Meaning
Localized contact forces acting between two curved surfaces under mechanical load dictate the maximum pressure that metallic or plastic interfaces can endure without permanent deformation. Concentrated Hertzian stress occurs at point or line contacts within tool assemblies, such as guide pin bushings or slide faces. Exceeding the elastic limit of the material at these contact regions causes premature wear and pitting.
Contact Interface
Alignment components in complex multi-plate molds experience high loads over tiny contact areas during locking. This concentration produces intense Hertzian stress that can easily exceed the yield strength of the hardened steel. When the guide locks engage, the forces are transmitted through the curved profiles of the pins.
Proper radius design helps distribute these loads, reducing the peak forces at the contact point.
Wear Mechanism
Repetitive cycling under high load conditions leads to surface fatigue and material transfer between mating parts. High Hertzian stress causes microscopic cracks to form just below the surface of the steel, where shear stresses are highest. These cracks propagate outward, leading to spalling, which creates small pits that catch on the mating surfaces during mold actuation.
This damage soon ruins the alignment of critical mold inserts.
Lubrication Effect
Synthetic greases formulated with extreme-pressure additives help mitigate surface distress in these high-load areas. The lubricant separates the surfaces and reduces the peak Hertzian stress by spreading the load over a slightly larger effective area.
