Hardened Tool Steel Shutoff Land Wear Baseline Profilometry
Hardened shutoff land profilometry establishes baseline surface texture to quantify parting wear and prevent flash in injection molds.
Abrasive Erosion
Meaning
Wear on mold or machine surfaces arises when reinforced polymer melts flow through narrow gates and runners under high pressure. This progressive degradation, known as abrasive erosion, typically occurs during the processing of thermoplastic resins that contain hard fillers such as glass fibres or ceramic particles. The scraping action of these suspended solids physically removes microscopic layers of steel from the flow channels over many cycles.
Such removal alters gate geometry and ruins part consistency.
Wear Mechanism
Friction between the filler particles and the metallic boundaries of the runner system is driven by local melt velocity. When high-speed flows pass through narrow or restrictive gates, abrasive erosion escalates rapidly. The high shear rates force the solid reinforcement fibers against the steel walls, initiating micro-scratching and furrowing.
This damage accumulates most severely in regions where the melt stream changes direction or accelerates.
Tooling Impact
Changes in the dimensions of the tool gate directly affect the injection pressure and the shear heating of the polymer. As abrasive erosion widens the gate, the flow resistance drops, which can cause incomplete packing or unbalanced filling in multi-cavity molds. Flash formation becomes common at the parting line because the enlarged opening allows material to escape.
Tool steels with high carbide content and surface treatments like physical vapor deposition are employed to resist this wear.
Operational Limit
Production volume before tool maintenance is dictated by the permissible tolerance of the gate orifice. The rate of abrasive erosion increases if regrind material is used because recycled glass fibers are shorter and can present more sharp, fractured ends. Once the gate diameter increases beyond the specified limit, the mold must be taken out of service for repair.
Laser cladding or insert replacement restores the original flow dimensions.