JP3180992B2 - Porous hydrostatic bearing and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION As means for improving the smoothness and accuracy of relative motion between solids and maintaining the same for a long time, a fluid, for example, oil or air, is supplied under pressure between the solids so that the solids move between solids. There is a fluid lubrication that makes the non-contact floating. As an example of this, there is a hydrostatic bearing in which a high-pressure fluid is supplied to a gap between a solid, that is, a gap between a shaft and a bearing to float in a non-contact manner. As an example of a method for supplying a fluid to a minute gap between a shaft and a bearing in a hydrostatic bearing, there is a method in which one of the shaft and the bearing is formed of a porous body. This hydrostatic bearing is characterized in that a porous body also serves as a fluid passage and a different function of a throttle. The present invention relates to a configuration and a manufacturing method of a passage and a throttle of a porous body in a hydrostatic bearing using the porous body.

[0002]

2. Description of the Related Art As a porous material for a porous hydrostatic bearing, a porous material produced by sintering powder of metal, carbon (graphite), or ceramic is used. There is only carbonaceous porous material and other materials can be said to be research level. Further, even if the material is a porous carbonaceous material, the applicable fluid is a gas (usually air), and the porous hydrostatic bearing itself can be said to be a developing technology. FIG. 5 is a cross-sectional view showing an example of a conventional hydrostatic bearing using a carbonaceous porous material, wherein 1 is a cylindrical hollow shaft serving as a rotating shaft, and 2 is also a cylindrical carbonaceous porous serving as a bearing. The body, or 3, is a face plate connected to both sides of the hollow shaft 1. 4 is a minute radial gap formed between the hollow shaft 1 and the carbonaceous porous body 2 in the radial direction; 5 is an axial gap formed between the face plate 3 and the carbonaceous porous body 2 in the axial direction; A case for holding the porous porous body 2, 7 is an air supply hole for passing compressed air through the case 6 to the carbonaceous porous body 2, and 8 is an air supply groove provided on the outer periphery of the cylinder of the carbonaceous porous body 2. , 9 are the radial gap 4 and the shaft gap 5
It is an exhaust port to make the air supply to the space independent.

Hereinafter, the function as a hydrostatic bearing will be described.
The compressed air supplied from the air supply hole 7 passes through the carbonaceous porous body 2 through the air supply groove 8, flows through the radial gap 4 and the shaft gap 5, and is released into the atmosphere. The pressure of the compressed air is
The inside is the same, but after being temporarily reduced by the flow path resistance in the carbonaceous porous body 2, the flow path resistance in the radial gap 4 and the shaft gap 5 is further received, and the pressure is released to outside the bearing as atmospheric pressure. . However, the flow path resistance in the carbonaceous porous body 2 does not change, but the flow path resistance in the radial gap 4 and the axial gap 5 greatly changes depending on the size of the gap (inversely proportional to the cube of the gap). Therefore, when the hydrostatic bearing receives some external force and, for example, causes a difference between the opposed radial gap 4 or the axial gap 5, the flow path resistance on the side where the gap is reduced increases, and the pressure in the gap increases by that amount. . However, the gap on the opposite side is just the opposite, so the pressure in the gap drops. As a result, the hydrostatic bearing acts so that the pressure in the opposed gap increases or decreases so that the flow path resistance in the opposed radial gap 4 and the opposed axial gap 5 is always constant. Usually, a value obtained by dividing a value obtained by converting a pressure change into a force by a change amount of a gap is referred to as a spring constant, that is, rigidity. The higher the rigidity and the higher the rotational accuracy, the higher the performance of the hydrostatic bearing. In addition, in the porous hydrostatic bearing, the flow resistance of the porous body is designed to be approximately 1/2 to 3/4 of the bearing gap. Therefore, if the bearing clearance can be designed to be small, the overall flow path resistance becomes large, so that a low-flow and high-rigidity hydrostatic bearing is obtained. On the other hand, most of the flow path resistance in the bearing gap is the friction resistance between the fluid and the gap wall surface, but the flow path resistance of the porous body is determined by the fluid and the porous material if the thickness of the fluid passage in the porous body is sufficiently smaller than the bearing gap. Although the friction resistance (capillary restriction) with the wall surface is mainly used, it is not easy to manufacture a porous body having a fluid passage finer than the bearing gap. Even if it can be manufactured, control of the flow path resistance between the inlet and the outlet of the fluid becomes a problem as described later.

