cleaning, pretreatment & surface preparation

BUFFING WHEELS AND EQUIPMENT

BY 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 elementsand how they interact to achieve desired quality, productivity, cleanability,corrosion resistance, reject elimination, and overall cost-effectiveness.

WHAT IS BUFFING?

Buffing is a mechanical technique used to bring a workpiece to final finish. Italso can be used to prepare the surface of a machined, extruded, or die-cast partfor plating, 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 othermore severe surface defects should be removed before buffing by polishing witha polishing wheel or abrasive belt.Buffing usually involves one, two, or three steps: cut buffing, intermediatecut, and color buffing. These operations normally are performed by what isreferred to as either “area” buffing or “mush” buffing.

Cut Buffing

A harder buff wheel and, generally, a more abrasive buffing compound, are usedto start the buffing process. In cut buffing, the buff wheel and workpiece areusually rotated in opposite directions to remove polishing lines, forming marks,scratches, and other flaws.

Color Buffing

When a mirror finish is specified, a color buff step may be required. Colorbuffing may be performed with a softer buff wheel and less aggressive abrasivecompounds. In color buffing, the buff wheel and workpiece are usually rotatedin the same direction. This enhances the cut buff surface and brings out themaximum luster of the product.

Area Buffing

For localized finishing, narrow buffing wheels, positioned tangentially to theworkpiece, are used. This is often is referred to as “area buffing.”

Mush Buffing

To finish larger parts or parts having several surface elevations, mush buffingmay be used. This involves the use of one or more wide buff wheels. In mushbuffing, a part is rotated or cammed through the buffing wheel. This techniqueis also used to finish multiple products simultaneously.

BUFFING COMPOUNDS

Buffing compounds are the abrasive agents that remove minor surface defectsduring the buffing phase of the finishing cycle. Buffing compounds are availablein paste or solid form. There are thousands of products from which to choose.The prime consideration in selecting a buffing compound is the substrate beingbuffed and the surface to be provided.Nonferrous products made of copper, nickel, chromium, zinc, brass, aluminum,etc., frequently are buffed with compounds containing silica (generallyamorphous, often “tripoli”). “Tripoli” is found in a small area of Oklahoma andis shipped all over the world. Steel products are normally buffed with compoundsof fused aluminum oxide, which is available in DCF collector fines and as gradedaluminum 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 products highreflectivity. Iron oxides are used to color buff gold, silver, copper, and brass. Limebasedbuffing compounds are used to generate mirror finishes on nickel products.Skilled buffing engineers can help manufacturers select the optimum equipment,buffing compounds, wheels, and buffing techniques. Cleaners and cleaningprocesses 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,and final luster. More closely woven, heavier, and stiffer materials are used onharder metals for greater cut and surface defect removal. Stiffness is a result ofheavier 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 itharder or softer, usually by varying convolutions of the face of the wheel. Thisinfluences aggressiveness. Part configuration dictates buff design, construction,thread count, etc.

Conventional buffs employ a circular disk of cloth cut from sheeting andsewn into a number of plies. For example, some materials require from 18 to 20plies to make a -in.-thick section. Multiple sections are assembled on a spindleto build the required face width. The density of these types of buffs is alsocontrolled by spacers that separate the plies of fabric or adjacent faces fromone another.

Industry standards for the inside diameter of airway-type buff wheels are3, 5, 7, and 9 in. As a rule, productivity and buff wheel life increase as outsidediameter increases and thread count and material content increases. Largerbuffs and higher shaft rotation speeds also increase productivity and buff life.The choice of buff center size depends on how far the buff material can beworn before the surface speed reduces to a point of inefficiency, or flexibilitydeclines to a point where contours cannot be followed. Airway buff flexibilitydecreases with use as wear progresses closer to the steel center. Most airway buffsare designed with as much material at the inside diameter as the outside diameter.

Flanges

Buffing wheels require flanges for safe operation. Flanges must be sized for thespecific inside diameter of each buffing wheel. It is important for all buffs that theflange be designed with sufficient strength to withstand the tremendous forcesand pressures exerted in buffing. If buffs are not well designed and fabricated,centrifugal forces at higher speeds and the shock from operations can cause failureof clinching teeth, breakage of rings, and breakdown of buff sections. MUSLIN BUFFSThe most commonly used fabrics for buffs are cotton muslins. As previouslynoted, fabrics are designated by thread count (e.g., 60/60, 80/80, 86/80). Thesedesignations 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

Flannels

Domet flannel (with nap on both sides) and Canton flannel (nap on one sideand twill on the other side) in various weights are used where other fabrics fail toproduce 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. Itis a coarse fiber twisted into strand groups and frequently woven into a fabric. Ithas a much lower thread count than cotton muslin, sometimes five by seven perinch, and offers the advantages of greater surface defect removal. Combination

sisal/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 adjacent clothplies. Alternating cloth and sisal improves compound retention, reduces unravelling,and moderates cut. Kraft paper alternated with sisal also has applications.

