For direct-buried outside plant copper telephone cable, the jacket is compounded from natural DGDA-2426 NT with a reported density of 0.941 g/cm³ (ASTM D792) and a melt index of 0.65 g/10 min (ASTM D1238, 190 °C/2.16 kg). The resin is not pre-dried unless pellets have been stored in unheated silos at relative humidity above 60%, in which case drying at 70 °C for 4 h prevents surface splay caused by condensation entering the feed throat. A carbon black masterbatch based on a 40 wt% carbon black concentrate is metered at 5.0–6.5 phr to give a final carbon black loading of 2.0–2.6 wt%, verified by ash content per ASTM D1603. A phenolic antioxidant is added at 0.08–0.12 wt%, and a metal deactivator at 0.05–0.10 wt% is used only when the cable core contains an uncoated copper shield requiring protection against copper-catalysed thermo-oxidative degradation. Extrusion is performed on a single-screw extruder with L/D ratio 24:1–30:1 and compression ratio 2.5:1–3.5:1, fitted with a barrier screw, a Maddock mixing section, and a 20/40/60 mesh screen pack. Zone setpoints are 160–175 °C in the feed section, 175–190 °C in the compression section, 190–205 °C in the metering section, 200–215 °C at the head, and 205–220 °C at the die; melt temperature is held between 210 °C and 225 °C. The upper limit is 240 °C because excursions produce oxidative degradation, gel particles, and surface melt fracture at the die lip. The first water trough is held at 45–60 °C, not ambient, to reduce frozen-in orientation, and the final trough is maintained at 20–30 °C. Jacket tensile properties are evaluated per ASTM D638, environmental stress crack resistance per ASTM D1693, and low-temperature brittleness per ASTM D746. The resulting sheath is integrated into direct-buried telephone distribution cables, where the final carbon black loading provides UV resistance during trench-side storage and installation.

What Cooling and Head-Pressure Modifications Are Needed for 144-Fiber Loose Tube Optical Cable Jacketing at 120 m/min?

Outdoor fiber optic loose tube cable jacketing at elevated line speed places different constraints on head pressure and cooling than copper telephone cable jacketing. The same natural DGDA-2426 NT is let down with carbon black masterbatch to a final carbon black loading of 2.2–2.6 wt%, but the additive package includes 200–400 ppm of fluoropolymer processing aid to lower die lip shear stress during prolonged runs above 100 m/min. A gear pump is inserted between the screw tip and breaker plate when line speed exceeds 120 m/min; melt pressure upstream of the screen pack is held at 18–30 MPa. Die pressure fluctuations greater than ±0.3 MPa cause periodic wall-thickness variation beyond ±0.05 mm on a nominal 1.2 mm jacket. The barrel profile is set 5–10 °C lower than in copper cable jacketing to raise melt viscosity and reduce sag in the catenary span between the crosshead and the first water trough. Cooling is staged in three troughs: first trough at 50–55 °C, second at 35–40 °C, and third at 20–25 °C. Rapid quench below 15 °C produces a density gradient that increases post-extrusion shrinkage above 3% after 24 h at 23 °C, which can axially displace loose tubes and create micro-bends in the optical fibers. Mechanical integrity is verified by crush and tensile tests of IEC 60794-1-2; environmental stress crack resistance is measured per ASTM D1693 at 50 °C in 10 vol% Igepal CO-630; and carbon black dispersion is checked by ASTM D5596. The terminal product is an outdoor loose tube optical cable sheath for duct or direct-buried routes where water-blocked loose tubes require a high environmental stress crack resistant outer polymeric layer.

