JP2009028634A - Cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method capable of effectively removing dust and pollutants stuck to a motor unit without affecting a bearing or the like even in a state the unit is completed. <P>SOLUTION: Inside the chamber in a pressure lower than a supercritical state, a nozzle unit for which a first nozzle for jetting supercritical carbon dioxide and a second nozzle for sucking and recovering the supercritical carbon dioxide are integrated is traversed relatively to the surface to be cleaned of an object to be cleaned, the supercritical carbon dioxide is jetted from the first nozzle to the surface to be cleaned, and particulates peeled off from the surface of the object to be cleaned or the pollutants dissolved from the surface of the object to be cleaned are sucked and recovered together with the supercritical carbon dioxide from the second nozzle. Thus, washing is surely executed without the secondary contamination of bearing oil, and since a large load is not given to the object to be cleaned, thereby preventing deformation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cleaning method for parts that require high cleanliness, and more particularly to a recording disk drive device, a spindle motor used therefor, and a cleaning method for the parts.

  In recent years, hard disk devices (hereinafter abbreviated as HDDs), optical disk devices, and the like have been required to significantly improve recording density, and as a result, the area per bit on the disk surface has been rapidly reduced. As a result, the distance between the recording disk and the head element for recording / reproducing the signal is allowed only a small value year by year in order to suppress the error rate of the reproduction signal, and the flying height of the head element is 10 nm. It is as follows.

  Here, if dust particles (submicron order) are caught between the head and the surface of the recording disk while the recording disk is rotating, the head element cannot float from the recording disk, and the head element and the head gimbal on which the head element is mounted There is a risk of crashing the assembly. In order to prevent the occurrence of such a crash, the cleanliness of the air in the recording disk drive device needs to be maintained at a high level.

  Also, when assembling HDD parts such as a spindle motor, the operator's sebum adheres to the motor, etc., and it is transferred to another part of the HDD during the recording disk mounting work, or may cause outgassing. May remain as a contamination to the recording disk or the head element, and the head may stick when the disk starts rotating.

  In order to keep the cleanness of the air at a high level, not only the HDD is sealed so as to prevent the inflow of dust by blocking the inside of the recording disk drive device from the outside air but also generating dust particles in the recording disk device. In addition, it is necessary to prevent adhesion / remaining of sebum on the surface of the HDD internal parts.

  Therefore, when assembling such a motor, each member is first cleaned with a cleaning solution to remove dust particles and oils (cutting oil, worker's sebum) adhering to the surface of the member, and then cleaned in a clean room, etc. It is necessary to assemble each member sequentially in a high-degree environment under strict control (dust generation from the assembly environment, worker's sebum, etc.).

  However, even if individual parts are cleaned, it is difficult to completely prevent various types of contamination during assembly, and in order to suppress dust in the motor completed state, cleaning in the unit state (motor completed state) has begun to be required. It was.

  Here, as a cleaning method in the unit, for example, as shown in Patent Document 1, ultrasonic cleaning is performed by applying a water-repellent member to the opening of the rotor hub and the base and immersing the entire motor unit in the cleaning liquid. There is.

  Furthermore, as shown in Patent Document 2, a sublimable substance (mainly dry ice) is jetted onto an object to be cleaned together with a carrier gas and a cleaning liquid, and energy when the sublimable substance collides and energy when the sublimable substance sublimates. There is something to clean with.

Moreover, as shown in Patent Document 3, oil and fat adhered to an object to be cleaned using a supercritical fluid obtained by pressurizing and heating CO2 gas to 75.2 Kg / cm ² and 31.1 ° C. or higher. There are some which wash away organic solvents, granular materials remaining on the surface of the object to be cleaned, exfoliated materials and the like.
JP 2006-314188 A JP 2003-211106 A Japanese Patent Laid-Open No. 10-24270

  However, even if a water-repellent film is formed in a minute gap as in the method described in Patent Document 1, ultrasonic cleaning is essential for cleaning in the unit state, and the water-repellent film can be easily destroyed. . If the water-repellent film is partially broken, cleaning liquid may enter the motor and the motor bearing oil may come off, or a serious defect such as a short circuit inside the motor may occur. Further, the peeled water-repellent film becomes dust and causes secondary contamination.

  In order to prevent the cleaning liquid from entering the gap between the rotor and the stator, an O-ring can be fitted into the gap between the rotor and the stator. It is necessary to prepare it every time, and the manufacturing cost is increased, and the defect rate can be increased due to defective maintenance of the jig. In addition, the contact between the O-ring and the motor parts, the sliding portion of the O-ring holding jig itself is unavoidable in principle, and there is a problem that the cause of dust generation increases.

  Also, as described in Patent Document 2, by causing dry ice to collide with a motor component such as a hub at high speed from the injection nozzle, an eccentric load is applied to the hub (moment load is applied), and as a result, the shaft / hub press-fit portion As a result, the press-fit accuracy is deteriorated (for example, axial surface runout axial repetitive run out; hereinafter abbreviated as ARRO), and the bearing is damaged to affect the motor performance. Also, the dry ice sprayed from the spray nozzle scatters together with the surface contaminants after cleaning the component surface, causing secondary contamination. Furthermore, before the dry ice is sprayed by the spray nozzle, the dry ice is charged in the supply pipe, the object to be cleaned is also charged, and the dust peeled off by the dry ice is adsorbed again. Had the problem of losing.

