WO1996009479A1

WO1996009479A1 - Method and device for providing an oil barrier on a component of a bearing system, and product manufactured by such a method and device

Info

Publication number: WO1996009479A1
Application number: PCT/IB1995/000749
Authority: WO
Inventors: Fridtjof Bremer
Original assignee: Philips Electronics N.V.; Philips Norden Ab
Priority date: 1994-09-23
Filing date: 1995-09-11
Publication date: 1996-03-28
Also published as: CN1135786A; KR960706027A

Abstract

A method and device for the application of an oil barrier (C) on a component (5) of a bearing system. A stamp (3) is raised from a reservoir (21) which contains a barrier fluid (21) comprising a solid substance and a solvent, whereby a quantity of barrier fluid forming a meniscus M1 and/or M2 on the stamp face (13) of the stamp (3) is taken along and is transferred in a rotationally symmetrical pattern onto the component (5) by the stamp (3). After evaporation of the solvent, the solid substance remains on the component and acts as an oil barrier. The solid substance has a surface tension such that it does not or substantially not allow itself to be wetted by lubricants. The invention renders it possible to provide oil barriers in a defined and reproducible manner on components in a mechanized process, without the risk of solid substance reaching locations where it is not desired, for example bearing surfaces (B).

Description

1

Method and device for providing an oil barrier on a component of a bearing system, and product manufactured by such a method and device.

The invention relates to a method of providing an oil barrier on a component of a bearing system, whereby a barrier fluid comprising a solid substance and a solvent is applied to a surface of the component in a rotationally symmetrical pattern, said solid substance remaining on said surface in the form of a film and acting as an oil barrier after evaporation of the solvent.

It is important in systems with maintenance-free bearings, such as self- lubricating porous sleeve bearings, hydrodynamic spiral groove bearings, ball bearings, etc. , to limit or entirely prevent the loss of lubricant, grease, or oil from the bearings. Lubricant loss may take place in two ways: by creepage and by evaporation. The lubricant which leaves the bearings may end up on components of the system where it is not desired, causing pollution of these components. In a computer hard disk drive system, for example, fitted with maintenance-free bearings, lubricant may end up on the hard disk owing to creepage and/or evaporation and pollute this disk. The term "bearing system" is understood to include any movable bearing, both rotary and translatory bearings. As for evaporation, the evaporation rate depends on the type of lubricant. Thus, for example, perfluoropolyethers are used as lubricants with low evaporation rates in vacuum equipment. To prevent lubricant leaking from the bearings through creepage, oil barriers are provided in various locations in the bearing system, insulating the bearings. These oil barriers at the same time protect sensitive components of the bearing system against pollution by leaking lubricant.

Such an oil barrier, which comprises a substance having a surface tension such that it cannot or only with very great difficulty be wetted with lubricants (oils and greases), for example a paraffin oil, prevents the lubricant from creeping over the oil barrier. The oil barrier is provided in the form of a barrier fluid. Such barrier fluids are commercially available and consist of 0.1 to 2% of the solid substance, while the remaining quantity is a solvent as a carrier of the solid substance. The solid substance is a copolymer and the solvent is a fluorine mixture. After a quantity of barrier fluid has been provided and the solvent has evaporated, the solid substance remains in the form of a film, forming an oil barrier. The method as described in the opening paragraph is known from the brochure: "Product Bulletin: NYEBAR TYPE K To Prevent Oil Migration" published by Nye Lubricants Inc. New Bedford MA, USA. The exact composition of a commercially available barrier fluid which can be used is also known from this publication. According to the known method, the barrier fluid can be provided in that the component to be treated is dipped in the barrier fluid, the barrier fluid is sprayed on the component, or the barrier fluid is applied with a brush. These methods of providing the barrier fluid are dependent on the individual operator, inaccurate, and non-reproducible. The surface area covered with the barrier fluid is not the same for each component. Barrier fluid may be applied in locations where it is not desired, such as bearing gaps, contact surfaces, ball races, etc. The known method is accordingly suitable only for providing oil barriers on comparatively large components and surfaces.