It is the clearance between the bearings that most affects the increase in rigidity of the hydrostatic bearing. This is because, as the gap becomes smaller, the pressure rises and falls in response to a minute gap change, and as a result, the rigidity becomes higher (inversely proportional to the gap). Inversely proportional to the cube). Furthermore, as a result of increasing the member accuracy in order to reduce the gap between the shaft and the bearing, the rotation accuracy is also improved by that much. As described above, the miniaturization of the bearing gap is directly linked to the high performance of the hydrostatic bearing by the high precision itself. However, high precision is greatly affected by the properties of the material to be processed, such as strength, hardness, expansion coefficient, dimensional stability, and the like. Compared with a ceramic material capable of high-precision processing, the carbonaceous porous body 2 having poor strength and hardness is a material unsuitable for precision processing, and thus has a drawback that restricts further increase in rigidity of a hydrostatic bearing. . Furthermore, since the carbonaceous porous body 2 has low strength, if the supply pressure is high, the carbonaceous porous body 2 is deformed or broken in the axial direction or the radial direction due to the internal pressure of the supply groove 8. For this reason, the carbonaceous porous body 2 has a disadvantage in that its size is large in strength compared to metals and ceramics. In particular, the disadvantage of the strength of the carbonaceous porous body 2 is that it is limited to application to a static pressure gas bearing (about 0.5 MPa) which requires a low supply pressure.
This makes application to a hydrostatic bearing (about 5 MPa or more) difficult. In addition, it goes without saying that the performance of the hydrostatic bearing will be adversely affected unless proper air supply to the bearing gap is performed even if high precision is realized. The design values of the diameter gap 4 and the shaft gap 5 are generally determined from the precision that can be processed. The supply air flow rate is determined by back-calculating the flow path resistance from the design value. However, in order to pass through the inside of the carbonaceous porous body 2 from the sole air supply hole 7 and supply the flow rate determined to the radial gap 4 and the shaft gap 5 at different locations, the shape and the transmittance of the carbonaceous porous body 2, Since the layout and the like of the air supply groove 8 are complicatedly related, the design thereof is not easy. Even if it can be designed, the production of the carbonaceous porous body 2 by the sintering method tends to change its quality depending on the conditions such as the particle size of the carbon powder, the binder, the pressure and the temperature at the time of molding, and the uniform and desired transmittance Carbonaceous porous material 2
Is not easy to obtain. As described above, in further improving the performance of the hydrostatic bearing, the carbonaceous porous body has various drawbacks in terms of member strength, suitability for high-precision processing, ease of design and manufacture, and the like.

On the other hand, if only the carbonaceous porous body 2 in FIG. 5 is replaced with a ceramic porous body, a hydrostatic bearing can be realized which has solved the drawbacks of the carbonaceous porous body such as low strength of the member and lack of suitability for high precision processing. . However, it does not lead to ease of design and manufacture. The biggest disadvantage of the conventional hydrostatic bearing using such a porous body is that the design and manufacture cannot be facilitated, and the cause is that the porous body has a different role of a fluid passage and a throttle. is there. That is, in the hydrostatic bearing of the conventional structure, the flow path resistance from the air supply hole 7 to the shaft gap 5 and the radial gap 4, that is, the amount of throttle of the fluid is not determined only by the transmittance of the porous body, and the structure and shape of the porous body are not determined. The close relationship has been a factor preventing easy design and manufacture. On the other hand, the porous body also serves as a fluid passage and a throttle, but the flow path resistance of the porous body is
There is a method in which the flow path resistance is manufactured to be slightly smaller than the actually required flow path resistance, and the flow path resistance after the bearing is manufactured is accurately controlled to the actually required transmittance. After manufacturing a bearing member corresponding to the carbonaceous porous body 2 in FIG. 5 using a porous body having a transmittance slightly smaller than the transmittance required as the example, the shaft gap 5 and the radial gap 4 are formed. A method shown in FIG. 6 in which the cross-sectional area of the fluid passage in the porous body is reduced by applying, for example, electroless nickel plating (hereinafter referred to as plating) to the surface of the porous body to control the transmittance, that is, the amount of restricting the fluid ( JP-A-64-6515)
There is.

