The centrifuge is a common piece of laboratory equipment that has the potential to cause serious injury if not properly used or maintained. There are a variety of types of centrifuges which operate at various speeds. General purpose bench top centrifuges can spin with the centrifugal force of 24,000 x g and ultraspeed centrifuges can generate forces of 1,000,000 x g. With the generation of such great force rotor failures can become deadly projectiles. The risk of your centrifuge becoming a safety hazard can be mitigated through proper preventive maintenance and strict adherence to manufacturer procedures and your internal laboratory safety procedures.
The primary component of the centrifuge is its rotor. There are several types of rotors with the most common being either fixed angle or swinging bucket. Fixed angle rotors are primarily used for differential centrifugation while swinging bucket rotors are primarily used for gradient work. Below are some examples of both a fixed angle and swinging bucket rotor. Rotors are also made from a variety of materials such as aluminum, titanium, stainless steel and carbon fiber.
Fixed Angle Rotor
Swinging Bucket Rotor
Below are some common causes of rotor failure:
- Incorrect Loading or Balancing
- Incorrect Attachment
Incorrect Loading or Balancing
An unbalanced rotor can create extreme vibrations and stresses the rotors. The following steps should be taken to ensure your rotors are balanced before activating the centrifuge:
- Always run centrifuge with ALL buckets in place
- Always load buckets symmetrically
- Always balance adjacent and opposing loads within manufacturer’s recommended tolerance
Rotors attach to the centrifuge using different methods. Superspeed centrifuge rotors are typically locked down to the centrifuge drive by tightening the lock knob. Lowspeed rotors are usually fastened by a locking pin. General purpose, small benchtop and micro-centrifuges use a locking nut or other mechanism to secure the rotor. Please check with your manufacturer to verify the method used to secure your rotor and always verify the rotor is locked down before starting the centrifuge.
If a swinging bucket rotor is used you must ensure the buckets are properly placed on the swinging arms, ALL buckets must be in place and the buckets should be cleaned and lubricated regularly to ensure the rotors freely swing out when spinning. You should also gently swing out each bucket to ensure a free easy motion before starting the centrifuge.
All rotors are designed with a maximum load tolerance at the maximum speed. An overloaded rotor ran at the standard maximum speed can result in a catastrophic failure. If the maximum load is exceeded then the maximum speed MUST be derated – ALWAYS check the manufacturer’s manual for maximum load values.
Surface corrosion is caused by long term exposure to moisture or chemicals. Over time surface corrosion can penetrate deep into the rotor and begin forming micro cracks. Micro cracks can enlarge under the centrifugal forces to the point where the rotor can break apart. The following steps should be taken to help prevent surface corrosion:
- Clean rotors between every use
- Thoroughly dry rotors between uses
- Remove adapters between runs
- Never use metallic objects to open or remove parts
- Always use cleaning, disinfection and sterilization agents that are chemically compatible with the rotor
Corroded rotors can become unsafe to use so it is vital that routine visual observations of the rotor are made to detect any type of rotor fatigue (cracks, bulges, or corrosion) that can lead to the eventual failure of the rotor and significant damage to your centrifuge.
Since rotors are exposed to high g-forces they do wear out. The molecular structure of the rotor changes as the metal elongates repeatedly and they will eventually fail. Since rotors can become unsafe due to excessive wear it is good practice to use a centrifuge use log for tracking the amount of time your centrifuge and rotors are being used as well as provide data on the wear and tear each rotor is receiving. The log can also be used to track the cleaning schedule of the equipment as well as your visual observations of the rotor. Follow all manufacturer’s guidelines and have your rotors inspected regularly by a trained technician.
In summary, there are many things involved in properly maintaining a laboratory centrifuge besides loading and spinning.
Please ensure you follow the guidelines outlined previously. A properly maintained centrifuge will help ensure the accuracy of your data, help extend the life of your centrifuge, and improve the safety culture within your lab.