Insulator Liquid Silicone Rubber RH-G605/40

In overhead transmission polymer insulator manufacturing, RH-G605/40 is processed as a two-part addition-cure liquid silicone rubber with a nominal hardness of 40 Shore A and a metering ratio of 1:1 by volume. The compound is degassed under vacuum of at least -0.095 MPa before entering a reciprocating screw injection unit, then injected onto a preheated pultruded epoxy-glass core at mold temperatures between 120 °C and 160 °C. Injection pressure on a 2,500 kN clamp-force LSR injection molding machine typically falls between 15 MPa and 35 MPa, but the critical processing threshold is not pressure; it is the interface temperature and primer coverage. The FRP core is preheated to 100 °C and treated with a silane coupling primer because residual amine species in the epoxy matrix can poison the platinum crosslinking system and produce a locally uncured elastomer layer at the core-sheath interface. Post-curing at 200 °C for 4 h is applied to remove siloxane volatiles and stabilize dielectric dissipation factor, tear strength, and compression set. End products—composite suspension and tension insulators in the 15 kV to 230 kV nominal voltage range—are qualified under IEC 61109 for mechanical load-time behavior and under IEC 62217 for interface integrity, water immersion, tracking and erosion, and hydrophobic transfer. The inclined-plane test under IEC 60587 at 4.5 kV applied voltage with a conductive NH4Cl contaminant is commonly specified for the silicone shed material; a typical acceptance boundary is an erosion depth not exceeding 25 mm and no puncture after 6 h. In field production, the dominant failure signature is not bulk dielectric breakdown but delamination at the core-sheath boundary, which is controlled by holding mold vacuum below 50 mbar and adjusting gate sequencing to prevent the low-viscosity melt from jetting across the primed core.

The tabulated test designations are applied to finished parts, not to the uncured raw component; lot-specific processing boundaries should be taken from the manufacturer’s certificate of analysis and the OEM material specification. Published data for this specific configuration is limited in open literature, but the ranges given reflect commonly applied processing and qualification windows for 40 Shore A addition-cure liquid silicone rubber compounds.

What Changes When a 40 Shore A Elastomer Is Overmolded Directly onto a Zinc Oxide Stack?

The process sequence begins with aligning metal-oxide varistor blocks on a mandrel, applying a controlled axial preload, and placing the assembly into a vacuum-capable mold. RH-G605/40 is then pumped through a static mixer at the same 1:1 ratio used for insulator housing work, but the injection speed is reduced to a creep-filling profile because the elastomer must not displace the preloaded blocks or entrap air at the block-to-block interface. Mold vacuum is held below 30 mbar; cure temperature is set between 130 °C and 150 °C, and the demolded part receives a 200 °C post-cure for 4 h to complete crosslinking and to minimize residual siloxane migration. The resulting polymer-housed surge arresters, typically from 3 kV to 36 kV system voltage, are tested according to IEC 60099-4 for operating duty, thermal stability, and short-circuit behavior with the specified overpressure relief device. The silicone housing contributes to polymer-type arrester performance by resisting erosion under contaminated surface wetting and by maintaining a hydrophobic surface state, while the encapsulated FRP structure provides mechanical containment. A production-relevant threshold risk is moisture entrapment between the zinc oxide blocks and the cured silicone: if the MOV stack is not preheated to 80 °C to 120 °C before injection, residual surface moisture vaporizes during cure and forms voids that increase partial discharge activity under IEC 60270 measurement. The material also must not be processed in molds previously used for condensation-cure RTV with organotin catalysts, because trace organotin compounds can poison the platinum addition-cure system and leave a tacky internal surface around the arrester stack.

Medium-voltage separable connectors and cable terminations use RH-G605/40 as the outer insulating body over conductive EPDM inserts, with the same 1:1 metering ratio and a cure window of 130 °C to 160 °C. The process is less sensitive to interfacial adhesion than to low compression set and tear resistance, because the connector must survive repeated installation and removal without splitting at the bus interface. Typical production uses multicavity cold-runner injection with vacuum-assisted venting and a 200 °C post-cure for 4 h, followed by dimensional inspection under ISO 815-1 compression set testing and ISO 34-1 tear strength verification. End products are 11 kV and 15 kV plug-in elbows, straight connectors, and dead-end receptacles qualified under IEC 60502-4 accessory type tests. An operational boundary for this part family is catalyst inhibition caused by sulfur-cured EPDM substrates; if a sulfur-cured insert has not been fully post-vulcanized or if sulfur blooming is present, the silicone surface in contact with the insert may remain uncured after demolding.

