ANALYSES OF CAST ROLL CRACKING IN A BIG KIND OF PAPER MACHINE

Macro and micro examination of failed roll in a big paper machine showed that the roll was made of cast iron.Craking originated at the bottom of threads in screw hole for connection.Intergranular fracture propagated along grain boundaries due to galvanic corrosion (or ferrite corrosion on the gray iron) combined with stress concentration at the thread notches during 4 years’ service.When the crack length attained threshold length,explosive cracking happened in the absence of deformation.Some suggestions are offered to prevent these kinds of accidence.