Curing in the microwave

[Robert Howle]

MIght be "batter" dependent.... I prefer grilled myself.

Robert

[Metalcaster]

No, I am pretty sure frying the material will not work .

I am currently testing on thick tall heavy pieces using the combination of Microwave in Mineral oil, then 20 minutes under UV which seems to dry the oil... then into the oven at 200 Of .... seem to be getting some pretty hard pieces which usually means it will cast good.
Will post pictures in a day or 2.

[Metalcaster]

[Stephen Attaway]

Do you have a way of measuring density for the oil-heated parts? Have you measured the temperature of the oil just after microwaving?

My working hypothesis is that bad casting occurs because the heating of uncured parts results in a change of dimensions of the part during the burnout process. This change in dimension causes the plaster to fail. For an uncured resin, the additional dimensional changes due to curing overstress the plaster and fails the resin. Heat-curing the parts makes them dimensionally stable so that they do not damage the plaster.

My attempts to measure density was to provide a quantitative measure that would allow us to compare different curing methods to show how well each fully cured the parts. Microwaving in water did not result in a measurable change in density. Heat-curing did result in a measurable change in density.

Fully cured parts are not only dimensionally stable, they are stiffer (i.e. harder). Jacobs introduces the term photomodulus to describe this linkage of mechanical properties to the degree of photon induced cross linking within the resin polymer. He developed both theory and experiments to show how Young's modulus changes with exposure.

Following Jacobs' photomodulus concept, measuring part stiffness (hardness) would also be a way to determine if a part was fully cured. Jacobs shows plots for photomodulus curves for 5 different resins. I would be interested in knowing if the B9 resin is similar, or the same as, the resins Jacobs tested.

The fact that the microwaving in oil produces parts that are stiff may indeed be a sign that they are good for casting. My guess is that not only is the complete cross linking of the polymer making them dense and stiff, it may be reducing the coefficient of thermal expansion. In general, the higher the Young's modulus, the lower the coefficient of thermal expansion. Said a different way, hard parts are not going to expand as much when heated as softer parts. For good casting results, a low coefficient of thermal expansion is likely a good thing.

I measured density (specific gravity) to use as a metric of curing because it is easier to measure than Young's modulus or coefficient of thermal expansion. I made the measurements using the same equipment that is used to measure gemstone SG or gold SG.

I realize that heat curing to maximizing density or Young's modulus may not be the full story. I can heat cure parts to the point that they crack. They are hard and dense but not so useful. Maybe, heating in oil stops the parts from becoming brittle.

I do worry that microwaving oil could result an outcome that ends in my being banished from the kitchen forever. For about $30, I can get a Presto FryDaddy Electric Deep Fryer on Amazon.

Stephen Attaway

[Metalcaster]

Hey Stephen, I agree with you on many points. I am pretty sure that I was reaching over 300 oF in the microwave and doing it a few times after allowing the material to cool . At the time, I have been testing the process and seeing what problems were being resolved. So far, I think I have a bunch of parts that cast out perfect. They are being de-vested now. Hope to have pictures up soon.
I have a few other tests to do. Namely engraved detail and lettering has a tendency to destroy itself in the casting process.
This is mostly due to the shrinkage of the material while it is in the oven for casting. I am going to be running some tests on these type of designs that have these specific problems to see if this new curing method works.

When using the Mineral oil for microwaving or for heat curing, make sure it is in a Pyrex bowl as it might crack under heat conditions. It is a Dow corning product for those who do not know where to find it... In the Kitchen!

All the equipment I use is no longer being used for any other purpose.
Bought a used microwave at the pawn shop for $20 It is much faster then Heat curing in an oven.

[Metalcaster]

PERFECTION!!!! got them. Microwave in the Mineral oil works fast and efficiently although it can get a tad messy.
12 rings cat at the same time.... all perfect, no pits, no holes, no issues at all....... Absolutely the best and smoothest RP castings

[akgold]

Nice

but I have ask what is that mosaic crystalline look on the surfaces of all the rings and the button?
is this yellow gold?

[TAJS]

It is brass

[Metalcaster]

It's brass. I use brass and bronze for production models and testing.

[Mine Art]

HI Metalcaster

That casting look very nice, can you share what type of Mineral oil ans where to buy it?
Thanks

Mike N.

[fcort]

wow this is all great information. Great cast too.

[Robert Howle]

Daniel, is baby oil and mineral oil same thing?


Robert

[Metalcaster]

Hi Robert, I do not know if it is the same as Baby oil as I have not read the label on baby oil. Mineral oil can be eaten/ taken internally for constipation , so that is a good thing in the sense that it's not dangerous to us Humans.
Mineral oil can be bought at any Pharmacy. Walgreens is where I bought mine, But CVS and many others carry it.

