GB2389632A

GB2389632A - Rolling bearing arrangement

Info

Publication number: GB2389632A
Application number: GB0322189A
Authority: GB
Inventors: Shigeru Okita; Kazuo Sekino; Toyohisa Yamamoto; Susumu Tanaka; Hiroyuki Ito; Akira Uchida; Kazuhiro Fujiu
Original assignee: NSK Ltd
Current assignee: NSK Ltd
Priority date: 1999-05-10
Filing date: 2000-05-09
Publication date: 2003-12-17
Anticipated expiration: 2020-05-09
Also published as: GB0322187D0; GB2389631A; GB2389632B; GB2389631B; GB0322189D0

Abstract

A rolling bearing comprising outer and inner rings 1, 3 having outer and inner ring raceways 4, 2 respectively, rolling elements 5, 19 which are disposed so as to rotate between the aforementioned raceways, an cage 6 for distributing the rolling elements evenly in their rotational direction between the raceways having cage pockets 8, 21 with openings 23 between 80-93 % (A) of the diameter C of the rolling element 5, 19 and wherein the rolling bearing arrangement is used with a fluoro-containing polymer lubricant 14 or in an atmosphere comprising a gas containing fluoride. The specific arrangement also comprises a weld line 26, a clamping area D and clamping fingers 24. The arrangement aims to reduce the wear on components, such as vacuum pumps, which operate in severe conditions and also improves the lubrication performance.

Description

f connected with the suction port into the pump main body and discharging

the same from the discharge port to evacuate the inside of the vessel.

The two rotor shafts are rotationally supported by 5 rolling bearings and usual bearing steels (SUJ2) are often used for the rolling bearings. Since high contact stresses are exerted repeatedly on inner and outer rings and rolling elements of the rolling bearing, it is necessary to harden the inner and outer rings and the rolling elements for 10 extending the rolling contact fatigue life. Accordingly, after forming the inner and the outer rings and the rolling elements of the rolling bearing with the bearing steels (SUJ2), quenching and tempering are applied.

Further, as lubricants for bearings used in reduced 15 pressure (including vacuum) atmosphere such as in vacuum pump apparatus, solid lubricants are sometimes used for preventing contamination of the reduced pressure atmosphere and the use of fluid lubricants such as lubricating oil has been increased in order to improve the life and the 20 reliability of the bearings. As typical examples, highly corrosion resistance and less evaporative fluoro-lubricating oil are used. Particularly, in high vacuum pumps used at a high speed rotation and in a high temperature circumstance depending on the case, fluoro-lubricating oil with higher 25 reliability have been used more frequently. Heretofore, in

the rolling bearings used in such a reduced pressure atmosphere including vacuum, only the lubricant is changed to the fluoro-lubricating oil but the accuracy of the bearings per se is left as it is in the usual specification

5 (for instance, at about JIS B 1514 for the accuracy).

On the other hand, fluoro-lubricating oil or fluoro grease which is excellent in heat resistance, less; evaporative and chemically stable is used also in a high temperature circumstance exceeding 200 C such as in heat 10 rolls for fixing portions of business machines. Such fluoro lubricating oil or fluoro-grease can include, for example, i lubricating oil or greases containing fluoro-containng polymers such as perfluoropolyether (PFPE) oil or fluoro grease using the PFPE oil as a base oil. Under the usual 15 working circumstances, there has been no problem for the lubrication with the lubricating oil or greases containing such fluoro-containing polymers.! However, business machines typically represented by copying machines (PPC), laser beam printers (LOP) , facsimile 20 (FAX) or composite machines thereof have tended to be adapted for more compact structure, energy saving, recycling performance and higher speed in recent years and, accordingly, it has been demanded for longer torque life with a smaller size and under severer conditions (high speed 25 and heavy load). Further, also in the field of the vacuum

( pump, rolling bearings capable of operating for a long time at higher temperature and under higher speed have been demanded in order to increase the capacity and make the structure compact. Further, also in the field for

5 manufacturing semiconductors and liquid crystal panels, operation for long time under large load and high speed is required for the rolling bearings to be used along with the enlargement for the size and high speed transportation of substrates. 10 Aside from them, as general materials for cages that hold rolling elements in an even distribution between an outer ring raceway and an inner r mg raceway, SPCC material, HB5Cl material and PA66 resin material have been used. For the rolling bearings required for corrosion resistance such 15 as support bearings in the vacuum pumps, cages for use in rolling bearings formed into a circular shape with a advanced resin material which is poor in the ductility but has corrosion resistance is used. In the cage for use in the rolling bearing, a plurality of pockets each receiving a 20 rolling element from an opening and holding the same rotatably are disposed each at a predetermined distance in the circumferential direction.

