Abstract: The article presents a five-year industrial validation of eliminating open gear drives in spiral classifiers by implementing a direct drive with a torque arm, alongside an assessment of cumulative effects on reliability, process efficiency, and operating economics. The relevance of the study is conditioned by the fact that a substantial share of the classifier fleet remains structurally obsolete: open gear trains constitute the root cause of mechanical instability (wear, lubricant leakage, misalignment) while simultaneously degrading the quality of diagnostic signals, thereby impeding the deployment of PdM/AI. The objective is to deliver a comprehensive, instrumentally substantiated evaluation of the long-term reliability and economic feasibility of direct drive under real-world conditions, and to demonstrate how removal of the failure root cause creates a data-ready mechanical platform for predictive maintenance and digital twins. The novelty consists in an industry-scale confirmation (January 2020, June 2025) of a fundamental transition from managing wear consequences to eliminating wear at the kinematic-scheme level: a sealed gearmotor (IP66) in combination with a torque arm and flanged connection obviates the open gear pair, dramatically elevating the vibration signal-to-noise ratio and rendering vibrodata coherent for PdM. It is shown that mechanical stabilization of the drive is in itself a critical precondition for trustworthy condition analytics. The principal findings confirm a multifactor modernization effect: a 33% increase in section throughput and a 19% rise in classification efficiency; 100% drive technical availability with zero unplanned downtime over 43,800 h; a lower confidence bound of MTBF at 14,600 h versus a characteristic service life of ~2,800 h for traditional drives; a persistently low vibration level < 2.0 mm/s (ISO 10816 category A) instead of 4.5–7.8 mm/s (C) for open gears; a 20% OPEX reduction and a 95% decrease in lubricant consumption, with payback in 14–18 months. The article will be of use to concentrator and plant managers, mechanical engineers, and reliability specialists.

DOI: 10.5267/j.esm.2025.12.001
Keywords: Spiral classifier, Direct drive, Torque arm, Reliability, Vibration diagnostics, Predictive maintenance