Other Natural Materials

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

Pieced Buffs

Pieced buffs are less expensive because they are made of lower-cost materials.The buffs are made of colored segments, unbleached segments and occasionallybleached material.

Combination Buffs

Often different materials are combined, especially sisal with cloth, and occasionallypaper as well as cloths of different specifications.

Synthetic Fibers

Unwoven nylon and other synthetics fibers, because of their water resistance, may be used wet or dry or with wax or grease lubricants. Buffs made of syntheticsare usually operated at slow speeds, typically 2,500 sfpm, to prevent meltingand streaking surfaces.

BUFF TREATMENTS

Treatments may be applied to fabrics (mill treatment) or to the buff after assembly(dip treatment). Buff fabrics are frequently hardened and stiffened to promotefaster cutting, softened for additional flexibility to conform to contours,strengthened for longer buff life, or lubricated to prevent burning. Buff fabricsmay also be treated to provide improved adhesion of buffing compound, toabrade for heavier cut, or to flameproof and make fire resistant. Treatmentsmust be applied evenly and uniformly to avoid creating hard spots that causeuneven buffing. The treatment must not deteriorate with buff age. Unsuccessfultreatments weaken the cloth and decrease buff life.

CONVENTIONAL, FULL-DISK BUFF DESIGNS

Unsewn Buffs

Conventional, full-disk buffs are made with die-cut cloth disks. Unsewn, conven-tional full-disk buffs may be used forluster (Fig. 2). Loose disks are turnedto allow the threads of the material tolie in different directions. This resultsin more even wear, avoiding a squareshape after being put into use. Onedisadvantage of this conventionaldesign is that the fabric can fray orravel. When held against a wheel rake,a cloud of threads may fly off. Thisshortens buff life, increases compoundconsumption, and adverselyaffects finish. Also available are solidbias sisal buffs, with every other layerbeing cloth, and rebuilt buffs madefrom reclaimed material.

CONVENTIONAL SEWN BUFFS

Conventional, full-disk buffs for heavier buffing (cut) are sewn in various ways(Fig. 3). Closer sewing is specified for cutting harder metals and for removingdeep imperfections.Concentric sewing causes a buff section to become harder as it wears closerto the sewing and softer after wear causes the sewing to break through. Spiralsewing results in more uniform density. Square sewing produces pockets thathelp the buff wheel to retain more buffing compound. Radial sewing, sometimescalled sunray sewing, and radial arc sewing provide other variations. Tangent,parallel, ripple, zigzag, cantilever, and petal sewing are used for similar reasons.Special sewing, other than spiral, which is done on automatic machines, involves

Folded or Pleated Buffs

Folded buffs consist of circles of cloth folded twice to form a quarter circle,resulting in a “regular-pocket” buff (18 ply), or, for more cut, three times, toform eighths of a circle to constitute a denser “superpocket” (34 ply). The segmentsare laid down to form a circle, with eachsegment overlapping the previoussegment. They are sewn around the arbor hole and partway to the periphery.The folds form pockets that hold compound and flex sufficiently for contourfollowingcapacity. Folded buffs share three design deficiencies: lack of centerventilation, a tendency to fray, and waste of material in the unused center.

Pleated Buff

Airway buff cloth may be accordion pleated to present more angles of materialto the surface of the product to be finished. Pleating results in more cloth anglesto reduce streaking and improve coloring characteristics. Better cutting is alsoachieved in some applications.

Packed Buffs

Buffs may be packed with spacers consisting of cloth or paper inserted betweenthe larger diameter plies. The same spacer principle is used between buff sections.Both measures result in a softer wheel face. The packed buff constructionis effective in contour buffing applications.A version of the packed buff, for threaded, tapered spindles (2-12-in. diameter),is used in the jewelry industry. The center is hardened, usually with shellac.The sides of the buff may be reinforced by leather disks.

