Classification and Characteristics of Rolling Bearings

Transcription

1 1. Classification Characteristics of Rolling Beas 1.1 Rolling bea construction Most rolling consist of s with raceway (inner outer ), rolling elements (either balls or rollers) cage. The cage separates the rolling elements at regular intervals, holds them in place within the inner outer raceways, allows them to rotate freely. Raceway (inner outer ) or raceway washer 1) The surface on which rolling elements roll is called the "raceway surface". The load placed on the bea is supported by this contact surface. Generally the inner fits on the axle or shaft the outer on the housing. Note 1: The raceway of thrust bea is called "raceway washer," the inner is called the "shaft raceway washer" the outer is called the "housing raceway washer." Rolling elements Rolling elements classify in two types: balls rollers. s come in four types: cylindrical, needle, tapered, spherical. s geometrically contact with the raceway surfaces of the inner outer s at "points", while the contact surface of rollers is a "line" contact. Theoretically, rolling are so constructed as to allow the rolling elements to rotate orbitally while also rotating on their own axes at the same time. s s function to maintain rolling elements at a uniform pitch so load is never applied directly to the cage to prevent the rolling elements from falling out when hling the bea. s of cages differ according to way they are manufactured, include pressed, machined formed cages. 1.2 Classification of rolling Rolling divide into two main classifications: ball roller. are classified according to their bea configurations: deep groove type angular contact type. on the other h are classified according to the shape of the rollers: cylindrical, needle, tapered spherical. Inner Deep groove ball bea Fig A Inner Cylindrical roller bea Fig. C Inner Tapered roller bea Fig. E Outer Inner Angular contact ball bea Fig.B Needle roller bea Fig. D Outer Inner Spherical roller bea Fig. F Rolling can be further classified according to the direction in which the load is applied; radial carry radial loads thrust carry axial loads. Other classification methods include: 1) number of rolling rows (single, double, or 4-row), 2) separable non-separable, in which either the inner or the outer can be detached. There are also designed for special applications, such as: railway car journal roller, ball screw support, turntable, as well as linear motion (linear ball, linear roller linear flat roller ).s of rolling are given in Fig Shaft raceway washer Housing raceway washer Thrust ball bea Fig. G Fig. 1.1 Rolling bea Shaft raceway washer Housing raceway washer Thrust roller bea Fig. H A-5

2 Single row deep groove ball B- 5 Single row angular contact ball B-43 Radial ball Duplex angular contact ball B-46 Four-point contact ball B-58 Double row angular contact ball B-60 Self-aligning ball B-65 for rolling bea unit* Single direction thrust ball B-255 Thrust ball Double direction angular contact thrust ball * High-speed duplex angular contact ball (for axial loads)* Rolling Single row cylindrical roller B- 77 Double row cylindrical roller B-102 Radial roller Needle roller * Single row tapered roller B-119 Double row tapered roller B-184 Spherical roller B-219 Cylindrical roller thrust * Needle roller thrust * Thrust roller Tapered roller thrust * Spherical roller thrust B-262 Fig. 1.2 Classification of rolling A-6

3 Ultra thin wall type ball * screw support * Railway car journal roller * Ultra-clean vacuum * SL-type cylindrical roller * Special application Insulated MEGAOHM TM series* Rubber molded * Clearance adjusting needle roller * Complex * Connecting rod needle roller with cage* followers* Cam followers* Linear motion Linear ball * Linear roller * Linear flat roller * Note: Beas marked with an asterisk are not contained in this catalog. For details, see the catalog devoted to the concerned type of bea. A-7

4 1.3 Characteristics of rolling Characteristics of rolling Rolling come in many shapes varieties, each with its own distinctive features. However, when compared with sliding, rolling all have the following advantages: (1) The starting friction coefficient is lower there is little difference between this the dynamic friction coefficient. (2) They are internationally stardized, interchangeable readily obtainable. (3) They are easy to lubricate consume less lubricant. (4) As a general rule, one bea can carry both radial axial loads at the same time. (5) May be used in either high or low temperature applications. (6) Bea rigidity can be improved by preloading. Construction, classes, special features of rolling are fully described in the boundary dimensions bea numbe system section roller Table 1.1 gives a comparison of ball roller Radial thrust Almost all types of rolling can carry both radial axial loads at the same time. Generally, with a contact angle of less than 45 have a much greater radial load capacity are classed as radial ; whereas which have a contact angle over 45 have a greater axial load capacity are classed as thrust. There are also classed as complex which combine the loading characteristics of both radial thrust Stard special The boundary dimensions shapes of conforming to international stards are interchangeable can be obtained easily economically over the world over. It is therefore better to design mechanical equipment to use stard. However, depending on the type of machine they are to be used in, the expected application function, a non-stard or specially designed bea may be best to use. Beas that are adapted to specific applications, "unit " which are integrated (built-in) into a machine's components, other specially designed are also available. The feature of typical stard are as follows: Table 1.1 Comparison of ball roller Contact with raceway Characteristics Load capacity 2a 2b Point contact Contact surface is oval when load is applied. Because of point contact there is little rolling resistance, ball are suitable for low torque high-speed applications. They also have superior acoustic characteristics. Load capacity is lower for ball, but radial are capable of bea loads in both the radial axial direction. r 2b Linear contact Contact surface is generally rectangular when load is applied. Because of linear contact, rotational torque is higher for roller than for ball, but rigidity is also higher. Load capacity is higher for rolling. Cylindrical roller equipped with a lip can bear slight radial loads. Combining tapered roller in pairs enables the to bear an axial load in both directions. Deep groove ball The most common type of bea, deep groove ball are widely used in a variety of fields. Deep groove ball include shield sealed with grease make them easier to use. Deep groove ball also include with a locating snap- to facilitate positioning when mounting the outer, expansion compensating which absorb dimension variation of the bea fitting surface due to housing temperature, TAB that are able to withst contamination in the lubricating oil. Table 1.2 of sealed ball Shield Non-contact ZZ Non-contact LLB Sealed Contact LLU Low torque LLH A-8

