Mechanical And Sealing Behaviors Of Expanded Polytetrafluoroethylene(ePTFE) Sealing Material

Polytetrafluoroethylene (PTFE) has widely used in electrical,mechanical and chemical applications due to its excellent physical characteristics such as high melting point,chemical resistance,heat resistance and low friction.As modified PTFE material,ePTFE greatly improve creep resistance,mechanical property and maintain all advantages of PTFE,which is more and more widely used in the sealing area.The mechanical behavior and sealing performance of ePTFE is studied in this paper.The effect of mechanical behavior,creep and thickness on sealing performance is investigated.Considering the creep of ePTFE gasket,the long-term sealing behavior is investigated through the ANSYS finite element simulation.The main contents and conclusions are as follows:(1) The mechanical properties is investigated by creep relaxation,compressibility and recovery,tension test.It is found that,due to the impact of material interface,the ultimate tensile strength and elastic modulus first increases with increasing thickness and then decrease with thickness.High density of ePTFE result in low compressibility and thickness cause high recovery.Creep relaxation of ePTFE increases with thickness increases.(2) The short-term tensile creep tests of different thickness ePTEF are carried out. It is shown that creep property of ePTFE is associated with the thickness.An appropriate Kohlrausch-Williams-Watts(KWW) model is used to explain the mechanism of thickness affecting the creep compliance and give a reasonable explanation from the perspective of the internal structure of the material.(3) Gas permeability of different thickness ePTFE gasket was investigated under different conditions,and the relations between sealing,creep,mechanical properties and thickness is analyzed.It is found that under low gasket stress ePTFE gasket is suitable for small fluctuations in the medium pressure conditions due to leakage rate greatly increases with medium pressure.Under high gasket stress ePTFE gasket is suitable for large fluctuations in the medium pressure conditions due to leakage rate have small changes.Because of the main leak way is interface leak and low recovery, Creep resistance determines the sealing performance. So,the short-term creep test is used to evaluate the performance of sealing material.The characteristic relaxation time τ can be as an sealing performance evaluation parameter. (4) Considering the viscoelastic properties of gasket materials,the finite element method(FEM) for long-term mechanical properties of bolted flange with ePTFE gasket is validated by experiment data.The relative error of simulation and experimental values is within10%.So,cosidering gasket creep,the method of ANSYS software calculating long-term mechanical behavior of bolted flange is feasible.Then the effect of gasket thickness and elastic modulus on bolt force is investigated through the finite element simulation.