Poor venting in feed section

Vent-type extruder shows material spewing at the vent port or low venting efficiency. 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. Equipment factors: First-stage screw conveying capacity too large causes the vent section to fill with melt. 2. Cooling/environmental factors: Vacuum pipeline at the vent port blocked. 3. Comprehensive factors: Unreasonable vent port design causes melt to block at the opening. 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: Adjust the conveying matching relationship between first-stage and second-stage screws. 2. Mold/tooling improvement and maintenance: Clean the vacuum pipeline. 3. Equipment inspection and system maintenance: Optimize vent port structure so it is not easily blocked by melt. 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 poor venting in feed section 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.