General
Performances and types
Selection criterions for metal O-rings
Coating and quality of finish
Sealing specification

Coating or electroplating

By means of coating or electroplating of the metal O-ring a higher adhesion and a more ductile (softer) surface is obtained, so that an adaptation to microscopic irregularities in the groove or flange can be enabled. Based upon the following formula the leakage of liquids can be determined approximately for non electroplated seals:

When the calculated leakage is &Mac179; 10-3 to &Mac179; 10-4 cm3/s, the effective leakage may possibly be zero owing to the surface tension. When leakage occurs it should be proportional to the sealing diameter and correspond to the value of the above equation multiplied by D/2 (D= sealing diameter). The effective leakage probably will be under the calculated value. Even helium impermeable connections may be prduced upon practical selected O-rings, coating or electroplating. The results range at a pressure difference of 1 bar and a leakage between 10-6 to 10-12 mbar.l/s.

Also uncoated rings and customized performances are additionally available to the following indicated coating materials:

temperature limit for coatings:

Quality of finish

Recommended qualities of finish of the groove and the jointing face of the flange:

• 0.4 µm Ra (N5) - for uncoated rings
• 0.8 to 2,54 µm Ra (N6-N8) - for electroplated or coated rings
• 0.4 µm Ra (N5) - for gases, vacuum or liquids of low viscosity (water)
• 0.8 µm Ra (N6) - for medium

Ghost lines on the groove surface or flange facing have to be free of dirt, grinding dust or other impurities.

The following surface roughnesses are usual in practical operation: