JP2009242548A - Grease composition, rolling device and ball bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grease composition having high effect of reducing fretting wear even when vibration is large, and also to provide a rolling device and a ball bearing having improved resistance to fretting and improved durability. <P>SOLUTION: The grease composition contains a base oil having a pressure viscosity coefficient of 25 GPa<SP>-1</SP>or more at 40°C. The rolling device and the ball bearing enclose the grease composition. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a grease composition used for lubricating various devices, equipment, a rolling device and a rolling bearing in which the grease composition is enclosed.

  For example, rolling bearings are used for the parts that rotate and support the rotating shaft of servo motors. However, especially when performing micro reciprocating motion or when receiving micro vibrations, the surface of the rolling element or rolling surface is used. Fretting occurs, causing various problems such as an increase in bearing torque and separation starting from the damaged part. Therefore, the countermeasure which reduces fretting wear is employ | adopted by employ | adopting a ceramic ball for a rolling element (refer patent document 1).

  However, since ceramic balls are more expensive than commonly used steel balls, it has also been attempted to reduce fretting wear by adding ultrafine particles to the grease composition enclosed for lubrication. . For example, a grease composition containing iron oxide ultrafine particles (see Patent Document 2), hydrophobized silica ultrafine particles (see Patent Document 3), and the like has been proposed.

JP 2005-188726 A JP-A-9-67588 JP 2006-169316 A

  However, with conventional lubricants containing ultrafine particles, the effect of reducing fretting wear can be obtained when vibration is small, but when vibration is increased, the effect of reducing fretting wear is not sufficient, and there is a strong demand for improvement. Yes.

  Therefore, an object of the present invention is to provide a grease composition having a high effect of reducing fretting wear even when vibration is large. Another object of the present invention is to provide a rolling device and a rolling bearing that are more excellent in fretting resistance and more durable.

In order to achieve the above object, the present invention includes a grease composition containing a base oil having a pressure viscosity coefficient at 25 ° C. of 25 GPa ⁻¹ or more at 40 ° C., and the grease composition is enclosed. A rolling device and a rolling bearing are provided.

Since the grease composition of the present invention contains a base oil having a pressure viscosity coefficient at 40 ° C. of 25 GPa ⁻¹ or more, it has a great effect of reducing fretting wear even when vibrations increase.

  Further, a rolling device or a rolling bearing in which such a grease composition is sealed does not need to use ceramic balls, and is inexpensive and has excellent fretting resistance.

  Hereinafter, the present invention will be described in detail.

(Grease composition)
The grease composition of the present invention, the pressure viscosity coefficient at 40 ° C. is 25 GPa ^-1 or more, preferably using 26 GPa ^-1 or more base oils. The pressure viscosity index is measured by a falling body viscometer. The type of the base oil is not limited as long as the pressure viscosity coefficient is satisfied, and examples thereof include various traction oils such as paraffinic, naphthenic, liquid paraffin, polyisobutylene, and synthetic isoparaffin.

Moreover, it is preferable that kinematic viscosity in 40 degreeC is 20-100 mm < ² > / s so that a base oil may show favorable lubrication performance in the wide temperature range from low temperature to high temperature.

  There is no limit to the thickener as long as the above base oil can be retained. For example, metal soap (aluminum soap, barium soap, calcium soap, lithium soap, sodium soap, etc.), composite metal soap (lithium complex soap, calcium complex soap, Aluminum complex soap, etc.), urea compounds (diurea, triurea, tetraurea, polyurea, etc.), silica gel, bentonite, urethane compounds, urea-urethane compounds, sodium terephthalate, and the like can be appropriately selected according to the purpose.

  In addition, various additives used in the grease composition can be added depending on the purpose. For example, amines such as phenyl-1-naphthylamine, phenols such as 2-tert-butylphenol, antioxidants such as sulfur and dithiophosphates; organic sulfonates such as alkali metals and alkaline earth metals, alkyls, Rust preventives such as alkyl alkenyl succinates, alkenyl succinate derivatives, partial esters of polyhydric alcohols such as sorbitan monooleate; extreme pressure agents such as phosphorus, zinc dithiophosphate, organic molybdenum; fatty acids, animal and vegetable oils Oil deactivators such as benzotriazole and the like can be added alone or in appropriate combination.

  Moreover, there is no restriction | limiting also in characteristics, such as the penetration degree of a grease composition.

(Rolling bearing)
In the present invention, the type of rolling bearing is not limited, and for example, a ball bearing shown in FIG. 1 can be exemplified. In the illustrated ball bearing, a plurality of balls 5 as rolling elements are held via a cage 7 between an inner ring 2 having an inner ring raceway 1 and an outer ring 4 having an outer ring raceway 3. A bearing space formed by the outer ring 4 and the balls 5 is filled with the above grease composition and sealed with a seal 6.

