Commentary
Commentary ●Classification and Characteristics of Rolling Bearings ●Classification and Characteristics of Rolling Bearings
1. Classification and characteristics of rolling bearings
1.1 Structure 1.2 Classification Outer ring Outer ring
Most rolling bearings consist of rings with a Rolling bearings are divided into two main Inner ring Inner ring raceway (inner ring and outer ring), rolling classifications: ball bearings and roller elements (either balls or rollers) and a cage bearings. Ball bearings are classified according Cage Ball Ball as shown in Fig. 1.1 (Figs. A to H). The cage to their bearing ring configurations: deep Cage separates the rolling elements at regular groove type and angular contact type. Roller intervals, holds them in place within the inner bearings on the other hand are classified and outer raceways, and allows them to rotate according to the shape of the rollers: cylindrical, Fig. A Deep groove ball bearing Fig. B Angular contact ball bearing freely. needle, tapered and spherical. Rolling bearings Raceway (inner ring and outer ring) or can be further classified according to the raceway washer1) (shaft or housing) direction in which the load is applied; radial Outer ring Outer ring
The surface on which rolling elements roll is bearings carry radial loads and thrust bearings Inner ring Roller called the “raceway surface.” The load placed on carry axial loads. Other classification methods the bearing is supported by this contact surface. include: 1) number of rolling rows (single, Cage Generally the inner ring fits on the axle or double, or 4-row), 2) separable and non- Cage shaft and the outer ring in the housing. separable, in which either the inner ring or the Roller Note 1: The raceway of thrust bearings is called the outer ring can be detached. “raceway washer,” the inner ring is called the “shaft There are also bearings designed for raceway washer” and the outer ring is called the special applications, such as: precision rolling Fig. C Cylindrical roller bearing Fig. D Needle roller bearing “housing raceway washer.” bearings for machine tools, bearings for special Rolling elements environments, as well as linear motion bearings Rolling elements are classified into two types: (linear ball bearings, linear roller bearings Outer ring Outer ring
balls and rollers. Rollers come in four types: and linear flat roller bearings). Types of rolling Roller Inner ring cylindrical, needle, tapered, and spherical. bearings are given in Fig. 1.2. For more detailed Cage Balls geometrically contact with the raceway information, please refer to the page that Roller surfaces of the inner and outer rings at “points”, introduces each bearing. Inner ring Cage while the contact surface of rollers is a “line” contact. Theoretically, rolling bearings are constructed to allow the rolling elements to rotate orbitally while also rotating on their own Fig. E Tapered roller bearing Fig. F Spherical roller bearing axes at the same time.
Shaft raceway washer Shaft raceway washer Cage Cages function to maintain rolling elements Ball Roller at a uniform pitch so a load is never applied directly to the cage and to prevent the rolling elements from falling out when handling the
bearing. Types of cages differ according to Cage Cage the way they are manufactured and include: pressed, machined and formed cages. Housing raceway washer Housing raceway washer Fig. G Thrust ball bearing Fig. H Thrust roller bearing
Fig. 1.1 Rolling bearing
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Commentary ●Classification and Characteristics of Rolling Bearings ●Classification and Characteristics of Rolling Bearings
Deep groove ball bearings ················ B- 17 Four-row cylindrical roller bearings ······························· C- 18
Angular contact ball bearings 1) ········ B- 57 Four-row tapered roller bearings ··································· C- 36 Duplex angular contact ball Radial ball bearings 1) ··············· B- 57 Ultra-thin section type ball bearings ····························· C- 58 bearings Four-point contact ball bearings ······ B- 58 SL type cylindrical roller bearings ·································· C- 66 Double row angular contact ball ULTAGE series bearings ······· B- 59 Sealed four-row tapered roller bearings for rolling mill roll necks [CROU···LL type]5) ··· C- 2 ULTAGE series Ball Self-aligning ball bearings ················· B- 79 Sealed spherical roller bearings [WA type]5) ··············· C- 6 bearings Special application ULTAGE series Ball bearings for rolling bearing unit 2) Spherical roller bearings with high-strength cage [EMA type]5) ··· C- 10 bearings ULTAGE series Deep groove ball bearings for high-speed servo motors [MA type]5) ··· C- 14
