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Basic Concepts of Rolling Bearings - Comprehensive Guide

This guide mainly introduces some basic concepts of rolling bearings: the definition of rolling bearings, the basic structure of rolling bearings, the names and roles of the components that constitute rolling bearings, some of the main dimensions of rolling bearings, the definition of terminology and parameter symbols, the level of tolerance and the grouping of the clearance, as well as the main features of rolling bearings and the basic requirements.China Roller Bearings Manufacturers.jpg

Basic Structure Of Rolling Bearings - Components

Today, bearings are one of the most commonly used machine components because their rolling motion makes almost any movement easier while reducing friction.

What is the primary function of a bearing?

  • Transmitting motion, i.e., they support and guide parts that rotate relative to each other.

  • Transmission of forces

Rolling bearings are critical essential elements widely used in all types of machinery. The International Organization for Standardization (ISO) defines roller bearings as components that facilitate rolling motion (as opposed to sliding movement) between parts experiencing loads and relative motion. These components encompass features with rolling tracks and rolling elements, with or without isolating or guiding elements.

Rolling bearings generally comprise an inner ring, an outer ring, a rolling element and a cage (Figure 1-1). In thrust bearings, the collar that fits with the shaft is called the shaft collar, and the collar that works with the housing or shell is called the seat collar (Figure 1-2). Because grease has a significant impact on the performance of the bearing, industry experts also say that the bearing consists of five major components, including oil.

The structures of radial bearings

The structures of thrust bearings

The inner ring is usually mounted on the shaft and rotates with the post; the outer ring usually plays a supporting role in the housing of the bearing or the shell of the mechanical parts, but in some applications, there are cases in which the outer ring rotates, the inner circle is fixed, or the inner and outer rings both rotate. 

What types of rolling elements are included in rolling bearings?

Rolling body rolling between the inner ring and outer ring, the type of ball, cylindrical roller, needle, tapered roller, spherical roller, etc., the size and number of the rolling body directly affect the bearing capacity. Keep frame will bearing rolling body isometric separation of a group, guide the rolling body in the correct track movement, and improve the bearing internal load distribution and lubrication performance.

1699777002114147.png  Ball  Ball bearing
 1699777135994053.png  Cylindrical roller  Roller bearing
 1699777157131727.png  Needle roller
 1699777176775655.png  Tapered roller (tapered trapezoid)
 1699777195245013.png  Convex roller (barrel-shaped)

How are common rolling bearing structures often represented?

In the bearing industry, the common terminology for components is: "01" usually denotes the outer ring, "02" denotes the inner circle, "04" indicates the rolling elements, "46" means the solid cage guided by the rolling elements, and "07" relates to the filled groove cage.

In practice, certain bearings may comprise more or fewer components to fulfil a specific field of application. Examples include bearings without inner or outer rings, bearings with neither inner nor outer rings (replaced by matching parts of the host machine such as shafts or housings), bearings without cages, or bearings equipped with sealing caps, seals and mounting adjustment locking devices.

With the continuous innovation of bearing technology, the trend of modularization and unitization of bearings is becoming increasingly obvious. A bearing unit is an integrated assembly of bearings and related components. Examples include automotive wheel hub bearing units, machine tool spindle bearing units and ball screw spindle bearing units. These units include bearings, housings and sometimes spindles. The selection of a spindle bearing unit depends on factors such as the type of machine tool, size, mounting method, accuracy, stiffness and mounting requirements.Bearing assembly.jpg

What are the types of rolling bearing cages?

What is a bearing cage?

Cages (also known as rolling element retainers) can play various roles in the normal operation of rolling bearings. The cage separates the rolling elements and avoids contact and wear between the rolling elements. The cage aligns the rolling elements on the raceways of the inner ring, preventing them from slipping, sliding or tilting and ensuring pure rolling. From the mounting point of view, the cage keeps the rolling elements on the inner ring to facilitate bearing mounting. Cages can also improve the lubrication of bearing raceways or retainer contact surfaces in some cases.

The following sections discuss the types of cages commonly used in each major bearing design (tapered, cylindrical, spherical, and ball bearings). Each cage type's basic geometry, materials, and manufacture are also discussed.

