Question: Detailed explanation of various assembly clearances

Technical requirements for the maintenance of various components of water pump units 1. Main shaft section 1) The taper and ellipticity of the shaft journals shall not exceed 1/2000 of the shaft diameter. However, it must not exceed 0.05 mm at most, and the surface must be free of defects; the surface roughness is required to be ▽3.2. 2) If the shaft bending exceeds the allowable value, it can be straightened using mechanical or heating methods. The allowable bending value of the shaft is shown in the table below (unit: mm). At the shaft diameter: middle of the shaft (1500 revolutions per minute), middle of the shaft (3000 revolutions per minute). For multi-stage pump shafts: ≤0.02, ≤0.10, ≤0.08, ≤0.05. 3) The key and the keyway must fit tightly together; the use of shims is not allowed. The fitting tightness between the key and the shaft’s keyway is shown in the table below (unit: mm). Diameter: 40–70, 70–110, 110–230. Key width and tightening force: 0.009–0.012, 0.011–0.015, 0.012–0.017. 2. Rotor section: 1) The degree of wobble of the rotor must not exceed the values specified in the table below (unit: mm). Part Radial vibration Axial vibration Shaft neck Bushing Ring Blade Wheel Balance disk Vibration degree ≤0.02 ≤0.05 0.08-0.12 ＜0.25 ＜0.03 2) Bushing (1) The bushing and the shaft cannot be made of the same material. In particular, the same type of stainless steel must not be used. (2) In media that do not cause corrosion, the shaft sleeves for mechanical seals can be made of steel grade 25 with a chromium plating on their surface; whereas the shaft sleeves for packing seals should have cemented carbide welded onto their surface, with a hardness of Rc50-60. (3) The perpendicularity of the shaft sleeve end face to the axis shall not exceed 0.01 mm. (4) The surface roughness of the contact surface between the bushing and the shaft shall be no less than ▽1.6, with a D/d fit. 3) Balance disc: The balance disc and the shaft are connected using a D/gd fit. 4) Impeller (1) The fit of the impeller on the shaft generally uses a D/gd fit. (2) The newly installed impeller should be made statically balanced; dynamically balanced if necessary. Rotor components must undergo dynamic balancing tests at the time of leaving the factory. The allowable residual unbalance mass on the outer diameter of the impeller when seeking static balance shall, for impellers operating at 3000 r/min, not exceed the tolerance limits specified for static balance in the table below. Outer diameter of impeller (mm) Maximum allowable static balance tolerance at the largest diameter of the impeller (g): ≤200 for 3; 5 for 201–300; 8 for 301–400; 10 for 401–500; 15 for 501–700; 20 for 701–900. (3) The impeller shall be balanced using the deburring method, but the thickness removed shall not exceed 1/3 of the wall thickness. (4) The impeller has no sand holes, perforations, cracks, or severe thinning of the wall thickness due to stamping. (5) When the impeller is fitted to the shaft, there should be a gap of 0.2–0.4 mm at the top of the key. 5) After the rotor and stator are assembled, the total axial play of the rotor is measured first; when centering the rotor, half of this total play should be used. 3. Bearing section 1) Sliding bearings: (1) The tightness between the bearing shell and the bearing cover should be 0.02–0.04 mm. The contact between the back of the lower bearing shell and its base should be even, with a contact area of 60%–80%; no shims shall be used at the back of the bearing shell. (2) The contact angle between the journal and the lower bearing shell should be 60–90°; the contact area must be uniform, with no fewer than 2–3 spots per square centimeter. (3) The clearance at the top of the bearing shell shall comply with the specifications in the table below (unit: mm). Axial clearance: Below 1500 r/min, 1500 r/min and above, 30–50, 0.075–0.160, 0.17–0.34; 50–80, 0.095–0.195, 0.20–0.40; 80–120, 0.120–0.235, 0.23–0.46; 120–180, 0.150–0.285, 0.26–0.53; 180–200, 0.180–0.330, 0.30–0.60. (4) The tungsten gold layer must bond well with the shell; there should be no cracks, pores, peeling, or inclusions. 