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metal finishingTHE INDUSTRYS RECOGNIZED INTERNATIONAL TECHNICAL AUTHORITY SINCE 1903

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79th Surface Finishing Guidebook Published as a 10th Issue by Metal Finishing Magazine

Fall 2011 VOLUME 109 NUMBER 11A

EDITORIAL STAFF

Publisher: Greg Valero

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Editor: Reginald E. Tucker

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Metal Finishing (ISSN 0026-0576) is published 10 times per year in January/February, March, April/May, June,July/August, September, October, November, November/December, and December by Elsevier Inc., 360 ParkAvenue South, New York, NY 10010. POSTMASTER: Send all address changes to Metal Finishing P.O. Box 141,Congress, NY 10920-0141. Metal Finishing is free to qualified metal finishers in North America. For others relat-ed to the field the subscription rate per year, including a copy of the Metal Finishing Guidebook and DirectoryIssue and the Organic Finish ing Guidebook and Directory Issue is: $123.00 in the U.S., $173.00 in Canada andMexico, $203 in Europe and Japan, $252, for all other countries $284. Prices include postage and are subjectto change without notice. For additional information contact Metal Finishing Customer Service, P.O. Box 141,Congers, N.Y. 10920-0141. Toll free (for U.S. customers); 1-800-765-7514. Outside the U.S. call 845-267-3490. Fax 845-267-3478. E-mail: [email protected]. Periodicals postage paid at New York and at addi-tional mailing offices.Change of Address: Postmaster: send address changes to Metal Finishing P.O. Box 141, Congers, N.Y.

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Copyright by Elsevier Inc. Permission for reprinting selected portions will usually be granted on written appli-

cation to the publisher.

At Aldoa we help customers quickly get

the plate on the parts using a combination

of published data, molecular behavior

and most importantly, functional trial and

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alloy deposits; Aldokote TCL a trivalent

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table of contentsmechanical surface preparation

Everything You Need to Know About Mechanical/Mass Finishing . . . . . . . . . . . . . . . .11Eugene Holzknecht

The Science of ScratchesPolishing and Buffing Mechanical Surface Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18Alexander Dickman Jr.

Buffing Wheels and Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31David J. Sax

Blast Finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45Daniel Herbert

Impact Blasting with Glass Beads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Robert C. Mulhall and Nicholas D. Nedas

chemical surface preparation

Controlled Cleaning by Measuring Surfactant Concentration . . . . . . . . . . . . . . . . . . . .57Daniel Schmann

Metal Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64Robert Farrell and Edmund Horner

Electrocleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74Nabil Zaki

The Art and Science of Water Rinsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80Ted Mooney

Advancements in Solvent Recovery Via Carbon Adsorption . . . . . . . . . . . . . . . . . . . . .89Joe McChesney

UltrasonicsA Practical Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96Kenneth R. Allen

Aqueous Washing Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102Edward H. Tulinski

Pickling and Acid Dipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111Stephen F. Rudy

Surface Preparation of Various Metals and Alloys Before Plating and Other Finishing Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119Stephen F. Rudy

electroplating solutions

New Technology for Electroplating Metal Layers Aims to ImproveThickness Control NEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135G. Carrasco, Dr. J. Harris, T.Beckett, E. Rubel

Determination of Phosphorous Electroless Nickel Deposits NEW . . . . . . . . . . . . . . .143Dr. V. Persits

Gold Post-Dip to Improve Corrosion Resistance Properties . . . . . . . . . . . . . . . . . . . .147Olaf Kurtz, Jrgen Barthelmes, Florence Lagorce-Broc, Taybet Bilkay, Michael Danker, andRobert Rther,

Troubleshooting RoHS-compliant Electroless Nickel . . . . . . . . . . . . . . . . . . . . . . . . . .156Duncan Beckett, John Szczypka, Boules Morcos, and Greg Terrell

Zincate-or Stannate-Free Plating of Magnesium, Aluminum, and Titanium . . . . . . .162John W. Bibber

4

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6High-Temperature Acid Copper Process for Plating Through-Holes . . . . . . . . . . . . .167Maria Nikolova, Jim Watkowski, Don DeSalvo, and Ron Blake

Brass and Bronze Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172Henry Strow

Decorative Chromium Plating UPDATED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177Donald L. Snyder

Functional Chromium Plating UPDATED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188Gene Barlowe

Copper Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .197Romualdas Barauskas

Gold Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .210Alfred M. Weisberg

Nickel Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .220George A. DiBari

Palladium and Palladium-Nickel Alloy Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .237Ronald J. Morrissey

Silver Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .239Alan Blair

Tin, Lead, and Tin-Lead Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .246Stanley Hirsch and Charles Rosenstein

Tin-Nickel Alloy Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .257S.K. Jalota

Zinc Alloy Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .261Edward Budman, Toshiaki Murai, and Joseph Cahill

Zinc Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .268Cliff Biddulph and Michael Marzano

hex-chrome alternatives

Alternatives to Dichromate Sealer in Anodizing Operations NEW . . . . . . . . . . . . . .275R. Mason, S. Clark, m. Klingenberg, E. Berman and N. Voevodin

Trivalent Passivates Need Trivalent Post-Dips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .288Bjrn Dingwerth

Trivalent Chromium for Enhanced Corrosion Protection on Aluminum Surfaces . .299Harish Bhatt, Alp Manavbasi, Danielle Rosenquist

Update on Alternatives for Cadmium Coatings on Military Electrical Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .308Rob Mason, Margo Neidbalson, Melissa Klingenberg, Parminder Khabra and Carl Handsy,

plating procedures

Barrel Plating UPDATED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .321Raymund Singleton and Eric Singleton

Selective Plating Process (Brush Plating, Anodizing and Electropolishing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .337Sifco Applied Concepts

Mechanical Plating and Galvanizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .351Arnold Satow

Electroless (Autocatalytic) Plating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .359James R. Henry

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8Automatic System for Endless Operation of Electroless Nickel . . . . . . . . . . . . . . . . .370Helmut Horsthemke

surface treatments

Electropolishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .376Kenneth B. Hensel

Antiquing of Brass, Copper, and Bronze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .382Mark Ruhland

Blackening of Ferrous Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .394Robert W. Farrell, Jr.

Anodizing of Aluminum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .401Charles A. Grubbs

Chromate Conversion Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .417Fred W. Eppensteiner and Melvin R. Jenkins

Trivalent Chrome Conversion Coating for Zinc and Zinc Alloys . . . . . . . . . . . . . . . . .428Nabil Zaki

control, analysis and testing

Accurate Thickness Testing Via Phase-Sensitive Eddy Current NEW . . . . . . . . . . . . .438Mike Justice

Volumetric Complexometric Method to Determine Sulfate Content inChromium Plating Solution NEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .442Dr. V. Persits

Control and Chemical Analysis of Plating Solutions . . . . . . . . . . . . . . . . . . . . . . . . . .448Sudarshan Lal

Examining the Hull Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .461Joe Fox

Chemical Analysis of Plating Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .471Charles Rosenstein and Stanley Hirsch

Thickness Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .484Norbert Sajdera

Choosing an Accelerated Corrosion Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .498Frank Altmayer

pH and ORP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .505Michael Banhidi

Microhardness Testing of Plated Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .511John D. Horner

Understanding Accuracy, Repeatability, and Reproducibility . . . . . . . . . . . . . . . . . . .516Francis Reilly

environmental controls NEW

Critical Factors Affecting Wet Scrubber Performance NEW . . . . . . . . . . . . . . . . . . . .518Kyle HankinsonWastewater Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .522Thomas WeberWaste Minimization and Recovery Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .536W.J. Mclay and F.P. Reinhard

finishing plant engineering, filtration & purification

Reducing Operational Costs Environmental Impact Via RigorousPlating/Finishing Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .562Dave Fister

Considerations in the Finishing Equipment Selection Process . . . . . . . . . . . . . . . . . .573CJI Systems

Finishing System Efficiency Upgrades for a Capital-Constrained Market NEW . . . .579Timothy Kurcz

Filtration and Purification of Plating and Related Solutions and Effluents . . . . . . . .593Jack H. Berg

Continuous Strip Plating of Electronic Components . . . . . . . . . . . . . . . . . . . . . . . . . . .609John G. Donaldson

Chemical-Resistant Tanks and Linings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .622C.E. Zarnitz

DC Power Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .632Dynapower & Rapid Power Corp.

