The International Organization of Standardization is a worldwide federation of national standards bodies. ISO 3601-3 specifies the quality acceptance criteria of O-rings used in fluid systems, the dimensions of which are standardized in ISO 3601-1, ISO 16031-1 and ISO 16031-2.
ISO 3601-3 also defines and classifies surface imperfections on O-rings and specifies maximum acceptable limits for these imperfections.
ISO 3601-3 is also applicable to O-rings to be used in aerospace construction.
Surface imperfections and flashes on O-rings are influenced by tolerance, finish, and cleanliness. These imperfections are formed during production of the O-rings by several causes, including:
- Inaccurate temperatures
- Inlcusion of air
- Inaccurate installation of the mold
- Inaccurate de-burring
- Insufficient flow of the elastomer
A flash is a very thin gage, sometimes a film-like material, which extends
from the parting line projection, and shall be removed.
The grade assigned to an elastomer defines the level of quality with regards to its surface condition. The grades are:
- Grade N – General Purpose – identifies acceptance criteria for O-rings intended for general use.
- Grade S – Special – identifies acceptance criteria for O-rings intended for applications requiring a higher level of quality and/or precision with respect to dimensional tolerances of surface imperfections.
- Grade CS – Critical Service – This grade identifies acceptance criteria for O-rings intended for applications requiring a much higher level of quality and/or precision with respect to dimensional tolerances of surface imperfections.