WO2017033699A1 - Rolling bearing - Google Patents

Abstract

Provided is a rolling bearing, wherein rust is prevented by a coating of phosphate being formed on the rolling contact surface of a bearing member, and the reduction in bearing service life is minimized. A rolling bearing 1 has a phosphate coating 6 over the entire inner ring surface including an inner ring track surface 2a, the entire outer ring surface including an outer ring track surface 3a, and the entire rolling element surface including the rolling surface 4a of a rolling element 4. The thickness of the phosphate coating 6 is 6 µm or more. When the surface of the coating is viewed from just above, 30% or more of the whole projected area of the coating is formed from a crystal grain with a projected area of 25 µm² or more.

Description

Rolling bearing

The present invention relates to a rolling bearing, and more particularly to a rolling bearing used for a general industrial machine.

A rolling bearing is known as a mechanical element used as a sliding mechanism of equipment. In a rolling bearing, since a plurality of rolling elements arranged between the inner ring and the outer ring continuously roll, the inner ring, outer ring, rolling element, and cage that are components of the rolling bearing are continuously in contact with each other. Stress is applied. In addition, when exposed to wind and rain in industrial machines used outdoors, or when cooling water or the like is used when processing products with the equipment, moisture may enter the bearing. Therefore, suppressing rolling fatigue and rusting caused by moisture due to long-time operation is important in preventing functional deterioration of the equipment.

In view of these points, rolling bearings with improved rolling fatigue resistance and rust prevention have been proposed so far. For example, Patent Document 1 reports that in rolling bearings used in steel plate rolling equipment, damage such as surface peeling due to corrosion wear is less likely to occur. In the rolling bearing of Patent Document 1, an inner ring, an outer ring, and a rolling element are manufactured by carbonitriding, and a plurality of rolling elements are held in a cage between raceway surfaces of the inner and outer rings. By forming a manganese phosphate salt coating on the rolling surface, it has succeeded in improving the life against rolling fatigue in a corrosive environment.

JP 2005-299838 A

For bearings that are exposed to the atmosphere, a phosphate coating treatment has been applied to prevent rust. For example, full-roller bearings used in sheaves are subject to rust prevention because they are exposed to wind and rain, while long life is required because they are used for a long time at low speed. Generally, when the phosphate coating treatment is performed, the bearing life (rolling fatigue life) is reduced as compared with the untreated product. This is considered to be caused by the fact that when the phosphate coating treatment is performed, the surface roughness of the bearing is deteriorated so that it becomes weak against rolling, and the phosphate peels off when operated under a high load. On the other hand, the phosphate coating has the effect of enhancing the lubricity of the bearing by retaining oil on the coating surface, so that the bearing life can vary depending on the film thickness and surface condition.

In Patent Document 1, as shown above, the life against rolling fatigue in a corrosive environment has been successfully improved. However, the relationship between the crystal size and film thickness constituting the coating and the bearing life is not clarified. Further, Patent Document 1 is directed to carburized steel as a base material, and it is not clear whether the above effect can be obtained even with bearing steel or the like.

The present invention has been made in order to cope with such a problem, and a rolling bearing in which a phosphate coating is formed on the surface of a rolling contact portion of a bearing member, has a rust prevention function, and suppresses a decrease in bearing life. The purpose is to provide.

The rolling bearing of the present invention is a rolling bearing having a phosphate coating on at least a part of the surface of the rolling contact portion, wherein the phosphate coating has a thickness of 6 μm or more, and the surface of the coating is viewed from directly above. In this case, 30% or more of the total projected area of the coating film is composed of crystal grains having a projected area of 25 μm ² or more. In particular, when the surface of the film is viewed from directly above, 40% or more of the total projected area of the film is composed of crystal grains having a projected area of 25 μm ² or more.

The rolling bearing includes an inner ring having an inner ring raceway surface on the outer periphery, an outer ring having an outer ring raceway surface on the inner periphery, and a plurality of rolling elements that roll between the inner ring raceway surface and the outer ring raceway surface, The surface of the rolling contact portion is at least one selected from the inner ring raceway surface, the outer ring raceway surface, and the rolling surface of the rolling element.

The above-mentioned rolling bearing is a cylindrical roller bearing or a tapered roller bearing. Moreover, this rolling bearing is a full roller bearing.

The surface of the rolling contact portion is the surface of a member made of bearing steel. The phosphate film is a manganese phosphate film. Further, the thickness of the phosphate coating is 6 to 7.5 μm.

Since the rolling bearing of the present invention has a phosphate coating with a film thickness of 6 μm or more and an optimized crystal size on at least a part of the surface of the rolling contact portion, it has a rust prevention function and is resistant to rolling fatigue. It is excellent in that it can suppress a decrease in bearing life.

It is sectional drawing which shows an example of the rolling bearing of this invention. It is sectional drawing which shows the other example of the rolling bearing of this invention. It is sectional drawing which shows the other example of the rolling bearing of this invention. It is a figure which shows a rolling fatigue test result (effect of a film thickness). It is a figure which shows a rolling fatigue test result (effect of a crystal size). It is a figure which shows a rolling fatigue test result (effect of a film thickness and crystal size).

Usually, in order to increase the rust prevention ability, a dense structure with small crystal grains is good, and for that purpose, the film thickness should be about 1 to 4 μm. In the present invention, a plurality of test pieces having different film thicknesses were produced and a rolling fatigue test was performed, and the relationship between the film thickness and the crystal size of the phosphate coating and the lifetime was investigated. A comparative study was conducted using a test piece having a phosphate coating having a thickness of 1 to 4 μm as usual and a test piece having a phosphate coating having a thickness of 6 to 9 μm, which is thicker than usual (examples described later). . As a result, it was found that “the film thickness of the phosphate coating” and “the crystal size constituting the phosphate coating” affect the bearing life. The present invention is based on such knowledge.

The rolling bearing of the present invention has a phosphate coating on at least a part of the surface of the rolling contact portion of a bearing member such as an inner ring, an outer ring, or a rolling element. The thickness of the phosphate coating is 6 μm or more, preferably 6 to 9 μm, more preferably 6 to 7.5 μm.

The phosphate coating can also be formed by immersing the target bearing member in the phosphating solution or spray-coating the phosphating solution on the bearing member. Among the phosphate treatments, manganese phosphate treatment is preferable. Examples of the treatment liquid used for the manganese phosphate treatment include an aqueous solution of a manganese phosphate compound composed of divalent manganese ions, iron ions, nickel ions and trivalent phosphate ions. The reaction process of film formation when this treatment liquid is used and steel is used as a base material is as follows. Free phosphoric acid is generated by the first dissociation of the aqueous manganese phosphate solution, and iron on the metal surface is dissolved by the free phosphoric acid. The hydrogen ion concentration on the metal surface decreases, the dissociation equilibrium of the manganese phosphate aqueous solution shifts in the direction of manganese phosphate formation, and insoluble manganese phosphate microcrystals precipitate on the metal surface to form a film.

The crystal particle diameter, film thickness, and film roughness constituting the film can be appropriately adjusted depending on the treatment liquid composition used. In phosphating, since the surface state of each bearing member greatly affects the crystal particle diameter of the coating film to be formed, it is preferable to degrease the surface of the member or clean it with ion exchange water before the treatment.

The rolling bearing of the present invention is characterized in that the phosphate coating formed on the surface of the rolling contact portion has a crystal size in a specific range in addition to the above film thickness. Specifically, when the surface of the formed phosphate coating is viewed from directly above, a range in which 30% or more of the total projected area of the coating is composed of crystal grains having a projected area of 25 μm ² or more. And That is, the phosphate coating satisfies the following formula.

100 × (Area composed of crystal grains having a projected area of 25 μm ² or more in the phosphate coating) / (total projected area of the phosphate coating) = 30%

Crystal grains having a projected area of 25 μm ² or more have a relatively large crystal size, and when this ratio increases, it is generally predicted that the rolling fatigue life will deteriorate. Excellent results have been obtained. This is considered to be because the surface of the phosphate coating becomes rough to some extent, so that the oil retention of the coating is increased and the lubricating action by the oil is optimized. Considering the results of Examples and the like described later, it is more preferable that 40% or more of the total projected area of the coating is composed of crystal grains having a projected area of 25 μm ² or more. .

