I've never heard of such a machine and I have spoken with several bank employees over the years about silver coins. Additionally, my father - who passed many years ago - was the president of a small, local bank with a few branches. He was keenly aware of silver coinage and accumulated a substantial amount of it, though he was not nearly as enthusiastic about it as I became.
The banks basically don't care about silver coins. It's not part of their business models and the amounts are so trifling as to not be worth their attention. Additionally, all banks consider coins of any sort to be a PITA...a necessary cost of doing business. Some banks will let their tellers keep any silver coins they find, as long as they replace them with modern coins of the same denomination.
It strikes me that banks have been limiting the amount of coins they keep on hand for several years, now. Few banks will give non-customers coins for cash and even my own banks no longer keep the amount on hand that they used to. I used to be able to go to my bank and ask to buy a roll or two of half dollars and they would happily oblige. In recent years, they usually claim that they don't have any rolls available.
The US Mint hasn't made silver circulating coins for roughly sixty years. Virtually all of them were long ago picked out of circulation. On the (very) rare occasions that I find a silver coin in change, I assume that kids found someone's silver stash and used the coins to buy candy.
Best
Doc
My mom used to be a teller back in the 80s in a small town bank. As long as their drawer had the correct amount of money in it, they were good. My mom (through my dad) was very aware of silver coins and "bought" every one she came across along with things like silver certificates, $2 bills, etc. She even got an entire bank bag of 1955 "wheat" pennies. (sorry collectors, no true double-die pennies - but lots of errors and so called poor-man's double die though).
I have been told that those automatic coin counter machines in banks, walmarts, grocery stores, etc have a place where it kicks out non-modern coinage and junk like paper clips. So they will spit out Canadian coins and yes even silver U.S. coins. And most people never think or care to look there. So you can sometimes find a silver coin or two there.