What are Bearings? Slide Bearings | Rolling-element Bearings | Fluid Bearings

Welcome back MechanicaLEi, did you know that
invention of bearings, in the form of wooden rollers, may predate the invention of wheels?
This makes us wonder, What are Bearings? Before we jump in check out the previous part
of this series to learn about what couplings are? Now, Bearing is a machine element that
constrains relative motion to only the desired motion and reduces friction between moving
parts. The design of the bearing may, for example, provide free linear movement of the
moving part or free rotation around a fixed axis; or, it may prevent motion by controlling
the vectors of normal forces that bear on the moving parts. A slide bearing is the simplest
type of bearing, comprising just a bearing surface and no rolling elements wherein a
journal which is the part of the shaft in contact with the bearing, slides over the
bearing surface. The simplest example of a slide bearing is a shaft rotating in a hole.
Plain bearings, in general, are the least expensive type of bearing. They are also compact
and lightweight, and they have a high load-carrying capacity.
A rolling-element bearing is a bearing which carries the load by placing balls or rollers
between two bearing rings called races. The relative motion of races causes rolling elements
to roll with minimal rolling resistance and with little sliding. They require fewer boundary
dimensions and can transmit heavy and variable loads of various forms. They can easily be
installed, serviced and replaced. Fluid bearings are bearings in which the load is solely supported
by a thin layer of rapidly moving pressurized liquid or gas between the bearing surfaces.
Since there is no contact between the moving parts, there is no sliding friction, allowing
fluid bearings to have lower friction, wear, and vibration than many other types of bearings.
When compared, a fluid bearing can be as simple as two smooth surfaces with seals to keep
in the working fluid. In contrast, a conventional rolling-element bearing may require many high-precision
rollers with complicated shapes. Hence, we first saw what bearings are, then saw what
simple type of bearing is and finally went on to see what rolling-element and fluid type
of bearings are?

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