Curing in the microwave

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akgold
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Re: Curing in the microwave

Post#61 » Thu Jan 15, 2015 5:52 pm

The last two are before pictures
I'm so far behind I think I'm First !!

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Metalcaster
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Re: Curing in the microwave

Post#62 » Thu Jan 15, 2015 9:28 pm

Hi Ak,
Never microwave the part in Alcohol. The alcohol absorbs into the material and will cause a reaction in itself.Alcohol is kind of detrimental both on the pdms and the B9 material. It does work as a first stage cleaner in an Ultrasonic.
Thicker pieces , the size you show need less microwave.
I will list the entire process so that it can be put on the wiki if others test it and it works .
Remove the part from the table:
1) clean prototype in Iso Alcohol with Ultrasonic. Other types of alcohol actually cause damage quickly. OR use dawn liquid dish washing soap in warm water (best in ultrasonic.) I prefer staying away from Alcohol.

2) put Mineral oil ( edible variety. CVS, Walgreens)in heat proof glass bowl . Pyrex or Dow corning...available at walmart and put the parts in the oil and into the Microwave.

3) Using 700 watt Microwave or lower wattage ( or adjustable) run it on the rotary table inside the microwave for 3 minutes. This will approach 300 0F the first time. after 10 minutes, the oil is still quite hot, so now you go another 3 minutes in the microwave. It could go higher/quicker with a more powerful Microwave. That is not desirable.
We know from Oven curing it must be done in stages to 345 degrees or so. With a microwave, It happens much quicker and if left too long or in a powerful Microwave, it will damage the pieces just like the oven does when you go directly in at high temp. That is why I suggest a 700 watt or lower Mic.

4) Pour oil back into the bottle using small plastic funnel. the parts will usually stay in the funnel. let them drip a while into the funnel. Use Air pressure to blast off most of the oil or Use Roberts Suggestion to heat dry the oil at (I believe he tried 150 oF) for an hour ( could be less time). Leaving excess oil did not seem to cause any ill effects.. it seems to absorb into the investment easily and may actually help the burn of the oil and resin

5) wax does not stick to oil easily, So I use my wax welder ( small soldering Iron with Variable light switch dimmer, very cheap!) I remove the resin base it was grown on and I weld a thin coating of wax onto the prototype where I will put the sprue. I do this so that I can really apply some heat to the wax so it actually mixes with the oil and dries into the B9 material. Now, I weld the sprue to that area. Works best with Bigger sprues as this will help the resin to leave.

6) Invest in any investment at it's strongest setting. Usually 38/100 ratio. I have tested on R&R Max and Plasticast. You can mix at 37/100 , but you will have to adjust your setting time. Let investment sit for 1 hour ( you can wait longer if you wish). With a programmable oven, raise the temperature to just below water boiling temperature . I use 200 oF for 3 hours.... then I ramp up to 1400 oF and I leave them at that temperature for at least 3 hours ( more time if you have a full oven). Then I ramp down to whatever my desired casting temperature is and cast after the temperature has settled in the flask.

7 Follow whatever procedure you do after casting. :-)

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akgold
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Re: Curing in the microwave

Post#63 » Thu Jan 15, 2015 10:47 pm

my microwave shows in put power 1200 output power 700 so I am assuming it is a 700 watt microwave.This is the first time I have seen cracks in my models that I notice.

trying it again on the new print cleaned it this time in dawn soap and water no ISO ( I use 99% ISO I don't know what others use.)
I am using an old pyrex 1 cup measuring cup. It is filled to 1/4 cup level (20 oz.) should I use a half a cup? how much oil are you all using?
---------------------------------------------------------------------------------------------------------------------------------------------------------
I check the temp of the oil this time after 3 minutes and it is right at 210 deg F. and a little smoky when I open the MW.
wait 10 minutes temp naturally drops and goes to 140deg
then second 3 minute exposure it goes to 240 then down to 180 no cracks that i saw still in the oil shoulda taken em out to look. but the last 3 min it went to 290 deg.
I'm so far behind I think I'm First !!

