The ball bearingslide bearings are basic supporting components which have strict requirements and are widely used in mechanical industry and residential appliances， and they are called as the mechanical joints。 It can be said that where there is rotation， there is a bearing。
The wide applications of the bearing determine the diversity and complexity。 The strict requirements determine the importance of the quality and performance。 They are the innovated versions of the traditional bearings。 The rotors and the stators of the these bearings are lubricated by using the balls and lubricants。 The ball bearing overcome the shortcomings of short service life and instable operation of the oil seal bearings， but the cost is not increase too much。 The ball bearings rotate through the round metal balls， and therefore， the rotation of the ball bearing can be activated easily。
The bearing have the advantages of small frication resistance， small power consumption， high mechanical efficiency， easy starting， size standardization， interchangeability， easy installation， convenient assembling， convenient maintenance， compact structure， light weight， narrowed axial dimension， high precision， high rotation speed， small wear and tear， and long service life。 Some have the performance of self-aligning。 They are suitable for large scale production with reliable and stable quality and high production efficiency。
Compared with the sliding bearing， they have many advantages。 They have smaller coefficient of friction and higher transmission efficiency than those of the sliding type， the friction coefficient of the general sliding bearings is 0。08 to 0。12， and the friction coefficient of the ball bearing is only 0。001 to 0。005。 They have achieved standardization， serialization and universalization， therefore， they are suitable for mass production and supply， and they are convenient to use and maintain。 They are made of steel and processed through heat treatment。 Therefore， the ball bearings have not only high mechanical properties and long life， and they can use less expensive non-ferrous metals than the sliding types during manufacturing process。
The bearing have small gaps inside the it， and all the parts are processed with high precision。 Therefore， they have high operation precision。 At the same timePlastic bearing， the rigidity of the bearings can be enhanced through pre-load method。 Some ball bearings are able to bear radial load and axial load simultaneously， and therefore， the support structure can be simplified。 These types have high transmission efficiency and less heat generation， therefore， they can reduce lubrication oil consumption， and lubrication and maintenance are relatively easy。