That is the reason the rotor turned freely after it cooled. Upper rotor is stuck and cannot be freed. Powders ingested into the pump Process gases are reacting with the lubricating oil. Making it sticky. No lubrication Failure of the cooling system.
High temperature can expand metal components and make the oil coke.
Lower rotor is stuck Pump is running too cold Powders ingested into the system Liquids ingested into the pump Wrong lubricant Poor or no lubrication to the lower unit. Process gas has entered the pump and corroded the internals The Mc Nally Institute 1986 S. Belcher Rd.