JP3607661B2 - Hydrodynamic porous oil-impregnated bearing and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a self-lubricating function by impregnating a bearing body made of a porous body such as sintered metal with lubricating oil or lubricating grease, and a lubricating oil film formed by the dynamic pressure action of a dynamic pressure groove. With respect to hydrodynamic porous oil-impregnated bearings that support the sliding surface in a non-contact manner, high rotational accuracy is required at high speeds, especially for spindle motors for polygon mirrors of laser beam printers (LBP) and magnetic disk drives (HDDs, etc.). It is suitable for a bearing such as a device that is driven at a high speed by applying a large unbalance load when a disk is placed, such as a spindle motor for DVD-ROM.
[0002]
[Prior art]
In the above-mentioned small spindle motors related to information equipment, further improvement in rotational performance and cost reduction are required. As a means for that purpose, the spindle bearing is replaced from a rolling bearing to a porous oil-impregnated bearing. Is being considered. However, since the porous oil-impregnated bearing is a kind of a perfect circular bearing, unstable vibrations are likely to occur where the shaft is small in eccentricity, and so-called whirling that tends to swing at half the rotational speed is likely to occur. There are drawbacks. Therefore, a conventional attempt has been made to support the shaft in a non-contact manner by providing a herringbone type or spiral type dynamic pressure groove on the bearing surface and forming a lubricating oil film in the bearing gap by the action of the dynamic pressure groove accompanying the rotation of the shaft. (Dynamic pressure type porous oil-impregnated bearing).
[0003]
As a conventional technique in which a dynamic pressure groove is formed on the bearing surface of a porous oil-impregnated bearing, there is one described in Utility Model Public Notice No. 19627 in 1988. In the technique described in the same reference, the formation area of the dynamic pressure groove on the bearing surface is subjected to surface crushing to seal the formation area of the dynamic pressure groove. In addition, as a method for forming dynamic pressure grooves on the bearing surface, a shaft-shaped jig in which a plurality of balls that are harder than a bearing material made of a soft metal such as brass or an aluminum alloy is arranged and held at equal circumferential intervals is used as the bearing material. A method is known in which a dynamic pressure groove forming region is plastically processed by pressing the ball against the inner peripheral surface of the material while applying a helical motion to the ball by rotating and feeding the jig. Japanese Patent No. 2541208).
[0004]
[Problems to be solved by the invention]
In the configuration described in Utility Model Notification 19627, 1988, the following problems arise. First, since the region where the dynamic pressure groove is formed is completely sealed, the circulation of oil, which is the greatest feature of the porous oil-impregnated bearing, is inhibited in that region. Therefore, the oil that has once oozed into the bearing gap is pushed into the axial central portion of the bearing surface by the action of the dynamic pressure groove and remains there. Since a large shearing action is acting in the bearing gap, the oil remaining in the bearing gap is easily denatured by the shearing force and frictional heat, and oxidation deterioration tends to be accelerated due to temperature rise. Therefore, the bearing life is shortened. Next, as other means for crushing the surface, other than plastic working, coating, etc. are mentioned, but the thickness of the coating film needs to be thinner than the groove depth, and a coating film of several μm is formed in the dynamic pressure groove. It is extremely difficult to apply only to the formation region.
[0005]
Further, in the method described in Japanese Patent No. 2541208, a material bulge occurs in a region adjacent to the dynamic pressure groove at the time of molding, and it is necessary to remove this with a lathe or reamer (Japanese Patent Publication No. 232958). Therefore, the number of manufacturing steps increases. Further, since a jig rotation driving mechanism and a feeding mechanism are necessary, the manufacturing equipment becomes complicated. Furthermore, since it is necessary to fix the bearing material with a chuck, the bearing surface is deformed by the chucking force, or the coaxiality with the outer peripheral surface is deviated.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide a manufacturing method capable of performing a molding process of a bearing surface having an inclined dynamic pressure groove with a simple facility, with a small number of man-hours and with high accuracy, and also in the interior of the bearing body and the bearing. The purpose is to ensure proper oil circulation between the gaps and to suppress the deterioration of the oil in the bearing gaps, thereby improving the bearing life.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is a method for producing a dynamic pressure type porous oil-impregnated bearing in which a bearing surface having an inclined dynamic pressure groove is formed on the inner periphery of a bearing body. Insert a core rod having a molding die corresponding to the shape with a predetermined inner diameter clearance on the inner peripheral surface of the cylindrical porous material, and lower the porous material together with the core rod so that the outer peripheral surface of the porous material is While press-fitting into the die with a predetermined outer diameter interference, pressure is applied from above and below with the upper and lower punches to apply pressure to the porous material, and the inner peripheral surface of the porous material has an outer diameter interference and an inner clearance. By pressurizing the core rod mold with an amount of pressure approximately equal to the difference between and the dynamic pressure groove on the inner peripheral surface of the porous material is formed by plastic working, and then the core rod is inserted into the porous material. In conjunction with the lower punch and core rod A structure including a step of releasing the core rod from the inner peripheral surface of the porous material by using the spring back of the porous material by releasing the compression force and removing the porous material from the die. .
