Metal-Backed Seal Rings
ROC Carbon Type MB carbon/graphite compressor seal rings are typically double-face seals that provide a critical seal to prevent fugitive emissions. The seals are installed over the shaft, sandwiched between the rotating seal ring and stationary sleeve. The hardness of carbon and lubricating properties of graphite combine to deliver long service. Type MB compressor seal rings have an outer metal ring to reinforce the carbon/graphite and preserve seal geometry at high speeds.
ROC metal-backed seals are available in both standard replacement styles and in custom configurations to solve specific operating problems.
Seal geometry is extremely important to service life. The two seal faces must be identical so that the seal rotates at one-half speed relative to the rotating seal ring, subjecting both seal faces to the same wear rate. If not identical, one seal face will wear excessively, shortening seal life. ROC seal surfaces are lapped and polished to within 1 helium light band (less than 12 millionths of an inch) for optimum sealing performance. Precise machining also produces perfectly round seals, preventing vibration that causes premature seal failure.
Shrink Fitting and Stress Relieving
To prevent stress buildup that can shorten seal life, ROC Carbon follows a proprietary procedure that involves shrink fitting the metal ring over the carbon/graphite, followed by full stress relieving. To further assure optimum geometry, larger ROC Carbon Type MB seal rings are shipped with a carbon/graphite plug that helps prevent seal damage during storage and handling. The plug is removed prior to installation.
Carbon/graphite grades are chosen to be compatible with the fluids being handled and with the mating seal surfaces. Typical carbon grades used are in our Materials Group A, with Shore Schleroscope hardnesses ranging from 77 to 95. For operating temperatures above 500° F, metal-impregnated carbon/graphite is used. The metal also has the appropriate corrosion resistance for the intended service.