Guys,
This is basic math here...100% of 10 does not mean its 100% of 11 or 15 or 60...or infinity.
After 10 minutes of use, at the 100% duty cycle window...the welder could very well go into overheat in the 11th, 15th or whatever minute the temperature senses its had enough. These numbers are not published or even valued because unless it is on a robot, no one typically will use it any where near the 60% duty cycle at maximum amps...Even on a robot, there are starts and stops.

Duty cycles are NOT figured by a complicated formula a welder when he is welding. No one says, OK , just welded for 5.59 minutes and now I have to let it cool down precisely 4.41 minutes before starting back to weld. Or I have welded on and off in 3 minute increments at this amperage, so my duty cycle is X. Its something that is intuitive.

The exception to this would be something like sub arc welding where a machine does have a rating based off a higher unit of time or a larger amp capability to keep normal welding with in normal temperatures.