Pieced Buffs

Pieced buffs may be used in place of sewn full-disk buffs. They are made fromremnants of cloth left over in the manufacture of other textile products. Suchbuffs require one of the types of sewing used for full disks in order to staytogether in use. The chief virtue of pieced buffs is their higher value owing tothe lower cost of materials. They usually are sold by the pound (see Table II).

BIAS-TYPE BUFF WHEELS

Bias buffs are more frequently used than conventional forms. They combineflexibility and cutting power. Bias buffs are cool running and resist burning.They are naturally ventilated. Side openings in flanges, center plates, and tabs,resulting in spacing between sections, enhance their cool-running characteristics.By using material cut on the bias, the threads form an “X” at the peripheryof the buff. Threads are held at a 45o angle by cross-threads. This minimizesfraying and raveling (Fig. 4).Strips of bias-cut fabric are sewn into continuous rolls. After the rolls arecut to proper length, they are wrapped around a hub or core. They are thenpulled to the desired inside diameter within the channel, usually by means ofsteel blades in an “Iris” machine. Straight-wound material wrapped aroundan oversized wheel results in a convoluted or “puckered” face; thus, the term“puckered” buff.The “puckered” face design of bias buffs tends to break up lines left in thesurface of a product from previous operations. Increasing the size of the drumsvaries the amount of pucker in the face. The bias buff can be adapted to various

contoured parts and degrees of cutting and coloring. An advantage of the “Iris”-made buff is the elimination of material beyond the inside diameter to the arborhole. Thus, more of the cloth is available for use. VENTILATED BIAS BUFFSAlthough the puckered characteristic of bias buffs results in cooler running,some operating conditions require additional cooling. Steel centers with holesand ridges are designed to collect and divert more air. The air cools the buffand the workpiece surface. Clinch rings permit use of reusable metal inserts for

substantial savings (Fig. 5).

PUCKERED BUFFS

Puckered buffs are rated by numbers. Higher numbers indicate greater clothcontent, buff density, and face convolutions (Fig. 6). Higher densities and closerconvolutions increase cutting and reduce streaking.

Open-Face Cloth Buffs

The open-face buff prevents loading, packing, clogging, and ridging duringfinishing operations. The plies are configured differently from the closedfacedesign. Buff material is wound singly or in groups of two, three, four, ormore plies. Open-face buffs may be “straight wound” or “spiral wound” for acorkscrew or cross-cutting action that further minimizes streaking. Buff densityvaries with the number of plies, the amount of cloth, thread count, fabricweight, and treatment of the cloth. Buff pressure, speed, angle to the part, clothstrength, compound absorption ability, ventilation, and cloth flexibility arevaried with buff design.Table II. Approximate Weight Table for Spiral Sewed Pieced Buffs

BIAS SISAL BUFFS

“Iris” equipment used to gather cloth buffs is adapted to sisal and other materials(Figs. 7-10). Some bias sisal buffs are tapered (wider at the outside thanthe inside diameter). This reduces gaps between hard sections that could causestreaking. The tapered bias sisal buff is a long-life, cool-running buff for steeland stainless steel. Hard bias sisal buffs also are used in place of some beltingoperations, as well as in deburring and brushing.

Open-Cloth Bias Sisal Buff

The open cloth bias sisal (OCBS) buff is used on contoured steel and stainlesssteel parts (Fig. 9). It consists of woven sisal and cloth, four plies of each(eight plies total), bound together by concentric sewing before Iris gathering.The buff is manufactured in endless strips, cut to length, rolled aroundsplit drums, and gathered into clinchrings by the “Iris” machine. A variationof the open-cloth bias sisal buff is theopen double-cloth bias sisal (ODCBS)buff. This design consists of two layersof cloth sewn together with one layer ofsisal to make a 12-ply buff of eight pliesof cloth and four plies of sisal.

Spoke Unit, or Finger Buff

Spoke unit or finger-type buffs combinegreat cutting power with the capacityto flex and accommodate contours andallow better workpiece coverage with

Fig. 4. Bias buff (left) versus conventional buff (right). Thread configurations of bias buffs alternate

warp and filler threads. Biasing provides design efficiency by exposing all thread ends to the surface

being buffed, reducing fraying of the fabric.