Referring to Fig. 11, size F for the opening of each pocket 30 is set to a value of 85 to 93% for the rolling 25 element diameter G. Accord m gly, each rolling element 31 is d I

assembled from the open m g 33 into each pocket 30 while circumferentially expanding fingers 32 of each pocket 30.

This can make easy assembling of the rolling element 31 to each pocket 30 and less drop off of the rolling element 31 5 assembled in each pocket 30 compatible.

Disclosure of the Invention i

By the way, in the rolling bearing for use in the vacuum pump used at a high speed rotation and, depending on 10 the case, in a high temperature circumstance, since lubrication in an oil bath is not possible and it adopts a splashing lubrication system using a gear or the like in view of lowering of lubricant membranes due to the temperature elevation of the lubricating oil or in order to 15 prevent contamination of the pump portion with the lubricating or, there is a worry of insufficiency for lubricating conditions such that the supply of the! lubricating oil tends to become insufficient. Further, since the fluoro-lubricating oil has higher specific gravity and 20 so-called nettability is deteriorated extremely compared with usual mineral lubricating oil, formation of the lubricant membranes tends to be difficult, which makes the lubricating conditions severer. Further, upon starting discharge of atmospheric air, excess axial load is applied, 25 although in a short period of time, on the bearing c

- ( supporting the rotor of the dry screw pump and axial load fluctuation is caused to the bearing. When such severe lubricating conditions are applied together to make the lubrication insufficient, it may be a worry of causing 5 peeling wear or peeling flaking to the raceway surface of the bearing.

Purther, when the oil bath lubrication with the fluoro-lubricating Oil is adopted, the height of the oil surface (height of the oil surface from the lower side of 10 the inner diametrical surface cuff a housing to the pitch circle dlamet:er of the bearirg) IS not suf ficient 1n view of the structure of the apparatus to sometimes make the lubrication unfavorable. That is, in duplex angular ball bearings or double row angular ball bearings as shown in Fig. 15 7 to Fig. 10, although the lubrication near the oil surface is favorable, the portion opposite to the oil surface iS lubricated by the rotation of the bearings, so that the lubrication state is not satisfactory, and wear between each of the cage, the rolling ring and the rolling element is 20 promoted to sometimes lead to the fracture of the cage, discoloration of the rolling elements and, thus, fracture of the bearing.

In the drawings, an outer ring 100, an inner ring 200, a rolling element 300 and a cage 400 are shown.

25 Further, the fluoro-lubricating oil reacts with iron

to form iron fluorides, which decompose, as a catalyst, the fluorolubricating oil. As described above, when the lubrication is insufficient, and the rolling element and the raceway surface of the bearing ring are in direct contact 5 with each other, the contact point is locally heated to an extremely high temperature, which decomposes the fluoro-

lubricating oil (PFPE oil and the like) sometimes to erode the surfaces of the rolling element, the bearing ring and the cage to shorten the life. In order to cope with such 10 problems, silicon nitride (Si3N.) has been used for rolling elements In view of the merit that it is excellent in adhesion resistance and scorch resistance with metals and light in weight in a high speed application used such as in machine tools or vacuum pump apparatus. However, when 15 temperature is locally raised by oil membrane breakage or the like, it causes another problem that the PFPE oil reacts with Si as the main ingredient of silicon nitride and, as a result, Si2F6 gas is evolved to embrittle the material and result in abnormal wear.

20 Such problems, may possibly occur quite in the same manner also in rolling bearings used, for example, in an atmosphere containing a gas comprising fluorides, in addition to the lubricating conditions with lubricating oil or grease containing a fluoro-containing polymer.

25 Further, aside from them, there is another problem in

the existent cage for use in rolling bearings. When a resin material with less deformability than the polyamide resin, for example, a advanced resin such as polyphenylene sulfide (PPS) resin is used as the material, the force exerted to 5 push-open fingers 32 of a pocket 30 upon assembling a rolling element 31 from an opening 33 to the pocket 30 (refer to Fig. 11) forms a bending moment on the entire cage to possibly cause cracks or breakages to a portion at the bottom of the pocket 30 of a reduced thickness (with less 10 strength), concretely, in the bottom of the pocket 30 having a weld 1lne 34, Particularly, for an axial load, when weld lines are formed at the bottom of the pockets by uneven numbers, they tend to form initiation points for the occurrence of cracks.