Types of bearing cages.jpg

1. Tapered roller bearing cage

Tapered roller bearing cage.jpgSteel Stamped Steel Cage - Tapered roller bearings are commonly used in a steel stamping frame-type cage. This cage selects low-carbon steel plates through mass production cutting, moulding and stamping processes. The stamping cage depends on mould processing; the product has high precision and interchangeability. The cell is highly efficient in production and can reduce the product's manufacturing cost. This cage type can be used in environments with high temperatures and harsh lubrication conditions.
100000264.pngPolymer Cage - Tapered roller-bearing cages made of polymer materials are mainly used in lubricated and self-sealing bearing assemblies. Typical polymer materials are nylon thermoplastic reinforced with glass fibres. Polymer cages can be produced in large quantities and offer greater design flexibility than steel-stamped cages. Polymer cages are lighter in weight and easier to assemble in production. In some applications, adding one or two rolling elements can be realized to increase the load rating of the bearing. However, there are temperature requirements, and generally, the temperature rise cannot exceed 107℃.
ba8ac7ea-b3f5-43aa-9d4e-d2107086f355.jpg_640xaf.jpgMachined Cage - Tapered roller bearings machined cages are of reinforced design, which can be used in high speed and heavy load conditions. The machined cage material can be alloy steel through the milling dumpling hole and other process processing. Bearing the assembly cage will be simpler, and the rolling element can be embedded through the cell fixed. According to the requirements, we can add additional oil hole lubrication. This type of cage is used on fewer occasions.
100000429.jpgPin Cage - The pin-type cage of tapered roller bearings uses pins that pass through the axial holes of hollow rollers to locate the rolling bodies. Tapered roller bearings pin-type cell consists of two cage rings and a set of pins, all the pins on one side of the threaded and cage ring connection, the other side of the use of welding and cage ring connection. This cage type is mainly used to design larger tapered roller bearings (outside diameter of more than 400mm). Pin cages are manufactured from machined steel and can usually increase the number of rollers. Pin cages are limited to low-speed applications (retaining edge speeds below 20m/s).

2. Spherical roller bearing cage

200000165.jpgStamped Steel Cage - The inner ring guides this cage and runs above the pitch circle. Each cage is case-hardened (nitrided) to increase wear resistance and higher strength, allowing the bearing to operate in the harshest environments. Grooved holes in the end faces improve lubricant flow. This reduces operating temperatures and extends bearing life.
200000099.jpgPin cages - Large-diameter spherical roller bearings can be equipped with these cages. Two pin cages for each row of rollers consist of two cage rings and pins through the centre of the rolling elements. The design of the pin cages allows for an increased number of rolling features, which increases the load-carrying capacity of the bearing.
300000099.jpgMachined Copper Cages - These are made of precision machined copper. Their rugged construction provides advantages in extremely harsh applications. The open-finger design allows lubricant to easily reach all surfaces, ensuring adequate lubrication and reducing bearing operating temperatures.

3. Cylindrical roller bearing cage

Cylindrical roller bearing cage.jpgStamped Steel Cages - Stamped steel cages for cylindrical roller bearings are manufactured from mild steel through a series of cutting, forming and piercing processes. These cages are in various designs for general-purpose use in cylindrical roller bearings. A special technique is the S-type cage for Series 5200 cylindrical roller bearings, which is mounted on and guided by the outer ring retaining edge. The beams of this type of cage are recessed, uniformly isolating the rolling elements and holding them on the outer ring. Stamped steel cages are easy to mass produce and can be used in high-temperature, poorly lubricated environments.
e6316d7e-88b3-4d2e-985b-dad0afb49bb7.jpgMachined Cages - Machined cages are also available for smaller sizes of cylindrical roller bearings, usually in brass. Machined cage designs for cylindrical roller bearings can provide even better performance in demanding applications. The cages are available in one-piece or two-piece designs.
pdgRVFJnS3yTHzTZe3alIg.jpg_366xaf.jpgPin Cage - The pin cage for cylindrical roller bearings consists of two cage rings and pins through the centre of the rolling elements. This cage type is used for large-diameter cylindrical roller bearings where machined brass cages cannot be used. When using this design, increasing the number of cylindrical rollers is often possible to improve the load-carrying capacity.

