Recently, I went looking for advice on what to use/how to use an ultrasonic cleaner for dirty bike parts. Here's what I've had really good luck with... this is at least partially for my own reference later
Ultrasonic Cleaner
I bought a device described as "New Stainless Steel 6 L Liter Industry Heated Ultrasonic Cleaner Heater w/Timer" on ebay from a beauty-supply-oriented seller. Note that there are several different devices which look very similar; and at least one of those is marketed under several different names at prices ranging from $100 to $500! The pictures on ebay include one view from the back, and if you look at the detailed view you can see the model number (in my case, PS-30A). I've seen the PS-30A sold for as much as $500 elsewhere. This is the one I bought:
ebay link that'll go stale eventually
The 6L model I got is not large enough to hold a 50T chainring. This was a bit of a error on my part, but not the end of the world. If I had it to do over again, I'd think real hard about going up a size or two.
Cleaning Fluid
To begin with, I tried plain water with a bit of dish washing detergent. This worked ok, but not as well as I hoped. The soiling on parts cleaned this way was softened, but it took a fair bit of scrubbing and rinsing to really make the parts clean.
A bit of research led me to
Branson MC-3, which is an ultrasonic-specific metal cleaning fluid that's specifically safe for aluminum. In many cases, they tell me, the soiled fluid may be flushed down the drain, but they advise checking with the appropriate authorities before you do that. In my case, I just plan to take the used fluid to the county waste transfer station with a copy of the MSDS and let them deal with it.
It's difficult to find MC-3 in smaller than a case of 4 gallon containers. There are a few sellers out there that sell the quart bottles, but I went with
Process Equipment & Supply who were recommended to me by a helpful person at Branson.
Cleaning parts with a ~8% solution of MC-3 & water at 50*C vs. a <1% solution of Dawn at 50*C was fairly night & day. Worked great for removing grease, dirt, oil, etc.
Rust Removal
MC-3 isn't a rust removal fluid. Branson does sell something which is, but it's pretty noxious stuff I think. In the end, I bought a small container of
Evapo-Rust from an auto parts store. I was able to soak my clean, but rusty, parts in Evapo-Rust for about 2h, and then clean in the MC-3 for 3 minutes (@ 50*C) and it worked great.
The Evapo-Rust label says it's safe for use in ultrasonic cleaners. I've read about people who fill their ultrasonic cleaner with water, and fill a glass or plastic container with the fluid they want to clean with, and set THAT into what amounts to a water bath in the ultrasonic cleaner. If you do that, you could go back & forth between Evapo-Rust and MC-3, but in my case I didn't need to do that (the rust I've been removing is on small parts).
Generally
Use gloves. I have thick chemical-resistant gloves that I've been using. The chemicals described above are reasonably safe, I think, and not terribly noxious, but still. Be careful. In particular, one must be careful with the not-yet-diluted MC-3.
Disclaimer
What the heck do I know about any of this stuff. You should be careful and not trust me.
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Follow-up:
I took an old chain out of the trash, cut it into four pieces, and took three of the pieces and cleaned them in the ultrasonic cleaner @ 50C for 2:30, 5:00 and 10:00 minutes, and then gave each a brief quick rinse in fresh water (no scrubbing at all). Some of the photos aren't as in focus as others, but I used a macro lens to try to get as close as I could. It seems to me there's a pretty clear difference between each of them (that is, it's cleaner after 10:00 than it was after 5:00, etc.). The chain is a little harder to tell how obviously clean it is after more than a couple of minutes ... but see below the cassette which was a bit clearer as to the cleaning power.
Photos are too large to attach, they're shared at
https://www.dropbox.com/sh/mritqgqg6...C0dY3jcQa?dl=0