"Foaming polyurethane" Topic

It has gas.

The parts puff up a bit.

Outside of pressure, any solutions?

I thought I stumbled upon one idea when I accidentally over filled the mould and it had a heap of waste on top. I think this allowed the resin to expand outside of the mould, lessening the internal expansion.

However 2 attempts have not recreated the result.

If you decide to go with a pressure pot, check YouTube's Rybonator channel -- he makes custom resin dice, using a pressure pot. Here is a link to his video, Dice Making Basics: Supplies: "The creator discusses essential tools like silicone, resin, and dyes, as well as optional equipment like a pressure pot and vacuum chamber."

He has a lot of knowledge and expertise displayed in his videos. Perhaps his videos will offer solutions and insights? Cheers!

Not real sure this will help much:

But with polyurethane that foams, adding heat makes it foam more. Playing around with the old "Mountains in Minutes" mix it yourself kits (yeas! I am that old), I discovered you can easily triple the volume of foam with applied heat.

So, the opposite should also e true. By chilling the urethane before mixing (or shooting out of the can, if you are working with that type) should reduce the resulting volume, and thus give you a denser, stronger, result.
Pre-chilling the mold would also help. Note that the reaction of the polymer curing produces heat on its own, so there will be limits to this effect.

The original Amber colored Gorilla Glue is a polyurethane that doesn't foam nearly as much, but still foams.
I have used that to make hedgerows. Lay down a bead, and dump sand, gravel or ballast. As it foams up, it entraps the stuff on top. Repeat to get the desired height.
I've also used it in buildings, to simulate brick and rubbish debris.

I've never tried to make hills or mountains with the insulation polyurethane, though.

If you have resin that has started foaming (which you don't want) it means one of the components, probably the polyhol, has become contaiminated with water. When you mix it with the isocyanate (the dark brown liquid) a reaction takes place that creates carbon dioxide.

This is essentially how polyurethane foam works. Water is added to the polyhol as a "blowing agent". The CO2 bubbles created by the reaction expand with the heat from the reaction, making a foam. There are other additives to get a nice uniform structure by managing the expansion and curing time.

Contaminiated resin lacks the additives and so the foaming is all over the place. There isn't much can do to remove the water.

I may have solved the problem??

Sat two foil lined tuna tins in a toaster oven with the door open, and it's regular top and bottom holes.

Put it on defrost, trying to get just over room temp, maybe 30 degrees C?

Stirred them with pop sticks for about 10 mins or so, enough to let the oven go on and off a few times, to suggest consistent temperature.

No fire ball.

Mixed and poured, seemed to cure rapidly (it's already easy cast!).

Casts show extremely low maybe no?? expansion.

Painting test is underway, as trimming expanded ones left areas where paint won't dry, possibly leaching resin??

If painting seems better, may have to heat larger batches. Have about 4 litres to use.

Hopefully I can put off buying more.

That painting test was only slightly tacky, a definite improvement.

I do wonder if washing the parts, after cutting/trimming would help? Another experiment I aim to do.

I just heated up about a cup each of resin in two large fruit tins in the open toaster oven on one bar defrost, lowest setting available.

The tins filled the height, so I kept pulling them out to stir well, every few minutes. For about an hour all up.

I felt like Bill Paxton, but there was no nuclear explosion in this movie.

Fumes? Probably? But nothing I really noticed. The dark resin may have gotten darker? Perhaps has some vapour release. But that was kind of the point of the exercise.

A couple of mini tests during the process, just a few drops of each in a plastic shot glass, seemed to work fine. None of the foaming I'd come to expect. Visible bubbles, but I'd consider that normal??

Poured into plastic jars with a good go with dry air blanket.

I'll leave them to cool, then test/try out hopefully tomorrow.

Just poured.

Yet to check.

Was thicker pouring in I think, but not foaming.

However after a few minutes, it started turning white, then began foaming on top of mould.

So it could go either was as far as the casts.

Three differences from when I did it last and it worked:

I did a larger batch this time, however I also warmed it longer, although it was in and out of the oven for mixing due to the size of the tins, which were only part filled.

I spraying in a lot of dry air blanket, however that's designed to be used with resin. However the resin was warm.

Perhaps the main difference is that on the successful pour, the resin was warm. This means it and any moisture in it had expanded already, likely the heat from the curing resin was no warmer, meaning it could not expand any further. I suspect this is the main solution, perhaps after the warming and stirring, warm before use???

I'll keep trying a bit longer.

Just pulled it out.

Failed.

I think I'll try it warm again, next.

Tried warming it before pouring, like I had done when first trying to warm and stir.

However, no success. Still puffed up parts.

There must be something that makes it work, as that one time, plus another previously when casting a bunch of cuffed up ones, it has worked.

I didn't stir it this time, just heated. But it was from what was already heated and stirred from yesterday.

Ah, ha.

A solid mould.

That would solve the issue, and the parts don't have undercuts.

Hmm…