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Metalcaster
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Re: Curing in the microwave

Post#64 » Fri Jan 16, 2015 9:32 am

Hi AK
I use a dow corning bowl from Walmart. Picture attached. I fill the bowl 1/2 way up. I use almost a 1/2 bottle of oil.
If you use too little oil, that may contribute to overheating as well.

Because A microwave heats/ cures through the entire piece quickly, It does not need the higher temperatures as in oven curing.
Attachments
Parts in Mineral oil.jpg
Parts in Mineral oil.jpg (66.42 KiB) Viewed 5877 times

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akgold
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Re: Curing in the microwave

Post#65 » Sat Jan 17, 2015 1:25 pm

this is the third time Printing these objects I posted earlier and the heating was a failure.
after cleaning once again in dawn soap in a cold ultrasound then rinsing and blowing off excess water to point of a dry surface
I put them in one half a cup of mineral oil in the microwave for just 3minutes
I removed them wiped with a towel to find after just 3 minutes in the oil, cracks began to form and some completely through the
edges of the models just like the pictures posted before.

This is just not working for me.
What can i say.
I'm so far behind I think I'm First !!

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akgold
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Re: Curing in the microwave

Post#66 » Sat Jan 17, 2015 1:36 pm

Metalcaster wrote:Hi Ak,
Never microwave the part in Alcohol. :-)


Yeah sorry that was a typo I meant ultrasonic I changed it I wondered why you said that. Went back and looked changed it.
I'm so far behind I think I'm First !!

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Re: Curing in the microwave

Post#67 » Sat Jan 17, 2015 6:02 pm

Hi Ak,
There has to be a reason it works for me and not for you... you want me to give your parts a try... ( no charge.) email the file to salesATracecarjewelry.com and I will test it when I come to work on monday... cast it on Tuesday in brass. I will also check my Microwave to see if it is 700 watts total ( which would probably mean around 300 watts actual out put).

The lines you have after washing In Isopropyl alcohol look more like what I got using denatured alcohol. I tried denatured alcohol and it worked very quickly to clean the parts of excess resin, BUT i could not get a single piece to cast and my parts had the same lines and cracking that your parts are showing.

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akgold
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Re: Curing in the microwave

Post#68 » Sat Jan 17, 2015 8:36 pm

Thanks for the offer
I am printing another one I had a failed print on this very same one. I had the first few layers attach to the build table and then the, since it was straight prints and flats all the way up it stuck to the NuVat Glass this time. Very strange.
I had one print of two half hearts looked like it shifted side ways but the other heart half was straight as an arrow
I don't see how that could have happened.
Cleaned the shafts for the bearings and the lead screw up the center reoiled lubed the sliders. just a basic tune up.
but I didn't recalibrate the table. I should have just in case as that was the problem last time it was printing like a champ and all of a sudden the prints were sticking to the Nuvat glass. the cool thing about this coating is I peeled the resin off the vat surface with no problem and wiped it all out washed with warm dawn soapy water and saw what i thought was the first indication of clouding on the NuVat coating. I thought oh well it had to happen sometime. then after I wiped it all down I used a little windex on both sides of the glass and the clouded area of the print disappeared. cool huh?

so this has happened one other time I don't know why but I have used this file 3 times with no problem and I just started a new print again this morning. (2.5hrs) each time, due to them being on their sides to get crisp letters vs. flat.
I tried them flat but the letters on the flat side didn't come out at all for some reason I figured the would be there after the base layers printed.
so anyways I am going to print it again and then I can send the file to you. it is on my thumb drive printing now.

I spent 3 hrs cleaning the vat and the b9 today. I also redid the stl changed it to angle it slightly.
I am wondering if straight vertical printed items are the problem. you can see the layers and the cracks follow the edges and continue inside along the layers for the most part.
I'm so far behind I think I'm First !!

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Stephen Attaway
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Re: Curing in the microwave

Post#69 » Sat Jan 17, 2015 9:05 pm

Not all mineral oils are the same (see http://aevnmont.free.fr/SACH-BOOKS/Petr ... 467_11.pdf). In general, the thicker the mineral oil the higher the flash point. Given that microwaving is heating the oil to 275F, that does not leave much margin for typical values of 300F for some mineral oils. The petroleum handbook references some mineral oils with flash points as high as 446F.

