The vibration issue in the high-speed centrifuge drive unit was thoroughly analyzed based on its drive components. The root causes of the vibration are multifaceted, including residual imbalance in the rotor, imbalance in the motor rotor, the connection method between the motor and drive assembly, and the damper settings. According to the kinetic principles, the equation governing the rotor’s behavior at a specific speed is G + M(e + y)ω² = (y + y). Among these factors, eccentricity (e) and deflection (y) have the most significant impact, which are closely related to the manufacturing precision of the rotor, the geometry of the drive shaft, and the positioning of the bearings. These issues lead to both radial and axial vibrations, with the primary effect being radial.
Upon reviewing the original design, it was found that there was no damping mechanism in the radial direction, resulting in repeated axial vibrations. Additionally, a 2 mm clearance was identified between the rotor and the rotor cover, which contributed to instability. The flexible coupling also played a role, as the rotor and motor each had residual imbalances. In a direct-drive system, these two sources must be connected, requiring a coupling that can effectively isolate them. However, the original coupling used a nylon sleeve with square holes, which offered limited damping but failed to meet the required performance standards.
To address these issues, we introduced a rubber vibration ring into the drive structure to reduce radial vibrations. The gap between the rotor and rotor cover was reduced from 2 mm to 0.1 mm. The coupling was redesigned into a Vientiane-type structure as shown in Figure 2, replacing the original nylon sleeve. After implementing these changes, the centrifuge reached 20,000 rpm within 3 minutes, and the self-vibration acceleration measured on the drive motor was 4 g.
Other factors affecting vibration include bearing selection, axial preload, and the type of grease used. Through extensive testing, it was confirmed that applying an axial preload using a spring eliminates internal bearing clearance and enhances vibration performance. Regarding grease, using too thick a lubricant can cause excessive heat. Initially, 7018 high-speed grease was used, but it caused the motor temperature to rise to 70–80°C when the speed reached 15,000 rpm. This was detrimental to the motor’s performance. Later, a specialized 12th high-speed bearing grease was adopted, significantly reducing the temperature to 40–50°C.
The position of the bearing support also influenced the drive shaft. A shaft with a 49 mm bearing span and a 65 mm overhang was tested, but the vibration frequency dropped to 5,000 rpm, and vibration increased sharply as speed rose. A new design with a 46 mm bearing span, a 40 mm overhang, and a 9 mm diameter overhang met the operational requirements.
In conclusion, solving the vibration problem of the high-speed refrigerated centrifuge's drive unit involved analyzing and improving various components. By referencing similar systems and making targeted adjustments, we achieved stable and efficient rotational performance. This project highlights the importance of detailed design and maintenance practices for high-speed centrifuges. The success of this work provides valuable insights for engineers working on similar equipment.
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