JP2010031909A - Sintered bearing and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably enhance support capacity of a sintered bearing having an inner recess part. <P>SOLUTION: This sintered bearing 1 is formed by sintering a green compact, and forms bearing surfaces 2 and 4 in two places separated in the axial direction of an inner peripheral surface, and has the inner recess part 3 forming an inside diametrical dimension of an area between bearing surfaces in a larger diameter than the bearing surfaces 2 and 4. The inner recess part 3 is formed in a predetermined shape in its whole by spring-back caused by releasing pressurizing force when molding the green compact. The inner recess part 3 and the first bearing surface 2, and the inner recess part 3 and the second bearing surface 4 have respectively crossing corner parts 3d and 3e. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sintered bearing and a manufacturing method thereof.

  Sintered bearings made of porous materials are usually used in a state in which the internal pores are impregnated with lubricating oil (sintered oil-impregnated bearings), and slide parts with the shafts as they move relative to the shaft to be supported. An oil film is formed on the shaft, and the shaft is supported by this oil film. Sintered bearings are suitable for various power transmission mechanisms and drive mechanisms because they can be manufactured at low cost and have many excellent features such as a self-lubricating function. In this type of sintered bearing, for example, Japanese Patent Laid-Open No. 2-8302 (Patent Document 1) and Japanese Patent Laid-Open No. 7-332363 (Patent Document) for the purpose of preventing oil film breakage and reducing torque during sliding with a shaft. As described in Document 2), there are cases where bearing surfaces are provided at two locations spaced apart in the axial direction on the inner peripheral surface, and an intermediate clearance portion having an inner diameter larger than the bearing surface is provided between the bearing surfaces.

  Patent Document 1 discloses that a sintered bearing having the above shape can be obtained as follows. First, the raw material powder is compacted to form a green compact having a substantially L-shaped cross section having an inner peripheral small diameter portion on one end side, and the green compact is sintered to obtain a sintered body. Next, by drawing the sizing core having a uniform outer diameter in the inner periphery of the sintered body, the inner peripheral small diameter part is formed at the other end of the sintered body, and both inner peripheral parts are formed. The inner peripheral surface of the small diameter portion is formed into a predetermined bearing surface.

On the other hand, Patent Document 2 discloses that a sintered bearing having the above shape can be obtained as follows. First, after the raw material powder is filled in the powder filling portion in a state where the guide core 102 is disposed on the inner periphery of the first die 101 having the small diameter inner peripheral surface 101a and the large diameter inner peripheral surface 101b, the small diameter outer peripheral surface 103a and the large diameter The raw material powder is compressed by the upper and lower punches 104 and 105 while the stepped first core rod 103 having the diameter outer peripheral surface 103b is press-fitted into the inner periphery of the raw material powder (powder filling part) (see FIG. 5A). As a result, the one end side region of the outer peripheral surface is formed with a large diameter and the other region is formed with a small diameter, and the other end side region of the inner peripheral surface is formed with a small diameter and the other region is formed with a large diameter. A first green compact 200 is obtained. Next, as shown in FIG. 5 (b), the first green compact 200 is inserted into the second core having the uniform inner diameter by the upper punch 113 while the core 112 having a uniform outer diameter is inserted into the inner periphery of the first green compact 200. Press fit into the inner periphery of the die 111. Thereby, the one end side area (area where the outer peripheral surface is formed to have a large diameter) of the outer peripheral surface of the first green compact 200 is deformed to the inner diameter side, and the second green compact in which the middle escape portion 202 is formed. 201 is obtained. Thereafter, the second green compact 201 is sintered to form a sintered body, and sizing is performed on both end side regions of the center relief portion 202 of the sintered body to obtain a sintered bearing having a predetermined shape. obtain.
JP-A-2-8302 Japanese Patent Laid-Open No. 7-332363

  However, in the sintered bearings formed as described in Patent Documents 1 and 2, it is difficult to obtain a uniform relief portion and thus a sintered bearing, and it is difficult to stably secure a high support capacity. It is. In particular, in the sintered bearing of Patent Document 2, the stepped surface 202b that connects the bearing surface on the upper side in FIG. 5B and the large-diameter inner peripheral surface 202a is not a surface formed in any process. Therefore, there is a problem that a predetermined amount of lubricating oil cannot be stably supplied to the upper sliding portion in the figure. This means that the supporting ability becomes unstable, which is disadvantageous for further improvement of the supporting ability. In addition, two steps are required to form a green compact having a predetermined shape, and a die having a different configuration needs to be used, resulting in high costs.