Given that Wallgreen's mineral oil works, will any mineral oil work? Will other oils work as the curing liquid? What is the lowest temperature that will cure the resin?

The flash point of mineral oil is low compared to other common oils. The most data I could find for oil was not on the flash point but for the smoke point (which is lower than the flash point). The table listed in Wikipedia for smoke point (http://en.wikipedia.org/wiki/Smoke_point) lists most of the common cooking oils. Refined avocado oil and safflower oil have smoke points above 500F. Refined soybean oil has a smoke point of 440F. Note that if the oils have not been refined, they will contain more volatile compounds and thus a lower smoke point. Clearly, if you are seeing smoke while microwaving, then you should start to worry that you are approaching the flash point of the oil.

I thought my capsule test in boiling water may be misleading due to the fact I am at an elevation of 7000 feet. Water boils at 198.7F at 7000ft. We know that 198.7 F did not result in a cure using the capsule test. Maybe at sea level, the higher 212 F temperature does cure the resin. Robert's microwaving temperature of 275 F produced great casting results. Will simply dipping parts in oil heated to 275F do the same thing as microwaving? Will 225F or 250F work?

I conducted additional capsule tests with thermal couples imbedded in the capsules. I use extra virgin olive oil as the heating oil. I selected extra virgin olive oil for testing due to its ready availability in the kitchen. The oil was heated on a hot plate. Following Mike’s by-line, I measured the oil temperature with two different thermal probes. I heated the oil to the desired temperature then immersed the capsule in the oil. It took about 5 minutes for the resin to reach stasis with the oil. After cooling I sliced the capsules open using a band saw. A capsule heated in 234.5F oil did cure. At 256.2F the resin did not cure. At 317.3F the resin was solid but soft/spongy. When this soft resin was exposed to UV at 395nm the resin became hard. Based on this result,it appears that 317.3F is the onset of solidification by heat cure. Some out gassing from the capsule was observed around 265F. The out gassing stopped at about 300F.

I reread Dawson's 2013 Santa Fe Symposium paper to better understand where the 345F oven cure temperature originated. It appears that this temperature was not the results of optimizing the heat curing process. For the heating in air test, weight change for raw resin starting at 100C (212F). For freshly printed resin, weight change did not start until 662F. The Differential Scanning Calorimetry test showed the onset of polymerization reaction indicated by heat flow at 200C (392F). My guess is that to avoid cracking, you should avoid rapid heat changes and minimize the cure temperature. It is hard for me to infer from Dawson's test an optimal heat treat. Cyclic heating in the microwave followed by cooling and re-heating may not produce the best outcome.

The volume reduction caused by additional curing can induce stress and lead to cracking. Thermal stress will also result when thermal gradients within a part are not linear. Cooling too fast or heating too fast could result in high thermal gradients. The geometry of the part will play a huge role in how parts cool and how thermal stresses build up. In addition, parts that can flex and deform with stress will be less likely to fracture than bigger parts. Said another way, I expect cracking during heat curing to depend on the part geometry.

I have not yet tired investing and casting the olive oil heated resin, so the jury is still out on how well/if olive oil heating will work.
capsule with thermal probe.jpg
Resin capsule with thermal couple heated to 256.2F did not solidify.


Regards,
Stephen Attaway

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Stephen Attaway
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Re: Curing in the microwave

Post#70 » Sat Jan 17, 2015 9:12 pm

Oops: Typo "A capsule heated in 234.5F oil did cure." should read " A capsule heated in 234.5F oil did NOT cure."
I will try to be more careful in the future.

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Metalcaster
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Re: Curing in the microwave

Post#71 » Sun Jan 18, 2015 1:06 pm

Lots of food for thought.
The reason for doing these tests is not so much to speed up the process.It is to learn how to make any component cure enough for casting purposes.Not all components cure enough for casting in any one system so far.


I have run my tests many times and only on a few parts where the castings were not satisfactory. On those parts, I ran the test in the microwave and then put them under UV cure for 20 minutes and then they cast fine. So, Some designs may not cure 100% in a microwave . Additional UV cure may be the final step for some tough to cast parts.

