In high-voltage AC transmission service, RH-G605/50 is processed as a two-part addition-cure liquid silicone rubber whose Part A and Part B are metered at a 1.00:1.00 weight ratio through a 32-element static mixer, followed by an in-line pigment masterbatch addition of 0.8–1.5 wt% of total compound when gray RAL 7035 or darker shed color is specified. The compound is used at 100 parts by weight of the finished insulation compound; no let-down with high-consistency silicone or EPDM is performed because diluting the pre-compounded alumina trihydrate content below 45 wt% shifts the tracking resistance from IEC 60587 Class 1A 4.5 kV to a Class 1B 3.5 kV boundary. On a 400-ton vertical LSR injection press with a 60 mm/20:1 L/D reciprocating screw, barrel zones are maintained at 18–32°C, the static mixer is cooled to 15–25°C, and the mold is held at 140–155°C with a curing time of 90–150 s for a 12 mm shed wall. Injection pressure is set at 80–120 bar and holding pressure at 60–80 bar; mold vacuum is pulled below 80 mbar before shot discard. The fiberglass-reinforced epoxy core rod, surface-prepared to Ra 3.2–6.3 μm and primed with a 0.01–0.03 mm dry-film silane adhesion promoter, is insert-loaded; end fittings are zinc phosphated and sealed with a boiling-water-resistant epoxy coating. Process control is dominated by scorch risk: when the screw remains idle for more than 180 s at a barrel temperature above 35°C, the mixed compound forms microgel particles that block the cold runner tips; the resulting batch-to-batch variance appears as surface defects at the lower shed root. Compliance for this application is governed by ISO 868:2003 hardness at 50 Shore A after post-cure, ISO 37:2017 tensile strength above 6 MPa, ISO 34-1:2022 tear strength above 20 kN/m, ASTM D257-14 volume resistivity above 1.0×10^15 Ω·cm, ASTM D149-20 dielectric strength above 20 kV/mm, IEC 60587:2007 tracking and erosion at 4.5 kV Class 1A, and IEC 61109:2008 in conjunction with IEC 62217:2012 for composite suspension and tension insulators. The terminal product classes are suspension insulators, tension insulators, braced line post insulators, and horizontal Vee insulators for 69 kV through 765 kV AC overhead lines, where the LSR shed must recover hydrophobicity after IEC 60815-1:2008 pollution class IV salt fog exposure. Published data for this exact grade after 10-year field exposure at 765 kV is limited; laboratory tracking and erosion results are not a substitute for full-scale insulator type testing under IEC 62217.

Can RH-G605/50 Maintain Interface Adhesion in Polymer-Housed Surge Arresters Under IEC 60099-4 Thermal Cycling?

Failures in polymer-housed metal-oxide surge arresters are most commonly observed at the interface between the varistor stack and the silicone housing after thermal cycling, not in the bulk LSR. In this application, RH-G605/50 Part A and Part B are metered at 1.00:1.00 by weight and the finished compound is used without ATH let-down; for deep-shed arresters with a 25–30 mm wall thickness, an internal release agent based on a saturated fatty acid ester may be added at 0.3–0.6 wt% of total compound to Part B only, but any addition above 0.6 wt% disrupts silane-mediated adhesion to the pre-treated fiberglass cage and produces interface void counts above 2% on C-mode scanning acoustic microscopy. The process uses a 150–250-ton vertical injection press with a 50 mm/18:1 L/D mixing screw, a 20–24°C cold runner, and a mold temperature of 125–145°C; injection speed is deliberately reduced to 15–30 mm/s and cavity pressure is capped at 40–60 bar, because zinc-oxide varistor blocks crack at local contact pressures above 70 bar during filling. The varistor stack is preheated to 60–80°C before insertion to reduce viscosity-front separation at the metal-silicone boundary, and the curing time is 180–300 s depending on the maximum shed thickness. Post-cure runs at 200°C for 4 h in a forced-air oven with 20 air changes per hour to remove volatile siloxane cyclics, which would otherwise deposit on pressure-release diaphragms. The relevant compliance set includes IEC 60099-4:2014 for metal-oxide surge arresters, IEEE C62.11-2020 for metal-oxide surge arresters for AC power circuits above 1 kV, IEC 62217:2012 for polymeric insulators, and IEC 60587:2007 for tracking and erosion at Class 1A 4.5 kV; insulation resistance tests follow ASTM D257-14, and dielectric strength is verified by ASTM D149-20 at 20 kV/mm minimum. The terminal products are distribution class arresters from 10 kV to 36 kV and station class arresters from 66 kV to 245 kV, including both normal and high-energy classes, where the LSR housing must withstand repeated 8/20 μs current impulses without surface rupture. Sulfur-containing or amine-containing additives are incompatible with the platinum cure system and must be excluded from the entire molding line, including mold cleaning agents.

