The "units" of speed could be miles/hour or feet/second or furlongs per fortnight. The "units" of Hz is "per second ["/sec"]."
60 Hz is some thing that happens 60 times per second. In this case what is happening 60 times per second is that the voltage goes from zero to a positive value and then back to zero and then to a negative value and then back to zero.
And at 60 Hz the cycle is completed in 1/60 = 16.7 milliseconds = 0.0167 seconds.
The crucible will work on 50 or 60 Hz. Find out what the nominal voltage is for your area. I think you will be just fine. I would verify with the manufacturer and your power company before you write that PO.