Pulling Vacuum on BJB Silicone Casting material

The de-gassing process on silicone is critical to producing an air free mold surface. This demonstrates how to mix and pull vacuum on the two-part casting silicone.

Category:

Science & Technology

Tags:

• silicone
• casting
• urethane
• mold
• making
• bjb

[BJBEnterprises]

Not likely. You really need about 28-29" of mercury on your vacuum to effectively pull the air out. At only 24" you will most likely just make the existing bubbles in the mixture combine into larger bubbles and then they won't rise to the surface. You'll end with something that looks like carbonated soft drink rather than crystal clear urethane. You might also look into a pressure-pot for producing high quality clear parts if you don't have access to a good vacuum system.

[lalobarrera99]

Thanks man... I have another 2 questions.

Can this machine remove the bubbles from the resine???

And, how much is this machine cost.

I need one....

[BJBEnterprises]

Yes, this will work with other casting resins as well. See the two video responses above for more info. You can contact us directly for pricing on the Vacuum Cart or pumps separately. The glass bell jar you see in the video is not something we sell. It is a piece of lab equipment.

[lalobarrera99]

How is that machine work??? I mean, what happen inside the cristal that makes the bubbles going up?

[BJBEnterprises]

There is a large pump attached to that glass "bell jar" from the bottom that pulls an extremely high vacuum. Similar to the effect a home or shop vacuum sucks dirt into a bag, this is on an extreme level compared to that. The bubbles you see in the silicone is air escaping the material essentially boiling out.. though there is no heat created. Bubbles in the silicone can cause voids and surface imperfections when making a mold so it is best to get rid of the bubbles before pouring.

[toranacar]

Hello

Basically I want to do the same, which is vacuum silicon to get the bubbles out.

I made up a vacuum chamber using an air compressor inlet for suction, I used frothed up milk to test if it works as frothed milk is full of bubbles but wasnt sure if it worked. Basically I vacuumed the milk and it almost spilled over then came back down, but there seemed to be more bubbles left until I opened the valve and it looked like the bubbles disappeared after the valve was opened. Is this correct?

[BJBEnterprises]

What happened in your experiment sounds about right. The material will foam up and if there is not enough room in the cup it will spill over. You must be ready to "break" the vacuum a couple times to avoid any spillage. You need to use a much larger container/cup than mixed material to allow it to foam up. If you have sufficient vacuum, the material will continue to bubble until it hardens so you must stop at a certain point. Watch our other video on pulling vacuum on urethanes.

[dolphin42]

I want to do a one time job with the clear urethane but the only vac pump I have pulls only about 24... will this be enough if I take a piece of plexi and a silicone gasket and a 1 gallon chamber...?

[toranacar]

Thank you for that. Your videos and explanation is greatly appreciated.