Hollow-core composite insulators for 72.5–245 kV instrument transformers impose a different process bottleneck: the bond between the LSR shed and the filament-wound epoxy-glass tube fails before the bulk elastomer fails. Formulation-wise, RH-G605/50 is used at 100 parts by weight of the A/B system, with Part A and Part B metered at 1.00:1.00 by weight; a silane coupling agent is not normally added to the liquid rubber because it shortens the mixed-pot life at 25°C from more than 24 h to 6–10 h and accelerates microgel formation in the static mixer. Instead, the filament-wound tube is abraded to Ra 3.2–6.3 μm and coated with a 0.01–0.03 mm dry-film primer containing 5–8 wt% vinyl-functional silane and a platinum-compatible adhesion promoter; the primed core is transferred to a 250-ton vertical LSR press equipped with a vacuum chamber evacuated to below 100 mbar before shot. The mold operates at 135–155°C; for a 12–15 mm shed wall, cure time is 120–150 s at an injection pressure of 60–100 bar and holding pressure of 50–70 bar. Unlike the overhead line insulator process, the hollow-core process uses a lower injection speed of 20–35 mm/s to prevent air entrapment around the inner bore, and the screw is purged with uncured compound after every interruption longer than 120 s to avoid platinum catalyst deactivation by epoxy amine exudate. The compliance framework for this application comprises IEC 60137:2017 for bushings above 1000 V AC and IEC 61869-1:2007 for instrument transformer insulation, with material acceptance tied to ISO 37:2017 tensile strength above 6 MPa, ISO 34-1:2022 tear strength above 20 kN/m, ISO 815-1:2019 compression set below 25% after 22 h at 175°C, and IEC 60587:2007 Class 1A 4.5 kV tracking resistance. The terminal products are current transformer bushings, voltage transformer bushings, wall bushings, and SF6-to-air bushings for 72.5 kV, 145 kV, and 245 kV installations, where partial discharge extinction below 5 pC at 1.5 times rated line-to-ground voltage is required after over-molding. Published data for this specific configuration is limited for very large-diameter bushings above 600 mm shed diameter; mold-filling simulation and trial runs are required before series production.

Cable Termination Sheds and Stress-Relief Components Molded Without Post-Cure Discoloration

Medium- and high-voltage cable accessories demand low permanent deformation during load cycling, but the processing limit for RH-G605/50 in this sector is not mechanical; it is the interaction between the platinum cure system and sulfur-cured EPDM or peroxide-cured XLPE surfaces that migrate into the mold atmosphere. The formulation addition ratio remains Part A : Part B = 1.00 : 1.00 by weight, used at 100 parts of the finished LSR compound; a color masterbatch is added at 1.0–1.5 wt% only when non-gray termination sheds are required, and no plasticizer, ATH booster, or catalyst adjustment is performed. The downstream production line for an outdoor cable termination shed typically uses a 120–180-ton vertical LSR injection press with a 20:1 L/D 50 mm screw, a 32-element static mixer cooled to 18–22°C, and a 12–16°C cold runner; the mold temperature is 120–140°C, and the cure time is 100–180 s for wall thicknesses of 6–12 mm. Injection pressure is limited to 50–90 bar because the thin shed lips are prone to flash at higher cavity pressure, and the parting line is equipped with a 0.02 mm vent insert to prevent air burns at the tip of the weather shed. Release is mechanical using PTFE-coated core pins; silicone-oil external release is incompatible with subsequent silicone over-molding and with high-voltage interface tracking. The compliance standards are IEC 60502-4:2022 for cable accessories above 30 kV, IEEE 48-2020 for cable terminations above 2.5 kV, and HD 629.1 S3 for European cable accessory test requirements; material acceptance includes IEC 60587:2007 Class 1A 4.5 kV, ASTM D149-20 dielectric strength above 20 kV/mm, and ASTM D257-14 volume resistivity above 1.0×10^15 Ω·cm. The terminal products are outdoor termination sheds for 15 kV, 35 kV, 66 kV, and 132 kV XLPE cable systems, plug-in separable connectors up to 42 kV, and deadbreak connector bodies. The material is not recommended for oil-filled accessory designs because aromatic hydrocarbons in insulating oil swell LSR and reduce tensile strength by more than 15% after 1000 h at 80°C.

