STUDY: Finishing 304 Stainless Steel
304 Stainless Steel
Using a handheld
tool to finish installed parts
commercial finish for 304 stainless steel looks dull and flat
when viewed alongside polished stainless steel. A pharmaceutical
manufacturing facility noticed this after ordering 65 stainless
steel electrical enclosures.
the company had accepted the normal "unfinished" look
of the 304 enclosures, but when they were viewed alongside polished
stainless vessels, piping and equipment, this commercial finish
contrasted sharply. Though functional, the 304 stainless was aesthetically
it was discovered that all welds on the enclosures needed to be
ground flat so they would not retain bacteria when the facility
was routinely steam cleaned.
with the fabricator making the electrical enclosures, a 180-grain
(brushed) finish was agreed upon for the welded boxes already
delivered and those yet to be manufactured, an all welds were
to be ground flat.
the desired effect, an initial attempt was made using an orbital
(disk-type) polisher to grind down the weld seams, and hand finishing
was used on the boxes' surfaces to the grained effect.
polisher was the logical first choice for the fabricator because
it was on hand and is used in the shop for grinding down welds
and other applications in which the surface finish is immaterial.
Also, a handheld tool was desirable for use on the boxes already
became immediately apparent in this procedure; the circular patterns
left by the disk sander could not be completely removed by the
hand polishing; and the hand finishing being performed at the
fabricator's shop and company's facility was labor-intensive,
time consuming and costly.
for achieving the specified finish on the metal would be to use
a floor-mounted, belt-type sander/polisher. The type of belt used
determines the finish. These machines are widely used for polishing
sheets of metal and any object which has flat surfaces. The drawbacks
for these machines in this instance are that the metal must be
physically passed over the belt, and the metal must be configured
so that all the surfaces to be polished will contact the belt.
In this case,
the exposed sides of the box, or cabinets, had different planes
or shapes, so it would be very difficult to polish any side with
a floor-mounted polisher. Also, as a practical matter, the boxes
were generally more than 100 pounds each, so it would have been
difficult for any shop worker to position and hold them against
the belt. The fabricator would have relatively few opportunities
to use a floor machine in other projects, so it was difficult
to justify the cost of a floor-mounted grinder. Obviously, a floor
mounted machine could not be used on the boxes already installed.
the fabricator chose an electric, handheld surface finisher that
uses cylindrical enclosures. The tool was chosen for its ability
to apply even pressure to the workpiece, and it could be used
on the enclosures already installed.
One of the
major drawbacks of the disk grinder was that it did not press
evenly across its contact area, creating marks in the metal. Removable
nylon roller guides on the front and back of the finishing tool
helped the operator maintain an even pressure as it moved across
the workpiece to provide a uniform finish.
tool could also be used on the installed enclosures. The offset
of the cylindrical wheel permitted the operator to grain or finish
surfaces up to the abutting walls. The tool used an 80/100 grit
sanding/polishing flap wheel to produce a finish corresponding
to the grain standard 80. The finishing tool was also used by
the fabricator to flatten the weld seams.
It is unlikely
that the cylindrical grinder/polisher will put disk grinder/polishers
on the shelf of or take the place of floor-mounted grinder/polishers.
In this instance, the handheld cylindrical grinder provided the
type of finish needed and the portability for off-site use.