Hi again, Its been a while since I've posted. I had somewhat of a breakthrough on eliminating the bubbles from my steering wheels. I thought maybe it would be of interest to some of you. I was trying to figure out a way to set up a system for vacuuming the resin into the mold like had been mentioned by guys earlier in this thread. I was having a hard time figuring out a way to do it practically ,when I thought of maybe using pressure to inject the resin into the mold.
I thought about it and realized it seemed a lot easier to accomplish than vacuuming so I decided to try it. Here is what I did: The mold has about a 5/16 in. hole for pouring in the resin. I took a piece of 5/16 in O.D. clear pvc hose and plugged it into the pour hole. It fit nice and snug so that was good.I made the hose about 3 ft long. I ran the hose through a fitting I made in the side of my pressure pot that sealed OK, not great ,but ok. I have a pressure regulator and gauge on the inlet air to the pressure pot. I mixed the resin parts A and B together and put it into the pressure pot .I then placed the end of the pvc hose into the cup of resin so that the end was at the bottom of the cup. I then put the lid on the pressure pot and tightened it down. Now by turning the pressure up on the pressure pot I could see the resin start flowing through the tube and into the mold.
I had the pressure at about 6 psi and in about 3 to 4 minutes I saw the resin start coming out of the vents at the perimeter of the steering wheel. I let the troughs, surrounding the vents ,fill up with resin for about another 30 seconds and then stopped the transfer. I then put the resin filled mold into my large pressure pot under 50 psi for 4 hours and to my amazement when i demolded I had no bubbles in the steering wheel, not a single one!
I then did a second wheel and this time I lost control of the transfer; I let the resin cup accidentally empty and it then pressurized air down into the mold. It ended up having bubbles in the finished wheel. The next time instead of using a metal lid on the small pressure pot ,that held the cup of resin, I used the clear lid off of my vacuum chamber. Then I could see the resin going down in the resin cup and I was able to control the transfer and stop it before I forced air into the mold.
Another thing I found is that if I degassed the part A and part B of the resin separately I could get a huge amount of air out of it. I was able to degas the part B for about 5 minutes before I got most of the bubbles out of it. Part A didnt take near as long. ( I read recently that if you degas until about half the surface of the resin is free of bubbles then its time to stop degassing). To get to this stage with the part B it took about 5 minutes. I also degassed briefly after I had mixed the two parts together but it only took about a minute to get the mixture to the point where half the surface of the resin was free of bubbles.
In summary, I think what might have been happening is that when I was just pouring the resin in it was also taking air in along with it; but when I was pressurizing it in there was no way for air to enter along with the resin.
Does that sound plausible?
I was using Smooth On 327 resin that has a 10 to 20 minute pot life. It took be about 8 to 10 minutes from the time I mixed A and B together until I had the mold under the 50 lbs of pressure.
I was going to upload a picture of a finished wheel but it looks like PhotoBucket is experiencing problems right now (9/6/12) so I will try to remember to do it later. Happy Casting