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Abstract: The measuring method is discussed for axial protruding amount of NJ type cylindrical roller bearings，and the reasons for high dispersion for axial protruding amount are analyzed． The axial protruding amount is controlled by marking process sign on non － reference end face of outer rings and improving machining accuracy of assembled parts，the axial protruding amount of batch bearings is guaranteed within the scope of the requirements．
Key words: cylindrical roller bearing; axial convex; tolerance; reference end face; machining accuracy
Symbol Description
a11-- Width of the outer ring reference end face side guard edge
a12-- Width of the outer ring non reference end face side guard edge
a21-- Width of inner ring edge guard
C -- Outer ring width
E -- Width of bearing raceway
Lw -- Roller length
Δ ——— Axial protrusion
Cylindrical roller bearings have a simple internal geometric structure, high manufacturing accuracy, large load-bearing capacity, good rigidity, and are widely used. Especially in situations where axial guidance is not required, adopting a floating bearing configuration is an economical solution. The floating bearing configuration is similar in structure to a clearance adjustable bearing, but its shaft needs to use axial clearance s to move relative to the bearing seat. The value of s is determined by the guidance accuracy and needs to ensure that it can prevent harmful axial preloading of the bearing even under adverse thermal conditions.
In the floating bearing configuration equipped with NJ type cylindrical roller bearings, length changes are compensated in the bearings. Both the inner and outer rings can be fitted with interference fit.
1. Question raising
The measurement method for the axial protrusion of cylindrical roller bearings is shown in Figure 1. The outer ring of the bearing is supported horizontally and uniformly at three points, with the inner ring with a retaining edge facing upwards. The height difference between the inner and outer ring end faces on the same side is measured, which is the protrusion of the inner ring end face relative to the outer ring end face. The protrusion can be positive or negative.
Figure 1 Principle of measuring axial protrusion of cylindrical roller bearings
When the host user installs the machine, it is found that there is a significant difference (discreteness) in the axial protrusion of two sets of NJ2240 bearings installed on the same shaft. It is necessary to select and match bearing parts to meet the requirements of the host, resulting in low production efficiency and high labor intensity for assembly workers. In order to better meet the performance requirements of bearings and improve efficiency, it is necessary to quantitatively explore the axial protrusion of NJ type bearings.
2. Theoretical calculation analysis
2.1 Axial protrusion Δ 1 (Supporting outer ring reference end face)
According to equation (1), the maximum protrusion is
2.2 Axial protrusion Δ 2 (Non reference end face of support outer ring)
The width a12 of the side guard edge on the non reference end face of the outer ring is
a12=C-a11-E. (2)
Axial protrusion Δ 2 is for
Δ 2=C - (a12+Lw+a21). (3)
According to equations (2) and (3)
Δ 2=a11+E-Lw-a21. (4)
According to equation (4), the maximum protrusion is obtained
According to equations (1) and (4), when supporting the reference end face of the outer ring, the width tolerance of the outer ring is relatively large, which has a significant impact on the protrusion amount; When the supporting outer ring is not the reference end face, the protrusion is not directly related to the outer ring width, and the tolerances of a11, Lw, a21, and E related to it are relatively small, which has a relatively small impact on the protrusion. The protrusion is the result of comprehensive factors. According to the product drawing, the inner and outer ring end faces are standardized, and the dispersion of the axial protrusion of the complete set of bearings is relatively small.
3. Process analysis
The process flow of NJ cylindrical roller bearing outer ring grinding is as follows: rough grinding of non reference end face → rough grinding of reference end face → rough grinding of outer diameter face → rough grinding of inner diameter face of retaining edge → rough grinding of outer raceway → fine grinding of non reference end face → fine grinding of reference end face → fine grinding of outer diameter face → fine grinding of inner diameter face of retaining edge → fine grinding of outer raceway → fine grinding of outer ring retaining edge → ultra fine outer raceway.