The above disadvantages could be obviated at least partly in that the barrier fluid is provided through the nozzle of a spraying tool. Practice has shown, however, that the nozzle becomes choked up fairly soon owing to quick evaporation of the solvent and becomes useless. This method is not suitable for the treatment of components in a mechanized process.

The present invention has for its object to eliminate the above disadvantages and to provide a method which is capable of providing oil barriers on a component of a bearing system in an accurate and reproducible manner, and which is particularly suitable for treating small components. Small components are here understood to be components having dimensions of the order of a few millimetres.

According to the invention, this object is substantially achieved in that the barrier fluid is provided by means of a stamp, the stamp being immersed in the barrier fluid in a reservoir and then raised from the reservoir containing the barrier fluid, so that a quantity of barrier fluid forms a meniscus on a stamp face and is carried along by the stamp, the stamp being pressed subsequently with the stamp face against the surface of the component to be coated, whereby eventually at least a portion of the barrier fluid carried along is transferred from the stamp to said surface.

The use of the stamping method according to the invention renders it possible to limit accurately the oil barrier to be provided, whose shape and dimensions are defined by the shape and dimensions of the rotationally symmetrical stamp face, these shape and dimensions of the stamp face in their turn being adapted to the shape and dimensions of the component to be treated. The accuracy and reproducibility of the process are positively influenced thereby. Since the immersed stamp is raised from the reservoir, the barrier fluid to be transferred to the stamp face forming at least one meniscus defined by the stamp face, the same quantity of barrier fluid is taken along each time, so that an accurate and reproducible dispensing of the barrier fluid to be provided is obtained and the reproducibility of the overall process is further improved. The risk of pollution of the bearing system with barrier fluid, i.e. barrier fluid entering locations where it is not desired, is practically nil owing to the exact limitation of the oil barrier. The method according to the invention renders it possible to provide barrier fluid on a comparatively large surface area in a single step, so in a comparatively short time, without the risk of loss of barrier fluid owing to droplets falling off during transfer, while in addition only a negligible quantity of the solvent can evaporate. Thanks to the accurate limitation of the oil barrier, the reproducible dispensing of the barrier fluid, and the high degree of reproducibility of the process in general, the method according to the invention is particularly suitable for treating components of a bearing system having comparatively small components of the order of a few millimetres. The oil barrier can be provided in a mechanized process and in a defined and reproducible manner by the method according to the invention. The durability and permanence of the oil barrier can be improved in that the provided film is cured for approximately 15 minutes at a temperature of approximately 100 °C in a manner known per se.

To provide an annular oil barrier on a cylindrical component of a bearing system, the barrier fluid must be provided in radial direction. In an alternative embodiment of the method according to the invention, a disc-shaped stamp is used for this purpose which is pressed with its edge against the component during the transfer of the barrier fluid, while the stamp and the component are made to rotate relative to one another. If the oil barrier is to be provided in an annular groove of the cylindrical component, the disc-shaped stamp is pressed with its edge into the annular groove of the component during the relative rotation, the edge of the stamp being adapted to fit the dimensions of the groove.

The invention also relates to a device for implementing the method. According to the invention, this device is substantially characterized by a reservoir, a stamp which is displaceable in vertical direction and which has a rotationally symmetrical stamp face, a drive system for displacing the stamp, and a holder for a component of a bearing system. The method according to the invention can be implemented in an accurate, reproducible, and reliable manner with this comparatively simple arrangement. Preferably, fluctuations in the barrier fluid level are kept within narrow tolerances. The reservoir is preferably closed off with a lid to limit evaporation of the solvent of the barrier fluid presen in the reservoir.

The simplest embodiment of a stamp having a rotationally symmetrical stamp face is a stamp with a plane circular end face on which a meniscus is formed which leaves a disc-shaped spot on the component after the transfer.

In a preferred embodiment of the device according to the invention, the stamp is provided with a central bore in the end having the stamp face. With the annular stamp face of the stamp according to this embodiment, the barrier fluid forms at least one annular meniscus on the stamp face, and an also annular distribution of the barrier fluid on the component is obtained.

