QINGDAO JBD MACHINERY CO.,LTD
How to Improve the Thickness Accuracy of a Blown Film Extrusion Line？
Jul 14, 2026
How to Improve the Thickness Accuracy of a Blown Film Extrusion Line？
Before implementing improvement measures, clarify the core factors triggering circumferential and longitudinal thickness deviation on blown film lines:
  1. Unstable melt output from screw pulsation, fluctuating feeding volume and inconsistent raw material melt index (MI)
  2. Uneven temperature distribution of extruder barrel and annular die, resulting in inconsistent melt viscosity around the die lip
  3. Unbalanced airflow of air ring, asymmetric bubble cooling speed and irregular bubble swing
  4. Die lip wear, blocked flow channels and uneven gap clearance around the die circumference
  5. Unstable traction speed, vibration of collapsing frame and unbalanced winding tension
  6. Lack of closed-loop thickness feedback control, relying entirely on manual visual adjustment

Part 1: Stabilize Raw Material & Feeding System to Eliminate Longitudinal Thickness Deviation

Longitudinal thickness fluctuation (thick/thin spots along film length) mostly originates from unstable melt supply, which can be solved via standardized material handling and feeding upgrades compatible with JBD extruders.

1. Strict Raw Material Consistency Control

  • Uniform raw material batches: Test melt index (MI) of each PE/LLDPE batch before production; mix new and recycled PCR plastic evenly to avoid viscosity fluctuation caused by inconsistent resin grades.
  • Full drying treatment: Dry recycled plastic flakes to moisture content below 0.05% to prevent bubble generation inside melt that disturbs stable extrusion output.
  • Precision filtration: Adopt multi-layer combined filter screens on JBD extruder heads to remove impurities blocking die micro-channels and local flow restriction.

2. Upgrade Gravimetric Feeding System (Recommended Core Upgrade)

Replace traditional volumetric feeders with loss-in-weight gravimetric feeders matched to JBD single-screw extruders. The Siemens PLC system synchronizes feeding speed with screw rotation speed, maintaining constant melt mass flow and eliminating periodic thickness variation caused by uneven feeding.

3. Install Precision Melt Gear Pump (Industry Standard High-Precision Upgrade)

Mount a melt pump between extruder screw outlet and annular die, a standard precision accessory supported by JBD’s equipment designpt.jbd-mac.... The gear pump isolates screw pressure pulsation, delivers linear stable melt flow to the die, and reduces longitudinal thickness deviation by over 60%. JBD’s full-line control system realizes linkage adjustment of screw speed and melt pump speed on the Siemens touchscreen.

Part 2: Optimize Extruder & Die Assembly to Reduce Circumferential Thickness Difference

Circumferential uneven thickness (striped thick/thin zones across film width) mainly comes from non-uniform melt distribution at the die lip; targeted mechanical and thermal optimization is required.

1. Precise Multi-Zone PID Temperature Control

All JBD extruders adopt independent multi-section PID heating modules with temperature fluctuation controlled within ±1~2°C, far lower than ordinary equipment’s ±5°C deviationpt.jbd-mac...:
  • Calibrate thermocouples of barrel, adapter and die regularly to eliminate temperature detection errors.
  • Balance heating power of each circumferential zone of the annular die; replace aging heating bands with uneven heat output that creates local high/low viscosity zones.
  • Set gradient temperature curve according to resin type: lower die lip temperature appropriately to reduce melt swelling difference around the circumference.

2. Maintain & Adjust Annular Die Lip Clearance

  • Regular cleaning: Remove carbonized plastic residue on die lips with soft copper scrapers; burnt material blocks melt flow and forms permanent thin film strips.
  • Fine-tune die adjusting screws: Equipped with 16–32 groups of micro-adjust screws on JBD spiral dies; evenly calibrate circumferential gaps after cleaning to keep tolerance within 0.01mm.
  • Select high-precision spiral flow channel die: JBD’s customized spiral die design realizes uniform melt shunting, effectively reducing natural circumferential flow deviation compared with straight manifold dies.

Part 3: Optimize Air Ring & Bubble Cooling System (Key for Uniform Film Solidification)

As the critical shaping link after die extrusion, unbalanced cooling airflow is the most overlooked cause of thickness inconsistency.