  In addition, as described in Patent Document 3, a method using a supercritical fluid that is an intermediate form of gas and liquid as a cleaning agent can be said to be a very effective means for high-level cleaning of a single part, but has a low viscosity and penetration. In the method of immersing in a supercritical fluid with good properties, even if a water repellent is applied, it penetrates through a slight gap. Here, since the supercritical fluid has a density close to that of a liquid, the solubility of nonpolar substances such as oil is large. Therefore, the supercritical fluid that has permeated from the slight gap to the oil retaining portion of the bearing has a problem that even the oil in the bearing portion is dissolved (oil loss).

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a cleaning method capable of cleaning without causing deterioration in accuracy of parts even after a motor is assembled.

  In order to solve the above-described conventional problems, a cleaning method according to the present invention includes a nozzle unit in which a first nozzle that ejects a supercritical fluid and a second nozzle that sucks and recovers the supercritical fluid are integrated. A step of preparing, a step of preparing a traverse device capable of moving the nozzle unit relative to the surface to be cleaned of the object to be cleaned, a step of setting the object to be cleaned at a predetermined position, and a nozzle unit by the traverse device The supercritical fluid is ejected from the first nozzle to the surface to be cleaned while being moved relative to the surface to be cleaned, and is separated from the surface of the object to be cleaned together with the supercritical fluid from the second nozzle. And a step of sucking and collecting the pollutant dissolved from the surface of the granular material or the object to be cleaned, and a step of removing the object to be cleaned from a predetermined position.

  As a result, the supercritical fluid can be ejected only on the intended surface of the object to be cleaned, so that the supercritical fluid can be prevented from entering the motor or the like. Further, dust adhering to the surface of the object to be cleaned can be removed by the impact energy ejected from the nozzle. Further, since the peeled granular material or dissolved contaminant can be sucked on the spot, there is no fear of secondary contamination. Furthermore, the impact when the supercritical fluid is ejected can be mitigated by sucking and collecting the supercritical fluid, and there is no possibility of causing deformation or the like even if it is a precision part / unit.

  In the cleaning method according to the present invention, carbon dioxide is ejected from the first nozzle as a supercritical fluid under conditions of a critical temperature or higher and a critical pressure or higher.

  By using carbon dioxide as a supercritical fluid, (1) carbon dioxide is a non-polar molecule, so it will dissolve oils and fats adhering to the object to be cleaned well during assembly, so the cleaning effect is high. (2) The critical condition of carbon dioxide is critical. The temperature is 31 ° C., the critical pressure is 7.4 Mpa, which is relatively low pressure, and is easy to handle. (3) The operating temperature is 31 ° C. to 90 ° C. Because it is the same, there is no need for special design considerations for the object to be cleaned. (4) It does not destroy the ozone layer like chlorofluorocarbon solvents, nor does it newly generate carbon dioxide, a greenhouse gas. Since it can be recycled and reused, it has less environmental impact, (5) the material itself is inexpensive, and (6) nonflammable, harmless and safe for workers.

  Further, the cleaning method according to the present invention is the cleaning method according to the first or second invention, wherein the object to be cleaned is set in a pressure environment below the critical pressure and cleaned with a cleaning fluid in a supercritical state. Is to do.

  As a result, the object to be cleaned is exposed to a gas such as carbon dioxide to the inside, but is not immersed in the supercritical fluid, and therefore, for example, the lubricating oil inside the bearing is not dissolved. That is, by using the supercritical fluid and the nozzle, spot-like supercritical fluid cleaning can be performed, and the supercritical fluid can be prevented from entering the motor or the like. Also, the supercritical fluid injected from the first nozzle is injected onto the object to be cleaned in the low-pressure chamber, so that the phase changes from the supercritical fluid state to the gas, and the volume expands as a gas. The material that does not dissolve in the supercritical fluid can be removed by the expansion pressure. As a result, two operations of extracting and removing contaminants dissolved in the supercritical fluid and removing contaminants not dissolved in the supercritical fluid can be performed at the same time, thereby reducing the equipment cost and tact time. I can do it.

  In the cleaning method according to the present invention, the pressure in the chamber is higher than the atmospheric pressure.

  This makes it easy to connect the second nozzle to a pressure environment as low as atmospheric pressure, and the nozzle is ejected from the first nozzle even though there is no need to provide a dedicated pump for suction recovery in the chamber. It becomes easy to reliably suck and collect the supercritical fluid to the second nozzle.

  Next, in the cleaning method according to the present invention, the tip of the nozzle outlet of the first nozzle has a substantially annular shape, and the second nozzle is sucked so as to surround the tip of the nozzle outlet of the first nozzle in a substantially ring shape. The mouth is formed.

  As a result, the supercritical fluid ejected from the first nozzle and the granular material separated from the surface of the object to be cleaned or the contaminant dissolved from the surface of the object to be cleaned can be reliably recovered, and secondary contamination can be recovered. It can prevent more reliably.

  The object to be cleaned of the cleaning method according to the present invention is at least grounded during cleaning.

