ML Plastic Pelletizing Machine (Granulator) with Compactor for soft plastics

ML plastic pelletizing machine (granulator) with compactor

Every pelletising line has to solve the same first problem: getting material to enter the screw at a steady rate. On rigid regrind that problem solves itself — the flake is dense, it falls, the screw grips it. On film it does not. Loose film bridges over the throat, it rides up the flight instead of being pulled down it, and the extruder ends up starved for seconds at a time while the hopper above it looks full.

This machine exists because of that. It is a 3-in-1 pelletising system that puts a compactor in front of the extruder, so what reaches the screw is no longer film at all — it is a warm, dense crumb that behaves like regrind. The client specification calls it a system that combines material pre-conditioning and energy-efficient extrusion, particularly suited to high-volume film recycling, and notes that the integrated compactor improves material flow characteristics while reducing the thermal degradation risks common in conventional film recycling.

Everything below follows from that one decision. Read it as a chain: what the compactor does, what it costs you in heat history, and how the extruder, the filter and the cutter behind it are sized around the result.

Why film cannot be fed straight into an extruder

The obstacle is bulk density. A cubic metre of loose washed film weighs a fraction of what the same volume of rigid regrind weighs, and an extruder screw is a volumetric device — it moves a fixed volume per revolution regardless of what is in it. Feed it film and the throughput collapses, not because the motor lacks power but because there is not enough mass in each turn of the flight.

The second obstacle is that film is springy and interlocking. It arches over the feed throat and holds itself there, so the hopper empties in slugs rather than in a stream. An extruder that alternates between starved and flooded cannot hold a stable melt temperature, and an unstable melt shows up in the pellet as inconsistent size and colour.

Neither problem is fixed by a bigger screw. Both are fixed upstream, by changing the material before it ever reaches the throat. That is the compactor’s entire job description in the specification: it receives loose plastic films and flakes and densifies the material before extrusion.

What actually happens inside the compactor

Inside the chamber, a rotating cutting disc carrying moving blades works against stationary blades fixed on the chamber wall. That counter-cutting action does two things at once. It reduces the film, and it drags it against itself and against the steel fast enough to generate heat by friction alone — the specification lists the heating system simply as friction heating. There is no heater band on this stage.

The material softens, tacks together and rolls into dense irregular crumb. It does not melt. That distinction is the whole point: the specification describes the effect as pre-plasticising, not plasticising. The compactor takes the material to the edge of softening and stops, because a fully melted charge would weld into a cake instead of discharging as free-flowing crumb.

Stopping at the right point is not something an operator can judge by eye, which is why the specification puts temperature sensors in the chamber to monitor and control the pre-heating process. On a machine that heats by friction, temperature is an output of load and residence time rather than something you dial in directly — the sensors are the only closed loop you have.

The practical consequence for a buyer: the compactor is the stage that determines whether your line runs steadily or hunts. It is worth asking how the temperature loop behaves on your specific material before worrying about screw diameter.

Integrated compactor, or a separate agglomeration step

The same densification can be bought as a standalone agglomerator sitting beside a conventional pelletiser. The specification is explicit about why this machine does not work that way: the integrated compactor eliminates the need for a separate agglomeration step.

What that removes is not one machine, it is a handling cycle. On the separate route the agglomerate has to be discharged, cooled enough to store, moved, and reloaded into the extruder hopper — and the heat the agglomerator just put into it is thrown away in the process. On the integrated route the crumb travels a few metres and enters the screw while it is still warm, which is where the specification’s claim of energy-efficient extrusion comes from.

It also removes a control boundary. Two machines with two control systems have to be balanced by an operator watching both. One machine with one control system balances itself, and the motor-load monitoring in the control section can act on the compactor and the extruder together.

The extruder behind the compactor

The extrusion stage is a single-screw configuration with vacuum degassing zones and multiple heating zones under PID control. Single screw is the right choice here precisely because the compactor exists: the reason film lines are sometimes pushed towards twin-screw designs is feeding, and feeding has already been solved upstream.