Fundamentals of Plating Rack Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .650Steen Heimke

Selection and Care of Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .659Jack H. Berg

Immersion Heater Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .665Tom Richards

appendix

Federal and Military Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .673

Data Tables and Conversion Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .682

indexes

Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .695

Advertisers Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .700

9

Metal Finishing's WWebinar Series offers the most successful lead-generation pro-gram available in the industry. As part of an online seminar designed to ed-ucate industry members about new technologies and hot topics or issues rel-ative to surface finishing, sponsor companies have the opportunity to presenttheir message to a captive audience. The program allows sponsors to capturethe contact details of registrants online and also provides comprehensive re-porting information via a profile of all registrants.

Also available are Enhanced Podcasts, a more cost-effective lead-generation ve-hicle that combines audio and visual elements in a single broadcast-all accessiblefrom the Metal Finishing website, www.metalfinishing.com. Program features,which are determined by the sponsor, may feature interviews with targeted in-dustry members combined with corresponding photos and/or PowerPoint pre-sentations.

LOOKING FOR

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Arnie Hoffman 847-559-0909 [email protected] Ramage 847-699-6899 [email protected]

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Everything You Need to Know AboutMechanical/Mass FinishingBY EUGEN HOLZKNECHT, RSLER METAL FINISHING USA, BATTLE CREEK, MICH.

Mechanical surface finishing, also known as mass finishing or vibratory finish-ing, is a surface finishing technology that has been around for more than sixdecades. At the time it was invented in the 1940s, mechanical surface finishingrevolutionized whole industries with regard to their surface finishing meth-ods. Large international companies like Volkswagen and Mercedes-Benz inGermany were literally queuing up to initially get a hold of rotary barrels and, lat-er on, the first mass finishing vibrators. Delivery times of 24 months or more werenot unusual.

Deburring previously was a purely manual operation with extremely highpersonnel costs, poor quality, and no consistency or repeatability of results.Then, all of a sudden, manual finishing operations could be replaced with amechanical process that significantly reduced personnel costs but, more impor-tantly, one that consistently produced higher-quality parts with a high degree ofrepeatable results.

SOPHISTICATED SUPERFINISHING OF HIGH-VALUE COMPONENTS

Over the years, mechanical surface finishing has evolved from a simple deburringmethod into a sophisticated technology covering a broad range of industries andapplications. Here are just a few examples of high-tech mechanical finishingapplications:

Grinding and polishing of medical implants, such as artificial knees,hips, ankles, etc. In the medical implant industry, special massfinishing processes have been replacing robotic grinding and buffingsystems (Fig. 1).

Superfinishing of automotive gears down to a surface roughness of

media. Selection of the right mediais key to the success of any surfacefinishing process. Hopefully, theinformation to follow will help pro-vide some pointers toward the rightmedia selection.

A VERSATILE TECHNOLOGY

FOR MANY FINISHING

APPLICATIONS

Mechanical surface finishing, gen-erally referred to as mass finish-ing, offers a wide range of finishingsolutions. While the removal ofburrs is the most commonly knownapplication, mass finishing offersmany other finishing solutions, ofwhich the most important ones are:

INTERACTION OF VARIOUS

MASS FINISHING

COMPONENTS

Frequently, mass finishing is con-sidered a low-tech technology thatis noisy, dirty, and wet. And manyusers do not pay enough attentionto selecting the right componentsrequired to optimize their finish-ing operation. The results of suchnegligence are usually high finish-ing cost and a high scrap rate usu-ally requiring a lot of rework.

All this could be easily prevented,if the users would pay a bit moreattention to the optimum interac-tion of the various componentsinvolved in any mass finishingprocess (Table 1):

Figure 7 shows an example of avibratory mass finisher.

VIBRATORY FINISHING

MEDIA: A LARGE VARIETY

FROM WHICH TO CHOOSE

In the old days, when the firstmass finishing methods were devel-oped, media consisted of crushedgrinding wheels, river pebbles, andslag. Over the last few decades, massfinishing media evolved into a high-

12

Deburring: Burrs are

removed, as if numerous

little files were grinding

on the part (Fig. 4).

Radiusing: Sharp edges

on the parts are ground

off and transformed into

smooth, round contours.

Surface smoothing:

Peaks are ground off

creating a smooth

surface.

Polishing: A

continuation of the

smoothing process

decorative and

functional surfaces are

polished to a high gloss finish with

extremely low Ra values (Fig. 5).

Ball burnishing/ball

polishing: Polishing of

mainly aluminum and

stainless steel parts with

media made from

stainless steel.

Degreasing: Oily, greasy

parts (e.g., stampings) are

cleaned (degreased) and at

the same time finished

(deburred, radiused, etc.).

Surface cleaning:

Intensive cleaning of

dirty parts (e.g.,

descaling, derusting)

(Fig. 6).

13

Figure 1: Medical implants in various finishing stages.

Figure 2: Automotive gear before (left) and after (right) superfinishing.

Figure 3: Various finished air foils.

Figure 4: Part before (left) and after (right) deburring.

Figure 5: A polished part.

Figure 6: Part before (left) and after (right) cleaning (descaling shown).

Figure 7: Vibratory mass finisher (Image courtesy of Rsler).

Figure 8: Mass finishing media from 60 years ago.

Figure 9: Modern mass finishing media.

Figure 10: Rsler test lab in Battle Creek, Mich.

Figure 1: Medical implants in various finishing stages.

Figure 2: Automotive gear before (left) and after (right)superfinishing.

Figure 3: Various finished air foils.

Figure 4: Part before (left) and after (right) deburring.

Figure 5: A polished part.

Figure 6: Part before (left) and after (right) cleaning(descaling shown).

Figure 7: Vibratory mass finisher (Image courtesy of Rsler).

Figure 8: Mass finishing media from 60 years ago.

Figure 9: Modern mass finishing media.

Figure 10: Rsler test lab in Battle Creek, Mich.

ly sophisticated product line consisting of different materials, geometric shapes,and sizes (Figs. 8 and 9). Today there are a huge variety of media that a user canchoose from. And if mass finishing has an artistic element, it lies in the selec-tion of the right media with regard to type, shape, and size.

Only with the right media choice can the desired surface finish be achieved.Many times the media selection process requires comprehensive and time-con-suming processing trials. But the payback for such efforts generally is substan-tial in the form of optimum and cost-effective finishing results. Figure 10 showsa partial view of a present-day test laboratory.

Main Types of Mass Finishing MediaMass finishing media are generally classified into the following categories:

Ceramic (including porcelain polishing media) Plastic (mainly polyester-based, but also including

urea/formaldehyde media) Steel media (in hardened carbon steel and stainless steel) Organic media (for example, granules made from corn cob and

walnut shells) Other media (for example, glass beads, polyamide micro-beads,

etc.), which play only a minor role in vibratory finishing and are notdiscussed further

The most commonly used mass finishing media are either ceramic- or plastic-based. They account for approximately 8090% of all media used in mass finishingapplications. All other media are specialties that are used for certain applications,

14

Ceramic and plastic media always have one common characteristic:They consist of a carrier that is mixed with certain types of abrasives!

