Full definition
Polytetrafluoroethylene (PTFE), commonly known by the brand name Teflon, is a high-performance fluoropolymer renowned for its exceptional chemical resistance, making it a preferred material for seals in demanding industrial applications. PTFE can withstand nearly all industrial chemicals, solvents, acids, and bases, with the notable exceptions of molten alkali metals and fluorinating agents at elevated temperatures. Its operational temperature range is impressive, from -200°C to +260°C for continuous use, which allows it to function effectively in diverse environmental conditions. Additionally, PTFE possesses an extremely low coefficient of friction (0.04-0.10), the lowest of any solid material, which significantly reduces wear and prevents the stick-slip phenomenon, a critical factor in maintaining the reliability of dynamic seals.
As a seal material, PTFE is available in several forms, each catering to specific industrial needs. Solid PTFE is commonly used to manufacture machined gaskets, backup rings, and piston/rod seals, particularly in chemical service applications. However, it does have limitations due to its tendency to cold flow (creep) under sustained load. This necessitates careful groove design and periodic retightening to maintain an effective seal. To address these limitations, filled PTFE variants are introduced. These are enhanced with materials like glass fiber (15-25%), which improves wear resistance and creep behavior; carbon or graphite, which enhances wear and thermal conductivity; bronze, which offers superior wear and thermal conductivity characteristics; and MoS₂ for dry lubrication properties.
Another innovative application of PTFE in seal technology is the spring-energized PTFE seal, which features a V-shaped or U-shaped PTFE jacket supported by an internal metal or elastomer spring. This design effectively addresses the cold-flow challenge while ensuring consistent sealing force and retaining the chemical resistance benefits of PTFE. PTFE-encapsulated O-rings are also noteworthy, consisting of a FEP or PFA outer jacket enclosing a silicone or FKM core, which enhances spring-back capabilities. These solutions meet stringent industry standards, including ASTM D4894/D4895, ensuring reliability and performance in critical sealing applications. Leading brands in the market include Parker (Parbak), Greene Tweed (Chemraz), and Bal Seal, which offer a range of PTFE sealing products tailored for various industrial requirements.