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VIDEO TUTORIAL
USED IN THIS PROJECT
Although not necessarily an exhaustive list, the following tools and materials, supplied by Easy Composites, were used in this project.
The quantity shown below is the approximate amount used in the project rounded up to the nearest available kit size or quantity.
TOOLS & EQUIPMENT
Total £0.00
VIDEO TUTORIAL
How and Why to Vacuum Degas RTV Silicone Rubber and Casting Resins
Video tutorial demonstrating how to degas silicone and casting resin and the benefits of degassing materials like RTV silicone rubber and casting resins (like Fast Cast polyurethane or water-clears) to improve your moulds and castings. We use our Complete Vacuum Degassing System and demonstrate how simple the process is and why we do it at various stages such as during silicone mould making, before pouring casting resins and also in-mould degassing.
Degassing is a highly effective process for removing trapped air from within mixed materials such as RTV Silicone Rubbers, Polyurethane Casting Resins, Infusion Epoxies - all sorts of materials where air can become entrapped when the two parts of the material are mixed together.
TUTORIAL BREAKDOWN
1. Examples
Example 1 - shows RTV Silicone in its cured state when no degassing has taken place. Air bubbles are clearly visible trapped within the silicone.
Example 2 - shows the same RTV Silicone in its cured state, after degassing in the Vacuum Degassing Chamber. It has no air entrapment whatsoever and has a completely clear appearance.
The piece that has been degassed will have improved tear strength and give improved surface finish.
Example 3 - Shows Water Clear Polyurethane Resin which was mixed and left to cure with no degassing. There are fine air bubbles trapped within the resin.
Example 4 - Shows the Water Clear Polyurethane Resin again which was mixed then degassed in the Vacuum Degassing Chamber before curing and is visibly perfectly clear with no air entrapment.
2. Vacuum degassing chamber
Degassing chambers are commonly used for degassing resins once they have been poured into a mould. This is particularly true of moulds with fine surface detail and undercuts. The reason for this is explained in the demonstration using a nitrile glove.
The glove experiment shows why degassing is advisable and the principle behind degassing.
The whiteboard diagram explains how the degassing process helps to achieve consistent results when using moulds with undercuts.
3. Featured products
The Easy Composites Complete Vacuum Degassing System is available with a choice of large or small DVP vacuum pump. The large vacuum pump will empty the chamber in around 30 seconds making it the right pump when working with materials with a shorter pot life such as fast cast polyurethane resins and water clear polyurethane whereas the small pump takes around 3 minutes to draw down making it more suitable for use degassing silicone rubbers.
Follow equipment set up according to the manufacturers instructions.
4. Degassing demonstration using RTV silicone rubber
The demonstration shows the mixing of the silicone rubber with the catalyst which has trapped air bubbles in the mix. The mix is placed into the chamber, the lid put on and valves turned to their correct position then turned on and very quickly you can see that the air starts to expand, frothing and foaming as it begins to degas. The air in the mixture continues to expand, making the mixture expand until it reaches the self collapse stage. The air bubbles expand to such an extent that they collapse and the mixture falls in on itself. When the degassing process is complete turn the pump off and turn the valve to put the air back into the chamber it quickly becomes apparent the extent the degassing has had upon the mixture.
The mixture is now perfectly clear and ready to be poured. Once poured it is placed back in the vacuum chamber and degassed for a 2nd time before being left to cure.
The 2 step degassing process has resulted in a perfect silicone mould, and it can be used on most materials where air entrapment can be a problem.
DISCUSSION (14)
Please share any questions or comments you may have about this video tutorial.
pbassred
What level of vacuum do you pull?
Easy Composites› Matt
As close to absolute vacuum as you can possibly get. There are a lot of different vacuum units but 99.98% vacuum is a common target (virtually -29.92 inches mercury).
Raul Vidal
How long do you keep the resin under vacuum? Is it more of a visual decision?
Easy Composites› Matt
Yes, it's definitely more of a visual decision and will vary from one material to another, including one silicone to another. It will also depend on how the silicone was mixed in the first place and so how much air was mixed into the silicone. For the silicone we degassed in this video it was around the 2 minute mark when the foam of bubbles collapsed; after this point there is not much benefit in continuing to degas.
Grey M
Can you use your chambers with a vacuum injector and a compressed air supply?