Component Function

Mass finishing machine (1) Induces the energy to put the parts/media mass into motion and

(2) Creates a "rubbing" action between parts and media

Water (1) Serves as a coolant for the process(2) Absorbs potential dust(3) Dissolves and distributes the compound in the work bowl

Compound (1) Dissolves dirt and grease from the parts surface(2) Cleans the media to keep its "grip" on the part surface(3) Together with the water flushes media- and metal-fines

from the work bowl

Media (1) Generates the desired surface finishdeburring, radiusing, smoothing, polishing, etc.by constantly "rubbing" on the part surface

(2) "Cushions" the parts from each other, thus avoiding impingement

Table 1: Selecting the Proper Components to Optimize Finishing Operations

such as pressure deburring, ball burnishing, drying, and dry polishing.Whereas in the case of ceramic media the carrier is clay, in the case of plastic

media the carrier is either polyester or urea resin.The most common abrasives used in ceramic and plastic media are:

Silica (sand) Brown and white fused alumina (aluminum oxide) Silicon carbide Zirconium

Depending on the application, mesh sizes can vary between 40 and 400. Thedifferent types of media, how they are made, and for what applications they aregenerally used, are subsequently described.

CERAMIC MEDIA (Fig. 11)Density: 95110 lbs/ft3.Production method: extruded or pressed.Firing temperatures: 2,1002,400F.Available shapes: triangle, star, ellipse, cylinder,arrowhead, tri-star, pyramid, cone, rhomboid, para-bolic, ball. Applications: Due to their relative high density,ceramic media are generally used for aggressivegrinding on tough metals, such as steel, stainlesssteel, titanium, and so on. However, certain ceramicmedia can also be used for fine grindingproducing

low Ra values on the part surface. Porcelain media, made from pure alumina, canbe used for polishing, producing a high-gloss surface.Limitations: Ceramic media can chip, and chips may lodge in bore holes andundercuts.

PLASTIC MEDIA (Fig. 12)Density: 6085 lbs/ft3 Production method: Abrasive/liquid resin mix ispoured into molds at room temperature; mix hard-ens within 1520 minutes.Available shapes: triangle, tri-star, double wedge,cone, pyramids of different shapes, parabolic. Applications: Due to their somewhat lower densi-ty, plastic media are generally used on softer metals,such as aluminum, zinc, and brass. Applicationsrange from relatively aggressive deburring/radiusingto pre-plate surface finishes.

STEEL MEDIA (Fig. 13)Density: 210250 lbs/ft3 (depending on size)Material: hardened carbon steel, standard carbonsteel, stainless steel.Production method: Cut to length fromwire/round bar and then forged.Available shapes: Sphere (ball), satellite, oval, angle-cut cylinder, etc.

15

Figure 11: Ceramic media

Figure 12: Plastic media

Figure 13: Steel media

Applications: Pressure deburring of steel parts, ball burnishing (or ball polishing)of mainly stainless steel parts, occasionally also aluminum parts.

ORGANIC MEDIAMaterial: Mostly corn cob or walnut shell granules.Applications: For drying of parts after vibratory finishing. Also used for high-gloss polishing of metal parts, mainly stainless steel, aluminum, titanium, etc.,in combination with a mixed-in polishing paste.

SELECTION CRITERIA: MEDIA SHAPE, SIZE, AND ABRASIVE

CONTENTMedia shape, size, and abrasive content are crucial for achieving the optimum sur-face finish.

MEDIA SHAPEThe geometry of the parts to be finished generally determines the shape of themedia to be used. A simple rule of thumb is:

Round and compact media (Fig. 14): Use for standard appli-cations. There is less danger of media lodging in the part; low-er danger of chipping (in the case of ceramic media); and low-er wear rate. Typical shapes include: cylinder, cone, ball.

Media with sharp edges (Fig. 15): For parts with complexgeometry and difficult-to-reach surfaces. Danger of chip-ping; higher wear rate. Typical shapes include: tri-star, tri-angle, arrowhead.

MEDIA SIZE The required finish usually determines the media size (Fig.16):

Small media size: Produces a smoother surface by havingmore contact with the part surface; usually requires longerprocessing times and more gentle processing.Large media size: Faster removal of burs and radiusing ofsharp edges on the parts; produces a rougher surface thansmall media; more aggressive grinding required.

ABRASIVE TYPESilica: For deburring/deflashing of relatively soft metals,

such as aluminum, brass, and zinc.Silicon carbide: For aggressive grinding on difficult-to-machine metals. Thisabrasive produces dark surfaces.Aluminum oxide: Characteristics are similar to silicon carbide.Zirconium: Used in plastic media for adding weight. Mainly used for fine grind-ing of all kinds of metals.

HOW DO YOU SELECT THE CORRECT MEDIA? BY ASKING THE

RIGHT QUESTIONS!Selecting the right media requires much experience and possibly, as mentioned

16

Figure 14: Round andcompact media.

Figure 15: Media withsharp edges.

Figure 16:Smalland largemedia.

earlier, processing trials. However, by asking the right questions, media selectionbecomes easier:

What is the desired surface finish?Aggressive deburring on steel parts requires a different media thanforexamplea surface smoothing application on aluminum parts. In thefirst case, a relatively fast-cutting, large-sized ceramic media may berequired, whereas in the latter a fine-grinding, small to mid-sized plas-tic media may be needed.

What is the desired wear rate?All vibratory finishing media wear! Of course, you want to select the mediathat will do the job at the lowest possible wear rate and, thus, cost!

Can chipping of the media be an issue?If media chipping is an issue, ceramic media usually is not an option.

What about separation of parts and media?After the finishing process, the finished parts must be separated from the media.With ferrous steel parts, magnetic separation may be an option. Otherwise,there must be a distinct difference in size between parts and media to allow sep-aration by vibratory screening.

And what of media lodging?Depending on the part geometry and size, media lodging may be an issue. Byselecting the right media size and shape, media lodging in the parts may beminimized or altogether prevented.

Last but not least: How about media color?If lodging cannot be prevented, the media should at least have a bright color sothat lodged media can be easily detected and removed from the part.

THE CORRECT MEDIA CHOICE MAKES ALL THE DIFFERENCE

Vibratory finishing media may not be the most exciting subject to talk aboutunless you are infected by the mass finishing virus! But considering the conse-quences of the wrong media choicepoor surface finish, high scrap rate, and lotsof rework (all of this associated with high cost) for the user of mechanical sur-face finishing it is definitely worthwhile to pay a bit more attention to this sub-ject. Hopefully, this article was able to shed some light on the various factors thatneed to be considered in the selection of vibratory finishing media for a specif-ic surface finishing task.

17

MECHANICAL SURFACE PREPARATION

THE SCIENCE OF SCRATCHESPOLISHING

AND BUFFING MECHANICAL SURFACE

PREPARATIONBY ALEXANDER DICKMAN, JR.

ALEXANDER DICKMAN, JR. CONSULTANT, LLC, SOUTHBURY, CT.

POLISHING

Mechanical finishing refers to an operation that alters the surface of a sub-strate by physical means such as polishing and buffing.

Polishing plays a vital role in the development of a quality product. The term pol-ishing is not to be confused with buffing. The definition of polishing is surfaceenhancement by means of metal removal and is generally done by an abrasivebelt, grinding wheel, setup wheel, and other abrasive media. A definite coarse linepattern remains after such a polishing operation. This polishing effect removes largeamounts of metal from a particular surface.

Buffing is the processing of a metal surface to give a specific or desired finish. Therange is from semibright to mirror bright or high luster.

