Journal bearings, also called sleeve bearing, sliding, or plain bearings, work by creating a wedge of fluid compression between the bearing and the rotating shaft. The journal is the hardened component of the entire structure which is mechanically supported by the bearing. However, the bearing pad materials are typically softer, utilizing substances such as lead and tin-based babbitt, copper-lead, bronze, carbon, PTFE, and sintered powdered metal.
Most journal bearings work on hydrodynamic lubrication, where a thin film of a lubricant?—most often an oil?—is applied between the journal and the bearing. Usually, wear-and-tear occurs during initialization since an oil film is absent when the shaft is at rest. This is why materials with low friction coefficients (the soft materials discussed above) are used to make the inner lining of the bearing pads.
Furthermore, the grooves within the bearing are used to evenly distribute oil throughout parts. Some journal bearing designs also use an auxiliary pump to enact pressure on the bearing until the shaft can start creating the hydrodynamic wedge.
Journal bearings working on the principles of fluid dynamics are the most preferred for modern-day gearboxes, apart from other turbomachinery instruments in the aviation industry. They have many desirable properties, such as efficient rotodynamic damping and good durability. Although all journal bearings work on the same principle of a journal sliding over an oil film, they are still categorized into different types based on their unique functions. Given below is a quick rundown of the different kinds of sliding-contact journal bearings used today:
Full Journal Bearings
These journal bearings have a 360 degree angle of contact between the bearing and the journal shaft. Commonly used in heavy-duty industrial equipment, these bearings can be used to lift loads along any circumferential direction. This is why they find a wide variety of applications.
Partial Journal Bearings
When the journal and the bearing make an angle of 120 degrees, they constitute the partial journal bearing system. Although partial journal bearings have a lower frictional coefficient than full journal bearings, they are worth utilizing only when the load is to be lifted in a single direction. This is why railroad axles most commonly employ partial journal bearings in their structure.
Apart from the classification based on the angle of separation, sliding contact bearings can also be classified into thick film, thin-film, and zero film bearings, based on the thickness of the lubricating layer involved.
As is evident from their names, thick-film bearings have the lubricant layer completely separating both working surfaces. On the other hand, thin-film bearings (boundary lubricated bearings) have some degree of contact between the lubricating surfaces, despite a lubricant layer present between the two. Meanwhile, zero film bearings work without any lubricant at all.
Clearance Bearings
Both full and partial journal bearings can be called clearance bearings since the diameter of their journal is lesser than that of the bearing. However, when the diameters of both the bearing and the journal are equal in a partial bearing, they are called fitted bearings.
Most machinery used in industrial applications are expected to serve their purpose for extremely long periods. If the bearings fitted inside them are damaged, their replacement/repair becomes an issue since they are regularly located above ground level, often in extremely unreachable spots. This is where sliding contact bearings serve some unique advantages, such as those given below:
Sourcing the best journal bearing for your unique requirements might be a bit of a hassle, especially when the market is already flooded with cheaper knock-off versions. Therefore, all journal bearing purchases should only be made from ASAP Sourcing Solutions.
Before You Go, You Should Consider Looking at Our NSN Parts Catalog. and Remember, ASAP Sourcing Solutions Has Some of the Fastest and Most Competitive Quotes On the Market.
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