TWI688716B - Retainer and bearing - Google Patents

Abstract

A retainer is applied in a bearing. The retainer is an annular structure and includes a main body portion and a protruding peripheral portion. The main body portion defines a central axis and includes a first surface, a second surface, a plurality of holes and at least one oil storage groove. The second surface is opposite to the first surface. Each of the holes is for receiving a rolling member. The oil storage groove is concaved from the first surface and/or the second surface. The oil storage groove is located between two neighboring holes of the plurality of holes, and the oil storage groove is communicated with the two neighboring holes. The protruding peripheral portion is disposed on an outer periphery of the main body portion. The protruding peripheral portion includes a first protruding portion and a second protruding portion. The first protruding portion is adjacent to the first surface and is protruded outwardly relative to the first surface and thus has a first height difference therebetween. The second protruding portion is adjacent to the second surface and is protruded outwardly relative to the second surface and thus has a second height difference therebetween.

Description

Retainer and bearing

The invention relates to a retainer and a bearing, and particularly relates to a retainer and a bearing which is beneficial for preventing leakage of lubricating fluid inside the bearing.

Bearings are important parts in contemporary machinery and equipment. The main function of bearings is to support mechanical rotating bodies, reduce the friction coefficient during their movement, and ensure the accuracy of their rotation.

In order to improve the lubricating effect, some bearings will be filled with lubricating fluid to effectively reduce the friction coefficient and extend the bearing life. The structure of the retainer in the bearing is closely related to the oil storage capacity and lubrication effect of the bearing. Therefore, the relevant operators are all committed to improving the structure of the retainer.

Taking Japanese Patent Application Publication No. JP2001041250A as an example, it discloses a retainer. The inner wall surface of the retainer includes a plurality of grooves and a plurality of protrusions (such as the elements shown in reference numerals 61 and 62 of FIG. 11 in this case). Containing lubricating fluid, the protrusion is used to maintain the axial position of the roller. However, the retainer does not have a structure to prevent the leakage of lubricating fluid. As the bearing runs, the lubricating fluid inside it will gradually lose and cause lubrication failure. In addition, the structure of the retainer is not conducive to the lubricating fluid in the groove The circulation between different holes is not conducive to the uniformity of lubricating fluid distribution. The retainer is provided with protrusions at the upper and lower openings of the hole, which also causes difficulty in demolding and reduces the yield of the retainer.

Taking Japanese Patent Application Publication No. JP2008223919A as an example, it discloses a retainer. The inner wall surface of the retainer includes a plurality of protrusions (such as the elements shown in FIG. 6 as reference numerals 16a and 16b in this case). The protrusions are used to retain the rollers. Axial position. However, the structure of the retainer is less effective in preventing leakage of lubricating fluid, and the retainer is provided with protrusions at the upper and lower openings of the hole, which also causes difficulty in demolding and reduces the yield of the retainer.

Therefore, how to develop a new retainer so that it can provide better lubricating effect, and can more preferably reduce the difficulty of demolding, has become the goal of the efforts of the relevant industry.

According to one embodiment of the present invention, a retainer is provided for a bearing. The retainer is an annular structure and includes a body portion and a flange portion. The body portion defines a central axis and includes a first surface, a second surface, In the plurality of holes and at least one oil storage groove, the second surface is opposite to the first surface, and the second surface and the first surface have a separation distance in a direction parallel to the central axis. Each hole penetrates the main body portion to communicate with the first surface and the second surface. Each hole is used to accommodate a rolling element. The oil storage groove is recessed from the first surface and/or the second surface. The oil storage groove is located adjacent to two of the plurality of holes Between the holes, and the oil storage tank communicates with two adjacent holes. The flange portion is disposed on the outer periphery of the body portion. The flange portion includes a first protrusion and a second protrusion. The first protrusion is adjacent to the first surface, and the first protrusion protrudes outward relative to the first surface and has a first For the height difference, the second protrusion is adjacent to the second surface, and the second protrusion protrudes outward relative to the second surface to have a second height difference. The retainer of the present invention can reduce the gap between the flange portion and other parts of the bearing (such as the first ring structure and the second ring structure) by providing the flange portion on the outer peripheral edge of the body portion to effectively prevent the bearing The internal lubricating fluid leaks out, which is beneficial to maintain the lubrication effect of the bearing and prolong the service life of the bearing. By connecting the oil storage tank with two adjacent holes, it is conducive to the uniformity of lubricating fluid distribution.