  The first object of the present invention is to stably increase the support capability of a sintered bearing having a middle relief portion. A second object of the present invention is to reduce the manufacturing cost of this kind of sintered bearing.

  A sintered bearing according to the present invention made to solve the first problem is obtained by sintering a green compact, and bearing surfaces are provided at two locations separated in the axial direction of the inner peripheral surface. Between the faces, there is a middle relief part whose inner diameter is formed larger than the bearing surface, and the whole middle relief part is formed by the spring back generated by releasing the pressurizing force at the time of compacting It is formed in a predetermined shape and has a corner portion where the bearing surface and the middle escape portion intersect. Here, “having a corner where the bearing surface and the middle relief portion intersect” can be said that the bearing surface and the middle relief portion are connected at the corner, and one end of the bearing surface. And a case where a smooth circular arc surface or the like is interposed between one end of the intermediate escape portion adjacent to the intermediate escape portion.

  As described above, in the sintered bearing according to the present invention, the entire middle relief portion is formed in a predetermined shape by the spring back generated by releasing the pressing force at the time of compacting, and the bearing surface and the middle relief are formed. It has the corner | angular part which a part intersects, It is characterized by the above-mentioned. In other words, the entire center relief portion is formed as a molding surface that follows the shape of the core pin used at the time of compacting, and the core pin is pulled from the inner periphery of the compact without contact with the inner peripheral surface of the compact. It means that it has been pulled out (in other words, it has not been pulled out from the inner periphery of the green compact by so-called forced removal). Therefore, if the core pin is formed in a predetermined shape, it is possible to avoid the variation in the shape of the middle escape portion between individuals and finish the middle escape portion with high accuracy. In addition, since the surface properties (surface open area ratio, etc.) of the entire center relief part can be homogenized, the amount of oil supplied to the sliding part with the shaft varies, and the support capacity between both sliding parts It is possible to prevent as much as possible a situation in which there is a difference between the two. From the above, according to the present invention, it is possible to improve the support capability of this kind of sintered bearing.

  The sintered bearing having the above-described configuration can be manufactured, for example, as follows. That is, the manufacturing method of the sintered bearing according to the present invention made to solve the second problem is to form a powder filling portion on the outer periphery of the core pin and pressurize the raw material powder filled in the powder filling portion. Thus, after the green compact is separated from the core pin using the step of forming the green compact fixed to the outer periphery of the core pin and the spring back generated in the green compact by releasing the applied pressure, And a step of pulling out the core pin in a non-contact manner with the inner peripheral surface.

  If it is said method, the shape substantially equivalent to a finished product shape can be obtained only through one process which shape | molds a green compact. Therefore, the process and equipment can be simplified compared to Patent Document 1 where the finished product shape has been obtained by drawing in the sizing process, or alternatively, the compacting process is completed in two processes. Compared to the configuration of Patent Document 2 that has obtained the product shape, the number of processes and owned equipment can be reduced, and the manufacturing cost can be reduced. Further, since the green compact can be separated from the core pin by utilizing the spring back generated in the green compact by releasing the applied pressure, no other separation mechanism is required. In addition, since the core pin is pulled out in non-contact with the inner peripheral surface of the green compact, the inner peripheral surface of the green compact formed into a predetermined shape (the region that becomes the middle escape portion and the bearing surface) is accompanied by the core pin being pulled out. No damage will occur. Further, in particular, in drawing processing as in Patent Document 1, it is necessary to make the bearing length relatively long in order to obtain a predetermined finished product shape. There are no restrictions.

  In the above method, the core pin is inserted into the inner periphery of the lower punch so as to be axially movable relative to the cylindrical lower punch, and the powder filling portion is formed by relative movement of the core pin and the lower punch in the axial direction. Can do. In this way, the green compact molding apparatus can be simplified as compared with the conventional configuration.