According to the process flow, the axial dimensions that the outer ring needs to ensure are the width tolerance of the reference end face side guard edge, the width tolerance of the raceway, and the total width tolerance of the ring; Instead of indirectly controlling the width of the side guard edge of the reference end face. That is to say, the width of the outer ring reference end face side guard is greater than the width of the non reference end face side guard.
In actual processing, due to the lack of printing marks on non reference end faces, if end face measurement is not carried out, it is difficult to visually distinguish which face is the reference plane, but in reality, two end faces are machined as reference planes. Moreover, GB/T 307.2-2005 "Principles and Methods for Measurement and Inspection of Rolling Bearings" does not have clear requirements for the axial protrusion of NJ type complete bearings, and the axial protrusion is not detected in actual operation. Therefore, during the manufacturing process of the bearing outer ring, the two end faces are used as reference grinding edges, and the actual difference between the outer ring reference end faces cannot be distinguished when fitting.
4. Response measures
(1) Make process markings on the end face. Make process markings on the non reference end face of the outer ring, and ensure that the inner and outer ring benchmarks are unified when fitting, that is, the inner ring typing end face (with a guard edge end face) is not on the same side as the outer ring process marking end face, eliminating errors caused by unclear identification of the ring end face benchmark. The usual installation reference is the non typing surface, with the typing surface facing outward.
(2) Improve the machining accuracy of assembled parts. For smaller bearings, a double end face grinder can be chosen to improve axial dimension consistency; For larger ring sizes, compress the width tolerance of the ring and the edge width tolerance, and process them in a more economical way.
To meet the requirement of axial protrusion, the difference between the maximum and minimum protrusions of bearings in the same batch should generally not exceed 0.15 mm. By making process marks on the non reference end face of the outer ring and improving the manufacturing accuracy of bearing sleeve parts, it can meet the user's usage requirements.
5. Example explanation
Taking NJ2244EM as an example, explain the difference in the protrusion of the bearing inner ring with retaining edge end face relative to the same side end face of the outer ring due to different outer ring testing reference surfaces, as well as the problem of large dispersion in the axial protrusion of bearings in the same batch. Known:
When the horizontal support outer ring reference end face, the axial protrusion Δ 1max=+0.11 mm, Δ1min=-0.38 mm. When the outer ring of the horizontal support is not the reference end face, the axial protrusion amount Δ 2max=+0.21 mm, Δ2min=-0.04 mm.
In actual production, due to the inability to distinguish the reference end face of the outer ring, the axial protrusion is -0.38~+0.21 mm, resulting in significant discreteness. By making process markings on the non reference end faces of the outer ring, the reference of the inner and outer ring end faces can be unified, and the axial protrusion can be controlled within -0.04 to+0.21 mm; By improving the level of process equipment and making the width of the retaining edge (16.5 ± 0.02) mm, the axial protrusion can be further controlled within+0.01-0.17 mm, which can meet the requirements of the host.
6. Conclusion
To meet the special requirements of the host for the axial protrusion of the bearing, the protrusion can be measured using a dial gauge, as shown in Figure 1, by uniformly supporting the non reference end face of the outer ring at three points horizontally; If the axial dimension of the part is determined by measurement, the protrusion of the end face can also be calculated according to equation (4).
By making process marks on the non reference end face of the outer ring and improving the machining accuracy of the assembled parts, the problem of large dispersion of axial protrusion of bearings can be solved, meeting the requirements of the main engine installation.
2023 December 2nd Week KYOCM Product Recommendation:
KYOCM cylindrical roller bearings can meet the challenges of applications faced with heavy radial loads and high speeds. Accommodating axial displacement (except for bearings with flanges on both the inner and outer rings), they offer high stiffness, low friction and long service life. KYOCM cylindrical roller bearings include single row cylindrical roller bearings, double row cylindrical roller bearings and four row cylindrical roller bearings.
Cylindrical roller bearings are also available in sealed or split designs. In sealed bearings, the rollers are protected from contaminants, water and dust, while providing lubricant retention and contaminant exclusion. This provides lower friction and longer service life. Split bearings are intended primarily for bearing arrangements which are difficult to access, such as crank shafts, where they simplify maintenance and replacements.
2023-12-20