Insulator Liquid Silicone Rubber RH-G6031-1

In transmission-class composite suspension and tension insulator housings, RH-G6031-1 is metered as a two-part addition-cure liquid silicone rubber at a volumetric ratio of 1:1 through a 10–16 element static mixer mounted directly on the injection gate. Piston-metering systems should hold shot-to-shot dosing variation below 1%, because uneven stoichiometry from worn check valves shifts the hydrosilylation cure and creates soft interfaces in the shed-to-sheath transition. The mixing head must be cooled below 30 °C; pot life of mixed A/B at 25 °C is in the range of 12–24 h, but heated runner sections above 80 °C reduce open time to minutes. ATH-filled insulator LSR grades with a filler loading around 60–80 phr exhibit a viscosity between 80 Pa·s and 150 Pa·s at 10 s⁻¹. Injection pressure at the gate should be 3–8 MPa; clamp force on a 110 kV suspension insulator mold with 2–4 cavities is typically 200–350 t (1.96–3.43 MN). Air venting at the shed root and along the sheath surface should maintain cavity pressure below 0.2 MPa to prevent void formation. On vertical presses below 200 t, full-flow fronts may hesitate at the shed-to-core transition, producing trapped gas pockets that exceed 100 µm in diameter and reduce impulse puncture strength.

Cure temperature is profiled from 120 °C at the core to 160 °C at the outermost shed. Centre-of-mass cure for a 25 mm shed cross-section reaches demoldable Shore A 35–45 in 180–240 s. Post-cure at 200 °C for 4 h completes hydrosilylation, reduces volatile siloxane content, and stabilizes dielectric loss below 0.002 at 50 Hz under ASTM D150. The terminal housing is assembled with forged steel end fittings and crimped onto the FRP core to produce suspension and tension composite insulators rated 110 kV to 220 kV under IEC 61109. Tracking erosion resistance is confirmed by IEC 60587 at 4.5 kV using 0.1% NH₄Cl at 0.6 mL/min; erosion depth is assessed below 2.5 mm.

Hollow Core Insulators Expose the Interface Between Epoxy FRP and Addition-Cure Silicone

Mandrel-wound glass-reinforced epoxy cores used in hollow composite insulators have surface porosity and residual amine species that interfere with platinum-catalyzed addition cure. The FRP core should be post-cured above 130 °C for 6 h, surface ground with 80–120 grit alumina, and cleaned with anhydrous isopropanol before primer application. RH-G6031-1 is overmolded at 1:1 ratio with an adhesion promoter added at 0.5–1.0 phr to the B component. A silane-grafted primer with methacryloxy functional groups couples the LSR to the glass-epoxy matrix. Without primer and low amine surface activity, interfacial peel strength under IEC 62217 thermal-mechanical stress falls below the bond-line requirement and flashover risk increases.

Rotating core molding machines with 4 independent heating zones are used for hollow insulator shed overmolding. Barrel temperature is held below 25 °C, while mold temperature at the core interface is limited to 130–140 °C to avoid thermal expansion mismatch between steel tooling and the FRP tube. Injection pressure is set to 2–5 MPa and injection speed is profiled to push the flow front across the shed root without jetting. The mixed compound is degassed in-line at ≤20 mbar and filtered through a 100 µm screen before entering the cavity. The resulting part is a hollow core composite insulator body rated 126 kV with shed spacing designed to IEC 60815 pollution class III.

On production lines, the most frequent failure mode is catalyst inhibition at the first 2–3 mm of the bond-line where epoxy amine bloom persists. Infrared surface inspection or dye penetrant field data show that uncured interfacial film increases dielectric loss at 1.2 U₀. Compression set after 22 h at 150 °C should remain below 20% for flange sealing. Final flange assemblies are tested according to IEC 61462 for hollow composite insulators and IEC 61109 for dielectric type tests.

What Limits Partial Discharge Threshold in Cable Termination Stress Cones?

Partial discharge inception in 15 kV and 35 kV separable connectors is governed by void density at the XLPE–silicone rubber interface and by dissipation factor of the stress cone elastomer. RH-G6031-1 is processed at 1:1 ratio with additional batch degassing at ≤1 mbar for 10–15 min in a thin-film rotary degasser before injection. The metering system must maintain component viscosity ratio ≤1.2 because unbalanced flow through a 12-element static mixer generates striation defects. These defects appear as optical haze and raise apparent charge above 5 pC at 1.73 U₀ in a shielded room test under IEC 60270.

The injected stress cone requires low dielectric constant, low dissipation factor, and stable compression set. Dielectric constant is measured between 2.8 and 3.1 at 60 Hz under ASTM D150. Dissipation factor is kept below 0.005 at 50 Hz. Compression set after 22 h at 150 °C should be ≤20% so that interfacial pressure on the XLPE cable does not relax below design value. Vacuum degassing equipment must maintain the mixed premix below 5 mbar immediately before injection; any pressure rise above 20 mbar indicates moisture or low-molecular-weight siloxane devolatilization and requires a longer venting step.

