Bridging / uneven feeding

Powder or granular material forms an arch-shaped cavity at the lower part of the hopper, and material cannot fall normally. 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: Material particle size distribution too wide causes increased friction between particles. 2. Comprehensive factors: Hopper cone angle too large. 3. Material/formulation factors: Material contains water or oil causing agglomeration. 4. Material/formulation factors: Hopper volume too small causes material compaction. 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: Select material with uniform particle size distribution. 2. Mold/tooling improvement and maintenance: Optimize hopper cone angle design (generally ≤60°). 3. Equipment inspection and system maintenance: Install an arch breaker/agitator or vibrator. 4. Material/formulation optimization: Control material moisture content and oil content. 5. Operating specifications and preventive measures: Appropriately increase the size of the hopper discharge opening.

This problem is a typical manifestation of bridging / uneven feeding 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.