PurposeTo create a seal, gasket has to fill up the voids in the flange surface present because of surface finish and any flange rotation (or relative distortion) between the two surfaces.
The flange surface will thus give a broad indication of which gasket materials are likely to be suitable. Finishes of standard raised face flanges usually fall within the range 3.2 to 12.5mm, but this may be expressed in micro inch or roughness number.
Surface JoiningThe recommended surface finish for the compressed fibre jointing (above a thickness of 1 mm) is 3.2mm to 12.5mm Ra (125m in 500min. CLA). These values are also used for graphite laminate (above a thickness of 0.8mm).
A surface finish of 1.6mm to 6.3mm Ra (63 to 200 in. CLA) is possible for tongue and groove flange facings or for very thin gaskets (0.4mm or below).
Surface finishes below 1.6mm are not recommended due to their negative effect on creep resistance of the gasket.
Surface for Spiral Wound GasketThis type of gasket requires a range of surface finishes dependent upon the application:
- General - 3.2mm to 5.1mm Ra (125min. to 200min. CLA)
- Critical - 3.2mm Ra (125min. CLA).
- Vacuum applications - 2.0mm Ra (80min. CLA)