JP2002323051A - Rolling bearing for hot metal plating equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling gearing which is excellent in corrosion resistance and an abrasion resistance against a molten metal and suitable for a hot dipping device. SOLUTION: For the rolling bearing having an outer ring 1, an inner ring 2 and a plurality of balls 3 which are rollably arranged between the outer ring 1 and the inner ring 2 and used for the metal hot-dipping device, a boron layer 5 with Vickers hardness of more than Hv 1000 obtained by boron diffusion coating is provided at least in an orbit face of the outer ring 1 and that of the inner ring 2 among orbit faces of the outer ring 1, those of the inner ring 2 and the rolling surface of the ball 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing having excellent corrosion resistance and wear resistance used for supporting a roll used in a molten metal plating apparatus while being immersed in a molten metal plating bath. .

[0002]

2. Description of the Related Art Rolling bearings used for supporting rolls in a hot-dip metal plating apparatus always come into contact with the molten metal, and therefore must be made of a material having excellent corrosion resistance to the molten metal. Steel is generally used as a material for forming a rolling bearing for a hot-dip metal plating apparatus, but the erosion of the hot-dip metal to the steel material is very strong.

In a rolling bearing used for a hot-dip metal plating apparatus, the degree of corrosion resistance to the molten metal directly affects the rolling life. A rolling bearing has been proposed in which a portion in contact with a roller is made of a ceramic material (Japanese Utility Model Laid-Open No. 61-90852). Japanese Patent Application Laid-Open No. 61-37955 discloses a technique for producing a roll for molten metal having excellent corrosion resistance, heat resistance, abrasion resistance and the like by plasma spraying a ceramic material. Japanese Patent Application Laid-Open No. 62-127457 discloses a technique for improving the high-temperature corrosion resistance of a metal base material by partially melting a ceramic material or a cermet film formed on the surface of the metal base material by irradiating a laser beam. .

[0004]

However, since a shaft and a housing used in a hot-dip metal plating apparatus are generally made of a metal material such as stainless steel having excellent corrosion resistance, a rolling bearing (particularly, a bearing ring) is used. Is made of a ceramic material, there is a difference in linear expansion coefficient between the material forming the shaft and the housing and the material forming the rolling bearing (for example, the linear expansion coefficient of SUS304 is 10 × 10 ^-6 / ° C, silicon nitride is 3 × 10 ^-6 /
° C).

When the rolling bearing is immersed in the molten metal or taken out of the molten metal for maintenance or the like, a repetitive load generated due to the difference in linear expansion coefficient described above is applied to the rolling bearing. As a result, there is a problem that the bearing ring may be cracked or chipped, and the rolling bearing may have a short life. In addition, when a coating of ceramics, cermet, or the like is coated on the surface of the base material by plasma spraying or the like, since the coating has pores, the molten metal enters through the pores and corrodes the base material. It turned out that there was.

[0006] Further, since the coating of ceramics, cermets and the like greatly differs in physical properties and mechanical properties from the metal material as the base material, when the roll is immersed in molten zinc at 450 to 460 ° C, the coating and the base material are formed. In some cases, peeling occurred at the interface with the material, and it was found that the rolling bearing was extremely unstable and poor in reliability. On the other hand, there are coating methods such as PVD, CVD or plating as a method of surface modification, but the hard coating obtained by these methods requires a base material and a base material to be applied to rolling members on which high shear stress acts. Have insufficient adhesion and film strength. In addition, there is often a problem that there is a limit to application to a member having a complicated shape.

Accordingly, the present invention solves the above-mentioned problems of the prior art, and provides a rolling bearing which is excellent in corrosion resistance and abrasion resistance to molten metal and can be suitably used in a molten metal plating apparatus. The task is to

[0008]

In order to solve the above problems, the present invention has the following arrangement. In other words, the rolling bearing for a molten metal plating apparatus according to claim 1 of the present invention includes an outer ring, an inner ring, and a plurality of rolling elements rotatably disposed between the outer ring and the inner ring. In a rolling bearing used for a hot-dip metal plating apparatus, at least one of the raceway surface of the outer ring, the raceway surface of the inner ring, and the raceway surface of the rolling element, the raceway surface of the outer ring and the raceway surface of the inner ring, Vickers hardness by diffusion infiltration treatment is Hv1
000 or more boride layers are provided.

