JPH11100587A - Vacuum pump roll bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a grease leak, to surely prevent a failure in lubricity and soiling of the periphery of a bearing and furthermore, to reduce raising of dust. SOLUTION: Within a bearing is housed a solid lubricating composition 4 having a lubricating component dispersed in and supported by a synthetic resin base. The lubricating composition 4 is a solidified substance of a mixture of lubricating grease or lubricating oil and an ultra-high molecular weight polyolefin powder and as the ultra-high molecular weight polyolefin powder, a polyethylene powder having an average molecular weight of 1×10<6> -5×10<6> is used. As the lubricating grease, the base oil is a fluorine-based oil and the thickening agent is a PTFE-based thickening agent and as the lubricating oil, either a fluorine-based oil, fluoro-silicone oil or an alkylcyclo-pentane oil is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing for a vacuum pump used in semiconductor manufacturing equipment and the like.

[0002]

2. Description of the Related Art There are various types of vacuum pumps for creating or maintaining a degree of vacuum. Among them, a vacuum pump having a relatively low degree of ultimate vacuum, as shown in FIGS. 2. Description of the Related Art A eyebrow pump is known as a kind of a pump (a pump that transfers a fluid by directly contacting a working part of a pump device). In this pump, two rotors (13, 14) are rotatably accommodated in a housing (12) having an intake port (10) and an exhaust port (11) with a phase difference of 90 °. The intake and exhaust are repeated by the rotational movement of (13, 14) to make the intake port (10) side in a vacuum state.

[0003] Both rotors (13, 14) are provided with rolling bearings (15).
It is supported rotatably by this rolling bearing (1
If normal grease is used as the lubricant in 5), there is a concern that the base oil of the grease will evaporate when the atmosphere around the bearings becomes vacuum. Therefore, conventionally, a grease using a fluorine-based oil having a low vapor pressure as a base oil has been used.

[0004]

At the start and stop of the operation of the vacuum pump, the atmosphere around the bearing changes from the atmosphere to the vacuum or from the vacuum to the atmosphere. Due to this change in air pressure, a pressure difference is created between both end faces of the bearing, so that the sealing plate attached to the end face of the bearing is removed to prevent grease scattering and dust prevention, and the grease sealed inside the bearing is released to the outside. May leak. Such leakage of grease may cause poor lubrication of the bearing, or cause problems such as grease entering the vacuum side of the pump and contaminating the surroundings. Further, since the grease generates a relatively large amount of dust, it is not suitable for use in an environment requiring high cleanliness, such as a semiconductor manufacturing apparatus.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a rolling bearing for a vacuum pump, which can prevent grease from leaking out and reliably prevent poor lubrication and contamination around the bearing. .

[0006]

In order to achieve the above object,
A rolling bearing for a vacuum pump according to the present invention is a bearing for supporting a rotating member of a vacuum pump, and contains a solid lubricating composition in which a lubricating component is dispersed and held in a synthetic resin base material inside the bearing. Is what you do.

The lubricating composition is preferably prepared by solidifying a mixture containing lubricating grease or lubricating oil and ultrahigh molecular weight polyolefin powder.

[0008] The base oil of the lubricating grease is preferably a fluorine-based oil, and the thickener is preferably a PTFE-based oil. On the other hand, lubricating oil
It is preferable to use any one of a fluorinated oil, a fluorinated silicone oil, and an alkylcyclopentane oil.

[0009] As the ultra-high molecular weight polyolefin powder,
It is desirable to use polyethylene powder having an average molecular weight of 1 × 10 ^{6 to} 5 × 10 ⁶ .

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to FIGS. 1 and 2A and 2B.

As shown in FIG. 1, the rolling bearing for a vacuum pump according to the present invention comprises a plurality of rolling elements (1), an outer ring (2), and a plurality of rolling elements (1) interposed between inner and outer rings (1) and (2). 3: a ball), and a solid lubricating composition (4) sealed in the inner space of the bearing between the inner and outer rings (1) and (2).

