Test Method for Rotor Unbalance in 3C Cabinet-Type Centrifugal Fans

Test Method for Rotor Unbalance in 3C Cabinet-Type Centrifugal Fans

When a 3C cabinet-type centrifugal fan rotates, it generates centrifugal force. This centrifugal force periodically impacts the bearings, causing vibration. Prolonged bearing vibration can damage the bearings of the 3C cabinet-type centrifugal fan, potentially causing the impeller to collide with the housing. First, use a vibration meter to measure the bearing vibration values and assess the rotor’s unbalance under operating conditions. 1. Select an area near the impeller on the 3C cabinet-type centrifugal fan shaft where rotation has stopped, wipe the surface clean, and verify that its true roundness meets the standard. 2. Start the 3C cabinet-type centrifugal fan at operating speed. Using a sharp pencil, slowly extend the centerline of that shaft section. If the pencil contacts the shaft surface, the extension will stop; however, as the shaft rotates, the pencil will move briefly. Afterward, retract the pencil and repeat the process several times until the next step. The selected shaft section is now complete. The motion must be light and steady. Be careful not to extend the pencil too far, otherwise the entire arc will be drawn on the shaft. If the extension is insufficient, contact between the pencil and the shaft will be inadequate, making it impossible to mark the line segment clearly and difficult to judge. While drawing the line, a vibration meter can be used to measure the bearing vibration value A. 3. After the 3C cabinet-type centrifugal fan has stopped, locate the centerline A-A of the line drawn on the shaft. Mark its position F on the other part of the shaft, then rotate line A-A to a horizontal position. At this point, the horizontal position A on the same side of the impeller is the unbalanced point, and the opposite side is point B. After prolonged practice, the impeller’s diameter is as follows: 1600 mm, speed 1480 rpm. 4. Restart the 3C cabinet-type centrifugal fan, redraw the lines on the shaft using the method described above, and measure the bearing vibration value B. Compare this with the original vibration value A to verify the change in the rotor’s vibration value. After the 3C cabinet-type centrifugal fan stops again, confirm whether the position mark F of the centerline of the newly drawn line segment aligns with the centerline A-A of the initially drawn line segment. If they align, verify that value B meets the standard requirements. Otherwise, if point B is present (i.e., B > A), the centerline of the new segment is 180 degrees relative to F, indicating excessive weight, which can be reduced accordingly. If the centerlines of the two lines do not overlap or are 180 degrees apart, this indicates an error between the two drawn lines, and they can be modified again.