JP2002295470A - Gas bearing spindle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas bearing spindle using graphite for a bearing sleeve capable of easily securing a bearing clearance even in the case when a rotation axis rotates at high speed, carrying out high precision work of graphite and with less possibility of damaging it. SOLUTION: The bearing sleeve 3 is constituted of a graphite made inside cylinder member 33 and a metallic outside cylinder member 34 externally fitted on the inside cylinder member 33 with a specified interference and a liner expansion coefficient of which is larger than graphite on the gas bearing spindle supporting the bearing sleeve 3 fitted in an outer diametrical surface of the rotation axis 1 with a clearance 11 for a gas bearing in between on a housing 2 through an elastic member (0 ring 41-44).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas bearing spindle used for a precision machine, a hole machine, an electrostatic coating machine and the like.

[0002]

2. Description of the Related Art FIG. 2 shows a journal bearing portion of a conventional gas bearing spindle (hydrostatic air bearing spindle). In this gas bearing spindle, as shown in the figure, a bearing sleeve 3 is fitted to an outer diameter surface of a rotating shaft 1 with a bearing gap 11 for a gas bearing therebetween, and both ends of the bearing sleeve 3 are connected to four Os.
It is supported on the housing 2 via rings 41-44. The O-rings 41 and 42 hermetically seal the circumferential space 22 between the housing 2 and the bearing sleeve 3 and attenuate whirling vibration of the rotating shaft 1 by its elasticity. The rotating shaft 1 is rotatably and non-contactly supported by a high-pressure gas supplied to the bearing gap 11, and is also non-contactly supported by the high-pressure gas in the axial direction (not shown).

The high-pressure gas for the gas bearing is supplied to a circumferential space 22 between the inner diameter of the housing 2 and the outer diameter of the bearing sleeve 3 through an air supply passage 21 formed in the housing 2. A plurality of bearing nozzles 31 and 32 formed in the vicinity of both ends provide a bearing gap 11 on the outer periphery of the rotating shaft 1.
It is to be spouted. It should be noted that in FIG.
A tool or the like can be attached to the right end of the drive shaft, and the rotating shaft 1 is driven by a drive unit (not shown).

[0004]

In recent years, in order to improve the seizure resistance of a gas bearing spindle, a bearing sleeve 3 has been developed.
Is formed of graphite having excellent lubricity, and the rotating shaft 1 is formed of a steel-based metal subjected to a surface hardening treatment. However, such a gas bearing spindle may cause the following problems. is there. (1) When the rotating shaft 1 rotates at high speed, heat is generated due to gas friction in the bearing gap 11, but the bearing sleeve 3 is generally elastically supported by the O-rings 41 to 44 and has poor heat transfer to the housing 2. Therefore, heat easily accumulates between the rotating shaft 1 and the bearing sleeve 3.

When the heat accumulates, the temperatures of the rotating shaft 1 and the bearing sleeve 3 rise. However, the linear expansion coefficient of graphite, which is the material of the bearing sleeve 3, is higher than that of the steel-based material, which is the material of the rotating shaft 1. Since it is small, the increase in the radial dimension is larger in the rotating shaft 1 than in the bearing sleeve 3. For this reason, when the rotating shaft 1 rotates at high speed, the bearing gap 11 gradually narrows, and in some cases, the gap becomes zero and the rotating shaft 1 and the bearing sleeve 3 may come into contact. This problem is more serious in high-speed rotation applications.

For example, when the bearing sleeve 3 is made to have a linear expansion coefficient α ₁
= 4 × 10 ^-6 / ° C graphite, rotating shaft 1 is linear expansion coefficient α ₂ = 1
When made of stainless steel of 7 × 10 ⁻⁶ / ° C., the inner radius of the bearing sleeve 3 (journal bearing radius) r ₁ = 20 mm, and the bearing radius gap C _r = 0.005 mm, the temperature rise of each member is uniform. Assuming that, a temperature rise of about 19 ° C. (=
At ΔT), C _r = 0. This can be calculated from the following equation.

ΔCr ₁ = r ₁ (α ₂ −α ₁ ) ΔT where ΔCr _{1 is the} amount of change in the bearing radial gap.