Thrust ball Single direction thrust ball bearings ··· B-253 ULTAGE series Precision rolling bearings for machine tools 5) ············· C- 76 bearings Double direction angular contact thrust ball bearings 1) Bearings for special environments 5) ······························ C- 76 High speed duplex angular contact ball bearings 1) (for axial load) Rubber molded bearings 5) ·············································· C- 76
Rolling MEGAOHMTM series insulated bearings 5) ····················· C- 77 bearings Cylindrical roller bearings ················· B- 93 Double row cylindrical roller Clutches/torque limiters 5) ·············································· C- 77 bearings 1) ·············· B- 94 Radial roller bearings Needle roller bearings 4) ···················· E- 2
Tapered roller bearings 1) ·················· B-127 Linear ball bearings 4) Double row tapered roller bearings ··· B-128 Roller Linear motion 4) bearings bearings Linear roller bearings Spherical roller bearings ··················· B-211 Linear flat roller bearings 4)
Thrust cylindrical roller bearings 4) ··· E- 2 Thrust roller bearings Thrust needle roller bearings 4) ········· E- 2
Thrust tapered roller bearings 3) Note: 1) See Precision Rolling Bearings (CAT. No. 2260/E) for bearings of JIS 5 class or above.
Thrust spherical roller bearings ········ B-254 2) See Bearings Units (CAT. No. 2400/E). 3) See Large Bearings (CAT. No. 2250/E). 4) See Needle Roller Bearings (CAT. No. 2300/E). Fig. 1.2 Classification of rolling bearings 5) See the section of “Introduction of catalogs and technical reviews” for the Cat. No of bearings marked with ＊5.
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Commentary ●Classification and Characteristics of Rolling Bearings ●Classification and Characteristics of Rolling Bearings
1.3 Characteristics 1.3.2 Ball bearings and roller bearings 1.3.3 Contact angle and bearing type 1.3.5 Standard bearings and special bearings Table 1.1 gives a comparison of ball bearings A contact angle is an angle made by a line that The boundary dimensions and shapes of 1.3.1 Characteristics of rolling bearings and roller bearings. connects the contact point of the inner ring, bearings conforming to international standards Rolling bearings come in many shapes and rolling element, and outer ring in the radial are interchangeable and can be obtained Table 1.1 Comparison of ball bearings and varieties, each with its own distinctive features. direction when a load is applied on the bearing roller bearings easily and economically all over the world. However, when compared with sliding (Fig. 1.3). It is therefore better to design mechanical Ball bearing Roller bearing bearings, rolling bearings all have the following Bearings with a contact angle of 45° or less equipment that can use standard bearings. Contact with 2b
advantages: 2b have a much greater radial load capacity and are However, depending on the type of raceway (1) The starting friction coefficient is lower and 2a r classed as radial bearings; whereas bearings machine they are to be used in, and the there is little difference between this and the Point contact Linear contact which have a contact angle over 45° have a expected application and function, a non- dynamic friction coefficient. Contact surface is oval Contact surface is greater axial load capacity and are classed standard or specially designed bearing may when a load is applied. generally rectangular (2) They are internationally standardized, when a load is applied. as thrust bearings. There are also bearings be best. Bearings that are adapted to specific interchangeable and readily obtainable. classed as complex bearings which combine the applications, and “unit bearings” which Because of point Because of linear (3) They are easy to lubricate and consume less contact, where there is contact, rotational loading characteristics of both radial and thrust are integrated (built-in) into a machine's Characteristics lubricant. little rolling resistance, torque is higher for roller bearings. components, and other specially designed (4) As a general rule, one bearing can carry both ball bearings are bearings than for ball bearings are also available. suitable for low torque bearings, but rigidity is radial and axial loads at the same time. and high-speed also higher. Contact angle The features of typical standard bearings are (5) May be used in either high or low applications. as follows: They also have temperature applications. superior acoustic (6) Bearing rigidity can be improved by characteristics. Deep groove ball bearing
