JP2012057800A - Fluid bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve bearing rigidity and to achieve cost reduction.SOLUTION: Oil films are formed in radial bearing gaps of first/second radial bearing parts R1, R2 to rotatably support a shaft member 2. A bearing sleeve 8 and the shaft member 2 are stored inside a housing 7, an internal space of the housing 7 is filled with lubrication oil, and an opening part of the housing 7 is sealed by a sealing member 9. A first sealing space S1 is formed on an inner peripheral surface 9a2 of the sealing member 9. The housing 7 and the sealing member 9 are formed by injection molding of resin.

Description

  The present invention relates to a hydrodynamic bearing device that rotatably supports a shaft member with an oil film formed in a radial bearing gap.

  As this type of hydrodynamic bearing device, a sintered metal bearing sleeve is fixed to the inner periphery of a bottomed cylindrical housing, and a shaft member is inserted into the inner periphery of the bearing sleeve. A structure in which a radial bearing gap is formed between the inner peripheral surface and the inner peripheral surface is known. In the housing, a seal member is disposed adjacent to the axial direction of the bearing sleeve, and by forming a seal space filled with lubricating oil between the inner peripheral surface of the seal member and the outer peripheral surface of the shaft member, Capillary action prevents leakage of lubricating oil filling the housing.

  As an example of a housing or a seal member, a machined product of free-cutting brass is known (for example, see Patent Document 1).

JP 2003-172336 A

  In recent years, for example, in HDD devices, the number of magnetic disks mounted tends to increase as the capacity increases (multi-layered), and the hydrodynamic bearing device that supports the shaft as the weight increases further improves the bearing rigidity. In particular, there is a demand for improvement in bearing rigidity (moment rigidity) against moment load. On the other hand, the demand for cost reduction is still severe, so it is not enough to simply improve the bearing rigidity, and it is also important to consider how to avoid the associated cost increase.

  The present invention is intended to provide a low-cost hydrodynamic bearing device with improved bearing synthesis in consideration of such circumstances.

  In order to achieve this object, a hydrodynamic bearing device according to the present invention includes a radial bearing portion that rotatably supports a shaft member with an oil film formed in a radial bearing gap, a housing that accommodates the radial bearing portion therein, In a hydrodynamic bearing device having a lubricating oil that fills an internal space and a seal member that seals an opening of a housing, a first seal space is formed on the inner peripheral surface of the seal member, and a second seal is formed on the outer peripheral surface. A space is formed, and the seal member is formed by resin injection molding.

  As described above, when the seal space is formed on the inner peripheral surface and the outer peripheral surface of the seal member, the shape of the seal member is complicated. However, if the seal member is formed by resin injection molding, it is much more than a turned product. Cost reduction can be achieved. In this case, in addition to only the seal member being a resin injection-molded product, both the seal member and the housing can be a resin injection-molded product, which can further reduce the cost.

  As a specific configuration of the seal member in the present invention, a first seal portion that forms a first seal space on the inner peripheral surface, an axial projection from one end surface of the first seal portion, and a second seal on the outer peripheral surface. The thing which has the 2nd seal part which forms seal space can be mentioned.

  In a hydrodynamic bearing device, oil is often circulated in the housing in order to eliminate an imbalance in the pressure of oil filled in the housing. When the seal member has the above-described configuration, it is necessary to form a groove for oil circulation on the one end surface of the first seal portion in order to realize oil circulation in the housing. When the seal member is a turning product, the groove must be formed by milling, which increases the manufacturing cost. However, if the seal member is a resin molded product as in the present invention, the seal member is molded. At the same time, a groove for oil circulation can be molded, and further cost reduction can be achieved.

  The present invention relates to a radial bearing portion that rotatably supports a shaft member with an oil film formed in a radial bearing gap, a housing that accommodates the radial bearing portion therein, a lubricating oil that fills the internal space of the housing, and an opening portion of the housing In the hydrodynamic bearing device having a seal member that seals, a first seal space is formed on the inner peripheral surface of the seal member, a second seal space is formed on the outer peripheral surface, and the housing is formed by resin injection molding. Formed.