In the above configuration, the dynamic pressure groove region on the bearing surface and the other region may be simultaneously formed by pressing the core rod forming die.
The porous material is preferably formed of a sintered metal, more preferably copper or iron, or a sintered metal mainly composed of both.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0009]
FIG. 1 illustrates one embodiment of a dynamic pressure type porous oil-impregnated bearing manufactured by the manufacturing method of the present invention. The porous oil-impregnated bearing 1 is configured so that, for example, in a scanner motor of a laser beam printer as shown in FIG. 2, a spindle shaft 4 that rotates at high speed by an example magnetic force between a rotor 2 and a stator is rotatable with respect to a housing 5. Non-contact support.
[0010]
The porous oil-impregnated bearing 1 is composed of a porous bearing body 1a and oil retained in the pores of the bearing body 1a by impregnation with lubricating oil or lubricating grease. The bearing main body 1a is made of, for example, copper or iron, or a sintered metal mainly containing both, and preferably contains 20 to 95% by weight of copper and has a density of 6.4 to 7.2 g / cm 3. Formed as follows. As the material of the bearing body 1a, a porous body having many pores obtained by sintering or foaming cast iron, synthetic resin, ceramics, or the like may be used.
[0011]
A bearing surface 1b is formed on the inner circumferential surface of the bearing body 1a so as to face the outer circumferential surface of the shaft to be supported via a bearing gap, and an inclined dynamic pressure groove 1c is formed on the bearing surface 1b. The bearing surface 1b in this embodiment has a first region m1 in which a plurality of dynamic pressure grooves 1c inclined in one direction with respect to the axial direction are arranged in the circumferential direction, and is axially separated from the first region m1. The second region m2 in which a plurality of dynamic pressure grooves 1c inclined to the other side are arranged in the circumferential direction, and an annular smooth region n positioned between the first region m1 and the second region m2. The The back (region between the dynamic pressure grooves 1c) 1d of the first region m1 and the back (region between the dynamic pressure grooves 1c) 1d of the second region m2 are respectively continuous with the smooth region n. The dynamic pressure groove 1c in the first region m1 and the dynamic pressure groove 1c in the second region m2 are symmetrical with respect to the axial center line of the bearing surface 1b. In the bearing surface 1b, surface openings are distributed over the entire region including the region where the dynamic pressure grooves 1c are formed, and mainly between the interior of the bearing body 1a and the bearing gap through the surface openings of the bearing surface 1b. Oil is circulated between the shafts, and the outer peripheral surface of the shaft is supported in a non-contact manner with respect to the bearing surface 1b. For example, the surface area ratio is set to a range of 5 to 40%, preferably 5 to 20% in the first region m1 and the second region m2, and preferably in a range of 2 to 30% in the smooth region n, preferably It can be set in the range of 2 to 10%. Further, the surface area ratio of the smooth region n can be made smaller than the surface area ratios of the first region m1 and the second region m2. Here, the “surface opening” means a portion where the pores of the porous body structure are opened on the outer surface, and the “surface opening ratio” means the area of the surface opening that occupies the unit area of the outer surface. Say percentage.
