Bushing vs Bearing

When you are constructing a robot or an electrical device, you sometimes come across bushings and bearings. What’s the difference between the two? There have been a lot of debates and discussions about the two. Interestingly, the automotive worlds and thus many people tend to use those two terms interchangeably. They often call the plastic-lined bearing with a bronze interlayer as a bushing. Of course, there are reasons why it is often called as a bushing. However, in the general sense, bushings and bearings are two different things.

Below, we are going to see the differences between bushings and bearings. We will also see the types of bushings and bearings available, as well as the general rules about when to use them.

What is a Bushing?

A bushing is essentially just a tube-shaped material with a hole in the middle with properties that make it suitable for a particular purpose. A bushing is often called “sleeve bearing” or “plain bearing”. Despite the simple appearance, a bushing is actually quite a sophisticated part. It is generally designed to be able to slide over a smooth rod with extremely low friction so that power consumption, noise, and wear can be minimized.

A bushing is using bronze powder that is fused together in a way that causes tiny pores in the metal. It is then impregnated with oil. Thereby, whenever the bushing contacts a shaft, the oil can be drawn to the surface by capillary action. This way, a bushing constantly deposits a thin film of lubricating oil on the surface – it is self-lubricating.

The first, obvious advantage of using a bushing is obviously the self-lubricating nature. You won’t have to lubricate it manually. It requires less maintenance. Second, it is quiet. Third, it can be used on non-hardened as well as hardened shafts. Fourth, it is usually more affordable than bearings.

There are at least two disadvantages of using a bushing. First, bushings, especially the cheap ones, tend to have wide tolerance levels, making a somewhat worse fit on the smooth rod. Second, a bushing needs to overcome static friction forces before moving, and this may cause jerky, uneven movements, especially if the linear motion system is worn or not properly aligned.

What are the Types of Bushing?

A bushing is often called as a plain bearing or a sleeve bearing.Bushings are relatively simple parts, so the different types of bushings may have quite some similarities. Different types of bearings are made with slightly different styles to suit different purposes. There are journal bearings, which are actually plain bearings used at the ends of railroad wheel sets’ axles; these journal bearings are no longer used in modern applications, replaced by rolling-element bearings. There are also rifle bearings, which are relatively small plain bearings used in rifles. There are also drill jig bushings, used to provide drill guidance during a precision drilling operation. However, perhaps the most different of all are electrical bushings, which also have a particularly different purpose; these are insulated devices that allow an electrical conductor to pass safely and securely through a grounded conducting barrier. Electrical bushings are used to withstand and contain the strength of the electrical field, which, if leaked or not properly contained, may cause burning and arcing to surrounding materials.

What is a Bearing?

The term “bearing” is obviously derived from the verb “to bear”; such naming is due to a bearing being a machine element that enables a part to bear (support) the other part.A bearing is a machine element that functions to constrain relative motions to only the desired motion, as well as to reduce the friction between the moving parts. Unlike the bushing, a bearing is much more complex, with various types differing in design, nature, and purpose. A bearing may be used to allow free linear movements or free rotation around a fixed axis. It can also be used to prevent a motion by controlling the vectors of the normal forces on the moving parts.

There are several advantages offered by bearings. First of all, the motion provided by a bearing is smoother than that of bushings. Instead of sliding, a bearing moves by rolling; hence, there is no static friction to overcome. The second advantage is that a bearing is usually built for a tighter tolerance level than bushings. Hence, a bearing can fit more tightly on the smooth rod, allowing for less slop and less backlash.

Needless to say, a bearing also has a number of disadvantages. The very first disadvantage the people usually mention is the price. Bearings are quite more expensive than bushings. Second, bearings must be used on hardened, preferably chrome-plated shafts; if the shaft is not hardened, a bearing will gradually cut into the material. Third, a bearing requires a lot more care and maintenance. The mechanisms used in a bearing may be prone to external disturbances, such as dust, dirt, or magnetic fields. You need to make sure that the bearing you are using is protected from such disturbances. Some types of bearing, such as the linear ball bearing, may require frequent lubrication or other kind of maintenance.

What are the Types of Bearing?

There are various types of bearing. The most common are rolling-element bearings, which include ball bearings and roller bearings. These bearings have rolling balls inside them to allow movements in the desired manners. There are also jewel bearings, in which the load is carried by rolling the axle slightly off from the center. Fluid bearings carry the load by using a gas or liquid. Magnetic bearings carry the load by using a magnetic field. Then, there are flexure bearings, which support motions by using a load element that bends.

BushingBearing
- A simple tube-shaped device with a hole in the middle- A relatively complex device with a particular mechanism to allow and control movement, such as a set of rolling balls
- Generally cheaper- Generally more expensive
- Self-lubricating, thus requiring less maintenance- Requires more care and maintenance
- Moves by sliding; may have jerky movements due to static friction movements- Moves by rolling; movements are smoother

Conclusion

A bushing is a relatively simple tube-shaped device with a hole, used to allow movements on a shaft by sliding. A bushing is a great choice for a non-hardened shaft, for a limited budget, and if self-maintenance is needed; however, a bushing may have less precise and jerky movements due to the static friction forces and wide tolerance. A bearing is a more complex device; it offers smoother, more precise movements. However, it is generally more expensive, can only be used on a hardened shaft, and requires more care and maintenance.

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