Allowing the mineral oil to soak into the part and dry overnight seems to be very helpful if you have time. Do not wash off the excess oil with anything.

The difference between running an uncured liquid in a capsule and actually a grown component off a machine is that the part off the machine is probably 65% cured or more ( guessing at %) before doing any of this. So, using the microwave for final curing is what i have been getting to work. Or any system that will work at the highest percentage rate. Oven curing also works most of the time, but not all the time.

Items that have real issues in casting are pieces that have deep thin engraving... Like engraved words or deep lines. I have found that by putting the designed parts back under UV Light and have the engraved lettering face the UV light source directly, I can force cure those areas and get them to cast. With the Microwave cure, I got 3 out of 4 parts with engraving to work... with no other curing. Does that mean this is the way...? No. I think we are all still experimenting with what works for our parts. There may be more then a dozen different un tested methods and combination of methods. really thick, heavy parts are also a problem as UV light does not penetrate all the way through... On the otherhand, A microwave does penetrate to cook the part from the inside out. The trick is to not overheat it and crack the parts... so Thats why I suggest multiple stage curing in a microwave.. You may need to cure it with a lot less power over a longer time... Just as you would do cooking foods.

At our factory, we get about 50 parts to grow cure and cast during the week... sometimes more.Certainly not all parts cure and cast correctly using ANY current system, so I am constantly tinkering with methods of cure.I am really glad that others are taking an interest in testing and working on this.

So far all the rings that I have done ( about 200 pieces) have worked with the microwave... some engraved pieces have failed, but got them by other experimentation. Heavy Pieces 1/8th inch thick have had some problems. Much heavier thicker parts can also be a problem. On the big heavy parts, B9 red by itself without mixing cherry seems to work best for casting.

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Robert Howle
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Re: Curing in the microwave

Post#72 » Sun Jan 18, 2015 5:54 pm

I would just like to mention one other thing that can be done on pieces as a test. When I was having trouble with casting after i replaced the large oven with the small one (before I added the air mod). I went back to the old Viper model method of adding a sprue vent to blow out any ash that might be present. This did work. I u don't under stand "venting" the model let me know and I will explain. Maybe possible that this might help with heavier pieces, if, ash is the issue.

Robert
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Stephen Attaway
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Re: Curing in the microwave

Post#73 » Sun Jan 18, 2015 6:30 pm

I did a follow on test where I heated the oil to 345F. The rapid heating of the liquid in the capsule resulted in off gassing and in one case failure of the resin capsule. The resin was spongy and soft. It may have been more olive oil than resin by the time it was up to temperature. It took longer to heat the oil to the correct temperature than it takes for me to heat resin in the oven. Also, heated olive oil at 345 made the whole house smell like popcorn.

I think I will start experimenting with some extreme UV light with an inert atmosphere.

Steve

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behold3d
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Re: Curing in the microwave

Post#74 » Tue Jan 20, 2015 8:59 am

Just fyi, denatured alcohol is fundamentally different that isopropyl alcohol and may effect your parts differently.

http://www.ehow.com/about_5519636_denatured-alcohol-vs-isopropyl-alcohol.html

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Metalcaster
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Re: Curing in the microwave

Post#75 » Tue Jan 20, 2015 12:07 pm

Definitely do not use denatured alcohol if you plan on casting... it will ruin the casting.
Been there... done that!

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RobertW
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Re: Curing in the microwave

Post#76 » Wed Jan 21, 2015 11:05 am

Metalcaster wrote:Definitely do not use denatured alcohol if you plan on casting... it will ruin the casting.
Been there... done that!


How will it "ruin" the casting?

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Metalcaster
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Re: Curing in the microwave

Post#77 » Wed Jan 21, 2015 1:29 pm

When I tried Denatured Alcohol, it seemed to take the excess off very quick and would also start to create lines in the piece... like it was dissolving the surface .
When I cast the pieces, they had very bad roughness .
I tried a few casts that way and they all had problems.
I went back to using Isopropyl Alcohol and had no more problems.

