Bamboo pattern / pulsating extrusion

Pipe or profile surfaces show periodic bamboo-like bulges or thickness fluctuations, with basically consistent bulge spacing, presenting a regular pulsed appearance. The essence of the bamboo pattern is periodic instability in the matching of extrusion and haul-off speeds, causing regular dimensional fluctuations along the longitudinal direction of the product. This defect is especially obvious in precision profiles and thin-walled pipes, seriously affecting dimensional accuracy and appearance quality.

1. Process parameter factors: Haul-off speed and extrusion speed do not match and fluctuate periodically. 2. Process parameter factors: Screw rotation speed fluctuation. 3. Equipment factors: Improper PID parameters for barrel temperature control cause periodic overshoot. 4. Operational factors: Uneven feeding in the feed section produces pulses. 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: Correct the haul-off-extrusion speed matching. 2. Mold/tooling improvement and maintenance: Check the stability of the screw motor and frequency converter. 3. Equipment inspection and system maintenance: Optimize temperature control PID parameters. 4. Material/formulation optimization: Check whether material discharge in the feed section is smooth. 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 the bamboo pattern is periodic instability in the matching of extrusion and haul-off speeds. The core of the solution is to eliminate speed fluctuation sources — stabilize the screw rotation speed transmission system, optimize the temperature control PID to eliminate periodic temperature overshoot, and ensure uniform feeding in the feed section.