  The filling of the raw material powder into the powder filling part is desirably performed gradually in correspondence with the axial relative movement amount of the core pin and the lower punch (volume increase amount of the powder filling part). This is because a green compact with a uniform density is formed. That is, after forming a powder filling part of a predetermined volume, the powder filling part is filled with the raw material powder at once. Excess air or the like is mixed in the powder filling part, and a compact powder of uniform density is formed. It is difficult to obtain.

  When the core pin is disposed on the inner periphery of the cylindrical lower punch so as to be relatively movable, and the powder filling portion is formed by the relative movement of the two, the hole diameter of the lower punch is that of the core pin having the inner peripheral surface forming portion. In order to be able to move relative to each other, at least the maximum outer diameter of the inner peripheral surface molding portion of the core pin needs to be set. At this time, a radial gap is formed between the lower punch and the core pin, and there is a possibility that the raw material powder may enter the gap if no effort is made on the base end side of the inner peripheral surface molding portion. When such a situation occurs, it becomes an obstacle to accurately forming the green compact, such as generation of burrs, misalignment of the core pin, and breakage of the mold. In view of this situation, as shown in FIG. 3 (a), the outer diameter dimension is equal to or greater than the maximum outer diameter of the inner peripheral surface molded portion adjacent to the proximal end side of the inner peripheral surface molded portion provided on the outer peripheral surface of the core pin. It is desirable to fill the powder filling portion with the raw material powder in a state where the protruding portion is provided and this protruding portion is disposed on the inner periphery of the lower punch.

  When pressurizing the raw material powder filled in the powder filling portion, it is desirable to pressurize evenly from both ends of the raw material powder. This is to obtain a green compact with a uniform density.

  Moreover, the release of the pressing force performed when the green compact is separated from the inner peripheral surface molding portion of the core pin may be performed in the order of radial pressing force → axial pressing force, or axial pressing force. → It may be performed in the order of the pressure in the radial direction. These can be appropriately selected.

  In the sintered bearing having the above-described configuration, the surface properties of the bearing surface and the middle escape portion, for example, the surface area ratio can be made different. Such a configuration can be obtained, for example, by forming a bearing surface by forming sizing only on one end side region and the other end side region of the peripheral surface of the sintered body after forming the sintered body. In this way, while ensuring high oil film rigidity at the sliding portion with the shaft, the lubricating oil can be smoothly supplied to the sliding portion with the shaft to improve the bearing performance, and the sizing process and The sizing device can be simplified and the manufacturing cost can be reduced.

  As described above, according to the present invention, it is possible to stably increase the support capability of a sintered bearing having a middle relief portion. Also, this kind of sintered bearing can be manufactured at low cost.

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

  FIG. 1 is a sectional view conceptually showing an example of a sintered bearing 1 according to the present invention. A sintered bearing 1 shown in the figure is made of a sintered metal porous body, and has internal pores impregnated with lubricating oil (sintered oil-impregnated bearing), and is incorporated in a spindle motor for HDD, for example. It is used to support a shaft to be supported (in this case, a spindle shaft, indicated by a two-dot chain line in the figure) in a relatively rotatable manner.

  The sintered bearing 1 has first and second bearing surfaces 2 and 4 spaced apart at two axial positions, and an inner diameter dimension between the bearing surfaces 2 and 4 larger than that of the bearing surfaces 2 and 4. And the corner portions 3d and 3e at which the bearing surfaces 2 and 4 intersect. More specifically, the middle escape portion 3 includes a large-diameter inner peripheral surface 3a, a tapered first step surface 3b connecting the large-diameter inner peripheral surface 3a and the first bearing surface 2, and a large-diameter inner peripheral surface 3a. The second step surface 3c is connected to the second bearing surface 4, and the first step surface 3b and the first bearing surface 2 are connected by a corner 3d, and the second step surface 3c and the second step surface 3c are connected to each other. The two bearing surfaces 4 are connected by corner portions 3e. The intermediate relief portion 3 is a molding surface that is molded in accordance with the outer peripheral surface shape (the shape of the molding portion 14a) of the core pin 14 used when molding the green compact 1 'described later. The radial dimensional difference between the bearing surfaces 2 and 4 and the large-diameter inner peripheral surface 3a varies depending on the application of the sintered bearing 1, but in the sintered bearing for a spindle motor as in this embodiment, the radius The size is in the range of 5 μm to 20 μm.