Polishing refers to an abrading operation that follows grinding and precedes buff-ing. The two main reasons for polishing are to remove considerable amounts of met-al or nonmetallics and smooth a particular surface. This operation is usually fol-lowed by buffing to refine a metallic or nonmetallic surface.

POLISHING WHEELS

Polishing wheels can be made up of a different variety of substrates such as muslin, can-vas, felt, and leather. Cotton fabric wheels as a class are the most commonly used medi-um for general all-round polishing due to their versatility and relatively modest cost.Polishing wheels can have a hard consistency, such as canvas disks, or a soft consistency,such as muslin, sewn together. The most popular wheels are composed of sewn sectionsof muslin disks held together by adhesives. The types of adhesives used include thosewith a base of silicate of soda and the animal-hide glue type.

Felt wheels are available in hard densities to ultrasoft densities. The outside periph-ery or face of the wheel must be kept true and be absolutely uniform in density over itsentire surface. Felt wheels can be easily contoured to fit irregularly shaped dimensions.Felt wheels are generally restricted to use with finer abrasive grain sizes.

In general, the more rigid polishing wheels are indicated where there is either aneed for rapid metal removal, or where there are no contours and a flat surface isto be maintained. Conversely, the softer types with flexibility do not remove met-al at such a high rate.

In addition to polishing wheels, precoated abrasive belts can be obtained inany grit size ready for polishing operations. Metallic and nonmetallic articles arepolished on such belts running over a cushioned contact wheel with the prop-er tension being put on them by means of a backstand idler. Where a wet pol-ishing operation is desired, the use of abrasive belts in wet operations needs tohave a synthetic adhesive holding the abrasive particles to the belt backing.This synthetic adhesive must have a waterproof characteristic.

When determining the belts grit size, the condition of the surface is what willdictate the aggresiveness of a belt. Too aggresive belt can put in larger imperfectionsthan those initially in the surface.

18

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BURR REMOVAL

The removal of burrs is a breaking of sharp edges. Burr removal is done by thefollowing methods: hand filing, polishing, flexible polishing, satin finishing,brushing, and tumbling. Functional parts do not necessarily need a decorativefinish and usually deburring becomes the final mechanical finish.

Burrs can be removed by hand methods such as filing, which is very labor-intensive making mechanical means preferred in most cases. Parts that containrestricted areas can be processed using set-up polishing wheels and muslin buffscoated with a greaseless compound. See the discussion on polishing wheels (above)and buffing. Processing methods will be determined by the configuration of the part.If a part contains a heavy burr yet the edges are straight, a rigid set-up wheel is need-ed. Where the contours are irregular and the burrs not excessive, a sewn or loose cot-ton buff with a greaseless compound works more efficiently. If extreme flexibilityis required, a string wheel with greaseless compound or a tampico wheel with alu-minum oxide, grease-based material is required.

BUFFING

Buffing is the processing of a metal surface to give a desired finish. Depending onthe desired finish, buffing has four basic categories: satin finishing, cutdown buff-ing, cut-and-color buffing, and luster buffing. Satin finishing produces a satin ordirectional lined finish; other types of satin finishing are brushed or Butler finishing.Cutdown buffing produces an initial smoothness; cut-and-color buffing producesan intermediate luster; and luster buffing (color buffing) produces high reflectiv-ity or mirror finish.

TYPES OF BUFFING COMPOUND COMPOSITIONS

Greaseless compound is used to produce a satin finish or a directional lined fin-ish. Greaseless compound contains water, glue, and abrasive. As its name implies,it retains the abrasive on the buffing wheel in a grease-free environment, leavingthe surface of the finished part clean and free of greasy residue. The principal usesof greaseless compound are for satin finishing or flexible deburring.

Generally, the abrasive contained in such compounds is silicon carbide or fusedaluminum oxide. Grades are available in abrasive sizing from 80 grit to finerdepending on the degree of dullness required on a particular base metal. Silicon car-bide abrasives are used for the finishing of stainless steel and aluminum. Aluminumoxide grades are used for brass and other nonferrous metals, as well as for carbonsteel prior to plating.

To produce a finer satin finish on nonferrous materials, fine emery and hard sil-ica are used. For Butler finishes on silver plate and sterling, fine buffing powdersof unfused aluminum oxide and soft silica are used. Greaseless compounds areapplied to a revolving buff by frictional transfer. The buff speed is 4,000 to 6,000surface feet per minute (sfm). The material then melts on the cotton buff, adheresto the peripheral surface, and dries in a short period of time. This produces a dry,abrasive-coated wheel with a flexible surface. The buffing wheels on which grease-less compounds can be applied are sewn muslin buffs, pocketed buffs, full disk loosebuffs, and string wheels. The coarser the abrasive particle, the duller the satin fin-ish; the finer the abrasive particle, the brighter will be the satin finish.

BAR COMPOUNDS

Bar compounds contain two types of ingredients; binder and abrasive. Thebinder can consist of one or more materials taken from animal or vegetable fatsas well as petroleum and similarly derived products. Animal fats are such mate-

20

rials as fatty acids, tallows, and glycerides. Waxes can be from vegetable, insect, orpetroleum-based products. Petroleum-based or vegetable-based oils also may be used.The animal and vegetable materials are more saponifiable and will produce awater-soluble soap when combined with alkali. Petroleum, mineral oils and waxesare unsaponifiable and, therefore, might create subsequent cleaning problems.

Each ingredient is added to the binder to transmit a specific effect to the bar com-pound such as lubricity, degree of hardness, or improved adherence to a buffingwheel. A binder also controls the amount of frictional heat that can be developedon a surface. This is called slip. There is a wide range of abrasives used in buffingcompounds, a few of which will be described.

BUFFING ABRASIVES

Aluminum Oxide and Other PowdersAluminum oxide powders, fused and unfused, are the abrasives most commonlyused in the buffing of hard metals. Chromium oxide is used to achieve the highestreflectivity (color) on stainless steel, chromium, and nickel plate. To achieve ahigh reflectivity (color) on brass, gold, copper, and silver, iron oxide is generally used.Aluminum oxide is chemically represented as Al

2O

3.

The unfused aluminum oxide is white in color. This is manufactured frombauxite or hydrated aluminum oxide by heating it at elevated temperatures. Thisheating process, called calcination, gives the abrasive the common name calcinat-ed alumina. The higher the calcination temperature, the more water of hydrationis driven off and the harder the crystalline material becomes.

When the calcinated temperature is about 950oC, the product produced is a softalumina having a porous structure. This type of abrasive is used for luster or col-or buffing. When the calcined temperature is about 1,250oC, a harder alumina is pro-duced. This type of abrasive is used for cutting. Soft aluminas are used to produceluster or a higher reflectivity on all metals, both ferrous and nonferrous. Theharder aluminas will cut and remove more metal from the surface of castings orextrusions of aluminum, brass, and other metals.

When alumina is heated to 1,850oC, fused aluminum oxide (Al2O

3) is produced.

This material is made in an electric furnace at approximately 2,000oC. Bauxite, whenmixed with alumina and other oxide materials, produces a specific crystallinestructure whose hardness can be varied to meet specified physical properties. Thisfused mass is then cooled and crushed. In the crushing process, the material isground, screened to the appropriate size, treated magnetically, and acid washed. Itis then rescreened to its final classification (grit sizing).

The difference between fused aluminum oxide and calcined alumina is thatthe fused oxide is of a crystalline structure that is much harder than that of the cal-cined alumina. Fused aluminum oxide is used mainly on abrasive belts or setupwheels for polishing. As for buffing, fused aluminum oxide is used for cutting downferrous metals. The abrasive sizing is generally from 60 grit to -325 grit for buffingcompounds.