FIG. 6 is a schematic view showing a cross section of a porous body which has been subjected to transmittance adjustment by plating, wherein 10 is a fleshy portion of the porous body, 11 is a hole existing between the fleshy portions 10, and 12 is a fleshy portion. 13 is a plating film attached to the surface of the portion 10, 13 is a bearing surface, 14
Is a bearing gap. Normally, a porous body produced by sintering or the like is bonded by thermally diffusing composition molecules and a sintering aid between sintered particles at a temperature equal to or lower than a melting point. Therefore, the pores formed between the particles have a three-dimensional structure in which the pores 11 are connected in a cluster as shown in the figure. Therefore, the transmittance of the fluid passing therethrough, that is, the flow path resistance is determined by the effect of the cross-sectional area between the holes 11 having the smallest cross-sectional area. The transmittance adjustment by plating is controlled by reducing the cross-sectional area between the holes 11 by the thickness of the plating film 12.
However, in this method, when the thickness of the plating film 12 is increased because the size of the cross-sectional area between the holes 11 is originally large, the plating film 12 is sealed from the small cross-sectional area between the holes 11 first. The outlet of the fluid on 13 decreases gradually. Conversely, it means that the cross-sectional area between the small holes 11 is sealed and controlled. As a result, the cross-sectional area between the large holes 11 remains roughly, making it difficult to supply a uniform fluid to the bearing gap 13. In addition, the holes 11 originally opened on the bearing surface 13 are left behind even after plating, and become useless gaps of the bearing to reduce the rigidity of the hydrostatic bearing, or a pneumatic hammer peculiar to the hydrostatic bearing, that is, air Causes self-excited vibration based on the compressibility of There are drawbacks.

In addition, the clearance of a porous bearing is usually 5 μm.
The following is common. In this case, when the flow resistance of the porous body is mainly determined by the frictional resistance (capillary restriction) with the wall surface of the porous body as described above, the diameter of the hole 11 is 5 μm or less.
In particular, the reduced portion of the cross-sectional area due to plating must be of the order of μm. If the diameter of the pores 11 is 5 μm or less, even if gas can enter the porous body, in addition to penetration of a liquid plating solution, there is a difficulty in controlling transmittance by plating itself. For this reason, since a porous body having pores 11 that is significantly larger than the bearing gap is used, transmittance control is inevitable in which residual pores 11 on the bearing surface and uneven supply of fluid are inevitable. Therefore, in actuality, the flow resistance of the porous body controlled by the plating is reduced in the ratio of the frictional resistance (capillary restriction) with the wall surface of the porous body, and the flow resistance (orifice restriction) from the small hole on the porous body surface and the bearing clearance are reduced. An aperture having a mixture of steps formed by the shape of the porous body surface and outflow resistance (surface aperture, self-generated aperture) due to voids and the like is mixed. Since these throttles have different characteristics as the throttle, the performance of the hydrostatic bearing varies as much as the mixing ratio. Capillary and orifice throttles show a constant flow resistance regardless of the change in bearing clearance, while surface and self-contained throttles have a lower flow resistance as the bearing clearance increases and a decrease in clearance decreases the flow resistance. Shows rising characteristics. As the effect of increasing the rigidity of the bearing, the better the mixing ratio of the capillary throttle and the orifice throttle, the better the result. The flow path resistance increases when the clearance between the bearings increases, and the flow path resistance decreases when the clearance decreases. However, such a throttle does not exist at present. As described above, it has been described that the configuration of the hydrostatic bearing using the transmittance control by plating has various disadvantages.

[0008]

SUMMARY OF THE INVENTION The present invention has been proposed to improve the above-mentioned drawbacks, and an object of the present invention is to provide a porous member provided with a new means for forming a fluid passage and a means for controlling a fluid restriction. An object of the present invention is to provide a hydrostatic bearing and a manufacturing method thereof.