As a method of preventing the phenomenon of the bearing radial gap being zero, it is conceivable to first set the bearing gap 11 large. However, if the bearing gap 11 is increased, the bearing rigidity is reduced. Is not applicable.
In addition, it is not preferable to increase the bearing gap 11 in suppressing whirling. On the other hand, a method of forming the rotating shaft 1 with a metal material having a small linear expansion coefficient as much as graphite is also conceivable, but such a material is generally expensive and is not a practical solution. (2) When the graphite bearing sleeve 3 is elastically supported, high-precision machining is required for the bearing sleeve 3 alone. However, graphite has a small longitudinal elasticity coefficient and the bearing sleeve 3 itself is thin, so high-precision machining is required. Is difficult. (3) Since graphite is brittle, there is a high possibility that the bearing sleeve 3 will be damaged when the graphite bearing sleeve 3 is inserted into or removed from the housing 2. Graphite bearing sleeves have various problems as described above.

An object of the present invention is to provide a gas bearing spindle using graphite for a bearing sleeve, which can easily secure a bearing gap even when the rotating shaft rotates at a high speed.
It is another object of the present invention to provide a gas bearing spindle that can process graphite with high precision and has a low possibility of damage.

[0010]

A gas bearing spindle according to the present invention has a bearing sleeve supported by a housing via an elastic member and fitted on an outer diameter surface of a rotating shaft with a gap for the gas bearing interposed therebetween. In the spindle, the bearing sleeve is constituted by a graphite inner cylinder member, and a metal outer cylinder member that is externally fitted to the inner cylinder member with a predetermined interference and has a linear expansion coefficient larger than that of graphite. .

Thus, even when the temperature of the bearing sleeve rises during high-speed rotation, the compressed inner cylinder member expands in the radial direction so as to follow the radial thermal expansion of the outer cylinder member. A bearing gap with the inner cylinder member can be easily secured. Further, since the outer cylinder member functions as a protection cylinder for the graphite inner cylinder member, damage to the inner cylinder particularly when the bearing sleeve is inserted into and removed from the housing can be prevented, and handling of the bearing sleeve using graphite becomes easy. .

More specifically, the interference between the inner cylinder member and the outer cylinder member may be based on a fitting standard such that an interference always exists between them in the normal rotation range. The bearing clearance can be secured stably.

As the metal of the outer cylinder member, desirably, a material such as stainless steel whose longitudinal elastic modulus is larger than that of graphite is used. Thus, when finishing the inner cylinder member bearing surface (inner diameter surface) of the bearing sleeve, the outer cylinder member made of a metal having a large longitudinal elastic modulus can be chucked and machined, and the inner cylinder member is deformed by the chuck. , And high-precision bearing surface processing can be performed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a hydrostatic air bearing spindle will be described below with reference to FIG.
FIG. 1 shows a journal bearing portion of a hydrostatic air bearing spindle. The configuration other than the bearing sleeve 3 is the same as that of FIG. In the hydrostatic air bearing spindle of the present invention, the bearing sleeve 3 is constituted by an inner cylindrical member 33 made of graphite and an outer cylindrical member 34 made of metal. The outer cylinder member 34 is the inner cylinder member 33
Is fitted with a predetermined interference by shrink fitting.

The inner diameter of the bearing sleeve 3, that is, the inner cylindrical member 3
The rotating shaft 1 is inserted into the inside diameter of the bearing 3 with a bearing gap 11 therebetween. The rotating shaft 1 is rotatably and non-contactly supported by high-pressure air supplied to the bearing gap 11, and is also non-contactly supported by high-pressure air in the axial direction (not shown).

High-pressure air is supplied to the peripheral space 22 from an air supply passage 21 formed in the housing 2, and is supplied to the outer cylindrical member 34.
Via the air introduction holes 35 and 36 formed in a plurality of
The air is introduced into the bearing gap 11 from the bearing nozzles 31 and 32 of the inner cylindrical member 33 formed in the same circumferential phase as the air introduction holes 35 and 36. In FIG. 1, a tool or the like can be attached to the right end of the rotating shaft 1 so that the rotating shaft 1 is driven by driving means (not shown).