TripoliTripoli is considered to be microcrystalline silica, which is made naturally. It is high-ly suitable for buffing of aluminum, brass, copper, and zinc die cast or otherwhite metals. Tripoli and silica can be used as a cutting abrasive or a so-called cut-and-color abrasive for nonferrous metals. Tripoli should not be classified as an amor-phous silica, but it is microcrystalline in nature. Crystalline silica may causedelayed lung injury for people when exposed to it over a long period. Users of prod-ucts containing these abrasives should be aware of this possibility and should

21

wear a mask and work in a ventilated area.

Silicon CarbideSilicon carbide (SiC) is of a crystalline structure that is harder than fused aluminumoxide. It is formed by mixing coke and silica in an electric furnace at approxi-mately 1,900 to 2,400oC. The material is cooled, ground, and sifted to the requiredgrit size similar to the processing of fused aluminum oxide. The crystalline struc-ture of SiC is a hexagonal.

Red RougeThe chemical formula for rouge is Fe

2O

3; it is also called jewelers rouge. Its

purity is 99% ferric oxide. The crystalline structure of ferric oxide is spherical.Rouge is used mainly on precious metals to give an exceptional high luster.

Green RougeThe chemical formula for chromium green oxide is Cr

2O

3. The hardness of chromi-

um oxide is 9 Mohs as opposed to iron oxide, which is 6 Mohs, and is used to pro-duce an exceptional luster or color on ferrous as well as nonferrous metals.

These abrasives mentioned represent a small percentage of material available togive a specific finish required on a particular substrate. See Table I for typicalhardness values.

Although the wheel speeds for buffing with grease bars will vary greatlyfrom job to job and operator to operator, the figures in surface feet per minutegiven in Tables II and III will serve as a guide for hand buffing operations.Buffing wheel speeds for automatic operation may vary with the design of themachine and the contact of the work to the wheel. It can, therefore, be more def-initely fixed without depending on the physical ability of the hand buffer to main-tain the correct position and pressure against the wheel.

LIQUID SPRAY BUFFINGLiquid spray buffing compositions have largely replaced bar buffing composi-tions on automatic buffing machines. Unlike the bar compound previously dis-cussed, liquid buffing compound is a water-based product. The liquid buffingcompound has three main constituents: water, binder, and abrasive. Water is usedas the vehicle to transport the binder and abrasive to a buffing wheel through a spraysystem. This water-based liquid is an oil/water emulsion. In this emulsion theabrasive particle is suspended and could be thought of as particles coated with abinder material. The emulsifying materials act as a device to hold the oil-soluble mol-ecules onto the water molecules.

Larger abrasive particles offer less surface area (when compared with the weightof that particle) than several smaller particles. Surface area and density play animportant role in the suspension of any liquid emulsion. Stability is the ability to

Table I. Hardness of Abrasive Materials

Abrasive Type Chemical Symbol Mohs Scale

Aluminum oxide (fused) Al2O

38-9+

Aluminum oxide (calcined) Al2O

38-9+

Tripoli-silica SiO2

7

Silicon carbide SiC 9.6

Iron oxide (red rouge) Fe2O

36

Chrome oxide (green rouge) Cr2O

38-9

22

keep the abrasive particle in suspension. When the abrasive particles tend to fall outof suspension, their weight factor is greater than the ability of the emulsifiedmaterial to maintain stability. Viscosity, therefore, plays an important role in a sus-pension. A totally unstable emulsion will settle out under all circumstances.

The flow characteristics of a liquid buffing compound are controlled generallyby the viscosity of that compound as well as its degree of slip. The viscosity stabil-ity of any emulsion is established by its thixotropic nature, which means the viscositybecomes lighter in direct proportion to the amount of shear to which the compoundis subjected.

As the degree of slip is increased, the flow characteristics of the compound willalso increase in direct proportion to the resultant change in slip or the resultantchange in the coefficient of friction.

The gel-type property of an emulsion is broken down by the action of thepump, thus producing viscosity changes. The changes are determined by theamount of shearing action of the pump and the length of time. This breakdown isnecessary to allow the transfer of the buffing compound from the pump to the spraygun, which often requires a significant distance.

The viscosity of a liquid compound is measured under a constant set of condi-tions. To measure viscosity, a representative sample from a batch is needed. This sam-ple must be in a state of equilibrium for a defined period and at a constant tem-perature. A viscometer is used with a specific spindle. This reading multipled by afactor will give a viscosity reading in centipoise. A deviation of 25% is normal.The control of viscosity of a compound is somewhat difficult. Variations in rawmaterials or the method of blending are two reasons for viscosity changes. Viscosityis an arbitrary measurement.

Liquid compounds are supplied to the spray guns by means of either air pressurefeed tanks or drum pumping equipment. Air pressure is varied depending on theviscosity of the liquid compound, the length and diameter of the fluid lines feed-ing the spray guns, and the actual number of spray guns. With one or two spray gunsclose to the tank, 10 to 15 psig tank pressure may be sufficient, while 6 to 8 gunscould require 40 to 45 psig tank pressure.

A drum pumping system is inserted into a steel drum. The pump then trans-fers the compound through a fluid line or manifold that feeds the guns.Depending on the size of the system, the drum pump is operated at 10 to 40 psigair pressure.

The spray gun is usually mounted in back of the buffing wheel so it will notinterfere with the operator and is at a distance from the buffing wheel face so thatcomplete coverage of the face of the buff is obtained with proper regulation ofthe spray gun. An opening in the dust collecting hood allows the compound tobe sprayed from this position. Where buffing machines are totally enclosed, thereare no hoods to interfere with the placement of the guns. The spray guns are actu-ated by air, which is released, in the case of manually operated lathes, by a footvalve that allows the buffer to keep both hands on the part being buffed. With

Table II. Wheel Speeds for Hand Buffing, sfm

Cutting Down Luster Buffing

Carbon and stainless steel 8,000-9,000 7,000-9,000

Brass 6,000-9,000 6,000-9,000

Nickel 6,000-9,000 6,000-8,000

Aluminum 6,000-9,000 6,000-7,000

Zinc and other soft metals 5,000-8,000 6,000-7,000

Chromium 7,000-8,000

23

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automatic machines, solenoids allow the flow of air to operate the guns. The sole-noids are connected to an electric timer where an on-time and an off-time canbe set depending on the frequency of the compound needed on the buff face.

A buffing head is a series of buffing wheels put together producing a buff face.This buff face can vary in length depending on contact time needed to do a certainjob function. To adequately apply buffing compound to the wheel face, spray gunmovers or multiple gun set-ups are usually employed. This allows the liquid com-pound to be applied across the entire buff wheel face. Spray guns will generally pro-duce a fan of 10 to 12 inches per gun.

In manual operations, the main advantage of the spray composition methodis to save the operator time. He or she does not have to stop buffing to apply thecake of conventional solid composition. The operator can remain buffing andapply the liquid compound by the use of a foot peddle, hence less motion is usedin applying the compound thus increasing productivity.

In the case of automatic machines, the spray equipment replaces mechanicalapplication. Shutdown time for regulation of mechanical applicators in most cas-es amounts to more than 25% of the theoretical maximum production time. Thisis almost entirely eliminated.

The advantages of liquid spray buffing for both automatic and manual buffingprocedures are as follows:

1. Optimum quantity of composition is readily controlled on the buff surface,the composition being supplied regularly rather than haphazardly. With buff-ing bars, an excess of composition is present when the first piece is buffed andan insufficient amount is present for the last piece of work before anotherapplication of the bar. If this were not true, the operator would handle the barof composition more often than the work. Using the spray method, thedesired amount of composition is present for each piece buffed.

