DoI is defined in ASTM D430/D5767.
Beyond Mechanical
Polishing?
At least one manufacturer offers
mirror-finish stainless steel that it
claims is superior even to the socalled No. 8 grades such as those
described above. Pacific Plus Specialties, based in Dallas, offers No. 8
(so-called True No. 8) and, superior
to that, CMP Super No. 8, produced
by ��chemical mechanical polishing.��
This is a technique almost universally
used in polishing of semiconductor
silicon wafers and associated copper
surfaces in electronics, but its use
for larger surfaces (nominal 1,200
�� 2,400 mm) is very rarely found.
The highest possible degree of
surface finish is usually desirable
for two distinct reasons. In the short
term, it��s desired both for aesthetic
and functional reasons. In the
longer term��months and years��
there��s abundant evidence that the
TaBle 2���oPTical Values for Mirror-finish saMPles
Sample
Gloss(GU)
R(spec)
DoI
Haze
R
77
76
96.6
0
0
79
82
95.6
1.6
A
89
97
96.5
0.7
smoother the surface, the slower
the corrosion or tarnishing, since it
is more difficult for such micron or
sub-micron sized particles to lodge.
What seemed to be identical grades
of mirror-finish stainless steel from
different manufacturers differed
significantly in their surface finish
and optical properties, though all
conformed to the relevant standard.
The shown measurements enable
such differences to be identified
and quantitatively characterized,
and the relevant standards could
usefully be revised to include such
measurements. There is not always a
simple relationship between surface
roughness and optical properties.
Manufacturers of this type of
product should provide purchasers
with technical information as to the
state of surface finish and not just
rely on the ill-defined classification
laid down in existing standards. n
Anselm Kuhn is with Metal Finishing
Information Services and can be reached
at office@finpubs.com. John Fletcher is
with Elcometer, elcometer.com.
LearnMORE
Lasers Put a Shine on Metals
To read how researchers at the Fraunhofer
Institute for Laser Technology ILT in Aachen
have developed a way of automating polishing
work, visit pfonline.com/news/lasers-puta-shine-on-metals(2).
Let���s get started
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