According to a second aspect of the present invention, there is provided a rolling bearing for a molten metal plating apparatus according to the first aspect, wherein the rolling element is made of a silicon nitride ceramic material. Features. Since the rolling bearing having such a configuration is provided with a high-hardness boride layer having a Vickers hardness Hv of 1000 or more on at least the raceway surface of the raceway surface and the rolling surface, the rolling bearing has high corrosion resistance to molten metal. Are better. Therefore, it can be suitably used as a rolling bearing for a molten metal plating apparatus which is always in contact with a molten metal. In addition, the boride layer has excellent wear resistance. If the Vickers hardness Hv of the boride layer is less than 1000, the contents of FeB and Fe ₂ B, which mainly form the boride layer, decrease, so that the corrosion resistance and wear resistance decrease.

Further, the boride layer (diffusible hard layer) formed on the raceway surface (or rolling surface) is peeled off because there is no clear interface with the base material of the raceway (or rolling body). Hard to do. Such a boride layer has a carbon content of 0.3-1.
It can be formed by subjecting a raceway (or rolling element) made of 0% steel to a boron diffusion and infiltration treatment.

If the bearing ring is made of steel, the linear expansion coefficient of the shaft or housing used in the hot-dip metal plating apparatus is close to the linear expansion coefficient of the bearing ring constituting the rolling bearing. When immersed in the molten metal or taken out of the molten metal for maintenance or the like, the repeated load generated due to the difference in linear expansion coefficient hardly acts on the rolling bearing. As a result, the bearing ring is unlikely to be cracked or chipped, so that the life of the rolling bearing is hardly reduced.

Further, since the boride layer is a diffusible hardened layer, there is no possibility that the boride layer is peeled off unlike a film formed by a conventional plasma spraying or a film formed by a coating method. Furthermore, the boron diffusion and penetration treatment for forming the boride layer can be applied to a member having a complicated shape. Such a boride layer is subjected to boron diffusion and infiltration treatment on a raceway (or a rolling element) made of the steel to be processed to diffuse and infiltrate boron into the surface of the processing target, and then quenched. ,
By performing tempering, it is formed uniformly on the surface of the object to be processed.

The boron diffusion and infiltration treatment includes a gas method, a powder method, an immersion method and the like. The gas method uses a mixed gas of diborane and hydrogen or a mixed gas of boron trichloride and hydrogen as a treatment agent.
Approximately 50 to 250 hours by performing the treatment for 6 hours.
A μm boride layer is formed. The powder method uses a mixed powder of boron or ferroboron, alumina and ammonium chloride as a treating agent, and has a treating temperature of 950 to 950.
By performing the treatment at 1050 ° C. for 1 to 5 hours, a boride layer of about 100 to 300 μm is formed.

However, the gas method is toxic to the treating agent.
In addition, the powder method has problems such as high processing cost. Ma
Generally, the boride layer has two layers (the surface layer is an FeB layer,
Is Fe _TwoB layer), but the surface FeB layer
Vickers hardness Hv reaches 1700-2000
The boride layer is Fe_TwoB single layer is preferred
New

Therefore, the immersion method is preferable as the boron diffusion and penetration treatment. Borax, sodium oxide and potassium oxide are used as the treating agent, and the treating temperature is 900 to 100.
By performing the treatment at 0 ° C. for 3 to 6 hours, a single boride layer of Fe ₂ B is formed. However, since it is gradually cooled after the boron diffusion and infiltration treatment, the base of the boride layer (core)
Is generally either ferrite, pearlite, or a mixed structure of ferrite and pearlite. With such a structure, the strength required for the rolling member cannot be obtained, and it cannot withstand high contact stress. Therefore, in a state in which the boron diffusion and infiltration treatment is performed, it can be used for a sliding member but cannot be applied to a rolling member such as a rolling bearing. Therefore, it is necessary to use a material that is hardened by quenching for the base steel, and it is necessary to further quench and temper after the boron diffusion infiltration treatment to impart sufficient strength to withstand high contact stress. There is.

In order to impart sufficient strength to the base material by quenching and tempering, and to obtain sufficient core strength to support the base of the boride layer, the steel preferably has a high carbon content. However, at the time of boron diffusion infiltration treatment, boron atoms having an atomic radius larger than carbon atoms enter from the surface of the base material, so that if the carbon content of the base material exceeds 1.0%, the boriding property is hindered, and There is a tendency that a layer is difficult to form.