15 The present invention has been developed for overcoming the problems described above and it is an object thereof to provide a rolling bearing of longer life even under severe lubricating conditions due to fluoro lubricating oil and provides a rolling bearing free from 20 occurrence of cracks or breakage to pockets having weld lines upon assembling a rolling element to the pocket of a cage. The present inventors have made investigations on the form of peeling wear or peeling flaking occurring in rolling 25 bearings lubricated with a fluoro-lubricating oil and have

recognized the following features a. Rolling elements of rolling bearings in which peeling has occurred to inner rings or outer rings are always worn.

5 b. In raceway surfaces of inner and outer rings and the rolling elements in which peeling has occurred, tracks formed by biting of obstacles such as wear part, cles and abrasive wears due to obstacles are observed.

c. Even when peeling does not occur to the inner 10 rings or the outer rings, it is sometimes observed that the rolling elements are damaged or worn.

d. Abnormal wear occurs in the pocket portion of the steel cage in a bearing in which the rolling elements are damaged or worn.

15 From the forgoing results' it is easily supposed that occurrence of peeling starts at first from the rolling element. Then, the mechanism is supposed as follows, 1. In bearings for use in a vacuum pump lubricated with a fluoro-lubricating o and further used under a high 20 rotation, lubricating conditions are extremely severe. That is, since the fluorolubricating oil has poor nettability, the lubricating oil less prevails in gaps and, further, the temperature is elevated at high rotation, the lubricating performance, particularly, around the cage is deteriorated.

25 Accordingly, the rolling element and the cage are sometimes a

( brought into an intimate contact with each other.

2. When the lubrication for the cage is insufficient, the pocket portion of the cage is sometimes worn by the contact with the rolling element, or the rolling element itself is 5 damaged to worsen the surface roughness.

3. The rolling element deteriorated for the roughness.

under the severe lubricating condition is in metal contact with the inner ring and the outer ring to cause peeling to the inner ring and the outer ring. Further, peeling in the 10 rolling element or the inner ring and the outer ring is promoted due to the abraded powder of the cage.

In view of the above, a rolling bearing according to claim 1 of the present invention comprises an outer ring having an outer ring raceway, an inner ring having an inner 15 ring raceway, and rolling elements rotatably disposed between the outer ring raceway and the inner ring raceway, and a cage for evenly distributing the rolling elements in the rotational direction of the rolling elements between the outer ring raceway and the inner ring raceway, and used 20 under either lubrication with a lubricating oil, or a grease containing a fluoro-containing polymer, or in an atmosphere containing a gas comprising fluorides, wherein the cage is formed with an advanced resin material into a circular shape, a plurality of pockets, each containing the 25 rolling element through an opening and rotatably holding the same, are disposed at predetermined locations on the circumference of the cage, the size for the opening of a pocket having a weld line has a value of 93% or more of the

( diameter of the rolling element, and the size for the opening of at least two other pockets is 80% or more to 93% or less of the diameter of the rolling element.

The rolling bearing according to claim 2 of the 5 present invention defined in claim 1 has a feature in that the cage is formed with either a PTFE resin material or a PPS resin material, and constituted by applying chamfering to inner and outer diametrical sides of the pockets and forming a through hole in the bottom of the pockets.

10 As the advanced resin material described above, advanced engineering plastics of excellent corrosion resistance specifically, polyphenylene sulfide (P1'S) resin, polyether ether ketone (PEET) resin and polybutylene terephthalate (PBT) resin are used suitably.

Brief Description of the Drawings

20 Fig. 1 is a longitudinal cross sectional view illustrating a comparative example of a rolling bearing.

Fig. 2 is an explanatory graph illustrating a relation between the hardness of the coating film and the 25 wear rate of the rolling element according to the present invention.

Fig. 3 is a perspective view illustrating an embodiment of a cage adopted for the rolling bearing according to the present invention.

5 Fig. 4 is a side elevational view for a main portion illustrating a pocket having a weld line in a cage used for the rolling bearing shown in Fig. 3.

