This part of ISO 6621 specifies those quality aspects which are capable of definition but not normally found on a drawing specification.
It covers the following :
— single-piece piston rings of grey, carbidic, malleable, spheroidal graphite cast iron or steel;
— multi-piece piston rings (oil control rings) consisting of cast iron parts and spring components;
— single-piece and multi-piece rings of steel, i.e. oil control rings in the form of strip steel components or steel segments (rails) with spring expander components.
In addition to specifying certain of the limits of acceptance relating to inspection measuring principles {covered by ISO 6621-2), this part of ISO 6621 also covers those features for which no recognized quantitative measurement procedures exist and which are only checked visually with normal eyesight (spectacles if worn normally) and without magnification. Such features (superficial defects) are additional to the standard tolerances of ring width, radial wall thickness and closed gap.
This part of ISO 6621 does not establish acceptable quality levels (AQL), it being left to manufacturer and purchaser to decide the appropriate levels jointly. In this case the recom-mendations of ISO 2859 should be followed.
The requirements of this part of ISO 6621 apply to all rings up to and including 200 mm diameter covered by the above classi-fication for both reciprocating internal combustion engines and compressors.