11/4 - Update: Made another bubble free clear PR cast today, this time with ultrasonics only. Still ran ultrasonics for about 6 minutes without catalyst. Added catalyst and stirred very carefully. May have to find a new use for the pressure pot. This is definitely a simpler and less expensive way to get into clear casting. Also a better chance of not getting resin in tube (not guaranteed, just a better chance). Would still like to hear if anyone else has tried this.
Original Post:
For a while, I have been considering the use of ultrasonics to get the bubbles out of clear resin casts. I got the idea from my days using this technique to get entrapped air out of solvents for liquid chromotography. Well, I finally got a small ultrasonic cleaning unit on ebay (the kind used to clean jewelry) for about $25 and have run several tests. Just looked at the cast I made last night and it is bubble free (will be my PITH pen). I did also use the pressure pot for insurance, but know that the ultrasonics did help.
Procedure for polyester resin is to pour desired amount in a mixing container and set this in about 1/2 inch of water in the ultrasonic cleaner before adding any catalyst. I ran the ultrasonics for about 6 minutes.
I was discussing this with a professor at one of the local universities. Our best theory is that the bubbles come from air disolved in the resin. As the resin heats up to cure or there are sharp edges or minute irregularities on the surface, the air comes out of solution in the form of bubbles. Vacuum degassing likely does the same thing as ultrasonics - it forces the air out of solution. Pressure, on the other hand probably does not shrink the bubbles, it merely forces them to go into solution. For those scientists or anyone else is interested in the theory, the mere shrinking of the bubbles by pressure cannot be explained by physics. The gas law says that pressure and volume are directly proportional, so an 2X increase in pressure can only descrease volume by 1/2. The pressure pot threads suggest running at 25 to 30 psi, or about 2 to 3 times atmospheric pressure. IMO, this is not enough to shrink bubbles to invisible, so I'm thinking any left after degassing are going back into solution.
For those who don't care how it works, I offer this as an alternative to vacuum. Ultrasonics degassing by itself may also work well if you don't want to make the investment in a pressure pot and compressor. Its a little lower in cost by itself.
Would love to hear from others if they decide to try this and can further develop the techinque.
Original Post:
For a while, I have been considering the use of ultrasonics to get the bubbles out of clear resin casts. I got the idea from my days using this technique to get entrapped air out of solvents for liquid chromotography. Well, I finally got a small ultrasonic cleaning unit on ebay (the kind used to clean jewelry) for about $25 and have run several tests. Just looked at the cast I made last night and it is bubble free (will be my PITH pen). I did also use the pressure pot for insurance, but know that the ultrasonics did help.
Procedure for polyester resin is to pour desired amount in a mixing container and set this in about 1/2 inch of water in the ultrasonic cleaner before adding any catalyst. I ran the ultrasonics for about 6 minutes.
I was discussing this with a professor at one of the local universities. Our best theory is that the bubbles come from air disolved in the resin. As the resin heats up to cure or there are sharp edges or minute irregularities on the surface, the air comes out of solution in the form of bubbles. Vacuum degassing likely does the same thing as ultrasonics - it forces the air out of solution. Pressure, on the other hand probably does not shrink the bubbles, it merely forces them to go into solution. For those scientists or anyone else is interested in the theory, the mere shrinking of the bubbles by pressure cannot be explained by physics. The gas law says that pressure and volume are directly proportional, so an 2X increase in pressure can only descrease volume by 1/2. The pressure pot threads suggest running at 25 to 30 psi, or about 2 to 3 times atmospheric pressure. IMO, this is not enough to shrink bubbles to invisible, so I'm thinking any left after degassing are going back into solution.
For those who don't care how it works, I offer this as an alternative to vacuum. Ultrasonics degassing by itself may also work well if you don't want to make the investment in a pressure pot and compressor. Its a little lower in cost by itself.
Would love to hear from others if they decide to try this and can further develop the techinque.