What is vacuuming and why should I do it?Updated 23 days ago
Vacuuming: A vacuum pump is like a vacuum cleaner. A vacuum cleaner is designed to pick up things such as dirt off of carpet using suction or vacuum. A vacuum pump is identical to a vacuum cleaner, except it will have MUCH more suction. A vacuum system is measured in the amount of vacuum it will pull. In technical terms, it is measured in inches of mercury. A common household vacuum will pull 1-2 inches of mercury. A good vacuum pump will pull 29-30 inches of mercury. A vacuum pump is used to suck the air from the mixed silicone or resin to assist in pouring air/void free molds or parts. The concept is that when we mix the silicone we mix in tons and tons of air into the mix. Ideally, we want to remove the air from the mixed rubber so it doesn't end up in our cured rubber mold. When you put the mixed rubber or resin that is full of tiny air bubbles under vacuum, it makes those air bubbles expand into big air bubbles which now have the buoyancy to float to the top and pop which removes them from your liquid rubber. If they remain small, they do not have the buoyancy required to float through the thick consistency of the rubber and get to the top. The thicker the rubber the harder it is for small bubbles to float and hence the need for the vacuuming rises. Some of Alumilite silicone and many of our resins have a thin enough viscosity the majority of air bubbles will rise to the surface without a need to vacuum. Other silicones that are higher in viscosity ... over 20,000 cps are recommended to be vacuumed to ensure a good mold or part is cast. Therefore, you must pull a vacuum to assure no air is entrapped. Once your vacuum reaches 29-30 inches of mercury, the mixed rubber or resin expand and begin to foam up. You will need a container around 4 times the size of the amount of material your are mixing/degassing. Once the material expands and foams up, the bubbles will start to break (meaning to fall quickly). After the silicone or resin falls, you will want to keep it under vacuum for another 2-3 minutes before removing from the vacuum chamber. During that 2-3 minutes, the material you are degassing may continue to pop bubbles which is okay but the mixed air you introduced while mixing is now gone. Then remove the material from the vacuum and let it sit for 1 minute. You will notice that almost all the air from the silicone or resin is gone. Now you are ready to slowly pour the rubber or resin into your mold box or mold. You may want to pull a second vacuum after the mold has been poured. This will remove any air that you may have entrapped while pouring. Remember, once the rubber has risen and fallen, it will not rise again.
