JP2011052714A - Multi-row combination angular ball bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide multi-row combination angular ball bearings which achieves stable high-speed rotation without causing a seizure fault of bearings arranged inside the multi-row bearings. <P>SOLUTION: Ball pitch circle diameters PCD2, PCD3 of the inside bearings 50, 60 in the second and third rows from the tool side out of bearings 40, 50, 60, 70 of the multi-row angular ball bearings are made smaller than the pitch circle diameters PCD1, PCD4 of the outside bearings 40, 70 in the first and fourth rows, and contact angles α2, α3 of the inside bearings 50, 60 in the second and third rows from the tool side are made smaller than the contact angles α1, α4 of the outside bearings 40, 70 in the first and fourth rows. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a multi-row combination angular contact ball bearing, and more particularly to a multi-row combination angular contact ball bearing that is applied to a machine tool spindle, a compressor, and the like and that can rotate at high speed.

  In recent years, the speed of machine tool spindles has been increased to improve machining efficiency, and the conventional gear drive and belt drive have poor transmission efficiency such as friction between teeth and heat generated by belt slip. The direct drive motor type with a ring and the so-called motor built-in type in which a motor is mounted inside the main shaft dominate.

  In particular, in a motor built-in type, when a high-output motor is mounted, the axial length of the entire main shaft becomes longer due to the axial length of the rotor and the stator. In such a case, in order to increase the bending rigidity of the spindle against the moment load on the spindle system generated by the machining force of the tool part at the tip of the spindle, a combination of three or four rows of angular contact ball bearings is used as a tool. There are very many cases used as side bearings.

  In the case of such multi-row combination bearings (for example, in the case of 4-row combinations), the second row and third row bearings on the inner side in the axial direction are obstructed by the heat generation and temperature rise of the first row and fourth row bearings. Therefore, it is difficult to release the heat generated by the rolling friction of the bearing itself to the outside, resulting in a so-called heat storage state where heat is trapped.

  As a result, the temperature of the rolling contact portion between the balls and the inner and outer rings increases, and seizure due to oil film breakage occurs very easily. Further, in the case of the motor built-in type, the heat generated in the rotor is transmitted through the shaft and is also transmitted to the bearing portion on the tool side.

  Also, in motor built-in types that generate heat from the motor, it is important to suppress thermal displacement in order to improve the accuracy of the main spindle, and in order to suppress the temperature rise of the main spindle due to heat generation of the bearing at high speed rotation and heat generation of the stator, In most cases, a structure in which cooling oil whose temperature is controlled is circulated in the outer cylinder portion.

  This outer cylinder cooling suppresses the temperature rise of the outer ring of the bearing, but the temperature rise of the inner ring of the bearing that is not in direct contact with the cooling portion cannot be suppressed. As a result, the temperature difference between the inner and outer rings of the bearing (inner ring temperature> outer ring) Temperature). In the case of a four-row combination bearing, the second-row and third-row bearings are located in the center of the circulation path of this outer cylinder cooling oil and the most effective cooling is obtained. Compared with the bearings, the temperature difference between the inner and outer rings tends to be larger. When the temperature difference between the inner and outer rings occurs, the internal clearance of the bearing decreases, the internal preload increases, the PV value of the rolling contact portion increases, and the seizure proceeds.

  In addition, at the time of high-speed rotation, the action of the centrifugal force of the balls is also added, and the internal preload is further increased to increase the risk of seizure.

  During high-speed cutting rotation, the tool load is small and the processing load generated by the cutting force is not large. Therefore, the internal load (internal preload) generated by the above factors is not the external load. Occupy. From the above, for example, the seizure failure of the bearing in the high-speed main shaft composed of four rows of multi-row combination bearings mostly occurs in the second and third rows.

  As a method of suppressing the heat generation of the inner bearings of the multi-row combination bearings and lowering the temperature between the bearings, the inner bearings have a larger curvature than that of the outer bearings (for example, see Patent Document 1), or the inner bearings. Is known (see, for example, Patent Document 2).

