Cooling-stage-validated thermal modeling of hybrid POM nanocomposite gears: Heat dissipation pathways and thermal hotspot localization under dry-running conditions

The thermal reliability of polymer gears operating under dry-running conditions is governed by the interaction between friction-induced heat generation, conductive heat dissipation, and localized thermal accumulation. However, the relationship between intrinsic thermal transport and component-level thermal reliability remains insufficiently understood. In this study, the transient thermal behavior of polyoxymethylene (POM) gears reinforced with carbon black (CB) and nano-calcium carbonate (NCC) was investigated through an integrated experimental–numerical approach. Thermal conductivity, specific heat capacity, transient temperature evolution, cooling behavior, wear, and surface degradation were experimentally characterized, while three-dimensional finite element simulations were used to analyze localized temperature fields and heat-transfer pathways. A cooling-stage-based validation strategy was introduced to evaluate the component-level cooling response under controlled conditions while excluding active friction-induced heating. Furthermore, localized heat-flux analysis, thermal hotspot localization, cooling-time-constant evaluation, and a Heat-Flow Intensity (HFI) index were employed to quantitatively characterize internal heat transport within the gear tooth, while a normalized Thermo-Tribological Performance Index (TTPI) was developed to provide a unified comparative assessment of thermal transport, cycle-normalized wear performance, and service durability. Thermal conductivity increased from 0.29 to 0.449 W m⁻ 1 K⁻ 1 with increasing nanofiller loading, leading to faster cooling and enhanced heat transport. However, the highest thermal conductivity did not provide the best thermal reliability because excessive nanoparticle loading was associated with increased friction-induced heating and surface degradation. Instead, the POM/CB/3NCC composite exhibited the best overall performance, combining efficient heat dissipation, reduced operating temperature, superior wear resistance, and the longest service life. The proposed framework, together with the HFI and TTPI indices, provides quantitative comparative tools for evaluating internal heat transport and integrated thermo-tribological performance of polymer nanocomposite gears and offers a potentially transferable basis for the thermal and tribological design of polymer transmission components.