So far I have tested the curing on 2 other materials and all the B9 materials and the process works. Have had ZERO artifacts and no issues... trying some slightly bigger pieces tomorrow.

[Robert Howle]

Does it actually come to a boil? If so u do for 3 min, cool for 10, then do it again for 3 min

[Robert Howle]

Does it actually come to a boil? If so u do for 3 min, cool for 10, then do it again for 3 min

[Devlin]

Great news, Thanks metalcaster for posting your results. I have been wondering for a while if glycerin would work well. You can also buy it at CVS, the flask point is 320F in an closed cup and 349F in an open cup.
the thing that make me think of it is it is suggested when using colorit a UV cured resin. the properties may work better than oil.

As of now I have not tried any microwave curing, looks like a viable option.

let me know if anyone has tried glycerin.

[Metalcaster]

Hi Robert,
I have not tried to boil it as It is working fine just the way it is now. I do not think I am exceeding 300 oF in the 3 minute time.
and this is so much quicker then any other way, I don't think I want it to boil.

What I have done today was I ran a heavier piece for 3 minutes, allowed it to cool and did this 5 times.... Only on the 5th try did I start to see some cracking in the part. That is in casting for tomorrow and I will see if It had any detrimental effects.

There are apparently many types of mineral oil.... Many are not for Ingestion purposes. I picked this type as it was considered safe to take internally.
I will try to look up the flash point/ boiling point later on. There are many different figures listed for this when I do a search, so it is best if I get an MSDS sheet from the brand I am using.

[Robert Howle]

Had to post latest casting and technique based on Metalcaster's process.

14k yellow gold head groups cast with no new metal (did use deox additive). These were done in my small oven with the air mod turned off, so no extra air flow in the oven (do have holes drilled near floor on both sides. 1 hr 300f, 1.5 hr 650F, 3 hr 1400f. down to 900f for casting. Satin cast 20.

These three prints 1:1 mix on 1.2 machine, 30 xy 30 Z.

NO UV cure used, Washed in soapy water in ultrasonic for 15 min. Dried in oven 15 min at 150F (make sure no water on print). Used baby oil (high grade mineral with fragrance, smells like baby powder when hot, not for ingestion, external use only) that i had for quenching certain gold parts.

Oil in pyrex measuring cup, 3 min on high, 10 min cool, 3 min on high, 10 min cool, 3 min on high. Remove with tweezers and placed on paper towel to drain 5 min. PLaced in oven at 150f for 15 min. (all oil gone assume it was absorbed).

Built tree, invested, placed in oven after 1 hr bench set. As good a casting as i have ever had.

Thanks so much Daniel and others that started this experiment. Next batch white gold.

I did check temp with metal thermometer after last 3 min heating. Max temp I measured was 275F.

Really do think since Mike's mention of oxygen inhibiting curing, that the heat does the trick because no O2 is in contact with the resin prints while submerged in oil. Please be careful if u try this as my pyrex measuring cup got really hot, had to handle with few layers of paper towel (suggest oven mitt or similar). I would def not over heat the oil. I have seen flash over boiling of other liquids when tongs or other objects introduced into super heated liquids. This will hurt u if you get a boil over on any part of your body. Remember water boils at 212F and mine got up to 275F.

Those small bumps are just where i cut off supports before curing. I did not pre finish these prints in any way. These are as close to flawless as I have ever seen, anytime, resin or wax. I am thrilled. Only time will tell, but very positive results so far. Thanks again Daniel.

Robert Howle

[Metalcaster]

Hi Robert,
Your Welcome . Glad to post whatever discoveries I can. I did a Larger ,thicker piece yesterday that I had trouble casting using the UV cure method . It worked perfect using the Mineral oil/Microwave.
Daniel G

[akgold]

so I did the walgreens mineral oil same bottle as posted earlier then did microwave 3min sit 10 then 3 min sit 10 then 3minand this is what it looks like
ruined all three having to reprint now was hoping to cast them tonight but this threw the monkey a wrench.

any thoughts on this?
I also cleaned the prints in 90% alcohol in * ultrasonic* for 3 to 4 minutes. just long enough to remove the resin

both pieces of the hearts are cracked to the point of no return.

I tried this in water the same way on some others that were tests not really usable due to letters not coming out.

same heating schedule but noticed that the two hearts has a slight bow in them after heating so I decided to try out the mineral oil since the water worked ok
it was a flop.
any thoughts on this?