WO2016147928A1

WO2016147928A1 - Housing, fluid dynamic pressure bearing device with same, and method for manufacturing housing

Info

Publication number: WO2016147928A1
Application number: PCT/JP2016/056958
Authority: WO
Inventors: 柴原　克夫
Original assignee: Ntn株式会社
Priority date: 2015-03-17
Filing date: 2016-03-07
Publication date: 2016-09-22

Abstract

The present invention relates to a housing (7) for a fluid dynamic bearing device, the housing (7) being a product which is formed by injection molding a resin, the housing (7) integrally having a cylindrical side section (7a) and a bottom section (7b) which closes one axial end of the side section (7a). The housing (7) has a gate mark (7b30) comprising a surface formed by a closure member (27) for closing an injection gate (26). The present invention also relates to a fluid dynamic pressure bearing device having the housing (7) and to a motor having the fluid dynamic pressure bearing device. The present invention further relates to a method for manufacturing the housing (7), the method having: a step in which a molten resin within a runner is injected into a cavity (23) through the injection gate (26); a step in which the injection gate (26) is closed by the closure member (27) to separate the molten resin within the runner (25) and the molten resin having been introduced into the cavity (23); and a step in which the molten resin having been introduced into the cavity (23) is cooled and solidified.

Description

Housing, fluid dynamic bearing device including the same, and method of manufacturing housing

The present invention relates to a resin housing used for a fluid dynamic bearing device and a method for manufacturing the same.

The fluid dynamic pressure bearing device supports the shaft member in a non-contact manner so as to be relatively rotatable by pressure generated in a fluid film (for example, an oil film) in a radial bearing gap between the outer peripheral surface of the shaft member and the inner peripheral surface of the bearing member. It is. Due to its high rotational accuracy and quietness, the fluid dynamic pressure bearing device has a spindle motor of an information device (for example, a magnetic disk drive device of an HDD), a polygon scanner motor of a laser beam printer, a color wheel of a projector, or an electric device. It is suitably used for small motors such as cooling fan motors.

The fluid dynamic pressure bearing device has, for example, a configuration including a shaft member, a bearing sleeve in which the shaft member is inserted in the inner periphery, and a bottomed cylindrical housing in which the bearing sleeve is fixed on the inner peripheral surface. In recent years, fluid dynamic bearing devices have been required to be further reduced in weight and cost, and in order to meet this requirement, a bottomed cylindrical housing may be integrally injection molded with resin. For example, in Patent Document 1 below, as shown in FIG. 15, a molten resin P is injected into a cavity from a runner 110a provided in a molding die through a gate 110b, thereby providing a bottomed cylindrical housing. A method of forming 107 is shown. In this case, in the state before the mold opening, as shown in the figure, the resin solidified in the runner 110a (runner resin portion) and the molded product (housing 107) are solidified in the gate 110b (gate resin portion). However, by performing mold opening, the gate resin portion is torn off, and the runner resin portion and the housing 107 are separated.

Thus, by sharpening the gate resin portion, sharp irregularities made of a filler or a resin piece are formed on the cross section. When a housing having such a sectional surface is incorporated into a fluid dynamic pressure bearing device, a filler, a resin piece, etc. dropped from the sectional surface may be mixed as contamination in the lubricating oil filled in the housing.

In the following Patent Document 1, the occurrence of contamination is suppressed by pressing and smoothing a jig on the split surface (gate trace) of the gate resin portion remaining in the molded product (housing).

Japanese Patent No. 4808457

However, if the step of pressing the jig against the gate trace of the housing is provided as described above, the manufacturing cost of the housing increases due to an increase in man-hours. Further, even if the jig is pressed to smooth the gate trace, it cannot be said that the falling of the filler or the resin piece can be reliably prevented, and the concern about the occurrence of contamination cannot be solved.

In addition, when the gate resin part is torn off by mold opening, the axial position of the gate mark varies. For example, if the gate resin portion is cut at a position deviated toward the runner resin portion, the gate mark protrudes greatly from the bottom of the housing, so that the gate mark may interfere with other members. On the other hand, if a part of the material at the bottom of the housing is taken to the runner resin portion side when the mold is opened, the gate mark is formed in a concave shape at the bottom of the housing, which may cause insufficient strength. Even when the gate trace is smoothed with a jig as described above, the variation in the axial position of the gate trace cannot be suppressed, and the problems associated therewith cannot be solved.

