down to you when it comes to the chemistry but 7 to 12 hours to me seems over kill. Once the PR jells are we really going to force more air out at 35-40 lbs pressure? I've been taking my castings out after 1 hr than into the toaster oven at 150 degrees. BTW I'm using a swing resin and 3 drops per Oz.and I also pre heat the resin in the oven for 30 min. @ 150 before adding the activator
I leave the castings in the pressure pot to cure for between 7 & 12 hours.



.
 
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Charles, I bow down to you when it comes to the chemistry but 7 to 12 hours to me seems over kill. Once the PR jells are we really going to force more air out at 35-40 lbs pressure? I've been taking my castings out after 1 hr than into the toaster oven at 150 degrees. BTW I'm using a swing resin and 3 drops per Oz.and I also pre heat the resin in the oven for 30 min. @ 150 before adding the activator

Roy,

Please, no bowing, just unmarked cash.

I know the discussion has been that once pressurized and gelled that the disolved O2 has been trapped and cannot escape again however, I have seen cured Silmar 41 form a vent in the inhibited surface and bubble after 7 hrs of pressure. If I remember correctly from a conversation with technical support, or a tech paper, uncured S41 resin is only very barely hydrophilic, and can/does absorb minute amounts of water. It is my untested theory that the water, as vapor(caused by the heat of curing), expands when the pressure is released, and bubbles out of the still soft resin.

The time to cure, using the recommended amount of MEKp, in the literature I have, and or read is that it requires 6-8 hrs, some brands list 12-24 hrs on 1/4" thick casting. So I leave the casts for 7hrs or so when I cast in the morning, 12hrs when I cast at night and unseal the pot in the morning.

Swing resins while they may be polyester resins are not the same as laminating resins(Silmar 41, EP4101, C'nC). They have extra/different promotors to help drive/accelerate the cure with the extra pigment or embedment load, up to 70% filler/pigments, so less load = faster cure. We really need to make a differentiation regarding which subtype of polyester resin we are using.

Silmar 41 has a viscosity between 400-600. When catalyzed at 1% has a time to gel of 20-30 minutes depending on temp, environmental conditions, thickness and load.

I typically catalyze at 0.5% of the resin volume in mL, I do not preheat the resin, but I do ultrasonic it for 16min, before pigmenting, and 8 min after pigmenting. I heat the dry/powder pigments, to drive off any moisture, before adding to the resin. I believe, perhaps anecdotally, that the US helps break up and mix the powdered pigments that may have lumped up. The US incidentally, does adds heat to the resin through molecular motion and absorbtion of the sound energy. The resin is significantly thinner after US than before.
 
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OKLAHOMAN

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Charles a bag of cash is on its way, I won't vouch that its unmarked as my 4 year old granddaughter had some crayons the last time we played Monopoly.
Thanks for your input...we all learn something everyday here.
 
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