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Bearings play a crucial role in ensuring the smooth operation of rotating machinery through a reduction in friction between two parts and the prevention of excessive wear. Namely, there are two types of bearings that are mainly used in various applications: ball bearings and journal bearings. In this article, we’ll discuss ball bearings compared to journal bearings; their differences, similarities, and various applications.

Journal Bearings

Journal bearings, also known as sleeve bearings or slide bearings, are the older and more basic type of bearing, called plain bearings. They usually consist of a shaft, referred to as a journal, that rotates inside a stationary bushing housed in a stationary support housing.

These bearings can be used in relatively low-speed applications, and their lubrication is tightly related to the journal’s rotational speed. Because of the speed dynamics, both hydrostatic and hydrodynamic bearings are appropriate in various high-demand circumstances. In both types, the space between the journal and the bearing is filled with a lubricant that prevents metal-on-metal contact, provides cushioning effects, and reduces friction between the two surfaces, no matter their material.

Hydrodynamic lubrication is most often used in high-speed applications in which the rotating shaft pressurizes the lubricant within the assembly, creating a thin fluid film that lowers friction.

Hydrostatic bearing systems must rely on external components, such as pumps and valves, to supply a continuous oil flow to lubricate and cool down the bearing assembly.

Structurally, there are three main types of journal bearings, and each one might contain a notable upgrade over the other. The most basic type is an integrated journal bearing, which is very compact and reliable but not easily maintained or even replaced.

The step-up from the integrated type is a bushed journal bearing, which consists of a bushing made of softer materials housed in a bearing shell made of steel or cast iron. The final type is a plummer journal bearing, which also consists of a bushing and a bearing shell, but both are held together by bolts or screws that can complicate application.

The latter type is the most expensive, but it’s unmatched in terms of maintenance and repairability, despite limitations such as the need for a very precise alignment between the shaft and the bearing.

Ball and Roller Bearings

A typical ball bearing, also known as a spherical roller bearing or an angular contact ball bearing, is a type of rolling element bearing. The ball bearing design consists of outer and inner rings, as well as a retainer. The inner ring’s outer circumference and the outer ring’s inner circumference have machined grooves called raceways that encapsulate the spheres separated by the retainer.

The ball bearing’s outer ring is often kept in a stationary support housing, whereas the inner ring is applied to a rotating shaft. The spherical bearings roll between the rings and reduce friction between the rings. Ball bearings are capable of handling heavy radial loads, as well as lighter axial loads.

All ball bearings are structurally very similar, with minor differences. Deep groove and angular contact ball bearings are the most common types, followed by self-aligning bearings and thrust bearings. It might be worth mentioning that the latter is designed to handle axial loads only.

What Are Roller Bearings?

Similar to ball bearings are roller bearings, which have cylindrical metal rollers instead of spherical rollers. The fact that they have larger contact points increases their surface area compared to spherical bearings, thus increasing their load capacity and shock resistance. There are other types of roller bearings, including tapered roller bearings, cylindrical roller bearings, and needle roller bearings. Compared to ball bearings, roller bearings have much greater durability, as they’re better suited for high loads.

It’s important to note that rolling element bearings have a finite lifespan, and they’ll eventually stop working due to typical wear and tear and other factors. In other words, these bearings have a pre-defined number of revolutions predicted based on statistical data.

This lifespan is influenced by shaft and bearing alignment, as well as lubrication, which may include packing the bearing full of grease lubricants or a thin liquid lubricant, applied either by hydrostatic or hydrodynamic means. In both cases, the rotational speed of the rolling elements is enough to create an oil film between parts of the bearing assembly.

How to Choose Which Bearing Will Work for Your Application

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The choice between different types of bearings always depends on the application in which the bearings are used. Even then, there are several different factors you’d have to consider:

Speed

Ball bearings are typically used in applications that involve relatively high speeds and lighter loads due to smaller contact points and generally lower friction. The same applies to roller bearings, which are capable of withstanding relatively higher speeds and higher loads.

In comparison, journal bearings don’t have any roller elements and are better suited for relatively low-to-moderate speeds or high-load environments. For example, ball bearings found their application in more precise, high-speed applications such as ball-bearing turbochargers.

This smaller contact point in ball bearings also means less friction, which makes them perfect for high RPM applications. Journal bearings have a much larger contact surface, which generally produces more friction.

Load

Ball bearings and many of their varieties, such as double-row ball bearings and roller bearings, are better suited for higher radial and axial loads due to less friction within the bearing assembly and the elasticity of the spherical element materials. Journal bearings can withstand some axial loads and low-to-moderate radial loads.

Clearances

Ball bearings have very low tolerance and are better suited for precise machinery, while journal bearings are less precise by machinist standards but are, in turn, better suited for heavy machinery. Additionally, they’re more compact and take up less space compared to journal bearings.

Lubrication

Journal bearings typically require more frequent lubrication due to their higher friction applications. Ball bearings have less friction and thus require less lubrication. However, the choice of lubricant and lubrication method depends mostly on the operation conditions, speed, load, and the associated costs of lubrication and lubrication systems.

Price

Since they’re more complex compared to journal bearings, ball bearings are a pricier option. However, their lower friction and longer life expectancy can offset the high initial costs.

When and Why Choose Journal Bearings?

When making a decision between a journal bearing and a ball bearing, it’s important to consider the bearing’s operational conditions, loads, speeds, and relevant factors to determine the best type of bearing for your specific application.

The best approach is to consult with a bearing expert, as they can provide valuable insight to help ensure that you made an informed purchase. Our product experts can help you find the journal or ball bearing solution for your project.