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I will be often asked if a vacuum chamber or a pressure pot is required in the fine artwork of mold making and casting. As with so many answers in life, a "yes" or "no" answer is not possible without first learning more information about the project. Except for water clear resin, where tiny air bubbles will obscure the clarity of a part, and such equipment is a must, my answer most often is, "It all depends. " That is bad, I am aware. So the objective of this article is to provide the specific answer you are searching for.
For everyday mold making and casting, you can pour your materials in a high, narrow stream as one part of your mold package to reduce the inevitable air bubbles. This allows air to escape as it travels down the narrow stream as you are pouring. Vibrating the mold, or mold box helps, as well, either mechanically, by knocking on it with your knuckles, or by putting a vibration source against the mold package, like a hand sander. These types of are all great studio room tricks that will definitely reduce air bubbles. But they do not eliminate them entirely. So if that is your goal, please read on.
So if you are planning to create molds and castings on a regular basis then you should bite the topic and acquire the variety of of equipment to achieve professional results. Just as that is one can do cabinetry using manual operating tools like a hand saw, better and faster results are often obtained through the electric table saw or chop saw. The right tools, for the right purpose, help in attaining steady acceptable results in any industry or hobby for that matter.
"What is the difference between the two and do I would like both" are the essential questions I most often receive. As the titles imply one chamber provides air pressure even though the other removes air pressure. Nevertheless only one actually removes air from your mold making and casting material - the vacuum holding chamber, while the other simply hides it--the pressure weed.
The pressure chamber works by providing up to 50-psi of atmospheric pressure. When you remember your high school science, normal sea level pressure is about 14. 7- psi. Hence, the greater pressure works to compress any air bubbles in your material and squeezes them down to almost microscopic size - thus making them appear to disappear. The air remains though, but you just can't view the pockets now. But, once you release the air pressure back to 14. 7-psi, the air bubbles will come back - that is unless air is contained as it might be if the material you were pressurizing solidified to a solid, like a hard resin, gypsum plast typer or epoxy. If your material was a mildew rubber though, such as silicone or polyurethane, the flexible rubber will not contain the compressed air bubbles and they would expand within the rubber normal again size, even though your rubber has cured.
Thus, the pressure pot is best suited when your mold making or casting material cures to a solid and the vacuum holding chamber is utilized to remove air from flexible rubbers. The vacuum chamber can also de-air solid resins and epoxies, too. But since it takes a lttle bit more time to create a vacuum, and certain resins are fast-cured, the pressure chamber is the tool of choice in those instances as it can be quickly pressurized, faster than a vacuum holding chamber can be evacuated.