  As will be described in detail later, the bearing surfaces 2 and 4 are sizing surfaces, while the middle relief portion 3 is a sizing surface. Therefore, the surface properties are different between the bearing surfaces 2 and 4 and the middle escape portion 3. Specifically, the surface opening ratio of the bearing surfaces 2 and 4 is smaller than the surface opening ratio of the middle escape portion 3. The middle escape portion 3 is not limited to the illustrated example, and can be formed in a single arcuate shape, for example.

  When the sintered bearing 1 having the above configuration and the spindle shaft rotate relative to each other, an oil film is formed in the bearing gap between the bearing surfaces 2 and 4 and the shaft by the seepage of the lubricating oil impregnated into the sintered bearing 1. The shaft is non-contact supported by the oil film so as to be relatively rotatable. Further, during relative rotation of the sintered bearing 1 and the spindle shaft, the lubricating oil is sequentially supplied from the middle escape portion 3 to the sliding portion (bearing gap) with the shaft. Therefore, the oil film breakage in the bearing gap is prevented as much as possible.

  The sintered bearing 1 having the above-described configuration is mainly manufactured through a compacting process, a sintering process, and a sizing process in order, and then completed through an oil impregnation process in which the internal pores are impregnated with a lubricating oil. Hereinafter, each step will be described.

(A) Compacting process In this compacting process, the compacting powder of a predetermined shape is obtained by compressing the raw material powder filled in the mold. FIG. 2 is a cross-sectional view conceptually showing the overall structure of the manufacturing apparatus 10 used for forming the green compact 1 ′, and shows a state in which the following constituent members are at the origin position. The manufacturing apparatus 10 shown in the figure includes a cylindrical upper punch 11 and a lower punch 12, a solid shaft-shaped core pin 14, and a cylindrical die 13 in which the lower punch 12 and the core pin 14 are disposed on the inner periphery. Are provided as main constituent members.

  The lower punch 12 can be moved relative to the die 13 in the axial direction (movable up and down), and the upper end surface 12b of the lower punch 12 is located on the same plane as the upper end surface 13b of the die 13 at the origin position. Yes. The core pin 14 can be moved relative to the lower punch 12 (and the die 13) in the axial direction. At the origin position, the upper end surface 12b is flush with the lower punch 12 and the upper end surfaces 12b and 13b of the die 13. It is comprised so that it may be located in. The upper punch 11 can be inserted into and removed from the die 13 by being relatively close to or away from the lower punch 12. In this embodiment, the die 13 constitutes a stationary side fixed to a stationary member (not shown), and the other members constitute movable sides that can be moved up and down independently by an appropriate driving mechanism (not shown).

  The core pin 14 is provided with an inner peripheral surface molding portion 14a for molding the inner peripheral surface of the green compact 1 '. The inner peripheral surface forming portion 14a is formed in order from the tip end side of the core pin 14 to form the first bearing surface 2, the middle escape portion 3, and the second bearing surface 4 of the sintered bearing 1 on the green compact inner peripheral surface. The first to third molding portions 14 a 1, 14 a 2, 14 a 3 are configured to follow the inner peripheral surface shape of the sintered bearing 1. The first molding part 14a and the second molding part 14a2, and the second molding part 14a2 and the third molding part 14a3 are connected at the corners, respectively. The core pin 14 further includes a protruding portion 14a4 having a larger diameter than the third molded portion 14a3 adjacent to the proximal end side of the third molded portion 14a3. This protrusion 14a4 is provided in order to prevent the raw material powder from entering the inner periphery of the lower punch 12 when filling the raw material powder described later. However, the outer diameter dimension of the protrusion 14a4 is the maximum outer diameter of the inner peripheral surface molding portion 14a (that is, the second molding portion so that the axial movement of the lower punch 12 and the core pin 14 is not hindered by providing this. 14a2), which is the same as or slightly larger in diameter. In addition, when the green compact 1 ′ is formed, a partial region on the upper end side of the core pin 14 is introduced into the inner periphery of the upper punch 11 (see FIG. 3B). Therefore, the total length of the first molding portion 14a1 of the core pin 14 is longer by a predetermined amount than the axial dimension of the region to be the first bearing surface 2 to be molded.

