JPH0587143A - Static pressure fluid bearing device - Google Patents

Abstract

PURPOSE:To prevent the seizure of a static pressure fluid bearing during high speed rotation and the contact of a thrust plate. CONSTITUTION:The bearing housing 4 of a static pressure fluid bearing 3 is provided with water-cooled jackets 5 so as to hold cylindrical static pressure pads 7 respectively opposed to the cylindrical outer surface of a rotary shaft 1 and a thrust plate 2. The rotary shaft 1 and the thrust plate 2 are made of silicon carbide or silicon nitride small in thermal expansion so as to prevent the generation of seizure caused by the decrease of a bearing clearance due to thermal expansion during high speed rotation. A deformation preventing member 9 is further provided on the face, opposite to the face jointed to the rotary shaft 2, of the thrust plate 2, so that the thrust plate 2 is prevented from coming in contact with the annular static pressure pads 7 because of deformation caused by centrifugal force during high speed rotation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrostatic bearing device used for a spindle of a precision machine tool, and more particularly to a hydrostatic bearing device suitable for a precision machine tool rotating at high speed.

[0002]

2. Description of the Related Art Hydrostatic bearings are widely used for spindles of precision machine tools because they have almost no friction and therefore have very small torque due to rotational friction and have extremely high rotational accuracy.

However, at the time of high speed rotation, the amount of heat generated by viscous friction of the pressurized fluid increases, so that the bearing housing is provided with a water cooling jacket, but the temperature rises significantly because there is no cooling means on the rotating shaft. As a result, the thermal expansion of the rotary shaft reduces the gap between the bearing and the rotary shaft, which may cause seizure.

A known example using ceramics for the rotating shaft is alumina (coefficient of thermal expansion 7 to 8 × 10 ^-6 ), but in this case, it is intended to reduce inertia and is called a heat countermeasure. In terms of points, there was no great difference in the coefficient of thermal expansion from that of steel, and they did not contribute.

Therefore, conventionally, a large bearing gap is set in advance to prevent seizure during high-speed rotation.

[0006]

According to the above-mentioned conventional technique, as described above, the bearing gap is set large for the purpose of preventing the seizure due to the thermal expansion at the high speed rotation, so that the bearing gap is too wide at the low speed rotation. Therefore, there is a problem that the bearing rigidity is reduced.

Further, at the time of high speed rotation, a large centrifugal force is applied to the thrust plate attached to one end of the rotating shaft, so that the thrust plate is deformed due to the imbalance of the tensile stress generated on both sides of the thrust plate, and as a result, the bearing is There was also a problem in that it touches and interferes with high-speed rotation.

The present invention has been made in view of the above-mentioned problems of the prior art. It prevents seizure during high speed rotation and reduces centrifugal force during high speed rotation without reducing the rigidity during low speed rotation. It is an object of the present invention to provide a hydrostatic bearing device in which the thrust plate is not deformed to prevent rotation.

[0009]

In order to achieve the above object, a hydrostatic bearing device of the present invention comprises a rotary shaft having a thrust plate, a cylindrical outer surface of the rotary shaft and a surface of the thrust plate. The bearing includes a static pressure bearing member facing each other and a bearing housing holding the static pressure bearing member. The rotary shaft and the thrust plate are made of one material selected from silicon carbide and silicon nitride. It is characterized by

The cylindrical outer surface of the rotating shaft and the thrust plate surface may be covered with a thin film having a smooth surface.

Further, a deformation preventing member having the same diameter as the rotary shaft may be provided on the surface of the thrust plate opposite to the surface joined to the rotary shaft.

[0012]

In the present invention, since the rotary shaft and the thrust plate are made of silicon carbide or silicon nitride, the coefficient of thermal expansion is smaller than that of the bearing housing, and the rotary shaft is rotated during high speed rotation with respect to the cooled bearing housing. Also, the thrust plate does not significantly expand and the bearing gap decreases, so that the thrust plate does not come into contact with the hydrostatic bearing member. Further, when the deformation preventing member is provided on the surface of the thrust plate opposite to the surface joined to the rotary shaft, it is possible to prevent the thrust plate from being deformed due to unbalance of expansion due to centrifugal force during high speed rotation.

[0013]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view showing a first embodiment, in which a rotary shaft 1 is provided with a thrust plate 2 at one end thereof, and the rotary shaft 1 and the thrust plate 2 are made of silicon carbide having a small coefficient of thermal expansion. Or made of silicon nitride. The hydrostatic bearing 3 supports the rotary shaft 1 and the thrust plate 2 in a non-contact state by the hydrostatic pressure of the pressurized fluid.
The bearing housing 4 and the water cooling jacket 5 are provided. The radial bearing portion of the bearing housing 4 holds a cylindrical hydrostatic pad 6 which is a hydrostatic bearing member, and the thrust bearing portion has a pair of annular hydrostatic pads 7. Is held. Further, the bearing housing 4 is provided with an air supply hole 8, and the pressurized fluid supplied from a well-known pressurized fluid supply source passes through the air supply hole 8 and the cylindrical static pressure pad 6 and each annular static pressure pad 7 are provided.
Is supplied to.

The bearing housing 4 is made of carbon steel, and the cylindrical static pressure pad 6 and the annular static pressure pad 7 are made of graphite. Further, a deformation preventing member 9 having the same diameter as the rotating shaft 1 is integrally joined to the surface of the thrust plate 2 opposite to the surface to be joined to the rotating shaft 1, and the deformation preventing member 9 serves as the rotating shaft and the thrust plate. Made of the same material.

