Optical cable quality depends not only on fiber performance but also on process control during cabling and sheathing production. Poor tension control, unstable stranding pitch, and inconsistent sheath concentricity can lead to attenuation increase, mechanical failure, and reduced service life.
This article explains five critical process control points that directly affect optical cable quality and demonstrates how modern optical cable manufacturing equipment can improve production consistency.
1.Pay-off Tension Control: Why Stable Tension Matters in Optical Cable Manufacturing
Process Principle
During cabling, the pay off tension of strength members (steel wire/FRP) and loose tubes must be precisely controlled. Too high a tension stretches the loose tube and alters the fiber excess length inside; too low a tension causes the loose tube to arch during stranding, leading to uneven pitch. Production experience shows that when pay off tension fluctuates by more than ±0.8N, the additional attenuation of the cable after temperature cycling from -40°C to 70°C can rise above 0.05dB/km, exceeding the national standard limit of 0.03dB/km.
Hongkai Tension Control Solution
Hongkai SZ stranding and cabling machines adopt independent servo motor active pay off + real time closed loop tension sensors. Each loose tube pay off is equipped with a tension dancer and a low friction cylinder. Tension signals are fed back to the PLC every 20 ms, and the PLC dynamically adjusts the pay off motor torque via a PID algorithm. In actual production (line speed 20 m/min), pay off tension fluctuation is stably maintained within ±0.4 N, better than the industry standard of ±0.5 N.
2.Stranding Pitch Control: How to Maintain Consistent Cable Structure
Process Principle
The SZ stranding pitch is one of the most important parameters affecting optical cable structure and performance. Pitch deviation leads to uneven stress on the fibers, causing microbending loss when the cable is bent. Traditional equipment relies on mechanical gear changes to set the pitch, which not only slows down changeovers but also causes pitch drift over time due to gear wear.
Hongkai Technical Solution
Hongkai uses a fully differential mechanical structure + stepless PLC setting, eliminating any gear change. The pitch value is entered directly on the touch screen (in mm), and the PLC controls the differential motor speed synchronously with the main capstan. The equipment also features a pitch calibration function – when the actual number of turns deviates from the set value, operators can correct the calibration parameter online. Customer production data shows that over 8 hours of continuous production, the maximum stranding pitch deviation is ±0.08 mm, with a CPK value of 1.33.
3.Binding Yarn Tension Control for Stable Optical Cable Production
Process Principle
The function of binding yarn is to fix the stranded loose tubes. Excessive yarn tension leaves longitudinal indentations on the loose tube surface, causing local wall thinning after sheathing; too low tension makes the binding loose and the cable core unstable. Moreover, tension differences between left hand and right hand binding affect cable roundness.
Hongkai Segmented Control Technology
Hongkai dual-head binder uses independent tension adjustment for left hand and right hand yarn, with an adjustment range of 0.5 N–5 N. Each side is equipped with a yarn break detection switch. During normal production, the yarn break switch is turned on; if a yarn breaks or tension becomes abnormal, the machine stops automatically and raises an alarm. In practice, when installing a yarn bobbin, care must be taken about the direction – the yarn should be taken from the top of the bobbin to avoid friction induced tension jumps. This design helps prevent loose-tube deformation and improves cable roundness.and a cable roundness above 98.5%.
4.How to Improve Sheath Concentricity in Optical Cable Production
Process Principle
In sheathing extrusion, concentricity between the tip and die has traditionally relied on manual adjustment by operators, requiring recalibration every 4–6 hours and varying between shifts. When concentricity falls below 98%, the thin side of the sheath is prone to cracking when the cable is subjected to lateral pressure.
Hongkai Online Closed-Loop Solution
Hongkai sheathing line is equipped with a high-precision laser diameter gauge (accuracy 0.2 μm, scanning speed 200 mm/s), located after the cooling trough and before the first capstan. The gauge collects outer diameter data in real time, and the PLC uses a PID algorithm to dynamically adjust the extruder screw speed, controlling outer diameter fluctuation within ±0.03 mm. At the same time, the system automatically evaluates sheath concentricity. Over 8 hours of continuous production, the average concentricity remains above 98% during continuous production, with wall thickness tolerance ≤ 0.04 mm (nominal 1.8 mm). This solution reduces adjustment time from 30–60 minutes (manual) to no intervention needed after initial calibration.
5.Temperature Cycling Performance in Optical Cable Manufacturing
Process Principle
One of the most important concerns for end users is signal attenuation change under extreme temperatures. Residual stresses introduced during cabling and sheathing, as well as uneven fiber excess length, translate into additional attenuation during temperature cycling. International standard IEC 60794-1-2-F1 requires additional attenuation ≤ 0.03 dB/km after 10 cycles from -40°C to 70°C.