The relationship expressed by the above formula in the phosphate coating is, for example, that a substantially uniform phosphate coating is formed at the target site, and a part of the phosphate coating is photographed with an optical microscope or SEM (scanning electron microscope). This can be confirmed by analysis. The crystal shape (plate shape, granular shape, needle shape, columnar shape, etc.) is not particularly limited, and the projected area can be confirmed by the above image analysis for any shape. The upper limit of the projected area of the crystal grains is not particularly limited as long as it is a size that is normally formed, but a specific example is about 25 to 50 μm ² . Further, the upper limit of the above range (30% or more) is not particularly limited, but a specific example is about 30 to 60%.

Further, there is a certain degree of correlation between the size of the crystal grains and the film thickness. Specifically, the larger the film thickness, the larger the crystal grain size on the coating surface. This is presumably because the crystal growth progressed by extending the coating treatment time in order to increase the film thickness. For example, when the film thickness is 3 μm or less, crystal grains having a projected area of 25 μm ² or more cannot be confirmed (5% or less in the above range).

Embodiments of the present invention will be described with reference to FIGS. 1 to 3 are all sectional views of a rolling bearing (cylindrical roller bearing). As shown in FIG. 1, the rolling bearing 1 includes, as bearing members, an inner ring 2 having an inner ring raceway surface 2a on the outer periphery, an outer ring 3 having an outer ring raceway surface 3a on the inner periphery, an inner ring raceway surface 2a and an outer ring raceway surface 3a. Are provided with a plurality of rolling elements 4 that roll between and a cage 5 that holds the plurality of rolling elements 4. In this embodiment, the phosphate coating 6 (black thick line) is formed on the entire inner ring surface including the inner ring raceway surface 2a, the entire outer ring surface including the outer ring raceway surface 3a, and the entire rolling element surface including the rolling surface 4a of the rolling element 4. is doing. As described above, the phosphate coating 6 is a coating with optimized film thickness and crystal size.

In the embodiment shown in FIG. 2, the phosphate coating 6 (black thick line) is formed on the entire inner ring surface including the inner ring raceway surface 2a and the entire outer ring surface including the outer ring raceway surface 3a. In this embodiment, the coating film is not formed on the rolling surface 4a. In the form shown in FIG. 3, the phosphate coating 6 (black thick line) is formed on the entire surface of the rolling element including the rolling surface 4 a of the rolling element 4. In this embodiment, the coating is not formed on the inner ring raceway surface 2a and the outer ring raceway surface 3a. 2 and 3 is the same as the phosphate coating of FIG.

The rolling bearing of the present invention is not limited to the examples shown in FIGS. 1 to 3, and a predetermined phosphate coating may be formed on at least a part of the surface of the rolling contact portion. Specifically, the rolling contact portion surface is an inner ring raceway surface, an outer ring raceway surface, or a rolling surface.

Examples of the material of the inner ring, outer ring, and rolling element that constitute the rolling bearing of the present invention and serve as a base material for the phosphate coating include, for example, bearing steel (high carbon chrome bearing steel JIS G 4805), case hardening steel (JIS G). 4104 etc.), high speed steel (AMS 6490), stainless steel (JIS G 4303), induction hardened steel (JIS G 4051 etc.). In the rolling bearing of the present invention, a lubricant such as lubricating oil or grease is lubricated by being interposed in the rolling contact portion (rolling surface) between the inner ring 2 and the outer ring 3 and the rolling element 4. The lubricant is not particularly limited, and any lubricating oil or grease can be used. These lubricants are retained on the surface of the phosphate coating, contributing to lubrication and extending the bearing life.

The rolling bearing of the present invention is not limited to the cylindrical roller bearing shown in FIGS. 1 to 3, and can be applied to any type of bearing. It is particularly suitable for cylindrical roller bearings and tapered roller bearings that are operated under high loads. Moreover, in these, it is suitable for the full roller bearing (SL bearing) which eliminated the cage.

A cylindrical roller (bearing steel) was coated to obtain a test piece. The formed phosphate coating was a manganese phosphate coating, and was formed by immersing the above-described cylindrical roller in a manganese phosphate treatment solution. A plurality of test pieces having different film thicknesses and crystal sizes were prepared by changing various conditions.

