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.
Vent Dieseling
Meaning
Compression-induced ignition of trapped air or gas within an injection mold cavity results in localized burning of the plastic part. This vent dieseling occurs when the air cannot escape through the designated vents fast enough during the high-speed injection phase. The rapid increase in pressure raises the temperature of the air above the auto-ignition point of the polymer.
Physical Process
Trapped gas pockets at the end of the flow path act as small combustion chambers. This vent dieseling leaves a charred, black mark on the part and can physically erode the steel surface of the mold. It often occurs in deep ribs or blind pockets where venting is difficult to implement.
System Adjustment
Reducing the injection speed can allow more time for the air to escape through existing vents. If vent dieseling persists, the vents may need to be cleaned or widened to improve the gas flow. Using a vacuum venting system is another method to ensure that all air is removed before the plastic arrives.
This adjustment requires careful synchronization with the injection cycle to avoid introducing new defects like flash or short shots.
Component Inspection
Burn marks on a cellular antenna housing are cause for immediate rejection because they indicate degraded material properties. Checking the depth and width of the vents with a feeler gauge ensures they remain within the specified limits. Consistent part weight and color are the primary indicators that the venting system is working correctly.