Non-Stop Melt Filtration & Screen Change Management for Recycled and Highly Filled Pelletizing Lines

On any pelletizing line the screen changer sits between the extruder outlet and the die head, and it is the last barrier the melt passes before it becomes pellets. Everything the extruder carried this far — printing ink and paper fibres from baled film, sand and stone dust from raffia bales, metal particles, cross-linked gels, carbonised polymer from dead spots in the barrel, filler grit and agglomerates from mineral-loaded recipes — is either caught on the screen pack or passes straight into the product.

What passes never stays hidden. Film customers see it as pinholes and specks, tape lines feel it as breaks on the loom, and every one of those complaints is traced back to a screen that was asked to work one change longer than it should have. Meanwhile the pressure across a loaded pack keeps climbing, and the difference between a routine plate shift and a burst screen is usually nothing more than when somebody decided to act.

This solution turns that decision into a set point. A hydraulic plate-type screen changer is installed between the extruder and the die on a machined adapter, melt pressure is measured on both sides of the pack, and the crew shifts plates at the set differential instead of waiting for trouble — one plate filters while the other is cleaned and repacked. The result is a filtration routine that takes minutes, keeps the melt moving, produces a record of screen consumption per tonne, and takes pellet cleanliness out of the hands of whoever happens to be on shift.

The problem

What the section changes

Keeps melt filtration from setting the pace of production on contaminated recycled and highly filled melts: screens are changed hydraulically at a set differential pressure instead of during a line stop, so die pressure stays steady and pellet quality does not depend on one operator's timing.

Where the customer starts

Plants pelletizing baled post-consumer film, woven raffia or mineral-filled recipes usually run some form of manually changed screen arrangement between the extruder and the die. The crew eases output or stops the line, opens the hot changer, digs out the loaded screen pack and restarts — on feed whose contamination changes from bale to bale, so the interval between changes is never quite predictable. Under production pressure, changes get deferred: upstream melt pressure climbs while the pack loads, die pressure starts to swing, and the line either trips on high pressure or lets contamination through into pellets that film and tape customers reject on sight.

Plants that change screens early instead pay a different way — polymer lost with every change, time lost on every restart, and screens consumed faster than anyone can account for.

Why the problem happens

As the screen pack traps paper fibres, printing ink residues, sand and stone dust, wood fibres, metal particles, gels and carbonised polymer, the pressure drop across it rises. A plate-type changer holds its plates closed against melt pressure; run too far past the intended change point, the pack deforms or the melt finds its way past the sealing faces, and what should have been a routine change becomes a leak or a burst that stops the line for a whole shift.

The damage before that point is quieter: die pressure that wanders as the pack loads shows up as pellet length and shape variation, and contamination that passes a loaded or torn pack becomes specks and pinholes in the customer’s film. On highly filled recipes the mechanism is harder still — coarse mineral particles and coating residues abrade the pack, so screen life is shorter and the change discipline matters more, not less.

Target output or state

Filtration that runs on records instead of nerve: plates shifted at a defined differential pressure, melt flowing through the shift, die pressure held inside the band agreed at commissioning, screen consumption becoming a number per tonne that the plant can plan and budget, and spent screens leaving the line through a safe, repeatable routine.

Process

The steps, in the order the material flows

Melt transfer from extruder to changer

Carries the melt from the extruder outlet straight into the heated changer body, so the polymer never leaves its process temperature window between barrel and die.

Role of the equipment
A flange adapter machined to the customer’s existing extruder outlet; the changer body carries its own heater zones matched to the line’s temperature controller.
Filtration on the active plate

Holds back paper fibres, ink residues, sand and stone dust, metal particles, gels, carbonised polymer and filler grit before the die, on the plate that is in the filtering position.

Role of the equipment
A screen pack specified per product grade — mesh count and layering chosen at order stage — carried on a plate that seals against melt pressure while its pair is being serviced.
Change-point monitoring and plate shift

Turns the change decision into a set point: when the pressure difference across the pack reaches the agreed value, the plates are swapped with the melt flowing, instead of the line being stopped to change a screen.

Role of the equipment
Pressure transducers upstream and downstream of the pack feed the local indication, and the hydraulic pack shifts the fresh plate into position in minutes under line pressure.
Seal and pressure check after the shift

Confirms, hot, that no melt is passing the sealing faces after a shift, and that die pressure has returned to its normal band before the line is called back to full rate.

Role of the equipment
A short purge and a visual and pressure check written into the shift procedure; heater zones hold the body at process temperature throughout.
Spent screen handling and pack preparation

Gets the loaded pack off the line safely and the fresh pack ready, so the next shift is a routine task rather than an improvisation.

Role of the equipment
A working position beside the changer, a covered bin for hot spent screens, and a consumption log that turns screen use into a number per tonne.

Material

What goes in, what comes out

Feed condition and requirements

Polymer melt at the extruder outlet, inside the grade’s temperature window, carrying the contamination profile of the feed — printing ink, paper fibres and stone dust on raffia and film lines; filler grit and coating residues on mineral-filled lines. Upstream separation and washing, where they exist, are part of the customer’s front end and stay there.

Output condition and boundaries

Filtered melt delivered to the die head at a stable pressure, with pellets free of the contamination classes named in the acceptance criteria, and a pressure record that shows every plate shift was made before the melt reached the alarm band.

Basis for the capacity figures

A screen changer is sized to the line it serves — the extruder’s output and the head pressure the recipes run at — not to the plant’s annual tonnage. Model size and plate count are fixed once the customer confirms the extruder interface, the grades to be run and the contamination they carry; no catalogue figure is quoted until then.