According to the aforementioned retainer, each hole may include a first opening and a second opening, wherein the first opening is provided on the first surface of the body portion, the second opening is provided on the second surface of the body portion, and each hole is on the first The opening or the second opening is provided with a dipper-shaped structure, and the dipper-shaped structure is composed of two arc-shaped inner walls adjacent to the first opening or the second opening. In this way, it is advantageous to carry the rolling element, and it can avoid that when the first opening and the second opening of the hole include the dipper-like structure at the same time, it is difficult to install the rolling element and the lack of mold release.

According to the aforementioned holder, the plurality of holes may include a plurality of first holes and a plurality of second holes, each first hole is provided with a dipper-like structure at the first opening, and each second hole is provided with a dipper-like structure at the second opening. In this way, when the first hole or only the second hole is only included, the retainer may cause friction with other components (such as the first ring structure and the second ring structure).

According to the aforementioned retainer, the plurality of first holes or the plurality of second holes may be arranged at equal angles. In this way, it is beneficial to maintain the consistency of the distance between the retainer and other components (such as the first ring structure and the second ring structure).

According to the aforementioned holder, the material of the holder may be plastic. With this, it is advantageous for the weight reduction of the retainer.

According to another embodiment of the present invention, there is provided a bearing including a first ring structure, a second ring structure, the aforementioned retainer and a plurality of rolling elements, the retainer is disposed in the first ring structure and the second ring structure Between the structures, the first top edge of the first protrusion of the flange portion is adjacent to the inner surface of the first annular structure, and the second top edge of the second protrusion of the flange portion is adjacent to the inner surface of the second annular structure, rolling The piece corresponds to the hole of the retainer. The bearing of the present invention, by including the aforementioned retainer, can effectively prevent the leakage of the lubricating fluid inside the bearing, and can improve the uniformity of the distribution of the lubricating fluid.

According to the aforementioned bearing, the first top edge and the first ring structure may have a first gap distance, the second top edge and the second ring structure may have a second gap distance, the first gap distance and the second gap distance The sum of can be 0.1 mm to 0.4 mm. Thereby, the effect of preventing leakage of lubricating fluid can be further improved, and friction between the first ring structure, the second ring structure and the retainer can be avoided.

According to the aforementioned bearing, the first ring structure may include a first ring protrusion, the first ring protrusion may be disposed on an inner surface of the first ring structure, and the second ring structure may include a second ring protrusion, the second ring The protrusion is disposed on the inner surface of the second ring structure, the first ring protrusion and the second ring protrusion are adjacent to form a shaft portion, and each rolling element is a first rolling element. The bearing may further include a third ring-shaped structure and a plurality of second rolling elements. The third ring-shaped structure is disposed between the first ring-shaped structure and the second ring-shaped structure and surrounds the shaft portion, and the second rolling element is disposed on the shaft portion and The third ring structure. The number of the aforementioned retainers is two, namely a first retainer and a second retainer, the first retainer is disposed between the first ring structure and the third ring structure and surrounds the shaft portion, and the second retainer is provided Between the third ring structure and the second ring structure and surrounding the shaft. By arranging the first rolling element and the second rolling element at the same time, it is beneficial to increase the bearing capacity of the bearing in the radial and axial directions.

In order to make the above-mentioned features and advantages of the present invention more obvious and understandable, the embodiments are specifically described below with the accompanying drawings for detailed description as follows.

Please refer to FIGS. 1 to 3, FIG. 1 is a perspective schematic view of the retainer 100 according to an embodiment of the present invention, FIG. 2 is a plan schematic view of the retainer 100 in FIG. 1, and FIG. 2 illustrates the retainer 100 is a surface, and the other surface of the retainer 100 has the same configuration as the aforementioned surface. FIG. 3 is a partial cross-sectional schematic view of the retainer 100 along the cut plane line AA in FIG. The schematic diagram is bilaterally symmetrical, and the right half is omitted here. The retainer 100 is used for a bearing (not shown). The retainer 100 is an annular structure and includes a body portion 120 and a flange portion 130. The body portion 120 defines a central axis O, and the body portion 120 includes a first surface 160, The second surface 170, a plurality of holes, and at least one oil storage tank 180. The second surface 170 is opposite to the first surface 160. The second surface 170 and the first surface 160 have a separation distance d1 in a direction parallel to the central axis O. The plurality of holes are a plurality of first holes 140 and a plurality of second holes 150, respectively. Each first hole 140 and each second hole 150 penetrate the body portion 120 to communicate with the first surface 160 and the second surface 170, and each first hole 140 and each second hole 150 are used to accommodate a rolling element (not shown) If the hole is not specified as the first hole 140 or the second hole 150, it means that the hole can be the first hole 140 or the second hole 150. In Fig. 2, the hole is elongated and can be used to accommodate rollers. However, the shape of the hole can be adjusted according to the shape of the rolling element. For example, the rolling element can also be a ball, and the hole can also be correspondingly set as a circle.