- Fig 5 is a side elevational view for a main portion 10 illustrating another pocket in a cage used for the rolling bearing shown in Fig. 3.

Fig. 6 is an explanatory view for the test method of a tensile strength of a cage used for a rolling bearing.

Fig. 7 is a vertical cross sectional view of a comparative duplex angular ball bearing.

Fig. 8 is a cross sectional view of a cage for the 20 angular ball bearing shown in Fig. 7.

Fig. 9 is a vertical cross sectional view of a comparative double row angular ball bearing.

Fig. 10 is a vertical cross sectional view of a cage for the angular ball bearing shown in Fig. 9.

( Fig. 11 is a side elevational view for a main portion illustrating a pocket having a weld line of a cage for a comparative rolling bearing.

5 A comparative example is to be described.

Fig. l is a cross sectional view for a rolling bearing of a comparative example. The rolling bearing is a deep groove ball bearing comprising a plural ity of rolling lo elements (balls) 5, an inner ring 3 situated inward thereof, and an outer ring 1 situated outward of the rolling elements in which the rolling elements 5 are guided under rolling while being held between the inner ring 3 and the outer ring 1. In the comparative example, rolling 15 grooves for guiding the rolling elements 5 are disposed in the inner ring 3 and the outer ring 1, and the rolling elements 5 are held being distributed evenly in the rolling grooves by a cage 6.

20 The comparative example is based on the rolling bearing put under a reduced pressure including vacuum and lubricated with a fluorolubricating oil as in a vacuum pump apparatus. Then, as an example of the comparative examples, cages made of plastic and of metal as comparative 25 examples were prepared as shown in the following Table 1.

Cages of an identical shape were manufactured by using nylon 66 as polyamide and polyphenylene sulfide (PPS), namely, thermoplastic material as plastic cases and by

using SPCC of low carbon steel plate as the steel plate and S50CM of tempered steel as metal cages.

( TABLE 1

Class of materials Metal m Ode Plasti c made \ Material SPCC S50CN Nylon 66 PPS - (GF25%)

Density (g/cm3) 7.86 7.86 1.14 1.64 Linear expansion coefficient 1.16 1. 18 710 27 Item (10-s x 1/ C) Young's modulus 210 210 3.3 7.5 1GPa) Tensile strength 280 440 90 160 (MPa} or more or more.

Hardness (note) *105 *180 **120 **120 or less or less Roughness (m) 0.025 0.025 2S 2S or less or less Normali- Tempered Not Glass Remark Bed strongfiber thened 2 5 9.

(Note 1) The hardness value is based on Hv scale for metal 5 made * and HRR scale for plastic made *.

On the other hand, the inner ring, the outer ring and the rolling element were made by using JIS hearing steel SUJ2, and quenched at 830 C to 850 C, and then only the 5 inner ring and the outer ring were tempered at 230 C to 260 C as a dimension stabilizing treatment, while the rolling element was tempered at a usual specification at

160 C to 200 C. They were finished by grinding, to which various kinds of cages described above were combined to 10 finally manufacture deep groove ball bearings 6206 having values according to JIS B 1518. For the roughness of the raceway surface, test bearings of different roughness to be described later were manufactured by changing the grinding method or applying finish grinding repeatedly.

Then, test conditions are to be described. A ball bearing life tester manufactured by Nihon Seiko Co. was used as a tester and basic rating life (106 rotation)Lo under clean lubrication was measured. As the lubricating 20 oil, a fluoro-lubricatlng oil J100 (perfluoropoly ether oil manufactured by NOK KLUEBER) and spindle oil RO#68 (paraffinic mineral oil) were used. Further, while these comparative examples are directed to the rolling bearing used in a reduced pressure atmosphere, the test was 25 conducted in this case in an atmospheric pressure for the sake of convenience, since the fluoro-lubricating oil, in particular, does not change so much either in vacuum or in atmospheric pressure. For making the lubricating condition

( severer, estimation was conducted at a test temperature between 80 C and 120 C assuming that the temperature of the lubricating oil rises to reduce the oil membrane.

5 (Life Test Condition) Name of Tester: Ball bearing life tester Test Load: P/C = 0.45 Number of Rotation of Bearing: 3000 rpm Test Temperature: 80 - 120 C 10 Lubricating oil:Fluoro-lubricating Oil J 100 Paraffinic Mineral Oil RO # 68 The test method is as described below.

