Diagnosis of Pre-Tightening Force Loosening for Top Cover Bolts in Generator Sets

Bolt loosening is a common mechanical failure in large-scale generator sets, especially the top cover bolts, which can lead to unstable operation, affecting the safety and efficiency of the unit. Real-time monitoring of bolt pre-tightening force and the early diagnosis of loosening are crucial for ensuring the long-term safe operation of the generator set. This study proposes a novel method for diagnosing faults in large-scale hydraulic units, with a particular focus on thread loosening failures. The proposed approach utilizes stress feature analysis and intelligent algorithms to enhance the diagnostic process. The study involves a detailed analysis of the stress transfer mechanism during bolt loosening, aiming to elucidate the relationship between changes in pre-tightening force and stress distribution in the surrounding bolts. A combined approach of monitoring the pre-tightening force and signal analysis is employed to facilitate the real-time tracking of dynamic changes. Experimental results show that loosening a single bolt causes stress distribution changes in the entire bolt group, particularly in the adjacent bolts. The study also introduces a diagnosis method combining pre-tightening force changes and VMD (Variational Mode Decomposition), which proves to be highly accurate in locating loosened bolts. Engineering applications validate that VMD analysis combined with the Spearman method effectively identifies changes in stress and has high accuracy and potential for diagnosing bolt loosening failures, providing valuable guidance for generator set maintenance.