Hello everyone. I’m hoping that you guys can help me with some investment mixing issues that I’m having. I’ve scoured the forums, and while I’ve found a bunch of threads discussing investment issues, none of them seem to address my particular problem. So here’s the issue:
When I mix investment powder and water at a water/powder ratio of 40:100, I initially get an okay consistency (like pancake batter). However, when I put it under vacuum the mixture thickens and boils sluggishly. When I remove it from the vacuum after only 30 seconds, it has thickened up substantially, and at this point there is no flow to it, so pouring it into a flask isn’t possible. The vacuum pump appears to be working properly - it boils water in just under 40 seconds and pulls at a normal 28.5 Hg. I have made a quick 1 minute video and posted it on youtube to show what is happening: https://youtu.be/9VnInUhn04w
Here is what I have tried:
I am mixing batches at a 40:100 water/powder ratio, weighing both water and powder. I have tried both distilled and deionized water at very close to recommended temperatures of 73 degrees for the water, and 75 degrees for the investment. After adding the investment to the water, I mix it with a mechanical mixer for 3 minutes. I have tried using different bowls/mixing utensils. I initially thought the problem could be the investment (newly purchased R&R Plasticast), so I ordered some Kerr Satin Cast, but I am still having the exact same problem with the Satin Cast.
So, this leads me to think that there’s an issue with the vacuum pump. The vacuum pump is only 6 months old, but it is regularly used to degas epoxy resin. I am unsure how using it to degas epoxy would affect the degassing of investment, but I admittedly know very little about vacuum pumps.
The vacuum pump is rated at 5 CFM. The vacuum table that I am using is the popular little one that Riogrande sells, and I believe they recommend a 3 CFM pump. From what I understand, a pump’s ability to suck air is limited by the size of the connected hoses, so there shouldn’t be much of a difference between the two as far as how much air is being sucked, with the small hose sizes that are being used. But, perhaps I am wrong and that extra 2 CFM is creating problems?
I am just about to purchase a new vacuum pump that is rated at 3 CFM, but first wanted to make this post to see if any of you are able to chime in with your experience.
Thanks for taking the time to read this rather long-winded post!