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tim.yoshi
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Re: Curing in the microwave

Post#78 » Fri Jan 23, 2015 7:21 am

Wow. Such an interesting thread. Regarding mineral oil, could you please describe it more? As I firstly thought about automotive motor oil :) Here, locally everybody is "saying mineral oil" in regards only to 15w-40 motor oil :) But then I saw photos of almost completely translucent jar and bottle, and understand that you talking about something other. Could anybody please explain to international what is it? :)

Also I read all thread but haven't saw nobody mentioned the obvious thing - why not to lower the power of microwave both by reducing it with settings (i.e. high, medium, defrost, low etc) and by increasing the volume of liquid? And hence just take one run of, say 5 minutes, or 10. Without hassle to turn on - turn off - turn on - turn off - turn on - turn off - turn on - turn off - turn on - turn off... (yes copypasted) :)

Here, in Ukraine, we likely have the most of the world's sunflower oil reserves and production :) It is cheap and widEEEEEly available here. We cook on it, rather then olive oil. Will it suit? Wiki says - Smoke point (refined) 232 °C (450 °F). It should be kinda close to olive oil likely.
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Stephen Attaway
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Re: Curing in the microwave

Post#79 » Fri Jan 23, 2015 10:52 am

My selection of olive oil was because it was in the kitchen and available. My test using olive oil was intended to determine the temperature needed to cure the resin. I interpreted the testing results as follows:
1) heating to 317F cured the resin but did not make it hard
2) heating in oven to 325 to 345F cured the liquid resin and made it fully dense and hard
3) out-gassing in the capsule test when dipped into 345F oil caused capsule to crack and the oil to mix with the resin.

Please understand that the capsule test may not be fully relevant to the casting process. These simple tests were to help me understand some of the parameters in the curing process. The resin does not fully cross link at 250F when heated in a microwave. Microwaving in oil may help with casting even though the resin is not fully curing. That said, I would like to understand how to get a fully dense (fully cross linked polymer) to insure that I start with as stable of geometry as possible.

I suspect the following phenomena are causing problems when casting:
1) dimensional changes due to additional cross linking (not fully cured when invested)
2) out gassing
3) uncured resin on the surface interacting with the plaster
4) thermal expansion of the resin relative to the thermal expansion of the plaster
5) poor oxygen supply to the resin in the oven resulting in the formation of carbon ash

For those uninitiated to the problems that can occur in casting, the following example may help.

bad casting.jpg
Everyone worked in this cast except this one ring.


bad ring casting.jpg
I hate it when this happens.


The photo above shows a simple ring that did not cast well. The ring was the only part in the cast that did not cast well. I have cast this ring without problems in the past. The ring was heat cured followed by a light hand painting/coating of resin to smooth/remove the print line. I used sun light to cured the coating, but it must have not fully cured due to oxygen interfering with the cross-linking on the surface.

To insure that the resin was fully burned out, I recorded the casting temperature for the casting. I followed Robert's suggestion and used an aquarium pump to insure proper air flow. I measured 1 liter per minute flow rate for the air. Below is a plot showing the temperature inside the flask and at the fresh air outlet from the aquarium pump. The pink curve is the probe inside the flask, and the blue curve is the probe in the air inlet. The combustion of the resin results in the thermal overshoot above the oven temperature at 650F. The initial part of the burnout was in a convection oven, so ignore that part of the cure.

casting setup.jpg
Air supply with location of thermal probe at air outlet. The probe in the flask is not visible in this photo.


burnout log.jpg
Burnout log with thermal probe located in the plaster and in the air outlet


In this example, the ring was fully cured except on the surface. It should be dimensionally stable. The other parts in the flask were almost perfect, indicating that the burnout was not the problem. I fully vented the part. I used plasticast investment and followed the rules for proper mix ratios. I allowed the plaster to cure for 6 hours before burnout. For this case, it appears that uncured resin on the surface of the part was the cause of the failure. The lesson learned is that the surface must be cured and "dry". Maybe hot microwaving in water or oil is providing a valuable surface treatment.

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noahbern
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Re: Curing in the microwave

Post#80 » Mon Jan 26, 2015 9:54 pm

Hi,

So I did the 3 mins in a 700w microwave waited 10 did another 3 and waited for it cool in the mineral oil. I saw lots of cracks lots it made parts brittle as well. Any help? Sorry I forgot my camera with pictures at work.

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