Coaxial Drop Cable Jacket Die Drawdown and Low-Frequency Attenuation Stability

RG6 and RG11 aerial coaxial drop cables use a thin HDPE jacket over an aluminium foil shield and braid. With DGDA-2426 NT, the jacket is extruded by tubing or semi-tubing crosshead methods with a die drawdown ratio between 1.5:1 and 2.2:1. The drawdown ratio is calculated from the die annulus area divided by the final jacket cross-sectional area; keeping the ratio below 2.2:1 prevents excessive orientation that can raise longitudinal shrinkage above 3% and loosen the cable shield under aerial tension. For outdoor aerial drop service, final carbon black loading is 2.3–2.6 wt% using a 40 wt% masterbatch at 5.8–6.5 phr. For indoor white premise cables, carbon black is omitted and a titanium dioxide concentrate is used at 4–7 phr with a hindered amine light stabilizer at 0.3–0.5 wt%. The white formulation has a narrower processing window because titanium dioxide increases melt viscosity; melt temperature is maintained at 205–215 °C, and die lip buildup is controlled with 200 ppm fluoropolymer processing aid. The crosshead is set with a tip/die land length ratio of 10:1–15:1, and the melt cone is drawn through a 5–15 mm air gap into a 40 °C first water trough. Concentricity is monitored continuously by x-ray or laser diameter gauge; eccentricity above 0.03 mm causes shield cutting during connector crimp. Jacket tensile and shrinkback are evaluated by mechanical and temperature cycling methods under IEC 61196-1; low-frequency attenuation stability is not jacket-controlled, but jacket shrinkback and moisture ingress are assessed through impedance and return loss measurements before and after thermal cycling. The terminal product is an aerial or premise coaxial drop cable jacket that maintains dimensional stability under connector termination loads.

Over a longitudinally welded aluminium armour on a three-core low-voltage underground distribution cable, DGDA-2426 NT is applied as an outer protective sheath with wall thickness between 1.8 mm and 3.2 mm. The compound consists of natural DGDA-2426 NT plus 5.5–6.5 phr of a 40 wt% carbon black masterbatch, 0.10–0.15 wt% phenolic antioxidant, and 200–400 ppm fluoropolymer processing aid. Where the armour is left bare or where copper screen wires are present under the jacket, 0.05–0.10 wt% metal deactivator is added to the melt to inhibit copper-catalysed thermo-oxidative degradation at processing temperatures. Extrusion is run at lower screw speeds and line speeds of 8–25 m/min because the thick wall must be cooled evenly to prevent sink marks and vacuum voids at the armour overlap. Melt temperature is held at 205–220 °C; barrel zone setpoints are 170 °C, 185 °C, 195 °C, 200 °C, and 205 °C from feed to die. Back pressure upstream of the screen pack is 15–25 MPa. The first water trough is set to 55–65 °C and the final trough to 20–30 °C. Tensile strength and elongation at break of the sheath are measured after ageing for 168 h at 100 °C per IEC 60502-1, and outer sheath carbon black content is checked by ASTM D1603. The material is not used as primary conductor insulation; dielectric stress is carried by the inner XLPE insulation layer. The terminal product is a mechanically protective outer sheath for buried low-voltage distribution cable.

When Aerial Self-Supporting Figure-Eight Drop Cable Jacketing Is Run on the Same Line as Cylindrical Cable

In aerial self-supporting figure-eight drop cable, the messenger wire and optical unit are encapsulated in a single extruded HDPE jacket with a thin web connecting the two lobes. DGDA-2426 NT is metered with carbon black masterbatch to a final loading of 2.4–2.8 wt%, and a phenolic antioxidant is added at 0.12 wt%. The melt is split into two channels before a single figure-eight die, and the web thickness is controlled by adjusting the air gap and the draw ratio of the molten web between die and first water trough. Published data for DGDA-2426 NT in figure-eight tooling is limited; production validation on the specific crosshead is required because web dimensions depend on die land geometry and melt temperature uniformity within ±3 °C. Line speed is reduced 15–25% relative to a cylindrical jacket of equivalent cross-sectional area because the thin web freezes before the two lobes, producing differential orientation and residual stress. Die temperature is set at 210–220 °C, first trough at 50–60 °C, and final trough at 20–25 °C. Eccentricity of the optical lobe is maintained below 0.08 mm. Jacket tear resistance and low-temperature brittleness are tested per ASTM D624 and ASTM D746, and outdoor weathering performance is controlled through carbon black dispersion testing per ASTM D5596. The terminal product is an aerial self-supporting optical drop cable sheath that integrates the messenger member and fiber unit without a separate protective covering.