Fit

Where this section belongs — and where it does not

Suitable when

Recycling pelletizing lines on printed film, woven raffia and mixed polyolefin feed, where contamination arrives with the bales and screen loads are real. Highly filled masterbatch and compounding lines, where grit and agglomerates load packs quickly while film-grade cleanliness is still expected. Any line where a stop for screens interrupts a production plan the rest of the plant depends on.

Not suitable when

Virgin, single-grade lines whose melt is clean enough that screens load slowly — for them a simple manual changer and a calm change routine can be the more economical answer, and this system would be bought to solve a problem that does not exist. Lines expecting the changer to remove dissolved odour or volatiles — that is a venting and deodorization task served by different equipment. And lines whose upstream sorting still lets metal reach the extruder — no screen pack is a substitute for front-end separation.

Conditions still to be confirmed

The customer’s extruder outlet and die head are measured before the adapter is made. The screen pack specification — mesh count and layering — is fixed per product grade at order stage, and the change point is set from the line’s own pressure behaviour at commissioning. Screens, seals and heater cartridges are budgeted by the customer as consumable wear parts.

Site and connections

What the section assumes around it

Utilities

Power supply: Hydraulic power pack and body heaters fed from the plant's three-phase supply; voltage and frequency follow the plant standard and are confirmed at order.
Water: Not required by the standard hydraulic changer.
Compressed air: Only where pneumatic-assist options are selected; confirmed per order.
Exhaust and ventilation: No exhaust of its own beyond the normal ventilation of the extruder area.

Spent screens and the polymer they carry are hot and contaminated; the working position and the bin for them belong in the layout plan, not after it.

Site constraints

Footprint: The changer occupies the section between extruder outlet and die, plus a working position for the open plate and the screens.
Headroom: Enough clearance to swing the plate open and lift a loaded screen out.
Environment: Indoor installation beside the existing extruder.

A small floor area for pack preparation and a covered bin for spent screens keep the change routine fast and safe.

Interfaces

Mechanical: Flange adapter machined to the customer's existing extruder outlet and die head bolt pattern.
Control: Hydraulic pack interlocked with the extruder's running status; transducer signals to local indication and to the line's alarm system.
Upstream and downstream: Nothing upstream changes; the die head is untouched, so pelletizing downstream is unaffected by the retrofit.

Targets

What the section is judged on

Unplanned stops caused by filtration: 0 stops per month Line stoppage and alarm records over the verification window
Die pressure through a plate shift: Inside the band agreed at commissioning bar Pressure trend records around each shift event
Pellet cleanliness against screen-passing contamination: No claims traceable to screen pass-through during the verification window claims The customer's own inspection and claim records
Screen consumption: Recorded per shift and within the estimate agreed at order screens per tonne Consumption log reconciled against production tonnage

How acceptance is judged

1. On the customer’s own material, the crew performs plate shifts at the set differential with the melt flowing, within the training period.

2. No leakage at the plate sealing faces during or after a shift, checked hot.

3. Pressure records show every shift made before the alarm band, with die pressure back inside its normal band immediately afterwards.

4. Handover documentation — the change procedure, the screen pack specification for each grade and the spares list — delivered and walked through with the crew.

Scope of supply

What is in the delivery — and what is not

Included in the scope of supply

Hydraulic screen changer (plate type) Heated body, plate-shift hydraulics and connection flanges machined to the confirmed extruder and die interface.
Melt pressure instrumentation Pressure transducers upstream and downstream of the screen pack, with local indication and alarm wiring into the line's controls.
Starter screen packs and spares list Initial packs in the mesh combination set for the customer's grades, plus the recommended wear-parts list.
Installation guidance, commissioning and training Erection support on site, first shifts demonstrated on the customer's own melt, and operators trained on the change and logging routine.

Not included in the scope of supply

Extruder and die head The customer's existing machine is retained; the retrofit sits between them.
Upstream metal separation and washing Front-end separation belongs to the recycling line and is quoted separately where asked.
Consumable screens beyond the starter set Screens, seals and heater cartridges are wear parts, budgeted and replenished by the customer.
Disposal of spent screens and loaded polymer Hot, contaminated waste is handled and disposed of under the customer's own site procedures.

Before a price

What we confirm before this becomes a quotation

01 Extruder and die interface details Flange drawings or measurements, the connection standard, and the output the line actually runs per grade.
02 Grades and contamination profile What the line pelletizes — baled film, raffia, mineral-filled recipes — and what the melt is expected to have left in it already.
03 Current screen practice How screens are changed today, how often, and what a change costs the line in time and polymer.
04 Utilities and layout Plant power standard, the space available between extruder and die, and where the crew actually stands during a change.

Request a Quote Send these points with your inquiry; the section can then be quoted against your line, not against an assumption.

Placeholder image: quotation reference photo, or a dimensioned layout sketch, 1200 × 900 px (4:3). It shows the space reserved for approved material and is not a photograph of our equipment. — **Placeholder · 1200 × 900 px (4:3)（占位图）** Replace with an approved quotation reference photo, or a dimensioned layout sketch at this size.（按此尺寸替换为正式图片。）

Photos

The section in the workshop

Placeholder · 1200 × 900 px (4:3)（占位图） Replace with an approved section photos, real workshop or installation views at this size.（按此尺寸替换为正式图片。）
Placeholder · 1200 × 900 px (4:3)（占位图） Replace with an approved section photos, real workshop or installation views at this size.（按此尺寸替换为正式图片。）