JPH05321940A - Bearing unit - Google Patents

Abstract

PURPOSE:To improve life and precision by manufacturing a bearing comprising an inner ring, an outer ring, and rolling bodies of ceramic, and manufacturing a housing and/or a shaft to be engaged with the bearing inner ring of low expansion alloy. CONSTITUTION:In a bearing unit, an inner ring 1, an outer ring 2, and rolling bodies 3 are manufactured of ceramic, while a shaft 6 and/or a housing 7 are manufactured of low expansion alloy. The low expansion alloy includes Ni by 25-40%, Co by 0-20%, C by 0.3-3.5%, and Si by 0.2-3.5%, and it also includes Mg or Ca by 0.01-1.0%, Mn 2.0% or less, sulfur by 1.0% or less, and phosphor by 1.5% or less as necessary to be Fe-based cast alloy having an average thermal expansion coefficient of 6X10<-6>/ deg.C or less under a room temperature to 200 deg.C. The ceramic is silica nitride, sialon, etc., having necessary strength, and an average thermal expansion coefficient of the silica nitride is about 3.5X10<-6>/ deg.C. In this constitution, breakage or backlash by a difference of thermal expansion an be restricted, thereby shaft rotation precision can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a machine tool that requires high speed rotation and high accuracy, and a bearing unit used in a high temperature environment or a corrosion resistant environment.

[0002]

2. Description of the Related Art In recent years, realization of high-speed rotation by weight reduction,
Also, it is becoming practical to manufacture bearings from ceramics for the purpose of high temperature durability and corrosion resistance. As an example of this, a fully ceramic bearing has been recently developed that uses silicon nitride as the main material and uses ceramics not only for the rolling elements (rollers, balls) inside the bearing except for the retainer (retainer), but also for the inner and outer rings. It was This bearing is designed to suppress the tensile stress generated in the metal shaft due to the difference in thermal expansion between ceramics and metal as much as possible by cutting a special spline (groove) in the metal shaft at the fitting part. Is.

[0003]

However, the effect of the above ceramic bearing, which is made of ceramics and the shaft is made of metal, is still insufficient in spite of its ingenuity, and especially when it is used at 100 ° C. or higher. ,
There is a problem that the life of the bearing is shortened due to the difference in thermal expansion. An object of the present invention is to avoid the thermal expansion difference between the shaft and housing and the bearing inner ring and outer ring, which has been a bottleneck in putting the above ceramic bearing into practical use. To provide the bearing unit that was used.

[0004]

According to the present invention, an inner ring,
The bearing mainly composed of the outer ring and the rolling elements housed therebetween is made of ceramics, and the housing surrounding the bearing and / or the shaft fitted to the inner ring of the bearing is made of a low expansion alloy. A bearing unit is provided.

[0005]

The bearing comprises an inner ring, an outer ring and rolling elements such as balls and rollers housed between them, and a retainer for holding the rolling elements. Further, this bearing constitutes a bearing unit from a housing which surrounds the bearing and a shaft which is fitted to the inner ring of the bearing. The bearing unit of the present invention is
The inner ring, the outer ring, and the rolling elements of the bearing are made of ceramics, and the shaft and / or the housing are made of a low expansion alloy.

As the low expansion alloy used here, Ni 25-40%, Co 0-20%, C 0.
3 to 3.5%, Si 0.2 to 3.5%, Mg or Ca 0.01 to 1.0%, Mn as required 2.
It contains 0% or less, sulfur 1.0% or less, and phosphorus 1.5% or less, and has an average coefficient of thermal expansion of 6 × 1 at room temperature to 200 ° C.
Fe-based casting alloy of 0 ^-6 / ° C or less, or N by weight ratio
i 25 to 40%, Co 0 to 20%, and optionally Mn 1.0% or less and Si 0.2% or less,
Average thermal expansion coefficient from room temperature to 200 ° C is 6 × 10 ^-6 /
A Fe-based forged alloy or a Fe-based rolled alloy having a temperature of ℃ or less is preferable.

Among the low expansion alloys having the above composition, typically, C 0.3 to 2.0% by weight and Ni 25 to 3 by weight ratio.
2%, Co 12 to 20%, Si 0.3 to 2.0%,
Nb 0.2-0.8%, Mg or Ca 0.01-0.
2%, Mn 1.0% or less, the balance is Fe containing impurities, and the average coefficient of thermal expansion from room temperature to 200 ° C. is 3 × 1.
^{0 -6 / ℃ ~4 × 10 -6} / ℃, cast iron average thermal expansion coefficient from room temperature to 400 ° C. is 4.5 × 10 ^-6 /℃~5.5×10 ^-6 / ℃ or weight ratio, C 0.8-3.0%, Ni
30-34%, Co 4.0-6.0%, Si 1.
0% -3.0%, Mn 2.0% or less, sulfur 1.0%
Hereafter, phosphorus has a composition of 1.5% or less, Mg is 1.0% or less, and the balance is Fe containing impurities. The average thermal expansion coefficient at room temperature to 200 ° C. is about 2 × 10 ⁻⁶ / ° C. to 3 × 10 5. ^-6 / ° C., such as cast iron is preferably not more than room temperature average coefficient of thermal expansion to 400 ° C. of about 9 × 10 ^-6 / ℃ However, it is also possible to use a low expansion alloy such as other Invar alloy and Kovar.