The lubricating composition (4) is a solid in which a lubricating component is dispersed and held in a synthetic resin base material, and can be produced, for example, by the following method. That is, a predetermined amount of lubricating grease or lubricating oil and a predetermined amount of ultra-high molecular weight polyolefin powder as a base material (matrix) are uniformly mixed, and at a gel point of the ultra-high molecular weight polyolefin powder or higher,
In the case where lubricating grease is used, the lubricating grease can be obtained by dispersing and maintaining the lubricating grease at a temperature lower than the drop point (for example, 150 to 200 ° C.) and cooling.

The ultra-high molecular weight polyolefin powder includes:
Powders made of polyethylene, polypropylene, polybutene, or copolymers thereof, or mixed powders each containing a single powder are used, and polyethylene powders are particularly preferred for vacuum pumps. The molecular weight of the ultra-high molecular weight polyolefin powder is such that the average molecular weight measured by a viscosity method is 1 × 10 ^{6 to} 5 × 10 ⁶ . Polyolefins having such an average molecular weight range are superior in rigidity and oil retention to low molecular weight polyolefins, and hardly flow even when heated to a high temperature. The blending ratio of the ultra-high molecular weight polyolefin is 1 wt% to 95 wt% based on the total weight of the lubricating composition (4).
% (% By weight) (the mixing ratio of the lubricating grease or lubricating oil is preferably 99% by weight to 5% by weight), but the lubricating composition has a desired degree of oil release, toughness, and hardness. It can be adjusted accordingly. The greater the amount of ultrahigh molecular weight polyolefin, the greater the hardness of the gel after being dispersed and maintained at a predetermined temperature.

As the lubricating grease, a base oil made of a fluorine-based oil and a thickening agent made of a PTFE (polytetrafluoroethylene) -based oil, and as the lubricating oil, a fluorine-based oil, a fluorine-based silicone oil or an alkyl It is good to use any of the cyclopentane oils.

In the case where the oil seeps out of the lubricating composition (4) excessively, the rate of oil release of the oil seeping out can be appropriately suppressed by adding an anti-leakage agent.
As the leaching inhibitor, a solid wax or a compound containing a low-molecular-weight polyolefin containing the same is used. Examples of the solid wax include vegetable wax such as carnauba wax and candelina wax, animal wax such as beeswax and insect white wax, and petroleum wax such as paraffin wax. Such a leaching inhibitor is 1 wt% based on the total weight of the lubricating composition (4).
It is advisable to mix at a ratio of 50 wt%. The higher the blending ratio, the more the oil separation rate can be suppressed and the speed of oil bleeding decreases, but if it exceeds 50% by weight, the strength of the lubricating composition decreases, which is not preferable.

The lubricating composition (4) is solidified by heating after filling the mixture before heat treatment into the inside of the bearing. After that, it may be incorporated in the bearing. If the content of the ultrahigh molecular weight polyolefin is 50% by weight or more, sufficient strength is ensured, so that, for example, a cage as one of the bearing components can be molded with the lubricating composition.

The oil gradually seeps out of the lubricating composition (4) housed in the bearing even in a stationary state, so that the bearing raceway surface can be reliably lubricated.
Since the lubricating composition has a high oil retaining force and the oil seepages gradually and stably even under the action of the centrifugal force during the operation of the bearing, the rotating members of the vacuum pump (the rotors 13 and 14)
Etc.) (see FIG. 4), it is possible to reliably prevent oil from leaking from inside the bearing due to a change in air pressure. In addition, since a sealing plate is not required, leakage of grease due to falling off of the sealing plate can be avoided, and the number of parts can be reduced.

A dusting test of the bearing containing the lubricating composition was performed, and it was confirmed that the bearing had extremely low dusting. Hereinafter, the outline of the test will be described. As a test bearing, a mixture of a lubricating grease (60 wt%) using a base oil of fluorinated oil and a thickening agent of PTFE and polyethylene (40 wt%) as a rolling bearing (NTN: model number 608) After that, the bearing was heated at 160 ° C. for 30 minutes to solidify the lubricating composition.

