Die head leakage

Melt leaks from abnormal outlets such as die flange connections or temperature measurement holes. When this defect appears in extrusion molded products, it is usually closely related to process links such as die design, screw plastication state, cooling and sizing system, or haul-off stability. Persistence of the defect will lead to out-of-tolerance product dimensions, unqualified appearance, or decreased mechanical properties, increasing scrap rate and rework costs. Timely diagnosis and troubleshooting from both extrusion process parameters and equipment status are basic requirements for ensuring stable continuous production.

1. Mold/tooling factors: Poor sealing of the connecting flange between die and head. 2. Comprehensive factors: Fastening bolts loose or insufficient preload after thermal expansion and contraction. 3. Comprehensive factors: Gasket/seal ring aged or wrongly selected. 4. Cooling and sizing factors: The cooling rate and uniformity of extruded products determine crystallinity, internal stress level, and dimensional stability. Uneven cooling causes pipe ovality, profile deformation, and internal stress concentration; the cooling water circuit layout and water temperature control must be optimized.

1. Process parameter optimization and adjustment: Regularly check and tighten die connecting bolts (tighten to specified torque in hot state). 2. Mold/tooling improvement and maintenance: Replace damaged sealing gaskets/seal rings. 3. Equipment inspection and system maintenance: Select appropriate sealing material according to process temperature (such as high-temperature graphite gaskets). 4. Systematic troubleshooting method: Troubleshooting of extrusion problems follows the sequence "temperature → pressure → speed → die → cooling". First check and stabilize the temperature control of each zone, then observe die head pressure fluctuations to judge the feed and screen condition, next verify the matching relationship between screw rotation speed and haul-off speed, further check the condition of the die flow channel and sizing sleeve, and finally optimize the cooling water circuit and water temperature distribution. Change only one variable at a time to confirm the effect. 5. Preventive management: Establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify countermeasures as PFMEA control points. Establish a regular equipment maintenance system and implement life management for key tooling such as dies/spinnerets/calender rolls/coating heads.

This problem is a typical manifestation of die head leakage in extrusion molding. The core of the solution lies in eliminating the root cause of the defect through systematic optimization of process parameters (temperature, speed, pressure) and precision correction of the die/sizing system. It is recommended to start with parameter adjustment and gradually go deeper into the equipment and tooling levels.