Acrylic under a vacuum

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SSobel

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Has anyone ever tried to put resin or acrylic into a piece of burl with tons of little holes? I was thinking of trying a soak in acrylic under a vacuum. Do you all think it will get deep into the pours or is it too thick?
 
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I have used pressure and vacuum on burls to get the resin in deep. If you use vacuum, make sure the wood is in a tub so it doesn't go all over the place. I made this mistake. Ruined the pressure pot. Also, don't use Alumilite as the open time is way to short.

Just my two cents worth.
 
I have not had good luck stabilizing (anything) using vacuum. The only thing I use vacuum for is to de-air the rubber prior to making molds.

The problem is that the act of sucking the air out of a piece of wood is, in itself, preventing the resin from entering the wood. I have experimented on soft redwood and achieved about 1/4" penetration on 26 hg vacuum, which equates to about 12lb of pressure.
Using a pressure pot at 60psi will yield much greater penetration and the air bubbles trapped within the wood will be crushed to a pinpoint.

Here is a photo of an example, the top was cast in resin using vacuum, the bottom was using pressure. Both use the same type of resin and was kept under vac/pressure until the resin was fully cured (about 10 hours).

By all means, experiment with the products you have at hand and keep notes on your process and results :wink:
 

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Vince_Hoffmann said:
I have not had good luck stabilizing (anything) using vacuum. The only thing I use vacuum for is to de-air the rubber prior to making molds.

The problem is that the act of sucking the air out of a piece of wood is, in itself, preventing the resin from entering the wood. I have experimented on soft redwood and achieved about 1/4" penetration on 26 hg vacuum, which equates to about 12lb of pressure.
Using a pressure pot at 60psi will yield much greater penetration and the air bubbles trapped within the wood will be crushed to a pinpoint.
Click to expand...

You are confusing the terms here, Vince. Stabilizing is the act of getting a stabilizing resin deep into the wood where it looks to me like you are using a casting resin and CASTING a piece. The difference being that a casting resin is a resin with a relatively high viscosity and a chemical reaction that causes the resin to polymerize. A stabilizing resin has a MUCH lower viscosity and is usually polymerized by heat and will not harden on its own.

You are correct that a vacuum is NOT a good method of getting casting resin deep into wood. The viscosity of the casting resin is just too high and the only way to do it effectively is to pull the vacuum and then release it before the resin goes off. Otherwise, any "overhangs" that are trapping air will still be a void in the cast.

One other thing, a vacuum of 26" Hg does not equate to a pressure of 12 psi but rather a reduction of pressure roughly equal to 12 psi from atmospheric pressure. In other words, pressure inside a 26" Hg vacuum is roughly equal to 1.74 psi.
 
Thanks for the clarifications MMan, perhaps my message was a bit confused. I always cast wood/resin blanks using pressure and have had excellent results, not so much with vacuum. I've attempted stabilization using Polycryl in a vacuum chamber, but with limited results with redwood. However, using Polycryl in a pressure pot yielded much better results. Polycryl does not catalyze and requires the piece to be removed to air dry.
My conclusion is that, regardless of the casting/stabilization material, pressure produces a much better end product.
 
Vince_Hoffmann said:
My conclusion is that, regardless of the casting/stabilization material, pressure produces a much better end product.
Click to expand...

I have to respectfully disagree with you on stabilizing! Casting, I absolutely agree with you 100%. I have done lots of extensive testing with stabilizing materials and have found that vacuum does a much better job for impregnating wood if the right type of resin is used. When you pressurize the wood for stabilzing, you are simply compressing the air inside the wood. As soon as you release the pressure, the air re-expands and pushes a lot of the resin back out of the wood. With vacuum, you are removing the air and when you release the vacuum, since nature always likes to be in balance, resin is pulled back in to displace where the air used to be and is held in by atmospheric pressure.

Then again, I am not talking about polycryl. I am very familiar with polycryl and have tested it in the past with fair results at best, both with pressure and vacuum. You are correct, it is an air drying material which is part of the reason my testing results were fair at best. Anything that has to "dry" has solvent carriers of some sort that have to evaporate. In the case of polycryl, it is water. The issue is that the amount of solids that are actually transported into the wood is very low and you are not left with much once the water has evaporated.

Not trying to be argumentative, sir! Just trying to pass along information based on a lot of testing.
 
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Funny thing yesterday I put two pieces of porous deer antler in pr resin under 55 psi. I use 3 drops of cat. hoping to slow down the hardening process so I could get penetration. A little more than 24 hrs. latter I removed them from the pressure pot and heard a pop. The resin was still quite runny and the compressed air expanded and excaped. I put it in a vacuum for a few min. then back in the pressure pot. I guess the question is how small a void will resin fill while also compressing air. I don't want to take over Sobels thread but I didn't know if I should start a new one since I think we're thinking on the same line. Thanks
 
That's a good point Kenny...I was thinking about different materials to experiment with and thought October cereals (as I was eating some). Put some cheerios on a 7mm tube, and soak in acrylic. My problem is knowing whether to acrylic will penetrate those holes better with pressure or vacuum. Maybe I'll try one of each...one of us pen making nerds has to have tried this.
 
