Plastic washing recycling line for rigid plastics

Plastic washing recycling line for rigid plastics

A rigid plastic washing line takes hard post-consumer and post-industrial plastic — bottles, drums, crates, pipe, pallets, appliance housings — and hands back clean dry flake that an extruder can run. The material arrives thick-walled, closed and often still holding whatever it used to contain, so the line has to cut it open before it can wash it. That order matters, and it is what separates a rigid line from a film line.

Ten machines stand between the infeed conveyor and the silo. Each one removes something the machine before it physically could not, and one of them — the sink-float tank — decides whether the finished flake is one polymer or several.

What this line runs on

HDPE, PP, ABS and PS plastics are commonly used in the production of packaging materials such as bottles, barrels, containers, casings and shells of household appliances, chemical drums, milk bottles, boxes, chairs, desks and pipes. Anything in that list can go on the conveyor.

What changes from one feedstock to the next is not the polymer but the shape of the contamination. A milk bottle carries a paper label and a cap of a different resin. A chemical drum carries product residue sealed inside it, and the residue does not come out until the drum is cut open. Crates and pallets carry grit ground into every rib, plus the occasional steel screw or metal handle. Pipe carries soil on the outside and nothing at all on the inside. Appliance housings carry foam, adhesive and metal inserts.

Size reduction is therefore a cleaning stage on a rigid line, not just a sizing stage. Until the wall is broken open, the washing section cannot reach half of what it is meant to remove.

Before

Four typical infeed conditions. Anything in this range feeds the same line; what changes is how much work the shredder and crusher have to do before the water gets a chance.

After

Washed rigid flake at 8–16 mm and under 1% moisture, taken from the silo. Colour is the only thing that changes across these four — the size, the cleanliness and the moisture are the same, because they are set by the machines rather than by the feed.

The lesson buried in those four pictures is a commercial one. The line cannot improve on the colour it is given, so whatever sorting happens on the infeed floor sets the ceiling on what the flake is worth. Everything downstream of the conveyor controls cleanliness and moisture, not value.

How the line is laid out

Material enters at the conveyor, goes through optional pre-shredding and then wet crushing, passes three separate cleaning principles in sequence, and finally goes through two stages of water removal before it reaches the silo. The run is deliberately linear. Wet rigid flake is heavy and it hangs up at every direction change, so the fewer transfers there are, the longer the line runs without anyone standing next to it.

Line capacity and what each tier costs you

Five standard tiers, from 200–300 kg/h up to 1800–2000 kg/h. Most buyers start with output. On a rigid line, the number worth studying second is manpower.

Read across that table and the shape of the economics shows up straight away. Output rises roughly sevenfold from the smallest tier to the largest, but installed power only goes from 100 kW to 250 kW and floor area only from 300 m² to 800 m². Manpower barely moves at all — 2–3 people on the smallest line and 3–5 on the largest. Labour cost per tonne is what falls fastest as the line grows, which is why rigid plants that have the feedstock supply tend to size up rather than run two small lines.

Water follows the same pattern: 4–5 m³/h at the bottom and 10–15 m³/h at the top. Installed power in the table is connected load rather than measured draw, because the crusher and the friction washers do not peak at the same moment.

Water, power and the people the line needs

Rigid washing is a wet process, but it is a comparatively thrifty one. Four stages draw water — the wet crusher, the friction washer, the sink-float tank and the high speed friction washer — and between them they need 4–5 m³/h at 200–300 kg/h rising to 10–15 m³/h at 1800–2000 kg/h.

Those are circulating figures, not fresh intake. Water leaves each stage dirty, drops its solids in settling and filtration, and comes back to the tanks. What has to be made up is the water that leaves clinging to the flake plus what evaporates — and on rigid flake that is a small amount, because a hard chip sheds water off its surface instead of holding it in folds. The material that genuinely leaves site is sludge: soil, sand, label fibre, glue and the sunk fraction from the float tank. Plan its disposal route before commissioning, not after.

Power runs from 100 kW on the smallest line to 250 kW on the largest. Manpower runs 2–3 at the bottom and 3–5 at the top, and most of those people are on the infeed side sorting by colour and pulling out what should never have arrived — metal, wood, PVC — rather than tending machines.

Key equipment, stage by stage

Ten machines, in the order material passes through them, grouped by the four jobs the line actually does: get material in and cut it down, clean it, take the water back out, and store what is left.

