Ball bearing monitoring employs time-frequency techniques to facilitate the early detection of faults; however, the presence of non-stationary or noisy signals can limit the effectiveness of these techniques, requiring advanced methods for reliable predictive maintenance. This study proposes a methodology for fault detection in complex systems,utilising Principal Component Analysis (PCA) to identify indicators with a higher probability of fault. Subsequent to this, the signal characteristics are decomposed using the Fast Fourier Transform (FFT). This technique is employed to identify the Hotelling component and the SPE (quadratic prediction error), with the objective of determining the state of health of the rolling bearings. This is achieved by extracting the frequencies and harmonics that characterise the fault. The Hotelling component considers elements in the main space with a higher energy representation for evaluation, while the SPE considers elements in the residual space. The results demonstrate a rapidly appreciable range of detection and dispersion of faulty signals. A comparative analysis of the KPCA-FFT and PCA-FFT results is performed. However, this study demonstrates that the combination of PCA-FFT with the Hotelling index test and SPE is more suitable for evaluating signals with defects.

This study assessed the quality of recycled aluminum pots produced through artisanal processes in Cameroon. The objectives were to identify production practices, analyze the chemical composition of finished products, and evaluate the process capability to comply with food safety standards. Results revealed a high variability in practices across regions, with a predominance of non-compliant practices. Notably, lead content significantly exceeded regulatory limits in 66.6% of samples, with levels reaching up to 0.152%. This contamination was primarily attributed to the lack of rigorous waste sorting, the introduction of foreign materials during melting, and a lack of quality control. Process capability analysis revealed very poor performance, with less than 3% of products meeting standards. These findings highlight the urgent need for measures to improve product quality and ensure compliance with regulatory requirements.