How to choose bearing size

Navigate the intricacies of bearing selection with this guide. Exploring the Bearing Size Chart, delve into size choices for rating life accuracy, static load, runout, rigidity, and environmental factors.

Bearing Size Chart

6000 Series Metric Bearing Size

6200 Series Metric Bearing Size

6300 Metric Bearing Size

6700 Series Bearign Size

6800 Series Bearing Size

6900 Series Bearing Size

600 Metric Series Bearing Size (Flanged)

MR Metric Series Bearing Size

1600 Metric Series Bearing Size

60/22-63/22 Metric Series Bearing Size

Miniature Bearings Bearing Size

Double Row bearings Bearing Size

Wide Bearings Bearing Size

Self-aligning Bearing Size

8700 Series Bearing Size

Why so many sizes?

Size is dependent on shaft size and application needs, as mentioned above. Since the size of a ball bearing has a significant effect on its performance and capacities, several sectors make use of bearings of varying sizes.

In general, the load capabilities of smaller bearings are lower. Space efficiency, rather than load capacity, is the primary consideration in their use. For very tiny applications, such semiconductor equipment, medical apparatus, or robots, miniature bearings—typically made as precise ball bearings—are used. Conversely, bearings with a wider diameter can support heavier loads. Heavy power tools, agricultural machinery, and mining and drilling equipment all make use of these. In addition, several companies provide the option to have bearings made to a specified size for those rare and unusual applications.

Size selection based on rating life

We need to calculate the basic rating life L10 and SKF rating life L10M for the bearing. This is based on the needed bearing life, which takes into consideration the probable impacts of rolling contact fatigue.

Consider the impact of rolling contact fatigue (RCF) when deciding on the right bearing size for a given application where the bearings will be running under normal operating conditions, such as normal speeds and good lubrication, and not under extreme or peak loads.

This section details the assessment criteria and the formulas for bearing rating life:

• The L10 or SKF rating life of a bearing is based on this fact.
• Efficient dynamic load rating base
• P, the dynamic bearing load equivalent
• A component that alters one’s lifestyle
• The consistency of the lubricant – the ratio of viscosity, κ
• Limit of fatigue load, Pu
• Partially contaminated, or ηc

Size selection based on accuracy

Dimensional Accuracy

Bearing dimensions may be accurately assessed by measuring the bore diameter (d), inner ring width (B), and outer ring width (C). The term “dimensional deviation” is used to characterize the discrepancy between a bearing’s real and nominal dimensions. Common metrics include the average of the inner and outer ring widths (ABs and ACs), the average of the bore and outer diameters (Admp and ADmp) on a single plane, and other similar metrics.

Machining Accuracy

Is a measure of the discrepancy between two measurements of the same bearing that causes the aforementioned example dimensions to vary. Since they take an average of the changes in both the inside and outside diameters in a single plane, Vdmp and VDmp are the most used measurements. VCs and VBs aren’t as common, but they’re still useful for measuring changes in ring width (both inside and out). A series variation’ is its range of values, but an observation’s “mean variation” is its average range of values across the observational period.

Running Accuracy

The eccentricity, also known as radial runout, and squareness, which are assessed by running accuracy, are two aspects of a bearing.

The internal and external radial runouts, Kia and Kea, respectively, are included into the shared measurements. Be careful while running to avoid assembly misalignment and vibration.

Size selection based on static load

This requires finding the static safety factor s0 and considering the possible effects of permanent deformation, which is based on the static load capacity of the bearing.

If any of the following are present, you must take permanent deformation into account when choosing or checking the bearing size:

• High loads are applied to the non-rotating bearing either continuously or intermittently in the form of peak loads.
• The bearing exhibits tiny, unpredictable motions when subjected to a load.
• Bearings undergo both continuous, normal operating loads (as measured by fatigue life-dimensional analysis) and transient, extraordinarily high peak loads (WHPT) as they spin.
• Due to the bearing’s low rotational speed (n < 10 r/min) while under load, its lifespan is short. If, for a given equivalent load P, the rating life equations yielded an extraordinarily low required basic dynamic load rating C, then a fatigue life-based bearing would be grossly overloaded while in service.

