1. Chassis: We hypothesized that the design and manufacturing of the chassis could be a source of noise: ① The chassis utilizes a box-like structure with non-continuous welds; variations in weld length and positioning lead to significant differences in chassis rigidity, potentially creating resonance effects that amplify even minor vibrational noise. ② Constructed from welded steel plates, the chassis lacks inherent vibration-damping or sound-deadening properties; if its natural frequency aligns closely with the gear meshing frequency, minor gear vibrations could trigger significant resonance, thereby increasing noise levels. We conducted tests to investigate these possibilities but found-across three separate trials-only a weak correlation between noise levels and factors such as chassis structure, rigidity, and frequency. Conversely, we observed a strong correlation between noise levels and the movement of internal components. Thus, we concluded that chassis design and manufacturing quality are not the causes of excessive noise.
2. Bearing Clearance: It was suggested that, given the noise originates near the drum assembly and transmission components, excessive clearance in the drum's sliding bearings might be the culprit. We carefully selected drum components to ensure the clearance between the bearing bore and the main shaft met design specifications and then tested the assembled units. Using a variable-frequency drive (VFD) motor to adjust speeds, we observed the impact of rotational speed on noise. Extensive testing revealed that speed is the primary factor influencing noise: higher drum speeds resulted in increased noise levels and more intense machine vibration. Clearance was a secondary factor-larger gaps between the main shaft and the bushing led to higher noise-while the chassis had the least impact. When the machine's baseline noise was low, variations in speed or shaft clearance did not result in excessive noise, indicating that excessive noise is not caused by large bearing clearances.