Bushing, also known as a plain bearing, is a mechanical assembly that reduces friction between a stationary component and a rotating shaft. The bushings support the rotating shaft on a hard shaft journal, which uses soft metal and an oil layer. The bushing, also known as a plain bearing, is typically used on machinery with rotating or sliding shafts.

The bushings are also called sliding bearings, journal bearings, and sleeve bearings. In order to protect the shaft journal, they are made of soft metal, such as Babbit metal or some other type of material. Depending on the particular application and load requirements, they can also be designed using different materials. For example, in some instances, bushes are used to align drilling operations' systems.

In this article, we'll discuss different types of bushings and different types of applications to consider when selecting the right bearing.

Difference Between Bushings and Bearings

The difference between bushings and bearings is that bushing is a type of bearing, with the latter being a general term for a mechanical assembly that allows motion between two components. However, unlike rolling-element bearings, which usually have rolling cylinders or balls, bushings are designed as a single-part device that supports a shaft.

Since they don't have rolling elements, which are typically designed with a finite life span, bushings are capable of running indefinitely, at least theoretically, provided sufficient lubrication. That's why they're used in extremely critical applications where the failure of roller bearings might have serious repercussions, leading to irreparable damage.

Bushings are mostly used in different types of turbomachines, such as steam turbines used in powerplants and compressors used in crucial pipeline applications. They're primarily employed in high-performance engines in the automotive and aerospace industries, but other low-speed applications like ship propellers also use bushings.

Due to their low cost and simplicity, plain bearings are also suitable for applications involving intermittent and linear motions. These bearings can be made of various bushing materials, from sintered bronze infused with graphite and oils to self-lubricating thermoplastics, nylon, PTFE, polyurethane, Vespel, etc.

In contrast to bushings, ball bearings are precision-made components that allow machinery to move at high speeds, with low friction, and high loads. The same can be said for thrust bearings and turntable bearings.

Different Types of Bushings

Several different types of bushings are used in machinery to provide a bearing surface that reduces friction between two components. Here are the most common types of bushings:

Hydrodynamic and Babbitted Journal Bearings

These bushing types are typically employed to support engine crankshafts and are designed using highly polished stainless-steel surfaces and connecting bearings, all of which are situated inside the crankcase.

The engine's main bearings run under a hydrodynamic regime. This indicates that, under normal operating conditions, an oil film formed by the rotating shaft serves as a barrier between the bearings and journals. This oil is fed through the holes into the bearings, ensuring that they're well-lubricated while preventing any chance of corrosion within the connecting bearings.

Numerous industrial turbomachines, including compressors and turbines, use journal bearings. However, these industries use hydrostatic bearings. This indicates that the shaft can be supported by an oil wedge even when the corresponding system is not in use.

Sleeve Bearings

Despite having a similar working principle to the aforementioned bearing designs, sleeve bearings as used for linear motion as frequently as they're used for rotary motion. Because of that, these machine components are interchangeably referred to as bearings or bushings.

However, unlike hydrodynamic and babbitted journal bearings, which frequently imply fairly complex mechanical systems with an integral lubrication system, sleeve bearings are relatively simple press-fitted components used in a variety of applications.

Sleeve bearings are frequently made of bearing sintered bronze or cast, and they occasionally have lubricant plugs inside. Depending on your application, there are various plastic bushings as well. There are two main types of sleeve bearings available: a plain cylindrical version and a flanged type that offers a bearing surface for axial loads.

Spherical Bearings

Spherical bearings are specifically designed to support the angular rotation between the control arm and linkages, though they weren't specifically designed to handle this rotation but reather to support the angular movement between the components. In addition, the friction between two surfaces is significantly decreased by a lubricating layer.

Spherical bearings differ from typical roller bearings; the latter belongs to the family of bearings with rolling elements, and while spherical bearings also have rotational capabilities, their primary use is angular motion.

The spherical inner race typically rotates angularly within bounds in the outer race, while oil provides a lubricating layer between contacting surfaces of spherical bearings. Certain heavy-duty applications demand additional ball rolls between the races to create motion with very little friction.

Drill Jig Bushings

Drill jig bushings are one of the most prominent workholding tools intended to offer drill guiding during precise metal drilling operations. However, since they're mostly used for tool guiding rather than actual workholding, they're mostly press-fitted components with changeable liners. Hence, they're made of harder materials than steel, with very tight tolerances to maintain excellent precision.

Bushing Applications and Industries

Contrary to rolling element bearings, which are designed with finite lives in mind, plain bearings with full-fluid lubrication have outstanding durability and a very long lifespan. As a result, they are utilized in demanding applications where bearing failure could have disastrous effects.

These include the steam turbines and compressors used in vital pipeline applications in power plants. Low-speed shafting, such as that used in ship propellers, frequently uses plain bearings as well. They're also a simple and cost-effective solution for the food processing industry, as well as end operations like intermittent applications.

Summary

It's simple to choose the best option for your production system once you grasp the design and applications of bushings. The aforementioned guide provides the distinction you require regarding bushings and the locations where they are used, allowing you to make the finest choice and ensure proper upkeep for increased production.

If you're looking for bushings and bearings, please visit Reid Supply, a prominent industrial component supplier with a broad assortment of bushings and bearings, which also has a vast downloadable library of professional literature and guides.