Bearings are one of the best known machine elements. Their main purpose is to allow movement and load transfer of rotating components relative to fixed housing. Besides these requirements bearings have to provide certain accuracy of the position of rotating components.
Ball bearings are the most represented type of bearings. Ball bearings are a part of “group” of bearings that all have similar construction with inner and outer ring and rotating components inside. They are called ball bearing because the rolling elements inside are metal balls. In this category there are also roller and needle bearings. The difference between them are in the difference of shape of rotating components. Other major type of bearings are sliding bearings that are simpler in construction and have their own set of positives and negatives.
Ball bearings are constructed out of outer and inner ring with raceways in which balls can run. Balls are usually contained in cages. These cages keep the balls equally spaced and in place during the rotation. Cages are important because without them all balls would move over to one side and fall out of the bearing. Other components are optional, but you can specify bearings with or without lubrication and with protective shields. There are also some different features that you could specify but they are not so common.
The shape of inner and outer rings determent the type of ball bearing. So there are angular, axial and deep-groove ball bearings. The main difference is in the loads that each bearing can transfer. If you look at the geometry of these bearings it is obvious why it is so. Read more about the loads on the ball bearings bellow.
On the picture above from left to right: Deep-groove, angular and thrust ball bearings.
Unlike sliding bearings that have to provide low sliding friction in order to provide a smooth rotation of the shaft, ball bearings have to overcome rolling friction. Rolling friction is always significantly lower than sliding one for the same material. Just remember rolling the car tire and pushing one without rolling. In the animation bellow you can see how this rolling movement is achieved. One ring, in this case outer, is stationery while the other one moves with the rotating element. Metal balls inside roll around to “connect” this stationary and rotating ring.
Loads on the ball bearings can be transmitted in the axial and radial directions. Axial direction is the direction of the shaft (blue color in the pictures bellow) and radial direction is the direction normal to the direction of the shaft (red color). Generally ball bearings can transmit less loads then sliding bearings. This is because the loads are transmitted from the one ring “through” metal balls and out of the other ring. Balls inside the raceways are transmitting the loads though point contact instead of the whole surface. The greater number of balls in the bearing the greater load the bearing can carry. The design of ball bearing assembly limits the number of balls inside that limits the load carrying. As you can probably tell the type of ball bearing determent’s the type of loads it is designed for.
Deep-groove ball bearing loads
Deep-groove ball bearings are designed to transmit primarily rotational and less axial load. You can see this illustrated in the picture below. This type off ball bearings is most commonly used because of its ability to transmit both axial and radial loads. Most applications require the transmission of primarily radial and small axial forces. Using deep-groove ball bearings can provide the perfect fit and the most cost effective solution. We will talk about determining loads and designing with ball bearings in future posts, so don’t forget to subscribe.
Thrust ball bearing loads
Thrust ball bearings are designed to transmit only axial loads. Any radial load will disassemble the thrust bearing and it will completely fail. Because of this thrust ball bearings are used almost always in combination with other type of bearings angular, deep-groove, roller or needle. They are used in applications where there is excessive axial loads for standard bearing types like angular or deep-groove. Or with types of bearings that cannot transmit any axial loads. Common application in machine design is the spindle of the milling machine. Because of high loads in the Z-axis of the machine. Other more common applications are in everyday life like in the rotating office chair. Here there are primarily axial loads from sitting on the chair. Other radial loads are transmitted usually with bushings.
Angular contact ball bearings are somewhere in between deep-groove and thrust ball bearings consigning load transmission. They have a construction where the outer and inner ring contact the ball bearings inside at an angle. If we compare the cross section of the angular ball bearing and a deep-groove ball bearing we can see that there is significantly more support for the ball bearing in axial direction with angular contact type. This is why angular contact ball bearings can transmit a lot more axial loads. This construction has its limitations. If you look carefully at the cross section picture bellow you can see that the blue arrows representing axial loads are acting on the outer ring on one side and the inner ring on the other side. This is the only “path” the force can take through the bearing. If the opposite where to occur it would disassemble the bearing and it would fail.
Angular contact ball bearings are used where there is a need to transmit higher axial forces. They must be used in pairs and mounted oppositely one from another because of the “path” of the force discussed above. When mounted in pairs the bearings are secured from failing with application of the force on the wrong ring. Common configurations of paring are shown in the picture bellow
To learn more about ball bearings check out some websites of the world’s leading bearing manufacturers. We have provided you with a list of the world’s top bearing manufacturers and their website for your convenience. You can download the list in the download section bellow: