Purging time factors of extruders

The purging time for any system varies depending on several factors:
1.The type of materials that need to be purged.
For example,transitioning from a LDPE to a LLDPE is much faster than going from a LLDPE to a Nylon.
2.The design of the extruder,the adapter and the die.
For example,a properly designed system with correctly seized flow passages
will be much easier to purge than one with many hangup spots or slow flow areas.
3.The size of the equipment.It is inevitable that larger equipment will be harder to
purge than smaller ones due to the sheer size differences.
For example,the residence time of a 4.5" extruder is much longer than that of
a 2.5" extruder.
As a result,the purge time will be longer in a 4.5"extruder.