  By forming the seal space (second seal space) on the outer peripheral surface of the seal member in this manner, the seal space can be disposed on the outer diameter side of the radial bearing gap of the radial bearing portion. Therefore, it is not necessary to arrange the radial bearing gap and the seal space side by side in the axial direction as in the prior art, and at least a part of both can be arranged in the axial direction. Accordingly, the axial dimension of the housing that accommodates the radial bearing portion and the seal space can be reduced. This means that the axial span between adjacent radial bearing portions can be expanded without changing the axial dimension of the housing. As a result, the bearing rigidity, particularly the moment rigidity can be further improved.

  When such a configuration is adopted, the shape of the housing becomes more complicated, so that the cost of a conventional metal material turning product is significantly increased. On the other hand, if the housing is a resin injection-molded product, even a housing having a complicated shape can be formed at low cost, so that an increase in manufacturing cost can be suppressed.

  The housing after injection molding is taken out of the mold while being attached to the outer periphery of the male mold (core) by mold opening. At this time, by forming a protruding surface that receives a protruding force from the protruding mechanism on the end face on the opening side of the housing, the molded product can be smoothly demolded. The projecting surface must have a sufficient pressure-receiving area to receive the necessary projecting force from the projecting pin, etc., but the outer peripheral surface of the housing is provided with a large-diameter outer peripheral surface and a small-diameter outer peripheral surface. If a large-diameter outer peripheral surface is arranged on the surface, the pressure receiving area required for the protruding surface can be easily secured, and smooth demolding becomes possible. In addition, by adopting such a configuration, it becomes possible to form the outer diameter side region of the seal member and other regions of the housing with substantially the same thickness, and the housing may be affected by variations in molding shrinkage. Inaccuracy can be avoided.

  According to the present invention, bearing rigidity can be increased while avoiding an increase in the axial dimension of the hydrodynamic bearing device, and this kind of effect can be obtained at low cost.

It is sectional drawing of the spindle motor for HDD incorporating the hydrodynamic bearing apparatus concerning this invention. It is sectional drawing of the hydrodynamic bearing apparatus concerning this invention. It is sectional drawing of a bearing sleeve. It is sectional drawing which shows the injection molding process of a housing. It is sectional drawing which shows the housing as contrast. It is sectional drawing in the AA line (refer FIG. 7) of a sealing member. It is a top view of the sealing member seen from the B direction (refer to Drawing 6).

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 conceptually shows one configuration example of a spindle motor for information equipment incorporating a fluid dynamic bearing device (fluid fluid dynamic bearing device) 1 which is a kind of fluid bearing device. This spindle motor for information equipment is used for a disk drive device such as an HDD, and includes a dynamic pressure bearing device 1, a disk hub 3 attached to a shaft member 2 of the dynamic pressure bearing device 1, and a radial gap, for example. The stator coil 4 and the rotor magnet 5 and the bracket 6 that are opposed to each other are provided. The stator coil 4 is attached to, for example, the outer peripheral surface of the bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The disk hub 3 holds one or more disks D such as magnetic disks on the outer periphery thereof. When the stator coil 4 is energized, the rotor magnet 5 is rotated by an electromagnetic force generated between the stator coil 4 and the rotor magnet 5, and the disk hub 3 and the shaft member 2 are rotated integrally therewith.

  FIG. 2 illustrates one embodiment of the hydrodynamic bearing device 1 used in the spindle motor. The hydrodynamic bearing device 1 mainly includes a shaft member 2, a bottomed cylindrical housing 7, a bearing sleeve 8 accommodated in the housing 7, and a seal member 9 that seals one end opening of the housing 7. Configured as a part. In the following description, for convenience of explanation, the description will proceed with the opening side of the housing 7 as the upper side and the opposite side in the axial direction as the lower side.

  The shaft member 2 is formed of a metal material such as stainless steel, and includes a shaft portion 2a and a flange portion 2b provided integrally or separately at the lower end of the shaft portion 2a. In addition to forming the entire shaft member 2 from metal, for example, by forming the entire flange portion 2b or a part thereof (for example, both end surfaces) from resin, a hybrid structure of metal and resin can be obtained.