15 Each type of tested bearings was provided by ten and the life test was conducted under the test conditions described above. For the judgement of the life, test was terminated at the instance the vibration value of the tested bearing on the tester reached twice as much as the 20 initial vibration value, and presence or absence of flaking on the raceway surface or wear in the rolling element or the pocket portion of the cage were confirmed. Further, the longest test time was set to 500 hrs and the subsequent test was terminated. Then, for the ten tested bearings, 25 total time of rotation till flaking or wear occurred to those 10% bearings from the side of the shorter life was determined according to a weible distribution function, which was defined as the life. The following Table 2 shows

the life time for Comparative Examples a - n lubricated with the paraffinic mineral oil RO#68 and Comparative Examples A - P lubricated with the fluoro-lubricating oil JIOO. Those with the life time exceeding 500 hrs are 5 indicated as terminated.

TABLE 2

Librcation condition Material for cage NTe of Tempera- SPCC S50CM Nylon 66 PPs Lubricat- ture (GF251) ing oil ROf68 80 C 4.05 (Q)ter- (d)ter- (g) ter- (k)ter minted minated minated nnnated Rol68 100 C 2.75 (b)ter- (e) ter- th)ter- (l)ter-

minated minated mnated mnated _ ROl68 110 C 2,20 _ _ ()ter- (m)ter minated mi nated ROf68 120.C 1.95 (c)ter_ (f) (j)ter- (n)ter minated 350 Hr mineted minated J100 BO C 5.60 A.350 Hr E:SO Hs I:tenm;_ M:te nated nated J100 100 C 3.85 B:250 Hr F:20 Hr J:termi- Nste nated nated J100 110 c 3.11 C: 100 Hr G:10 Hr R:termi- O:teri_ nated nated J100 120CC 2.60 D: 10 Hr H: 5 Hr L: 480 Hr P:termi nated

( An embodiment of the rolling bearing according to the present invention is to be described. Like the comparative examples described above, the embodiment is also based on the rolling bearing used in reduced pressure including 5 vacuum such as in vacuum pump apparatus and lubricated with fluoro-lubricating oil. Then, in this embodiment, a cage for holding the balls is formed with an advanced resin material into a circular shape instead of the deep groove ball bearing or the angular ball bearing used in the 10 comparative examples described above.

Fig. 3 is a perspective view illustrating an embodiment of a cage adopted in the rolling bearing according to the present invention, Fig. 4 is a side elevational view for a main portion of a pocket having a 15 weld line in a cage for use in the rolling bearing in Fig. 3, Fig. 5 is a side elevational view for a main portion illustrating other pocket of a cage for use in the rolling bearing shown in Fig. 3. Further, Fig. 2 is a plan view for explaining a test method of a tensile strength of the cage 20 for use in the rolling bearing.

Referring to Fig. 3 to Fig. 5, in a cage 20 for use in rolling bearing, a reinforcing material such as glass fibers is incorporated by about 5 to 15% by weight ratio to an advanced resin material such as polyphenylene sulfide 25 (PPS) resin and formed into a circular shape without applying annealing.

In the cage 20 for use in the rolling bearing, pockets 21, 22 are disposed in plurality (by the number of seven in

( Fig. 3) at a predetermined distance in the circumferential direction each being opened upward in Fig 3. Each of the pockets 21, 22 contains a rolling element 19 of the rolling bearing (not illustrated) through an opening 23 and holds 5 the same rotatably.

Each of the pockets 21 and 22 has a pair of fingers 24, and each rolling element 19 is assembled through the opening 23 into each of the pockets 21 and 22 so as to circumferentially expanding the finger 24 for each of the 10 pockets 21 and 22, By the injection molding of the advanced resin material, a weld line 26 is formed at the junction of the molten resin injected from gates 25, and the size A for the opening of the pocket 21 having the weld line 26 (inter 15 finger size) (Fig. 4) is set to a value larger than 93% of the rolling element diameter C (for example 93 to 110%) .

Further, the opening size B for each of other pockets 22 is set to a value for 80 to 93% of the rolling element diameter C. Accordingly, the clamping area D by the finger 20 24 of the pocket 21 with the weld line 26 (Fig. 4) is smaller than the clamping size E (Fig. 5) by the finger 24 of each of the other pocket 22.

