Cast iron injection housing.
ASTM A 536 Grade 65-45-12 ductile iron.
The cast iron injection piston housing had been subject to approximately one million cycles in a plastic injection moulding system. Seven identical failures of localized damage to the ring seal on cast iron injection piston housings had occurred.
Approximately 1.5 years, or one million cycles.
Visual examination of the region of localized damage revealed areas of large craters surrounded by smaller craters or micro-pits. Such damage is typical of cavitation damage.
Cavitation damage is defined as the wearing away of metal through the formation and collapse of cavities in a liquid, subject to rapid and intense pressure changes. In this situation, the liquid was the oil used to lubricate the piston and housing. The rapid movement of the piston through the housing caused the swift and intense pressure surges in the oil, resulting in the cavitation damage.