Centrifugal fan maintenance quality standard

In industrial production in various fields, the use of ventilation systems is inseparable. The commonly used equipment is centrifugal fans. In order to ensure that centrifugal fans can work effectively, they need to be regularly repaired and maintained, including various parts of centrifugal fans. .

1)Maintenance quality standard of centrifugal fan coupling

1. The coupling and shaft are matched with H7/js6.
2. There should be no gap between the coupling bolt and the elastic ring, and there should be a certain tightening force. The outer diameter of the elastic ring should have a clearance of 0.5~1.0mm when the hole is matched, and the bolt should be locked with a spring washer or a stop washer.
3. The alignment of the unit should conform to Table 1.

Table1: Allowed values ​​in the unit pair (table value)< /span>mm
Coupling form	Outer circle radial	End face
Elastic pin type	0.08	0.06
rigidity	0.06	0.04
Diaphragm style	0.10	0.08

4. The clearance between the two ends of the elastic pin coupling is 2~6mm.
5. During the alignment inspection, each group of adjusting shims shall not exceed 4 pieces.
6. Diaphragm coupling maintenance standard:
(1) When installing the half-coupling, preheat the half-coupling to 120℃. After installation, make sure that the shaft end is 0~0.5mm lower than the end face of the half-coupling;
(2) The sum of the lengths of the coupling short joint and the two diaphragm groups is compared with the distance between the end faces of the two half-couplings, and the difference is 0~0.4mm. There is no distortion after the sheet is installed;
(3) The diaphragm transmission torque bolt should be tightened with a torque wrench to the torque specified in the manufacturer’s data.
(4) Use the method of surface coloring flaw detection to detect the diaphragm connecting bolts, and replace them in time if any defects are found.

2)centrifugal fan impeller maintenance quality standards

1. The impeller should be colored to check that there are no cracks, deformations and other defects.
2. When the rotational speed is lower than 2950r/min, the upper limit of the static unbalance allowed by the impeller should conform to Table 2.

Table2: The upper limit of the unbalanced weight allowed by the impeller</span >
Impeller outer diameter/mm	401~500	501~600	601~700	701~800	801~1000	1000~1500
Unbalanced amount/g	10	12	15	17	20	25

3. The blade turntable of the impeller should not be significantly thinned.

3. Maintenance quality standard of centrifugal fan spindle

1. The cylindricity tolerance value at the main journal bearing should conform to Table 3.

Table3: Main journal cylindricity tolerance< span>mm
Shaft diameter	≤150	＞150~175	＞175~200	＞200~225
Cylindricity tolerance	0.02	0.025	0.03	0.04

2. The spindle straightness tolerance value should conform to Table 4.

Table4: Spindle Straightness Tolerancemm
Fan speed/(r/ min)	≤500	＞500~1500	＞1500~3000
Straightness tolerance value	0.10	0.07	0.05

3. The main shaft should be checked for coloring, its surface is smooth, free of cracks, rust and pitting, and there should be no mechanical damage and defects elsewhere.
4. The surface roughness of the journal is Ra0.8.

4 )centrifugal fan bearing maintenance quality standards

1. Rolling bearings

(1) The rolling elements and raceway surfaces of the rolling bearing should be free of corrosion and marks, and the cage should be free of defects such as deformation and cracks;
(2) The matching between the shaft and the rolling bearing bearing both axial and radial loads is H7/js6, the matching between the shaft and the rolling bearing only bearing the radial load is H7/k6, and the matching between the outer ring of the bearing and the inner hole of the bearing box is Js7/h6;
(3) For fans using axial thrust rolling bearings, the axial clearance between the outer ring of the rolling bearing and the gland is 0.02~0.10mm;
(4) When the rolling bearing is hot loaded, the heating temperature should not exceed 100 ℃, and it is strictly forbidden to directly heat it with flame;
(5) The axial clearance between the outer ring and gland of the free end bearing should be greater than the thermal elongation of the shaft, and the reference value of thermal elongation should conform to Table 5.

Table5: thermal axial elongation
Temperature/℃	0~100	＞100~200	>200~300
Extension per meter of shaft length/mm	1.20	2.51	3.92

 

2. Sliding bearing bushing

(1) The surface of the bearing lining should be free of defects such as cracks, blisters, interlayers or shelling;
(2) The contact between the bearing bush and the journal should be uniform, the contact angle should be 60°~90°, and the contact point within the contact angle should not be less than 2~3 points/cm2;
(3) The bearing backing and the bearing seat hole should be evenly fitted, and the contact area: the upper bearing body and the upper cover are not less than 40%, and the lower bearing body and the lower seat are not less than 50%. Bearing backing interference is -0.02~0.03mm;
(4) Bearing top clearance conforms to Table 6, bearing side clearance is 1/2 top clearance;

Table6: Bearing Top Clearance mm
Shaft diameter	50~80	＞80~120	＞120~180	＞180~250
Bearing clearance	0.10~0.18	0.15~0.25	0.23~0.34	0.34~0.40

(5) The bearing thrust clearance is generally 0.20~0.30mm, and the contact area between the thrust bearing surface and the thrust disc should not be less than 70%.

5) centrifugal fan rotor maintenance quality standards

The allowable values ​​of circular runout and full runout of each part of the rotor should conform to Table 7.

Table7: The allowable value of the beating of each part of the rotor< span>mm
Measurement part	External circle of impeller	Spindle journal	Coupling outer circle	Both sides of the outer circle of the impeller	Coupling outer edge	The thrust surface of the thrust plate
Bounce category	Circle beat	Circle beat	Circle beat	Full beat	Full beat	Full beat
allowed values	0.07	0.02	0.05	0.01	0.05	0.02

6)Quality standard for centrifugal bearing seal maintenance

1. The radial radius gap between the front cover plate of the impeller and the casing seal ring of the centrifugal fan is 0.35~0.50mm; the end face and radial clearance between the impeller inlet ring and the casing should not exceed 12mm.
2. When the shaft seal adopts felt seal, only one joint is allowed, and the position of the joint should be placed on the top.
3. The gap between the casing sealing cover and the shaft is generally not more than 1~2mm on each side.
4. The shaft seal adopts the expansion ring type or the labyrinth type, and its sealing clearance should conform to Table 8.

Table8: upper limit value of shaft seal clearancemm
Sealing gap	Sealing gaps on each side
	Installation value	Upper limit
Seal in plain bearing housing	0.15~0.25	0.35
Seal inside the enclosure	0.20~0.40	0.50

7) centrifugal fan casing and bearing box maintenance quality standards

1. The casing should be free of cracks and pores; the welded casing should be well welded.
3. For the integrally installed bearing box, take the middle face of the bearing seat as the benchmark, and check that the vertical and horizontal deviations are 0.1mm/m.
4. Vertical and horizontal installation levels of the split bearing box:
(1) The horizontal deviation of the longitudinal installation of the facets in each bearing housing should not be greater than 0.04mm/m;
(2) The horizontal deviation of the lateral installation of the facets in each bearing box should not be greater than 0.08mm/m;
(3) The installation level deviation at the spindle journal should not be greater than 0.04mm/m.