Seven Pelletizing Methods Compared: Strand, Water Ring, Underwater, Hot Face

The pelletizer is chosen by the polymer, not by the budget. This table compares all seven methods we build on the criteria that actually decide the purchase: filler ceiling, water contact, pellet shape and fines. A reference pelletizing methods compared page from Kerke.

Updated 6 November 2026

Reviewed by Kerke process team

Basis commissioning records, parameter table

A pelletizing mistake shows up months later as dust in the customer's bag, moisture in their dryer or tails in their mould. Choose by polymer first, filler level second, pellet shape third.

The comparison

**Table 1.** Seven pelletizing methods by application window.
Method	Filler ceiling	Water contact	Pellet shape	Best for
Water-cooled strand	≤ 50%	Full immersion	Uniform cylinder	PET, PA, engineering plastics, low-filled masterbatch
Air-cooled strand	≤ 60%	None	Uniform cylinder	PVC, biodegradable, materials that must stay dry
Water strand (special for PET)	—	Full immersion	Cylinder, low dust	PET bottle flake and sheet grade, IV-critical
Water ring hot face	70–85%	Spray + ring	Lens / half-round	Filler masterbatch, carbon black
Air-cooled hot face	85–90%	None	Irregular, low bulk density	PVC, HFFR, WPC, high filler
Underwater	≤ 70%	Full chamber	Round, dense	TPE/TPU, EPP beads, hot melt
Spray / mist	≤ 60%	Light	Round	Sticky or low-melting products

Why water contact is the deciding column

Water is a cooling medium and a contaminant at the same time. For PET, moisture hydrolyses the chain and destroys IV. For PVC, water plus residual heat means hydrolysis of the stabiliser system and corrosion in the bag. For PLA, water at 60 °C starts the same hydrolysis the product is designed for in a compost heap.

So the sequence of questions is: does the polymer tolerate water (PET tolerates it if dried afterwards; PVC does not) → does the filler level allow a strand (above 50% the strand embrittles) → does the application need a specific pellet shape (bead products need round, dense pellets).

What each option costs you downstream

Strand lines are the cheapest to buy and the most labour-intensive to run: a broken strand stops the line and the operator rethreads it.
Water ring removes the strand handling problem but adds 8–12% surface moisture, so a centrifuge and a fluid-bed dryer are part of the price.
Air-cooled hot face needs no dryer at all, which is why PVC lines use it even though the pellet shape is irregular.
Underwater gives the best pellet quality and the highest cost per kg/h; the water circuit must be temperature-controlled to ±2 °C.

How we choose for a customer

We run the material on the lab line with the pelletizer we think is right, then send pellets plus a note on fines percentage, bulk density and moisture. If the pellet does not feed in your downstream machine, the trial has failed early and cheaply — which is the point of doing it before the order.

FAQ

Water ring or underwater for TPE?

Underwater. TPE and TPU need round, dense pellets and the water chamber holds temperature more evenly than a ring. Water ring gives lens-shaped pellets that bridge in some feeders.

Why does my strand break at 60% filler?

There is not enough polymer left to hold the strand together through the bath. Above roughly 50% move to water ring, above 82% to air-cooled hot face.

Can one line run two pelletizing methods?

Yes, if the die and discharge are designed for it. The pelletizer is a module; the die plate and the water circuit are what need to be swapped.

Where these numbers come from

Values are drawn from the Kerke parameter table, commissioning records and service reports from lines in the field. Temperature windows and consumption figures are typical ranges — confirm on your own material before they become a production setpoint.

Tell us your material — we will tell you the line

Send 25–50 kg and we run it on our lab extruder: pellets, running video and a capacity report back in 3–7 days.

Get a quote Send material for trial

Pelletizing methods compared — the short version

Note on Pelletizing methods compared: every figure on this page is a reference range measured on Kerke's own test line in Nanjing, not a catalogue maximum. If your material differs from the one in the table, send 25–50 kg and we will replace the range with a measured number.