1. MECHANICAL FINISHING
Precision Finishing Processes
in Centrifugal Barrel Equipment
Methods promise faster cycling in select applications.
By David A. Davidson, Society of Manufacturing Engineers, 2006 Chair: Deburring
Technical Committee, Spokane, Wash.
L
arge numbers of parts can be uniformly edge
and surface finished in mass finishing equip-
ment. Process development in recent years has
facilitated the creation of very refined surfaces by
processing parts in a series of successively finer
processes in high-energy centrifugal equipment.
Nearly all manufactured and fabricated compo-
nents require some edge and surface finish prepa-
ration prior to final assembly. Although many parts
today are still individually handled and processed
with hand tools or hand-held power tools, it has
become almost universally accepted that utiliza-
tion of mass finishing techniques are preferred for
both their economic and technical merits, whenev-
er possible. Utilizing energy developed from motion
imparted to the containers or vessels in mass fin-
ishing equipment, loose abrasive, or polishing
media can produce a wide range of desirable edge
and surface effects.
Roughly machined, milled, molded, stamped, or
cast parts can be transformed into attractive parts
free or burrs, sharp edges, and corners with uni-
form surfaces that can range from the utilitarian
to the highly aesthetic. Among the specific tasks
these processes are specified to perform are clean-
ing, deburring, descaling, surface smoothing, edge-
break, radius formation, removal of surface con-
taminants from heat treat and other processes,
preplate, prepaint or coating surface preparation,
blending in surface irregularities from machining
or fabricating operations, producing reflective sur-
faces with nonabrasive burnishing media, refining
and polishing surfaces, and developing superfinish
or microfinish equivalent surface profiles.
CENTRIFUGAL BARREL FINISHING
Although many types of manufactured components
with high-volume output are abrasively processed
with barrel and vibratory finishing equipment,
many different types of parts with specialized or
precision edge and surface finish requirements are
processed in high-energy centrifugal barrel equip-
ment (see Figures 1–3).
Centrifugal barrel finishing (CBF) is a high-energy
finishing method (see Figure 4), which has come into
widespread acceptance in the last 25 to 30 years.
Although not nearly as universal in application as
vibratory finishing, many important CBF applications
have been developed in the last few decades.
Similar in some respects to barrel finishing, in
that a drum-type container is partially filled with
media and set in motion to create a sliding action of
the contents, CBF is different from other finishing
methods in some significant ways. Among these are
the high pressures developed in terms of media con-
tact with parts, the unique sliding action induced
by rotational and centrifugal forces, and accelerat-
ed abrading or finishing action. As is true with
other high-energy processes, because time cycles
are much abbreviated, surface finishes can be
developed in minutes, which might tie up conven-
tional equipment for many hours.
The principle behind CBF is relatively straightfor-
ward. Opposing barrels or drums are positioned cir-
July/August 2006 65
Figure 1: Centrifugal barrel finishing equipment, shown here, is
used to produce very refined surface finishes.The equipment is
very versatile—it can be used for both highly abrasive and pol-
ishing processes. The large, 220-liter-capacity machine to the
left can process large numbers of small parts in production, or
it can process larger parts by segregated processing in individ-
ual chambers or fixturing. The smaller machine has a total
capacity of 12 liters and is useful for smaller operations such as
dental laboratories, jewelry manufacturing, and precision screw
machine applications. It has a much higher degree of portabili-
ty than similar equipment in that it can be rolled from location
to location, and use single-phase, 110V current. (Photo courtesy
of Mass Finishing, Inc.)
2. cumferentially on a turret. (Most systems have
either two or four barrels mounted on the turret;
some manufacturers favor a vertical setup, and oth-
ers a horizontal orientation for the turret.) As the
turret rotates at high speed, the barrels are coun-
terrotated, creating very high G-forces or pressures,
as well as considerable media sliding action within
the drums.
Pressures as high as 50 Gs have been claimed for
some equipment. The more standard equipment
types range in size from one cubic foot (30 L) to 10
cubic feet, although much larger equipment has
been built for some applications.
