Sealing technology manual for the process industry - PTFE

General properties • Density: 2.10 to 2.30 g/cm3 • Hardness 55 to 60 Shore D • The thermally reliable application range of PTFE is be- tween –200 °C and +250 °C (–328 °F and +482 °F). At tem- peratures above +400 °C (+752 °F), highly toxic pyrolysis products such as fluorophosgene (COF2 ) are released • Special types of PTFE can be welded • To a certain degree, PTFE has an innate memory-effect, which means that it seeks to go back to its original shape. This is based on the extremely long chains of molecules that build up PTFE Products • Rotary shaft seals • Bellows • U-packings • Slide bearings • V-Seal set packings • O-rings Thanks to its composition, PTFE (polytetrafluoroethylene) has a number of excellent properties for the food, chemi- cal and pharmaceutical industries. The chemical resistance exceeds that of all elastomer materials and thermoplas- tics. Thus, a broad portfolio of applications in almost all media is possible. The extremely large thermal application range of this mate- rial allows it to even be used in contact with liquid gases. It should be kept in mind that the material is not elastic; as such, it cannot simply be used to replace elastomer materials. The excellent chemical resistance of PTFE is based on the strong bond between the carbon and fluorine atoms, which is due to the strong electronegativity of fluorine. In order to break these bonds, the contacting materials need to use a lot of energy which is not possible in most food and phar- maceutical applications. PTFE is extremely resistant to all acids, bases, alcohols, ketones, benzines, oil and other sub- stances. The material is only non-resistant to very strong reducing agents, such as solutions of alkali metals (e.g. so- dium) in liquid ammonia or very strong oxidizing agents, such as elemental fluorine at high temperatures. PTFE has a very low coefficient of friction. This means that it glides as well over PTFE as wet ice over wet ice. In addi- tion, the static friction is equal to the dynamic friction, so that the transition from standstill to movement takes place without jerking. The “stick-slip” effect is thereby prevented. There are almost no materials that adhere to PTFE, since its surface tension is extremely low. The surface may be prepared for bonding by targeted etching. PTFE APPENDIX PRODUCT PORTFOLIO MATERIALS RESISTANCE & PURITY ENGINEERING PLASTICS ELASTOMERIC MATERIALS TECHNICAL FUNDAMENTALS INTRODUCTION 49

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