Choosing a plastic extruder is not primarily a capacity decision. Capacity is the last thing you settle, because two of the earlier choices — screw type and L/D ratio — narrow the field before kg/h ever comes up.
This article covers the extruder families used in real pipe, profile and recycling lines, how to read a model code, and what to confirm before signing. The figures come from the published configurations of the plastic extrusion machine and plastic recycling machine ranges SUHUI builds.
Two machines share a name and almost nothing else.
What Counts as a Plastic Extruder in an Industrial Line
An industrial plastic extruder is a screw rotating inside a heated barrel that melts polymer and pumps it under pressure to a die. It runs continuously at hundreds of kilograms per hour. Search results for the term also return two other things entirely, and mixing them up wastes a lot of time.
The first is the extruder on a desktop 3D printer. That is a filament drive plus a small hot end. It handles grams per hour, has no compression screw and no melt pressure to speak of, and shares only the word. The second is the hobbyist recycling extruder sold as a kit or built from plans. Those are real screw extruders, but at a scale and duty rating that has nothing to do with a production line.
Everything below refers to the industrial machine. If a specification sheet does not state screw diameter, L/D ratio, drive power and output in kg/h, it is not describing one.
The Three Extruder Families Used in Pipe, Profile and Recycling Lines
Three families cover essentially all plastics extrusion. A single screw is one screw in one bore. A conical twin screw is two intermeshing screws that taper from a wide feed end to a narrow discharge end. A parallel twin screw is two intermeshing screws of constant diameter, rotating either in the same direction or in opposite directions.
Three geometries, three different ways of conveying and shearing material.
| Family | How it conveys material | Shear and thermal history | Where SUHUI uses it |
|---|---|---|---|
| Single screw | Drag flow — material moves because it sticks to the barrel more than to the screw | Longer residence time, shear depends on screw speed and channel depth | HDPE and PPR pipe lines, SJ and HSJ series |
| Conical twin screw | Positive displacement — material is pushed forward in closed chambers between the screws | Short, controlled and repeatable; large feed area tapering to high discharge pressure | PVC pipe lines, SJZ series |
| Parallel twin screw | Positive displacement at constant diameter, with mixing elements along the length | Tunable by screw element configuration, strong distributive mixing | Largest PVC pipe sizes, SJP series; PVC and rigid plastic pelletizing |
The practical difference between drag flow and positive displacement shows up in two places. Positive displacement handles powder and irregular regrind without slipping, and it gives a shorter, more predictable time at temperature. Drag flow is simpler, cheaper per kilogram of output and perfectly adequate for polymers that tolerate heat.
Which of the two twin screw directions of rotation applies is a separate question with its own trade-offs. Our article on the twin screw extruder covers co-rotating and counter-rotating designs, and the single screw vs twin screw extruder comparison works through the choice in detail.
The Polymer Decides the Screw Before Output Does
Screw type follows the polymer, not the production target. A material that tolerates heat and melts predictably under shear runs on a single screw. A material that degrades if it is held hot, or arrives as a powder blend rather than pellets, needs the positive conveying and short thermal history of a twin screw.
The material property that drives the choice is thermal stability, not viscosity.
| Polymer | Screw type | Why |
|---|---|---|
| HDPE, PP, PPR and other polyolefins | Single screw | Thermally stable, melts predictably under shear, tolerates a long residence time. A single screw is the efficient answer and SUHUI’s HDPE and PPR pipe lines use SJ and HSJ series machines throughout |
| Rigid and flexible PVC | Conical twin screw, parallel twin at the largest sizes | PVC degrades rather than simply discolouring when it is held hot, and it is usually processed as a dry blend powder. Twin screws convey powder positively and give a short, repeatable thermal history |
| Filled, reinforced or compounded material | Parallel twin screw | Distributive mixing along the screw length is needed to disperse filler or additive evenly, which a single screw cannot do well |
| Mixed or contaminated recycled feed | Depends on the polymer, plus filtration and venting | The base polymer still sets the family. What changes is everything around the screw — see the recycling section below |
This ordering is worth insisting on with a supplier. If the first question you are asked is how many kilograms per hour you want, rather than what material you are running, the configuration is being built backwards.
What the Second Number in a Model Code Tells You
Extruder model codes carry two numbers and both mean something. In SUHUI’s HDPE range, SJ65/33 is a single screw of 65 mm diameter at an L/D ratio of 33. In HSJ75/38 the screw is 75 mm at an L/D of 38. The first number is size, the second is barrel length relative to that size.
