During the last two decades, there has been a revolution in the advancement and use of highly engineered plastics in bushing applications. Plastic bearings are now designed to stand up to high speeds and loads, temperature extremes, caustic chemicals, and a wide range of other application requirements and environmental factors. In this Tech Talk, uncover the top 5 reasons for replacing PTFE-lined bearings with engineered plastic options.

1. Thicker wear surface

A PTFE-lined bearing is composed of a metal shell and a very thin coating of polytetrafluroethylene, or PTFE, applied to the inside as the wear surface of the bearing. These types of bearings typically have a maximum wear surface of 0.025 mm, or about 0.001 inches. As the PTFE lining is stripped or worn off during operation, the metal shell becomes exposed, creating a metal-on-metal effect between the bearing and the shaft; this can cause serious shaft damage, or seizing of the bearing. This issue is most common when bearings are used in oscillating applications, or where high edge loads are present.

In comparison, engineered plastic bearings are comprised of advanced polymer compounds, which contain particles of solid lubricant embedded in millions of tiny chambers throughout the entirety of the material. During operation, these particles of solid lubricant are transferred onto the shaft to help lower the coefficient of friction and rate of wear, and eliminate the risk of metal-on-metal contact. This allows the acceptable amount of wear to be determined by the type of application, unlike PTFE-lined alternatives, which will fail if the wear exceeds the 0.025 mm lining's thickness.

2. Resistance to corrosion and chemicals

3. Weight savings

PTFE-lined bearings weigh much more than a full plastic option. When using a heavier bearing, no matter what the material, more energy is required to operate the bearing system. This can be problematic, especially in vehicle applications, such as automobiles, aerospace applications, recreational vehicles, and bicycles.

In contrast, plastic bearings are extremely lightweight, approximately 80% less than a PTFE-lined option. The reduced weight can reduce fuel consumption and carbon dioxide output, reducing the overall drive power requirement. To compare, an iglide® G300 plastic bearing weighs in at 0.23 oz, or 6.5 grams, while a comparable size PTFE-lined bearing comes in at 1.2 oz, or just over 34 grams.

4. Constant coefficient of friction

Thanks to the very low values of PTFE, the coefficient of friction of a PTFE-lined bearing is usually very good during the beginning of the bearing's service life. However, the very thin PTFE layer will be worn away over time, creating a rapid increase in the COF as metal-on-metal contact occurs. On the other hand, iglide® plastic bearing materials are a homogenous blend of base polymers, strengthening fibers, and solid lubricants. With particles of lubricant throughout the entire bearing thickness, the bearings have a brief start-up phase while they mate with the shaft surface, after which the COF remains constant throughout the entirety of the bearing's service life. See a comparison of iglide® bearings compared to PTFE-lined in terms of rotation vs COF in the above graph.

In-house testing was also carried out to investigate how friction between the plain bearings and their shafts changed through the service life/wear of the bearing. The COF of iglide® plastic bearings and metallic PTFE-lined bearing options were tested as brand new parts, then after 100 hours of rotation. This test was performed at 0.33 ft/s (0.1 m/s) under a load of 145 psi (1 MPa). Results showed that while both bearings exhibited the same COF as new parts, as wear occurred, the COF of the PTFE-lined bearings increased exponentially, as opposed to only a nominal increase in COF by the iglide® bearings.

5. RoHS compliance

Since 2006, RoHS (Restriction of the use of Hazardous Substances) has steadily tightened guidelines set to limit the values of industrially-necessary, yet potentially harmful substances, including lead, hexavelent chromium, mercury, polybrominated biophenyls, polybrominated diphenyl ethers, and cadmium in the manufacture of electronics and electrical equipment.