We have industrial ultrasonic cleaners here at work. After much testing we figured out that a 12-16% concentration of Brulin 815 gave a great result. It turns out that a chemistry optimized for ultrasonic cleaning is the right answer. Surprise!
You need a basic (high pH) solution, not too much, and run it at 140-160 degrees to start. From there you can dial it in
We tested Simple Green. Awful smell and barely mediocre results.
You need the right chemical/water concentration and the right temperature to get good results. Ultrasonic cleaning works by creating vapor bubbles that collapse violently and knock the material loose. The chemistry does the rest. Too cool and the bubbles don't form adequately, too hot and they don't collapse with enough force. Too high a chemical/water ratio and the bubbles don't form (not enough water in the mix). Too low a chemical/water ratio solution and the chemical cleaning action is compromised.
We clean up varnish on labyrinth seals in about 3 minutes with this unit. If there was caked up carbon it might take 20 min. Granted it is 12 KW at 20 KHz so a very powerful unit. Optimization of chemistry and temperature is key. For reference we clean 10 foot long heat exchanger bundles which have finned tubes caked with carbon and varnish. Takes a few hours to do a good job. All the **** and oil destroys the cleaning solution though. We use a little titration kit to test the remaining capability of our chemistry.
We buy 815 by the barrel because the tank is about 450 gallons.
The key lesson for any user: there is a correct window of temperature and chemistry ratio for your ultrasonic cleaner. Too much or too little is not good. And cleaners optimized for ultrasonic use work way better.