When the resin includes a fibrous filler, as shown in FIG. 16, when the housing 107 and the runner resin portion are separated by performing mold opening, the material of the bottom portion 107b of the housing 107 is taken by the runner resin portion. Thus, not only the recess 130 is formed, but also the fibrous filler 120 contained in the resin of the bottom 107b may be pulled out. A hole penetrating the bottom 107b of the housing 107 is formed by the recess 130 formed in the bottom 107b and the trace 140 from which the fibrous filler is pulled out, and the inside of the housing 107 is filled through this hole. Oil may leak out. In particular, when the bottom portion 107b is thinned in order to further reduce the size and weight of the housing (for example, when the thickness of the shaft center of the bottom portion 107b is 1 mm or less), the above-mentioned concern becomes remarkable.

In view of the circumstances as described above, the technical problem to be solved by the present invention is to prevent the occurrence of contamination in the injection molding of a bottomed cylindrical housing with resin, and the axial position of the gate mark. Is managed with high accuracy to avoid interference with other members and strength reduction.

In addition, another technical problem to be solved by the present invention is that when a housing having a bottomed cylindrical shape is injection-molded with resin, a situation in which a hole penetrating the housing is formed is avoided, and the inside of the housing is filled. It is to reliably prevent leakage of the lubricating fluid (for example, oil) to the outside.

In order to solve the above-mentioned problems, the present invention provides a method for manufacturing a housing for a fluid dynamic bearing device integrally including a cylindrical side portion and a bottom portion that closes one axial end of the side portion. A step of injecting the molten resin in the runner into the cavity through the injection gate, and closing the injection gate with a closing member, thereby the molten resin in the runner and the molten resin filled in the cavity There is provided a method of manufacturing a housing, comprising a step of dividing, and a step of cooling and solidifying a molten resin filled in the cavity.

The present invention also provides a housing for a fluid dynamic bearing device, which is integrally molded with a cylindrical side portion and a bottom portion that closes one axial end of the side portion, and is injection-molded with resin. Provided is a housing having a gate mark made of a surface.

As described above, in the housing manufacturing method according to the present invention, after injecting the molten resin into the cavity, the injection gate is closed with the closing member (needle valve), so that the molten resin in the cavity and the molten resin in the runner are Divide. Thus, after the molten resin in the cavity is cooled and solidified, when the mold is opened, the boundary between the resin solidified in the cavity (housing) and the resin solidified in the runner is not torn. Can be separated. At this time, by molding the gate trace of the housing with the closing member, the gate trace becomes a smooth molding surface that follows the closing member, so that the filler and the resin piece can be reliably prevented from falling off. Moreover, the axial position of the gate trace can be managed with high accuracy by setting the axial position of the closing member with high accuracy.

In the above case, when the mold is opened after the molten resin in the cavity is cooled and solidified, the resin (housing) solidified in the cavity and the resin solidified in the runner are already separated. . For this reason, at the time of mold opening, a part of the material of the housing is not torn off and taken by the runner resin portion, and the fibrous filler contained in the resin of the housing is not pulled out. Therefore, even when the bottom portion of the housing 7 is thinned (specifically, when the thickness of the gate mark forming portion is 1 mm or less), it is ensured that a hole penetrating the bottom portion is formed. Can be prevented.

The injection gate is preferably provided on the axis of the molding surface for molding the end surface of the bottom of the housing. By injecting the molten resin from the injection gate, the molten resin can be uniformly distributed to the bottom and sides of the housing, and the formation of a weld line can be avoided. In this case, the gate mark is provided on the axial center of the end surface of the bottom of the housing.

The fluid dynamic pressure bearing device according to the present invention includes the above housing, a bearing sleeve fixed to the inner peripheral surface of the side portion of the housing, a shaft member inserted into the inner periphery of the bearing sleeve, and the bearing sleeve. A radial bearing portion that supports the shaft member in a radial direction with a fluid pressure in a radial bearing gap formed between an inner peripheral surface of the shaft member and an outer peripheral surface of the shaft member; an end surface of the shaft member; and a bottom portion of the housing A thrust bearing portion that supports the shaft member in the axial direction with a fluid pressure in a thrust bearing gap formed between the end face on the inner side.

