JPH0733848B2 - Porous static pressure gas bearing - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a static pressure gas bearing using porous ceramics, and more particularly to a stable and highly rigid porous gas bearing. The slicing machine is a machine tool used for cutting and grooving ceramics, and the spindle that rotates the grindstone rotates at a high speed at a speed suitable for the workpiece and has high rigidity, so it can be easily obtained at the factory. Operates at maximum supply pressure The bearing of the present invention can be used as a bearing where such stable high speed rotation and high rigidity are required.

[0002]

2. Description of the Related Art Conventionally, a porous body is disposed on a bearing surface, pressurized gas is supplied to the gap between the bearing surfaces through the porous body, and an air layer on the bearing surface holds the shaft structure. Pressure gas bearings are known.

Porous sintered metal, carbon and ceramics have been conventionally used as the material for the porous body. Of these, if porous sintered metal or porous carbon is used, the bearing surface will be crushed and the bearing surface will be crushed. There was a problem that it was not possible to obtain a proper static pressure gas bearing.

[0004]

On the other hand, when the porous ceramics are used, the above-mentioned problem of the blinding does not occur. However, for example, the Japan Society of Mechanical Engineers, Proceedings C
As disclosed in Vol. 55, No. 511, "Load Characteristics of Porous Ceramics Static Pressure Air Bearings", static pressure gas bearings using porous ceramics are subject to instability caused by self-excited vibration (pneumatic hammer). However, it has a problem that it is stable only under extremely limited conditions, and that it is impossible to mass-produce a highly rigid and stable static pressure gas bearing.

The object of the present invention is to solve the above problems,
An object of the present invention is to provide a porous static pressure gas bearing having a structure capable of mass-producing stable and highly rigid static pressure gas bearings.

[0006]

In the porous hydrostatic bearing of the present invention, the flow rate per unit area Q [s1 / (min.cm
² )] is 10 ^-3 (0.01P ² + 0.02P -0.03) ≤Q ≤0.01P ² + 0.02P -0.03 ---- (1) where P: Supply pressure [kgf / cm ² · G] It is characterized by using the porous ceramics.

[0007]

In the above-mentioned structure, if the flow rate per unit area of the porous ceramics on the bearing surface is set to a predetermined value or less, as will be apparent from the examples described later, the other characteristics of the porous ceramics may not be affected. This is because it was found that self-excited vibration does not occur in normal use, and a stable and highly rigid porous hydrostatic gas bearing can be obtained.

The lower limit is not specified, but if Q is less than 10 ^-3 (0.01P ² + 0.02P -0.03), the rigidity is low and the bearing cannot be used in many cases, so the lower limit is Q. = Up to 10 ^-3 (0.01P ² + 0.02P -0.03) is preferable.

Further, in order to obtain a porous ceramics having a predetermined air permeability, it is necessary to change the molding pressure at the time of molding in the usual manufacturing method of preparing powder, molding and firing to obtain a sintered body. It was found that the desired air permeability can be easily obtained with good reproducibility by changing the firing temperature during firing.

In the present invention, any other characteristics are possible as long as the flow rate per unit area of the porous ceramics satisfies the above equation (1), but in order to achieve this flow rate, The characteristics of porous ceramics are usually in the following ranges. That is, the average pore diameter: 0.5
~ 10 μm, open porosity: 10-30%, pore volume: 0.02-0.08
cc / g, water absorption: 2-8%, molding density: 2-5 g / cc.

[0011]

1 is a sectional view showing the structure of an example of a porous static pressure gas bearing according to the present invention. In FIG. 1, 1 is a porous ceramics layer having a predetermined flow rate, 2 is a gas supply unit for supplying gas such as air through the porous ceramics layer 1,
3 is a shaft structure to be supported. The bearing size of the grindstone spindle of a general slicing machine is d = 25-60mm, D
= 30-80 mm, 1 = 25-60 mm. In order to support the shaft structure 3 by the porous static pressure gas bearing having the above-described structure, first, after mounting the shaft structure 3 with a clearance of 5 to 20 μm provided on the cylindrical bearing surface of the porous ceramic layer 1, a predetermined period is set. This can be achieved by rotating the shaft structure 3 while the gas having the pressure of 1 is supplied to the gas supply unit 2.