Another preferred embodiment of the device according to the invention i characterized in that the stamp has an annular raised rim on the stamp face. The raised rim divides the stamp face into two concentric support faces, so that the barrier fluid can form double meniscus on the stamp face. The barrier fluid can be provided on two mutually perpendicular surfaces of the component thanks to this measure.

In a further preferred embodiment of the device according to the invention, the stamp has an annular groove in the stamp face, so that a comparatively large quantity of barrier fluid can be transferred by the stamp and applied to a comparatively larg surface of the component, possibly divided over two or three mutually perpendicular surfaces.

For providing an annular oil barrier on a cylindrical component of a bearing system in an annular groove of the component, a yet further preferred embodiment of the device according to the invention is used, which is characterized in that the stamp is constructed as a rotatable wheel, and the holder for the component is rotatable, the device being further provided with a drive system for driving the holder. The wheel is brought int contact with the rotating component during the application of the barrier fluid on the component, so that the wheel is caused to rotate by the component.

A component of a bearing system provided with at least one oil barrier which is provided by the method according to the invention is characterized by an even thickness of the oil barrier, uniform dimensions, a clean appearance, and a clear boundary particular with portions which must not come into contact with the barrier fluid. To avoid lubricant losses or pollution by lubricant in a bearing system, four oil barriers are usually necessary, two on the moving part and two on the stationary part of the bearing system, on 5 pair at each end of a bearing gap. The oil barrier has a thickness of approximately 0.5 μm.

The use of oil barriers is particularly effective and advantageous in maintenance-free bearing systems which must comply with very high requirements, inter alia as to their life. Such bearing systems are used, for example, in scanner motors for video recorders. The provision of oil barriers on components of the bearing system of these motors may be carried out by the conventional methods in view of the comparatively large dimensions of the components, for example, rotor spindles of approximately 6 mm diameter. When the method according to the invention is used, however, the oil barriers can be applied as part of a process and with the advantages explained above. The invention can be applied in a very efficient and advantageous manner to electric motors designed for driving the hard disk of a computer and comprising a rotor part and a stator part, the rotor part and the stator part forming a bearing system and being journalled relative to one another by means of a dynamic groove bearing. These motors are of a very compact design and have comparatively small dimensions, in particular the components to be treated. In a practical embodiment, the bearing spindle has a diameter of approximately 2.5 mm. As was explained above, the method according to the invention is particularly suitable for treating components of comparatively small dimensions of the order of a few millimetres, i.e. also for applying oil barriers on components of the dynamic groove bearing mentioned above. In spite of the comparatively small dimensions, the oil barriers applied by the method according to the invention are characterized by an even thickness and clearly defined proportions.

The invention will be explained in more detail with reference to the drawing, in which: Fig. 1 diagrammatically shows a device for carrying out the method according to the invention;

Figs. 2, 3 and 4 show the stamp of Fig. 1 in various embodiments;

Fig. 5 shows an embodiment of the device with a rotary stamp; and

Fig. 6 shows an electric motor for the hard disk drive of a computer, whose bearing system is provided with oil barriers applied by the method and the device according to the invention.

