Polymer Melt Filter Cleaning Best Practices

Clean and reuse polymer melt filter with proper cleaning 

In polymer manufacturing, filter performance is only as reliable as its maintenance routine. You can choose the right filter media and fine-tune your system, but long-term performance still comes down to one thing: cleaning. 

Effective cleaning helps maintain melt purity, reduce downtime and extend the life of your polymer melt filter inserts. If you're processing high-value polymers like polycarbonate, polyamide or other highly engineered plastics, proper cleaning can mean the difference between smooth production and ongoing problems. 

Why filter cleaning matters

Polymer melt filtration is critical in removing gels, black spots, unmelted particles and other impurities that compromise end-product quality. But filtration isn’t just about the filter; it’s about the entire system. Treat cleaning as a strategic process. not just a reactive maintenance task, because it plays a core role in system performance. 

Cleaning a polymer melt filter regularly and correctly can: 

• Maintain melt purity and process stability 
• Prevent unplanned shutdowns and production losses 
• Reduce operating costs over time 
• Extend the service life of the reusable polymer candle filter  

John Crane’s Seebach® large area filter, replaceable filter element; metal fibre fleece media 

Additionally, a structured cleaning programme should include inspection, testing and data collection to verify performance after cleaning and allow the user to individually track cleaning performance. These measures help identify when a filter has reached the end of its useful life and ensure only effective filters go back into operation. 

Cleaning is a notable ongoing cost in polymer production, so choosing polymer melt filters that can withstand repeated cleaning cycles becomes a crucial selection criterion. 

The role of reusability in stainless-steel filter media

Stainless-steel filter elements are widely used in polymer melt filtration. These include wire mesh, mesh laminates and fibre fleece, all known for their durability under high-temperature, high-pressure and chemically aggressive conditions. One of the greatest advantages of stainless steel polymer filter candles is that they can be cleaned and reused multiple times, delivering operational and environmental benefits. 

John Crane’s Seebach® Candle Filter  

Key benefits of reusability include: 

• Reduced waste: Reusing filters decreases the volume of spent filters sent to landfill or recycling 
• Lower total cost of ownership: Fewer replacements and longer service intervals reduce long-term costs 
• Less downtime: Reusable filters, paired with the right cleaning strategy, enable faster changeouts and more reliable operation 

Industries such as PA, PET, PC polypropylene, polyester fibres and film manufacturing can especially benefit from the high thermal and mechanical tolerance of stainless-steel filters. 

Standard cleaning methods for melt filters

No single cleaning method suits every situation. The choice of method depends on the polymer type, filter media, and the type and extent of contamination, especially for high-value polymer melt filter systems. Below are the most common cleaning methods for polymer melt filters: 

• Thermal cleaning 
  Thermal techniques like furnace or fluidised bed cleaning are widely used to remove residual polymer. The high temperatures in the absence of oxygen and sometimes using overheated steam, which acts as a solvent, degrade and depolymerise built-up material without damaging stainless-steel structures. The filter media limits the maximum temperature exposure, which usually should not exceed 380°C 
  
  • Suitable for metal mesh and laminates 
  • Efficient for polymers that degrade cleanly with heat 
  • Ideal for filters with high thermal stability
  • In combination with steam preferable for any polymer made by polycondensation 

• Solvent-based cleaning 
  Solvent cleaning can be a viable alternative for polymers that don’t fully degrade with heat. This method uses chemical solvents to dissolve residue, but it requires carefully matching the solvent type to the polymer and the filter material. 
  • Effective for stubborn or low-temperature polymers 
  • Least stress inducing method to remove organic impurities  
  • Operators must handle and dispose of solvents in line with safety and environmental regulations. 
     
• Ultrasonic cleaning 
  Ultrasonic baths use high-frequency sound waves to dislodge contaminants from fine or pleated filter surfaces. This method protects delicate geometries that physical scrubbing might damage. 
  • Non-invasive and thorough 
  • Can be combined with solvent, heat and pressure 
  • Best for precision filters with tight pore size control 
  • Requires pre-cleaning for heavily fouled filters 
  • Least stressful method to filter media and less likely to accelerate wear 
     
• Mechanical or manual cleaning 
  It is necessary, prior to passivation, drying and quality control (weight/tightness), to eliminate inorganic impurities such as extruder barrel abrasion, sand, dust, black spots, etc. The most common method is high-pressure washing from multiple directions, where the filter element setup can be adjusted to optimise the accessibility of the core media. In some cases, manual cleaning may be applied to rugged stainless-steel mesh. However, this method risks deforming the filter structure and altering pore size, especially when performed without proper training or tools. 
  
