Insulator Liquid Silicone Rubber RH-G603/40

Grade RH-G603/40 is a two-part, platinum-catalyzed addition-cure liquid silicone rubber formulated for electrical insulator housings, cable accessories, stress cones, and high-voltage equipment where the cured elastomer functions simultaneously as a dielectric envelope and an outdoor weathering barrier. The model designation includes a nominal cured hardness of 40 Shore A. It is supplied as a pumpable A/B system with a specified mixing ratio of 1:1. Because the manufacturer’s lot-specific certificate of analysis governs release limits, the numerical values cited in this document are drawn from public technical data for 40 Shore A insulator-grade addition-cure LSR systems and are representative targets, not product release specifications. End users must verify exact values against the active datasheet before mold design, cure-cycle programming, or electrical qualification. Unlike peroxide-cured high-consistency silicone rubber, RH-G603/40 does not require two-roll milling and can be processed in closed-loop liquid injection molding equipment.

The primary application envelope is injection overmolding of suspension and post insulator weathersheds, hollow composite insulator sheds, surge-arrester housings, and medium-voltage cable jointing. In such applications the cured material must maintain low-temperature flexibility at −40 °C, resist tracking under contaminated wet conditions, and retain hydrophobic recovery after dry-band arcing. The uncured compound exhibits shear-thinning behaviour and remains pumpable at 25 °C, but undergoes rapid addition cure when the mold temperature exceeds approximately 120 °C. The material is therefore handled in a cooled metering system and cured in heated tooling.

How Does Platinum-Catalyzed Addition Cure Constrain Processing of RH-G603/40?

The A and B components are combined by a piston or gear metering unit, passed through a static mixer with 12–24 elements, and injected into a cooled runner system. Mixing ratio tolerance is typically ±0.5%; deviations beyond ±1% alter crosslink density and can shift cured hardness by several Shore A points. The mixed viscosity at 25 °C is shear-thinning and generally reported for this hardness class between 100,000 and 500,000 mPa·s at low shear. Injection pressures in liquid silicone molding commonly fall between 5 and 25 MPa depending on part geometry, gate dimensions, and runner length. A water-cooled barrel maintained at 20–30 °C prevents premature gelation before the material enters the heated cavity.

At mold temperatures of 120–180 °C, thin sections can reach a demoldable state in 10–60 s; cure time increases nonlinearly with section thickness because silicone exhibits low thermal diffusivity. Insulator sheds thicker than 10 mm require stepped cure profiles or extended holding to avoid under-crosslinked interior regions. Cold-runner systems are specified to keep the liquid below 40 °C until the gate; hot-runner designs are unsuitable because of premature crosslinking. Gate land lengths are typically kept below 2 mm where possible to prevent excessive pressure drop. Venting slots of 0.01–0.03 mm are used because the low-viscosity uncured compound flashes through larger clearances. Production lines using closed-loop LSR injection machines with clamp forces from 1,000 to 5,000 kN report that insufficient clamping produces flash and dimensional drift.

The addition-cure system produces no volatile cure byproducts, but platinum catalyst inhibition is a process-limiting hazard. Amines, sulphur-containing compounds, tin soaps, and plasticizer off-gassing from certain PVC materials can create uncured surface films; production lines therefore avoid amine-based mold release agents and sulphur-vulcanized rubber residues. Metering system seals and static-mixer elements are specified as stainless steel or polyacetal to limit catalytic contamination. Demolding may require brushed or polished tool steel. External mold release is generally avoided to preserve surface hydrophobicity; if release is unavoidable, diluted isopropanol-based silicone-compatible agents are used. Amine or sulphur-containing release films are incompatible.

Lot-to-lot variation is monitored by rheometry. Cure curve torque maximum and scorch time are recorded on a moving die rheometer at 160 °C. Changes in torque maximum above ±10% indicate filler dispersion or inhibitor imbalance and require metering calibration. The mixed material in a static mixer has a finite working life at room temperature. Production stoppages longer than 24 h require purging of the static mixer with component A or a dedicated purge compound to prevent gel formation in the mixer.

Within the electrical qualification envelope, the cured material is assessed against wet-process tracking and erosion, dielectric strength, volume resistivity, and hydrophobic recovery after discharge activity. The following table lists representative target values for 40 Shore A insulator-grade addition-cure LSR systems. The values are not a substitute for lot-specific certificates.

