The vibration issues in the high-speed centrifuge drive unit were thoroughly analyzed based on its mechanical components. The root causes of the vibration are multifaceted, primarily stemming from residual imbalance in the rotor, imbalance in the motor rotor, the connection method between the motor and the drive assembly, and the damping settings. According to dynamic principles, the equation governing the rotor's behavior at a given speed is G + M(e + y)CO: (y + y). Among these factors, the eccentricity (e) and deflection (y) of the rotor play the most significant role. These parameters are closely related to the manufacturing accuracy of the rotor, the geometry of the drive shaft, and the positioning of the bearings. Such imbalances can lead to both radial and axial vibrations, with the radial direction being the most affected.
Upon reviewing the original design, it was found that there was no radial damping mechanism in place, leading to repeated axial vibrations. Additionally, a clearance of 2 mm was observed between the rotor and the rotor cover, which contributed to the instability. Another factor was the flexible coupling. Since both the rotor and the motor may have residual imbalances, these two sources must be connected in a direct-drive system. Therefore, an effective coupling is necessary to isolate these imbalances. However, the original coupling used a nylon sleeve with square holes, which provided limited damping but failed to meet the required performance standards.
To address these issues, we introduced a rubber vibration ring to the original drive structure, effectively isolating radial vibrations. The gap between the rotor and the 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 three minutes, and the self-vibration acceleration on the drive motor was measured at 4 g.
Other factors affecting vibration include:
1. **Bearing selection** – Choosing the right type of bearing is crucial for stability.
2. **Axial preload of the bearing** – Applying proper axial preload helps eliminate internal clearance and enhances vibration performance.
3. **Grease choice** – High-speed applications require low-viscosity grease. Initially, 7018 high-speed grease was used, but it caused excessive temperature rise (70–80°C) at 15,000 rpm. Switching to a specialized 12th high-speed bearing grease significantly improved performance, reducing the motor temperature to 40–50°C.
4. **Bearing support position** – The original shaft had a bearing span of 49 mm and an overhang of 65 mm, which led to increased vibration. After redesigning the shaft with a bearing span of 46 mm and an overhang of 40 mm, the vibration frequency dropped from 12,000 rpm to 5,000 rpm, and the system operated more smoothly at higher speeds.
In conclusion, solving the vibration problem in the high-speed refrigerated centrifuge drive unit involved a comprehensive analysis of multiple factors. By referencing similar systems and making targeted modifications, we achieved stable and efficient rotational performance. This project not only resolved the issue but also provided valuable insights for future designs and maintenance of high-speed refrigerated centrifuges. The approach taken reflects our own innovation and has practical significance for engineers working in this field.
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