[0012]
When relative rotation occurs between the bearing body 1a and the shaft, the oil in the bearing gap is directed toward the smooth region n by the dynamic pressure grooves 1c formed in the first region m1 and the second region m2 so as to be inclined in opposite directions. Since the oil is drawn in and collected in the smooth region n, the oil film pressure in the smooth region n is increased. Therefore, the formation effect of the lubricating oil film is high. In addition to the spine 1d, the smooth region n also serves as a support surface for supporting the shaft, so that the support area is increased and the bearing rigidity is increased. The ratio r of the axial width of the smooth region n is set in the range of r = 0.1 to 0.6, preferably in the range of r = 0.2 to 0.4, where the bearing width is 1. Is good. The dynamic pressure groove 1c only needs to have a shape inclined with respect to the axial direction. For example, the dynamic pressure groove 1c may have a continuous shape in the axial direction as shown in FIG. 3 (in this case, it does not have an annular smooth region). A spiral shape may be used.
[0013]
FIG. 4 shows the flow of the oil O in the axial section when the shaft 4 is supported by the porous oil-impregnated bearing 1 having the above-described configuration. As the shaft 4 rotates, the oil O retained in the pores inside the bearing body 1a oozes out from the both sides in the axial direction of the bearing surface 1b and the vicinity of the chamfer portion into the bearing clearance, and further, the bearing clearance is reduced by the dynamic pressure groove. It is pulled toward the axial center. The oil O pulling action (dynamic pressure action) increases the pressure of the oil film interposed in the bearing gap, thereby forming a lubricating oil film. Due to the lubricating oil film formed in the bearing gap (the lubricating oil film formed by the dynamic pressure action of the dynamic pressure groove), the shaft 4 is supported in a non-contact manner with respect to the bearing surface 1b without causing unstable vibration such as a whirl. The The oil O that has oozed into the bearing gap returns to the inside of the bearing body 1a mainly from the surface opening of the bearing surface 1b due to the pressure generated by the rotation of the shaft 4, circulates inside the bearing body 1a, and again becomes a bearing. It oozes out from the surface 1b and the vicinity of the chamfer portion into the bearing gap.
[0014]
The bearing body 1a of the porous oil-impregnated bearing 1 shown in FIG. 1 has a cylindrical shape as shown in FIG. 12, for example, obtained by compression-molding and firing a metal powder mainly composed of copper or iron, or both. For example, sizing → rotational sizing → bearing surface forming can be performed on the sintered metal material 1 ′.
[0015]
The sizing process is a process of sizing the outer peripheral surface and the inner peripheral surface of the sintered metal material 1 ′. The outer peripheral surface of the sintered metal material 1 ′ is pressed into a cylindrical die and a sizing pin ( Press fit (circular cross section). In the rotational sizing process, a sizing pin having a substantially polygonal cross-section (a part obtained by partially flattening the outer peripheral surface of a pin having a circular cross-section and leaving an arc portion at a circumferentially equidistant position) of the sintered metal material 1 ′ It is a step of sizing the inner peripheral surface while being press-fitted into the inner peripheral surface and rotating the inner peripheral surface. In the bearing surface molding step, the bearing surface 1b is formed by pressurizing a molding die having a shape corresponding to the bearing surface 1b of the finished product 1a onto the inner peripheral surface of the sintered metal material 1 ′ subjected to the sizing process as described above. This is a step of simultaneously forming the formation region of the dynamic pressure groove 1c and the other region (the spine 1d and the annular smooth region n). This process is as follows, for example.
[0016]
FIG. 5 illustrates a schematic structure of a molding apparatus used in the bearing surface molding process. This apparatus has a cylindrical die 20 for press-fitting the outer peripheral surface of the sintered metal material 1 ′, a core rod 21 for forming the inner peripheral surface of the sintered metal material 1 ′, and both end surfaces of the sintered metal material 1 ′ in the vertical direction. The upper and lower punches 22 and 23 to be pressed from the main parts are configured as main elements. As shown in FIG. 5 (b), an uneven mold 21 a corresponding to the shape of the finished bearing surface 1 b is provided on the outer peripheral surface of the core rod 21. The convex portion 21a1 of the molding die 21a forms a region of the dynamic pressure groove 1c on the bearing surface 1b, and the concave portion 21a2 forms a region other than the dynamic pressure groove 1c (the back 1d and the annular smooth region n). The step (depth H) between the convex portion 21a1 and the concave portion 21a2 in the molding die 21a is about the same as the depth of the dynamic pressure groove 1c in the bearing surface 1b (for example, about 2 to 5 μm), but is very small. In FIG.
