Extrusion of Wanma Macromolecule WMPE-1311H for 0.6/1 kV distribution cable insulation is performed on a 60 mm single-screw extruder with an L/D ratio of 24:1 and a compression ratio of 2.5:1. Barrel zone set points are 145°C, 160°C, 170°C, and 180°C; the flanged head and die are held at 190°C. Melt temperature at the die exit is kept below 210°C to suppress scorch. The grafted silanol condensation reaction accelerates sharply at elevated temperatures. A breaker plate carrying a 180/100/60 mesh screen pack removes unmelted gel particles and foreign inclusions. If pressure upstream of the screen pack exceeds 350 bar, the pack is replaced before shear heating drives the melt into the scorch regime. Dry blending with a catalyst masterbatch is performed in a low-shear tumbler mixer for 3 min to avoid tin catalyst segregation. The compound must not be mixed with amine-based additives or masterbatches containing free amines. Amines accelerate silanol condensation and promote premature crosslinking in the extruder. Storage of unextruded compound requires sealed moisture-tight packaging. Exposure to ambient humidity above 60% RH for more than 4 h can produce surface pre-crosslinking, which appears as pimples and rough insulation surfaces during extrusion.

Extruder zone	Set temperature
Zone 1	145°C
Zone 2	160°C
Zone 3	170°C
Zone 4	180°C
Flange/die	190°C
Melt temperature limit	210°C
Screw L/D	24:1
Compression ratio	2.5:1

The insulated core is cooled in a water trough held at 50–80°C before coiling. Crosslinking is completed in a sauna chamber at 80–95°C and 90–100% RH for 4–8 h for insulation walls up to 1.0 mm. Thicker walls require longer residence time because moisture diffusion follows a square-root time dependence. Crosslink density is verified by hot set testing according to IEC 60811-2-1. A 200 mm specimen is loaded to 0.2 MPa at 200°C for 15 min. Elongation under load must not exceed 175%, and permanent set after recovery must not exceed 15%. Gel content measured by ASTM D2765 extraction in boiling xylene is commonly held between 65% and 75% for moisture-cured silane XLPE. Lower gel content degrades hot-set performance. Higher gel content increases modulus and may reduce low-temperature impact resistance. The finished insulation is rated for continuous conductor temperature of 90°C and short-circuit temperature of 250°C under IEC 60502-1. Insulation resistance stability is assessed after immersion in water at 20°C according to IEC 60167, with acceptance limits defined by the cable specification.

What Processing Adjustments Are Required for EN 50618 Photovoltaic Cable Insulation?

For 1500 V DC photovoltaic wire manufactured to EN 50618:2014 or IEC 62930:2017, WMPE-1311H is used as the primary insulation layer over tinned copper conductors from 1.5 mm² to 35 mm². Insulation wall thickness is selected from the construction tables in the standard. The primary insulation is normally protected by an ultraviolet-stabilized halogen-free sheath. Direct UV exposure of the silane XLPE primary insulation is not specified unless a carbon black masterbatch is added. Carbon black addition lowers volume resistivity and may reduce insulation resistance after damp heat conditioning. Therefore the grade is usually run unmodified and protected by the outer sheath. Extrusion temperature profiles are similar to low-voltage cable insulation, but line speed is governed by the downstream heat soak tunnel rather than the extruder screw. The tunnel is operated at 80–90°C and 90% RH with residence time of 6–10 h to complete moisture crosslinking through the wall before the insulation is wound onto payoff drums. Incomplete crosslinking is detected by hot set testing according to IEC 60811-2-1. The photovoltaic specification adds damp heat exposure at 85°C/85% RH for 1000 h. After damp heat, the insulation must show no cracking and must retain dielectric strength. Long-term thermal endurance at 120°C is evaluated according to EN 60216-1. North American photovoltaic wire constructions are evaluated to UL 4703. Water treeing resistance in DC wet conditions is assessed by long-term immersion tests under positive and negative polarity. Published data for this specific silane XLPE grade in photovoltaic applications is limited, so each cable construction requires full type testing by the cable manufacturer.Thin-wall automotive primary wire insulation with wall thickness from 0.20 mm to 0.40 mm imposes melt filtration and concentricity demands that are not present in building wire. WMPE-1311H is processed on a 45 mm single-screw extruder with L/D 20:1 and a screw compression ratio of 2.0:1. The lower compression ratio reduces shear heating in small cross-sections. Melt filtration through a 120/80 mesh pack is applied to remove particles larger than 70 µm. A particle above one-third of the wall thickness creates a high-voltage pinhole risk. Barrel set points are 135°C, 150°C, 160°C, and 175°C; die temperature is 185°C. The crosslinked insulation is evaluated to ISO 6722 for Class C temperature rating at 125°C. Long-term ageing at 125°C for 3000 h determines acceptance. Class D at 150°C is generally outside the usable range of unmodified silane XLPE unless additional antioxidant packages are developed; irradiation-crosslinked polyethylene or fluoropolymers are used for those constructions. Fluid immersion tests in gasoline, diesel, engine oil, ethylene glycol, and battery acid are part of ISO 6722. Silane XLPE shows limited resistance to hot engine oil. Engine-bay harness sections usually require secondary protection such as conduit or polyamide overbraid. Scrape abrasion resistance of the crosslinked insulation is improved relative to thermoplastic polyethylene, but it is lower than polyamide. Harness design places abrasion points under tape or loom.

