Air bubbles in Alumilite resin

[Austin T]

Been castin resin for a little while and the one issue that keeps plaguing my castings is air bubbles. How can I prevent these?I've tried heating my molds and warming the two parts before I pour them and it seems to help a little but I still have them.

[GeeBee]

Try pouring the resin into the miles slowly, pouring it too fast traps the air in the resin, also I find vibrating the mold once the resin has been poured helps a lot in removing the air

Edited February 16, 2014 by GeeBee

[Erik Smith]

Where are the bubbles showing up? Sometimes you can run a slightly dulled toothpick into the resin in the mold before it sets to break bubbles from small cavities.

You can make a pressure pot too...mine was about $75...

[Austin T]

What I'm mostly casting right now are rims. The bubbles tend to sink into either the lip of the rim or where the nut's go. It's really only in these areas that I'm having issues with. For example I just poured a rear bumper today for a 43rd scale mustang and it came out great with no air bubbles.

Edited February 17, 2014 by Austin T

[935k3]

The pressure pot is probably the best solution. The pros that do it for a living use them. You could try vibrating by setting the poured mold on on of those vibrating football games that does work we have used this at work for casting cross sectioning samples. My boss got one at yard sale. You can still get them new. Another method I saw on youtube was to stand up and pour into the mold sitting on the floor. Th length drives the air out before it hits the mold, you would need to aim carefully for this method.

Edited February 17, 2014 by 935k3

[Austin T]

The pressure pot is probably the best solution. The pros that do it for a living use them. You could try vibrating by setting the poured mold on on of those vibrating football games that does work we have used this at work for casting cross sectioning samples. My boss got one at yard sale. You can still get them new. Another method I saw on youtube was to stand up and pour into the mold sitting on the floor. Th length drives the air out before it hits the mold, you would need to aim carefully for this method.

I pressure pot is out of the question for me. Right now I'm just casting for myself and friends. If I do start selling products I will probably invest in a pressure pot. One thing I've been thinking about doing was making a little table I can put my molds on that vibrated. I have a few old phones lying around and my father used a vibrating component out of a phone before on a reloading press with good results so I might go this path with it.

[Erik Smith]

Yeah, wheels tend to catch bubbles on the edge of the outer rim and lug nuts - that's when I use a toothpick to pick the bubbles out. I switched from the brown alumilite to their white - it sets up slower and allows time to get at the bubbles trapped in the trouble spots. I don't think a pressure pot is necessary with simple casting - helps, but you can do just fine without.

[Evil72gto]

You can try what I did to solve that problem. Gloss coat your master before you make your mold. A glossy surface tends to let the rubber flow over the part better then if it was a flat or a semi gloss finish on the part. With the gloss coated part there is less surface tension for the rubber to try to flow around giving you a better finished part in the end. When you pour your resin into the mold it tends to flow into all the areas of the mold that you normally get air bubbles in. And also using a mold release will help a lot. Molds release helps to get the resin to flow better into the mold as well. I hope this helps I have been casting parts now for the better part of 10 years.

[Skydime]

Try pouring the resin into the miles slowly, pouring it too fast traps the air in the resin, also I find vibrating the mold once the resin has been poured helps a lot in removing the air

Maybe try pressing a palm sander with no paper against the mold? I saw this trick on a show about making concrete countertops before.

[Jeremy Jon]

Austin, what mold release agents are you using now? Try dusting with baby powder, I find it works much better over the spray mold release agents

The above suggestions are all good ones, another is what does your mold look like? Maybe post a photo for us

The reason being, is in my own trial&error, learning that the initial mold design makes ALL the difference in the world too, and perhaps some improvements there might help you also

I'm by no means an expert, in fact I am working on my skills now to get components reliably resin cast, and it's more work than many people think

For example, I continue to copy photos from online, and ask questions about method & materials specifically, to increase my own learning, the pics I can go back a look at often to help improve my own techniques

[Art Anderson]

What I'm mostly casting right now are rims. The bubbles tend to sink into either the lip of the rim or where the nut's go. It's really only in these areas that I'm having issues with. For example I just poured a rear bumper today for a 43rd scale mustang and it came out great with no air bubbles.

