Vacuum sizing section blockage

Scale or impurities accumulate in the vacuum sizing tank causing cooling water holes or vacuum holes to block. 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. Cooling/environmental factors: Cooling water hardness too high produces scale. 2. Mold/tooling factors: Product surface precipitates or release agents deposit in the sizing section. 3. Cooling/environmental factors: Microbial growth in cooling water. 4. Operational factors: Not cleaned and maintained on schedule. 5. 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.

1. Process parameter optimization and adjustment: Use softened water or deionized water as cooling water. 2. Mold/tooling improvement and maintenance: Regularly clean the vacuum sizing section. 3. Equipment inspection and system maintenance: Add cooling water treatment agents (scale inhibitors, biocides). 4. Material/formulation optimization: Establish a regular maintenance system. 6. 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 vacuum sizing section blockage 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.