  This prevents static charges caused by internal friction when the supercritical fluid is transported at high speed in the first and second nozzles and pipes, and prevents reattachment of particles such as once separated particles. it can.

  Further, the object to be cleaned of the cleaning method according to the present invention is such that the ionization is performed after cleaning.

  As a result, static electricity generated during cleaning can be removed from the object to be cleaned, and small powder particles scattered in the clean room after cleaning can be prevented from being drawn to the surface of the object to be cleaned.

  Further, the cleaning method according to the present invention provides a plurality of nozzle units for cleaning the surface of an object to be cleaned that is substantially rotationally symmetric around the rotation center axis, and the plurality of nozzle units rotate at least during cleaning. It is moved relatively so as to be arranged substantially evenly with respect to the central axis.

  Thereby, since it arrange | positions in the substantially equal position with respect to the center axis | shafts of to-be-cleaned objects, such as a hub of a motor, an offset load is no longer applied with respect to to-be-cleaned objects. As a result, it is possible to prevent the perpendicularity of the hub with respect to the shaft from deteriorating and the ARRO of the disk when the disk is attached to be deteriorated.

  In the cleaning method according to the present invention, the suction force generated by the air current sucked from the second nozzle is larger than the jet power that the supercritical fluid ejected from the first nozzle gives to the surface of the object to be cleaned. It is.

  Thereby, it becomes possible to reliably collect the supercritical fluid ejected from the first nozzle and the granular material separated from the surface of the object to be cleaned or the contaminant dissolved from the surface of the object to be cleaned.

  Further, the cleaning method according to the present invention measures the force that the nozzle unit applies to the object to be cleaned, and the ejection state of the first nozzle or the second nozzle so that a load exceeding a predetermined value is not applied to the object to be cleaned. At least one of the suction states is controlled.

  Thereby, it is possible to suppress an excessive force from being applied to the object to be cleaned, and to minimize the deformation of the object to be cleaned.

Moreover, the cleaning method according to the invention is such that the tip of the first nozzle is farther from the surface to be cleaned of the object to be cleaned than the tip of the suction port of the second nozzle.
Thereby, it becomes easy to reliably recover the supercritical fluid, the granular material, or the contaminant without scattering.

  Further, in the cleaning method according to the invention, the part is placed in the chamber, the atmosphere in the chamber is replaced with a gas having a composition almost the same as that of the supercritical fluid, and then the pressure in the chamber is increased. It is a thing.

  Accordingly, moisture in the atmosphere in the chamber can be removed, so that condensation in the chamber can be prevented when an object to be cleaned is taken out.

  In the cleaning method according to the invention, the pressure in the chamber is reduced while the temperature in the component or the chamber is controlled to be 0 ° C. or higher and 100 ° C. or lower.

  This prevents the object to be cleaned from condensing when taken out from the chamber. Moreover, even if there is moisture in the chamber, it is possible to prevent dew condensation due to adiabatic cooling during decompression. In addition, since the solubility of carbon dioxide in oil is lower as the temperature is higher, the effect of discharging carbon dioxide dissolved in oil during supercritical fluid cleaning from oil is also high.

  Further, in the cleaning method according to the present invention, before shipping the parts, the pressure is lowered to a predetermined pressure (preferably an absolute pressure of 0.9 kPa or less) for a predetermined time (preferably 30 minutes or more) for less than atmospheric pressure. It is a thing.

  As a result, it is possible to prevent the carbon dioxide gas melted in the oil from rapidly expanding into bubbles in the bearing gap due to sudden decompression and causing oil leakage.

  According to the present invention, it is possible to apply supercritical fluid cleaning capable of reliably removing oils and fats as a cleaning method to cleaning a motor in a completed state. That is, oils and fats, powder particles on the product surface, etc. can be reliably removed and recovered without causing adverse effects such as deformation caused by jetting of the supercritical fluid on the object to be cleaned.

  Moreover, since the motor can be effectively cleaned in a unit state by traversing the object to be cleaned with the injection nozzle and the suction nozzle as an integrated structure, the cleanliness of the motor can be dramatically improved.

  In addition, since the motor surface can be cleaned in the unit state after the motor is assembled, it is less necessary to clean the parts that make up the outer surface of the motor in advance. Management can be greatly simplified.

  In addition, since it is possible to simplify the management of dust adhering to the motor during assembly (the degree of cleaning of the components themselves and the clean environment during assembly), the cost can be greatly reduced (equipment and quality control).

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a cross-sectional view of a spindle motor to which the cleaning method according to Embodiment 1 of the present invention is applied. This spindle motor is used for driving a recording disk and constitutes a part of a recording disk device such as an HDD.
<Configuration of spindle motor>
The spindle motor includes a base 100 constituting a stator (stationary member) 2, a rotor hub 101 made of aluminum or an iron alloy material constituting the rotor 1, and a rotor 1 for rotatably supporting the rotor 1 with respect to the stator 2. A hydrodynamic bearing device is provided.

  The hydrodynamic bearing device includes a hollow cylindrical sleeve 102, a shaft 106, and a disk-shaped thrust plate 105 that closes a lower portion of the sleeve 102. The sleeve 102 is formed of a metal material such as iron, iron alloy, copper, or copper alloy, and is fixed to the base 100.

