Troubleshooting overheating issues during sub-micron grinding?

Hey there all, I am searching for some recommendations concerning how to achieve ultra-fine particles with a new ink I am developing. I have been utilizing a vintage bead mill (grinding machine); however, I am having a tough time achieving consistent nano level yield. I have modified the speed of my milling operation and switched to utilizing smaller ceramic beads. Despite my best efforts the machine continues to run too hot when grinding down to sub-micron size particles. Have others experienced heat issues while attempting to process sub-micron sized particles? Would it be advantageous to consider upgrading our cooling system or investing in a new machine?