Easy Composites› Matt
You could however the problem with venturi vacuum generators is that they don't tend to achieve particularly high levels of vacuum. It's normally at the very high end of the vacuum scale (28" mercury or 99% vacuum) that the degassing really starts to happen, especially for materials like silicone which can be quite reluctant to self-collapse until the highest vac levels are reached. Venture vacuum generators are typically nowhere near that level of vacuum.
Zaks S4
Is there a difference between a pressure pot and a degassing chamber? If yes, what are they best for?
Easy Composites› Matt
Yes, they're basically the opposite things to each other. A degassing chamber is evacuated to remove all the air - materials are degassed because the trapped air inside the liquid expands (in the low pressure) and bubbles out. A pressure pot is pressured with multiple times atmospheric pressure (example 5 bar) which compresses bubbles in a liquid. The advantage to degassing is that the material can be removed from the degassing chamber once degassing has occurred and can cure at ambient pressure. With a pressure pot, the trapped air is still inside the liquid and so it must be cured inside the pressure pot under pressure, otherwise as soon as the pressure it let off, the trapped air will expand again. It might help to think that a pressure pot shrinks the air bubbles and then the curing process locks in the trapped air at this reduced volume. A degassing chamber removes the trapped air.
windthrop grumman
Can you please explain what a 2 stage vacuum pump is compared to a 1 stage vac pump, I don't understand the difference.
Easy Composites› Matt
Dual stage pumps are normally required to reach the very highest levels of vacuum. For sensitive processes like degassing, resin infusion or prepreg laminating, it really does make a difference whether you're at 99.9% vacuum or 99.99% vacuum. The higher the vacuum, the more effective the degassing (or prepreg or infusion) will be. Dual stage pumps generally cost a little more but they're worth investing in if you're doing composites work. Probably the most important area would be out-of-autoclave prepreg where the ultimate vacuum level is absolutely critical to achieving a pinhole free finish.
Dinh Phong Tran
So basically we can use vacuum degassing for removing bubble out of silicon rubber and epoxy resin. No more money to spend on pressure pot ? Am I right ?
Easy Composites› Matt
Well, yes and no. They do a similar job but it's not the same job, although often you could use one or the other. A pressure pot shrinks down bubbles to a tiny size and needs to hold them there, compressed like this, until the resin or whatever material you're working with, cures. A degassing chamber makes the air expand and be expelled from the liquid, atmospheric pressure is then restored whilst the material is still in its uncured state - which compressed any traces of residual air down to almost zero volume, and then the material is allowed to cure.
cncmodeller g
If degassing PU resin in the mould does that encourage the resin to flow into all the parts of the mould or is that reliant on viscosity? I want to cast fine model aircraft parts.
Easy Composites› Matt
Yes; if you run a degas and then re-pressurise cycle whilst the resin is still within its pot-life then this will effectively force the resin into all the fine surface detail (including smaller undercuts or difficult areas. If the undercuts are large then you need a slight surplus of resin (almost like a 'header') that can feed resin into the undercuts when your re-pressurise the chamber.
Kirkland Shunk
Can a degassing chamber be used to degas resin, as well as silicone? If it can, would you degas the resin after mixing it before pouring or could you degas after pouring into the mold?
Easy Composites› Matt
Yes you can. Some people prefer to degas the resin both before pouring and after. The only limit is the practicality of fitting the mould into the chamber if the mould is very large.
afadario
Does this work for degassing fast-curing resin like polyurethane? Mine is cures in 3 minutes. My idea is pour it to my mold then put it to vacuum camber until resin cured… will this work?
Easy Composites› Matt
Yes but if you have such a quick resin then you might want to reduce the volume of the chamber by loading it with some ballast (like house bricks or something else to take up the space in the chamber); this will mean that the same pump will draw down the chamber to vac pressure more quickly. Don't forget that it's essential you re-pressurise the chamber before the resin cures - simply loading it in a pulling a vac until it cures would definitely be wrong and won't give you good results.
Ivan Spinning
I degas the resin, cast it in the mold, and put the mold again in the vacuum chamber. In this situation am I allowed to have no vent holes in the mold? They are no longer necessary, right?
