What is the purpose of dimples in PTFE in bridge bearings?Posted in Bridge Engineering | Email This Post |
PTFE is a flurocarbon polymer which possesses good chemical resistance and can function in a wide range of temperature. The most important characteristic of this material is its low coefficient of friction. PTFE has the lowest coefficients of static and dynamic friction of any solid with absence of stick-slip movement. The coefficient of friction is found to decrease with an increase in compressive stress. However, PTFE do have some demerits like high thermal expansion and low compressive strength.
In designing the complementary contact plate with PTFE sliding surface, stainless steel plates are normally selected where the plates should be larger than PTFE surface to allow movement without exposing the PTFE. Moreover, it is recommended that the stainless steel surface be positioned on top of the PTFE surface to avoid contamination by possible accumulation of dirt and rubbish on the larger lower plates. Lubricants are sometimes introduced to reduce the friction between the PTFE surface and the upper stainless steel plate. Dimples are designed on PTFE surfaces to act as reservoirs for lubricant and these reservoirs are uniformly distributed over the surface of PTFE and normally they cover about 20%-30% of the
surface area. Hence, the PTFE may be designed with dimples to avoid the lubricant from squeezing out under repeated translation movements.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.