Designing Deep Groove Ball Bearing Applications: Finding the Optimal Lifespan

There are many factors to consider when choosing a bearing for your application. Besides the load and size requirements, you also need to think about how long the bearing needs to last in your specific industry or application type.

To estimate the service life of a bearing, you can use the L10 calculations. But that’s not enough. You also need to make sure that the bearing design meets the end-user’s expectations for durability.

In this article, you will learn about considerations for design life and the different variables that affect bearing life. Additionally, you’ll learn how to determine how many hours of operation you should aim for from your bearing selection. Using this information will help you design mechanical systems that last longer and perform better.

Industry Guidelines

When determining the number of hours of rating life to design for with deep groove ball bearings, industry guidelines can provide valuable reference points. Meeting or exceeding recommended design life should be considered foundational for ensuring the satisfaction of your eventual end users.

Keep in mind that individual industries will have customers with different expectations of reliability. For instance, some industries will have end users that expect to rebuild their equipment on an annual basis. In other industries, users may expect 5 or even 10 years of service before replacement parts are required. Because of this, it becomes important to know and adhere to the common expectations of the industry you’re designing for. 

Below is a table showing general examples of target design life according to application.

Application	Design Life (hrs.)
Motors
Very Small Motors	1,000 – 2,000
Small Motors	8,766 – 15,000
Medium Motors	20,000 – 40,000
Large Motors	43,830 – 60,000
Specific Application Examples
Agricultural equipment	3,000 – 8,000
Beater mills	20,000 – 30,000
Briquette presses	20,000 – 30,000
Grinding spindles	1,000 – 2,000
Machine tools (machinery)	10,000 – 30,000
Mills – Small Cold	5,000 – 6,000
Mills – Large Multipurpose	8,000 – 10,000
Mining machinery	4,000 – 15,000
Paper machines	50,000 – 80,000

Quick Calculation Table

If you’re far enough along in your design process to know the load that will be imposed on your ball bearing, then the C_r/P factor chart (below) can save a lot of time in the selection process. We’ve designed the chart to allow engineers the ability to skip the L10 calculations for common machinery and speeds. This chart will help you determine the dynamic load capacity required of your bearing selection in order to achieve the service life desired.

Remember that your desired service life should adhere to the expectations of your industry. Also, note that the life hours are equal to hours of actual operation.

So how does the table work? It’s simple. The C_r/P factor should be multiplied by the imposed load on your bearing. The resulting number is the dynamic load capacity required of your bearing selection. Let’s walk through an example.

Step 1: Find your desired service life on the left side of the chart. Let’s say we’re designing for a “General Industrial Application” and we want it to be quite reliable. The chart suggests that we should design for 40,000 hours of service life.

Step 2: Locate the RPM of the application across the top of the chart. Our example bearing will be rotating at 1200 RPM.

Step 3: Follow the row and column until they intersect to locate your C_r/P Factor. 40,000 hours and 1200 RPM intersect at a C_r/P Factor of 14.2

Step 4: Multiply your C_r/P Factor by the load that will be imposed on your bearing. In this example we will use an imposed load of 100 lbs. So our calculation would look like this: 
14.2 x 100 = a required dynamic load capacity of 1,420 lbs.

Step 5: Review catalogs for bearings that have a dynamic load capacity that meets or exceeds the number calculated in Step 4. A bearing with a dynamic load capacity of 1,420 lbs. or more will be likely to have a service life that meets or exceeds the desired 40,000 hours of operation.

NOTE: This chart is intended to give engineers a quick tool for bearing selection and should not be considered a guarantee of service life. Several factors can shorten the service life of a bearing including improper installation, lubrication, or handling.

Variables to Consider

Several variables should be considered when deciding on the number of hours of rating life for a deep groove ball bearing. These factors play a significant role in determining the optimal lifespan and reliability of the bearing within your specific application. Here are some key variables to take into account:

1. Type of application: C_r/P tables and L10 Calculations can’t account for things like missed maintenance or particle contamination. It’s wise to consider the probability of these issues in your specific design. Considering operational temperatures, lubrication intervals, and contamination are recommended.
2. Reliability expectations: The guidelines for design life may not match the reliability expectations of your targeted users. It is recommended that you double-check the specifics of your industry to ensure the accurate use of the tables above.
3. Warranty timelines: Ensure that you have a very clear understanding of the warranty policies of your company. Typical service life calculations may not clear your company’s warranty period so your own designations for desired service life may be required.
4. Frequency of use: Because life hours are equal to hours of operation, remember to consider how the design life hours will translate into the yearly calendar. An industry that only uses their equipment part-time will require fewer life hours to clear a calendar year than equipment that operates continuously.

By carefully considering these variables, engineers can make informed decisions about the number of hours of rating life to design for in a deep groove ball bearing application. It’s important to remember that these variables are interconnected. A comprehensive understanding of the application’s demands will optimize the bearing selection for longevity and reliable performance.

Bearing Service Life Is a Key Factor in Mechanical Design

Selecting the appropriate service life for deep groove ball bearings is a critical aspect of engineering design. By considering factors such as the application you are designing for and reliability necessary, you can quickly dial into options using the C_r/P chart. 

Remember, proper installation and maintenance are equally important for maximizing bearing longevity. Armed with these insights, you are well-equipped to make informed decisions and design mechanical systems that stand the test of time.