Introduction Types of bearings Rolling Contact Bearings Construction Classification Bearing Types Bearing Life Merits & Demerits

Introduction to Introduction to bearingsbearings Objective of bearing is to provide relative positioning and rotational freedom while transmitting a load between two parts.

In rolling contact bearings as the name implies the friction is of rolling type.

It is much smaller than the sliding type.

Rolling Contact BearingsRolling Contact Bearings

load is transferred through rolling elements such as balls, straight and tapered cylinders and spherical rollers.

Journal (sleeve) BearingsJournal (sleeve) Bearings load is transferred through a thin film of

lubricant (oil).

Types of bearingsTypes of bearings

Rolling Contact BearingsRolling Contact Bearings

Rolling contact bearings are also known as

antifriction bearings.

The load, speed, and operating viscosity of the

lubricant affect the friction characteristics of a rolling

bearing.

These bearings provide coefficients of friction

between 0.001 and 0.002.

The designer must deal with such matters as fatigue,

friction, heat, lubrication, kinematics problems,

material properties, machining tolerances, assembly,

use and cost

The rolling contact bearings are composed of four elements.

i.Outer raceii.Inner raceiii.Rolling elementiv.Cage of retaining ring

Roller contact bearing With its parts

i.Outer ring (or) Outer raceii.Inner ring (or) inner raceiii.Rolling elementsiv.Cage or retaining ring

Construction Diagram :

Classification of rolling bearings

i.Ball Bearing•Deep groove (Conrad) bearing•Filling notch ball bearing•Angular contact bearings (AC)

ii. Roller Bearing •Cylindrical bearings•Needle bearings•Tapered bearings•Spherical bearings

Classified into two types

Ball BearingsBall Bearings

Deep groove bearingDeep groove bearing

Single row of deep groove ball bearing can combinational of radial and thrust load.Load capacity is limited by the number of ballsPrimarily designed to support radial loads, the thrust capacity is about 70% of radial load capacity

Filling notch ball bearings

Bearings have the same basic radial construction as Conrad type. However, a filling notch (loading groove) permits more balls to be used.Radial load capacity is 20 – 40% higher than Conrad type.Thrust load capacity drops to 20% (2 directions) of radial load capacity.

Angular contact Ball bearings (AC)

The centerline of contact between the balls and the raceway is

at an angle to the plane perpendicular to the axis of rotation.

Used for high radial and thrust load applications

RADIAL AND ANGULAR BEARINGRADIAL AND ANGULAR BEARING

Standardization of bearings

Roller Bearings

Roller bearings have higher load capacity than ball

bearings, load is transmitted through line contact instead

of point contact.

Helical rollers are made by winding rectangular

material into roller. Due to inherent flexibility they are

capable of taking considerable misalignment.

A roller with length much larger than diameter is

known as needle roller and are used where radial space is

limited. Cage nay be absent in needle roller bearings.

ROLLER BEARINGSROLLER BEARINGS

If a bearing is clean, properly lubricated and mounted and is operating at reasonable temp., failure is due to fatigue caused by repeated contact stresses (Hertzian stress)

Fatigue failure consists of a spalling or pitting of the curved surfaces

Failure criterion – spalling or pitting of an area of 0.01 in2, Timken company (tapered bearings)

Spallingcrack initiates below the curved surface at the location of

maximum shear stress, propagates to the surface causing surface damage.

LIFE number of revolution or hours of operation, at constant speed, required for the failure criterion to develop.

L10 = 500 (hours) x 33.33 (rpm) x 60 = 106 = 1 million revolutions

For ball bearings and spherical bearings:

For tapered bearings manufactured by Timken:L10 = 3000 (hours) x 500 (rpm) x 60 = 90 x 106 = 90 million revolutions

– defines the number of revolution or hours of operation, at constant speed, in such a way that of the bearings tested (from the same group) will complete or exceed before the first evidence of failure develops. This is known as life.

Basic Dynamic Load Rating, C constant radial load that a group of bearings can carry for L10 life.

Bearing LifeBearing Life

Bearing lifeBearing life

PRELOADING OF BEARINGPRELOADING OF BEARING

Preloading or Duplexing is used to eliminate the play or clearance in either radial or axial direction of ball bearing to be used for precision machine tool.

• Low starting and good operating friction torque.

• East of lubrication

• Requiring less axial space.

• Generally, taking both radial and axial loads.

• Rapid replacement

• Warning of impending failure by increasing

noisiness.

• Good low-temperature starting.

Merits of Rolling contact bearingsMerits of Rolling contact bearings

• Greater diametric space.

• More severe alignment requirements.

• Higher initial cost.

• Noisier normal operation.

• Finite life due to eventual failure by

fatigue.

• Ease of damage by foreign matter.

• Poor damping ability.

Demerits of rolling element bearings:Demerits of rolling element bearings: