Complete Solution to Eliminate Stringing on Female Groove of PVC Wall Panels

(Practical priority: Adjust process first → Modify formula second → Repair mold last)

I. Quick Emergency Adjustments

No formula change or mold disassembly required; immediate results, priority operation

1. Precise Zoned Mold Temperature Control (Simplest Operation)

1. Independently lower the temperature of female groove die lip by 5~10℃. The female groove is the high-incidence area of stringing. Excessively high temperature causes massive lubricant precipitation; keep the temperature of main panel unchanged to ensure proper plasticization.

2. The overall die head temperature shall not exceed 175℃. For Ca-Zn stabilization system, control at 165-172℃; local overheating of female groove is strictly prohibited.

3. If carbon deposits or wax buildup form on the die lip, gently clean the corners of female groove with a copper shovel. Wire brushes are forbidden to avoid scratching the polished mold surface.

2. Matching Extrusion and Haul-off Speed

1. Reduce haul-off speed by 10%~15% appropriately to lower stretching of melt, preventing soft material at female groove corners from being pulled into fine filaments.

2. Stabilize screw speed to avoid uneven output caused by fluctuating rotation, which leads to accumulated melt and stringing.

3. Slightly reduce back pressure by 5~10 bar to cut down shear heat generated by screw and mitigate high-temperature precipitation of additives.

3. Optimization of Calibration & Cooling System (For Wax Precipitation & Condensation Stringing)

1. Increase cooling water flow of calibrator and control water temperature below 20℃. Install independent side spray pipes at female groove position to rapidly cool the buckle area.

2. Raise calibration vacuum properly. Insufficient vacuum causes profile shaking and friction stringing on female groove; excessive vacuum shall be avoided to prevent female groove deformation.

3. Widen the distance between die head and calibrator sleeve by 5~10mm for slight pre-cooling of melt before calibration, reducing wax condensation and mold adhesion.

4. Raw Material Moisture Control

After high-speed mixing, fully cool the powder to below 40℃ before feeding. Pre-dry damp calcium powder and recycled materials, as water vapor will carry lubricants to adhere to die lip and form filaments.

II. Formula Adjustment (Fundamental Solution)

80% production line stringing issues stem from unbalanced lubrication

1. Optimize External Lubricants (Core Modification)

1. Cut the dosage of low-melting paraffin wax and stearic acid by 0.2~0.5 parts. Such small-molecule substances easily precipitate and stick to molds.

2. Replace partial short-chain external lubricants with macromolecular ester lubricants and PE wax (high molecular polyethylene wax), which feature better compatibility and less precipitation under high temperature.

3. For high calcium-filled formula: add 0.3~0.6 parts internal lubricant (glyceryl monostearate, G60) to fully wet calcium carbonate and avoid wax filaments brought out by exposed fillers.

2. Stabilizer System Modification

Ca-Zn stabilizers are prone to precipitation. A small amount of epoxidized soybean oil can be added to restrain bleed-out of low-molecular components.

Do not arbitrarily increase stearic acid as auxiliary stabilizer, which will worsen stringing.

3. Improve Melt Strength to Reduce Stretch-induced Filaments

1. Add 0.5~1 part ACR foaming regulator / impact modifier ACR to enhance melt toughness, so the melt will not break into fine fuzz under stretching.

2. Limit recycled material addition within 15%. Accumulated additives in recycled materials easily cause precipitation and stringing.

4. Auxiliary Improvement

Add 0.1~0.2 parts anti-bleeding additive to block the migration of lubricants to mold surface.

III. Mold Renovation (Long-term Fundamental Solution for Structural Defects of Female Groove)

Carry out this step if process and formula adjustments fail to solve the problem

1. Chamfer female groove edges: convert sharp right angles to R0.3~R0.5 rounded corners to eliminate high-shear dead zones and reduce material adhesion.

2. Repolish female groove die lip to mirror finish, remove scratches and pits to eliminate material sticking points.

3. Fine-tune flow channel clearance of female groove: narrow die lip clearance slightly if material output at female groove is too thick, ensuring uniform extrusion speed of the whole panel and avoiding stringing from local overflow.

4. Clean dead zones of die head flow channel and polish accumulated material grooves to prevent long-term retention, decomposition and precipitation of small-molecule additives.

IV. Daily Production Maintenance & Prevention

1. Clean the mold with PVC purging compound for 5-10 minutes before shutdown per shift to wash away wax buildup on die lip.

2. Disassemble and clean die head every 3~7 days to thoroughly remove carbon deposits and precipitated wax layer on female groove.

3. Standard mixing process: discharge materials from high-speed mixer at 110~120℃, complete full cooling mixing for even lubricant distribution and avoid local excessive lubrication.

4. Avoid long-term overloaded high-speed production, as continuous high temperature will accelerate lubricant precipitation.

Simple Troubleshooting Sequence (On-site Quick Operation Flow)

1. Remove wax deposits on female groove die lip → Lower female groove temperature, strengthen calibration cooling, slow down haul-off speed (Visible improvement within 10 minutes)

2. If ineffective, adjust formula: reduce paraffin wax, replace with high molecular PE wax, supplement internal lubricants

3. For recurring long-term defects: renovate mold with rounded corners and re-polish female groove