Centrifugal barrel finishing is a mass finishing process that uses centrifugal force to rapidly deburr, finish, and impart compressive stress on metal surfaces. Parts are loaded into barrels along with abrasive media, which are spun at high speeds up to 50 times normal gravity. This compacts the load and causes the media to smoothly slide against the parts under high pressure, removing burrs in a fraction of the time of other processes. The process is highly consistent and can achieve very fine surface finishes while processing a wide variety of high-precision and fragile components.

1. MR81-231
The Centrifugal Barrel Process-
Precision Deburring and
Surface Finishing
abstract
Centrifugal Barrel Finishing (CBF) is one of the three major mass finishing
processes, mass finishing being the most generally used mechanical
deburring and surface finishing technique in the metal working industry. The
mass finishing processes are standard in most metal working organizations
because they are both versatile and economical. CBF is a very rapid process
capable of handling high-precision and fragile components to deburr, descale
and generate edge and corner radii. While finishing components, CBF can
also impart very high compressive stress in the surface of those parts. so
improving resistance to fatigue failure. This paper outlines recent develop-
men&of equipment and process methods while offering a guide to equipment
selection and a comparison with other finishing techniques in terms of both
process capability and economics of the CBF process.
authors
J. Bernard Hignett
Vice President
The Harper Company
Richard D. Gillott
Sales Engineer
The Harper Company
conference
SME 1981 International Tool & Manufacturing
Engineering Conference
April 27-30, 1981
Detroit, Michigan
index terms
Abrasive Machining
Abrasive
Barrel Finishing
Deburring
Finishing
Metal Finishing
Polishing
Society of Manufacturing Engineers l One SME Drive l P.O. Box 930
Dearborn, Michigan 48128 l Phone (313) 271-l 500

2. INTRODUCTION
By definition, mass finishing is the processing of parts by loading them into a
container, usually with some finishing medium, water and compound, and creating
motion of the container to cause the media to rub against the components, so refining
edges and surfaces for either decorative or functional purposes. Normally, either
abrasive media or compound, or both are used so that the action is to grind away burrs,
radius exposed edges and corners and refine surfaces. Non abrasive processing may be
used to burnish surfaces, generally for decorative purposes, also to roll over any
burrs and blunt any sharp edges.
The first mass finishing equipment consisted of tumbling barrels, wooden drums
which were approximately half-filled with parts to be finished, natural stones, water
and usually a little soap. The open-ended oblique barrels were convenient, easy to
rinse out and check parts during processing, but very slow and not always producing
uniform results. Closed drums, rotating about a horizontal axis, require more labor
to operate, are not quite as slow, and produce uniform results. Conventional tumbling
barrels were the standard mass finishing process until only twenty years ago and are
still in general use. While very slow and limited in capabilities, the process is
intrinsically of low cost and can achieve excellent and consistent results.
The first substantial developments of the old tumbling methods took place in the
mid 1940's with the introduction of manufactured media, first random-shaped fused
aluminum oxide materials and then preformed shapes of ceramic bond with abrasive grain
bonded in. Compounds were developed to enhance the cut or the surface finish capabil-
ities of these media, and these developments resulted in much extending the scope of
the tumbling barrels, speeding up the process somewhat, ensuring complete consistency
of the process and enabling somewhat more awkward shapes to be processed and better
surface finishes achieved.
During the early 1950's, vibratory finishing equipment was developed, first tub
type vibrators and then bowl type. It was the development of these machines that had
the major impact on the deburring and surface conditioning processes within industry.
Vibratory equipment offers much faster processing than tumbling barrels, far greater
capability to handle larger and more complex parts as well as soft metal components,
and permits the deburring and finishing operations to become automated. It is only
twenty years ago that the new ceramic and plastic bonded media and controllable
vibratory equipment began to be fairly widely used. Only then did mass finishing
really develop from the old image of the dirty, noisy back room with its crude metal-
removal operation into a universal metalworking process.
The centrifugal barrel finishing process was developed during the late 1950's and
was first used in the metalworking industry as a deburring and surface conditioning
tool during the early 1960's. The first machines were of small capacity so that early
process development was for the deburring and finishing of very small precision parts
such as watch components,
orthodontal
instrument parts, precision miniature bearings, dental,
and jewelry components. The process was used primarily to handle the tasks
that could not be processed by conventional tumbling barrels and vibratory equipment _
primarily parts that were being deburred and finished by laborious hand techniques,
As industry demands became more sophisticated, requiring many parts to have bet-
terfinal edge and surface condition,
steadilygrew in importance.
and as parts became evermore complex, CBF
Automated equipment was developed in the early 1970's,
andvery high speed processing by
barrel to be an economical genera
automatic Harperizing (TN)'enabled
1 purpose deburring and surface fin
the centrifugal
ishing machine.
MR81-231

