Sleeve bearings, also known as plain bearings, journal bearings, or bushings, are the most common type of plane bearing suitable for various applications. They're single-piece components press-fitted into housing that carries linear, oscillating, and rotating shafts. They improve linear motion by absorbing friction, thus enabling motion between two components.

These types of bearings are more affordable than the typical ball bearings; they're reliable, straightforward, and quite rugged, which makes them suitable for various applications. Additionally, their lack of moving parts makes them more resilient to hostile operating conditions and suitable for both high-speed and low-speed applications.

More robust sleeve bearings are exceptionally low wear and can withstand heavy loads and high temperatures. They can correct for misalignment of the other components and have a high shock load resistance in their contact region.

In this article, we'll discuss sleeve bearings, their design, their numerous advantages, and specifications, and we'll even mention a few applications that are quite useful.

 

Source: Wikimedia Commons

 

 

Sleeve Bearing Design

Sleeve bearings come in a few different varieties. For example, a flanged bearing withstands radial and axial loads, which is why it's the most popular cylindrical bearing amongst machinists and mechanical engineers. On the other hand, thrust bearings are a viable solution for massive side loads, and basic cylinder bearings are the best options for purely radial loads.

There are two common designs you’ll encounter most frequently: flanged and cylindrical. The bearing surface for an axial load is provided by a projecting flange on one end of a flanged sleeve, whereas a cylindrical bearing has straight outside and interior diameters and sits flush inside the housing.

There are also a number of variables to optimize the bearing performance, including geometry, number of lobes, materials, and type of lubrication, which can be pressure-fed or self-lubricating — the latter of which demands the use of an oil ring.

Sleeve bearings have several benefits, including reduced installation and maintenance costs and significant noise reduction at low speeds.

Source: Wikimedia Commons

Reduced Noise

If a perfect bearing system, lubricating oil film would prevent any metal-to-metal contact, thereby eliminating all bearing noise. However, because both the shaft and the bearing have rough surfaces, at least on a microscopic level, the bearing could produce a scraping or a grinding sound. Sleeve bearings are generally quiet and remain low-noise until they begin to run out of oil.

Noise issues are easily solvable by adding more lubricant to the assembly. In contrast, ball bearings are considered relatively noisier than sleeve bearings due to a larger number of assembly components, which act as noise sources. Additionally, noise levels don't increase towards the end of sleeve bearing's life expectancy the way they do with ball bearings.

Low Maintenance

Sleeve bearings are very straightforward components and don't have any moving parts, so their maintenance usually comes down to adequate lubrication. Besides aiding friction, lubrication also prevents the plain bearing and shaft from "polishing" one another. This may sound counterproductive because bearings should have the lowest friction coefficient. In this case, however, it may trigger a so-called "stick-slip effect."

Since they don't have moving parts and are usually press-fitted inside the bearing's housing, lubrication is usually the only maintenance necessary to prevent any damage to the housing. Any damage to the receptive body that holds the bearing would require additional repairs.

Easy Installation

Easy installation is one of the main advantages of sleeve bearings since they're usually press-fitted over the shaft or inside the mating component. Some on-shaft applications use two-part bearings that are secured to the shaft via screws.

The easy installation is somewhat contrasted by a more complicated disassembly. Two-part bearing assemblies aren't usually too difficult to remove, but the single, individual one-piece components can become stuck within a housing. This is usually solvable by the use of pin-punch tools and a few light hammer taps, but it always implies a damaged bearing. Luckily, they're really affordable.

Common Sleeve Bearing Applications

Source: Wikimedia Commons

As previously explained, the sheer durability, wear resistance, and high-load capacity design of sleeve bearings make them suitable for a range of light- and heavy-duty applications, such as:

• Automotive Industry — mostly in transmission shafts and crank components;
• Agriculture — linkage assemblies on attachments;
• Off-road Industry — clevis bearings for hydraulics;
• Marine Industry — used mainly for propeller shafts;
• Food Industry — used in lift and tilt devices in processing and packaging applications.

How are Sleeve Bearings Lubricated?

Sleeve bearings are usually made of compressed powder metal, which makes them microscopically porous. Thus, any lubrication applied outside the bearing will result in oil being drawn up through the pores to lubricate the inner cylinder. Some applications require specifically designed lubricants such as liquid metal or graphite.

Self-lubricating bearings, on the other hand, have lubricants impregnated within the porous material of the bearing, using either liquid or solid lubricants. The type of lubricant is usually determined by the application's requirements, such as operating temperatures. As the bearing operates, the lubricant seeps through the porous material in the sliding layer, lubricating its surface.

Sleeve Bearing Specifications

Sleeve rings have several crucial dimensions you'd need to know when selecting an adequate part:

• Clearance — the distance in the shaft's radial movement within the bushing. This should be selected based on the normal operating conditions.
• ID and OD — these refer to the inside diameter and the outside diameter of the bushing, not accounting for the radius of the flange.
• Length — overall length of the sleeve bearing.
• Load — usually expressed in pounds per square inch.
• Rotating Speed — related to several crucial factors, like material, speed, surface finish, hardness, lubrication, alignment, etc.
• PV value — P stands for a specific load, while V stands for sliding speed, both of which have a massive influence on the service life of the bearing. Generally speaking, a lower PV value indicates a longer service life.

Conclusion

Sleeve bearings are press-fitted components that reduce noise, vibrations, and friction between two moving parts using a sliding motion. They're made of a variety of different materials, making them suitable for various different applications. If you want to learn more about sleeve bearings or bearings in general, please visit Reid Supply and head over to their extensive library containing the latest industry news, as well as professional literature.