Uneven coextrusion layer thickness

Interlayer separation and delamination occur in multilayer coextruded products, interlayer adhesion strength is insufficient, and peel force tests are below standard required values. Poor coextrusion interlayer adhesion can occur in multilayer pipes (such as PE-aluminum-PE composite pipes), multilayer films, and composite sheets. Interlayer separation causes the product to lose the design function of the composite structure — barrier layer failure, reinforcement layer detachment, adhesive layer cracking, and the overall performance of the product drops significantly.

1. Process parameter factors: Unstable control of the extrusion output ratio of each layer's extruder. 2. Mold/tooling factors: Die flow channel design causes uneven melt distribution of each layer. 3. Process parameter factors: Viscosity differences of each layer's material cause inconsistent flow front speeds. 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: Stabilize extrusion output and pressure of each layer's extruder. 2. Mold/tooling improvement and maintenance: Optimize flow channel geometric parameters of each layer in the die. 3. Equipment inspection and system maintenance: Adjust each layer's material viscosity so their rheology is close at coextrusion temperature. 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 uneven coextrusion layer thickness 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.