  The housing 7 is integrally formed of a cylindrical small diameter portion 7a, a large diameter portion 7b disposed on one end side of the small diameter portion 7a, and a bottom portion 7c that seals the other end opening of the small diameter portion 7a. The outer peripheral surface 7b1 (large diameter outer peripheral surface) of the large diameter portion 7b is formed to have a larger diameter than the outer peripheral surface 7a1 (small diameter outer peripheral surface) of the small diameter portion 7a. Similarly, the inner peripheral surface 7b2 of the large diameter portion 7b is also formed of the small diameter portion 7a. It has a larger diameter than the inner peripheral surface 7a2. A boundary surface 7e between the inner peripheral surfaces 7a2 and 7b2 is formed in a flat surface shape in a direction orthogonal to the axial direction. The inner bottom surface 7c1 of the bottom portion 7c is formed with a dynamic pressure groove region (shown in black in FIG. 2) serving as a thrust bearing surface. In this region, a plurality of dynamic pressure generating portions arranged in a spiral shape, for example, are formed. A dynamic pressure groove (not shown) is formed. The small-diameter outer peripheral surface 7a1 is fixed to the inner peripheral surface of the bracket 6 shown in FIG.

  The housing 7 is formed by resin injection molding. In order to prevent deformation due to a difference in molding shrinkage when the resin is solidified, each portion 7a to 7c of the housing 7 is formed to have a substantially uniform thickness.

  The resin forming the housing 7 is mainly a thermoplastic resin. For example, as the amorphous resin, polysulfone (PSF), polyethersulfone (PES), polyphenylsulfone (PPSU), polyetherimide (PEI) As the crystalline resin, liquid crystal polymer (LCP), polyether ether ketone (PEEK), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), or the like can be used. The type of filler to be filled in the resin is not particularly limited. For example, as the filler, fibrous filler such as glass fiber, whisker-like filler such as potassium titanate, and scaly filler such as mica. A fibrous or powdery conductive filler such as carbon fiber, carbon black, graphite, carbon nanomaterial, or metal powder can be used. These fillers may be used alone or in combination of two or more.

  FIG. 4 shows an injection molding process of the housing 7. As shown in the figure, the housing 7 injects molten resin into a cavity from a dotted gate 14 provided at the axial core portion of the female mold 13 out of two molds (male mold 12 and female mold 13) that are clamped. To be molded. The configuration and number of gates are arbitrary, and a plurality of dotted gates or disk gates can be adopted. The gate position is also arbitrary. For example, the gate 14 can be disposed on the outer peripheral edge of the bottom 7c.

  When the mold is opened after the resin is solidified, the molded product is taken out from the female mold 13 while being attached to the male mold 12. Thereafter, the housing 7 is separated from the male mold 12 by pressing the opening-side end surface 7 f with a protruding mechanism provided on the male mold 12, for example, a protruding pin 15. The protrusion of the housing 7 can be performed by, for example, a protrusion ring or a protrusion plate in addition to the protrusion pin.

  The bearing sleeve 8 is formed in a cylindrical shape with a porous body made of a sintered alloy, for example, a sintered metal mainly composed of copper. The sintered metal is impregnated with lubricating oil. In addition, the bearing sleeve 8 can be formed of a solid metal material, for example, a soft metal such as brass.

  On the inner peripheral surface 8a of the bearing sleeve 8, two upper and lower dynamic pressure groove regions (shown in black in FIG. 2) serving as radial bearing surfaces are provided apart in the axial direction. In these two regions, as shown in FIG. 3, a plurality of dynamic pressure grooves G arranged in a herringbone shape, for example, are formed as dynamic pressure generating portions. The dynamic pressure groove G in the upper region is formed asymmetrically in the axial direction. In this region, the axial length X1 of the upper dynamic pressure groove is slightly longer than the axial length X2 of the lower dynamic pressure groove. It is larger (X1> X2). On the other hand, the dynamic pressure grooves G in the lower region are formed symmetrically in the axial direction, and the axial lengths of the upper and lower dynamic pressure grooves G are equal in the region. A region serving as a radial bearing surface having the dynamic pressure groove G can also be formed on the outer peripheral surface of the shaft portion 2 a of the shaft member 2.

  A dynamic pressure groove region (shown in black in FIG. 2) serving as a thrust bearing surface is formed on the lower end surface 8b of the bearing sleeve 8. In this region, for example, a plurality of dynamic pressure grooves (not shown) arranged in a spiral shape are formed as dynamic pressure generating portions.

