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Standard rules for fit tolerances of bearings and shafts

1、 Rolling bearings

① When the inner diameter tolerance zone of the bearing forms a fit with the shaft tolerance zone, the tolerance code of the transition fit in the general basic hole system will become an over fit, such as k5, k6, m5, m6, n6, etc., but the over fit amount is not large; When the bearing inner diameter tolerance is combined with h5, h6, g5, g6, etc. to form a fit, it is no longer a clearance and becomes an over fit.

② The outer diameter tolerance zone of bearings is a special tolerance zone due to its different tolerance values from general reference axes. In most cases, the outer ring is fixed when installed in the outer shell hole, and some bearing components require structural adjustment, so their fit should not be too tight. They often fit with H6, H7, J6, J7, Js6, Js7, etc.


In general, the axis is marked as 0 to+0. If it is not frequently disassembled, it is+0. 005 to+0. The interference fit of 01 is sufficient, and if frequent disassembly and assembly is required, a transitional fit is sufficient. We also need to consider the thermal expansion of the shaft material itself during rotation, so the larger the bearing, the better it is -0. The clearance fit between 005 and 0 should not exceed a maximum of 0. Clearance fit of 01

1. The bearing and shaft are matched using a base hole system, while the bearing and shell are matched using a base shaft system.

The values of bearing dimensional tolerance and rotational accuracy shall comply with the provisions of GB307-84 for corrosion-resistant pumps.

2. According to GB1031-83, the roughness Ra value of the journal and the hole in the bearing box that are matched with the bearing should be less than 1.6 μ m. The roughness Ra value of the bearing box hole is less than 2.5 μ M.

3. When using GCr15 and ZGCr15 steel to manufacture bearing rings and rollers, the hardness values of the rings and rollers should be between 61 and 65HRC; When manufactured with GCr15SiMn and ZGCr15SiMn steel, the hardness value should be between 60 and 64HRC. The hardness inspection method and the uniformity of the hardness of the same part shall comply with the provisions of JB1255.

4. The radial and axial clearance of the bearing bottom should comply with the regulations of GB4604-84.

5. The raceway of the inner and outer rings of the rolling bearing should be free of peeling and severe wear, and there should be no rear cracks on both the inner and outer rings; The ball should be free from wear, the cage should not be severely deformed, and there should be no abnormal noise or vibration during rotation. When stopped, the gap should gradually stop.

6. For C-grade tolerance tapered roller bearings, the contact accuracy between the rollers and the bottom of the raceway of the ring is determined by the water pump with a certain load. After coloring inspection, the contact marks should be continuous, and the contact length no should be less than 80% of the roller busbar.

2、 Sliding bearing

1. For radial thick wall tiles

① Measure the bearing clearance and bearing shell clearance using lead pressing method, shaft lifting method, or other methods. The shaft clearance should meet the requirements, and the bearing shell clearance should be 0-0.02mm.

② Check all components to ensure there are no damage or cracks, and the bearing pads should be free of peeling, air holes, cracks, grooves, and eccentric wear burns.

③ The contact condition between the bearing pad and the journal should be checked using the coloring method, and the inspection angle should not be between 60 ° and 90 ° (if the speed is higher than 1000r/min, take the gap limit, and if the speed is lower than 1000r/min, take the upper limit). Within the contact range, the contact should be uniform, with 2-4 pairs of contact points per square centimeter. If the contact is not good, good scraping and grinding must be carried out.

④ Clean the bearing box, ensure that all oil holes are unobstructed, and there are no cracks or leaks after being removed.

⑤ The back of the tile and the bearing seat should be tightly and evenly fitted, and inspected by coloring method. The contact area should be no less than 50.

2. For radial thin-walled tiles

① The axle tile alloy layer and tile shell should be firmly and tightly bonded to the soil, and there should be no phenomenon of delamination or peeling after being obtained. The surface of the alloy layer and the inner bottom of the two halves of the tile should be smooth and flat, with no defects such as cracks, pores, double skin, slag inclusions, and bumps allowed.

② The surface of the back of the bearing and the inner hole of the bearing seat should be tightly and evenly fitted, and inspected by coloring method. If the inner diameter is less than 180mm, the contact area should be no less than 85, and if the inner diameter is larger than or equal to 180mm, the contact area should be no less than 70.

③ The clearance and contact condition between the bearing bush and the journal are ensured by the machining accuracy, and the contact area is generally allowed to be scraped. If the axial contact is uniform, it can be slightly trimmed.

④ After assembly, use a 0.02mm feeler gauge to check the split surface inside the belt, and it should be able to be inserted and qualified.

3. For thrust bearings

① The bearing pads should be free of wear, deformation, cracks, scratches, delamination, rolling and burn defects; The contact mark with the thrust disc should be uniform, the contact area should be no less than 70, and the entire circumference of each tile should be evenly distributed; The thickness difference of the same set of tiles should not be greater than 0.01mm, and the Babbitt alloy of the tiles should be rounded in the direction of rotation to enter the oil wedge, using profit lubricating oil; The load-bearing surface of the back is flat and smooth.

② The adjusting gasket should be smooth, flat, and free from bending. A layer of gasket with a thickness difference of no greater than 0.01mm should be used.

③ After assembly with bearing cover, repeatedly use the push shaft method to measure the clearance of the thrust bearing, and the value should be taken within the range of calculation. The clearance between the thrust bearing on the side of the shaft displacement probe measured using that method must be consistent, and the bottom indication zero position of the rod displacement probe must be adjusted according to regulations.

④ The horizontal joint surface of the bearing shell is tight and not misaligned. The bottom oil hole for measuring oil temperature is aligned with the tile cover hole, and there is no deviation. The oil hole is clean and unobstructed.

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