In this fluid dynamic pressure bearing device, since the bottom of the housing is in contact with the high-pressure lubricating fluid filled in the thrust bearing gap, it is preferable to provide a gate mark made of a molding surface to reliably prevent the formation of a through hole. . In particular, when a thrust dynamic pressure generating portion that generates a dynamic pressure action on the lubricating fluid filled in the thrust bearing gap is formed on the end face of the shaft member or the inner end face of the bottom of the housing, the thrust bearing gap It is more preferable to apply the present invention because the fluid pressure of the gas is further increased.

As described above, according to the present invention, it is possible to reliably prevent the occurrence of contamination due to the dropping of the filler and the resin piece, and to manage the axial position of the gate trace with high accuracy, so that the gate trace and the other member Problems such as insufficient strength due to interference and formation of recesses can be avoided.

Further, according to the present invention, by forming the gate trace formed in the housing with the closing member, a situation in which a through hole is formed in the gate trace formation portion of the housing is avoided, and fluid leakage from the inside of the housing is ensured. Can be prevented.

It is sectional drawing of the spindle motor incorporating the fluid dynamic pressure bearing apparatus. It is sectional drawing of the said fluid dynamic pressure bearing apparatus provided with the housing which concerns on one Embodiment of this invention. It is sectional drawing of the bearing sleeve provided in the said fluid dynamic pressure bearing apparatus. It is a bottom view of the said bearing sleeve. It is a top view of the housing. It is sectional drawing of gate vicinity vicinity of the said housing. It is sectional drawing of the metal mold | die which carries out the injection molding of the said housing, and shows the state before inject | pouring molten resin in a cavity. It is sectional drawing of the said metal mold | die, and shows the state with which the cavity was filled with molten resin. It is sectional drawing of the cavity in the XX line of FIG. 8A, and shows the state which filled the molten resin in the cavity. It is sectional drawing which shows the state which obstruct | occluded the gate of the said metal mold | die with the needle valve. It is an expanded sectional view showing a state before inserting a needle valve into a gate. It is an expanded sectional view which shows the state which inserted the needle valve in the gate. It is sectional drawing which shows the state which opened the said metal mold | die. It is an expanded sectional view near the gate mark of the housing concerning other embodiments of the present invention. It is an expanded sectional view near the gate mark of the housing concerning other embodiments of the present invention. It is sectional drawing of the housing which concerns on other embodiment of this invention. It is sectional drawing which shows the state which filled the cavity of the injection mold of the conventional housing with the molten resin. FIG. 16 is a cross-sectional view showing a state where the injection mold shown in FIG. 15 is opened and the resin in the runner and the resin in the cavity are separated.

1 to 6, a case where a fluid dynamic bearing device having a housing 7 according to an embodiment of the present invention is incorporated in a spindle motor of an HDD disk drive device will be described.

A spindle motor shown in FIG. 1 includes a fluid dynamic pressure bearing device 1, a disk hub 3 fixed to a shaft member 2 of the fluid dynamic pressure bearing device 1, a stator coil 4 and a rotor magnet opposed to each other via a radial gap. 5 and a bracket 6. The stator coil 4 is fixed to the bracket 6, and the rotor magnet 5 is fixed to the disk hub 3. A housing 7 of the fluid dynamic bearing device 1 is fixed to the inner peripheral surface of the bracket 6. The disc hub 3 holds a predetermined number (two in the illustrated example) of discs D. When the stator coil 4 is energized, the rotor magnet 5 rotates, and accordingly, the disk D held on the disk hub 3 rotates integrally with the shaft member 2.

As shown in FIG. 2, the fluid dynamic bearing device 1 includes a bearing sleeve 8, a shaft member 2 inserted into the inner periphery of the bearing sleeve 8, and a bottomed cylindrical shape in which the bearing sleeve 8 is fixed to the inner peripheral surface. The housing 7 and a seal member 9 disposed in the opening of the housing 7 are provided. In the following description of the fluid dynamic bearing device 1, the opening side of the housing 7 in the axial direction is referred to as “upward” and the opposite side is referred to as “downward”. .

The shaft member 2 is formed of a metal material such as stainless steel. The shaft member 2 includes a shaft portion 2a and a flange portion 2b provided at the lower end of the shaft portion 2a. The outer peripheral surface of the shaft portion 2a is formed in two axially spaced locations, cylindrical surfaces 2a1, 2a2 that are radially opposed to a radial bearing surface of a bearing sleeve 8 to be described later, and the axial directions of the cylindrical surfaces 2a1, 2a2. An escape portion 2a3 having a smaller diameter than the cylindrical surfaces 2a1 and 2a2 and a tapered surface 2a4 provided above the cylindrical surface 2a1 and having a diameter reduced toward the upper side are formed. The outer diameter of the shaft portion 2a (in particular, the outer diameter of the cylindrical surfaces 2a1 and 2a2) is, for example, about 1 to 4 mm.

