What’s a Sleeve Bearing?

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A sleeve bearing is a porous cylindrical bearing with an internal rotating cylinder that can be lubricated with oil, molten metal, graphite, or polymers. They are made of compressed powder metal and can be shielded from dust and dirt with seals. Sleeve bearings are used in many machines, but can fail from lack of lubrication.

A sleeve bearing is a type of cylindrical bearing. It gets its name from having a single internal rotating cylinder inside it. Sleeve bearings are porous, so they suck in oil applied to the outer sleeve.

Sleeve bearings are a kind of plain bearing, i.e. bearings with few moving parts. Many spherical ball bearings have an inner ring, which is lined with smaller balls on the inside. Unlike regular ball bearings, a sleeve bearing has only two moving parts; the outer sleeve and the inner rotating cylinder. They are also known as journal bearings, after the technical term for the outer sleeve. The outer path of a sleeve bearing can be entire, split, or clamped between halves.

Sleeve bearings can be made of compressed powder metal, such as bronze or copper. Because of the material they are made of, metal is microscopically porous. When they are oiled on the outside, the oil will be sucked in through the pores to lubricate the inside cylinder.

A sleeve bearing can be lubricated in a number of ways besides oiling. Sometimes molten metal or graphite is used. Some man-made polymers can lubricate moving parts without seizing in extremely low temperatures. Other sleeve bearings are lined with porous wood and oiled so that the oil is sucked out more easily.

Although self-lubricating, sleeve bearings often fail from lack of lubrication. The inner bearing may wear at the sleeve until the space is no longer perfectly cylindrical. This could cause the bearing to rattle when it moves, adversely affecting the movement of the mechanism. Other times, there may not be enough lubricant or the lubricant may become viscous due to adverse temperature conditions. When there is not enough lubrication, the bearing will stop moving.

Because of these problems, sleeve bearings are often elaborately shielded from dust and dirt by means of seals. A designer or mechanic must carefully consider where a sleeve bearing will be located in a machine before using it. They are criticized for being finickier than ball bearings as inadequate lubricant will cause them to stop completely rather than wear out gradually over time.

A sleeve bearing is an integral part of many machines used in everyday life. Automobiles, household appliances, fans and office machines can all use sleeve bearings.

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