Heat-Shrink Tubing Expansion and Recovery Without Split Defects

Production of heat-shrinkable tubing from WMPE-1311H begins with extrusion of a tube having controlled wall thickness and diameter. The tube is crosslinked by moisture exposure at 80–95°C and 90% RH until gel content reaches at least 70% by ASTM D2765. The crosslinked tube is then heated to 130–150°C and expanded over a mandrel to a diameter ratio of 2:1 or 3:1. The expanded tube is cooled under compressed air while still on the mandrel to freeze the oriented molecular network. Recovery occurs when the recovered tube is heated to 120–150°C. Longitudinal splitting during expansion occurs when gel content is below 65% or when wall thickness eccentricity exceeds 10%. Crosslink density must be high enough to give hot-set elongation below 100% at 200°C and 0.2 MPa load. Standard low-voltage cable insulation limits of 175% are not sufficient for 3:1 expansion. Tensile strength, elongation, dielectric strength, and heat shock requirements are tested according to UL 224 and CSA C22.2 No. 198.1. Recovered wall thickness increases by approximately the expansion ratio. The pre-expansion wall must be thinner than the final target. Concentricity is controlled at the extrusion stage because post-expansion correction is not possible.

When Halogen-Free Flame-Retardant Fillers Are Compounded into Silane XLPE

For building wire and control cable requiring halogen-free flame retardance, WMPE-1311H is dry-blended with a silane-compatible masterbatch containing aluminum hydroxide and magnesium hydroxide. Total filler loading ranges from 80 phr to 150 phr. Filler addition raises melt viscosity and screw torque by 30–60% compared with unfilled compound. The metering zone barrel temperature is reduced by 10–20°C to avoid releasing water of hydration from the filler. Maximum melt temperature is limited to 190°C. Above this temperature, water release from aluminum hydroxide creates porosity and surface roughness. The masterbatch must be dried at 80°C for 4 h to reduce moisture below 0.1% before mixing. Excess moisture in the filler masterbatch can trigger premature silanol condensation in the extruder, causing gel particles and uneven insulation surfaces. Flame retardance is assessed by IEC 60332-1-2 for vertical flame propagation on single insulated conductors. Halogen acid gas emission is tested by IEC 60754-1 and IEC 60754-2. Smoke density is measured by IEC 61034-2. Because hydrated fillers increase modulus, crosslink density must be raised by 10–15% to compensate for the stiffening effect and retain hot-set compliance. The exact FR masterbatch addition is determined by the cable specification because increasing filler loading reduces tensile elongation and insulation resistance.

Standard	Test objective
IEC 60332-1-2	Vertical flame propagation on single insulated conductor
IEC 60754-1	Halogen acid gas emission from combustion
IEC 60754-2	pH and conductivity of evolved gases
IEC 61034-2	Smoke density under defined combustion conditions

In industrial instrumentation cable insulation rated 300/500 V and continuous conductor temperature of 90°C, long-term insulation resistance stability under humid conditions is the controlling parameter. WMPE-1311H is extruded on a 45 mm single-screw extruder with L/D 20:1; insulation wall thickness is 0.6–1.2 mm. The compound must be pre-dried if exposed to ambient humidity above 60% RH, because surface moisture produces pimples. Insulation resistance is measured after 5 min electrification in water at 20°C according to IEC 60167. Typical XLPE volume resistivity at 20°C exceeds 10¹⁴ Ω·cm. For marine or shipboard instrumentation cable to IEC 60092-351, qualification includes low-smoke and flame-retardance requirements where specified. Published WMPE-1311H data for this specific configuration is limited. The cable manufacturer must perform complete type testing. Water absorption after immersion in distilled water at 70°C for 168 h is assessed. Absorbed water reduces insulation resistance until the cable is dried; the acceptance limit is set by the end-use specification.