By subjecting this test piece to forced circulation of turbine oil VG68 at a contact surface pressure of 4.16 GPa and a load speed of 20400 cpm under line contact where cylindrical rollers are brought into contact with each other, and measuring the load time until occurrence of peeling. Rolling fatigue resistance (peeling time (min)) was evaluated. The relationship between the stripping time thickness 4, 5 the relation between crystal size (projected area 25 [mu] m ² or more crystalline fraction) and the release time, the film thickness and crystallite size (projected area 25 [mu] m ² or more crystalline proportion ) And the peeling time are shown in FIG.

Here, the film thickness of the phosphate coating was determined from the difference in the diameter values of the test pieces before and after the treatment. As for the crystal size, an image obtained by observing an arbitrary range of the phosphate coating with an optical microscope at a magnification of 200 times is directly above the observation stage of the optical microscope among the coatings recognized in the rectangular frame of the observation image. The ratio of the area composed of crystal grains having a projected grain size of 25 μm ² or more when viewed from the direction to the total area (total projected area) of the rectangular frame was calculated from the above formula.

First, the influence of the film thickness and the crystal size on the peeling time will be considered. As shown in FIG. 4, the peeling time can be extended by increasing the film thickness (6 μm or more). Further, as shown in FIG. 5, the peeling time can be extended by increasing the proportion of crystals having a projected area of 25 μm ² or more (30% or more).

Next, the effect of both the film thickness and crystal size (combination) on the peeling time will be considered. As shown in FIG. 6, when the film thickness is in the range of 6.5 to 7.5 μm, the ratio of crystals having a projected area of 25 μm ² or more and the peeling time tend to increase as the film thickness increases. When the film thickness is in the range of 7.5 to 9.0 μm, there is a tendency that the ratio of crystals having a projected area of 25 μm ² or more and the peeling time decrease conversely as the film thickness increases. This is presumed that the crystal growth progressed uniformly while having a monodispersity in the particle size distribution within the range of the film thickness up to 7.5 μm, and the particle size distribution within the range of the film thickness exceeding 7.5 μm. It is presumed that the monodispersity collapsed and the crystal growth progressed non-uniformly. From this, it is considered that the film thickness of the phosphate coating is more preferably 6 to 7.5 μm in order to realize a longer bearing life.

In addition, from FIG. 5 and FIG. 6, the crystal ratio with a projected area of 25 μm ² or more is preferably 40% or more. Within this range, the peeling time can be further extended and a long bearing life can be realized.

The rolling bearing of the present invention is suitable as a rolling bearing for general industrial machines that are used for a long time in harsh environments such as sheaves, cranes, etc., which are loaded with high loads and easily exposed to wind and rain. Available to:

DESCRIPTION OF SYMBOLS 1 Rolling bearing 2 Inner ring 2a Inner ring raceway surface 3 Outer ring 3a Outer ring raceway surface 4 Rolling element 4a Rolling surface 5 Cage 6 Phosphate coating

Claims (8)

1. A rolling bearing having a phosphate coating on at least a part of the surface of the rolling contact portion,
   When the thickness of the phosphate coating is 6 μm or more and the surface of the coating is viewed from directly above, 30% or more of the total projected area of the coating is composed of crystal grains having a projected area of 25 μm ² or more. Rolling bearing characterized by being made.
2. ^{2. The} structure according to claim 1, wherein when the surface of the coating is viewed from directly above, 40% or more of the total projected area of the coating is composed of crystal grains having a projected area of 25 μm ² or more. Rolling bearing.
3. The rolling bearing includes an inner ring having an inner ring raceway surface on an outer periphery, an outer ring having an outer ring raceway surface on an inner periphery, and a plurality of rolling elements that roll between the inner ring raceway surface and the outer ring raceway surface. ,
   2. The rolling bearing according to claim 1, wherein the surface of the rolling contact portion is at least one selected from the inner ring raceway surface, the outer ring raceway surface, and the rolling surface of the rolling element.
4. The rolling bearing according to claim 1, wherein the rolling bearing is a cylindrical roller bearing or a tapered roller bearing.
5. The rolling bearing according to claim 4, wherein the rolling bearing is a full complement roller bearing.
6. 2. The rolling bearing according to claim 1, wherein the surface of the rolling contact portion is a surface of a member made of bearing steel.
7. The rolling bearing according to claim 1, wherein the phosphate coating is a manganese phosphate coating.
8. 2. The rolling bearing according to claim 1, wherein the thickness of the phosphate coating is 6 to 7.5 μm.

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