The same code format means different things for single screw and conical twin screw machines.
L/D is length divided by diameter, so 33 means the screw is thirty-three screw diameters long. A longer barrel gives more residence time and more shear length, which means more thorough melting and more pumping capacity at the same screw speed. It also costs more, takes more floor space and adds thermal load, so it is not free.
The effect is visible directly in SUHUI’s two HDPE series. The 33D series covers Φ20–1,200 mm pipe. The 38D series covers up to Φ20–1,600 mm with higher throughput at comparable screw diameters — HSJ75/38 is rated at 550–650 kg/h where SJ75/33 is rated at 400 kg/h.
Conical twin screws are labelled differently and it catches people out. SJZ65/132 does not mean L/D 132. It means the conical screws measure 65 mm at the small end and 132 mm at the large end. Reading it as an L/D ratio produces an absurd number, which is the quickest way to spot the mistake.
How Screw Diameter Maps to Output and Product Size
Screw diameter is the capacity lever once the family is fixed. Bigger screws move more material, so output rises with diameter and drive power rises with it. What does not rise is line speed, because larger products contain far more material per metre of length.
| Extruder | Family | Output | Pipe range it serves | Motor power |
|---|---|---|---|---|
| SJ65/33 | Single screw | 180–220 kg/h | Φ20–110 mm HDPE or PPR | 55–75 kW |
| SJ75/33 | Single screw | 300–400 kg/h | Φ40–250 mm | 110 kW |
| SJ90/33 | Single screw | 500 kg/h | Φ160–450 mm | 160 kW |
| SJ120/33 | Single screw | 1,000 kg/h | Φ500–800 mm | 280 kW |
| HSJ120/38 | Single screw, long barrel | 1,300 kg/h | Large-diameter HDPE | — |
| SJZ55/110 | Conical twin | 180 kg/h | Φ20–63 mm PVC | 22 kW |
| SJZ80/156 | Conical twin | 350–400 kg/h | Φ75–315 mm PVC | 55 kW |
| SJZ92/188 | Conical twin | 600–800 kg/h | Φ160–630 mm PVC | 75–110 kW |
| SJP130/28 | Parallel twin | 1,100 kg/h | Φ500–800 mm PVC | 160 kW |
Output tracks screw diameter within a family, but the two families are not directly comparable.
Two readings of that table are worth spelling out. First, the conical twins deliver comparable output at noticeably lower motor power than the single screws — SJZ80/156 gives 350–400 kg/h on 55 kW where SJ75/33 gives 400 kg/h on 110 kW. Positive displacement conveying is more efficient than drag flow. That does not make it the better choice for polyolefins, because PVC and HDPE are different materials with different melting behaviour, but it does mean power draw alone is a misleading way to compare quotations across families.
Second, and this is the trap in reading the table as a shopping list — the extruder you need is not always the biggest one your budget reaches. SUHUI’s PVC32 configuration serves Φ16–32 mm pipe from an SJZ65/132, a mid-range machine, because that product simply cannot consume what a larger extruder delivers. Sizing up past what the product can absorb buys idle capacity and a machine running below its efficient window, which is where wear accelerates.
Why a Recycling Line Uses a Different Extruder Setup
A recycling pelletizing line uses the same three families, but the machine around the screw is configured differently. Recycled feed varies in bulk density, carries solid contamination and carries volatiles. Each of those adds hardware that a virgin-material extrusion line does not need, and it changes what you should be comparing between quotations.
Same screw families, three extra subsystems.
Feeding. Virgin pellets flow under gravity. Washed film flake does not — it is light and fluffy and bridges above the feed throat. This is why SUHUI’s PP PE film compacting pelletizing line puts a compactor ahead of the extruder rather than feeding flake directly, and why rigid streams are granulated to a controlled 3–8 mm before they reach the screw on the rigid plastic granulating pelletizing line.
Melt filtration. On a virgin line a screen pack is insurance. On a recycling line it is a working process stage sized for the actual contamination load, with a screen changer that swaps screens without stopping production. Both SUHUI pelletizing lines specify melt filtration with a screen changer as a named stage rather than an accessory.
Pelletizing head. An extrusion line ends at a die that makes a product. A recycling line ends at a die that makes pellets, and the cutting method is part of the extruder package — the rigid line offers underwater or strand pelletizing to 2–5 mm, while the PVC granulating pelletizing line uses die-face hot cut with air-cooled cyclone conveying to 2–4 mm.