The porous ceramics layer 1 can be obtained by an ordinary ceramics firing method, that is, by preparing a powder having a predetermined composition, molding the prepared powder, and firing the molded body after molding. At that time, the porous ceramics layer 1 having a predetermined flow rate can be obtained by changing the molding pressure during molding or by changing the baking temperature during baking as described later. The porous ceramics layer 1 is preferably made of a material having a uniform pore distribution and not clogged even when processed, and porous zirconia, porous alumina, porous aluminum nitride, porous silicon carbide, porous Preference is given to using silicon nitride.

FIG. 2 is a diagram showing an apparatus used to determine the limit at which self-excited vibration is generated by receiving a shaft structure by an actual porous hydrostatic gas bearing. The size of each bearing is d = 50
-60 mm, D = 55-75 mm, 1 = 50-60 mm. In the device shown in FIG. 2, a distance measuring sensor, an acceleration pickup 4 and an FF are provided in a porous static pressure gas bearing having the same structure as in FIG.
The T-analyzer 5 is provided, the vibration when rotating at each rotation speed is measured, and it is considered that the self-excited vibration is generated when the frequency component that is not synchronized with the rotation speed is generated. In addition,
The pressure supplied from the gas supply unit in FIG. 1 was 7 kgf / cm ² G. This is because the higher the supply pressure, the higher the bearing rigidity and the maximum pressure that can be easily supplied in the factory.

The flow rate per unit area of the porous ceramics layer 1 was actually changed by the apparatus shown in FIG. 2 to find the number of revolutions at which self-excited vibration occurred, and the result shown in FIG. 3 was obtained. It was In Fig. 3, the numbers indicate the test No., the meaning of the frame of the numbers is □: 2000 rpm or less, and the flow rate curve of the bearing in which the vibration component which is not synchronized with the rotation speed occurs is Δ: 2000 rpm or more and 30000 rpm or less, The flow rate curve of the bearing where the vibration component not synchronized with the rotation speed is
Up to pm, it means the flow rate curve of the bearing in which the vibration component not synchronized with the rotation speed did not occur, and the double frame shows the flow rate curve which is the boundary condition. As is clear from FIG.
The flow rate Q flowing per unit area is Q = 0.01P ² + 0.02P-0.
It can be seen that a stable porous hydrostatic gas bearing without self-excited vibration can be obtained if the amount is 03 or less. In addition, the flow rate Q per unit area is Q = 1.2 × 10 ^-3 P ² + 0.01P -7.8 × 10 ^-3
In the following cases, it can be seen that a more stable porous hydrostatic gas bearing can be obtained because it is stable up to 30,000 rotations, which is the maximum rotation speed of the device confirmed by the experiment. On the other hand, the rigidity is (1)
It was measured to be 15 kgf / μm or more under all conditions that satisfy the formula.

Further, in order to investigate the influence of the molding pressure and the firing temperature at the time of manufacturing the porous ceramics layer 1, the molding pressure and the firing temperature at the time of molding are changed for ceramics of the same composition, and the other conditions are the same. When porous ceramics were manufactured and the flow rate thereof was investigated, the flow rate can be controlled by changing the molding pressure and the firing temperature, and this method is for obtaining the porous ceramics having the predetermined flow rate of the present invention. However, since the molding pressure and the firing temperature are closely related to each other, it is necessary to consider the relationship between them when controlling the actual air permeability.

[0016]

As is apparent from the above detailed description, according to the present invention, even the flow rate per unit area of the porous ceramics layer of the porous static pressure gas bearing is as described above.
By controlling so as to satisfy the formula (1), it is possible to obtain a stable and highly rigid bearing free from self-excited vibration even in a pressurized gas bearing using ceramics. Further, in controlling the flow rate of the ceramic layer described above, the porous ceramic layer having a predetermined air permeability can be easily obtained by changing the molding pressure or the firing temperature.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configuration of an example of a porous pressurized gas bearing of the present invention.

FIG. 2 is a diagram showing a state of checking occurrence of self-excited vibration in the present invention.

FIG. 3 is a graph showing the influence of the flow rate per unit area flowing through the porous layer on the maximum rotation speed in the present invention.

[Explanation of symbols]

 1 Porous Ceramics Layer 2 Gas Supply Section 3 Axis Structure 4 Distance Measuring Sensor and Accelerometer 5 FFT Analyzer

Claims (1)

[Claims] 1. A flow rate per unit area Q [s1 on the bearing surface
/ (min ・ cm ² )] is 10 ^-3 (0.01P ² + 0.02P -0.03) ≤
Q ≦ 0.01P ² + 0.02P −0.03 (However, P: Supply pressure [kgf / cm
Porous hydrostatic gas bearing, characterized in that using a porous ceramic is ² · G]).