Centrifugal fan

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Centrifugal fan 1. Structure and principle of centrifugal fans 2. Maintenance of centrifugal fans: Disassembly and inspection of centrifugal fans: 1) Disconnect all pipes and connections connected to the equipment. 2). Remove the coupling guard, disconnect the coupling, and check the unit alignment data. 3). Disconnect the expansion joint at the equipment inlet and the flow regulator, then remove the end cover and the backflow cylinder. 4) Remove the partition at the motor end of the fan. 5) Use a special pulling tool to remove the impeller; if it is too tight, use a copper rod to tap on the impeller hub while pulling – make sure to rotate the impeller as you tap, and place a wooden block under the impeller to support it. 6) Remove the motor and take out the backup wheel at the bearing housing end. 7) Take off the cover of the bearing housing and check the amount of play in the rotor (lift the rotor shaft and use a dial indicator to measure the bearing clearance). 8) Remove the bearing cover and lift out the rotor. 9) Inspect the oil seal, bearings, and shaft: ① Oil seal: No signs of aging or cracks. ② Bearings: Rolling bearings – the surfaces of the rolling elements and raceways should be free from corrosion or defects. The cage should be free from defects such as deformation or cracks, and the bearing should not be used beyond its designed service life. ?2) The fit for rolling bearings that are subjected to both axial and radial loads is H7/js6. The fit for rolling bearings in which the shaft bears only radial loads is H7/k6. The fit between the outer ring of the bearing and the inner hole of the bearing housing is Js7/h6. ?3) For fans equipped with axial thrust rolling bearings, the axial clearance between the outer ring of the rolling bearing and the gland should be 0.02mm–0.10mm. ?4) When installing the rolling bearings thermally, the heating temperature should not exceed 100°C; it is strictly prohibited to heat the bearings directly with a flame. ?5) The axial clearance between the outer ring of the bearing at the free end and the gland should be greater than the thermal expansion amount of the shaft. The reference values for thermal elongation are shown in Table 4 below. Table 4: Axial thermal elongation. Heating temperature: ℃ 0–100, 100–200, 200–300. Elongation per meter of shaft length: mm 1.2, 2.5, 13.9, 2.③ The shaft’s surface should be smooth, without any visible scratches, wear marks, cracks, rust, or pitting; the surface roughness of the shaft journal should be Ra0.8. Color flaw detection inspection can be performed if necessary. The cylindricity tolerance at the main journal bearing shall comply with Table 2 below. Table 2: Tolerances for the cylindricity of the spindle journal, in mm. Journal diameter: ≤150, 150–175, 175–200, 200–225. Cylindricity tolerances: 0.02, 0.025, 0.03, 0.04. The tolerances for the straightness of the spindle shall comply with those specified in Table 3 below. Table 3: Tolerance for spindle straightness in mm
Fan speed: r/min ≤ 500, 500–1500, 1500–3000
Straightness tolerance values: 0.1, 0.07, 0.05

3. Installation of centrifugal fans
1) Install bearings.
2) Clean the bearing housing.
3) Install the rotor; prepare a plan in advance and pay attention to safety during installation.
4) Install the upper cover of the bearing housing, as well as the front and rear bearing caps.
5) Install the impeller.
6) Install the partition; pay attention to the proper installation of the asbestos rope.
7) Install the air volume control mechanism and the front and rear flexible connections.
8) Install the auxiliary pipelines.
9) Install the coupling; refer to the table below for alignment standards:
Allowable misalignment value for the unit in mm
Coupling type: Outer diameter, radial direction, end face
Flexible pin type: 0.08, 0.06
Rigid type: 0.06, 0.04
Diaphragm type: 0.1, 0.08

4. Standards for a properly installed centrifugal fan
1) Components: All components of the main and auxiliary units must be complete and of quality that meets technical requirements. Instruments for measuring current, temperature, pressure, etc., as well as control and regulation devices, are complete, accurate, and sensitive. Are the fan foundations and frames stable and reliable? Are the fastening and connection bolts complete and secure? Is there no looseness? Pipes, valves, supports, pipe clamps, etc. are installed properly, firmly and completely, with clear markings. The axial displacement of the rotor and the clearances between various components meet the technical requirements and specifications. It has good anti-corrosion and insulation properties, meeting the technical requirements. 2) Operational performance: The equipment runs smoothly, without any abnormal vibrations or noises, and the motor’s temperature rise and current levels are within acceptable limits. The equipment has reached its designed capacity and can meet production needs. Is the lubricating oil and cooling system in good condition? The oil temperature, oil pressure, and oil quality meet the design specifications and regulatory requirements. 3) Technical documents: Complete technical files and records related to the design, manufacturing, inspection, installation, and acceptance of the equipment are available. There are complete operating procedures and maintenance rules for the equipment. Records of equipment operation, maintenance, defects and their resolutions, as well as technical summaries of major overhauls, are all complete. The drawings for key components, wear-prone parts, and the overall equipment layout are all available. 4) Equipment and surrounding environment: The equipment, pipelines, and surrounding area should be free of oil stains, dust, water accumulation, and other debris, and kept clean. 5) Hygiene: The equipment shows no signs of leakage.