Fig. 5. Steel clinch ring (left) and steel clinch ring buff

with open center (right). Buffs that are constructed

by the clinch ring or “Iris” machine method have

superior ventilation and cloth biasing, and optimal

material utilization.

fewer buffing heads. Spokeunit or finger-type buffs are made from materialsthat include soft cloth, stiff cloth, sisal,and coated abrasives. The material ismanufactured into units, or fingers,sewn into endless belts, cut to length,wrapped around split drums, and gathered

by an “Iris” machine into steelteeth. The spoke unit or finger sisalbuff is usually made with woven sisalinterlaced with 86/80 cloth. Acid or

rope sisal is sometimes used. The clothmay be mill or dip treated (Fig. 10).The spoke or unit bias buff runs

cooler than standard bias buffs andhas a knee-action flexibility that givessuperior contour-following ability. The width and number of the individual unitsis varied within limits. The range of buff density, or hardness, is varied by choiceof materials, treatments, (buff center size) plies, and type of radial stitching. Somecomplex products are best finished with this type of buff.

FLAP BUFFS

The flap buff (Fig. 11) utilizes separate flap units placed at right angles to thedirection of rotation of the wheel. Each flap supports the other to produce asmooth running wheel. Flap wheels were originally designed for bumper polishingand buffing operations. Flaps are made of coated abrasives, sisal, cloth andcombinations thereof.

POLISHING WHEELS

Polishing wheels are usually made of conventional cloth buff sections glued orcemented together. Canvas disks are cemented to the sides to protect the sewing.Glue or cement is applied to the face. Faces are struck with a pipe at anglesand cross-angles to form a uniform crisscross of cracks on the polishing surfaceand provide sufficient resiliency to allow the wheel to make better contact witha workpiece.Buff sections used to make polishing wheels are generally spiral sewn andmade of various types of cloth, sisal, canvas, or sheepskin. Solid, one-piece woolfelt, and bull neck and walrus hide are occasionally used.Conventional straight buff sections that are glued together may cause streakingduring polishing. An alternative involves inserting pie-shaped segments or

other spacers between the buff sections to result in a “nonridge” polishing wheelthat eliminates streaking. Various abrasive and adhesive combinations are usedto grind, polish, and satin finish. These include liquid, graded aluminum oxideabrasives, greaseless compounds and burring bar compositions.

BUFFING EQUIPMENT

Significant improvements have been made in buff wheels and buffing compoundsto provide consistent and predictable performance. This has helpedmanufacturers of automated buffing machines to develop automated equipmentfor low- as well as high-volume requirements and to minimize labor andoverhead in the finishing operation.

Fig. 6. Cloth bias buffs in order of increased

density from closed face (left to right: 0, 2, 4, 6)

to open face (far right) design.

MACHINE DESIGN

Mechanical buffing systems have a motor-driven shaft to which the buff wheelis applied. In addition, most machines will have a positioning mechanism, afinishing lathe, and workpiece-specific fixtures.

POSITIONING MECHANISM

Automated buffing machines orient parts against the media by mechanicalmethods to duplicate or replace human motions. They rotate, oscillate, tilt, andindex the wheel and/or the workpiece.

Fig. 7. Conventional sisal buff. Fig. 8. Bias sisal buff.

Fig. 9. Open cloth sisal buff. Fig. 10. Spoke unit or finger sisal buff.

Finishing LatheThe finishing lathe is a device located inrelation to the positioning mechanism.It allows a buff wheel to contact one ofmore surfaces of the workpiece at predeterminedlocations.

Fixturing

The workpiece fixture or tooling is used toposition a part during the buffing cycle.Buffing machines can incorporate singleor multiple fixtures. Fixtures can also bedesigned to automatically reorient a workpieceduring the buffing cycle. Buffingfixtures are unique to each part being processed,although some may be adapted to anassortment of similarly shaped parts. Thedesign of fixtures is extremely important.

Unless a part can be fixtured properly at areasonable cost, the economical utilizationof finishing equipment cannot be justified.

TYPES OF BUFFING MACHINES

Buffing machines fall within three broadcategories: manual, semiautomatic, andfully automated.

Manual Machines

Manual buffing machines are used in low-volume applications and applicationsinvolving the buffing of extremely complex workpieces. Manual machines, whenused in conjunction with the proper buff wheel and buffing compound, can bemanipulated.

Semiautomatic Machines

Semiautomatic buffing machines are used in lower volume applications where asingle finishing operation is performed on a variety of parts. Initial investmentand fixturing and operating costs are low.Semiautomatic finishing machines can be used with a single- or double-endlathe. One operator can be employed to load, unload, and operate equipment.Semiautomatic machines hold the workpiece and present it to the buff wheel. Atimed cycle controls dwell and retraction. Only one fixture is required for eachmachine for each type of part finished. Because the machine supports the part,operator fatigue is minimized. Various types of rotation also can be performed,depending on the type of semiautomatic machine selected.Production of semiautomatic buffing machines depends on part configurationand the degree of finishingrequired. By using a double-end jack with two semiautomatics,an operator can load one machine while the other is finishing a part.This can double production without increasing labor costs.

