The sheathing line for XLPE-insulated medium-voltage distribution cable to IEC 60502-2:2014 is configured as a 90 mm single-screw extruder with 30:1 L/D ratio and 2.8:1 compression ratio, fitted with a melt pump and pressure die. Borstar LE8706 Natural is metered as 100 parts by mass of the outer sheath compound. When direct-burial UV and mechanical requirements under HD 620 S2 Part 10C are enforced, a carbon black masterbatch is added at 2.5±0.3 parts by mass to achieve a carbon black content of 2.0–2.5% by mass and dispersion rating no greater than 2 under IEC 60811-505:2012. Melt temperature at the die is held at 205±5°C with barrel zones from feed to head at 175°C, 185°C, 195°C, 205°C, and 210°C. Melt pressure is maintained between 180 bar and 240 bar, and screw speed is clamped at 35–60 min⁻¹ to avoid shear heating above 215°C, above which the bimodal high-molar-mass fraction can generate gel particles observed as surface pimples on the sheath. Cooling is staged in three troughs at 20±2°C, 35±2°C, and 45±2°C over a total cooling length of 24 m, supporting line speeds of 15–40 m/min. Sheath thickness is maintained at 2.0–3.4 mm for 12/20 (24) kV three-core constructions, and the jacket layer constitutes approximately 8–14% of total cable mass. The finished product is XLPE-insulated medium-voltage distribution cable for buried or ducted urban networks, rated from 6/10 (12) kV through 18/30 (36) kV depending conductor size.

What Processing Window Prevents Post-Extrusion Shrinkage in Fibre Optic Loose-Tube Cables?

Fibre optic loose-tube cable sheathing imposes residual stress constraints that are not present in copper conductor cable jackets because a 0.9–1.5 mm jacket with axial shrinkage above 1% produces microbending attenuation in 12–288 fibre counts and breaches the 0.5% maximum permitted by IEC 60794-1-2:2017 for outdoor duct cables. The formulation is run at 100 parts by mass Borstar LE8706 Natural with 3–5 parts by mass of a PE-based colour masterbatch; no processing aid is introduced, and the melt flow rate of 0.7 g/10 min under ISO 1133-1:2022 is retained unless recycled PE regrind is added, which is limited to 10 parts by mass because higher addition dilutes the bimodal tie-molecule population and reduces environmental stress crack resistance in contact with cable filler gels. The extrusion process uses a 65 mm 24:1 L/D single-screw extruder with barrier mixer and a pressure die sized 7.5 mm above the cable core diameter; barrel temperatures are set at 160/170/180/185/190°C, die temperature at 195°C, and melt temperature is held at 190–200°C, below the 210°C upper limit published in the manufacturer’s processing guideline. After the crosshead, the cable enters a water trough segmented at 15°C, 28°C, and 40°C; pay-off and take-up tension is maintained at 12±4 N on aramid strength members to prevent core displacement but not high enough to indent the jacket at line speeds of 30–60 m/min. The terminal product is an outdoor loose-tube or central-tube fibre optic cable for FTTx backbone and distribution networks, compliant with ITU-T G.652.D fibre parameters and IEC 60794-3-10:2014 for duct installation, but not compliant with NFPA 262 plenum requirements because the compound is not flame retardant.

When Coaxial Drop Cable Abrasion Resistance Is Measured at −20°C, Which Compound Variables Dominate?

Coaxial drop cable outer jackets respond to cold abrasion through crystalline lamellae thickness distribution and the high-molar-mass fraction of the bimodal molecular weight distribution, not merely Shore D hardness. Borstar LE8706 Natural is introduced at 100 parts by mass; outdoor drop cable jackets add a UV-stabilized carbon black masterbatch at 2.5±0.3 parts by mass to meet weathering resistance under IEC 61196-1:2021 and EN 50117-1:2018, while indoor-outdoor variants use 4–6 parts by mass non-black pigment masterbatch. The jacket is extruded on a 45–50 mm 24:1 L/D single-screw line directly over the aluminium foil or braid shield at melt temperature 180–195°C, screw speed 50–90 min⁻¹, and line speed 60–120 m/min. The die gap is set at 1.8 times the final jacket thickness of 0.8–1.2 mm to permit draw-down without melt fracture, while the shear rate in the die land is kept below 800 s⁻¹ to avoid reducing low-temperature impact strength in cold-climate drop installations. The terminal product is RG-6 and RG-11 coaxial drop cable for HFC, direct-to-home satellite, and cable television systems; the jacket layer typically constitutes 22–28% of cable mass, and the finished cable must pass the jacket cold-bend test at −20°C without visible cracking.

Industrial instrumentation and control cable sheathing in onshore process plants is specified against resistance to oils, wet trenches, and sunlight where vertical-tray flame propagation is not mandated. Borstar LE8706 Natural is processed at 100 parts by mass with carbon black masterbatch at 2.5±0.5 parts by mass or colour masterbatch at 4–6 parts by mass; the natural resin contains stabilizers sufficient for extrusion but not for long-term outdoor exposure unless carbon black is added. The compliance framework is ANSI/ICEA S-73-532/NEMA WC 57 for control cables with thermoplastic PE jackets, while IEC 60092-350:2020 for shipboard cable materials applies only if project-specific fire performance requirements are waived or replaced, because the compound is not flame retardant and will not meet IEC 60332-3-22 vertical tray flame propagation. On production floors, the jacket is applied using a 60 mm 25:1 L/D single-screw extruder with a crosshead die over screened pairs, foil shields, and binder tapes; melt temperature is 190–205°C, die pressure 140–180 bar, screw speed 30–50 min⁻¹, and line speed 15–35 m/min for cable diameters of 8–18 mm. The process requires low die swell and a draw ratio below 2.0:1, otherwise the jacket indents the underlying polyester binder tape and reduces insulation resistance under wet conditions. The terminal product is 300/500 V or 0.6/1 kV instrumentation and control cable for outdoor open-air installations, chemical plant trays, and buried ducts where thermoplastic sheathing is permitted in non-hazardous or adequately protected routes.

Low-Voltage Overhead Bundled Cable Sheathing in Rural Energy Distribution

The use of a bimodal LLDPE jacket in low-voltage ABC lines is governed by long-term UV ageing, tracking resistance under pollution, and peel adhesion to the phase insulator. In this application, the compound is used at 100 parts by mass, and 2.5±0.5 parts by mass of carbon black masterbatch is added to achieve the UV protection level required by HD 626 S2:2018; the carbon black primary particle size is specified below 25 nm without agglomerates larger than 60 μm, because larger agglomerates initiate surface tracking across the sheath under wet polluted conditions. Production is carried out on rotating capstan lines with a 75 mm 25:1 L/D single-screw extruder, pressure extrusion die, and a cooling trough divided into 4 m stages at 20°C, 30°C, 45°C, and 50°C; melt temperature is 200±5°C, and line speed is restricted to 25–50 m/min to limit sheath eccentricity below 5% over the assembled phase conductors. Sheath thickness is set at 1.4–2.0 mm for 0.6/1 kV bundled configurations of 2–5 conductors, with the jacket representing 8–12% of total cable mass. The terminal product is a self-supporting low-voltage overhead bundled cable for rural distribution networks, designed for span lengths of 30–80 m without a separate messenger wire, and tested in accordance with HD 626 S2 and national variants such as NF C33-209 for French installations.