JP 2005-299761 A JP 2006-322496 A

  However, the multi-row ball bearing described in Patent Document 1 does not clearly describe how much the actual effect is. Moreover, since only the curvature of the bearing is changed, it is difficult to distinguish the actual product, and there is a possibility of making a wrong combination in the manufacturing process or at the customer assembly site. Further, in the multi-row angular contact ball bearing described in Patent Document 2, when the clearance between the outer ring and the housing is increased, the rigidity of the main shaft (radial direction and moment direction) decreases. Originally, all bearings should receive a cutting load and a vibration load accompanying the processing, but in this case, they cannot be received and problems such as fretting are likely to occur.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a multi-row combination angular ball bearing that can achieve stable high-speed rotation without causing seizure failure of the inner bearing. .

The above object of the present invention can be achieved by the following constitution.
(1) In a multi-row combination angular contact ball bearing in which three or more angular contact ball bearings are arranged in the axial direction,
A multi-row combination angular contact ball bearing characterized in that a ball pitch circle diameter of the angular ball bearing arranged on the inner side in the axial direction is smaller than a ball pitch circle diameter of the angular ball bearing arranged on the outer side in the axial direction.
(2) A contact angle of the angular ball bearing disposed on the inner side in the axial direction is smaller than a contact angle of the angular ball bearing disposed on the outer side in the axial direction. Row combination angular contact ball bearing.
(3) The multi-row combination angular contact ball bearing according to (1) or (2), which supports a machine tool main shaft.

  According to the multi-row combination angular contact ball bearing of the present invention, an angular contact ball bearing in which the ball pitch circle diameter of the angular contact ball bearing (hereinafter also referred to as “inner bearing”) disposed on the inner side in the axial direction is disposed on the outer side in the axial direction. Since it is smaller than the ball pitch circle diameter (hereinafter also referred to as “outer bearing”), the dmn value of the bearing is reduced, and the bearing heat generation at the center of the combined bearing is reduced. As a result, the temperature distribution of the entire bearing becomes uniform, the occurrence of a large temperature difference between the inner and outer rings of the inner bearing is suppressed, and an increase in the internal preload during high-speed rotation of the inner bearing can be suppressed. Can be reduced. Therefore, the seizure risk of the inner bearing can be set to the same level as that of the outer bearing, and the thermal load can be balanced. Further, the moment rigidity of the bearing can be improved due to the difference in the ball pitch circle diameters.

  In addition, since the contact angle of the inner bearing is smaller than the contact angle of the outer bearing, the smaller the contact angle, the smaller the slip generated in angular ball bearings having a contact angle such as spin slip and gyro slip, and further the inner bearing The amount of heat generated can be suppressed, and a difference in the amount of heat generated between the outer bearing and the inner bearing can be provided to further improve the seizure resistance of the bearing. Furthermore, the moment rigidity of the bearing can be further improved by the contact angle difference.

It is sectional drawing which shows the main axis | shaft apparatus with which the multi-row combination angular contact ball bearing of this invention was applied as a front side bearing. It is sectional drawing of the multi-row combination angular contact ball bearing which concerns on one Embodiment of this invention. It is a figure for demonstrating the provision method of a fixed position preload. It is sectional drawing of the multi-row combination angular contact ball bearing which concerns on the 1st modification of this invention. It is sectional drawing of the multi-row combination angular contact ball bearing which concerns on the 2nd modification of this invention. It is sectional drawing of the multi-row combination angular contact ball bearing which concerns on the 3rd modification of this invention.

  Hereinafter, a multi-row combination angular contact ball bearing according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a spindle device 20 to which the multi-row combination angular ball bearing of this embodiment is applied. The main shaft device 20 is a motor built-in system, and a hollow rotating shaft 22 is provided in the center in the axial direction, and a draw bar 23 is slidably inserted into the shaft core of the rotating shaft 22. . The draw bar 23 is provided with a tool holder 24 to which a tool T is attached, and the draw bar 23 is urged in the counter tool side direction (right direction in the figure) by the force of the disc spring 27, whereby the tool holder 24. Is fitted to the tapered surface 28 of the rotary shaft 22. As a result, the tool T is integrally attached to the rotary shaft 22 together with the draw bar 23 and the tool holder 24.

  Further, the rotary shaft 22 is rotated to the housing H by front bearings 40, 50, 60, 70 which are multi-row combination angular ball bearings supporting the tool side and a rear bearing (not shown) supporting the counter tool side. It is supported freely.

