Quality management audit checklist

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Surface Finishes
Background
The finish quality of a machined surface is very important in industries that require sanitary
surfaces such as Food, Biotech, Pharmaceutical, and Semiconductor manufacturing. There
are a number of ways to define the Surface Finish, and this
Tech Talk
attempts to give a
simple overview of the common terms. Surface finish measurement procedures, general
terminology, definitions of most parameters and filtering information can be found in American
Standard ASME B46.1 - 2002, Surface Texture, and in International Standards, ISO 4287 and
ISO 4288.
Common terms
Ra
The most common surface roughness parameter is Ra, or Arithmetic Average
Roughness. It basically reflects the average height of roughness component
irregularities from a mean line. Ra provides a simple value for accept/reject
decisions. It is a default parameter on a drawing if not otherwise specified, and is
available even in the least sophisticated measuring instruments. Ra is not a good
discriminator for different types of surfaces as it is incapable of differentiating
between “spiky” and “scratched” surfaces having the same Ra.
Rp
Maximum Peak height
Rv
Maximum Valley depth
Ry
maximum Peak-to-Valley Roughness height
Rz
Mean Roughness Depth. It is the average distance between the highest peak and
the deepest valley in five sampling lengths, or cutoffs. Rz is more sensitive then Ra
to the changes in surface finish because maximum profile heights, and not the
averages, are being examined.
Grit
Number of abrasive grains per given area
EP Electro polish
Polished Finish
The high end of the sanitary finishes is an electro-polished ID which yields a 10 or 15 μ-inch
Ra maximum roughness. These electro-polished products are generally used in very high
purity applications.
Mill Finish Industrial
32 Ra Sanitary
20 & 15 Ra Pharmaceutical
20 RaEP
Pharmaceutical
15 RaEP
Ultra-Pure Applications
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Surface Finishes Cross-Reference Chart
Common
Name
Grit
#
USA
Finish
#
Ra
Microinch
EP Range
Ra Microinch
Ra
Micron
Rmax
Microinc
h
Rmax
Micron
Appx RMS
Micron
ISO
#
ASTM Std
Ra Microinch
Japanese
Std
2000
50 7875 200
N12
1000
25
3940
100
N11
500
12.5 1968 50
N10
Mill Plate
60
1
250
50 max
6.3
985
25
N9
140 max
125
3.2 492 12.5
N8
Satin Sheet
80
2
40-60
70 max
80
63
1.6
6.3
N7
100-
120
3
52
58
Commercial #4 120 4
40-60
3A Sanitary
150
4
30-35
42 max
15-20
42-47
45 max
ANSI #4
32
0.8 126 3.2
N6
Sanitary Finish
180
4
20-30
30 max
15-20
34
25 max
Buff #100
Biotech Finish
200-
220
4
20-25
25 max
240
6
15-20
10-15
17
8-20
16
0.4
63
1.6
17 max
N5
6-15
320
7
8-12
12 max
14
12
0.3
59
1.5 13-14
Buff #200
8
0.2
31
0.8
9
N4
Buff #300
Mirror Finish 400
8
4-8
Super Mirror
Finish
500
8
3-8
<4
Super Mirror
Finish
500 8
4
0.1
16
0.4
4-10
N3
Buff #400
appx
2
0.05
8
0.2
N2
1
0.025 4
0.1
N1
THIS INFORMATION IS SUPPLIED “AS IS” WITHOUT A GUARANTEE OF ANY KIND. Clipper Controls Inc. does not guarantee that the data is suitable for your particular application, nor do we
assume any responsibility. © Clipper Controls Inc. 2006