On the other hand, if the carbon content is less than 0.3%, the strength of the core portion sufficient to support the base of the boride layer cannot be obtained. As described above, in order to satisfy all of the thickness and hardness of the boride layer and the hardness of the core, it is necessary to use steel having a carbon content of 0.3 to 1.0% as the base material. Is preferred. If the carbon content of the steel is 0.4 to 0.9%, all of the thickness and hardness of the boride layer and the hardness of the core can be made more preferable.

The thickness of the boride layer is 30 to 20.
Preferably, the thickness is 0 μm. If the thickness is less than 30 μm, sufficient corrosion resistance may not be obtained, and the boride layer may be depleted as the rolling bearing is used, exposing the substrate. On the other hand, in order to ensure stable corrosion resistance over a long period of time, it is preferable that the boride layer is thick. However, for this purpose, it is necessary to perform treatment at a high temperature for a long time, so that the cost becomes high. Can not expect. In order to make the above disadvantages less likely to occur, the thickness of the boride layer should be 5
More preferably, it is 0 to 200 μm.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a rolling bearing for a hot-dip metal plating apparatus according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a structure of a thrust ball bearing which is one embodiment of a rolling bearing for a hot-dip metal plating apparatus of the present invention. Thrust ball bearing of FIG. 1 (manufactured by Nippon Seiko Co., Ltd., identification number 51305, outer diameter 52 mm, inner diameter 25 m
m, width 18 mm) are an outer ring 1, an inner ring 2, a plurality of balls 3 arranged to be able to roll between the outer ring 1 and the inner ring 2, and a plurality of balls between the outer ring 1 and the inner ring 2. And a Ta-made machined die holder 4 for holding the holder 3.

On the raceway surface of the outer race 1 and the raceway surface of the inner race 2, boride layers 5, 5 having Vickers hardness of Hv1000 or more are provided by boron diffusion and penetration treatment. The thickness of the boride layer 5 is 30 to 200 μm.
The outer ring 1 and the inner ring 2 have a carbon content of 0.3 to 1.0.
%, And the ball 3 is made of a silicon nitride ceramic material.

Since such a thrust ball bearing is provided with the high hardness boride layer 5 on the raceway surfaces of the outer ring 1 and the inner ring 2, it has excellent corrosion resistance to molten metal. Therefore, it can be suitably used as a rolling bearing for a hot-dip galvanizing apparatus (for example, a rolling bearing used for a zinc immersion roll of a continuous hot-dip galvanizing apparatus) which is always in contact with a molten metal.
The thrust ball bearing also has excellent wear resistance due to the boride layer 5.

The present embodiment is an example of the present invention, and the present invention is not limited to the present embodiment. For example, in the present embodiment, the boride layer 5 is provided on both the raceway surface of the outer ring 1 and the raceway surface of the inner ring 2, but only one of them may be provided. Further, the ball 3 may be made of the above-mentioned steel, and a boride layer may be provided on a rolling surface thereof.

Further, in the present embodiment, the thrust ball bearing has been described as an example of the rolling bearing. However, the rolling bearing of the present invention can be applied to various other types of rolling bearings. For example, radial rolling bearings such as deep groove ball bearings, angular ball bearings, cylindrical roller bearings, tapered roller bearings, needle roller bearings, and self-aligning roller bearings,
This is a thrust type rolling bearing such as a thrust roller bearing.

(Example) In order to evaluate the corrosion resistance of the boride layer, an immersion test in a molten zinc bath was performed. The test material was a ball for rolling elements and was finished to JIS grade G5.
A boring layer provided on the surface of an inch ball was used.
As shown in Table 1, the materials were as follows: Example 1 was a steel having a carbon content of 0.3%, Example 2 was a steel having a carbon content of 1.0%, and Comparative Example 1 was SUS440C (bored layer). Is not provided).

Such a test material was immersed in a zinc bath (450 ° C.) for 50 days, and the degree of surface erosion was examined.
Table 1 shows the results. The wall thickness reduction in Table 1 indicates the maximum erosion depth from the surface of the ball. As can be seen from Table 1, Examples 1 and 2 provided with a boride layer
Little surface erosion was observed. On the other hand,
The surface of Comparative Example 1 having no boride layer was melted and eroded.

[0026]

[Table 1]

Next, a description will be given of the result of evaluating the life by a rotation test using a bearing having substantially the same configuration as the above-described thrust ball bearing. The thrust ball bearing used in the test is composed of the inner ring, outer ring, and balls of the materials shown in Table 2 (steel (C 0.3%) means steel with a carbon content of 0.3%, (C1.0%) means steel having a carbon content of 1.0%). The raceway surfaces of the inner ring and the outer ring are shown in Table 2
A boride layer having a thickness as shown in FIG. Table 2 shows the surface hardness of the inner ring and the outer ring (the hardness of the raceway surface, that is, the hardness of the boride layer) and the core hardness of the inner ring and the outer ring.

