This article from Igus explains the five major advantages that technopolymer bearings - often referred to as 'plastic bearings' offer over traditional alternatives.
Some engineers hesitate to use plastic bearings in their designs, maybe because they have trusted metal and bronze bearings for years or they simply do not believe that plastics can handle the tough applications or environmental conditions. Plastic bearings, however, can endure extreme temperatures, heavy loads and high speeds. However, it's important to understand both the advantages and disadvantages of the options available.
Metal-backed polymer bearings based on PTFE (polytetrafluoroethylene) have a steel backing bonded to a porous bronze sintered layer that is impregnated and overlaid with the filled PTFE bearing material. This thin lining can be scratched off by contaminants, resulting in metal-to-metal contact between the bearing and shaft. This increases the coefficient of friction (COF), leading to higher wear rates and, ultimately, damage to the shaft.
With sintered-bronze bearings, oil is drawn from the bearing as it rotates on the shaft (minimum speed of 1m/s). The oil creates a thin film that separates the bearing and shaft, preventing wear and shaft damage. At high speeds, a low COF is achieved. However, shaft oscillation, slow speeds, irregular use or uneven loads can prevent the film lubrication from being maintained. As a result, the coefficient of friction and wear rates increase. This type of bearing should really never be used for linear motion.
Self-lubricating polymer bearings contain solid lubricants embedded in millions of tiny chambers within the fibre-reinforced material. During operation, the bearing transfers lubricant onto the shaft to help lower the COF. Unlike a sintered-bronze bushing, polymer bearings release solid lubricants as soon as the bearing or shaft is set in motion, regardless of the speed. The fibre-reinforced materials inside the bearing withstand high forces or edge loads. Plastic bearings can also be used on many different shaft types.
In addition, it is important not to confuse high-performance plastic bearings with bearings manufactured from 'standard' polymer grades. With iglidur plastic plain bearings, the life of the bearing can be calculated accurately according to wear rates, actual testing results and specific application parameters. Igus provides the Expert System - a database in which users enter the maximum loads, speeds, temperatures, and shaft and housing materials; the system then calculates the appropriate plastic bearing and its expected lifetime based on real-world testing.
Five major benefits of plastic bearings
Iglidur plastic plain bearings are tested, predictable and readily available machine components. They offer many advantages, but these five would make the top of any engineer's list:
1 - Freedom from maintenance. Plastic plain bearings can replace bronze, metal-backed and custom injection-moulded bearings in almost any application. Their resistance to dirt, dust and chemicals make plastic bearings 'fit-and-forget' components.
2 - Cost savings. Plastic plain bearings can reduce costs by up to 25 per cent. They feature high wear resistance, a low coefficient of friction and can replace more costly alternatives in a variety of applications.
3 - No messy lubricants. Self-lubricating bearings transfer lubricant onto the shaft to help lower the coefficient of friction and are impervious to dirt, dust or other contaminants. There is no need for oils or greases that are messy, require regular replenishment and can be damaging to the environment.
4 - Consistent coefficient of friction (COF). Plastic bearings are designed to maintain a low COF consistently over the lifetime of the bearing. Compared to metal-backed bearings, which can become scratched and increase the COF, plastic bearings often last longer.
5 - Resistance to corrosion and chemicals. Plastic bearings can be used in wash-down applications, salt water and harsh chemicals without compromising performance. Water can even be considered as a lubricant for plastic bearings.
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