  • Should only be used when other methods are not an option 
  • Risk of damaging filter integrity is high 
  • Not recommended for sintered or pleated media 

Matching the cleaning method to filter media

Not all filters can withstand all cleaning methods. Effective cleaning must preserve three critical properties: 

• Pore size uniformity: Consistent filtration performance depends on maintaining precise pore dimensions 
• Layer bonding: Crucial in sintered or laminated filter media, where bonded layers and fibers give the filter its strength and integrity 
• Mechanical strength and dimensional stability: Cleaning should not warp, compress or thin the media, which could lead to performance degradation or failure 

This is why matching the cleaning method to the filter design is so important. For example, polymer candle filters must maintain structural integrity during cleaning to ensure continued performance and allow for repeated use.  

Cleaning frequency and system design considerations

No universal rule exists for how often to clean a polymer melt filter. Instead, the cleaning frequency depends on the specifics of your process. Factors that influence cleaning intervals include: 

• Polymer type and its contamination load 
• Melt flow rate and viscosity 
• Filter area and system configuration 
• Process requirements 

Advanced system designs, such as duplex or multi-bank filtration systems, enable one filter to remain in service while the other is cleaned. These setups offer: 

• Continuous operation: No need to halt production during cleaning 
• Improved reliability: Avoidance of process interruptions or melt degradation due to clogged filters 

Operators should monitor specific performance indicators to determine when a filter should be cleaned. These include: 

• Rising differential pressure (ΔP): A sign of clogging or reduced flow compensated by increasing rpm in extruders or gear pumps 
• Decreasing flow rate: Suggests the filter is nearing blockage 
• Changes in melt clarity or product quality: Indicates accumulated contaminants such as gels 

Key indicators of filter element condition

Knowing when to retire or reclean a polymer candle filter depends on a few simple tests and observations: 

• Weight loss/gain: A filter that weighs less after cleaning may have lost material or structure. An element that gained weight might have accumulated ashes or mineral impurities that can no longer be washed out. 
• Bubble point or 10 lpm test failure: Indicates filter media perforation by mechanical damage and/or the presence of large or inconsistent pores. Increasing bubble point results after a cleaning cycle can indicate dirt accumulation or filter media compression during the process. 

Remove filters that fail these checks to protect downstream equipment and product quality. 

Cleaning efficiency and its impact

Cleaning effectiveness has a direct impact on: 

• Filter onstream life: Well-cleaned filters last longer and require less frequent changeouts 
• Product consistency: Clean filters maintain melt purity and prevent defects 
• Resource use: Efficient cleaning means fewer chemicals, less labour and reduced energy costs 

Inadequate cleaning shortens filter life and can increase scrap rates, affect equipment performance and drive up operating costs. 

Cleaning as a core reliability strategy

Too often, teams treat cleaning as a reactive task, done only when something goes wrong. However, cleaning should be part of a proactive maintenance strategy in high-performance polymer filtration systems. 

A well-defined cleaning programme does more than protect your filters: 

• Improves product quality by ensuring consistent melt purity 
• Extends equipment life by preventing irreversible fouling or deformation 
• Supports ESG goals by reducing waste and resource use 
• Lowers operating cost through fewer filter replacements and line stoppages 

When paired with the right filter design and system layout, frequent and planned high-performing cleaning supports the plant’s reliability and consistent production quality. 

John Crane's role in polymer melt filter reliability

John Crane designs filtration solutions that are easy to clean and built for repeated use. Our depth filters, metal mesh laminates and pleated fleece elements, including polymer candle and leaf disc filters, offer high thermal and mechanical durability, making them suitable for repeated cleaning cycles. 

With application-specific engineering support, our filters help maintain uptime and melt quality. When cleaning methods align with filter media and system design, manufacturers can extend filter life, reduce downtime and build a more sustainable, cost-effective process. 

Want to learn more about polymer filtration best practices? 
Explore our related blogs on selecting stainless-steel media and tailoring filter performance through pore size and porosity. 

Part 1: Polymer melt filter optimisation

Part 2: Polymer melt filter optimisation