February 13, 2014

Coatings: Cure-Alls or Just Options?

Coatings that once were only associated with frying pans are successfully finding their way into the gun world—in a variety of colors.

 

Technically, browning and blueing are metal finishes, not coatings. They are both controlled oxidation processes employed to color the metal itself. Browning has been around longer than blueing, since about 1780, but blueing is the more popular finish. The bead-blasted or “satin” stainless-steel finishes have also gained popularity in recent years.

A stainless-steel finish won’t rust, but it will scratch. Depending on the depth of the damage, minor scratches can be rubbed out. American Gunsmith used a metal golf-club refinishing kit on a slightly scratched Smith & Wesson 4006 and got excellent results. We understand a similar kit expressly for guns is now available, though at a slightly higher cost.

Electroless Nickel Plating

Courtesy, American Gunsmith

Electroless nickel plating works basically like this, although the processes mentioned above are a bit more detailed and some are proprietary.

Parkerizing is a manganese-iron process that is highly wear-resistant, and results in a dark gray or black, textured finish. A Parkerized finish will rust and scratch, but not as easily as a blued or browned finish. Minor scratches are more difficult to repair on Parkerized finishes because of the color matching required.

Teflon Coatings

Aside from “satin” stainless-steel finishes, all finishes will rust if not properly maintained. Coatings, however, won’t rust. The most highly rust- and corrosion-resistant coatings known contain Teflon, invented by DuPont.

We were unable to learn how Teflon coatings are applied, because the Teflon coaters we spoke to insisted it was “a proprietary process.” We checked with DuPont on the subject, and they sent us a sizable package of information from the company’s Industrial Finishes Group, which leads us to believe there’s nothing proprietary about it at all.

According to DuPont: “Applying a Teflon coating is a relatively easy process using normal coating equipment and techniques. Where special application techniques are necessary, the specific product Fact Sheet will indicate what deviations from normal procedures are necessary.” The Fact Sheets are available to anyone upon request from DuPont.

There are several kinds of Teflon, but the two that appear to be used in gun work are Teflon-P and Teflon-S. Both produce a baked-on, self-lubricating coating that can be applied to carbon steel, stainless steel, aluminum, or any other metal able to withstand the curing temperature.

Teflon-P is a powder that must be mixed with a binder. It requires the substrate to be sand- or bead-blasted to provide good adhesion for the primer. Teflon-S is a liquid that requires no blasting, but it adheres better if the substrate is bead-blasted. Teflon-S requires no primer. Since Teflon-S and its many variations are the types most widely used in coating guns, we studied the DuPont technical data on application procedures.

A gun being prepped for Teflon coating has to be every bit as clean and grease-free as a gun being prepped for blueing. To assure all surface contamination is removed, baking the piece at or slightly above the curing temperature is recommended.

In most cases, compressed air and standard spray equipment are the most suitable for applying Teflon-S. The spray gun should be held perpendicular to the piece using a flat, rectangular action, since “whipping” the spray gun in an arc tends to produce bubbles in the wet film, and will cause excessive beading on the edges of the part being coated. Normal distance for the spray gun is 4 to 12 inches. Any closer than that will make the finished product look rippled; any farther away will cause the spray to be dry and rough. Alternatives to spraying are dip-and-flow techniques, as well as rolling on the coating. Brush application is restricted to small repairs.

After the application of the wet Teflon, curing is required, which is done in an oven at temperatures up to 900 degrees. The temperature referred to is the temperature of the metal itself, which must be maintained long enough to set the film of Teflon. This helps to explain why a gun being coated must be completely disassembled. (Springs can’t be placed in a curing oven because they might lose their set.) Specific curing times, available from DuPont, depend on the type of metal and the type of Teflon-S. We have been told that using the wrong curing time can result in discoloration, film embrittlement, and loss of adhesion.

Teflon goes on so thinly that any milling or machine marks can be seen in the substrate metal. Once cured, however, battery acid, muriatic acid, or handling by people with “acid hands” don’t faze it. Nevertheless, Teflon is not a hard finish, and it will scratch. One method of repairing scratches is to feather the area, carefully apply Teflon with an air brush to cover it, then rebake. If the gun has been coated with Teflon-S, you can’t use Teflon-P to touch up any dings—the two don’t mix.

Teflon-S is available in black, blue, and clear. The clear can be colorized before application to produce just about any color of coating—including pink (if you’re so inclined). Teflon can be applied to fiberglass, wood, and telescopic sights, then air dried. It cannot be applied to the interior of a barrel because the coating, thin as it is, could create pressure problems. Another problem we heard of involves the difficulties one refinisher had with blueing a gun once it had been Teflon coated. It seems the coating had to be removed to the depth it had penetrated the substrate metal, which was too deep for safety’s sake in the refinisher’s opinion. As a result, he no longer accepts orders to blue guns that have previously been Teflon coated.

On the other hand, one Teflon coater says all he does is bead blast the coating off, clean and reblue the gun. “What you end up with looks like a bead-blasted, matte-blue finish,” he says.

Most of the firms involved in Teflon coating were reluctant to quote us prices, preferring to set their fees after seeing the job. However, we have seen law-enforcement and dealer prices for handgun coating starting at $60, while rifles started at $80. Coatings of shotguns and other types of firearms generally run between $70 and $85. Delivery times vary as much as the prices do.

We next talked to Gene Heller, an experienced gunsmith and gun coater who runs his own operation, The Armorer, in Smyrna, New York, about other chemical-based coatings.