The specification credits the pre-conditioning with better melt homogeneity, and the mechanism is straightforward. A screw fed with uniform warm crumb sees a consistent load along its length, so each heating zone does the job its PID loop was tuned for. A screw fed with alternating slugs of cold film and air does not, and the melt leaving it carries that inconsistency forward.

Vacuum degassing matters more on film than on most feedstocks. Film carries surface moisture and printing residues into the barrel, and volatiles that are not pulled out of the melt end up as voids and streaks in the pellet.

Filtration and cutting: the two choices you actually make

Two decisions on this line are genuinely yours to make, and both sit after the screw.

Screen changer

The screen changer is hydraulically powered, and the specification offers plate type, piston type and laser filter. Filtration is quoted at 40–120 mesh as the common range. Post-consumer film is the dirtiest feed a pelletiser sees — paper label fibre, sand that survived washing, the occasional metal fine — so screen change frequency, not screen fineness, is usually what limits a shift. That is what pushes buyers towards the piston and laser options.

Pelletiser and cutter

The specification lists water-ring and strand (spaghetti) type, with water cooling. Both produce a saleable pellet; what differs is the shape of your line and how you inspect it.

Water-ring is the shorter installation: the die head carries a multi-hole die with 2–8 mm hole diameter and rotary knives cut against its face, with the pellets quenched in the ring of water immediately. Strand cutting pulls the melt out as spaghetti through a bath before cutting, which costs floor length but lets an operator see a broken or thin strand and react before a whole batch goes off-spec.

Control system

Supplied as HMI with PLC, or button type. It controls temperature profiles, monitors motor load and throughput, and carries overload protection and an emergency stop system.

Motor load monitoring earns its place on a film line specifically. Film bulk density varies bale to bale in a way rigid regrind does not, so compactor load is the earliest signal that the feed has changed — it moves before extruder amps do and well before pellet quality does. If you are choosing between the HMI and the button-type build, that trend readout is the thing you are actually buying.

Sizing: compactor volume, not just kilograms per hour

Five models, quoted on clean LDPE film from 150–250 kg/h up to 900–1100 kg/h, with installed power from 205 kW to 700 kW.

Note that the throughput figures are qualified: they are for clean LDPE film. Heavier contamination, thicker gauge or mixed feed will not hit the top of the band, and any supplier quoting a single number without naming the material is quoting a best case.

Compactor volume is the row worth reading twice. It runs 300 L on the ML85-100 and 1500 L on the ML180-200 — a fivefold increase against roughly a 4.4-fold increase in rated throughput. The chamber is sized against the volume of material arriving, and low bulk density feed arrives as a lot of volume for very few kilograms. If your film is lighter or fluffier than clean LDPE, the compactor is the component that runs out of capacity first, not the screw.

Extruder diameter is quoted as a pair on every model — ⌀85/⌀100 through ⌀180/⌀200 — because the barrel behind the compactor and the barrel doing the final work are not the same size.

What this line runs on

The specification covers film-to-pellet and foam-to-pellet: HDPE, LDPE and LLDPE packing and agricultural film; shopping bags; industrial film scrap including multilayer packaging film; PP woven bags; BOPP labels; CPP film; and EPS and EPE foam.

One entry on that list carries a condition worth reading carefully. PP woven bags are listed as suitable after pre-cutting by a crusher or shredder. A whole woven sack will not present itself to the cutting disc the way loose film does — it wraps. If woven sacks are a meaningful share of your feed, size a shredder into the project at the same time, not after commissioning.

Foam is the opposite case and the one where a compactor pays back fastest. EPS and EPE arrive at a bulk density so low that transporting them is already uneconomic; densifying on site is often the point of buying the machine at all.

Models & specification

See the line running

Frequently asked questions