A screen changer is the filtration unit mounted between the extruder and the die. It removes contaminants from the polymer melt before they reach the product. The type you choose determines how often your line stops — and how much production you lose every year.
For a complete explanation of how melt filtration works, see our Polymer Melt Filtration guide.
A screen changer is a filtration device installed inline between the extruder barrel and the die head. Its primary function is to remove solid contaminants — carbonised polymer, gels, metal particles, paper, aluminium foil, and other foreign matter — from the polymer melt before it enters the die.
The filtration element itself is a wire mesh screen pack, typically made of stainless steel, rated from 20 mesh (840 μm) for coarse recycling applications to 400 mesh (37 μm) for fine fiber spinning. As the screen captures particles, differential pressure (ΔP) across the filter rises. The screen changer is the mechanism that replaces saturated screens — with or without stopping the extruder, depending on the type.
Beyond contamination removal, the screen changer plays a second critical role: melt pressure stability. A screen pack near saturation causes pressure spikes upstream that destabilise the bubble in blown film, create thickness variations in cast film, and generate surface defects in fiber and sheet. The filtration technology you choose directly determines how stable your melt pressure is — and therefore how consistent your product quality is. For a detailed technical comparison, see breaker plate vs screen changer.
Screen changers fall into two fundamental categories: discontinuous (line stops or pauses for screen replacement) and continuous (screen is replaced or cleaned while the line runs). The right choice depends on your contamination level, throughput, product quality requirements, and acceptable downtime.
| Type | Line during change | Changeover time | Melt pressure | Best for |
|---|---|---|---|---|
| Manual slide plate | Full stop required | 15–45 min | Unstable at saturation | Low-volume, clean resins, R&D lines |
| Hydraulic (discontinuous) | Brief flow interruption | Seconds–2 min | Pressure spike at swap | Medium lines, moderate contamination |
| Dual-bolt / double-slide | Partial flow maintained | <1 min | Moderate spike | Film and fiber, virgin polymer |
| Continuous (AP Series — self-cleaning) |
Line runs — no stop | Zero (continuous) | Stable | Film, fiber, sheet, coating |
| Automatic belt (GorillaBelt — recycling) |
Line runs — no stop | Zero (no line stop) | Stable, handles high ΔP | Post-consumer recycling, contaminated streams up to 10% |
| Laser melt filter (ScrapeAway — recycling) |
Line runs — no stop | Zero (no line stop) | Stable, continuous cleaning | Recycled melts with solid contaminants (elastomers, unmelted particles) |
For a detailed comparison of all types — including benchmarks and a decision framework — see the guide to continuous vs discontinuous screen changers →
ΔP is the operational signal that a screen pack needs replacement or cleaning. On a manual screen changer, the operator monitors upstream pressure: when it climbs beyond a set threshold, the line stops for a screen change. On a screen changer that keeps the line running, the ΔP signal shows when to clean or renew the filter: the screen is cleaned or advanced without interrupting melt flow.
The distinction matters for product quality. A manual system running a screen pack to near-saturation operates with rising and unstable melt pressure for much of each screen life cycle. A blown film line sees this as bubble instability; a cast film line sees it as gauge variation. A self-cleaning system maintains constant filtration area and therefore constant ΔP throughout operation — the AP Series keeps melt pressure stable during the cleaning cycle. For the complete engineering explanation of how differential pressure, screen packs, and contamination interact, see the guide to polymer melt filtration.
For a complete diagnostic guide to the causes of melt pressure variation, see melt pressure instability: causes and solutions →
Enter your throughput, change frequency, and shift schedule. With the Cofit Lost Production Calculator, calculate the production you lose every month and the annual revenue impact — in under two minutes.
The correct screen changer type is determined by four variables: contamination level of the incoming polymer, required filtration fineness, throughput rate, and product quality tolerance for pressure variation. Running the wrong type does not fail immediately — it erodes OEE (Overall Equipment Effectiveness) silently, through accumulated downtime, scrap, and quality rejects.
Among screen changers that keep the line running, three designs serve different application profiles. Self-cleaning cartridge systems — such as the AP Series — use a backflush of melt, activated by the operator through the flow valves, to clean the screen in place while melt flows through the alternate filtration path. The screen is never removed from the line; cleaning is activated by the operator with a key, without stopping the line. This design is suited to low-to-moderate contamination in film, fiber, sheet, and extrusion coating applications, where fine filtration fineness is required.
Automatic belt screen changers — such as the GorillaBelt — advance a filter belt automatically through the melt stream. As one section of belt becomes saturated, a fresh section advances. There is no cleaning cycle: saturated belt exits the melt zone and is replaced. This design handles contamination levels up to 10% by weight — the operating range that defines most post-consumer recycling streams — without pressure disturbance.
Scraping melt filters — such as ScrapeAway — keep the same filtering surface clean while it filters: fixed scrapers remove contaminants from two laser-drilled filter discs, and an automatic discharge system carries them out. This design is suited to recycled melts contaminated with elastomers, unmelted particles and other solid foreign matter, with filtration from 100 to 1,000 µm.