When the rotary shaft 1 is rotated at a high speed, the amount of heat generated by viscous friction of the pressurized fluid supplied by the cylindrical static pressure pad 6 and the annular static pressure pad 7 increases, and the rotary shaft 1 and the thrust plate 2 are heated. The temperature rises. However, as described above, since the rotary shaft 1 and the thrust plate 2 are made of a material having a smaller thermal expansion coefficient than the material forming the bearing housing 4, the diameter expansion due to thermal expansion is made of, for example, the same carbon steel as the bearing housing 4. Remarkably less than the case. On the other hand, since the bearing housing 4 is cooled by the water cooling jacket 5, the thermal expansion is small.

Therefore, even during high speed rotation, the gap between the rotary shaft 1 and the thrust plate 2 and the cylindrical static pressure pad 6 and the annular static pressure pad 7 does not cause seizure without large fluctuations in the housing.

For example, a rotating shaft having a shaft diameter of 110 mm is rotated at a high speed in a radial hydrostatic bearing having a bearing gap of 5 μm, and a heat difference of a pressurized fluid causes a temperature difference of 10 ° C. between the rotating shaft and the bearing. At this time, when the rotary shaft and the bearing housing are both made of carbon steel (coefficient of thermal expansion 10.7 × 10 ⁻⁶ ), the bearing gap decreases by about 6 μm, so the rotary shaft and the bearing come into contact with each other. When the rotating shaft is made of silicon carbide (coefficient of thermal expansion 4.0 × 10 ⁻⁶ ),
Since the reduction of the bearing gap is about 2 μm, the rotating shaft and the bearing do not come into contact with each other.

At this time, the rotating shaft 1 and the thrust plate 2 are subjected to a treatment (a surface smoothing treatment) such as a plating treatment to coat the surface with a metal thin film, thereby reducing the surface roughness and vibrating by self-excited vibration. Is less likely to occur, and it is desirable to reduce friction with the pressurized fluid.

During high speed rotation, the thrust plate 2 tends to expand outward in the radial direction due to centrifugal force and bend in the direction of the surface to which the rotary shaft 1 is joined. Since the deformation preventing member 9 is integrally joined to the surface and both surfaces expand in the same manner, there is no bending as described above. Therefore, unlike the conventional case, the thrust plate 2 does not come into contact with the bearing during high speed rotation.

FIG. 2 is a schematic cross-sectional view showing a second embodiment. In this embodiment, a pair of thrust plates 12a, 12b are attached to both ends of a rotary shaft 11, and the outer surfaces of the thrust plates 12a, 12b are attached. Anti-deformation members 19a and 19b are joined to the rotary shaft 11, the thrust plates 12a and 12b, and the anti-deformation member 19, respectively.
a and 19b are made of silicon nitride (coefficient of thermal expansion 2.8 × 10 ⁻⁶ ). The hydrostatic fluid bearing 13 includes a bearing housing 14 made of carbon steel, and the bearing housing 14 holds a hydrostatic bearing pad 16 which is a hydrostatic bearing member facing the rotating shaft 11 and the thrust plates 12a and 12b. Moreover, it is provided with an air supply hole 18 and is cooled by a water cooling jacket 15.

The temperature of the rotating shaft 1 and the thrust plates 12a, 12b rises remarkably during high speed rotation, but both of them are made of silicon nitride, which has a smaller coefficient of thermal expansion than the carbon steel forming the bearing housing 14. There is little radial and axial expansion. That is, since the reduction of the bearing gap due to the expansion of the shaft diameter and the reduction of the thrust bearing rigidity due to the axial expansion of the rotary shaft are slight, the contact with the bearing does not hinder the high speed rotation.

The operation of the deformation preventing members 19a and 19b is the same as that of the first embodiment, and the description thereof will be omitted.

[0024]

Since the present invention is constructed as described above, it has the following effects.

Without setting a large bearing gap in advance,
That is, seizure during high speed rotation can be prevented without impairing the rigidity of the bearing during low speed rotation.

Further, it is possible to prevent the thrust plate from being deformed by centrifugal force during high speed rotation. Therefore, it is suitable for high speed rotation and has excellent bearing performance without lowering the rigidity at low speed rotation.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first embodiment.

FIG. 2 is a sectional view showing a second embodiment.

[Explanation of symbols]

 1, 11 rotating shaft 2, 12a, 12b thrust plate 3, 13 hydrostatic bearing 4, 14 bearing housing 5, 15 water cooling jacket 6 cylindrical hydrostatic pad (hydrostatic bearing member) 7 annular hydrostatic pad 16 hydrostatic bearing Pad (hydrostatic bearing member) 8,18 Air supply hole 9,19a, 19b Deformation prevention member

Claims (3)

[Claims] 1. A rotary shaft having a thrust plate, a hydrostatic bearing member facing the cylindrical outer surface of the rotary shaft and a surface of the thrust plate, and a bearing housing holding the hydrostatic bearing member. The hydrostatic bearing device, wherein the rotary shaft and the thrust plate are made of one material selected from silicon carbide and silicon nitride. 2. The hydrostatic bearing device according to claim 1, wherein the cylindrical outer surface of the rotating shaft and the surface of the thrust plate are covered with a thin film having a smooth surface. 3. The static prevention member according to claim 1, wherein a deformation preventing member having the same diameter as the rotating shaft is provided on the surface of the thrust plate opposite to the surface joined to the rotating shaft. Hydrodynamic bearing device.