Easy Composites› Matt
This is a little complicated. The kind of process you're describing where you can pour into a complex mould, with undercuts and not need any vents on these undercuts would usually require a vacuum casting machine where the resin is poured into the mould under vacuum; in this situation no vents are needed and the resin will flow, under gravity, into all areas of the mould, including unvented undercuts. If you don't have a vacuum casting machine (a degassing chamber is not a vacuum casting machine) then you can achieve something quite similar but it's done in a slightly different way. You would need your silicone mould to have some extra 'header' area to hold some extra resin - you then fill the mould (and the header) with the casting resin and then pull a vacuum on the mould. The vacuum would cause the air trapped in the undercuts to expand and bubble out (through the header and out of the top, where you fill the resin in from). Once this has happened, you allow the pressure back into the chamber which compressed the air in the undercuts down to almost no volume. As this happens, it creates a vacuum in the undercuts which draws resin in from the rest of the casting to fill the voids. Surplus resin in the 'header' is then drawn down into the main body of the casting. The end result should be that all the undercut areas are filled properly with resin.
Higgins_123
How do you clean the vacuum pump oil?? I've tried filtering through kitchen towels and freezing and separating to remove water (what they recommend for freeze drying pumps) but my oil is still cloudy???
Easy Composites› Matt
We would strongly recommend replacing the oil at this stage. You can help reduce contamination, especially by particulate matter by using an inline filter such as our VF1 Vacuum pump inlet filter. However, having now got contaminated oil it really does need replacing, not filtering or cleaning.
Aj Amori
Great video!! I'm looking to purchase a vacuum pump. Can you tell me the specs of the pump you use in the video? I was told I need a 7 CFM pump that can pull -28 inches of mercury to degas my Smooth Sil 940 platinum silicone rubber.
Easy Composites› Matt
The exact pump we used in this video (and the smaller model shown) are no longer available from us but have been replaced by two very nice pumps from Italian manufacturer DVP. The closest of these two pumps to the VP3400 (in the video) would now be the EC.20, you can find the full spec for this pump on its product page. The most important number when choosing a vacuum pump for degassing is the vacuum level that the pump can achieve, this is really the number that will determine how well your material will degas. In the case of our current vacuum pumps, they both achieve better than 29.92 inches of mercury (99.98% vacuum), which - in vacuum terms - is much higher than 28 inches of mercury. From our experience, 28 inches of mercury would not be a high enough level of vacuum to properly degas most silicones. As for the CFM of the pump, this is just its throughput and doesn't relate to the ultimate level of vacuum achieved and so the CFM rating of the pump only affects how quickly the pump will empty your chamber and so how quickly the degassing will happen. A 1CFM pump and 50°CFM pump that both achieve 29 inches of mercury will degas the same silicone in exactly the same way, only the 20°CFM pump would do it quicker.
metals
The instruction manual with my pump says that shut off the pump when the needle on the gauge is no longer moving or has reached the max. I am doing that but I find that it has never gotten rid of all the bubbles properly in the epoxy.
Easy Composites› Matt
We tend to run the pump throughout any degassing operation. The pumps we offer are perfectly capable of being run throughout the degassing operation. Degassing resin also depends on the viscosity of the material. Some resins degas easier than others. Also be aware some resins have a solvent content which can outgas during very high levels of vacuum which can effectively mean they bubble indefinitely, not really remove entrapped air but instead boiling off the solvent or volatile content in the resin and altering its make-up.
Titan Terrain Studio
When you're done degassing the mold the 2nd time, do you leave it inside the chamber to fully cure after releasing the vacuum? I did this with some molds recently for the first time but ran into some issues with bubbles popping up slowly over time.
Easy Composites› Matt
You can do either as it shouldn't make any difference to the cure as long as you are careful removing the mould from the chamber, however, the essential thing would be to ensure that - if you're leaving the mould inside the chamber - you let the air pressure back into the chamber once you're done degassing; it's the restoration of atmospheric pressure that will compress any residual air down to basically zero volume and produce a properly degassed material. If you leave the resin or silicone to cure under vacuum then you're totally defeating the objective and the material will cure with aeration.
LEAVE A COMMENT OR QUESTION
USED IN THIS PROJECT
Although not necessarily an exhaustive list, the following tools and materials, supplied by Easy Composites, were used in this project.
The quantity shown below is the approximate amount used in the project rounded up to the nearest available kit size or quantity.
TOOLS & EQUIPMENT
Total £0.00
DISCUSSION (14)
Please share any questions or comments you may have about this video tutorial.
pbassred
What level of vacuum do you pull?
Easy Composites› Matt
As close to absolute vacuum as you can possibly get. There are a lot of different vacuum units but 99.98% vacuum is a common target (virtually -29.92 inches mercury).