The bearing sleeve 8 has a cylindrical shape, and is formed of, for example, a sintered metal, specifically, a copper-based, iron-based, or copper-iron-based sintered metal. On the inner peripheral surface 8a of the bearing sleeve 8, radial bearing surfaces are provided in two regions separated vertically, and a radial dynamic pressure generating portion is formed on each radial bearing surface. In the present embodiment, herringbone shaped dynamic pressure grooves 8a1 and 8a2 as shown in FIG. 3 are formed as radial dynamic pressure generating portions. The region indicated by cross-hatching in the figure represents a hill that is raised to the inner diameter side than the other regions (hereinafter the same). In the illustrated example, the dynamic pressure groove 8a1 formed on the upper radial bearing surface has an asymmetric shape in the axial direction. Specifically, the dynamic pressure groove 8a1 above the annular hill portion provided substantially at the center in the axial direction. The axial dimension L1 is larger than the axial dimension L2 of the dynamic pressure groove 8a1 below the annular hill. On the other hand, the dynamic pressure groove 8a2 formed on the lower radial bearing surface has an axially symmetric shape.

The lower end surface 8b of the bearing sleeve 8 functions entirely as a thrust bearing surface, and a thrust dynamic pressure generating portion is formed on the thrust bearing surface. In the present embodiment, a spiral dynamic pressure groove 8b1 as shown in FIG. 4 is formed as the thrust dynamic pressure generating portion. The illustrated dynamic pressure groove 8b1 is a pump-in type that pushes the lubricating fluid into the inner diameter side. As shown in FIG. 3, an annular groove 8d1 and a plurality of radial grooves 8d2 provided on the inner diameter side of the annular groove 8d1 are formed on the upper end surface 8d of the bearing sleeve 8. As shown in FIGS. 3 and 4, a plurality (three in the illustrated example) of axial grooves 8 c 1 are provided on the outer peripheral surface 8 c of the bearing sleeve 8 at equal intervals in the circumferential direction.

The housing 7 is a resin injection molded product having a bottomed cylindrical shape. As shown in FIG. 2, the housing 7 of the present embodiment integrally includes a cylindrical side portion 7 a and a disc-shaped bottom portion 7 b that closes the opening at the lower end of the side portion 7 a. A thrust bearing surface that forms a thrust bearing gap is provided on the upper end surface 7b1 of the bottom 7b, and a thrust dynamic pressure generating portion is provided on the thrust bearing surface. In the present embodiment, a spiral dynamic pressure groove 7b10 as shown in FIG. 5 is formed as the thrust dynamic pressure generating portion. The illustrated dynamic pressure groove 7b10 is a pump-in type that pushes the lubricating oil filled in the thrust bearing gap into the inner diameter side. Of the upper end surface 7b1 of the bottom portion 7b, a recess 7b2 is provided in a region on the inner diameter side of the thrust bearing surface (formation region of the dynamic pressure groove 7b10). A recess 7b4 is provided in the axial center of the lower end surface 7b3 of the bottom 7b (see FIG. 2). The housing 7 in the illustrated example has a thickness of 2 mm or less, preferably 1 mm or less, more preferably 0.8 mm or less, at a formation portion (axial center in the illustrated example) of a gate mark 7b30 described later in the bottom portion 7b of the housing 7. It has become. In the illustrated example, the thickness of the bottom 7b is the thinnest at the axial center. Moreover, in order to ensure intensity | strength, it is preferable that the thickness of a bottom part shall be 0.3 mm or more.

On the surface of the housing 7, a gate mark 7b30 is provided. In this embodiment, the gate mark 7b30 is provided on the lower end surface 7b3 of the bottom 7b of the housing 7. Specifically, as shown in FIG. 2, the axis of the lower end surface 7 b 3 of the bottom 7 b of the housing 7, more specifically, the axis of the recess 7 b 4 provided on the lower end surface 7 b 3 of the bottom 7 b A gate trace 7b30 of the gate is provided. The gate mark 7b30 is continuously provided on the same plane as a region adjacent to the outer diameter side (the bottom surface of the recess 7b4 in the illustrated example).

