Moving a nearly finished
part from the last machining operation to the loading dock can be
a laborious process, taking days instead of hours or less, especially
if the part sits in a batch waiting its turn for hand deburring
or other form of final finishing.
Steel media,
applied through either barrel or vibratory equipment, can take huge
chunks out of down time while providing polished, clean interiors
and exteriors, even with delicate parts. And it simultaneously provides
manufacturers with a long-term capital investment carrying a life
expectancy of a decade or more.
In 1909 George
E. Abbott experimented with methods to burnish a bright finish
on small metal parts. At that time only steel balls were available,
and since a sphere can neither reach into corners, nor recesses
smaller than its diameter, early parts showed clearly delineated
non-finished areas.
During the
ensuing years engineering sophistication grew, and the range of
finishing applications expanded. New shapes, improved metallurgy
and manufacturing, extensive research, plus better compounds and
finishing equipment have all provided new uses for steel media,
reducing costs while improving productivity and quality.
Since steel
media lasts a decade or more and can perform in one step, it usually
pays for itself in about a year. Steel media produces fewer rejects
from lodging, and creates better fitting parts for reduced assembly
time and increased wear resistance. When the proper shapes and sizes
have been chosen, the uniformity of steel media ensures it will
contact all critical areas and will not lodge anywhere. When correctly
applied and maintained, it will hold its shape for years.
Steel media
is most often made from high-quality, high-carbon, casehardened
and stress-relieved steel, as well as 302 high-quality stainless
steel. The controlled uniform shapes are essential in complex areas
where lodging could be a problem. Proper heat treatment and stress-relief
combine to form tough, long-lasting media.
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| Variety
of sizes and shapes of steel media
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Steel media
weighs approximately 300 pounds per cubic foot, therefore it cushions
and supports parts in the mass, delivering quick contact and fast
peening of edges. Its substantial weight exerts added pressure to
a mass of components. As pieces force their way through the media,
the pressure and increased resistance are especially effective in
reducing finishing times. Cycle times are normally 5-20 minutes.
Steel media also is non-consumable. With proper care it is not used
up in the finishing process.
Systems are
designed to efficiently clean soils and remove chips remaining from
machining operations in parts having such diverse features as milled
grooves, threaded holes, slots, stampings, die cast and headed parts.
Steel media scrubs oxides from zinc, aluminum, brass, copper and
other materials and is highly effective at removing nuclear residues
from metal tools. It also works with biodegradable compounds and
does not contribute pollutants to the waste stream.
Deburring
One
of its most cost effective uses is in deburring operations. During
cleaning, many parts obtain a burnished finish. Although steel media
is not used to cut down on a heavy buff, it is widely used for peening
or hammering sharp edges. As a result of its size control and ability
to access all areas, complicated castings are successfully deburred
in large quantities often in less than 15 minutes. OSHA requirements
have been met using this process.
Another common
use for steel media is deflashing thermoset plastics, a process
that has been successfully used for years at leading manufacturers
of thermoset electrical components. Non-abrasive steel media does
not damage surfaces, and time cycles are normally short (7-12 minutes).
Complex ceramic insulators with intricate cavities are successfully
deflashed using this process.
Burnishing
Sometimes
called "ball-burnishing," burnishing produces smooth mirror-like
finishes on surfaces ranging from matte to polished. In addition,
as steel media presses on a part, the working action imparts compressive
stress, and its surface becomes work-hardened. The process often
can replace steel shot blasting as a work-hardening step. Parts
processed with steel media have longer cycle lives and greater resistance
to wear as a result of this compressive stress action.
As an added
benefit to its cleaning and burnishing capabilities, steel media
enhances plating operations. Prior to plating, parts that may appear
smooth often are marked by micro-imperfections, which can distort
the plating process. The weight of steel media flattens these minute
irregularities and prepares a surface for satisfactory plating.
Plated
Parts
When
plated parts are finished with steel media, a compacting action
spreads the surface of the softer plate to fill and pinpoint holes.
This process helps eliminate porosity and increases the corrosion
resistance created by the plating process. This action is especially
critical during the deposition of nickel or other solutions that
typically do not fill the depressions, but follow the contours of
the metal.
Steel media
also is essential in solving finishing problems resulting from the
complexity of modern parts manufacture. To achieve this it must
be understood that each piece of steel media in the mass is an individual
polishing tool, and must be flaw free for optimal performance without
damage. The media also must maintain its original dimensions to
prevent lodging or other problems associated with size reduction.
Shape
Selection
Abbott
requires all shapes, except pins and diagonals, to be checked for
dimensional tolerance to plus or minus 0.010 inch during production,
the most stringent standard in the industry. Tight tolerances on
all flanges, sloping edges, tapers, curves and points assure contacts
in angles, grooves, and figured surfaces that eliminate or reduce
the potential for lodging.
Abbott also
has developed proprietary techniques to ensure that its shapes receive
uniform heat treatment for longer life. Ball surfaces are equidistant
from a common center, and hardness penetration is uniform. However,
formed shapes such as cones and ball cones, can become brittle in
the thinner, flanged sections. Media shapes are case hardened, then
tempered for stress relief.