Raul Vidal
How long do you keep the resin under vacuum? Is it more of a visual decision?
Easy Composites› Matt
Yes, it's definitely more of a visual decision and will vary from one material to another, including one silicone to another. It will also depend on how the silicone was mixed in the first place and so how much air was mixed into the silicone. For the silicone we degassed in this video it was around the 2 minute mark when the foam of bubbles collapsed; after this point there is not much benefit in continuing to degas.
Grey M
Can you use your chambers with a vacuum injector and a compressed air supply?
Easy Composites› Matt
You could however the problem with venturi vacuum generators is that they don't tend to achieve particularly high levels of vacuum. It's normally at the very high end of the vacuum scale (28" mercury or 99% vacuum) that the degassing really starts to happen, especially for materials like silicone which can be quite reluctant to self-collapse until the highest vac levels are reached. Venture vacuum generators are typically nowhere near that level of vacuum.
Zaks S4
Is there a difference between a pressure pot and a degassing chamber? If yes, what are they best for?
Easy Composites› Matt
Yes, they're basically the opposite things to each other. A degassing chamber is evacuated to remove all the air - materials are degassed because the trapped air inside the liquid expands (in the low pressure) and bubbles out. A pressure pot is pressured with multiple times atmospheric pressure (example 5 bar) which compresses bubbles in a liquid. The advantage to degassing is that the material can be removed from the degassing chamber once degassing has occurred and can cure at ambient pressure. With a pressure pot, the trapped air is still inside the liquid and so it must be cured inside the pressure pot under pressure, otherwise as soon as the pressure it let off, the trapped air will expand again. It might help to think that a pressure pot shrinks the air bubbles and then the curing process locks in the trapped air at this reduced volume. A degassing chamber removes the trapped air.
windthrop grumman
Can you please explain what a 2 stage vacuum pump is compared to a 1 stage vac pump, I don't understand the difference.
Easy Composites› Matt
Dual stage pumps are normally required to reach the very highest levels of vacuum. For sensitive processes like degassing, resin infusion or prepreg laminating, it really does make a difference whether you're at 99.9% vacuum or 99.99% vacuum. The higher the vacuum, the more effective the degassing (or prepreg or infusion) will be. Dual stage pumps generally cost a little more but they're worth investing in if you're doing composites work. Probably the most important area would be out-of-autoclave prepreg where the ultimate vacuum level is absolutely critical to achieving a pinhole free finish.
Dinh Phong Tran
So basically we can use vacuum degassing for removing bubble out of silicon rubber and epoxy resin. No more money to spend on pressure pot ? Am I right ?
Easy Composites› Matt
Well, yes and no. They do a similar job but it's not the same job, although often you could use one or the other. A pressure pot shrinks down bubbles to a tiny size and needs to hold them there, compressed like this, until the resin or whatever material you're working with, cures. A degassing chamber makes the air expand and be expelled from the liquid, atmospheric pressure is then restored whilst the material is still in its uncured state - which compressed any traces of residual air down to almost zero volume, and then the material is allowed to cure.
cncmodeller g
If degassing PU resin in the mould does that encourage the resin to flow into all the parts of the mould or is that reliant on viscosity? I want to cast fine model aircraft parts.
Easy Composites› Matt
Yes; if you run a degas and then re-pressurise cycle whilst the resin is still within its pot-life then this will effectively force the resin into all the fine surface detail (including smaller undercuts or difficult areas. If the undercuts are large then you need a slight surplus of resin (almost like a 'header') that can feed resin into the undercuts when your re-pressurise the chamber.
Kirkland Shunk
Can a degassing chamber be used to degas resin, as well as silicone? If it can, would you degas the resin after mixing it before pouring or could you degas after pouring into the mold?
Easy Composites› Matt
Yes you can. Some people prefer to degas the resin both before pouring and after. The only limit is the practicality of fitting the mould into the chamber if the mould is very large.
afadario
Does this work for degassing fast-curing resin like polyurethane? Mine is cures in 3 minutes. My idea is pour it to my mold then put it to vacuum camber until resin cured… will this work?
Easy Composites› Matt
Yes but if you have such a quick resin then you might want to reduce the volume of the chamber by loading it with some ballast (like house bricks or something else to take up the space in the chamber); this will mean that the same pump will draw down the chamber to vac pressure more quickly. Don't forget that it's essential you re-pressurise the chamber before the resin cures - simply loading it in a pulling a vac until it cures would definitely be wrong and won't give you good results.
