Release time : 2015-06-12 10:00:42
IGUS has written about the characteristics of three different types of self-lubricating bearings which are said to be maintenance-free, reducing the workload on factory technicians.
In the past, maintenance departments had to painstakingly lubricate bearings on the plant floor. However, three types of self-lubricating plain bearings are now used in most modern plants.
These include oil-filled sintered bronze bearings from the 1930s, self-lubricating metal-polymer bearings from 1950, and lubrication-free solid polymer bearings which were developed in the 1960s.
Each type of self-lubricating bearing has different wear rates and operation characteristics under specific loads, temperatures and speeds. Dust, dirt and chemicals also affect different bearings in a variety of ways. Noise levels and performance as well as the shaft materials used in the application will also affect the choice of bearing.
Oil-filled sintered bronze bearings use capillary action to create a film of oil which lubricates the works. These bearings have a low coefficient of friction, high precision and rotational speeds up to 365 surface metres per minute.
These types of bearings need high speed and rotational motion to draw the oil out and create the lubricant effect. If the shaft oscillates, or the application requires slow speed and intermittent use, the process will be affected, resulting in squeaking and increased friction.
If the bearing is exposed to high temperatures, the oil can also break down. Also, the bearings have low chemical resistance and are sensitive to dirt, edge pressure and impacts.
Metal-polymer bearings have a metal backing and a thin polymer liner. The liner contains a solid lubricant which is transferred onto the shaft during movement. These bearings have include a low coefficient of friction and high load capacity. They are also suitable for high temperatures.
Disadvantages of this type of bearing include high sensitivity to dirt, susceptibility to corrosion and inferior handling of vibrations. If there are high edge loads or oscillating movements, the polymer liner will be stripped off.
The third type is injection-moulded solid polymer bearings. These are made of a mixture of thermoplastic materials with embedded reinforcing fibres and solid lubricant. They run dry, so dirt particles do not stick to the surface.
These bearings are strong and resistant to high forces and edge loads. They have low wear rates, are resistant to chemicals and have lower noise levels. They are also corrosion-resistant and have high load capacities. Depending on the type of plastic, they may also be suited for high-temperature applications.
Another factor to consider when choosing a bearing is the nature of the shaft, which is in direct contact with the bearing. If the shaft is too rough, it can wear down the bearing. If the shaft is too smooth, not enough lubricant will be transferred, resulting in higher wear. Precision-ground shafts are best paired with sintered bronze bearings, while solid polymer bearings can run on all types of shafts.