  The manufacturing apparatus 10 used in the compacting process mainly has the above-described configuration, and the compact 1 'is compression-molded in the following manner.

  First, as shown in FIG. 3A, the lower punch 12 is lowered, and a powder filling portion 15 having a predetermined volume is formed by the inner peripheral surface 13 a of the die 13, the upper end surface 12 b of the lower punch 12, and the outer peripheral surface of the core pin 14. The raw material powder 16 is filled in the powder filling portion 15. The raw material powder 16 is filled up to substantially the same height as the upper end surface 13 b of the die 13. The filling of the raw material powder 16 into the powder filling unit 15 is gradually performed in a manner corresponding to the volume increase amount of the powder filling unit 15 (the descending amount of the lower punch 12). If the raw material powder 16 is filled at a time after the powder filling portion 15 having a predetermined volume is formed, excess air or the like is mixed in the powder filling portion 15 (between individual raw material powders 16), and the green compact has a uniform density. This is because 1 'may not be molded. Since the powder filling portion 15 is formed by lowering the lower punch 12 with respect to the core pin 14, the overall configuration of the manufacturing apparatus 10 is simplified compared to the conventional configuration shown in FIG. .

  In the filling stage of the raw material powder 16, the protruding portion 14 a 4 of the core pin 14 is always disposed on the inner periphery of the lower punch 12. By doing in this way, the situation where the raw material powder 16 enters between the inner peripheral surface 12a of the lower punch 12 and the outer peripheral surface of the core pin 14 can be avoided as much as possible, and the green compact 1 ′ having a predetermined shape can be accurately obtained. Can be molded. The raw material powder 16 is mainly composed of a metal powder such as Fe, Fe-based alloy, Cu, Cu-based alloy, a binder such as Sn, and a solid lubricant such as graphite or molybdenum disulfide as necessary. The added one is used.

  By the way, when the density difference between the both ends of the sintered bearing 1 becomes large, there is a possibility that the supporting ability becomes unstable. Therefore, in the filling stage of the raw material powder 16, the lower end of the powder filling portion 15 (upper end surface 12 b of the lower punch 12) is connected to the core pin 14 by the axial dimension substantially equal to the compression amount of the raw material powder 16 by the upper punch 11. The compression amount in the compression stage of the raw material powder 16 shown in FIG. 3B is made substantially equal in the vertical direction so as to be positioned below the boundary portion between the three molded portions 14a3 and the protruding portions 14a4.

  That is, in this embodiment, after filling the raw material powder 16 into the powder filling unit 15, the upper punch 11 is lowered and the lower punch 12 is raised at the same time (the upper punch 11 and the lower punch 12 are relatively moved closer to each other). ) To uniformly pressurize the raw material powder 16 filled in the powder filling unit 15 from both ends (see FIG. 3B). Thereby, the green compact 1 'fixed to the outer periphery of the inner peripheral surface molding portion 14a of the core pin 14 is obtained. Since the green compact 1 ′ is molded as described above, the density between both ends is substantially equal.

  After the green compact 1 ′ is formed as described above, the green compact 1 ′ is moved from the inner periphery of the die 13 by raising both punches 11 and 12 and the core pin 14 while maintaining this state. Take out (release the radial pressure applied to the green compact 1 '). Then, as shown in FIG. 3 (c), when the upper punch 11 is further raised to release the axial pressure applied to the green compact 1 ′, it is accumulated inside the green compact 1 ′. The elastic restoring force that has been released is released, and a spring back is generated in the green compact 1 ′. As a result, the inner peripheral surface of the green compact 1 ′ expands in diameter. Is separated. At this time, a minute radial gap is formed between the inner peripheral surface of the green compact 1 ′ and the inner peripheral surface molding portion 14 a of the core pin 14. The gap width is such that it can be pulled out without contact with the inner peripheral surface of the green compact 1 ′. This is because when the core pin 14 is pulled out from the inner periphery of the green compact 1 ′, the core pin 14 is pulled out so-called forcibly so that the inner peripheral surface of the green compact 1 ′ is not damaged.