The operation of the embodiment is to be described below. In the cage 20 for use in the rolling bearing, since 25 the clamping size D by the finger 24 of the pocket 21 with the weld line 26 is smaller than the clamping size E by the finger 24 of each of other pockets 22, when the rolling element 19 is assembled to each of the pockets 21 and 22,

( the force exerted when the finger 24 of the pocket 21 having the weld line 26 is expanded in the circumferential direction by the rolling element 19 can be made smaller compared with that for the finger 24 of each of other 5 pockets 22.

Accordingly, the rolling element 19 is assembled smoothly with no excessive force being exerted to the finger 24 in the pocket 21 with the weld line 26, so that neither crack nor breakage occurs to the portion of the 10 weld line 26 (bottom of the pocket 21). Further, in each of the other pockets 22, both easiness for assembling the rolling element into each of the pockets 22 and less drop off of the rolling element 19 assembled into each pocket 22 are ensured at the same time.

15 When the size A for the opening of the pocket 21 (inter-finger size) having the weld line 26 is set to loot or more, since the clamping size D by the finger 24 is eliminated, the rolling element 10 can be assembled further smoothly. 20 Then, a tensile test was conducted for the cage 20 for use in rolling bearing in the embodiment while varying the various conditions in accordance with the following method.

That is, referring to Fig. 6, in a state of situating the cage for use in the rolling bearing such that the gate 25 25 of the cage for use in the rolling bearing is on the right in Fig. 6, while the weld line 26 is on the left in Fig. 6, a pair of die members 27 are disposed to an inner diametrical portion of the cage. Each of the die members 27

( is formed into a semi-circular shape and has a somewhat smaller diameter than the inner diameter of the cage, Then, each of the die members 27 was pulled in the directions opposite to each other (in the vertical direction in Fig. 5 6) till the cage for use in the rolling bearing was fractured to measure the load upon breakage.

Various conditions and the results are shown in Table 13. The number means herein the number of the cage. All breakage occurred at the portion of the weld line 26.

10 Further, in Table 13, all the value for the load upon breakage are mean values.

TABLE 1 3

Bearing No. Number Aesin CF con- Anneal- Load on material tent ing breakage ratio (kgf) 6205(Comp. Example) 4 PPS. 20% no 16 6205(Exaple) 4 PPS 10% no 45 620 6 ( coup. Example, 3 PPS 2 0 % no 3 2 6 2 0 6 ( coup. Example) 3 PPS 20% applied 27 6206 (E:xmpl.) 4 PPS 10% no 55

( As can be understood from Table 13, those with the content ratio of the reinforcing materials such as glass fibers as 20% by weight show smaller load upon breakage companied with those with the content ratio of reinforcing 5 materials as 10% by weight. Further, those applied with annealing showed smaller load upon breakage compared with the those applied with no annealing.

Also, the cage 20 for use in roller bearing according to the embodiment with varying the various conditions are 10 assembled in the roller bearing, and we investigated whether the cracks are occurred on cage assembled.

The various conditions and the results are shown in Fig. 2. The all of the cracks are occurred on the portion of weld line 26.

TABLE 1 4

Bering No. Number Resin CF con- Anneal- Occurrence of crack material tent ing upon nag insertion _ ratio to bernq 6205(Cop. Exomple) TO PPS 2 0% no cracked 6205(Exmple) JO PPS 10 % no not cracked 6206(Comp. Example) 1O PPS 20% no cracked 6206(Cop. Example) 1 0 PPS 20% applied cracked 6206(Example) 1O PPS 10% no not cracked.

As can be understood from Table 14, when the content ratio of the reinforcing materials such as glass fiber is set to 20% by weight, cracks occurred to the pocket having the weld line 26 irrespective of the presence or absence of 5 annealing treatment.

As described above, in accordance with the embodiment, the size A for the opening of the pocket 21 having the weld line 26 is set to a value larger than 93 of the rolling element diameter C (for example, 93 to 110%), and the size 10 B for the opening of each of other pockets 22 is set to a value of 80 to 93% of the rolling element diameter C. Accordingly, drop off of the cage 20 for use in the rolling bearing from the rolling bearing can be prevented reliably and occurrence of cracks or breakage at the bottom of the 15 pocket 21 having the weld line 26 can be prevented reliably upon assembling of the rolling element lo to each of the pockets 21 and 22.

