What Machines Are Needed for a Plastic Recycling Line

A plastic recycling line is not one machine. It is a set of machines, and only four of them are genuinely unavoidable: something that reduces size, something that washes, something that removes water, and something that turns the output into a sellable form. Everything else on a quotation is a decision, not a requirement.

That distinction is the whole point of this page. Most equipment lists are organised by process order, which tells you what happens but not what to buy. This one is organised by whether you actually need the machine — four you cannot skip, three that depend entirely on your material, and a set that routinely appears on quotations for projects that do not need them. If you want the stages in process order instead, that is the plastic recycling process from bale to pellet.

The Four Machines You Cannot Skip

Whatever the material and whatever the scale, these four functions have to exist somewhere in the line. The machine names change; the functions do not.

Size reduction — and whether that means one machine or two

Nothing can be washed until it is small. The question is whether you need a shredder, a crusher, or both, and that follows from the size of what arrives.

If your input arrives as bales, drums, pallets, purgings or pipe, you need a plastic shredder machine first — a slow, high-torque machine that turns bulk into feedable pieces. A twin-shaft shredder handles the roughest mixed and rigid input; a single-shaft shredder with a horizontal pusher gives a more controlled output size because it works against a screen. Choosing between the types by material is worked through in how to choose a recycling shredder.

If your input already arrives loose and hand-sized — bottles, bottle crate contents, light containers — you can go straight to a heavy-duty crusher. The crusher runs fast against a perforated screen and produces flake in the 12–20 mm range, which is what the wash stages downstream are designed for.

Buying both when one would do is one of the most common ways money leaves a project early. Buying only a shredder and expecting flake is the other.

The washing line

This is the largest single item in almost every project and the one that decides your output grade. A plastic recycling washing line is a sequence of tanks, screws and washers rather than a single unit, and the sequence differs by material class.

Rigid material — drums, crates, containers, thick-wall scrap — runs on a washing line configured for rigid plastics. Film runs on a washing line for soft plastics, which is a genuinely different machine, not the same one with a different label; film floats, tangles and holds water in ways rigid flake does not. Bottles have their own configuration again, the bottle-to-flake PET line, which puts label and cap removal ahead of crushing.

Whether that line needs hot washing at 85–95 °C with 1–3% alkali or whether cold is sufficient is a material question with a large cost attached, addressed in hot wash versus cold wash.

Dewatering and drying

Wet flake cannot be sold and cannot be extruded. A centrifugal dryer running at around 1500 rpm throws off free water and brings moisture down to 0.5–2%. A hot-air stage after it takes the flake below 1%, which is where most buyer specifications sit.

Skipping the second stage to save money is a false economy that shows up later as hydrolysis during extrusion — the polymer chains shorten, the melt viscosity drops, and the material is permanently worth less. The drying stage is cheap relative to what it protects.

The pelletizer — or the deliberate decision not to buy one

This is the one “essential” that is actually a fork in the road, and it deserves more thought than it usually gets.

You can stop at clean, dry flake and sell it. Many profitable plants do exactly that, because flake is a real commodity with real buyers and the capital saved is substantial. Or you can add a plastic pelletizing machine, melt the flake, filter the melt and cut pellets — which lifts the price per tonne and widens the buyer pool, because pellets meter accurately through a moulder’s feeder and flake does not.

If you do pelletize, the machine follows the material. Rigid flake goes to an SJ pelletizing line for rigid plastics. Film needs a pelletizing machine with a compactor, because loose film will not feed into a screw on its own. Clean, dry PE film offcuts from a converter — a much easier input than post-consumer film — can go through an air-cooling mini granulator without a water bath at all.

Which route pays depends on who is buying, not on which machine is better. The comparison is set out in plastic regrind and how buyers judge its value.

The Three That Depend Entirely on Your Material

These three are essential on some projects and pure waste on others. There is no general answer, only a material-specific one.

Sink-float tank — only if your stream is mixed density

A sink-float separation tank separates polymers by whether they float in water. PET and PVC sink; PE and PP float. If you are processing PET bottles with PE caps and PP label film, it does most of the polymer separation in the line and you cannot do without it.

If you are processing a single-polymer stream — clean HDPE drums from one supplier, factory offcuts of known material — it separates nothing, because everything in the tank has the same density. It still costs floor space, water and power. The test is simple: is there more than one polymer in your feed, and do they differ in density? If the answer to either half is no, the tank is not doing work.

Friction washer — only if the dirt is stuck on

A high-speed friction washer cleans by abrasion: flake is driven against screens and against itself at speed, and adhering dirt comes off mechanically. It is the right machine for material carrying soil, pulp, paper fibre or dried residue.

For lightly soiled input it duplicates what the rinse tanks already do, while adding power draw and a wear part that has to be replaced. Heavily contaminated post-consumer film and agricultural material need one; clean industrial scrap generally does not.

Squeezer — almost only for film

Washed film comes out of the line carrying far more water than rigid flake, and a centrifugal dryer alone will not get it low enough. A plastic squeezer and densifier mechanically presses and partly plasticises the film, driving out water and densifying the material so the pelletizer can feed it.

On a rigid-flake line it is redundant. This is the clearest example in the whole list of a machine that is genuinely mandatory for one material class and genuinely pointless for another, which is why a single “standard recycling line” specification should always be treated with suspicion.

How Capacity Decides the Machine List

The other half of the specification is scale, and it is worth understanding that a bigger line is not the same line with larger motors. The configuration logic changes: labour density falls, water per tonne does not, and at certain points a second dewatering stage or a different feed arrangement becomes necessary rather than optional.

