Factors to Consider When Sizing a Deep Groove Ball Bearing

Are you on the hunt for a deep groove ball bearing but finding it difficult to begin determining necessary considerations? Look no further! In this article, we delve into the key considerations that should be taken into account when sizing deep groove ball bearings, ensuring a proper fit and maximizing the lifespan of your bearings. 

Deep groove ball bearings are widely used in various industries, playing a critical role in enabling smooth and efficient rotational motion. These versatile bearings are designed to handle both radial and axial loads, making them essential components in a vast array of applications.

Selecting the appropriate size for a deep groove ball bearing involves careful evaluation of various factors including nominal dimensions, load ratings, internal clearance, and limiting speeds. Understanding the application requirements and considering the specific operating conditions, you can ensure optimal performance, reliability, and longevity of the bearing.

While starting with size constraints of the equipment or application you are designing is a solid first step, there are several other critical factors to explore. In this article, we will go over nominal dimensions, load ratings, internal clearance, and limiting speeds.

Nominal Dimensions

First and foremost, your deep groove ball bearing (or 6000 series bearing) needs to fit where it’s going to be installed. If it doesn’t fit, it won’t work. Plain and simple. Manufacturers catalogs provide a bearing’s dimensions and should be the “go-to” for referencing when it comes to a size guide. Find ours here! In order to get started on sizing your 6000 series bearing, you will need a basic understanding of how to measure a bearing and how nominal dimensions work.

Nominal dimensions are the sizes used to describe the approximate characteristics of a bearing rather than the exact dimensions.

Here are the most commonly measured and referenced parts of a bearing:

• Inside diameter (or ID) is the diameter of if the inside of the bearing bore
• Outside diameter (or OD) is the diameter outermost ring of the bearing
• Width or length through bore (LTB)

These measurements are typically what you will find in a manufacturer’s catalog and are most commonly used to describe a bearing’s dimensions. 

Many bearings are manufactured to the metric system and are measured in millimeters. You can easily convert a measurement knowing that 1 inch = 25.4 mm. For example – a bearing with a bore size of 45mm is 1.7717 inches (45 ÷ 25.4 = 1.7717). 

Establishing nominal dimensions of possible options for your deep groove ball bearing is a great start to unlocking the perfect fit for your deep groove ball bearing. Next up, we will dive into load ratings.

Load Ratings

It’s not just about fitting; the imposed loads on the bearing are equally important. Selecting a bearing solely based on fit may lead to failure and damage if it cannot withstand the loads it encounters. To address this, thoroughly review the manufacturer’s catalogs for information on dynamic and static load ratings. Bear in mind that opting for a high-precision bearing won’t increase its load capacity. Instead, a bearing’s load capacity depends on the material it’s constructed from, size of rolling elements and other factors. 

Consider selecting a heavier cross section or double row ball bearing if your ball bearing’s load capacity is too low. For example – moving from a 6000 series to a 6200 series. This increases the load rating but also changes the OD and overall width of the bearing. Be sure to double check that the nominal dimensions of the application design are compatible with the dimensions of the double row ball bearing.

Once you have determined that the bearing fits and is capable of withstanding the imposed loads of your application. The next step is getting more familiar with internal clearance. 

Internal Clearance

What does internal clearance actually mean? Internal clearance is the amount of internal free movement before installation. It allows a small amount of displacement in either the inner ring or outer ring depending on which one is in a fixed position. This displacement can occur in either a radial or an axial direction. These are called radial internal clearance and axial internal clearance. Although axial internal clearance may not be listed, due to geometry, for ball bearings axial clearance can typically be assumed to be around 8-10 times the radial clearance. 

Bearings manufactured with higher internal clearances allow for higher interference fits (when there is an interference between the bearing ring and its mating part) in the housing or on the shaft. This prevents friction and creates room for heat expansion.

It is important to note that not all applications benefit from more internal clearance. High precision applications such as wood planers do not allow for much wiggle room because the consistency would be compromised. 

Excess internal clearance can be avoided by increasing the press fit. Increasing the press fit is done by increasing the interference fit of the installation to minimize the internal clearance.

In the majority of high-precision applications, reduced running or even preload is needed to enhance system rigidity but some other potential reasons to have reduced running clearance or preload in a bearing include:

• Enhanced stiffness
• Reduced noise level
• Improved shaft guidance
• Elimination of issues cause by too much clearance
• Improved running accuracy
• Prevent skidding in high-speed applications during rapid starts and stops and under very light or no-load conditions

The key is to select a bearing with an internal clearance closest to the application’s needs. Does the shaft need room to expand? If so, a higher clearance bearing is likely to be required. Does the application require high precision and high rigidity? If so, less internal clearance will most likely do the trick.

Clearance ratings (or C codes) determine the amount of room for expansion there is between the races of the bearing. The clearance ratings are measured in the following scale:

• C1
• C2
• C0 or CN
• C3
• C4
• C5

C0 or CN are considered to be the “normal” clearance rating. However, C3 is more commonly found and is a better fit in a large variety of applications. Because of this, C3 has become more of the industry standard. Some bearings are not marked with a C code. Most of the time, those bearings are rated C0/CN. 

Clearance ratings are an important aspect to consider when sizing deep groove ball bearings because they allow “wiggle room” and room for expansion. This helps avoid premature failures and damage.

Limiting Speed

With fit, loads, and internal clearance addressed, it’s time to consider the limiting speed of your deep groove ball bearings. The manufacturer’s catalog or website typically provides the limiting speed or speed ratings. It is crucial to operate your application below the listed speed rating to avoid bearing failures and damage.

Determining factors of a bearings limiting speed are: cage style and material, any contact seals that are installed on the bearing, ABEC rating, and the kind of lubrication used inside of the bearing. For example – a bearing using grease will have a lower limiting speed than one using oil. Likewise, a bearing with a lower ABEC rating will have a lower limiting speed as opposed to one with a high ABEC rating. 

In the case of 2RS (2 rubber seals), the seals make contact with the inner ring of the bearing which creates drag and extra friction. This lowers the limiting speed for 2RS bearings.

Speed ratings and rotational speed are in their own category but should also be considered when selecting clearances as the two work hand-in-hand. The faster a bearing spins, the more heat it generates. Clearance is a great way to dissipate heat in most cases. 

Selecting a lubricant compatible with your bearing’s limiting speed and operating temperature is essential for smooth operation and a prolonged lifespan. Fast-moving parts generate friction and heat that can quickly degrade lubrication. Always find a lubricant that matches your bearing’s temperature and speed ratings.

ABEC tolerance categorizes a bearing’s speed rating, offering classes of odd numbers ranging from 1 to 9. Higher ABEC ratings indicate tighter tolerances, resulting in better precision, higher efficiency, and suitability for high-speed applications. However, it’s worth noting that higher precision bearings only affect the limiting speed, not the load capacity. Consequently, they are more expensive and unnecessary for every application. Be mindful not to overspend when you are sizing your deep groove ball bearing!

Limiting speeds help prolong a bearings life by reducing operating temperatures, drag and friction and should always be considered when sizing deep groove ball bearings.

Conclusion

Selecting a deep groove ball bearing involves careful evaluation of various factors including nominal dimensions, load ratings, bearing clearance, and limiting speed. By understanding the application requirements and considering the specific operating conditions, engineers can ensure optimal performance, reliability, and longevity of the bearing.

Designing applications involves numerous moving parts, but understanding the critical factors involved in the decision-making process is key. Using the considerations we discussed will help you when choosing your deep groove ball bearings. Additionally you can consider the lubrication method, bearing material, and sealing options to further enhance the overall performance and service life of the deep groove ball bearing.