Steel media-nigro-87

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1987
0C ALL RIGHTS AESER
MR87-160
Vibratory Finishing with
Steel Media
author
STEPHEN J. NIGRO
Product Manager, Steel Media
Abbott Ball Company
West Hartford, Connecticut
abstract
Steel medra fmishing systems are a simple, economrcal, versatrle. and envrron-
mentally safe method of clearung. firushmg, deburrrng and structurally treatmg
workpreces in the mass manufacturmgfinishing process. The variety of avatlable steel
media, used in conjunctton with vibratory finrshmg equipment and cleanrng agents,
can produce a multrtude of high quality fmrshes that enhance the finish, appearance,
and structural Integrity of the workpreces
conference
Deburring and Surface Conditioning ‘87
February 17-l 9, 1987
Phoenix, Arizona
index terms
Vibratory Finishing
Deburring
Media
Finishing
Society of Manufacturing Engineers l One SME Drive l P.O. Box 930
Dearborn, Michigan 48121 l Phone (313) 271-l 500

2. SME TECHNICAL PAPERS
This Techmcal Paper may not be reproduced in whole or in part in any
form mcluding machine-readable abstract, wlthout permission from the
Society of Manufacturing Engineers. By publishing this paper, SME does
not provtde an endorsement of products or services which may be discussed in
the paper’s contents.

3. MR87-160
INTRODUCTION
Steelmediais manufacturedin a numberof standardandcustomshapesandsizes. The function
of the mediais to (throughtheprocessof friction andvibration) impactuponworkpiecessuchas
castings,forgings,andmachinedpartsin order to altertheir surfacestructuresor removeforeign
matter.
The mediais usedwith vibratoryfinishing machinery,which combinesthemediawith the
workpiecesandgivesthe mediaits impetusthroughoscillatingmotion. The machineryis designed
to operateaspart of the manufacturingprocessproper,or asa separateprocessin which the media,
workpieces,and compoundsolution,arecycledtogetherto achievethe desiredeffect. With
completionof thecyclethe mediais separatedfrom the workpiecesto bereused.
This paperprovidesan introductionandbackgroundto steelmediamassfinishing by examining
the manufactureandusesof steelmedia,its advantagesanddisadvantages,andits application
within the contextof vibratory finishing systems.
THE STEEL MEDIA
MANUFACTURE OF STEEL MEDIA
Steelmediais madefrom steelwire usingthe cold headingprocess.The mediacanbe
fabricatedfrom eitherlow carbonsteelor stainlesssteel. The steelwire is segmentedandformed
into slugsby the headersbetweenpunchandblock dies. The sizeand shapeof thediesdictatethe
sizeandshapeof the mediabeingproduced. Although scoresof headerssimultaneouslydraw and
cut the wire, the shapesareessentiallyproducedoneat a time.
The formed shapesarethencut down; a processin which theyareloadedinto tumbling bar&s
and,in muchlike theprocessof vibratory finishing itself, the shapesaretumbledagainsteachother
to bring them to standarddimensions.A mixtureof aluminumoxide, water,anda cleaningagent
areaddedasthe barrelis rotatedto assistin smoothingtheedgesof the media.
The mediais thenheattreatedat anapproximatetemperatureof 1600°Fin orderto achievecase
depthandimparthardnessto themedia. Naturalgasis addedto theretort (holdingcell) that
containsthe mediaandsubsequentlythe shapesabsorbcarbonfrom the gas,which givesthem their
hardness.After heattreating,themediais quenchedin eitherwateror oil dependingon the sizeof
the finishing media.
Tempering,the next operation,is critical in theproductionof steelmediabecauseit drawsthe
hardnessbackto relievestressesin the structureof the mediaby allowing the gramof the steelto
realignitself. In turn this affectsmediaresistanceto fracturewhile the degreeof hardnesscontrols
the media’sresistanceto wear. Both of thesecharacteristicsareverified, along with size,in a
seriesof quality control checks,beforethe mediais polishedto a surfacefinish of lessthan 5 rms.

