Centrifugal fans are machines that utilize input mechanical energy to increase gas pressure and discharge the gas; they are widely used for ventilation and induced draft applications in factories, mines, tunnels, cooling towers, vehicles, ships, boilers, and industrial furnaces. The main shaft is a critical component connecting the fan impeller to the motor bearings; since any wear or bending can compromise the fan's operational precision, materials with high hardness and excellent wear resistance are typically selected for its construction.
The main shaft serves to support the rotating impeller and transmit mechanical energy from the drive unit; it must possess sufficient strength and rigidity to handle this power transmission and support the impeller without inducing vibration. Consequently, main shafts for large centrifugal fans are usually forged and precision-machined from high-strength alloy steels, such as 35CrMo, 35CrMoA, 42CrMo, 45 steel, 40Cr, and 20Cr2Ni4MoV. Standard centrifugal fans often utilize 45 steel or 40Cr, while some smaller models may even use 304 stainless steel.
Proper assembly of the main shaft is equally vital to the fan's operational quality. Before assembling the shaft with the coupling and bearings, all protective coatings must be removed to ensure the mating surfaces are clean and free of damage-specifically, the shaft and journal areas should be inspected for cracks, scuff marks, or other defects. If scuff marks or damage are found, they should be smoothed with a file (provided this does not impair the equipment's performance) and then polished with oil-soaked abrasive cloth or an oilstone. During assembly, the clearance between the main shaft and the bearing shell should be set such that the top clearance is 0.015–0.020 times the journal diameter, and the side clearance is 1/2 to 2/3 of the top clearance. Contact points between the bearing shell and the journal should number between 12 and 18, or cover an area of 25×25 mm². Finally, the radial misalignment between the fan shaft and the motor shaft must not exceed 0.05 mm, and the horizontal alignment tolerance is 0.2 mm/m. Furthermore, strict cleanliness must be maintained during the assembly of bearings and spindles; the bearings should remain in their original packaging until the moment of installation onto the shaft to prevent dust and debris from entering the spindle assembly and causing wear.