The gate mark 7b30 is a molding surface formed by the front end surface of a closing member (needle valve) to be described later. That is, the gate mark 7b30 is not a surface cut after the resin is solidified or a surface subjected to post-processing (molding or machining) after cutting, but a molded surface formed simultaneously with the injection molding of the housing 7. . In addition, as shown in FIG. 6, in the region where the gate trace 7 b 30 is formed in the lower end surface 7 b 3 of the bottom 7 b, the fibrous filler 10 is pushed into the inside, and the dotted line in the figure There is no fibrous filler 10 ′ protruding from the surface of the housing 7 as shown in FIG.

The resin forming the housing 7 is mainly a thermoplastic resin, for example, a crystalline resin, specifically, a liquid crystal polymer (LCP), polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), polyether ether ketone (PEEK). ) Etc. can be used. For example, a fibrous filler such as glass fiber or carbon fiber is blended with the above resin, and in this embodiment, carbon fiber is blended. The average fiber length of the carbon fibers is, for example, 100 to 200 μm. The carbon fibers of the present embodiment include those having a fiber length longer than the thickness in the axial direction at the gate mark 7b30 formation portion (axial center in the illustrated example) of the bottom 7b of the housing 7. The average diameter of the carbon fiber is, for example, 6 to 8 μm. The blending ratio of the carbon fiber to the resin is, for example, 5 to 40 wt%. The filler to be blended into the resin is not limited to the above, but instead of the fibrous filler or in addition to the fibrous filler, glass flakes, glass beads, metal powder, carbon black, graphite, carbon nanomaterial, etc. You may mix | blend. The fillers shown above can be blended alone or in admixture of two or more.

The seal member 9 is formed in an annular shape with resin or metal, and is fixed to the upper end portion of the inner peripheral surface 7a1 of the side portion 7a of the housing 7 (see FIG. 2). The lower end surface 9 b of the seal member 9 is in contact with the upper end surface 8 d of the bearing sleeve 8. The inner peripheral surface 9a of the seal member 9 is opposed to the tapered surface 2a4 provided on the outer peripheral surface of the shaft portion 2a in the radial direction, and a wedge-shaped seal space in which the radial dimension is gradually reduced downward therebetween. S is formed. When the shaft member 2 rotates, the seal space S functions as a capillary force seal and a centrifugal force seal, and prevents leakage of the lubricating oil filled in the housing 7 to the outside.

潤滑 Lubricating oil as a lubricating fluid is injected into the fluid dynamic bearing device 1 composed of the above components. Thereby, the internal space of the fluid dynamic bearing device 1 including the internal holes of the bearing sleeve 8 is filled with the lubricating oil, and the oil level is always maintained within the range of the seal space S. In addition to the lubricating oil, grease or magnetic fluid may be used as the lubricating fluid.

When the shaft member 2 rotates, a radial bearing gap is formed between the inner peripheral surface 8a (radial bearing surface) of the bearing sleeve 8 and the outer peripheral surface (cylindrical surfaces 2a1, 2a2) of the shaft portion 2a. Then, the pressure of the oil film in the radial bearing gap is increased by the dynamic pressure grooves 8a1 and 8a2 formed on the inner peripheral surface 8a of the bearing sleeve 8, and the first radial bearing portion R1 that rotatably supports the shaft member 2 in a non-contact manner. A second radial bearing portion R2 is configured.

At the same time, a thrust bearing gap is formed between the upper end surface 2b1 of the flange portion 2b and the lower end surface 8b (thrust bearing surface) of the bearing sleeve 8, and the lower end surface 2b2 of the flange portion 2b and the housing 7 A thrust bearing gap is formed between the upper end surface 7b1 (thrust bearing surface) of the bottom portion 7b. Then, the dynamic pressure groove 8b1 formed on the lower end surface 8b of the bearing sleeve 8 and the dynamic pressure groove 7b10 formed on the upper end surface 7b1 of the bottom 7b of the housing 7 increase the pressure of the oil film in each thrust bearing gap. The first thrust bearing portion T1 and the second thrust bearing portion T2 are configured to support the shaft member 2 in a non-contact manner so as to be rotatable in both thrust directions.

