Hot runner leakage is a frequent fault in injection molding production, contaminating mold cavities, damaging product appearance, causing raw material waste and production downtime, and even burning out heating coils and thermocouples in severe cases. Leakage is mainly caused by assembly gap deviation, abnormal temperature, excessive pressure impact, aging accessories and installation misalignment. Troubleshooting from external observation to internal inspection and from simple to complex maintenance can quickly locate and solve faults.
On-site Preliminary Visual InspectionFirst cut off the injection molding machine's injection function and turn off the hot runner temperature control power supply, waiting for the hot runner temperature to drop to a safe range to avoid high-temperature scalding and circuit short circuits. Visually confirm the leakage position to distinguish between hot nozzle end leakage, splitter plate joint surface leakage, flange connection leakage or glue seepage at wiring and outlet positions, narrowing down the fault scope. Observe the leaked material state: thin overflow is mostly due to excessive temperature reducing melt viscosity, while massive hard glue seepage usually results from excessive assembly gaps and failed sealing parts, quickly determining basic inducements. Check mold opening and closing conditions to eliminate leakage caused by template deformation and extrusion dislocation.
Temperature System Troubleshooting and Rectification
Temperature imbalance is the most common cause of hot runner leakage. Excessively high actual temperature reduces melt viscosity, making it easy to seep out from tiny gaps. Check temperature control box parameters to ensure consistency between measured and set temperatures; if hot nozzle and splitter plate temperatures exceed the standard by more than 15℃, melt viscosity decreases sharply, causing leakage. For high-temperature materials like PC, PA and PPS, hot runner temperature shall not exceed the material forming upper limit; for general plastics, hot runner temperature is 5-10℃ lower than barrel temperature. Check thermocouple positions for offset, wear or detachment, as inaccurate temperature measurement leads to virtual high temperature and actual overheating leakage. Inspect aging heating coils for local overheating, which continuously softens melt and forms seepage channels by scouring sealing areas. Rectify faults by lowering abnormal area temperatures, re-fixing thermocouples and replacing aging heating accessories to ensure uniform and stable hot runner temperature.
Injection Pressure and Parameter Troubleshooting and AdjustmentExcessively high injection pressure and packing pressure continuously impact the hot runner's internal sealing structure, expanding assembly gaps and triggering leakage. Check actual injection and packing pressure values; thick-walled products and high-viscosity materials are prone to excessive pressure, with high-pressure melt squeezing splitter plate and hot nozzle connections, breaking through sealing limits and overflowing. Adopt segmented injection molding to reduce terminal filling pressure and packing pressure, shortening packing time to decrease cumulative melt impact force inside the hot runner. Improve melt fluidity for long flow length products to lower injection resistance, reducing extrusion force on the hot runner sealing structure and preventing pressure impact-induced leakage.
Assembly Gap and Sealing Structure In-depth InspectionIf leakage persists after adjusting temperature and parameters, disassemble the hot runner to check splitter plate and hot nozzle joint surface flatness, which may deform or scratch after long-term high-temperature use, causing poor fitting and seepage gaps. Focus on high-temperature resistant sealing gaskets for aging, hardening and fracture; failed seals lose elasticity and become the core cause of splitter plate leakage. Verify hot nozzle extension length: excessively long nozzles prop against cavities, while excessively short ones leave excessive gaps, both causing displacement and leakage during injection. Flange and machine nozzle connection leakage is mostly due to concentricity deviation and poor spherical fitting, which can be improved by correcting concentricity and polishing fitting surfaces. Control assembly pre-tightening force uniformly: insufficient force leads to poor fitting, while excessive force cracks accessories and causes permanent deformation, with bolts locked evenly according to standard torque.
Raw Material and Shutdown Operation Standardized InspectionExcessive raw material moisture generates water vapor expansion at high temperature, increasing internal pressure and breaking through sealing gaps to cause leakage. Strictly implement raw material drying standards and control recycled material proportion. Standardize shutdown operations: lower hot runner holding temperature for short-term shutdown to avoid long-term high-temperature retention and material carbonization; empty residual melt inside the runner for long-term shutdown to prevent cold material solidification and expansion damaging sealing structures. Avoid frequent switching of raw materials with large viscosity differences to prevent adaptive failures and sudden leakage.
Mold Structure and Cooling System Matching InspectionUnbalanced mold cooling indirectly induces hot runner leakage. Excessively close cooling water channels around hot nozzles cause frequent cold and hot alternation of metal parts, with repeated thermal expansion and contraction expanding assembly gaps. Optimize cooling pipeline layout to keep away from hot runner core sealing positions, ensuring hot runner operating temperature is not interfered by the mold cooling system. Check cavity pressure distribution: local air trapping causes sudden pressure rise, transmitting reverse pressure to the hot runner and triggering abnormal leakage. Reasonably arrange exhaust grooves to balance internal cavity pressure and reduce reverse pressure impact. For multi-cavity hot runners, check flow balance to prevent melt backflow and seepage from splitter plates due to unbalanced filling resistance.
Targeted Solutions for Different Leakage Positions
Adjust hot nozzle extension height and lower front-end temperature, reduce injection buffer pressure, polish fitting surfaces or replace worn hot nozzle heads to solve end leakage; replace new high-temperature resistant seals, grind splitter plate fitting surfaces and lock screws evenly to reduce internal melt accumulation pressure to eliminate splitter plate seepage; correct injection nozzle concentricity, trim spherical contact surfaces and clean internal cold materials to lower initial injection pressure and improve flange connection leakage; strengthen wiring sealing protection and lower ambient temperature to prevent melt seepage along line gaps, cleaning overflow materials timely to avoid circuit burnout; unify temperature and pressure parameters, stabilize injection pressure and standardize startup/shutdown holding procedures to eliminate intermittent leakage.
Daily Preventive Maintenance Key PointsRegularly inspect hot runner temperature curves and calibrate temperature control equipment daily, conducting comprehensive disassembly and maintenance every three months to clean carbon deposits and residual impurities in runners, replacing aging seals and heating elements in advance. Debug hot runner assembly dimensions before new molds are put into service, conducting low-pressure and low-speed trial operation to confirm no leakage before mass production. Select matching hot runner specifications according to raw material fluidity, using sealing-enhanced structures for high-fluidity materials. Establish a complete daily maintenance system to reduce downtime maintenance and ensure continuous and stable injection molding production.