That PVC pelletizing line also confirms the polymer rule from the other direction. Its published extruder type is conical or parallel twin screw — the same families used on PVC pipe, chosen for the same reason. The polymer does not stop being heat-sensitive because the feed is recycled.
What to Confirm Before Signing for an Extruder
Most extruder disputes trace back to something that was assumed rather than written down. The specification that matters is not just the headline output figure — it is the conditions under which that figure was measured, and who is responsible when the material you actually run behaves differently from the sample.
| What to confirm | Why it matters | What a weak answer looks like |
|---|---|---|
| Output measured on which material and which grade | kg/h varies with melt flow index, bulk density and moisture. A figure quoted on virgin pellets will not hold on regrind | A single kg/h number with no material stated |
| Screw and barrel material and surface treatment | Filled, reinforced or contaminated feed is abrasive. Screw wear shows up as falling output months after commissioning | “Alloy steel” with no treatment or hardness stated |
| Whether a trial run with your own material is possible | It is the only test that answers the output question for your feedstock rather than a reference one | Trial offered only on the supplier’s material |
| L/D ratio, stated explicitly | It decides melting quality and the realistic output ceiling, and it is the number most often left out of a quotation | A model code given without explaining what the second number is |
| Melt filtration and venting, if recycled feed is in scope now or later | Both are far cheaper designed in than retrofitted onto a commissioned barrel | Treated as an optional accessory rather than a line stage |
| Who owns the ramp to rated capacity after installation | An extruder that reaches rated output only on paper is a commissioning dispute waiting to happen | Responsibility ends at delivery or at mechanical installation |
Six things to have in writing before the order.
Pricing sits deliberately outside that list. An extruder price depends on screw diameter, L/D, drive power, control specification and the downstream hardware it has to match, so any figure quoted without those is not comparable to another. SUHUI quotes against a material and a product specification rather than publishing a machine price list.
Frequently Asked Questions
What is a plastic extruder?
It is a machine that melts plastic and pumps it under pressure through a die. A screw rotates inside a heated barrel, conveying and compressing the polymer until it is a uniform melt, then delivering it at steady pressure to tooling that gives it a shape.
What are the main types of plastic extruders?
Three families. Single screw, used for polyolefins such as HDPE, PP and PPR. Conical twin screw, used for PVC. Parallel twin screw, used for the largest PVC sizes, for compounding and for filled or reinforced material. The polymer decides the family before output does.
Is a 3D printer extruder the same as an industrial plastic extruder?
No. A 3D printer extruder is a filament drive with a small hot end, working in grams per hour with no compression screw and no melt pressure. An industrial extruder is a screw in a heated barrel producing hundreds of kilograms per hour. They share a name and almost nothing else.
What does the second number in an extruder model code mean?
For a single screw it is the L/D ratio, so SJ65/33 is a 65 mm screw thirty-three diameters long. For a conical twin screw it is the large-end diameter, so SJZ65/132 tapers from 65 mm to 132 mm. Reading a conical code as an L/D gives an absurd number.
What industries use extruder machines?
Pipe and fitting production, window and door profile manufacture, cable and wire sheathing, packaging film and sheet, and plastic recycling. In recycling the extruder is the pelletizing stage, turning washed flake back into pellets a converter can buy.
Do I need a single screw or a twin screw extruder?
Start from the polymer. Polyolefins such as HDPE, PP and PPR run efficiently on a single screw. PVC needs a twin screw because it degrades if held hot and is usually a powder blend. Filled or compounded material needs a parallel twin for its mixing capability.
Can one extruder run more than one polymer?
Within a family, usually yes. A single screw sized for HDPE will run PP and PPR with a temperature profile change. Crossing families is the problem — putting PVC through a single screw built for polyolefins gives it nowhere to go but degrade, and the screw geometry is wrong for a powder blend in the first place.
Which Extruder Family Each Line Runs
- Plastic Extrusion Machine Range — screw choice mapped onto complete lines, with published price ranges by product
- HDPE Pipe Extrusion Line — where the SJ and HSJ single screws in the table above actually run
- PVC Pipe Extrusion Line — the conical twin screw case, with calibration, cutting and belling built around it
- PPR Pipe Extrusion Line — the same single screw families at smaller diameters, single-layer or multi-layer
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