3. -2-
THE CENTRIFUGAL BARREL PROCESSTODAY
Centrifugal barrel equipment is used for the following applications:
Deburring
Deflashing
Descaling
Edge and corner radiusing
Surface stock removal
Refining surfaces (functional surface finishing)
Improving appearance (decorative surface finishing)
Generating compressive stress in surfaces
(improvement of resistance to fatigue failure)
Grinding of materials
The specific applications where CBF will probably offer the best mechanical
finishing method in an organization are:
1. When there is considerable manual deburring
2. When components are high precision.
3. When parts to be deburred and finished are f
4. When surface finishes better than those achi
are required.
5. When there is a wide variety of components
when equipment has to be very versatile.
and surface finishing.
ragile.
eved by other mass fin
to be processed during
ishing processes
a short period-
.
6. When inventories and work in progress need to be reduced, or when very short
process cycles are truly beneficial.
7. When floor space is at a premium.
8. When resistance to fatigue failure has to be improved.
HOWCBF WORKS
Centrifugal barrel equipment is comprised of a number of drums mounted on the
periphery of a turret. The turret rotates at high rpm in one direction while the
drums are rotated at a slower speed in the opposite direction. Parts to be deburred
and finished are loaded into each of the drums, normally together with media, water
and some form of compound. Turret rotation creates a high centrifugal force of up to
50 times earth's gravity, compacting the load within the drums into a tight mass.
Rotation of the drums causes activity of this tightly packed mass, the media slides
against the parts being processed, removing burrs and improving surfaces.
The abrading action while under the high centrifugal force results in very short
process cycles for a simple reason: While a product rubbed lightly by an abrasive is
not affected greatly, the same abrasive can dramatically affect the surface condition
of the product when rubbed with pressure increased 50 times. Process cycles will
usually be less than l/50 of the time needed to deburr or finish parts in other mass
finishing equipment.
MR81-231

4. -3-
With most modern CBF machines the speed of the turret rotation (G force) is
variable. By varying the G force it is possible to utilize the same abrasive media
for heavy grinding operations at high speed and for surface finish improvement at a
lower speed, hence combining two processes to a single automatic operation.
Varying the pressure with which the abrasive is pressed against components speeds
up the finishing process, reduces costs, improves work flow and enormously enhances
the versatility of available abrasive media. But the real values of centrifugal bar-
rel equipment extend beyond these opportunities to reduce costs. Because drums rotate
in the direction opposite to rotation of the turret, a completely smooth sliding action
of the media against the components is produced within the drums. There is no possi-
bility of parts falling or banging against each other, and there is no impingement of
media against parts. This action is completely consistent so reproducible results are
achieved, very high tolerances can be maintained, extremely fragile components can be
processed, and surface finishes even finer than one micro inch rms are obtainable.
Figure 1 and 2 show the principle of operation of CBF equipment.
Fffi.1
ETION WITHIN A CENTRIFUGAL BARREL WHINE
MEt81-231

