Excessive moisture content in raw material

A "crackling" sound is heard during extrusion, and the product shows bubbles, silver streaks, or surface water marks. 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. Material/formulation factors: Raw material storage environment humidity high. 2. Equipment factors: Drying equipment efficiency insufficient or drying time inadequate. 3. Material/formulation factors: Material re-absorbs moisture after drying. 4. Die design factors: The geometry of the die flow channel, the land length, and the outlet dimensions directly affect melt flow stability and product dimensional accuracy. Unreasonable flow channel design (presence of dead corners, excessively large convergence angle) is an important root cause of melt fracture, material buildup, and flow marks, and must be addressed starting from optimization of the die structure. 5. 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: Improve raw material storage conditions (sealing, dehumidification). 2. Mold/tooling improvement and maintenance: Ensure drying temperature and time meet material requirements (e.g., PET needs drying at 120-160℃ for 4-6h). 3. Equipment inspection and system maintenance: Use immediately after drying or store sealed temporarily; should not be exposed to air for a long time. 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 excessive moisture content in raw material 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.