  Specifically, a minute radial gap is formed between the minimum inner diameter portion of the inner peripheral surface of the green compact 1 ′ and the maximum outer diameter portion (here, the second molding portion 14 a 2) of the core pin 14. In such a radial clearance, the spring back amount (expansion amount) of the inner peripheral surface of the green compact 1 ′ is larger than the radial dimension difference between the second molded portion 14 a 2 and the third molded portion 14 a 3 of the core pin 14. Thus, it can be obtained by adjusting the pressing force, the composition of the raw material powder 16, and the like.

  After the radial gap is formed between the outer peripheral surface of the core pin 14 and the inner peripheral surface of the green compact 1 ′ as described above, the core pin 14 is lowered as shown in FIG. When the core pin 14 is pulled out from the inner periphery of the body 1 ', a green compact 1' having a predetermined shape is completed. From the above-described configuration, the core pin 14 can be pulled out of contact with the inner peripheral surface of the green compact 1 ′, and therefore the inner peripheral surface of the green compact 1 ′ is damaged as the core pin 14 is pulled out. Absent. The green compact 1 'is transferred to the sintering process.

  In the present embodiment, after the green compact 1 ′ is taken out from the inner periphery of the die 13 (after the radial pressure is released), the axial pressure applied to the green compact 1 ′ is applied. Although it was made to cancel, you may take the reverse procedure. That is, the upper punch 11 is first lifted to release the axial pressure, and then the lower punch 12 and the core pin 14 are lifted together to take out the green compact 1 ′ from the inner periphery of the die 13 (radial direction). The pressure may be released).

(B) Sintering Step In this sintering step, the green compact 1 ′ obtained in the green compacting step is heated to the sintering temperature of the used metal powder to obtain a sintered body 1 ″. Depending on the type of metal powder used, the sintering operation may be performed in a non-carburizing atmosphere in order to avoid carburizing by sintering.

(C) Sizing Step In this sizing step, an appropriate pressing force is applied to the sintered body 1 ″ obtained in the sintering step to size the sintered body 1 ″. 4 (a) and 4 (b) conceptually show a sizing process. Specifically, FIG. 4 (a) is a cross-sectional view showing a stage immediately before sizing, and FIG. 4 (b) is a cross-sectional view during sizing. Respectively.

  The sizing device 20 shown in the figure corresponds to a cylindrical die 23 for press-fitting the outer peripheral surface of the sintered body 1 ″, and the inner peripheral surface of the sintered body 1 ″ (strictly speaking, it corresponds to the bearing surface of the inner peripheral surface. A core rod 24 for forming a region, that is, a region on both ends of the middle escape portion), and an upper punch 21 and a lower punch 22 for restraining both end surfaces of the sintered body 1 ″ are provided as main components. The surface 23a and the outer peripheral surface 24a of the core rod 24 are made constant in diameter.In this manufacturing apparatus 20, the die 23 is on the stationary side, and both punches 21 and 22 and the core rod 24 are moved up and down by an appropriate drive mechanism (not shown). Specifically, the upper punch 21 is extrapolated to the outer periphery of the core rod 24, and both can be lifted and lowered independently, and the lower punch 22 can be lifted and lowered independently of the upper punch 21 and the core rod 24. It is.

  In the sizing apparatus 20 having the above configuration, first, as shown in FIG. 4A, the sintered body 1 ″ is disposed on a predetermined portion in the apparatus, here, the lower punch 22. From this state, the upper punch 21 is disposed. Then, the core rod 24 is lowered, and the core rod 24 is inserted into the inner periphery of the sintered body 1 ″, and both end faces of the sintered body 1 ″ are constrained by the upper punch 21 and the lower punch 22. This state is maintained. If the upper punch 21, the lower punch 22, and the core pin 27 are moved downward together and the sintered body 1 "is press-fitted into the inner periphery of the die 23 as shown in FIG. 4B, the sintered body 1" As a result, the one end side region and the other end side region of the inner peripheral surface of the sintered body 1 ″ are pressed against the outer peripheral surface 24a of the core rod 24. The surface layer of the region causes plastic flow and the core A nip on the outer circumferential surface 24a of the head 24, a predetermined bearing surfaces 2,4 is molded.