In the present embodiment, the space on the outer diameter side of the flange portion 2b of the shaft member 2 is sealed via the axial groove 8c1 of the outer peripheral surface 8c of the bearing sleeve 8, the annular groove 8d1 and the radial groove 8d2 of the upper end surface 8d. It communicates with the space S. Thereby, the space on the outer diameter side of the flange portion 2b is always in a state close to atmospheric pressure, and generation of negative pressure in this space can be prevented. In particular, in this embodiment, since the dynamic pressure grooves 8a1 and 8a2 formed in the upper region of the inner peripheral surface 8a of the bearing sleeve 8 have an axially asymmetric shape, the lubrication of the radial bearing gap with the rotation of the shaft member 2 is performed. A pumping force that pushes oil downward is generated. As a result, the lubricating oil circulates in the path of the radial bearing gap → the thrust bearing gap of the first thrust bearing portion T1 → the axial groove 8c1 → the annular groove 8d1 and the radial groove 8d2 → the radial bearing gap. It is possible to reliably prevent local negative pressure from being generated in the filled lubricating oil.

Hereinafter, a manufacturing method (injection molding method) of the housing 7 will be described with reference to FIGS.

As shown in FIG. 7, the mold 20 for injection molding the housing 7 includes a fixed mold 21 and a movable mold 22. The movable mold 22 moves in the vertical direction in the figure, and the cavity 23 is formed by clamping the fixed mold 21 and the movable mold 22. The cavity 23 includes a cylindrical portion 23a for forming the side portion 7a of the housing 7 and a disk portion 23b for forming the bottom portion 7b. In the present embodiment, the mold 20 is disposed so that the moving direction of the movable mold 22 (that is, the mold opening / closing direction) is horizontal.

The fixed mold 21 is provided with a nozzle 24, a runner 25 provided on the inner periphery of the nozzle 24, and an injection gate 26 (hereinafter simply referred to as “gate 26”) that connects the runner 25 and the cavity 23. . The gate 26 is a dotted gate, and is provided on the axis of the molding surface 21 a that molds the outer end surface of the bottom 7 b of the housing 7. The nozzle 24 is provided with a heater (not shown), thereby configuring a so-called hot runner that always maintains the resin in the runner 25 in a molten state (in the figure, the molten resin is indicated by dots). ). The mold 20 is provided with a closing member that opens and closes the gate 26. In the present embodiment, a needle valve 27 as a closing member is provided on the inner periphery of the nozzle 24. The outer diameter of the needle valve 27 is substantially the same as the inner diameter of the gate 26, and the gate 26 can be closed by fitting the both together. The needle valve 27 is moved vertically between the closed position (see FIG. 7) for closing the gate 26 and the open position (see FIG. 8) for opening the gate 26 by a driving means such as a cylinder (not shown). It can be moved.

With the fixed mold 21 and the movable mold 22 clamped, the needle valve 27 is retracted upward from the inner periphery of the gate 26 as shown in FIG. 8A, so that the runner 25 and the cavity 23 pass through the gate 26. The molten resin in the runner 25 is injected from the gate 26 into the cavity 23. At this time, the molten resin injected from the gate 26 provided at the axis of the molding surface 21a of the fixed mold 21 flows to the outer diameter side through the disk portion 23b of the cavity 23 (see the arrow in FIG. 8B), and further to the cavity 23 flows downward in the figure (see the arrow in FIG. 8A). Thereby, molten resin spreads uniformly in the circumferential direction in the cavity 23, and formation of a weld line can be avoided.

Thus, in the state where pressure is applied to the molten resin filled in the cavity 23, as shown in FIG. 9, the needle valve 27 is advanced downward in the figure and inserted into the inner periphery of the gate 26. 10A and 10B, the molten resin in the gate 26 is pushed into the cavity 23 by the needle valve 27. When the gate 26 and the needle valve 27 are fitted, the gate 26 is closed, and the molten resin in the cavity 23 and the molten resin in the runner 25 are separated. In this state, the molten resin in the cavity 23 is cooled, so that the resin in the cavity 23 is solidified and the housing 7 is molded. At this time, the shape of the tip surface of the needle valve 27 is transferred to the axial center of the outer end surface (upper end surface in FIG. 9) 7b3 of the bottom 7b of the housing 7, and the gate mark 7b30 is formed. As described above, the fibrous filler 10 exposed on the surface of the gate mark 7b30 of the housing 7 does not protrude from the surface by solidifying the molten resin in the cavity 23 while being pushed in at the tip of the needle valve 27. All are embedded in the housing 7 (see FIG. 6). Thereby, the gate mark 7b30 becomes a smooth molding surface that follows the tip surface of the needle valve 27. Moreover, the axial position of the gate mark 7b30 can be managed with high accuracy by setting the axial position of the distal end surface of the needle valve 27 with high accuracy.