The flange portion 130 is disposed on the outer periphery (not otherwise labeled) of the body portion 120. The flange portion 130 includes a first protrusion 131 and a second protrusion 132. The first protrusion 131 is adjacent to the first surface 160. The first protrusion The portion 131 protrudes outward with respect to the first surface 160 to have a first height difference H1. In detail, the first top edge 133 of the first protrusion 131 and the first surface 160 have a first height difference H1, and the second protrusion 132 Adjacent to the second surface 170, the second protrusion 132 protrudes outward relative to the second surface 170 to have a second height difference H2. In detail, the second top edge 134 of the second protrusion 132 and the second surface 170 have Two height difference H2. In other words, the thickness d2 of the flange portion 130 along the central axis O is greater than the thickness of the body portion 120 along the central axis O (ie, the separation distance d1 between the second surface 170 and the first surface 160 in the direction parallel to the central axis O) . This can effectively prevent leakage of lubricating fluid. In addition, in the present embodiment, the first height difference H1 is equal to the second height difference H2. However, the present invention is not limited to this. In other embodiments, the first height difference H1 may also be different from the second height difference H2, depending on actual needs.

Please also refer to Figure 4 to Figure 6, Figure 4 is an enlarged schematic view of the X site in Figure 2, Figure 5 is a schematic cross-sectional view of the X site in Figure 4 along the cut line BB, Figure 6 is A schematic cross-sectional view of the X portion in Fig. 4 along the cut plane line CC. The first hole 140 includes a first opening 141 and a second opening 142, the first opening 141 is disposed on the first surface 160 of the body portion 120, the second opening 142 is disposed on the second surface 170 of the body portion 120, and the first hole 140 is The first opening 141 is provided with a dipper-like structure 143. The dipper-like structure 143 is composed of arc-shaped inner walls 144, 145 adjacent to the first opening 141. In detail, the arc-shaped inner walls 144, 145 are retracted inward to form a dipper-like structure 143, whereby the size of the first opening 141 is smaller than the diameter of the rolling element and can carry the rolling element. Please also refer to FIG. 7, which is a schematic cross-sectional view of the Y part in FIG. 2. The second hole 150 includes a first opening 151 and a second opening 152. The first opening 151 is disposed on the first surface 160 of the body portion 120, the second opening 152 is disposed on the second surface 170 of the body portion 120, and the second hole 150 is The second opening 152 is provided with a dipper-like structure 153, and the dipper-like structure 153 is composed of arc-shaped inner walls 154, 155 adjacent to the second opening 152. The material of the retainer 100 may be plastic, such as thermoplastic plastic, and the thermoplastic plastic may be, but not limited to, polyimide (PI) resin or polyetheretherketone (PEEK) resin. The metal material is beneficial to the weight reduction of the retainer 100. In addition, the retainer 100 can be manufactured by injection molding, and the matching holes (140, 150) include only a single dipper-like structure (143, 153), which is beneficial to the demolding of the retainer 100, and can increase the retainer 100 can be manufactured Sex.

Please also refer to FIG. 8 and FIG. 5, FIG. 8 and FIG. 1 are schematic diagrams of the retainer 100 in FIG. 1 for fixing the rolling element 30, when the retainer 100 is installed on the first part 10 and the second part 20 of the bearing In between, the rolling element 30 is disposed in the first hole 140, the first component 10 and the first surface 160 of the retainer 100 have a distance d3, and the second component 20 and the second surface 170 of the retainer 100 have a distance d4, if maintained Only the first hole 140 is provided in the retainer 100. Since the size of the second opening 142 is larger than the diameter of the rolling element 30, the rolling element 30 is forced to move downward by the first component 10, which will cause the spacing d3 to decrease and the retainer 100 and the first component 10 Friction occurs. Similarly, if the retainer 100 is only provided with the second hole 150, it is not conducive to maintaining the size of the distance d4. Therefore, the retainer 100 of the present invention includes the first hole 140 and the second hole 150 at the same time, which is beneficial to maintain the distance between the retainer 100 and other components (such as d3, d4), and can avoid the retainer 100 and the first component 10 or the second member 20 generates friction. In this embodiment, the number of the second holes 150 is three, as indicated in FIGS. 1 and 2, the remaining holes are the first holes 140, and the second holes 150 are arranged at an equal angle, that is, two The included angle between the second holes 150 is 120 degrees. However, the present invention is not limited to this. For example, in other embodiments, the number of the second holes 150 may be two, and between two adjacent second holes 150 The included angle may be 180 degrees, and the equiangular configuration helps maintain the consistency of the distance between the retainer 100 and other components (such as d3 and d4).