  A rotor 30 is fitted on the outer peripheral surface of the rotary shaft 22 between the front bearings 40, 50, 60, 70 and the rear bearing. The stator 32 arranged around the rotor 30 is fixed to the outer cylinder 29 by fitting a cooling jacket 33 shrink-fitted into the stator 32 into the outer cylinder 29 constituting the housing H. Therefore, the rotor 30 and the stator 32 constitute a motor, and by supplying electric power to the stator 32, a rotational force is generated in the rotor 30 and the rotating shaft 22 is rotated.

  As also shown in FIG. 2, the front bearings 40, 50, 60, 70 are composed of outer rings 41, 51, 61, 71, inner rings 42, 52, 62, 72, and contact angles α1, α2, α3, α4. Angular balls each having balls 43, 53, 63, 73 as rolling elements arranged with a ring and retainers 44, 54, 64, 74 holding the balls 43, 53, 63, 73 at substantially equal intervals. Ball bearings, with the first and second row front bearings 40 and 50 counted from the tool side and the third and fourth row front bearings 60 and 70 arranged in a rear combination. A fixed position preload is applied. The fixed position preload is a method of applying preload to the combination bearing. As shown in FIG. 3, in the case of rear combination, an appropriate clearance (Δa) is set between the combined end faces, and the bearing Can be externally fitted to the shaft, tightened in the axial direction using a bearing nut or the like, and brought into close contact with the clearance (Δa is set to 0), whereby a preload corresponding to the clearance can be applied to the bearing.

Outer rings 41, 51, 61, 71 of the front bearings 40, 50, 60, 70 are fitted in a front bearing housing 31 fixed to the outer cylinder 29 and are bolted to the front bearing housing 31. The outer ring presser 38 is fixed to the front bearing housing 31 in the axial direction via a plurality of outer ring spacers 35. Further, the inner rings 42, 52, 62, 72 of the front bearings 40, 50, 60, 70 are externally fitted to the rotary shaft 22, and a plurality of inner ring spacers 36 are connected by nuts 39 fastened to the rotary shaft 22. And is fixed in the axial direction with respect to the rotating shaft 22.
Note that FIG. 2 shows the outer ring spacer 35 and the inner ring spacer 36 omitted, but the multi-row combination angular ball bearing of the present invention has either a structure having a spacer or a structure having no spacer. Including cases.

  In addition, a cooling path is formed between the outer peripheral surface of the front bearing housing 31 and the cover 34 that is fitted on the front bearing housing 31, and each of the front bearings 40, 50, 60,. 70 is cooled.

  Here, out of the front bearings 40, 50, 60, 70, the ball pitch circle diameters PCD2, PCD3 of the front side bearings (inner bearings) 50, 60 in the second and third rows from the tool side in the axial direction are arranged in one row. The fourth and fourth rows of axially outer front bearings (outer bearings) 40, 70 are smaller than the pitch circle diameters PCD1, PCD4 (PCD1, PCD4> PCD2, PCD3). In the present embodiment, since the contact angles α1, α2, α3, α4 of the front bearings 40, 50, 60, 70 are the same, the ball pitch circle diameters PCD1, PCD4 of the outer bearings 40, 70 are the same, The ball pitch circle diameters PCD2 and PCD3 of the inner bearings 50 and 60 are the same (ie, PCD1 = PCD4> PCD2 = PCD3), the first and fourth rows of outer bearings 40 and 70, and the second and third rows. The inner bearings 50 and 60 can be shared.

  With this configuration, the dmn value of the inner bearings 50, 60 is smaller than the dmn value of the outer bearings 40, 70, and the bearing heat generation at the center of the combination bearing is reduced. As a result, the temperature distribution of the entire bearing becomes uniform, the occurrence of a temperature difference between the inner and outer rings that increases at the inner bearings 50 and 60 is suppressed, and an increase in internal preload when the inner bearings 50 and 60 rotate at high speed can be suppressed. Thus, the seizure risk can be reduced. Therefore, the seizure risk of the inner bearings 50 and 60 can be set to the same level as that of the outer bearings 40 and 70 so that the thermal load can be balanced. Further, the moment rigidity of the bearing can be improved due to the difference in the ball pitch circle diameters.

