Gate-bleed and drooling occur when molten plastic slowly leaks from the nozzle tip during the injection cycle or when the mold is open. This issue causes stringing, parts with excess material, clogged vents, and increased downtime for cleaning. While nozzle design and valve gate performance play roles, temperature control governed by thermocouples is one of the most influential factors. Proper thermocouple performance can significantly reduce or eliminate drooling.
Drooling often occurs when the nozzle tip temperature is too high. Excessive heat reduces melt viscosity so much that material flows through the gate under low pressure. Drifting or poorly placed thermocouples may report lower temperatures than reality, leading operators to increase heat unnecessarily. Accurate thermocouples maintain the minimum effective temperature to prevent unwanted flow.
Conversely, temperatures that are too low can cause unstable flow that also contributes to inconsistent gate behavior. Thermocouples ensure the tip remains within the ideal thermal window where the melt stays fluid but does not seep out.
Fast-response thermocouples quickly compensate for temperature loss when the mold opens. Without rapid recovery, the tip may cool slightly, causing inconsistent freezing and restart leakage. Quick thermal recovery maintains stable gate conditions.
Thermocouple placement near the nozzle tip is critical. Sensors located too far from the gate cannot accurately reflect tip temperature, leading to incorrect control. Proper placement ensures the measured temperature matches the actual gate environment.
In valve gate systems, temperature stability synchronizes with pin actuation. If temperature fluctuates, the melt may remain too fluid or freeze prematurely, causing either drooling or stringing. Stable thermocouples support reliable valve performance.
By maintaining accurate, responsive, and well-placed temperature control, thermocouples effectively reduce gate-bleed, drooling, and stringing, improving productivity and part quality.
