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How to keep the centrifuge vibration within the normal range
Author: BLLA Published: 2013-1-16 Visits: 2238
The centrifuge is designed to allow certain processing errors, so that the vibration of the centrifuge is controlled within the normal range.However, if the user uses it improperly, this design balance will be broken, leading to serious accidents.
The rotor can rotate smoothly only when the working speed of the centrifuge is not at the critical speed.For low-speed centrifuges with low working speeds, the critical speed is generally increased as much as possible to make the centrifuge run below the critical speed.The shaft of this centrifuge is very thick and rigid, and is called a rigid shaft.When the speed requirement is high, the critical speed should be reduced as much as possible. The shaft should be made thinner and less rigid. It is called a flexible shaft. Modern ultracentrifuges use flexible shafts.
The critical speed is related to the centrifuge and the rotor.A centrifuge can be equipped with several types of rotors, so the centrifuge's vibration damping design should be considered for the tolerance of various rotors.The working range of the centrifuge is very wide, from thousands of revolutions per minute to tens of thousands of revolutions per minute. The higher the rotation speed of the centrifuge vibration, the greater its danger.
Once the vibration occurs at high speed, the centrifuge should be stopped immediately with the fastest downshift, and all personnel should leave the site quickly to avoid personal injury in the event of a shaft break.The power must not be cut off. As soon as the power is cut off, the brakes (rapid speed reduction) are gone, and the rotor stalls very slowly.Accidents are generally caused by improper operation of the centrifuge, such as the rotor is not properly placed on the main shaft, the rotor cover is not properly closed, and the rotor basket that is thrown away is not properly placed.The structure of this accident is accompanied by a huge sound, a certain centrifuge of 300 ~ 400kg suddenly rotates more than 270 degrees.Open the cover to see the rotor lying in the cavity. Take out the rotor and observe that the outer surface of the rotor is seriously scratched and discolored. The inner wall of the centrifuge chamber will also be damaged, and even the refrigerant leaks.Sometimes the rotor and rotor cover are separated, the liquid in the test tube is spilled into the cavity, and the main shaft is broken or severely bent.Due to the repeated occurrence of such accidents caused by improper user operations, modern centrifuges generally have imbalance protection functions.That is, once the vibration of the rotor is greater than a certain size when the centrifuge is started, the centrifuge will automatically stop at a reduced speed. Centrifuges with this performance sometimes fail to report and cannot ensure that no accidents occur.
Centrifuge rotor machining errors and centrifuge installation errors will cause the centroid of the rotor to deviate from the centrifuge spindle to varying degrees, so vibrations will occur when the rotor rotates, and these vibrations will be inherent to the centrifuge drive system at certain specific speeds The frequency resonates, which causes the entire system to vibrate strongly.The speed at which this occurs is called the critical speed.
The rotor will cause vibration when it rotates at high speed, but the flexible shaft has "self-aligning effect".Its working principle is that the rotor produces a disc effect during high-speed rotation, and the elastic reaction force when the flexible shaft is bent pulls the rotor deviating from the geometric centerline of the spindle back to the geometric centerline of the spindle and the vibration disappears.Of course, at this time, the amount of imbalance in the rotor must also have a certain limit. If the limit is exceeded, the vibration will not disappear.