The Purpose of using dimples for PTFE for pot and spherical bearing
Pot bearing and spherical bearing are used widely in the bridge construction industry. Pot bearing and spherical bearing composed of many components and has many functions. Pot and spherical bearing allow releasing of stresses generated due to increase and decrease of superstructure span due to thermal variation, shrinkage, and creep deformation. The Bearing will release these stresses by allowing the superstructure translation movement in one or two directions.
The mechanism of bearing movement is by sliding. Sliding materials will slide against a hard mat. PTFE (Polytetrafluoroethylene) used commonly as sliding materials. Sliding material should have a low friction coefficient. PTFE possesses low static and dynamic friction coefficient, which make it very suitable to slide against hard material such as stainless steel without creating high friction force. PTFE possesses excellent chemical resistance, and it can operate under a wide range of temperature. Also, the coefficient of friction for PTFE decreased with increasing compressive force. The demerits of PTFE is low compressive strength and high thermal expansion.
Stainless steel plate size should be larger than PTFE to prevent the exposing of PTFE plate to the environment and protect it from deterioration. Also, it should be placed above the PTFE plate to avoid the ingress of dirt or any harmful materials.
Lubricants are used to reduce the friction between the PTFE plate and stainless steel mat. dimples in PTFE plate are used as reservoirs for those lubricants. Dimples will cover 20% to 30% of PTFE plate. also, dimples can be used to prevent the squeezing of lubricants out from PTFE under repeated cycles of translation movements