Rolling Bearings
When the bore diameter tolerance zone of a bearing matches the shaft tolerance zone, in the general base hole system, the tolerance symbols originally designated for transition fits will become overfit fits, such as k5, k6, m5, m6, n6, etc., but the overfit amount is not significant. When the bore diameter tolerance symbol matches with h5, h6, g5, g6, etc., it no longer forms a clearance fit but becomes an overfit fit.
② The bearing outer diameter tolerance zone is a special tolerance zone as the tolerance values differ from those of general reference shafts. In most cases, the outer ring is fixed in the housing bore. However, some bearing component structures require adjustment, and the fit should not be too tight, often matching with H6, H7, J6, J7, Js6, Js7, etc.
Appendix:
Typically, the shaft is marked at 0 to +0.005. If it's not frequently disassembled, an interference fit of +0.005 to +0.01 is sufficient. For frequent disassembly, a transition fit is appropriate. We must also consider the thermal expansion of the shaft material during rotation, so for larger bearings, an clearance fit of -0.005 to 0 is recommended, and it should not exceed a clearance of 0.01.
1. Bearings are matched with shafts using a basic hole system, while bearings are paired with housings using a basic shaft system.
Bearings dimensional tolerances and rotational accuracy values comply with the provisions of GB307-84 for corrosion-resistant pumps.
2. The shaft journals and bearing housing bores are in accordance with the GB1031-83 specification. The surface roughness Ra value of the shaft journals is less than 1.6μm, and the surface roughness Ra value of the bearing housing bores is less than 2.5μm.
In the manufacturing of bearing rings and rollers with GCr15 and ZGCr15 steel, the hardness values of the rings and rollers should be between 61~65HRC. For the production using GCr15SiMn and ZGCr15SiMn steel, the hardness should be between 60~64HRC. The method for checking the hardness and the uniformity of hardness in the same part are in accordance with the regulations of JB1255.
Ensure that the radial and axial clearance of the bearing should comply with the GB4604-84 standard.
5. The inner and outer raceways of the roller bearing should be free of spalling and severe wear; neither the inner nor the outer race should have cracks. The balls should be free of wear, the cage should not be severely deformed, and there should be no abnormal noise or vibration during rotation. When stopping, it should gradually decelerate.
6. For C-tolerance spherical roller bearings, the contact degree between the rollers and the raceway bottom should be inspected under a certain load with the pump. The color inspection should reveal continuous contact marks, with the contact length not being less than 80% of the roller flange.
Slide Bearing
1. Regarding radial thick-walled tiles
Measure the bearing clearance and shell filling volume using methods such as lead pressing, lifting the shaft, or others. The shaft clearance should be suitable for immediate use, and the shell filling volume should be between 0 to 0.02mm.
All components should be inspected for any damage or cracks, and bearing shells should be free from peeling, pores, cracks, grooves, and uneven burnishing.
③ The condition of contact between the bearing shell and shaft neck should be inspected using the dye method. The inspection angle should not be between 60° to 90° (for speeds above 1000 rpm, the lower limit is applied; for speeds below 1000 rpm, the upper limit is applied). Within the contact area, ensure even contact by aiming for 2 to 4 contact points per square centimeter. If the contact is not good, proper scraping and finishing must be performed.
④ Cleaned the bearing housing, all oil holes are unobstructed, no cracks or leakage observed.
The back of the瓦 should be tightly and evenly adhered to the bearing seat. Inspect using the coloring method, ensuring the contact area is no less than 50.
2. Regarding radial thin-walled tiles
The alloy layer on the bearing shell should be firmly and tightly bonded with the shell, with no subsequent delamination or peeling. The surface of the alloy layer and the inner bottom faces of the two halves of the shell should be smooth and even, with no defects such as cracks, blowholes, double skins, inclusions, and scratches.
② The back of the shell and the inner surface of the bearing seat should be tightly and uniformly fitted together. Inspected by the coloring method, the contact area should not be less than 85% for diameters less than 180mm, and for diameters greater than or equal to 180mm, the contact area should not be less than 70%.
③ The fit between the shaft sleeve and the shaft neck is ensured through machining. Generally, the contact area should not require scraping and lapping. If the contact along the axial direction is not uniform, slight adjustment may be needed.
After assembly, check the inside mating surfaces with a 0.02mm feeler gauge; it should NOT be able to fit to ensure compliance.
3. Thrust Bearings
The shaft sleeve should be free of wear, deformation, cracks, scratches, spalling, crushing, and burn defects; the contact marks with the thrust plate should be even, and the contact area should be no less than 70%, with the entire circumference evenly distributed among the sleeve segments; the thickness difference among the sleeve segments in the same group should be no more than 0.01mm, and the Babbitt metal should be rounded in the direction of rotation to form the oil wedge, allowing the use of high-quality lubricating oil to enter; the back bearing surface should be flat and smooth.
The shims should be smooth, flat, free of warping, and consist of a single layer with no thickness variation greater than 0.01mm.
After assembly with bearing caps, the thrust bearing clearance should be repeatedly measured using the push shaft method, and the value should be within the specified range. The measurement using this method must be consistent with that obtained using an axis displacement probe, and the probe's bottom indicator must be adjusted to zero as per regulations.
④ The bearing housing horizontal mating surface is tight, with no misalignment. The bottom oil temperature measuring hole aligns with the bearing cap hole, with no deflection. The oil holes are clean and unobstructed.
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