Best Bearings Types and Uses 2024

A bearing is a machine element that constrains relative motion between moving parts to only the desired motion. For example, a bearing may:

• provide free linear movement, or
• provide free rotation around a fixed axis.

Many bearings also minimize friction. Bearings permit smooth low-friction movement between two surfaces. Bearings are broadly classified according to the type of operation, the motions allowed, or to the directions of the loads (forces) applied to the parts. The most common bearing is the plain bearing which uses surface rubbing contact, often with a lubricant. The most sophisticated bearings are very precise. There are, of course, many types of bearings with varying shapes, materials, lubrication, principles of operation, etc. One of the important functions of bearings is to reduce friction and thus reduce wear and facilitate extended use at high speed. The friction in the bearing is reduced by virtue of its shape, its material, by separation of surfaces by fluid, and by electromagnetic field. A combination of these methods can be applied in any given bearing. For example, a bearing cage may be made of plastic, and it is separated by the rollers/balls, which reduce friction by their shape and finish.

Concept: 

The basic concept of bearing is simple – things roll better than they slide. The wheels of a car act like bearings. If a car had skis instead of wheels, it would be very difficult to move on the road. If things slide one above the other, friction resists the movement. But if the 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.

Load on bearings: 

There are two kinds of loading on bearings – radial and thrust. The loads depend upon where the bearing is used. It may be all radial loading, all thrust loading, or a combination of both. For example, the bearing of an electric motor faces only radial load. The bearing in the stool (for example: the barstool) is subjected to thrust load. It is loaded purely in thrust, and the entire load comes from the weight of the person sitting on the stool. The bearings in a car wheel are subjected to both thrust and radial loads. The radial load comes from the weight of the car. The thrust load comes from the cornering forces when you go around a turn.

Principles of Bearings Operation: 

The following are six common principles of operation:

Plain bearing  

Bushing, journal bearing, sleeve bearing, and rifle bearing.

Roller-element bearing 

Ball bearings and roller bearings.

Jewel bearing 

The load is carried by rolling the axle slightly off-center.

Fluid bearing  

A gas or liquid carries the load.

Magnetic bearing

The load is carried by a magnetic field.

Flexure bearing  

The motion is supported by a load element that bends.

Bearing Motions:

Following are the common motions that bearing permit:

Axial rotation

For example, shaft rotation

Linear motion 

For example, a drawer.

Spherical rotation

For example, ball and sprocket joint. 

Hinge motion

For example, door, elbow, knee.

Bearings Loads: 

Bearings can support forces in various directions. Prominent among them are – radial, axial (thrust bearings), or bending moments perpendicular to the main axis. Loads acting perpendicular to the axis of the bearing are called axial loads. Although radial bearings are designed primarily for straight radial service, they will withstand considerable thrust loads when deep ball tracks in the raceway are used.

Loads applied parallel to the axis of the bearing are called thrust loads. Thrust bearings are not designed to carry radial loads. When loads are exerted both parallel and perpendicular to the axis of the bearings, a combination of radial and thrust bearings is used.

Bearings Speeds: 

Different types of bearings are designed to operate at different operating speeds. Speed is specified as the maximum relative surface speed in meters / second. The performance of rotational bearings is stated as DN where D is the mean diameter (in mm) of the bearing and N is the rotational rate in revolutions per minute. Plain bearings handle low speed. Rolling element bearings are faster. Fluid and magnetic bearings are limited by centripetal force.

TYPES OF BEARINGS

Many different kinds of bearings are designed to handle radial load, thrust load, or some combination of the two.

Plain Bearings: 

A plain bearing is any bearing that works by sliding action, with or without lubricant. This group comprises practically all types other than rolling-element bearings. Plain bearings are often referred to as either sleeve bearings or thrust bearings, terms that designate whether the bearing is loaded radially or axially.

Lubrication is critical to the operation of plain bearings, so their application and function are also often referred to according to the type of lubrication principles used. Thus, terms such as hydro-dynamic, fluid-film hydrostatic, boundary-lubricated, and self-lubricated are designations for particular types of plain bearings. Most bearings are oil-lubricated. The designed rings are still puer effective arrangements for providing supplementary lubrication.

Antifriction Bearings: 

Ball, roller, and needle bearings are classified as antifriction bearings because in them friction is reduced to the minimum. They may be divided into two main groups: radial bearings and thrust bearings. Except for special designs, ball and roller bearings consist of two rings, a set of rolling elements, and a cage. The cage separates the rolling elements and spaces them evenly around the periphery (circumference of the circle).