  After sizing the sintered body 1 ″ as described above, the upper punch 21, the lower punch 22 and the core rod 24 are moved up in conjunction with this state, and the sintered body 1 is moved from the die 23. "Take out. Next, when the upper punch 21 and the core rod 24 are further raised, the elastic restoring force accumulated in the sintered body 1 ″ is released, and the inner diameter dimension of the sintered body 1 ″ is expanded (spring back). A minute radial gap is formed between the inner peripheral surface of the body 1 ″ and the outer peripheral surface of the core rod 24. When the core rod 24 is extracted, the sintered bearing 1 in the finished product shape is obtained. Since the core rod 24 used has a uniform outer diameter, the bearing surfaces 2 and 4 of the sintered body 1 ″ (sintered bearing 1) sized as described above and the region between the bearing surfaces (medium) The surface portion is different from the escape portion 3). Specifically, the bearing surfaces 2 and 4 are subjected to a crushing process, and the surface open area ratio becomes smaller than that of the middle escape portion 3. Then, the released sintered bearing 1 is transferred to the oil impregnation process.

(D) Oil impregnation step In this step, the sintered bearing 1 formed into a predetermined shape through the sizing step is impregnated with the lubricating oil, thereby completing the sintered bearing 1 in which the internal pores are impregnated with the lubricating oil. The impregnation of the lubricating oil into the internal pores of the sintered body bearing 1 is performed, for example, by immersing the sintered bearing 1 in a lubricating oil bath filled with the lubricating oil for a certain period of time in a predetermined reduced pressure environment. Is called. At this time, in order to perform the impregnation of the lubricating oil reliably and in a short time, the impregnation operation may be performed while the lubricating oil is heated.

  As described above, in the sintered bearing 1 according to the present invention, the entire intermediate relief portion 3 is formed by the spring back generated by releasing the pressing force at the time of compacting, and the bearing surfaces 2 and 4 are formed. And corner portions 3d and 3e where the middle escape portion 3 intersects. That is, as described above, the entire inner relief portion 3 is formed as a molding surface that is molded following the inner peripheral surface molding portion 14a (second molding portion 14a2) of the core pin 14, and the core pin 14 is compacted. It means that the green compact 1 'is pulled out from the inner periphery of the body 1' in a non-contact manner. Therefore, it is possible to avoid the occurrence of variations in the shape of the middle escape portion 3 among individuals, and to finish the middle escape portion 3 with high accuracy. Moreover, since the surface properties (surface open area ratio, etc.) of the entire middle escape portion 3 can be homogenized, a difference occurs in the amount of oil supplied to the two sliding portions formed between the shaft, It is possible to prevent as much as possible a situation in which a difference occurs in the support capability between both sliding portions. Therefore, the support capability of the sintered bearing 1 is stably increased.

  Further, since a shape substantially equal to the finished product shape can be obtained only by the molding process of the green compact 1 ′, the process and apparatus are compared with Patent Document 1 in which the finished product shape is obtained by drawing in the sizing process. The number of steps can be reduced compared to the configuration of Patent Document 2 in which the configuration is simplified, or alternatively, the compacting step is performed in two steps to obtain a finished product shape. Further, since the green compact 1 ′ is separated from the core pin 14 by utilizing the spring back of the green compact 1 ′ by releasing the applied pressure, no other separation mechanism is required. In particular, in the drawing process as in Patent Document 1, it is necessary to take a relatively long bearing length in order to obtain a predetermined finished product shape. Nor. From the above, the manufacturing cost of the sintered bearing 1 can be reduced.

  In addition, since the sizing is applied only to both the bearing surfaces 2 and 4, while ensuring high oil film rigidity at the sliding portion with the shaft, the sliding portion with the shaft has a relatively large surface opening ratio. Abundant oil can be supplied from the escape portion 3. Thereby, high bearing performance can be maintained stably. Further, since the sizing is performed only on both the bearing surfaces 2 and 4, the sizing process and the sizing device can be simplified, and the manufacturing cost can be further reduced.

  In the above, the case where the present invention is applied at the time of manufacturing a sintered bearing having a uniform outer diameter has been described. However, the form of the sintered bearing described above is merely an example, and the configuration of the present invention is not limited to the outer diameter. It is of course possible to apply to sintered bearings whose dimensions are different in the axial direction. The present invention is suitable not only for manufacturing sintered bearings that rotate relative to the shaft, but also for manufacturing sintered bearings that move linearly relative to the shaft, and this type of sintered bearing. is there.

