JPH05223124A - Rolling bearing - Google Patents

Abstract

PURPOSE:To provide a longer rolling fatigue life and higher function in rolling bearing used at a high temperature and high speed. CONSTITUTION:At least either of an outer ring or an inner ring where a ceramic rolling element is incorporated is formed of powder high speed steel of HRC 65 or more in hardness. In the powder high speed steel, there is not giant carbide which effects an adverse influence on the rolling fatigue life of a bearing in its structure, and heat ray expansion coefficient is next to iron which is a material for forming a housing. Therefore, a bearing provided with a bearing ring made of powder high speed steel not only has good service life characteristic even at a high temperature and high speed, but also has no fear of generating creep between the outer ring and the housing due to a temperature change, and increased fitting allowance between the inner ring and a shaft.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing used under high temperature and high speed such as a rolling bearing incorporated in a gas turbine, a turbocharger of an automobile, a high speed rotating spindle for machine tools and the like. Regarding

[0002]

2. Description of the Related Art Rolling bearings, which are incorporated in a gas turbine, a high-speed rotating spindle of a machine tool and used at high temperature and high speed, have been made of heat resistant steel such as M50 material instead of bearing steel such as SUJ2. It was

However, in recent years, due to remarkable progress in ceramics technology, high-temperature and high-speed rolling bearings using ceramic rolling elements have become widespread and their effectiveness is being recognized. Also, although the temperature conditions are not strict, in the rotary spindle for machine tools used at ultra high speed,
A ceramic rolling element or bearing ring, which has a small specific gravity and is less affected by rotational centrifugal force, has been put to practical use because it is advantageous for ultra-high speed rotation.

[0004]

It is known that a rolling bearing incorporating a ceramic rolling element has a rolling fatigue life of a bearing ring lower than that of a general bearing because the hardness of the ceramic is high. This tendency is remarkable especially in the case where the bearing ring is made of heat-resistant steel. this is,
This is because a large amount of giant carbide remains in the structure of the conventional melt-processed heat-resistant steel, and a partial high surface pressure is generated at the contact portion between the giant carbide and the ceramic rolling element.

This problem can be solved to some extent if both the rolling elements and the races are made of ceramics. However,
Since the coefficient of linear thermal expansion of the ceramic and that of iron, which is a material for forming the shaft and the housing, are greatly different, the interference between the housing and the outer ring and between the shaft and the inner ring changes due to the temperature rise. Due to a change in the fit tightening margin, the risk of inner ring splitting due to increased creep between the housing and outer ring and increased fit stress between the shaft and inner ring increases. In order to solve this problem, it is known that the fitting between the ceramic inner ring and the shaft is loosened and the inner ring is tightened in the width direction by a special tightening means, so that the tightening margin between the inner ring and the shaft is always maintained properly. ing. However, according to this means, there is a risk of deteriorating the rotation accuracy of the shaft.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a rolling bearing which can maintain a proper tightening margin between a shaft and a housing even under high temperature conditions even at high speeds and can extend rolling fatigue life. It is what

[0007]

Means for Solving the Problems The technical means of the present invention for achieving the above object is to provide at least one of an outer ring and an inner ring of a rolling bearing incorporating a ceramic rolling element with a hardness HR.
That is, it was formed of powder high speed steel of C65 or more.

The above-mentioned powder high-speed steel is a steel forged by hot isostatically pressing a raw material powder of gas atomized powder produced by rapid solidification in a hot-pressing treatment device, and is a high-melting speed steel with the same toughness level. Compared with steel, it has high wear resistance and excellent grindability, and it has almost no precipitation of huge carbides, and it has suitable physical properties as a bearing material.

[0009]

The powder high-speed steel having hardness HRC65 or higher is, for example, HAP series HAP40, H manufactured by Hitachi Metals Co., Ltd.
Known as the product name such as AP70, the rolling bearing in which the ceramic rolling element is incorporated into the bearing ring made of this powder high speed steel is as shown in the experimental results described later.
Very suitable for bearings used at high temperature and high speed.