  A disc-shaped thrust plate 105 is fixed to the sleeve 102 by a method such as adhesion, caulking, press-fitting, or welding. The opposite side (upper side in the figure) of the sleeve 102 to which the thrust plate 105 is fixed is open, the open end of the sleeve 102 is inclined toward the inside of the hydrodynamic bearing device, and the gap with the shaft 106 is open. Since it is arranged so as to become narrower from the end toward the hydrodynamic bearing device, it functions as the taper seal portion 108 and stably holds the lubricating oil 107 as a lubricant in the gap between the shaft 106 and the sleeve 102. ing. Further, on the inner peripheral surface side of the sleeve 106, a radial dynamic pressure generating groove (not shown) having a herringbone shape is formed side by side in the axial direction. The radial dynamic pressure generating groove may have a spiral shape. The surface of the sleeve 106 may be subjected to a surface hardening process such as a nickel plating process.

  The shaft 106 is a member made of a metal material and having a cylindrical outer peripheral surface with a diameter of 2 to 4 mm, and is inserted into the inner peripheral surface of the sleeve 106 in a rotatable state. Further, a disc-shaped thrust flange 109 is joined to the lower end of the shaft 106 by a method such as welding, press-fitting, adhesion, or screw tightening. Since the shaft 106 is used as an axis of rotation center, for example, a hard material such as SUS is used.

  The thrust flange 109 is a disk-shaped member, and is attached to the lower end side of the shaft 106 (the closed side of the hydrodynamic bearing device) as described above. The thrust flange 109 is disposed in a space surrounded by the step portion of the sleeve 102 and the thrust plate 105. The lower surface of the thrust flange 109 faces the thrust plate 105, and the upper surface of the thrust flange 109 faces the sleeve 102. A thrust dynamic pressure generating groove is formed on at least one surface of the facing surface.

  The thrust plate 105 is a member on a disc attached so as to cover the bottom surface of the hydrodynamic bearing device, and a thrust dynamic pressure generating groove (not shown) is formed on one side of the opposing surface of the opposing thrust flange 109. ing. The surface on which the thrust dynamic pressure generating groove is formed is not limited to the configuration of the present embodiment, and may be formed on any one of the opposing surfaces while forming a gap in the axial direction. That is, a thrust dynamic pressure generating groove may be formed on the lower surface of the thrust flange 109 or the upper surface of the thrust flange 109.

  Further, the shaft 106 including the radial dynamic pressure generating groove and the thrust dynamic pressure generating groove, the gap between the sleeve 102 and the inner peripheral cylindrical portion, and between the thrust flange 109 and the sleeve 102 and between the thrust flange 109 and the thrust plate 105. The gap is filled with lubricating oil 107.

  The rotor hub 101 which is the rotor 1 has a substantially bowl-like shape, a through hole is formed in the center portion, and the shaft 106 is fixed by adhesive press fitting, welding or the like. A substantially annular rotor magnet 104 is attached to the inner periphery of the rotor hub 101 and faces the stator core 103 in the radial direction. A disk mounting surface is formed on the upper surface of the rotor hub 101.

The rotor magnet 104 is attached in the circumferential direction on the inner peripheral surface side of the rotor hub 101. On the other hand, a sleeve 102 is fixed to the base 100 by bonding, adhesive press fitting, welding, or the like. A stator core 103 around which a coil 110 is wound is fixed substantially coaxially with the sleeve 102 by a method such as adhesion. A rotating magnetic field is generated by the rotor magnet 104 and the stator core 103 to apply a rotational force to the rotor hub 101.
<Regarding supercritical carbon dioxide>
A supercritical fluid is a unique fluid that is in a state where the temperature and pressure (critical point) at which gas and liquid can coexist is exceeded, and that exhibits different properties from ordinary gas and liquid. FIG. 9 is a state diagram of carbon dioxide. It is well known that carbon dioxide is a gas at normal temperature of 1 atm, becomes solid (dry ice state) at −80 ° C. and 1 atm, and liquefies at −20 ° C. and 20 atm. If the pressure is further increased to a critical pressure Pc (75.2 kgf / cm ² ) or higher and the temperature is set to a critical temperature Tc (31.1 ° C.) or higher, the phase changes to a supercritical state. At this time, the supercritical fluid has the property of gas that penetrates everywhere (diffusibility) and the property of liquid that dissolves the components (solubility), and has the feature that its density can be changed drastically continuously.
<Configuration of cleaning device>
FIG. 2 shows a block diagram of a cleaning apparatus to which the cleaning method of this embodiment is applied. In the chamber 50, a main body (described later) including a cleaning mounting base 3, a nozzle unit 24, and the like for fixing an object to be cleaned is installed. The nozzle unit 24 has a role of injecting supercritical carbon dioxide onto the object to be cleaned and sucking and collecting the contaminant together with the contaminant. Here, the carbon dioxide whose pressure has been increased by the pressure increasing device 43 and whose temperature has been adjusted is in a supercritical state. Then, the pressure and flow rate of the supercritical carbon dioxide are controlled by the supply pressure control device 17 a and supplied to the nozzle unit 24. Carbon dioxide is recovered after washing by controlling the pressure and flow rate on the recovery absorption side by the recovery pressure controller 17b. Further, the pressure of the supercritical carbon dioxide is lowered by the decompression device 41 and sent to the separation tank 42. This separation tank 42 is for separating contaminants and dust adhering to the object to be cleaned from carbon dioxide. Then, clean carbon dioxide is sent out from the separation tank 42 and recirculates to the booster 43 again.

