Curing in the microwave

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Metalcaster
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Re: Curing in the microwave

Post#21 » Wed Dec 31, 2014 4:06 pm

Correct me if I am wrong, but, the reason docs investment would work better for cured material ( i don't know or think it will work for uncured) is that it is considered an investment used for Platinum and has tremendous strength. It is also much more difficult to break out and clean off the piece. You can definitely use Platinum investment for B9 resin, but it is overkill , much more money in all areas.

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Robert Howle
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Re: Curing in the microwave

Post#22 » Wed Dec 31, 2014 9:07 pm

@RobertW-- Why introduce another variable into the equation. Complete curing is just the way to eliminate one more possible issue.

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ckl81
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Re: Curing in the microwave

Post#23 » Fri Jan 02, 2015 2:03 am

I was testing with microwave curing. I put all the prints in the cup with water, then turn on high temp for 10mins. These are the casting result. I have not calibrated my oven yet. So, there are some small holes in those bangles, but easy fix. The surface looks no different from the uv curing. Thank you OP for the microwave curing method.

Ken
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Re: Curing in the microwave

Post#24 » Fri Jan 02, 2015 12:20 pm

Nice castings

Thanks posting up the result, I was waiting for it


Mike N.

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Robert Howle
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Re: Curing in the microwave

Post#25 » Fri Jan 02, 2015 1:17 pm

I guess enough people have tried the boiling method. I'm going to give it a test myself. will post results.

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mikej
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Re: Curing in the microwave

Post#26 » Fri Jan 02, 2015 1:43 pm

The fact that the part is under water may keep the cure inhibiting oxygen off the surface, allowing a faster/better surface cure?
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noahbern
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Re: Curing in the microwave

Post#27 » Fri Jan 02, 2015 5:00 pm

Looks good but you NEED more air in the oven!

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Stephen Attaway
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Re: Curing in the microwave

Post#28 » Fri Jan 02, 2015 7:48 pm

Does the microwave heat the resin more than the water? Would simply placing the part in boiling water do the same thing?

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Robert Howle
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Re: Curing in the microwave

Post#29 » Fri Jan 02, 2015 8:53 pm

I'm not sure, but it seems to be the heat with the water blocking the oxygen that aids in curing. Water boils at 212 F so u are not reaching the oven cure temp of 345 F that is recommended. Since oxygen inhibits curing (reason layers don't stick to oxygenated PDMS) It would seem to be as Mike suggests. Only speculation at this point. I know at some pt. there were attempts to cure in the microwave without the water. This did not work, ruined some prints.

I have a sterilizer (UV with ozone generator) and I put some prints in and in just a few minutes the surface got fuzzy looking. Not sure what was going on, but did't try to cast or cure this way again. Thinking about disconnecting the Ozone generator and just using the UV. Haven't done this yet. Just want as a backup for UV curing. If it turns out that the boiling water method is a dependable method for curing, this will be a mute point.

Printer settings, resin mixes (ie, 1:1), and curing methods, are ongoing adventures. I, for one, am enjoying the experimentation while still being able to print great models. The evolution of the B9 is still happening and hopefully will continue for some time as we all work together to get every "micron" of benefit from Mike's great machine.

Robert Howle
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Stephen Attaway
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Re: Curing in the microwave

Post#30 » Sun Jan 04, 2015 6:37 pm

Where does the recommendation for oven cure at 345 F temperature for two hours come from. Is 345 F temperature that is specific to this polymer resin? Is it based on testing or is there a theoretical reason based on this resin?
Thanks,
Steve

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Robert Howle
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Re: Curing in the microwave

Post#31 » Sun Jan 04, 2015 8:22 pm

All of the information is in a paper written by Gary Dawson, the jeweler that helped the B9 creator with the resin testing for the very beginning. Gary recommended 4 degree F per minute ramping to 345 F and hold for 1 hr.

Castability

"RED RESIN: Our original B9R1-RED resin has been well-documented to directly cast with little modification to a typical jewelry-industry lost-wax casting system. The printed object MUST be fully cured prior to casting with either light (UV light box, available online for around US$30...search term: acrylic nail curing box) or heat, ramp at 4deg to 345 deg F and hold for one hour. We also suggest using “Plasticast®” as your investment, following Ransom & Randolph instructions for either a 6 hour or 12 hour burnout."

This is copied from Dawson Distributions FAQ section of his home page.

