Common Causes of Material Leakage on Plastic Extruder Screen Changer

1. Damaged & Failed Sealing Parts (Most Frequent Issue)

1. The PTFE/FKM O-rings or packing gaskets are aged, carbonized under high temperature or cracked. Long-term operation above 200°C hardens rubber seals and eliminates elasticity; seals wear out much faster during recycled plastic processing.

2. Seals are installed crookedly, squeezed and cut during sliding plate feeding, leaving gaps for melt leakage.

3. Carbon deposits, burnt plastic residues or metal burrs left inside seal grooves prevent full surface contact between fitting faces.

2. Improper Assembly of Screen Pack & Breaker Plate

1. The outer diameter of the screen stack exceeds the breaker plate size. Woven wire mesh gets clamped between sealing surfaces and creates persistent gaps.

2. The screen pack is misplaced or sticks out on one side, propping up the sliding plate and causing uneven compression.

3. Uneven thickness of multi-layer screens creates bulges, leading to loose sealing pressure on partial areas.

3. Insufficient Clamping Force from Hydraulic System

1. Hydraulic station pressure is set too low. The sliding plate slightly backs off when melt pressure rises, resulting in slow leakage or burst spillage.

2. Oil cylinder leakage, internal valve leakage or pipeline pressure loss weakens pressure holding capacity; clamping pressure drops gradually during production.

3. For bolt-type manual screen changers: Bolts are not tightened evenly diagonally, leading to inadequate compression on one side.

4. Scratched or Deformed Fitting Surfaces of Sliding Plate & Base

1. Hard impurities and broken metal wires score or pit the sliding plate’s sealing face; tiny grooves cannot be fully sealed.

2. Long-term unilateral stress warps the sliding plate and exceeds flatness tolerance, resulting in partial poor contact.

3. Knocks and abrasions create chipped edges on the breaker plate outer circle, destabilizing support and forming gaps.

5. Abnormal Melt Pressure & Processing Temperature

1. Extruder head pressure exceeds the rated pressure of the screen changer, pushing melt through micro gaps.

2. Overheating reduces melt viscosity. Low-viscosity materials like PE and EVA easily seep through tiny clearances.

3. Rapid temperature rise causes uneven thermal expansion of sealing components, temporarily widening gaps.

6. Operational Errors During Screen Replacement

1. Production starts before the sliding plate is fully pushed into position and locked firmly, which often triggers sudden massive melt ejection.

2. Large burnt plastic lumps remain in flow channels after cleaning, jacking up the sliding plate and forming clearance gaps.

3. Frequent rapid screen changes accelerate seal aging due to repeated drastic temperature fluctuations.

7. Long-term Equipment Wear

1. Excessive clearance of sliding rails makes the plate swing left and right, leading to misalignment after locking.

2. Loose bolts connecting the screen changer flange and extruder head shift overall stress distribution.

Quick Troubleshooting Sequence

1. Check hydraulic clamping pressure first

2. Inspect O-rings for damage and carbon buildup in seal grooves

3. Verify whether the screen pack is oversized or offset

4. Check sliding plate sealing face for scratches and pits

5. Conduct a trial run with reduced head melt pressure to rule out overpressure

Professional Glossary for Foreign Trade

• material leakage:

• FKM / PTFE sealing O-ring

• insufficient hydraulic pressure

• scratched sliding plate

• offset screen pack

• carbon buildup in seal groove

• excessive melt pressure

• breaker plate

• sliding plate screen changer