The working process of a horizontal rotor in a centrifuge.
Release time:
2012-02-20
Overview:
For the operation of a centrifuge, balancing the rotor is key to achieving good separation results.
The swing-out rotor, also known as the horizontal rotor (or "leveling rotor"), features centrifuge tubes placed in a basket that is symmetrically suspended from the rotor. As the rotor spins, the centrifugal force causes the basket to swing from a vertical position to a horizontal position; hence, it is also referred to as an external swinging rotor or a leveling-basket rotor.
1. Installation method of the suspended platform
2. Wall effects (welleffects)
When the rotor spins in a centrifuge, the direction of the centrifugal force is radial and forms a symmetrical sector in the horizontal cross-section. Only particles located precisely along the central axis of the centrifuge tube align perfectly with the direction of the centrifugal force field; particles at other positions will collide with the tube wall during sedimentation and settle along the tube wall. The tube-wall effect is less pronounced in swinging-bucket rotors than in fixed-angle rotors.
The sedimentation paths of particles in the centrifuge tube are perpendicular to the axis of rotation. Initially, particles at the center of the sample zone will settle radially. However, particles near the tube wall will collide with the wall first. Since the distance from the tube wall varies among particles, they will reach the bottom of the tube at different times, causing the zone to broaden. This can also lead to particle aggregation into clumps, convective disturbances, and other abnormal phenomena.
3. Rotor balancing
For the operation of centrifuges, rotor balancing is crucial to achieving good separation results. The balancing methods for different numbers of baskets (tubes) are illustrated in the figure. The weighing error for balancing the weights corresponding to the tubes must be kept within 0.1 g, and the baskets must be placed symmetrically about the rotor axis. Some centrifuges require that all baskets be installed according to their designated positions.
4. The separation process of the rotor by centrifugal force
a. First, prepare the gradient and load the sample. Then, hang (or install) the rotor basket onto the rotor (when the centrifuge is not rotating, the basket hangs vertically). b. As the rotor accelerates, the basket begins to swing upward. Once the rotational speed reaches above 800 rpm, the basket assumes a horizontal position at a 90° angle to the rotor’s axis of rotation, and no reorientation of the gradient occurs. c. Under the action of the centrifugal force field, particles in the sample sediment toward the bottom of the tube, separating into discrete bands according to their differences in sedimentation coefficients or buoyant densities. d. When the rotor decelerates and comes to a stop, the basket returns to its original vertical position, and no reorientation takes place within the test tube.
5. The radius-volume relationship of the rotor's swing.
In this formula, rt represents the distance between the rotation center and the top of the liquid surface.
If the effect of the hemispherical tube bottom is taken into account, the following equation can be used:
In the formula, b represents the total volume of the solution contained within the tube; V denotes the volume of the solution from the meniscus to the point at distance r; r is the distance between the axis of rotation; Wt is the thickness of the tube bottom; t is the wall thickness of the tube; D is the radius of the centrifuge tube’s bore; and Rmax is the maximum radius of the rotor.
1. Installation method of the suspended platform
2. Wall effects (welleffects)
When the rotor spins in a centrifuge, the direction of the centrifugal force is radial and forms a symmetrical sector in the horizontal cross-section. Only particles located precisely along the central axis of the centrifuge tube align perfectly with the direction of the centrifugal force field; particles at other positions will collide with the tube wall during sedimentation and settle along the tube wall. The tube-wall effect is less pronounced in swinging-bucket rotors than in fixed-angle rotors.
The sedimentation paths of particles in the centrifuge tube are perpendicular to the axis of rotation. Initially, particles at the center of the sample zone will settle radially. However, particles near the tube wall will collide with the wall first. Since the distance from the tube wall varies among particles, they will reach the bottom of the tube at different times, causing the zone to broaden. This can also lead to particle aggregation into clumps, convective disturbances, and other abnormal phenomena.
3. Rotor balancing
For the operation of centrifuges, rotor balancing is crucial to achieving good separation results. The balancing methods for different numbers of baskets (tubes) are illustrated in the figure. The weighing error for balancing the weights corresponding to the tubes must be kept within 0.1 g, and the baskets must be placed symmetrically about the rotor axis. Some centrifuges require that all baskets be installed according to their designated positions.
4. The separation process of the rotor by centrifugal force
a. First, prepare the gradient and load the sample. Then, hang (or install) the rotor basket onto the rotor (when the centrifuge is not rotating, the basket hangs vertically). b. As the rotor accelerates, the basket begins to swing upward. Once the rotational speed reaches above 800 rpm, the basket assumes a horizontal position at a 90° angle to the rotor’s axis of rotation, and no reorientation of the gradient occurs. c. Under the action of the centrifugal force field, particles in the sample sediment toward the bottom of the tube, separating into discrete bands according to their differences in sedimentation coefficients or buoyant densities. d. When the rotor decelerates and comes to a stop, the basket returns to its original vertical position, and no reorientation takes place within the test tube.
5. The radius-volume relationship of the rotor's swing.
In this formula, rt represents the distance between the rotation center and the top of the liquid surface.
If the effect of the hemispherical tube bottom is taken into account, the following equation can be used:
In the formula, b represents the total volume of the solution contained within the tube; V denotes the volume of the solution from the meniscus to the point at distance r; r is the distance between the axis of rotation; Wt is the thickness of the tube bottom; t is the wall thickness of the tube; D is the radius of the centrifuge tube’s bore; and Rmax is the maximum radius of the rotor.
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