preloading. Load capacity is lower Load capacity is higher Contact angle The most common type of bearing, deep groove Construction, classes, and special features for ball bearings, but for rolling bearings. ball bearings are widely used in a variety of Load capacity of rolling bearings are fully described in the radial bearings are Cylindrical roller Fig. 1.3 Contact angle fields. Deep groove ball bearings can include capable of bearing bearings equipped with boundary dimensions and bearing numbering loads in both the radial a lip can bear slight axial shielded bearings or sealed bearings with grease system section. and axial direction. loads. Combining 1.3.4 Load acting on bearing to make them easier to use. tapered roller bearings in pairs enables the Types of loads applied on rolling bearings are Deep groove ball bearings also include bearings to bear an axial given in Fig. 1.4. A moment load is caused by an bearings with a locating snap-ring to facilitate load in both directions. unbalanced load and misalignment. positioning when mounting the outer ring, expansion compensating bearings which absorb dimension variation of the bearing fitting surface due to housing temperature, and TAB bearings that are able to withstand contamination in the lubricating oil.
(a) Radial load (b) Axial load (c) Moment load Fr Fa Table 1.2 Configuration of sealed ball bearings Shielded type Sealed type Fig. 1.4 Types of load Type and Non-contact Non-contact Contact Low torque code type ZZ type LLB type LLU type LLH Structure
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Commentary ●Classification and Characteristics of Rolling Bearings ●Classification and Characteristics of Rolling Bearings
Angular contact ball bearing Table 1.3 Contact angle and symbol Cylindrical roller bearing Tapered roller bearing
The line that unites the point of contact of the Contact angle Cylindrical roller bearings use rollers for rolling Tapered roller bearings are designed so the inner ring, ball and outer ring runs at a certain elements, and therefore have a high load inner/outer ring raceway and apex of the tapered angle (contact angle) in the radial direction. Contact angle and contact angle symbol capacity. The rollers are guided by the ribs of the rollers intersect at one point on the bearing Angular contact ball bearings are generally Contact angle 15° 30° 40° inner or outer ring. The inner and outer rings can centerline. By receiving a combined load from Contact angle 1) designed with three contact angles. (Refer to symbol C A B be separated to facilitate assembly, and both the inner and outer ring, the rollers are pushed Table 1.3) Note: 1. Contact angle symbol has been abbreviated as “A”. can be fit with a shaft or housing tightly. If there against the inner ring rib and are guided by the Angular contact ball bearings can support an are no ribs, either the inner or the outer ring can rib. axial load, but cannot be used by themselves move freely in the axial direction. Cylindrical Induced force is produced in the axial Table 1.4 Configuration of double row angular because of the contact angle. They must instead roller bearings are therefore ideal to be used as direction when a radial load is applied, so it must contact ball bearings be used in pairs or in combination. (Refer to so-called “free side bearings” that absorb shaft be handled with a pair of bearings. The inner Type Non-contact Contact Open type Shielded Table 1.5) and type ZZ sealed type sealed type expansion. In the case where there are ribs, the ring with rollers and outer ring come apart, thus code LLM LLD Angular contact ball bearings include double bearing can bear a slight axial load between the facilitating mounting with clearance or preload.
row angular contact ball bearings for which the Structure end of the rollers and the ribs. Cylindrical roller Assembled clearance is however hard to inner and outer rings are combined as a single bearings include the HT type which modifies manage and requires special attention. Tapered unit. (Refer to Table 1.4) The contact angle of the shape of the roller end face and ribs for roller bearings are capable of supporting large double row angular contact ball bearings is 25°. increasing axial load capacity, and the EA type loads in both the axial and radial directions. There are also four-point contact bearings and E type with a special internal design for NTN also has a line of case hardened steel Table 1.5 Combinations of duplex angular that can support an axial load in both directions enhancing radial load capacity. The EA type is bearings designed for longer life (ETA-, etc.). contact ball bearings by themselves. These bearings however require standardized for small-diameter sizes. NTN tapered roller bearings also include Type caution because problems such as excessive and Back-to-back Face-to-face Tandem Table 1.6 shows the basic shapes. bearings with two and four rows of tapered symbol arrangement DB duplex DF arrangement DT temperature rise and wear could occur rollers for extra-heavy loads.
