JPH04300420A - Porous static pressure gas bearing - Google Patents

Abstract

PURPOSE:To obtain a porous static pressure gas bearing having structure by the use of which the mass production of a stable and highly rigid static pressure gas bearing is possible. CONSTITUTION:Porous ceramics 1 whose flow Q per unit area is Q<=0.01P<2>+0.02P-0.03 (where, P: air supply pressure), are used for the bearing surface of a static pressure gas bearing consisting of the bearing surface retaining a shaft structure body 3, and a gas supply portion 2 supplying gas to this bearing surface.

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. A slicing machine is a machine tool used for cutting and grooving ceramics, etc. The spindle that rotates the grindstone rotates at a high speed that matches the workpiece and has high rigidity, so it can be easily obtained in factories. operated 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

[Prior Art] Conventionally, a porous static material is provided on a bearing surface, and pressurized gas is supplied through the porous material into the gap on the bearing surface, and the shaft structure is held by the air layer on the bearing surface. Pressurized gas bearings are known.

Conventionally, porous sintered metals, carbon, and ceramics have been used as materials for this porous body. Among these, when porous sintered metal or porous carbon is used, the bearing surface will be damaged due to machining of the bearing surface, so unless it is reprocessed which requires a huge amount of man-hours, it will be stable and have high rigidity. There was a problem in that it was not possible to obtain a static pressure gas bearing.

0004

[Problems to be Solved by the Invention] In this respect, when porous ceramics are used, the above-mentioned problem of eyelids does not occur. However, for example, the Transactions of the Japan Society of Mechanical Engineers C
As disclosed in "Load Characteristics of Porous Ceramic Hydrostatic Air Bearings" in Vol. The problem is that it is stable only under extremely limited conditions, making it impossible to mass-produce highly rigid and stable hydrostatic gas bearings.

[0005] The purpose of the present invention is to solve the above-mentioned problems,
The present invention aims to provide a porous hydrostatic gas bearing having a structure that allows mass production of stable and highly rigid hydrostatic gas bearings.

[0006]

[Means for Solving the Problems] The porous hydrostatic bearing of the present invention has a flow rate Q [s1/(mi) per unit area on the bearing surface.
n ・cm2)] is Q≦0.01P2+0.02P-0.03
-----(1) However, P: Supply pressure [
kgf/cm2·G] is used.

[0007]

[Operation] In the above-mentioned configuration, if the flow rate per unit area of the porous ceramic on the bearing surface is kept below a predetermined value, as will be clear from the examples described later, other characteristics of the porous ceramic will be affected. This is because it has been found that even if there is, it is possible to obtain a stable and highly rigid porous hydrostatic gas bearing that does not generate self-excited vibration during normal use.

[0008] The lower limit is not particularly stipulated, but Q = 10-3 (0.01P2 + 0.02P
If it is less than -0.03), the rigidity is too small and it is often impossible to use it as a bearing, so the lower limit is Q = 10-3 (0.03).
．． 01P2 +0.02P -0.03).

[0009] Furthermore, in order to obtain porous ceramics having a predetermined air permeability, it is necessary to change the molding pressure during molding in the usual manufacturing method in which powder is prepared, molded, and fired to obtain a sintered body. Alternatively, it has been found that a desired air permeability can be easily obtained with good reproducibility by changing the firing temperature during firing.

[0010] In the present invention, as long as the flow rate per unit area of the porous ceramic satisfies the above formula (1), any other properties are possible; however, in order to achieve this flow rate, The properties of porous ceramics are usually in the following ranges. That is, average pore diameter: 0.
5 to 10 μm, open porosity: 10 to 30%, pore volume: 0.02 to 0.08 cc/g, water absorption rate: 2 to 8%
, molding density: in the range of 2 to 5 g/cc.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 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 ceramic layer having a predetermined flow rate; 2 is a gas supply unit that supplies gas such as air through the porous ceramic layer 1;
3 is a shaft structure to be supported. The bearing dimensions of the grinding wheel spindle of a general slicing machine are d = 25 to 60 m.
m, D=30 to 80 mm, 1=25 to 60 mm. The shaft structure 3 is supported by the porous hydrostatic gas bearing having the above-mentioned structure. First, the shaft structure 3 is mounted on the cylindrical bearing surface of the porous ceramic layer 1 with a gap of 5 to 20 μm, and then This can be achieved by rotating the shaft structure 3 while supplying gas at a pressure of .