Tracking and erosion performance is formulation-dependent. Outdoor insulator grades commonly incorporate alumina trihydrate or surface-treated silica to suppress dry-band arcing damage. The representative value above should not be used as a substitute for full IEC 62217 insulator qualification, because final performance depends on shed geometry, bonding to the fibre-reinforced polymer core, and interface void content. Dielectric strength is measured on 2 mm slabs; thicker sections and voids reduce the usable field gradient. Volume resistivity is measured after conditioning at 23 °C and 50% relative humidity to avoid moisture-induced surface leakage confounding the result.

Low-molar-mass siloxane migration provides hydrophobic recovery after corona or discharge exposure. A clean cured surface typically shows a static water contact angle above 100°; after hydrophobicity loss, recovery occurs within 24–72 h at room temperature. In enclosed switchgear or relay compartments, volatile siloxane outgassing is controlled by post-curing at 200 °C for 2–4 h, if low cyclic siloxane emissions are required. Compression set at 150 °C for 22 h is often below 25%, which supports seal integrity in cable accessories. Thermal endurance per IEC 60216 commonly supports continuous service at 150 °C with excursions to 200 °C; continuous use above 200 °C requires a documented life curve. The cured compound is formulated to comply with EU RoHS Directive 2011/65/EU and REACH Regulation EC 1907/2006 for restricted heavy metals and cyclic siloxane declarations, subject to lot-specific declaration.

Comparative Performance Boundaries Against HCR and RTV Silicone Insulator Materials

RH-G603/40 occupies a processing position between solid peroxide-cured high-consistency silicone rubber and condensation-cure room-temperature-vulcanizing silicone. The liquid state permits closed-loop metering and injection molding; the addition-cure reaction avoids the volatile peroxide decomposition products released by HCR and the condensation byproducts generated by RTV systems. These differences influence void formation, bond-line integrity, and long-term electrical insulation in thick sections.

In comparison with porcelain or glass insulation, the polymeric housing is lighter and provides hydrophobicity transfer under wet pollution, but its mechanical fracture toughness is lower and the device requires an FRP rod core. The product is not recommended for direct long-term immersion in hot mineral oil, ketones, esters, or aromatic hydrocarbons; swelling can exceed dimensional tolerance. Field repair is outside the intended processing window because the material requires controlled metering and heat cure. Compared with condensation-cure RTV, the addition-cure system cures rapidly with heat but does not cure at room temperature in thick sections unless post-cured; this restricts field repair use and favours factory molding.

Within the same liquid silicone rubber family, a 40 Shore A grade offers lower modulus than 50–60 Shore A housing grades, which can reduce stress on bonded FRP interfaces during thermal cycling. It provides higher tear strength and mechanical durability than 20–30 Shore A grades used for cable accessory bodies. The selection depends on the required compressive stress relaxation and the expected mechanical load from wind and ice. Compared with unfilled or low-filler silicone elastomers, the insulator-grade formulation is modified with mineral fillers to improve erosion resistance; the exact filler type and loading are datasheet-controlled because they affect dielectric loss, tear strength, and hydrophobicity recovery.

When RH-G603/40 Is Processed Below 20 °C or Above 85% Relative Humidity

Storage and handling constraints arise at low temperature and high humidity. Sealed original containers should be kept at 5–30 °C. Below 20 °C, component viscosity increases and may cause feed starvation in pump-driven metering units; below 10 °C, the A/B components should be conditioned to 23 °C±2 °C before mixing. At relative humidity above 85%, condensation on chilled mold surfaces or damp substrates can produce steam during cure and leave voids at the silicone-substrate interface. Pre-drying of FRP rods and metal inserts at 80–110 °C until moisture content stabilises is required when ambient humidity exceeds 60%.

Cross-contamination with amine-cured epoxy resins, polysulphide sealants, or sulphur-vulcanized EPDM must be controlled, because these materials can create uncured surface films even when the bulk cure appears complete. Contact with certain heavy-metal surfaces may contribute to surface cure inhibition; therefore, metering equipment contact surfaces are specified as stainless steel or polyacetal. Metering systems should be flushed with inhibited silicone oil or component A; chlorinated solvents are not required and may attack silicone seals.

Published data for the specific RH-G603/40 lot configuration may differ from the representative class values shown above, particularly where the manufacturer has introduced proprietary filler treatments or inhibitor packages. Electrical qualification and mold trials should therefore be run on the exact lot intended for production.