Please refer to FIG. 1, FIG. 2 and FIG. 6, the body portion 120 may further include a plurality of oil storage grooves 180. The oil storage grooves 180 are disposed on the first surface 160 and the second surface 170 of the body portion 120, and the first surface The recess 160 and the second surface 170 are formed and arranged in a cross shape. The oil storage groove 180 is located between two adjacent holes, and the oil storage groove 180 communicates with the two adjacent holes, thereby facilitating the flow of lubricating fluid between different holes. Conducive to the uniformity of lubricating fluid distribution. In other embodiments, the oil storage groove 180 may be provided only on the first surface 160 or the second surface 170 of the body portion 120. In addition, the number of the oil storage groove 180 may be only one. By providing the oil storage groove 180, the bearing can be lifted up. The content of lubricating fluid.

FIG. 9 is a schematic cross-sectional view of a bearing 1000 according to another embodiment of the present invention. The bearing 1000 includes a first ring structure 200, a second ring structure 300, a cage 100, and a plurality of rolling elements 400. The cage 100 is disposed between the first ring structure 200 and the second ring structure 300. Corresponding to the hole provided in the retainer 100, in order to clearly show the retainer 100, the left rolling element 400 is omitted. The first top edge 133 of the first protruding portion 131 of the flange portion 130 is adjacent to the inner surface 210 of the first ring structure 200. The first top edge 133 and the inner surface 210 have a first gap distance d5. The second top edge 134 of the second protrusion 132 is adjacent to the inner surface 310 of the second ring structure 300. The second top edge 134 and the inner surface 310 have a second gap distance d6, a first gap distance d5 and a second gap distance d6 The sum (d5+d6) is 0.1 mm to 0.4 mm. Thereby, the effect of preventing leakage of lubricating fluid can be further improved, and friction between the first ring structure 200, the second ring structure 300, and the retainer 100 can be avoided. The size of the rolling element 400 can be flexibly adjusted according to equipment requirements. As shown in the right side of FIG. 9, the sum of the first gap distance d5 and the second gap distance d6 is the diameter r1 of the rolling element 400 and the flange portion 130 along the central axis O The difference of the thickness d2.

Please refer to FIGS. 10 to 12, FIG. 10 is a perspective schematic view of a bearing 2000 according to another embodiment of the present invention, FIG. 11 is an exploded schematic view of the bearing 2000 in FIG. 10, and FIG. 12 is a diagram in FIG. A schematic cross-sectional view of the bearing 2000 along the cutting plane line DD. The bearing 2000 includes a first ring structure 500, a second ring structure 600, a third ring structure 800, a first retainer 100a, a second retainer 100b, a plurality of first rolling elements 900 and a plurality of second rolling elements 950. In FIG. 12, the first rolling element 900 and the second rolling element 950 are omitted to clearly show the relationship between the remaining elements. The bearing 2000 may be a rotary table bearing (RTB). The bearing 2000 is provided with the first rolling element 900 and the second rolling element 950 at the same time, which is beneficial to increase the bearing capacity of the bearing 2000 in the radial and axial directions.