Fully Automatic Machines

Fully automatic machines are used in high-volume applications and where multiplesurfaces of a workpiece must be finished. The two most common types ofautomatic buffing machines are rotary automatic and straight-line machines.

Rotary Automatic Machines

Rotary machines have round tables with finishing heads located around theperiphery of the table. This type of machine is typically used to finish simple,round parts requiring high production. The number of finishing heads andproduction determine the size of the rotary.The table of the rotary machine can move continuously or index to start, stop,dwell, and then start again, with the length of the dwell controlled by a timer.The configuration and area of the product to be finished determine which isbest. Production is higher on a continuous rotary machine because the tabledoes not stop rotating. On an indexing rotary machine, because of the stop,dwell, and start cycle, production is lower. Parts that have surfaces that are difficultto reach and require more dwell time in certain areas may be finished on anindexing rotary machine to obtain the dwell time necessary. On each table thereare rotating spindles on which the parts are fixtured for the finishing sequence.Rotary tables may have a greater number of fixtures than indexing tables, sincethe production and simple configuration make it more appropriate to be runon a continuous machine due to the ease of reaching all surfaces.

Straight Line Machines

There are various types of straight-line automatic finishing machines. Normally,linear workpieces are finished on straight-line machines. Straight-line machinesalso can be used to finish round parts if extremely high production is required.There is less limitation on workpiece size as with rotary equipment.With straight-line automatic machines, finishing heads can be placed on bothsides of the machine. In addition, various heads can be incorporated into thesystem for buffing and polishing. With rotary equipment, the outside peripheryof a rotary table is used.Various types of straight line machines include:Horizontal return straight lineNarrow universal straight lineOver and under universal straight lineReciprocating straight lineOpen-center universalThe size or length of these straight-line machines can be designed and built

to accommodate the desired end result; floor space is the only major limitation.Each machine normally requires only one operator for load/unload. All operationsof these machines are controlled from a push-button panel located nearthe operator for starting, stopping, and controlling various functions.

COMPUTER NUMERICAL CONTROL BUFFING MACHINES

Buffing machine manufacturers can build equipment offering the same levelsof control and flexibility available from computer numerical control (CNC)metal-cutting machines. Separate CNC workcells can be designed to combinebuffing with deburring operations within a given and limited series of processsteps. It also is possible to integrate a complete sequence of manufacturingoperations through a universal, plant-wide parts handling system to combinefabricating, machining, deburring, polishing, buffing, painting, plating, andpackaging. Such systems have a significant impact on material handling costs,daily in-process inventory levels, direct labor costs, plant floor spacerequirements,safety, and overall productivity.CNC buffing systems offer a number of significant advantages. Equipmentis programmed on the shop floor for reduced setup time. Buffing cycles can bereprogrammed to accommodate changing production requirements. Productiondata are automatically collected to support statistical process control requirements.Most important, quality is improved because part-to-part tolerances areconsistent and repeatable.

WORKPIECE HANDLING

Significant advancements have been made in materials handling technologyas it relates to buffing. A broad range of application-specific options is offered.These include pick-and-place workpiece load/unload systems, “blue steel” rollerconveyor systems, lift-and-carry and shuttle-type in-line part transfer systems,trunnion-type transfer tables, power-and-free conveyor systems, robotic worktables,and automated guided vehicles for transferring parts between machines.

SUPPORTING TECHNOLOGY

Buffing systems are increasingly becoming turnkey, integrated installations. Inaddition to the basic machine, equipment builders can offer a variety of supportingsystems to ensure increased performance and improved quality.Electronic options, beyond programmable controllers and computer numericalcontrol systems, include the use of load torque controls, sensors, proximityswitches, encoders, digital read-out devices, laser gauging, and LED programmablecounters. Other supporting systems include quick-change and modularwheel assemblies, automatic tool compensation, automatic buffing compoundapplication systems, dust collection systems, and automatic workpiece shuttleand load/unload systems.

SUMMARYEffective buffing is accomplished through the proper selection of buffing compound,the buff wheel, and the buffing machine. In most instances, it is recommendedthat prototype or test parts be processed under production conditions to establish process parameters and prove production rates and quality.