Ball Bearings: 

Ball bearings are very common because they can handle both radial and thrust loads. But they can handle a small amount of weight. A ball bearing uses spheres that are between the outer race and the inner race. These spheres only contact the inner and outer races at very small points, which helps them spin very smoothly. But this also means that the spheres have a very small contact area holding the load. Therefore, overloading can deform the balls and the bearings may be ruined. 

Ball bearings have low load capacity in comparison to other kinds of rolling-element bearings, but they can tolerate some misalignment of the inner and outer races.

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. This helps it spin very smoothly.

In most applications, one race is stationary and the other is attached to the rotating assembly (e.g., a hub or shaft). As one of the bearing races rotates it causes the balls to rotate as well. Because balls are rolling they have a much lower coefficient of friction than if two flat surfaces were sliding against each other. 

Parts of ball bearing: 

Ball bearings are also called “Deep-groove Ball Bearings”, because of their constructional aspects. The balls are made to run in deep grooves formed in the inner race and outer race of the bearing. The basic parts of a ball bearing are:

Inner race: 

This is the part that is mounted on the rotating shaft and tends to rotate the shaft.

Outer race: 

This is the part that is mounted to the housing and is stationary. This also serves as a means for transferring the loads from the bearing to the housing.

Rolling element “balls”: 

These are the elements that carry the load distributing it throughout the raceways. They tend to rotate about the inner race, but not at the speed the inner race rotates.

Cage: 

This is an important element in the bearing. This acts as a barrier between the balls preventing them from bumping into each other.

Besides the normal ball bearing, bearings are available with certain special constructional features like shielded bearings and sealed bearings.

Shielded ball bearing: 

A shielded ball bearing shields the rolling elements from the external dirt. The shield is normally made of plastic or special rubber.

Sealed ball bearing: 

A sealed ball bearing is completely sealed with lubricant inside. It prevents the flow of other lubricants into the rolling element area. It also prevents the inside lubricant i.e. grease from getting out of the rolling element area.

Double-row ball bearings: 

When the load-carrying capacity of a single-row bearing is inadequate, double-row deep groove ball bearings are used. While they have the same outside and bore diameters as single-row bearings, these double-row bearings are slightly wider and offer considerably higher load-carrying capacity than single-row bearings. They can carry axial loads acting in both directions in addition to radial loads.

Load carrying capability: 

The ball bearing has a good capability to run at high speeds but is average in carrying loads. They can carry only medium loads and hence find use in almost all household items such as ceiling fans, mixies, grinders, etc. These bearings are not used in applications that require heavy axial load to be carried.

Radial bearings: 

Deep-groove bearings are the most widely used ball bearings. In addition to the radial loads, they can carry substantial thrust loads at high speeds in either direction. They require careful alignment between the shaft and housing. Self-aligning bearings come in two types: internal and external. In internal bearings, the outer-ring ball groove is ground as a spherical surface. 

Externally self-aligning bearings have a spherical surface on the outside of the outer ring, which matches a concave spherical housing. Double-row, deep-groove bearings embody the same principle of design as single-row bearings Double-row bearings can be used where high radial and thrust rigidity is needed and space is limited. They are about 60 to 80 percent wider than comparable single-row groove bearings, and they have about 50 percent more radial capacity. Angular-contact thrust bearings can support a heavy thrust load in one direction combined with a moderate radial load. High shoulders on the inner and outer rings provide steep contact angles for high thrust capacity and axial rigidity. 

Thrust bearings: 

In a sense, thrust bearings can be considered to be angular-contact bearings. They support pure thrust loads at moderate speeds, but for practical purposes their radia! load capacity is nil. Because they cannot support radial loads, ball thrust bearings must be used together with radial bearings. Flat-race bearings consist of a pair of flat washers separated by the ball complement and shaft-piloted retainer, so load capacity is limited. Contact stresses are high, and torque resistance is low. One-directional, grooved-race bearings have grooved races very similar to those found in radial bearings. Two-directional, groove-race bearings consist of two stationary races, one rotating race, and two ball complement.

Roller Bearings: 

Roller bearings are designed to carry heavy loads. For example, they are used in conveyor belt rollers, where they must hold heavy radial loads. The primary roller is a cylinder, which means the load is distributed over a larger area. The contact between the inner and outer race is not a point but a line. This spreads the load over a larger area. This enables the bearing to handle larger amounts of load. This structure can, however, handle primarily radial loads, but is not suited for thrust loads. Where space is limited, a needle bearing can be used. Needle bearings work with smaller diameter cylinders, so they are easier to fit in smaller applications.

Roller bearings thus include the types:

• Tapered rollers

• Cylindrical rollers
• Needle rollers

The two styles are: “non-tapered rollers” (cylindrical and needle) and “tapered rollers”. The most apparent difference between the two types is the shape of the rollers and the curvatures of the races. In a non-tapered roller bearing, the centers of each part run parallel to one another. In the tapered roller, if the Imaginary lines were run through the outer race and inner race, they would taper off and eventually coincide at a point.

