Vibration and flexible systems for high speed centrifuges

Long-term production experiments and the factors that Shanghai Kamaishu encountered in the after-sales service caused a lot of high-speed centrifuge vibration. The vibration of the centrifuge is one of the important indicators to measure the performance of the centrifuge. Generally, vibration damping can take two methods: active vibration reduction and passive vibration reduction. Active vibration reduction is designed to avoid the operating speed of the centrifuge far from the critical speed of the rotating system (the high-speed centrifuges in the laboratory generally design the critical speed to be much lower than the working speed). In addition, dynamic balancing must be performed during rotor machining. Passive damping is the separation of possible vibrations from the frame and foundation with various types of dampers.

Generally, in the centrifuge design, the active vibration reduction and the passive vibration reduction are simultaneously applied to the high-speed centrifuge. Generally, the vibration reduction can be considered in three parts; (1) The main shaft bearing housing is designed as a flexible vibration damping type; (2) Flexible connection between the main shaft and the motor; (3) The entire drive system is flexibly coupled to the frame.

Rubber dampers generally meet the vibration reduction requirements of high-speed centrifuges. In the case where the structure of the damper is fixed, the greater the rubber hardness, the higher the critical speed of the system. The damper with too low hardness cannot meet the requirements and is easily damaged.

In addition to the above three parts using the flexible damping type, the elastic joint can be used between the rotor and the main shaft. The US solwa company produces a ~RC-z high-speed refrigerated centrifuge with a layer of silicone rubber between the main shaft and the rotor. SiliconeRubbet), which absorbs vibration further. In addition to the vibration isolation effect, various vibration damping measures also reduce the critical speed of the rotating system, so that the working speed is far away from the critical speed. This is why some high-speed centrifuge spindles are thick and not very long, and the entire system is still operating above the critical speed.

There are two types of shafts for laboratory high speed centrifuges. A shaft is slender and has a large flexibility, so that it can be self-aligning. The other type of shaft is shorter and shorter, and the bending deflection of the shaft itself is small, but the layer damper still makes the operating speed of the system above the critical speed, so the system is still a flexible system. Although it is also a flexible system, the difference between the slender flexible shaft and the more rigid shaft is that the automatic centering of the elongated flexible shaft mainly causes the rotor to rotate about its center of mass by bending the shaft. The more rigid shaft is automatically centered by the relative relative displacement of the components in the entire rotating system.

Based on this, Shanghai Kamaishu believes that the slender shaft should be made of spring steel, and the shorter and thicker shaft should be more reasonable.

The main shaft of the US Type 2-21, East Germany VACZ5 and Hitachi 20PR-52D centrifuges belongs to the former case, which is a slender, flexible shaft, while the Shanghai Biochemical Institute's 20000 rpm high-speed centrifuge and Beijing Bio The main shaft of the high-speed centrifuge of the physical institute belongs to the second case, that is, the shaft with higher rigidity. The diameter and length of the spindle depend on the power required by the centrifuge's rotating system and the type of construction of the instrument, but mainly depends on the power requirements. Because the shafting structure of the laboratory high-speed centrifuge is much the same. American J2-3 type, East Germany VAC2 5 type centrifuge pump r partial vacuum. Thus the shaft is a typical elongated flexible shaft. The centrifuges of the Shanghai Biochemical Institute and the Beijing Biophysical Institute are vacuuming and consume a lot of power. Therefore, a shaft that is thick and short and has a large sag is selected.

After the spindle is determined, the lack of flexibility of the rotating system can be compensated by the vibration oscillator. Therefore, it does not make sense to say whether the spindle itself is rigid or flexible. Whether the system itself is flexible depends not only on the flexibility of the shaft itself, but also on the flexibility and mounting of the various damping devices. Thus, strictly speaking, in high-speed centrifuges, the concept of a flexible shaft and a rigid shaft seems to be inappropriate, but should be distinguished by a flexible rotating system.


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