Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Reexamination Certificate
1999-11-03
2002-01-29
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
C384S902000, C384S907000, C384S912000, C428S550000, C428S552000, C428S565000, C428S676000, C508S103000, C508S104000, C508S105000
Reexamination Certificate
active
06342306
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bearing material having a porous sintered metal layer and a porous hydrostatic gas bearing using this bearing material.
2. Description of the Related Art
Porous hydrostatic gas bearings have hitherto attracted attention as having excellent high-speed stability and high load carrying capacity, and although various studies have been made, there are yet a number of problems to be overcome in their practical use.
As for the porous hydrostatic gas bearing, a bearing material which is formed by combining a porous sintered metal compact with a backing metal provided with means for supplying a compressed gas is frequently used. As the material for forming the porous sintered metal compact in this bearing material, a material which mainly consists of bronze, an aluminum alloy, or stainless steel, particularly a material which mainly consists of bronze, is frequently used.
As the bearing material used for the porous hydrostatic gas bearing, sufficient gas permeability and the surface roughness on the order of 10
−3
mm are required. However, in the case where the above-described bearing material is used for the hydrostatic gas bearing, the porous sintered metal compact itself has satisfactory gas permeability in a way, but since the dimensional accuracy and surface roughness of the porous sintered metal compact are not sufficient, its surface is subjected to machining in many cases.
This machining is mainly effected by lathe turning, milling, and grinding, but loading of the surface of the porous sintered metal compact is caused by such lathe turning, milling, and grinding, which substantially affects its gas permeability (drawing characteristic). In grinding, in particular, plastic flow takes place in the surface of the porous sintered metal compact, and burrs are consequently caused.
In addition, the porous sintered metal compact is combined with the backing metal provided with the means for supplying a compressed gas as described above, and in the case of, for example, a porous hydrostatic radial gas bearing, a means for press-fitting a hollow cylindrical porous sintered metal compact to a hollow cylindrical backing metal is adopted in this combining process.
In the case of a simple slide bearing, no particular problem occurs even if such a press-fitting means is adopted. In the porous hydrostatic gas bearing, however, since a very small gap is present between the contact portions of the two members which are apparently tightly press-fitted to each other, there are cases where the leakage of the gas from this gap is greater than the essential circulation of the compressed gas in the porous sintered metal compact.
The leakage of the gas from this gap leads to a decline in the performance such as a reduction of the load capacity as the porous hydrostatic gas bearing, so that it is preferable to prevent this leakage as much as possible.
To cope with this problem, if the interference is made large and fitting is effected with a large press-fitting force, the gap in this portion can be eliminated substantially completely. On the other hand, however, there is the possibility of occurrence of plastic flow of the sintered metal on the outer surface side of the porous sintered metal compact subjected to extremely large drawing by the backing metal. Hence, a problem newly arises in that, after fitting to the backing metal, the circulation of the compressed gas is substantially hampered on the fitted surface side of the porous sintered metal compact.
SUMMARY OF THE INVENTION
The present inventors discovered that a bearing material having a porous sintered metal layer fabricated under particular fabrication conditions is capable of maintaining gas permeability allowing its use as a porous hydrostatic gas bearing even after the bearing material is subjected to machining.
Accordingly, it is a primary object of the present invention to provide a bearing material capable of maintaining gas permeability, satisfactorily allowing its use as a porous hydrostatic gas bearing even after the bearing material is subjected to machining.
A secondary object of the present invention is to provide a bearing material which is free of unintended leakage of a supplied compressed gas.
A tertiary object of the present invention is to provide a porous hydrostatic gas bearing using the aforementioned bearing material.
The bearing material for a porous hydrostatic gas bearing in accordance with the present invention comprises: a backing metal; and a porous sintered metal layer sintered onto at least one surface of the backing metal, particles of an inorganic substance being contained at grain boundaries of the porous sintered metal layer.
In the bearing material in accordance with the present invention, component materials of the porous sintered metal layer are integrally joined to the backing metal on at least one surface of the backing metal.
In a preferred example, the porous sintered metal layer contains at least tin, nickel, phosphorus, and copper, and further contains iron or manganese, and the particles of the inorganic substance are those of at least one of graphite, boron nitride, graphite fluoride, calcium fluoride, aluminum oxide, silicon oxide, and silicon carbide.
The backing metal of the bearing material in accordance with the present invention is preferably formed of a metal selected from a group essentially consisting of iron, an iron alloy, copper, and a copper alloy. In a case where the backing metal is formed in a hollow cylindrical shape to form a porous hydrostatic gas radial bearing, the porous sintered metal layer is sintered onto an inner cylindrical surface of the backing metal, whereas in a case where the backing metal is formed in a planar shape to form a porous hydrostatic gas thrust bearing, the porous sintered metal layer is sintered onto one planar surface of the backing metal. It should be noted that the porous sintered metal layer in accordance with the present invention is also applicable to a linear motion bearing, i.e., a so-called slider.
The porous hydrostatic gas bearing in accordance with the present invention uses the aforementioned bearing material, and means for supplying a compressed gas to the porous sintered metal layer is provided in the backing metal.
In the porous hydrostatic gas bearing in accordance with the present invention, the roughness of the exposed surface of the porous sintered metal layer is 10
−3
mm or less.
The particles of the inorganic substance in accordance with the present invention are those of at least one of graphite, boron nitride, graphite fluoride, calcium fluoride, aluminum oxide, silicon oxide, and silicon carbide. These substances do not undergo plastic deformation, which is otherwise the case with many metallic materials, and they are inorganic substances.
If such particles of the inorganic substance are compounded in a dispersed manner in a substrate formed of tin, nickel, phosphorus, and copper, as well as iron, manganese or the like in the porous sintered metal layer, such inorganic substances themselves do not undergo plastic deformation in machining. Additionally, since the inorganic substances function to disrupt and alleviate the plastic deformation of metal portions in the substrate of the porous sintered metal layer, it is possible to suppress the loading of the porous sintered metal layer in machining.
As for the porous sintered metal layer, a mixed powder composed of 4 to 10% tin, 10 to 40% nickel, 0.5 to 4% phosphorus, 3 to 10% graphite by weight, and the balance consisting of copper is pressed to fabricate a hollow cylindrical or planar green compact, and this green compact is inserted into the hollow cylindrical backing metal in contact with its inner peripheral surface or placed on the flat surface of the planar backing metal, the backing metal being formed of such as iron, an iron alloy, copper, or a copper alloy. This assembly is sintered in a reducing atmosphere or a vacuum at a temperature of 800 to 1,150° C. for 20 to 60 mi
Ozawa Hideo
Tomita Hirotsugu
Tsuji Hiroshi
Jones Deborah
Koehler Robert R.
Nixon & Vanderhye
Oiles Corporation
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