Matt McCormack, applications engineer for SKF gives us a little insight into what design engineers are frequently asking him. Here, he specifically focuses on the basics of the bearing selections process. With the variety of high-specialized bearing options, it can be daunting just to decide where to begin. May we suggest this article as a starting point.
This article was taken from a short presentation by McCormack and has been edited for length and clarity.
There are as many as 40 different ball bearing types, roller bearing types, plane bearing heads, journal bearing heads, bushing type. That’s just the basic families. 40 different types. And then you can go on even further in the variations of those types and of course the different sizes. You can have hundreds of thousands of different bearings to choose from. And this is just a small portion of what’s out there on the market. So it can be a little intimidating for our customers to try to understand, “well, which one do I use?”
So when we look at the central question in the center of this diagram to your right, you have bearing selection, and that’s question. How do I select this bearing? And around this central question we have in-, influencing factors. These aren’t all the factors but these are some of the most common we use. So if we start with how much load the bearings can support, that’s gonna influence what style of bearing you use. With a light load, for example, maybe we can get away with using a ball bearing.
If it’s a heavy load application, we might have to use a load bearing. Of course how fast is it gonna go? If it’s very low speeds, if it’s only a few RPM, that’s much different than the design in a bearing that can go to 80,000 RPM. It’s on the machine tool. .
And what kind of contamination is this bearing going to see? If this is a food and beverage plant application, you’re more than likely gonna see quite a bit of contamination from a washout cycle at the end of a shift. The different caustic detergents, the cleaning and killing of bacteria: that can get easily inside the bearing and damage the seal, damage the lubricant and corrode the bearing.
Does there need to be a common misalignment? If there’s some inherent misalignment in the system, we will need to design a bearing that can handle misalignment and maybe not use a freebase style bearing that won’t be able to tolerate that misalignment.
Accuracy: how accurate does the bearing need to be? If it’s going into a shopping cart wheel, we don’t need an accurate bearing. We can get away with an inexpensive bearing. But if it’s going into a CNC machine where we’re gonna be making a large amount of parts every day, we need higher accuracy solution.
Then of course is the size. If it’s going into a dentist’s drill, we need a bearing the size of a popcorn kernel. If it’s going in a wind turbine, we need a bearing that’s several feet or even meters in diameter.
Temperature: what kind of temperatures will the bearing be exposed to? Is it going into an Alaskan offshore drilling platform that needs to live in -50 degrees fahrenheit? Or is it going into the Saudi Arabian desert?
And then lastly, bearing life. How long do you know this bearing will last for? Some think the bearing will last maybe a month or two, other need a few years just to get through the warranty period, and then there are others that want their bearing to last for the lifetime of the operator, 10, 20, 30, 40 years, so they don’t have to worry about it.
These are all things that we think about as applications engineers. This is by no means a comprehensive list of the different influence factors in bearing selection but these are some of the major concerns. These help narrow down the bearing selecting process. To the left is just an example of a chart used as a selection guide in application engineering. On the left-hand side here you have different bearing types: ball bearings, double ball bearings, roller bearings, self-laying bearings. On the top there are different types of performance characteristics that customers might want out of a bearing. If you had a fan inside of a hotel room, for example, we might want the bearing to be very low noise, so you want a low noise bearing. Or you might want to have a bearing that can handle a very high axial loads, or a bearing designed to handle shock loads well.
So this is just a primer on the kinds of things we need to think about and we go through when we go thorugh our bearing selection process. This process is fairly complicated, which is one of the reasons why it’s always good to consult other applications engineers. Looking at the whole picture is generally something that takes years of experience to get through the selection process and make sure you’re getting right bearing.