Comparable components have been given the same reference numerals in the drawings. The device 1 diagrammatically depicted in Fig. 1 substantially comprises a stamp 3 which can be moved reciprocally in vertical direction in accordance with double arrow A and which is driven by a conventional drive system (not shown). A tubular component 5 to be treated having a bore 7 is shown, i.e. a component of a bearing system o which an oil barrier C must be provided, indicated with a fat full line. The broken line B on the inner circumference of the bore 7 indicates a bearing surface, for example the spiral grooves of a spiral groove bearing. Reference numeral 9 denotes a holder for the component 5. The stamp 3 is also of tubular shape, at least the end portion shown, and is provided with a bore 11. The end face of the stamp 3 forms a rotationally symmetrical stamp face 13, here an annular stamp face. An annular raised rim 15 is provided on the stamp face 13, whereby the annular stamp face 13 is subdivided into two concentric annular faces 17 and 19. H is th height and D3 the diameter of the raised rim 15, and Dl and D2 are the external and interna diameters of the stamp 3. Symbols dl and d2 indicate the external and internal diameters of the component 5. A reservoir 21 contains a barrier fluid L which is known per se and whose composition has been discussed above. As was also noted earlier, the reservoir 21 may be provided with a lid (not shown) so as to prevent evaporation of solvent from the barrier fluid as much as possible. The internal diameter D2 of the stamp 3 is greater than the internal diameter d2 of the component 5. The diameter D3 of the raised rim 15 is greater than the external diameter dl of the component. The device operates as follows: in the idle position of the device 1, the stamp 3 is fully immersed in the barrier fluid L in the reservoir 21, below the level N of the fluid. To apply a quantity of barrier fluid in certain areas of the component 5, the stamp 3 is raised into an operational position, and the concentric annular face 17 of the stamp face 13 is brought into contact with a portion of the component 5 which is to be coated. In this movement, the stamp 3 carries along a certain quantity of the barrier fluid L, which forms two meniscuses on the stamp face 13: a meniscus Ml on the annular face 17 and a meniscus M2 on the annular face 19. The moment the concentric annular face 17 of the stamp face 13, i.e. the barrier fluid on the stamp face, comes into contact with the bottom of the component 5, a portion of, i.e. about half the barrier fluid carried along will spread over the region indicated with the full line C owing to the surface tension. After the return of the stamp 3 into the idle position and after evaporation of the solvent, within a few minutes, a colourless transparent film of a solid substance remains on the component 5, forming an oil barrier C with a thickness of approximately 0.5 μm. As mentioned above, this film may be cured, if so desired. The quantity of barrier fluid transferred depends on a large number of factors such as: the geometry of the stamp and of the surface to be coated, the transport time between idle and operational positions of the stamp, the contact time between stamp and component, flow behaviour and wetting characteristics of the barrier fluid, the possible degree of pollution of the stamp and the surface to be coated, etc. It should also be taken into account that a fluid spreads itself more easily over an internal angle than over an external angle. Generally, it is preferable to use a barrier fluid comprising a solid substance whose surface tension is lower than that of the usual lubricants. A suggestion is a substance with a surface tension lower than 18 mN.m"¹. In the embodiment shown in Fig. 1, the geometry, i.e. shape and dimensions, of the stamp 3, is so adapted to the geometry of the component 5 that a certain quantity of transferred barrier fluid spreads itself over the end face of the component as well as over a portion of the outer circumference, while it should be absolutely prevented that barrier fluid enters the bore 7 and the bearing surface B with the spiral grooves. To given an idea of sizes and dimensions occurring in practice, the dimensions of a practical application are listed here: the component 5 to be treated had an internal diameter d2 of 2.5 mm and an external diameter dl of 3.8 mm. The stamp 3 had an internal diameter D2 of 3 mm and an external diameter Dl of 6 mm. The diameter D3 of the raised rim 15 was 4 mm and its height H 0.5 mm. The volume of barrier fluid transferred was approximately 0.5 mm . The stamp was made from hardenable stainless steel, and the component was made from bearing bronze.

Fig. 2 shows the stamp 3 in an embodiment without bore, where the stamp face 13 is subdivided by the raised rim 15 with height H and diameter D3 into a lowered central circular face 23 and an annular face 25 with an external diameter Dl, so that a central chamber is formed on the stamp face.

The component 5 in this embodiment is formed by a shaft 27 with a shaft tip 29 of diameter d and height h. The barrier fluid is provided on the portion of the shaft tip indicated with the full line C, while the outer circumference of the shaft 27 serves as a bearing surface B and should remain free from barrier fluid. The barrier fluid to be transferred forms a double meniscus on the stamp face 13, one on the central circular face 23 and one on the annular face 25, which have flown together into a double meniscus M. The diameter D3 of the raised rim is greater than the diameter d of the shaft tip 29 to be coated.

