Powder Coating And Polishing Basics

Add color and shine to your ride. From the December 1997 issue of Motorcycle Cruiser.

For as long as humans have been working with metal, we have been polishing it for the simple pleasure that the sheen brings to the viewer. Naturally, we want our motorcycles to be shiny too. When compared with mankind's longstanding relationship with polished metals, powder coating is a relative newcomer--but one that's steadily gaining popularity in both the manufacturing and customizing aspects of motorcycling. While one process is old-fashioned and brutish, requiring hard physical labor, and the other is high-tech, employing electricity, heat, and epoxies, both can be used individually to create stunning finishes on motorcycles. Combining the two produces a synergistic relationship that can become the crowning touch of a custom project.

Powder Coating

Powder coating is a dry finishing process in which a powder, consisting of finely ground particles of pigment and resin, is given an electrostatic charge and sprayed on the part to be coated. The charge holds the powder to the part until the curing oven melts and fuses the powder to a uniform coating. Since the powdered paint doesn't contain the volatile organic compounds (VOCs) found in most liquid paints, powder coating is an environmentally friendly process that provides a durable finish. Scott Andrews, owner of Andrews Powder Coating, Inc., understands what customizers want from a powdercoater. When we approached him for this project, he suggested we combine polishing and powder coating, and even recommended that we have all the venting holes in the discs powder coated, a process which requires that the whole disc be masked and each hole uncovered to accept the powder.

When parts arrive at Andrews Powder Coating, the process starts with surface preparation. Andrews sandblasts parts with aluminum oxide to make sure any previous coatings are completely removed. Aluminum oxide etches the surface of the metal, providing "traction" for the powder to mechanically bond while making the powder coat more durable. If the parts were previously powder coated, he will have them chemically stripped before the sandblasting to be doubly sure that the surface is ready for the powder coat. Next, the parts get prebaked at 400 degrees for about 20 minutes. Andrews feels that the prebaking of parts is one of the characteristics of a top-notch powder coater. The prebake temperature is approximately 20 degrees hotter than the actual powder-coat baking temperatures so it bakes out any impurities that may be lurking within the metal's pores (a process called "outgassing"). If these impurities are not cooked out, they could bubble up under the finished powder coat, making it possible for a small chip to cause whole sections of the coating to fall off.

After the initial surface preparation, Andrews sends the parts for polishing to Derek Stankovich at Distinctive Metal Polishing. Upon their return from Distinctive, the parts receive a solvent bath and another prebake. Then the polished portions of the part, and any other sections that should not be powder coated (such as the piston holes in the calipers), are carefully masked with high-temperature-resistant tape. The masked parts make their way to the paint booth where they are hung on electrically grounded racks. The powder is given a 30,000- to 90,000-volt charge and is sprayed onto the part, where it adheres to material much as dust clings to a TV screen. One advantage of powder coating over painting is that if the person applying the powder is not happy with the thickness or look of the powder, he can brush or blow it off with compressed air and reapply. Also, areas of the part that are too time-consuming to mask may simply be wiped off with a finger. However, unlike liquid paints, powder-coated candy colors, such as the candy blue used on our Valkyrie's wheels and calipers, require multiple coats of powder. Candy colors require that a layer of silver be baked on before a translucent color is applied over the silver, making candy colors cost more than plain colors. Andrews says high-end powder coaters will always wait for the parts to cool down to the ambient temperature before the second color's application. Spraying the powder on hot parts results in uneven coverage and an inferior finish.

The oven is where the action takes place, and Andrews' oven is a sight to behold. Large enough to hold an entire car frame, the 24-foot-deep oven once baked an 8-foot round, 14-foot tall bird cage. Since the metal of the part must become hot enough to melt the powder for optimum adhesion, the time parts spend in the oven is determined by their size and weight. Calipers will bake for 20 minutes at 380 degrees during the application of the base color, while wheels need to roast for a full 45 minutes. Curing the final coat takes longer (40 minutes for a caliper and almost an hour for a wheel) to assure that the powders have fully melted and bonded to the surface of the part. Once the parts have cooled, the masking tape can be removed from the finished part.

Polishing

Heat plays an important but different role in polishing. Instead of using heat to bond a substance to the metal, the heat of friction in polishing--reaching temperatures as high as 400 degrees--causes the surface of the metal to fuse together, closing its pores. Polishing is, in its most basic sense, the progressive elimination of scratches through the use of finer and finer abrasives. The sheen comes from making the scratches in the metal so fine that they are invisible to the naked eye. In the final stages of polishing, rouges (compounds of grits, lubricants, and metals that help to bring out the metal's natural color highlights), not sandpapers, provide the ultra-fine abrasives. Although brute force plays the primary role in polishing, a polisher's finesse with the detail work demarcates the class polishers from the masses.

When a part arrives at Distinctive Metal Polishing, Stankovich sands the part to remove the large imperfections (including brand names, part numbers, and casting seams) from the surface. Large faces of the part get the treatment from a belt sander shod with 220-grit sandpaper. Smaller sections of the part require a sanding wheel, a hand-held belt sander, or a Dremel, depending on the intricacy required. Detail work is time-consuming, but Stankovich says the use of hand-held tools separates a show-quality polishing job from an average one. He estimates that about 80 percent of the time he spends on polishing motorcycle parts is consumed by the Dremel. For example, nine-spoke cast Harley wheels and eleven-spoke A.C.E. Tourer wheels require around 40 hours of labor, simply because of the tight spaces in the spokes. After the 220-grit sanding, a 400-grit sanding takes out sanding scratches, continuing the process of eliminating scratches.