Not sure which design fits your process? Request a technical alignment.
Screen changers are used across all major thermoplastic extrusion processes. The filtration requirements — fineness, contamination tolerance, pressure stability — differ significantly between applications. Here is the engineering rationale for each.
The most demanding application for melt pressure stability. Gel particles at 100 μm and above cause pinholes and fish-eyes that fail optical testing. Continuous self-cleaning filtration is strongly recommended on all high-volume film lines. See the complete guide to blown film extrusion filtration →
Sub-70 μm filtration protects spinnerets from micro-contaminants that cause filament breaks. At 325–400 mesh, ΔP rises rapidly — continuous self-cleaning filtration is usually the preferred choice.
Post-consumer and post-industrial streams contain metal, paper, elastomers and cross-linked polymer, which saturate fine screens within minutes. GorillaBelt handles up to 10% contamination by weight without line stops; ScrapeAway continuously removes solid contaminants from laser-drilled filter discs.
Thermoforming sheet requires surface uniformity and consistent gauge. Gel inclusions cause optical defects and localised weak points in the finished part. 150–200 mesh filtration with stable pressure is the baseline specification.
Pipe extrusion tolerates brief pressure variations better than film, but potable water and gas pipe grades still require clean melt and consistent output. Screen changers at 80–150 mesh are standard; continuous systems eliminate gauge drift on long production runs.
Insulation continuity and coating adhesion require defect-free melt at the die. Contaminants cause voids, pin-holes, and coating breaks that fail electrical testing. Fine filtration at 150–250 mesh with continuous operation is the industry standard.
Factors that erode production on a manual screen changer line:
1. Multiple stops per shift for screen replacement
2. Pressure instability during restart (scrap generation)
3. Scrap during stabilisation phase after restart
4. Increased operator workload and intervention frequency
5. Lower annual sellable tonnage relative to nominal capacity
Use the Cofit Lost Production Calculator to quantify these losses for your specific line parameters — throughput, change frequency, shift schedule, and output value.
Cofit engineers screen changers for plastic extrusion that keep the line running. Three product families cover the full range, from fine-filtration film and fiber applications to contaminated and highly contaminated recycling streams.
Continuous filtration for blown film, cast film, stretch film, fiber spinning, sheet and extrusion coating. Self-cleaning cycle keeps melt pressure stable — no line stops for screen changes, no pressure spikes, no scrap at changeover.
Automatic belt filtration for post-consumer recycling, industrial waste, and highly contaminated polymer streams. Handles contamination levels up to 10% by weight — the operating range that saturates conventional screen changers. Belt advances automatically; no cleaning cycle, no pressure disturbance.
Continuous filtration for contaminated recycled melts. Two laser-drilled filter discs, fixed scrapers and an automatic discharge system remove contaminants without stopping the line, with filter discs that stay in service for weeks or months.
A manual screen changer requires the extruder to be stopped — or flow to be significantly reduced — to replace saturated screen packs. Each change takes 15–45 minutes and generates scrap during restart. An automatic or continuous screen changer replaces or cleans screens while the extruder runs, with no interruption to melt flow and no pressure spike. A continuous screen changer greatly reduces these stops: the filter is cleaned or renewed while the line keeps running. The AP Series self-cleaning design, the GorillaBelt automatic belt design and the ScrapeAway laser melt filter all keep the line running: it never stops for screen maintenance.
Post-consumer recyclate contains paper, aluminium foil, sand, metal fragments, cross-linked polymer, and rubber. For recycling applications Cofit offers two technologies: the GorillaBelt automatic belt screen changer, which advances fresh belt automatically through the melt zone as the saturated section exits, and the ScrapeAway laser melt filter, which scrapes contaminants off laser-drilled filter discs while it filters. The GorillaBelt handles contamination up to 10% by weight without pressure disturbance and without line stops, on LDPE, HDPE, PP and mixed polyolefin streams; ScrapeAway handles solid contaminants such as elastomers and unmelted particles, with melt loss below 1%. The right choice depends on material, contamination and target filtration: request a technical alignment.
For PET-specific recycling filtration requirements, see the complete guide to PET recycling filtration.
Yes — and this is often the higher-value benefit. Manual screen changers operating near saturation cause melt pressure instability that directly degrades product quality: bubble instability in blown film, gauge variation in cast film, filament breaks in fiber spinning, and surface defects in pipe and sheet. Continuous screen changers eliminate the saturation cycle entirely, maintaining stable ΔP throughout production. Upgrading from manual to continuous filtration usually reduces gel counts, improves film optical properties and reduces the reject rate from pressure-related defects — benefits that add to the reduced downtime.
Not sure which system you need? Read: Breaker plate vs screen changer →
Blown film applications: Blown Film Extrusion Filtration: The Complete Engineering Guide →
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