Die buildup / die lip buildup

Melt residue gradually accumulates at the die outlet; initially a thin layer of adhesion, it gradually thickens over time and eventually falls off as irregular lumps embedded in the product surface, forming surface black spots or raised defects. Die buildup (die lip buildup) is a common problem in long-term continuous extrusion production, and is more likely to occur especially when processing formulations containing large amounts of additives. The buildup shedding cycle ranges from several hours to several days, seriously affecting product appearance consistency.

1. Mold/tooling factors: Die temperature too high causes material degradation and coking. 2. Mold/tooling factors: Small molecular substances or additives in the raw material precipitate at the die lip. 3. Mold/tooling factors: Unreasonable die outlet flow channel design causes dead corner retention. 4. Mold/tooling factors: Melt residence time in the die too long. 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: Appropriately reduce die temperature. 2. Mold/tooling improvement and maintenance: Check the small-molecule additive formulation in the raw material. 3. Equipment inspection and system maintenance: Optimize die flow channel design to eliminate dead corners. 4. Material/formulation optimization: Regularly clean the die and apply coating treatment to reduce adhesion. 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.

The essence of die buildup is the precipitation, adhesion, and accumulation of low-molecular substances and degradation products in the melt at the die outlet. The core of the solution is "cool down + clean die + optimize formulation": appropriately reduce die temperature to reduce precipitation drive, regularly clean the die to keep the outlet smooth, and optimize the formulation to reduce low-molecular additive content.