2. With a deficiency of composition of buffing compound present, the buff-ing cloth is worn excessively. Spray compositions, eliminating this defi-ciency of coating, also eliminate this cause of unnecessary buff wear.

3. Solid buffing dirt is packed into the crevices of the work when an excessof buffing composition is present. The serious cleaning problem pre-sented by this dirt is well known. As there need be no excess of composi-tion using the spray method with properly formulated compositions,cleaning after buffing is greatly simplified.

4. Significant savings can be realized in compound consumption, becauseall the liquid composition brought to the lathe can be used. There are nonubbins left over.

5. Where high pressures exist between the work and the buffs, a deficiencyof compositions has often resulted in such a high frictional heat that themuslin buff catches fire. The spray method eliminates this hazard bykeeping the buff properly coated at all times; however, a spray composi-tion must be selected that does not constitute a fire hazard, which wouldbe present if a liquid composition were composed of volatile, combustiblefluids.

When using bar compound on an automatic machine, wheel speeds must bemaintained in the higher range to generate sufficient friction to exceed the melt-ing point of the bar; however, much lower wheel speeds may be used when liquidcompounds are used. The ability to slow down the surface feet enables more intri-cate parts to be buffed. The lower buffing wheel speeds with large buff faces and liq-

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uid compound allow the slowly rotating work to bepushed up into or mushed into the buff wheel. Although the amount of

work per unit of time might be lowered, this is compensated by increasing the buffcontact time on the work by using wide-faced buffs.

Airless spray systems provide a significant breakthrough in developing a high-ly efficient method of applying liquid buffing compositions for automatic and semi-automatic buffing operations. Such a system uses high fluid pressures in therange of 600 to 1,800 psi. Specially designed, air-activated drum pumps generate suchhigh fluid pressures and deliver custom-formulated, heavy viscosity liquid buffingcompounds to special automatic spray guns with tungsten carbide insert noz-zles. Much like the action of a watering hose, the high fluid pressures force the heavyliquid buffing compounds through the orifice of the spray gun for controlledfracturing of the compound. This high velocity spray is capable of penetrating notonly the wind barrier around a rotating buff, but has enough force behind it toimpregnate the cloth buff up to a 1.5-in. depth, depending upon the constructionand speed of the buff. Overspray, so common to regular external atomizing spraysystems, is practically eliminated.

Deep saturation of the buff with the compounds provides more consistentand uniform finishes, with reduced compound consumption up to 35%. Extendedbuff life also reduces changeover downtime. Operating costs are further reduced withlower compressed air consumption because airless spray guns do not requireatomizing air to apply the compounds.

Airless spray buffing systems presently in operation limit applications to custom-formulated, heavy viscosity liquid buffing compounds containing tripolis andunfused aluminum oxides. Properly designed drum pumping systems must be used.High pressure fluid hose and fittings are also necessary. The high fluid pressuresgenerated in airless spray buffing systems make it necessary to exercise certain pre-cautions. When adjusting the spray guns, operators must be careful not to allow theforce of the spray to come in contact with exposed skin, since the force of compoundis strong enough to break the skin.

Liquid abrasive compounds offer so many recognized advantages that theiruse is now accepted by the finishing industry as standard procedure for high pro-duction buffing.

POLISHING AND BUFFING OF PLASTICS

Due to the dies used to mold plastic, little buffing or polishing is required.Some do require removal of flash, parting lines, sprue, projections, gates, andimperfections from areas that may need further surface finishing. Plastics cut andmachined generally need abrasive finishing to bring back their original luster usingbelt polishing and buffing. Plastic compounds are formulated to remove largeamounts of stock without generating too much frictional heat between the partand the wheel (preventing crazing of the plastic). Some buffing compoundscontain built-in antistatic materials so that the buffed surface resists the adhe-sion of airborne lint. When buffing plastic, the material becomes staticallycharged.

On surfaces of plastic laminates, where fibrous fillers are completely covered witheither a thermoplastic or thermosetting plastic, polishing and buffing recom-mendations are the same as those given for the particular plastic binder involved.

Heavy flash removal, sprues, flat surfacing, and beveling on thermosetting andthermoplastic articles are usually done with wet belt sanding. Special waterproofabrasive belts are most generally used. The abrasive grit size is determined by theamount of flash that must be removed.

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For flexible polishing of thermosetting plastic articles, greaseless compound pro-vides a dry and resilient abrading face for removal of light or residual flash, imper-fections in the surface, and cutting tool marks, or for smoothing out irregularities onthe contours left by the belting operation. Thermoplastic articles readily distort withfrictional overheating. To avoid this problem minimum work pressure against the coat-ed buff wheel and low peripheral speeds are needed. To assure low frictional heat devel-opment, grease sticks also can be applied to the coated buffing wheel. This givesadded lubrication and lowers the amount of drag, which produces the heat buildup.

BUFFING OF PLASTICBuffing is usually divided into cutdown and luster or color buffing. Cutdownbuffing produces a semigloss finish from the dull, sanded surface resulting frombelt sanding or greaseless compound operations. This semigloss finish is ade-quate as a final finish in some cases. Where a higher luster is required, this cutdownbuffing is the intermediate operation prior to the final high luster buffing.

The most popular buffs used are full disk sewn 80/92 count cloth for cutdownand full disk loose, bias type, or ventilated 64/68 count for luster. Buffing pressureshould be at a minimum and the buff speed slow to prevent burning the plastic.Keeping the buff well lubricated with buffing compound in the cutdown operationhelps minimize the burning.

MILL AND ARCHITECTURAL FINISHES (STAINLESS STEEL)The main concern of most fabricators of stainless steel is to remove welds andmachining marks, and blend and sim-ulate the final finish with the originalmill finish or the sheet or coil stock.To refine the area of welds and machin-ing marks, standard rough polishingprocedures used are as those previous-ly discussed. Note that the final sur-face finish must closely approximatethe original mill finish. There are eightbasic stainless steel mill finishes used inthe industry by product designers andarchitects. Mill finish Nos. 3, 4, 6, 7,and 8 are produced mechanically usingsome type of abrasive media and buff-ing wheels. Finish Nos. 3 and 4 haveproven to be the most popular amongfabricators of dairy, kitchen, cafeteria,chemical equipment, and architecturaland decorative structures. The simplestway to produce these blended finishes iswith string wheels coated with grease-less abrasive compositions containing80, 120, or 180 grit abrasive, operatingat relatively low speeds.

Narrow, flat, or curved areas can eas-ily be blended with a portable powertool and a string wheel up to 8 inches inface width. Medium or very wide areasare finished with a string wheel log held

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ISO 9001: 200 Certified

Manufacturers of fine polishingcompounds for over 8 years.

For Metal, Fiberglass, Marble and Paint

All compounds are crystalline silica free.

Private labeling available.

CUSTOM KITS LUBRICANTS

SPECIALTY DEGREASERS

4800 South St. Louis AvenueChicago, Illinois 60632, U.S.A.

Phone: 773-847-1111Fax: 773-847-3399www.kocour.net

email: [email protected]

BARS LIQUID PASTE BUFFS BELTS


with two hands or by two operators. Such a polishing log is made up of string wheelsections on a desired width shaft of a sufficiently powered portable tool. Thegreaseless compound is applied to the rotating string wheel log and allowed to drya few minutes. String wheel blending is then quickly accomplished in the directionof the lines of the original mill finish.

Mill finishes Nos. 6, 7, and 8 are most generally used on consumer products,although on some architectural sections they are produced for contrasting patterns.

BASIC STAINLESS STEEL SHEET FINISH DESIGNATION

The following list of stainless steel sheet finish designations includes a briefdescription of how each finish is obtained.

