How to calibrate a blown film machine if the herringbone clamp or traction roller is not aligned with the center of the machine head?

 

Principle of mechanical imbalance: In the production of blowing film, the alignment accuracy of herringbone fixture and the center line of traction roller directly influences the quality of film forming. When the deviation between the two and the center line of the die head exceeds 0.5mm, the film will produce obvious transverse stress during the tensile process. This uneven distribution of stress can lead to regular oscillations and, in severe cases, spiral distortion of the film bubble. Experimental data show that for every 1mm deviation, the transverse thickness fluctuation rate of the film increases by 12%-15%, which leads to the decrease of product qualification rate. In a certain company's production line, for example, the scrap rate due to center misalignment was as high as 18% before calibration and fell below 3% after calibration.
Typical Process Defects

1. Edge thickness anomaly: When the thickness difference the edges of the film is more than 15 microns, a "wavy edge" phenomenon occur during winding. This wavy edge deformation not only affects the appearance of the product, but also reduces subsequent sectioning efficiency by more than 30%.
2. Surface Stripe Defect: Uneven pressure of the traction rollers will cause longitudinal stripes on the film surface. This defect is especially evident in the production of transparent films, which leads directly to the downgrading of products.
3. Risk of membrane bubble rupture: Deviation of the angle of the herringbone clamp can lead to a decrease in membrane bubble stability. Statistics from one company show that for every additional degree of angle deviation, the rupture frequency increases by 300%, severely limiting continuity of production.

 

 

(I) Basic Calibration Process

Mechanical Centering Three-Step Method

1. Laser Positioning Benchmark Establishment: A high-precision laser tracker projects a vertical benchmark line at the machine head exit, with the error controlled within ±0.02mm/m. A company's practice shows that using this technology reduces center positioning time from 2 hours to 40 minutes.
2. Clamping Plate Angle Adjustment: Using the principle of pentaprism beam refraction, the opening angle of the herringbone clamping plate is adjusted to within the theoretical value of ±0.5°. Digital angle meter data shows that improved angle accuracy increases film bubble stability by 40%.
3. Roller Parallelism Detection: A multi-plane automatic rotating laser system is used to ensure that the deviation between the traction roller and the cooling air ring centerline is <0.1mm. After implementation on a production line, the transverse thickness uniformity of the film improved by 25%.

Dynamic Balance Verification
Running at rated speed for 30 minutes, an infrared thermal imager is used to monitor the roller surface temperature distribution; the temperature difference should be <2℃. Simultaneously, a tension sensor collects film running data to verify that the traction force fluctuation range is within ±2N. A company's verification showed that after achieving dynamic balance, the number of film breaks decreased by 75%.

(II) Specialized Calibration Technologies

Hinge Clamp Precision Adjustment

1. Angle Optimization: Dynamically adjust the clamp opening angle according to film specifications; 2-3° is recommended for LDPE film, and 3-5° for HDPE film. After implementing differentiated adjustment, a company expanded the product's adaptability range by 30%.
2. Contact Surface Treatment: Utilize nano-coating technology to reduce the coefficient of friction to 0.1-0.15, effectively reducing the risk of film bubble adhesion. Tests show that the continuous operating time of the equipment is extended by 2 times after coating treatment.

Traction Roller System Calibration

1. Pressure Equalization Adjustment: Configure a dual-channel pressure control system to ensure that the roller surface pressure difference is <0.5 bar. After improving pressure uniformity, the film surface roughness is reduced to below Ra0.5μm.
2. Speed ​​Synchronization Control: Employ a servo motor drive system, controlling speed fluctuations within ±0.5%. After implementation on a production line, the product length error rate decreased from 1.2% to 0.3%.

 

(I) Key Parameter Control Standards

Parameter Item	Technical Requirement	Detection Method	Acceptance Criterion
Centerline Deviation	≤0.1mm	Laser Interferometry	Average of three measurements ≤0.08mm
Splint Opening Angle	Theoretical Value ±0.5°	Digital Protractor	Display Fluctuation ≤0.3°
Roller Parallelism	≤0.05mm/m	Laser Tracking System	Maximum Deviation ≤0.04mm/m
Temperature Uniformity	Temperature Difference ≤2°C	Infrared Thermography	Difference between Highest and Lowest Temperature ≤1.8°C

 

(II) Addressing Frequently Asked Questions
Post-calibration Bubble Vibration

1. Airflow System Inspection: Use An anemometer to check wind speed differences of less than0.5 m/s between regions. Adjusted, one company saw a 60 percent 60% the bubble vibration amplitude.
2. Die Gap Optimization: Adjust to a range of 0.8 -1.2 mm to ensure uniform output >95%. The experimental results showed that the standard deviation of film thickness can be reduced by 40% by increasing gap accuracy.

Longitudinal Stripes on film

1. Roller Surface Accuracy Inspection: The surface roughness traction roller should be less than Ra0.8 μm. After ultra-precision machining, the stripe defect disappearance rate reached 90%.
2. Transmission System Overhaul: Gearbox backlash was controlled between 0.05 and0.1mm. After repairs, one company found the incidence of stripes dropped from 15% to 2%.

 

Film Quality Inspection

1. Thickness Measurement: continuous collection of 100m film data using an online thickness gauge; standard deviation should be less than 1.5 microns. A company verification showed that the calibrated thickness fluctuation range narrowed to ±0.8μm.
2. Tensile strength test: test according to GB/T 1040.3 standard with the longitudinal/transverse strength ratio of 1:1.1-1:1.3. Tests showed that products that met the criteria improved tear resistance by 25%.

Equipment operation monitoring

• Continuous operation test: less than one rupture of membrane shall be recorded within 24 hours. After one production line was implemented, 72 hours of continuous trouble-free operation was achieved.
• Energy Consumption Monitoring: energy consumption per unit of product decreased by 8%-12% compared to pre-calibration, and one enterprise saved more than half a million yuan a year in electricity costs.

 

Regular Calibration Cycle

1. Daily Inspection: Check the centerline reference mark every shift, using a laser level for rapid verification.
2. Periodic Calibration: Perform a comprehensive calibration every 500 production hours, focusing on checking the wear of vulnerable components.
3. Overhaul Calibration: Perform precision calibration every 2000 production hours, replacing key transmission components and readjusting mechanical precision.

Digital Maintenance System

1. IoT Sensor Network: Real-time monitoring of roller vibration spectrum, with an abnormal vibration early warning accuracy rate of 95%.
2. Equipment Health Record: Utilizing big data analysis to predict calibration needs; one company's predictive maintenance increased equipment utilization by 18%.
3. AR Assistance System: Remote expert guidance via smart glasses reduces calibration time by 40% and increases operational accuracy to 99%.

This technology system has been applied by several leading companies in various industries. Practice shows that after implementing systematic calibration, the overall equipment efficiency (OEE) increases by 25%-30%, the first-pass yield rate increases to over 98.5%, and annual maintenance costs decrease by 40%. It is recommended that companies establish standardized calibration operation manuals based on the characteristics of their own equipment, and conduct regular skills certification for operators to ensure consistent and stable calibration quality. Through the deep integration of digital technologies and traditional processes, blown film production is moving towards a higher-precision intelligent manufacturing era.