What Air Separation Removes

The published FAQ for the WX series answers the removal question by listing fractions, not polymer names: light film, paper labels, fines and light contaminants from mixed plastic, plus light impurities in municipal solid waste fractions. That list is worth reading against the contamination tables of the washing lines we build. The PET bottle washing line page, for example, publishes paper and film labels, caps and rings, sand, organic residue and metal as its handled contamination — and the first two of those, paper and film, are precisely the fractions an air separator lifts before any water is spent on them.

The mechanism is a density split, not an identification. Material falls through a horizontal air duct; the air flow deflects light particles into a separate collection chamber while heavier plastic continues its fall path. Two fractions leave the machine separately, each ready for further sorting or processing. Nothing is washed, nothing is dissolved and nothing is identified — the machine simply exploits the weight difference between the plastic you want and the light contamination you do not.

Film is the clearest case. Loose film floats where rigid scrap sinks, which is one of the published reasons a film washing line is built around gentle conveying and wet cutting in the first place. When film arrives inside a rigid-plastic stream — shopping bags in a bottle bale, stretch wrap on a bale of housings — the air duct catches it while it is still light, dry and easy to lift, instead of letting it reach the wash water where it floats, clumps and loads the tanks.

Where It Sits: Between Crushing and Washing

The published position for the WX series is explicit: it is designed for inline operation between crushing and further sorting or washing. That placement is not incidental — it follows from what the two neighbouring stages do to the material.

Upstream, the PS-series crusher sets flake size with interchangeable screens published at 3, 5, 8, 10 and 15 mm. The crusher page makes the connection directly: washing efficiency depends on particle size, which is why the PS series is specified by the size the next stage needs. Air separation is one of the stages that benefits — a crushed, screened stream flows through the duct as a predictable curtain of particles instead of entangled pieces, so the air sees the density difference rather than a tangle.

Downstream, the wet section runs better for what never reached it. Every kilogram of film and paper kept out of the wash water is capacity the friction washer can spend on the soil that actually needs scrubbing — the published FW series runs at 500-800 rpm with 2-12 m³/h of water across models, and larger or heavily contaminated lines put two or three washers in series. water heated and pumped through a closed loop is one of the running costs of a washing plant; the water that costs least to treat is the water that never had to carry paper pulp.

The published flow in both directions also leaves room for a second air pass. Because the two fractions are discharged separately, the heavy fraction can continue to washing or densifying while the light fraction is reprocessed, baled for sale as a mixed light stream, or routed into a dedicated film line if the volume justifies it.

The WX Series: Published Numbers

The WX series is published as a three-model range, and the specification shows the machine scaling along two axes: duct width and fan power. The published figures:

Two details in that table repay attention. First, the particle-size column widens with the duct: 5-50 mm on WX-600, 5-60 mm on WX-800, and the published working range of 5-80 mm across the series on WX-1000. A PS-series screen set at 8 or 10 mm drops comfortably inside every one of those windows, which is part of why the crusher-then-air-separator pairing is the natural order. Second, the capacity ranges overlap between models — the top of WX-600 meets the bottom of WX-800 — because throughput is not the only selection criterion. The published note under the table is blunt: separation efficiency depends on material characteristics, moisture content, air volume and damper settings, so the model is chosen for the material as much as for the tonnage.

The other published design point is footprint. Where a vertical separation column needs height and floor area, the horizontal duct works with the material's own fall path and keeps installation length short — the stated reason the series suits space-constrained plants. Retrofitting an air stage into an existing crusher-to-washer layout is one of the common requests the compact length exists to answer.

The Two Feed Conditions: Moisture and Particle Size

The published selection points reduce the operating discipline to a short list, and two items dominate. The first is moisture: material moisture above roughly 10% causes particles to stick together and separation quality drops. Wet film wraps around wet film; damp paper mats onto flake; the density split the whole machine relies on stops being visible to the air stream. This is why the WX sits before the wet stages, fed with dry crushed material — and why material that has already been washed needs to be dewatered and dried before any second air pass. The published dewatering guide puts the horizontal screw press at 3-15% outlet moisture by model and the series dryer at 2% or lower after thermal drying, and our post on fixing dewatering before blaming the dryer covers how that number is reached.

The second condition is particle size. The published working range is 5-80 mm depending on model, and the bottom of the window matters as much as the top: fines below the working range behave like dust, and dust follows the air wherever the air goes. Crusher screens are the control — the published 3-15 mm screen options let the plant set the flake size so the majority of the stream sits inside the separator's window, while the fraction that falls outside it is small enough to handle elsewhere.

The remaining selection point is tuning. The multi-stage dampers are adjusted to the density difference in your mix — a stream of PET bottles against film runs at a different setting than a mixed rigid stream against paper, and the dampers are the published mechanism for making that adjustment without hardware changes.

How Air Separation Fits With Downstream Sorting

The WX page closes its equipment notes with a pairing rule: air separation is often paired with electrostatic or optical sorting downstream. The division of labour is straightforward. Air separation works on density difference and takes out the light fraction early; it does not identify polymers. Electrostatic and optical machines make the polymer-level decisions on the heavy fraction — the published silicone, rubber and PVC sorting work is one example of what a dry downstream stage looks like, covered in our post on sorting look-alikes from PET flake.

The order matters because every sorter downstream performs better on a lighter, cleaner, more homogeneous feed. A optical or electrostatic unit that receives film and paper mixed into the flakes spends capacity on particles it cannot classify; the same unit after an air separator receives the heavy fraction only. Air separation is the cheap, low-energy first decision — a fan and a duct against 11 to 30 kW of published fan power — that lets the more expensive decisions run on the material they were built for.

What to Send With the Enquiry

The published invitation is short: send a sample and your target separation. In practice that breaks into four inputs that decide the configuration:

• The material mix — what the heavy fraction is (bottles, housings, pipe, mixed rigid) and what the light fraction is (film, paper, foam, fibre). The density difference between them sets the damper strategy.
• Moisture — whether the stream arrives dry from a crusher or wet from an earlier wash. Above roughly 10% moisture, the published expectation is that particles stick and separation drops.
• Particle size — the crusher screen in use, so the stream can be matched to the published 5-80 mm working window of the right model.
• The target — what clean means on the heavy fraction, and whether the light fraction has a destination of its own.

The published efficiency of 92% or higher is then confirmed the published way: a material test, on site or in our workshop. That test also sets the damper positions your mix actually needs, so the machine arrives tuned rather than generic. For readers mapping a whole line around this stage, our posts on the film washing line route and on where a friction washer does its work cover the wet side that usually follows.

Frequently Asked Questions