Archive: Feb 2020

Cast vs. Oil-Impregnated Bronze Bushings

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As a broader category, bronze bushings are desirable for their longevity and resistance properties, but there are still significant differences between cast bronze bushings and oil-impregnated bronze bushings. While similar in many ways, these component types are manufactured using completely different processes, and these processes lend themselves to different physical characteristics.

At Bunting Bearings, our oil-impregnated bronze bushings are made by the powder metal process while the cast variety are produced through more traditional machining methods. It’s important to understand how this distinction affects the final product, as one type may be more appropriate for your application than the other.

Oil-Impregnated Bronze Bushings

Oil Impregnated Bronze Bushings

Oil-impregnated bronze bushings are characterized by their ability to self-lubricate. This effect is possible because of the powder metallurgy process:

  • Bronze powder is gravity fed into a die set which is the desired bushing size. The powder is then pressed to connect the powder particles together.
  • The powder particles in the part are then bonded together in a furnace. The furnace temperature is just high enough to bond the particles without melting the metal.
  • This sintering procedure is the key to oil impregnation. Sintering, by nature, decreases the porosity of the product as it bonds the powder particles together, but it’s possible to control the degree to which this happens.
  • For oil-impregnated bronze bushings, the final porosity is maintained at around 25%, meaning that there are still tiny, interconnected capillaries woven throughout the material.
  • To finish the manufacturing process the bushing is then pressed through a calibration set of tools to the required tolerances. The bushing is then vacuum impregnated which forces oil into the interconnected porosity.

Benefits and Applications

Powder metallurgy was originally developed as a cost-effective alternative to standard machining and remains an extremely economical option. In most cases, it is one of the most efficient methods of high-volume production, which translates into cost savings on the consumer end. Oil impregnation also eliminates the need for lubricants and frequent maintenance.

Oil-impregnated bushings originated as an automotive component, however they are used in many other industries. Generally, our oil-impregnated bronze bushings are best-suited for low-to-moderate loads, but they do tolerate high-velocity loads better than many alternatives. They also function well across a wide temperature range of approximately 10–220°F, meaning that they are suitable for use in outdoor and industrial environments.

Cast Bronze Bushings

Cast Bronze Bushings

Unlike oil-impregnated bushings, cast bronze bushings are not formed from powder. Instead, they are formed from a solid or hollow bronze cast bar that undergoes machining processes designed to achieve a precise final shape.

  • First bronze is continuous or centrifugally cast into a solid or hollow bar.
  • Most modern manufacturers use a CNC lathe to cut the cast bar to its final size, although other machining techniques may be used for forming or finishing the bushing.

Benefits & Applications

Cast bronze bushings do not begin as a powder, so they are able to maintain a finer grain structure and therefore a higher degree of strength. In general, cast bronze bushings are also stronger, more durable, and more reliable under compressive force. This combination of properties makes cast bushings an ideal choice for applications involving heavier loads. A sintered bronze bushing of comparable size would simply be unable to withstand the same forces as a cast one.

Bunting Bearings’ Selection of Bronze Bushings

Regardless of your decision between cast and oil-impregnated bronze bushings, Bunting Bearings is ready to fulfill your order with durable, high-quality components. Our extensive catalog includes both plain and flanged bushing designs made from cast bronze. Oil-impregnated options are also available in a comparable range of designs, all of which conform to ASTM standards for chemical properties, physical properties, and tolerances.

At Bunting Bearings, we’ve earned our reputation as a trustworthy provider for stock and custom components. As one of the largest providers of bronze bearings in the nation, we are dedicated to offering exactly the parts you need at the right prices.

For details specific to your project, request a quote or contact our experienced team today.