Amelioration de la procedure d'essai d'eclatement de joints d'etancheite a base de teflon.

摘要

The objective of this work is to improve a HOt Blow-out Test procedure to determine the maximum operating temperature of Teflon-based gaskets. In parallel, an experimental fixture is developed to measure the thermal expansion coefficient of such material. This study aims to analyze the relaxation of PTFE gasketed joints due to creep at high temperature. The determination of the safe operating temperature limit of PTFE-based gaskets requires a good knowledge of its capacity to resist creep-relaxation due to temperature exposure in the short and long term. The aim of this work is to improve the HOBT standard procedure " Standard Test Method for Hot Blowout and Thermal Cycling Performance for Polytetrafluoroethylene (PTFE) Sheet or Sheet-Like Gaskets" which is under adoption by the ASTM F03 gasket committee.;Based on a previous work, the introduction of a fixed number of cycles of heating and cooling in the HOBT test procedure has shown that the cumulative permanent deformation (ratcheting damage) which has impact on reduction of the gasket stress can be taken into account. The effect of holding temperature for a short period of time will be investigated. The modified HOBT rig allows measurement of the gasket compression during the test in order to accurately quantify the cumulative permanent deformation. Several types of PTFE-based gaskets will be tested in order to cover a wide range of gaskets to justify the generalization of the modified procedure.;The different steps to achieve this project are listed below: 1. Improve the HOBT test rig by implementing a device to measure gasket compression and it variation with the thermal cycles. 2. Study the effects of the number of thermal cycling and the holding temperature on the gasket stress and the cumulative permanent deformation and the short term creep on the hot blowout characteristics of PTFE-based gaskets. 3. Development of a small fixture to measure the coefficient of thermal expansion of gasketing materials under high loads. This fixture can also measure other mechanical properties such as load compression and short term creep at high temperature. 4. Tests of hot blowout, load compression, creep and measurement of the coefficient of thermal expansion will be conducted on several PTFE-based gaskets.