In the embodiment shown in Fig. 3, the stamp 3 with external diameter Dl is provided with a bore 11 with diameter D2. An annular groove 31 with a depth G is provided on the stamp 3 in the stamp face 13 and is formed by two oblique ring surfaces 33 and 35 which enclose an angle with the stamp face 13. The tubular component 5 to be treated, provided with a bore 7, has an external diameter dl and an internal diameter d2. Th end of the component to be coated is provided with an annular collar 37 so that the free end of the component is stepped. The collar 37 has an internal diameter d3 and a height K. The internal diameter D2 of the stamp 3 is greater than the internal diameter d2 of the component 5 and smaller than the internal diameter d3 of the collar 37. The external diameters of the stamp 3 and the component 5 are substantially the same. The barrier fluid forming a meniscus M on the stamp face 13 is applied to three mutually perpendicular surfaces on the collar 37 of the component 5 indicated with a broken line C. No barrier fluid will reach the inner circumference of the bore 7, which circumference forms a bearing surface B.

In the embodiment shown in Fig. 4, the stamp face 13 of the stamp 3 is subdivided by the raised rim 15 of diameter D3 into a raised circular central platform 39 with a height H and an annular face 41 with a diameter Dl. The component 5 is disc-shaped and has a bore 7 of diameter d2, a bearing surface 45, and an annular end face 47 with an external diameter d3. The component 5 has a length L in axial direction. The barrier fluid forms two meniscuses on the stamp face 13, i.e. a meniscus Ml on the platform 39 and a meniscus M2 on the annular face 41. The diameter D3 of the platform 39 is smaller than the diameter d2 of the bore 7. The diameter Dl of the annular face 41 is smaller than the diameter d3 of the end face 47 on the component 5. The barrier fluid is provided on the end face 47 and in the bore 7 of the component 5, and creeps further upward in the bore 7. The adapted geometry of the stamp face of the stamp prevents the barrier fluid from creeping up too far and reaching the bearing surface 45.

Fig. 5 shows the device 1 in a special embodiment for providing an annular oil barrier on a cylindrical component of a bearing system, for example, in a groove 51 of a component 5. For this purpose, the stamp 3 of the device is constructed as a rotatable wheel 53 whose outer edge is adapted to the desired profile of the oil barrier to be provided, i.e. to the profile of the groove 51. The wheel 53 is mounted with rotation possibility in a bearing 55 and can be reciprocally moved between an idle position and an operational position by means of a drive system 59 with motor 61. The component 5 is centred and secured in a holder 9 which can be made to rotate by means of a drive shaft 63 and a motor 65. A bearing for the drive shaft 63 has reference numeral 67. A reservoir 21 i filled to the level N with barrier fluid. The reservoir 21 is partly closed off with a cover 69. The frame of the device is numbered 71. 9

In the idle position, the wheel 53 is in the reservoir 21, below the barrier fluid level N. During its displacement into the operational position the wheel 53 carries along a quantity of barrier fluid. In the operational position, the wheel hits with its outer edge against the component 5, which has in the meantime been made to rotate. The wheel is also made to rotate through contact with the rotating component, and the barrier fluid carried along by the wheel is transferred from the wheel 53 onto the component 5, i.e. into the groove 51 of the component.