5. -4-
Considering the forces applied to a particle or a component at the center of the
drums in Figure 1:
VI2A, = R
1
where V = velocity of the particle in a circle
A = radial acceleration of the particle
R = distance of the particle from the center of the turret
G = A/32
V = 277 Rl (RPS)
where RPS = speed of rotation of the turret in revolutions per second.
The force exerted on any particle at the center of the drum, equivalent to G,, can
therefore be defined as:
2
G, = & = 47T2 R
1
(RPS)2 = 1 . 234R, (W2
1 32 -
Clearly, any particle at the outside periphery of one of the drums of the machine has
a different force exerted upon it, equivalent to G2 where:
G2
= 4R2n2 (RPS)2 = 1.234R2 (RPS)2
32
It is apparent that the particle at Position 2 will have a greater weight of media and
other parts resting upon it than at Position 1. The force applied at Position 2 is
therefore markedly greater than at the center of the drum.
By design, with most centrifugal barrel machines,
than R,.
R2 is approximately 50% greater
These proportions result in the smoothest action.
Figure 2 shows the approximate configuration of the load within the drum of a
centrifugal barrel machine when it is in action. Because of the variation of force
applied on different particles in different drum locations, the action within the mass
of parts and media takes place throughout the load; it is not restricted to a sliding
action just along the outer surface of the load. This is the reason why process cycles
are generally faster than the simple increase of force would at first indicate. It is
also the reason action within the load is maintained as a completely smooth slide.
Figure 2 also indicates the reason why CBF employs counter-rotation of turret and
drums and why there is no waterfalling action of parts against media. It is not possi-
ble for any particle to come free from the complete load within the drum as will invar-
iably happen in conventional barrel tumbling equipment, Any tendency for a particle
to come loose from the load will of course be overcome by the fast orbiting of the
entire load in the direction of motion.
It may be significant to note that the converse of this smooth action does apply
if turret and drum rotation are the same. This non-standard motion results in a radi-
cal waterfalling or impingement action. Clearly, this is highly undesirable for nor-
mal deburrinq and finishinq operations but there are some aoolications where the
motion can o?fer real merii;. '
. .
Experiments conducted in Japan by M. Matsunago and H. Kobayashi (1.) have deter-
rate but also the
amount of finish-
mined that not only does the turret speed have a factor in the work
interior configuration of the drum itself plays a major role in the
ing accomplished.
MR81-231

6. :he
nd
r
The resu_ 1
of drums that
the most stab1
efficient and
ts of these experiments are shown in Figure 3 and indicate, for the size
was investigated, that hexagonal and heptagonal drums appear to have
e and optimum finishing efficiency,with octagonal drums a little less
other sizes significantly weaker.
Fig. 3. Photograph of drums of various profiles.
Figure 3
Figure 4 i
; sectional profi
' wear of the chi
s a graph plotting the wear of the abrasive chips against the cross-
le of the drum. From this graph it will be seen that the greater the
ps, the greater the amount of material removed from the work pieces.
Fig. 4. Effect of drum profile on finishing efficiency.
IO
9 i
l --’ /St RUN
--.. -
x--l; 2ndRUN
A
A---h 3 r-d RUN
0
/” *;
/’
A
L “1
FL
-----5.
x e
1
3 4 5 6 7 8 9 /o // /2 C/RCULR_P_
/tUfi?ER O! S/DES O/IQU/fRTZ%?9f
POLYGON
Figure 4
MR81-231