Once the surface has been sanded, the sisal wheel, covered with a nylon and denim-like material, begins the actual polishing. Brown or black rouge, equivalent to 1200- to 1400-grit, begins to bring out the metal's luster. The final step in polishing is running the metal under a cotton wheel with green rouge, which, at 2000-grit, is a true polishing rouge. The previous rouges just took out scratches. The chromium in the green rouge bonds with the metal, giving the polished metal its characteristic sheen. Since chromium is transparent, the individual character of the metal seems to shine from within the part itself.

Back on the Bike

Both Andrews and Stankovich stressed the need for care when reassembling the polished and powder-coated parts. Parts that will hold fluid should be thoroughly flushed (water or alcohol will work fine) and dried before reassembly, and all seals should be checked to make sure no powder coating ended up on the mating surfaces.

Representatives of American Honda, who were nice enough to let us use their Valkyrie in this project, asked us to state that calipers and other brake components were not designed to be powder coated or polished and that the stresses of these processes may impair the ability of the parts to function up to the manufacturer's specifications. While neither Stankovich, Andrews, nor anyone at Motorcycle Cruiser has heard of problems associated with powder coating or polishing, extra care should be taken during the assembly and a test of full functionality should be conducted after modifying anything on a motorcycle as important as the brakes. We routinely check the calipers during our cleaning and maintenance regimen.

Since a polished part's pores are only closed, not sealed, and since oil, dirt, and water will age polished metal, Stankovich recommends a regular cleaning schedule to keep the metal shiny, but he warns against using metal polish to clean newly polished parts. Instead, he recommends using corn starch to clean oily finger prints off the metal. Weekly wipe-downs will keep light dirt away, and occasional soap and water washes followed by carnauba wax will protect the metal. Stankovich says a major cleaning every six months with a quality metal polish followed by carnauba wax will keep the polish looking fresh. However, he warns not to use wheel cleaners or gritty polishes, which may dull the finish.

Powder coating also needs some special care. Avoid contact with battery acids, acetone-based solvents, carburetor cleaners, contact cleaners, and brake fluid, all of which will partially dissolve the surface of the coating, diminishing its shine and durability. Andrews recommends washing with soap and water and protecting the powder coat with wax. Parts that are powder coated and not polished can be cleaned with a wheel cleaner that is listed as safe for clear-coated wheels. Any brake fluid that drips onto coated parts can be removed easily with alcohol. Also, never clean the parts while they are hot.

Powder coating and polishing the Valkyrie's wheels, calipers, caliper brackets, and discs gives the bike a unique look without replacing the parts. When compared with the cost of aftermarket replacements of these parts, the $500 (all parts combined) powder coat, including the candy and the $305 for [polishing, are cost-effective investments that pay dividends every time someone comments on how great the bike looks.

The author, who used to be Associate Editor of Motorcycle Cruiser, is now freelancing and invites you to visit his website: www.EvansBrasfield.com.

RESOURCES

Andrews Powder Coating, Inc.
9410 Desoto Ave., Unit E
Chatsworth, CA 91311
(818) 700-1030
www.powdercoater.com

Distinctive Metal Polishing
18328 Gault St.
Reseda, CA 91335
(818) 344-2160
www.dmpolish.com

Powder Coating Institute
2121 Eisenhower Ave. Suite 401
Alexandria, VA 22314
www.powdercoating.org

For more articles on how to maintain and modify your motorcycle, see the Tech section of MotorcycleCruiser.com.

For more articles on custom bikes and articles about how to customize and modify your motorcycle, see the Custom Section of MotorcycleCruiser.com.

The detail work done to these parts can't be fully appreciated in photos. For example, the inside edges of every hole and cut-out in the disc have been powder-coated candy blue. Photography by Dean Groover (www.DeanGroover.com)
Sandblasting the component both removes any of its existing surface coatings and roughens the underlying metal to improve the powder coating's adhesion to it.
Before our Valkyrie's parts are powder coated or polished, Scott Andrews prebakes them at 400 degrees in his huge oven to cook out any impurities trapped in the pores of the metal.
High-temp tape covers polished areas.
The gun gives the powder a negative charge to make it stick to the part.
After our Valkyrie's calipers made their final trip through the baking oven and cooled, Andrews removed the the tape from the polished areas, giving us the first look at the finished parts.
The four stages of polishing. The top section is the original etched part . The left side has just gotten the first sanding. The black part on the right has been sisal polished, and the bottom lug shows the final polish.
Polishing starts with sanding off seams, lettering, etc.
A sign of a quality polisher: Stankovich hand assembles the smaller sanding wheels from larger pieces of sandpaper, thus making it possible for him to sand more intricate parts.
Derek Stankovich uses a hand-held belt sander to remove the Valkyrie caliper bracket's identification markings. His efforts with hand tools make Stankovich's work stand out.
Stankovich spends 80 percent of his time with the Dremel, making sure the nooks and crannies shine as brightly as the big flat surfaces.
Stankovich applies the fine green rouge to the cotton wheel. This final polish creates the shine, revealing the beauty of the metal.
Now shinier and more colorful, our parts are ready to install.