  Next, a schematic configuration of the main body in the chamber 50 of the cleaning apparatus will be described. FIG. 3A is a plan view of the main body portion in the chamber 50, and FIG. The stator 2 of the spindle motor is fixed to the cleaning mount 3 by a clamp 4. The cleaning mount 3 is grounded by a grounding means 14 to prevent the spindle motor from being charged. The grounding means is preferably connected to the rotor 1 when the object to be cleaned is the rotor 1, and is preferably connected to the stator 2 when the object to be cleaned is the stator 2.

  As shown in FIGS. 4 (a) and 4 (b), the cleaning apparatus includes a first nozzle 25 for injecting supercritical carbon dioxide to clean the spindle motor, and separated particles such as dust 7 (particles). A nozzle unit 24 is provided that is integrated with a second nozzle 26 that sucks and collects body and dissolved contaminants (contamination) together with supercritical carbon dioxide. The detailed configuration of the nozzle unit 24 will be described later. The first nozzle 25 is connected to the cleaning fluid supply pipe 5, and the second nozzle 26 is connected to the suction recovery pipe 6.

The nozzle unit 24 is fixed to the traverse units 11 and 12 and the rotary table 13 provided so as to be movable / rotatable in the horizontal direction, the vertical direction, and the rotation axis direction with respect to the spindle motor. Thereby, the nozzle unit 24 can be moved relative to the cleaning surface of the object to be cleaned.

  In addition, since the object to be cleaned has a substantially rotationally symmetric shape around the rotation center axis, a plurality of the nozzle units 24 are prepared for cleaning the surface of the object to be cleaned. The traverse units 11 and 12 and the rotary table 13 are relatively moved with respect to the rotation center axis.

The cleaning mount 3 is provided with a heating device (not shown) and is disposed on the cleaning device base 18 by the elastic support portion 15. The elastic support portion 15 is provided with a plurality of load sensors 16 for measuring a load applied to the spindle motor by injection. Then, the reaction force when the cleaning agent is injected / sucked is measured and fed back to the pressure control device 17 to control the injection force and the suction force.
<Configuration of nozzle unit>
As shown in FIG. 4B, the nozzle unit 24 is peeled off together with a first nozzle 25 for injecting supercritical carbon dioxide 20 for cleaning the object to be cleaned and supercritical carbon dioxide partially sublimated. The dust particles 7 and the like, and the second nozzle 26 that sucks and collects the recovered material 10 in which dissolved contaminants are mixed are integrated.

  Here, the second nozzle 26 is disposed so as to surround the first nozzle 25. Here, the tip of the second nozzle 26 is configured to protrude further than the tip of the first nozzle. The first nozzle 25 is made of a metal or conductive flexible tube and is grounded.

  Further, a heating device (not shown) is installed near the tip of the first nozzle 25 to warm the carrier gas and prevent the supercritical carbon dioxide 20 from being clogged in the supply pipe.

The diameter of the first nozzle is preferably about 1 to 3 mm. Thereby, the jet power of supercritical carbon dioxide jetted from the first nozzle can be suppressed to the order of about 1 to 10 kgf.
<Operation of device and cleaning action>
Next, operation | movement of this cleaning apparatus is demonstrated using the process flowchart shown in FIG. First, the object to be cleaned is fixed to the cleaning mount 3 in the chamber 50 using the clamp 4. At this time, the object to be cleaned is set to be grounded by the grounding means 14. Next, the atmosphere in the chamber 50 is replaced with carbon dioxide gas. This replacement is intended to remove moisture in the atmosphere and remove unnecessary gas components other than carbon dioxide, so that the supercritical state can be easily maintained. Preheat the item to be cleaned as necessary. This prevents condensation during cleaning. A plurality of objects to be cleaned may be set at the same time. Then, the pressure in the chamber 50 is increased to a critical pressure or less. The rising pressure at this time is preferably about 1/5 to 4/5 of the pressure of the supplied supercritical carbon dioxide and lower than the critical pressure. This is because the supercritical fluid is ejected at a high speed (several tens to several hundreds m / sec) due to the difference between the pressure in the chamber 50 and the pressure of the supercritical fluid to be supplied. A force to peel off difficult-to-remove dust is generated. Further, since the pressure is in a gas state, the volume increases in inverse proportion to the pressure. Accordingly, in addition to the impact of the collision, the cleaning fluid itself rapidly expands, so that dust can be more easily separated. Furthermore, since there is a pressure difference between the inside and outside of the chamber 50, the cleaning fluid ejected from the first nozzle 25 can be surely adjusted only by adjusting the pressure so that the second nozzle 26 is balanced (or close to) the outside air side pressure. Since it can collect | recover from the 2nd nozzle 26, it can prevent that a supercritical fluid permeates into other than a to-be-cleaned surface.

  Next, the plurality of nozzle units 24 are moved relative to the object to be cleaned (here, a spindle motor), and arranged so as to be substantially at the target positions around the rotation axis.