4. TYPES OF STEEL MEDIA
The geometryof steelmediais importantbecauseit determineshow the mediawill finish a given
workpiece.In the early 1900’s,steelballs werefit usedfor burnishinga bright finish on small
metalparts. However, a variety of shapesandsizeshavesinceevolvedto matchthe increased
engineeringsophisticationof vibratory finishing and thecontoursof variousworkpieces. Now, a
variety of operationsareperformedin additionto simpleburnishingwith a substantiallyincreased
numberof steelmediashapes.Thesescientifically designedshapescombineinto an interlocking,
compactmassthat increasespressureandimprove finishing.
PIGURE 1depictsthe standardtypesof media:
ECLIPSE ABC0 CONE PIN
DIAGONAL BALLCONE OVALBALL
Fig. 1 Proper selection of media
shapes will prevent lodging.
ECLIPSE BALL
Flatteningat polesis characteristicof ballsproducedfor the majority of applications. Size
range: 3132”through98”
ABC0 BALL
Theseballs maintainroundnessfor morecritical finishing requirements.Sizerange: 3/32”
through 5%
CONE
Centerflange andtaperedcrownsprovide contactsin anglesandon curvedsurfaces.Small
sizesideal for ornamentaldesigns. Sizerange: l/8” through 1”
PIN
Tapering to pointed ends,pins reachinto therecessesof figured work andgrooves,deflash
through-holesandcleanthreadedareas. Diameters: 3/64”through5132” Lengths: up to l/2”
DIAGONAL
Bevelededgesof diagonally-cutends(alsocalledangle-cutcylinders)provide effectivefinishing
action in comers. Cylindrical body offers wide areacontacts. Sizerange: l/16” through3/g’
BALLCONE
Designedto combinethe actionof balls andconeswith onescientifically-proportionedshape.
Sizerange: l/8” through5/W
0vALBAI.L
Introducesoscillating motion to finishing massandprovidesmoresurface-tosurfacecontact
thanballs. Used for finishing coin blanks. Sizerange: l/8” through3/V
CUSTOM SHAPES
A variety of customshapesfor uniquefinishing requirementscanbe custom-engineered.These
shapescan bedesignedto finish especiallycomplexor difficult parts.

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~~87-160-3
APPLICATIONS OF STEEL MEDIA
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Steelmediain vibratory finishing is applied in two generalareas- partsfinishing, andcleaning.
Steelmediarequiresthe useof vibratory machineryor standardtumbling barrelsin orderto achieve
its objective. The machineryprovidesthe vibratory or rotary motion which is the principle action
that causesthe processing of the workpieces.
The mediais easily separatedfrom the parts,affords careful control of part contact,andallows
edgecontact. The sizeandshapeof the mediacontrolsthe degreeof contactwith the partsbeing
finished. Steelmediais usually smallerthan the workpiecesbeingprocessed,which facilitates easy
separationof the mediafrom the workpiecesby meansof internal or externalseparation.
PARTS CLEANING AND CHIP REMOVAL
By being non-abrasiveandnon-wearing, steelmedia,coupled with a good compound
containing cleaningpropertiesanda built-in corrosion inhibitor, actually scrubsurfacesand
interiors resulting in a mosteconomicallyeffkient removal of both organic andinorganic soils.
This methodof cleaning is now commonly usedto removea wide variety of soils on many typesof
materials. Common carbonsteelsto exoticssuchassilver andgold arecleanedin vibratory
equipment. Systemsareableto efficiently removesoils from machining operations,stampings,
headedparts, aswell asoxides from zinc, aluminum, brass,copper, and more. This unique
scrubbingactionandaccessibilityactively removesmetalchipsfrom machiningoperations,milled
grooves,threadedholes,slots,etc., while at the sametime removing soil from the parts.
For example,oneof the mostdifficult cleaning applicationstoday involves the removal of
nuclearresiduesfrom metal tools, (SME technicalpaper,“MB79 - 747”- “Vibratory Finishing As
a DecontaminationTechnique”discussesthis topic). Disposalof residueis greatly reducedbecause
steelmediais cleananddoesnot createadditional soils.
An important factor when consideringsteelmediain vibratory equipmentasa cleaning systemis
that many parts,while being cleanedin steelmedia,obtain a burnishedfinish or are&burred with
greatsuccessat the sametime. The processcanoften eliminate the needfor secondaryor painting
operations.
Sincecleaning is achievedprimarily through the useof only the steelmedia,or when necessary,
with addition of phosphate-freeandbiodegradablesolutions,the mediaqualifies asan
environmentallysafealternativeto conventionalcleaningsystemswhich employ toxic solvents.
PARTS FINISHING
DEBURRING
Steelmediais excellentfor &burring. Although steelmediais not usedto cut down a heavy
burr, it is a widely usedmethodfor peeningor hammeringsharpedgesto very acceptable
conditions. Extremely complicatedcastingsaredeburredin largequantitiesdue to the sizecontrol
and accessibilityto all part areasafforded by the media. Steelmediareducessharpnesswith such
speedandsuccessthat the deburring cycle is usually lessthan 15minutes. OSHA requirementsare
also met using this process.

