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Merlin

Degassing polyurethane resin cannot remove myriad of bubbles

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Hi,

9cfm pump gets to 28.5inch (sometimes 28.7)  never 29, bought for this purpose, its a good pump.  Javac 231.

7-8 min potlife resin. SG2000L

Resin goes in chamber after mixed B into A, pump on etc , 3 mins elapsed since mix started, I watch loads of bubbles about  2mm dia covering top surface and also filling the drinking beaker down to base, 1inch worth of resin in there. I see thin wisps of something, a gas ? but then I look closer and its gone.

I expect them to rise but they just sit there, some activity of bursting at surface but not much, .

One must not overdo this else resin will boil. you get then loads of bigger bubbles and the resin is getting warmer and sets up with a resin froth !

After a while with nothing happening and not wishing to boil the resin I let air in, so I have resin with lots of small bubbles floating in it, I repeat the degassing and again achieve nothing more than before.

 

THis cannot be used for pouring into mould and I also need to place that into chamber as there are some areas that may trap air I cannot vent easily.

 

what is going on ?

 

room 23 deg humidity 55 my gubbins says. Its a normal UK day, blue sky some grey cloud nuking the sunset, doesnt feel humid as such.

 

I cant seem to degass resin before it sets up, as for time to degass beaker then degass mould as well, impossible. How does one cope with such dual needs ?

 

this is setting up and its not a liquid through which bubbles can rise after 5 mins if not even 4 mins, it has the consistency of a milkshake even at 3 mins.

 

I also need to add in aluminium powder and thats 1:1 by weight at the least, I have tried 1.5:1 for a more aluminium effect and its like paste, impossible to degass, let alone pour, like the remains of choc icing or polyfilla setting on a plate end up with a metal muffin. Yet its sold for adding into ply resins then pouring !

 

Merlin

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I think that resin with this kind of pot life is generally not very suitable for vacuum degassing, it's still not enough time before the reaction sets in. However, your resin may have absorbed moisture, which causes excessive bubble production.

I de-gas only my clear resin which has a pot life of around 15min and doesn't produce much heat on its own.

 

Either mix very carefully and cast without degassing, just into the open mould or use a pressure pot setup.

 

For the aluminum powder, decant and measure your required quantity of the thicker part of the resin first (usually the polyol), mix in the powder, then de-gas just this mix.

Then add the other part, mix carefully and cast.

 

J

 

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I have never had the opportunity to use a vacuum to de-gas, I just pour it and hope but one think I have experienced is bubbling whilst the resin goes off and that is caused by moisture in the resin. I now have my resin cans opened for the minimum time to decant some into a jar and the lid goes back on. I only decant as much as I need. It still bubbles if the resin has been on the bench for any length of time though. I work in centrally heated room so it obviously does not ned much moisture for the resin to do that. This might not apply to you at all but it's all grist to the mill!

 

Simon

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Is your resin old? The more times you take the top off the containers, the greater the chance there is of moisture getting into the resin, a squirt of an inert gas into the containers will prevent moisture build up. If your patters have a lot of detail and you are using fast cast resins, you might be better off pressure casting rather that vacuum degassing. You can make a pressure chamber from a cheap pressure cooker, you won't need to degas the resin prior to pouring. Alternativly, try Axson F31 resin - it has a very low viscosity (and a very short pot life so don't try degassing the resin after mixing), short vacuum (not to a full 1 bar) your castings after pouring.

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