I used to keep a supply of toothpicks handy. To "dull them", I simply dipped the ends of them into the resin, and then set them aside. When cured out, they had just the tiniest, but smooth, ball end on them.

Using such instruments, the quickest way to get rid of those little bubbles in wheel rim edges and lug nut detail, is to simply use such blunted toothpick to "chase" the air bubbles out of where they are being trapped. Simply sliding the end of such a toothpick around the circumference of the wheel rim, down all the way into the edge generally got rid of the problem there, and simply pressing the toothpick into the lug nut details in the mold did the same thing there as well.

One of the keys is to do this quickly, before the resin starts to "kick" from liquid to gel to hard solid. Also, heating the molds beforehand only exacerbates this air bubble problem, as the warmer the mold and/or resin is, the faster the resin kicks, starts to cure. If anything, keeping the resin cooler can greatly extend its working time.

Art

[Steven Zimmerman]

I buy those little 'childrens' paint brushes at Walmart ( packs of 30, about a buck fifty) and trim the bristles down to about a quarter inch in length. Much easier to handle than toothpicks, and quicker. I pour on the average of 16 wheels at a time, so speed is of the essence. I also use a spray mold release; baby powder is too slow, too messy, and sometimes leaves a 'cast look' surface on your resin part. It also seems to double the life of my molds.....I also found, when casting small pieces like wheels, the resin does not build up enough heat to cure completely. I pop my molds in a dehrydator for 15 minutes, and let cool before removing from the mold................'Z'

[Jeremy Jon]

Steve, do you use the bristle brush to paint the resin into crevices, or to poke away at the resin as it fills, so to release air bubbles? Just wondering your technique there?

Edited February 24, 2014 by Jeremy Jon

[shucky]

Austin, I use tiny metal picks (similar to the tooth pick idea) which came from hobby lobby to whisk away any tiny air bubbles in those areas you describe. If you wipe the pick off quickly it'll last forever. I've always used these instead of toothpicks because they have a much finer tip to them. I also run the pick horizontally over the mold (for 1 piece molds) through the resin but not touching the mold itself to remove any bubbles. The bubbles follow the pick as you move it through the resin leaving a bubble free casting. I also use a spray mold release (Price Driscoll) and a quick dusting of baby powder on a heated mold.

[my66s55]

I have held off answering this until I tested this answer myself. I had just visited my local Smooth On distributer at the time this question was asked. While there, I asked why the Smooth Cast resin that advertises no bubbles, was coming out with bubbles big time. He explained it to me thusly. Pour parts A and B into your separate containers. Instead of mixing them right away, let them sit for 5 to 10 minutes to gas out. Remove any visable bubble and combine slowly into the mixing container. stir gently as to not creat any new bubbles. Pour into mold gently. My results, perfect casting with no bubbles.

[Joeys Models]

I use Smooth On too. The way I make my molds is differt from what others use here. When I pour my molds. its a closed mold. Meanning I pour resin into the mold threw funnels. In the mold has runners and gates. Any area that I see that will trap air. Such as the rim of your wheel. I cut a vent into the mold to have somewere for the air to go out of the mold. I use a peice of .072 stainless steal tubing to punch a small hole into the top half of the mold. It has to bee tubbing. As it goes into the mold. It will cut a small core out of the rubber. I push it all the way threw to the top of the mold. This way the air and resin will flow freely into the mold. Eventhough I use Smooth On 310. It is a no air bubble resin. I still use a pressure pot for curing. no more than 35 psi is need to collaps and bubbles trapped in the mold. Useing this method. I never have any air bubbles.

[Skip]

When I worked in a tooling shop years ago we used to use a vacuum pump to first draw the bubbles out of parts A & B resin and mold materials prior to mixing.

I've seen the Foodsaver Vacuum Sealer at garage sales for as low as $5 and $10 - $20 on Craig's List. These have a small Vacuum pump on them, along with the jar lid attachment some sort of vacuum setup should be pretty easy to make. The vacuum is low enough on the Foodsaver that quart or gallon jars or acrylic containers can be used with relative safety, they are designed to use canning jars. High vacuum and glass don't mix, glass things come apart like a bomb blast!

[Steven Zimmerman]

Jeremy, I fill the mold with resin, then work the areas I know might have bubbles with the brush.