[0009]

In order to achieve the above object, the present invention provides a hydrostatic bearing for supplying a fluid to a gap between solids to float in a non-contact manner, wherein the hydrostatic bearing is connected to a fluid supply hole, and A porous body having an opening in a part of the bearing gap is included in the dense ceramic, and the opening of the bearing gap of the porous body is a porous body formed by embedding and fixing small-diameter particles with a binder. A feature of the present invention is a porous ceramic hydrostatic bearing. further,
The present invention relates to a method for manufacturing a ceramic porous hydrostatic bearing in which a porous body connected to a fluid supply hole and having an opening in a part of a bearing gap is included in a dense ceramic. A method for manufacturing a ceramic porous hydrostatic bearing, wherein a porous body is integrally formed by a slurry casting method, and small-diameter particles are embedded and fixed in an opening of the bearing gap of the porous body with a binder. It is assumed that. In other words, the present invention provides, as a first means, that is, as a configuration of the fluid passage, a porous body which is connected to the fluid supply hole inside the dense ceramic and has an opening in a part of the bearing gap. A part of the porous body extending from the fluid to the bearing gap is limited to a fluid passage, thereby forming a hydrostatic bearing component having no throttle control function. As a second means, that is, as a fluid restricting control, by embedding and fixing particles smaller than the cross-sectional area of the opening in the opening of the porous body having an opening in a part of the bearing gap to form a porous body, The cross-sectional area of the partially porous body opening is reduced to control the flow path resistance, that is, the fluid restriction. The above two means limit the role of the porous body only as a fluid passage, and the control of the fluid restriction is separately controlled by a method of embedding and fixing particles. Therefore, it is characterized in that the formation of the fluid passage and the control of the throttle are separated and independent, as well as the strength and accuracy of the hydrostatic bearing member made of ceramic porous material.

[0010]

In the present invention, since the restriction of the fluid passage is controlled by embedding and fixing small-diameter particles in the opening constituting the bearing surface, it is possible to control the restriction with high precision.

[0011]

Next, an embodiment of the present invention will be described. FIG.
FIG. 1 is a cross-sectional view of an embodiment showing the structure of a hydrostatic bearing of the present invention. In the drawing, reference numeral 15 denotes a ceramic partially porous body made of ceramic in which a partially porous body is integrally formed inside a hollow cylinder. is there. Reference numeral 16 denotes a part of the ceramic partial porous body 15, which is a porous body integrally formed in the ceramic partial porous body 15 and serves as a fluid passage. Reference numeral 17 denotes a shaft gap outlet made of the same material as the porous body 16. The ceramic porous body 15 is annularly opened at the axial end face. Reference numeral 18 denotes a radial gap outlet made of the same material of the porous body 16 and is also opened in an annular shape toward the inside of the hollow cylinder of the ceramic partial porous body 15. 7 is a ceramic partial porous body 15
Are air supply holes formed in the porous body 16 from the outside. However, at this stage, the porous body 16 is set to have a transmittance that greatly exceeds the fluid supply amount required for the shaft gap 5 and the radial gap 4. The opening of the porous bearing gap is formed by embedding and fixing small-diameter particles with a binder. With such a structure, if a pressurized fluid is supplied to the air supply hole 7, the fluid is diverted from the porous body 16 to the shaft gap outlet 17 and the diameter gap outlet 18, and the fluid flows through the shaft gap 5 and the diameter gap 4 respectively. It passes through and is released outside the bearing at atmospheric pressure. The function as the hydrostatic bearing is not different from that of the conventional carbonaceous porous body 2, and therefore the description is omitted.

Next, an example of a method for manufacturing the ceramic partial porous body 15 will be briefly described. In order to form a porous portion having a specific shape inside the ceramic, a shape forming method called a slurry casting method is used. The usual slurry casting method is
When a slurry (hereinafter, referred to as a slurry) in which ceramic particles and a sintering aid are dispersed in water is poured into a gypsum mold having a desired outer frame shape, moisture in the slurry is gradually absorbed by the gypsum mold, The ceramic particles land on the mold. As a result, a cast product of ceramic particles equivalent to a gypsum mold is completed. This is dried and sintered to form a ceramic, which is a slurry casting method. Although the ceramic obtained by the slurry casting method is dense and has high strength, it is impossible to make a specific portion of the ceramic into a porous body by simple slurry casting. In order to make a specific portion of the ceramic a porous body, the shape of the specific portion is equal to that of the specific portion.
A sponge made of (polyvinyl acetal) is set in a gypsum mold in advance, and a slurry is poured thereinto to produce a cast product containing the sponge. If this is sintered, the sponge sublimates during sintering. As a result, a porous ceramic can be produced only in a specific portion.