6. ~~87-160-4
BURNISHING
Ball burnishing,asis sometimesreferredto, is usedto producesmooth,mirror-like finisheson
parts. Metal surfacesvary greatly,from mattetype finishesto smooth,polishedtypesin which
surfacereflectivity is improved. A mattesurfaceis non-reflectivebecauseit hasnumeroushills and
valleysor ridgesandgrooves. Burnishingwith steelmediapeensdown theseimperfectionsand
producessmoothandbrilliant surfaces.The actionin vibratoryequipmentprovidesinterior action
aswell asexterior soburnishedfinishescanbeobtainedon insidedimensionalareasaswell ason
outsidesurfaces.
DBFLASHING
Deflashingor removingflash from typesof thermosetplasticshasbeenaccomplishedfor years
by leadingmanufacturersof thermosetelectricalcomponents.By beingnon-abrasive,thereis no
damageto surfacesandprocessingtime cyclesarenormally short- usually7 - 12minutes.
Complexceramicinsulatorswith intricatecavitiesarealsosuccessfully&flashed usingthis
process.
SURFACE MODIFICATION
Surfacemodificationreducesroughness,surfacearea,andimprovessoil and stainresistancein
a workpiece. The mediapoundsdown thesurfaceto createuniformity andsmoothness.This
resultsin lesssurfaceareaandlessroughnesson a part Also, resistanceto soil and stainsis
achievedbecausethe microscopicpeaksandvalleyswhich entrapthe soil on mostworkpiecesare
modified by thepoundingactionof the media. This applicationis commonlyusedfor food
processingequipment,which requiresa high degreeof cleanliness.
ADVANTAGES OF STEEL MEDIA
Steelmediais not abrasiveby nature,anddoesnot createnor absorbsoils. Therefore,it is not
likely to cut or scratchworkpieces. Sinceit is not abrasive,it will not changethedimensionof
partssuchasinvestmentcastings,in which tolerancesmustbemaintained. The mediadoesnot
createsoils,therefore,workpiecescomeout extremelycleanandno secondaryoperationsare
requiredto cleanpartsafter they areunloadedfrom a vibratoryfinishing machine.Steelmediais
hardenedto rockwell C 60 minimum;therefore,it maintainsits dimensionandshapewith
continueduse.
Becauseof thedensityof massin steelmediaat approximately300 lbs. per cubicfoot, it
deliversvery fast finishesin burnishing,deburring,degreasing,anddeflashingoperations. Cycle
timesaregenerallylessthan 15minutes. It alsohasanaveragelife of aroundtenyears.
Steelmediadoesnot wear thelining from finishing equipment,so thecostof relining machines
eliminated. Despiteits mass,it canbeused
to processfragile parts; if the small-sizedmediais used,it canactuallycushionandsupportparts
within the finishing mass.
.

7. ~~87-160-5
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%
Wear
20
60
STEEL MEDIA~DIA
Fig. 2 Typical wear rates: example, l/2” dia. media.
IMPARTING COMPRESSIVE STRESSES
As steelmediapeensa workpiece,the part’ssurfaceis work-hardened. The working actionin
partsproducescompressivestressasa beneficialby-productof the finishing process.In many
instances,the processcanreplacesteelshot-blastingasa work hardeningstep. Partsprocessed
with steelmediathushavelongerlife cyclesandgreaterresistanceto wear.
Polyurethane-Lined
Chamber ,
I Top ET Weight~
DrainLever I Y/- ’
Fig. 3 Typical vibratory machine for mass finishing.

