Flanges 41/2 inch OD and smaller are made from 304 electroslag remelt (ESR) bar stock. ESR is a refining process that produces stainless steel with higher purity, fewer inclusions and more uniform grain structure to eliminate microscopic leak paths. Larger CF flanges are made from Argon Oxygen Decarburization (AOD) 304 stainless steel. This material is certified to meet ASTM-240 and has less than 0.01% sulfur to prevent sulfur stringers. Grain size is 3 to 6 per ASTM E-112. Maximum inclusion size is 2.5 per ASTM E-45. Normally our standard CF material is in the low carbon range for 304 stainless steel. As specials 304L and 316L material can be supplied in AOD or roll-forged rings.
Machining is consistent with good UHV practice. Machine coolant is sulfur free to reduce outgassing. State-ofthe- art CNC machine centers are used to produce flanges with consistent high quality. Flanges are machine washed in approved aqueous detergent after machining. Chem-cleaning and clean room packaging are available.
CF flanges utilize an OFHC copper gasket to produce a vacuum tight seal up to 10-13 Torr, even when baked repeatedly to 450÷C. When the copper gasket is compressed between the knife edges of CF flanges, its material flows laterally to fill surface imperfections. Ebara offers CF flanges in rotatable as well as nonrotatable versions. (Refer to diagram on page 48.) When components of several systems are used interchangeably, the use of rotatable flanges is recommended. Assembly is facilitated by rotating the receiver portion of the flange to align its bolt holes with those of the mating flange. The insert is welded to the tube or component and contains the knife edge portion of the CF flange.
Nonrotatable CF flanges, unlike rotatable, contain both sealing surface and bolt holes in one unit. This makes the nonrotatable flange less expensive, and therefore the preferred choice when mating component orientation is not a concern. All fittings are priced with a rotatable flange opposing a nonrotatable. For fittings with all nonrotatable flanges subtract the difference in price between a rotatable and nonrotatable flange of the desired size multiplied by the number of additional nonrotatable flanges.