[0013] The cast product before sintering manufactured by the slurry casting generally exhibits properties like black ink used when writing characters or pictures on a blackboard, and thus is easily formed into a desired shape by cutting or the like. Can be processed. However, since it shrinks due to sintering, it is necessary to manufacture it accordingly. However, after sintering, the ceramic is transformed into a dense and high-hardness ceramic, so that only grinding and polishing can be applied, but extremely high finishing accuracy can be obtained. In addition, when producing partially porous ceramics by the slurry casting method, if ceramic particles are not filled in all the pores of the sponge, nests will form inside,
A sponge having a coarse pore density is more suitable for slurry casting. Therefore, it is more advantageous to form a porous body having a large transmittance, that is, a coarse porous body, than forming a porous body having a small transmittance, that is, a dense porous body. As described above, the slip casting has a difficulty in producing a dense porous body having a small transmittance, but has an advantage that the precision can be improved. However, as described above, increasing the rigidity of the hydrostatic bearing is closely related to minimizing the bearing gap, and the higher the precision, the greater the flow resistance in the bearing gap. Also need to be increased in proportion to this. However, although the ceramic porous body formed by slurry casting is suitable for high precision, it is not suitable for obtaining a porous body having high density and large flow path resistance. However, because of low flow resistance, it is suitable as a fluid passage. The foregoing has described the structure of the hydrostatic bearing according to the present invention, particularly the configuration of the fluid passage made of ceramic, and an example of the method of manufacturing the same. Hereinafter, a new method of controlling the aperture will be described.

FIG. 2 shows the method of controlling the restriction according to the present invention applied to the fluid outlet, that is, the shaft gap outlet 17 or the radial gap outlet 18 in the ceramic partial porous body 15 manufactured by the slurry casting shown in FIG. It is a schematic diagram of an enlarged cross section. However, the structure of the porous body is the same as that of FIG. 1 for easy understanding. Reference numeral 19 denotes small-diameter particles for transmittance control embedded and fixed in the holes 11 existing in the openings of the fluid passages of the ceramic partial porous body 15. By embedding and fixing the small-diameter particles 19 in the fluid outlet of the ceramic partial porous body 15, the cross-sectional area of the fluid passage is reduced to control the passage rate, that is, the flow passage resistance. The embedding of the small-diameter particles 19 is performed by filling the small-diameter particles 19 into the partially porous ceramic body 15 and fixing the same. Hereinafter, the embedding and fixing of the small-diameter particles 19 will be described.

FIG. 3 is a schematic view showing an example of a device configuration for embedding and fixing the small-diameter particles 19. Reference numeral 17 denotes a shaft gap outlet of the fluid on the ceramic partial porous body 15;
Is a circular gap outlet, 20 is a ring seal for individually masking the axial gap outlet 17, 21 is a cylindrical seal for individually masking the radial gap outlet 18, 22 is a small particle 1
A slurry in which 9 is dispersed in a tetraethoxysilane-based binder; 23, a dropper for removing the slurry 22;
Reference numeral 24 denotes a spatula for removing an excessive slurry 22.
Reference numeral 25 denotes a vacuum pump for evacuating the inside of the ceramic partial porous body 15, and 26 denotes a ceramic partial porous body 1.
A separator for removing the small-diameter particles 19 and the vanida liquid that have passed through 5, a vacuum gauge 27 for observing the pressure in the separator 26, a filter 28 for allowing the vacuum pump 25 to pass anything but gas, Reference numeral 29 denotes a vacuum hose that connects the ceramic partial porous body 15, the separator 26, the filter 28, and the vacuum pump 25. Hereinafter, a procedure for embedding the small-diameter particles 19 will be described.