The first ring structure 500 includes a first ring protrusion 520 disposed on the inner surface 510 of the first ring structure 500, and the second ring structure 600 includes a second ring protrusion 620 disposed on the second ring structure 600 On the inner surface 610, the first ring protrusion 520 and the second ring protrusion 620 are adjacent to form the shaft 700, and the third ring structure 800 is disposed between the first ring structure 500 and the second ring structure 600 and surrounds the shaft 700, the first retainer 100a is disposed between the first ring structure 500 and the third ring structure 800 and surrounds the shaft 700, and the second retainer 100b is disposed between the third ring structure 800 and the second ring structure 600 And around the shaft portion 700, the first rolling element 900 is disposed in the holes (not otherwise labeled) of the first retainer 100a and the second retainer 100b. The second rolling element 950 is disposed between the shaft portion 700 and the third ring structure 800. The first ring protrusion 520 includes a first step portion 521 and a second step portion 522, which are sequentially disposed on the inner surface 510 of the first ring structure 500. The outer diameter r3 of the second step portion 522 is smaller than that of the first step portion 521 The outer diameter r2 forms a space 710 in the shaft portion 700 for accommodating the second rolling element 950. The first holder 100a and the second holder 100b may be the same as the holder 100, and for the elements in the first holder 100a and the second holder 100b, reference may be made to the elements with the same name in the holder 100. In this embodiment, the first top edge of the flange portion of the first holder 100a has a first gap distance (not otherwise labeled) from the first ring structure 500, and the second edge of the flange portion of the first holder 100a The top edge and the third ring structure 800 have a second gap distance (not otherwise labeled), and the sum of the first gap distance and the second gap distance is 0.1 mm to 0.4 mm. The first top edge of the flange portion of the second holder 100b and the third ring structure 800 have a first gap distance (not otherwise labeled), the second top edge of the flange portion of the second holder 100b and the second ring The structure 600 has a second gap distance (not otherwise labeled), and the sum of the first gap distance and the second gap distance is 0.1 mm to 0.4 mm. In conventional bearings, because the retainer is not provided with a flange portion, the retainer needs to be configured with a large thickness to prevent the gap between the retainer and the bearing from being too large and the oil leakage is serious. The present invention can further reduce the thickness of the body portion by providing the flange portion And reduce the weight of the retainer.

Oil retention test: The first test bearing is assembled, and its structure is the same as that of bearing 2000, but the first retainer 100a is replaced with a control retainer without a flange portion (that is, both heights H1 and H2 in Figure 3 are 0). Inject the same weight of lubricating fluid into the first ring structure and the third ring structure of the first test bearing and the third ring structure and the second ring structure (at this time, the weight is W0) to make the first test bearing Run at 10 rpm for 1 hour, and then measure the weight of the remaining lubricant in the first and third ring structures of the first test bearing and in the third and second ring structures (W1 ), and calculate the weight (△W) of the leaked lubricant, △W = W0-W1. The test results are listed in Table 1. From Table 1, it can be seen that the retainer of the present invention can effectively reduce the weight of the leakage lubricant.

Torque test: Assemble the second test bearing and the control test bearing, the structure of which is the same as that of the bearing 2000, but the control retainer in the control test bearing has no flange and contains only the first hole, using a torque meter (brand: IMADA; model : FB-20K) Measuring the torque values of the second test bearing and the control test bearing respectively to obtain 4 kgf and 4 kgf. From the test results, it can be seen that the present invention reduces the first gap distance and the second gap distance by providing the flange portion, It does not reduce the effectiveness of the bearing.

Compared with the prior art, the retainer of the present invention can effectively prevent the leakage of lubricating fluid inside the bearing by providing a flange portion, which is beneficial to maintaining the lubrication effect of the bearing and extending the service life of the bearing. By connecting the oil storage tank with two adjacent holes, it is conducive to the uniformity of lubricating fluid distribution.

Further, the retainer of the present invention may include a first hole and a second hole at the same time, which is beneficial to avoid contact friction between the retainer and other parts of the bearing, such as the first ring structure and the second ring structure, and each hole only With a dipper-like structure, it can improve the manufacturability of the retainer. The above are only the preferred embodiments of the present invention, and all changes and modifications made in accordance with the scope of the patent application of the present invention shall fall within the scope of the present invention.

10: The first part 20: Second part 30, 400: Rolling parts 100: retainer 100a: the first retainer 100b: second retainer 120: Main body 130: flange 131: The first protrusion 132: Second protrusion 133: First top edge 134: Second top edge 140: the first hole 141, 151: first opening 142, 152: second opening 143, 153: Dipper structure 144, 145, 154, 155: curved inner wall 150: Second hole 160: first surface 170: second surface 180: oil storage tank 200, 500: first ring structure 210, 310, 510, 610: inner surface 300, 600: second ring structure 520: First ring protrusion 521: First stage 522: Second stage 620: Second ring protrusion 700: Shaft 710: Space 800: third ring structure 900: the first rolling element 950: second rolling element 1000, 2000: Bearing d1: separation distance d2: thickness d3, d4: spacing d5: first gap distance d6: second gap distance r1: diameter r2, r3: outer diameter H1: First height difference H2: Second height difference O: central axis X, Y: location