8. MR87-160-6
VIBRATORY FINISHING SYSTEM
In additionto theworkpiecesandthe mediathereatetwo otherelementsthatmakeup a
vibratory massfinishing system.Thesearethe vibratory equipmentand thecompoundsolution.
In or&r to obtaindesirableresults,propervibratory equipmentis essential.The equipmentmust
beableto supportanddrive the densemassof steelmedia(approximately300 poundsper cubic
foot). Propercompoundsolutionsarealsorequiredto control the interactionbetweenmedia,
machinery,andworkpieces,aswell asto ensurethat theworkpiecesam cleanedof foreign matter.
VIBRATORY MACHINERY
Vibratory finishing machinesoperateby rotatingeccentricweightsattachedto a shaftdriven by
varying degreesof horsepower(dependingupon the sizeof thefinishing machin . Theseeccentric
weightsvibrate the fmishing vessel(eithertub or bowl), which is supportedby %ptings. The
coefficientof friction betweenthelining of thevesselandthemediacausethe feedand(or) roll
within the finishing mass.
Most manufacturersof vibratory finishing equipmenthavemachinesdesignedfor both steel
mediaandpre-formedtypesof media(althoughmachinesdesignedfor steelmediawill operatewith
any type of media). Propergusseting,springplacementandhorsepowerareespeciallyimportantin
the designof finishing equipmentfor usewith steelmedia,dueto its increasedweight
Eccentric weight system
Unbad
Fig. 4 Cross section and action of vibratory machine.
COMPOUND SOLUTION
The function of the solution- is to dissolveoily soilsandremoverust. Steelmediaalone
vibrating in a machinewould only spreadsoilsaround. It is the solutionthatemulsifiesthe soil,
whetherit be organicor inorganic. In the caseof rust,acidicburnishingcompoundsremove
oxidation, and,by meansof a flow-through system,areremovedfrom the machines.
Flow-through is when a compoundsolutionis addedto the finish-media,passedthroughthe media
andevacuatedfrom themachineryvia drains.
The vibratory compoundpump systemis designedto mix compoundwith waterandintroduceit
into the machine. The pump is designedsothatthe flow rateof thecompoundsolutioninto the
finishing machinecanbe monitored. Consistencyis animportantfactor to ensureproperfinishing.

9. MR87-160-7
Steel,or anyother media,is driven by the motionof wall of the finishing machine. If the
coefficientof friction betweenthe wall of the machineandthemediais lost,thentheactionof the
massis alsolost. Solutionsarespecificallydevelopedto control the degreeof lubricity between
mediaandmachine.Too muchlubricity would slow the massdown to whereit becomes
ineffective.
The solutionalsoinhibits corrosionof mediaandparts. When ftishing workpiecesin steel
media,very activemetalsurfacesarecreated. Properinhibitorshavebeendevelopedthatwill
maintainsteelmediafree from corrosionup to 60 or 90 days,andinhibitors havebeendevelopedto
retardcorrosionof non-ferrousmetalssuchastheoxidation that appearson aluminumpieces. The
compoundsolution alsocontrolspart color andluster,andasa secondarybenefit,removesthe heat
generatedby the friction betweenmediaandmachinery.
The flow rateof the solutionalsoaffectsactionof the mass,cleaning,anddrain rate. If the flow
rateis too great,flooding canoccurasdrainsareoverburdenedand subsequentdampeningof
mediaactioncanoccur.
SUMMARY
Vibratory finishing with steelmediahasbecomean industrialstandard.Thousandsof
installationscurrentlyusesteelmediain anincreasingnumberof applications.Reductionsin cost,
time,materialsandmediaitself all resultfrom theuseof steelmediain vibratoryequipment.
Processflexibility is an addedbenefit. Operationsthat wereformerly performedby hand,on burr
benches,or in multiple, dedicatedprocesses,cannow bedoneusingsteelmediain vibratory
finishing. Deburring,descaling,deflashingmetalandplastic,removingdie lines,preplate
finishing, degreasing,cleaningandburnishingareall donewith the sameequipment. Steelmedia
reducesfinishing cost,improvesproductivity andimprovesquality. Fewerrejects,reduced
assembly,increasedwearresistanceandbetterfitting partsaretheresults.
The initial costof steelmediais morethan thatof consumabletypesof media.However,since
consumablemediarequiresreplacementfrom two to four timesa year,its long term costswill
outpacethatof steelmedia. Vibratory equipmentcostis competitivewith othertypesof mass
finishing equipment. Thesefactors,whencombinedwith the savingsrealizedfrom reducedcycle
times,theability of the mediato perform multiple processessimultaneously,andtheinherent
durability of steelmedia,area clearindicationof this technology’seconomyandperformance.