What Is a Bush Bearing?

Posted on Jan 8, 2021

Bush Bearing

A bush bearing, also known as a bushing or bush, is one classic type of independent plain bearing. It is a mechanical component which is designed to provide a bearing surface for rotary applications, reducing friction between the spinning shafts and stationary supporting elements. 

What Are Bush Bearings?

A bush bearing, also known as a bushing or bush, is one classic type of independent plain bearing. It is a mechanical component which is designed to provide a bearing surface for rotary applications, reducing friction between the spinning shafts and stationary supporting elements. 

Generally, bush bearings rely on plastic, soft metals like babbitt or oil film to bear and protect the shafts on the hardened shaft journals. Depending on the use and the load requirements, bush bearings can be made of a variety of materials. Unlike most bush bearings that are inserted in the housing of rotary applications, linear bush bearings are secured with a radial feature. For instance, mold one retaining ring onto the outer diameter of the bush bearing which fits the groove in the housing or using double retaining rings. These arrangements can reduce the risks that the force applying on the bushing presses the bearing out, retaining and securing the bush bearings more firmly. 


Plain Bearing

A bush bearing is the most common type of plain bearings. Plain bearings are widely utilized in devices that have rotating or sliding shafts. Without rolling elements, plain bearings are also called journal bearings, slide bearings or sleeve bearings. Plain bearings are the most cost-efficient type of bearings. Moreover, plain bearings are compact and light in weight, having ideal load capacity. These benefits make the bearing popular in industrial applications. For example, plain bearings are used in a wide variety of engines, turbomachines like steam turbines, compressors and so on. They are also preferred in applications that operate at relatively lower speed, such as propeller shafts of ships. Since the bearings can reduce the cost and are simple to add in the system, they are also suitable for a wide range of linear, intermittent motion applications.


Materials and Lubrications

Unlike other types of bearings that have rolling elements, bush bearings rely on fluid lubrication. Typically, they are utilized in relatively critical applications where bush bearings’ failures will lead to severe problems. Due to the mentioned reasons, materials that the bush bearings are made of play an important role when selecting the right bearing. Plain bearings’ materials can range from sintered bronze which needs to work with oil to other thermoplastic styles which are suitable for working on drying applications with embedded lubricants. The plastic style is more likely to see in food processing production lines which do not require strength and other properties of metal bearings. Bush bearings are typically impregnated with oil which is helpful for reducing the friction and providing lubrication. They are usually pressed in powdered metal or applying bronze cast.

:: Read more : Flange Bearings Explained in All Their Varieties


Different Types of Plain Bearings


● Hydrodynamic Journal Bearings:

One classic application of hydrodynamic journal bearings is bearing the engine crankshaft. The core bearing itself is mounted in the crankcase, and the smooth surfaces are the journal of the core bearing and the connecting rod bearing. Journal bearings which act as engine bearings operate in the hydrodynamic regime, in general, the journals and bearings are separated by the oil wedge which is created when the shaft is spinning. Since they are hydrostatic, the engine shaft can still be supported by the film when it is not working. This type of bearings is widely used in turbines and compressors. Typically, the surfaces of journal bearings are lined with babbitt, which is a soft white metal material that is suitable for supporting film lubricants. While contacting a hardened shaft, babbitt journal bearings can provide forgiving surfaces.


● Bush Bearings:

Bush bearings are similar to hydrodynamic journal bearings, however, in addition to rotary applications, they are also popular for linear motion applications. They are commonly referred to bushing, sleeve bearing or simply bearing. Bush bearings are simpler than journal type, they can be inserted for the host applications from guidepost to caster bearings. When it comes to the materials, the bush bearings are typically made from bronze which is sintered or cast. The materials often are filled with various lubricants, for example, graphite. Various thermoplastics are also common sleeve bearing materials. 

Typical styles of bush bearings include sleeve bush bearing, flanged bush bearing, split bush bearing, and clenched bush bearing. They are all sleeve alike components with different inner diameters, lengths and outer diameters. Sleeve bush bearings are entirely solid; split bush bearings have a cut along the length; clenched bearings have clenches or clinches across the cut along its length; flanged bush bearing is similar to sleeve bearing but has flange at the end which develops outward from the outer diameter radially. The flange of flanged type bushing can ideally position the bush bearing when providing a thrust bearing surface. The inch sizes of bush bearings use the SAE numbering system to ensure the dimensions by using the format IIOO-LL. II is the inner diameter in sixteenths of an inch. OO is the outer diameter which is also in sixteenths of an inch. LL is the length in eighths of an inch.


● Spherical Bearings:

This type of plain bearing provides angular rotation between control arms or links. Without rolling elements, the inner race of spherical bearings spins angularly within limits while the lubricants provide the lubricating layer between surfaces. In critical applications like ones in the aerospace industry, the small bearing balls will roll between the races, generating very little friction in the motions of control linkages. Another common application of this style is for rod ends. 


● Drill Jig Bushings:

Drill jig bushings can guide the drill in high precision drilling applications. In metal drilling operations, the bearings are widely used as single components which particularly suit the press or the renewable form that are replaceable liners. This kind of bearings work to guide that for supporting use. They are mostly made from much harder steels and have tighter tolerance to keep the precision for drilling machines operations.


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