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Surface imperfections (O-Rings)

Defects and tolerances are referred to DIN 3771/4, which lists a number of common imperfections and maximum allowable measured defects as per table 6.

Category of surface imperfections letter symbol maximum acceptable limits (mm)
grade N
cross section (mm)
grade S
cross section (mm)
0
2,25
2,25
3,15
3,15
4,50
4,50
6,30
6,30
8,00
0
2,25
2,25
3,15
3,15
4,50
4,50
6,30
6,30
8,00
off register and mismatch (offset) a 0,08 0,10 0,13 0,15 0,15 0,08 0,08 0,10 0,12 0,13
combined flash, offset and parting line projection b 0,10 0,12 0,14 0,16 0,18 0,10 0,10 0,13 0,15 0,15
backrind c 0,18 0,27 0,36 0,53 0,70 0,10 0,15 0,20 0,20 0,30
d 0,08 0,08 0,10 0,10 0,13 0,05 0,08 0,10 0,10 0,13
excessive trimming Departure from a circular cross section due to trimming is permissible providing the resulting surface is smoothly blended and is within the tolerances
flow marks, radial orientation is not permissible e 0,05 X int.diam. 0,05 X int.diam.
1,50 1,50 6,50 6,50 6,50 1,50 1,50 5,00 5,00 5,00
f 0,08 0,08 0,08 0,08 0,08 0,05 0,05 0,05 0,05 0,05
foreign materials non fills, identations, including parting line identations g 0,60 0,80 1,00 1,30 1,70 0,15 0,25 0,40 0,63 1,00
h 0,08 0,08 0,10 0,10 0,13 0,08 0,08 0,10 0,10 0,13
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