Comparison of various international surface roughness systems is given in Table 2.1.
2.2.20 Factors That Affect Roughness Measurements
Relative values between different roughness systems will vary by up to 20% depending on the metal-cutting process by which they were generated. Even when considering just grinding, the abrasive type can alter the ratio of Rz to Ra, CBN often giving a higher ratio to alumina. This
|
Class |
R |
b |
V |
Class |
Class |
||||||
|
Ra |
Rt |
Rz |
RMS |
CLA |
PVA |
France |
France |
France |
France |
China |
Russia |
|
(Rm) |
(Rm) |
(Rm) |
(Rin.) |
(Rin.) |
(Rin.) |
(Rm) |
(pm) |
(Rm) |
(Rm) |
||
|
0.025 |
0.2 |
0.16 |
1.12 |
1 |
6.3 |
12C |
0.13 |
0.08 |
0.15 |
N1 |
12 |
|
0.05 |
0.3 |
0.32 |
2.2 |
2 |
12 |
11C |
0.25 |
0.15 |
0.3 |
N2 |
11 |
|
0.06 |
0.5 |
0.38 |
2.7 |
2.4 |
16 |
11B |
0.3 |
0.18 |
0.36 |
N2 |
11 |
|
0.08 |
0.6 |
0.5 |
3.6 |
3.2 |
20 |
11A |
0.4 |
0.24 |
0.48 |
N2/N3 |
11 |
|
0.1 |
0.8 |
0.63 |
4.5 |
4 |
25 |
10C |
0.5 |
0.3 |
0.6 |
N3 |
10 |
|
0.12 |
1 |
0.75 |
5.3 |
5 |
32 |
10B |
0.6 |
0.37 |
0.73 |
N3 |
10 |
|
0.16 |
1.25 |
1 |
7.1 |
6.3 |
40 |
10A |
0.8 |
0.48 |
0.97 |
N3/N4 |
10 |
|
0.2 |
1.5 |
1.25 |
9 |
8 |
50 |
9C |
1 |
0.61 |
1.22 |
N4 |
9 |
|
0.25 |
2 |
1.6 |
11.2 |
10 |
63 |
9B |
1.25 |
0.76 |
1.52 |
N4 |
9 |
|
0.31 |
2.5 |
2 |
14 |
12.5 |
80 |
9A |
1.6 |
0.95 |
1.8 |
N4/N5 |
9 |
|
0.4 |
3.2 |
2.5 |
18 |
16 |
100 |
8C |
2 |
1.2 |
2.4 |
N5 |
8 |
|
0.5 |
4 |
3.2 |
22.4 |
20 |
125 |
8B |
2.5 |
1.5 |
3 |
N5 |
8 |
|
0.63 |
5 |
4 |
28 |
25 |
160 |
8A |
3.2 |
1.9 |
3.8 |
N5/N6 |
8 |
|
0.8 |
6.3 |
5 |
35.5 |
31.5 |
200 |
7C |
4 |
2.4 |
4.8 |
N6 |
7 |
|
1 |
8 |
6.3 |
45 |
40 |
250 |
7B |
5 |
3 |
6 |
N6 |
7 |
|
1.25 |
10 |
8 |
56 |
50 |
320 |
7A |
6.3 |
3.8 |
7.6 |
N6/N7 |
7 |
|
1.6 |
12.5 |
10 |
71 |
63 |
400 |
6C |
8 |
4.7 |
9.4 |
N7 |
|
TABLE 2.1 Guideline Comparisons of International Surface Finish Systems |
|
Roughness Renault Citreon Citreon Roughness Quality |
difference also shows up cosmetically when looking visually at surfaces ground with alumina or CBN. When changing from lapping to fine grinding, the change in appearance of the finish can be dramatic, changing from a matt-pitted surface to a shiny but scratched surface, both of which have comparable surface roughness values. The type of grinding process will also affect the appearance in terms of the grind line pattern. For example, in face grinding of a shoulder using, for example, a 2A2 or 6A2 wheel, the grind gives a cross-hatch appearance as in Figure 2.6(a). In angle approach grinding, the face is produced with line contact and the lines are concentric with the journal diameter as in Figure 2.6(b).