When an 800 V Busbar Is Insert-Molded Without an Adhesion Primer

For power distribution units in electric vehicles and stationary battery systems, RH-G605/40 is injection-molded around nickel-plated copper busbars in a three-axis insert cell. If the substrate is not plasma-activated and a silane primer is not applied, the elastomer forms only a mechanical interference fit; subsequent thermal shock from -40 °C to 150 °C produces interfacial separation and exposes creepage paths. The recommended process sequence is vapor degreasing, atmospheric plasma treatment at 2 kW to 5 kW generator output, primer application, and insert preheating to 90 °C to 120 °C before mold closure. The LSR is metered at 1:1 and injected at low shear to avoid displacing the busbar; cure temperature ranges from 130 °C to 150 °C, followed by 200 °C for 4 h post-cure. The finished part—an insulated busbar section or battery disconnect unit cover—is evaluated for flammability at the final wall thickness under UL 94 V-0, for creepage and clearance under IEC 60664-1, and for high-voltage leakage across the overmold boundary. Material compliance for the European market is assessed under RoHS Directive 2011/65/EU and REACH Regulation 1907/2006, with lot-level analytical data used to verify restricted phthalate and polycyclic aromatic hydrocarbon content. In this application, the main process conflict is not cure inhibition but heat transfer from the copper insert: busbars thicker than 8 mm act as chill bars, delaying cure at the contact surface and requiring a slower cure profile than unfilled mold cavities. If the mold is opened on a fixed timer rather than a cure-monitoring signal, the inner surface can be under-cured while the outer surface is fully crosslinked, producing a part that passes Shore A hardness on the exterior but fails dielectric adhesion after thermal cycling.

Bushing Sheds on Filament-Wound FRP Cores

Dry-type transformer and switchgear bushings in the 72.5 kV to 145 kV class are manufactured by overmolding RH-G605/40 shed profiles onto a machined filament-wound FRP tube. The 1:1 mix is injected through sequential needle gates into a vented mold held at 140 °C; vacuum below 30 mbar is maintained during filling because shed crests and root corners are prone to air entrapment in unvented molds. The FRP tube is primed on its bonded surface, and the primer is cured at 25 °C for 30 min before silicone injection. Post-curing at 200 °C for 4 h reduces low-molecular-weight siloxane content and improves tracking resistance. The resulting dry-type bushings are qualified under IEC 60137 for insulation systems above 1000 V and are often subjected to partial discharge measurement under IEC 60270 at rated voltage to detect voids at the FRP–silicone interface. The boundary condition most often overlooked is moisture absorption by the filament-wound core: if the FRP tube is stored at relative humidity above 60%, it must be preconditioned at 80 °C until moisture content is below 0.1%; otherwise water vapor released during molding produces interfacial bubbles that are detectable as a rise in apparent charge above 10 pC in the finished bushing.

Cold-shrink cable joint insulation requires lower processing complexity than bushing overmolding but imposes a separate storage-state compression set requirement. RH-G605/40 is injection-molded as a thick-walled tube at 1:1 ratio with a 140 °C cure, post-cured at 200 °C for 4 h, and then expanded over a removable spiral core. The expanded part may remain in warehouse storage for up to 24 months before installation, so compression set tested under ISO 815-1 at 100 °C for 22 h is a routine lot-acceptance parameter. The product is used as the insulating layer in 11 kV to 33 kV XLPE cable joints qualified under IEC 60840 or IEC 60502-4 accessory test sequences, depending on system voltage. The main operational incompatibility is with mineral oil: although lightly oil-contaminated surfaces can be wiped, long-term immersion in free mineral oil is outside the intended application envelope because oil absorption alters volume resistivity and can increase the dielectric loss factor at elevated temperature.