depending on the load conditions. Structure In addition to these, there are cylindrical roller bearings with multiple rows of rollers and the SL type of full complement roller bearings without r r a cage.
r: Distance between load centers Table 1.6 Types of cylindrical roller bearings Type NUP Type Type NU Type NJ Type NH code Type N Type NF (NJ HJ) Subunit dimensions
2α E Design Type NU Type NJ Type NUP E : Outer ring (cup) nominal small-end diameter α : Nominal contact angle
Fig. 1.5 Tapered roller bearings
Type N Type NF Type NH
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Commentary ●Classification and Characteristics of Rolling Bearings ●Classification and Characteristics of Rolling Bearings
Spherical roller bearing Thrust bearing Needle roller bearing Bearing unit Equipped with an outer ring with a spherical There are many types of thrust bearings that Needle roller bearings use needle rollers as A unit comprised of a ball bearing inserted into raceway surface and an inner ring which holds differ according to the shape of the rolling rolling elements. The needle rollers are a various types of housings. The housing can be two rows of barrel-shaped rolling elements, element and application. maximum of 6 mm in diameter and are 3 to 10 bolted onto machinery and the inner ring can be NTN spherical roller bearings are able to adjust Allowable rotational speed is generally times as long as they are in diameter (JIS B1506 easily mounted on the shaft with a set screw. center alignment to handle inclination of the low and special attention must be paid to rolling bearings roller). Because the bearings This means the bearing unit can support axle or shaft. lubrication. use needle rollers as rolling elements, the rotating equipment without a special design to There are a variety of spherical roller bearing cross-section is thin, but they have a high load allow for mounting. A variety of standardized types that differ according to their internal In addition to the types shown in Table 1.8 capacity for their size. Due to the large number housing shapes are available, including pillow design. below, there are various other types of thrust of rolling elements, bearings have high rigidity block and flange types. The outer diameter In addition to cylindrical bore inner rings, bearings for special applications. and are ideally suited to oscillating motion. of the bearing is spherical just like the inner spherical roller bearings can be produced with There are various types of needle roller diameter of the housing, so it is capable of Table 1.8 Types of thrust bearings a tapered bore inner ring. The tapered bore bearings, and just a few of the most aligning itself on the shaft. Type Single direction thrust ball Needle roller thrust bearing can easily be mounted on a shaft by bearing bearings representative types are covered here. For For lubrication, grease is filled inside the means of an adapter or withdrawal sleeve. details, see the catalog “Needle roller bearings bearing, and foreign particles are prevented The bearing is capable of supporting heavy AXK type (CAT. No. 2300/E).” from entering with a shaft riding seal and slinger loads, and is therefore often used for industrial shield. AS type raceway washer machinery. When a heavy axial load is applied For details, see the catalog “Bearing unit Table 1.9 Main types of needle roller bearings to the bearing, the load on rollers of one row is GS/WS type raceway washer (CAT. No. 2400/E).” Structure Type not applied, and can cause problems. Attention Needle roller bearing with cage Thrust cylindrical roller Thrust self-aligning roller must therefore be paid to operating conditions. bearing bearing
Table 1.7 Types of spherical roller bearings Grease fitting ULTAGE Type B type C type 213 type Ball Housing EA type EM type Spherical outer ring Solid type needle roller bearings
Structure Allowable angle Slinger Special rubber seal Structure
Drawn cup needle roller bearings Setscrew with ball
Fig. 1.6 Bearing unit with grease fitting Cam follower Roller follower
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