No adapter or transformer will fix the "cycles" (HERTZ) issue.
On 60hz (here in the USA) the machines' 50hz motors and timers will be 20% faster. I am not sure if this is a fire-hazard or not per se.
HOWEVER here, our 220v is a split-phase double-hot system. In places with 220 (line to ground/neutral) it is not. Generally for safety BOTH SIDES A 220v CIRCUIT (HERE) must be protected by a fuse and BOTH sides must be switched for safety.
If you do decide to use those appliances here
1- never leave them unattended.
2- never leave them plugged-in when not in use.
Other than a motor-generator set to provide the "proper" 220v 50hz/Hertz current I don't know how to advise you.
I have heard of a 220v Miele vacuum cleaner used here on our current, but in all fairness there is no additional load to such a motor (except when the bag is full) and it is probably very well air-cooled, and densest run for 2 hours continuously!
If you are DYING to try them, get a Euro power-strip (of adequate amperage) or extension cord, cut off the male end (LOL) and add a USA 220v plug that fits your (female)receptacle.
PLEASE BE CAREFUL.
The rest of the world will laugh, but we are not used to 220v power here and generally need to fear and respect it for the dangers involved.
The joy of 110-120 volts is if you do anything stupid or careless you get to live to do it again.
P.S. so yes the difference between 220 to 240 volts can be considered generally "in name only" and is, for the most part, meaningless.
Perhaps we should convert the whole world to 220v 60 hertz and be done with it!