Further, the reinforcing materials such as glass fiber was incorporated by about 5 to 15% by weight ratio to the 20 advanced resin material such as polyphenylene sulfide (PPS) and the annealing was not applied. Accordingly, strength at the portion of the weld line 26 could be ensured together with excellent corrosion resistance, and occurrence of cracks or breakage at the bottom of the pocket 21 having 25 the weld line 26 can be prevented more reliably.

Further, the cage 20 for use in the rolling bearing according to theembodiment is applicable to any of rolling bearings having rolling elements and, for example, it is

( applicable to cylindrical thrust bearings, tapered roller bearings and self-aligning roller bearings.

Improvement in the shape of the cage: 5 The bearing life can be extended also by configurating the cage 6 as in the following shape. A hole 10 (through hole) of a desired shape is perforated at the bottom 9 of the pocket 8, a lubricating agent is intruded through the hole 10 to improve the lubricating performance between the 10 cage 6 and the rolling elements 5 thereby enabling to extend the bearing life. There are no particular restrictions for the size of the hole 10 (hole diameter), shape or the number of the holes (one or plurality of holes for one pocket) and optional design is possible within the 15 scope of the present invention.

Further, chamfering 11 is applied to the inner and outer diametrical sides for the surface of the cage pocket 8 to facilitate intrusion of the lubricating agent thereby improving the lubricating performance between the cage 6 20 and the rolling elements 5. Further, an angle of inclination for the chamfering 11 is not particularly limited but selected optionally within the scope of the present invention.

Further, well-known structures are applicable to the 25 shape of the cage 6 with no restrictions excepting for providing the through hole 10 and the chamfering 11 described above.

Improvement in the material and the shape of the cage:

( Further, it is also within the scope of the present invention to make the material for the cage 6 with the PTFE (polytetrafluoroethylene) resin material or PPS (polyphenylene sulfide) resin material and to provide the 5 through hole 10 for the pocket bottom 9 as described above and provide the chamfering 11 on the inner and the outer diametrical sides on the surface of the pocket 8.

Although not restricted in the present invention' the bearing life can further be extended by adopting the 10 following specifications in a case of using balls for the

rolling element S. Generally, the radial size for the grooves of the inner and outer ring raceway surfaces 2, 4 is adapted as 50.5 to 60% for the ball diameter and it is desirable to 15 adopt 52 to 54\ for the inner ring and 53 to 56t for the outer ring in view of the PV value (P: contact pressure, V: sliding speed).

It has been known that the bearing life is made longer as the radial size of the groove is smaller in view of the 20 relation with the contact pressure but, if it is too small, the contact ellipse with the raceway surface becomes excessively large tending to cause sliding and sometimes shorten the bearing life by sliding wear. Accordingly, even if the bearing life is shortened by increasing the contact 25 pressure, the bearing life is extended relatively by lowering the sliding speed.

Further, the bearing life can be extended by adopting the carbonitrided bearing material or nitrided bearing

( material having a long life even under lubricating conditions with incorporation of dusts.

The present invention is based on that it concerns a rolling bearing used in a reduced pressure atmosphere 5 such as in vacuum pump apparatus, and a rolling bearing for supporting heat rolls and the like in the fixing portion of business machines.

Fluoro-lubricant is used in both of the cases in view of corrosion resistance and less evaporative amount in lO and heat resistance and less evaporation amount and chemical stability for the use in high temperature circumstance in O. By the way, although the fluoro-lubrlcant has an advantage being less evaporative and more chemically stable 15 compared with the mineral oil type lubricant, it involves problems ln that the lubrication is insufficient since the specific gravity is higher and the nettability is poor (insufficient formation of oil membrane), the lubricant can not easily prevail through narrow gaps (for example between 20 the pocket of the cage and the rolling element) and, accordingly, peeling damages such as peeling wear or peeling flaking tends to occur on the raceway surface of the bearing ring or the rolling element to lower the life.

In addition, it has been found that the peeling damages 25 tend to occur easily on the rolling surface of the rolling element or the pocket portion of the cage (made by steel).