[0017]
In a state before press-fitting into the die 20, there is an inner diameter clearance T between the inner peripheral surface of the sintered metal material 1 ′ and the forming die 21 a (based on the convex portion 21 a 1) of the core rod 21. The size of the inner diameter clearance T (diameter amount) is, for example, 50 μm. The press-fitting allowance (outer diameter interference S: diameter amount) of the outer peripheral surface of the sintered metal material 1 ′ to the die 20 is, for example, 150 μm.
[0018]
After the sintered metal material 1 ′ is positioned and arranged on the upper surface of the die 20, as shown in FIG. 6, the upper punch 22 and the core rod 21 are lowered, and the sintered metal material 1 ′ is press-fitted into the die 20, Further, it is pressed against the lower punch 23 and pressurized from above and below.
[0019]
The sintered metal material 1 ′ is deformed by receiving a pressing force from the die 20 and the upper and lower punches 22 and 23, and the inner peripheral surface is pressed against the forming die 21 a of the core rod 21. The amount of pressurization of the inner peripheral surface is substantially equal to the difference between the outer diameter interference margin S and the inner diameter clearance T, and the surface layer portion from the inner peripheral surface to a predetermined depth is pressed to the molding die 21a of the core rod 21 to cause plastic flow. Raise and bite into the mold 21a. Thereby, the shape of the molding die 21a is transferred to the inner peripheral surface of the sintered metal material 1 ′, and the bearing surface 1b is formed into the shape and dimensions shown in FIG. 1 (at the same time, the outer peripheral surface of the sintered metal material 1 ′ is also Sized.)
[0020]
After the formation of the bearing surface 1b is completed, as shown in FIG. 9, the lower punch 23 and the core rod 21 are raised in conjunction with the core rod 21 inserted into the sintered metal material 1 ′ ((2) in FIG. 9). The state of ▼), the sintered metal material 1 ′ is pulled out from the die 20 (the state of FIG. 9 (3)). When the sintered metal material 1 ′ is pulled out of the die 20, a spring back is generated in the sintered metal material 1 ′ and its inner diameter is enlarged (see FIG. 7), so that the sintered metal material is not destroyed without breaking the dynamic pressure groove 1c. The core rod 21 can be extracted from the inner peripheral surface of the material 1 ′ (the state shown in FIG. 9 (4)). Thereby, the bearing main body 1a is completed. In the manufacturing process of an ordinary perfect circle bearing (sintered oil-impregnated bearing having no dynamic pressure groove on the bearing surface), as shown in FIG. 8, the bearing surface (inner peripheral surface) is sized and then sintered. In a state where the metal material 1 ″ is press-fitted into the die 20 ′, the sizing pin 21 ′ {circular cross section: does not have the forming die 21a as shown in FIG. 5B) is raised and the sintered metal material 1 is raised. Then, the sintered metal material 1 "is pushed up by the lower punch 23 'and taken out from the die 20'. This procedure is performed to form a bearing surface having an inclined dynamic pressure groove. If it is used for, when the sizing pin (core rod) is extracted from the inner peripheral surface of the sintered metal material, the shape of the dynamic pressure groove is destroyed.