  Then, the cleaning fluid 9 is ejected and the sublimate is sucked and collected together with the contaminants. At this time, in addition to the dissolving ability of supercritical carbon dioxide itself, it is ejected into the chamber 50 having a pressure lower than the supercritical pressure, so that the supercritical fluid is accelerated and collides with the surface to be cleaned at a high speed. Remove deposits. At this time, if the supply pressure of the supercritical fluid is changed so as to have a triangular wave shape having a fluctuation range corresponding to several atmospheres or intermittent, dust can be more effectively separated by the collision of the cleaning fluid.

  After that, the object to be cleaned is taken out by removing electricity or heating with an ionizer as required. When a plurality of objects to be cleaned are attached to the cleaning mounting base 3, the cleaning may be performed sequentially.

  Here, when the pressure of the chamber 50 is reduced in order to take out the cleaning object from the chamber 50, the temperature of the chamber 50 or the object to be cleaned is 0 ° C. or higher and 100 ° C. or lower, preferably 20 ° C. or higher and 80 ° C. or lower. While adjusting the temperature. This prevents a decrease in temperature due to adiabatic expansion during decompression, and prevents moisture in the atmosphere from condensing and dew condensation when the object to be cleaned is taken out from the chamber 50.

  FIG. 10 shows the Bunsen coefficient indicating the saturation solubility of various gases in mineral oil. The Bunsen coefficient is the volume (ml) when the amount of the gas dissolved in 1 ml of solution when the gas is 1 atm and the gas is brought to 0 ° C. However, in FIG. 10, it is displayed as a percentage. As shown in FIG. 10, the higher the temperature, the more difficult the carbon dioxide dissolves. However, air is easier to dissolve at higher temperatures, but its solubility is lower by an order of magnitude compared to carbon dioxide. Since the fluid bearing oil is an ester oil, there is a slight difference from the value in FIG. Further, the amount of dissolution increases in proportion to the gas partial pressure. Therefore, when the object to be cleaned includes a hydrodynamic bearing device, the gas in the chamber 50 is replaced with normal air before the object to be cleaned is taken out from the chamber 50, and in that state, a pressure lower than atmospheric pressure ( Desirably, the absolute pressure is 0.9 kPa or less), and is maintained for a predetermined time (desirably 30 minutes or more). Furthermore, it is preferable that the temperature at that time is also high (about 40 to 100 ° C.). Since the chamber 50 is filled with high-pressure carbon dioxide gas during supercritical fluid cleaning, the carbon dioxide dissolves in the oil, and if shipped as it is, if exposed to an environment with low air pressure during transportation or the like, It is conceivable that carbon dioxide becomes bubbles and stays in the bearing, and as a result, oil leaks from the bearing seal portion. In order to prevent this phenomenon after shipment, excess carbon dioxide gas can be discharged as soon as possible by increasing the temperature before shipping and exposing it to a reduced pressure environment, causing problems in the market. The probability of occurrence can be reduced.

  The dirt adhering to the surface of the object to be cleaned 30 is peeled off or dissolved in supercritical carbon dioxide and removed (cleaned) from the object to be cleaned. The dirt removed from the object 30 is sucked and collected by the second nozzle 26 together with the supercritical carbon dioxide partially sublimated. Therefore, since the cleaning fluid 9 and the separated dust and contaminants do not scatter around the first nozzle, there is no possibility of secondary contamination of the object to be cleaned after cleaning. Furthermore, since supercritical carbon dioxide itself is 31 ° C. or more and is used in a small amount, there is no fear of causing thermal shock to the object to be cleaned even if it is ejected into the chamber 50 and the pressure is lowered and adiabatic cooling is performed. However, if the cleaning time becomes long, the temperature of the object to be cleaned is too low, and there is a possibility that moisture in the air will be absorbed and condensed after cleaning. In order to prevent this, the object to be cleaned may be heated in advance, or the object to be cleaned may be heated during or after cleaning.

  According to the present embodiment, since the nozzle unit 24 can move relative to the object to be cleaned 30, the surface of the object to be cleaned 30 can be thoroughly cleaned. Further, since the second nozzle (suction nozzle) 26 is provided integrally with the first nozzle (injection nozzle) 25, the contaminants peeled off or dissolved by the injected supercritical carbon dioxide are the second. The nozzle 26 immediately collects by suction. Therefore, the peeled contaminants are not diffused into the surrounding environment by jetting, and secondary contamination can be prevented.

  Moreover, the 1st nozzle 25 and the 2nd nozzle 26 are integrated as above-mentioned, and are jetting and suctioning. As a result, the injection force applied to the object to be cleaned can be relatively weakened by the suction force, so that it also has the effect of reducing the stress applied to the object to be cleaned when supercritical carbon dioxide is injected. Further, the injection force and the suction force are measured by a load sensor 16 disposed on an elastic support 15 that elastically supports the cleaning mount 3 and fed back to the pressure control device 17 so that the load applied to the object to be cleaned is always constant. It becomes possible to control. With these configurations, it is possible to prevent deterioration of the assembly accuracy of the object to be cleaned (motor) and damage to the bearing due to the load at the time of supercritical carbon dioxide injection, which the conventional example has. If the suction force is set to be slightly larger than the injection force per nozzle (about 1N to 50N), the supercritical fluid injected from the nozzle 25 is reliably recovered by the second nozzle 26, and the parts are deformed. There is no problem that it is said.

