Centrifugal Fan Shaft

A Centrifugal Fan Shaft has to perform three mechanical duties at the same time： It transmits torque from the motor to the impeller, carries the entire static and dynamic load of the rotating assembly and is so rigid that its own vibration level or critical speed, is always well above the fan's operating speed. When the operating speed approaches the critical speed of the shaft, then resonance begins and as the vibration level increases, suddenly the shaft breaks. As per engineering principles, the operating speed must not exceed 75~80% of the critical speed that means that the critical speed must be 1.3~1.7 times the maximum operating RPM. Its only engineering control is the diameter of the shaft. The large diameter reduces the bending of the impeller under load, which raises the critical speed to a safe margin above the operating speed.

The material used to make the fan shaft or other components mainly depends on its service life and temperature resistance. Carbon steel - Q235 / 1018~1060 / EN8 is used as standard for general-purpose fans for temperatures up to 400°C. On the other hand, 42CrMo alloy steel is used for heavy load, high torque and high-speed industrial applications (such as ID fans, FD fans, or large centrifugal blowers). Because its tensile strength is more than 1,080 MPa and its fatigue resistance is also excellent. As a result, the bending, twisting or extreme pressure it can withstand during continuous operation cannot be handled in the long term by ordinary carbon steel. SS316L is used for corrosive chemical environments and offshore applications. When the temperature rises above 500°C, ordinary alloy steel loses its structural limits or capacity. Therefore, in those cases, heat-resistant alloy steel like SS304, SS321 or Inconel grade is used, which can easily operate at a high temperature range. For all fans operating at high temperatures, it is recommended to use a shaft cooling device if the temperature of the shaft on the bearing side exceeds 150°C. In addition, each Centrifugal Fan Shaft is manufactured strictly according to the specifications of the engineering drawing. Its keyway, interference fit zone and bearing seat diameter are all precision machined.