2) The fit between the inner ring and the shaft of the rolling bearing (1) is shown in the table below (unit: mm). Axial clearance fit Axial clearance fit 18-30 0.002-0.027 80-120 0.003-0.046 30-50 0.003-0.032 120-180 0.004-0.055 50-80 0.003-0.038 (2) The fit between the outer ring and the shaft is as shown in the table below (unit: mm). Axial clearance fit Axial clearance fit 18-30 +0.029~-0.008 80-120 +0.045~-0.014 30-50 +0.033~-0.010 120-180 +0.052~-0.014 50-80 +0.038~-0.012 Note: (+) indicates clearance ； (–) indicates a surplus quantity. (3) The clearances in ball and roller bearings are as shown in the table below (unit: mm). Bearing diameter, radial clearance, new ball bearings, new roller bearings; maximum allowable wear: 20–30, 0.01–0.02, 0.03–0.05, 0.1; 35–50, 0.01–0.02, 0.05–0.07, 0.2; 55–80, 0.01–0.02, 0.06–0.08, 0.2; 85–120, 0.02–0.03, 0.08–0.10, 0.3; 130–150, 0.02–0.04, 0.10–0.12, 0.3. (4) In pumps where rolling bearings are used for axial thrust support, the outer ring of these rolling bearings should not be compressed; generally, a clearance of 0.04–0.08 mm should be left. (5) Special tools should be used when assembling and disassembling rolling bearings ； If possible, hot loading is the preferred method; the oil temperature used for heating should be around 100°C, and direct heating with flames is strictly prohibited. (6) The rollers of the rolling bearing and the surfaces of the raceways should be free from corrosion, pits, and spots, with smooth contact and no abnormal noises. 4. Sealing device 1) Nut (1) The diameter clearance between the nut and the shaft sleeve is generally 0.75–1.00 mm. (2) The perpendicularity of the plane where the gland of the mechanical seal contacts the gasket to the axis centerline shall be ≯0.02 mm. (3) The diameter clearance between the gland and the inner wall of the packing box is generally >0.20 mm. (4) The thickness of the gasket between the mechanical seal gland and the packing box should be maintained at 1–3 mm. (5) A radial gap of 1–2 mm in the axial direction should be maintained between the root of the anti-rotation groove in the static ring of the gland and the anti-rotation pin, to prevent the sealing ring from not being pressed tightly and to avoid stress buildup. 2) Packing ring: (1) The diameter clearance between the packing ring and the shaft sleeve is generally 1–1.5 mm. (2) The diameter clearance between the packing ring and the packing box is 0.15–0.20 mm. 3) The diameter clearance between the filler bottom sleeve and the shaft sleeve is generally 0.70–1.00 mm. 4) The diameter clearance between the balance sleeve and the shaft sleeve is generally 0.5–1.2 mm. 5) The diameter clearances between the shell mouth ring and the impeller mouth ring, as well as between the intermediate support ring and the intermediate shaft sleeve, are shown in the table below (unit: mm). Flange diameter: Standard clearance and replacement clearance for the shell flange and impeller flange, as well as for the intermediate support and intermediate shaft sleeve. Standard clearance: <100 – 0.40~0.60; 1.00 – 0.30~0.40; 0.80. Replacement clearance: ≥100 – 0.60~0.70; 1.20 – 0.40~0.50; 0.90. 5. Coupling: 1) The fit between the coupling and the shaft should be of type D/gd. 2) The axial clearance between the two end faces of the coupling is generally 2-6 mm. 3) When installing the toothed coupling, it should be ensured that the outer teeth are located in the middle of the width of the inner teeth. 4) When installing the elastic cylindrical pin coupling, its rubber ring and pin should be in an interference fit with a certain degree of tension. The diameter clearance between the rubber ring and the coupling hole should be 1-1.5 mm. 5) The concentricity deviation of the coupling shall meet the requirements shown in the table below (unit: mm). Type, Radial, Axial, Tooth shape: <0.08, <0.06; Elastic pin type: 0.10, 0.06; Spring leaf type: 0.15, 0.10; Fixed type: 0.06, 0.04. 6) When checking for concentricity, no more than four shims should be used per group under the motor.