  In addition, since the plurality of nozzle units 24 are arranged so as to be almost evenly balanced with respect to the rotation axis, the uneven load due to the injection force, the deterioration of press-fitting accuracy with respect to the shaft 106 of the rotor hub 101 due to the uneven load, and the bearing Can prevent damage.

  In addition, when carbon oxide is transported supercritically in the supply pipe, static electricity is generated due to mutual friction and friction with the inner wall of the pipe constituting the supply pipe, and as a result, dust is re-applied to the object to be cleaned. In some cases, it adheres and a good cleaning effect cannot be obtained. However, in the present embodiment, the object to be cleaned, the cleaning mounting base 3 to which the object to be cleaned is fixed, and the first nozzle 25 are grounded so that they are not charged and the separated dust is immediately recovered. Therefore, a good cleaning effect can be obtained. If the charge cannot be completely suppressed even after that, the ionization may be performed by an ionizer as soon as possible after cleaning. This minimizes particulate adsorption due to static electricity.

  In addition, the cleaning mounting base 3 of the cleaning device has a heating device and a heating device (not shown) for heating the carrier gas at the tip of the injection nozzle. As a result, the problem that the object to be cleaned is condensed after cleaning can be solved.

<Modification of First Embodiment>
Although the first embodiment of the present invention has been described above, the present invention is not limited to the first embodiment, and various modifications can be made without departing from the scope of the invention.

(A)
In the description of the first embodiment, the one applied to the apparatus for cleaning the object to be cleaned from the direction parallel to the rotation axis (vertical direction) is used. As a modification, as shown in FIG. It is also possible to inject and wash supercritical carbon dioxide from a direction perpendicular to the axis (horizontal direction). Further, in order to have a combination of the description of the first embodiment and this modification, it is also possible to provide an electromagnetic rotation mechanism in the nozzle unit base so that the vertical direction and the horizontal direction can be arbitrarily selected. is there.

(B)
In the above description, the object to be cleaned is a motor unit (spindle motor) in which the bearing portion is also completed. However, as shown in FIGS. 5 and 6, it is possible to clean the rotor hub 101 and the like in a single item. .

(C)
In the above description, the object to be cleaned is a motor unit (spindle motor) in which the bearing portion is also completed, but it is also possible to clean the base 2 in a single product state as shown in FIG. When it is not necessary to consider the unbalanced load on the object to be cleaned as in the case of the base 2, or when the object to be cleaned is not axisymmetric about the rotation center axis, a plurality of nozzle units 24 need to be arranged uniformly. However, it can also be implemented with a single nozzle unit 24.

(D)
In the above description, the configuration in which only the supercritical carbon dioxide is ejected from the first nozzle has been described, but the present application is not limited to this. For example, a supercritical carbon dioxide supply pipe for supplying supercritical carbon dioxide and a carrier gas supply pipe for supplying carbon dioxide or air as a carrier gas around the first nozzle are coaxially provided from the pressure control device. It is good also as a structure connected and connected.

  Supercritical carbon dioxide is sucked out of the supercritical carbon dioxide supply pipe at a high speed by the negative pressure generated by the carrier gas flowing through the carrier gas supply pipe at a high speed. At this time, the supercritical carbon dioxide is cooled by adiabatic expansion that occurs abruptly to become dry ice pellets.

  The dry ice pellets are accelerated as they are generated to become a cleaning fluid mixed with a carrier gas, and are sprayed at high speed (several tens to several hundreds m / sec) toward dust and contaminants adhering to the surface of the object to be cleaned. Due to the collision energy when the dry ice pellets injected from the first nozzle collide and the expansion pressure that accompanies the sublimation of the dry ice pellets, the dirt attached to the surface of the object to be cleaned is peeled off or becomes liquefied carbon dioxide. It is dissolved and removed (cleaned) from the object to be cleaned. The dirt removed from the object to be cleaned is sucked and collected by the second nozzle together with the dry ice partially sublimated. Accordingly, since the cleaning fluid 9 and the separated dust and contaminants do not scatter, there is no possibility of causing secondary contamination after cleaning. Furthermore, although the temperature of dry ice itself is low, since it instantly sublimes due to collision energy, there is no concern that the object to be cleaned will be excessively cooled to cause thermal shock.

(E)
In the description of the above embodiment, the cleaning apparatus main body is grounded in the chamber for maintaining the pressure, but the present invention is not limited to this. For example, in an ordinary clean room environment, there is no problem even when working in an area where partitions are provided to prevent accidents such as frostbite due to the supercritical fluid being splashed.

(F)
In the above description, the motor shown in FIG. 1 is taken as an example, but the applicable range of the present invention is not limited to this, and it is needless to say that the present invention can be applied to any other form of motor. .

  The cleaning method according to the present invention can reliably perform cleaning without deteriorating the shape accuracy and performance of the apparatus even when the apparatus is completed or semi-completed, and particularly requires high cleanliness. It is useful as a cleaning method for information-related devices such as HDDs, semiconductor-related elements, and video devices.

