Common Misconceptions in the Maintenance of Explosion-Proof Centrifugal Fans
1. When aligning the couplings between the motor, fluid connections, and the explosion-proof centrifugal fan, do not use the following two methods for alignment.
(1) Using auxiliary flat blocks and a feeler gauge to measure radial and axial misalignment.
(2) With the two coupling halves not in contact, secure a dial indicator to the stationary coupling half so that the probe can measure the radial and axial misalignment of the rotating coupling half.
Reasoning: The positioning accuracy of explosion-proof centrifugal fan couplings is extremely high, requiring coaxiality within 0.05 mm during normal operation. Due to contamination on the coupling itself, the actual coaxiality value often exceeds this tolerance by several or even ten times, causing severe vibration in the explosion-proof centrifugal fan. Method (1) is generally used for rough alignment in applications with lower requirements, but it is not suitable for aligning explosion-proof centrifugal fans. Method (2) does not account for the impact of geometric errors and instead relies on high-temperature fans.
Correct Method: Temporarily connect the two coupling halves of the centrifugal fan using 2–3 bolts to achieve synchronous rotation. Measure the radial and axial vibration values using three (quick alignment method) or two dial indicators, then adjust to meet the specified requirements.
Second, for explosion-proof centrifugal fans using couplings, the methods described above are centered on maintaining coaxiality within 0.05 mm. However, the effects of thermal expansion differences between the explosion-proof centrifugal fan, the hydraulic coupling, and the motor (relative to the centerline) under high-temperature conditions are often overlooked. Alternatively, even with careful consideration, the operating temperature of the explosion-proof centrifugal fan remains high, so it is necessary to lower the centerline when the system is cold.
Reasoning: During normal operation of the explosion-proof centrifugal fan, the temperature of the fluid coupling (up to 80°C) is higher than that of the motor and bearing housing (oil-lubricated), resulting in greater thermal expansion. Therefore, the centerline must be shifted slightly downward in the cold state. The high-temperature environment of the explosion-proof centrifugal fan’s propeller configuration must not be used as the basis for calculating high thermal expansion of the centerline.
Correct Method: To ensure that the centerlines of the explosion-proof centrifugal fan, fluid coupling, and motor theoretically align in a straight line during normal operation under high-temperature conditions, the centerline of the fluid coupling is intentionally set lower than that of the motor. For explosion-proof centrifugal fans, this difference is generally 0.1–0.2 mm.
3. When installing the rear bearing cover, the fixed and free end covers were not installed correctly.
Cause Analysis: To accommodate thermal expansion caused by high temperatures on the fan shaft, the manufacturer designed a non-fixed bearing at the rear. During installation, the fixed bearing must be strictly positioned, while the expansion side of the free bearing must remain unrestricted. If installed after replacement, the shaft’s free expansion is restricted, which may lead to equipment failure.
Correct Method: Based on the length of the bearing end cover inserted into the flange section, install the shorter upper and lower halves of the flange on the opposite side. This ensures reliable positioning of the other end cover and prevents insufficient alignment caused by the thickness of the sealing ring.
1. When aligning the couplings between the motor, fluid connections, and the explosion-proof centrifugal fan, do not use the following two methods for alignment.
(1) Using auxiliary flat blocks and a feeler gauge to measure radial and axial misalignment.
(2) With the two coupling halves not in contact, secure a dial indicator to the stationary coupling half so that the probe can measure the radial and axial misalignment of the rotating coupling half.
Reasoning: The positioning accuracy of explosion-proof centrifugal fan couplings is extremely high, requiring coaxiality within 0.05 mm during normal operation. Due to contamination on the coupling itself, the actual coaxiality value often exceeds this tolerance by several or even ten times, causing severe vibration in the explosion-proof centrifugal fan. Method (1) is generally used for rough alignment in applications with lower requirements, but it is not suitable for aligning explosion-proof centrifugal fans. Method (2) does not account for the impact of geometric errors and instead relies on high-temperature fans.
Correct Method: Temporarily connect the two coupling halves of the centrifugal fan using 2–3 bolts to achieve synchronous rotation. Measure the radial and axial vibration values using three (quick alignment method) or two dial indicators, then adjust to meet the specified requirements.
Second, for explosion-proof centrifugal fans using couplings, the methods described above are centered on maintaining coaxiality within 0.05 mm. However, the effects of thermal expansion differences between the explosion-proof centrifugal fan, the hydraulic coupling, and the motor (relative to the centerline) under high-temperature conditions are often overlooked. Alternatively, even with careful consideration, the operating temperature of the explosion-proof centrifugal fan remains high, so it is necessary to lower the centerline when the system is cold.
Reasoning: During normal operation of the explosion-proof centrifugal fan, the temperature of the fluid coupling (up to 80°C) is higher than that of the motor and bearing housing (oil-lubricated), resulting in greater thermal expansion. Therefore, the centerline must be shifted slightly downward in the cold state. The high-temperature environment of the explosion-proof centrifugal fan’s propeller configuration must not be used as the basis for calculating high thermal expansion of the centerline.
Correct Method: To ensure that the centerlines of the explosion-proof centrifugal fan, fluid coupling, and motor theoretically align in a straight line during normal operation under high-temperature conditions, the centerline of the fluid coupling is intentionally set lower than that of the motor. For explosion-proof centrifugal fans, this difference is generally 0.1–0.2 mm.
3. When installing the rear bearing cover, the fixed and free end covers were not installed correctly.
Cause Analysis: To accommodate thermal expansion caused by high temperatures on the fan shaft, the manufacturer designed a non-fixed bearing at the rear. During installation, the fixed bearing must be strictly positioned, while the expansion side of the free bearing must remain unrestricted. If installed after replacement, the shaft’s free expansion is restricted, which may lead to equipment failure.
Correct Method: Based on the length of the bearing end cover inserted into the flange section, install the shorter upper and lower halves of the flange on the opposite side. This ensures reliable positioning of the other end cover and prevents insufficient alignment caused by the thickness of the sealing ring.
