Bimetallic Bushes

For this article’s purposes, I have selected bronze bushings for comparison to radial ball bearings. Of course, there are many different materials used to manufacture bushings. Categorically, bushings are made from bronze, polyamide, steel, wood, ceramic, and countless other mixtures of materials.
In a nutshell, standard stock Powdered Metal Bronze Bushings are manufactured from SAE 841-copper (87-90%), tin (8-9%), carbon, and other elements. As a powdered metal bronze material, it provides interconnected reservoirs for oil. The material is Vacuum impregnated with SAE 30 oil during the manufacturing process (approx. 19% by vol).
This process produces a Self-lubricating bushing. When the bushing is in motion, oil rises to the surface for lubrication and restores itself when at rest.

Bushings are ideal for heavy loads at moderate speeds or light loads at high speeds – max Pv 50,000, P-Load 2,000, V-SFM-1,200.
Effective in a temperature range of +10°F to + 175°F with standard oil. Standard tolerances vary by size.
What is important is how compact the bushing cross section is as compared to a radial ball bearing. The compact size and self-lubricating feature make bronze bushings ideal in many applications where radial ball or roller bearings simply would not fit. The high load carrying capacity at medium speeds is another major consideration for using bronze bushings instead of ball or roller bearings.

Design differences between bushings and bearings impact functionality, performance, and suitability. The design of a bushing is simple, typically cylindrical, and comprises an outer surface that contacts the bore or housing and a smooth inner surface fitted around the shaft.
In contrast, a radial ball and or roller bearings design consist of an outer raceway, an inner raceway, and rolling elements such as balls or rollers. The rolling elements minimize the contact area reducing friction and allowing for smoother operation at higher speeds and loads.
The design differences between bushings and bearings impact their load-carrying and speed capacity.
Generally Ball bearings are designed to carry medium to higher loads and operate at higher speeds. Generally Roller bearings are designed to carry higher loads at lower speeds. Bearings allow for better distribution of loads and reduced stress concentrations, improving the bearing’s service life and reliability.
To illustrate the design differences between bushings and bearings, let’s consider this example. Assume a shaft with a diameter of 2 inches rotating at a speed of 300 rpm. The load on the shaft is 125 lbs, and the temperature in the application is 150°F.
If a bushing were used in this application, the load would be directly transferred to the bore or housing, generating frictional forces that could lead to wear and damage. A properly sized self lubricating bronze bushing however would in this case possibly be the correct choice if the application had space restrictions.
In contrast, if a bearing were used in this application, the rolling elements would reduce the contact area between the inner and outer raceways, minimizing friction and wear. The bearing’s design would allow for better distribution of loads and reduced stress concentrations, improving its service life and reliability.

Material properties differ between bushings and bearings and should be considered when selecting a bearing or bushing for an application. Bushings are typically made from materials such as bronze, brass, steel or plastic, while bearings are often made from steel or ceramic. These materials have distinct advantages and disadvantages that impact their performance and durability in specific applications.
Bronze and brass are popular materials for bushings due to their high strength, corrosion resistance, and low coefficient of friction. Bronze bushings can handle high loads and provide long service life in low-speed, high-load applications, such as in agriculture and construction equipment. Brass bushings are commonly used in low-load, high-speed applications, such as in pumps and compressors.
Plastic bushings, on the other hand, offer excellent chemical resistance, low coefficient of friction, and good wear resistance.
Steel bearings can handle high loads and provide long service life in high-speed, high-load applications, such as in automotive and industrial equipment.
Ceramic bearings offer superior wear resistance and can operate at higher speeds and temperatures than steel bearings.

Bushings require minimal maintenance since they have a simple design and do not require lubrication. However, they may need to be periodically inspected and replaced if they wear out or become damaged. Inspecting bushings for wear can be done visually or by measuring the clearance between the shaft and the bushing. If the clearance exceeds the manufacturer’s specifications, the bushing should be replaced.
Bearings may require regular lubrication to reduce friction and prevent wear depending upon the application . Many bearings are sealed for life and will never require additional lubrication.