After masking the portion other than the shaft gap outlet 17 filled with the small-diameter particles 19 using the ring seal 20 or the cylindrical seal 21, the inside of the ceramic partial porous body 15 is evacuated by operating the vacuum pump 25. Next, when the slurry 22 in the dropper 23 is supplied onto, for example, the shaft gap outlet 17, the slurry 22 is vacuum-sucked into the porous material, and as shown in FIG. The small-diameter particles 19 stagnate in the cross-sectional area between the holes 11 having the smallest cross-sectional area, and this triggers the small-diameter particles 19 to fill the inside of the passage of the porous body. However, since the binder in the slurry 22 is a viscous liquid, most of the binder is removed through the gap between the small-diameter particles 19, but the small-diameter particles 19 and the binder attached to the wall surfaces of the holes 11 are left behind. Since the binder is cured after a certain time, a large number of small-diameter particles 19 can be embedded and fixed in the holes 11. After the curing, firing in a furnace can greatly increase the bonding strength of the binder.

FIG. 4 is a schematic enlarged view of the situation where the small-diameter particles 19 are embedded and fixed, as viewed from the bearing surface 13 side in FIG. 1
Numeral 0 denotes a fleshy portion of the ceramic partial porous body 15, 30 denotes a new passage for a fluid newly opened between the embedded and fixed small-diameter particles 19, and 31 denotes a hardening that is left behind between the wall surface of the fleshy portion 10 and the small-diameter particles 19. It is a binder that did. As shown in the figure, the pores 11 existing between the fleshy portions 10 are hard to be distinguished because the pores 11 are filled with small-diameter particles 19 and the porous body is formed. A large number can be formed three-dimensionally, and the cross-sectional area of the fluid passage can be greatly reduced. Although the schematic diagram shows the small-diameter particles 19 having the same diameter and the binder 31 having the same thickness for easy understanding, the size of the pores 11 of the ceramic partial porous body 15 to be controlled in actual embedding and fixing is controlled. Although it is related, the diameter of the small-diameter particles 19 and the viscosity of the binder 31 can be selected, and these are used for controlling the slurry 22 multiple times, or controlling the exhaust pressure by the vacuum pump 25 or the like. Many conditions exist. Therefore, it is not difficult to select a condition for setting the transmittance of the shaft gap outlet 17 and the diameter gap outlet 18 shown in FIG. 1 to a target value.

Hereinafter, the tetraethoxysilane-based binder will be briefly described. The chemical structure of the basic tetraethoxysilane is

Embedded image It reacts with water in the presence of a catalyst to produce silica (SiO ₂ ) as follows. Si (OC ₂ H ₅ ) ₄ + 2H ₂ O → (catalyst) → SiO ₂
+ 4C ₂ H ₅ OH It contains about 28% silica and tetraethoxysilane, ethanol and the like. What has been further concentrated to a silica content of about 40% by partial hydrolysis is generally used as a silica raw material. A hydrolyzate obtained by mixing a solvent, water, an acidic catalyst and the like is used for vanida. It is considered that ordinary hydrolyzate is a colloidal dispersion of SiO _{2 in an} alcohol solvent, and when particles are mixed and applied to this hydrolyzate, an SiO ₂ film is formed in such a way as to wrap the particles or fill the gaps Is done. By this action, the particles are fixed to the surface of the object, or the particles are solidified and formed. Typical uses are a sand-type solid agent used for precision casting such as lost wax and a show process, and a surface hardening agent for plastic materials. In addition, extremely fine S
The viscosity can be adjusted by mixing iO ₂ fine particles. Further, when SiO ₂ is used, the chemical resistance at the time of washing the fluid passage is excellent, the plating is easy because it is hydrophilic, and the resistance change due to swelling is small because it has moisture resistance.
Since it is resistant to heat, it is easy to reinforce the fixing force by reheating after determining the resistance. Furthermore, since SiO ₂ has a solvent (hydrofluoric acid), it can be removed without damaging the ceramic, so that the resistance can be readjusted and the base ceramic can be recycled. In the above, two means relating to the configuration of the fluid passage and the control of the fluid restrictor for improving the drawbacks of the conventional hydrostatic bearing have been described.