  In FIG. 2, the contact angles α1, α2, α3, α4 of the front bearings 40, 50, 60, 70 are the same (α1 = α2 = α3 = α4). However, as shown in FIG. The contact angles α2 and α3 of the inner bearings 50 and 60 in the third and third rows may be smaller than the contact angles α1 and α4 of the outer bearings 40 and 70 in the first and fourth rows (α1, α4> α2). , Α3).

  As a result, the slip generated in the angular ball bearing having a contact angle such as spin slip and gyro slip is reduced, and further, the heat generation amount of the inner bearing is suppressed, and the heat generation amount difference between the outer bearings 40 and 70 and the inner bearings 50 and 60 is given. The seizure resistance of the bearing can be further improved. Furthermore, the moment rigidity of the bearing can be further improved by the contact angle difference.

  In this embodiment, the four-row angular contact ball bearing has been described. However, the multi-row angular contact ball bearing of the present invention only needs to have at least three rows, and as shown in FIG. A row angular contact ball bearing may be sufficient, and as shown in FIG. 6, it may be a 3 row multi-row angular contact ball bearing.

  Specifically, in the six-row angular contact ball bearing shown in FIG. 5, the outer rings 81 and 91, the inner rings 82 and 92, the balls 83 and 93, and the holding are held between the outer bearings 40 and 70 and the inner bearings 50 and 60. Intermediate rows of angular ball bearings 80, 90 each having a container 84, 94 are arranged. In this case, the ball pitch circle diameter of each bearing is the ball pitch circle diameter of the outer bearings 40 and 70> the ball pitch circle diameter of the intermediate row bearings 80 and 90> the ball pitch circle diameter of the inner bearings 50 and 60 (PCD1, PCD4> PCD5, PCD6> PCD2, PCD3). Further, the contact angle of each bearing is the contact angle of the outer bearings 40 and 70> the contact angle of the intermediate row bearings 80 and 90> the contact angle of the inner bearings 50 and 60 (α1, α4> α5, α6> α2, α3). ).

  Further, as shown in FIG. 6, in the case of a three-row angular contact ball bearing having only one inner bearing 50 between the outer bearings 40, 70, the ball pitch circle diameter of each bearing is the outer bearing 40, The ball pitch circle diameter of 70> the ball pitch circle diameter of the inner bearing 50 may be set (PCD1, PCD4> PCD2). Further, the contact angle of each bearing may be set such that the contact angle of the outer bearings 40 and 70> the contact angle of the inner bearing 50 (α1, α4> α2).

  However, in the case of even-numbered combination bearings, it is desirable that the bearings at the same position counted from the outside in the axial direction have the same contact angle. For example, in the case of the four-row combination bearing shown in FIG. 4, the contact angles α1, α4 of the first and fourth outer bearings 40, 70 from the tool side, and the second and third inner bearings 50, 70, When the contact angles α2 and α3 of 60 are made equal, when fixed position preload is applied, the additional loads Fa1, Fa2, Fa3, and Fa4 due to preload of the individual bearings are Fa1 = Fa4, Fa2 = Fa3, and Fa1 + Fa2 = Fa3 + Fa4. Become. Accordingly, the first and fourth rows, and the second and third rows have the same preload, so that a preload balance can be achieved.

  Here, for example, if the contact angles are different, such as the first row: 20 °, the second row: 16 °, the third row: 16 °, the fourth row: 18 °, the bearings in the third row and the fourth row The contact surface pressure (particularly the third row) due to the preloads 60 and 70 becomes larger than the bearings 40 and 50 in the first row and the second row, which is somewhat disadvantageous for seizure. However, on the contrary, when the temperature difference between the inner and outer rings of the bearing 50 in the second row is larger than the bearing 60 in the third row, seizure of the bearing 50 in the second row needs to be made harder than the bearing 60 in the third row. If there is, the contact angle of the bearings 40 and 70 in the first row and the fourth row may be changed as described above.

  Also, in the case of odd-numbered combination bearings, the bearings that are located in the axially intermediate portion and the bearings whose contact angle faces in the opposite direction to the radial direction when combined on the back are the bearings at the same position counted from the outside in the axial direction. In comparison, it is preferable to increase the contact angle.