( Accordingly, for coping with the foregoings, the present invention provides a long life rolling bearing in a working circumstance, For improving the corrosion resistance (due to the 5 effect of the fluorolubricant or the like) in the application use of supporting bearing in vacuum pumps, the cage tending to suffer from peeling damages is made of resins such as PPS, PEEK or PET. While injection molding is adopted for the manufacturing method, since cracks tend to 10 be formed by weld lines, the opening for the portion is made wider than the opening portion for other pocket portions and the opening for other pocket is narrowed in order to prevent drop off of the rolling element. The life of the cage is extended by preventing cracks upon forced 15 drawing of the cage after the injection molding and the assembling of the rolling bearing, thereby reducing the cost of the rolling bearing in the application use for the! vacuum pump and preventing the damages in the weld portion of the cage, to provide a long life rolling bearing. I 20 In the cage using the fluorolubricant, materials of high corrosion resistance and usable at high temperature such as PTFE or PPS are used. Since the fluoro-lubricant is less prevailing through the gap between the cage and the rolling element because of poor nettability, a through hole 25 is formed in the pocket bottom or chamfer is applied to inner and outer diametrical surfaces of the pocket surface for improving this, thereby preventing peeling damages to the cage, to provide a long life rolling bearing.

( INDUSTRIAL APPLICABILITY

As has been described above, according to the rolling bearing of claim l in the present invention, since the size for the opening of the pocket having the weld line among 5 the rolling element pockets of the cage formed with an advanced resin material into a circular shape is made to a value of 93% or more of the diameter of the rolling element, and the size for the opening of other at least two pockets are made to a value of 80% or more to 93 or less 10 of the diameter of the rolling element, cracks or breakage in the bottom of the pocket having the weld line can be reliably prevented upon assembling the rolling element to each of the pocket while reliably preventing the drop off of the cage from the rolling bearing.

15Further, according to the rolling bearing of claim 2 in the present invention, since the cage is constituted with the PTFE resin material or the PPS resin materials, or! chamfer is formed to the inner or the outer diametrical sides of the pocket and the through hole is formed in the I 20 pocket bottom, the abrasion powder of the cage is less caused, the lubricant is not deteriorated, indentations are less caused to the raceway surface and the lubrication performance can be improved, so that long life can be attained under the condition with fluoric lubrication.

( À CLAIMS

1. A rolling bearing comprising an outer ring having an outer ring raceway, an inner ring having an inner ring 5 raceway, and rolling elements rotatably disposed between the outer ring raceway and the inner ring raceway, and a and a cage for evenly distributing the rolling elements in the rotational direction of the rolling elements between the outer ring raceway and the inner ring raceway, and used lo under either lubrication with a lubricating oil, or a grease containing a fluorocontaining polymer, or in an atmosphere containing a gas comprising fluorides, wherein the cage is formed with an advanced resin material into a circular shape, a plurality of pockets, each containing the 15 rolling element through an opening and rotatably holding the same, are disposed at predetermined locations on the circumference of the case, the size for the opening of a pocket having a weld line has a value of 93% or more of the diameter of the rolling element, and the size for the 20 opening of at least two other pockets is 80t or more to 93% or less of the diameter of the rolling element.

2. A rolling bearing according to claim 1, wherein the cage is constituted with the PTPE resin material or a PPS resin material, and constituted by applying chamfering to 25 inner and outer diametrical sides of the pockets and forming a through hole in the bottom of the pockets.

3. A rolling bearing substantially as described with reference to the accompanying drawings.

Claims

( <, l'cll(!llt'. g> x lNVES r1R IN l'hOPLE Application No: GB 0322189.2

Examiner: David J Evans Claims searched: 1-2 Date of search: 2 October 2003

Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims A US 5516214 A (KA K U M OTO)

A EP 0486218 A1 (INTER N ATIO N AL BUSINESS M A C HINES

CO RP.) =

A JP 07217659 A (KO Y O SEIK O)

As, Categories: X Document mdcatmg lack of novelly or mvenove step A Documcut ndicalng technahgiLI backgrourxI and/or state of Ate art Y Document indicating lack of mventivc step If combined P Document published on or after the declared pnorty date hu'beforc wok one or more other documents of same category the filing date of this mvennon & Member of the same patent family E Patent document published on or after but with priority date tariler Dan the filing date of flus application Field of Search:

Search of GB, EP, WO & US patent documents classified in the fO]Iowilig areas Ot the UKCV: F2A Worldwide search of patent documents classified in the following areas of the IPC7: F16C The following online and other databases have been used in the prt paration of this search report: | EPODOC, WPI & PAI. l 3k An Executive Agency at tht Department of Trade and Industry