Bearings

Nizwa College of Technology

BEARINGS- INTRODUCTION

• Bearings are machine elements which are used to support a rotating member called as shaft.

• They transmit the load from a rotating member to a stationary member known as frame or housing.

Bearing Motions

Common motions permitted by bearings are:

• Axial rotation e.g. shaft rotation

• Linear motion e.g. Carriage over the bed, drawer in the table

• spherical rotation e.g. ball and socket joint

• Hinge motion e.g. door

Bearing Loads

• Radial Load

• ThrustLoad

• Combination of both.

Fr

Radial load Thrust load Radial &Thrust load

Bearing Loads-Radial load

The bearings that support the shafts of motors and pulleys are

subject to a radial load.

Bearing Loads-Thrust load

The bearings in this stool are subject to a thrust load

Bearing Loads-Combination of Radial &Thrust load

The bearings in a car wheel are subject to both thrust and radial loads.

Bearing ClassificationOn the basis of contact they have between

the rotating and the stationary member

• Plain bearings

(Sliding contact)

• Rolling bearings

(Rolling contact)

Plain bearings-Sleeve Bearing

Advantages : It takes up less space. It has a rigid constructionIt will carry loads more effectivelyIt is suitable for larger diameter shaftsIt is cheap to manufacture and cost less. They operate more silently. They have good shock load capacity.

Disadvantages: It has higher frictional resistanceIt is more difficult to lubricateThere are limited choice of designs available

Sliding contact- Sleeve Bearing

Solid Sleeve

Suitable to radial load

only

Slit Sleeve

Adjustable to compensate

wear

Split Sleeve

Suitable for large diameters

shafts

Rolling BearingsThe concept behind a ball bearing is very simple: • Things roll better than they slide• Two surfaces can roll over each other, the

friction is greatly reduced. • Bearings reduce friction by providing

smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against.

• These balls or rollers "bear" the load, allowing the device to spin smoothly.

Rolling BearingsAdvantages• The rolling bearings have a lower frictional

resistance than plain bearings• The Lubrication of rolling bearings is easier

because they can be "grease packed'• A greater choice of roller bearing designs are

available than for plain bearingsDisadvantages• It takes up more space than plain bearings• The rolling bearings are not as rigid as plain

bearings• More nosier in operation than plain bearings

Types of rolling Bearings

• Ball bearings,

• Roller bearings,

• Tapered roller bearings.

• Ball thrust bearings,

• Roller thrust bearings and

Ball bearings

Cutaway view of a ball bearing

Ball bearings• In a ball bearing, the load is transmitted from the

outer race to the ball and from the ball to the inner race

• Since the ball is a sphere, it only contacts the inner and outer race at a very small point, which helps it spin very smoothly

• But it also means that there is not very much contact area holding that load, so if the bearing is overloaded, the balls can deform and spoil the bearing

• Less expensive and suitable for lighter loads and applications

Rolling Element Bearing Parts

Bore

Outer Race

Inner Race

Ball

Cage or Separator

Roller bearing

•Common roller bearings use cylinders of slightly greater length than diameter. •Roller bearings typically have higher radial load capacity than ball bearings, but a low axial capacity and higher friction under axial loads. •If the inner and outer races are misaligned, the bearing capacity often drops quickly compared to either a ball bearing

Roller bearingAdvantages• They can carry greater radial loads• The geometric shape of the rolling element

can be varied• They are having greater area of contact

with the race waysDisadvantages• Not suitable to take much thrust load• Expensive

Taper Roller Bearings

•Tapered roller bearings use conical rollers that run on conical races.•Tapered roller bearings support both radial and axial loads, and generally can carry higher loads than ball bearings due to greater contact area. •Taper roller bearings are extensively used in Machine spindles and gear boxes using helical gears• The disadvantage of this bearing is that due to manufacturing complexities, tapered roller bearings are usually more expensive than ball bearings

Needle Bearing

A variation of the roller type of bearing is called a needle bearing, uses cylinders with a very small diameter. This allows the bearing to fit into tight places. Advantages•Smaller diameter rollers (Needles) enable larger area of contact and greater load carrying capacity.•Less space is occupiedDisadvantages•More area of contact resulted in more frictional resistance to motion.

Ball Thrust Bearing

•Ball thrust bearings like the one shown are mostly used for low-speed applications and cannot handle much radial load. •Lead screws and feed rods use this type of bearing at its end.

Roller Thrust Bearing

Roller thrust bearings like the one illustrated can support large thrust loads. They are often found in gear sets like machine transmissions between gears, and between the housing and the rotating shafts. The helical gears used in most transmissions have angled teeth and this causes a thrust load that must be supported by this type of bearing