How to degassing treatment of casting silicone

Degassing treatment of casting silicone
Casting silicone is easy to be drawn into air and form bubbles during the mixing process. These bubbles will affect the quality and precision of the silicone mold, so degassing treatment is very critical. The following introduces the method, principle and precautions of degassing treatment of casting silicone:
Vacuum degassing method
Operation method: Pour the mixed casting silicone into the container of the vacuum degassing machine, cover the lid and seal it. Start the vacuum degassing machine, set the appropriate vacuum degree (generally between - 0.08MPa and - 0.1MPa) and degassing time (usually 5-10 minutes). Under vacuum environment, the bubbles in the silicone will expand and rise to the surface and rupture due to the internal and external pressure difference, thereby achieving the purpose of degassing. After degassing is completed, turn off the vacuum degassing machine first, then slowly release the vacuum, and take out the silicone for subsequent operations.
Principle: Use a vacuum pump to extract the air in the container, reduce the internal pressure, and make the internal pressure of the bubbles in the silicone greater than the external pressure, causing the bubbles to expand and become larger, and then escape from the silicone.
Precautions: Make sure that the vacuum degassing machine is well sealed to prevent air leakage from affecting the degassing effect. Different types of casting silicone may have different requirements for vacuum degree and degassing time, which need to be adjusted according to the product manual. In addition, the degassing time should not be too long, otherwise the silicone may overreact or thicken, affecting its fluidity and performance.
Natural degassing method
Operation method: Pour the mixed casting silicone into a container, and then place the container in a stable place to allow the bubbles in the silicone to rise and burst naturally. In order to speed up the rising speed of the bubbles, you can gently stir the silicone or vibrate the container slightly, but be careful to avoid generating new bubbles. The natural degassing time is long and may take several hours or even longer, depending on the amount of silicone and the number of bubbles.
Principle: Relying on the buoyancy of the bubbles themselves, they gradually rise to the surface in the silicone and burst and disappear.
Note: This method is suitable for simple mold making with low requirements for bubbles, or for use without vacuum degassing equipment. During the natural degassing process, keep the environment quiet to avoid external interference that causes the silicone to shake and generate new bubbles. At the same time, pay attention to the choice of containers, and try to use containers with smooth surfaces to reduce the possibility of bubble attachment.
Centrifugal degassing method
Operation method: Put the mixed casting silica gel into the centrifugal tube of the centrifugal degassing machine, and distribute it reasonably according to the amount of silica gel and the capacity of the centrifugal tube. Set the appropriate centrifugal speed (generally 1000-3000 rpm) and time (usually 3-5 minutes). Start the centrifugal degassing machine. Under the action of centrifugal force, the bubbles in the silica gel will be thrown to the edge or surface of the container, thereby achieving degassing. After the centrifugation is completed, carefully remove the silica gel to avoid reintroducing bubbles.
Principle: Use centrifugal force to separate bubbles with lower density from silica gel with higher density, and the bubbles move to the edge or surface of the container under the action of centrifugal force.
Precautions: When using the centrifugal degassing method, ensure the balance of the centrifuge tube to avoid unstable operation or damage of the centrifugal degassing machine due to imbalance. Different types of silica gel have different tolerance to centrifugal speed and time. It is necessary to determine the optimal parameters through experiments to avoid damaging the structure or performance of the silica gel due to excessive centrifugal force.