Meaning
Damage to sliding metal surfaces occurs when localized friction causes micro-welding and subsequent tearing of the contact areas. Severe material transfer during adhesive galling disrupts the movement of tooling components. This localized welding occurs under high contact pressure when lubrication fails or is absent during the moulding cycle.
The phenomenon usually terminates when the sliding components seize completely.
Wear Mechanism
Slideway degradation begins with the disruption of the protective oxide film on the metal surface. High surface temperatures and compressive stresses during injection mould operation then force bare metal atoms into direct contact, initiating localized cohesion. Material is plucked from one surface and transferred to the mating surface as the sliding motion continues.
This transfer creates rough protrusions that gouge the opposing component on subsequent strokes, leading to rapid mechanical breakdown of both sliding faces.
Tooling Impact
Mould ejector pins and sliding cores frequently experience this form of surface damage when high clamping forces or thermal expansion increase contact stresses. This failure mode causes surface defects on moulded parts because the seized pins cannot retract smoothly. Production must stop to replace damaged inserts and pins, which increases the overall cost of moulding.
Prevention Strategy
Surface treatment of moving tool components reduces the likelihood of localized micro-welding. Tooling alloys can be coated with physical vapor deposition treatments or subjected to surface hardening treatments to increase surface hardness and minimize metal-to-metal adhesion. Maintaining a hardness differential of at least five Rockwell C units between mating sliding components prevents similar microstructures from welding easily.
