What’s a Mech Bushing?

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Mechanical bushings are used to reduce friction and wear between mechanical parts or limit movement. They consist of a rotating rod or shaft that slides through a bore lined with a bushing. Materials used include Babbitt metal, plastic, aluminum, rubber, bronze, carbon, and ceramics. They should not be confused with normal bearings.

A mechanical bushing is a sleeve-like lining used to reduce friction and wear between mechanical parts or to limit or restrain the movement of parts. Sometimes called plain bearings, mechanical bushings are used to line a hole in a stationary part of a mechanism and are effective at spreading friction and wear across the surface of the bushing rather than directing it to one point.

The most basic elements of bushing mechanics consist of a rotating rod or shaft that slides through a bore lined with a mechanical bushing. The stem is thus able to rotate inside the bushing with the bushing, relieving the stem from the friction and wear generated by the rotation.

In an internal combustion engine, the crankshaft is an example of the typical mechanical rolling bearing that is lubricated. The connecting rods are connected to the rotating crankshaft with the rotation of the crankshaft pushing the connecting rods up and down. The connection point of the steel piston rod and the polished steel shaft is a hole in the piston rod which is lined with the bushing. This particular bushing aids in the lubricating action of the engine oil in dissipating the friction of the rotating shaft.

An example of a non-lubricated mechanical bushing would be that used in the through-hull fitting of the propeller shaft on an inboard powered boat. The propeller shaft slides from the transmission, through a hole in the hull, and into the water. This hole or fitting is lined with an anticorrosive, polymer or bronze pad that dissipates friction and reduces wear to both the hull and shaft. Additionally, this fitting is designed to prevent water from entering the boat.

Babbitt metal, which is often referred to as white metal, and plastic are used far more often than any other material in the manufacture of mechanical bushings due to their effectiveness in reducing friction, as well as their light weight and relatively low cost. Other materials used in ordinary bushing include aluminum, rubber, bronze, carbon and various ceramics.

A mechanical bushing or plain bearing should not be confused with a normal bearing. A normal bearing is usually constructed of a more durable material, is less prone to being lubricated than the introduction of lubrication, and is very often a moving part in itself, as is the case with a ball bearing.

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