It is sectional drawing which shows notionally an example of the sintered bearing which concerns on this invention. It is sectional drawing which shows notionally the whole structure of the manufacturing apparatus used at a compaction process. The flow of a compacting process is shown conceptually. (A) is a cross-sectional view of the stage where the raw material powder is filled in the powder filling part, (b) is a cross-sectional view of the compacting stage, and (c) is the pressure Sectional drawing of the stage after powdering, (d) is a sectional view of the stage where each component of the apparatus has returned to the origin. The flow of a sizing process is shown notionally, (a) A figure is a sectional view of the stage which has arranged a sintered compact in an apparatus, and (b) figure is a sectional view of the stage which performs sizing to a sintered compact. . FIG. 1 conceptually shows a manufacturing process of a sintered bearing that has been conventionally employed. FIG. 1A is a sectional view conceptually showing a second compacting process, and FIG. 2B is a conceptual view showing a sizing process. It is sectional drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sintered bearing 1 'Compact 1 "Sintered body 2, 4 Bearing surface 3 Middle escape part 3a Large diameter inner peripheral surface 3b, 3c Step surface 3d, 3e Corner | angular part 10 Manufacturing apparatus (for compacting processes)
12 Lower punch 14 Core pin 14a Inner peripheral surface molding part 14a2 Second molding part 14a4 Projection part 15 Powder filling part 16 Raw material powder

Claims (10)

A bearing surface is provided at two locations in the axial direction of the inner peripheral surface that are sintered with the green compact, and an inner clearance portion having an inner diameter dimension larger than the bearing surface is formed between the bearing surfaces. A sintered bearing comprising:
Sintering characterized in that the entire center relief part is formed in a predetermined shape by the springback generated by releasing the pressing force during compacting, and has a corner where the bearing surface and the center relief part intersect bearing.   The sintered bearing according to claim 1, wherein the surface properties of the bearing surface and the intermediate relief portion are different. A bearing surface is provided at two locations in the axial direction of the inner peripheral surface that are sintered with the green compact, and an inner clearance portion having an inner diameter dimension larger than the bearing surface is formed between the bearing surfaces. A method for producing a sintered bearing comprising:
Forming a powder filling part on the outer periphery of the core pin, and pressing the raw material powder filled in the powder filling part to form a green compact fixed to the outer periphery of the core pin;
A step of separating the green compact from the core pin using springback generated in the green compact by releasing the pressure, and then pulling the core pin out of contact with the inner peripheral surface of the green compact;
The manufacturing method of the sintered bearing characterized by including.   The core pin is inserted into the inner periphery of the lower punch so as to be axially movable relative to the cylindrical lower punch, and the powder filling portion is formed by relative movement of the core pin and the lower punch in the axial direction. Method for manufacturing a sintered bearing.   The method for manufacturing a sintered bearing according to claim 4, wherein filling of the raw material powder into the powder filling portion is gradually performed in accordance with an axial relative movement amount of the core pin and the lower punch. Adjacent to the base end side of the inner peripheral surface molding portion provided on the outer peripheral surface of the core pin, a protrusion having an outer diameter dimension equal to or larger than the maximum outer diameter of the inner peripheral surface molding portion is provided.
The method for manufacturing a sintered bearing according to claim 4 or 5, wherein the raw material powder is filled in the powder filling portion in a state where the protruding portion is disposed on the inner periphery of the lower punch.   The manufacturing method of the sintered bearing in any one of Claims 3-6 which pressurize equally the raw material powder with which the powder filling part was filled from the both ends side.   The method for manufacturing a sintered bearing according to any one of claims 3 to 7, wherein the axial pressure is released after the radial pressure is released.   The method for manufacturing a sintered bearing according to any one of claims 3 to 7, wherein the radial pressure is released after the axial pressure is released.   After the core pin is pulled out of the green compact, the green compact is sintered, and a step of forming a bearing surface by sizing one end side region and the other end side region of the inner peripheral surface of the obtained sintered body is further performed. The manufacturing method of the sintered bearing in any one of Claims 3-9 containing.

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