Artificially Defected Washers for Thrust Bearings and Life Test Methods for Thrust Bearings

Abstract

To provide a race with artificial defects suitable for life testing of thrust bearings. [Solution] A thrust bearing washer 20 with artificial defects has a flat surface (back surface) 10a opposite to the raceway surface 11 of the washer 10 of a thrust bearing 1, and has a hole (artificial defect) 30 formed from the opposite surface 10a toward the deepest part 11a of the raceway surface 11. A thrust bearing 1 equipped with such a thrust bearing washer 20 with artificial defects is rotated under load to cause internally initiated flaking starting from the artificial defect 30, and the value of the rolling fatigue life is determined based on this.

Description

[Technical Field]

[0001] The present invention relates to an artificially flawed thrust bearing washer and a life test method for a thrust bearing using a thrust bearing equipped with an artificially flawed thrust bearing washer. [Background technology]

[0002] Generally, the rolling fatigue life of a rolling bearing is defined as the total number of bearing revolutions until the first damage due to material fatigue occurs on the raceway surface formed on the bearing ring or the rolling surface of the rolling elements. Of the damage that can occur on raceway surfaces and rolling elements, internally initiated spalling on the raceway surface originates from tiny defects (non-metallic inclusions) present in the surface layer. In other words, when a rolling bearing is in operation, in the load zone, shear stress is repeatedly applied below the raceway surface every time the rolling elements pass over the raceway. As a result, the value of this shear stress is particularly high in the defective area, and after long periods of operation, cracks will initiate from the defects, and these will further propagate, resulting in internally initiated spalling.

[0003] Therefore, when evaluating the rolling fatigue life of a rolling bearing, it is important to investigate in advance through experiments how the location and size of a defect, etc., affect the occurrence of subsurface-initiated flaking.Therefore, for example, Patent Document 1 proposes a raceway with an artificial defect, in which a hole is formed from one end surface of the raceway of a rolling bearing to the other, and this hole is used as an artificial defect. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-340808 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the artificial defect proposed in Patent Document 1 is a hole that penetrates from one end face of the bearing ring to the other, which poses a problem in that it is difficult to process in annular bearings such as thrust bearings, because the end faces are curved.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a bearing washer with artificial defects suitable for life testing of thrust bearings, and a method for life testing of thrust bearings. [Means for solving the problem]

[0007] The above object of the present invention is achieved by the following configuration [1] relating to an artificially defective bearing washer for a thrust bearing.

[0008] [1] The surface opposite to the raceway surface of the thrust bearing raceway is flat, 10. A thrust bearing washer with artificial defects, comprising: a hole formed from said opposite surface toward the deepest portion of said raceway surface.

[0009] Furthermore, preferred embodiments of the present invention relating to the thrust bearing washer with artificial defects relate to the following [2] to [3].

[0010] [2] The artificially defective race for thrust bearing according to [1], wherein the distance between the deepest part and the tip of the hole is 35 to 500 μm. [3] The artificially defective race for a thrust bearing according to [1] or [2], wherein the diameter of the tip of the hole is 100 to 500 μm.

[0011] The above object of the present invention is achieved by the following configurations [4] and [5] relating to a life test method for a thrust bearing.

[0012] [4] A life test method for a thrust bearing, characterized in that a thrust bearing equipped with an artificially defective thrust bearing race according to any one of [1] to [3] is rotated while applying a load, thereby causing internally initiated flaking that originates from the artificial defect, and determining the value of the rolling fatigue life based on this. [5] For a thrust bearing having an artificial defect bearing washer for a thrust bearing according to any one of [1] to [3], a plurality of types of artificial defect depths D and diameters φ of the holes corresponding to the artificial defects are prepared, rotating the thrust bearing with a predetermined load applied thereto, and observing the deterioration state of the raceway surface of the raceway washer with the artificial defect at predetermined time intervals from the start of rotation; A life testing method for thrust bearings, characterized in that the rolling fatigue life is estimated by determining the correlation between the rotation time and the deterioration state from the observation results. [Effects of the Invention]

[0013] According to the thrust bearing washer with artificial defects of the present invention, the surface of the thrust bearing washer opposite the raceway surface is made flat, and the holes representing the artificial defects are formed on the opposite surface, so that the flat surface on the opposite side can be easily drilled. Furthermore, during drilling, the depth of the holes can be set accurately as desired.

