Journal Bearings vs. Ball Bearings – What's the Difference?

Ball and roller bearing provide the same support of shafts through any mechanical means. Journal or bronze sleeve bearings rely on fluid films, usually oil that support rotating shafts. Both bearings are used to check radial and axial loads by bearings and bushes suppliers. 

Let’s know in brief the difference between these bearing types with examples.

Ball or Roller Bearings

A typical roller or ball bearing consists of inner and outer raceways. A carrier separates several spherical, cylindrical, semi-cylindrical, or tapered elements. It often seals designed to keep dirt out the grease in. The inner race is often pressed lightly onto a shaft when installed, and the outer race is held in the housing. The designs are available for handling pure radial loads, axial loads, and combined loads.

Ball bearings are defined as point contact that each contacts the race in a small patch. Now roller bearings have line contact rather than point contact. It enables them higher shock resistance and great capacity. These rolling element bearings do not have infinite lives. And eventually, they fail from fatigue or any other mechanisms. They are designed on a statistical basis that specific numbers are expected to fail or set after many revolutions that have accumulated. Bearing manufacturing company defines this as the useful life of bearing.

In bearing life, shaft and bearing alignment play a critical role. For higher misalignment bearing capacity, self-aligning bearings are used. The bearing carrier is eliminated to increase the radial load capacity, and the space between the races is filled with many balls or rollers. Wear and friction in these roller bearings are higher than those using a carrier. Because of rubbing between adjoining rolling elements. Know this before and replace your bearing before it’s too late.

In any critical applications, the machine tool spindles where shaft runout is a concern; for example, bearings and bushings may be preloaded to take up any clearance in the tightly tolerance bearing assembly.

Journal Bearings 

Journal or sleeve bearings make proper use of pressure wedge of fluid. That creates forms between the rotating shaft and the bearing. The part of the shaft connected by the bearing is called the journal. And it is usually hardened for wear-resistance. While bearing pad material is generally softer material such as tin and lead-based, bronze, copper-lead, carbon, etc.

As the shaft rotates in the bearing bushing clearance, it tends to watch and climb up the bearing wall. It generates a high-pressure area in the oil film that supports the shaft journal. As the load on the shaft differs, so too, the region of high pressure varies. It makes journal bearings quite tolerant of overload and shock loads.

A bearings and bushes supplier has developed with full hydrodynamic lubrication that runs forever as there is no wear. Upon startup, wear occurs, and since there is no supportive oil film, the shaft is at rest. Thus, soft materials are preferred for bearing liner. That is particularly material with low frictional coefficients. Some designs depend on an auxiliary pump that pressurizes the bearing until the shaft produces the hydrodynamic wedge.

The bearings are simulated by the misalignment between bearing and shaft as it is likely to hamper the formation of fluid film.

Choose a Journal or Rolling-element Bearing

Journal bearings have lower initial costs than rolling-element bearings. You may offset these savings if equipment such as pressurizing pumps needs to be used. The journal bearings require less radial space than rolling element bearings, but they need more axial length. 

Journal bearings are more capable of managing overload and shock compared to the ball and roller bearings. They can run quieter, especially when rolling element bearings begin to wear. They are less prone to fatigue. It is because the oil separates the journal and roller bearing dirt. And other particles have little impact on a journal bearing’s operation.

Rolling-element bearings are the preferred choice because of their low starting friction. 

They are more adapted to handle misalignment between shaft and bearing as they have self-aligning designs available to increase this capacity. The journal bearings can carry axial loads, but a bearing manufacturing company designs rolling bearings to handle radial and axial force.

For example, the railway cars used journal bearings on the wheel axles. The equivalent load was applied to the bearing whether the car is still or moving. Multiple locomotives were required to get the train moving as one was sufficient to keep it rolling. The rolling element bearings have all but replaced journal bearings on railcar axles.

Conclusion:

There are different types of bearings categorized by bearing and bushes suppliers. According to their direction and magnitude of the force, they can support, and the optimal bearing type is selected, considering the machine’s structure.