I've done it using Post Oak burl. Have everything ready, I place the burl blanks in "boats or forms" of triple layered heavy duty aluminum foil, fill with resin, place in a vacuum chamber for about 5-8 minutes, remove, place in pressure pot at 60 psi. the gel time for the stuff I use is about 20-30 minutes, need to get into the pressure pot a few minutes before it starts to gel. Give them plenty of time to harden, I left mine overnight as that was convenient. The vacuum removes most of the air and allows the pressure to collapse any remaining air bubbles to very small dimensions. Worked very well.

From Curtis's info you can see that a good vacuum can remove about 90%+ of the air.

It won't fill voids that are completely sealed off, but in my experience those are few and small.

The problem with pressure only, any trapped bubbles will reduce in volume by less 1/8 at 60 psi. If you remove about 90%+ of the air the trapped bubble volume goes to about 1/80, better vacuum, smaller trapped bubbles.
 
FYI: polyester resin users who also use vacuum: The styrene solvent in polyester resin will boil out of the solution at 28" Hg. I would suggest to not exceed 27"Hg. Just to be sure when I do use vacuum on polyresin I keep the vacuum at 26" Hg.
Do a good turn daily!
Don
 
mhbeauford said:
The problem with pressure only, any trapped bubbles will reduce in volume by less 1/8 at 60 psi. If you remove about 90%+ of the air the trapped bubble volume goes to about 1/80, better vacuum, smaller trapped bubbles.
Click to expand...

Are you sure about this, Martin? I am no engineer by any means but my understanding of Boyle's Law, which covers this, is that for every atmosphere of pressure you add, you reduce the volume of a gas by half. The first 14.7 psi cuts the volume of air to 1/2, then the next 14.7 cuts it in half again. Since 60 psi is roughly 4 atmospheres, what does that give us? I am not good with that kind of math but it sure seems like it is more than reducing it by less than 1/8 since the first atm already reduced it by 1/2.

Regardless, if one is using Alumilite, it is a moot point, since there is not enough time to pull full vacuum, release, and then put it in a pressure pot! However, I don't believe he was talking about Alumilite so thus I stray! Also, based on my years of experience with pressure casting, I find that pressure eliminates virtually all bubbles in my castings.
 
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Last week I had the opportunity to do both on the same set of blanks. I pressure cast, with 2 color PR, on a rectangular 4x6 block of punky stuff from Aussie land. Casting went great...expected results. But there were large area's still soft as Jell-o. I know PR isn't a replacement for stabilizing, so into the vaccum tank it went. After the curing process...I received the expected results...3 great looking pen blanks using 2 seperate processes.
 
Curtis first I would like to say thanks for your willingness to help others. With your knowlege of casting I would like to ask your opinion about something I saw on you tube. A person was making a silicon mold for casting a flexible drinking glass for a film prop. While putting the silicon mold in a pressure pot he said the pressure, 40-60lbs., would desolve the air bubbles. I've heard the term shrinking them to a very minute size to the point they "disappear" but never disolve. Whats your take on this? Thanks
 
Kenny Durrant said:
Curtis first I would like to say thanks for your willingness to help others. With your knowlege of casting I would like to ask your opinion about something I saw on you tube. A person was making a silicon mold for casting a flexible drinking glass for a film prop. While putting the silicon mold in a pressure pot he said the pressure, 40-60lbs., would desolve the air bubbles. I've heard the term shrinking them to a very minute size to the point they "disappear" but never disolve. Whats your take on this? Thanks
Click to expand...

Kenny,

That is beyond my pay grade as to what actually happens to the air! Whether it dissolves or is just so small you can't see it is irrelevant to me as long as the bubbles are gone! And you are most welcome for the help! Give me a call sometime if you want to further discuss some of these issues.
 
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mhbeauford said:
I've done it using Post Oak burl. Have everything ready, I place the burl blanks in "boats or forms" of triple layered heavy duty aluminum foil, fill with resin, place in a vacuum chamber for about 5-8 minutes, remove, place in pressure pot at 60 psi. the gel time for the stuff I use is about 20-30 minutes, need to get into the pressure pot a few minutes before it starts to gel. Give them plenty of time to harden, I left mine overnight as that was convenient. The vacuum removes most of the air and allows the pressure to collapse any remaining air bubbles to very small dimensions. Worked very well.

From Curtis's info you can see that a good vacuum can remove about 90%+ of the air.

It won't fill voids that are completely sealed off, but in my experience those are few and small.

The problem with pressure only, any trapped bubbles will reduce in volume by less 1/8 at 60 psi. If you remove about 90%+ of the air the trapped bubble volume goes to about 1/80, better vacuum, smaller trapped bubbles.
Click to expand...

Correction: should be reduced TO less than 1/6, missed typed and my in the head calculations were a little off.:redface: Actually V2 = V1*P1/P2 where P1 and V1 are first pressure and volume and P2 and V2 are second pressure and volume pressure is ABSOLUTE pressure, ie 14.7 psi plus gauge reading approximately at sea level. As Curtis has pointed out atmospheric pressure varies with altitude and local barometric pressure. As I have discussed with Curtis, solubility of air in resin also increases directly with absolute pressure and the air in small bubbles can be absorbed at higher pressure.
 
Thank you for the conversation today on the phone, Martin! I have been misunderstanding Boyle's law for a while now! I enjoy being educated on physics issues and appreciate the time you took with me!

One thing to keep in mind, however, if you are using Alumilite, there is really not enough time to pull a full vacuum, release, and put in your pressure pot. I have pulled the vac in the pressure pot and then released and added pressure but did not find that it made much difference and was not worth taking the chance that my resin would be going off before I got it to full pressure.
 
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