The above-mentioned cast iron can obtain an average coefficient of thermal expansion close to that of ceramics with a desired average coefficient of thermal expansion by setting the above composition range. Among them, Ni and Co are particularly preferable. Outside the above range, the desired average coefficient of thermal expansion cannot be obtained. Further, by adding Mn and Si in the above range, the oxygen level in the material is suppressed, and the melt fluidity and workability due to the deoxidizing effect are improved. These low expansion alloys are preferable from the viewpoint of cost because they can be cast in the atmosphere and can be produced in an arbitrary shape when used as a casting material, but when used as a casting material, they are low in strength when they lack reliability. Expanded alloys, although generally expensive, can also be used as forged or rolled materials.

The ceramics used for bearings include silicon nitride, sialon, silicon carbide, alumina, aluminum titanate, etc., which have the required strength. Incidentally, the average thermal expansion coefficient of silicon nitride is about 3.5 × 10.
^-6 / ° C, the average coefficient of thermal expansion of alumina is 7.0 x 10 ^-6 /
℃. As a method of fixing the bearing, shaft, and low expansion alloy used for the housing, conventional fitting methods such as press fitting and clearance fit can be used, but in addition, by casting with low expansion alloy The bearing outer ring and the housing are integrated, and the shaft and the bearing inner ring are integrated. Further, a mode in which the low expansion alloy of the present invention is used as a cushioning material between the conventional steel housing and / or shaft and the bearing made of ceramics is also preferable.

[0010]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to these examples. FIG. 1 is a schematic sectional view showing an example of a bearing in a bearing unit of the present invention, and FIG.
A sectional view and FIG. 3 are sectional views taken along line BB of FIG. 1 to 3
In, the bearing 5 is composed of the inner ring 1, the outer ring 2, the sphere 3 housed between the inner ring 1 and the outer ring 2, and the retainer 4 that holds the sphere 3. FIG. 4 is a schematic sectional view showing an example of the bearing unit of the present invention.
The inner side of the metal shaft 6 is made of the low expansion alloy of the present invention.
Is fitted and fixed, and the outer peripheral portion of the outer ring 2 of the bearing 5 is surrounded by a housing 7 made of the low expansion alloy of the present invention to form a bearing unit. And
The shaft 6 is usually connected to a drive motor 8.

Next, a concrete implementation result will be described. (Example 1, Comparative Examples 1 and 2) Low expansion cast iron (composition (weight ratio): Ni 28.0%, Co 14%, C 0.9
%, Si 1.2%, Mg 0.03%, Nb 0.3
%, Mn 0.3% or less, the balance being Fe),
A prototype of a rotary machine in which the inner ring, the outer ring, and the sphere of the bearing were made of silicon nitride was manufactured (Example 1). For comparison, S4
A rotary machine composed of a shaft made of 5C and NiCr steel and a bearing made of silicon nitride was prototyped (Comparative Examples 1 and 2). A life test was performed on these rotary machines at a rotation speed of 120 rpm under a high temperature environment of 400 ° C. The results are shown in Table 1.

[0012]

[Table 1]

(Example 2, Comparative Examples 3 to 4) Low-expansion cast iron (composition (weight ratio): Ni 33.0%, Co 5.5
%, C 2.0%, Si 2.0%, Mn 0.3% or less, Mg 0.03%, the balance being Fe), and the precision of this shaft rotation for a precision lathe using a silicon nitride bearing. Was determined (Example 2). In addition, S45C on the axis,
The precision of a precision lathe using NiCr steel and a bearing made of silicon nitride was also compared for the accuracy of shaft rotation (Comparative Examples 3 to 4). The results are shown in Table 2.

[0014]

[Table 2]

[0015]

As described above, the bearing unit in which the bearing is made of ceramics and the shaft and / or the housing is made of low expansion alloy as in the present invention,
It is possible to suppress breakage due to the difference in thermal expansion, which has been a problem in the past, and also to prevent looseness due to the difference in thermal expansion due to temperature change. As a result, for example, the shaft rotation accuracy of a machine tool is improved,
This has a remarkable effect that the machining accuracy of the workpiece can be improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of a bearing in a bearing unit of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG.

FIG. 4 is a schematic sectional view showing an example of a bearing unit of the present invention.

[Explanation of symbols]

 1 inner ring 2 outer ring 3 ball 4 cage 5 bearing 6 metal shaft 7 housing 8 drive motor

Claims (3)

[Claims] 1. A bearing mainly composed of an inner ring, an outer ring and rolling elements housed therebetween is made of ceramics, and a housing surrounding the bearing and / or a shaft fitted to the inner ring of the bearing is made of a low expansion alloy. A bearing unit manufactured by. 2. The low expansion alloy comprises Ni 25-by weight ratio.
40%, Co 0 to 20%, C 0.3 to 3.5%, S
i 0.2 to 3.5%, Mg or C as required
a 0.01-1.0%, Mn 2.0% or less, sulfur
1.0% or less and phosphorus 1.5% or less, room temperature to 20
F having an average coefficient of thermal expansion at 0 ° C. of 6 × 10 ⁻⁶ / ° C. or less
The bearing unit according to claim 1, which is an e-based casting alloy. 3. The low expansion alloy is Ni 25 to 25 in a weight ratio.
40%, 0 to 20% Co, and optionally Mn
1.0% or less, Si 0.2% or less, room temperature to 20
F having an average coefficient of thermal expansion at 0 ° C. of 6 × 10 ⁻⁶ / ° C. or less
The bearing unit according to claim 1, which is an e-based forged alloy or an Fe-based rolled alloy.