Temperature control inside an extruder is one of those topics that every production manager acknowledges… yet few truly monitor with discipline. Once the line starts running and the output looks “acceptable,” most factories let the temperature drift a little. Five degrees here, eight degrees there — nothing dramatic.
But for modern cables, especially thin-wall insulation and high-precision communication wires, those small fluctuations accumulate and turn into quality instability, scrap, and customer complaints.

This article looks at what actually happens when temperature zones drift, why some materials are more sensitive than others, and what practical steps keep your extrusion line stable at scale.

1. What “Temperature Fluctuation” Really Means on an Extruder

When technicians talk about temperature fluctuation, they usually mean barrel zones not holding their setpoints. But in reality, extrusion temperature instability comes from several overlapping sources:

• Barrel zone overshoot and undershoot

• Inconsistent screw shear heating

• Die head thermal cycling

• Material feed variation

• Unstable cooling at the water trough

• Line speed changes causing shear temperature shift

So even if your controller only shows a 3–5°C drift, the actual melt temperature can swing 10–20°C depending on screw load and polymer grade.

For PVC, LSZH, TPE — that’s the difference between glossy and dull, soft and brittle, uniform and streaky.

2. How Temperature Instability Translates Into Cable Quality Defects

Below are the most common defects factories see when melt consistency breaks down. These are not generic effects — these are the real production consequences we see across PVC, LSZH, PE, TPE, XLPE (pre-vulc), and similar compounds.

2.1 Diameter Instability

When melt viscosity changes, the pressure at the die head fluctuates. This causes:

• Oversized sections

• Undersized sections

• Ovality drifting beyond tolerance

If QC starts seeing back-and-forth diameter swings within a 20–40 meter interval, melt temperature is the first thing to check.

2.2 Surface Gloss Inconsistency

Too hot → overly glossy, easy to smear
Too cold → matte areas, micro-orange-peel texture
Drifting → alternating gloss bands along the cable

This is one of the top reasons customers reject high-visibility automotive or appliance cables.

2.3 Insulation Bubbles or Micro-Voids

Under-plasticization from low melt temperature means material doesn’t fully fuse.
Over-temperature promotes gas expansion.

Both show up as:

• small pinhole-type voids

• bubble traces under the insulation

• weak insulation bonding on copper

2.4 Poor Adhesion and Mechanical Performance

TPE and LSZH particularly hate temperature instability. Fluctuations make:

• tear strength inconsistent

• elongation unstable

• cold bend performance unpredictable

The customer only sees the failure; you see the rework.

2.5 Die Drool and Build-Up

Temperature swings change viscosity at the die lip. Combined with contamination, you get die drool — and that leads to spiral marks, black dots, and unclean surface lines.

3. Why Extruder Temperature Fluctuates Even With a “Working” Machine

Factories often assume the heating system is the problem.
Most of the time, the root causes are elsewhere:

3.1 Screw Wear

A worn screw increases material slip and reduces compression.
Result: inconsistent shear heating → inconsistent melt temperature.

3.2 Poor Barrel Contact or Old Heater Bands

Loose bands, uneven contact, or slow-response heaters cause local hot/cold zones.

3.3 Inconsistent Material Feeding

If the feeding section has bridging, humidity, or granule decomposition, the screw load changes — and with it, melt temperature.

3.4 Running Too Fast for the Cooling System

If your water trough, vacuum sizing, or cooling tank cannot keep up, melt temperature stabilizes slower and fluctuates longer.

3.5 Bad PID Settings

Some older extruders “hunt” around the setpoint because the PID parameters were never calibrated for the current screw, material, or heating unit.

4. Practical Optimization Strategies for Real Cable Factories

This is where factories usually separate themselves — not by expensive upgrades, but by disciplined process control.

4.1 Stabilize the Material Before It Enters the Extruder

Material moisture, temperature, and bulk density should be consistent.
A 10-minute pre-drying/pre-heating step solves many temperature drift problems.

4.2 Tighten Zone Control Based on Melt Temperature, Not Setpoints

Factories often rely on barrel readings.
Professionals check actual melt temperature using:

• a melt thermocouple

• pressure feedback at the die

This allows finer corrections.

4.3 Improve Shear Stability

If your screw is worn, replace or refurbish.
A healthy screw stabilizes melt temperature far better than heater bands.

4.4 Upgrade Heater Bands and Insulation

Modern ceramic or cast aluminum bands lift consistency immediately.
Adding insulation blankets reduces external heat loss.

4.5 Control Line Speed Ramp-Up

Sudden speed changes modify shear and melt temperature.
Use smooth, predictable ramp curves when adjusting production speed.

5. When To Consider an Equipment Upgrade

Even well-maintained extruders eventually fall behind modern cable quality requirements.
If you are producing thin-wall, micro-coax, or automotive cables, it may be time to upgrade to a more stable extrusion solution.

Your readers often turn to suppliers such as:

• New-generation extruder lines: tighter temperature loops, stronger PID control

• Better screw designs: for LSZH, TPE, XLPE, high-speed PVC

• Integrated OD gauge feedback systems for closed-loop control

These changes reduce drift, improve stability, and reduce scrap at high line speeds.

Closing Thoughts

Temperature isn’t just a number on your panel.
It is the backbone of extrusion stability — and the deciding factor for consistent dimensions, smooth appearance, and material performance.

Cable manufacturers who keep their thermal process under control get: