Types of Construction
Just as the applications for plain bearings in technical devices and machinery are diverse, so too are the materials from which they are manufactured. The material used largely determines the strength and, consequently, the load-bearing capacity, thermal conductivity, as well as the friction, wear and corrosion behaviour — and ultimately the suitability for each specific application.
Sintered plain bearings
Oil-impregnated porous sintered plain bearings are usually made from bronze or iron. They typically have a pore volume of 15 to 30%, which is impregnated with oil after the sintering process, forming a lubricant reservoir that generates hydrodynamic lubrication. Due to the high thermal conductivity of copper, bronze sintered bearings exhibit better friction and wear behaviour than iron sintered bearings. However, since iron is a significantly more cost-effective raw material, iron sintered bearings offer a price advantage and are therefore used primarily where high cost pressure exists in manufacturing. These bearings are suitable for medium to high sliding speeds (up to over 20 m/s, optimum at 1 to 3 m/s) and low loads.
Compacted solid lubricant sintered plain
bearings consist of a bronze, iron or nickel alloy and contain a high proportion of solid lubricants (up to over 30% by volume), which are finely distributed throughout the entire metallic matrix, enabling maintenance-free operation. In contrast to porous oil-impregnated sintered bearings, these sintered bearings are non-porous or only marginally so. Due to the solid lubricant content, plain bearings made from these materials can be used at temperatures where oil- and grease-lubricated (sintered) plain bearings can no longer be employed, owing to the limited temperature resistance of such lubricants. These bearings are primarily used under high loads and low sliding speeds (sliding speed up to max. 2 m/s).
Bronze plain bearings
Solid-lubricated, maintenance-free
These bearings consist of cast bronze alloys (or brass alloys) fitted with a large number of bores, into which a solid lubricant is pressed. Graphite, PTFE, and molybdenum disulfide — or combinations thereof — are typically used as solid lubricants (also referred to as dry lubricants). During operation, the micro-abrasion that occurs causes the lubricant contained in the bores to be released into the bearing gap, thereby ensuring separation between shaft and bearing. Like solid lubricant sintered plain bearings, this bearing type is used under high loads and low sliding speeds (sliding speed up to max. 2 m/s).
Oil- and grease-lubricated
These bearings also consist of cast bronze alloys (or brass alloys), which are partially fitted with lubrication grooves that serve as grease reservoirs. This bearing variant is maintenance-intensive, as a permanent and sufficient oil or grease lubrication must be ensured. These bearings are used across a wide range of sliding speeds — from low speeds (e.g. with grease lubrication) up to extremely high sliding speeds (in the case of hydrodynamic plain bearings).
Plastic plain bearings
A cost-effective bearing type, available in maintenance-intensive (oil- and grease-lubricated) and maintenance-free (PTFE) versions. They offer the advantage that no metal seizure can occur and are electrically insulating. The disadvantages are that they cannot withstand high temperatures and require greater bearing clearance, which compromises guiding accuracy.
Composite plain bearings
Typically consisting of a steel backing onto which a porous bronze layer is sintered, into which a plastic sliding layer is rolled. Here too, a maintenance-free variant is available, featuring a PTFE running surface, as well as a maintenance-intensive version consisting of a low-wear plastic fitted with so-called lubrication pockets that serve as grease reservoirs.
