Rolling bearing

Details Rolling bearing Rolling bearing

2001-02-07

2003-08-05

Yee, Deborah (Department: 1742)

Metal treatment

Stock

Ferrous

C148S325000, C148S328000, C148S906000, C384S912000

Reexamination Certificate

active

06602360

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a rolling bearing, in particular a rolling bearing suitable for engine auxiliary machines (alternator, electromagnetic clutch, compressor, intermediate pulley or water pulley) to be used at high temperatures, high vibrations and under circumstances where lubricate film formation is difficult owing to or a water invasion.
2. Description of the Related Art
Recently, in company with making automobiles small sized and light weight, auxiliary machines of engines have also been demanded to provide high performance and high output together with making the small size and the light weight. For example, bearings for alternators are acted on through belts with high vibration or high load (around 4 G to 20 G at the acceleration of gravity) accompanying rotation of high speed simultaneously with working of the engine. Therefore in the conventional bearing for the alternator, a problem has been present that exfoliation is easy to occur at an earlier period of service especially in the bearing face of the outer ring being a stationary ring.
It is considered that the exfoliation at an early period of the service is generated because the bearing face of the outer ring and the rolling faces of the rolling elements easily contact in that the formation of an oil film is difficult in company with increase of stress by high vibration, and a water content of around 0.1% in a grease or a water invasion during car washing, dissolve the grease.
Of shortening life of the bearing in case of the water invasion into the bearing, described in “Wear, 24 (1973) 107-118, The Effect of Hydrogen on the Rolling Contact Fatigue Life of AISI 52100 and 440C Steel Ball” by J. A. Cirura and other.
This literature sets forth, as results of four ball rolling tests, that the life in the test where a water was mixed in the lubricant was reduced to around {fraction (1/10)} of the life in other tests where the water was not mixed therein, and further as results of rolling fatigue tests using steel balls of hydrogen charge as rolling elements, that the life in the test where stainless steel (SUS440C) balls were used was longer than the life in the test where steel balls made of high carbon chromium bearing 2 category (SUJ2).
There have been proposed many techniques for preventing the early exfoliation so as to lengthen the life of the bearing to be served under the high vibration and high load.
For example, Japanese Patent Unexamined Publication No. Hei. 3-173747 proposes, in a grease sealed bearing, that at least the bearing ring at the stationary ring-side is made of martensite based stainless steel. It is described to employ, as the martensite based stainless steel, 13% Cr-0.3% C steel having a tempered martensite fabrication (e.g., SUS420J2), otherwise 13% Cr- or 18% Cr-high carbon stainless steel (e.g., SUS440A being 13% Cr-0.7% C steel and SUS440C being 18% Cr-1% C steel).
Japanese Patent Unexamined Publication No. Hei. 4-28845 proposes the use of a steel containing lower carbon (C) and higher chromium (Cr) (C: 0.65 to 0.90 wt %, Cr: 2.0 to 5.0 wt %, Si: 0.15 to 0.50 wt % and Mn: 0.15 to 1.0 wt %) in comparison with SUJ2 which has hitherto been used. It is described to use steel materials where the above steel is, as needed, added with at least one kind of Ni (0.2 to 0.5 wt %), Mo (0.1 to 2.0 wt %) and V (0.05 to 1.0 wt %).
According to this description, the early exfoliation is caused by generation of a white structure in steel which occurs by cohesion of carbon. Thus, by employing steels of low carbon, the carbon is prevented from diffusion to be a cause of cohesion for attaining the long life.
Japanese Patent Unexamined Publication No. Hei. 5-26244 describes that the early exfoliation is caused by invasion of hydrogen into steel generated in company with decomposition of grease and hydrogen embrittlement caused thereby. It is therefore proposed therein to employ a steel containing Cr 1.5 to 6% for at least the bearing ring at the stationary ring-side. There is described that an oxide film of Cr is formed on the surface of the bearing ring so that a rolling surface (orbital surface) is made inactive, and so the grease is prevented from decomposition, or even if it is decomposed, the hydrogen generated thereby is avoided from invasion into the steel (bearing ring).
Further, as a measure for preventing the early exfoliation of the stationary ring, a fatigue mechanism of the bearing for alternators is explicated at the 1st article to the 14th article of “SAE Technical Paper: SAE 950944 (open Feb. 27 to Mar. 2, 1995), and it discloses to change the sealed greased from E grease to M grease. The M grease has a high damper effect, and if using to the bearing to be served under high vibration and high load, it fully absorbs vibration and load, and it is possible to prevent the early exfoliation of the stationary ring.
However, some of the prior techniques cannot actually provide the disclosed effects, and even if providing, there remains a room for improving several respects of workability of a steel to be served, hardness for the bearing members, corrosion resistance, and cost.
For example, as described in pp. 551 to 554 of “Preparatory Manuscript for Japan Tribology Congress (Tokyo, May 1995)”, the bearing for auxiliary machine of engine to be used under the high vibration and high load creates self-rotating slide at an entrance side of the stationary ring. Cr oxidized film to be formed with a steel of 1.5 to 6% Cr is easily broken by the self-rotating slide, and so it will be difficult to prevent the early exfoliation of the stationary ring by the method disclosed in Japanese Patent Unexamined Publication No. Hei. 5-26244.
Further, in “WEAR 199 (1996) p 245 to 252, Occurrence of brittle flaking on bearing used for automotive electrical instruments and auxiliary device” by Tamada and others, it is described that in the rolling fatigue test of line-contact by test pieces of hydrogen charge, test pieces of stainless steel of 13% Cr make change of white structure and breakage similar to test pieces of SUJ2 or SUJ3.
Also even in a case of the M grease, the formation of the oil film might be often insufficient in an atmosphere at high temperature exceeding 150° C. In addition, if difference in atmospheric temperature is large, a dew easily occurs within the bearing, and a water by the dew might go into the lubricant.
SUMMARY OF THE INVENTION
The invention has been made in view of these problems involved with the conventional technique, and with respect to the rolling bearings to be used at high vibration, high load and under the using conditions where the water might mix into the lubricant, the invention is accordingly to provide such a rolling bearing enabling to prevent the early exfoliation in the rolling surface of the outer ring as the stationary ring and to largely lengthen the bearing life.
The object can be achieved by a rolling bearing, according to the present invention, comprising:
a stationary ring;
a rotary ring; and
a plurality of rolling elements rotatably interposed between the stationary and rotary rings,
at least the stationary ring is made of an iron-steel material containing alloying components of
0.40% to 1.20% by weight of carbon (C);
0.7% to 2.0% by weight of at least one of silicon (Si) and aluminum (Al);
0.2% to 2.0% by weight of manganese (Mn);
0.1% to 3.0% by weight of nickel (Ni) and 3.0% to 9.0% by weight of chromium (Cr),
where Cr-equivalent amount defined by following formula (1) is 9.0 wt % to 17.0 wt %,
Cr-equivalent amount (%)=[Cr]+2[Si]+1.5[Mo]+5[V]+5.5[Al]+1.75[Nb]+1.5[Ti]  (1)
 in the formula, [Cr], [Si], [Mo], [V], [Al], [Nb] and [Ti] show containing percent (wt %) of Cr, Si, Mo, V, Al, Nb and Ti in the iron-steel material, and
wherein the at least the stationary ring has a rolling surface which is subjected to quenching an

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