Today's KNOWLEDGE Share
⚙️ Extrusion Series Part 1: Choosing an Extruder Isn’t About Size but It’s About Suitability
▪️ Bigger isn’t always better. Smaller isn’t always worse.
Think of an extruder screw like a car engine.
A massive V8 looks great on paper, but if you’re stuck in city traffic, all that power turns into heat, waste, and noise.
Same thing on a cable line: run thin insulation on a big screw, and the melt lingers too long in the barrel.
Residence time stretches, temperature control drifts, and you start cooking polymer instead of shaping it.
Flip it. A small screw is a 1.3-liter turbo which is fast, efficient, perfect for low-wall runs.
But overload it with thick walls or high throughput and it gasps; pressure spikes, melt swings, higher shear rate and mixing turns uneven.
▪️ What Actually Matters
1. Barrel diameter → defines throughput capacity.
2. L/D ratio → controls how completely the polymer melts and mixes.
3. Compression ratio → stabilizes melt pressure; critical for different materials (LSHF ≠ XLPE ≠ PVC).
4. Die & crosshead size → must match the incoming core OD to keep centering and pressure stable.
▪️ Rough Sizing Guide
45–70 mm extruders
→ Typically handle 20–110 kg/hr (≈0.3 – 1.8 kg/min).
→ Good for small conductors and thin-wall jobs where melt demand is low.
90–120 mm
→ Comfortable around 120–380 kg/hr (≈1.5 – 6.5 kg/min).
→ Covers most LV and MV single-core work because the kg/min requirement matches a wide range of incoming diameters.
150 mm and above
→ Push 400+ kg/hr (≈7 – 15+ kg/min).
→ For big cores, thick sheaths, or very high line speeds where melt demand skyrockets.
▪️ Residence Time - The Silent Killer
Run a small cable on oversized extruder and the material just sits there… slowing being pushed out.
Example: for a 95 mm² cable with 1.8 mm XLPE insulation, a 120 mm extruder gives roughly 6 minutes from hopper to die.
Use a 200 mm instead, and that same polymer can take 30 minutes to reach the die.
That extra resident time invites premature cross-linking and gel formation which effectively spoiling your insulation before it even sees the crosshead.
▪️ Bottom Line
It’s not a diameter contest.
A well-matched 70 – 90 mm extruder will outperform a bored 120 – 200 mm any day if polymer, temperature, screw design, and residence time are all balanced with the required material output.
So pick by job, not by ego.
A good extruder, like a good engine, doesn’t shout.
It hums with steady flow, clean pressure, and perfect control.
Should I go for the screw design, crosshead or material for extruders next?
source : Hazim Shafik
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