meucci2009
Member
I know this is proably a repeat I am sorry I just cant find a direct answer to my question, I understand the pressure part its to push the liquid in the cracks and all and get the bubbles out but what is the vacuum part for.
Vacuum explain please
- Thread starter meucci2009
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KenV
Member
The theory most assume is that vacuum will pull degass the contents of the vacuum chamber. In most cases it is more successful at boiling off solvents.
its_virgil
Member
Vacuum will allow the air "dissolved" in the liquid to release. As the air is released the liquid will bubble and appear to be boiling. So, vacuum is used to degass the resin. Pressure, on the other hand, will keep the air in solution much like the pressure in a bottle of soda or champaigne will keep the air in solution. Remove the cap, release the pressure and some of the air will be released as bubbles. For casting polyester resin I no longer use either. I don't do worthless wood nor do I cast alumilite. So, I can't speek intelligently on those two topics.
Do a good turn daily!
Don
Do a good turn daily!
Don
Glass Scratcher
Member
Some families of resins like polyurethanes will have a component that will absorb moisture from the atmosphere once it is unsealed. Vacuum degassing will draw the moisture out of the component. Polyurethanes tend to foam with water present.
Some polyester resins are slightly polar, and will also attract water from the atmosphere, and vacuum degassing can be of a benefit as water will inhibit curing and cause some bubble formation. If degassing polyester resins do not exceed 27"Hg as the styrene solvent in PR will boil out of solution at 28"Hg.
For mold making with Silicones vacuum degassing the A&B compounds before mixing, and after mixing while not required on some hobby silicones is required on many others. Hobby silicones can benefit from vacuum degassing as well.
Some polyester resins are slightly polar, and will also attract water from the atmosphere, and vacuum degassing can be of a benefit as water will inhibit curing and cause some bubble formation. If degassing polyester resins do not exceed 27"Hg as the styrene solvent in PR will boil out of solution at 28"Hg.
For mold making with Silicones vacuum degassing the A&B compounds before mixing, and after mixing while not required on some hobby silicones is required on many others. Hobby silicones can benefit from vacuum degassing as well.
Alumilite
Member
Applying vacuum to your resins will apply negative air pressure to the resin and the air inside of the resin (the air you generated and created during stirring) and will cause the air bubbles to expand significantly. Once the bubbles expand, the bouyancy of those bubbles also dramatically increases which allows the bubbles to float to the top and pop. This process removes the air you introduced into the resin during the mix process and any other air that may have been trapped in the resin.
Imagine 500 tiny champagne size air bubbles throughout a container of thin syrup. Those air bubbles would love to float to the top but simply do not have the bouyancy to force their way through the thick liquid to get to the top before the syrup in the case, resin, begins to cure (anywhere from 5 to 20 minutes depending on what type of system you are using ... PR or urethane). They would however eventually get there if they had overnight to slowly make their way to the top. But once the materials gel, the tiny air bubbles are stuck and typically expand a little during the exotherm of the resin curing making them even more visible. However, bubbles the size of a gum ball would float to the top fairly quickly. Therefore, vacuum is used to greatly expand the size and bouyancy of the bubbles to help them quickly float to the top of the thick resin and pop eliminating them from your material and providing you with perfectly bubble free material to cast.
Pressure on the other hand does exactly the opposite. It does not push the bubbles out of the resins. It simply crushes them so small the human eye can not see them and holds them in that size and shape until the resin cures in which the bubbles can no longer expand and become visible. This is the reason why you must keep the resin under pressure until it is hard enough to contain the bubbles in that size. If you apply pressure to the resin, it will crush the bubbles, however if you were to release the pressure prior to the resin curing, the bubbles would simply return. If the pressure forced them out of the resin, there would be no reason to leave it under pressure until it cured. You could simply pressure the resin to evacuate the bubbles and then remove it from the pressure to cure under normal conditions. But the fact that when you do this the bubbles come back is proof that they are still in the resin, just so small you can not see them. I'd love to know if you could see them with a microscope?? Hmm.
We have a video on our site demonstrating how the vacuum works. Skip the first 4 minutes and 30 seconds where we tell people how to hook up the vac pump and chamber and go directly to the 4:30 point in the video where you see Charlie tying off the rubber glove and putting it in the chamber. This will show you how much negative air pressure you are putting on the material and how the air in your resin will expand and gain bouyancy.
Looks like you'll have to cut and paste the following link/address:
http://alumilite.com/ProdDetail.cfm?Category=Equipment&Name=Vacuum Chamber
We also have a picture/text tutorial on pressure casting that can be found:
http://alumilite.com/HowTos/PressureCastingClear.cfm
(the pictures aren't the best but I think you'll get the idea)
Hope this helps you visualize the difference and affect pressure and vacuum have on your resins.
