MDC established its high standing in the vacuum components world after becoming one of the first licensed manufacturers of Varian’s patented ConFlat® metal-seal flange, known today to most MDC customers as the De-Seal CF metal-seal flange.
The reliable sealing performance of MDC’s Del-Seal CF flanges is a result of a unique seal design and geometry which “captures” a metal gasket material. When a flat OFE copper gasket is pressed between the conical sealing edges of two Del-Seal CF flanges, a lateral cold flow of the gasket material occurs. This cold flow is limited by a vertical flange wall or capture groove that is concentric to the sealing knife edge. Further material flow away from the seal area is severely limited and high interface pressures are developed. These pressures cause gasket material to fill minor surface imperfections and produce a highly reliable seal. At high temperatures, the “capturing” geometry maintains high pressures despite softening of the gaskets. Del-Seal CF flanges can be baked to 450°C and cooled to -200°C and are suitable for vacuum service levels of 1x10-13 Torr. They are ideally suited for the rigorous demands of ultra-high vacuum (UHV) environments and capable of maintaining seal integrity through high-temperature excursions. Del-Seal CF flanges are 100% compatible with the equivalent Varian Conflat® metal seal flanges.
Del-Seal CF flanges are classified as genderless flanges since the seal geometries on both mating flanges are identical. They are available in both rotatable and nonrotatable geometries with clearance or threaded bolt holes, and for standard tube sizes from .25 to 14.0 inches in diameter. MDC discourages resealing a Del-Seal CF flange with a previously used metal gasket and strongly recommends the installation of a new metal gasket every time a flange is fastened. When flange fasteners are tightened to their specified sealing torques a gap will remain between the mating flanges, which is normal and desirable. Tightening the flanges metal-to-metal is not necessary to achieve a UHV hermetic seal.
OFE copper, which stands for “Oxygen Free Electronic or Electrolytic grade Copper”, is the metal gasket material of choice for most UHV sealing applications. For special applications which preclude the use of pure copper, various metal gasket materials including nickel, aluminum and silver plated copper are also available.
MDC also offers specialized elastomer gaskets made of DuPont Dow Elastomers Viton® material. These can be used within existing UHV systems fitted with MDC Del-Seal CF flanges and allow frequent and repeated assembly and disassembly. These elastomer gaskets have rectangular cross sections and fit within the standard knife edge seal geometry of a Del-Seal CF metal seal flange. Note that the use of elastomer gasket seals in metal seal flanges will reduce the system’s minimum and maximum temperatures and its vacuum ratings to -20°C, 150°C and 1x10-8 Torr, respectively. The torque required to make a leak tight seal with an elastomer gasket will be reduced to 7-10 lb-ft.