7. -6-
Previous tests by Matsunaga and Kobayashi indicated that the sliding action be-
tween the chips and work pieces was the major factor in improving "finishing efficiency."
In square and pentagonal drums the mass moving more intermittently resulted in insuffi-
cient action. In circular drums the mass slides continuously at the drum wall, meaning
inadequate mixing action existed within the drums. Nonagonal and dodecagonal drums act
like circular drums because angle between sides is too obtuse. Hence, the conclusion
was drawn that hexagonal and heptagonal drums combined sufficient mixing action with
good sliding action thus giving the most beneficial results.
Similar testing in the USA and England indicates that the ideal shape of drum
depends upon the size of drum, the shape of the side walls, the plane in which drums
and turrets rotate, the type of product to be processed and the action required in
small-sized drums, circular cross-section generates the smoothest action and adequate
mixing presents no problems. In the largest sizes of machines, circular drums with
some sort of ribbing prove the most effective.
PROCESSING MATERIALS
In CBF equipment similar media are used as in other mass finishing processes but
usually of smaller particle size and of harder nature. In other mass finishing equip-
ment use of small media results in greatly extended process cycles, sometimes negligi-
ble action. In CBF equipment the G force can be increased to ensure fast enough action
and small media can be selected to pass through holes and achieve sufficient action in
recesses, slots and grooves. The finer the media used, the finer the surface finish
that can be obtained, hence capability of CBF to obtain finer finishes than other mass
finishing equipment. When uniformity of action on all edges and corners of fairly
complex shaped components is needed, this can only be done with fine media. Experi-
ments run by Hignett (2$ show the relationship of edge and corner radii generated in
centrifugal barrel equipment using different sized media of different shapes.
It is normal to select harder types of media for centrifugal barrel finishing than
for the other mass finishing processes to enhance process capabilities and to reduce
costs. In general, harder media offer greater efficiency, i.e., amount of metal remov-
al for a given weight loss of media is greater with the harder materials. A more im-
portant economic benefit by the use of hard media is that reclassification as those.
media wear down is required less frequently. Hard media are those which generally have
less abrasive properties than the softer materials so that in CBF equipment running at
low G forces with finishing compounds it is possible to obtain very fine finishes. The
same media running at high G force with abrasive compound can have very abrasiveaction
so the capability of carrying out heavy stock removal followed by fine finishing in a
single process is greater with harder media than soft.
Ceramic Bonded Media
These media are porcelain or other vitreous material with or without abrasive
grains imbedded in them. Properties of these media are changed by alteration of the
proportion of the abrasive to bonding material,
size.
the type of abrasive and its grain
Ceramic media with no abrasive are used for fine finishing and burnishing.
Media with 50% aluminum oxide abrasive of about 60 grit are the fastest materials for
deburring edge generation and stock removal. Modern manufacturing methods with proper
coordination between media manufacturers and equipment manufacturers have resulted in
these materials being the most generally used in all mass finishing processes includ-
ing CBF.
mai-

8. -7-
Plastic Media
Plastic media normally contain between 40% and 70% by weight of abrasive bonded
into polyester or urea formaldehyde resins. Like ceramic media, basic abrasives are
quartz, silica, fused aluminum oxide and silicon carbide in various grain size, shapes
may be triangles, pyramids or cylinders in a multiplicity of sizes.
Plastic media are normally of lower density and softer nature than the ceramic
materials, resulting in less abrasive action but greater cushioning effect between
parts, particularly when processing softer materials such as zinc and aluminum.
Plastic media generate smaller radii compared with surface metal removal than similar
shaped and sized ceramic media and are therefore useful when uniformity of action is
desirable. Major application for these media is for surface improvement of parts to
achieve a pre-plate finish.
Random Manufactured Media
Fused and sintered aluminum oxide nuggets have greater application in CBF than
other mass finishing, primarily because they are very economical materials readily
available in fine mesh sizes. The sintered aluminum oxide media are of particular
value,being so hard,and capable of finishes below two microinches AA on virtually any
metal, yet at elevated G forces capable of substantial stock removal.
Metal Media
Metal shapes, usually steel and most generally balls, are important mass finish-
ing materials partly due to the high density, also uniformity of size and shape.
When used for non abrasive operations , steel media maintains its size indefinitely and
is no longer a consumable material. Pins and tacks offer means of removing fine burrs
from holes and small recesses but the major use of steel media is for burnishing appli-
cations. While used in CBF equipment, steel media are not as important in these mach-
ines as for other mass finishing processes because there is no real asset in using
media that are intrinsically dense as CBF can develop effective density to meet speci-
fic requirements when using any type of media.
Dry Media
Mixtures of corn cob, walnut shell, hardwood sawdust with fine abrasives and some
bonding agent offer means of achieving very fine finishes indeed. Because these media
are so fine, there is little cushioning effect between components being processed so
that parts quite frequently have to be handled on fixtures or in individual compart-
components such-as molds, dies, bearing races
tolerances and without generating significant
Iments. However, drv media are able to achieve finishes of below one microinch AA or
and rollers, while maintaining exact
radii on sharp edges.
Other Media
Natural materials such as flint stone, 1
have occasional application within centrifuga
imestone, granite, corundum and novaculi,
1 barrel equipment but because they are
te
softer than manufactured materials and less consistent, the applications are very lim-
ited. Similarly, wood, non abrasive plastic, cloth and glass media may on rare occa-
sions be of some use but these are more likely to find application for less sophisti-
cated finishing operations than those where CBF equipment has greatest merit.
mai-

9. -a-
COMPOUNDS
While compounds are generally used during processing in CBF machines, they are of
substantially less importance than for other mass finishing processes. The reasons
for this are that the process cycles with CBF are short, media will not get dirty and
glaze over, there is less need for corrosion inhibition and much less likelihood of
any back deposit of soils upon components being processed. The most important reason
for using compounds in CBF equipment is to enable a cut-down operation to be carried
out by use of an abrasive compound and then, by automatically switching to a finishing
compound,change the process to one of fine finishing.
Abrasive Compounds
These compounds are usually fine grained aluminum oxide or silicon carbide, the
former either calcined or fused, together with some cleaning and probably mild corro-
sion inhibition agents. All abrasive compounds can be neutral with neutral and harm-
less products that go into solution.
Non Abrasive Compounds
Liquid or powder compounds for CBF equipment are formulated for achieving fine
finish on components, softening of water, corrosion inhibiting and occasionally en-
hancing the color of the material being finished. All standard CBF compounds are mild,
harmless and biodegradable.
SELECTION OF THE PROPERMATERIALS FOR YOUR APPLICATION
When selecting media and compounds for use in CBF equipment the following items
should be considered:
1.
2.
3.
4.
5.
6.
7.
8.
The capability of the media to perform the required operations, deburring, radius-
ing, surface finishing, etc., or a combination of these operations.
Means of achieving optimum parts-to-media ratio. In general, the larger the media
particle size, the better cushioning effect between components is achieved.
The size and shape of media must be selected to avoid any jamming in
recesses.
holes or
The size and shape of media particle must also be selected to reach
to be processed.
into a11 areas
Media must normally be of a type that will not fracture; fine particles can create
lodging problems and also affect results.
CBF media should normally be tough and firmer than standard mass finishing media
because they are performing more arduous tasks. Low wear rate represents in-
creased efficiency.
Media must be of size and shape to be easy to separate from the components being
processed.
When media size is critical, shape should be one permitting easy reclassification.
Media and compounds must be readily available, of reliable and consistent quality.
mai- 31

10. -9-
10. Media and compound suppliers should be used who are capable of offering technical
service as well as reliable supply.
11. Materials must be the most economical that perform to optimum efficiency.
12. Materials should be matched to enable multiple processing to be carried out in a
single operation for many applications.
CAPABILITIES OF CENTRIFUGAL BARREL EQUIPMENT
CBF is the fastest mass finishing process for any product. It is therefore a
process which can offer minimum floor space, minimum inventory and work in process,
normally the best work flow pattern. CBF is also able to process more delicate parts,
higher precision parts and parts requiring finer surface finishes than other mass
finishing methods. It is the most versatile process offering means of removing other-
wise inaccessible burrs and finishing into holes and recesses,handling the smallest
components and parts of over a thousand pounds weight.
Selection of the best mass finishing process for any application will invariably
depend not only upon quality of result to be achieved from the type of component being
finished, but also the product mix, batch quantities, total throuqhput, the cost and
qua
the
ccl
how
1.
ity of labor and supervision, space available, degree of automation required, and
philosophy of the company towards the finishing department. A few examples of ex-
ent applications for centrifugal barrel finishing might give a better picture of
the process can be effectively used:
Fluid Connectors - Finishing
Figure 5: Tee Connectors
Elbows, tees and different shapes and sizes of connectors used in hydraulic,
pneumatic and gas apparatus are processed in centrifugal barrel equipment.
The main purpose of processing these is for burr removal although, as with
most components entering the finishing department, there are a number of
functions that will be performed simultaneously such as descaling, surface
finishing, cleaning, and in some cases rust inhibiting.
MR81-231

11. -lO-
The CBF machine shown in Figure 6 is capable of processing up to 2,000 parts
cycle times ranging from 10 minutes to 60 minutes, compared to process cycles
in
from 4 to 14 hours in conventional equipment followed by electro-polishing.
The CBF machine has not only reduced finishing costs by 60%, but it has reduced
work in process and has generated a better work flow.
Figure 6: New Style Model 2HA-18 Harperizer
2. Carburetor Throttle Plates - Edge finishing and radius generation
The parts shown in Figure 7 are finished in CBF equipment to generate edge radius
and improve surface condition to improve air flow and heating of the blade within
the carburetor. Prior to CBF these plates were ground to improve the surface
finish but this created a burr on the O.D. which then had to be removed by a sec-
ondary finishing operation, leaving a non uniform edge radius. With CBF, both
surface improvement and edge radiusing are performed simultaneously with consis-
tent results while reducing costs 50%.
Using a CBF machine shown in Figure 6, 4,000 plates are processed per hour in
process cycles of 15 minutes to achieve a .003-.005 radius. Since the CBF equip-
ment has been installed, scrap and rework have been reduced by 75%.
MR81-231

12. Figure 7: Throttle Plates
3.I
I
Figure 8: Jet Engine Blade
MR81-231

13. -12-
There are, currently, tremendous demands upon aircraft engine manufacturers to
improve performance and efficiency of their products. Improvement of surface
finish upon some of the blades and vanes from 30 microinches AA to 15 micro-
inches AA can result in improved efficiency of the engine Of Several Percentage
points. Such an improvement also results in longer engine life between overhauls,
easier inspection and assembly of the product, reduced scrap, reduced rework and
fewer operational problems. Centrifugal barrel finishing offers means of obtaining
surface finish on blades and vanes of better than 10 microinches AA while giving
means of generating more precise and uniform leading and trailing edge radii on
those blades. Deburring, generation of the edge radii and improvement Of surface
finish can all be combined into single Harperizing process cycles.
.Typical process cycles used in CBF equipment are 15 to 30 minutes. Finishing
costs can be reduced by more than 50% compared with the manual filing and polish-
ing operations together with conventional mass finishing techniques.
4. Grinding of Bearing Balls
Centrifugal barrel finishing is used to grind bearing balls before and after
hardening. While the process only marginally improves sphericity of the parts
it will maintain precise tolerances and be entirely consistent in results.
Typical rates of stock removal are ,006" reduction in diameter of half-inch ball
before hardening and .004" per hour after hardening. The machine shown in
Figure 9 will handle 3,000 lbs. of balls per load and using this equipment, total
grinding costs are reduced by more than 25% compared with conventional techniques.
In addition, Harperizing of the hardened ball generates compressive stress in the
surface which produces a better condition for the final lapping operations.
Similar heavy stock removal CBF applications are used for all forms of bearing
rollers.
. w-
5. Stainless Steel Coil Springs
The improvement of edge and surface condition of most components reduces the risk
of premature fatigue failure. Surface imperfections act as stress risers and removal
of these will invariably improve performance of any highly stressed component. For.
critical parts it is desirable to achieve very high surface finishes to remove stress
risers and also to enable inspection to ensure that those stress risers have been
removed. Removal of burrs and absolutely uniform radii on all sharp edges will im-
prove performance. While peening,.surfaces and edges, CBF will simultaneously gener-
ate very high ComPressive stresses to all edges and surfaces of the part with abso-
lute uniformity. This results in components having greater resistance to fatigue
strength than can be achieved by a combination of other mass finishing operations
followed by shot peening.
The capability to improve resistance to fatigue failure has been demonstrated by
a manufacturer of stainless steel coil springs. Test results on springs finished by
Conventional tumbling followed by shot peening showed fatigue failure occurring be-
tween 160,000 and 360,.000 cycles. The springs that had been processed in CBF equip-
ment (at cost of 50% of the standard items) failed between 360,000 and 520,000, a
performance improvement of 60%.
6. Refrigerator and Air Conditioner Flapper Valves
Surface finish, edge radius and improve fatigue strength.
MR81-231
E
5
1C
11
1;
1:
L
t
a