Cold-runner injection tooling with pneumatic needle shut-off is preferred. The gate is placed at the high-field region opposite the cable insertion bore to avoid knit-line partial discharge sites. Mold temperature is held at 140 °C; injection pressure at the gate is 4–8 MPa. Cure time for a 15 mm thick stress cone is 60–120 s, followed by post-cure at 200 °C for 2 h. The finished cable accessory is tested under IEEE 386 or IEC 60502-4 for partial discharge below 5 pC at 1.73 U₀ and for withstand voltage at 2.5 U₀ for 30 min.

During direct molding of station-class surge arrester housings over 10 kA metal-oxide varistor stacks, RH-G6031-1 must accommodate aluminium flange tolerance stack-up and a tangential surface gradient up to 0.5 kV/mm under wet pollution. The material is injected on a multi-cavity aluminium tool at 150 °C with gate pressure limited to 2–6 MPa. Alternating large and small sheds create undercuts that require tear strength above 18 N/mm under ASTM D624 Die B; lower tear strength leads to de-molding fractures at the small-diameter shed root and creates partial discharge sources in service.

Tracking and erosion performance is evaluated by IEC 60587 at 4.5 kV with 0.1% NH₄Cl and 0.6 mL/min contaminant flow for 6 h. Erosion depth is controlled below 2.5 mm, and tracking current should not exceed 60 mA for a 50 mm test distance. Polymer surge arresters are type-tested to IEC 60099-4, including short-circuit mechanical strength and thermal charge. Hydrophobicity recovery after surface corona at 80% relative humidity is checked under IEC TS 62073; receding contact angle should recover above 80° within 72 h after contamination.

The LSR injection barrel is held below 25 °C to avoid precure during charge and recharge cycles. Shot volume is sized to 105–110% of cavity volume to compensate for flash and to maintain packing pressure at 0.5–1.0 MPa during crosslinking. Finished surge arrester housings are assembled with venting seals at the lower flange to prevent moisture ingress; the terminal product covers distribution and station-class arresters from 3 kV to 220 kV.

When Tracking Failure Extends Beyond the Shed Root on 500 kV Bushings

Resin-impregnated paper (RIP) and oil-impregnated paper bushings use LSR shed profiles to increase creepage distance without increasing porcelain mass. At 500 kV, the shed root is the highest erosion risk because contamination accumulates at the flange transition and concentrates electrical stress. RH-G6031-1 should be qualified for 14–16 mm of creepage per kV under IEC 60815 pollution class IV. Inclined-plane testing under IEC 60587 at 4.5 kV for 6 h with 0.1% NH₄Cl and 0.6 mL/min flow should show erosion depth no greater than 2.5 mm and total failure time beyond 6 h.

Vertical injection of LSR sheds onto a RIP condenser core requires a low-clamp-force tool because the core surface compression limit is 0.5 MPa. The tool is heated to 130–150 °C and injection is performed at 3–6 MPa. Gate locations are positioned at alternating shed roots to prevent weld lines in the highest tangential field regions. Post-cure at 200 °C for 4 h removes residual siloxane species that could contaminate mineral oil in oil-impregnated bushings. However, continuous mineral-oil immersion above 100 °C is not recommended for this grade; fluorosilicone or oil-resistant barriers are required for lower, oil-submerged sections.

Bushing shed profiles are tested for wet power-frequency withstand and lightning impulse under IEC 60137. Partial discharge at 1.5 U_m should remain below 10 pC. Thermal cycling from -40 °C to +80 °C for 100 cycles should not develop cracks at the shed root; adhesion is verified by a 90° peel test exceeding 2.5 N/mm. Terminal hardware is assembled with corona rings to grade the first and last shed boundary fields.

Instrument Transformer Encapsulation and Control Winding Potting

Outdoor metering units and control winding assemblies use RH-G6031-1 as an insulating encapsulant where a soft, high-voltage-enduring layer is required between primary and secondary circuits. The A/B components are mixed at 1:1 by weight and degassed at ≤2 mbar until the foam cap settles, typically 10 min for a 500 g batch. The mixture is poured into an epoxy-coated housing preheated to 80 °C, then cured at 120 °C for 30 min in a vented oven. Exotherm is less than 15 K on a 500 g shot, avoiding thermal stress on ferrite cores and reducing cracking in the secondary winding encapsulation.

Electrical acceptance testing follows IEC 61869-1 for instrument transformers and ASTM D149 for dielectric strength. Volume resistivity under ASTM D257 should remain above 1×10¹⁴ Ω·cm after 168 h at 85 °C and 85% relative humidity. Partial discharge under IEC 60270 at 1.2 U_m is controlled below 5 pC. Because the potting layer is non-structural, the housing must provide mechanical support; continuous tensile load on the encapsulant should not exceed 0.1 MPa. The terminal product is an outdoor metering transformer rated from 11 kV to 35 kV.