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In high-performance cable insulation extrusion, achieving a diameter tolerance of ±0.005 mm is no longer a benchmark reserved for only a few top-tier manufacturers—it has become a competitive requirement. For Jinghan Machinery, founded in 1998 and rooted in advanced Taiwanese extrusion technology, this level of precision reflects decades of R&D, control-system refinement, and continuous equipment innovation.

This article dives directly into the core engineering mechanisms—screw geometry, chemical foaming behavior, thermal stability, and real-time diameter feedback control—that allow modern foaming extruders to meet demanding tolerance requirements in applications such as single-layer insulation, FOAM-SKIN chemical foaming, dual-layer foamed structures, and color-strip injection extrusion.

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1. Why ±0.005 mm Tolerance Matters in Foaming Extrusion

In insulation extrusion for communication cables, RF cables, coaxial cables, and high-frequency data cables, extremely small deviations in outer diameter directly influence:

• Capacitance stability (±0.5 pF)

• Signal attenuation and impedance

• Concentricity (>93%)

• Material density distribution

• Mechanical strength under bending and pulling

Foamed insulation is especially sensitive because chemical foaming creates a cellular microstructure. Any disturbance in temperature, back pressure, screw shear, or melt homogeneity immediately affects foam ratio and expands tolerance errors. Therefore, consistent precision depends on highly optimized mechanical, thermal, and control subsystems—areas where Jinghan Machinery has invested heavily.

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2. Screw Engineering: Where Precision Begins

Modern foaming extruders achieve tight diameter tolerance largely because of scientifically optimized screw design. In foaming insulation systems, screw geometry is not only responsible for plasticizing but also for stabilizing the gas–melt mixture during foaming nucleation.

Key screw innovations that reduce diameter fluctuation:

(1) Non-stick and non-chromium-loss screw surface treatment

• Prevents material adhesion

• Maintains stable melt pressure

• Supports rapid color change without residue

• Ensures consistent inner-wall lubrication, reducing micro-pulsation in melt output

(2) Compression ratio matched to foaming kinetics

Chemical foaming requires carefully controlled shear energy. Excessive shear collapses cells; insufficient shear traps unbroken powder or moisture.

The optimized compression ratio in modern foaming screws creates:

• Uniform cell nucleation

• Even gas distribution in the melt

• Stable volumetric output, thus reducing OD pulsation

(3) Balanced metering section for high line speed + high precision

The metering zone determines the volumetric consistency of the melt delivered to the die. Jinghan Machinery’s foaming screws maintain stability even during:

• High-speed extrusion

• Quick production changeovers

• Material transitions (e.g., HDPE → FRPE)

This consistency is a major reason foaming extruders can achieve stable ±0.005 mm outer diameter.

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3. Temperature Control: The Core Driver of Foam Stability

Chemical foaming extrusion is highly temperature-sensitive. A variation of even ±2 ℃ can alter foam density, cell expansion, and capacitance. Jinghan Machinery’s system maintains internal temperature fluctuation within ±1 ℃, using:

SCR Power Control

• Smooth, jitter-free heating curve

• No thermal overshoot during ramp-up

• Immediate response to load changes

Imported High-Precision Temperature Controller

• PID auto-tuning for each heating zone

• High sampling rate ensures real-time compensation

• Stabilizes melting curve during long production runs

Thermal Uniformity → Foam Uniformity → OD Stability

A perfectly controlled melt temperature ensures that the foam ratio remains consistent along the extrusion path, directly contributing to ultra-tight diameter tolerance.

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4. Real-Time Diameter Feedback: Closing the Loop

Precision extrusion today is not purely mechanical—it relies on smart control algorithms. Jinghan’s system integrates:

Electrostatic Capacitance Monitoring

• Measures O.D. and insulation thickness in microseconds

• Detects deviations before they accumulate

• Sends correction signals to the haul-off system

Automatic Closed-Loop Adjustment

The control system:

1. Monitors diameter in real time

2. Feeds data to the servo or inverter system

3. Adjusts screw speed or puller speed

4. Restores OD stability immediately

This intelligent feedback loop ensures consistent tolerance during:

• Acceleration (start-up)

• Deceleration

• Material transition

• High-speed continuous extrusion

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5. Integrated Auxiliary System → Smaller Footprint, Higher Stability

Traditional extrusion lines rely on multiple standalone devices:
wire storage → wire extraction → wire metering → wire take-up.

Jinghan Machinery redesigned these into a single integrated module, producing:

• Shorter overall line length (reduced by 5+ meters)

• Minimized vibration and mechanical shock

• More stable tension control

• Simplified operator workflow

Fewer mechanical interfaces mean fewer sources of fluctuation that could affect diameter tolerance.

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6. Production Capacity and Foam Quality: Why Screw & Temperature Are the Core

High-output extrusion traditionally conflicts with precision control. However, modern foaming extruders overcome this through:

Optimized Screw Design + Thermal Stability = High-Speed Capability

• Maintain stable pressure balance

• Prevent melt surge

• Control foam-cell uniformity even at high throughput

Direct influence on production quality:

• OD tolerance: ±0.005 mm

• Capacitance: ±0.5 pF

• Concentricity: >93%

The combination of mechanical precision, thermal control, and intelligent electronics ensures that production speed no longer compromises product stability.

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7. Technical Summary Table

Technical Factor	Contribution to ±0.005 mm Tolerance
Optimized Screw Geometry	Stabilizes melt flow, consistent volumetric output
Non-Stick Screw Surface	Prevents pressure spikes, improves foaming consistency
±1 ℃ Temperature Control	Maintains uniform foam-cell structure
SCR Power Regulation	Eliminates heating oscillation
Real-Time Capacitance Feedback	Immediate correction of diameter deviation
Integrated Auxiliary System	Reduces mechanical disturbance and tension variation

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8. FAQ: Deep Technical Insights for Engineers

Q1: Why is temperature precision more critical in foaming extrusion than in solid extrusion?

Because chemical foaming relies on thermal decomposition, any temperature drift alters cell structure, which directly affects diameter, capacitance, and density.

Q2: How does screw design affect capacitance stability?

Foaming uniformity determines dielectric behavior. A screw that stabilizes melt pressure ensures consistent foam density, resulting in more stable capacitance.

Q3: Can high-speed extrusion still maintain ±0.005 mm tolerance?

Yes—if the line integrates optimized screw geometry, highly stable thermal zones, and closed-loop diameter monitoring.

Q4: Why is concentricity above 93% significant?

High concentricity ensures uniform electric fields in communication cables and reduces signal attenuation.

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Conclusion

The ability to reach ±0.005 mm diameter tolerance in modern foaming extruders is the result of deep engineering integration: advanced screw design, ultra-stable temperature control, intelligent feedback algorithms, and compact mechanical architecture. For Jinghan Machinery, these innovations reflect a 25-year commitment to advancing cable manufacturing technology through precision, reliability, and continuous R&D.

High-performance foamed insulation—once difficult to control—is now a repeatable, stable, and scalable process, unlocking new levels of efficiency and quality for global cable manufacturers.

http://www.jinhanmachinery.com
Jinghan Machinery

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