14. 7.
a.
9.
10.
11.
12.
13.
14.
15.
16.
17.
-13-
Hand Tools
Scale removal, edge and surface finish improvement.
Watch Parts - to deburr and surface finish.
Fuel Nozzles - to deburr and surface finish.
Fine and Costume Jewelry - decorative edge and surface finishing.
Orthodontal Bands and Brackets - to deburr, clean and finish.
Glass and Plastic Molds - to clean, descale and finish.
Carbide Tooling - to condition edges.
Fuel Pump Bodies - to deburr and finish uniformly.
Transmission Chain, Side Plates, Rollers and Bushings
Deburr, edge radius, surface finish and rust inhibit.
Castings and Die Castings - to deburr and surface finish.
Automotive Distributor Cams and Weights
NEW DEVELOPMENTS
- to descale, deburr and surface finish.
IN CBF
AUTOMATION
Figures 9, 10 and 11 show some of the automatic CBF machines in production today.
Like other mass finishing processes, when very high production systems are required
there are a number of standard units which can have complete material handling systems
adapted to suit specific requirements.
The machine shown in Figure 9 is capable of processing up to 3,000 lbs. of com-
ponents per load. As with all automated Harperizers the process cycle can be set to
run initially at a very high speed to remove burrs and grind surfaces very quickly.
At the end of this process the machine can change automatically to a slower speed,
add water and a finishing compound, and refine the edges and surfaces, thus combining
two processes into a single operation. For general deburring and surface finishing,
process cycles rarely exceed 30 minutes; this type of equipment typically handles more
than 6,000 lbs. of components each hour.
MR81-231

15. Figure 9: Model 2VH 36 x 30 Automatic Harperizer
The machine shown in Figure 10 is a somewhat smaller unit. This particular unit
has material handling arranged to handle different components in each of the two drums.
With its internal pre-load units, separators and dryers the machine is suited to han-
dle a very wide variety of different components. Such equipment can incorporate media
storage and automatic selection of media and compound in the correct quantities and it
is also possible to have numeric control to select the correct process cycle for each
of the different components to be deburred and finished.
Figure 10: Smaller CBF Machine (Model 2VH 28 x 32)
MR81-231

16. -15-
Figure 11 shows a more automatedmeansof material handling with a Harperizer
where parts and media can be fed into the machine while it is running. During the
process cycle water and compounds can be added to change from fast deburring to fine
surface finishing. At the end of the process cycle the machine can automatically
slow down to feed the load out of the drums for subsequent drying and into the assem-
bly department. Such equipment requires no operator involvement at all.
Figure 11: Model "Auto G" Harperizer
A new range of centrifugal barrel machines where drums are removable for reload-
ing purposes offers an alternative means of automating the finishing department where
the variety of processes and batch sizes do not enable the automatic machines pre-
viously described to be effectively utilized.
Figure 12 shows a standard removable-drum Harperizer having four containers.
Containers are pre-loaded at a central material handling system capable of handling
drums for a number of machines. Robots can load drums into machines and equipment is
designed to be numerically controlled to set process cycles and speeds and to enable
water and compounds to be added during the process cycle. One finishing department
utilizing equipment of this type used a single machine to process 50 different types
of components each day, ranging in size from less than l/4" to 12" long, with all
metals and a broad range of process requirements. Operator error has been eliminated
as has virtually all costs of inspection.
MR81-231