  In such a ball bearing, the inner ring raceway 1 and the ball 5, the outer ring raceway 4 and the ball 5 collide with each other due to vibration, and the inner ring raceway 1, the outer ring raceway 2, and the ball 5 are damaged. The base oil of the grease composition enters the gap between the balls 5 and the gap between the outer ring raceway 3 and the balls 5 to reduce fretting wear. Therefore, it is suitable as a rolling bearing or the like that supports the rotating shaft of the servo motor that is susceptible to vibration, and the ball 5 does not need to be made of ceramic and can be made inexpensive.

  In addition, as a kind of rolling bearing, besides a ball bearing, a roller bearing with a cage, a total rolling bearing, a total roller bearing, and the like can be given, and the rolling surface may be a single row or a double row.

(Rolling device)
Examples of the rolling device include a ball screw and a linear guide, but there is no limitation other than enclosing the above grease composition. Like the rolling bearing, the rolling device of the present invention is inexpensive and excellent in fretting resistance.

  Hereinafter, the present invention will be further described with reference to examples and comparative examples.

Example 1
A test grease A containing traction oil (pressure viscosity coefficient at 40 ° C. 27 GPa ⁻¹ , kinematic viscosity at 40 ° C. 30 mm ² / s) and a urea compound was prepared. The penetration degree is 247.

(Comparative Example 1)
Test grease B containing ether oil (pressure viscosity coefficient at 40 ° C. 19 GPa ⁻¹ , kinematic viscosity at 40 ° C. 100 mm ² / s) and a urea compound was prepared. Incidentally, the blending degree is 290.

(Comparative Example 2)
Test grease C containing mineral oil (pressure viscosity coefficient at 40 ° C. of 17 GPa ⁻¹ , kinematic viscosity at 40 ° C. of 130 mm ² / s) and lithium soap was prepared. In addition, the penetration degree is 275.

(Fretting test)
The test greases A to C prepared above were enclosed in equal amounts in a single-type thrust ball bearing (invention number: 51305) having an inner diameter of 25 m, an outer diameter of 52 mm, and a height of 18 mm to produce a test bearing. Then, the test bearing was mounted on a fretting tester manufactured by Nippon Seiko Co., Ltd. shown in FIG. In the test bearing, in order to accurately measure the maximum height (Ry) of the damaged portion, a disk test piece in which the lower race is lapped is used.
・ Maximum surface pressure: 3.2 GPa
・ Maximum rocking speed: 20mm / s
・ Number of oscillations: 10,000 times ・ Amplitude ratio: 0.5 to 2.0

  The amplitude ratio is a ratio “A / b” between the contact circle radius (a) and the amplitude (A) as shown in FIG. As shown in FIG. 4, the disk test piece is worn as the rocking occurs, and wear powder accumulates on the circumference of the contact ellipse, and the portion is greatly damaged. Therefore, by comparing the maximum height (Ry) of the damaged portion, the effect of reducing fretting wear can be evaluated.

  The test was performed for each predetermined amplitude ratio, and the lower race surface of the test bearing before and after the test was observed with an interference microscope to measure the maximum height (Ry) of the damaged portion. The ratio of Ry before and after the test of the test bearing (Ry after test / Ry before test: damage ratio) was obtained. The less damage, the closer the damage ratio is to 1. FIG. 5 is a graph showing the damage ratio for each amplitude ratio. If the amplitude ratio is 0.5 or less, there is no difference in the degree of damage in any test bearing, but if it exceeds 0.5, there is a difference in the degree of damage. Begins to appear and becomes more pronounced as the amplitude ratio increases. From this, it can be seen that in an environment where vibration is intense, the effect of reducing fretting wear is increased by using a base oil having a large pressure viscosity coefficient according to the present invention.

It is sectional drawing which shows an example of a ball bearing. It is a schematic diagram which shows the fretting test machine used in the Example. It is a schematic diagram for demonstrating an amplitude ratio. In a fretting test, it is a mimetic diagram showing the state where a disk specimen is worn. It is a graph which shows the relationship between an amplitude ratio and a damage ratio obtained in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner ring track 2 Inner ring 3 Outer ring track 4 Outer ring 5 Ball 6 Seal 7 Cage

Claims (4)

A grease composition comprising a base oil having a pressure viscosity coefficient at 40 ° C. of 25 GPa ⁻¹ or more.   A rolling device in which the grease composition according to claim 1 is enclosed.   A rolling bearing, wherein the grease composition according to claim 1 is enclosed.   4. A rolling bearing according to claim 3, wherein the rolling bearing is used for a rotating shaft of a servo motor.

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