[0021]
FIG. 10 shows an inner diameter clearance T, an outer diameter interference margin S, and a springback amount when the bearing surface forming process described above is performed on a sintered metal material 1 ′ having an inner diameter φ3, an outer diameter φ6, and a width 3 mm. The relationship is shown. As shown in the figure, there is a certain correlation between the inner diameter clearance T and the outer diameter interference S and the amount of spring back. If the inner diameter clearance T and the outer diameter interference S are specified, the spring back at that time is determined. It can be seen that the amount is also specified. According to the experiment, if the springback amount is set to about 4 to 5 μm (diameter amount) at a predetermined depth H (2 μm to 3 μm: substantially equal to the depth of the dynamic pressure groove 1c to be formed), the dynamic pressure Since the sintered metal material 1 ′ can be extracted from the core rod 21 without breaking the groove 1c, it is desirable to set the inner diameter clearance T and the outer diameter interference margin S so as to obtain this amount of springback. When the radius of the springback amount of the sintered metal material 1 ′ is larger than the depth H, the mold 21a can be released without interfering with the inner peripheral surface of the sintered metal material 1 ′. However, even when the radius of the springback amount of the sintered metal material 1 ′ is smaller than the depth H and the molding die 21a slightly interferes with the inner peripheral surface of the sintered metal material 1 ′, the sintered metal It is only necessary to add a diameter expansion amount (radial amount) due to material elasticity of the material 1 ′ so that the forming die 21a can be released from the inner peripheral surface of the sintered metal material 1 ′ without breaking the dynamic pressure groove 1c. Therefore, the dimension setting based on the above experimental result is an example, and the present invention is not limitedly interpreted thereby.
[0022]
In addition, after the formation process of the bearing surface 1b is completed, you may size the bearing surface 1b using a normal sizing pin (circular cross section). In this case, when the spine 1d and the smooth region n on the bearing surface 1b are sized by the sizing pins, the surface area ratio of these regions becomes smaller than the surface area ratio of the formation region of the dynamic pressure grooves 1c. Also, in the molding process of the bearing surface, only the formation area of the dynamic pressure groove is formed by the molding die, and then the area other than the formation area of the dynamic pressure groove is sized (using a sizing pin with a circular cross section) or rotational sizing (cross section) It is also possible to finish by partially flattening the outer peripheral surface of the circular pin and using a sizing pin that leaves an arc portion in the circumferentially equidistant position.
[0023]
When the bearing main body 1a is manufactured through the steps as described above, and this is impregnated with lubricating oil or lubricating grease to hold the oil, the dynamic pressure type porous oil-impregnated bearing 1 having the form shown in FIG. 1 is completed.
[0024]
A comparative experiment of shaft runout performance was conducted using a perfect circle bearing (sintered oil-impregnated bearing having no dynamic pressure groove on the bearing surface) and a dynamic pressure type porous oil-impregnated bearing (sintered oil-impregnated bearing) manufactured by the above method. In the experiment, a test bearing was incorporated into a CD-ROM actual motor as shown in FIG. 13, a commercially available CD was mounted, and the shaft run-out with respect to the rotational speed was measured. The result is shown in FIG. From this figure, it can be understood that the dynamic pressure type porous oil-impregnated bearing of the embodiment is more effective in suppressing the shaft runout than the perfect circle bearing.
[0025]
In the above-described embodiment, the bearing surface is formed on the sintered metal material 1 ′. In addition, the bearing surface can be formed in the forming process. Forming is a process in which a forming pin serving as an inner mold is inserted inside the outer mold, a powder material is filled between the inner mold and the outer mold, and then compressed in the axial direction to form a cylinder. In this forming step, by forming a molding die as shown in FIG. 5B on the outer peripheral surface of the forming pin, as shown in FIG. 1 on the inner peripheral surface of the molded product (compression molded body) simultaneously with forming. It is possible to form a bearing surface having a proper shape. If the compression molding force is removed after pressure compression, the molded product (compression molded product) can be removed from the forming pin using the spring back of the molded product (compression molded product). Will not collapse. The powder material is a metal powder material, for example, containing copper, iron, or both as a main component. The molded product after forming is baked and then commercialized through a sizing process, an oil impregnation process, and the like.
[0026]
In the above description, the case where the mold for the bearing surface is released using the spring back of the porous material or the compression molded body is exemplified, but in addition, the mold can be elastically contracted and expanded. It may be structured (for example, the mold is divided into slits), and after the bearing surface is molded, the mold may be elastically reduced in diameter and released. Further, by changing the shape of the molding die according to the shape of the bearing surface (the shape of the dynamic pressure groove), various shapes of the bearing surface can be similarly formed. Furthermore, even when a plurality of bearing surfaces are formed on the inner peripheral surface of one bearing body so as to be separated from each other in the axial direction, a core rod or a forming pin formed by separating a plurality of molding dies on the outer peripheral surface in the axial direction should be used. Thus, a plurality of bearing surfaces can be formed simultaneously.
