BS ISO 6621-5:2020 pdf download.Internal combustion engines — Piston rings.
4 Visible defects
4.1 General Visible defects are divided into two principle classes as described in 4.2 to 4.5. The first class covers those defects frequently found in castings and includes such defects as porosity, sand inclusions, cavities, etc. The second class of defect covers mechanical abrasions which may occur during forming, machining or handling of the rings, and includes scratches, dents, chipping, burrs and cracks. Inspection of piston rings for such defects is generally carried out visually, without magnification, by inspectors having normal eyesight, corrected if necessary. It is not intended that every ring be rigorously inspected for size and distribution of defects, but rather that the values given in the tables and text be used as a general guide. However, in case of doubt, the values given should be used as the means of judging the quality of the rings.
4.2 Pores, cavities and sand inclusions Such defects are permissible on uncoated surfaces and edges provided that the values given in Table 1 for size, number and spacing are not exceeded.
4.3 Scratches, indentations, depressions and cracks
4.3.1 Scratches
Isolated scratches are permissible provided that:
— no burrs are produced exceeding the permissible values given in 4.4.1.1;
— on turned peripheral surfaces, they are not deeper than the tool marks;
— on non-turned peripheral surfaces, they are not deeper than 0,004 mm;
— on the side faces, they are not deeper than 0,01 mm; and
— on other surfaces, they are not deeper than 0,06 mm.
4.3.2 Indentations, depressions
Indentations and depressions are permissible provided that:
— the values given in Table 1 for number and spacing of defects are met;
— no burrs are produced exceeding the permissible values given in 4.4.1.1; and
— they do not exceed the values for size and depth given in Table 2.
Rings of a plated/coated/nitrided type shall not have indentations or depressions on the periphery.
NOTE Indentations arising from hardness measurements on the side faces are acceptable provided that they do not exceed the limits given in Tables 2 and 11.
4.3.3 Cracks
No cracks are permissible in the base material.
See also 4.5.4 for chromium-plated peripheral surfaces and 4.5.6 for nitrided surfaces.
4.4.2 Chipping and similar defects on peripheral edges and peripheral edges at the gap.
Chipping and similar defects are permitted at these points provided that:
— they are free of loosely adhering particles;
— no burrs are produced exceeding the values permitted in 4.4.1.1;
— they do not exceed the values given in the following tables:
— Table 5 for plain rings;
— Table 6 for chromium plated or nitrided rings;
— Table 7 for spray coated rings;
— Table 8 for PVD (excluding DLC) coated rings;
— Table 9 for chamfers on all rings.
Typical defects are illustrated in Figures 1 and 2.BS ISO 6621-5 pdf download.