Both pressure and vacuum eliminate bubbles ?

In summary: I think the two methods are very different and that a vacuum chamber is better suited for getting rid of bubbles.
  • #1
Stephen Tashi
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To get bubbles out of plastic resin that's to be used in casting, the uncured resin can be put in a vacuum chamber. However, I notice that a pressure chamber is also advocated for getting out bubbles (e.g. http://www.smooth-on.com/faq_display.php?faq_id=81 ). Are bubbles in a plastic resin in some sort of delicate equilibrium state so that both more pressure and less pressure can be used to eliminate them ?
 
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  • #2
Stephen Tashi said:
To get bubbles out of plastic resin that's to be used in casting, the uncured resin can be put in a vacuum chamber. However, I notice that a pressure chamber is also advocated for getting out bubbles (e.g. http://www.smooth-on.com/faq_display.php?faq_id=81 ). Are bubbles in a plastic resin in some sort of delicate equilibrium state so that both more pressure and less pressure can be used to eliminate them ?
It seems to me that a vacuum chamber allows the bubbles (and dissolvables) to escape, by causing them to form and rise to the surface. A compression chamber drives them into solution, and, if you can cast rapidly enough, prevents them from coming out of solution. Just a thought.
 
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  • #3
My understanding is that the two methods are very different.

In both cases bubbles are typically formed when the resin is mixed.

Then in the case of pressure moulding the resin is poured into the mould and subjected to increased pressure. As your link says.. "The bubbles are collapsed into solution and the result is a bubble free casting". So the gas is still in the resin just not in the form of a visible bubble.

In the case of vacuum casting the resin is degassed before it's put into the mould. During degassing individual bubbles becomes larger which increases their buoyancy so they rise to the surface more easily. Gas dissolved in solution is also removed so there might be more bubbling than you expect..

 
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  • #4
CWatters said:
My understanding is that the two methods are very different.

In both cases bubbles are typically formed when the resin is mixed.

Then in the case of pressure moulding the resin is poured into the mould and subjected to increased pressure. As your link says.. "The bubbles are collapsed into solution and the result is a bubble free casting". So the gas is still in the resin just not in the form of a visible bubble.

In the case of vacuum casting the resin is degassed before it's put into the mould. During degassing individual bubbles becomes larger which increases their buoyancy so they rise to the surface more easily. Gas dissolved in solution is also removed so there might be more bubbling than you expect..


This does a much better job of articulating what I was trying to say in post #2.
 

Related to Both pressure and vacuum eliminate bubbles ?

What is the difference between pressure and vacuum in eliminating bubbles?

In pressure, the external force is applied to the surface of the liquid, while in vacuum, the external force is taken away from the surface of the liquid. Both methods work to reduce the size and number of bubbles in a liquid, but the mechanism is different.

Why do bubbles form in liquids?

Bubbles form in liquids due to the presence of gas or air trapped in the liquid. This can occur during the production or mixing process, or due to chemical reactions within the liquid. Bubbles can also form due to changes in temperature or pressure.

How does pressure eliminate bubbles?

Applying pressure to a liquid forces the bubbles to decrease in size and rise to the surface. This is because the gas or air within the bubble is compressed, making it less buoyant and causing it to rise to the surface. As the bubbles rise, they burst and the gas is released, resulting in a bubble-free liquid.

Can any liquid be treated with pressure or vacuum to eliminate bubbles?

Yes, both pressure and vacuum can be used to eliminate bubbles in any liquid. However, the effectiveness of these methods may vary depending on the viscosity and surface tension of the liquid. Some liquids may require higher pressure or longer exposure to vacuum in order to completely remove bubbles.

Are there any risks or drawbacks to using pressure or vacuum to eliminate bubbles?

Applying pressure or vacuum to a liquid can cause changes in the physical properties of the liquid, such as density and viscosity. This may affect the overall quality of the liquid. Additionally, care must be taken when handling pressurized or vacuum-sealed containers to avoid accidents.

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