That is, the rolling fatigue life of high-speed powder steel is about twice that of SUJ2 steel, the life is not significantly reduced even under high temperature conditions, and the effect of centrifugal force during rotation at high speed is small. Therefore, both the outer ring and the inner ring, or one or both of them are made of powder high-speed steel, and the rolling bearing that incorporates the ceramic rolling element makes use of the advantages of the powder high-speed steel and ceramics to reduce the rolling fatigue life. Longer life,
It facilitates the realization of high functionality at high temperature and high speed.

[0011]

EXAMPLES Examples of the present invention will be described with reference to the cylindrical rolling fatigue life test data of FIG. 1, the bearing life test data of FIG. 2, and the representative physical property data of FIG. And explain.

The life test of FIG. 1 is performed on powder high speed steel, SUJ.
2. 12φ × 22 made of various ceramic materials
The rolling fatigue life of the roller was measured when the roller and the SUJ2 steel ball were brought into point contact with each other. The results show the following. The high-speed powder steel has hardness H
It is a HAP material such as HAP40 (trade name) of RC65 or more, and this is the same also in the case of the powder high speed steel shown in FIGS. 2 and 3.

(A) The rolling fatigue life of powder high speed steel is
When the rolling partner is SUJ2, it is inferior to ceramics but has a long life of about twice as long as SUJ2.

(B) In molten high-speed steel, the remaining giant carbide is unavoidable, and the remaining giant carbide shortens the rolling fatigue life of the bearing. However, there is no giant carbide in the powder high-speed steel. It is a suitable material for rolling bearings.

The life test of FIG. 2 is to measure the rolling fatigue life of a bearing in which the bearing ring is made of various materials such as powder high speed steel, SUJ2 and ceramics and the rolling elements are made of ceramics. The results of this life test show the following.

(C) A rolling bearing incorporating a ceramic rolling element, which uses a bearing ring made of powdered high-speed steel, is better than a bearing which uses a SUJ2 or M50 bearing ring at room temperature. The bearing life is 2.5 times or more longer, especially 5 times or more than that of M50 heat-resistant steel. This is confirmed stably when the hardness of the powder high speed steel used is HRC65 or more.

(D) A rolling bearing using a bearing ring made of powdered high speed steel exhibits a good long life even under a high temperature condition of 200 ° C. From this point as well, it is understood that the powder high-speed steel is suitable as a material for high-temperature high-speed rolling bearings such as gas turbines.

FIG. 3 shows typical physical property values of various materials such as powder high-speed steel, SUJ2, and ceramics. From these values, the following can be understood.

(F) The longitudinal elastic modulus of powder high speed steel is SUJ
Larger than 2. This characteristic indicates that, for example, when the inner ring made of powdered high-speed steel rotates at high speed, expansion of the inner ring due to rotational centrifugal force is small and change in groove diameter dimension of the inner ring is small.

(G) The thermal linear expansion coefficient of powder high-speed steel is considerably larger than that of ceramics, and is close to SUJ2. Therefore, in the case of the ceramic bearing ring, the change in the fitting interference between the shaft and the housing due to the temperature change has been a problem, but in the case of the powder high speed steel bearing ring, it can be said that there is no such problem.

From the above data, the use of powdered high-speed steel in the bearing ring of a rolling bearing which is used at high temperature and high speed by incorporating a ceramic rolling element improves the characteristics of life and function. It is clear that it is extremely effective above. Further, the powdered high speed steel bearing is slightly more expensive than a heat resistant steel bearing such as M50, but has an economical advantage that it is cheaper than a ceramic bearing.

[0022]

According to the present invention, the rolling fatigue life of the rolling bearing in which the ceramic rolling element is incorporated is improved, and the creep between the housing and the outer ring or the excessive tightening margin between the inner ring and the shaft is generated. Eliminates the danger of. Therefore, it is possible to provide a rolling bearing most suitable for use at high temperature and high speed such as a gas turbine or a turbocharger of an automobile.

[Brief description of drawings]

FIG. 1 is a table showing the results of a cylindrical rolling fatigue life test.

FIG. 2 is a table showing the results of a bearing life test.

FIG. 3 is a table showing representative physical property values.

Claims (1)

[Claims] 1. A rolling bearing incorporating a ceramic rolling element, at least one of an outer ring and an inner ring of which is HRC6.
A rolling bearing characterized by being made of powder high-speed steel having a hardness of 5 or more.