JPH08247138A - Sleeve for dynamic pressure bearing - Google Patents

Abstract

PURPOSE: To provide a sleeve for dynamic pressure bearing which can facilitate working, is excellent in corrosion resistance and start/stop durability and has good dimensional accuracy. CONSTITUTION: A dynamic pressure generating groove 11 is formed at the bearing surface 10a of a sleeve 10 consisting of aluminum alloy, and anodic oxidation coating 12 by anodic oxide coating of 2.5μm or less in thickness if formed at the bearing surface 10a at least. Aluminum alloy of soft metal facilitates to process the dynamic pressure generating groove and the anodic oxide coating improves corrosion resistance and surface hardness. The thickness of the anodic oxide coating 12 is lower than an ordinary case, so it is possible to ensure dimensional accuracy necessary to exhibit dynamic pressure bearing feature, and prevent generation of scratches resulting from sliding at the time of starting and stopping.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a sleeve for a dynamic pressure bearing, and more particularly, to a sleeve for a dynamic pressure bearing which has a thin film having corrosion resistance and durability and does not require post-processing, and has good dimensional accuracy. Regarding

[0002]

2. Description of the Related Art In a conventional dynamic pressure bearing, in particular, a dynamic pressure air bearing using air as a working fluid, a dynamic pressure generating groove 2 is formed on an outer peripheral surface 1a of a shaft 1 made of stainless steel, as shown in FIG. It is processed by etching. On the other hand, the sleeve 3 made of structural steel that cooperates with the shaft 1 has Nidax plating (product name, nickel plating surface impregnated with Teflon on the surface of the sleeve to ensure corrosion resistance and start-stop durability. ) Has been used. In the case of a dynamic pressure bearing, the outer peripheral surface 1a of the shaft 1 and the bearing surface 3a, which is the inner peripheral surface of the sleeve 3, rotate in contact with each other when the bearing is started and stopped. The plating film prevents abrasion and deterioration of corrosion resistance and durability.

[0003]

However, in order to etch the groove for generating a dynamic pressure on the outer peripheral surface of the stainless steel shaft, at least the masking step, the etching step and the neutralization step are required in the groove processing step. Therefore, there is a problem that the processing takes time and the cost becomes high.

Further, the cost of the Nidax plating is high. In addition, since there is a large variation in the thickness of the plating film, it is difficult to ensure the predetermined dimensional accuracy.
0 μm plating is applied, and after the plating, the bearing sliding surface and the surface requiring accuracy are not removed by plating (10-2
Finishing grinding is performed again in a machining allowance range of 0 μm, and processing is performed to a predetermined dimensional accuracy. Therefore, there is a problem that an additional man-hour is required and the cost is further increased in addition to the cost of the plating itself.

Therefore, the present invention has been made in view of such conventional problems, and provides a sleeve for a dynamic pressure bearing which is easy to process, has excellent corrosion resistance and start / stop durability, and has good dimensional accuracy. The purpose is to do.

[0006]

According to the present invention which achieves the above object, a dynamic pressure generating groove is provided on a bearing surface of a sleeve made of an aluminum alloy, and at least the bearing surface has a thickness of 2.5 μm or less. It is characterized in that an anodized film is formed by the treatment.

[0007]

[Function] Since the sleeve for the dynamic pressure bearing is made of aluminum alloy which is a soft metal, the bearing surface is grooved for generating the dynamic pressure.
Grooving becomes easy. The sleeve surface is anodized to improve corrosion resistance and surface hardness. In addition, the thickness of the anodized film formed by the alumite treatment is made thinner than usual, 2.5 μm or less, to secure the dimensional accuracy required to fulfill the dynamic pressure bearing function of the sleeve. With this film thickness, it is possible to prevent the occurrence of scratches due to sliding during start / stop.

If the thickness of the anodic oxide coating exceeds 2.5 μm, the dimensional accuracy changes greatly and the function as a dynamic pressure bearing deteriorates. Further, if the thickness of the anodized film is 5 μm or more, the surface roughness of the film becomes poor. On the other hand, it was found that when the thickness of the anodic oxide film is 2.5 μm or less, the film surface roughness is hardly deteriorated.

Therefore, the thickness of the anodic oxide coating of the present invention is specified to be 2.5 μm or less.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an embodiment of a sleeve for a dynamic pressure bearing of the present invention. The sleeve 10 is made of an aluminum alloy, and a bearing surface 10a, which is an inner peripheral surface thereof, has a groove 11 for generating dynamic pressure.
Is provided. Then, on the entire surface of the sleeve 10, as shown in FIG.
As shown in, the anodized film 12 having a thickness t of 2.5 μm or less is formed by the alumite treatment.

The sleeve 10 is made of an aluminum alloy round bar (which may be a die cast product or a forged product) as a material, and is roughly obtained through the following manufacturing steps. (1) Cutting process A round bar of material is cut and finished to a predetermined size. (2) Grooving step The dynamic pressure generating groove 11 is formed on the inner peripheral surface of the cut one by plastic working by ball rolling. Here, ball rolling means a jig in which a plurality of hard balls are radially arranged at the tip of the shaft so as to slightly project from the inner peripheral surface of the sleeve.
The groove for dynamic pressure generation is rolled on the inner circumferential surface of the sleeve while rotating in the left or right direction and pushing in the axial direction.

(3) Ridge removal processing This is to remove the bulge around the groove for dynamic pressure generation caused by the plastic working by ball rolling, if necessary. Finish processing. Next, the pretreatment of the alumite treatment is performed in the usual manner by the following washing steps (4) to (7).

(4) Degreasing (5) Washing with water (6) Washing with alkali (7) Washing with water (8) Alumite treatment (electrochemically applying an anodized film) In the alumite treatment of the present invention, the formed anode is formed. Unlike the usual alumite treatment, the thickness t of the oxide film 12 is regulated to 2.5 μm or less.