Media used in these types of processes tend to be
a great deal smaller than the common sizes chosen
MECHANICAL FINISHING
66 www.metalfinishing.com
Figure 2: Centrifugal barrels are being used to develop very
demanding finish specifications, such as that shown here on
both the cast acrylic denture and dental partial frame. To pro-
duce precision finishes of this order, multiple process cycles in
the correct sequence are required that utilize differing media
types, including (1) ceramic abrasive media, (2) plastic fine fin-
ishing media, and (3) dry process polishing media. Processes
utilizing similar sequential steps are also specified for medical,
aerospace, bearing, electronic, automotive, and jewelry applica-
tions.The aesthetically desirable surface finishes developed on
the dental parts shown here also have important functional
characteristics, including reduced plaque adhesion and metal
fatigue resistance. (Photo courtesy of Mass Finishing, Inc.)
Figure 3: Close-up photo showing acrylic dentures and ceramic
media in processing step 1 as outlined in the caption for dental
parts shown in Figure 2. In this view, a 30-liter-capacity machine
is shown with four separate removable hexagonal barrel com-
partments with polyurethane linings. Typically, the abrasive
cycles in this type of processing are done in conjunction with an
aqueous solution in addition to the abrasive media, making for
a “wet process.” The final process often makes use of soft pol-
ishing media in a dry environment. (Photo courtesy of Metal
Finishing, Inc.)
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3. July/August 2006 67
MECHANICAL FINISHING
for barrel and vibratory process-
es. The smaller media, in such a
high-pressure environment, are
capable of performing much
more work than would be the
case in lower-energy equip-
ment. They also enhance access
to all areas of the part and con-
tribute to the ability of the
equipment to develop very fine
finishes. In addition to the abil-
ity to produce meaningful sur-
face finish effects rapidly, and
to produce fine finishes, CBF
has the ability to impart com-
pressive stress into critical
parts that require extended
metal fatigue resistance.
Small and more delicate parts
can also be processed with confi-
dence, as the unique sliding
action of the process seems to
hold parts in position relative to
each other, and there is general-
ly little difficulty experienced
with part impingement with
proper media and part loading.
Dry process media can be used in
certain types of equipment and is
useful for light deburring, polish-
ing, and producing very refined
isotropic superfinishes.
Practicality and questions of
cost effectiveness often deter-
mine whether high-energy
methods are selected over con-
ventional barrel or vibratory
processes. If acceptable surface
finishes can be developed in a
few hours, conventional equip-
ment is usually the most eco-
nomic alternative. CBF equip-
ment’s strong suit is the ability
to develop surface finishes that
may require lengthy time cycles
in conventional equipment and
the capability to develop a wide
range of special surface finishes
required for demanding and
critical applications.
REFERENCES:
Davidson, D.A., “Micro-Finishing
and Surface Texture,” Metal
Finishing, 100(7):10–12; 2002.
Davidson, D.A., “Mass Finishing
Processes,” 2005 Metal Finishing
Guidebook and Directory,
103(6A):78–89; 2005.
Hignett, J. Bernard, “Centrifugal
Barrel Deburring and Surface
Conditioning–Some Recent
Developments,” Technical
Paper: MR79-567, Society of
Manufacturing Engineers,
Dearborn, Mich.; 1979.
Gillespie, Laroux, Deburring and
Edge-Finishing Handbook,
Society of Manufacturing
Engineers, Dearborn, Mich.;
1999.
For more information, contact
Dave Davidson at (e-mail) ddavid-
son@mgnh.dyndns.org or visit
www.deburringsolutions.com. mf
Figure 4: Four barrels are mounted at the periphery of a
large turret. Each barrel is loaded with media, parts,
and water to approximately 50% to 90% full. During
operation, rotation of the large turret creates a cen-
trifugal force on the media and parts inside each barrel.
This force compacts the load into a tight mass, causing
the media and parts to slide against each other, remov-
ing burrs and creating superior finishes.This action also
reduces the cycle time needed to complete the finish-
ing of the parts by up to a factor of 30 over conven-
tional vibratory and barrel equipment. (Diagram cour-
tesy of Mass Finishing, Inc.)
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