Hongkai Process Guarantee
Hongkai equipment ensures temperature-cycling performance from three aspects:
Cabling stage: Precise pay-off tension and pitch control ensure uniform distribution of fiber excess length.
Sheathing stage: Laser-diameter closed-loop guarantees uniform wall thickness, avoiding stress concentration.
Material compatibility: The screw design is suitable for various sheath materials such as PVC, LSZH, HDPE, and TPU. Each material has its own temperature-process curve stored in the PLC recipe.
Tested by customer third-party laboratories, cable samples produced with Hongkai cabling and sheathing lines show a maximum additional attenuation at 1550 nm of 0.027 dB/km after 10 cycles from -40°C to 70°C, fully meeting the standard requirement.
International Compliance and Export Experience
| Export Region | Compliance Requirements | Hongkai Equipment Status |
| European Union | CE certification (mechanical safety EN ISO 12100, electrical safety EN 60204-1) | Electrical system designed to EN standards; can assist with certification |
| USA | UL 508A industrial control panels | UL-certified components optionally available |
| Southeast Asia | No mandatory certification, but requires manuals and training | Provides Chinese/English manuals + on site training |
| Middle East / Africa | High temperature environment adaptability | Maximum operating ambient temperature 45°C, redundant cooling on key components |
Cumulative exports: As of 2025, Hongkai equipment has been sold to 15+ countries and regions including Saudi Arabia, UAE, India, Vietnam, Indonesia, Nigeria, Kenya, Russia, and Ukraine, with cumulative shipments exceeding 150 units/sets.
Hongkai Equipment Key Parameters (Measured Data)
| Equipment Type | Key Parameter | Hongkai Measured Value | Industry Benchmark |
| SZ stranding & cabling machine | Tension control accuracy | ±0.4 N | ±0.5 N |
| SZ stranding & cabling machine | Stranding pitch deviation | ≤ ±0.08 mm | ≤ ±0.1 mm |
| Sheathing line | Concentricity | 98.6% (average) | ≥ 98% |
| Sheathing line | Wall thickness tolerance | ≤ 0.04 mm | ≤ 0.05 mm |
| Temperature cycle test | Additional attenuation -40°C~70°C | ≤ 0.027 dB/km | ≤ 0.03 dB/km |
| Whole plant commissioning | Installation to production | 3–4 weeks | Typically 6–8 weeks |
| Changeover time | Switching product specifications | ≤ 1.5 hours | Typically 4–6 hours |
Conclusion: Turning Process Control Points into Equipment Selection Criteria
When purchasing optical cable equipment, decisions should not focus solely on price and capacity, but on how well the equipment guarantees the five process control points described above: pay off tension closed loop, stepless pitch setting, independent segmented binding tension control, online concentricity correction for sheathing, and temperature cycle verification. These are not marketing slogans – they are quantifiable technical indicators.
Guangdong Hongkai Optical Cable Equipment Technology Co., Ltd. is a professional optical cable equipment manufacturer in China, providing SZ stranding machines, optical cable sheathing lines, FTTH cable production lines, and turnkey factory solutions, and supports whole-plant planning and overseas delivery. For technical specifications or field production data for specific models, please contact the Hongkai technical team.
FAQ
Q: What factors affect optical cable cabling quality?
A: The key factors include pay-off tension stability, stranding pitch accuracy, yarn binding tension uniformity, sheath concentricity, and temperature cycling performance. These critical process control points directly affect the mechanical strength, attenuation performance, and service life of the optical cable.
Q: Why is tension control important in SZ stranding?
A: Tension control directly affects excess fiber length (EFL) and stranding pitch stability. Excessive tension may stretch the loose tubes and alter the designed excess fiber length, while insufficient tension can cause loose tube buckling and uneven pitch distribution, resulting in increased attenuation. Precise tension control is essential for ensuring consistent optical cable quality.
Q: How does stranding pitch affect optical cable performance?
A: Variations in stranding pitch can lead to uneven stress distribution on the optical fibers. During cable bending, this may cause micro-bending losses and increased signal attenuation. A uniform and stable stranding pitch ensures proper fiber distribution within the cable core, improving bending performance, tensile strength, and long-term reliability.
Q: What equipment is required for optical cable manufacturing?
A: A typical optical cable production line includes a fiber coloring and rewinding machine, secondary coating (loose tube extrusion) line, SZ stranding line, yarn serving machine, tape wrapping machine, and sheathing extrusion line. Supporting equipment generally includes pay-off stands, capstans, take-up systems, and quality inspection instruments. Depending on the cable design, additional equipment such as tight-buffer production lines and FTTH drop cable production lines may also be required.