This kind of deformation can cause the rolling elements to flatten or the raceways to develop indentations. You have the option of evenly spacing the indentations across the raceway or scattering them at random. The spacing should correspond to the spacing of the rolling elements. Stationary or slowly oscillating bearings that support loads big enough to induce permanent deformation will generate significant vibration and friction when subjected to continuous rotation. Alterations to the fit characteristics between the housing and shaft, or an increase in the internal clearance, are other possible outcomes.

Size selection based on bearing runout and rigidity

Bearing runout is the geometric misalignment that occurs as a shaft is rotated, affecting both the center and the shaft. It is not a problem to modify the spinning components of cutting tool spindles.

Due to strict manufacturing tolerances, choosing a high-precision bearing for this application during engineering will decrease system runouts.

Bearing rigidity—the resistance to the force that causes the shaft to move—is essential for reducing shaft runout. When the rolling element hits the racetrack, the bearing stiffens. Pressure on the rolling element generates elastic deformation and rigidity.

Conventional bearing stiffness classifications include:

• Radial rigidity

• Axial rigidity

High bearing stiffness requires more force to move the shaft.

Precision angular contact bearings will be examined first. These bearings commonly have offset inner and outer raceways. The offset is reduced by inserting angular contact bearings, enabling the balls to press into the raceway without external effort. Preloading stiffens bearings before application forces.

Size selection based on the environment

Standard Conditions (Normal Load, Speed, and Temperature):

• In most cases, activities with relatively low loads, speeds, and temperatures should be perfectly fine using metric bearings from the 6000, 6200, or 6300 series. These shows typically have a massive fan base.

High-Speed Applications:

• Selecting bearings from the 60/22-23/22 Metric Series or designated high-speed versions of the 6000 or 6200 series is advised for applications necessitating operation at high speeds.

Heavy Load Applications:

• For uses involving higher axial or radial stresses, bearings from the 6700, 6800, or 6900 series might be an excellent choice. Heavy weights are usually no problem for this series.

Miniature Size Requirements:

• For applications where space is at a premium, the MR Metric Series and Miniature Size Bearings are ideal choices for small bearings. Their intended usage is in small applications.

Flanged Bearings:

• In cases where more axial stability is required, flanged bearings from the 600 Metric Series are an excellent choice.

Double Row Bearings:

• A bearing with two rows of rollers is a good option when you require a strong and durable one that can handle heavier loads. The 5200, 5300, and additional series are available as well.

Self-Aligning Bearings:

• The self-aligning 2200 or 2300 series of bearings can be useful in cases where shaft misalignment is expected.

Harsh Environments (Contaminants, Moisture):

• If your application is exposed to difficult conditions caused by pollution, dampness, or chemicals, it may be worth investigating bearings with specific coatings or seals. When it comes to protecting themselves from environmental threats, certain series may fare better than others.

Wide Bearings:

• Consider using bearings with tailored coatings or seals in situations where chemicals, humidity, or pollution pose a threat to your application. It is possible that certain species are more equipped than others to deal with threats encountered in the wild.

Specialized Applications (8700 Series, 16000 Series):

• Bearings from the 8700 or 16000 series, for instance, could work for certain jobs. Among these, the 8700 series stands out for its extraordinary endurance in harsh environments.

Temperature Extremes:

• Bearings made of heat-resistant materials or lubricants designed to withstand high temperatures should be considered for uses where temperatures may reach dangerous levels.

Corrosive Environments:

• In areas prone to corrosion, it could be required to use bearings made of or coated with materials that resist corrosion.

What issues arise from mismatched bearing sizes?

Incompatible bearing sizes can cause uneven load distribution, friction, heat, vibration, shaft and housing damage, less precision, higher energy consumption, installation hassles, higher operating costs, catastrophic failure, difficulty finding replacement parts, less warranty coverage, and safety risks. Choose the right size bearing to avoid these issues.