4. Ball Bearing Cage

Stamped and welded steel cage.jpgStamped and Welded Steel Cage - This type of cage consists of two molded half cages welded together. This type of cage is the standard for deep groove ball bearings without filler grooves and provides high strength and rigidity while ensuring uniformity of the balls in the cage gap. It is suitable for high-temperature applications but not for applications with eccentrics.
Molded Nylon Finger Cage.jpgMoulded Nylon Finger Cage - This type of cage is a one-piece molded design. Rolling bodies snap into place. These cages are molded from nylon 66, which provides good thermal stability and moisture regulation. This cage type is used in most wide inner ring (WIR) ball bearings. The polymer can withstand continuous operating temperatures up to 250°F (120°C) and transient temperatures up to 300°F (150°C) and provides a non-corrosive, self-lubricating material that is abrasion-resistant and resistant to most solvents, oils, and greases. This type of cage can be used in eccentric applications.
Molded reinforced nylon cage.pngMoulded Reinforced Nylon Cage - This type of cage is a one-piece outer ring-guided or roller-guided cage. This cage type is molded from nylon 66 with 30% fiberglass for improved dimensional stability in wet environments. The polymer resists continuous operating temperatures up to 250°F (120°C), withstands transient maximum temperatures of 300°F (150°C), is non-corrosive, self-lubricating, and has good wear resistance.
Slippery has good abrasion resistance to most solvents, oils, and greases.

Ball Bearing Machined Phenolic Resin Cage.jpg

Machined Phenolic Resin Cage - This cage type is a one-piece design, often guided by an inner and outer ring. This type of cage is lightweight, oil-absorbent and suitable for high-speed applications. This type of cage is precision machined, which reduces the impact of the balls and cage at high speeds. However, the cage does not hold the balls during bearing handling.

Ball Bearing Cast Brass Cage.jpg

Machined brass cages for ball bearings.jpg

Brass and Steel Cages - Ball bearing cages made of brass or steel are designed for heavy-duty applications. Optional cage configurations include one-piece machined steel or two-piece riveted brass cages. Most are designed with either an inner or outer ring guide. This type of cage can be created with silver plating if desired. The silver leaf lubricates the ball-cage contact surface during startup, thus preventing ball slippage.

Main Dimensions of Rolling Bearings

The main dimensions of rolling bearings are the dimensions that determine the boundary of the bearing, indicate its contour, and the important measurements for mounting the bearing onto the shaft or shell. The main bearing inner diameter d, bearing outer diameter D, bearing width (height) degree B (H), sets of bearing width T, chamfer size r, etc., are shown below. For the internal relevant dimensions, belong to the design size, in principle, is not specified.


Metric bearing diameter (d), in the 0.6 ~ 2500mm range of 90 kinds of standard size. See the table below.

Nominal Bearing Bore d/mmStandard Inner Diameter/mmStandard of Reference
131,1.5,2,2.50.5mm interval
3103,4,…91mm interval
203520,22,25,28,30,32Standard number R20 series
3511035,40,…1055mm Interval
110200110,120,…19010mm Interval
200500200,220,…48020mm interval
5002500500,530,…2 500Standard R40 series

Features of Rolling Bearings

Although there are many types and brands of rolling bearings, and they have their inherent characteristics, compared with plain bearings, they have the following common advantages:

  • 1)The coefficient of friction of the rolling bearing is small. Thus, the friction resistance and the starting friction torque are small, and the power consumption is less;

  • 2)The external dimensions have been international standardization, serialization, generalization, suitable for mass production, good interchangeability, easy to install, dismantle and maintain;

  • 3) rolling bearing internal clearance is very small, has high processing accuracy, and can be applied by applying preload to improve bearing rigidity, which is very important for precision machinery;

  • 4) rolling bearing transmission efficiency, less heat generation, easy lubrication and maintenance, saving lubricant;

  • 5)Wide adaptable range of load, rotational speed and working temperature; a small change of working conditions has little effect on the performance of bearings;

  • 6) Generally, most types of bearings can simultaneously withstand radial and axial load, simplifying the structure.

However, rolling bearings also have certain disadvantages, mainly:

  • 1)The ability of rolling bearings to withstand loads is much smaller than that of plain bearings of the same volume. Therefore, the radial size of rolling bearings is large. Thus, the load-bearing and the requirement of the radial size of small occasions is more than the use of plain bearings.

  • 2)The vibration and noise of rolling bearings are large, especially in the late stage of use, so it is difficult for rolling bearings to be competent for occasions requiring high precision and not allowing vibration.

  • 3)Rolling bearings are particularly sensitive to foreign metal matter; once the bearing enters the foreign value, it will produce intermittent large vibration and noise, making it easy to cause early damage to the bearing.

Rolling bearings and sliding bearings, compared with the advantages and disadvantages of each, each occupy certain application occasions. Therefore, the two can only partially be replaced. However, due to the outstanding benefits of rolling bearings, rolling bearings have developed into the main mechanical support type, more and more widely used.