Rolling device

Details Rolling device Rolling device

2000-10-04

2002-08-13

McAvoy, Ellen M. (Department: 1764)

Solid anti-friction devices, materials therefor, lubricant or se

Lubricants or separants for moving solid surfaces and...

Silicon dioxide, silicic acid, orthosilicate, or...

C508S182000, C508S206000, C508S582000, C508S590000, C384S462000

Reexamination Certificate

active

06432887

ABSTRACT:

This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-034233, filed Feb. 12, 1999; and No. 11-079636, filed Mar. 24, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a rolling device, particularly to a rolling device using a lubricant.
In general, in a rolling device such as a ball-and-roller bearing or a rectilinear device, abrasion of the rolling body and the member in contact with the rolling body is prevented by circulating or sealing a lubricant such as a lubricating oil like a mineral oil or poly-&agr;-olefin oil or a grease within the rolling device.
Such a rolling device can be used under the ordinary use conditions without giving rise to a problem. However, where the rolling device is driven under, for example, a high temperature, high speed or vacuum condition, the lubricant is scattered to the outside of the rolling device, or the lubricant is evaporated to generate a gas. As a result, the outer environment of the rolling device is contaminated. For that reason, a fluorine-based grease is used in many cases as a lubricant of the rolling device in an apparatus used in a clean room such as a semiconductor manufacturing apparatus, a liquid crystal panel manufacturing equipment and a hard disk manufacturing equipment; a vacuum equipment in which the rolling device is exposed to a vacuum condition such as a vacuum pump; and the equipment used under high temperatures.
The fluorine-based grease is a mixture of a liquid fluorinated polymer oil as a base oil and a solid fluorinated polymer as a thickener. In general, the fluorine-based grease is very low in its volatility, and the amount of the grease scattered to the outside of the rolling device or evaporated is very small. It follows that the outer environment of the rolling device is relatively unlikely to be contaminated.
However, the liquid fluorinated polymer contained in the fluorine-based grease has in general a high viscosity, leading to a difficulty, particularly where the rolling device using the fluorine-based grease as a lubricant is driven at a high speed. Specifically, since the lubricant has a large resistance to stirring, the torque is rendered excessively high so as to increase the heat generation. As a result, in the case of the ball-and-roller bearing, the inner ring, the outer ring, and the rolling body are expanded. It follows that the clearance between the adjacent members is diminished so as to make the load excessively large at the contact surfaces between the inner ring and the rolling body and between the outer ring and the rolling body. As a result, an abnormal abrasion and seizing are brought about so as to render the rolling device unusable in a short time. Naturally, the rolling device must be renewed frequently.
Also, in recent years, the evacuation capacity and the evacuation rate tend to be increased in the vacuum pump. To be more specific, the rotating speed of the rolling device used in the vacuum pump is sharply increased nowadays. Therefore, the heat generation is increased so as to bring about the abnormal abrasion and seizing as described above. As a result, the rolling device is rendered unusable in a short time and the vacuum pump is rendered inoperable in a short time.
As described above, where a fluorine-base grease is used as a lubricant of a rolling device operated under a high temperature, high speed or vacuum condition, an abnormal abrasion and seizing tend to be derived from the high viscosity of the fluorine-based grease. Naturally, it is desirable for the rolling device used under a high temperature, high speed or vacuum condition to be driven without inviting contamination of the outer environment and an increased torque.
The problem described above takes place not only under a high temperature, high speed or vacuum condition but also under a low temperature condition. When it comes to a rolling device used in, for example, an equipment for cooling or freezing an electronic element, the temperature elevation is derived from the resistance to stirring accompanying the driving of the rolling device. As a result, where a mineral oil, poly-&agr;-olefin oil or the like is used as the lubricant of the rolling device, the outer environment of the rolling device, e.g., the coolant used for the cooling or freezing, is contaminated. Thus, the cooled element such as the electronic element is contaminated with the lubricant component. Also, since, in this case, the evaporation and disappearance of the lubricant are promoted by the coolant, a sufficient lubricity ceases to be obtained by the use for a short time. Under the circumstances, the fluorine-based grease was widely used in the past as a lubricant of the rolling device under the condition requiring a low temperature and a clean environment as in the refrigerator and freezer.
However, the ordinary fluorine-based grease has a high viscosity, as already pointed out. Particularly, the fluorine-based grease has a very high viscosity under a low temperature condition, giving rise to an increase in the resistance to stirring, i.e., an increase in the torque of the rolling device. As a result, it is impossible to drive the rolling device in some cases. Also, even if the rolling device can be driven, an excessively large load is applied to the motor for driving the rolling device. In addition, the heat generation accompanying the driving of the motor is rendered excessively large so as to evaporate the lubricant and, thus, to contaminate the coolant.
It should also be noted that some of the fluorine-based greases has a high vapor pressure. Where such a fluorine-base grease is used as a lubricant of the rolling device used under the low temperature condition, the evaporation caused by the heat generation noted above is rendered more prominent. In this case, the evaporation and disappearance of the lubricant are promoted by the coolant, as pointed out above, with the result that a sufficient lubricity ceases to be obtained in a very short time.
In accordance with miniaturization of the design rule of the electronic element in recent years, demands for preventing contamination tend to become severer and severer against the cooling and freezing equipment of the electronic element. Also, in accordance with miniaturization and energy saving of the cooling and freezing devices, the torque of the rolling device constituting a part of the driving section tends to be decreased so as to suppress the loss of the power and to prolong the life of the driving section, thereby achieving a mechanism free from maintenance.
However, the lubricant used in the conventional rolling device gives rise to an increase in the torque and to contamination of the cooled member. In addition, the lubricant gives rise to the problem that a sufficient lubricity ceases to be obtained in a short time. Under the circumstances, it is desirable for the rolling device used under low temperature conditions to be driven without giving rise to contamination of the outer environment and to an increase in the torque.
The problem derived from the lubricant is generated not only in the case where the rolling device is used in the apparatus described above. In other words, the problem derived from the lubricant is also generated in the case where the rolling device is used for the other purposes, as described below.
As widely known to the art, a ball-and-roller bearing using grease as a lubricant is utilized in general in the electrical components of an automobile, an alternator that is an auxiliary member of an engine, an intermediate pulley, an electromagnetic clutch for an automotive air conditioner, etc.
Diminishment of an engine room is required for the automobile in accordance with popularization of a front-wheel-drive vehicle intended to miniaturize and decrease the weight of the automobile and with requirement for an enlarged cabin. Such being the situation, vigorous efforts are being made in an attempt to miniaturize and decreas

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