Such a thrust ball bearing was mounted on a bearing rotation tester manufactured by Nippon Seiko Co., Ltd., with an axial load of 980 N, and immersed in a zinc bath (450 ° C.).
It was rotated at a rotation speed of 00 rpm. The components of the zinc bath are as follows: Al: 0.1 to 5%, Fe: 0.1% or less, P:
b: 0.1% or less, with the balance being Zn. The rotation time until the torque value increased to three times the initial value was defined as the life of the thrust ball bearing. Table 2 shows the results. In addition, the torque life of Examples 3 to 5 is 1 times the torque life of Comparative Example 2.
It is shown as a relative value when.

[0029]

[Table 2]

It can be seen that the life of the thrust ball bearings of Examples 3 to 5 having the boride layer is better than that of the thrust ball bearing of Comparative Example 2 having no boride layer. And
Of the thrust ball bearings of Examples 3 to 5, the life of Example 5 in which the material of the ball was silicon nitride was the best. FIG. 1 shows the correlation between the carbon content of the steel constituting the inner ring, the outer ring, and the balls and the torque life, and FIG. 2 shows the correlation between the thickness of the boride layer and the torque life. The curves 11 and 21 in the graphs of FIGS. 1 and 2 are the results when the inner ring, the outer ring, and the rolling element are all made of steel and have a boride layer on the surface, and the curves 12 and 21 are the same. 22 is the result when the inner and outer rings are made of steel and have a boride layer on the surface, and the balls are made of silicon nitride.

As can be seen from the graph of FIG. 1, when the carbon content was 0.3 to 0.1%, the torque life was excellent, and especially when the carbon content was 0.3 to 0.9%. . If the carbon content exceeds 1.0%, the torque life is inferior.
This is considered to be due to the fact that if the carbon content exceeds 1.0%, a boride layer is difficult to form, and the rolling members such as the inner ring and the outer ring do not have sufficient corrosion resistance. . It is also considered that the thickness of the boride layer is not sufficient, so that the boride layer wears down with the rotation of the bearing, resulting in abnormal wear that exposes the substrate.

On the other hand, when the carbon content is less than 0.3%, the torque life is inferior. This may be due to insufficient hardness of the core. 1 and 2, the inner ring, the outer ring, and the rolling members of the rolling elements are made of steel having a carbon content of 0.3 to 1.0%, and have a surface of 30 μm.
With a boride layer of m or more, the rolling member will have excellent corrosion resistance and a strong core, and as a result, the thrust ball bearing will have an excellent life.

[0033]

As described above, the rolling bearing for a hot-dip metal plating apparatus according to the present invention has at least one of the raceway surface of the outer race, the raceway surface of the inner race, and the raceway surface of the rolling element. Since the bearing surface has a boride layer with a Vickers hardness of at least Hv1000 due to boron diffusion and infiltration treatment, it has excellent corrosion resistance and abrasion resistance to molten metal, and can be used suitably for molten metal plating equipment. It is.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a structure of a thrust ball bearing which is one embodiment of a rolling bearing for a hot-dip metal plating apparatus of the present invention.

FIG. 2 is a graph showing a correlation between a torque life and a carbon content.

FIG. 3 is a graph showing a correlation between a thickness of a boride layer and a torque life.

[Explanation of symbols]

 1 outer ring 2 inner ring 3 ball 5 boride layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) F16C 33/32 F16C 33/32 F-term (Reference) 3J101 AA02 AA32 AA42 AA53 AA62 BA10 BA70 DA01 EA02 EA44 EA78 FA08 FA31 GA60 4K027 AA02 AB42 AD11 AD17

Claims (2)

[Claims] An outer race, an inner race, and a plurality of rolling elements rotatably disposed between the outer race and the inner race;
In a rolling bearing used in a hot-dip metal plating apparatus, boron diffusion is performed on at least the raceway surface of the outer ring and the raceway surface of the inner ring among the raceway surface of the outer ring, the raceway surface of the inner ring, and the rolling surface of the rolling element. A rolling bearing for a hot-dip metal plating apparatus, wherein a boride layer having a Vickers hardness of Hv1000 or more by infiltration treatment is provided. 2. The rolling bearing according to claim 1, wherein the rolling element is made of a silicon nitride ceramic material.