Ivan Spinning
I degas the resin, cast it in the mold, and put the mold again in the vacuum chamber. In this situation am I allowed to have no vent holes in the mold? They are no longer necessary, right?
Easy Composites› Matt
This is a little complicated. The kind of process you're describing where you can pour into a complex mould, with undercuts and not need any vents on these undercuts would usually require a vacuum casting machine where the resin is poured into the mould under vacuum; in this situation no vents are needed and the resin will flow, under gravity, into all areas of the mould, including unvented undercuts. If you don't have a vacuum casting machine (a degassing chamber is not a vacuum casting machine) then you can achieve something quite similar but it's done in a slightly different way. You would need your silicone mould to have some extra 'header' area to hold some extra resin - you then fill the mould (and the header) with the casting resin and then pull a vacuum on the mould. The vacuum would cause the air trapped in the undercuts to expand and bubble out (through the header and out of the top, where you fill the resin in from). Once this has happened, you allow the pressure back into the chamber which compressed the air in the undercuts down to almost no volume. As this happens, it creates a vacuum in the undercuts which draws resin in from the rest of the casting to fill the voids. Surplus resin in the 'header' is then drawn down into the main body of the casting. The end result should be that all the undercut areas are filled properly with resin.
Higgins_123
How do you clean the vacuum pump oil?? I've tried filtering through kitchen towels and freezing and separating to remove water (what they recommend for freeze drying pumps) but my oil is still cloudy???
Easy Composites› Matt
We would strongly recommend replacing the oil at this stage. You can help reduce contamination, especially by particulate matter by using an inline filter such as our VF1 Vacuum pump inlet filter. However, having now got contaminated oil it really does need replacing, not filtering or cleaning.
Aj Amori
Great video!! I'm looking to purchase a vacuum pump. Can you tell me the specs of the pump you use in the video? I was told I need a 7 CFM pump that can pull -28 inches of mercury to degas my Smooth Sil 940 platinum silicone rubber.
Easy Composites› Matt
The exact pump we used in this video (and the smaller model shown) are no longer available from us but have been replaced by two very nice pumps from Italian manufacturer DVP. The closest of these two pumps to the VP3400 (in the video) would now be the EC.20, you can find the full spec for this pump on its product page. The most important number when choosing a vacuum pump for degassing is the vacuum level that the pump can achieve, this is really the number that will determine how well your material will degas. In the case of our current vacuum pumps, they both achieve better than 29.92 inches of mercury (99.98% vacuum), which - in vacuum terms - is much higher than 28 inches of mercury. From our experience, 28 inches of mercury would not be a high enough level of vacuum to properly degas most silicones. As for the CFM of the pump, this is just its throughput and doesn't relate to the ultimate level of vacuum achieved and so the CFM rating of the pump only affects how quickly the pump will empty your chamber and so how quickly the degassing will happen. A 1CFM pump and 50°CFM pump that both achieve 29 inches of mercury will degas the same silicone in exactly the same way, only the 20°CFM pump would do it quicker.
metals
The instruction manual with my pump says that shut off the pump when the needle on the gauge is no longer moving or has reached the max. I am doing that but I find that it has never gotten rid of all the bubbles properly in the epoxy.
Easy Composites› Matt
We tend to run the pump throughout any degassing operation. The pumps we offer are perfectly capable of being run throughout the degassing operation. Degassing resin also depends on the viscosity of the material. Some resins degas easier than others. Also be aware some resins have a solvent content which can outgas during very high levels of vacuum which can effectively mean they bubble indefinitely, not really remove entrapped air but instead boiling off the solvent or volatile content in the resin and altering its make-up.
Titan Terrain Studio
When you're done degassing the mold the 2nd time, do you leave it inside the chamber to fully cure after releasing the vacuum? I did this with some molds recently for the first time but ran into some issues with bubbles popping up slowly over time.
Easy Composites› Matt
You can do either as it shouldn't make any difference to the cure as long as you are careful removing the mould from the chamber, however, the essential thing would be to ensure that - if you're leaving the mould inside the chamber - you let the air pressure back into the chamber once you're done degassing; it's the restoration of atmospheric pressure that will compress any residual air down to basically zero volume and produce a properly degassed material. If you leave the resin or silicone to cure under vacuum then you're totally defeating the objective and the material will cure with aeration.
LEAVE A COMMENT OR QUESTION
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