Rapid prototyping of a sprinkler thermal trigger via RTV silicone molding of a low-melting-point alloy

This study presents a new manufacturing method that utilizes room-temperature-vulcanized silicone molding to create low-melting-point alloy fuse links for fire sprinkler thermal triggers, an unexplored safety-critical application. The research addresses limitations of conventional sheet-metal forming by redesigning the trigger mechanism of an upright sprinkler, consolidating five components into a simplified four-part assembly featuring a stepped-cylinder fuse link and conical-tipped rods. Material characterization revealed a melting-onset temperature of 71 °C. Tensile testing confirmed a yield stress of 37.5 MPa and an ultimate tensile strength of 41.26 MPa, demonstrating adequate mechanical integrity for load-bearing applications. The silicone molding process, using vacuum-assisted gravity casting at 80 °C, achieved high-fidelity replication with 0.17% linear shrinkage and produced up to 50 parts per mold cavity. Functional validation confirmed zero leakage during hydrostatic pressure tests up to 34.5 bar and consistent thermal activation at 71.8 °C under both unloaded and pressurized conditions, providing preliminary validation according to selected National Fire Protection Association and Factory Mutual (FM) test conditions. The response time index classified the sprinklers as standard response. This hybrid manufacturing strategy bridges the gap between rapid tooling and safety-critical actuator production, eliminating the need for expensive sheet-metal forming dies, substantially reducing assembly complexity, and offering a cost-effective alternative for low- to medium-volume production.