Unpolished Finish No. 1: A dull finish produced by hot rolling to specifiedthickness, followed by annealing and descaling.

Unpolished Finish No. 2D: A dull finish produced by cold rolling to specifiedthickness, followed by annealing and descaling. May also be accomplished by a final,light roll pass on dull rolls.

Unpolished Finish No. 2B: A bright finish commonly produced in the sameway as No. 2D, except that the annealed and descaled sheet receives a final, lightcold-roll pass on polished rolls. This is a general purpose, cold-rolled finish, andis more readily polished than the No. 1 or No. 2D finishes.

Polished Finish No. 3: An intermediate polished finish generally used where asemipolished surface is required for subsequent finishing operations following fab-rication, or as a final finish with a 50- or 80-grit abrasive compound.

Polished Finish No. 4: A general purpose bright polished finish obtained witha 100 to 180 mesh abrasive, following initial grinding with coarser abrasives.

Buffed Finish No. 6: A soft satin finish having lower reflectivity than No. 4 fin-ish. It is produced with a greaseless compound, #200 grit, top dressed with whiterouge or chromium green rouge.

Buffed Finish No. 7: A highly reflective finish produced by buffing a surface thathas first been refined to approximate a No. 6 finish, then buffed lightly with a whiterouge without removing satin finish lines.

Buffed Finish No. 8: The most reflective finish commonly produced. It isobtained by flexible polishing with successively finer abrasive compounds, thenbuffing extensively with a very fine chromium green rouge bar compound.

FINISHES FOR ARCHITECTURAL ALUMINUM

Due to the different aluminum alloys, variations in final surface finish may occur.Variations may also occur by the type of buffing equipment used, type and size ofthe buff wheels, peripheral speed of the buff, the type of abrasive composition usedand operators technique. When using automatic equipment, the operator techniqueis replaced by a mechanical system controlling such variables as pressure, time cycle,conveyor speed, and contact time against the buffing wheel, resulting in a more con-sistent finish.

Aluminum and its alloys are soft metals with a high frictional coefficient. As pre-viously discussed, tripoli or silica is used for a cutdown or cut-and-shine operationon aluminum. Calcined alumina compounds are used for shine on the aluminumsurface.

DESCRIPTION OF ARCHITECTURAL FINISH DESIGNATIONS

Series (a) As fabricated. No buffing or polishing required.Series (b) Medium bright soft textured satin finish.Series (c) Bright buffed finish over soft texture satin.

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Series (d) Bright buffed finish on original surface.Series (e) Coarse directional satin finish.Series (f) Medium directional satin finish.Series (g) Fine directional satin finish.Series (h) Hand-rubbed satin-type finish (small areas only).Series (i) Brushed finish.Series (j) Nondirectional satin finish.

GENERAL RECOMMENDATIONSThe following recommendations are step-by-step instructions for obtaining the des-ignated architectural finishes.

Series (b) Finishes: Polish with a wheel coated with an abrasive and cementpaste with 80 to 150 grit on sewn or ventilated buffs, lightly lubricated with specialbar or liquid lubricants. Buff speed 6,000 sfm. Final polish with a wheel coated withan abrasive and cement paste with 320 grit using the same buff and same speed.

Series (c) Finishes: Polish with an abrasive and cement paste coated wheel, 320grit on sewn or ventilated buff. Light lubrication with special bar or liquid lubricant.Bright buff with clean working tripoli bar compound or liquid tripoli buffingcompound on ventilated, sewn, or loose buff. Buff speed 7,000 sfm.

Series (d) Finishes: Bright buff only over original surface as for series (c) finish-es. No prior polishing required.

Series (e) Finishes: Coarse satin finish with greaseless compound of 80 gritover glue base buff sizing on a ventilated or sewn buff, or with liquid abrasive 80 griton the same type buff. Lubricate the dried compound head with a special bar or liq-uid lubricant. Buff speed 6,000 sfm.

Series (f) Finishes: Medium satin finish with greaseless compound, 120 grit, overa blue base buff sizing on ventilated or sewn buffs, or with liquid abrasive 120 griton the same type buff. Lubricate dried compound head with a special bar or liquidlubricant.

Series (g) Finishes: Fine satin finish with greaseless compound, 150 grit, on a ven-tilated, sewn or loose buff, or with liquid abrasive 150 grit on the same type of buff.Lubricate dried compound head with a special bar or liquid lubricant. Buff speed6,000 sfm.

Series (h) Finishes: Hand rubbed finish, using coarse steel wool lubricated witha special liquid lubricant. Final rubbing with No. 0 steel wool.

Series (i) Finishes: Brush type finish produced with string wheels coated withgreaseless compound, 80 grit. String wheel speed 6,000 sfm. Buff head may requiresome light lubrication with a special bar lubricant, depending on alloy of alu-minum. Nylon impregnated wheels are also used for this finish.

Series (j) Finishes: Brush type finish produced with a string wheel coated withgreaseless compound, 80 grit, but operated at a slow speed of 2,000 to 3,000 sfm.May also require some light lubrication with a special bar lubricant. Again, nylonimpregnated wheels may also be used.

When high production satin finishing is required for series (e), (f), (g), and (i),use a liquid greaseless abrasive. Such compositions may be applied automaticallywith properly designed spray equipment. Light lubrication of the satin finishedhead, when required, is done with nonmisting, low atomizing spray equipment.

SAFETY REQUIREMENTS OF POLISHING AND BUFFINGDue to increased concern for industrial and environmental safety, state and federalauthorities have drawn up guidelines for controlling industrial hazards. Theseguidelines protect the user as well as the environment.

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Buffing processes propel dust particles, cotton lint, abrasive dust, and metallicdust into the air. Microcrystalline silica, or tripoli, which is used in buffing com-pounds, is a good example of such dust. According to OSHA permissible exposurelimits, exposure to airborne crystalline silica shall not exceed an 8-hour time-weighted average limit as stated in 29 CFR Part 1910 1000 Table Z-3 for MineralDusts, specifically Silica: Crystalline: Quartz (respirable). The threshold limit val-ue and biological exposure indices for the 1987-1988 American Conference ofGovernmental Industrial Hygienists is 0.1 mg/m3 (respirable dust).

Excessive inhalation of dust may result in respiratory disease including silicosis,pneumoconiosis, and pulmonary fibrosis.

The International Agency for Research on Cancer (IARC) has evaluated Monographson the Evaluation of the Carcinogenicity Risk of Chemicals to Humans, Silica and Some Silicates(1987, Volume 42), that there is sufficient evidence for carcinogenicity of crys-talline silica to experimental animals and limited evidence with respect to humans.

A conventional particulate respiratory protector is required based on consider-ations of airborne concentrations and duration of exposure. Refer to the most recentstandards of the American National Standard Institute (ANSI Z.88.2), theOccupational Safety and Health Administration (OSHA) (29 CFR Part 1910 134),and the Mine Safety and Health Administration (MSHA) (30 CFR Part 56). The useof adequate ventilation and dust collection is also required.

Grinding, polishing, or buffing operations that generate airborne contami-nants in excess of exposure limits into the breathing zones of employees should behooded and exhausted as necessary to maintain legal exposure limits. A hoodused for the control of contaminants from a grinding, polishing, or buffing oper-ation should be connected to an exhaust system that draws air through the hoodto capture air contaminated by the operation and to convey the contaminated airthrough the exhaust system.

Where large quantities of exhaust air cause negative pressures that reduce theeffectiveness of process exhaust systems or cause a carbon monoxide hazard due toback-drafting of flues of heating devices, provisions shall be made to supply cleanmake-up air to replace the exhausted air. The make-up air supply, where necessary,should be adequate to provide for the combined exhaust flows of all exhaust ven-tilation systems, process systems, and combustion processes in the workplacewithout restricting the performance of any hood, system, or flue.

