alumilite and bubbles

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airrat

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I poured some PR cactus blanks the other day and with just using the pressure pot they came out without any bubbles.

Today I poured some with alumilite and put them in the pressure pot and they both have bubbles. Does alumilite need to be vacuumed first or did I miss a step with it.
 
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Dario

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My theory is that on cactus blanks... the air ends up IN the cactus fibers when you pressurize it. With plain blanks, they don't have anywhere to go/hide and you just end up compressing the bubbles.

I believe I've heard/read from Curtis that de-gassing is recommended. Another option mentioned by another member is the use of ultra-sonic cleaner...one claimed you won't even have to pressurize it. Haven't tried casting yet so cannot speak from experience.
 

MesquiteMan

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Tom,

Your problem is most likely that your cactus skeletons are not dry enough. Urethane resins in general DO NOT tolerate moisture or water AT ALL. I use a drying process that gets the skeletons bone dry before casting and do not have any problems.

As for any of the other stuff, it is not needed, at least in my experience. I do not de-gass or use vacuum at all. Ultrasconic will not do it either, IMO, due to all the voids and pockets naturally in the cactus skeleton. It might help the resin itself but once you pour it, you have just introduced air back in.

Try drying the skeletons THOROUGHLY before casting and I bet your problems will mostly go away. OH yeah, you will get a few small bubbles with Alumilite even with the best practices.
 

airrat

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Thanks Curtis, I do believe they were a little wet. I did not mention we had dyed the skeletons. I will try it again after leaving them out in the heat for a day or so.
 

BRobbins629

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Ultrasonics and vacuum degasing only work with resins that have air or other gases in solution. These methods work well for polyester and epoxy resins, but in the case of urethanes (which Alumilite is) a volatile gas is a byproduct of the curing reaction so these techniques have no effect on that. For Alumilite, pressure during curing is the only way to reduce/eliminate the bubbles. Drying the cactus or whatever else you're casting will help, but will not eliminate all.
 

Alumilite

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Curtis is correct. Moisture, as we've mentioned quite a bit lately, causes havic with urethanes. Typically if you have moisture in the cactus and you pressure cast it thinking it was dry, the result will be air bubbles not throughout the piece but closely attached to the cactus itself. There may be a small number of sporadic tiny bubbles floating randomly off of the cactus but most will be sitting on or very close to the surface of the cactus itself.

If you have moisture in the resin, in a dye, in a filler, or in the mold box you will typically see more random air bubbles throughout the part. They are typically spread out very evenly throughout the pour and in worst cases it will foam out of the box completely as we saw in airrat's case with the pearl colorant he tried.

To the question of whether you can vacuum or degas Alumilite, the answer is yes. 95% of all Alumilite Clear users will simply mix the resin, vacuum it to remove all of the mixed in air and then pour a perfectly clear part. In a situation such as this how to ... http://www.alumilite.com/index.php?page=show_info&type=HOWS&id=47 ... we recommend also pressure casting the resin once it has been vacuumed and poured due to the resin more than likely creating air bubbles as it fills the detailed mold of the tail light lense. So in this example we not only recommend degassing the resin before pouring to remove all of the air we whipped in while mixing but also pressure cast it to eliminate any air bubbles in the mold that we may have created while pouring it. This process is still rare that you have to do both. Typically people either vacuum or pressure the Alumilite Clear with the large majority only vacuuming to effectively remove all the air out of the cast.

200767135956_Clear%20Pour%20Vacuumed.jpg
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Here is a picture of a piece I poured yesterday and the left over resin poured in a cup. All I did was mix, vacuum, and pour the resin and the parts came out perfect with absolutely no air (without using any pressure). So stating that pressure during curing is the only way to reduce/eliminate the bubbles of Alumilite resin is simply not accurate. Vacuuming Alumilite has been used for close to 20 years and is a perfectly suitable mean of removing air from the urethane resins whether they be clear, opaque, or flexible.

Mike
Alumilite
800 447-9344
 
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