However, needless to say, in the first means of the embodiment, the production of a ceramic in which only a specific portion is made of a porous body can be carried out by a usual sintering method in which ceramic particles are sintered and bonded. In short, it is characterized in that the porous body is made to have a transmittance that does not act as a restrictor for a fluid as in the related art. As described above, in order for the porous body to act as a fluid restrictor, FIG.
That the average diameter of the holes shown in (1) is equal to or smaller than the gap between the bearings, and that the flow path resistance of the porous body is ２〜 to ／ of the flow path resistance of the bearing gap.
Is desirable. However, if the fluid passage configuration and the throttle control of the present invention are used, even if the average diameter of the pores is one order of magnitude or more larger than the bearing gap, the flow resistance of the porous body is 1/100 of the flow resistance of the bearing gap.
Needless to say, there is no problem even if the number is 10 or less, but the easiness of manufacture has priority. Incidentally, the permeability K of the porous body suitable for the configuration of the fluid passage of the present invention is expressed as follows: K = (Q · L) / (△ PA) (cm ³ / sec) · c
m / cm ² · cmH ₂ O gas flow rate Q (cm ³ / sec), permeation thickness L (cm),
When the pressure difference ΔP (cmH ₂ O) and the permeation cross-sectional area A (cm ² ) are defined, the value of K is around 1 × 10 ^-2 , and the average pore diameter is about 50 μm to 150 μm. It is easy to manufacture and suitable for controlling the aperture. Alumina (AL ₂ O ₃ ) is usually used for the ceramic material, but is not limited to this. For example, silicon nitride (Si) may be used.
Needless to say, N) or silicon carbide (SiC) may be used.

In the second means of the embodiment, the material of the small-diameter particles is not specified, but silicon oxide (SiO ₂ ) of the same material as the tetraethoxysilane-based binder is suitable, but is not limited thereto. Needless to say, ceramic or metal powder or originally small porous particles may be used. It goes without saying that the size of the small-diameter particles also needs to be selected according to the design of the target porous material and the hydrostatic bearing. Further, the small-diameter particles were embedded and fixed with a tetraethoxysilane-based binder, but the present invention is not limited to this, and it is needless to say that the transmittance may be adjusted by conventional electroless plating after temporary fixing. Is embedded and fixed in a porous body with a binder to form a porous body. In the above, the new configuration means of the fluid passage made of the ceramic porous body and the new restriction forming means made of the porous body have been described in detail using the embodiments. In the configuration of the fluid passage in the conventional porous hydrostatic bearing, the passage of the porous body itself is configured as the control means of the flow path resistance, whereas the configuration of the fluid passage of the present invention is opposite to the conventional one. It is configured so as not to be a control means of the flow path resistance. The construction method is completely opposite to the conventional one, and there is a great difference. Further, the flow path resistance control means in the conventional porous hydrostatic bearing controls the flow resistance of the porous flow path constituting the fluid passage, whereas the flow path resistance control means of the present invention employs a porous body constituting the fluid passage. Controls the flow resistance of a porous body in a porous body having completely different densities and manufacturing methods. That is, the porosity to be controlled is completely different, and there is a great difference.

[0021]