Here is what the three material classes actually look like across their capacity ranges. These are installed power divided by rated throughput, with operators expressed per tonne per hour so the tiers can be compared directly.

PET bottle-to-flake

Rigid — drums, crates and pipe

Soft — film and woven bags

Four things fall out of those three tables that change how a line should be specified.

Scale works on energy and barely works on water. A rigid line going from 250 to 1,900 kg/h drops from 400 to 131 kWh per tonne, a fall of two thirds. Over the same range water only goes from 16–20 down to 5.3–7.9, and most of that is the smallest tier having been over-specified in the first place. All three classes flatten out on water by mid-range. Sizing up to dilute a water bill does not work.

Material class matters more than capacity. A soft line at 1,500 kg/h draws 253–400 kWh per tonne; a rigid line at the same tonnage draws 128. That is a bigger gap than the entire range of either table. If you have a choice of stream, this decision outweighs the capacity decision.

Labour is where rigid lines win and PET lines lose. At 1,500 kg/h a rigid line needs 2.1–3.6 people per tonne per hour and a PET line needs 5.3–6.7 — the extra bodies are all on the sorting belt. In a high-wage economy that single row can outweigh the equipment price difference.

The tiers are not evenly spaced in value. On PET the step from 1,500 to 2,000 kg/h buys throughput and no efficiency at all: 200 kWh per tonne at both. On rigid the step from 1,500 to 2,000 is slightly worse per tonne than staying put, 128 up to 131. Those two tiers exist for plants that need the tonnage, not for plants chasing unit cost.

What Gets Added to a Quotation That You Might Not Need

Nothing in this section is a bad machine. Each solves a real problem. The question is whether you have that problem.

A second washing tank. Sold as extra cleaning. It is genuinely useful for heavily contaminated input, and it is a tank of standing water for anything already reaching specification after the first. Ask which contaminant it removes that the existing sequence leaves behind, and ask it as a specific question.

Buffer silos at every transfer. A buffer silo decouples two machines so that a brief stop upstream does not starve the machine downstream. That matters at the junctions where flow is genuinely uneven — typically before the pelletizer. Putting one at every transfer point adds cost and floor area to smooth out variation that is not there.

Optical sorting on a single-polymer line. Expensive and impressive. If your input is one known polymer from a known supplier, it has nothing to identify.

Capacity you are not going to feed. The most expensive item on this list. A line sized for 3,000 kg/h running on 800 kg/h of available feedstock costs more to buy, more to power and more to staff, and the per-tonne economics that justified the larger machine never arrive because the tonnes never arrive. Size the line to the material you can actually secure, not to the material you hope to secure in year three. The full picture of where money goes is in what adds up in plastic recycling plant cost.

A supplier who answers “which problem does this machine solve on my material?” with a specific, checkable answer is worth listening to. One who answers with “every complete line has one” is describing their catalogue, not your project. Once the list is settled, what each of those machines adds to the bill is worked through separately, one machine at a time, with the scope-of-supply lines that decide whether two quotations can be compared at all.

How the Machines Connect

The connective equipment is where inexperienced buyers under-budget, because it is unglamorous and it does not appear in the headline capacity figure. It is also where most commissioning problems originate.

Belt conveyors move material between stages and set the working height of everything they feed. Get an inlet height wrong and a machine that is perfectly specified on paper cannot be fed without a platform that was not in the budget.

Screw loaders lift dry flake into hoppers. Simple, cheap, and the reason nobody is carrying buckets.

Buffer silos, used where they belong, absorb the difference between a batch-like upstream process and a continuous downstream one.

Water circulation and treatment is the item most often missing from a first budget. A washing line consumes water continuously, and unless you are prepared to buy and discharge that volume every shift, you need recirculation, filtration and sludge handling. This is a system, not an accessory, and local discharge rules decide how large it has to be.

The control cabinet is what makes the line one line instead of eight machines standing near each other. Interlocks that stop the upstream machine when a downstream one trips, a single start sequence, and consistent alarm logic are the difference between a plant that runs and a plant where somebody watches a jam propagate. The rest of the auxiliary equipment range covers these supporting units.

What Changes If You Buy the Machines Separately

Buying machine by machine from different suppliers is legitimate, and sometimes it is the right call — particularly when you already own working equipment and are extending a line rather than building one. It moves four things onto your side of the table.

Capacity matching. Rated capacities are quoted on the supplier’s reference material, not yours. Two machines both rated 1,000 kg/h can deliver quite different real throughput on the same feed, and the line runs at the speed of its slowest stage regardless of what the others are rated at.

Physical interfaces. Discharge height, inlet height, chute geometry, flange sizes, water connections. Every mismatch becomes a fabricated transition piece made on site, and site fabrication during commissioning is the most expensive way to build anything.

Control integration. Separate machines arrive with separate control panels and no shared interlocks. Someone has to design and build the logic that ties them together, and that someone is now you or a contractor you hire.

Responsibility when output misses specification. This is the real cost. On a single-supplier line, the output specification is one company’s obligation. On a mixed line, a moisture problem can be blamed on the washer by the dryer supplier and on the dryer by the washer supplier, and both can be partly right. You end up arbitrating a technical dispute between vendors while your line is not producing.

None of that argues against buying separately. It argues for knowing which of those four you are taking on before the order, rather than discovering them during commissioning.

Frequently Asked Questions