The Water You Remove Mechanically Is Water You Never Evaporate

A washed plastic stream comes out of the last rinse tank carrying water on every surface, in every fold of film, and inside every hollow shape that survived crushing. There are only two ways to get it out: mechanically, by spinning or squeezing it away, or thermally, by boiling it off in a dryer. The first costs electricity for a motor. The second costs energy for every kilogram of water and takes time in a drum whose length and heat input are fixed once it is built.

That is why dewatering is a selection decision and not an accessory. On the film washing line the published sequence ends with squeezing followed by thermal drying, and the line is published at an outlet moisture of 2% or lower after drying — the squeezing stage is what decides how much work the drying stage is asked to do. On the PP/PE rigid line the order is the same: dewatering, then drying, and the same published 2% outlet moisture is a figure for the whole line, achieved only if the stage before it did its job.

Put in the terms the dewatering machine product page uses: less water carried into the dryer means lower energy cost and higher drying stability. The second half of that sentence matters as much as the first. A dryer fed a fluctuating wet load does not produce a stable output moisture, and an unstable output moisture is what a granulator notices.

Two Structures, Two Mechanisms

The published range splits into two machines that share a purpose and nothing else:

• Vertical (VD) — centrifugal. Flake is thrown against a perforated drum and the water leaves through the screen while the plastic stays inside. The published application is PET flakes and rigid plastic regrind, at a dewatering rate of 95% or higher.
• Horizontal (HD) — screw press. Material is conveyed by a screw through a chamber and compressed, so water is pressed out of the mass instead of being thrown off individual particles. The published applications are PE/PP film, woven bags and agricultural film, at an outlet moisture of 3-15% by model.

The difference is not a preference. A centrifuge needs particles that behave individually: a flake entering the drum is thrown outward, sheds its surface water and leaves. Film does not behave like that. A wet film sheet folds onto itself, traps water between layers and wraps rather than drains, which is why the film line's published process uses squeezing for the water and describes the machine choice as one made for film rather than scaled down from a rigid-plastic line.

Read the published note on the dewatering page carefully, because it states the selection rule and the rating rule in one line: the choice is set by material form, not by capacity alone, and vertical machines are rated by dewatering rate while horizontal machines are rated by outlet moisture. Those two ratings are not interchangeable, and comparing them directly is the single most common error in a line comparison sheet.

Published Model Data

Both series are published model by model, and both are also available as standalone units for integration into an existing line. The figures below are the published values, not test results for a specific material.

Vertical centrifugal (VD series)

Horizontal screw press (HD series)

Look at the shape of the two tables rather than the individual numbers. On the vertical series every model is published at the same dewatering rate, and what changes with size is throughput and drum diameter. On the horizontal series the outlet moisture rises with model size on the same capacity ladder — 3-5% on HD-300, 5-8% on HD-500, 8-15% on HD-800 — because a larger screw press is asked to pass more material through the same compression length. The published note says this explicitly: horizontal machines are rated by outlet moisture, which rises with throughput on the same model.

That has a direct consequence for how you read a quotation. If your target is a dry cake and your capacity is large, you are not simply buying the biggest horizontal model — you are trading moisture against throughput, and holding both means either a larger drying duty or a different structure. On rigid flake the vertical series avoids the trade entirely: every model removes 95% or more of the water, and the model number only sets how many kilograms per hour pass through it.

Where the Machine Sits in the Line

Dewatering is never the first or the last stage. In the published sequences it always follows washing and always precedes drying:

• Rigid PP/PE line — feed, crushing, friction washing, float-sink separation, dewatering, drying. The float-sink stage ahead of it is what removes metal, stone and heavy plastics, so the dewatering machine receives a clean, single-material stream.
• PET bottle line — de-labeling, crushing, hot washing, density separation, then dewatering and drying. Caps and rings float off in the density stage before the flake reaches the dewatering machine.
• Film line — bale opening, anti-wrapping feed, wet size reduction, intensive washing, squeezing, thermal drying. Here the squeezing stage is the dewatering stage, built for film rather than adapted from a rigid route.

The stage immediately upstream matters for a mechanical reason. The friction washer is published as sitting between crushing and float-sink separation, or between washing stages, and it specifies that material should be pre-crushed to roughly 10-30 mm. That same size window is what lets a dewatering machine work: too coarse and the mass does not compress evenly, too fine and the screen blinds. When a dewatering unit underperforms, the cause is often three stages upstream in the crusher screen size, not in the machine.

One more positioning note that is easy to miss when reading a capacity table: film lines are published as sized by wet throughput, which is lower than the dry figure for the same model. Bulk density, not kilogram count, is the constraint. A film plant that sizes on dry tonnage buys a machine that runs at a fraction of the line above it.

Four Selection Mistakes That Show Up Repeatedly

• Comparing a dewatering rate with an outlet moisture. "95% or higher" and "3-5%" describe different quantities. A 95% dewatering rate on a feed that arrives at 40% water still leaves water in the product; the two figures only become comparable once you know the infeed condition of your own material.
• Buying the largest horizontal model to chase dryness. On the HD series outlet moisture rises as model size increases, from 3-5% on HD-300 to 8-15% on HD-800. Larger is for throughput, not for a drier cake.
• Using one machine for both film and flake. The published answer is that it can be done but efficiency drops. Film folds and holds water in layers; flake drains and spins free. If a plant runs both streams, the dewatering stage is where the compromise becomes visible in the dryer's energy bill.
• Treating dewatering as the drying stage. Mechanical removal has a floor. Where the target moisture is below what the machine reaches, a thermal dryer follows and is sized on the dewatering machine's outlet moisture — which is exactly why the choice made here sets the capital cost of the stage after it.

There is a fifth case that is a configuration issue rather than a mistake: heavily wetted or irregular material, where the published guidance is an inclined configuration that avoids blocking in the chamber.

What to Send With the Enquiry

The published prompt on the dewatering page is short: tell us the material and the target moisture. Behind that sentence sit four inputs that decide the model, and having them ready turns a quotation into a specification:

• Material form — rigid flake or regrind, PE/PP film, woven bags, agricultural film, or a mix. This decides the structure before any capacity number is discussed.
• Throughput — kilograms per hour at the point where the machine will sit, not at the plant infeed, and for film the wet figure the line is sized on.
• Infeed water content — how wet the stream arrives from the last rinse or friction washer. It is the missing half of any dewatering-rate comparison.
• Target moisture at the dryer or the granulator — the number your next stage actually needs. If it is below what mechanical removal reaches, plan the dryer at the same time and size it on the dewatering outlet.

All four are answered by a material trial on a representative sample, which is also where the published figures get replaced by a number for your plant. For an existing line the practical question is narrower still: what is the moisture at your dryer infeed today, and how much of the dryer's duty is water that a correctly sized dewatering machine would have removed for the price of a motor?

Frequently Asked Questions