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Before
and after shot of part finished with Abcut steel media
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Filigrees and
engravings on silverware and other detailed parts presented a new
challenge. These designs require a pointed object to achieve an
overall finish. Thus, pins were developed in double-pointed sizes
to reach into these intricate areas. The resultant ball, cone, and
pin mixture is common for finishing a variety of detailed components.
Other specialized
shapes were later developed to secure surface contacts on irregularly
machined pieces. These shapes include diagonals, (a cylindrical
steel section with each end cut off at a slant); ball-cones (which
differ from the cone in that one side is a cone, the other side
a half-ball); and oval balls (a football-shaped piece that provides
wider area contacts than a ball, and somewhat more vigorous tumbling
action.)
Steel media
now consists of a multitude of interlocking, compact, scientifically
designed shapes and sizes to match virtually every product contour,
increase pressure and improve finishing action. Unique shapes are
also available.
Durability
When
conducting a value analysis of steel media, its "wear resistance"
is a major component that should be considered. Steel media will
maintain its size tolerances, thus eliminating wear-related size
changes and the inevitable lodging problems sure to follow. The
media's metallurgical structure is engineered to prolong its life
and eliminate the hidden costs of frequent re-ordering.
When the proper
media is chosen, consistent performance and repeatability is assured.
If proper maintenance procedures are followed for protecting the
steel media between uses, many years will elapse before replacement
is necessary. Also, steel media will not wear the lining of barrel
equipment, saving costly downtime and relining of the equipment,
even when using compound solutions.
Non-abrasive,
non-wearing steel media coupled with a good cleaning compound containing
a built-in corrosion inhibitor, scrubs surfaces and interiors economically
and efficiently. This method removes both organic and inorganic
soils from various materials ranging from common carbon steels to
exotics such as silver and gold.
Compounds are
excellent for cleaning parts in conjunction with ferrous steel media.
Although they are acidic, rusting due to improper maintenance can
be prevented by using a compound solution containing corrosion inhibitor
properties or by using steel media made from stainless steel.
Compounds are
developed specifically as inhibitors for dipping ferrous and non-ferrous
parts after processing. The ferrous inhibitors can be used directly
in the media mass over weekends and shutdown periods to insure extra
corrosion protection. Proper compound and inhibitor selection will
protect the long life of steel media and improve cleaning productivity.
Foremost among
the specialized types of media developed by Abbott is the ABCUT
line. ABCUT provides accurate deburring and a bright finish on steel,
zinc and aluminum parts, in one clean, economical process. The grooves
in the media surface deburr and remove material without changing
the part shape, often eliminating the need for hand finishing or
other secondary finishing processes. This product closely resembles
many miniature files working on the burrs of the part.
Stainless
Steel Media
There
is stainless steel media designed for specialized finishing operations.
Also, more acidic compounds have been developed for use with stainless
steel media to dramatically cut finishing times. A descaling cycle
is typically cut in half when chemistry with less than 4.0 or higher
than 10 ph is used. Other finishing operations are also improved
with these chemistries.
Stainless steel's
inherent ability to resist corrosion often eliminates the need for
compound solutions and rust inhibitors. When compounds are required,
lower-cost compounds may be substituted. Corrosion-resistant stainless
steel reduces the storage, maintenance and handling costs, and maintenance
procedures for overnight and longer-term shut downs are considerably
simplified.
Stainless steel
media also eliminates iron impregnation of components from chemical
interactions during some finishing processes. Uncontaminated part
surfaces are especially important to manufacturers of medical equipment,
surgical tools, food processing equipment and similar items.
Equipment
Barrel
finishing is achieved using optimized concentration and control
of working pressures; efficient application of these pressures directly
to the part without dissipation; and uniform contact of finishing
media on all part surfaces. Other process parameters affect desired
surface finish characteristics and run times, from the mix of media
shapes and compound to barrel speed and height-to-width ratio as
it affects cascading action.
Open-faced
barrel design provides variable cascading, and is also used where
acids might risk explosion in a closed barrel. The tilting angle
of the barrel determines the rate of cascading action. A more horizontal
position produces no cascading with gentle rotation that's suitable
for polishing; a steeper angle generates parts and media cascading
that approaches the levels of a closed barrel. A closed barrel design
permits the full rotation of the parts and media for more aggressive
action in longer, unattended cycles.
Vibratory
Equipment
To
obtain the desired results with vibratory equipment, the system
must be able to support and drive the density of the steel media.
Internal or external separators designed into this equipment will
allow ease of operation and integration with in-line automation.
External part-media
separators allow parts to vibrate onto a screen deck while the media
returns to the vibratory equipment by conveyor. Internal separators
have built-in screen decks and a gate, allowing media and parts
to flow onto the screen deck where media returns to the equipment
and only the parts vibrate out. The media never leaves the equipment.
Both types greatly increase the production rate by eliminating handling.
Smaller systems
are perfect for jewelry, die castings, small decorative parts, fittings,
medical and precision components. Larger systems are suited for
production runs of larger parts in higher quantity. Since the geometry
of steel media is most important, a specification sheet aids in
its measurement.
