Moving parts in machinery involve relative sliding or r […]
Moving parts in machinery involve relative sliding or rolling motion. Examples of relative motion are linear sliding motion, such as in machine tools, and rotation motion, such as in motor vehicle wheels.
Most bearings are used to support rotating shafts in machines.
Rubbing of two bodies that are loaded by a normal force (in the direction normal to the contact area) generates energy losses by friction and wear.
Appropriate bearing design can minimize friction and wear as well as early failure of machinery.
The most important objectives of bearing design are to extend bearing life in machines, reduce friction energy losses and wear, and minimize maintenance expenses and downtime of machinery due to frequent bearing failure.
In manufacturing plants, unexpected bearing failure often causes expensive loss of production. Moreover, in certain cases, such as in aircraft, there are very important safety considerations, and unexpected bearing failures must be prevented at any cost.
During the past century, there has been an ever-increasing interest in the friction and wear characteristics of various bearing designs, lubricants, and materials for bearings. This scientific discipline, named Tribology, is concerned with the friction, lubrication, and wear of interacting surfaces in relative motion.
Several journals are dedicated to the publication of original research results on this subject, and several books have been published that survey the vast volume of research in tribology.
The objectives of the basic research in tribology are similar to those of bearing design, focusing on the reduction of friction and wear. These efforts resulted in significant advances in bearing technology during the past century. This improvement is particularly in lubrication, bearing materials, and the introduction of rolling-element bearings and bearings supported by lubrication films. The improvement in bearing technology resulted in the reduction of friction, wear, and maintenance expenses, as well as in the longer life of machinery.
The selection of a proper bearing type for each application is essential to the reliable operation of machinery, and it is an important component of machine design.
How are jet engines lubricated?
What lubricates the main shaft bearings in a jet engine?
Bearings evolved from journal bearings — devices to allow wheels to rotate on shafts.
Further load-carrying capability and friction reduction resulted in ball-bearings and roller bearings.
These bearings, strategically placed, also reduce or eliminate “shaft whipping”.
Then bearings began to be called upon to carry axial loads also, and so the taper roller bearing and the ball-thrust bearing was born.
For low-profile applications, the needle bearing was invented.
Today, there are hundreds of types and millions of sub-types for every application.