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Stephen Attaway
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Re: Curing in the microwave

Post#32 » Sat Jan 10, 2015 6:11 pm

I did an experiment to determine how well resin cured in a microwave. I wanted to know if simply boiling a part would cure resin. I built a resin capsule (10 mm x 10mm), filled it with liquid resin, and then sealed it closed using a short exposure with a UV flashlight. I had two small holes in the jar top and used a syringe to make sure that no air bubbles were present.

resin jar.jpg
B9 layout for resin "jar"


I placed the capsule in an uncovered dish with about 1 cup of water. I microwaved it for 5 minutes on high, checked the water level, and continued for an additional 5 minutes. For the boiling water test, I placed the part in boiling water for 10 minutes.

The microwave did not appear to cure the resin.
uncured microwaved resin.jpg
Uncured microwaved resin

As you might guess, boiling in water also did not cure the resin inside the capsule.

When I cured a capsule in a convection oven for about two hours at 325F, the resin was fully cured.
heat cured at 325F.jpg
Fully cured with 325F heat


The lack of cure in the microwave was not the results I was expecting.

In a second set of tests, I tried to measure the change in density of printed parts that are heat-cured.
I first measured the specific gravity (SG) of uncured 1:1 mix based on a 10 cc sample size and found SG with no cure = 1.093 g/cc. The SG of the capsule filled with resin before curing was 1.12 to 1.13 g/cc. After boiling and microwaving, the SG of the capsule was 1.09 to 1.13. After-heat curing, the SG of the resin was 1.169 g/cc.

I printed several large rings (see setup below) to serve as test parts. The rings weight 6.2 g and were 8 mm thick. The as printed SG was measured in the range of 1.176 to 1.180 g/cc. After heat-curing, I measured SG in the range of 1.191 to 1.96 g/cc. I also measured .1 to .2 g of weight loss on these test parts during heat treatment. Heat-curing also produced a 0.3% change in length for my test parts. Microwaving did not change the density of the printed parts.
ring test part.jpg
Ring test part (46 mm tall)
ring test part.jpg (55.37 KiB) Viewed 4862 times


What can we infer from this simple tests?
1) heat-curing makes parts denser (more cross linking)
2) some weight loss (out-gassing) occurs during heat-curing
3) parts shrink during heat-curing
4) 325F appears to cure the resin (this is good because I was getting cracks at 345F, but not at 325F)
5) microwaving does not cure resin

Casting results show that microwaving parts improve casting results. Microwave heating does appear to "treat" printed parts. Microwaving is not the same thing as heat-cure. Maybe microwaving/boiling removes unexposed resin from the surface.

Regards,
Stephen Attaway

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Robert Howle
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Re: Curing in the microwave

Post#33 » Sat Jan 10, 2015 6:24 pm

Thanks, great to know. Thanks for all the testing.

Robert
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akgold
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Re: Curing in the microwave

Post#34 » Sat Jan 10, 2015 7:09 pm

I am not so convinced by this test using liquid resin.
a resin model is exposed layer by layer to harden the liquid into a solid.
then the curing of the exposed model is another process.
Curing by heat of resin is going to harden due to temps but is it actually cured ?

so the only way to test this is to cure a model already exposed to light.

with the container filled with resin being cured in the microwave you have no way of knowing if the container itself was cured.
Resin will also harden and cure both if it is exposed to sun light

the real test has yet to be presented to understand depth of cure. so a thick item printed may not be cured to it's core but the outer surfaces exposed to UV light are using the UV method. short of cutting it in half and using some sort of identification of cured and uncured printed models we really don't even know if the UV is actually curing it to it's core.

my take on it is that so far the only way we know if an item has been cured "enough" is when we cast the item and it yields a model with or without porosity. poor casting we blame the curing time or method when it could even be a combination of partially cured model and mistakes made heating the metal or inconsistencies in mixing or heating the metal to cast.
casting white gold is much different than casting yellow gold so a YG casting may show great results but casting it in WG using the same model and curing times might well have a whole different outcome.

Try pouring the resin in a glass of water and see what happens to it in the microwave.
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Stephen Attaway
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Re: Curing in the microwave

Post#35 » Sat Jan 10, 2015 9:48 pm

After heat-curing, I measured SG in the range of 1.191 to 1.96 g/cc.


Looks like I made a typo, the range measured should read 1.191 to 1.196.

Steve

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brumbaer
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Re: Curing in the microwave

Post#36 » Sun Jan 11, 2015 4:53 am

Interesting test. Many thanks for doing them.

Some random thoughts

What would be nice to have are the values for UV curing (i.e. .5, 1, 1.5 hour under UV light)
It would be intersting to see how deep the UV cure reaches. I could imagine that the cure stops at a certain depth, especially with the stronger pigmented resins.

Looking at the results, I think, we see different effects.

I.e.
Curing - what UV light does
Drying out - what happens in an oven, probably in addition to curing. Drying out resin might look like cured resin, but still be different.
Other - rearrangment, removing of resin or breaking up of large bubbles or whatever.

I assume that UV curing will not reach in very far and as microwaving seems to improve the results this leads to the thought, that
a model casts well, if It is sealed in. i.e. being in a shell of cured resin, and that it does not have to be cured through and through.

Emperical data might be contaminated because they are usually done with rings which are round and the distance between core and surface is often not that big, so that it might be cured to the core without heat curing.

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Metalcaster
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Re: Curing in the microwave

Post#37 » Sun Jan 11, 2015 12:54 pm

Hi Guys,
Throwing My 2 cents in here. I was the person who mentioned way back that I had tried direct Microwave curing and it did not work well.. I even kep the parts in a microwave running at full power for as much as 20 minutes. Diferent materials reacted differently, but none were castable.

Using the 50/50 mix , Mike's settings on a 1.2 machine:

My next experiment had been using water and a microwave. I would run the microwave for 3 minutes on with a tall jar 1/2 filled with water and 5 or 6 parts in the water. I would allow the water to cool down and run it again for 3 minutes , cool down and run again. I then tried direct casting and it was Sometimes good and sometimes not. I did find that I could cure the resin in a UV curing system with a rotary device to rotate the parts for 10 to 20 minutes and the pieces became harder . These cast pretty good.

My Next experiment which seems to work BEST is:
I bought Mineral oil from CVS and put that in the jar instead of water. WHY ?
Oil can reach higher temperatures then water as the water can only reach boiling temperature.
So, i put 10 pieces made of the 50/50mix into my Mineral oil jar into the microwave.
1st noticeable difference between water and mineral oil..
In water, air bubbles cling to the surface of the parts, probably creating some issues.
In Oil, there were no air bubbles on the parts.

I cured the parts in mineral oil for 3 minutes in a 700 watt Microwave on full power. This was so hot that you could not touch
the glass without getting a bit of a burn. I allowed it to cool down and did it again for 3 minutes. ( do not know if it was needed to do twice) I put small and larger parts into casting and they all came out perfect with no failures.

My reasoning is the Mineral oil gets absorbed into the material a little and helps cure it. Since the oil is a combustible product, this may help in the "burning of the resin" . I have done this many times and the results have been very good.

I suspect we could use other types of liquid that are combustible, but there could be a danger in that while microwaving... so far, the mineral oil seems to be safe running for 2 to 4 minutes at a time. I do not suggest running oil in the microwave for 10 to 15 minutes as that MAY have an undesired effect.


Dealing with mineral oil, you should wear rubber gloves. AIR BLAST Excess OIL AT THIS TIME using compressed air.All the oil will not be gone, so expect there will be some left on the pieces.

IF you leave the pieces out to dry overnight, in the morning, they will appear to have absorbed all the oil which is a good thing, but not necessary.
Also, to attach the wax casting sprue so it does not come off, first use your wax pen to melt some wax directly onto the part and allow it to cool. Then weld your casting sprue to that location. The reason for doing it this way is so the first wax melted can get hot enough and bond to the part through the oil coating. This makes it easier to weld the sprue to that area without it constantly falling off.

I have been developing different methods of curing because My factory also does large parts and we use all kinds of materials. Curing and casting larger parts can sometimes be problematic.

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Robert Howle
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Re: Curing in the microwave

Post#38 » Sun Jan 11, 2015 2:58 pm

Thanks Daniel, will give the mineral oil a try.

Robert
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Re: Curing in the microwave

Post#39 » Sun Jan 11, 2015 6:46 pm

Hope it works as well for you as it does for me. Certainly shortens the time to cure by quite a bit!

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Stephen Attaway
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Re: Curing in the microwave

Post#40 » Sun Jan 11, 2015 8:28 pm

Do you think deep frying the resin will work?

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