Tapered roller bearings: 

This type of bearings can handle large radial and thrust loads. Because of their lead versatility, they are found in car hubs, where they are usually mounted in pairs facing opposite directions so that they can handle thrusts in both directions. Car wheels are required to carry large loads both radial and thrust.

In profile, the tapered roller bearing resembles the wide edge of a cone rather than a circle. There are two major benefits to this design. First, true rolling motion is obtained. Secondly and more importantly, the bearing can handle all loads radial, thrust, or both – in any combination. 

The first benefit of the tapered roller bearing is its cone-shaped design. Each roller in the bearing can align itself perfectly between the tapered faces of the cup and cone, without guidance by the cage. As each roller revolves around the cone, a wide area of contact is made between the large end of the roller and the rib. This wide area of contact compels each roller to maintain accurate alignment. With each roller perfectly aligned between the two races, the bearing works to maximum productivity. Each roller has an equal share of the total workload.

The second benefit – is the bearing’s ability to support radial and thrust loads simultaneously.

One construction feature makes tapered roller bearings unique from most other designs: the races are separable. When mounted, the inner race (cone) and rollers are assembled as one unit and the outer race (cup) as another. Industry standards in size and design permit cups and cones to be interchanged when necessary.

Tapered roller bearings are used in automobiles, trucks, tractors, and various farming vehicles, including:

• Transmissions
• Transfer cases
• Rear axle shafts
• Differentials
• Front wheels
• Trailer wheels

Cylindrical roller bearings: 

The cylindrical type consists of four basic roller bearing parts: inner race, outer race, cage, and rollers. The cylinder-shaped rollers are kept evenly spaced by the cage, which guides their turning movement on the flat surface of the two Taces. Some types have flanges or ribs, projecting from the edge of one or both of the races. This supports the rollers while permitting limited free axial movement of the shaft in relation to the housing.

The benefits of cylindrical roller bearings are:

• High capacity under radial loads
• Accurate guiding of the rollers
• Limited free axial movement (single flange design only)

A few examples of application of cylindrical roller bearings are:

• Transmissions
• Differentials
• Rear Axle Shafts

Needle roller bearings: 

The needle roller bearing is a variation of the cylindrical roller bearing. According to “Marks Standard Handbook for Mechanical Engineers”, a needle bearing is a roller bearing with rollers whose length are at least four times their diameter. They are used to reduce friction on a rotating surface. The main difference is in roller design capacity. The rollers are thinner in diameter, but there are more rollers per bearing. Full complement needle roller bearings do not have a cage. In this type of bearing one roller pushes against the other holding everything in place.

In these bearings, there is less added clearance (the difference between the diameter of the shaft and the diameter of the bearing) so they are much more compact. Radial needle bearings are cylindrical and use rollers parallel to the axis of the shaft. Thrust needle bearings are flat and use a radial pattern of needles.

The benefit of needle roller bearing is its good capacity under radial loads. Needle bearings are very much used in automobile components, pumps, compressors, etc. Its applications include the following:

• Transmissions
• Alternators
• Steering gears
• Universal joints

The drive shaft of a rear-wheel drive vehicle typically has at least eight needle bearings (four in each U joint). Ball thrust bearings: These bearings are designed to handle thrust loads in low-speed low-weight applications. They cannot handle much radial load. For example, barstools make use of ball thrust bearings to support the seat. Turntables also use this type of bearing.

Roller thrust bearings: 

Roller thrust bearings, like ball thrust bearings, handle thrust loads. The difference lies in the amount of weight the bearings can handle, Roller bearings can support much larger amounts of thrust coatings can support much in car transmissions, where they are used to support helical gears. The helical gears are angled which causes a thrust load that must be supported by a bearing, Gear support in general is a common application for roller thrust bearings.

Journal bearings: 

These bearings are sometimes called friction bearings. These are simple bearings in which the crankshaft (journal) rotates in the bearing with a layer of oil separating the two parts. These bearings are usually used inside engines and are very efficient when the engine is operating at high RPM and with good oil pressure. These bearings do not work well at low RPM.

These are cylindrical or ring-shaped bearings designed to carry radial loads. The simplest and most widely used bearings are cast-bronze and porous-bronze (powdered-metal) cylindrical bearings. Cast bronze bearings are oil-, or grease-lubricated. Porous bearings are impregnated with oil and often have an oil reservoir in the housing.

Specialized bearings: 

There are several kinds of bearings that are manufactured for specific applications. For example, magnetic bearings are found in high-speed devices, because they have no moving parts. Giant roller bearings are used to move extremely large and heavy loads, such as buildings and large structural components.