Then, as shown in FIG. 11, the movable mold 22 is moved away from the fixed mold 21 to perform mold opening. At this time, since the housing 7 and the resin in the runner 25 are already separated, a part of the solidified resin is not torn off when performing mold opening. Thereby, since the gate mark 7b30 of the housing 7 is a smooth molding surface, it is possible to prevent the filler and the resin piece from dropping off from the gate mark 7b30 and to prevent the occurrence of contamination. Further, since the axial position of the gate trace 7b30 is set with high accuracy, the gate trace 7b30 protrudes greatly downward from the bottom portion 7b and interferes with other members, or the gate trace 7b30 is formed in a concave shape so that the bottom portion 7b A situation where the strength is insufficient can be avoided. Furthermore, when the mold is opened, a part of the bottom 7b of the housing 7 that moves together with the movable mold 22 may be taken to the fixed mold 21 side, or the fibrous filler 10 contained in the bottom 7b of the housing 7 may be pulled out. Therefore, it is possible to avoid a situation where a hole penetrating the bottom 7b is formed.

The present invention is not limited to the above embodiment. Hereinafter, although other embodiment of this invention is described, the site | part which has a function similar to said embodiment attaches | subjects the same code | symbol, and abbreviate | omits duplication description.

Since the gate mark 7b30 according to the present invention is formed on the tip surface of the needle valve 27, the gate mark 7b30 can be arranged at an arbitrary axial position by adjusting the axial position of the needle valve 27 at the time of forming. it can. Therefore, as shown in FIG. 2, the gate trace 7b30 is provided flush with the area adjacent to the outer periphery thereof, and as shown in FIG. 12, for example, the gate trace 7b30 is positioned above the area adjacent to the outer periphery thereof in the figure. You may form by making it indent. In this case, since the gate trace 7b30 does not protrude downward in the figure from the lower end surface 7b3 of the bottom portion 7b, interference between the gate trace 7b30 and other members can be reliably avoided.

Alternatively, as shown in FIG. 13, the gate trace 7b30 may be formed so as to protrude downward in the drawing from the region adjacent to the outer periphery thereof. In this case, since the bottom portion 7b is not thinned by the formation of the gate mark 7b30, it is possible to avoid a decrease in strength of the bottom portion 7b.

In the above embodiment, the recess 7b4 is provided in the shaft center of the lower end surface 7b3 of the bottom 7b of the housing 7, and the gate mark 7b30 is provided in the recess 7b4. However, the present invention is not limited to this. For example, as shown in FIG. 14, the entire region of the lower end surface 7b3 of the bottom portion 7b may be a flat surface without a step, and a gate mark 7b30 may be provided on the axis. In this case, in order to reliably avoid interference between the gate trace 7b30 and other members, the gate trace 7b30 is formed flush with the lower end surface 7b3 of the bottom portion 7b as shown in FIG. It is preferable that a part of the lower end surface 7b3 of the bottom portion 7b is recessed as shown in FIG.

Further, the position of the gate 26 of the mold 20 forming the housing 7 is not limited to the above. For example, a dotted gate may be provided at the axis of the molding surface of the mold 20 that molds the inner side end surface (the upper side end surface 7b1 in FIG. 2) of the bottom 7b. Alternatively, a plurality of dotted gates spaced apart in the circumferential direction may be provided on the molding surface that molds the outer or inner end surface of the bottom 7b. However, it is preferable to provide a dotted gate at the center of the molding surface for molding the end surface of the bottom portion 7b in order to allow the molten resin to spread uniformly in the cavity 23 and prevent a weld line from being formed.

In the above embodiment, the herringbone-shaped dynamic pressure grooves 8a1 and 8a2 are formed on the inner peripheral surface 8a of the bearing sleeve 8. However, the present invention is not limited to this. A step-shaped dynamic pressure groove extending along the direction may be formed. Further, in the above embodiment, the dynamic pressure grooves 8a1 and 8a2 are formed at two locations separated in the axial direction of the inner peripheral surface 8a of the bearing sleeve 8, but these may be continuous in the axial direction, or Only one set of herringbone-shaped dynamic pressure grooves may be formed.