Conveyor

Transports material to the shredder. Gear motor drive, with high side walls that suit varied material — drums and crates roll, and a flat belt would lose them over the edge.

Shredder

Single-shaft or twin-shaft shredder, optional, pre-shreds plastics to increase throughput of the whole line and eases the burden on the crusher. Siemens PLC control.

On rigid feed this machine earns its keep in a way it does not on film. A sealed drum or a stacked pallet cannot enter a crusher whole, and even if it could, the residue inside would never be exposed to water. Pre-shredding opens the part. Everything the washing section does afterwards depends on that having happened.

Heavy-duty wet crusher

Breaks plastics and shredded chunks into smaller particles of 8–16 mm. Wet crushing pre-washes the material and avoids the problem of flying dust and smoke. Turning large material into small pieces in this module improves the washing result and makes the final product easy to pack. V rotor and blade design, easy operation.

Crushing under water does two jobs at once on rigid feed. It sizes the material, and it catches the grit that thick wall releases the instant it fractures — grit that would otherwise ride downstream embedded in the flake and end up in somebody’s extruder screw.

Friction washer

Deep cleaning of flakes. Stainless steel internals, thick wear-resistant blades and rotor design, high speed design at 700–1000 rpm, with dynamic balance treatment on the rotor.

This is the stage that takes off what is stuck rather than what is loose: label paper, glue residue and the film of dirt that survives crushing. It works by making flake rub against flake, so it needs a full chamber to work properly — a friction washer running half fed cleans noticeably worse than the same machine running full.

Sink-float washing tank

For washing and separation of plastic material of varying density. Separates HDPE and PP, which float, from sand and metals, which sink. Stainless steel construction, with a thumb wheel under frequency inverter control.

This is the only stage on the line that separates by density rather than by force, and on rigid feed it does something no other machine can: it sorts polymer from polymer. HDPE and PP float and stay with the product. Sand, stones, metal fines and grit sink and leave. ABS and PS are the ones to watch — both are denser than water, so they go down with the dirt rather than floating clear of it. If your feed genuinely mixes them with HDPE and PP, decide before commissioning which fraction you are selling.

High speed friction washer

Deep cleaning of flakes. High speed and efficiency washing equipment running at 1200 rpm, with dynamic balance treatment.

The final mechanical pass, after density separation has already taken the heavy contamination out. Running it last is deliberate: there is no point spending friction energy on grit that the float tank was going to remove anyway.

Screw loader

Transports material with water to downstream equipment. All parts in contact with water are made of stainless steel.

Dewatering machine

A centrifugal dryer that reduces moisture efficiently, with a rotor given dynamic balance treatment and an octagonal screen. Each vane top side is equipped with a stainless steel block, replaceable after wearing. Runs at 1440 rpm.

The replaceable wear block matters more than it sounds, and it matters more here than on a film line. Rigid flake is abrasive, it carries residual grit, and vane tips are the fastest-wearing surface in the whole drying section. On machines without replaceable tips the entire rotor becomes a consumable.

Pipe drying system

Stainless steel pipe lines, a hot air drying device and a strong blower.

Centrifuging throws off the free water. Heated air in the pipe run takes off what is left clinging to the flake surface, and that is the step that gets rigid flake under 1% moisture. Rigid has an advantage here that film never gets: a hard chip has no folds or creases to trap water in, so surface drying finishes the job and no squeezer is needed.

Silo

Stainless steel construction, sized to order.

What comes out, and where it goes

One product, specified by two numbers: flake at 8–16 mm with moisture under 1%. Both come straight off the machines — the size from the wet crusher screen, the moisture from centrifuging plus pipe drying — so they hold whatever colour or feedstock you put in the front.

That specification is what makes rigid flake straightforward to sell. Under 1% moisture means an extruder does not have to boil water out of the feed before it can melt it, and 8–16 mm chips have a high bulk density, so they meter evenly into a screw and they ship without paying freight on air. Rigid flake at this spec goes three places: straight into an on-site pelletising line, out to compounders as a washed regrind, or directly into injection and extrusion moulders who are willing to run regrind alongside virgin material.

The variable that decides price is colour, and colour is decided on the infeed floor. Natural and single-colour flake resell highest; mixed-colour flake sells into applications where the part is going to be black or dark anyway. No stage on this line can undo a mixed infeed, which is why the sorting table in front of the conveyor pays for itself faster than any machine behind it.

See the line running

Models & specification

Frequently asked questions