After the formation of the anodic oxide film is completed, following the usual method, (9) washing with water (10) sealing treatment (closing fine pores on the film surface) (11) inspection.

When the aluminum alloy sleeve 10 is subjected to the alumite treatment, the surface of the sleeve is slightly removed by the alkali cleaning as a pretreatment, and the inner diameter is increased. Due to the subsequent formation of anodized film by the alumite treatment, the inner diameter of the sleeve tends to be smaller. Therefore, by controlling the alkali cleaning time and controlling the thickness of the anodized film to 2.5 μm or less, the two cancel each other out, and the dimensional change of the sleeve before and after the alumite treatment can be almost eliminated, which is high. It is possible to secure dimensional accuracy.

Further, by carrying out the alkali cleaning, fine burrs on the bearing sliding surface caused by cutting the outer shape of the sleeve for the dynamic pressure bearing, rolling the dynamic pressure generating groove, etc. are removed. Another advantage is that the deburring process such as brushing or taping, which is performed in the conventional manufacturing process of the sleeve for the dynamic pressure bearing, can be omitted. That is, when the alumite treatment that is usually performed is applied, the thickness of the anodized film is approximately 5 μm or more, so the dimensional accuracy changes too much and the dimensional accuracy of the sleeve that functions as a dynamic pressure bearing is secured. Although it was difficult to do so, by suppressing the thickness of the anodic oxide film to 2.5 μm or less, it was possible to put the sleeve for dynamic pressure bearing of the alumite treatment into practical use for the first time. The thickness of the anodized film is 2.5 μm.
If the thickness is less than 5 μm, the indentation hardness of the sleeve surface will be lower than in the case of 5 μm or more, but a slight anodic oxide film on the bearing sliding surface can secure sufficient surface hardness to prevent scratches. The inventors of the present invention have found that the influence on the starting / stopping durability required for the dynamic pressure bearing does not cause any particular problem. Furthermore, the surface roughness deteriorates with normal alumite treatment, but the thickness of the anodic oxide film is 2.5 μm.
In the following cases, the surface roughness is hardly deteriorated, so that the practical effect is extremely large.

The material of the shaft of the mating member that cooperates with the dynamic pressure bearing sleeve of the present invention will now be described. The material of the shaft is SUS30, which is austenitic stainless steel.
3, SUS304 with nitriding treatment or ceramic coating is closer to the thermal expansion coefficient of aluminum alloy than SUS440C of martensitic stainless steel, so there is little change in bearing clearance even when ambient temperature changes. preferable. Also in terms of corrosion resistance, austenitic stainless steel is preferable because it is less likely to rust than martensitic stainless steel. Further, since the surface of austenitic stainless steel is soft, the surface can be hardened by performing a nitriding treatment or a ceramic coating as a surface treatment, which is preferable in terms of bearing performance and handling.

Incidentally, the sleeve 1 for the dynamic pressure bearing of the above embodiment.
At 0, the dynamic pressure generating groove 1 is formed on the inner peripheral surface (bearing surface) 10a.
1 is provided, but it is also applied to a dynamic pressure bearing in which a groove for dynamic pressure generation is provided with the outer peripheral surface 10b as a bearing surface so as to cooperate with the inner peripheral surface of a mating member (eg, housing) instead of the shaft. it can. In that case, a groove for dynamic pressure generation is formed on the outer peripheral surface 10b of the dynamic pressure bearing sleeve 10. The groove processing is not limited to the plastic processing and the cutting processing. Alternatively, the groove other than the groove may be masked after the alumite treatment, and the groove may be formed by shot blast processing or electrolytic etching. Also in this case, the post-machining of the bearing surface for ensuring the dimensional accuracy is unnecessary, and therefore the machining is easy. Further, it is preferable to use an aluminum alloy anodized aluminum alloy as the counterpart member that cooperates with the dynamic pressure bearing sleeve, because the thermal expansion coefficient can be made equal and the bearing clearance does not change even when the ambient temperature changes.

In the above embodiment, the dynamic pressure bearing sleeve 10 is provided with the anodized film by alumite treatment on the entire surface, but the present invention is not limited to this, and the anodized film is the dynamic pressure bearing sleeve. It may be formed only on the surface which will be the bearing surface. Further, the groove shape of the dynamic pressure generating groove 11 is not limited to that shown in the figure, and any point may be used as long as it can effectively generate the dynamic pressure.

[0020]

As described above, according to the present invention, since the dynamic pressure generating groove is formed on the bearing surface of the sleeve made of aluminum alloy and the anodized film is formed by the alumite treatment, It is easy to obtain, and there is an effect that a sleeve for a dynamic pressure bearing having excellent corrosion resistance and start / stop durability can be obtained. The thickness of the anodized film is 2.5μ.
Since it is set to m or less, there is an effect that a sleeve for a dynamic pressure bearing having no burrs and good dimensional accuracy can be obtained without special post-processing of the bearing surface after the alumite treatment.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a dynamic pressure bearing sleeve showing an embodiment of the present invention.

FIG. 2 is an enlarged view of a portion II in FIG.

FIG. 3 is a cross-sectional view of a conventional dynamic pressure bearing (sleeve and shaft).

[Explanation of symbols]

 10 sleeve 10a bearing surface 11 dynamic pressure generating groove 12 anodized film

Claims (1)

[Claims] 1. A dynamic pressure generating groove is provided on a bearing surface of a sleeve made of an aluminum alloy, and an anodized film having a thickness of 2.5 μm or less is formed by alumite treatment on at least the bearing surface. Sleeve for dynamic pressure bearing.