Glass Filled Polymer Injection Tool Wear Mechanisms
Glass filled polymer injection tool wear stems from fiber micro-ploughing and matrix erosion, requiring hard powder metallurgy steels or duplex PVD coatings.
Shear Rate Erosion
Meaning
A degradation process in which high velocity and localized shear stresses in the molten material wear away the protective oxide layer or the metal of the mold gates during high-pressure injection molding leads to premature tooling failure. In manufacturing processes using highly filled polymers, shear rate erosion removes tool steel from narrow restrictions, altering the molded part dimensions over time. This wear alters the gate geometry and leads to cosmetic and structural defects in the molded products.
The wear ceases to be significant when molding non-abrasive unfilled resins or when using hardened carbide gate inserts.
Material Wear
Abrasive fibers and fillers suspended in the polymer melt act as microscopic cutting tools under high shear conditions. This continuous abrasion wears down the tool surface, especially at the gate where the flow velocity reaches its maximum. The mechanical fit and gate volume change, which leads to overpacking or flash on the molded part.
Process Parameter
High injection speeds increase the shear rate, which accelerates the removal of the protective steel layer. Monitoring these speeds during production protects the tooling and ensures consistent part quality.
Defect Avoidance
Utilizing hardened tool steels or replaceable inserts at the gate region prevents the rapid degradation of the mold. This design choice maintains the structural integrity of the gate over long production runs.