When a 25 kV AC electrified railway network specifies hydrophobic recovery after a 1000 h salt fog test, the compound’s preloaded alumina trihydrate content should remain undiluted, and the only permitted adjustment is a UV-stabilizer masterbatch at 0.5–1.0 wt% of total compound to shift the ISO 4892-3 UV-A weathering limit beyond 5000 h without surface chalking. RH-G605/50 is metered at Part A : Part B = 1.00 : 1.00 by weight and processed at 100 parts by weight of the final elastomer compound; addition of phenyl-substituted silicone oil below 2 wt% has been proposed to lower injection pressure, but this practice retards hydrophobicity recovery after corona exposure and is therefore excluded from the railway insulator formulation. The production process uses a 180-ton vertical injection press with a vacuum chamber below 80 mbar, a mold temperature of 130–150°C, and an injection speed of 20–35 mm/s; metal end fittings are sand-blasted to Sa 2.5 and primed with a two-part epoxy zinc phosphate layer before insertion. Cure time for an 8 mm shed wall is 80–120 s, and post-cure is fixed at 200°C for 4 h to reduce cyclosiloxane volatiles below 0.1 wt%, so that surface deposition on the contact wire in tunnels is avoided. Compliance is aligned with EN 50124-1:2017 for insulation coordination in railway applications, EN 50163:2004 for traction supply voltages, and IEC 61109:2008 for composite insulators, while tracking performance is tested to IEC 60587:2007 Class 1A 4.5 kV and mechanical integrity to ISO 37:2017 and ISO 34-1:2022. The terminal products are catenary cantilever insulators, section insulators, tunnel support insulators, and return-circuit insulators for 25 kV 50 Hz and 15 kV 16.7 Hz electrified lines, where the LSR must withstand direct application of de-icing chemicals without losing hydrophobicity. Amine-based mold release and condensation-cure RTV repair pastes must not share the same production area because airborne amine species poison the addition-cure reaction at the shed surface.

38 kV Metal-Enclosed Switchgear Bushing Inserts and Low-Pressure Fault Containment

38 kV metal-enclosed switchgear bushing inserts and support insulators are molded from RH-G605/50 with the same two-part metering ratio of 1.00:1.00 by weight, but the process window is narrower than for overhead insulators because the insert is a 4–8 mm thin-wall component over a 25 mm diameter copper conductor, not a thick shed. The formulation uses no filler addition and no pigment masterbatch, because any additive above 0.2 wt% alters the dielectric loss tangent under oil and creates a visible surface haze on the conductor interface. The downstream production cell is a 100-ton vertical LSR injection press with a 40 mm/20:1 L/D screw and a 16-element static mixer; mold temperature is 120–135°C, injection pressure is 40–60 bar, and cure time is 60–120 s for wall thicknesses of 4–8 mm. The copper conductor is pre-coated with a platinum-compatible silane adhesion promoter, and the mold is evacuated to below 60 mbar before injection to eliminate interfacial voids that would initiate partial discharge at the conductor edge. The quality gate is partial discharge measurement below 5 pC at 1.2 times rated voltage in accordance with IEC 60060-1, plus insulation resistance above 1.0×10^15 Ω·cm by ASTM D257-14 and dielectric strength above 20 kV/mm by ASTM D149-20. Compliance is governed by IEC 62217:2012 for polymeric insulators and IEC 60060-1 for high-voltage test technique, with the product’s fire resistance verified by limited oxygen index testing under ISO 4589-2:2017 at or above 28%. The terminal products are 38 kV bushing inserts, spout insulators, and support insulators for metal-clad switchgear and gas-insulated switchgear up to 38 kV, where the LSR must survive internal arc overpressure without fragmentation. Operational boundaries include a maximum storage time of 6 months in sealed drums below 30°C, and any exposure to relative humidity above 60% without nitrogen blanketing raises the risk of hydrolytic degradation of the adhesion promoter system.