[0014] Therefore, the rolling fatigue life of the thrust bearing due to internally initiated spalling can be determined more accurately. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a partially cutaway perspective view showing the overall structure of a thrust bearing. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an example of a bearing washer with artificial defects for a thrust bearing, taken along the axial direction of the bearing washer. [Figure 3] FIG. 3 is a schematic diagram showing a method of forming a hole in the bearing washer according to FIG. [Figure 4]FIG. 4 is a graph showing the "correlation between artificial defect depth D and L50 life" obtained in the example. [Figure 5A] FIG. 5A is a metallurgical microscope photograph showing a cross section around a hole after a thrust bearing incorporating a race with an artificial defect has been rotated for a predetermined period of time, in which the artificial defect depth D is 35 μm. [Figure 5B] FIG. 5B is a metallurgical microscope photograph showing a cross section around a hole after a thrust bearing incorporating a race with an artificial defect has been rotated for a predetermined period of time, in which the artificial defect depth D is 50 μm. [Figure 5C] FIG. 5C is a metallurgical microscope photograph showing a cross section around a hole after a thrust bearing incorporating a race with an artificial defect has been rotated for a predetermined period of time, in which the artificial defect depth D is 100 μm. [Figure 5D] FIG. 5D is a metallurgical microscope photograph showing a cross section around a hole after a thrust bearing incorporating a race with an artificial defect has been rotated for a predetermined period of time, in which the artificial defect depth D is 200 μm. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will be described below. Note that this embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications and improvements can be made to this embodiment, and such modifications and improvements can also be included in the present invention.

[0017] In this embodiment, there is no limitation on the type or material of the thrust bearing, and various thrust bearings can be used. For example, as shown in Fig. 1, a thrust bearing 1 is configured by holding a plurality of rolling elements 15 between a pair of annular washers 10 in a freely rollable manner by a cage 18.

[0018] Next, Figure 2 is a cross-sectional view showing an example of an artificially defected bearing washer for a thrust bearing, taken along the axial direction of the washer. As shown in Figure 2, the artificially defected bearing washer for a thrust bearing of the present invention (hereinafter referred to as "artificially defected bearing washer") 20 has a flat surface 10a (hereinafter referred to as "back surface") opposite to the raceway surface 11 of the thrust bearing washer 10, and has a hole 30 formed from the back surface 10a toward the deepest part 11a of the raceway surface 11. Note that this hole 30 corresponds to the "artificial defect."

[0019] To form the hole 30 in the bearing washer 10, as shown in Figure 3, it is advisable to press the electric discharge electrode rod 40 from the back surface 10a of the bearing washer 10 toward the deepest part 11a of the raceway surface 11, preferably perpendicular to the back surface 10a (up and down direction in Figure 3). Note that the symbol F in Figure 3 indicates the pressing direction. In the thrust bearing 1, because the back surface 10a of the bearing washer 10 is flat rather than curved, the hole 30 can be easily formed perpendicular to the back surface 10a toward the deepest part 11a of the raceway surface 11.

[0020] As the electric discharge machining electrode rod 40 is pushed in, as shown in Figure 2, the opening diameter of the hole 30 on the back surface 10a of the washer 10 increases and gradually narrows toward the tip 30a of the hole 30, so that the tip portion of the hole 30 becomes approximately hemispherical, and the hole 30 takes on a shape similar to a so-called "triangular cone."

[0021] Furthermore, by changing the amount of pressing of the electric discharge machining electrode rod 40, it is possible to arbitrarily set the distance between the tip 30a of the hole 30 and the deepest part 11a of the raceway surface 11. This distance corresponds to the "depth D of the artificial defect" shown in FIG.

[0022] The shallower the artificial defect depth D, the more the influence of internal defects in shallower regions of the raceway surface 11 can be estimated, but if it is too shallow, it becomes difficult to distinguish between the influence of defects present on the surface of the raceway surface 11, and there is a risk that the influence of only internal defects in the surface layer cannot be adequately detected. For this reason, the artificial defect depth D is preferably 35 μm or more, and more preferably 100 μm or more and 500 μm or less.

[0023] Furthermore, the smaller the diameter φ of the tip of hole 30 (see FIG. 2), the more easily the effects of smaller internal defects can be detected, but the more difficult the hole drilling process becomes. On the other hand, if the diameter φ of the tip of hole 30 is too large, the internal defects will become too large. Therefore, the diameter φ of the tip of hole 30 is preferably 100 to 500 μm. As mentioned above, the tip of hole 30 is approximately hemispherical, and therefore, in this specification, "the diameter φ of the tip of hole 30" means the same length as the diameter of a hemisphere having the same volume as the hemisphere at the tip of hole 30.

[0024] The artificially defective washer 20 is configured as described above, but to detect the rolling fatigue life of a thrust bearing, it is advisable to prepare a number of types of holes 30 corresponding to the artificial defects, each with a different artificial defect depth D and diameter φ, and rotate the thrust bearing 1 incorporating the artificially defective washer 20 under a predetermined load, and observe the state of deterioration of the raceway surface 11 of the artificially defective washer 20 at predetermined time intervals from the start of rotation. Then, by finding a correlation between rotation time and the state of deterioration from the observation results, it is possible to estimate the rolling fatigue life of the thrust bearing and reflect this in an actual product. [Example]

[0025] The present invention will be described in more detail below with reference to examples.

[0026] A thrust bearing (bearing number 51305) was prepared, and an electrode rod for electrical discharge machining was pressed perpendicular to the back surface of one of the raceway washer raceways, from the back surface to the deepest part of the raceway surface, to create a raceway with an artificial defect. Both the thrust bearing raceway washer and steel balls (3 / 8 inch) were made of through-hardened SUJ2.

