Screen Changers in Film Extrusion

In a film extrusion production line, the screen changer is a core piece of equipment that ensures product quality and production stability, and its selection requires comprehensive consideration of process requirements, material properties, and cost budgets. The following is a detailed analysis:

I. Core Requirements for Screen Changers in Film Extrusion

1. Continuous Production Stability

Film production is sensitive to melt pressure fluctuations, necessitating the avoidance of issues such as film breakage and uneven thickness. Continuous screen changers (e.g., dual-column screen changers) enable screen changes without machine shutdown, controlling pressure fluctuations within ±2 MPa to ensure product stability.

2. Filtration Precision and Efficiency

High transparency requirements for films necessitate the filtration of minute impurities. It is recommended to use screens with over 200 mesh, combined with multi-layer gradient structured screens (e.g., sintered metal fiber screens), achieving an initial filtration precision of up to 40 μm and enhancing anti-pollution capability by 300%.

3. High-Temperature and High-Pressure Resistance

Film extrusion temperatures typically range from 200°C to 280°C, requiring screen changers to withstand temperatures ≥300°C and pressures of 25-30 MPa. For instance, hydraulic column-type continuous screen changers, employing nitrided alloy steel, can endure high-temperature and high-pressure conditions.

II. Recommended Types of Screen Changers for Film Extrusion Production Lines

Advantages:

Dual-station alternating operation allows one screen to filter while the other is being changed, ensuring uninterrupted material flow.

Hydraulic-driven screen changing speed ≤0.3 seconds, with minimal pressure fluctuations, suitable for high-speed film production lines (e.g., BOPP, BOPET).

Integrated backflushing function extends screen lifespan to over 100 uses, reducing replacement frequency.

Application Example:

After adopting a hydraulic dual-column screen changer, film thickness tolerance was reduced from ±5% to ±1.5%, with a 40% decrease in waste rate.

2. Belt-Type Fully Automatic Screen Changer (High-End Scenarios)

Advantages:

Screen length up to 20 meters, enabling continuous screen changing driven by pressure, without manual intervention.

Suitable for long-process film production (e.g., cast films, optical fiber coatings), with material flow fluctuations<0.5 MPa during screen changes.

Water-cooled sealing design reduces raw material waste, achieving an energy savings rate of 15%.

Technical Parameters:

Temperature resistance: ≤350°C

Pressure resistance: ≤40 MPa

Adjustable screen mesh: 100-500 mesh

3. Hydraulic Backflushing Screen Changer (High-Contamination Conditions)

Advantages:

Online backflushing technology maintains 75% of the filtration area operational during screen changes, with nearly zero pressure fluctuations.

Dual-column four-station design provides a larger filtration area, suitable for recycled material or highly filled film production.

Applicable Scenarios:

Recycled PE film production lines with high impurity content and screen clogging.

High-capacity production lines requiring frequent screen changes (e.g., annual output of ten thousand tons).

By scientifically selecting and reasonably applying screen changers, the stability and product quality of film extrusion production lines can be significantly enhanced, while reducing energy consumption and maintenance costs.