The hydrostatic air bearing spindle according to the present invention is constructed as described above, and the bearing clearance 11
When the heat is generated in this case, the temperature of the entire bearing sleeve 3 increases due to the heat. However, since the inner cylinder member 33 is fitted with a tight fit, the outer cylinder member 34 is thermally expanded, thereby loosening the tightness of the inner cylinder member 33, and the inner diameter of the inner cylinder member 33 is expanded beyond the thermal expansion. Accordingly, the margin for the disappearance of the bearing gap 11 due to the outer diameter expansion of the rotating shaft 1 can be made larger than that of the conventional structure in which the bearing sleeve 3 is constituted only by graphite.

For example, if graphite is used for the inner cylinder member 33 and stainless steel is used for the rotary shaft 1 and the outer cylinder member 34 and the physical properties and dimensions are as shown in Table 1, it is assumed that the temperature rise of the members is uniform. The amount of decrease in the bearing gap 11 is given by the following equation 1.
Approximately 0.35 μm at a temperature rise of 19 ° C. and 55 ° C.
Is calculated to be about 1.0 μm.

[Table 1]

[Formula 1]

From the calculation, the bearing radial gap C _r = 0 is about 270 ° C., but at 100 ° C., the shrinkage allowance q = 0 of the inner cylinder member 33 and the outer cylinder member 34 becomes zero. Therefore, the allowable limit value of the temperature rise is 100 ° C.

As a result, the margin for temperature rise is about five times that of the conventional gas bearing spindle shown in FIG. 2 in which the bearing sleeve 3 is made of graphite and the dimensions of each part are completely the same. (Actually, it is necessary to consider the safety factor, but it is not considered in this calculation.)

The embodiment of the present invention has been described above. However, the present invention is not limited to the above embodiment, and various modifications can be made. Although the bearing is used, the present invention can be applied to other bearing types such as a porous hydrostatic bearing, and can also be applied to a dynamic pressure bearing.

[0022]

As described above, according to the present invention, the bearing sleeve is composed of the graphite inner cylinder member and the metal outer cylinder member, and the outer cylinder member is fitted to the inner cylinder member with a predetermined interference. Even if the temperature of the bearing sleeve rises due to heat generated in the bearing gap due to high-speed rotation, the graphite inner cylinder member also thermally expands following the radial thermal expansion of the outer cylinder member, accompanying the radial thermal expansion of the rotating shaft. A decrease in bearing clearance can be suppressed. Further, since the graphite inner cylinder member is protected by the metal outer cylinder member, it is possible to prevent the inner cylinder member from being damaged when the bearing sleeve is inserted and removed from the housing. Also, by making the longitudinal modulus of elasticity of the metal used for the outer cylinder member larger than that of graphite,
When finishing the inner cylinder member bearing surface of the bearing sleeve, the outer cylinder member made of metal with a large longitudinal elastic modulus is chucked and machined to suppress deformation of the inner cylinder member by the chuck, resulting in a high-precision bearing. Surface processing can be performed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a journal bearing portion of a gas bearing spindle according to the present invention.

FIG. 2 is a sectional view of a journal bearing portion of a conventional gas bearing spindle.

[Explanation of symbols]

1 rotating shaft 2 housing 3 bearing sleeve 11 bearing gap 21 supply passage 22 laps like space 31, 32 bearing nozzles 33 graphite in tubular member 34 metallic outer sleeve members 35 and 36 air inlet holes 41 to 44 O-ring C _r bearings Radial gap

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3J011 AA04 AA08 BA02 DA01 QA04 SE02 3J012 AB11 BB01 CB10 FB20 HB02 3J102 AA02 CA31 EA02 EA13 FA01 FA30 GA07

Claims (4)

[Claims] 1. A gas bearing spindle in which a bearing sleeve fitted on an outer diameter surface of a rotary shaft with a gap for a gas bearing is supported by a housing via an elastic member, wherein the bearing sleeve is made of a graphite inner cylinder. A gas bearing spindle comprising: a member; and a metal outer cylinder member having a linear expansion coefficient larger than graphite, which is externally fitted to the inner cylinder member with a predetermined interference. 2. An inner cylinder member and an outer cylinder member of a bearing sleeve maintain an interference in a normal rotation range.
2. A gas bearing spindle according to claim 1. 3. The gas bearing spindle according to claim 1, wherein the outer cylinder member is formed of a metal having a modulus of longitudinal elasticity larger than that of graphite. 4. The gas bearing spindle according to claim 3, wherein the outer cylindrical member is formed of stainless steel.