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 Axial rotation e.g. shaft rotation 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 &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 Classification On 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 construction It will carry loads more effectively It is suitable for larger diameter shafts It is cheap to manufacture and cost less. They operate more silently. They have good shock load capacity. Disadvantages: It has higher frictional resistance It is more difficult to lubricate There are limited choice of designs available

Sliding contact- Sleeve Bearing Split Sleeve Suitable for large diameters shafts Solid Sleeve Suitable to radial load only Slit Sleeve Adjustable to compensate wear

Rolling Bearings Things roll better than they slide The 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 Bearings Advantages 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 bearings Disadvantages 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 Outer Race Inner Race Ball Cage or Separator Bore

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 bearing Advantages 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 ways Disadvantages 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 occupied Disadvantages 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