  A circulation groove 8d for circulating the lubricating oil is formed in the axial direction at one place on the outer peripheral surface of the bearing sleeve 8 or at a plurality of places arranged equally in the circumferential direction. Both ends of the circulation groove 8d are open to both end faces 8b, 8c of the bearing sleeve 8.

  The seal member 9 is integrally formed with a disk-shaped first seal portion 9a and a cylindrical second seal portion 9b protruding in an axial direction from one end surface 9a1 of the first seal portion 9a so as to have an inverted L-shaped cross section. . In the present embodiment, the outer peripheral surface 9b1 and the inner peripheral surface 9b2 of the second seal portion 9b are both formed in a cylindrical surface, but the inner peripheral surface 9a2 of the first seal portion 9a is a tapered surface whose diameter is expanded upward. It is formed into a shape. As shown in FIGS. 6 and 7, a radial circulation groove 10 for circulating the lubricating oil is formed on the one end face 9a1. This circulation groove 10 is formed at one place or a plurality of equally spaced places (three places in FIG. 7) in the circumferential direction across the end face 9a1. The seal member 9 is also formed of a resin injection-molded product, like the housing. Usable base resins and fillers are the same as those in the housing 7 and will not be described.

  In assembling the hydrodynamic bearing device 1, after the shaft member 2 is accommodated in the housing 7, the bearing sleeve 8 is fixed to the inner peripheral surface of the housing 7, and the seal member 9 is fixed to the upper end of the outer peripheral surface of the bearing sleeve 8. Is done. Thereafter, when the internal space of the housing 7 is filled with lubricating oil, the fluid dynamic bearing device 1 shown in FIG. 2 is obtained. The housing 7 and the bearing sleeve 8 can be fixed, and the bearing sleeve 8 and the seal member 9 can be fixed by press-fitting or bonding, or press-fitting (press-fitting with an adhesive). After assembly, the end surface 9a1 of the first seal portion 9a constituting the seal member 9 contacts the upper end surface 8c of the bearing sleeve 8, and the lower end surface of the second seal portion 9b is the boundary surface 7e on the inner periphery of the housing 7. It is opposed via an axial gap 11. Further, the seal member 9 is disposed on the inner diameter side of the large diameter portion 7 b of the housing 7.

  When the shaft member 2 rotates, the two upper and lower dynamic pressure groove regions serving as the radial bearing surfaces of the inner peripheral surface 8a of the bearing sleeve 8 are opposed to the outer peripheral surface of the shaft portion 2a via the radial bearing gap. Further, the dynamic pressure groove region serving as the thrust bearing surface of the lower end surface 8b of the bearing sleeve 8 faces the upper end surface 2b1 of the flange portion 2b via the thrust bearing gap, and the thrust bearing surface of the inner bottom surface 7c1 of the housing bottom portion 7c The resulting dynamic pressure groove region faces the lower end surface 2b2 of the flange portion 2b via a thrust bearing gap. As the shaft member 2 rotates, dynamic pressure of the lubricating oil is generated in the radial bearing gap, and the shaft member 2 is supported in a non-contact manner so as to be rotatable in the radial direction by the oil film of the lubricating oil formed in the radial bearing gap. Is done. Thus, the first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 in a non-contact manner so as to be rotatable in the radial direction are configured. At the same time, the dynamic pressure of the lubricating oil is generated in the thrust bearing gap, and the shaft member 2 is supported in a non-contact manner so as to be rotatable in the thrust direction by the lubricating oil film formed in the two thrust bearing gaps. Thereby, the 1st thrust bearing part T1 and the 2nd thrust bearing part T2 which non-contact-support the shaft member 2 rotatably in a thrust direction are comprised.

  The inner peripheral surface 9a2 of the first seal portion 9a forms a first seal space S1 having a predetermined volume with the outer peripheral surface of the shaft portion 2a. In this embodiment, the inner peripheral surface 9a2 of the first seal portion 9a is formed in a tapered surface shape that gradually increases in diameter upward, and therefore the first seal space S1 exhibits a tapered shape that gradually decreases in the downward direction. . The outer peripheral surface 9b1 of the second seal portion 9a forms a second seal space S2 having a predetermined volume with the large-diameter inner peripheral surface 7b2 of the housing 7. In this embodiment, the inner peripheral surface 7b2 of the large-diameter portion 7b of the housing 7 is formed in a tapered surface shape that gradually increases in diameter upward, so that the first and second seal spaces S1, S2 face downward. The taper shape is gradually reduced. Accordingly, the lubricating oil in the seal spaces S1 and S2 is drawn in a direction in which the seal spaces S1 and S2 become narrow due to the drawing action by the capillary force, and thereby the upper end opening of the housing 7 is sealed. The seal spaces S1 and S2 also have a buffer function that absorbs the volume change accompanying the temperature change of the lubricating oil filled in the internal space of the housing 7, and the oil level is always in the seal spaces S1 and S2. The volume of the first seal space S1 and the second seal space is smaller in the first seal space S1.

  In addition, while the inner peripheral surface 9a2 of the first seal portion 9a is a cylindrical surface, the outer peripheral surface of the shaft portion 2a facing this may be formed in a tapered surface shape. In this case, the first seal space S1 is further provided. Moreover, since a function as a centrifugal seal can be provided, the sealing effect is further enhanced.

  As described above, the dynamic pressure groove G of the first radial bearing portion R1 is formed to be axially asymmetric, and the axial dimension X of the upper region is larger than the axial dimension Y of the lower region. Therefore, when the shaft member 2 rotates, the pulling force (pumping force) of the lubricating oil by the dynamic pressure groove G is relatively larger in the upper region than in the lower region. Due to the differential pressure of the pulling force, the lubricating oil filled in the gap between the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface of the shaft portion 2a flows downward, and the thrust of the first thrust bearing portion T1 It circulates along the path of the bearing gap → the axial circulation groove 8d → the radial circulation groove 10 and is again drawn into the radial bearing gap of the first radial bearing portion R1.

  In this way, the configuration in which the lubricating oil flows and circulates inside the housing 7 prevents a phenomenon in which the pressure of the lubricating oil filled in the housing 7 becomes a negative pressure locally. Problems such as generation of bubbles accompanying the generation, leakage of lubricating oil and generation of vibration due to the generation of bubbles can be solved. The first seal space S1 communicates with this lubricating oil circulation path, and further, the second seal space S2 communicates with the axial clearance 11, so that bubbles are mixed into the lubricating oil for some reason. Even when the bubbles circulate with the lubricating oil, the lubricating oil in the seal spaces S1 and S2 is discharged from the oil surface (gas-liquid interface) to the outside air, and the adverse effects of the bubbles are further effectively prevented. The

  The axial circulation groove 8 d can be formed on the inner peripheral surface of the housing 7, and the radial circulation groove 10 can be formed on the upper end surface 8 c of the bearing sleeve 8.

  In the present invention, as described above, the seal space S2 is formed not only by the inner peripheral surface of the seal member 9 but also by the outer peripheral surface. Conventionally, since both the radial bearing gap and the seal space are formed using the outer peripheral surface of the shaft portion 2a, both must be arranged side by side in the axial direction, and the required space in the axial direction increases. In contrast, when the second seal space S2 is formed on the outer peripheral surface of the seal member 9 as in the present invention, the second seal space S2 can be formed on the outer diameter side of the radial bearing gap. As shown in FIG. 2, the formation region of the second seal space S2 and the formation region of the radial bearing gap (in the illustrated example, the radial bearing gap of the first radial bearing portion R1) can be overlapped in the axial direction. Further, since the amount of oil necessary for securing the buffer function is also secured in the second seal space S2, the amount of oil to be retained in the first seal space S1 is reduced, and the low volume of the first seal space S1 is reduced. That is, the thickness of the first seal portion 9a can be reduced. For the above reasons, the axial dimension of the bearing sleeve 8 can be increased while suppressing an increase in the axial dimension of the bearing device. As a result, the span between the two radial bearing portions R1 and R2 can be lengthened, the bearing rigidity (particularly the moment rigidity) can be improved, and it is possible to cope with the multi-stacking of disks in the HDD device.

