Casting with Alumilite's Flex 30

Posted in Custom Workstation

I just cast some items and am waiting for them to cure. I'll relate my experience working with Flex 30 here. It's a straightforward process, but there are annoying little things to take into account. For a newbie, the process can be confusing because people online don't consistently use the proper terms to explain things. Even the official instructions aren't clear on what "post-curing" is or at what point in the process to do it.


[OVERVIEW]
According to the data sheets, Flex 30 is like a "soft rubber gasket" when cured. For a customizer, this makes it ideal for things like hair, skirts, jackets, etc. It's a 2-part urethane casting rubber, Part A and B are mixed 1:1 by WEIGHT. We have about 5 minutes to mix and pour before it begins to gel.

I'm casting some skirt flaps in rigid Apoxie Sculpt molds, Sculpey Firm molds, and a head in a latex mold as an experiment.




[MATERIALS]
Because you don't have time to dick around, set up the work area beforehand.

Here's all you need:
-Plastic wrap or newspaper (To cover work surfaces because this will get messy.)
-Gloves (Just do it, this stuff feels horrible on skin)
-Scale (Make sure it can measure light weights, like grams and ounces. It should also have a "tare" function. Don't eyeball this, you'll get poor results.)
-Oven (I use a small one.)
-Flex 30
-Mixing stick (Like wooden popsicle sticks, though smooth plastic or metal ones are recommended.)
-Flexible mixing containers (Like little medicine cups or plastic drinking cups. The flexibility lets us control the pour. Buy these in bulk because you can't reuse them.)
-Your molds
-Mold Release (I used Stoner's Rocket Release, a paintable mold release. I'm assuming "paintable" means you can paint the cast item. It's actually a 12oz. spray can, so you can't apply it with a brush.)


[PROCESS]
There are things to do before we can even get to mixing.

•Spray your molds with the mold release and let it dry or whatever for a few minutes, only a light layer is needed. This Rocket Release shoots a fine mist so there's no risk of it pooling up. (I had to flip the head mold inside-out to spray the inner latex surface.)

•Shake the two Flex 30 bottles and let them sit for like half an hour. This is to mix the "raw ingredients" in each bottle, and to let the generated bubbles pop.

•When casting thin parts, pre-heat your molds to about 130F-150F because they need more heat to cure properly. Yes, you will pour into the heated mold.

•Part B is like syrup and gets thick when it's cold, so make sure you get it to like 75F at least so it's easier to work with. Put the bottle in a bucket of warm water.

•There are paper membranes sealing the bottle, remember to remove those. Just carefully cut out the centers because they're impossible to peel off. Also remove the white caps and snip he tips off the bottles so you can, you know, pour the liquids out.


Ok, now we can mix and pour. The mix ratio is 1:1 by WEIGHT. I used 15g/15g of A/B, and it looked like enough material for two or three 6-inch scale heads. (FYI: The full bottle of Part A weighs 500 grams and Part B weighs 510 grams. Maybe you can do the math and mix by volume.)


•Place a mixing cup on the scale and zero it out. Now pour the amount you need of Part A. This stuff is watery, be careful not to make a mess.

•Do the same for Part B in its own cup, making sure it's the same WEIGHT as Part A. This stuff is thicker and won't splash around.

•Since Part A flows a lot better, you can pour it into the Part B cup. Make sure the cup can hold the full amount, obviously.

•Mix them steadily with the stick, don't go too fast to avoid generating bubbles. You only have 5 minutes, so use your best judgement. The cup will warm up, it's supposed to do that.

•Now you can pour. Squeezing the mouth of the container will result in a slower, narrower pour, this is necessary when pouring into small mold openings like this head mold. (I made a mess lel)


Oh, great, we're done right? NOPE. Since I'm casting thin items, now I need to "post-cure". This means I have to heat the whole thing for a while so it cures properly before demolding. So, a few minutes after pouring I popped everything in the oven for 2 hours at 130F, and now I'm waiting for the results.


=============================================


[PART 2]

After an hour in the oven some of the skirt pieces were still tacky, but they were solid enough to be demolded. I peeled 2 of them off the molds easily thanks to the mold release, then popped them back in the oven for another hour.

I figured the head cast would be a huge pain to separate because the latex is as flexible as the Flex 30...and it was. After removing the Apoxie Sculpt shell, I grabbed a rounded tool and worked it between the latex mold and the Flex 30 cast. It was like trying to separate two gummy bears that had melted together. Eventually I pulled them apart, surprisingly with no damage. The mold release did its job again. The head was tacky like the skirt flaps.

The latex mold looked like new, however, the head was gross. The cheeks are speckled with air bubbles, the chin is just a giant pock mark, the nose has a bubble, etc. However, there are sections of the head that look great. I think this means that after I sprayed the latex with mold release and flipped it inside-out again, I accidentally rubbed off the mold release from the ugly areas, allowing bubbles to accumulate there. So, make sure you don't touch the inside of the mold once you've sprayed the mold release.

Anyway, the head went back in the over with the skirt flaps.

After another hour, the head and 3 of the skirt pieces weren't so tacky anymore. Once they coooled off they felt like normal rubbery things. One of the skirt pieces that I had left in the mold stayed tacky and even had uncured sections underneath. I have no idea why this would happen since I poured everything at the same time and the other flaps are fine. Meh.



The big circular chunk is what was left in the mixing cup. For whatever reason, that thing didn't cure properly either, it was sticky and gross so I trashed it.

I made a mess when pouring, so here's a pic with the excess trimmed off the skirts:



You can see bubbles in the skirt pieces, most of them are under the surface though. Now I'll wait until tomorrow to paint them.


========================

[PART 3]

The pieces that cured properly aren't tacky anymore, the one skirt piece that didn't cure is still tacky. No idea why that happened. :/

Went ahead and painted the head and a skirt piece. I didn't wash them, just straight paint.

Here you can see how squishy Flex 30 is, the head goes back to the original shape after compression. Painted with Tamiya Flat Flesh, the paint dried normally and there's no tackiness.



Here I used P3 Thamar Black, again with no problems. After a few minutes I drybrushed some grey on it to see all those terrible bubble holes better lol.



The Flex 30 picks up every detail, just like latex. It feels like a gummy bear. It stretches well, the skirt pieces are about an inch big and can stretch to double the length without being damaged.

I like this material, it's perfect for what I need it for, unfortunately those freaking bubbles ruin everything and I can't afford a pressure pot. For small stuff like this, I'd rather just use latex like I've been doing.

As for costs...

-Flex 30 costs about $45 to $50 for two 14oz. bottles. It's enough to cast a ton of small stuff.

-I'm asking Alumilite if they recommend degassing or a pressure pot for bubble free casts.

--------

UPDATE
Here's Alumilite's response on degassing versus pressure casting:

“Pressure is the way to go with short open times.

It can be degassed by vacuum as well, just need to have everything ready, and a vacuum chamber that will have a pump strong enough to get to 26" relatively quick.

If you are going to use pressure your silicone molds need to be degassed as well.”