[0027]
【The invention's effect】
According to the present invention, the core rod having a molding die corresponding to the shape of the bearing surface is the inner die, the die is the outer die, the core rod molding die is pressed against the inner peripheral surface of the porous material, Since the dynamic pressure groove is formed on the inner peripheral surface by plastic working, the bearing surface having the inclined dynamic pressure groove can be formed with simple equipment, with less man-hours and with high accuracy.
[0028]
The dynamic pressure type porous oil-impregnated bearing manufactured by the manufacturing method of the present invention has high molding accuracy of the bearing surface, and surface openings are distributed over the entire region of the bearing surface including the region where the dynamic pressure groove is formed. Since an appropriate oil circulation is ensured between the inside of the bearing and the bearing gap, the effect of forming a lubricating oil film is high, and the bearing has a good and stable bearing function and at the same time has a high durability life.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing one embodiment of a dynamic pressure type porous oil-impregnated bearing manufactured by a manufacturing method of an embodiment.
FIG. 2 is a longitudinal sectional view conceptually showing a motor incorporating a porous oil-impregnated bearing.
FIG. 3 is a longitudinal sectional view showing another embodiment of the dynamic pressure type porous oil-impregnated bearing.
FIG. 4 is a diagram schematically showing an oil flow in an axial section when a shaft is supported in a non-contact manner by a dynamic pressure type porous oil-impregnated bearing.
FIG. 5A is a longitudinal sectional view showing an outline of a forming apparatus used for forming the bearing surface, and FIG. 5B is a side view showing a forming die for forming the bearing surface.
FIG. 6 is a diagram showing a molding process of a bearing surface.
FIG. 7 is a view showing a molding process of the bearing surface.
FIG. 8 is a view showing a process of forming a bearing surface in a conventional perfect circle bearing.
FIG. 9 is a diagram showing a process of forming a bearing surface according to the embodiment.
FIG. 10 is a graph showing the relationship between the inner and outer clearances and the amount of springback.
FIG. 11 is a diagram showing the results of a comparative test of shaft runout when using a conventional perfect circle bearing and the dynamic pressure type porous oil-impregnated bearing of the embodiment.
FIG. 12 is a longitudinal sectional view showing a sintered metal material.
FIG. 13 is a longitudinal sectional view conceptually showing an experimental apparatus used for a shaft runout comparison test.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Dynamic pressure type porous oil-impregnated bearing 1a Bearing main body 1b Bearing surface 1c Dynamic pressure groove 21a Mold

Claims (5)

A method for producing a dynamic pressure type porous oil-impregnated bearing in which a bearing surface having an inclined dynamic pressure groove is formed on the inner periphery of a bearing body,
Insert a core rod having a molding die corresponding to the shape of the bearing surface with a predetermined inner diameter clearance on the inner peripheral surface of the cylindrical porous material,
The porous material is lowered together with the core rod, the outer peripheral surface of the porous material is press-fitted into the die with a predetermined outer diameter , and the upper and lower punches are pressed from above and below to press the porous material. The porous material is pressed by applying a pressing force to the material and pressing the inner peripheral surface of the porous material to the mold for forming the core rod with a pressurizing amount approximately equal to the difference between the outer diameter interference and the inner clearance. The above-mentioned dynamic pressure groove is formed by plastic working on the inner peripheral surface of
Thereafter, the lower punch and the core rod are raised in conjunction with the core rod inserted into the porous material, the porous material is removed from the die, and the compression force is released to release the porous force. A method for producing a dynamic pressure type porous oil-impregnated bearing, comprising a step of releasing the core rod from the inner peripheral surface of the porous material by using a springback of the material. 2. The method for producing a hydrodynamic porous oil-impregnated bearing according to claim 1, wherein a region of the dynamic pressure groove on the bearing surface and the other region are simultaneously formed by pressurizing the core rod forming die. The method for producing a dynamic pressure type porous oil-impregnated bearing according to claim 1 or 2, wherein the porous material is formed of a sintered metal. The method for producing a dynamic pressure type porous oil-impregnated bearing according to claim 3, wherein the sintered metal contains copper, iron, or both as a main component. A dynamic pressure type porous oil-impregnated bearing manufactured by the manufacturing method according to claim 1.

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