Fig. 6 is a strongly enlarged (scale 10:1) diagrammatic drawing of an electric motor 81 designed for the hard disk drive of a computer, where a number of components are provided with oil barriers by the method and device according to the invention. The electric motor 81 essentially comprises a stator part 83 and a rotor part 85 which form a bearing system. The hard disk to be driven is diagrammatically indicated with 87. The stator part 83 substantially comprises a base plate 89, a fixedly arranged stator spindle 91, and a coil 93. These components are fixedly interconnected by suitable methods such as welding, forcing, gluing. The rotor part 85 comprises a hub portion 94, a shell 95, an iron ring 96, and a closing plate 97. These portions of the rotor part are also fixedly interconnected. The stator spindle 91 serves as a central bearing for the entire electric motor and is provided with an annular groove 51, a flange 98, and a spindle tip 99. The base plate 89, stator spindle 91, hub portion 94, and closing plate 97 are provided with oil barriers indicated with full lines C, which barriers were provided by the method and the device according to the invention. Thus the oil barrier C on the base plate 89 was provided with a stamp according to Fig. 3. The spindle tip 99 of the stator spindle 91 was treated with a stamp as shown in Fig. 2, while the oil barrier C in groove 51 was provided with the device of Fig. 5. The stamp shown in Fig. 1 was used for treating the hub portion 94, and the closing plate 97 was treated with the stamp of Fig. 4. The bearing system comprises a continuous bearing gap which runs alongside the broken lines B. The flange 98 of the stator spindle 91 is provided with spiral grooves B on both axial surfaces and serves as an axial bearing in conjunction with corresponding axial bearing surfaces on the closing plate 97 and the hub portion 94. The circumference of the stator spindle 91 from the flange 98 to the groove 51 serves as a radial bearing in conjunction with a spiral groove pattern B on the inner circumference of the hub portion 94. The bearing gap of the bearing system is limited by two oil barriers each time on either side, i.e. at the side of the spindle tip 99 and the side of the groove 51 on the stator spindle 91, one on the rotor part and one on the stator part. The oil barrier in the groove 51 of the stator spindle may be regarded as an additional safety measure.

The quantity of barrier fluid provided may be checked for deviations fro the nominal quantity in the process of implementing the method in that the levels of the meniscuses are registered by means of video cameras.

Furthermore, a substance may be added to the barrier liquid which renders it possible to check where barrier fluid is or is not present on the component by means of an UV lamp.

Claims

CLAIMS:

1. A method of providing an oil barrier on a component of a bearing system, whereby a barrier fluid comprising a solid substance and a solvent is applied to a surface of the component in a rotationally symmetrical pattern, said solid substance remaining on said surface in the form of a film and acting as an oil barrier after evaporation of the solvent, characterized in that the barrier fluid is provided by means of a stamp, the stamp being immersed in the barrier fluid in a reservoir and then raised from the reservoir containing the barrier fluid, so that a quantity of barrier fluid forms a meniscus on a stamp face and is carried along by the stamp, the stamp being pressed subsequently with the stamp face against the surface of the component to be coated, whereby eventually at least a portion of the barrier fluid carried along is transferred from the stamp to said surface.

2. A method as claimed in Claim 1 for providing an annular oil barrier on a cylindrical component of a bearing system, characterized in that a disc-shaped stamp is used which is pressed with its edge against the component during the transfer of the barrier fluid, while the stamp and the component are made to rotate relative to one another.

3. A device for implementing the method as claimed in Claim 1 and 2, substantially characterized by a reservoir, a stamp which is displaceable in vertical direction and which has a rotationally symmetrical stamp face, a drive system for displacing the stamp, and a holder for a component of a bearing system.

4. A device as claimed in Claim 3, characterized in that the stamp is provided with a central bore in the end having the stamp face.

5. A device as claimed in Claim 3 or 4, characterized in that the stamp has an annular raised rim on the stamp face.

6. A device as claimed in Claim 3, 4 or 5, characterized in that the stamp has an annular groove in the stamp face.

7. A device as claimed in any one of the Claims 3 to 6, characterized in that the stamp is constructed as a rotatable wheel, and the holder for the component is rotatable, the device being further provided with a drive system for driving the holder.

8. A component of a bearing system provided with at least one oil barrier, which oil barrier is provided by the method as claimed in Claim 1 or 2.

9. A bearing system with components which are movable relative to one another and which are each provided with at least one oil barrier, which oil barriers are provided by the method as claimed in Claim 1 or 2.

10. An electric motor, in particular designed for a hard disk drive of a computer, comprising a rotor part and a stator part, wherein the rotor part and the stator part form a bearing system and are journalled relative to one another by means of a dynamic groove bearing, characterized by oil barriers on the rotor part and on the stator part and on either side of the dynamic groove bearing, which oil barriers are provided by the method as claimed in Claim 1 or 2.