Bearing

         The bearing in its current form was developed towards the end of the 19th century. It was initially made by hand.

Nowadays, bearings are one of the most commonly used machine parts because their rolling motion make almost all movements easier and they help reduce friction.

 

Rolling bearings are machine elements and serve to support shafts and axles. Depending on their design, they absorb radial or axial loads and simultaneously enable rotation of the shaft or the components mounted on an axle. The force is transmitted via spherical or roller-shaped rolling elements. The advantages include the following points:

• low friction even when starting from standstill.  
• low cooling and lubrication requirements, grease lubrication usually sufficient. 
• radial, axial and combined loading capacity achievable with little effort. 
• almost backlash-free or preloaded operation possible. 
• rolling bearings are available worldwide as ready-to-install standard part series

 

Rolling bearings and sleeve bearings

In a sleeve or plain bearing, the axle and the bearing move in opposite directions on a sliding surface. By contrast, the two components of a rolling bearing that move towards one another – the inner and outer rings – are separated by rolling elements. This design generates significantly less friction than a sleeve bearing.

Radial bearings and Axial bearings

Bearings can transmit loads in a radial direction or an axial direction and in many cases there is a combination of both radial and axial loads to transmit.

Both designs are available as ball bearings or roller bearings. The choice of bearing design depends upon the application in question.

Bearing Types

Rolling bearings are divided into different bearing types and designs. Based on the ball bearing which represents the starting point, the starting point for the technical development of rolling bearings, today there are a large number of bearing types used for very specific operating conditions. Any design of a rolling bearing, however, will be a technical compromise determined by a wide variety of criteria. Rolling bearings are selected according to:

• the available installation conditions, 
• the type and extent of the load,   
• speeds or motion cycles in general,   
• the required guidance accuracy of the machine and plant components, 
• the rigidity of the bearings,   
• the ambient conditions,   
• the installation and removal options

A part from the technical parameters of a rolling bearing, such as static and dynamic load carrying capacity and permissible speeds, the bearing clearance or preload, the appropriate cage modification and the required lubrication method must be considered when selecting the bearing type.

 

Components

Bearings usually consist of the following components:

·         Two rings or discs with raceways

·         Rolling elements in the form of rollers or balls

·         A cage which keeps the rolling elements apart and guides them

 

Inner Ring / Outer Ring

The inner and outer ring are usually made from a special high-purity, chrome alloy steel. This material has the necessary hardness and purity – both important factors for a high load rating and a long service life.
Special materials such as ceramic and plastics are also used. Although plastics cannot withstand extremely high temperatures, they are considerably lighter than steel. This makes them invaluable in sectors such as the automotive industry, where every gram matters.

 

Rolling Elements

Rolling elements are either balls, rollers, cones, spheres or needles. They are usually made from a special high-purity, chrome alloy steel. Special materials such as ceramic and plastics are also used.

The rolling elements roll on the specially formed raceways of the rings or discs and are kept apart and guided by the cage.

 

Cage

The cage is responsible for keeping the rolling elements apart and guiding them. The materials used include steel, brass and plastic. Solid metal cages can be produced using machining techniques, while pressed cages are made from sheet metal. Similarly, plastic cages can be machined from solid plastic or injection moulded.

 

Bearings Prefixes & Suffixes

*Prefixes are mainly used to identify bearing rolling component.

*Suffixes identify special designs, variants & characteristics, which differ in some way from the original design or from the current basic design

Bearing suffix:

• Z. Steel shield on one side of bearing

• 2Z Steel shields on both the sides of bearing

• ZZ Rubber shields on both the sides of bearing

• K Tapered bearing bore in the ratio of 1:12

• W33: Lubricating groove and 3 holes on outer race

• W33X Lubricating groove and 6 holes on outer race

• C3 Normal bearing clearance (Clearance more than C2)

• C4 More bearing clearance (Clearance more than C3)

• J Pressed steel cage

•F Machined steel cage

Bearing Can be Identified based on their starting nos 

• Ball bearings No’s start with 1&6.
• Spherical roller bearings 2
• Angular contact bearings 7
• Taper roller bearings 3
• Cylindrical roller bearings start with NU

 

Bearing Fail Reasons.

• Over lubrication. 
• More or less bearing clearance 
• Jerk loads.
• Bearing manufacturing defects.
• Operating bearing at higher vibration and temperature for long time.
• Wrong methods of bearing installation. 

Bearing Clearance 

Bearing clearance is the clearance or gap between outer race or inner race and rolling elements. And in journal bearings it is the clearance between shaft and bearing liners

Calculate the bearing clearance of bearing having bore diameter D 

As a thumb rule Bearing clearance minimum = 0.00185 X D

Bearing clearance maximum = 0.00254 X D

 

 

 

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