As described above, since the structure of the fluid passage in the hydrostatic bearing of the present invention is made of ceramic and the role of the porous body as the fluid passage can be limited, the following effects can be obtained. (1) The porous body only needs to be a fluid passage having a sufficiently high transmittance, and therefore, there is not much required precision in the configuration dimensions, the transmittance of the porous body, and the homogeneity and variation thereof. (2) The porous body is a minimum necessary as a fluid passage, and most of the bearing structure can be made of a dense ceramic having high strength and hardness. Accordingly, the supply pressure can be increased as well as the size of the hydrostatic bearing can be reduced by this amount, so that application to a hydrostatic bearing is also possible. (3) It can be made of ceramic suitable for high-precision processing. Therefore, high rigidity, low air supply flow rate, high rotational accuracy, etc., which are closely related to the high precision of the hydrostatic bearing, can be achieved. Further, the throttle control of the fluid passage in the present invention has the following effects because the porous body is formed by embedding and fixing small-diameter particles in the porous body opening constituting the bearing surface. (4) The aperture control can be performed with a high degree of accuracy by controlling the transmittance while observing the flow path resistance. (5) Since the density of the porous material in the porous body can be changed by selecting the size of the small-diameter particles, the viscosity of the binder, and the like, the control range of the fluid restriction can be greatly expanded. (6) The small number of small fluid outlets can be formed in the porous body by reducing the porous density, and the distribution of fluid supply to the bearing gap can be made uniform. (7) Since a large number of small fluid outlets, that is, orifice throttles, which are superior as throttle characteristics on the bearing surface, can be formed, the rigidity of the hydrostatic bearing can be increased. (8) Since the pores of the porous body opened on the bearing surface can be filled with the small-diameter particles and the binder, the useless gap can be reduced by that much, and the rigidity of the bearing can be increased, and the pneumatic hammer can be reduced. In addition to overcoming the design and manufacturing disadvantages of conventional porous hydrostatic bearings, it has many advantages that can greatly improve the application range and overall performance of porous hydrostatic bearings. A low-flow, high-rigidity, high-speed, and high-accuracy hydrostatic bearing utilizing the advantages can be realized.

Although the present invention has been described in detail by taking the hydrostatic lubrication between the shaft and the bearing as an example, if the shaft and the bearing are replaced with a guide and a slider, or a screw shaft and a nut, the shaft and the bearing can rotate. The guide, the guide and the slider are linear guides, and the screw shaft and the nut are helical guides, all of which are guides. Therefore, it is needless to say that the basic concept of the configuration method of the fluid passage and the throttle in the porous hydrostatic bearing of the present invention can be applied to all hydrostatic lubrication mechanisms. Further, the hydrostatic bearing according to the present invention can be applied to non-contact fluid lubrication using liquid as well as gas, and its performance can be remarkably improved as compared with the prior art. Therefore, if the present invention is applied to a spindle, a guide, a stage, a hydrostatic screw, or the like as a mechanical component using the present hydrostatic lubrication, the characteristics thereof can be fully utilized.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment showing a structure of a hydrostatic bearing of the present invention.

FIG. 2 is a schematic view of an enlarged cross section obtained by performing the aperture control method of the present invention.

FIG. 3 is a front view of a schematic diagram showing an example of an instrument configuration for embedding and fixing small-diameter particles.

FIG. 4 is a cross-sectional view of a schematic enlarged view showing a state of a bearing surface in which small-diameter particles are embedded and fixed.

FIG. 5 is a cross-sectional view showing an example of a conventional hydrostatic bearing using a carbonaceous porous body.

FIG. 6 is a schematic diagram of a cross section of a porous body having undergone plating transmittance adjustment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 rotating shaft 2 carbonaceous porous body 3 face plate 4 diameter gap 5 shaft gap 6 case 7 air supply hole 8 air supply groove 9 exhaust port 10 fleshy portion 11 void 12 plating film 13 bearing surface 14 bearing gap 15 ceramic partial porous body 16 Porous body 17 Shaft gap outlet 18 Diameter gap outlet 19 Small diameter particles 20 Ring seal 21 Cylindrical seal 22 Slurry 23 Dropper 24 Spatula 25 Vacuum pump 26 Separator 27 Vacuum gauge 28 Filter 29 Vacuum hose

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F16C 32/06 B28B 1/26 C04B 33/28 C04B 38/06

Claims (2)

(57) [Claims] 1. A hydrostatic bearing for supplying a fluid to a gap between solids to float in a non-contact manner, wherein a porous body connected to a fluid supply hole and having an opening in a part of the bearing gap is made of a dense ceramic. A ceramic porous hydrostatic bearing, wherein the opening is formed inside the porous body and is formed by embedding and fixing small-diameter particles with a binder. 2. A method of manufacturing a ceramic porous hydrostatic bearing in which a porous body connected to a fluid supply hole and having an opening in a part of a bearing gap is included in a dense ceramic. And forming the porous body integrally by a slurry casting method, and embedding and fixing small-diameter particles into an opening of the bearing gap of the porous body with a binder.