Mike
Alumilite
800 447-9344
Imagine 500 tiny champagne size air bubbles throughout a container of thin syrup. Those air bubbles would love to float to the top but simply do not have the bouyancy to force their way through the thick liquid to get to the top before the syrup in the case, resin, begins to cure (anywhere from 5 to 20 minutes depending on what type of system you are using ... PR or urethane). They would however eventually get there if they had overnight to slowly make their way to the top. But once the materials gel, the tiny air bubbles are stuck and typically expand a little during the exotherm of the resin curing making them even more visible. However, bubbles the size of a gum ball would float to the top fairly quickly. Therefore, vacuum is used to greatly expand the size and bouyancy of the bubbles to help them quickly float to the top of the thick resin and pop eliminating them from your material and providing you with perfectly bubble free material to cast.
Pressure on the other hand does exactly the opposite. It does not push the bubbles out of the resins. It simply crushes them so small the human eye can not see them and holds them in that size and shape until the resin cures in which the bubbles can no longer expand and become visible. This is the reason why you must keep the resin under pressure until it is hard enough to contain the bubbles in that size. If you apply pressure to the resin, it will crush the bubbles, however if you were to release the pressure prior to the resin curing, the bubbles would simply return. If the pressure forced them out of the resin, there would be no reason to leave it under pressure until it cured. You could simply pressure the resin to evacuate the bubbles and then remove it from the pressure to cure under normal conditions. But the fact that when you do this the bubbles come back is proof that they are still in the resin, just so small you can not see them. I'd love to know if you could see them with a microscope?? Hmm.
We have a video on our site demonstrating how the vacuum works. Skip the first 4 minutes and 30 seconds where we tell people how to hook up the vac pump and chamber and go directly to the 4:30 point in the video where you see Charlie tying off the rubber glove and putting it in the chamber. This will show you how much negative air pressure you are putting on the material and how the air in your resin will expand and gain bouyancy.
Looks like you'll have to cut and paste the following link/address:
http://alumilite.com/ProdDetail.cfm?Category=Equipment&Name=Vacuum Chamber
We also have a picture/text tutorial on pressure casting that can be found:
http://alumilite.com/HowTos/PressureCastingClear.cfm
(the pictures aren't the best but I think you'll get the idea)
Hope this helps you visualize the difference and affect pressure and vacuum have on your resins.
Mike
Alumilite
800 447-9344
meucci2009
Member
ok I understand that thank you mike Alumilite, so whats the reason for building a tank that has both pressure an vacuum options on the tank
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Glass Scratcher
Member
Physical shop space. You only have to have 1 tank.
hilltopper46
Member
Type "%20%Chamber" (omit quotation marks but include percent signs) at the end of the address to make it work.
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Alumilite
Member
Good question regarding vacuum and pressure in one unit. Lets first explain why you would want to do both ... vacuuming the resin takes care of the bubbles you mixed in but still doesn't cover you for the bubbles created or trapped when pouring. You could have perfectly bubble free resin but when you pour the resin it cascades in the bottom of the mold as well as flows around and traps bubbles in whatever you might be encapsulating, you now need to get rid of those bubbles or risk wasting the pour.
Shop space is definitely an advantage but also ease of use. Sometimes people will just have a two way valve on the tank which allows them to much more efficiently switch from vacuum to pressure. Some rapid prototypers would also briefly vacuum the resin in the mold and then quickly switch to pressure in attempt to pull big air pockets out before pressure casting. This is typically not needed when casting blanks. Vacuuming the resin often is violent and pulls a lot of resin out of the mold with the air (makes a pretty big mess and risks short pours due to the material that ends up out of the mold).
Typically vacuum is the preferred method when using silicone rubber and pressure is preferred when casting resins.
Mike
Alumilite
800 447-9344
Shop space is definitely an advantage but also ease of use. Sometimes people will just have a two way valve on the tank which allows them to much more efficiently switch from vacuum to pressure. Some rapid prototypers would also briefly vacuum the resin in the mold and then quickly switch to pressure in attempt to pull big air pockets out before pressure casting. This is typically not needed when casting blanks. Vacuuming the resin often is violent and pulls a lot of resin out of the mold with the air (makes a pretty big mess and risks short pours due to the material that ends up out of the mold).
Typically vacuum is the preferred method when using silicone rubber and pressure is preferred when casting resins.
Mike
Alumilite
800 447-9344