In brief
A plain bearing is a bearing in which the shaft and bearing surface slide on one another, separated by a lubricating film or a low-friction material.
Contents
What is Plain bearing?
A plain bearing has no rolling elements. The shaft rotates or moves linearly in a bush or bearing shell. Depending on the design, a load-bearing lubricating film separates the surfaces, or the bearing material itself ensures low friction. Plain bearings are insensitive to shocks, run quietly, require little installation space and are also suitable for oscillating movements and slow rotation, where rolling bearings tend to develop false brinelling.
Hydrodynamic plain bearings build up the lubricating film through the rotation itself; they are used in large turbomachinery, compressors and electric motors. Hydrostatic bearings receive oil pressure from an external pump. Maintenance-free or low-maintenance bushes are made of oil-impregnated sintered bronze, composite materials with a sliding layer or plastic. Key parameters are inner and outer diameter, width, material, permissible surface pressure, sliding speed and temperature range.
Wear becomes apparent through increased bearing clearance, scoring or seizure marks. Common causes are lack of lubricant, dirt, edge loading due to misalignment and operation outside the permissible load.
In practice: maintenance and procurement
For a bush, state the inner and outer diameter, width, any flange dimensions, material and type of lubrication. For large bearing shells from turbomachinery, a drawing or the manufacturer part number is usually required, because the lining and tolerances are specific to the plant.
Synonyms and abbreviations: sleeve bearing · bushing · journal bearing · plain bush · slide bearing
Frequently asked questions
What is the difference between a plain bearing and a rolling bearing?
In a rolling bearing, balls or rollers roll; in a plain bearing, surfaces slide on one another. Rolling bearings have low starting friction and are standardised. Plain bearings cope better with shocks and vibration, run more quietly and need less radial space. With correct lubrication, hydrodynamic plain bearings achieve very long service lives, but they are sensitive to oil starvation.
What is a maintenance-free plain bearing?
This refers to bushes that do not need relubrication. They are made, for example, of composite materials with a low-friction sliding layer, oil-impregnated sintered bronze or engineering plastics. Their load capacity and sliding speed are limited, and service life depends on the wear of the sliding layer. They are widely used for slow oscillating and linear movements.
What information is needed to replace a plain bearing bush?
Important are inner and outer diameter with tolerance, width, for flanged bushes the flange diameter and flange thickness, material and details of lubrication. Type of movement, load, temperature and medium are also helpful. Since the same dimensions are offered in different materials, the original material should be known if possible.
How can a worn plain bearing be recognised?
Typical signs are noticeable shaft play, unusual noises, increased temperature, rising vibration levels or metal particles in the lubricant. With circulating oil bearings, bearing temperature and oil analysis indicate the condition at an early stage. Scoring, seizure marks or melted-out sliding layers are visible on removal.