First, two test bearings were assembled on a spindle, and while changing the bearing load (axial load), particles of 0.3 μm or more were counted by a particle counter, and outgas was measured.
The result shown in (A) was obtained. However, the rotation speed is 50 rpm,
The measurement time is 150 hours, and the degree of vacuum is 10 ^-6 Torr or less.

From FIG. 2 (A), it can be understood that the amount of dust (total number) is extremely low at 5 or less under all load conditions, and that no harmful CF-based outgas is generated. .

Next, as a lubricant, a bearing (comparative product) using lubricating grease in which the base oil is a diester oil type, the thickener is lithium soap (comparative product), the base oil is a fluorine-based oil, and the thickener is PTFE
When the amount of dust generation was measured for each of the bearing using the lubricating grease (conventional product) and the test bearing (product of the present invention), the results shown in FIG. 2 (B) were obtained. However, the rotation speed is 200 rpm and the axial load is 1 kgf
It is.

From FIG. 2B, it can be understood that the product of the present invention generates much less dust than the comparative product and the conventional product.

As is clear from the above two test results, the product of the present invention has extremely low dust generation, and thus is suitable as a bearing used in a high cleanliness environment such as a semiconductor manufacturing apparatus.

The bearing according to the present invention is not limited to the deep groove ball bearing shown in FIG. 1, but can be widely applied to rolling bearings in general (angular ball bearings, cylindrical roller bearings, etc.). Further, the present invention is not limited to the eyebrow pump shown in FIGS. 3A and 3B, and can be applied as a rolling bearing for various other types of pumps (such as a scroll pump).

[0025]

As described above, according to the present invention, the oozing of the oil is gradually and stably performed by the solid lubricating composition. Leakage of oil from inside the bearing can be reliably prevented. Further, since a sealing plate is not required, leakage of grease due to falling off of the sealing plate can be avoided, and further, cost can be reduced by reducing the number of parts. Further, since it generates extremely low dust and hardly generates outgas as compared with conventional products, it can be used even in an environment requiring high cleanliness such as a semiconductor manufacturing apparatus.

[Brief description of the drawings]

FIG. 1 is a sectional view of a rolling bearing for a vacuum pump according to the present invention.

FIG. 2 is a diagram showing measurement results of the number of generated particles and outgas (A)
FIG. 7B) and a diagram (B diagram) showing the results of a comparison test between a conventional product, a comparative product, and the product of the present invention.

FIGS. 3A and 3B are a cross-sectional view illustrating an example of a vacuum pump (FIG. A) and a cross-sectional view taken along line CC in FIG.

[Explanation of symbols]

 Reference Signs List 1 inner ring 2 outer ring 3 rolling element (ball) 4 lubricating composition 13, 14 rotating member (rotor)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C10M 107: 04 105: 52 107: 50 105: 04 119: 22) C10N 20:04 40:00 40:02

Claims (5)

[Claims] 1. A bearing for supporting a rotary member of a vacuum pump, wherein the bearing contains a solid lubricating composition in which a lubricating component is dispersed and held in a synthetic resin base material. Rolling bearing. 2. The rolling bearing for a vacuum pump according to claim 1, wherein the lubricating composition is obtained by solidifying a mixture containing lubricating grease or lubricating oil and ultrahigh molecular weight polyolefin powder. 3. The rolling bearing for a vacuum pump according to claim 2, wherein the base oil of the lubricating grease is a fluorine-based oil and the thickener is a PTFE-based oil. 4. The rolling bearing for a vacuum pump according to claim 2, wherein the lubricating oil is one of a fluorinated oil, a fluorinated silicone oil, and an alkylcyclopentane oil. 5. The rolling bearing for a vacuum pump according to claim 2, wherein the ultrahigh molecular weight polyolefin powder is a polyethylene powder having an average molecular weight of 1 × 10 ^{6 to} 5 × 10 ⁶ .