17. -16-
Figure 12: Large Six-Drum CBF Unit
Chemically Accelerated Centrifugal.Barrel Finishing
The use of chemical polishing solutions and chemical accelerators is now well
established, incorporating the positive attributes of both chemical polishing and of
Harperizing while overcoming some of the disadvantages. Absolute consistency of work
on all surfaces, corners and edges can be achieved. The process is controllable and
capable of generating substantial radii. Surface defects can be removed. It is not
necessary to ensure components are as thoroughly cleaned as for normal chemical pol- ._
ishing, and some of the problems normally associated with effluent disposal of the
chemical solutions can be overcome. Chemically accelerated centrifugal barrel finish-
ing is most applicable to the finishin
3
of complex shaped ferrous parts where
(1) uniformity of finish is needed; (2 there are recesses and holes which would be
difficult to finish without chemical accelerators, and (3) very fine finishes are
needed. Generally, finishing costs are much higher than conventional centrifugal
barrel finishing and more precise control is needed.
Slow Speed and Controlled Activity Equipment
Figure 13 and 14 show CBF equipment designed for slower speed running than the
standard very heavy duty units and having lower cost per unit volume. Such machines
with the capability of generating forces up to approximately ten times earth's gravity
are well suited for the more economical and less demanding applications. For example,
the machine in Figure 14 can process 20 cu. ft. of die castings or steel stampings per
load with process cycles normally of only about 15 minutes. Such a machine costs only
half that of standard high speed equipment. These machines greatly widen the scope
for CBF beyond the traditional applications for ultra-high speed, ultra-high precision
and high quality deburring and surface conditioning.
MR81-231

18. -17-
On occasions there is some merit in having independent control of speed of rota-
tion of the drums from the speed of rotation of the turret. For very large soft metal
components slow speed rotation of the drums at moderately high G forces enables bulk
processing to be achieved with high standards of edge and surface finish.
Figure 13: Small capacity low-speed CBF machine
Q-..--___ 9&“-e-- i-
Figure 14: Large capacity low-speed CBP machine
MR81-231

19. -18-
Grinding and Milling CBF Equipment
Figure 15 shows a modified CBF machine. This unit has the drums and turretrotat-
ing in the same direction and produces a totally different action from standard CBF.
While in standard CBF the load within the drums is maintained in a very closely packed
mass where there is no possibility of impingement, in the "DB" (dogboning) type CBF
machines activity is one of almost exclusively impingement motion with very little
slide of parts against media. As the load is moved by the rotation of the drums,
turret rotation pulls the drum wall away from the load itself, causing every particle
within that drum to impinge against the opposite metal wall of the drum.
This type of action is of benefit for grinding powders and ore, for breaking up
ceramic materials and for "hammering" action on some components, which is required in
a number of specialized industrial applications. The bearing industry makes use of
such machines for achieving rounded ends on roller bearings before grinding.
The "DB" process does enable autogenous grinding of some materialsthatwould have
had to be processed in ball or rod mills by conventional means - obviously a truly
enormous benefit.
Figure 15: Modified CBF machine
MR81-231

20. SUMMARY
I Automated deburring and surface conditioning is at last being treated seriously
p by most of the metalworking industry. The average mechanical finishing cost for most
1 components is 5% of total production cost, and re-work, rejects and replacements under
; guarantee as a result of inadequate finishin g
: other manufacturing operations.
are still out of proportion with the
The mass finishing processes offer most manufactur-
; ing organizations means of producing more consistent quality products at lower cost.
Centrifugal barrel finishing is one of the newer deburring and surface condition-
t ing techniques offering all the basic advantages of the other mass finishing methods
i; and overcoming many of the disadvantages. High speed, capability to handle high pre-
L cision parts and generate very high compressive stresses are of vital' importance.
c
Equipment is now available to meet a broad range of production requirements and re-
cent developments extend capabilities permitting much improved standards of automation
and even greater versatility. CBF is one of the important contributions towards more
scientific handling of burrs and surface finish.
MR81-231 I

21. -2o-
BIBLIOGRAPHY
1. M. Matsunaga and H. Kobayashi, "Some Experiments on Centrifugal Barrel Finishing"
Metal Finishing (A), Vol. 64, No. 5, p. 57.
2. J. B. Hignett, "Centrifugal Barrel Finishing-A Comparative Media Evaluation"
Metal Finishing, August 1976
3. J. B. Hignett, "Centrifugal Barrel Deburring and Surface Conditioning -
Some Recent Developments," SME Technical Paper MR79-567
4. F. Schafer, 'Entgraten," Krausskopf-Verlag, 1975
5. J. B. Hignett, "Centrifugal Barrel Finishing".
Cost Guide for Automatic Finishing Process, SME, 1981
6. MFSA Quality Metal Finishing Guide, "Mass Finishing," Vol.1, No. 3, lMl2-79
MR81-231