1. Ensure Air Ring Concentricity & Uniform Air Outlet Gap

  • Center the air ring and die strictly: Measure four-direction air gap between air ring inner wall and die with feeler gauges; gap deviation must be controlled below 0.5mm, otherwise asymmetric cooling will lead to bubble tilt and thickness stripes.
  • Clean air ring air ducts regularly: Remove dust and plastic powder blocking air outlets, which cause local insufficient cooling and inconsistent film draw-down ratio.

2. Upgrade Automatic Adjustable Dual-Layer Air Ring

Replace fixed air rings with JBD-supported automatic air rings with segmented airflow regulation. The Siemens control system receives thickness detection data and dynamically adjusts air volume of each air outlet zone in real time to balance circumferential cooling speed.

3. Equip Internal Bubble Cooling (IBC) System for Wide Film Lines

For wide-width blown film production, add an IBC internal cooling unit matched with JBD extruders. IBC stabilizes bubble internal air temperature and flow, eliminates bubble swing, and greatly improves circumferential thickness uniformity for films over 1200mm width.

Part 4: Add Closed-Loop Automatic Thickness Control System (Fundamental Intelligent Improvement)

Manual adjustment cannot respond to real-time thickness drift; closed-loop online detection + automatic correction is the ultimate solution for stable gauge accuracy, perfectly compatible with JBD Siemens SMART LINE control platform.

1. Install Online Thickness Gauge

Choose infrared or beta-ray thickness sensor installed above the collapsing frame, continuously scanning film circumferential thickness data in real time, and transmit deviation signals to the central PLC control cabinet.

2. Link Detection Data with Executing Components

The Siemens touchscreen of JBD equipment automatically processes thickness data and triggers synchronous correction actions:
  • If local thickness exceeds tolerance: Adjust corresponding air ring zone airflow or fine-tune die lip gap servo motors;
  • If overall longitudinal thickness drifts: Automatically fine-tune melt pump output and extruder screw speed;
  • For periodic bubble swing: Adjust traction rotating speed and IBC air flow parameters.

3. Equip Rotating Traction Unit

JBD’s optional rotating haul-off mechanism slowly rotates the film bubble horizontally during traction, evenly distributing circumferential thickness deviation across the whole roll and avoiding concentrated thick/thin strips on finished film rolls.

Part 5: Optimize Traction, Collapsing & Winding Auxiliary Equipment

Minor vibration and tension instability of downstream auxiliary equipment will amplify thickness deviation, requiring standardized daily calibration:
  1. Collapsing frame maintenance: Check bearing wear regularly to eliminate vibration that distorts bubble shape; keep herringbone plates horizontal and symmetric.
  2. Constant tension winding system: Adopt magnetic powder clutch tension control on JBD winding units to avoid film stretching (thinning) or loose wrinkling caused by fluctuating winding tension.
  3. Traction speed stabilization: Use variable frequency servo traction motors with speed fluctuation controlled within ±0.1m/min, matching melt pump delivery speed synchronously via PLC linkage.

Part 6: Standard Daily Operation & Maintenance SOP for Sustained Thickness Accuracy

Even with high-precision hardware, irregular maintenance will gradually deteriorate thickness consistency; formulate fixed operating procedures for JBD blown film lines:
  1. Pre-production calibration: Test die temperature, air ring concentricity and thickness sensor zero point before each startup; run 30min empty melt circulation to stabilize thermal field.
  2. Periodic disassembly maintenance: Clean extruder screw, adapter and die every 7–10 production days to remove carbon deposits affecting melt flow.
  3. Real-time parameter monitoring: Operators track melt pressure, barrel temperature and thickness curve on the Siemens touchscreen; adjust parameters immediately once deviation exceeds the preset threshold.
  4. Regular spare part replacement: Timely replace aging heating bands, worn screw flights and blocked air ring ducts to avoid gradual accuracy degradation.

Comprehensive Benefit Analysis of Thickness Accuracy Optimization for JBD Blown Film Lines

  1. Raw material savings: Stable thickness reduces film overdesign margin by 8–12%, cutting PE resin consumption per ton of finished products;
  2. Scrap rate reduction: Circumferential thickness deviation controlled within ±3μm lowers defective film waste by over 20%;
  3. Stable downstream processing: Uniform thickness improves printing, lamination and bag-making yield, enhancing customer order satisfaction;
  4. Extended equipment service life: Stable melt pressure and balanced cooling reduce screw, die and traction component wear frequency.


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