Cross section of spindle motor Block diagram of the cleaning apparatus according to Embodiment 1 of the present invention. (A) The top view of the washing | cleaning apparatus to which the washing | cleaning method in Embodiment 1 of this invention is applied, (b) The cross-sectional view of the washing | cleaning apparatus to which the washing | cleaning method in Embodiment 1 of this invention is applied. (A) Schematic diagram showing the relationship between the nozzle unit of the cleaning apparatus to which the cleaning method in Embodiment 1 of the present invention is applied and the traverse apparatus, (b) of the cleaning apparatus to which the cleaning method in Embodiment 1 of the present invention is applied. Cross section of nozzle unit (A) The top view of the washing | cleaning apparatus which applied the washing | cleaning method in the modification (A) of Embodiment 1 of this invention, (b) The washing | cleaning method in the modification (A) of Embodiment 1 of this invention was applied. Cross section of cleaning device Cross-sectional view of a cleaning apparatus to which the cleaning method in the modification (B) of the first embodiment of the present invention is applied. Cross-sectional view of a cleaning apparatus to which the cleaning method in the modification (C) of the first embodiment of the present invention is applied Process flow diagram of cleaning method in embodiment 1 of the present invention Carbon dioxide phase diagram Saturation solubility diagram of various gases in mineral oil

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotor 2 Stator 3 Cleaning mount 4 Clamp 5 Cleaning fluid supply pipe 6 Suction collection pipe 7 Dust 9 Cleaning fluid 10 Collected substance 11, 12 Traverse unit 13 Rotary table 14 Grounding means 15 Elastic support part 16 Load sensor 17 Pressure control apparatus 17a Supply pressure control device 17b Recovery pressure control device 18 Cleaning device base 20 Supercritical carbon dioxide 24 Nozzle unit 25 First nozzle 26 Second nozzle 30 Object to be cleaned 41 Decompression device 42 Separation device 43 Boosting device 50 Chamber 100 Base DESCRIPTION OF SYMBOLS 101 Rotor hub 102 Sleeve 103 Stator core 104 Rotor magnet 105 Thrust plate 106 Shaft 107 Lubricating oil 108 Tapered seal part 109 Thrust flange 110 Coil

Claims (14)

Preparing a nozzle unit in which a first nozzle for ejecting a supercritical fluid and a second nozzle for sucking and collecting the supercritical fluid are integrated;
Preparing a traverse device capable of moving the nozzle unit relative to the surface to be cleaned;
Setting the object to be cleaned at a predetermined position;
While the nozzle unit is moved relative to the surface to be cleaned by the traverse device, the supercritical fluid is ejected from the first nozzle to the surface to be cleaned, and from the second nozzle. A step of sucking and collecting the granular material separated from the surface of the object to be cleaned together with the supercritical fluid or the contaminant dissolved from the surface of the object to be cleaned;
And a step of removing the cleaning object from a predetermined position.   The cleaning method according to claim 1, wherein the supercritical fluid is carbon dioxide having a temperature higher than a critical temperature and higher than a critical pressure.   The component is set in a chamber that maintains an environment that is not lower than the critical temperature of the supercritical fluid and lower than the critical pressure of the supercritical fluid, and the supercritical fluid is ejected to the component. The cleaning method according to claim 1.   The cleaning method according to claim 3, wherein the pressure in the chamber is higher than atmospheric pressure.   The tip of the nozzle outlet of the first nozzle has a substantially annular shape, and the suction nozzle is formed so that the second nozzle surrounds the periphery of the tip of the nozzle of the first nozzle in a substantially ring shape. The cleaning method according to any one of claims 1 to 4, wherein:   The cleaning method according to claim 1, wherein the object to be cleaned is grounded at least during cleaning.   The cleaning method according to claim 1, wherein the object to be cleaned is neutralized by an ionizer after cleaning.   In order to clean the surface of an object to be cleaned that has a substantially rotationally symmetric shape around the rotation center axis, a plurality of the nozzle units are prepared, and at least during the cleaning, the plurality of nozzle units are substantially set with respect to the rotation center axis. The cleaning method according to claim 1, wherein the cleaning method is relatively moved so as to be evenly arranged.   The supercritical carbon dioxide ejected from the first nozzle has a larger suction force due to the airflow sucked from the second nozzle than the jet power given to the surface of the object to be cleaned. The cleaning method according to any one of claims 1 to 8.   The force exerted by the nozzle unit on the object to be cleaned is measured, and the spraying state at the first nozzle or the suction state at the second nozzle is not applied to the object to be cleaned. 10. The cleaning method according to claim 1, wherein at least one of them is controlled.   The cleaning method according to claim 5, wherein the tip of the first nozzle is farther from the surface to be cleaned of the object to be cleaned than the tip of the suction port of the second nozzle. 3. The method according to claim 2, wherein the part is placed in the chamber, the atmosphere in the chamber is replaced with a gas at a room temperature and a normal pressure having substantially the same composition as the supercritical fluid, and then the pressure in the chamber is increased. The cleaning method described.   The cleaning method according to claim 2, wherein the pressure in the chamber is reduced while controlling the temperature in the component or the chamber. The cleaning method according to any one of claims 1 to 13, wherein the pressure is lowered to a predetermined atmospheric pressure or less for a predetermined time before the parts are shipped.