Polymer Degradation Mechanics in Glass-Filled Injection Tooling Cavities
Glass fiber erosion and shear scission alter gate dimensions and matrix integrity, requiring modular PM steel inserts and strict vent land depth maintenance.
Gas Burning
Meaning
Thermal discoloration resulting from compressed air or volatiles trapped within a mold cavity appears as localized charring on the part surface. The phenomenon of gas burning occurs when the injection speed is too high to allow air to escape through vents. It is restricted to the mold cavity environment and does not include external fire hazards.
Venting Efficiency
Adequate escape paths for air prevent the buildup of high pressure. When vents are clogged or too small, gas burning manifests at the end of the flow path. Regular cleaning of the parting line maintains proper airflow.
Injection Speed
Rapid filling of the mold increases the compression rate of trapped gases. Because the temperature of the air rises according to the gas laws, gas burning becomes more likely as the fill time decreases. Adjusting the velocity profile helps manage the internal pressure.
Surface Finish
Dark spots or degraded polymer textures indicate that the material has reached its decomposition temperature. If gas burning is visible, the mechanical integrity of the plastic at that location is compromised. Parts with these defects are typically rejected during quality control.
Proper gate placement ensures that the melt front pushes air toward the vents without trapping pockets.