Dust collection equipment is available in numerous designs utilizing a numberof principles and featuring wide variation in effectiveness, first cost, operating andmaintenance costs, space, arrangement, and materials of construction. Consultationwith the equipment manufacturer is the recommended procedure in selecting a col-lector for any problem where extensive previous plant experience on the specific dustproblem is not available. Factors influencing equipment selection include:

1. Concentration and particle size of contaminant2. Degree of collection required3. Characteristics of air or gas stream4. Characteristics of contaminant5. Method of disposal under Federal, State, and Local Regulations.

There are many other aspects of buffing and polishing than these briefly discussedhere. Though this very important contributor to the metal-finishing industry is moreof an art than a science, basic engineering principles can be applied to this opera-tion. With the proper melding of buff and compound, applied in a controlledfashion, optimum finish and maximum economy can be achieved.

For questions or comments, contact the author at [email protected].

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BUFFING WHEELS AND EQUIPMENTBY DAVID J. SAX

STAN SAX CORP., DETROIT; WWW.STANSAXCORP.COM

Three elements to a successful buffing operation are the buff wheel, the buffingcompound, and the buffing machine. It is necessary to understand all of these ele-ments and how they interact to achieve desired quality, productivity, cleanabil-ity, corrosion resistance, reject elimination, and overall cost-effectiveness.

WHAT IS BUFFING?

Buffing is a mechanical technique used to bring a workpiece to final finish. It alsocan be used to prepare the surface of a machined, extruded, or die-cast part forplating, painting, or other surface treatment. The objective is to generate asmooth surface, free of lines and other surface defects.

Buffing is not a process for removing a lot of metal. Deep lines and other moresevere surface defects should be removed before buffing by polishing with apolishing wheel or abrasive belt.

Buffing usually involves one, two, or three steps: cut buffing, intermediate cut,and color buffing. These operations normally are performed by what is referredto as either area buffing or mush buffing.

Cut BuffingA harder buff wheel and, generally, a more abrasive buffing compound, areused to start the buffing process. In cut buffing, the buff wheel and workpieceare usually rotated in opposite directions to remove polishing lines, formingmarks, scratches, and other flaws.

Color BuffingWhen a mirror finish is specified, a color buff step may be required. Color buff-ing may be performed with a softer buff wheel and less aggressive abrasive com-pounds. In color buffing, the buff wheel and workpiece are usually rotated in thesame direction. This enhances the cut buff surface and brings out the maximumluster of the product.

Area BuffingFor localized finishing, narrow buffing wheels, positioned tangentially to theworkpiece, are used. This is often is referred to as area buffing.

Mush BuffingTo finish larger parts or parts having several surface elevations, mush buffing maybe used. This involves the use of one or more wide buff wheels. In mush buffing,a part is rotated or cammed through the buffing wheel. This technique is also usedto finish multiple products simultaneously.

BUFFING COMPOUNDS

Buffing compounds are the abrasive agents that remove minor surface defects dur-ing the buffing phase of the finishing cycle. Buffing compounds are available inpaste or solid form. There are thousands of products from which to choose. Theprime consideration in selecting a buffing compound is the substrate beingbuffed and the surface to be provided.

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mechanical surface preparation

Nonferrous products made of copper, nickel, chromium, zinc, brass, alu-minum, etc., frequently are buffed with compounds containing silica (generallyamorphous, often tripoli). Tripoli is found in a small area of Oklahomaand is shipped all over the world. Steel products are normally buffed with com-pounds of fused aluminum oxide, which is available in DCF collector fines andas graded aluminum oxide in a range of grit designations.

Special abrasives are available for other purposes. For example, chromium oxideis widely used to give stainless steel, chromium- and nickel-plated productshigh reflectivity. Iron oxides are used to color buff gold, silver, copper, andbrass. Lime-based buffing compounds are used to generate mirror finishes onnickel products.

Skilled buffing engineers can help manufacturers select the optimum equip-ment, buffing compounds, wheels, and buffing techniques. Cleaners and clean-ing processes must be matched to the soil to be removed.

BUFFING WHEELS

Fabrics used in buffing are designated by thread count and fabric weight. Countis measured by threads per inch; weight by the number of linear yards per poundof 40-inch-wide fabric. Heavier materials have fewer yards per pound. Lowerthread count and lighter weight materials are used for softer metals, plastics, andfinal luster. More closely woven, heavier, and stiffer materials are used on hard-er metals for greater cut and surface defect removal. Stiffness is a result of heav-ier weight, higher thread count fabrics, more material, specialized treatments,sewing, and overall buff design.

Buff wheel construction determines the action of the buff by making it hard-er or softer, usually by varying convolutions of the face of the wheel. This influ-ences aggressiveness. Part configuration dictates buff design, construction,thread count, etc.

Conventional buffs employ a circular disk of cloth cut from sheeting and sewninto a number of plies. For example, some materials require from 18 to 20 pliesto make a -in.-thick section. Multiple sections are assembled on a spindle to buildthe required face width. The density of these types of buffs is also controlled byspacers that separate the plies of fabric or adjacent faces from one another.

Industry standards for the inside diameter of airway-type buff wheels are 3, 5,7, and 9 in. As a rule, productivity and buff wheel life increase as outside diam-eter increases and thread count and material content increases. Larger buffsand higher shaft rotation speeds also increase productivity and buff life.

The choice of buff center size depends on how far the buff material can be wornbefore the surface speed reduces to a point of inefficiency, or flexibility declinesto a point where contours cannot be followed. Airway buff flexibility decreaseswith use as wear progresses closer to the steel center. Most airway buffs aredesigned with as much material at the inside diameter as the outside diameter.

FlangesBuffing wheels require flanges for safe operation. Flanges must be sized for thespecific inside diameter of each buffing wheel. It is important for all buffs thatthe flange be designed with sufficient strength to withstand the tremendous forcesand pressures exerted in buffing. If buffs are not well designed and fabricated, cen-trifugal forces at higher speeds and the shock from operations can cause failureof clinching teeth, breakage of rings, and breakdown of buff sections.

MUSLIN BUFFS

The most commonly used fabrics for buffs are cotton muslins. As previously not-

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ed, fabrics are designated by thread count (e.g., 60/60, 80/80, 86/80). These des-ignations refer to the threads per inch in the warp and fill, respectively. Fabricweights typically run from 2.5 to 3.5 yd/lb. (Table I).

OTHER BUFF MATERIALS

FlannelsDomet flannel (with nap on both sides) and Canton flannel (nap on one side andtwill on the other side) in various weights are used where other fabrics fail to pro-duce a high enough luster. Coloring of jewelry products is a typical applicationfor such buff materials.

SisalSisal is a natural hemp fiber used for fast-cut buffing of steel and stainless steel.It is a coarse fiber twisted into strand groups and frequently woven into a fabric.It has a much lower thread count than cotton muslin, sometimes five by sevenper inch, and offers the advantages of greater surface defect removal. Combinationsisal/cloth buffs are effective designs (Fig. 1). The sisal plies frequently are clothcovered to omit the tendency of the sisal to cut the cotton threads of adjacentcloth plies. Alternating cloth and sisal improves compound retention, reducesunravelling, and moderates cut. Kraft paper alternated with sisal also has appli-cations.

Other Natural MaterialsOccasionally, other materials are used to form buffs. For example, woven woolbuffs are used on plastics, soft metals, and sterling silver. Sheepskin buffs are usedto avoid surface drag or smear when buffing metals that contain lead. Russet(bark-tanned) sheepskin is used for cut. White alum (alum-tanned) sheepskin isused fo

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