Moly-Coats

Heller says, “The toughest one I offer contains molybdenum disulfide. It’s not as slippery as Teflon, but it’s self-lubricating and very durable. It comes in a myriad of colors from flat and gloss black, to greens, browns, tans, red, white, and blue. It’s a thermo-setting coating, less porous than Teflon, and goes on everything from aluminum to pot metal. Many U.S. and European police departments use it. I use it in my camo work and as part of a clear-coat, stainless-steel powder finish,” Heller said.

Moly-coats, we discovered, can be used on springs, since curing temperatures range from 275 to 400 degrees. Some are even air dried, like paint, instead of being baked on. Surfaces to be moly-coated should be blasted first. Heller uses 80-grit alox at 75 to 80 psi to enhance adhesion. The blasting also serves to reduce reflective qualities. If high gloss is what the customer wants, however, there are molys that can be spray-applied that are very shiny.

In responding to our “how tough is it?” query, Heller related an experiment conducted by a car fanatic who used a Sandstrom Corporation moly coating on a 289-cubic-inch Ford V-8. The guy tore the whole engine down, sandblasted it, and sprayed everything in sight with the Sandstrom coating. He then reassembled the engine, reinstalled it in the car, and ran it for weeks—with no oil and no damage to the “molyized” V-8.

Chrome and Nickel Plating

Far beyond chemical coatings in surface hardness are nickel- and chrome-plated finishes. Of the two, Bob Cogan of Accurate Plating and Weaponry favors chrome.

“The bonding of the chrome to the steel,” Cogan says, “is better than with nickel. I’ve seen the bond between nickel and steel in a magnum handgun blow away. Chrome adheres like it’s been welded on, and it doesn’t plate the bores or inside cylinders. Chrome is also harder.”

“Nickel has a Rockwell in the high 30s. Chrome is Rockwell 65 to 70. The gunmetal would give before the chrome, whether the finish is black or bright,” he added.

Cogan’s prices include disassembly and assembly. Hard chrome or nickel plating costs $120 for pistols and revolvers, $152 for rifles and basic shotguns, and $185 to $205 for double-barrel or over/under shotguns. Black chrome costs $160 for handguns, $215 for rifles and basic shotguns, and $260 to $280 for double-barrel and over/under shotguns. Depending on the finish desired, delivery times run four to eight weeks.

Jim Kelly of Metaloy Industries agrees with Cogan. His firm uses a proprietary process called “Metaloy,” which was developed during World War II for electrodepositing extremely hard chromium. Metaloy, he says, “produces a superior degree of adherence and uniformity not attainable in conventional chromium plating.”

Technical information sheets that American Gunsmith received say Metaloy’s composition aids in lubricant dispersion, and reduces or eliminates galling, seizing, and high friction. It will not cause a buildup in excess of .0002, has a hardness in excess of 70 Rockwell C, a coefficient of friction less than half that of steel against steel, and withstands temperatures up to 2,300 degrees Fahrenheit.

Kelly offers three “Metaloy Chrome” finishes. His standard, after removal of any blue or rust, is smooth satin. His light starburst, achieved by glass-bead blasting all parts, provides a smooth, satin-silver finish. The firm’s heavy starburst finish is accomplished with larger glass beads and produces a matte-silver surface. The heavy starburst finish isn’t recommended for revolvers, Kelly says, because it makes them harder to clean. He does, however, suggest this finish for guns that are in poor to bad shape. Alloy guns cannot be plated, although Kelly’s firm will plate the steel parts, and bead-blast the alloy portions to make them match.

Nickel, the other hard coating we looked into, can be applied either with electricity or electrolessly. Electroless nickel plating has some advantages over regular nickel plating; namely, electroless nickel deposits form a uniform thickness over the surface that is being plated. It is also whiter than regular nickel. A gun plated with electroless nickel looks much like it was made from satined stainless steel.

Suggested prices on the Metaloy coating run $100 for handguns; $135 for bolt-action rifles; $150 for pump, levers, or automatics; $115 for break-open shotguns or rifles; and $120 for double-barrel shotguns. Delivery times range from two to six weeks.

Ed House, a former gunsmith who now devotes his full time to a unique electroless nickel process he calls Nitex, has been putting his coating on guns for more than 12 years. Applied via a proprietary combination of heat and chemical treatments, the coating has been tested to show no rust after 96 hours or more of continuous salt-spray contact. If a rupture in the coating does occur, which can happen through age or abuse, rust has shown no indication of migrating under the Nitex coating, as it does under a regular nickel-plated surface.

Another fault of nickel that House’s coating is said to overcome is separation from the substrate. Adhesion of Nitex to base metal ranges from 30,000 to 60,000 psi, exceeding the base metal’s own adhesive force. Microhardness of the coating is equivalent to Rockwell 49C, regardless of thickness, which can be held to 1.3 microns (0.00005 inch). The maximum plating depth is 125 microns (0.005 inch), with the recommended minimum to ensure no porosity at 10 microns (0.0004). In terms of wear resistance, the coating compares favorably with hard chrome (unless the gun does duty in sandstorms). Good wetability gives Nitex the edge over chrome, which tends to shed lubricants. Nitex is not as slippery as Teflon, but unlike Teflon, it can be displaced on bore interiors and springs, and is guaranteed not to crack or peel as long as it’s given minimum care.

Summing up the basic features responsible for the superior corrosion resistance of Nitex, House says, “The coating remains inert with a passivity that lasts indefinitely and is resistant to a large group of acids and chemicals. The degree to which it seals the substrate to prevent penetration is another factor. Moreover, the extreme uniformity of thickness, including hard-to-reach areas that cannot be metal coated by other means, is another advantage.”

Coatings experts routinely caution that no coating can overcome a poor substrate-prep job, and no coating should be used in cases calling for major cosmetic surgery. A gouge taken out of a barrel or slide is still a gouge—and no coating available, by itself, is going to cure that.

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