Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-12-21
2004-04-27
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C384S448000, C384S492000, C148S906000
Reexamination Certificate
active
06725720
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rolling bearing which is incorporated into steelworking facilities (facilities for processing steel into products) or paper machine facilities and which is to be used under harsh conditions such as high contact pressure or high temperatures.
The present invention also relates to a rolling bearing for use in railcars such as the Shinkansen (bullet train), a narrow-gauge line, or a freight train.
The present invention further relates to a rolling bearing which is to be used in, e.g., machine tool facilities, for a long period of time at high speed rotation and is subject to high-cycle rolling contact fatigue.
More particularly, the present invention relates to a rolling bearing which is resistant to cracking or flaking, which would otherwise shorten the life of the bearing, and which is ensured of having a stable and prolonged life.
Moreover, the present invention also relates to an ultrasonic detection and inspection method suitable for use in inspecting imperfections in a bearing raceway ring of the rolling bearing, such as presence of non-metallic intevening material in a position immediately below a bearing raceway surface of the bearing raceway ring.
Presence of non-metallic intevening material in a position immediately below a bearing raceway surface of a bearing raceway ring has hitherto been known to greatly affect the life of a rolling bearing. For this reason, there has conventionally been adopted a method of extending the life of a bearing by limiting the amount of non-metallic intevening material in steel during a phase of producing steel material for bearing. As described in, e.g., Japanese Patent Application Laid-Open (i.e., Japanese Patent Unexamined Publication) Nos. 145883/1994, 56640/1991, 117804/1993, and 192790/1994, there has already been proposed a technique aimed at prolonging the life of a bearing. Taught by the technique is that the bearing life can be prolonged by specifying the number of pieces of oxide-based intervening material (imperfections) consisting primarily of Al
2
O
3
or the number of pieces of Ti-based intervening material (imperfections) consisting primarily of TiN, each existing in a given area of subject steel.
Since a rolling bearing employed in paper machine facilities is used with an inner ring thereof being subjected to fitting stress, hoop stress is exerted on a bearing inner ring in a high-temperature environment, which raises a problem of cracking originating from large pieces of non-metallic intervening material located in the vicinity of an inner-diameter surface. In order to address the problem, there has been adopted a measure for preventing occurrence of cracking, by means of carburization of a bearing surface to there by impart compressive stress to the surface. As described in, e.g., Japanese Patent Application Laid-Open No. 307457/1994, there has already been disclosed a technique of preventing occurrence of hoop stress cracking in an inner ring having fitting stress exerted thereon, which would otherwise be caused in a high-temperature environment, by means of carbonitriding medium carbon steel for preventing occurrence of cracking.
In the case of a bearing for use in a railcar typified by the Shinkansen, in which the bearing is continuously used over a long period of time at high speed, one can predict that the bearing is subject to high-cycle rolling contact fatigue and that a serious accident will arise if the bearing is exfoliated and short-lived. With a view toward reducing the amount of non-metal intervening material in steel, steel having a limited amount of oxygen has been used as bearing material in such an application, or steel having a reduced amount of intervening material existing in a given area of subject steel has been used as bearing material, as described in connection with the related art.
Ultrasonic flaw detection is employed for detecting flaws in steel used in a bearing. With the objective of detecting flaws, such as macro-streak-flaws or imperfections caused by a hole not having been crimped, a steel manufacturer inspects all steel bars and all cross sections thereof, through ultrasonic flaw detection. As a result of removal of the imperfections that have been found through inspection, large imperfections in steel material used for a bearing have been eliminated. As the flaw detection method, there has already been known a normal beam method (see “Special Steel” Vol. 46, No. 46, pg. 31), wherein flaw detection is effected by causing ultrasonic waves to propagate from an outer circumferential surface of rolled steel to the inside thereof, in water or on a table.
However, flaws that can be detected in the rolled steel by ultrasonic flaw detection measure several millimeters in length. In-some instances, flaking or cracking has originated in actually-used bearings, within a short period of time, from large non-metal intervening material of hundreds of micrometers or from an aggregate into which small simple substances have coagulated. Highly accurate detection of flaws of such sizes has been impossible for two reasons. Namely, one of which is that flaws are detected at high speed through inspection during the steelworking process in order to improve productivity, and the other of which is that a steel product is inspected while remaining in a rolled state and having rough crystal grains therein and a rough surface layer. Accordingly, large noise resultantly arises during the course of detection of flaws.
Presence of large non-metallic intervening material has been well known to exert a great influence upon extending the life of a rolling bearing. If presence of such large non-metallic intervening material can be detected beforehand at the time of manufacture of a bearing, an extension of the life of a manufactured bearing can be expected. A steel product to be used for a bearing is subjected to ultrasonic flaw detection in a billet phase during a steel working process or a rolled-round bar phase. However, a flaw detection frequency is as low as 2 through 7 MHz. Hence, a damping factor of ultrasonic waves traveling through steel is low. In terms of roughness of a billet surface and productivity, the time required to pass a steel product through a flaw detector must be minimized. For these reasons, only imperfections of tens of millimeters in length (and hundreds of microns in width) can be detected.
Progress toward increasing load and contact pressure has recently been made in steelworking facilities, and demand for higher temperatures in the field of paper machinery has recently become stricter. For these reasons, a usage environment of a rolling bearing to be incorporated into the facilities has become harsher.
In relation to a rolling bearing used in steelworking facilities and paper machine facilities, there exists demand for a longer life and elimination of products which suddenly become short-lived or which suffer occurrence of cracking. In a production framework in which lines are inspected and maintained at given time intervals, if a rolling bearing used in the line has become short-lived or susceptible to cracking, the line must be deactivated, thereby inflicting an enormous loss. Therefore, there is a need for a rolling bearing which does not become short-lived at high contact pressure and under heavy fitting stress and which obviates a concern about occurrence of cracking and has a stable, long life.
Even in connection with a bearing for use in a railcar, such as the Shinkansen, which is to be continuously used for a long period of time at high speed, a user environment of a bearing has recently become more harsh. In association with an increase in the speed of the Shinkansen, a rolling bearing is exposed to fatigue that is higher in cycles than that having arisen in the related art. Journal of Japanese Society of Tripologists Vol. 45, No. 7 (2000), pg. 27, states that a maintenance-free Shinkansen has recently been planned. In view of facilitating business management of a railroad company, and that there is a desire for increasi
Kiuchi Akihiro
Matsumoto Yoichi
Murakami Yasuo
Miller Rose M.
NSK Ltd.
Sughrue & Mion, PLLC
Williams Hezron
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