In the above embodiment, the case where the spiral-shaped dynamic pressure grooves 8b1 and 7b10 are formed on the lower end surface 8b of the bearing sleeve 8 and the upper end surface 7b1 of the bottom portion 7b of the housing 7 has been described. Alternatively, a dynamic pressure groove having another shape such as a herringbone shape or a step shape may be formed.

In the above embodiment, the case where the dynamic pressure generating portions (dynamic pressure grooves) are formed on the inner peripheral surface 8a, the lower end surface 8b of the bearing sleeve 8 and the upper end surface 7b1 of the bottom portion 7b of the housing is shown. The dynamic pressure generating portions may be formed on the outer peripheral surfaces (cylindrical surfaces 2a1, 2a2) of the shaft member 2 facing these surfaces through a bearing gap, the upper end surface 2b1 and the lower end surface 2b2 of the flange portion 2b. Further, both the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface of the shaft member 2 may be cylindrical surfaces to constitute a perfect circle bearing. In this case, a dynamic pressure action is generated in the lubricating fluid in the radial bearing gap due to the swing of the shaft member 2.

Further, in the above embodiment, the shaft rotation type fluid dynamic pressure bearing device in which the shaft member 2 rotates is shown. However, the present invention is not limited to this, and the shaft on which the shaft member 2 is fixed and the bearing sleeve 8 and the housing 7 rotate. The present invention can also be applied to a fixed fluid dynamic bearing device or a fluid dynamic bearing device in which both the shaft member 2 and the bearing sleeve 8 rotate.

Further, the fluid dynamic pressure bearing device described above is not limited to a spindle motor of an HDD, but may be applied to a spindle motor of another information device, a polygon scanner motor of a laser beam printer, a color wheel of a projector, or a fan motor of an electric device. Can do.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic pressure bearing apparatus 2 Shaft member 7 Housing 7a Side part 7b Bottom part 7b30 Gate mark 8 Bearing sleeve 9 Seal member 10 Fibrous filler 20 Mold 21 Fixed mold 22 Movable mold 23 Cavity 24 Nozzle 25 Runner 26 Injection gate 27 Needle Valve (blocking member)
R1, R2 Radial bearing part T1, T2 Thrust bearing part S Seal space

Claims

A housing for a fluid dynamic bearing device comprising a resin injection-molded product integrally having a cylindrical side portion and a bottom portion closing one axial end of the side portion,
A housing having a gate mark made of a molding surface.
The housing according to claim 1, wherein a thickness of the gate mark formation portion is 1 mm or less.
The housing according to claim 1 or 2, wherein the gate mark is provided on an axis of an end surface of the bottom portion.
The housing according to any one of claims 1 to 3, wherein the resin includes a fibrous filler.
The housing according to any one of claims 1 to 4, a bearing sleeve fixed to an inner peripheral surface of a side portion of the housing, a shaft member inserted into an inner periphery of the bearing sleeve, and the bearing sleeve A radial bearing portion that supports the shaft member in a radial direction with a fluid pressure in a radial bearing gap formed between an inner peripheral surface of the shaft member and an outer peripheral surface of the shaft member; an end surface of the shaft member; and a bottom portion of the housing A fluid dynamic bearing device comprising: a thrust bearing portion that supports the shaft member in the axial direction with a fluid pressure in a thrust bearing gap formed between the end face on the inner side.
The fluid according to claim 5, further comprising a thrust dynamic pressure generating portion that is formed on an end surface of the shaft member or an inner end surface of the bottom portion of the housing and generates a dynamic pressure action on the lubricating fluid filled in the thrust bearing gap. Hydrodynamic bearing device.
A motor comprising the fluid dynamic bearing device according to claim 5, a stator coil, and a rotor magnet.
A method for manufacturing a housing for a fluid dynamic bearing device integrally having a cylindrical side portion and a bottom portion that closes one axial end of the side portion,
Injecting the molten resin in the runner into the cavity via an injection gate, and cleaving the molten resin in the runner and the molten resin filled in the cavity by closing the injection gate with a closing member And cooling and solidifying the molten resin filled in the cavity.
The method for manufacturing a housing according to claim 8, wherein the molten resin includes a fibrous filler.
The method for manufacturing a housing according to claim 8 or 9, wherein the injection gate is provided at an axis of a molding surface that molds an outer end surface of the bottom portion.