Types of Bearings

   

                                   What is a Ball Bearing ?

A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races.

The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit the loads through the balls. 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 the balls are rolling they have a much lower coefficient of friction than if two flat surfaces were sliding against each other.

                  What Is the Purpose of Bearings?

The main purpose of bearings is to prevent direct metal to metal contact between two elements that are in relative motion. This prevents friction, heat generation and ultimately, the wear and tear of parts. It also reduces energy consumption as sliding motion is replaced with low friction rolling.

They also transmit the load of the rotating element to the housing. This load may be radial, axial, or a combination of both. A bearing also restricts freedom of movement of moving parts to predefined directions as discussed above

Advantages of ball bearings:

• Good wear resistance
• Do not need much lubrication
• Provide low friction, thus little energy loss
• Long service life
• Easy to replace
• Small general dimensions
• Comparatively cheap
• Can handle thrust loads

Disadvantages of ball bearings:

• May break due to shocks
• Can be quite loud
• Cannot handle large weights

                      Types of Bearings

                             Roller Bearings

                                                     

Roller Bearings are mechanical assemblies that consist of cylindrical or tapered rolling elements usually captured between inner and outer races. They provide a means of supporting rotating shafts and minimizing friction between shafts and stationary machine members. Roller bearings are used primarily in machinery with rotating shafts that require the support of heavier loads than ball bearings provide. Tapered roller bearings are often used to accommodate higher thrust loads in addition to the radial loads. Types range from cylindrical to spherical rollers. Roller bearings are standardized like ball bearings, albeit to a lesser degree. Considerations include

• Higher load capacities than ball bearings
• Can withstand high axial loads

                            Mounted Bearings

Mounted Bearings are mechanical assemblies that consist of bearings housed within bolt-on or threaded mounting components and include pillow blocks, flanged units, etc. They provide means of supporting rotating shafts and minimizing friction between shafts and stationary machine members. Mounted bearings are used primarily in machinery with exposed rotating shafting. They are used as take-up devices on the ends of conveyors and as flanged units along intermediate points. The bearings can be rolling element or journal bearing configurations. Mounted bearings are designed for bolt-on mounting and ease of replacement. Other varieties of mounted bearings include rod end bearings and cam followers. Considerations include

• Housed units reduce mounting concerns, protection issues
• Cartridge designs ease replacement
• Shafts usually held in place with set screws
• Allow adjustment of the supported components
• Mainly used for low/mid speed applications

                              Linear Bearings

Linear Bearings are mechanical assemblies that consist of ball or roller elements captured in housings and used to provide linear movement along shafts. Linear bearings are used primarily in machinery that requires linear movement and positioning along shafts. They also may have

secondary rotational features depending on the design. Considerations include

• Lower friction and higher accuracies compared with bushings
• Costlier and more complex than bushings

                                Slide Bearings

Slide bearings are mechanical assemblies designed to provide free motion in one dimension between structural elements. Slide bearings are used primarily in the structural support of bridges as well as commercial and industrial buildings. These parts accommodate thermal movement, allow for end-beam rotation, and isolate components of the structure against vibration, noise, and shock. Other types of slide bearings include those used on truss base plates, heat exchangers, and process equipment.

                             Jewel Bearings

Jewel bearings are mechanical devices used in light rotating applications such as watches, meter movements, gyroscopes, etc. where loads are small and the supported rotating shafts are tiny. Jewel bearings are constructed from a range of synthetics, with ruby and sapphire being particularly common. 

                        Frictionless Bearings

Frictionless bearings are mechanical or electro-mechanical alternatives to conventional bearings that provide controllable shaft support through air, magnetic fields, etc. for critical, high precision applications. 

        Applications and Industries

Bearing applications span across virtually every industry which employs moving components and equipment. For example:

• Ball and roller bearings are used in machinery of all kinds, from boiler feed pumps to automotive transmissions.
• Mounted bearings are especially common on conveyors, in shaft linkages, and particularly where long lengths of shafting must be supported by housed units where the bearing is not protected by another housing such as a transmission case.
• Linear bearings are used exclusively in linear applications such as slide tables.
• Slide bearings are used primarily for load-bearing application in large civil engineering projects such as bridges where they accommodate a limited range of movement, unlike the other bearings here, where motion—either radial or linear—is the main concern.
• Jewel bearings are restricted to very small devices and movements and do not rely on any rolling elements.
• Frictionless bearings are any of the other special-purpose designs that include air bearings, magnetic bearings, etc.

While bearings are used nearly everywhere, there are some industries that use so many or have specific requirements for durability, cleanliness, etc. that they warrant mentioning here. Some of these industries are:

• Aerospace
• Agricultural
• Automotive
• Machine Tools
• Medical
• Mining

                 Considerations

When selecting a bearing for a particular application, there are several considerations to keep in mind, including bearing friction, temperature, and lubrication. Along with the specific design and construction of the bearing, these three interacting factors can affect the overall performance.

  Important Attributes In Selection

Bearing Type

For ball bearings, the Conrad, or non-slot fill bearing is the most common, whose design dispenses with a filling slot and instead relies on displacing the inner race to load the balls and a cage to keep them evenly spaced. For roller bearings, bearing type requires a selection of roller type, be it cylindrical, tapered, spherical, etc. Mounted units require a type selection of ball, roller, or spherical, as well, and then an additional selection of style, as defined below. Linear bearing types range from ball bearing cages—essentially bare cages holding balls that are often used as die-post bushings—to recirculating ball designs where the balls roll linearly along the shaft and then return to their starting points through channels on the non-shaft sides of the bearings.

Style

This attribute applies solely to mounted units, where a distinction must be made between the housing for the bearing, among them the choice of pillow blocks, flanges, take-ups, etc.

Material

Material choice for ball and roller bearings is generally limited to a few specialty steel alloys, some plastics, occasionally ceramics, etc. while mounted units have more material choices owing to the additional materials available for housings.

Seal/Shield

Ball bearings exposed to the environment can be ordered with seals and/or shields where shields provide some protection of the bearing elements from dirt ingress with minimal added friction and seals provide shaft contacting lips that exclude moisture but do add to the friction on the bearing. Seals and shields can be added on both sides, either side, alone or in combination. The image to the right shows a radial bearing in cross section with shields on both sides.

Race

Ball bearings races fall generally into two designs: angular contact and radial. Angular contact bearings (image right) load the balls at angles to the perpendicular radial planes, whereas radial contact bearings (image above) load the balls through the perpendicular planes. Angular contact bearings are generally preferred where axial loading is a consideration. Deep groove bearings are commonly associated with radial contact bearings. Cup and cone bearings are common on bicycle wheels where the bearings are loosely packed between cones and the cones are adjusted for play.

Locating

Mounted pillow block units are classified as expandable and non-expandable and in situations where two are more pillow block bearings are installed for shaft support one will ordinarily be specified as non-expandable and the other as expandable which allows the bearing to accommodate slight growth of the shaft. Some units are configured to allow either option.

Maximum Static and Dynamic Loads

Bearing loading is based on static and dynamic values and the choice of which governs is a function of the operating conditions the bearing will see.

                                            CONCLUSION

 So, I hope you all have understood much about Ball Bearings and it's different types. Thank you very much for giving this precious time of yours.

Authors: Arya Kokare, Piyush Kolhatkar , Akshay Khubchandani , Shreyash Khandwe,Harsh Khandelwal,Vaibhav Khandagle

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