  For example, in the case of the three-row combination bearing shown in FIG. 6, the contact angles α1 and α2 of the first and second row bearings 40 and 50 from the tool side and the contact angle α4 of the third row bearing 70 are the radius. The additional loads Fa1, Fa2, and Fa3 due to the preload of the bearings in each row are Fa1 + Fa2 = Fa3, and Fa3> Fa1> Fa2, and the bearing 70 in the third row is 1 Since a preload is applied to the bearings 40 and 50 in the second and second rows, the contact surface pressure due to the preload increases. Therefore, the contact angle α4 of the third row bearing 70 is made larger than the contact angle α1 of the first row bearing 40 (α1 <α4 and α1> α2), so that the preload of the third row bearing 70 is increased. An increase in contact surface pressure due to a load can be suppressed.

  In addition, this invention is not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably.

  The present invention can be particularly effective for a high-speed main shaft such as a motor built-in main shaft, but is not limited thereto. In addition to a low-speed main shaft, a preload is also applied to a belt drive, a gear drive, a motor direct drive, etc. It is effective and applicable even when the temperature rise due to heat generation of the bearing is high by setting it large.

  Furthermore, the rolling elements can be made of not only iron but also a lightweight ceramic (for example, silicon nitride) material, thereby suppressing an increase in preload due to centrifugal force during high-speed rotation, and further improving seizure resistance. it can. In this case, all the rolling elements of the row may be made of a ceramic material, or only the inner bearing may be made of a ceramic material in order to further improve the seizure resistance of the inner bearing. Furthermore, when the ball pitch diameter of the outer bearing is increased or the contact angle is increased to increase the seizure risk of the outer bearing, the ceramic material may be used only for the outer bearing.

The lubrication conditions are not limited to grease lubrication, and any lubrication method such as oil-air lubrication, oil mist lubrication, underlace lubrication, and jet lubrication may be applied.
Further, as a method of combining the bearings, in addition to the back surface combination, a front surface combination (a combination in which the contact angle is a reverse C shape) may be used.

  In addition to the multi-row combination bearings of single row bearings, for example, in FIG. 2 and FIG. 4, double row ball bearings in which the first row and the second row, and the third row and the fourth row are respectively integrated. May be a backside combination or a frontal combination, and in FIG. 5, a double row ball bearing in which the first row, the second row, the third row, the fourth row, the fifth row, and the sixth row are respectively integrated. It is good also as a back surface combination and a front surface combination.

(Test 1)
Here, various bearing characteristics were compared using the inventive products A to C shown in the present embodiment (the combined bearings in FIGS. 2 and 4) and the conventional product. The bearing dimensions and test conditions are listed below together with Table 1. In the devices A to C, the first and fourth rows, and the second and third rows are bearings having the same specifications, and the four-row combination has a symmetrical arrangement structure.

<Bearing dimensions (common specification for conventional and conceived products)>
・ Inner diameter: φ100mm
・ Outer diameter: φ150mm
・ Width: 24mm
・ Ball diameter: 11.112mm
・ Combination: 4 rows back combination angular contact ball bearing <Test conditions>
・ Number of revolutions: 6,000 min ^-1
・ Preload clearance: -17μm
・ Lubrication: Grease lubrication

From Table 1, when the conventional product is set to 100, the heat generation ratio in the second and third rows of the inventive product falls to about 80% or less (20-23% decrease). Moreover, the increase in the total calorific value is a result of less than 2%. Here, the 2% increase is due to the fact that the ball pitch circle diameter and contact angle of the outer bearing are slightly larger than those of the conventional product, but since the rate of increase is small, the effect on the temperature characteristics of the entire bearing is small.
As can be seen from the calculation results, the internal temperature of the second and third rows of bearings is lower than that of the conventional product by adopting the present invention, the temperature difference between the inner and outer rings is reduced, the increase in internal preload is suppressed, and seizure hardly occurs. Become.