The porous ceramic layer 1 can be obtained by the usual ceramic firing method, that is, by preparing powder of a predetermined composition, molding the prepared powder, and firing the molded body after molding. At this time, the porous ceramic layer 1 having a predetermined flow rate can be obtained by changing the molding pressure during molding or changing the firing temperature during firing, as will be described later. The porous ceramic layer 1 is preferably made of a material that has a uniform pore distribution and does not become clogged even when processed, such as porous zirconia, porous alumina,
Preferably, porous aluminum nitride, porous silicon carbide, porous silicon nitride are used.

FIG. 2 is a diagram showing an apparatus used to determine the limit at which self-excited vibration occurs when a shaft structure is received by an actual porous hydrostatic gas bearing. The dimensions of each bearing part are d=5
0~60mm, D=55~75mm, 1=50~60m
It is in the range of m. In the device shown in FIG. 2, a distance measurement sensor, an acceleration pickup 4, and an FFT analyzer 5 are installed in a porous hydrostatic gas bearing with a structure similar to that in FIG. 1, and vibrations when rotated at each rotation speed are measured. Self-excited vibration is considered to have occurred when a frequency component that is not synchronized with the rotational speed occurs. Note that the pressure supplied from the gas supply section in FIG. 1 was 7 kgf/cm2G. This is because the higher the supply pressure, the higher the bearing rigidity, and because this is the highest pressure that can be easily supplied within the factory.

When the flow rate per unit area of the porous ceramic layer 1 was varied and the rotational speed at which self-excited vibration occurred was actually determined using the apparatus shown in FIG. 2, the results shown in FIG. 3 were obtained. Ta. In FIG. 3, the numbers indicate test no. In addition to indicating, the meaning of the number frame is □: 2000 rpm
Below, the flow rate curve of a bearing in which a vibration component that is not synchronized with the rotation speed is generated, Δ: 2000rpm or more
pm or less, the flow rate curve of a bearing in which a vibration component that is not synchronized with the rotation speed has occurred, ○: The flow rate curve of a bearing that has not generated a vibration component that is not synchronized with the rotation speed up to 30,000 rpm, and a double frame. shows the flow rate curve serving as the boundary condition. As is clear from Fig. 3, the flow rate Q per unit area is Q = 0.01P2 + 0.02P - 0.0
It can be seen that as long as the value is 3 or less, a stable porous hydrostatic gas bearing without self-excited vibration can be obtained. Also, the flow rate Q per unit area is Q = 1.2 × 10-3P2 + 0.01
If P -7.8 × 10-3 or less, it is stable up to 30,000 rotations, which is the maximum rotation speed of the device confirmed in experiments.
It can be seen that an even more stable porous hydrostatic gas bearing can be obtained. On the other hand, the rigidity was actually measured to be 15 kgf/μm or more under all conditions satisfying equation (1).

In addition, in order to investigate the influence of the molding pressure and firing temperature during the production of the porous ceramic layer 1, the molding pressure and firing temperature during molding were varied for ceramics of the same composition, and other conditions were kept the same. When porous ceramics were manufactured and the flow rate was investigated, the flow rate could be controlled by changing the molding pressure and firing temperature, and this method was used to obtain the porous ceramics having a predetermined flow rate of the present invention. However, since molding pressure and firing temperature are closely related, it is necessary to consider the relationship between them when actually controlling the air permeability.

[0016]

Effects of the Invention As is clear from the above detailed explanation, according to the present invention, even the flow rate per unit area of the porous ceramic layer of the porous hydrostatic gas bearing can be reduced to the above (
1) If controlled so as to satisfy the formula, a stable and highly rigid bearing without self-excited vibration can be obtained even in a low-pressure gas bearing using ceramics. Further, in controlling the flow rate of the ceramic layer described above, a porous ceramic layer having a predetermined air permeability can be easily obtained by changing the molding pressure or changing the firing temperature.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of an example of a porous low-pressure gas bearing of the present invention.

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

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

[Explanation of symbols]

1 Porous ceramic layer 2 Gas supply section 3 Shaft structure 4 Distance measurement sensor and acceleration pickup 5 F
FT analyzer

Claims (2)

[Claims] [Claim 1] A flow rate per unit area Q[
s1/(min・cm2)] is Q≦0.01P2
+0.02P -0.03 (P: Supply pressure [kgf
A porous hydrostatic gas bearing characterized in that it uses porous ceramics that have the following properties: /cm2 ・G]). 2. The flow rate Q per unit area of the porous ceramic is 10-3 (0.01P2 +0.02P
-0.03) ≦Q≦0.01P2+0.02P -
The porous hydrostatic gas bearing according to claim 1, wherein the porous hydrostatic gas bearing has a diameter of 0.03.