  On the other hand, since the housing 7 and the seal member 9 whose shapes are complicated in accordance with such a configuration are made of resin injection-molded products, the cost of these members is suppressed, and the inexpensive hydrodynamic bearing device 1 is provided. It becomes possible to provide. In particular, since the shape of the seal member 9 is substantially cylindrical, it is difficult to form the radial groove 10 in the end surface 9a1 in the case of a metal material cut out, and the seal member 9 is significantly increased in cost. In the case of resin injection molding, since the radial groove 10 can be molded simultaneously with the molding of the seal member 9, the cost can be further reduced.

  Further, as shown in FIG. 2, since the outer peripheral surface of the housing 7 is formed with a larger diameter on the opening side than other places (large-diameter outer peripheral surface 7 b 1), the large diameter located on the outer diameter side of the seal member 9. A sufficient thickness can be secured by the portion 7b. Therefore, after the resin is solidified in the injection molding process, a sufficiently large pressure receiving area can be secured by the protruding surface 7f even when the molded product is protruded by the protruding pin 15 or the like, and smooth protrusion by the protruding pin or the like can be achieved. It becomes possible. In addition, since the entire housing 7 including the large-diameter portion 7b can be made to have a substantially uniform thickness, it is possible to avoid deterioration in the accuracy of the housing 7 due to variations in the amount of molding shrinkage. For comparison with the present invention, the housing 7 ′ of FIG. 5 is formed by forming the outer peripheral surface of the portion 7b ′ corresponding to the large diameter portion 7b to the same diameter as the other portions. In this case, the protruding surface 7f ′ Therefore, it is difficult to secure a sufficient pressure receiving area, and the portion 7b ′ corresponding to the large diameter portion 7b is thinner than the other portions, so that the amount of molding shrinkage varies.

  In the above description, the case where the dynamic pressure grooves of the first and second thrust bearing portions T1 and T2 are formed on the end surface 8b of the bearing sleeve 8 and the inner bottom surface 7c1 of the housing bottom portion 7c is exemplified. A dynamic pressure groove as a dynamic pressure generating portion may be formed in one or both of 2b1 and 2b2.

  Further, the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2 are exemplified by the configuration in which the dynamic pressure action of the lubricating oil is generated by the herringbone-shaped or spiral-shaped dynamic pressure grooves, but the radial bearing portion R1, A so-called step bearing, a wave bearing, or a multi-arc bearing can also be adopted as R2, and a step bearing or a wave bearing can also be adopted as the thrust bearing portions T1 and T2. Further, as the radial bearing portions R1 and R2, so-called perfect circle bearings having no dynamic pressure generating portions can be adopted, and as the thrust bearing portions T1 and T2, pivot bearings that contact and support the end portions of the shaft members are adopted. You can also

1 Fluid bearing device (fluid dynamic pressure bearing device)
2 Shaft member 3 Hub 4 Stator coil 5 Rotor magnet 6 Bracket 7 Housing 7a Small diameter portion 7a1 Small diameter outer peripheral surface 7b Large diameter portion 7b1 Large diameter outer peripheral surface 7c Bottom portion 7f Protruding surface 8 Bearing sleeve 9 Seal member 9a First seal portion 9b Second Seal portion 10 Circulating groove 12 Male die 13 Female die 14 Gate R1 First radial bearing portion R2 Second radial bearing portion S1 First seal space S2 Second seal space T1 First thrust bearing portion T2 Second Thrust bearing

Claims (2)

A radial bearing portion that rotatably supports the shaft member with an oil film formed in the radial bearing gap, a housing that houses the radial bearing portion therein, lubricating oil that fills the inner space of the housing, and a seal that seals the opening of the housing In a hydrodynamic bearing device having a member,
A fluid dynamic bearing characterized in that a first seal space is formed on the inner peripheral surface of the seal member, a second seal space is formed on the outer peripheral surface, and the seal member is formed by injection molding of resin. apparatus.   A seal member includes a first seal portion that forms a first seal space on the inner peripheral surface, and a second seal that protrudes axially from one end surface of the first seal portion and forms a second seal space on the outer peripheral surface. The hydrodynamic bearing device according to claim 1, wherein a circulation groove is formed on the one end face of the first seal portion.

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