Tuesday, January 29, 2013

Bubble, Bubble, Toil and Trouble? There are bubbles in my ComposiMold!


Why Bubbles? Stick a rock into warm water and let the water cool and you will see how bubbles can form. Hot water holds more air because there is more space within the water molecules. But when it cools, the air has to go somewhere as the water molecules come closer together, so it creates bubbles that come out of solution and adhere to the surfaces within the cup.

But the bubbles can easily be removed by reducing the surface tension on the parts. A touch of Bubble Buster and the bubbles will rise to the surface and off the rock. This is how bubbles can form with ComposiMold and PowerMold and also how you can remove bubbles from your mold. Here is a breakdown of different methods:

 Bubble Buster: The first approach we discuss is the use of Bubble Buster. Bubble Buster is a PVA/water solution that reduces the ability for the bubbles to adhere to the surface of the master. To use, just spray, dip, or coat the Bubble Buster over the part you are molding. Be sure to get lots of the PVA/water solution in the cracks and corners. You don't have to let the Bubble Buster dry before pouring on the PowerMold or ComposiMold. If needed, use a mold release (vegetable oil, Vaseline, or mineral oil will be fine for most molds) before putting on the Bubble Buster.

Bubble Buster sprayed on to your master before making your mold
 
Sealing: The Bubble Buster will reduce most bubbles from adhering to your master and thus give better molds, but if you are still getting bubble in y our mold, then there are many other potential solutions.

Is your original part sealed? Air that is in the plaster can come out and into the ComposiMold. This is probably the cause if you are using plaster, clay, or wood as the master. To solve, seal the master first with several layers of polyurethane spray, shellac, or other wood sealers. Elmers-like glue (PVA glue) works well to seal parts.

 
Pulling Out the Bubbles: Are the bubbles getting stuck in cracks or undercuts?For any undercuts, you will likely have to pull the bubbles out so they can float to the surface instead of get stuck under the ledges (undercuts). Use a toothpick or small screw driver to pull the bubbles away with a toothpick. Even better: soak the toothpick with Bubble Buster and then pull away the bubbles.PowerMold is thicker than ComposiMold, so pulling away the bubbles will be more difficult with PowerMold, but the same approach works. If at any point, the PowerMold is too thick, take a hot air gun and warm it up more, but be careful not to overheat above 200 F.

 
Mold Release: You may also have too much mold release, so the interaction causes bubbles. This seems to happen quite a bit when you use a vegetable oil as a mold release or don’t let your silicone mold release dry first, but other mold releases may have this affect. Be sure to wipe off any access mold release. You can use Bubble Buster over your mold release without any harm.

You may have bubbles in the ComposiMold from bubbling in the microwave. It may be worthwhile to remelt the ComposiMold and let it cool at room temperature so the bubbles can rise to the top and escape.

Pouring: You may be putting bubbles in when you pour the ComposiMold into the container. The best way to avoid this is to just pour gently into the lowest area of the mold so the ComposiMold rises up over the part. Be sure any holes are filled with the ComposiMold and you are not trapping air. You can also use a toothpick to pull bubbles out as you are filling your mold box.

 
Heating: You can also adjust the heating: Heat up your original slightly with a hot air gun and let the

ComposiMold cool before pouring it on your part. The ComposiMold will be thicker when you pour, but it will still fill most gaps. The heating and cooling reduces the temperature difference between the ComposiMold and master and reduce bubbles from forming.

If you are still having bubbles (and your master is sealed well) another approach is to brush on the ComposiMold or PowerMold and then if necessary heat the PowerMold while on your mold with a hot air gun to break up any bubbles with the hot air gun. Be careful with this approach that you don’t overheat your master or the PowerMold. Heat jJust enough to keep it warm and break up the bubbles. When you pour the rest of the ComposiMold over your master, it will re-melt this layer, but that won’t matter as the bubbles will already be out of the layer against the master.

 
We do also get asked about degassing with a vacuum and this approach does not seem to work very well. It will make a mess as the ComposiMold expands. We think because the vacuum reduces the boiling point and makes the ComposiMold boil.

 The great advantage of PowerMold and ComposiMold is that it can be reused and re-melted. So any mistakes or bubbles that you don’t get out can be fixed by heating that area or remelting and making the mold over again. Let us know what other methods you find that work for you and keep experimenting!

 

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