  Further, as the contact angle difference between the outer bearing and the inner bearing is increased, the reduction rate of the heat generation ratio between the outer bearing and the inner bearing is changed. In other words, if the contact angle difference between the outer bearing and the inner bearing is too large, the heat generation amount of the outer bearing will increase excessively, and the heat difference difference between the two will become too large, and the seizure risk will increase. It will be reversed by the bearing. Accordingly, the contact angle of each row is preferably 10 ° or more at the minimum (inner bearing) and 30 ° or less at the maximum (outer bearing), more preferably 15 ° or more and maximum (at the inner (bearing)) (maximum ( The outer bearing is preferably 25 ° or less, more preferably 15 ° or more at the minimum (inner bearing) and 20 ° or less at the maximum (outer bearing). An appropriate angle difference may be selected in accordance with the high-speed characteristics of the main shaft (frequency and risk of seizure) such as the main shaft bearing arrangement, number of combination rows, motor capacity, and outer cylinder cooling efficiency.

(Test 2)
Next, the bearing moment stiffness was compared under the following test conditions using the inventive products A to C having the same bearing dimensions as those described above and the conventional product.

<Test conditions>
・ Preload clearance: -17μm
・ Tilt angle: 30 ”(seconds)

  From the calculation results in Table 2, it can be seen that the bearing moment rigidity can be improved as an incidental effect of the product of the present invention. In particular, the device C can be expected to have about 10% improvement in moment rigidity compared to the conventional product. The bending rigidity in the radial direction of the main shaft is determined by a combination with the bending rigidity of the shaft itself in addition to the bearing rigidity. By improving the moment rigidity of the bearing, the bending of the shaft itself is also reduced. Therefore, the actual bending rigidity of the main shaft can be expected to be more effective than this calculation result.

(Test 3)
Next, the bearing axial rigidity was compared under the following test conditions using the inventive products A to C having the same bearing dimensions as those described above and the conventional product.

<Test conditions>
・ Preload clearance: -31μm
・ External axial load: 3000N

  From the calculation results in Table 3, it can be seen that the bearing axial rigidity increases as a further incidental effect of the product of the present invention. In particular, the device C increases by about 8% compared to the conventional product.

(Test 4)
Furthermore, under the following test conditions, the load sharing ratios of the first and second rows of bearings when an axial load was applied, and the contact surface pressure ratio of the second row to the first row were compared.

<Test conditions>
・ Preload clearance: -17μm
・ External axial load: 3000N

  From the calculation results shown in Table 4, when an axial load is applied, in the first and second rows on the load side, the first row having a larger contact angle has the effect of increasing the load sharing. That is, when an external load in the axial direction is applied at high speed rotation, the load load in the second row, which is the inner bearing, can be reduced, and it can be understood that the inner bearing is less susceptible to damage such as seizure.

  From the calculation results shown in Table 5, it can be seen that the ratio of the contact surface pressure between the inner and outer ring grooves of the second row bearing and the ball of the present invention product is lower than that of the conventional product. The degree of decrease in the inventive product seems to be only about 2 to 5% compared to the conventional product. However, the presence or absence of seizure increases the PV value at the rolling contact portion, increases local heat generation, and cuts the oil film. It is determined by whether the boundary point of whether or not, so-called critical point is exceeded.

  The preload of the high-speed bearing for the main shaft needs to increase the rigidity of the main shaft bearing as much as possible and is set in the vicinity of this critical point. The reduction in surface pressure is significant.

20 Spindle device 22 Rotating shaft 30 Rotor 32 Stator 40, 50, 60, 70, 80, 90 Front bearing (multi-row angular contact ball bearing)
α1, α2, α3, α4, α5, α6 Contact angle PCD1, PCD2, PCD3, PCD4, PCD5, PCD6 Ball pitch circle diameter H Housing

Claims (3)

In a multi-row combination angular contact ball bearing in which three or more angular contact ball bearings are arranged in the axial direction,
A multi-row combination angular contact ball bearing characterized in that a ball pitch circle diameter of the angular ball bearing arranged on the inner side in the axial direction is smaller than a ball pitch circle diameter of the angular ball bearing arranged on the outer side in the axial direction.   The contact angle of the angular ball bearing disposed on the inner side in the axial direction is smaller than the contact angle of the angular ball bearing disposed on the outer side in the axial direction. Ball bearing.   The multi-row combination angular contact ball bearing according to claim 1, wherein the multi-row combination angular contact ball bearing supports a machine tool main shaft.

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