[0027] The diameter of the tip of the electric discharge machining electrode rod was 0.2 mm, and the depth of the hole in the artificially defective race, i.e., the artificial defect depth D, was adjusted by adjusting the push amount to 35 μm, 50 μm, 100 μm, and 200 μm, so that a total of four races with artificial defects were produced with different artificial defect depths D. The diameter φ of the tip of the hole was approximately 0.3 μm.

[0028] The L50 life was determined using a thrust life tester for thrust bearings incorporating the above-mentioned artificially flawed races with different artificial flaw depths D. The test was carried out under a load of 900 kgf (surface pressure: 3.4 GPa) for 1000 min -1 The thrust bearing was continuously rotated at a rotation speed of 1000 rpm. Lubrication was performed with 150 ml of ISO-VG68. The results are shown in Table 1 and graphed in Figure 4.

[0029] [Table 1]

[0030] As shown in Table 1 and Figure 4, the closer the internal defect is to the raceway surface, the earlier it will lead to spalling.

[0031] In addition, thrust bearings incorporating races with artificial defects of different artificial defect depths D were continuously rotated under the same conditions as above, and then the races with artificial defects were removed and the cross sections along the artificial defects were observed.

[0032] Figures 5A to 5D show metallurgical microscope photographs of the cross section around the hole of a thrust bearing incorporating an artificially flawed raceway after it had been rotated for a specified period of time. Figure 5A shows the case where the artificial defect depth D was 35 μm, Figure 5B shows the case where the artificial defect depth D was 50 μm, and Figure 5C shows the cases where the artificial defect depth D was 100 μm and D was 200 μm. Only when the artificial defect depth D was 35 μm was etched with 2% nital during cross-sectional observation. Based on the L50 life results above, rotation was terminated after 5 hours for thrust bearings incorporating raceways with artificial defects of D=35 μm, after 3 hours for thrust bearings incorporating raceways with artificial defects of D=50 μm, after 11 hours for thrust bearings incorporating raceways with artificial defects of D=100 μm, and after 25 hours for thrust bearings incorporating raceways with artificial defects of D=200 μm.

[0033] Note that the black lines extending from the holes 30 in each figure correspond to cracks, and the areas corresponding to these cracks are shown enclosed in dotted lines (parts A and B) in each figure. Only when the artificial defect depth D = 35 μm in Figure 5A was a crack directed toward the raceway surface 11 (i.e., the black line from the tip 30a of the holes 30 directed toward the raceway surface 11) observed (see part A in Figure 5A), and this is thought to be the cause of the shortened L50 life. On the other hand, when the artificial defect depth D = 50 μm in Figure 5B, when the artificial defect depth D = 100 μm in Figure 5C, or when the artificial defect depth D = 200 μm in Figure 5D, no cracks were observed from the tip 30a of the holes 30 directed toward the raceway surface 11 (see part B in Figures 5A to 5C).

[0034] In this way, by detecting not only surface defects on the raceway surface 11 but also internal defects in shallower regions, it is possible to know the deterioration state of the thrust bearing in more detail. Therefore, it can be said that it is useful to use a race with artificial defects that can be manufactured by changing the artificial defect depth D, as in the present invention. [Explanation of symbols]

[0035] 1 Thrust bearing 10 Raceway 10a Back side (surface opposite to the raceway surface) 11 Raceway surface 11a (Deepest part of the orbital plane) 15 Rolling elements 18 Cage 20 Raceway with artificial defects 30 holes (artificial defects) 30a (hole) tip 40 Electrode rod for electrical discharge machining

Claims

1. The surface of the thrust bearing washer opposite to the raceway surface is flat, 10. A thrust bearing washer with artificial defects, comprising: a hole formed from said opposite surface toward the deepest portion of said raceway surface.

2. 2. The thrust bearing washer with artificial defects according to claim 1, wherein the distance between the deepest part and the tip of the hole is 35 to 500 μm.

3. 2. The thrust bearing washer with artificial defects according to claim 1, wherein the diameter of the tip of the hole is 100 to 500 μm.

4. A life testing method for a thrust bearing, comprising: rotating a thrust bearing equipped with an artificially defective thrust bearing race according to any one of claims 1 to 3 while applying a load, thereby causing internally initiated flaking to occur with the artificial defect as a starting point, and determining a value of rolling fatigue life based on the result.

5. For a thrust bearing including the thrust bearing washer with artificial defects according to any one of claims 1 to 3, a plurality of types of holes corresponding to the artificial defects are prepared, each having a different artificial defect depth and diameter, rotating the thrust bearing with a predetermined load applied thereto, and observing the deterioration state of the raceway surface of the raceway washer with the artificial defect at predetermined time intervals from the start of rotation; A life testing method for thrust bearings, characterized in that the rolling fatigue life is estimated by determining the correlation between the rotation time and the deterioration state from the observation results.

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