5 Angular contact ball The line that unites point of contact of the inner, ball outer runs at a certain angle (contact angle) in the radial direction. Beas are generally designed with three contact angles. Angular contact ball can support an axial load, but cannot be used by single bea because of the contact angle. They must instead be used in pairs or in combinations. Angular contact ball include double row angular contact ball for which the inner outer s are combined as a single unit. The contact angle of double row angular contact ball is 25. There are also four-point contact that can support an axial load in both directions by themselves. These however require caution because problems such as excessive temperature rise wea could occur depending on the load conditions. Table 1.3 Contact angle Contact angle Cylindrical roller Uses rollers for rolling elements, therefore has a high load capacity. The rollers are guided by the ribs of the inner or outer. The inner outer s can be separated to facilitate assembly, both can be fit with shaft or housing tightly. If there is no ribs, either the inner or the outer can move freely in the axial direction. Cylindrical roller are therefore ideal to be used as so-called "free side " that absorb shaft expansion. In the case where there is a ribs, the bea can bear a slight axial load between the end of the rollers the ribs. Cylindrical roller include the HT type which modifies the shape of roller end face ribs for increasing axial road capacity. And the E type with a special internal design for enhancing radial load capacity. The E type is stardized for small-diameter sizes. Table 1.6 shows the basic configuration for cylindrical roller. In addition to these, there are cylindrical roller with multiple rows of rollers the SL type of full complement roller bea without cage. Contact angle contact angle Contact angle Contact angle 15 C 30 A 40 Note 1: Contact angle has been abbreviated as "A". 1 B Table 1.6 s of cylindrical roller Symbol NU type N type NJ type NF type NUP type NH type NJ+HJ Table 1.4 of double row angular contact ball Open Shield ZZ Non-contact sealed LLM Contact sealed LLD Drawings NU type NJ type NUP type N type NF type NH type Table 1.5 Combinations of duplex angular contact ball Back-to-back duplex DB Face-to-face duplex DF Tem duplex DT r r A-9

6 Tapered roller Tapered roller are designed so the inner/outer raceway apex of the tapered rollers intersect at one point on the bea centerline. By receiving combined load from inner outer, the rollers are pushed against the inner rib roll guided with rib. Induced force is produced in the axial direction when a radial load is applied, so must be hled by using a pair of. The inner with rollers outer come apart, thus facilitating mounting with clearance or preload. Assembled clearance is however hard to manage requires special attention. Tapered roller are capable of supporting large loads in both the axial radial directions. NTN with 4T-, ET-, T- U attached to the name conform to ISO JIS stards for sub-unit dimensions (nominal contact angle, nominal small end diameter of outer ) are internationally interchangeable. NTN also has a line of case hardened steel designed for longer life (ETA-, ET-, etc.). NTN tapered roller also include with two four rows of tapered rollers for extra-heavy loads. Spherical roller Equipped with an outer with a spherical raceway surface an inner which holds two rows of barrelshaped rolling elements, NTN spherical roller are able to adjust center alignment to hle inclination of the axle or shaft. There are variety of bea types that differ according to internal design. Spherical roller include as type equipped with an inner with a tapered bore. The bea can easily be mounted on a shaft by means of an adapter or withdrawal sleeve. The bea is capable of supporting heavy loads, is therefore often used in industrial machinery. When heavy axial load is applied to the bea, the load on rollers of another row is disappeared, can cause problems. Attention must therefore be paid to operating conditions. Table 1.7 s of spherical roller Stard (B type) C type 213 type E type Thrust Sub-unit dimensions 2α E There are many types of thrust that differ according to shape of rolling element application. Allowable rotational speed is generally low special attention must be paid to lubrication. In addition to the ones given below, there are various types of thrust for special applications. For details, see the catalog devoted to the concerned type of bea. E nominal small end diameter of outer α Nominal contact angle Fig. 1.3 Tapered roller Table 1.8 s of thrust Single direction thrust ball bea Needle roller thrust bea AXK type AS type raceway washer Cylindrical roller thrust bea GS/WS type raceway washer Spherical roller thrust bea Center alignment angle A-10

7 Needle roller Needle roller use needle rollers as rolling elements. The needle rollers are a maximum of 5 mm in diameter are 3 to 10 times as long as they are in diameter. Because the use needle rollers as rolling elements, the cross-section is thin, but they have a high load capacity for their size. Because of the large number of rolling elements, the have high rigidity are ideally suited to wobbling or pivoting motion. There is a profusion of types of needle roller, just a few of the most representative types are covered here. For details, see the catalog devoted to the concerned type of bea. Table 1.9 Main types of needle roller Needle roller bea with cage Bea unit A unit comprised of a ball bea inserted into various types of housings. The housing can be bolted onto machinery the inner can be easily mounted on the shaft with a set screw. This means the bea unit can support rotating equipment without special design to allow for mounting. A variety of stardized housing shapes is available, including pillow flange types. The outer diameter of the bea is spherical just like the inner diameter of the housing, so it capable of aligning itself on the shaft. For lubrication, grease is sealed inside the bea, particle generation is prevented by a double seal. For details, see the catalog devoted to the concerned type of bea. Grease fitting Housing Spherical outer Solid type needle roller Slinger Special rubber seal Shell type needle roller Setscrew with ball Fig. 1.4 Oil-lubricated bea unit follower Cam follower A-11