FIG. 1 is a schematic perspective view of a holder according to an embodiment of the present invention. Figure 2 is a schematic plan view of the retainer in Figure 1. Fig. 3 is a schematic partial cross-sectional view of the retainer in Fig. 2 along the cutting plane line A-A. FIG. 4 is an enlarged schematic view of the X portion in FIG. 2. FIG. 5 is a schematic cross-sectional view of the X portion in FIG. 4 along the cutting plane line B-B. FIG. 6 is a schematic cross-sectional view of the X portion in FIG. 4 along the cutting plane line C-C. FIG. 7 is a schematic cross-sectional view of the Y site in FIG. 2. Fig. 8 is a schematic diagram of the retainer in Fig. 1 for fixing the rolling element. Fig. 9 is a schematic cross-sectional view of a bearing according to another embodiment of the present invention. Fig. 10 is a schematic perspective view of a bearing according to still another embodiment of the present invention. Figure 11 is an exploded view of the bearing in Figure 10. Figure 12 is a schematic cross-sectional view of the bearing in Figure 10 taken along the cutting plane line D-D.

100: retainer

120: Main body

130: flange

140: the first hole

150: Second hole

160: first surface

180: oil storage tank

O: Central axis

Claims (8)

A retainer is used for a bearing. The retainer has a ring structure and includes: A body part defines a central axis. The body part includes: A first surface; A second surface opposite to the first surface, the second surface and the first surface having a separation distance in a direction parallel to the central axis; A plurality of holes, each of which penetrates the body portion to communicate with the first surface and the second surface, and each of the holes is used to accommodate a rolling element; and At least one oil storage groove formed by being recessed from the first surface and/or the second surface, the oil storage groove is located between two adjacent holes of the plurality of holes, and the oil storage groove is in communication with the two adjacent holes; and A flange portion is provided on an outer periphery of the body portion, and the flange portion includes: A first protrusion adjacent to the first surface, the first protrusion protruding outward with respect to the first surface to have a first height difference; and A second protrusion is adjacent to the second surface, and the second protrusion protrudes outward relative to the second surface to have a second height difference. The holder according to claim 1, wherein each of the holes includes a first opening and a second opening, the first opening is provided on the first surface of the body portion, and the second opening is provided on the body portion The second surface, and each of the holes is provided with a dipper-shaped structure in the first opening or the second opening. The dipper-shaped structure is composed of two arc-shaped inner walls adjacent to the first opening or the second opening. The holder according to claim 2, wherein the plurality of holes includes: A plurality of first holes, each of the first holes is provided with the dipper structure in the first opening; and A plurality of second holes, each of the second holes is provided with the dipper structure in the second opening. The holder according to claim 3, wherein the plurality of first holes or the plurality of second holes are arranged at equal angles. The holder according to claim 1, wherein the material of the holder is plastic. A bearing including: A first ring structure; A second ring structure; As described in any one of claims 1 to 5, the retainer is provided between the first ring structure and the second ring structure, and a first top edge of the first protrusion of the flange portion is adjacent to An inner surface of the first ring structure, a second top edge of the second protrusion of the flange portion is adjacent to an inner surface of the second ring structure; and The plurality of rolling elements correspond to the plurality of holes provided in the retainer. The bearing according to claim 6, wherein the first top edge and the first ring structure have a first gap distance, and the second top edge and the second ring structure have a second gap distance, the first The sum of a gap distance and the second gap distance is 0.1 mm to 0.4 mm. The bearing according to claim 6, wherein the first ring structure includes a first ring protrusion provided on the inner surface of the first ring structure, and the second ring structure includes a second ring protrusion , Disposed on the inner surface of the second ring structure, the first ring protrusion and the second ring protrusion are adjacent to form a shaft portion, each rolling element is a first rolling element, and the bearing further includes: A third ring structure disposed between the first ring structure and the second ring structure and surrounding the shaft portion; and A plurality of second rolling elements are provided between the shaft portion and the third ring structure; The number of the retainers is two, which are a first retainer and a second retainer respectively. The first retainer is disposed between the first ring structure and the third ring structure and surrounds the shaft, The second retainer is disposed between the third ring structure and the second ring structure and surrounds the shaft portion.

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